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THE

ANATOMY OF VERTEBRATES,

VOL. I.

Works by the same Author

LECTURES on the COMPARATIVE ANATOMY and
PHYSIOLOGY of the INVERTEBRATE ANIMALS, delivered at the
Royal College of Surgeons. Second Edition (1855), illustrated by
numerous "Woodcuts 8vo. 21s.

On the CLASSIFICATION and GEOGRAPHICAL DIS-
TRIBUTION of MAMMALIA, being the Lecture on Sir R. Reade's
Foundation, delivered before the University of Cambridge, in the
Senate House, May 1859. To which is added an Appendix on the Gorilla,
and on the Extinction and Transmutation of Species. With 9 Figures
on Wood 8vo. 55.

INSTANCES of the POWER of GOD as manifested in His
Animal Creation : a Lecture delivered before the Young Men's Christian
Association, November 1863. With 11 Figures Crown 8vo. 1*.

London : LONGMANS, GREEN, and CO.

<

c:

ox Tin.

fir

ANATOMY OF VERTEBRATES.

^ --

VOL. I. " * " A

v> *

FISHES AND EEPTILES.

•

BY

RICHARD OWEN, F.R.S.

RUPEItlSTKNDBNT OF THE NATURAL HISTORY DEPARTMENTS 0>" TIIK 1UUTISH MUSEUM.
FOREIGN ASSOCIATE OF THE INSTITUTE OF FRANCE, ETC.

LONDON :
LONGMANS, GREEN, AND CO.

1866.

LONDON
BY SPOTTISVVOODB AX D CO.

NEW-STREET SQUARE

PREFACE.

THE PRESENT WORK completes the outline of the Organisation
of the Animal Kingdom which was begun in that on the Inverte-
brates.1 They may be regarded as parts of a whole, having the
same general aim, and, together, form a condensed summary of
the subjects of my ( Lectures on Comparative Anatomy and
Physiology, according to the Classes of Animals,' delivered in the
Theatre of the Royal College of Surgeons of England in the
years 1852, 1853, and 1854.

In the choice of facts, as then and since acquired by science,
I have been guided by their authenticity and their applicability
to general principles.

In the first, regard has been had to the agreement of several
observers, or to the nature of the fact as making it acceptable on
the testimony of a single expert. Appearances that require helps
to vision are those that call for multiplied concurring testimony,
and on such alone are offered the descriptions and illustrations of
the microscopical characters of ( tissues ' premised to most of the
chapters.

In the second aim, the parts and organs, severally the subjects
of these chapters, are exemplified by instances selected with a
view to guide or help to the power of apprehending the unity
which underlies the diversity of animal structures ; to show in
these structures the evidence of a predetermining Will, producing

1 Lectures on the Comparative Anatomy and Physiology of the Invertebrate
Animals, 8vo. 1843; 2nd eel. 8vo. 18oo.

vi PREFACE.

them in reference to a final purpose ; and to indicate the direction
and degrees in which organisation, in subserving such Will, rises
from the general to the particular.

Anatomy, or the ( Science of the Structure of Organised
Bodies,' is primarily divided into ' Phytotomy,' or that of plants,
and ' Zootomy,' or that of animals. When particular provinces,
classes, or species of animals have monopolised the time and skill
of anatomists, such special knowledges have received particular
denominations : such as ( Malacotomy,' or anatomy of mollusca ;
' Entomotomy,' or anatomy of insects ; ( Ichthyotomy,' or anatomy
of fishes ; ( Ornithotomy,' or anatomy of birds, &c.

An animal may be dissected in order to a knowledge of its
structure, absolutely, without reference to or comparison with any
other, its species being regarded as standing alone in creation.
The knowledge so gained, from the very limitation of the field of
enquiry, may be most accurate and minute, most valuable in its
application to the repair of accident, the remedy of injury and
decay, and the cure of disease. Such, e.g., is f Anthropotomy,'
or the anatomy of man, and ' Hippotomy,' or that of the horse.
Besides the numerous and excellent works on these special sub-
jects, I may cite the ' Traite Anatomique de la Chenille du Saule,'
4to., 1762, by LYONNET ; the ( Anatome Testudinis Europaeae,'
fol., 1819, by BOJANUS; the ( Anatomic Descriptive du Melolon-
tha vulgaris? 4to., 1828, and the ( Anatomic Descriptive du Chat,'
4to., 2 vols., by STRAUS-DURCKHEIM ; also, in application of the
science to art, ' The Camel, its Anatomy, Proportions, &c.,' fol.,
1865, by ELIJAH WALTON ; as unsurpassed examples of this
monographical kind of anatomical science. As applied to Man it
is commonly called ' Human Anatomy,' and is, in strictness of
speech, one of the manifold ways of human work.

But the anatomist may apply himself to a particular organ
instead of a particular species, either exhaustively in one animal,
or by tracing such organ or system throughout the animal king-
dom. The ( Neurotomies ' and ' Neurographies ' to which JOSEPH
SWAN, e.g., has devoted a laborious life, the ' Osteographie ' of

PREFACE. vii

DE BLAINVILLE, and my own ' Odontography/ are examples of
this way of anatomy. JOHJST HUNTER assembled the evidences
of his labours, in the unique and grand department of his Museum
illustrative of anatomy properly so called, in series according to
the organ, beginning with the simplest form, followed in succession
by the progressively more complex conditions of the same organ,
the series culminating, in most cases, with that which exists in
the human frame. The mechanism of the organ is here unfolded,
and its gradations were compared, to discover its mode of work-
ing ; and, as ( Physiology ' mainly consists in such determinations
of functions or final aim, this kind of investigation of organic
structures might be termed ' Physiological Anatomy.' 1

( Homological Anatomy ' seeks in the characters of an organ
and part those, chiefly of relative position and connections, that
guide to a conclusion manifested by applying the same name to
such part or organ, so far as the determination of the namesakeism
or homologv has been carried out in the animal kingdom. This

o./ o

aim of anatomy concerns itself little, if at all, with function, and
has led to generalisations of high import, beyond the reach of one
who rests on final causes. It has been termed, grandiloquently,
' Transcendental ' and ( Philosophical ;' but every kind of anatomy
ought to be so pursued as to deserve the latter epithet.

A fourth way of anatomy is that which takes a particular
species in the course of individual development, from the impreg-
nated ovum, tracing each organ step by step in its evolution up
to the adult condition. It is called ' Embryology ' and ' Develop-
mental Anatomy.'

A fifth way of anatomy is that which investigates the structure
of an animal in its totality, with the view of learning how the
form or state of one part or organ is necessitated by its functional
connections with another, and how the co-ordination of organs is
adapted to the habits and sphere of life of the species ; but does

1 See ' Descriptive and Illustrated Catalogue of the Physiological Series of Com-
parative Anatomy in the Museum of the Royal College of Surgeons,' 4to. 5 vols.
1832-1840; 2nd ed. vol. i. 18.V2.

viii T'REFACE.

not stop here, having for its main end the comparison of these
associated modifications and iiiterdependencies of organs in all the
species of animals. As their degrees of affinity and the characters
and circumscription of natural groups are hereby illustrated, this
way may be termed ' Zoological Anatomy.'

In the hands of the anatomist the microscope has been mainly
applied to the constituent parts of an organ, called * tissues ;' and
the results of such research, combined with those of chemical
tests, constitute a sixth sort of anatomy called ' Histology.' It
has been termed ( Microscopical Anatomy,' but this is essentially
only a more refined method of the scrutiny of organic parts. In
so far, however, as ( Histology ' treats of structure according to
the proximate tissues common to different organs, it corresponds
with the branch of the science which BICHAT, its founder, called,
loosely, e Anatomie Generale.' l

Finally, a seventh way in which the highest generalisations in
biological science may be aimed at is that which is taken when
we pursue investigations of form and structure beyond the animals
that are to those that have been. Here, however, the anatomist
is limited, as a rule, to such tissues and organs as are petrifiable,
e.g., corals, shells, crusts, scales, scutes, bones, and teeth ; but he
has been stimulated to a degree of minuteness and accuracy of
observation in this field of research to which few of the other
ways and aims would have led him. In applying the results of
such researches to the restoration of extinct species, physiology
has benefited by the study of the relations of structure to function
requisite to obtain an insight into the food, habits, and sphere of
life of such species ; and zoology has gained an immense accession
of subjects through such determinations, with improved systems
of classification due to the expanded survey of organic nature
opened out by ' Paleontology.'

The word ' Anatomy ' is still commonly used to signify ( Anthro-
potomy,' or ( Human Anatomy.' Almost all begin the study of
the science, as medical students, with the dissection of the human

1 Anatomie Generale, appliqiu'e a la Physiologie, &c., Svo. 1801.

PREFACE. ix

•

body, and most end there ; but no special anatomy can be rightly
and fully understood save on the basis of the general science of
which it is an integral part. The reason lies in the diversities of
organic structure being subordinated to a principle of unity. Of
this principle, apprehended as an ( idea ' or truth of reason, the
understanding receives evidences in number and comprehen-
sibility differing in different natural groups of the animal king-
dom. Illustrations of the ' idea ' will be found in the chapters on
the Articulate Province and other parts of the ' Lectures on In-
vertebrates,' and, in accordance with the present phase of ana-
tomical science, more abundantly in the present Work. True it is
that in the first steps to organisation we seem to see a tendency to
disintegration, to a reduction of the primary whole to the sub-
ordinate characters of a part. The first centre of sarcode, or
undifferenced organic matter, however originated, yet with de-
finite tendencies to formal character and course of growth (as in a
Foraminifer, e.g.), buds forth a second centre of identical nature;
this a third, and so on, until a group of such exists as an assem-
blage of coherent homogeneous or like parts. These, if clothed by
a delicate crust of characteristic structure, constitute a chambered
shell, straight, bent, or spiral, each chamber occupied by the
same vital sarcode, outshooting filamentary food-getting processes
through the shell-pores ; in which seeming complexity the inci-
pient unity or ( whole ' is reduced to the ' part ' called innermost
chamber, or is conceivable as a lesser whole in the larger one.
The Annelides offer a familiar example of such repetitions of a
primal complexly organised whole, by successive buddings in a
linear direction ; the nerve-centre, the muscles, the skeleton-seg-
ment, perhaps heart and gills, being regularly repeated in each,
and thereby reducing the original whole to one of many parts of
a segmented unity.

Almost every organ in the progressively differenced organism
initiates itself under a similar character of irrelative repetition,
suggestive of operance akin to that of inorganic polar growths, as
in a group of crystals, wherein each exemplifies the characters

x PREFACE.

•

of the mineral or crystalline species, but is subject, like vital
growths, to occasional malformation.

As this principle of growth by multiplication of like parts is
manifested more commonly and extensively in plants, it is illus-
trated in the ( Invertebrate Volume ' 1 under the term ( Vegetative

o

Repetition.' In the vertebrate series it is exemplified by the
hundreds of similar teeth in the jaws of many of that low class
(Pisces^ in which true dentinal teeth first appear in the animal
kingdom. The numerous and similar many-jointed terminal divi-
sions of the pectoral limbs of the fishes thence called e Kays,' the
multiplied similar endoskeletal segments of the vertebral column of
these and other cartilaginous fishes, of murasnoids and serpents, are
likewise lingering exemplifications of the low irrelative principle
of development.

In the vertebral embryo the first appearance of the parts of the
skeleton, in gristle or bone, is a segmental one ; in fishes the mus-
cular system shows much, and in all Vertebrates a little, of the
like segmental constitution of the trunk ; the same idea is suggested
by the symmetrical and parial origins of the nerves, and phy-
siologists have mentally recognised a corresponding segmental
condition of the myelon or spinal chord, which is visibly exem-
plified in certain fishes. But these appearances are concealed by
the general tegument ; not exposed, as in the Articulates, in which
the segmented skeleton is at the same time tegument. A Verte-
brate may be defined as a clothed sum of segments. But in this
highest province of the animal kingdom growth by repetition of
parts rapidly gives place to the higher mode of development by
their differentiation and correlation for definite acts and complex
functions. Nevertheless, I am constrained by evidence to affirm
that in the vertebrate as in the invertebrate series there is mani-
fested a principle of development through polar relations, work-
ing by repetition of act and by multiplication of like parts, con-
trolled by an opposite tendency to diversify the construction and
enrich it with all possible forms, proportions, and modifications of

1 Op. cit. 2nd ed. p. 541.

PREFACE. xi

parts, conducive to the fulfilment of a pre-ordained purpose and
a final aim : these opposite yet reciprocally complemental factors
co-operating to the ultimate result, with different degrees of dis-
turbance, yet without destruction, of the evidences of the typical
unity. 1

Thus, the dentition of Vertebrates will be seen to pass from
irrelative sameness and multitude to the state in which the teeth
in the same jaw are classed according to diversities of form and
function, and where each tooth has its own character, bears its
own name and symbol.

In like manner may be traced the gradations by which the
terminal divisions of the limb ascend from the multitude of many
jointed rays, swathed in a common sheath of integument, to indi-
vidual freedom, with reduction of number and of joints, and with
a special form and action ; according to which each digit in the
human hand, e.g., has its special name and symbol, and can be
combined in action with any other digit for a particular purpose.
The same principle, through reduction of number with differen-
cing of the parts, is exemplified by the fact that the competent
anthropotomist will distinguish and name each of the four and
twenty ' true vertebra' of the human skeleton.

In the Mammalian class there are four muscular pulsatile
cavities concerned in the propulsion of blood ; but they differ from
those cavities in the Annelide, in each having its own special
structure and powers, and being in such relation with another
cavity that the whole can combine to effect two complete but
mutually related systems of circulation, the four pulsatile cavities
constituting one complex and perfect ' heart.' The ox has four
bags for the digestion of food ; but they differ from those cavities
of the Polyyastria, not only in their minor number and more de-
finite structure as bags, but by each performing a distinct part in
the process of digestion, and combining with the rest, in mutual

1 This idea will be found more fully exemplified in my work, ' Principes d'Osteolo-
gie Comparee,' Sro. (Paris) 1855, p. 366, et seq.

xii PREFACE.

subserviency, to tlie completion of the most perfect act of that
function, the conversion, namely, of grass into flesh.

Thus, in tracing through the animal series this course of parts
and organs, we pass from the many and the like to the few and
the diverse.

A * homologue ' is a part or organ in one organism so answer-
ing to that in another as to require the same name.

Prior to 1843 the term had been in use, but vaguely or
wrongly.1 ( Analogue ' and 'analogy' were more commonly
current in anatomical works to signify what is now definitely
meant by ( homology.' But f analogy ' strictly signifies the
resemblance of two things in their relation to a third ; it im-
plies a likeness of ratios. An ( analogue ' is a part or organ in
one animal which has the same function as a part or organ in
another animal. A ' homologue ' is the same part or organ in
different animals under every variety of form and function.

In the Draco volans (Vol. I. fig. 163) the fore-limbs are
' homologous' with the wings of the bird (Vol. II. fig. 1); the
parachute is ( analogous ' to them.

Relations of homolosry are of three kinds ; the first is that

o«/

above defined. When the ( basilar process of the occipital bone '
in Man is shown to answer to the distinct bone called f basioc-
cipital ' in the fish, the special liomology of that anthropotomical
process is determined ; as such homologies are multiplied, the
evidence grows that man and fish are constructed on a common
type.

A wider relation of homology is that in which a part or series
of parts stands to such general type. When the ( basilar process
of the occipital bone ' is determined to be the l centrum ' of the
last cranial vertebra, its general liomology is enunciated.

The archetype skeleton represents the idea of a series of
essentially similar segments succeeding each other in the axis

1 ' Les organes des sens sont Jwmologues, comme s'exprimerait la philosopliie
allemaude ; c'cst-a-dire, qu'ils sont analogues dans leur mode de deYeloppement.'-
Geoffroy St. Hilaire, Annales des Sciences Nat., torn. xii. 182o, p. 34-1.

PKEFACE. xiii

of the body ; such segments being composed of parts similar in
number and arrangement. Accordingly, a given part or appen-
dage in one segment is repeated in another, just as one bone is
represented in the skeletons of different Vertebrates ; and this
representative relation in the segments of the same skeleton is
( serial homology.' As, however, the parts can be namesakes
only in a general sense, as e centrums,' ' ribs,' &c., and since they
must be distinguished by special names according to their special
modifications, as tf basioccipital,' ' mandible,' f coracoid,' ' humerus,'
£c., I have called such serially related or repeated parts ( homo-
types.' The basioccipital is the homotype of the basisphenoid,
and the humerus is the homotype of the femur : when the basi-
occipital is shown to repeat in its f vertebra ' the element which
the ( odontoid process ' represents in the succeeding vertebra, or
the basisphenoid in the preceding one, its f serial homology ' is
indicated.

The extent to which serial homologies can be determined
shows the degree in which vegetative repetition prevails in the
organisation of an animal.

The study of homologies is comparatively recent ; much of this
field of research remains for future cultivators, especially in
regard to the muscular and nervous systems.

When engaged in the f third way ' of anatomy, and in making
known the results of such labour as applied to the skeleton,1 I
found a great impediment in the want of names of bones. For
these, when first studied, had been mostly described under phrases
suggested by forms, proportions, or likeness to some familiar
object, which they present in the human body. A reform of this
nomenclature was an essential first step, and it is gradually
making its way against the usual impediments.

The best workman uses the best tools. Terms are the tools of
the teacher ; and only an inferior hand persists in toiling with a
clumsy instrument when a better one lies within his reach. But
* he has been used to the other.' No doubt ; and some extra

1 On the Archetype and Homologies of the Vertebrate Skeleton, 8vo. 1848; and
On the Nature of Limbs, 8vo. 1849.

xiv PREFACE.

practice is necessary to acquire the knack of applying the new
tool. But in this acquisition a small capital of trouble will have
been invested with a sure return of large profits. A single sub-
stantive term is a better instrument of thought than a paraphrase.1
But the substitution of such terms for definitions is still more
advantageous when they are susceptible of becoming adjectives by
inflection. Thus the term ( notochord ' for ( chorda dorsalis ' or
' dorsal chord ' enables one to predicate of species or groups of
vertebrates as being ' notochordal ; ' that single epithet implying
that the embryonal body in question is, in them, persistent. A
like advantage cleaves to ( myelon ' for ( chorda spinalis ' or
' spinal chord ;' the Physiologist, e.g., can then speak of f myelonal
functions,' and the Pathologist of ' myelonal' disease, with the cer-
tainty of being understood to signify properties and affections of
the s spinal chord ;' not, as in ' spinal disease,' that of its case, or
e spinal column/ In regard to the part so called and its con-
stituent ' vertebras,' their modifications are so many, so charac-
teristic, so important, especially in the application of Anatomy to
Paleontology, that I was early compelled in the latter kind of
labour to substitute single pliable terms for the phrases ( trans-
verse process,' ( oblique ' or ' articular process,' 6 body of the
vertebra,' ' vertebral lamina,' ( vertebral rib,' ' sternal rib,' &c.,
by which the parts of the ' vertebra ' were then designated.

But the single names of parts and constituents of the skeletal
segment called ' osteocomma ' or f vertebra ' have not merely the
advantage above illustrated, as where the adjective ' neurapo-
physial ' can be applied to a f ridge,' notch, or ( foramen,' in the
vertebral lamina (neurapophysis) ; the vertebral terminology in
use in the present Work indicates a profound truth which is
hidden by the language of anthropotomy. The terms ( pleur-
apophysis' and ( hajmapophy sis ' imply parts of the segment corre-

1 ' Superoccipital,' e.g., for ' pars occipitalis stride sic dicta partis occipitalis ossis
spheno-occipitalis ' of the eminent anthropotomist SOEMMERING. (See TABLE OF
SYNONYMS, &c., appended to Vol. II.) Similarly, in the present Work, I use the word
{ Vertebrate ' as a substantive. We do not speak of a ' Confederate ' animal, and the
added word is as unnecessary in regard to the ' Vertebrate ' one.

TREFACE. xv

lative in independency of development and elemental grade with
the ( neurapophysis,'- -a fact of high generalisation not only
ignored but impliedly contradicted bv the reckoning of the

O J. «/ */ O

' vertebral rib ' and the ' sternal rib,' or ' rib-cartilage,' as bones
distinct from, and countable with, that which the anthropotomist
equally holds to be a single bone under the name e vertebra.'
Furthermore, as each distinctly recognisable part or thing must
have its verbal sign, for the purposes of intelligible predication of
its nature and qualities, the course of knowledge of the vertebral
column would have enforced the origination of such signs irre-

o o

spective of the abstract need of improving the mental tools of
anatomy.

When it came to be discovered that ( the transverse process
of a cervical vertebra ' was other, and more than, as well as
formally different from, the ' transverse process of a dorsal ver-
tebra,' and that this process was a different thing from the
' transverse process ' of a l lumbar ' or ( sacral ' vertebra, the re-
sults of such analysis necessitated the creation of a correspondent
nomenclature.

' Transverse processes,' as such, are, as JOHANNES MULLER
first pointed out, of two kinds ; they are, in relation to hori-
zontally disposed vertebrates, f upper ' and ' lower ' -in our no-
menclature, ( diapophyses ' and f parapophyses.' Both kinds exist
in the ' transverse processes ' of the neck from the crocodile
upwards ; and the seeming unity of the outstanding part in
birds and mammals is caused by the soldering thereto of a third
element — the ' cervical rib ' of the herpetotomist, the ( styloid
process ' of the ornithotomist. ]

Referring to the ( Introductory Chapter ' of the ( Archetype
of the Vertebrate Skeleton,' 2 for further illustrations of the
advantage of single well-defined terms, I will here only show
how such advantage may be affected by reason of an unsettled
definition.

The anatomical term { organ ' has diverse significations. The

Macartney. Art. ' Birds,' Rees' Cyclopaedia. * Op. cit.

xvi PREFACE.

chief constituent idea is ' work for a special end :' thus, the heart
is the ' organ ' of circulation ; the lungs, the ( organ ' of respira-
tion ; the liver, the c organ' of bilification, &c. But also, incipient
stages in the development or formation of parts are called the
6 organs ' of such; e.g., the periosteum is the ' organ of bone,'
the pulp is the ' dentine organ;' other parts of the growing
complex tooth are the ( enamel organ,' f cement organ,' &c. The
parts in which independent cells, with special powers, originate,
are also called the ( organs' of such; as, e.g., the ovary is the
' organ of ovulation ;' the testis the ' organ of semination.' It
is obvious, however, that the part which the more or less con-
densed cellular basis, or ( stroma,' of the ovary or the testis may
take in the production of the gerrn-cells or sperm-cells and sperma-
tozoa is very different from that which the heart performs in the
motion of the blood, or the lungs in the mutation of the air
inspired.

Zoological anatomy is now an indispensable instrument to the
classifier, if not to the determiner, of the species of animals. The
anatomist properly so called, but commonly qualified as the
f comparative ' one, makes known the results and applications of
his comparisons of structure in zoological as well as homologi-
cal or anatomical works. The ( Regne Animal ' and the f Lepons
d' Anatomic Comparee ' of CUVIER exemplify these different appli-
cations and ways of exposition of his science.

As a zoologist or classifier, the anatomist avails himself of the
definite modification and full development of a part or organ, in-
dicating, and predicating of such conditions by special terms,
for the required characters. The ( fin,' the ( hoof,' the ( paw,' the
6 foot,' the ' hand,' are to him so many kinds of limbs, the presence
or absence of which serve to differentiate his groups ; anthropo-
tomical terms of parts of the brain reaching their full and cha-
racteristic development in Mammals or in Man, e.g., ffornix,'
6 corpus callosum,' ( hippocampus minor,' l posterior cerebral lobe,'
&c., serve and are used, absolutely, for the same end ; so likewise

PREFACE. xvii

with regard to special forms and proportions of teeth indicated by
the terms ' canine/ f carnassial,' ' tusk,' &c.

The absolute way in which the things or characters so desig-
nated are affirmed or denied in zoological definitions is essential to
their purpose.

Amongst the characters by which CUVIER differentiated the
hoofed quadrupeds which he had restored from their frag-
mentary fossil remains in the building-stone of Paris, the most
important in his estimation was 'the presence of canines' in
one (Paloeotheriwn), their absence in the other (Anoplotherium).1
Nevertheless, Homological Anatomy easily indicates in the series
of nine teeth in the ( morceau de conviction,'2 on which the
character was founded, the teeth answerable to those which,
because their pointed crowns projected beyond their neighbours
in the Palasothere, were called and characterised as ' canines.'
Now here was a temptation to an aspirant to scientific notoriety
( to meet ' the great anatomist ( by a flat contradiction,' and
'affirm that the Anoplotherium possessed canine teeth.' I allude
to such abuse because, of late, a practice has been creeping
in, to the opprobrium of some of our English zootomists, of repre-
senting a zoological definition of a part which an anatomist may
have given in a classificatory work, as the exponent of his homo-
logical knowledge and descriptions of such part in its various
modifications and grades of development.

CUVIER, in his characters of the order Bimana, affirms that
Man is the only animal possessing ( hands ' and ( feet : '
( L'homme est le seul animal vraiment Mmane et bipede.'3 The
Quadruma?ia are distinguished as having ' hands' instead of ' feet,'
a ' hand' being defined as having the thumb opposable — ' le pouce
libre et opposable aux autres doigts, qui sont longs et flexibles.'4

The aim of the author in the zoological work above cited was
to impart obvious and easily apprehended differential characters

1 ' Le plus important fut celui qui m'apprit que cette espece n'a point de dents
canines.' — Rechcrches sur les Ossemens Fossiles, 4to. 1822, torn. iii. p. 14.

2 Ibid. 3 Regne Animal, torn. i. p. 70. 1829. 4 Ibid. p. 85.

VOL. I. a

xviii PREFACE.

of the organ which observation had shown to define the groups.
The naturalist, thus enabled to place his subject in its proper
class or order, is not concerned, as such, in knowing the homo-
logical or transcendental relations of the part or character which
has afforded him the means of effecting what he wished to do.

LINN/EUS, to whom mainly is due the discernment of the power-
ful instrument of well-defined terms in acquiring a systematic
Science of Nature, and to whom we owe our best knowledge of
its use, so named the guiding parts of plants and animals, for such
arbitrary or special application, in botany and zoology : to this
end he differentiates the ( bract,' the ' spath,' the ( sepal,' the
{ petal,' from the ' leaf,' as things distinct.

What would be thought of the botanical critic who, quoting the
definition of the flowers of Cyperaceous plants, as consisting, for
example, of s glumes,' should meet the statement by affirming that
they were ( nothing but little bracts,' and who, then, with a show
of profounder research, should proceed to expound the ' bract ' as
being the first step by which the common leaf is changed into a
floral organ ? The answer is obvious. But what next might be
said, if it were pointed out that the objector had obtained this
very notion from the ( Prolepsis Plantarum,' or other homological
writings of the author criticised, where such philosophical con-
siderations, foreign to the classificatory work, were the proper aim
and object ? So, with regard to the zoological definitions and
characters of CUVIER. Those which I have cited are open to the
opposite averment that, ' The " hind hands " of the Quadrumana
are nothing but " feet ; '' ' and the contradictor might then proceed
to demonstrate, with much show of original research, the homology
of the ' astragalus,' ' calcaneum,' f cuboides,' ( cuneiform bones,'
&c., in order to establish his discovery that a hand and foot are
all one.

It is true that if the homological descriptions in the ' Lemons
d' Anatomic Comparee ' had been quoted, as well as the zoological
definitions in the e E-egne Animal,' the immortal author of the
latter work would be shown to have had previous possession of
the pretended discovery. Moreover, in the ' Cinquieme Lepon,

PREFACE. xix

Articles VJI.-IX. " Des os clu pied," ' l the frame of the hind
feet of Man, Ape, Lion, Seal, Elephant, &c., is shown to consist
of homologous bones. Nevertheless the great zootomist, in his
labour and character as zoologist, does not hesitate to define and
differentiate the ' foot,' the ' hand,' the ' paw,' the ' fin,' and the
( hoof,' respectively : nor does he deem the demonstration of the
unity underlying the diversity to make the f man ' an f elephant '
or a ' seal,' any more than it makes him a f dog ' or an ' ape ' !

The ' corpus callosum ' is defined as ' a horizontal mass of trans-
verse fibres covering the lateral ventricles, and exposed by divari-
cating the cerebral hemispheres.' If a group of mammals want
such commissural fibres, and another group possess them, the
classifier will avail himself of a well-defined term expressing such
difference, without prejudice to his reception of any homological
determination of the parts, or their rudiments,2 in anatomical
works of the applier of the term.

Only by ignoring such indication of the e rudiniental com-
mencement of the corpus callosum,' may a semblance of superior
knowledge be assumed by him who asserts, as an antagonistic
proposition to an affirmation of its absence as a zoological cha-
racter, that the Marsupialia, e.g., do possess the ( great com-
missure,' or ( corpus callosum.'3

So likewise with other well-defined parts of the human brain,
the homologues of which may not be traceable to the same extent

QJ V

down the mammalian series. KUHL, e.g., in Ateles Belzebutli*
TIEDEMAXN in the Macaque5 and Orang,6 VAN DER KOLK and
VROLIK in the Chimpanzee,7 and myself in the Gorilla,8 had

1 Le9ons d'Anat. Comparee, vol. i. 1799.

2 As given in the 'Philosophical Transactions' for 1837, p. 41.

3 Proceedings of the Royal Society, No. 72, and March 23, 1865.

4 Beitrage zur Zoologie tind vergleichenden Anatomic, 4to. 1820, zweite Abtheilung,
p. 70, Taf. vii.

5 Icones cerebri Simiamm, fol. 1821, p. 14, fig. iii. 2.

6 Treviranns, Zeitschrift fiir Physiologie, Bd. ii. S. 25, Taf. iv.

7 Nieuwe Yerhandliugeu der erste Klasse van het Koningl. Nederlandsche Instituut.
Amsterdam, 1849.

8 Fullerian Lectures on Physiology, Royal Institution (March 18, 1861); reported,
with copies of diagrams, in ' Athenpeum/ March 23rd, 1861, p. 395.

a 2

xx PREFACE.

severally shown all the homologous parts of the human cerebral
organ to exist, under modified forms and grades of development,
in Quadrumana. But because the presence or absence of the
( ergot,' or ( pes hippocampi minor,' as defined by TIEDEMAXN
(see Vol. II. p. 273 of the present Work), had been used as a
zoological character, the anatomical world has been deluged, since
the date of the last under-cited work, with descriptions and figures
of the homologous part in the Orang and other Quadrumana, as a
new discovery mainly serviceable as a battery of contradictory
affirmations.

Nevertheless the distinctive characters of the human brain, &uch
as the manifold and complex convolutions of the cerebral hemi-
spheres, their extension in advance of the olfactory lobes and
farther back than the cerebellum, thereby defining a posterior
lobe, with the corresponding ( horn of the lateral ventricle ' and
' hippocampus minor,' are as available to the zoologist in classifi-
cation as are the equally peculiar and distinctive characters of
the calcaneum, hallux, and other structures of the foot.

So much, in connection with the ( fifth way ' and application of
anatomy, I regret to find myself compelled to state, in order to
expose and stigmatise procedures which consist in representing
the homological knowledge and opinions of an author by his de-
finitions in a purely zoological work, and in suppressing all re-
ference to the descriptions and statements in the anatomical
writings of the same author, where his actual knowledge and

o O

opinions on the nature and homology of parts are given, and
where alone they can be expected to be found.

Somewhat analogous to the course of observation pursued
through the animal kingdom, from the lowest to the highest

O O o

species, is that which traces each organ through the several
phases of its development in the same species.

The right use of sense, in both ways, stores the understanding,
empirically, with a series of facts, as the raw material for reasoning
up to their principles. But Embryology has this inferiority, that

PREFACE. xxi

every species is such db initio, and takes its own course to the full
manifestation of its specific characters, agreeably with the nature
originally impressed upon the germ.

A perch, a newt, a dog, a man, does not begin to be such only
when the embryologist may discern the dawnings of their respect-
ive specific characters. The embryo derived its nature, and the
potency of self-development according to the specific pattern, from
the moment of the impregnation ; and each step of development
moves to that consummation as its end and aim.

This truth has been masked to some apprehensions by the
course of the developmental steps from the general to the par-
ticular ; the initial ones, more especially, offering likenesses or
analogies to finished lower species exemplifying degrees of organi-
sation in the animal kingdom. Each step differs in degree of
difference from the analogous grade at which a lower species rests,
and inversely as the advance of such species. Accordingly, the
less the degree of difference, and the wider the resemblance or
analogy spreads between the embryonal phase and the parallel
grade in the series of species.

The formation of the germ-mass (Vol. I. figs. 1-4, 422,452) —
the first step after impregnation — is a general phenomenon in
animality (Vol. ' On Invertebrates,' figs. 48-56, 73, 74, 80-84,
181, 209-212, 232) ; thereat and thereby the man resembles and
behaves like the monad.1 But, the germ-mass completed, the
vertebrate at once circumscribes itself or withdraws into its
vertebrality. The proteine substance is the seat of a chemical
differencing, leading to excess of albumen along one tract,
balanced by excess of gelatine along a parallel tract. Thus are
laid down the bases of the myelencephalon and vertebral axis.
The s notochord ' is soon followed by the protovertebral specks
in double parallel series (Vol. I. fig. 5; Vol.11, fig. 133): the
embryonal trace is established, and it is one of a vertebrate.

The formation of neural and hnsmal arches next follows ; and

1 Compare the above-cited figures with fig. 17, 'Lectures on Invertebrates,' 2nd
*d. p. 29.

xxii PREFACE.

the phenomenon of the appearance of the latter, in which the
blastemal is accompanied by a vascular arch, with clefts inter-
vening between contiguous arches, especially at the fore part of
the embryo, has led to the idea that a reptile, bird, or mammal,
is a fish before it becomes what it is tending to. True it is, that

o

the embryos of these air-breathers float in fluid, and not any of
them breathe the air until birth or exclusion, or near to exclusion ;
but they do not breathe water : the oviparous air-breather has one
kind of temporary lung, the mammiferous embryo another kind,
each alike special to the class. From the vascular loops accom-
panying the haemal arteries branchiae are not developed ; one only
of the interhaemal fissures is deepened on each side, brought into
communication with the pharynx, and straightway converted into
the ( eustachian tube,' according to the precocious rate of growth
and development characteristic of the special organs of sense
and their appendages. No true branchial or piscine breathing
apparatus is at any time, or in any degree, manifested in the
embryo of an air-breathing vertebrate. The deepening and open-
ing of several interhremal fissures in the embryo of a perch, and
the subsequent course of development therewith of gill-arches arid
gills, with their subservient mechanism of branchiostegal rays and
the opercular lid or door, are as distinctive manifestations of the
original nature of the fish, as is the vascular lining; of the egs: that

O ' O oO

of the bird, or the vascular arrangement for borrowing breath
from the mother that of the foetal mammal.

At the incipient stages of these provisional and deciduous
respiratory conditions the circulation in the embryo lizard, fowl,
beast, is like that of a fish in its simplicity ; but, as TREVIRANUS1
rightly remarked, it is far from being identical ; there are, indeed,
characters of the circulating organs at this grade of simplicity,
which not only distinguish the embryo of the air-breather from

»/ O »'

that of the water-breather, but also the embryo of the mammal
from that of the bird or reptile ; so soon is the course of deve-
lopment affected by the specific taint !

1 Gr. R. in ' Zeitschrift fiir Physiologie/ vol. iv. ; and 'Edinburgh New Philosophical
Journal.' ]83'2. vol. xiii. p. 75-86.

PREFACE. xxiii

Marked deviations from the archetype characterising existing
species are directly approached in the progress of development.

If, as, e.g., in a thoracic or jugular fish, the position of the
pelvic limbs departs from the typical one, these limbs bud out in
the embryo in that special and anomalous place. When a higher
species departs from type by a thoracic position of the scapular or
occipital limbs, they likewise bud out in such special position. In
both cases the haemal arch, sustaining such appendages, is libe-
rated from the rest of its segment for the special needs of the
species, and the embryo of such never shows it fixed. At most,
perhaps, the general character and typical connections may be
indicated by the closer contiguity of the detached scapular arch to
the rest of its proper occipital segment; as, e.g., in the embryo of
birds and long-necked ruminants, to be removed to a distance
determined by the later growth of the series of vertebras inter-
vening between head and chest.

To infer from such developmental phenomena that the throat-
fins of the cod are not the displaced homologues of the hind legs
or pelvic limbs of air-breathers, and that the fore-legs of such are
not the homologues of the typically situated and connected scapu-
lar limbs of fishes, is an abuse or misuse of the empirical facts
ascertained by observation of embryonal phenomena.

V V

In like manner the developmental phenomena of the skull of
an avian and mammalian species, succeeding those that broadly
and intelligibly mark out the four pairs of neurapophyses and
corresponding haemal arches, plainly indicating the seginental or
vertebral type of the skull, depart therefrom to attain the par-
ticular character of the face and mouth of the species. After
the first budding indications of the halves of the maxillary (fore-
most cranial haemal) arch, the development of it, as upper jaw,
with that of the palate, pterygoid, and zygomatic appendages,
obeys the impress of impregnation, and proceeds directly to es-
tablish the specific characters of such jaw in the particular bird
or beast ; the points of ossification, their deposit in membrane or
gristle, and subsequent growth, having no other or deeper signifi-

xxiv PREFACE.

cation. If a species be gifted with acute hearing, and the move-
ments of the ear-drum require several ossicles, these, like the
labyrinth, grow to full size in the embryo, appropriating the
blastema of the contiguous hremal arch, and proportionally re-
ducing, by arresting the development of, the pleurapophysis of
such arch. The inherited tendency to a special or specific form
which thus influences early developments and growth of parts has
misled some who have mistaken such for homological or archetypal
characters. But the determination of these characters is arrived
at by other routes of research ; and, so reached, such determination
serves to explain many of the phenomena of development which
otherwise would remain as mere empirical facts.

Embryology, e.g., shows that in the human foetus the sternum
is developed from a series of ossific centres (Vol. II. p. 555, fig.
364), whilst the co-articulated clavicle — as long a bone — is de-
veloped from a single ossific centre, and a contiguous rib, though
of greater length, is also hardened from a single ossific centre ;
but embryology affords no explanation of the reason of such dif-
ference. That is afforded by a knowledge of the archetype
skeleton, which teaches that the sternum — reckoned as a single

o

bone in anthropotomy — consists of a series of vertebral elements,
but that the rib and the clavicle are single elements.

Embryology shows that the canon-bone of a ruminant, re-
garded as a single bone by the veterinarian, is developed from five
ossific centres ; two on the same transverse line near the middle,
one on the upper, and a pair which soon coalesce at the lower end.
But no clue is afforded to the signification of these several cen-
tres : embryology is no criterion of their homologies ; these are
determinable on other grounds or f ways of anatomy.'

A knowledge of the f Nature of Limbs,' derived from homolo-
o-ical studies leading to a recognition of the archetype, could alone
determine that two only out of those five centres represent dis-
tinct bones in the typical pentadactyle foot of the mammal; the
rest having no such signification, but serving to perfect the ulti-
mate growth as ' epiphyses.' So likewise with the collar-bone

PREFACE, xxv

and rib. At a period long subsequent to the deposition of the
first centre of bone, a second appears at the sternal end of the
human clavicle, and two are added to complete the head and
tubercle of the lib, the shaft of which had been ossified by growth
from a single centre.

Recognition of the archetype skeleton elucidates the empirical
facts of embryology, and teaches us to distinguish between the
points of ossification of a bone in a higher vertebrate which sig-
nify or answer to bones that retain their distinctness in lower
vertebrates, and the points of ossification which merely help out
the growth or have their final purpose in the exigencies of the
vouno- animal. A lamb or foal, e.o\, can stand on its fore legs

J O

shortly after it is born, and soon begins to run and bound. The

•/

shock to the limbs themselves is broken at this tender a«;e by the

c^ »>

cushions of cartilage at the ends of the shafts, and which continue
for some time to be interposed between the ' epiphyses' and * dia-
physis.' The jar that might affect the large and pulpy brain 01
the immature man is similarly diffused and intercepted by the
' epiphysial ' extremities of the vertebral centrums.

Such final purpose in the several centres of ossification of the
vertebral bodies and the long bones of the limbs of mammals does
not apply to those of reptiles ; and no epiphyses with interposed
cartilage attend the growth of the limb-bones of saurians and
tortoises. But, when the reptile moves by leaps, ossification of
the long limb-bones by distinct centres again prevails; the ex-
tremities of the humeri and femora are ' epiphyses ' in the frog.

Embryology affords no criterion between the ossific centres that
have a ( homological ' and those that have a ' ideological ' signifi-
cation. A knowledge of the archetype skeleton is requisite to
teach how many and which of the separate centres that appear
and coalesce in the human, mammalian, or avian skeleton, re-
present and are to be reckoned as distinct bones, or elements of
the archetype vertebra. For the want of this guide great and
estimable anatomists have gone astray. Thus CUVIER, comment -

- on the arbitrary enumeration of the single bones in the human

» o

xxvi PFxEFACE.

skeleton, affirmed that to learn their true number in any given
species we must go to the first osseous centres as these are
manifested in the foetus ; ! and GEOFFROY ST. HiLAiRE2 concurred
in this view.

In the cartilages called ' epiphysial,' that eke out the ends
and margins of bones, ossification begins later than does that of
the bone itself. The times of appearance of the osseous nucleus
in the coracoid process and acromion of the human scapula well
exemplify this difference ; in the coracoid, e.g., at the first year,
in the acromion at the fifteenth year. Embryology teaches the
facts but affords not the reason.

Special homology shows that the coracoid is a distinct bone, the
acromion a mere process, in the vertebrate series. General ho-
mology gives the ground of the distinctness — the coracoid being
the hasmapophysis of the ha3mal arch of which the scapula proper
is the pleurapophysis. In most mammals this haamapophysis is
stunted and terminates freely, like that of the last (floating) rib.
In Monotrenies it attains and articulates with its haemal spine, as
in the ' true rib,' and keeps this normal extent and condition
through all the lower vertebrates. It is the typical state of the
coracoid, which is departed from in all vertebrates above Mono-
tremes : but such typical state is not passed through in the
course of their development. As in that of other modified hasmal
arches, the maxillary, e.g., so in the scapular arch, the special con-
dition of the aborted haamapophysis is gained directly, not through
any intervening transitory manifestation of the general character.
So far is embryology from being a criterion of homology.

In regard to what I have reckoned a ( seventh way of ana-

1 ' Pour avoir le veritable nombre des os de chaque espece, il faut remonter jusqu'aux
premiers noyaux osseux tels qu'ils se montrent dans le foetus.' — Lemons d' Anatomic Com-
paree, 8vo. ed. 1835, torn. i. p. 120.

2 ' Ayant imagine de compter aufant d'os qu'il y a de centres d'ossification distinct?,
et ayant essaye de suite cette mauiere de faire, j'ai eu bien d'apprecier la justesse de
cette idee.' — Annales du Museum, torn. x. p. 344. See, however, the remarks on this
point in my ' Lectures on the Comparative Anatomy of the Vertebrate Animals/ Svo.
1846, p. 37, et seq.

PREFACE. xxvii

tomy,' I would remark that the existing kinds of vertebrates
constitute part only, perhaps but a small proportion, of those
which have lived. Two large primary groups of fishes have
almost wholly passed away ; but the Polypterus, Lepidosteus, and
sturgeon yield the anatomist some insight into the structural
modifications of the Ganoidei of AGASSIZ ; whilst the shark, the
skate, and the cestracion give a fuller knowledge of those of the
Placoidei.

Present reptiles form a mere fragmentary remnant of the great
and varied class of cold-blooded air-breathing vertebrates which
prevailed in the mesozoic age. More than half of the ordinal
groups of the class, indicated by osteal and dental characters, have
perished ; and it is only by petrified faeces or casts of the intestinal
canal, by casts of the brain-case, or by correlative deductions from
characters of the petrifiable remains, that we are enabled to gain
any glimpse of the anatomical conditions of the soft parts of such
extinct species : by such light some of the perishable structures of
these animals are indicated in the text.

As vertebrates rise in the scale and the adaptive principle pre-
dominates, the law of correlation, as enunciated by CuviER,1 be-
comes more operative. In the jaws of the lion, e.g., .there are
large laniaries or canines, formed to pierce, lacerate, and retain its
prey. There are also compressed trenchant flesh-cutting teeth, which
play upon each other like scissor-blades in the movement of the
lower upon the upper jaw. The lower jaw is short and strong ;
it articulates to the skull by a transversely extended convexity or
condyle, received into a corresponding concavity, forming a close-
fitting joint, which gives a firm attachment to the jaw, but almost
restricts it to the movements of opening and closing the mouth.

1 ' Tout etre organise forme un ensemble, un systeme unique et clos, dont les parties
se correspondent mutuellement, et concourent a la meme action definitive par une re-
action reciproque. Aucune de ces parties ne peut changer sans que les autres changent
aussi ; et par consequent chacune d'elles, prise separement, indique et donne toutes les
autres.' — Discours siir hs Revolutions de la Surface du Globe. 4to. 1826, p. 47. In
this definition Cuvier apprehended, exclusively, the operance of the differencing and
adapting pole, and the law become^ limited in its application accordingly.

xxviii PREFACE.

The jaw of the Carnivore developes a plate of bone of breadth
and height adequate for the implantation of muscles, with power
to inflict a deadly bite. These muscles require a large extent of
surface for their origin from the cranium, with concomitant
strength and curvature of the zygomatic arch, and are associated
with a strong occipital crest and lofty dorsal spines for vigorous
uplifting and retraction of the head when the prey has been
griped. The limbs are armed with short claws, and endued with
the requisite power, extent, and freedom of motion, for the wield-
ing of these weapons. These and other structures of the highly-
organised Carnivore are so co-ordinated as to justify CUVIER in
asserting that ( the form of the tooth gives that of the condyle, of
the blade-bone, and of the claws, just as the equation of a curve
evolves all its properties ; and exactly as, in taking each property
by itself as the base of a particular equation, one discovers both
the ordinary equation and all its properties, so the claw, the
blade-bone, the condyle, the femur, and all the other bones in-
dividually, give the teeth, or are given thereby reciprocally ; and
in commencing by any of these, whoever possesses rationally the
laws of the organic economy will be able to reconstruct the entire
animal.' l.

The law of correlation receives as striking illustrations from
the structure of the herbivorous mammal. A limb may termi-
nate in a thick horny hoof. Such a foot serves chiefly, almost
exclusively, for locomotion. It may f paw the ground,' it may
rub a part of the animal's hide, it may strike or kick ; but it
cannot grasp, seize, or tear another animal. The terminal ungu-
late phalanx gives, as CUVIER declares, the modifications of all
the bones that relate to the absence of a rotation of the fore-leg,
and those of the jaw and skull that relate to the mastication
offered by broad-crowned complex molars.

But there are certain associated structures for the coincidence
of which the physiological law is unknown. f I doubt,' writes

1 Op. cit. p. 49.

PREFACE. xxix

CUVIER, ' whether I should have ever divined, if observation had
not taught it me, that the ruminant hoofed beasts should all have
the cloven-foot, and be the only beasts with horns on the frontal
bone.' l I may add that we know as little why horns should be in
one or two pairs in those ungulates only which have hoofs in one
or two pairs ; whilst in the horned ungulates with three hoofs
there should be either one horn, or two odd horns placed one be-
hind the other, in the middle line of the skull ; or why the ungu-
lates with one or three hoofs on the hind foot should have three
trochanters on the femur, whilst those with two or four hoofs on
the hind foot should have only two trochanters.2

' However,' continues CUVIER, ( since these relations are con-
stant, they must have a sufficing cause ; but as we are ignorant
of it, we must supply the want of the theory by means of observa-
tion. This will serve to establish empirical laws if adequately
pursued, as sure in their application as rational ones.'3 'That
there are secret reasons for all these relations observation mav

«/

convince us, independently of general philosophy.' f The con-
stancy between such a form of such organ and such another form
of another organ is not merely specific, but one of class with a
corresponding gradation in the development of the two organs.'4

' For example, the dentary system of non-ruminant ungulates
is generally more perfect than that of the bisulcates ; inasmuch
as the former have almost always both incisors and canines in the
upper as well as the lower jaw ; the structure of their feet is in
general more complex, inasmuch as they have more digits or hoofs
less completely enveloping the phalanges, or more bones distinct

1 Op. cit. 50. - Quarterly Journal of the Geological Society, p. 138. 1847.

3 ' Puisque ces rapports sont constants, il faut bien qu'ils aient une cause suffisante,
maiscorame nous ne la connaissons pas, nous devons suppleer au defaut de la theorie
par le moyen de 1'observation.' — Op. cit. p. 50.

4 ' En effet, quand on forine un tableau de ces rapports, on y remarque non seulement
une consistance specifique, si 1'on peut s'exprimer ainsi, entre telle forme de tel organe
et telle autre forme d'nn organ different ; mais Ton apergoit aussi une Constance
classique et une gradation correspondante dans le deyeloppement de ces deux organes,
qui montrent, presque aussi bien qu'un raisonnement effectif, leur influence mutuelle.' —
Op. cit. p. 51.

xxx PREFACE.

in the metacarpus and metatarsus, or more numerous tarsal bones ;
or a more distinct and better developed fibula ; or a concurrence
of all these modifications. It is impossible to assign a reason for
these relations ; but, in proof that it is not an affair of chance,
we find that whenever a bisulcate animal shows in its dentition
any tendency to approach the non-ruminant ungulates, it also
manifests a similar tendency in the conformation of its feet.' After
citino- similar instances of such constant relations, CUVIER as^ain

O O

declares that the palaeontologist f must avail himself of the method
of observation' as a supplementary instrument when the reason or
law of such relations is undiscovered ; and that he is most suc-
cessful in the reconstruction of a whole from a part, who applies
to the task ' efficacious comparison,' guided by ' tact (adresse) in
discerning likeness.' l

As we descend in the scale of life from the grade illustrative
of ( Cuvier's Law,' the method of empirical observation becomes
more and more essential, the tact with which it is applied being,
however, in the ratio of the discernment of the correlations of
structures. The results of the combined methods of interpreting
fossil remains are leading to views of life transcending the gains
to zoology as a record of well-classed species, or to physiology as
illustrative of final purpose. A progress from more generalised
to more specialised structures, analogous to that exemplified in
existing grades of animal life and in successive phases of individual
development, is appreciable in the series of species which have
succeeded one another upon our planet.

Certain structures which are transitory or rudimental in exist-
ing species are persistent and developed in extinct.

The caudal vertebrae are laid down in a gradually decreasing
series of cartilaginous nuclei, in the embryo of modern bony fishes ;
but in the course of ossification they become massed and blended
together to form the base of a vertically extended symmetrical
tail-fin. In all palaeozoic fishes the initial embryo-state persists,
and the tail-fin, through the length of the upper lobe retaining the

1 Op. eit. p. 52.

PREFACE. xxxi

terminal series of vertebras, is unsyrnmetrical. The process of
differencing which leads to the ( homocercal ' type begins in the
mesozoic period and prevails in the neozoic. (See TABLE OF
STRATA, &c., p. xxxviii.)

A corresponding modification of the caudal vertebra? prevails
in neozoic birds ; but the embryos of the existing species show
the terminal vertebra distinct, in a tapering series, before they
are massed into the 'ploughshare bone;' and such, doubtless, was
the law of development in all the extinct species which have left

tertiary ornitholites. But the earliest and as yet sole evidence

«> •/

of the fossil skeleton of a mesozoic bird shows the retention of
the embryo condition, with ordinary growth of the vertebra?.1

Modern ruminants are hornless when born, and have the me-
tnpodials supporting the phalanges of the cloven foot distinct ;
at an earlier foetal period rudiments of upper fore-teeth start in
the gum but do not get beyond it. The eocene mammal that first
indicates the ruminant type retained the transitory, and developed
the aborted, characters of its successors. The metacarpals and
metatarsals never coalesced to form a ' canon-bone ;' the upper
canines and incisors were functional, but small and equal-sized ;
and, as horns never sprouted, CUVIER called the extinct beast
( weaponless' (Anoplotherium). In modern horses the digit on
each side the one supporting the hoof is undeveloped, and is
represented by a concealed rudiment of the metapodial called
( splint-bone.' In the miocene horses these metapodials reached
their full length and supported hoofed digits, but of small size,
like the ' spurious hoofs ' of the ox. The eocene mammal initia-
ting the type had these hoofs so developed as to form a functional
tridactyle fool. Moreover, in the Palaotherium, certain teeth
(symbolised in the present Work as p 1 ) which are rudimental and
deciduous in the horse, were persistent and functional. The mesozoic
marsupials manifested a lower or less differenced state of dentition,
either by the degree of sameness of form (Phascolothere), or by the
superior number (Thylacothere) of the molar series of teeth.

1 Philosophical Transactions, 1863, pp. 33, 45, pis. I. and III.

xxxii PREFACE.

The ( rudiments ' of parts and organs which are retained un-
developed, or do not acquire the state capable of acting, or ( per-
forming the function ' done by them in other species, are of two
kinds : one exhibits the totality of the organ in miniature, as,
e.g., lacteal glands and nipples of the male mammal; the other
is a part of an organ, as, e.g., the few concealed caudal vertebra
in the sloth, to which other vertebra are added, with concomitant
growth, to make the organ perfect for its function, as in the tail
of the Megathere. Some rudiments show beginnings of parts
which rise to perfection in higher species of the existing series ;
others are remnants of organs that were fully developed and func-
tional in extinct species. TIEDEMANN'S ( scrobiculus parvus in
loco cornu posterioris ' in the brain of Macacus,1 and the part
which VROLIK believed himself entitled to regard as an indication
of the 'hippocampus minor' in the brain of Troglodytes,- are
beginnings of structures which show their full development in
the human brain, and merit the nomenclature assigned to them
in anthropotomy.

The filamentary limb of Protopterus (Vol. I. fig. 101, A), the
didactyle limb in Ampliiuma (Ib. B), the tridactyle homologue in
Proteus, are bemnnino-s of organs which attain full functional de-

~ o o

velopment in higher vertebrates. The styliform metacarpals and
metatarsals in Equus, on the other hand, are remnants of parts
of digits which were entire in Hipparion, and were functionally
developed in Palceotherium.

Ruminants which habitually frequent heated arid plains or
deserts, as the giraffes and camels, e.g., have lost the digits (ii
and v, Vol. II. fig. 193, ox) that add to the resistance of the hoof
on swampy ground, as in the bison, elk, and reindeer (Ib. fig.
311).

The visual organ degenerates in species inhabiting dark caves
or recesses (Amblyopsis (Vol. I. fig. 175), Heteropygii, Proteus,

1 Icones cerebri Simiarum, fol. p. 1 1, fig. iii. 2.

2 Versl. en Mededeel. der Kon. Ak;id.,xiii. 1862, p. 7.

PREFACE. xxxiii

the craw-fish of the ( Mammoth Cave,' and numerous insects and
arachnidans).

Lepidopus, Trichiurus, Stromateus, exemplify fishes which lose
the ventral fins entirely with age ; they are rudimental in Gem-
pylus, Psettus and Centronotus ; Soleotalpa has only the right
ventral developed and the left rudimental ; the pectoral fins are
rudimental in many pleuronectoids, either on both sides, as in
Buglossus and Achirus., or on the blind side only, as in Monochir
and many species of Synaptura. The ( adipose fin ' of certain
Siluroid and Salmon old fishes is a rudimental dorsal, sometimes
showing traces of rays.

The prevalence of birds in New Zealand without wings (Dinor-
nis\ or too feebly developed for the purpose of flight (Apteryx,
Brachypteryx, Notornis, &c.), is associated with the absence in
those islands of any higher form of life exercising destructive
mastery of organisation, until the immigration of the human race.
The wings of such birds, like the eyes of the cavern fishes and
crustaceans, would seem to have degenerated for want of use ;
their legs, by which locomotion was exclusively exercised, to have
gained in size and strength.

LAMAKCK,1 adverting to observed ranges of variation in certain
species, affirmed that such variations would proceed and keep pace
with the continued operation of the causes producing them ; that
such changes of form and structure would induce corresponding
changes in actions, and that a change of actions, when habitual,
became another cause of altered structure ; that the more frequent
employment of certain parts or organs leads to a proportional
increase of development of such parts, and that as the increased
exercise of one part is usually accompanied by a corresponding
disuse of another part, this very disuse, by inducing a proportional
degree of atrophy, becomes an added element in the progressive
mutation of organic forms.

Concomitant changes of climate, and other conditions of a coun-

1 Philosophic Zoologique, torn. i. chaps, iii. vi. vii.
VOL, I. b

xxxiv PKEFACE.

try affecting the sustenance or well-being of its indigenous animals,
may lead not only to their modification but to their destruction. I
have, in another work, pointed out the characters in the animals
themselves calculated to render them most obnoxious to such ex-
tirpating influences ; and have applied the remarks to the expla-
nation of so many of the larger species of particular groups of
animals having become extinct, whilst smaller species of equal
antiquity have remained.

( In proportion to its bulk is the difficulty of the contest which,
as a living organised whole, the individual of such species has to
maintain against the surrounding agencies that are ever tending
to dissolve the vital bond and subjugate the living matter to the
ordinary chemical and physical forces. Any changes, therefore,
in such external agencies as a species may have been originally
adapted to exist in, will militate against that existence in a degree
proportionate, perhaps in a geometrical ratio, to the bulk of the
species. If a dry season be gradually prolonged, the large mam-
mal will suffer from the drought sooner than the small one ;
if such alteration of climate affect the quantity of vegetable food,
the bulky Herbivore will first feel the effects of stinted nourish-
ment ; if new enemies are introduced, the large and conspicuous
quadruped or bird will fall a prey, whilst the smaller species con-
ceal themselves and escape. Smaller animals are usually, also,
more prolific than larger ones.' l

The actual presence, therefore, of small species of animals in
countries where larger species of the same natural families for-
merly existed, is not the consequence of any gradual diminution
of the size of such species, but is the result of circumstances,
which may be illustrated by the fable of the ' Oak and the Reed ; '
the smaller and feebler animals have bent and accommodated
themselves to changes which have destroyed the larger species.
They have fared better in the ' battle of life.'

Accepting this explanation of the extirpation of species as true,

1 On the Genus Dinornis (Part iv.), Zool. Trans., vol. iv. p. 15 (February 1850).

PREFACE. xxxv

MR. WALLACE J has applied it to the extirpation of varieties ; and
as these do arise in a wild species, he shows how such deviations
from type may either tend to the destruction of a variety, or to
adapt a variety to some changes in surrounding conditions, under
which it is better calculated to exist, than the type-form from
which it deviated.

ISTo doubt the type-form of any species is that which is best
adapted to the conditions under which such species at the time
exists ; and as long as those conditions remain unchanged, so long
will the type remain ; all varieties departing therefrom being
in the same ratio less adapted to the environing conditions of
existence. But if those conditions change, then the variety of the
species at an antecedent date and state of things may become
the type-form of the species at a later date, and in an altered
state of things.

In his work ( On the Origin of Species by Natural Selection,'2
MR. DARWIN more fully exemplifies, conjecturally, the reciprocal
influence of external conditions and inherent tendencies to variety,
in carrying on, as he believes, the deviations from type to specific
and higher degrees of difference.

All these, however, are conceptions of what may have, not
observations of what have, originated a species. Applied to
the structures which differentiate Troglodytes from Homo? or
Chiromys from Lemur* they are powerless to explain them : and
the structural differences in these instances are greater than in
many other species maintaining their distinction by sexual in-
capacity to produce fertile hybrids.

An innate tendency or susceptibility in an offspring to differ
from a parent is a fact of observation : when carried beyond a
certain point the issue is called, from its rarity, a f monster.' But
this tendency and its results are independent of internal volitions
and external influences.

1 Proceedings of the Linnean Society, August 1858, p. 57. - Svo. 1859.

3 On the Classification and Geographical Distribution of the Mammalia, Svo. 1859,
p. 92. 4 Transactions of the Zoological Society, vol. v. p. 86.

b2

xxxvi PREFACE.

Therefore, with every disposition to acquire information and
receive instruction as to how species become such, I am still com-
pelled, as in 1849, to confess ignorance of the mode of operation
of the natural law or secondary cause of their succession on the
earth. But that it is an ( orderly succession,' or according to
law,1 and also ' progressive ' or in the ascending course, is evident
from actual knowledge of extinct species.

The inductive basis of belief in the operation of natural law or
' secondary cause ' in the succession and progression of organised
species, was laid by the demonstration of the unity of plan under-
lying the diversity of animal structures, as exemplified by the
determinations of special and general homology ; by the discovery
of the law of ' Irrelative repetition ; ' by observation of the ana-
logies of transitory embryonal stages in a higher animal to the
matured forms of lower animals ; and by the evidence that in the
scale of existing nature, as in the development of the individual,
and in the succession of species in time, there is exemplified an
ascent from the general or lower to the particular or higher con-
dition of organism.

The most intelligible idea of homologous parts in such series
is that they are due to inheritance. How inherited, or what may
be the manner of operance of the secondary cause in the pro-
duction of species, remains in the hypothetical state exemplified
by the guess-endeavours of LAMARCK, DARWIN, WALLACE, and
others.

In the lapse of ages, hypothetically invoked for the mutation
of specific distinctions, I would remark that Man is not likely to
preserve his longer than, contemporary species theirs. Seeing
the greater variety of influences to which he is subject, the
present characters of the human kind are likely to be sooner
changed than those of lower existing species. And, with such

1 BADEN POTVELL, quoting from my Work ' On the Nature of Limbs,' 8vo. 1849, p.
86, writes: — ' To what actual or secondary cause' ('Essays on the Unity of Worlds,'
1855, p. 401), instead of, 'To what natural laws or secondary cause the orderly suc-
cession and progression of species may have been committed, we are, as yet, ignorant.'

PREFACE. xxxrii

change of specific character, especially if it should be in the
ascensive direction, there might be associated powers of pene-
trating the problems of zoology so far transcending those of our
present condition, as to be equivalent to a different and higher
phase of intellectual action, resulting in what might be termed
another species of zoological science.

With the present psychical and structural characteristics of the
human species, it may be reasonably concluded that those of other
existing species, especially of the distinctly marked vertebrate
classes, will be, at least, concurrent and co-enduring ; and, in that
sense, we may accept the dictum of the French zoologist:- -f La
stabilite des especes est une condition necessaire a Fexistence de
la science d'Histoire Naturelle.' At the same time, indulging with
LAMARCK in hypothetical views of transmutative and selective
influences during aeons transcending the periods allotted to the
existence of ourselves and our contemporaries, as we now are, we
may also say: — ( La nature n'offre que des individus qui se suc-
cedent les uns aux autres par voie de generation, et qui provien-
nent les uns des autres. Les especes parmi eux ne sont que
relatives, et ne le sont que temporairement.'

Pleistocene

lauie oj Virata ana uraer oj appearance

of Vertebrate Life upon the Earth.

•

3

a

c3

•d

i

VI

•r-t

m

*

VI
<D

ft
0)

fi
OJ

o

VI
• rH

DQ

FH

FH

0

02
O
4»a

f*

a>

4^>

0)
H

MAN by Eemains.

TERTIARY or NEOZOIC

Turbary.
Shell Marl.
Glacial Drift, i g
Brick Earth. JjJ

\ by Weapons.

Norwich "j
Eed r Crag.
Coralline /

Pliocene

Mammals under present geographical
distribution.

o*

Faluns.
Molasse.

Miocene

Euminantia. ^ Quadrumaua.
& Proboscidia. ,v o**

Gyps.

London )
™ ,. h Clays.

Plastic J J

[Eocene

^ ^ ^

Eodentia. ^cS"

Ungulata. Carnivora.

SECONDARY or MESOZOIC

Maestricht.
Upper Chalk.
Lower Chalk.
Upper Greensand.
Lower Greensand.

Cretaceous

Cycloid. ] Mosasaurus.
Ctenoid, j FISHES< Polyptychodon.
BIKDS, by Bones.
Procoelian Crocodilia.
Pterodactyles.

Weald Clay.
Hastings Sand.

d

"S

Iguanodon.
>^^lVT:iT'<iit>iiil'j — -~Cliplomfl, bv Bonp«!

Kimmeridgian.
Oxfordian. p
Kellovian.
Forest Marble.
Bath-Stone.
Stonesfield Slate.
Great Oolite. ,4
Lias.

o

Pliosaurus.
Birds by Bones and Feathers. g'

Marsupials. ^ ^ ^ g

Ichthyopterygia. "V O /3y ^
MAMMALIA .,.

U. New Eed Sandstone.
Muschelkalk.
Bunter.

<a

•H
5

AVES, by Foot-prints.
Sauropterygia.
Labyrinthodontia,

PRIMARY or PALAEOZOIC

Marl-Sand.
Magnesian Limestone.
L. New Eed Sandstone.

PH

•M Sauria.
" Chelonia, by Foot-prints.

Coal-Measures.
Mountain Limestone.
Carboniferous Slate.

1

§ REPTILIA ganocephala.

W 'S. •

U. Old Eed Sandstone.
Caithness Flags.
L. Old Eed Sandstone.

1

O

0>

fi

^ /ganoid. ^
'3 placo-ganoid. ^
PISCES! placoid. ^°

Wenlock.

I

%°'

Llandeilo.

^ \^X^-^c^V°V°\^%cV

Lingula Flags.

02

^ ^ ^^ &<3& ^

Cambrian.

Fucoicls. Zoophytes.

CONTENTS, OR SYSTEMATIC INDEX.

CHAPTER I.
CHARACTERS OF VERTEBRATES.

SECTION PAGE

1. Developmental characters . . 1

2. Structural characters .... . . 3

3. Piscine modification .... ..... 4

4. Reptilian modification ... . 5
o. Avian modification .... ... 6

6. Mammalian modification . 6

7. Genetic and thermal distinctions . 6

8. Sub-classes of Haematocrya, or Cold-blooded Vertebrates ... 7

9. Orders of Hsematocrya 9

CHAPTER II.
OSSEOUS SYSTEM OF H.EMATOCRYA.

10. Composition of Bone ... .... 19

11. Development of Bone , . . 21

12. Growth of Bone ...... 23

13. Classes of Bone ........... 26

14. Type-segment, or Vertebra .... .27

15. Archetype Skeleton . . 29

16. Development of Vertebrae ......... 30

17. Vertebral column of Fishes .... .... 34

18. Vertebral column of Batrachia ........ 46

19. Vertebral column of Ichthyopterygia ....... 50

20. Vertebral column of Sauropterygi a . . . . . . . 51

21. Vertebral column of Ophidia ........ 53

22. Vertebral column of Lacertia ........ 57

23. Vertebral column of Chelonia ........ 60

24. Vertebral column of Crocodilia ........ 65

25. Vertebral column of Pterosauria ........ 70

26. Development of the Skull 71

27. Skull of Plagiostomi 76

28. Skull of Protopteri .......... 82

xl CONTENTS.

SECTION PAGE

29. Skull of Batraclria ....

30. Skull of Osseous Fishes ....

31. Skull of Chelonia 126

32. Skull of Crocodilia 135

33. Skull of Ophidia H6

34. Skull of Lacertilia 154

35. Skull of lehthyopterygia 158

36. Skull of Dicynodontia 159

37. Skull of Pterosauria . . . . . . . . . . 161

38. Scapular arch and appendages of Hsematocrya 161

39. Pectoral limb of Fishes 163

40. Pectoral limb of Reptiles 169

41. Pelvic arch and limb of Fishes 179

42. Pelvic arch and limb of Reptiles . . . . . . . . 181

43. Dermoskeleton of Fishes ......... 193

44. Dermoskeleton of Eeptiles ......... 198

CHAPTER III.
MUSCULAR SYSTEM OP H^EMATOCRYA.

45. Structure of Muscle 200

46. Myology of Fishes 202

47. Myology of Reptiles .......... 215

48. Locomotion of Fishes .......... 243

49. Locomotion of Serpents ......... 259

50. Locomotion of Limbed Reptiles ........ 262

CHAPTER IV.
NERVOUS SYSTEM OF KLEMATOCRYA.

51. Nervous Tissues ......... 266

52. Myelencephalon of Fishes ......... 268

53. Myelencephalon of Reptiles 290

54. Myelencephalic membranes in Hgematocrya 296

55. Nerves of Fishes ........... 297

56. Nerves of Reptiles .......... 309

57. Sympathetic nervous system . . . . . . . . . 318

58. Sympathetic nervous system of Fishes ....... 320

59. Sympathetic nervous system of Reptiles . . . . . . 321

60. Appendages of the Nervous System ....... 323

61. Organ of Touch in Hsematocrya ........ 325

62. Organ of Taste in Reptiles . . . . . . . . . 327

63. Organ of Smell in Hamatocrya ........ 328

64. Organ of Sight in Fishes ......... 331

65. Organ of Sight in Reptiles ......... 337

66. Organ of Hearing in Fishes ......... 342

67. Organ of Hearing in Reptiles .... ... 347

68. Electric Organs of Fishes 350

CONTENTS. xli

CHAPTER V.
DIGESTIVE SYSTEM OF H^EMATOCRYA.

SECTION PAGE

69. Dental Tissues 359

70. Teeth of Fishes 368

71. Teeth of Eeptiles 385

72. Alimentary canal of Fishes .... . . 409

73. Liver of Fishes 425

74. Pyloric appendages and pancreas of Fishes ...... 428

75. Alimentary canal of Reptiles ... . 433

76. Liver of Reptiles ....... 448

77. Pancreas of Reptiles ....... 453

CHAPTER VI.
ABSORBENT SYSTEM OF HJEMATOCRYA.

78. Connective tissue : serosity ..... 455

79. Absorbents of Fishes .... 456

80. Absorbents of Reptiles ...... . . 458

CHAPTER VII.
CIRCULATING AND RESPIRATORY SYSTEMS OF ILEMATOCRYA.

81. Blood of Fishes . . .... 463

82. Veins of Fishes . .... 464

83. Heart of Fishes ..... 470

84. Gills of Fishes .... . 475

85. Arteries of Fishes ...... . 488

86. Air-bladder of Fishes . 491

87. Blood of Reptiles . 500

88. Veins of Reptiles 501

89. Heart of Reptiles 505

90. Gills of Batrachians ... . 512

91. Arteries of Reptiles .... 516

92. Lungs of Reptiles 521

93. Larynx of Reptiles .... 527

94. Respiratory actions of Reptiles . . 530

CHAPTER VIII.
URINARY SYSTEM OF HJ5MATOCYRA.

95. Kidneys of Fishes ... . 533

96. Kidneys of Reptiles . . . 537
9". Adrenals of Hsematocrya ... 542

YOL. I. C

xlii CONTENTS.

CHArTEK IX.

TEGUMENTARY SYSTEM OF II^MATOCHYA.

SECTION PAGE

98. Composition of Tegument ,"> i.>

99. Teguments of Fishes 546

100. Teguments of Keptiles 550

CHAPTER X.
PECULIAR AND DUCTLESS GLANDS AND REPRODUCIBLE PARTS.

101. Scent-glands of Eeptiles 562

102. Poison-glands of Reptiles ......... 563

103. Thyroid body or gland of Hsematocrya ....... 564

104. Thymus body or gland of Reptiles ....... 565

105. Reproducible parts in Hsematocrya ....... 566

CHAPTER XI.
GENERATIVE SYSTEM OF HJEMATOCRYA.

106. Male organs of Fishes 568

107. Female organs of Fishes 571

108. Male organs of Batrachians 576

109. Male organs of Reptiles 579

110. Female organs of Batrachians and Reptiles ...... 583

CHAPTER XII.
GENERATIVE PRODUCTS AND DEVELOPMENT OF ILEMATOCRYA.

111. Semination of Hsematocrya 589

112. Ovulation in osseous Fishes and Batrachians ..... 592

113. Ovulation in cartilaginous Fishes and scaled Reptiles . . . . 597

114. Fecundation in Fishes 599

115. Development of Fishes .......... 601

116. Growth and nests of Fishes ......... 611

117. Fecundation in Reptiles ......... 614

118. Oviposition in Reptiles ......... 616

119. Development of Batrachians . . . . . . . . . 619

120. Development of Reptiles 630

ERRATA.

Below Cuts 134, 135, 136, 137, for ' xxxm.,' read ' xxiu '

Page 396, eight lines from top, /or ' premaxillary,' read ' vomerine.'

,, 448, eighteen lines from top, /or ' timical,' read ' tumid.'

,, 512, eleven lines from bottom, transpose ' fig. 399, R ' to tenth line, after ' ventricle.'

„ 6'25, four lines from top, for ' fig. 435,' read ' fig. 424, &.'

„ 630, five lines from bottom, for ' bodies,' read ' borders.'

THE

ANATOMY OF VERTEBRATES.

CHAPTER I.

CHARACTERS OF VERTEBRATES.

§ 1. Developmental characters. — Vertebrates, like lower animals,
begin in a semifluid nitrogenous substance called ( plasma,' fig. 1 , A,
a ; primarily differentiating into albumen, fibrine, lemma, ib. £, c l,
nuclei and cells ; in winch lat-
ter form the individuality of
the new organism first dawns
as a nucleated ( germ-cell ' or $
germinal vesicle, ib. d.

By the evolution of albumi-
nous granules and oil-particles
plasma becomes f yolk,' fig. 1,
B,C ; the germinal vesicle may
be obscured by endogenous
multiplication of granules, gra-
nular cells and oil-globules,
which combine with those of
the yolk to form its germinal
part : an outer layer of ( lem-
ma,' D, ch, completes the un-.
impregnated vertebrate egg.

For further developement
another principle is needed,
viz. the hyaline nucleus or

•* Stages of derelopement of the ovarian egg of a vertebrate

prodllCt Of the Sperm-Cell, fig. animal (Gasterosteus). CLXXVI.

2, called ( spermatozoon.' Its reception by the egg, as at a, I, fig.

3, is followed by the formation of a germ-mass. This mass is due

1 Gr. lemma, skin ; also called 'primary' or 'basement' membrane ; distinguished,
through its relations, as * ncurilemma, sarcolemma, adcnolemma ' or the limitary
membrane of gland-follicles, £c.

ANATOMY OF VERTEBKATES.

to a series of self-splittings of the impregnated centre, which

' fissiparous' progeny assimi-
late or incorporate more or
less of the yolk. In fig. 4, A,
d is the impregnated germ-
yolk ; c the fluid between it
and the zona,^/; f is albumen
from which the chorion, cho,
arises. In B, fig. 4, is shown
the first division or segmen-
tation of the germ-yolk ; c
shows the second division; and
D, a later stage in which the
properties of the impregnated

Stages of developement of the ovarian egg of a verte- haV6

brate animal (cowled). CLXXVI. and distributed by fissiparous

multiplication amongst the countless nucleated cells which form
the germ-mass.

Thus far the vertebrate germ resembles in form, structure, and
2 behaviour, the infusorial monad and the germ-

stage of invertebrates. The next step impresses
upon the nascent being its ' vertebrate ' type.
Linear rows of the nucleated cells coalesce and
become converted into the nervous axis, which
under the form or appearance of a double chord,
fig. 5, ch, marks the dorsal or f neural ' aspect
with three of the embryonal rudiment. The nutritive organs

spermatoa, and their „ . . ., ., , i •

nucleus the 'spermato- grow irom the opposite side. Along the mter-

zoon ' (Cock). CLXXVII. • i • i j i i • P-I 11

space is laid the basis ot the skeleton, as a
gelatinous cylinder, in a membranous sheath, called f notochord,' *
3 which developes a pair of plates ( neurad ' 2

to enclose the nervous axis, and a pair of
plates ( haamad ' 3 to enclose the vascular
axis and organs of vegetative life. Flesh
and skin coextend with the enclosing plates.
This formation of two distinct parallel
cavities — ( neural ' and e haemal ' -under
symmetrical guidance in the vertical or
{ neuro-haamal ' direction, with a repeti-
tion of parts 011 the right and left sides,
transverse or ( bi-lateral '

I

Vertebrate egg, impregnated by the
spermatozoa (Rabbit). CLXXVI.

1 The ' chorda dorsalis' of embryologists. 2 Backward in man, upward in beasts.

3 Forward in man, downward in beasts.

ANATOMY OF VERTEBRATES.

3

Stages of developement of a vertebrate germ (Rabbit), evil.

symmetry, constitutes the chief developmental characteristic of
the vertebrate animal.

The twofold symmetry is shown in the bone-segment, fig. 7 ;
also in the flesh-segment surrounding the skeletal one in fig. 6,
in which the mid point 4

marks the f noto-
chord ; ' with the neu-
ral canal above, the
haBinal canal below ;
both surrounded by
the two neural and
two haemal masses of muscles on each side.

The lancelet, Branckiostoma, fig. 23, superinduces its distinc-
tive characters upon this stage. Aponeurotic septa accompany the
pairs of nerves and divide the longitudinal muscular masses into
segments. At the next rise segmentation is shown by the develop-
ment of cartilage, forming pairs of plates, fig. 5, v,
commonly corresponding with the pairs of nerves
sent off from the neural axis, and with the pairs
of vessels from the haemal axis. As these plates
ossify, ossification commonly also begins at cor-
responding points of the notochord, dividing it
into as many central parts as there are peri-
pheral plates or arches, and constituting skeletal
segments or ' vertebrae ; ' according, or reducible
to, the type, fig. 7.

§ 2. Structural characters. — The series of ( vertebrae/ under
their several modifications, as the neural or haemal organs
may predominate, constitute the vertebral column. The
neural axis consists of ' encephalon' or brain, and of
( myelon' or spinal chord. The organs of the five senses
- touch, taste, smell, hearing, and sight - - are usually
present. The blood-discs, fig. 8, speedily acquire the red
colour which, by their number and minuteness, they

* J Section of

impart to the whole blood. The heart is a compact mus-

Corm of a Rabbit (Barry)

OF

cular organ, of two or more cavities, propelling the blood, ment;tauofa
through a closed system of arteries and veins, directly to
the breathing-organ, and, in most vertebrates, directly also to the
body. The breathing-organ communicates with the pharynx. The
alimentary canal has distinct receptive and expellent apertures,
usually at opposite ends of the trunk. The mouth is provided
with two jaws, placed one above or before the other, working
in the direction of the axis of the body. The muscles surround

B 2

ANATOMY OF VERTEBRATES.

the bony or gristly levers on which they act. The limbs do not
exceed two pairs. The sexes are distinct, and the individual
is developed directly from an impregnated ovum. Under the

vertebrate plan of structure animals
grow to a greater size and live a
longer time, than under any of the
invertebrate plans.

^^^^1 § 3. Piscine modification. — All
pleurapophysis vertebrates, during more or less of
their developmental life-period, float
in a liquid of similar specific gravity
to themselves. A large proportion,

constituting the lowest organised and

~ ~

first developed forms of the pro-
vince, exist and breathe in water,

and are called ( fishes.' Of these a few retain the primitive
vermiform condition and develope no limbs : in the rest they are
( fins,' of simple form, moving by one joint upon the body, rarely
adapted for any other function than the impulse or guidance

8

||neural spine

zygapophysis J||% neurapophysis
cliapophysis _.f^ ^_

£ 2~~rc |LI " '''"''•vor*-

parapopliysis ^i^_^,_x3

ijJiff hremapophysis
zygapophysis :;F «O

ll hajmal spine
Ideal typical vertebra. CXLV.

d

g

Blood-discs, each magnified 300 diameters linear, a, Man ; &, Musk-deer ; c, Goose ; d, Crocodile ;

e, Frog ; /, Siren ; g, Cod-flsh ; 7i, Skate. CXLV.

of the body through the water. The shape of the body is usually
such as is adapted for moving with least resistance through a
liquid medium. The surface of the body is either smooth and
lubricous, or is smoothly covered by overlapping scales, is rarely
defended by bony plates or roughened by tubercles, still more
rarely armed with spines.

The neural axis presents but one local enlargement, at the fore
end, forming the ( encephalon ; ' it is small, and consists of a suc-
cession of simple ganglionic masses, most of which are appro-
priated to the function of a nerve of special sense. Touch is
feebly exercised, and an organ for that sense rarely developed.

ANATOMY OF VERTEBRATES. 5

The tongue, as an organ of taste, is hardly conspicuous; the
framework supporting it relates chiefly to the mechanism of swal-
lowing and breathing, and is suspended to a pedicle common to it
and the mandible. Of the organ of hearing there is no outward
sign ; but the essential internal part or ( labyrinth ' is present,
and its semicircular canals are, in most fishes, largely developed.
The labyrinth is devoid of a ( cochlea,' and is rarely provided with
a proper chamber, but is lodged, in common with the brain, in
the cranial cavity. The eyes are usually large, seldom defended
by eyelids, and never served by a lacrymal apparatus. The ali-
mentary canal is commonly short and simple, with the divisions
less clearly marked than in higher vertebrates; the short and
wide gullet being hardly distinguishable from the stomach. The
pancreatic function appears to be performed by commonly more
or fewer crecal appendages to the duodenum. The heart consists
essentially of one auricle receiving the venous blood, and one
ventricle propelling it to the gills, or organs submitting that blood
in a state of minute subdivision to the action of aerated water.
From the gills the arterial blood is carried over the entire body
by vessels, the circulation being aided by the contraction of the
surrounding muscles. The blood is cold, or with a temperature
rarely above that of the surrounding medium. The coloured
discs are, in some fishes, subcircular, fig. 8, g\ in others,
subelliptical, ib. h, or elliptical ; comparatively large, but not
the largest amongst vertebrates. The primordial renal glands
(corpora Wolffiana) are persistent, and secrete the urine from
venous blood. Such are the leading anatomical characters of the
class Pisces — Fishes.

§ 4. Reptilian modification. — Many fishes have a bladder of air
between the digestive canal and kidneys, which, in some, com-
municates by an air-duct with the gullet ; but its office is chiefly
hydrostatic. When, in the rise of structure, this air-bladder
begins to assume the vascular and pharyngeal relations, with the
form and cellular structure of lungs, the limbs acquire the
character of feet; at first, as in Lepidosiren, fig. 41, 99, thread-
like and many-jointed - - then bifurcate, or two-fingered, with the
ordinary elbow and wrist-joints of land-limbs (Amplmima), fig.
100, B, D, — next, three-fingered, as in Proteus, — or four-fingered,
but reduced to the pectoral pair, as in Siren. From these gill-
retaining transitional forms, up to and including crocodiles, all
cold-blooded vertebrates, with lungs, breathing air directly, are
called Reptiles (Reptilia, Cuv.). The heart has two auricles;
the ventricle, in most, is imperfectly divided, and more or less of

6 ANATOMY OF VERTEBRATES.

the venous blood is mixed with the arterial blood which circulates
over the body. The lungs retain the form of bags, with cellulo-
vascular walls, varying as to thickness, and are situated, with the
other organs of vegetative life, in a common thoracic-abdominal
cavity.

§ 5. Avian modification.- -When the lungs become spongy, and
the cavity of the air-bag is obliterated by the multiplication of
vascular cellules, and when a four-chambered heart transmits the
venous blood to the lungs, and pure arterial blood to the body,
the temperature is raised, and is maintained at from 90° to 105°
Fahr., whatever may be that of the surrounding medium. Of
these hot-blooded vertebrates, one class has the lungs fixed, and
communicating with air-cells extending into the abdomen, and

o ~

usually other parts of the body ; this class is oviparous, is clothed
with feathers, and has the pectoral limbs modified as wings ; it is
called Aves — Birds.

§ 6. Mammalian modification. — In the other class of warm-
blooded animals, the spongy lungs are freely suspended and
confined to a thoracic cavity, defined by a midriff from the
abdomen ; the class is hair-clad, viviparous, and suckles the
young, whence it is called Mammalia - - Mammals.

§ 7. Genetic and thermal distinctions.- The broad and well-
marked characters afforded by the respiratory system will probably
give permanence to the division, so convenient for most purposes,
of the vertebrate province into the four great classes above
defined, viz. Pisces., Reptilia, Aves, Mammalia.

But many important relations and affinities are thereby masked.
Although the last two classes agree, as ' hot-blooded vertebrates,'
in their higher cerebral developement, and in the more complex
heart and lungs, birds, by genetic and developmental characters,
as well as by the general plan of their organisation, are more
intimately and naturally allied to the oviparous saurian s than to
the viviparous mammals. In their generation and development,
modern batrachians differ from other cold-blooded air-breathers,
and agree with fishes. Present knowledge of extinct forms more
clearly exposes the artificial nature of the primary groups of the
oviparous vertebrates. An important link, the Pterosanria, or
flying reptiles, with wings and air-sacs, fig. 108, more closely
connecting birds with the actual remnant of the reptilian class, has
passed away. Other extinct orders (Ganocepliala and Laln/rintho-
dontia) have demonstrated the artificial nature of the distinction
between fishes and reptiles, and the close transitions that connect
together all the cold-blooded vertebrates.

ANATOMY OF VERTEBRATES. 7

Thus vertebrates might be binarily divided into oviparous, I.
II. in., and viviparous, iv. ; into aiiallantoic or branchiate and
allantoic or abranchiate ; into H&matothermal,1 having the four-
chambered heart, spongy lungs, hot blood, and Hcematocryal?
having less perfect breathing organs, less complex heart, with cold
blood ; and each of such divisions are artificial and convenient.
It suits my present purpose to adopt the latter.

§ 8. Subclasses of Hcematocrya. - With the best insight —
peering into the dark vistas of the remote past - - that one can
command into the nature of the strange forms which then

o

perished, and combining with pakeontological research the results
of anatomical and developmental scrutiny of existing vertebrates,
the following seem to be the best defined cold-blooded groups,
each with such characters in common as leads to their beino; called

O

' natural,' and of a value which may be expressed by the term
6 sub-class.'

I. DERMOPTERI. III. PLAGIOSTOMI.

II. TELEOSTOMI. IV. DIPNOA.

V. MONOFNOA.

Subclass I. DERMOPTERI. — Body vermiform, limbless; endo-
skeleton membrano- cartilaginous and notochordal,3 ribless ; skin
scaleless, lubricous ; a vertical fin-fold bordering the hind part of
the body, without fin-rays ; myelon opaline, ductile, elastic ; no
sympathetic nerve ; organ of smell single ; eyes wanting, or very
small ; "optic nerves not crossing each other ; auditory labyrinth
of one or two semicircular canals ; mouth jawless, or suctorial ;
alimentary canal straight, simple, without crecal appendages,
pancreas, or spleen. Branchial function independent of the mouth ;
heart, without ' bulbus arteriosus ; ' a pulsatile portal sinus ; no
swim-bladder ; testes and ovaria elongated plates without ducts ;
generative outlet peritoneal ; ova numerous, small, simultaneously
developed, and impregnated externally ; cleavage of yolk entire ;
no amnios or allantois ; a metamorphosis, as, e. g. from Ammo-
ccetes to Petromyzon, after the third year from the egg.

Subclass II. TELEOSTOMI.4- -Body pisciform, with medial and

1 Gr. /Kiima, blood ; thermos, hot.

2 Gr. haima, blood; cruos, cold.

Retaining the notochord or primitive basis of the vertebral column.

This word (from Gr. telos, end or completion ; fifonui, mouth ;) refers to the com-
pletion of the mouth by opposing upper and lower jaws, and also to its terminal
position, opening at the fore end of the head.

8 ANATOMY OF VERTEBRATES.

parial fins, supported by rays ; endoskeleton in most, more or
less ossified ; hyoid arch attached to tympanic pedicle ; scapular
arch attached to the occiput ; no sternum : skin defended by scales
or plates ; brain with predominant mesencephalon ; myelon opake,
inelastic ; a sympathetic nerve ; organ of smell double ; eyes usually
large, with bony sclerotic ; auditory labyrinth with three semi-
circular canals, in the cranial cavity ; mouth formed by upper and
lower jaws, opening at the fore part of the head, and admitting the
respiratory currents ; intestine, in most, with pyloric appendages
and spleen ; anus in front of urethra ; air-bladder in most ; gills,
free ; branchial outlet single on each side, defended by a bran-
chiostegal flap, with one or more rays ; testes (' milt ') and ovaries
(* roe ') large, with continuous ducts in most ; ova very numerous
and small, simultaneously developed, and impregnated, usually,
externally ; no amnios or external allantois.

Subclass III. PLAGIOSTOMI. — Endoskeleton cartilaginous, or
partially ossified; scapular arch detached from occiput; exo-
skeleton as osseous granules or tubercles ; body with medial and
parial fins, the hinder pair pelvic in position ; caudal-fin with
produced upper lobe ; brain with the prosencephalon predominant ;
auditory labyrinth in a special chamber ; mouth, in most, a wide
transverse slit, opening below the head; intestine with a spiral
valve, pancreas, and spleen ; no air-bladder ; bulbus arteriosus
with numerous rows of valves ; gills, in most, fixed, and with
several branchial outlets on each side ; testes of moderate size,
with sperm-duct and copulatory apparatus ; ovaries with few and
large ova, successively developed and conveyed away by a
detached oviduct ; ova impregnated and, in some, developed in-
ternally ; embryo without amnios or allantois, and with deciduous
external gills.

Subclass IV. DIPNOA. — Endoskeleton more or less ossified ;
ribs wanting, or short and free; parial members as legs ; brain with
predominant prosencephalon ; optic nerves not decussating ; audi-
tory labyrinth in a special chamber, but with only the ( fenestra
vestibuli ; ' nostrils communicating with the mouth ; intestine,
with pancreas and spleen ; air-bladder as a pair of lungs, com-
municating by a duct and glottis with the ha3mal side of the
pharynx; heart, in most, with one ventricle and two auricles.
Testes of moderate size, with sperm-ducts, but no intromittent
organs or claspers ; ovaries with detached oviducts ; ova simulta-
neously developed, and, in most, impregnated externally. Embryo
without amnios or allantois, and with external gills.

ANATOMY OF VERTEBRATES. 9'

Subclass V. MONOPNOA. — Encloskeleton ossified ; exoskeleton
in most as horny scales, in some as bony scutes ; one occipital
conclyle ; vomer usually single ; trunk-ribs long and curved. Brain
with predominant prosencephalou. Labyrinth with both fenestra
vestibuli and fenestra rotunda ; a tympanum in most ; lungs ;
heart with two auricles, and with the ventricle more or less
completely divided. Testes with ducts and intromittent organ.
Ovaria with detached oviducts. Ova successively developed,
impregnated with copulation. An ainnios and allantois. No
metamorphosis.

§ 9. Orders of H^EMATOCKYA.

Subclass I. Order I. CIKROSTOMI.

Body compressed ; mouth a longitudinal fissure with sub-rigid
cirri on each side. Pulsating vessels or sinuses in place of heart.
Blood pale ; free pharyngeal branchial filaments, and a branchial
dilatation of the ossophagus.

Gen. Branchiostoma. Ex. Lancelet.

Order II. CYCLOSTOMI.

Body cylindrical; heart distinct; branchial artery without
bulb ; branchia3 sacciform, with external spiracles, six or seven on
each side, blood red. Mouth subcircular, suctorial, but longitu-
dinal when closed. Olfactory sac communicating with, or produced
into, a canal.

Gen. Mijxine. Ex. Hag-fish.

Petromyzon. Ex. Lamprey.

Subclass II. A. Arterial bulb with one pair of valves ; optic
nerves decussating ; vertebras biconcave.

Order III. MALACOPTERI.

Skin, in most with cycloid scales, in a few with ganoid plates ;
rarely naked. Fins supported by rays, all of which (save the first
in the dorsal and pectoral, in some) are ( soft,' or many-jointed ;
a swim-bladder and air-duct ; peritoneal outlets in many.

10 ANATOMY OF VERTEBRATES.

Suborder I. APODES.

Fam. 1. SymbranchidcB. Ex. Cuchia.

2. Mur&nidcR. Ex. Eel.

3. Gymnotidcs. Ex. Gymnotus.

Suborder II. ABDOMINALES.

Fam. 1. Heteropygii. Ex. Amblyopsis.

2. Clapeidce. Ex. Herring.

3. Salmonidcs. Ex. Salmon.

4. Scopelid(R. Ex. Saurus.

5. Characinidce. Ex. Myletes.

6. Galaxidce. Ex. Galaxias.

7. Esocidce. Ex. Pike.

8. MormyridcE. Ex. Mormyrus.

9. CyprinodontiddB. Ex. Umber.

10. Cyprinidce. Ex. Carp.

11. Siluridce. Ex. Sheat-fish.

12. Alepisauridce. Ex. Marine Sheat-fish.

Suborder III. PHARYNGOGNATHI.
Fam. 1, Scomber-esocidce. Ex. Saury-Pike.

Order IV. ANACANTHINI.

Endoskeleton ossified ; exoskeleton in some as cycloid, in others
as ctenoid scales ; fins supported by flexible many-jointed rays ;
ventrals beneath or in advance of the pectorals, or wanting ; swim-
bladder, when present, without a duct.

Fam. 1. Ophididce. Ex. Ophidium.

2. Gadidce. Ex. Cod.

3. Pleuronectidce. Ex. Plaice.

Order V, ACANTHOPTEKI.

Endoskeleton ossified ; exoskeleton, in most, as ctenoid scales ;
fins with one or more of the first rays unjointed or inflexible
spines ; ventrals, in most, beneath or in advance of the pectorals ;
duct of swim-bladder obliterated.

ANATOMY OF VERTEBRATES. 11

Suborder I. PPIARYNGOGNATHI.

Fam. 1. Chromidce. Ex. Chromis.

2. Cyclo-labridce. Ex. AVrasse.

3. Cteno -lab r idee. Ex. Pomacentrus.

Suborder II. ACANTHOPTERI VERI.

Fam. 1. Prrcidce. Ex. Perch.

2. Sqiiammipennes. Ex. Chastodon.

3. SparidcB. Ex. Sea-bream, Gilthead.

4. Scicenidce. Ex. Maigre.

5. Ldbyrinthobranchii. Ex. Anabas or Tree-climber.

6. Muyilidce. Ex. Mullet.

7. Atlierinidce. Ex. Sand-smelt.

8. SplujrainidcR (cycloid). Ex. Barracuda.

9. ScombcridfB (cycloid). Ex. Mackerel.

10. Sclerof/t'iildtf. Ex. Gurnard, Miller's thumb.

11. Taitioidci. Ex. Riband-fish.

12. Teuthyidce. Ex. Lancet-fish,

13. Fistnl<irid(E. Ex. Pipe-mouth.

14. Gobiidce. Ex. Goby.

15. BlenniidcB (cycloid). Ex. Wolf-fish.

16. Lopliiida* (skin muricate or naked). Ex. Angler.1

Order VI. PLECTOGXATHI.

Endoskeleton partly ossified ; exoskeleton as ganoid scales,
plates, or spines ; ventrals wanting in most ; maxillary and pre-
maxillary immoveably connected on each side of the jaw ; swini-
bladder without air-duct.

Suborder SCLERODERMI.
Fam. 1. B alistiii i. Ex. File-fish.

Suborder APLEURI (ribless).

Fam. 1. Ostraeiontidce. Ex. Trunk-fish.
2. GymnodontidcB. Ex. Globe-fish.

1 This selection of the chief family-diversities of the vast, acanthopterotts order is
designed, like the families cited under other orders, merely to exemplify it by familial-
fishes with vernacular names. For the characters and affinities of all the present
known acanthopterous ftimilie^, see Dr. Gun tiler's excellent woik, CLXXIV.,
vol. iii.

12 ANATOMY OF VERTEBRATES.

Order VII. LOPHOBKANCHII.

Endoskeleton partially ossified, without ribs ; exoskeleton ganoid ;
gills tufted ; opercular aperture small ; swim-bladder without air-
duct. Males marsupial.

Fain. 1. HippocampidcB. Ex. Sea-horse.
2. Syngnathidcs. Ex. Pipe-fish.

B. Arterial bulb muscular, with more than one row of valves.
Optic nerves not decussating.

Order VIII. GANOIDEL

Endoskeleton cartilaginous, partly bony, or ossified ; in a few
recent and in most paleozoic extinct forms, notochordal ; exo-
skeleton as ganoid scales or plates ; fins usually with the first
ray a strong spine ; caudal fin in most unsymmetrical ; a swim-
bladder, often cellular, and with an air-duct ; intestine in many
with a spiral valve.

Suborder I. LEPIDOGANOIDEI.

Fain. 1. Salamandroidei. Ex. Lepidosteus, Polypterus.

2. Pycnodontidte. Ex. Pycnodus.

3. Lepidoidei. Ex. Dapedius.

4. Leptolepidce. Ex. Leptolepis.

5. Acanthodei. Ex. Acanthodes.

6. DipteridcB. Ex. Dipterus.

7. Ccelacanthi. Ex. Ccelacanthus.

8. HoloptychidcB. Ex. Holoptychius.

Suborder II. PLACOGANOIDEI.
Fam. 1. Sturionidae. Ex. Sturgeon.

o

2. Ostracostei. Ex. Pterichthvs.

*/

Subclass III. Order IX. HOLOCEPHALL

Endoskeleton cartilaginous, subnotochordal ; cranial wall com-
plete ; tympanic pedicle confluent therewith ; endoskeleton as
placoid granules. Anterior dorsal fin with a strong spine ;
mouth terminal, beak- shaped; dental plates and columns fused
with the jaws. Optic nerves not decussating. Valves of bulbus
arteriosus multiserial. Gills laminar, with a small proportion of

ANATOMY OF VERTEBRATES. 13

the border free ; a single external gill-aperture on each side ;
opercular and branchiostegal rays. Oviparous ; ova few and large.

Fam. 1. Chimceridce. Ex. Chimasra, Callorhynchus.

2. EdaphodontidcB. Ex. Edaphodus, Ischiodus, Elasmodus.

Order X. PLAGIOSTOMI.

Endoskeleton cartilaginous or partially ossified; vertebra
biconcave ; exoskeleton as placoid granules or tubercles, spiny in
some. Mouth transverse on the lower surface of the head. Optic
nerves commissurally united, not decussating. Valves of bulbus
arteriosus multiserial. Gills attached to the skin by the outer
margin, with intervening gill-apertures, five or more in number,
on each side ; no operculum.

Suborder I. CESTRAPHOEI.1
(Spine in front of each dorsal fin ; back teeth obtuse.)

Fam. 1. Hybodontidce. Ex. Hybodus.

2. Cestraciontidce. Ex. Cestracion.

Suborder II. SELACHII. (Sharks, branchial apertures lateral.)

Fam. 1. NotidanidcE. Ex. Grey Shark.

2. Spinacidce. Ex. Piked Dog-fish.

3. Scylliadce. Ex. Spotted Dog-fish.

4. Nictitantes. Ex. Tope.

5. Lamnidce. Ex. Porbeagle.

6. Alopecidce. Ex. Fox Shark.

7. Scymniidce. Ex. Greenland Shark.

8. Squatince. Ex. Monk-fish.

9. Zyycenidce. Ex. Hammer-head Shark.

Suborder III. BATIDES. (Rays, branchial apertures inferior.)

Fam. 1. Pristidce. Ex. Saw-fish.

2. Rhinobatidce. Ex. Rhinobates.

3. Torpedinidce. Ex. Electric ray.

4. Raiidce. Ex. Skate.

5. Trygonidce. Ex. Sting Ray.

6. Myliobatidce. Ex. Eagle Ray.

7. CephalopteridcB. Ex. Cephalopterus.

1 Kestra, a weapon ; phero, I bear. Many extinct species of this group are known
only by their fossil weapons, called ' Ichthyodorulites.'

14 ANATOMY OF VERTEBRATES.

(Transitional) Order XI. PROTOPTERI.

Endoskeleton notochordal, partly cartilaginous, partly osseous ;
no occipital condyle ; vomer undivided ; temporal fossa3 roofed
over by bone ; pleurapophyses short, with free extremities ; exo-
skeleton as subcuticular cycloid scales ; scapular arch attached to
occiput ; proximal ends of hyoidean and tympano-mandibular
arches distinct. Vertical fin a continuous border to the com-
pressed tail. Pectoral and ventral fins subulate, many jointed ; the
former fringed beneath ; the latter pelvic in position ; the pelvis
unattached to the spine ; gills filamentous, free, in a branchial
chamber with a single vertical outlet; branchial arches uncon-
nected with the hyoid ; air-bladder double, lung-like, with air-duct,
glottis, and pulmonary vein. Prosencephalon predominant in
brain; nasal sacs sublabial with two remote extra-buccal aper-
tures ; auditory labyrinth in a distinct chamber ; bulbus arteriosus
long, with two longitudinal valves ; intestine with a spiral valve,
vent anterior to urethra ; ovaria distinct from oviducts.

Fam. Sirenoidei. Ex. Lepidosiren.

Subclass IV. Order XII. GANOCEPHALA. (Extinct.)

Endoskeleton notochordal and osseous ; no occipital condyle ;
vomer divided ; temporal fossa3 roofed over by bone ; hyoid arch
not connected with tympanic pedicle ; branchial arches (?) un-
connected with hyoid ; exoskeleton as subganoid scales ; pleur-
apophyses short and free. Teeth with converging inflected
folds of cement at their basal half. Pectoral and pelvic limbs
short, slender, three or four digitate ; natatory.

Genus Dendrerpcton.
Archeyosaurus.

Order XIII. LABYRINTHODONTIA. (Extinct)

Head defended, as in Ganocephala, by a continuous casque of
externally sculptured and unusually hard and polished osseous
plates, including the supplementary "post-orbital" and "super-
temporal ' bones, but leaving a " foramen parietale." Two occi-
pital condyles. Vomer divided and dentigerous. Vertebral
•bodies, as well as arches, ossified, biconcave. Pleurapophyses of
the trunk, long and bent. Exoskeletou, in some, as small ganoid

ANATOMY OF VERTEBRATES. 15

scales. Teeth rendered complex by undulation and side branches
of the converging folds of cement, whence the name of the order.

Genus Mhombopholis.

Labyrinthodon.

Order XIV. BATRACHIA.

Endoskeleton ossified ; two'occipital condyles ; vomer divided,
in most dentigerous ; temporal fossa? unroofed ; scapular arch
detached from occiput ; ribs as processes, or short, straight and free;
skin nude, often lubricous. Limbs digitate, trisegmental. Intestine
without spiral valve, vent posterior to urethra. Embryonal gills,
in some retained, in most lost ; with a metamorphosis associating
a tail-less body with pulmonary respiration and a heart of two
auricles and one ventricle.

Suborder T. OPIIIOMORPHA.
Fam. Cceciliadce. Ex. Cecilia.

Suborder II. ICHTHYOMORPHA.

Fam. Proteidce. Ex. Siren, Proteus.

Salamandridce. Ex. Newt, Salamander.

Suborder III. THERIOMORPHA. Annra.

Fam. 1. Aglossa. Ex. Pipa or Surinam Toad.

2. Ranidce. Ex. Frog.

3. Hylidce. Ex. Tree-frog.

4. BufonidcR. Ex. Toad.

Subclass V. Order XV. ICHTHYOPTERYGIA.1 (Extinct.)

Body fish-like, without neck ; limbs natatory, with more than
five multiarti dilate digits ; vertebra many, short, biconcave ; no
sacrum ; anterior trunk-ribs with bifurcate heads ; an episternum
and clavicles ; post-orbital and supra-temporal bones ; a foramen
parietale ; maxillaries small ; premaxillaries long and large.
Teeth confined to maxillary, premaxillary, and premandibular
bones, implanted in a common alveolar groove, penetrated by
converging folds of cement at the base ; nostrils two, small, near

1 Gr. ichthyft, a fish ; pteryx, a fin.

1C ANATOMY OF VERTEBRATES.

the orbits ; orbits large ; a circle of sclerotic plates. Skin naked
forming a vertical tail-fin (inferential).

Genus Ichthyosaurus.

Order XVI. SAUPvOPTERYGIA. (Extinct.)

Body, in most, with a long neck ; limbs natatory, with not
more than five digits ; an episternmn and clavicles ; vertebrae
with flattened, or slightly cupped, articular surfaces ; a sacrum
of one or two vertebra? for the attachment of the pelvic arch,
in some ; ribs with simple heads ; no post-orbital and supra-
temporal bones ; large temporal and other vacuities between
certain cranial bones ; a foramen parietale ; two antorbital nostrils ;
teeth simple, in distinct sockets of premaxillary, maxillary,
and premaiidibular bones, rarely on the palatine or pterygoid
bones ; maxillaries larger than premaxillaries.

Genera Plesiosaurus, Pliosaurus, Nothosaurus, Placodus.

Order XVII. ANOMODONTIA. (Extinct.)

Teeth wanting, or limited to a single maxillary pair, having the
form and proportions of tusks ; a ( foramen parietale ; ' two ex-
ternal nostrils ; tympanic pedicle fixed ; vertebrae biconcave ; an-
terior trunk-ribs with a bifurcate head, ischiopubic symphysis
continuous.

Fain. Dicynodontia.

A long ever-growing tusk in each maxillary bone ; pre-maxil-
laries connate, forming with the lower jaw a beak-shaped mouth,
probably sheathed with horn. Sacrum of more than two verte-
brae. Limbs ambulatory. Ex. Dicynodon.

Fain. Cryptodontia.

Upper as well as lower jaw edentulous ; premaxillaries distinct
and produced. Ex. Rhynchosaurus.

Premaxillaries confluent, short. Ex. Oudenodon.

Order XVIII. CHELONIA.

Trunk-ribs broad, flat, suturally united, forming with their

ANATOMY OF VERTEBRATES. 17

vertebrae, the sternum, and dermal bones, an expanded
thoracic-abdominal case, into which the limbs, tail, and, usually,
the head, can be withdrawn ; sacrum of more than two vertebrae ;
no teeth ; external nostril single, a cavum tympani ; body covered
by horny scales in most ; ventricle of heart single.

Limbs natatory. Genus Chelone. (Turtles.)

T • n T .7 . f Triom/x. (Mud turtles.)

-Limbs amphibious. < 7-, /™v

[ Emys. (lerrapeiies.)

Limbs terrestrial. Testudo. (Tortoises.)

Order XIX. LACERTILIA.

Vertebra? procoelian, with a single transverse process on each
side, and with single-headed ribs ; sacral vertebrae wanting, or

O O7

not exceeding two ; two external nostrils ; eyes with moveable
lids ; body covered by horny, sometimes bony, scales.

Limbs natatory, no sacrum. Ex. Mosasaurus. (Extinct.)
Limbs ambulatory, a sacrum. Ex. Lacerta, L.
Limbs abortive, no sacrum. Ex. Anguis.

Order XX. OPHIDIA.

Vertebrae very numerous, procoelian, with single-headed hollow
ribs ; 110 sacrum ; no visible limbs ; two external nostrils ; no
cavum tympani ; eyeball covered by an iinmoveable transparent
lid. Body covered by horny scales. Teeth anchylosed to jaw.

Order XXI. CROCODILIA.

Teeth in a single row, implanted in distinct sockets ;
external nostril single and terminal or sub-terminal. Anterior

O

trunk vertebrae with par- and di-apophyses, and bifurcate ribs ;
sacral vertebra? two, eacli supporting its own neural arch ; this
arch usually articulated by suture. Tail long, vertically com-
pressed; feet short, webbed. Skin protected by bony, usually
pitted, plates. Ventricle of heart double.

Suborder AMPHICCELIA (vertebra? cupped at both ends).

Ex. Teleosaurus.

Suborder OPISTHOCCELIA (vertebra? convex in front, concave

behind). Ex. Streptospondylus.

Suborder PROCCELIA (vertebra? concave in front, convex

behind). Ex. Crocodilus.
VOL. r. c

18 ANATOMY OF VERTEBKATES.

Order XXII. DINOSAURIA. (Extinct.)

Cervical arid anterior dorsal vertebra? with par- and di-apo-
physes, articulating with bifurcate ribs ; a few anterior vertebrae
more or less convex in front and cupped behind ; the rest
with flat or slightly concave articular ends ; dorsal vertebrae with
a neural platform ; sacral vertebrae exceeding two in number ;
body supported on four strong, ambulatory, unguiculate limbs.
Skin in some armed by bony scutes. Teeth confined to upper
and lower jaws ; implanted in sockets. Ventricle of heart double
(inferential).

Genera, Iguanodon, Scelidosaurus, Megalosaurus.

Order XXIII. PTEROSAUKIA. (Extinct.)

Pectoral members, by the elongation of the anti-brachium
and fifth digit, adapted for flight. Vertebras proco2lian ; those
of the neck very large, those of the pelvis small. Anterior
trunk-ribs with bifurcate heads. Most of the bones pneumatic.
Head large ; jaws long, and armed with teeth. Ventricle of
heart double (inferential).

Genera, Dimorphodon , Hamplwrliynclius, Pterodactylus.

ANATOMY OF VERTEBRATES. 19

CHAPTER II.

OSSEOUS SYSTEM OF IOEMATOCRYA.

§ 10. Composition of bone. — The vertebrate organisation will
be first described as manifested in the great cold-blooded series,
tinder the diverse modifications, and progressive stages, indicated
by the characters of the foregoing subdivisions of the class.
But before entering upon the details of the osseous system, some
observations must be premised on the vertebrate skeleton in general.

The original substance of all animals consists of a fluid with

o

granules and cells. In the course of developement tubular tracts
are formed, some of which become filled with ' neurine ' or nervous
matter ; others with f myonine ' or muscular matter ; other portions
are converted into vessels, glands, &c. ; but a great proportion
of substance, akin to primordial, remains as ( cellular tissue.'
This, as a rule, becomes hardened in certain parts of the body of
vertebrates by earthy salts, chiefly phosphate of lime. Thus
the tissues called ' osteine ' or bone, and 6 dentine ' or tooth,
are constituted ; between which the chief distinction lies in the
mode of arrangement of the earthy particles, in relation to the
maintenance of a more or less free circulation of the nutrient
juices through such hardened or calcified bodies.

Fishes have the smallest proportion, birds the largest propor-
tion, of the earthy matter in their bones. The animal or soft
part in all is chiefly a gelatinous substance.

PROPORTIONS OF EARTHY OR HARD,1 AND OF ANIMAL OR SOFT, MATTER IN
THE BONES OF THE VERTEBRATE ANIMALS.

FISHES.

Salmon Carp Cod

Soft . . , . 60-62 40-40 34-30

Hard. 39-38 59 -60 6570

100-00 100-00 100-00

1 This has been termed inorganic ; but that the combination of phosphorus and
calcium has ever taken place in nature save under the influences of a living organism,
remains to be proved.

c 2

ANATOMY OF VERTEBRATES.

REPTILES.

Soft .
Hard .

Frog

35-50

64-50

100-00

Snake

31-04

68-96

100-00

Lizard
46-67
53-33

100-00

MAMMALS.

Porpoise

Ox

Lion

Man

Soft .

. 35-90

3 1 -00

27-70

31-03

Hard .

. 64-10

69-00

72-30

68-97

100-00

100-00

100-00

100-00

BIRDS.

Soft .
Hard .

Goose
32-91
67-09

100 00

Turkey

30-49

69-51

100-00

Hawk
26-72
73-28

100-00

From the above table it will be seen that the bones of the
fresh-water fishes have more animal matter, and are, consequently,
lighter than those of fishes from the denser element of sea-
water ; and that the marine mammal called Porpoise differs little
from the sea-fish in this respect. The batrachian Frog has more
animal matter in its bones than the ophidian or saurian reptiles,
and thereby, as in other respects, more resembles the fish. Ser-
pents almost equal birds in the great proportion of the osseous
salts, and hence the density and ivory-like whiteness of their
bones.

The chemical nature of the hardening particles, and of the soft
basis of bone, is exemplified in the subjoined Table, including a
species of each of the four classes of Vertebrata :-

CHEMICAL COMPOSITION OF BONES.

Hawk

Man

Tortoise

Cod

Phosphate of lime, with trace of fluate

of lime ......

64-39

59-63

52 66

57-29

Carbonate of lime ....

7-03

7-33

12-53

4-90

Phosphate of magnesia

0-94

1-32

0-82

2-40

Sulphate, carhonate, and chlorate of

soda ......

0-92

0-69

0-90

1-10

Glutiu and chondrin ....

25-73

29-70

31-75

32-31

Oil

0-99

1-33

1-34

2-00

100-00

100-00

100-00

100-00

ANATOMY OP VERTEBEATES.

21

§ 11. Developement of bone.- -The primitive basis, or l blas-
tema,' of bone is a subtransparent glairy matter containing
numerous minute corpuscles. It progressively 9

acquires increased firmness ; sometimes assuming
a membranous or ligamentous state, usually
a gristly consistence, before its conversion into

O t/

bone. The change into cartilage is noted by
the appearance of minute nucleated cells ; which
increase in number and size, and are a^oreo-ated

in rows, with intercellular tracts, where the ossi-

v<

&\m

\ ^~~~^ \^e& } \]ij&

fication is about to begin, as in fig. 9. These \ ^Ql^j^f^pf,

1 ^SaTV^N ^2 !

rows, in the cartilaginous basis of long bones,
are vertical to its ends ; in that of flat bones

Section of temporary carti-

thev are vertical to the margin. The cells la?p. winch has undergone

n •* a -, p ' £ n the last stage towards ossi-

iiirthest from the seat ot ossification are fiat- fication. CL.
tened and in close contact ; nearest that seat they become enlarged
and separated. In fig. 9, a is the intercellular or ( intercolumnar '
tissue ; b the enlarged cell-wall ; c
the nucleus. The first appearance
of bone is that of minute granules
in the intercolumnar and intercellu-
lar tissue, fig. 10, a. Canals are
next formed in the bone, by absorp-
tion, which ultimately receive blood-
vessels, and become the ' vascular
canals.' The immediate nutrition of
bone is provided for by the produc-
tion of nilllUte ' plasmatiC Canals ' Transverse section of temporary cartilage in
P , , the Jlrr-i staw of ossification. CL.

irom the vascular on; .

In most fishes the plasmatic canals are free from partial dilata-
tions, and appear as in the magnified section of bone, fig 11; where
a shows the area of the ' vascular canal,' and b the orifices of the
( plasmatic canals,' exposed in a longitudinal section of a vascular
canal. In some fishes, e. g. the Garpike (Belone), partial dilatations
do occur in the plasmatic canals, of the form shown in fig. 12, d; and
in a Sea-bream {Sargus) of that marked c ; in the Frog they are
wider and more defined, as in the two dilatations shown at a. In
serpents, e. g. the Python, they are commonly, where best defined,
of the elongate oval form shown in l, 2, and 3, fig. 13 ; but in
transverse section they appear as in 5 and 6. In the bird, e. g.
the Goldfinch, they have the form shown in b, fig. 12. In human
bone they assume the forms represented in fig. 14. When so
defined they are termed f lacunae ' or ( bone-cells ; ' and, in some

22

ANATOMY OF VERTEBRATES.

degree, characterise, by their shape and size, the osseous tissue of
the respective vertebrate classes. In the concentric laminae sur-

11

Plasrnatic canals in a fish-bone, a transverse, 6 longitudinal, section
of vascular canal (.TOMES, CL.)

rounding the vascular canal, fig. 15, a, a, the bone-cells are
arranged concentrically, between the laminae, with the long axis

12 13

0

Forms of bone-cells in Python and Boa Constrictor. CL.

in the direction of the circular line of the plate. Most of the
plasmatic tubes continued from the bone-cells pierce the plates at

ANATOMY OF VERTEBRATES.

23

Vlv

right angles in their course to the vascular canal, with which they
communicate ; and they form the 14

essential vehicle of the material
for future growth.

§ 12. Growth of bone. — In
fishes the bones continue to grow
throughout life, and their peri-
phery, whether in the flat bones of
the head which overlap each other,

Or in the thicker boneS that inter- The foruis assumed by the bone-cells in man. CL.

lock, is cartilaginous or membranous, and the seat of progres-
sive ossification. The long bones of most reptiles retain a layer
of ossifying cartilage beneath the terminal articular cartilage ;
and growth continues at their extremities while life endures.

15

Transverse section from the dense portion of the human femur. CL.

Some of the Ions; bones in frogs, birds, and most of those in mam-

O O 7 J

mals, have their ends distinct from the body or shaft of the grow-
ing bone ; these separately ossified ends are termed ' epiphyses ' :
the seat of the active growth of the shaft is in a cartilaginous
crust at the ends supporting the epiphyses. "When these coalesce
with the shaft, growth in the direction of the bone's axis comes to

24 ANATOMY OF VERTEBRATES.

an end; but there is a slower growth going on over the entire peri-
phery of the bone, which is covered by a membrane, called the
( periosteum.' In this membrane, the vascular system of a bone,
except the vessel supplying the marrow-cavity, undergoes the
amount of subdivision which reduces its capillaries to dimensions
suited for penetrating the pores leading to the vascular canals,
figs. 11 and 15, a, a.

Thus bone is a living and vascular part, growing by in-
ternal molecular addition and change, and having the power of
repairing fracture or other injury. The shells and crusts of
molluscous and crustaceous animals are unvascular; they grow
by the addition of layers to their circumference, may be cast off
when too small for the growing body, and be reproduced of a
more conformable size. When fractured, the broken parts may
be cemented together by newly superadded shell-substance from
without ; but are not unitable by the action of the fractured sur-
faces from within.

Extension of parts, however, is not the sole process which
takes place in the growth of bone ; to adapt a bone to its destined
office changes are wrought in it by the removal of parts pre-
viously formed. In fishes, indeed, we observe a simple unmodi-
fied increase. To whatever extent the bone is ossified, that part
remains, and consequently most of the bones of fishes are solid or
spongy in their interior, except where the ossification has been
restricted to the surface of the primary gristly mould.1 The bones
of the heavy and sluggish turtles and sloths, of the seals, and of
the whale-tribe, are solid. But in the active land quadrupeds, the
shaft of the long bones of the limbs is hollow, the first formed
osseous substance being absorbed, as new bone is being deposited
from without. The strength and lightness of the limb-bones are
thus increased after the well-known principle of the hollow column,
which Galileo, by means of a straw picked up from his prison
floor, exemplified, as an evidence of design, in refutation of a
charge of Atheism brought against him by the Inquisition. The
bones of birds, especially those of powerful flight, are remarkable
for their lightness. The osseous tissue itself is, indeed, more
compact than in other animals ; but its quantity in any given
bone is much less, the most admirable economy being traceable
throughout the skeleton of birds in the advantageous arrange-

1 In this case, exemplified in bones of the Lophius, Gyrosteus, and the lower
fiatrachia, fossilisation, which affects only the ossified crust, leaves the appearance,
through the solution of the unossified cartilage, of a wide medullary cavity, which
might mislead the Palaeontologist in his inferences.

ANATOMY OF VERTEBRATES. 25

ment of the weighty material. Thus, in the long bones, the cavi-
ties analogous to those called 'medullary' in beasts, are more
capacious, and their walls are much thinner : a large aperture
called the ' pneumatic foramen,' near one end of the bone, com-
municates with its interior ; and an air-cell, or prolongation of the
lung, is continued into and lines the cavity of the bone, which is
thus filled with rarefied air instead of marrow. The extremities
of such air-bones present a light open net-work, slender columns
shooting across in different directions from wall to wall, and these
little columns are likewise hollow.

In the mammalian class, the air-cells of bone are confined to
the head, and are filled from the cavities of the nose or ear, not
from the lungs. Such cells are called ( frontal sinuses,' ' an-
trum,' ( sphenoidal,' and e ethmoidal sinuses,' in man. The
frontal sinuses extend backward over the top of the skull in the
ruminant and some other quadrupeds, and penetrate the cores of
the horns in oxen, sheep, and certain antelopes. The most re-
markable developement of cranial air-cells is presented by the ele-
phant ; the intellectual physiognomy of this huge quadruped beino-
caused, as in the owl, not by the actual capacity of the brain case,
but by the vast extent of the pneumatic cellular structure between
the outer and inner plates of the skull-wall.

In all these varied modifications of the osseous tissue, the cavi-
ties therein, whether mere cancelli, or small medullary cavities
as in the Crocodile, or large medullary cavities as in the Ox, or
pneumatic cavities and sinuses as in the Owl, are the result of
secondary changes by absorption, and not of the primitive consti-
tution of the bones. These are solid in their commencement in
all classes, and the vacuities are established by the removal of
osseous matter previously formed, whilst increase proceeds by
fresh bone being added to the exterior surface. The thinnest-
walled and widest air-bone of the bird of flight was first solid,
next a marrow-bone, and finallv became the case of an air-cell.

•/

The solid bones of the Penimin. and the medullary bones of the

o j

Apteryx, exemplify arrested stages of that course of developement
through which the pneumatic wing-bone of the soaring Eagle had
previously passed.

But these mechanical modifications do not exhaust all the
changes through which the parts of a skeleton, ultimately becom-
ing bone, have passed ; they have been previously of a fibrous
or of a cartilaginous tissue, or both. Entire skeletons, and parts
of skeletons, of vertebrate animals exhibit arrests of these early
stages of developement ; and this quite irrespective of the grade of

26

ANATOMY OF VERTEBRATES.

the entire animal in the zoological scale. The capsule of the eye-
ball, for example, in man, is a fibrous membrane ; in the Turtle, it
is gristle ; in the Tunny, bone. The skeletal framework of the
Lancelet (Branchiostoma) does not pass beyond the fibrous stage
of tissue-change. In the Sturgeon and Skate it stops at the gristly
stage, and hence these fishes are called ' cartilaginous.' In most
fishes, and all air-breathing vertebrates, it proceeds to the bony
stage, with the subsequent modifications and developements above
recited.

§ 13. Classes of bone.- -Bony matter is variously disposed in
the bodies of vertebrate animals. The Trunk-fish, fig. 16, dn, dp,
dh, the Crocodile, and the Armadillo are instances of its accumu-
lation upon or near the surface of the body ; and hence the ball-
proof character of the skin of the largest of these mailed examples.
The most constant position of bone is around the central masses
of the nervous, ib. n, and vascular, ib. h, pi, systems, with rays
thence extending into the middle of the chief muscular masses,
formmo* the bases of the limbs. Portions of bone are also deve-

o

loped to protect and otherwise subser , j the organs of the senses,
and in some species are found encasing mucus-ducts, and buried
in the substance of certain viscera — as, e. g. the heart in the
Bullock and some other large quadrupeds. Strong membranes,
called ' aponeurotic,' and certain tendons, become bony in some
animals; as, e. g. the ( tentorium' in the Cat, the temporal fascia
in the Turtle, the ( leaders ' of the leg-muscles in the Turkey, the
nuchal ligament in the Mole, and certain tendons of the abdominal

O '

muscles of the Kangaroo, which, so ossified,
are called the ( marsupial-bones.' The pri-
mary classification of the parts of the osseous
system is, therefore, according to their pre-
valent position, as in the cases above cited.
The superficial or skin-bones constitute the
( dermo-skeleton' ; * the deep-seated bones, in
relation to the nervous axis and locomotion,
form the ( neuro-skeleton' ;2 the bones con-
nected with the sense-oro-ans and viscera

o

form the ' splanchno-skeleton';3 those de-
veloped in tendons, ligaments, and aponeuroses, the ( sclero-
skeleton.'4

1 Gr. derma, skin, and skeleton.

2 Gr. neuron, nerve, and skeleton.

3 Gr. splaychnon, viscus, or inward part, and skeleton.

4 Gr. scleros, hard, and skeleton.

Segment of neuro- and derrao-
skcletons, Ostracion

ANATOMY OF VERTEBRATES. 27

In the arrangement of the parts of the dermo-, splanchno-, and
sclero-skeletons, no common pattern is recognisable. One can
but discern a purpose gained by such bony plates, cases, or rods,
in special relation to the habits and well-being of the creatures
manifesting them ; but the diversity in the number, size, shape,
and relative position of dermal, tendinal, and visceral bones seems
interminable. The neuro-skeleton, which is the main part of the
osseous system, and might be termed the ( skeleton proper,' ex-
emplifies not only the principle of design and adaptation, but
that of unity of composition. Its parts are arranged in a series
of segments following and articulating with each other in the
direction of the axis of the body.

§ 14. Type segment or vertebra. — Each complete segment,
called ' vertebra,' consists of a series of osseous pieces arranged
according to a type or general plan, exem- 17

plified in fig. 17 ; in which they form a
hoop or arch above, and another beneath,
a central piece. The upper hoop, encircling
a segment of the nervous axis, is called the
neural l arch, N ; the lower hoop, encircling
a part of the vascular system, is called the
haemal2 arch, H: their common centre is
termed the ( centrum.'3 The neural arch
is formed by a pair of bones, called f neura-
pophyses,'4 n, n, and by a bone sometimes
cleft or bifid, called the ' neural spine,'
ns : it also sometimes includes a pair of
bones, called ' diapophyses ' 5 d, d. The haemal arch is formed by
a pair of bones, called ( pleurapophyses,'6 ^/; by a second pair,
called ( haemapophyses,' 7 h ; and by a bone, sometimes bifid, called
the fha3mal spine,' hs. It also sometimes includes parts, or
bones, called ' parapophyses.'8 Bones, moreover, may be developed
which diverge as rays from one or more of the above parts.

The parts of a vertebra which are developed from independent
centres of ossification are called ( autogenous ; ' those that grow
from previously ossified parts are called ' exogenous : ' the autoge-
nous parts of a vertebra are its ' elements,' the exogenous parts
are its ' processes.' No part, however, is absolutely autogenous

1 Gr. neuron, nerve. 5 Gr. dia, across, and apophusis.

2 Gr. haima, blood. 6 Gr. pleuron, rib, and apophusis.
8 Gr. kentron, centre. 7 Gr. for blood, and apophusis.

* Gr. for nerve, and apophusis, a pro- B Gr. para, transverse, and apophusis.

jecting part.

28

ANATOMY OF VERTEBRATES.

genous,

18

7tS

C'ranial scginen or vertebra

throughout the vertebrate series ; and some parts, usually cxo-
are autogenous in a few instances.

The vertebral elements are, the centrum
c, the neurapophyses n ; the neural spine
ns, the pleurapophyses pi, the haemapo-
physes h, and the haemal spine hs. The
exogenous parts are the diapophysis d, the
parapophysis/*, the zygapophysis z,} the ana-
pophysis a,2 the metapophysis m,3 the hypa-
pophysis, fig. 17, y,4 and the epapophysis,
fig. 17, e.5 Of the autogenous parts, the
neural spine is most commonly exogenous;
of the exogenous parts, the parapophyses,
diapophyses, and hypapophyses, are sometimes autogenous.

Vertebrae are subject to many and great modifications — e. g. as
to the number of the elements retained in their composition, as to
the form and proportion of the elements, and even as to the relative
position of the elements ; but the latter modification is never
carried to such a degree as to obscure the general pattern or
type of the bony segment.

Sometimes, as in the example, fig. 18, of the third segment of
the human skeleton, the neural arch, N, is much expanded, the
hsemal one, H, is contracted ; and, in the expanded neural arch,
the autogenous diapophyses, d d, are wedged between the neura-
pophyses, n, and the enormously expanded neural spine, ns. More
commonly, as in the example from the thorax, fig.
1 9, the haamal arch, hs, is much expanded, the neural
one n, contracted ; and the parapophysis is repre-
sented sometimes by the exogenous growth from
the centrum, commonly by that, p, from the rib pL
Sometimes, again, as is exemplified in the neck of
the bird, fig. 20, and the tail of the Crocodile, both
neural and haemal arches are alike contracted, the
pleurapophyses, pi, being excluded from the latter,
and standing out as continuations of the confluent
diapophyses and parapophyses ; and the hcemal arch
being formed, either by haemapophyses (Crocodile), fig. 7, or
hypapophyses (bird), fig. 20, hy. Such vertebras deviate but
little from the ideal type, under its less developed condition,
as in fig. 7. The segments are commonly simplified and made

Thoracic segment or
vertebra

1 Gr. zugos, junction, and apophusis.

2 Gr. ana, backwards, and apophusis.

3 Gr. meta, between, and apophusis.

Gr. Jnipo, below, and apophusis.
Gr. epi, above, and apophusis.

ANATOMY OE VERTEBRATES. 29

smaller as they approach the end of the vertebral column ; one
element or process after another is removed, until the vertebra
is reduced to its centrum, as in the subjoined diagram, fig. 21,
of the archetype vertebrate skeleton.

§ 15. Archetype skeleton. — In this scheme, which gives a side
view of the series of segments or ( vertebra? ' of
which the skeleton is composed, the extreme
ones are the seat of those modifications, which,
according to their kind and degree, impress
class-characters upon the type.

The four anterior neurapophyses, 14, 10,

n 6, 2, give issue to the nerves, the terminal ^•^v->&*™r pl
modifications of which constitute the organs
of special sense. That of smell, 4, 19. is

1 . Cervical segment or

situated in advance of its proper (nasal) seg- vertebra

meiit, which becomes variously modified to enclose and protect
it. The organ of sight, lodged in a cavity or 'orbit' be-
tween its own (the frontal) and .the nasal segment, is here
drawn above that interspace. The nerve of taste perforates
the neurapophysis of the third segment, 6, or passes by
a notch between this and the frontal segment, to expand in the
sense-organ, or ' tongue,' which is supported by the haemal spine,
41, 42, of its own (parietal) segment. The fourth is the organ
of hearing, 16, indicated above the interspace between the neura-
pophysis of its own (occipital) and that of the antecedent (parietal)
vertebra, in which it is always lodged ; the surrounding vertebral
elements being modified to form the cavity for its reception, which
is called f otocrane.'

The jaws are the modified haemal arches of the first two seg-
ments. The mouth opens at the interspace between these haemal
arches ; the position of the vent varies (in fishes), but always
opens behind the pelvic arch, s, 62, 63, p, when this is ossified.

Outlines of the chief developements of the dermoskeleton, in
different vertebrates, which are usually more or less ossified, are
added to the neuroskeletal archetype ; as, e. g. the median horn
supported by the nasal spine, is, in the rhinoceros ; the pair of
lateral horns developed from the frontal spine, n, in most rumi-
nants ; the median folds, D i, D 11, above the neural spines, one or
more in number, constituting the ' dorsal ' fin or fins in fishes and
cetaceans, and the dorsal hump or humps in the buffaloes and
camels ; similar folds are sometimes developed at the end of the
tail, forming a ' caudal ' fin, c, and beneath the haemal spines^
constituting the ( anal ' fin or fins, A, of fishes.

30

ANATOMY OF VERTEBRATES.

The different elements of the pri-
mary segments are distinguished by
peculiar markings : —

The neurapophyses by diago-
nal lines, thus —

The diapophyses by vertical
lines-

The parapophyses by horizon-
tal lines-

The centrum by decussating
horizontal and vertical lines —

The pleurapophyses by diago-
nal lines —

The appendages by dots- -'.'..'..
The neural spines and haemal spines
are left blank.

In certain segments the elements
are also specified by the initials of
their names :-

ns is the neural spine.
n is the neurapophysis.
pi is the pleurapophysis.
c is the centrum.
h is the haemapophysis, also indi-
cated by the numbers 21, 29,

44, 52, 58, 63, 64. l

hs is the haemal spine.

a is the appendage.
The centrum is the most constant
vertebral element as to its existence,
but not as to its ossification. There
are some living fishes, and formerly
there were many, now extinct, in
which, whilst the peripheral elements
of the vertebra become ossified, the
central one remains unossified ; and
here a few words are requisite as to
the developement of vertebrae.

§ 16. Developement of vertebras. —
The central basis of the neuroskeleton
is laid down in the embryo of every
vertebrate animal as a more or less

1 See 'TABLE OF SYNONYMS, Special Homologies,' for the names of the bones
indicated by numbers.

ANATOMY OF VERTEBRATES.

31

cylindrical fibrous sheath, filled with simple cells containing jelly.
The centrums, or 6 bodies of the vertebras,' are developed in and
from the notochord. The bases of the other elements are laid
down in fibrous bands, diverging from the notochord, and giving
the first indication of the segrnental character of the skeleton.
In Dermopteri the neu-

adipose substance

inner layer

outer layer -
of fibrous capsule

neural canal

fibrous band,

or basis of
gelatinous chorda

ral and haemal canals are
formed by a separation of
the layers of the outer
division of the sheath of

, i i -I n or» A Transverse vertical section of vertebral column of Myxine. xxi.

the notochord, ng. 22. A

transverse partition divides the larger portion of the neural canal,
lodging the myelon, from a smaller portion above containing
adipose tissue. In the Lancelet the substance of the noto-
chord, fig. 23, ch, consists of a number of circular discoid
or flattened vesicles, pressed one upon another within the
sheath, like a pile of coins in a purse ; the sheath is strength-
ened by a longitudinal filamentary ligament above and below.
Aponeurotic septa pass off, with each pair of nerves, to the
interspaces of the muscular segments, giving attachments to
the fibres. A median vertical membrane rises from the neural

23

Diagram of anatomy of the Lancelet, Branchiostoma

sheath, and beyond the abdominal cavity descends from the hremal
sheath, passing between the right and left series of myocommata.
The dermo-neural and dermo-haemal spines are indicated by short
linear series of firmly adhering flattened cylindrical cells. The
next step in the skeletal tissues is shown in a pair of jointed
cartilaginous filaments, fi ;. 23, h9 which bound or strengthen the
borders of the longitudinal oral slit, each cartilage supporting on
conical prominences the oral cirri (ib. f, f) : numerous carti-
laginous filaments strengthen the sides of the branchial cavity, ib.
a, with intervening fissures, not opening upon the skin. In the
Lamprey cartilaginous neurapophyses, fig. 24, n, n, strengthen the
sides of the neural canal, In the Sturgeon, fig. 25, the inner

32

ANATOMY OF VERTEBRATES.

layer of the notochordal capsule has assumed the texture of tough
hyaline cartilage; and not only are firm opakc cartilaginous
neurapophyses present, but also parapophyses, pleurapophyses,

Fore part of skeleton, Lamprey (Pctromyzon)

and neural spines. The part of the iieurapophysis bounding the
true neural canal is usually distinct from that bounding the fat-
filled fissure above. The parapophyses are united by a con-
tinuous plate of cartilage forming an inverted arch beneath the

aorta, in the trunk, ana-
logous to that formed by
bone in the lower neck-
vertebra of birds, fig. 20.

iuterneural cartilage

ueural spine

filiro-adipose
canal

neural canal
gelatinous chorda

inner layer of •
fibrous capsule as
hyaline cartilage

O Pleurapophysis

In the ChimcBra
der subossified

ngs

parapophysis
- interhitmal cartilage

hanual canal
Abdominal vertebra, Sturgeon

in the

o

nous sheath of the noto-
chord, which are more
numerous than the neu-
ral arches. These, where unconflueiit with each other, are
distinct also from the parapophyses, which in the tail bend
down to form the hoemal arches. In the Mediterranean Grey
Shark (Notidanus cinereus) the vertebral centres are still feebly
and irrelatively marked out by numerous slender rings of hard
cartilage in the notochordal capsule, the number of vertebra? being
more definitely indicated by the neurapophyses and parapophyses ;
but these remain cartilaginous.

In the Lepidosiren the peripheral vertebral elements, fig. 41, ??,
ns, p, hs, are ossified, but the notochord, ch, with a thicker and
condensed capsule, remains. In the Piked Dog-fish (^Acanthias)
the vertebral centres coincide in number with the neural arches,
and are defined by a thin plate of bone, shaped like an hour-
glass, and forming the conical cavity at each end of the centrum :
the rest of which is cartilaginous external to the ' hour-glass,' and
subgelatinous within its terminal cavities. In the Spotted Dog-
fish (Scyllium) the two thin bony cones of each centrum are con-

ANATOMY OF VERTEBRATES.

33

Vertical transverse section of
centrum of Selache maxima

fluent at their apices, which are perforated, and the notochord,
reduced to a beaded form, is continued through them : the
exterior of the bony cones is occupied by
a clear cartilage. In the Porbeagle Shark
(JLamna corniibica) further ossification of
the conical plate has reduced the central
communication to a minute foramen. Os-
seous plates have also been developed in
the exterior clear cartilage : these plates
are triangular, parallel with the axis of the
vertebra, their apices converging towards
the centre : the interspaces are filled by
cartilage. In the great Basking Shark
[Selache maxima) fig. 26, the longitudinal bony laminae are more
numerous and shorter than in Lamna, are peripheral in position,
and extend about one-third of the way towards the centre of the
interspace between the terminal cones, the rest being occupied by
a series of concentric cylinders of bone, interrupted by four
conical converging cavities, filled by cartilage ; of these, two, n, n,
are closed by the bases of the neurapophyses, and two, p, p, by
those of the parapophyses. There is a transition from the cylin-
drical to the longitudinally lamellar structure, the exterior and
largest of the cylinders sending out processes which join the in-
ternal margins of the converging lamellae In the Monk-fish
(Squatina) the osseous part of the centrum between the termi-
nal cones is entirely in the form of concentric layers, few in number,
and decreasing in breadth as they approach the centre. In the
Cestracion there are no concentric cylinders, but only longitudinal
Iamella3, radiating from the centre to the circumference, and giving
off short lateral plates as they diverge.

In the Topes ( Galeus), the Blue Sharks ( Carcharias), and in
most sharks which possess the nictitating eyelid, may be seen the
most advanced stao-e of ossification in the cartilaginous fishes :

o o

the entire centrum, save at the four cavities closed by the neur-
and par-apophyses, is occupied by a coarse bone, more compact
where it forms the smooth exterior surface and that of the ter-
minal articular cavities. In osseous fishes (most Teleostomi) the
neur- and par-apophysial cavities are obliterated by bone, and
the neur- and par-apophyses are confluent, or suturally joined,
with the centrum ; but they retain a greater proportion, than in
higher classes, of the primitive gelatinous basis, which fills up the
deep cone or cup at each end of the centrum, fig. 27, c c. Only
in the ganoid Lepidosteus, among fishes, does ossification so extend

VOL. i.

D

34

ANATOMY OF VERTEBRATES.

Scants

Lepidosteus

as to obliterate the front cavity, and protrude into the hind cavity
of the preceding vertebra, fig. 28 ; thus establishing a cup-and-

ball articulation on the ' opisthocoelian ' plan.
The cup-and-ball structure prevails throughout
the air-breathing, land-seeking, or terrestrial,
Hcematocrya. So interlocked, the vertebra? are
better fitted to support the body in air, and
transfer its weight to legs. Sometimes the cup
is behind, as in the land-salamander, the Surinam
toad (JPipa), and some extinct crocodiles, thence
called Streptospondylus ; but, as a general rule, existing reptiles
have ( procoelian ' vertebra, or with the cup in front. In many

extinct reptiles {Sauropterygia9 Dinosauria) ossi-
fication was so advanced as to leave no cavity
at either end of the centrum ; and these parts
were coarticulated by flattened or almost flat-
tened surfaces, as in mammals. Finally, both
extinct and recent Keptilia aiford instances in
which the parts or elements of the vertebra have
coalesced into one bone.

The progressive stages in the developement of
a vertebra, which have been illustrated by the chief of those at
which it is arrested in the cold-blooded series, bear a close analogy
to those by which it reaches the coalesced condition as a single
bone in the warm-blooded classes. The principal secondary and
adaptive modifications will next be pointed out which mark with
special characters the collective trunk-vertebras in H&matocrya.

§ 17. Vertebral column of Fishes.- -In the Sturgeon (Aci-
penser), fig. 29, the first five or six neural arches are confluent
with each other and with the parapophyses, forming a continuous
sheath of firm cartilage (fig. 62), inclosing the fore part of the
notochord, ib. «, and myelon, and perforated for the exit of
the nerves. The tapering end of the notochord is continued
forward into the fused basal elements of the cranial vertebras,
ib. g, g", and backward into the base and upper lobe of the
tail-fin, fig. 29, c. The vertebras are represented by their
peripheral elements, and principally by the neural and haemal
arches. The pleurapophyses are limited to about twelve of
the anterior trunk-vertebras, are articulated by simple heads
to parapophyses, fig. 62, p, and rapidly shorten in the two or
three hinder pairs ; the large ones sometimes consist of two or
three pieces joined end on end, like the modified occipital rib,
called f scapula.' Vegetative repetition of perivertebral parts

ANATOMY OF VERTEBRATES.

35

not only manifests itself in the double pleur-
and neur-apophyses on each side, but in small
interneural and interhaemal cartilages, fig. 25.
These peripheral cartilages are more feebly
developed in Spatularia.

In the Chimseroicls (Holocephali) the bases
of the neur- and par-apophyses of about ten
of the anterior trunk-vertebras coalesce and
form a continuous accessary cartilaginous

«/ o

covering of the fore part of the notochord ;
and the confluent neural spines here form a
broad and high compressed plate. Between
the neurapophyses are wedged accessory in-
terneural cartilages.

In NotidanuSyAcanthias, Centrina,and. Scym-
nus, the interneurals, fig. 30, z, resemble the
neurapophyses, ib. n, inverted, and are in-
terposed, like wedges, between them, with
the apices reaching the centrum. In Scyttium,
Mustelus, Sphyrna, and Carcharias, the in-
terneurals resemble the neurapophyses in size
and shape, but occupy a position above the
intervertebral joint. In Galeus the ( vegeta-
tive repetition ' is further exemplified by four
stellate points of ossification, one of which is
intervertebral ; and above these are rudiments
of neural spines. The spinal nerve directly
perforates the neurapophysis ; or, when the
two roots escape separately, one also per-
forates the interneural. The pleurapophy-
ses are short and simple cartilages, either
wedged into the interspaces of the parapo-
physes (Notidanus, Carcharias, Scymnus),
or attached to the ends of the parapophyses
( Galeus) of, say, the twenty-six anterior verte-
brae. In Acanthias there may be forty pairs
of such riblets, fig. 30, pi.

In the flat Plagiostomes (Skates, fig. 64,
Rays, Torpedos) vegetative repetition mani-
fests itself in the multiplication of vertebrae,
and especially of the central elements ; which,
as indicated by their rudimentary ossification
in Chim&ra, are commonly more numerous

D 2

\ o

Skeleton of Sturgeon,
(Acipenser Sturio). cxiv.

36

ANATOMY OF VERTEBRATES.

than the neural arches ; nor are interneural and interhaemal pieces
wanting. In Raia clavata these ( ossa intercalaria ' constitute the

chief part of the neural arch, at the
anterior part of the vertebral column ;
whilst the neurapophyses resume
their ordinary share in its formation
at the posterior part of the column.
In Zygcena there are interspinal
cartilages. In Rhinobatus a single
spine answers to two vertebral bodies,
and we may well suppose this mul-
tiplication of central pieces to have
been carried still farther in the pri-
maeval fossil Ray (Spinachorhinus)
from the lower Lias.

In the anchylosed cervical verte-
brae of the Skate the short centrums
are indicated by transverse bars along
the middle of the under part. In
the Monk-fish (^Squatina) the body
of the atlas is confluent with the
basioccipital, but the neural arch re-
mains distinct.

The parapophyses in most Rays
pass forward, and then backward, the
angle of one fitting, like an articular
process, into the notch of the para-
pophysis in advance : they do not
support pleurapophyses ; they gradu-
ally bend down behind the pelvic
arch, and complete the haemal canal
about six vertebra? beyond it; the
ha3inal spines become flattened in the
tail of some Rays.
In osseous fishes a trunk-vertebra consists of a biconcave body,
fig. 27, c, of a pair of neurapophyses, fig. 31, n, usually develop-
ing a spine, ib. ns, from their point of coalescence above the
neural canal ; and of a pair of parapophyses, ib. p ; to which
are added in the abdominal region in most fishes, and also in the
caudal region of some, a pair of pleurapophyses^ pi, figs. 31, 32.
Ossification usually commences in the bases of the neur- and
par-apophyses, and in the terminal cones of the centrum ; it
may proceed to blend the six points into one bone, and fill

Forepart of skeleton, Piked Dog-fish
(Acanthias}. XLIII.

ANATOMY OF VERTEBRATES.

37

31

32

Abdominal vertebras (Hugil)

Abdominal vertebras,
Pike (Esox)

up the hollow outside the cones, as indicated by the dotted
tract in the section, fig. 27. But, in some, a communicating
aperture is left between the
terminal cones, as indicated
by the dotted line in fig. 31.
In many fishes the plates
by winch the bone attains
the periphery of the centrum
leave interspaces permanent-
ly occupied by cartilage,
forming cavities in the dried
or fossil bone, or giving a
reticulate surface to the sides
of the centrum. The bases of the neur- and par-apophyses
sometimes expand so as to wholly inclose the centrum before
coalescing therewith ; as, for example, in the Tunny, where
the line of demarcation may be seen at the border of the articu-
lar concavity.

In the Pike the neurapophyses seldom, in the Polypterus and
Amia, never, coalesce with the centrum : the letter s shows the
neurapophysial suture in fig. 32. In the Salmonidce the neur-
apophyses remain distinct from both the centrum and from each
other, in the anterior vertebra ; where each developes a long and
slender spine.1 The parapophyses remain for some time distinct
from the body of the vertebra, as well as from the ribs. In the
anterior vertebra of the Carp the neurapophyses remain distinct,
as they do in the atlas of many other fishes, and a suture is ob-
servable between the parapophyses and centrum in embryo Cypri-
noids. In each vertebra the summits of the two neurapophyses
usually become anchylosed together, and to their spine ; but in the
Lepidosiren, fig. 41, the spine retains its character as a distinct
element, and is always attached by ligament to the top of the
neurapophysis, as it is in the Sturgeon, fig. 25. In the anterior
abdominal vertebrae of the Tetrodon, each of the neurapophyses,
though they coalesce in the interspace of the two spines to form
the roof of the neural canal, sends up its own broad truncated
spine ; and these are not much-developed oblique processes, but
gradually approximate and blend together, to form the single
normal spine at the fifth abdominal vertebra.2 In the Barbel
the neural arches also support two spines, but one is placed
behind the other.

1 XLIV. vol. i. p. 16, No. 46.

Ib. vol. i. p. 81.

38

ANATOMY OF VERTEBRATES.

Terminal caudal vertebra?, Sword-fish, xxm.

The interspaces of the neural arches are occupied by a fibrous
aponeurosis — the remains of the primitive covering of the neural

axis : but in
most fishes the

arches are ad-

j» /^

™/^>

ditionally con-
nected toge-
ther by articu-
lar or oblique
process e s
(zygapophy-
ses ) : in the
Pike the ante-
rior one, fig.

32, 2, is present, which barely touches the neural arch in advance ;
in Polypterus it overlaps that part. In the Perch a posterior
zygapophysis projects to receive the overlapping anterior one,
the relative positions being the reverse of those in most air-
breathing vertebrates. But, in some fishes, a second pair of
zygapophyses are developed, which resemble the normal pair
in higher vertebrates in relative co-adaptation, but seem to
grow as exogenous processes, from the centrum itself, fig.
31, z. It is also peculiar to fishes to have articular processes
developed from the parapophyses, as, e. g. in the abdominal region
of the Rays, and from the caudal vertebra? of the Sword-fish, fig.

33, z. In the Tunny these pi'ocesses are branched, and form a
network about the haemal canal. In Loricaria peculiar accessory
processes are sent out from the neural arch of the seven anterior ver-
tebra3 which abut against the lateral shields of the dermo-skeleton.
The parapophyses are short in some fishes (Sahno, Clupcea., Amia),
of moderate size in many, and longest in the Cod-tribe, fig. 34,
p, where they expand in the abdominal region and sustain
the air-bladder which adheres to their under surface. In one species
of Gadus, the bladder sends processes into deeper cavities of the
parapophyses, foreshowing, as it were, the pneumatic bones of
birds. The parapophyses gradually bend lower down as they
approach the tail, where, in many fishes, they unite to form the
haemal canal. In Lepidosteus the canal is formed by the pleura-
pophyses : whilst these, in Amia., Thynnus, and some others, are
appended to the parapophysial inverted arches, like haemal spines.
In Lepidosiren the elements p, fig. 41, which in the abdomen
represent either pleurapophyses or long parapophyses, bend down
in the tail to form the haemal arch. Not until we reach the
Batrachia in the ascensive comparison do we find true ' ha3ma-

ANATOMY OF VERTEBRATES. 39

pophyses,' fig. 43, h, forming the haemal arch in the tail, and
coexisting there with par- and pleur-apophyses, ib. p, and pi.

The pleurapophyses of fishes correspond to what are termed in
Comparative Anatomy, ( vertebral ribs,' and in Human Anatomy
( false or floating ribs : ' for, with few exceptions, of which the
Herring is one, fig. 37, their distal ends are not connected with
any bones analogous to sternal ribs or sternum ; i. e. the abdomen
is unclosed below by the osseous parts completing the haemal arch.
The true homologues of sternal ribs and sternum retain the primitive
aponeurotic texture, and may be well seen in the Bream, ex-
tendino: from the ends of the vertebral ribs. These elements, or

o

pleurapophyses, figs. 31, 32, pi, are usually appended to the
extremities of the parapophyses, p, the articulation frequently pre-
senting a reciprocal notch in each. But, in some bony fishes, as
Platax, the ribs articulate with the bodies of the vertebrae, in de-
pressions behind the parapophyses ; and in Polypterus beneath the
parapophyses, as in the cartilaginous Heptanchus, Carcharias, and
Alopias.

Between the floating ribs extends an aponeurosis, the remains
or homologue of the primitive fibrous investment of the abdomen
in the Lancelet and Lamprey. In the Salmon and Dory the ribs
continue to be attached to some of the parapophyses after they are
bent down, as in the Amia and Tunny, to form the haemal canal

V J

and spine in the tail. The costal appendages of the first vertebra of
the trunk are usually larger than the rest, and detached from the
centrum ; at least if we regard as such the styliform bones which
project from the inner side of the scapula?, and which have been
described as coracoids (Cuvier), and sometimes as displaced iliac
bones (Carus) : by the muscles attached to these styliform bones
the succeeding ribs are drawn forward and the abdomen expanded
in the Cyprinoids. Pleurapophyses are entirely absent in the
Sun-fish, Globe-fish (Diodon), the Tetrodon, the Pipe-fish (Fistu-
laria and Syngnafhus), the Lump-fish and the Angler. Of all
osseous, or rather semi-osseous, fishes, Lophius presents the simplest
vertebral column : the abdominal vertebrae are not only devoid of
ribs, but have the feeblest rudiments of parapophyses. The bodies
of the vertebra? interlock at their lower and lateral parts by a short
angular process fitting into a notch in the next vertebra ; the lower
border of this notch represents the lower transverse process in
other fishes : it is obsolete in the anterior abdominal vertebra? ;
begins to appear about the middle ones ; shows its true character
in the tenth; and elongates, bending downward, backward, and
inward, to coalesce with its fellow, and form the haemal arch at
the twelfth or thirteenth vertebra, from which the haemal spine is

40

ANATOMY OF VERTEBRATES.

developed. The interlocking process of the anterior vertebra dis-
appears as the true inferior transverse process is increased. The
side of the neural arch is perforated for the nerve, and that of the
haemal arch for the blood-vessel. The anterior abdominal vertebra

3 , of the Tetrodon are

firmly clamped to-
gether by the para-
pophyses.

A vegetative same-
ness of form prevails
in fishes throughout
the vertebral column
of the trunk, fig. 34,
which is made up of
only two kinds of ver-
tebras, characterised
by the direction of
the parapophyses, p :
these in the abdomi-
nal region are lateral,
usually stand out and
support ribs : but in
the caudal region
bend down to form,
either by direct co-
alescence or by the
ribs that continue to
be attached to them
in a vertical position,
the hremal arch.

The atlas is usu-
ally distinguished by
some modification of
the anterior articular
end of the centrum,
by the persistent
suture of the neural
arch, or by the ab-
sence or detachment
of its pleurapophy-
ses. Peculiar pro-
cesses are sometimes

Skeleton of the Haddock (Gadus cegleflnus) SCnt off from the

ANATOMY OF VERTEBRATES.

41

'•

under part of the centrum, as, e. g. the two which articulate with
the basioccipital in the Arapaima gig as. As the centrum of the
atlas retains its normal relations to the other elements, and the
ordinary mode of articulation with the body of the second verte-
bra, this shows no ' odontoid process ' in fishes.

The number of vertebrae varies greatly in the different osseous
fishes : the Plectognathi (Diodon., Tetrodon) have the fewest and
largest: the apodal fishes (Eels, Gyninotes) have the
most and smallest, in proportion to their size. It is not
easy to determine the precise number, on account of the
coalescence of some of the vertebra, or at least of their
central elements, in particular parts of the column. In-
stances of anchylosis of some of the anterior vertebra?,
analogous to that noticed in the cartilaginous Sturgeons,

o o o y

Chimaerae, Rhinobates, and some Sharks, occur also
amongst the osseous fishes, as in many Siluroid and Cy-
prinoid species, in Loricaria and Dactylopterus. Fig. 35
represents the four singularly elongated anchylosed ante-
rior vertebrae in the Tobacco-pipe fish (Fistularia tabac-
caria). A coalescence of several vertebrae is more con-
stant at the opposite end of the column in osseous fishes,
in order to form the base of the caudal fin, when this is
symmetrical in form, as in fig. 33, and in most existing
species of Teleostomi. But this modification is arrested
at different stages in the piscine class. In Cyclostomi
the gristly parts of the vertebrae continue distinct, with
gradual reduction in size to the taper end of the long tail :
in Protopteri the bony representatives of the caudal ver-
tebrae behave in the same way: the notochord persists in
both orders. In Mur&nidce, where it is changed into cen-
trums, these also gradually diminish in size, and remain distinct
to the tail-end. The continuous vertical fold of skin bordering
the compressed, long, and slender termination of the vertebral
column is not specialised as a caudal fin.1 In Plagiostomi, Holo-
cephali, Sturionidce, and many Ganoidei, the caudal fin, fig.
29, c, is formed chiefly by the haemal spines and appendages,
developed to support a lower 6 lobe ;' the vertebrae continue
distinct to the end of the tail, which bending upward, seems to
form an upper lobe longer than the lower : to this unsymme-
trical tail-fin the term ( heterocercal ' is applied. By decreased

1 This primitive embryonal basis of the piscine tail-fin is not to be confounded,
because it is symmetrical as to shape, with the extreme stage of developemental modi-
fication constituting the true ' homocercal ' type of most existing fishes.

42 ANATOMY OF VERTEBRATES.

number, with progressive confluence, of the caudal vertebrae, the
e upper lobe ' becomes gradually reduced in length, until the
symmetrical shape is attained. But this coexists in the Salmon,
Perch, and many extinct Ganoids with an unsymmetrical bend
of the coalesced caudal vertebra? into the base of the upper lobe.
In true ( homocercals ' the terminal bodies of the caudal vertebras
are not separately established in the primitive notochord, but are
continuously ossified to form a common, compressed, vertically
extended, and often bifurcated bony plate, fig. 33, n'h', from
which the neural and haemal arches and their spines

o f*

radiate : from these elements alone can the number of
vertebras of such caudal fin be estimated ; normal de-
velopement proceeding here in the peripheral elements,
as throughout the vertebral column in Lepidosiren, whilst
it is arrested in the central parts of the vertebrae. In
the Sun-fish ( Orthagoriscus mola) it would seem as if a
row of rudimental vertebra? had been blended together
at right angles to the rest of the column, in order to
support the rays of the short, but very deep caudal
fin, which terminates the suddenly truncated body of
this oddly shaped fish.

It is rare to find anchylosis save at the ends of the
vertebral series in fishes : sometimes, however, in the
PleuronectidcB, a kind of sacrum is formed by such bony
union of the bodies, c, and ha?mal spines, hs} of the
first two of the caudal series, as in fig. 36 ; ! in which
the broad and deep haemal spines are concave forwards,
and form a sort of pelvic posterior wall of the abdomen.
In the Halibut (JHippoglossus) the parapophyses of the
corresponding vertebra? with those of the last abdominal
are similarly united, though the bodies remain distinct.
In Loricaria both the upper and lower arches of a con-
siderable part of the caudal region are blended together
into an inflexible sacrum ; but, as a general rule, there
exists no such impediment to the lateral inflections of
the tail in the present class.

The number of trunk- vertebra? is a useful specific
character in Ichthyology ; and in counting them the
coalesced caudals are usually reckoned as ( one.' In the
Sun-fish ( Orthagoriscus} I find but 8 abdominal and 8
caudal vertebra? by distinct bodies. In a Globe-fish
^ Tetrodon) there are 7 abdominal and 10 caudal vertebra? :

1 Osteol. Collection, Mus. Coll. Chir. No. 188 ; xuv. i, p. 50.

ANATOMY OF VERTEBRATES.

43

total, 17. 1 In the Conger there are 162 vertebras ; in the
Ophidium, 204 ; in the Gymnotus, 236 ; and even this number
is surpassed in some Plagiostomes.

Although the vertebras maintain a considerable sameness of
form in the same fish,, they vary much in different species. The
bodies are commonly subcylindrical ; as deep, but not so broad,
as they are long ; more or less constricted in the middle, in some
to such a degree as to present an hour-glass figure. In Spina-
chorhinus they are extremely short ; in Fistularia extremely
long ; in Tetrodon 2 they are much compressed ; in Platyceplialus
they are more depressed ; in the tail of the Tunny the entire ver-
tebra is cubical,3 with the ends hollowed as usual, but the four
other sides flat, the upper and lower ones being formed, in the
connected series, by the neural and haemal arches of the vertebra
in advance, flattened down and, as it were, pressed into cavities
on the upper and under surfaces, of the centrum of the next
vertebra; so that the series is naturally locked together in the
dried skeleton ; and these arches cover not the neural and haamal
canals of their own, but of the succeeding, centrum.

The principle of vegetative repetition is manifested, in osseous
fishes, by the numerous centres of ossification,
from which shoot out bony rays affording ad-
ditional strength to many of the intermuscular
aponeuroses. In this system of bones may
be ranked those spines which are attached to,
or near to, the heads of the ribs, and extend
upward, outward, and backward, between the
dorsal and lateral masses of muscles, fig. 32, i p,
fig. 21, pi, a. These ' scleral ' spines are
termed, according to the vertebral element
they may adhere to, ( epineurals,' ' epicen-
trals,' and ( epipleurals ' ; though each may
shift its place, rising or falling gradually along
the series of vertebra?. All three kinds are
present in the herring, fig. 37, in which n a
is the ( epineural,' p a the ( epicentral,' pi a the epipleural spines.
The latter have been called ' upper ribs,' and in Polypterus are
stronger than the ('under') ribs themselves. In Esox and
Thymallus the epineural and epicentral spines are present: in
Cyprinus the epineural and epipleural ones : in Perca and Gadus
the middle series only is found, passing gradually from the

Abdominal vertebra,
Herring (flupea)

1 Osteol. Collection, Mus. Coll. Chir. No. 357, p. 81.

2 Ib. No. 357. 3 Ib. No. 247. XLIV. i, p. 62.

44

ANATOMY OF VERTEBRATES.

par- to the pleur-apophyses : in Salmo only the upper series
exists, developed from the second to the antepenultimate abdo-
minal neurapophysis, in S. Eriox.1 There are, however, gristly
representatives of epipleurals. In Gtyphysodon the epipleurals
are anchylosed to the ribs, foreshowing their normal condition
in the bird's thorax. According to the seat of their develope-
ment they belong to the ( scleroskeleton : ' by their attachments
to bone they are ( vertebral appendages.'

The vertical folds of skin from the middle line, constituting
the azygos fins, are the seat of ossifications in most fishes, develop-
ing a second row of spines, figs. 34, 38, dn, dn, above the neural,
n, and a corresponding row, dh, dk, below the haemal, h, spines.
Some of these dermal bones, in certain fishes, project as hard
enamelled weapons from the surface of the body. From the
bases of the dermal spines, other spines (fig 34, in, Hi) usually
shoot downward into the intervals of the neural and haemal spines.
In deep-bodied fishes they are broad and strong, as e. g. in the
Cock-fish, fig. 38 ; in the flat-fishes they are double, figs. 39 and
40 ; and these modifications are usually repeated above and
below. Both interneural and interha3inal spines are commonly
shaped like daggers, plunged in the flesh to the hilt, which is re-

38

Aryyrciosus seiipinnis

presented by the part to which the fin-ray (dermoneural or
dermohamial spine) is attached. In the plaice tribe (Pleuro-
nectidce) these superadded dermal ossifications are developed
above the cranial as well as the corporal vertebra? (fig. 39, dn),

1 XLIV. i, p. 16. CLIII.

ANATOMY OF VERTEBRATES.

45

and along the whole haemal region of the trunk, from the head to
the tail. This want of correspondence with the number of the
true segments of the endoskeleton, and the seat of developement
of the inter- and dermo-neurals and inter- and dermo-hsemals, with
some minor considerations, led me, in 1845, to substitute for the
views and illustration of the typical vertebra} proposed by GeofFroy
St.-Hilaire, l and then accepted and taught by Professor R. E.
Grant 2 in this country and by others abroad, the interpretation of
the supposed type-exemplar, which is contrasted with Geoffroy's in
fig. 40. The names applied by the French philosophical anatomist
to the several parts of the combined endo- and exo-skeletal segment

39

Pleuronectes Solea. XLIII.

are opposite the left hand of the reader : those applied to them
in my ' Archetype of the Skeleton ' are opposite the right hand.

The small exogenous process standing out from the sides
of the centrum is a dismemberment of the parapophysis ; in
the first caudal vertebra it is given off from the base of the
parapophysis, increases in length in the second caudal, rises upon
the side of the centrum in the third, and becomes distinct from
the parapophysis in the fourth : it diminishes and disappears in
the ninth and tenth caudal vertebra. In Polypterus and Murae-
noids a transverse process coexists, from the same cause, with the
parapophysis. This, in the twenty-fifth trunk-vertebra of
Murcena Helena,* bifurcates, and in the following vertebrae the

1 Memoires du Mus. 4to, is. 1822, p. 119, pi. v.

2 Lectures on Comp. Anat. p. 58. 3 XLIV. p. 14. No. 37-

46

ANATOMY OF VERTEBRATES.

o

•g

i

to

a
6

^

o

p

fissure deepens and the fork elongates, until at the seventy-third
the lower prong descends at a right angle to the upper one, and,
meeting its fellow, forms the hamial arch. There are no true
40 hrcmapophyses in the tail of fishes : the elements there

composing the luemal arch are parapophyses, pleura-
pophyses, or both combined. In the abdomen only are
hremapophyses represented by the supporting bones of
the ventral fins, fig. 41, 64. The slender ossicles
along its under part in the Herring, fig. 37, dh, are
dermal bones, which, like the scutes of serpents, are
connected with the lower ends of the ribs, pi.

In the subclass Protopteri the notochord, fig. 41,
ch, persists : the neural arches, n, ns, are ossified :
the haemal arches in the abdomen are represented
by parial bones, p, attached to the notochordal sheath,
and curving outward, like the long parapophyses in
the Cod, and the short pleurapophyses in the Amia
and Salamander, with which they, more probably,
are homologous. These riblets bend down and

o

meet at the beginning of the tail, p, to form the
ha3inal arch and support the ha3inal spines, hs, along
that region. As in fishes, the Lepidosiren also cle-
velopes in the continuous vertical fin-fold the acces-
sory ossicles marked in, ih, in the cut.

§ 18. Vertebral column of Batrachia. — Neither
inter- nor dermo-neurals are present in any gano-
cephalan or batrachian. In the former amphibious
order the notochord persists, but with beginnings of
the ossification of centrums : } in Batrachia it is con-
verted into a series of separate centrums. These in
the Ichthyomorphs are biconical, and deeply cupped
at both ends, through the same arrest of ossification
as in fishes : the developement of the vertebra goes
through the same piscine stage in the Iarva3 of the
Theriomorphs, as indicated by the dotted lines d, fig.
42 ; in the mature quadrupedal stage of these Ba-
trachia, ossification converts one terminal cup into a
ball ; which may be the front one, as in Pipa, or the
hind one, as in Rana, and most frogs and toads. In
the Land- Salamander, also, ossification goes to this
- and exo-ske- stage, with the ball in front.

lotal elements of a
caudal vertebra of
the Plaice, n.

1 Lectures on Comp. Anat. p. 194, Fig. 84.

£
•a

o

ft

ANATOMY OE VERTEBRATES.

47

The Siren lacertina has between eighty and ninety trunk-vertebrae.
They have many longitudinal ridges, the neural arch has coalesced
with the centrum, the neural spine forms the highest ridge and
bifurcates posteriorly to terminate upon the zygapophysis. A

41

/is -m

Skeleton of Lepidosiren anncctcns. xxxin.

hypapophysial ridge forms, by defect of ossification on each side,
the under part of the centrum. A parapophysial ridge extends
from a short anterior parapophysis to the longer parapophysial
part of the posterior transverse process. A diapophysial ridge
extends above, and nearly parallel with the former, from the
anterior zygapophysis to the diapophysial part of the posterior
transverse process. Thence a third short ridge is continued to the
posterior zygapophysis. The vacuities between these several ridges
resemble those in the vertebras of some fishes. The body of the
atlas extends forward like a short odontoid process : short par-
arid di-apophysial plates are developed from each side of the atlas,
which has also the posterior zygapophyses. In the second vertebra
the par- and di-apophysial plates have united to form a compound

42

30

Skeleton of Tadpole of Itana csculenta

transverse process, which supports a short straight pleurapophysis.
These elements are similarly developed from six or seven succes-
sive vertebrae. In the tail the vertebra is compressed and vertically
extended by the bending down of the parapophysial plates to form
two vertical walls, intercepting a haamal canal. In the Proteus,
which has about sixty trunk-vertebras, the third to the ninth in-
clusive support short ribs, attached to the lower (parapophysial)

48

ANATOMY OF VERTEBRATES.

half of the transverse process : they are wanting
in the twenty-one following vertebrae, and re-
appear, well developed, in the thirty-first, where
they form with cartilaginous haemapophyses, a
pelvic arch. In the Menopome, fig. 43, the
second to the nineteenth vertebrae support short
straight pleurapophyses, articulated to the ends
of transverse processes formed by par- and di-
apophyses, which intercept by their terminal
confluence an arterial canal. These processes,
t, are enlarged in the twentieth vertebra, s, and a
second rib-like piece, 62, the homotype of the
second part of the scapula in fishes, is articulated
to the short and thick rudimental rib, pi; the
inferior or haemal arch 63, 64, beincf cartilaginous.

•* o o

The segment thus completed by the haemal arch,
represents a so-called ( sacral : vertebra : the
second division of its rib answers to the ' ilium,'
62, and the haemal cartilage to the ( ischium,' or
cpubis.' Transverse processes t, progressively
decreasing in length are developed from the six
succeeding vertebrae. Bony pleurapophyses pi,
are attached to the first of these, and cartila-
ginous rudiments of the same element to the
three following. Haemal arches are anchylosed
to the under part of the centrum of the second
to the twelfth caudal vertebra inclusive, and
these become more compressed to the end of the
tail, for the support of a vertical fin. The neural
arches are broad, depressed, anchylosed to the
centrum : they are complete to the fourteenth
caudal vertebra. The body of the atlas pre-
sents an odontoid process between the two arti-
cular surfaces for the occipital condyles ; it is
deeply cupped behind, as are the succeeding
vertebrae at both ends. This vertebra has neither
di- nor pleur-apophyses.

The skeleton of the Newt ( Triton) resembles
that of the Menopome in its general characters ; the
neural and haemal spines are more produced in the
long tail, supporting there the chief swimming
skeleton of the Menopome organ of this aquatic batrachian.^ In one kind

are more developed, occasioning the sub-

8

m

or Protonopsis

ANATOMY OF VERTEBRATES.

49

Gl

f"

genus called Pleurodeles. In the land Salamander the backbone
is strengthened by the ball-and-socket articulation of the trunk-
vertebrae. Cuvier notices a curious inconstancy in the place of
attachment of the pelvic arch, sometimes to the fifteenth,, some-
times to the sixteenth,
and in one instance sus-
pended by the right pier
to the sixteenth, by the
left to the seventeenth,
vertebra, in Salaman-
dra atra.1

The ophiomorphous
batrachia are remark-
able for the multiplicity,
the theriomorphous for
the paucity, of distinct
vertebra? in the trunk ;
these latter have the
ball-and-socket articula-
tion. The frog, fig. 44,
A, has nine vertebrae
and the coccygeal style
c ; but by coalescence of
this with the sacrum,
and of the atlas with the
second vertebra, in the
Surinam toad (Pipa), the
number of distinct trunk-
segments is in that
species reduced to seven.

In Rana boans the
atlas has no diapophy-
ses ; but they are present
and of great length in
the succeeding vertebrae
to the sacrum inclusive, where they are thick and support by
their truncate ends two long rib-like bones, ib. A, 62, which
expand at their distal ends, and unite there to two partially
anchylosed bony plates, 64, which complete the haemal arch of the
ninth segment of the trunk. The superior developement of this
arch relates to the great size and strength of its appendages —

1 CLI. torn. v. pt. ii. p. 413,
E

SC'

TVii

Skeleton of frog, A ; vertebra B and carpus c of toad.

50 ANATOMY OF VERTEBRATES.

the hinder extremities- -in the tailless order, especially the frogs.
In the seven vertebrae between the atlas and sacrum, two zyga-
pophyses looking upward are developed from the fore part, and
two looking downward from the back part of the neural arch ;
there is also a short spine.

In the Toad (Bufo vulgaris) the number of trunk-vertebrae, fig.
44, B, is the same as in the Frogs, but the diapophyses of the third
and fourth vertebra? are relatively longer, those of the sacral
vertebra, s, relatively shorter, broader, and expanded so as to over-
lap the ilia, which are shorter and more arched. In Cystignathus
pachypus the sacral diapophyses are subcylindrical. In Pipa the
diapophyses of the second and third vertebra are of unusual
length, and support semi-ossified, short, flattened pleurapophyses.
The diapophyses of the four succeeding vertebras are short and
slender ; those of the sacrum are more expanded than in the toad,
and rest upon the anterior halves of the iliac bones. The coccy-
geal style shows, in most anourans, a simple anchylosed neural
canal, and also a haemal canal, as at h, D, fig. 44.

In the Ophiomorphs ( Ccecilice) the vertebras, besides being very
numerous, are biconcave.

§ 19. Vertebral column of Ichthyopterygia. — In an extinct
order (Ichthyopterygia) of Dipnoal Reptiles, modified for marine
life, but breathing air, the trunk-vertebras were very numerous,
very short, and biconcave ; the centrums remained distinct from
the neural and haemal arches, and were ligamentously, not sutur-
ally, united thereto. In the Ichthyosaurus communis, fig. 105,
there are about 140 vertebras ; in the anterior sixteen a short
parapophysis is developed from the side of the centrum, and
a diapophysis from the base of the neural arch ; but this soon
begins to project from the neurapophysial border of the centrum,
and then from the side of the centrum below that border. It
continues gradually to sink in position until, at about the fortieth
vertebra, it blends with the parapophysis, which alone continues
to represent a transverse process, as far as at about the eightieth
vertebra,1 where it disappears and the succeeding centrums become
compressed, indicating the vertical position of the dermal tail-fin
which they supported. The atlas and axis centrums become
anchylosed by flat surfaces ; but each supports its own neural
arch. Between the lower part of the atlas and the occipital
condyle is a wedge-shaped hypapophysis, representing the part
called ' body of the atlas ' in anthropotomy : a similar bone is

1 A dislocation or fracture commonly occurred at this part between the death and
final imbedding of the decomposing animal ; CLXI.

ANATOMY OF VERTEBRATES. 51

wedged between the atlas and axis, a third between this and the
third vertebra ; all tending to strengthen and stiffen, the part of
the vertebral column sustaining the skull, and adding to its power
of displacing the water in the agile movements of this ancient
predatory aquatic animal.1 As in Fishes, also, the continuity of
the broad occiput with the trunk was uninterrupted by any cervical
constriction. The ribs commence at the second vertebra, but by
a bifurcate head ; and so continue, articulating with both par- and
di-apophyses until the confluence of those processes, when they
become single-headed. The ribs rapidly increase in length, which
is greatest at the middle of the thoracic-abdominal cavity, and
then gradually diminish to short and straight appendages, resem-
bling detached transverse processes, in the tail. The longer ribs
are grooved longitudinally ; their lower ends are united to ha^m-
apophyses, subdivided into tAVO or three overlapping slender
portions, the lowest articulating with a median transverse style,
pointed at each end, representing the haemal spine, and completing
the lijemal arch in the abdomen. In the tail the haemapophyses
are simple, and attached by ligament, above to the centrum, and
below to one another.

§ 20. Vertebral column of Sauropterygia. — In this extinct
order of aquatic Reptiles the vertebral bodies had their terminal
articular surfaces either flat or slightly concave, or with the
middle of such cavity a little convex. In certain genera the
neck-vertebra3 were uncommonly numerous ; this was remarkably
so in the Plesiosaurus, fig. 45, in which those vertebra? consist of
centrum, neural arch, and pleurapophyses. The latter are wanting
in the first vertebra ; but both this and the second have the
hypapophyses. The cervical ribs are short, and expand at their
free end. They articulate by a simple head to a shallow pit, which
is rarely supported on a process, on the side of the centrum.
The body of the atlas articulates with a large hypapophysis
below, with the neurapophysis above, with the body of the axis
behind, and with part of the occipital condyle in front ; and all
the articulations, save the last, may become obliterated by
anchylosis. The hypapophysis forms the lower two-thirds, the
neurapophysis contributes the upper and lateral parts, and the
centrum forms the middle or bottom of the cup for the occipital
condyle. The second hypapophysis becomes ^confluent with the
inferior interspace between the bodies of the atlas and axis.2 As
the cervical vertebra? approach the dorsal, the costal pit gradually

1 CLXV. 2 CLXVI.

E 2

52

ANATOMY OF VERTEBRATES.

45

df

Skeleton of Plesiosaurus. CLXIII.

rises from the centrum to the
neurapophysis. This takes
place at the fortieth vertebra
in the Plesiosaurus homalo-
spondylus of the Whitby Lias,
but, in the PL doliclwdeirus,
fig. 45, of the Dorsetshire
Lias, at about the thirtieth, c.
The dorsal region is arbitrarily
commenced by the vertebra in
which the costal surface begins
to be supported on a diapo-
physis ; this progressively in-
creases in length in the second
and third dorsal, continues as
a transverse process to near
the end of the trunk, and on
the vertebra, s, between the
iliac bones, 62, it subsides to the
level of the neurapophysis. In
the caudal vertebras the costal
surface gradually descends from
the neurapophysis upon the
side of the centrum ; it is
never divided by the longitu-
dinal groove which, in most
Plesiosauri, indents that sur-
face in the cervical vertebras.
The neural arches are com-
monly unanchylosed with the
centrum. The long and large
spinous processes, in contact
along the trunk and base of the
neck, must have restricted the
bending movements chiefly to
the lateral directions. The
pleurapophyses gain in length,
and lose in terminal breadth,
in the hinder cervicals ; and
become long and slender ribs
in the dorsal region, curving
outward and downward so as
to encompass the upper two-

ANATOMY OF VERTEBRATES. 53

thirds of the thoracic-abdominal cavity. They decrease in length
and curvature as they approach the tail, where they are reduced
to short straight pieces, as in the neck, but are not terminally
expanded ; they cease to be developed near the end of the tail.
The hsemapophyses in the abdominal region, are subdivided,
and with the haemal spine or median piece, form a kind of
6 plastron' of transversely extended, slightly bent, median and
lateral, overlapping bony bars, occupying the subabdominal space
between the scapular, 52, and pelvic, 64, arches. In the tail the
hasmapophyses are short and straight, and remain, as in the
Ichthyosaurus, ununited both above and below. One Sauro-
pterygian genus, Tanystropheus, had the centrum, in certain
vertebras, so long and hollow as to simulate a limb-bone. In
another genus, (Pliosaurus) they were as short, in the cervical
region, as in the Ichthyosaurus. In a third genus (Nothosaurus}
two vertebras are recognised as sacral by their thick, straight, and
convergent pleurapophyses, of which the first overlaps the second.
In a fourth genus the wedge-shaped hypapophyses occur at the
lower interspaces of the dorsal and lumbar vertebras, whence its
name, Sphenosaurus.

§ 21. Vertebral column of Ophidia. — Amongst existing Reptiles,
the Serpents ( Ophidia) surpass all others in the vast number of
their vertebras, which, with incomplete hasmal arches, compose the
skeleton of the long, slender, limbless trunk, fig. 46.

In all these vertebras the autogenous elements, except the
pleurapophyses, fig. 46, pi, coalesce with one another, and the
pleurapophyses become anchylosed to the diapophyses in the tail.
There is no trace of suture between the neural arch, fig. 47,
ns, z, and centrum, c. The outer substance of the vertebra is
compact, with a smooth or polished surface. The vertebras are
( proccelian ; ' that is, they are articulated together by ball-and-
socket joints, the socket being on the fore part of the centrum, fig.
47 A, where it forms a deep cup with its rim sharply defined ;
the cavity looking not directly forward, but a little downward,
from the greater prominence of the upper border : the well-turned
prominent ball terminates the back part of the centrum rather
more obliquely, its aspect being backward and upward, fig. 47,
c. The hypapophysis, h, is developed in different proportions
from different vertebras, but throughout the greater part of the
trunk presents a considerable size in the cobra, 46, hy, and
crotalus, figs. 47, 47 A, h : it is shorter in the python and boa.
A vascular canal perforates the under surface of the centrum, and
there are sometimes two or even three smaller foramina. In the

54

ANATOMY OF VERTEBRATES.

46

23

python a large, vertically oblong, but short diapophysis extends
from the fore part of the side of the centrum obliquely backward :

it is covered by the ar-
ticular surface for the
rib, is convex lengthwise
and convex vertically
at its upper half, but
slightly concave at its
lower half. In the
rattlesnake the diapo-
physis developes a small,
circumscribed, articular,
tubercle, ib. ^/,-for the
( vertebral rib ' or pleur-
apophysis, pl\ a parapo-
physis, d! ', extends down-
ward and forward below
the level of the cen-
trum ; the anterior zy-
gapophysis, z, is sup-
ported by a process,
ib. d" 9 from the upper
end of the diapophysis.
The base of the neural
arch swells outward
from its confluence with
the centrum, and de-
velopes from each angle
a transversely-elongated
zygapophy sis ; that from
the anterior angle, z,
looking upward, that
from the posterior angle,
z' ', downward ; both sur-
faces being flat, and
almost horizontal, as in
the Batrachians. The
neural canal is narrow ;
the neural spine, ns, is of
moderate height, about

Skeleton of the cobra (Naija tripudians}

equal to its

terior extent ; it is compressed and truncate. A wedge-shaped
process, ' zygosphene,' zs, is developed from the fore part of the

ANATOMY OF VERTEBRATES.

55

47

ns

Two vertebra? of the Rattlesnake
(Grotalus)

base of the spine ; the lower apex of the wedge being, as it were,
cut off, and its sloping sides presenting two smooth, flat, articular
surfaces. This wedge is received into a cavity, the ' zygantrum,'
excavated in the posterior expansion of the neural arch, and
having two smooth articular surfaces to which the zygosphenal
surfaces are adapted. Thus the vertebrae of serpents articulate
with each other by eight joints in addition to those of the cup and
ball on the centrum ; and interlock by parts reciprocally receiving
and entering one another, like the joints called tenon-and-mortice
in carpentry, fig. 47. In the caudal vertebras, the hypapophysis
is double, the transition being effected by
its progressive bifurcation in the posterior
abdominal vertebrae. The diapophyses be-
come much longer in the caudal vertebrae,
and support in the anterior ones short ribs
which usually become anchylosed to their
extremities.

The pleurapophyses or vertebral ribs
have an oblong articular surface, concave
above and almost flat below in the Python,
with a tubercle developed from the upper
part, and a rough surface excavated on the fore part of the ex-
panded head for the insertion of the precostal ligament. They
have a large medullary cavity, with dense but thin walls, and a
fine cancellous structure at their articular ends. Their lower end
supports a short cartilaginous hasmapophysis, which is attached
to the broad and stiff abdominal scute. These scutes, alternately
raised and depressed by muscles attached
to the ribs and integument, aid in the glid-
ing movements of serpents ; and the ribs,
like the legs in the centipede, subserve
locomotion ; but they have also accessory
functions in relation to breathing and con-
striction. The anterior ribs in the cobra,
fig. 46, pi, are unusually long, and are
slightly bent ; they can be folded back one
upon another, and can be drawn forward,
or erected, when they sustain a fold of
integument, peculiarly coloured in some
spectacled cobra - - and which has the effect of making this
venomous snake more conspicuous at the moment when it is
about to inflict its deadly bite. The ribs commence in the
cobra, as in other serpents, at the third vertebra from the head.

Front view of a vertebra,
Rattlesnake

species

— e.g., the

56 ANATOMY OF VERTEBRATES.

The centrum of the first vertebra coalesces with that of the
second, and its place is taken by an autogenous hypapophysis :
this, in the python, is articulated by suture to the neurapophyses ;
it also presents a concave articular surface anteriorly for the lower
part of the basioccipital tubercle, and a similar surface behind for
the detached central part of the body of the atlas, or ' odontoid
process of the axis.' The base of each neurapophysis has an
antero-internal articular surface for the exoccipital tubercle, the
middle one for the hypapophysis, and a postero-internal surface
for the upper and lateral parts of the odontoid ; they thus rest on
both the separated parts of their proper centrum. The neura-
pophyses expand and arch over the neural canal, but meet
without coalescing. There is no neural spine. Each neura-
pophysis developes from its upper and hinder border a short
zygapophysis, and from its side a still shorter diapophysis. In
the second vertebra, the odontoid presents a convex tubercle
anteriorly, which fills up the articular cavity in the atlas for the
occipital tubercle ; below this is the surface for the hypapophysial
part of the atlas, and above and behind it are the two surfaces
for the atlantal neurapophyses. The whole posterior surface of
the odontoid is anchylosed to the proper centrum of the axis, and
in part to its hypapophysis. The neural arch of the axis de-
velopes a short ribless diapophysis from each side of its base ; a
thick sub-bifid zygapophysis from each side of the posterior
margin ; and a moderately long bent-back spine from its upper
part. The centrum terminates in a ball behind, and below this
sends downward and backward a long hypapophysis.

At the opposite extreme of the elongated body, two or three
much simplified vertebrae are usually found blended together ; they
support the horny rings forming the warning rattle of the Cro-
talus. There is no sternum in true Ophidia.

The skeleton of the Python (P. tigris)1 has 291 vertebras, of
which the 3rd to the 251st support movable ribs. The 74
anterior vertebrae develope hypapophyses. The skeleton of the
Boa constrictor* has 305 vertebras, a hypapophysis being developed
from the 60 anterior ones. In the skeleton of a Rattle-snake
(Crotalus horridus^ with 194 vertebras, 168 support movable
ribs, and all these develope hypapophyses, fig. 47, h, as long as the
neural spines, ns. In the Naja, fig. 46, as many vertebrae have
the lower process, but of less length. In the Rough Tree-snake
(Deirodon sealer)* with 256 vertebras, a hyj apophysis projects

1 XLIV. vol. i. No. 602, p. 123. 2 Ib., No. G30, p. 132.
3 Ib., No. 640, p. 135. 4 Ib., No. 638, p. 134.

ANATOMY OF VERTEBRATES.

57

48

from the 32 anterior ones,, directed backward in the first ten, and
forward in the last ten, where they are unusually long, and tipped
with a coat of hard dentine ; these perforate the oesophagus, and
serve as teeth. The jaws are merely roughened by rudiments of
teeth. The relation of this singular condition of the cervical
hypapophyses and the modification of the dental system to the
food of the Deirodon will be explained in the chapter on teeth.

§ 22. Vertebral column of Lacertia. - The anguine or snake-
like reptiles, with fixed upper-jaws and a
scapular arch, pass gradually, by other forms
with rudiments of limbs (Pseudofms), to the
slender-bodied lon^-tailed lacertians. The dis-

o

tinction is effected through the establishment
of a costal arch in the trunk, completed by the
addition of a hasmal spine (sternum) and haama-
pophyses (sternal ribs) to the pleurapophyses
or vertebral ribs, which are alone ossified in
Ophidia.

The vertebra of the trunk have the same procoelian character,
i. e., with the cup anterior and the ball behind, fig. 48 ; the latter,
c, being usually less prominent, more oblique, and more trans-
versely oval than in serpents. The vertebras also are commonly
larger, and always fewer in number than in the typical Ophidia.

Those of the Iguanas retain the superadded articular surfaces
of the zygosphene, fig. 48, zs, and zygantrum ; but I have not
met with these superadded processes in other lacertians. In the

49

Trimk vertebra, Iguana

Fore part of skeleton of a Lizard

Geckos the vertebra are, exceptionally, biconcave. ! The ribs do
not begin to be developed so near the head as in Ophidia, Not
only the atlas and dentata, but the third vertebra, fig. 49, and
sometimes, as in the Monitor ( Varanus)^ the four following verte-
bras, are devoid of pleurapophyses : when these first appear they

See those of the subgenus Rliynchocephalus, XLIV. vol. i. No. 662, p. 142.

58

ANATOMY OF VERTEBRATES.

50

are short, as at a ; but elongate in succeeding vertebras, b to e ;

and usually at the eighth,
or ninth, fig. 49, /, 6,
(Lacertci), from the head
or tenth ( Varanus), they
are joined through the
medium of ossified haema-
pophyses to the ster-
num. Two( Varanus),i\\TQQ
( Chameleo, Iguana), or four
(Cyclodus), following ver-
tebrae are similarly com-
pleted; and then the haama-
pophyses are either united
below without intervening
sternum ( Chameleo), or two
or three of them are joined
by a common cartilage to
the cartilaginous end of
the sternum. The haama-
pophyses afterwards pro-
ject freely, and are reduced
to short appendages to
the pleurapophyses. These
also shorten, and sometimes
suddenly, as, e. g., after
the eighteenth vertebra in
the Monitors ( Varanus), in
which they end at the
twenty-eighth vertebra, as
they began, viz., in the
form of short straight ap-
pendages to the diapo-
physes.

The Draco volans, fig.
50, is so called on account
of the wing-like expansions
from the sides of its body,
supported, like the hood of
the cobra, by slender elon-
gated ribs. In this little

Skeleton of Draco volans j^^ ^^ ^ twenty

vertebra? supporting movable ribs, which commence apparently

ANATOMY OF VEKTEBKATES. 59

at the fifth. Those of the eighth vertebra first join the sternum,
as do those of the ninth and tenth ; the plenrapophyses of the
eleventh vertebra suddenly acquire extreme length ; those of the
four following vertebras are also long and slender ; they extend
outward and backward, and support the parachute formed by the
broad lateral fold of the abdominal integuments. The pleurapo-
physes of the succeeding vertebra? rapidly shorten. The sacrum
consists of two vertebrae. There are about fifty caudal vertebra?.

The semi-ossified sternum in the Iguana has a median
groove and fissure, and readily separates into two lateral
moieties. The long stem of the episternum covers the outer
part of the groove, where it represents the c keel ' of the sternum
in birds.

The two sacral vertebra? retain, in most Lacertians, the cup-
and-ball joints ; and in the Scincks, where they coalesce, the
second presents a ball to the first caudal. Haamapophyses are
wanting in the first caudal, commence in the second, but are
displaced to the interval between this and the third ; they are
confluent at their distal ends, and there produced into a spine :
these ' chevron bones ' are continued usually along two-thirds of
the tail. In most of the caudal vertebra? the anterior third of
the centrum is marked off by a line, just anterior to the dia-
pophyses, where the tail snaps off, when a lizard escapes, leaving
the part that has been seized in the hands of the baffled pursuer.
The ossification of the centrum from two points, and their in-
complete anchylosis has prospective relation to the liability of
lizards to be caught by their long tail, and lends itself to their
escape. The epiphysial line does not extend through the thin
and brittle neural arch, which readily snaps when the two parts
of the centrum to which it is anchylosed are separated. Lizards
reproduce the lost tail ; but the vertebral axis is never ossified in
the new-formed part.

In the slow-worm (Anyuis) there are 111 vertebra?, 61 of which,
beginning at the fourth, support free ribs. The transverse pro-
cesses of the tail are formed by short anchylosed pleurapophyses,
which are bifurcate in the second and third caudals. The hypa-
pophyses are, also, anchylosed to the centrum ; but, instead of
remaining distinct, as in true Ophidia, they unite at their lower
ends and complete the haamal arch. The vertebra? of the Amphis-
bcena have no neural spine.

The lacertian modifications of the atlas and axis1 agree in the

1 XLIV. vol. i. pp. 139 — 149.

GO

ANATOMY OF VERTEBRATES.

main with those in the Python. In Istiurus the cervical hypa-
pophyses are compressed, distinct, and articulated to the inter-
space between their own vertebra and the one in advance. The
caudal vertebras are remarkable for the great length of their
neural spines.

In the Chameleon the ribs commence at the fourth vertebra,
and those of the sixth are articulated by semiossified cartilages to
the sternum, as are the three following pairs ; in the next eight
or ten pairs the long and slender cartilages meet and unite to-
gether at their extremities. There are two lumbar and three
sacral vertebras ; the tail is long and prehensile. In the
Iguana tuberculata twenty-one vertebras, commencing with the
fifth, support free ribs, and those of the ninth first join the
sternum.

§ 23. Vertebral column of Chelonia.- -This column is most ex-

51

Skeleton of Emijs Enroptca. xxxvin.

traordinary in those Reptilia to which, in the manifold modifica-
tions of the organic framework, has been given a portable abode,
in compensation for inferior powers of locomotion and the want
of defensive weapons.

ANATOMY OF VERTEBRATES.

61

The expanded thoracic-abdominal case, fig. 51, K, K, into
which, in most Chelonians, the head, the tail, and the four ex-
tremities can be withdrawn, and in some of the species be there
shut up by movable doors closely fitting both the anterior
and posterior apertures- -as, e.g., in the box-tortoises (Cino-
sternon, Cistudo)- -}uas been the subject of many investigations;
and not the least interesting result has been the discovery
that this seemingly special and anomalous superaddition to the
ordinary vertebrate structure is due, in a great degree to the
modification of form and size, and, in a less degree, to a
change of relative position, of ordinary elements of the vertebrate
skeleton.

The natural dwelling-chamber of the Ckelonia consists chiefly,
and in the marine species (Clielone) and soft-turtles (Trionyx)
solely, of the floor and the roof:
side-walls of variable extent are
added in the fresh-water species
(Emys) and land-tortoises ( Tes-
tudo). The whole consists
chiefly of osseous ' plates ' with
superincumbent horny ( scutes,'
except in Trionyx said. Sphargis,
in which these latter are

52

wanting.

ffi7

10

Carapace of the Loggerhead Turtle (Chelone
caouannci)

The roof, or ( carapace,' fig.
52, consists of a ' median ' series
of symmetrical plates, ch, s i to
511, and of two ' lateral ' series
forming a pair, pi i to pi 8, the
whole being surrounded by a
circle of ' marginal ' pieces, in i

to py, completed anteriorly by ch, the first of the median
series. Of the median series eight, s i to s 8, are attached to
the spines of eight subjacent vertebra? : the lateral or parial
plates, pi i to pi 8, are attached to, and more or less blended
with, the ribs of the same vertebra? ; and the ends of these ribs
usually articulate by gomphosis with a corresponding number
of the marginal pieces, of which, however, there may be from
twenty-four to twenty-six, including the two median and symme-
trical ones, ch and py. That these marginal pieces are the least
essential parts of the carapace is shown, not only by their incon-
stant number, but by their partial or total absence in some of the
soft-turtles (Gymnopus, Sphargis).

62 ANATOMY OF VERTEBRATES.

The median pieces, s i to s 11, are called the f neural' plates;
the lateral pieces, pi i to pi 8, the ' costal ' plates ; the term
6 marginal ' is restricted to those peripheral pieces which form pairs,
m i to in 12 ; the anterior symmetrical piece, ch, constant in all
Chclonia, is called the ' nuchal ' plate ; the posterior symmetrical
piece, py, which is wanting in all the Trionycidce, is the f pygal '
plate. The neural arch, connate with the first neural plate, s i, is
supported partly by the centrum of the vertebra to which the first
pair of free ribs is articulated, and which, therefore, is reckoned
as the first dorsal vertebra : these ribs are small and slender,
attached at both their extremities, the outer end abutting against

' ~ C?

the under part of the first pair of costal plates, which they help
to sustain. The second to the ninth dorsal vertebrae inclusive,
being those which are more immediately connected with the neural
and costal plates, are the ( vertebra of the carapace : ' their
characters, though not less artificial than those which distinguish
the ( dorsal ' or ( lumbar ' vertebrae of other reptiles, are much
more marked and constant. The eighth vertebra of the cara-
pace is succeeded by one, winch in some species (e. g. Clielone
caouanna) supports a pair of short ribs, in others ( Trionyx) none,
and which is therefore reckoned a ' lumbar ' vertebra ; this is
followed by two other vertebra?, with short and thickened ribs,
abutting against the iliac bones and representing the e sacrum,'
fig. 51, G : as these three vertebras are not immediately united with
the ninth, tenth, and eleventh ( neural plates,' they have less claim
than the first dorsal vertebra to be regarded as entering into the
composition of the carapace.

The ' plastron,' fig. 53, or floor of the thoracic-abdominal
chamber, consists, in all recent Chelonia, of nine pieces. The
median and symmetrical piece, s, is the ( entosternal ; ' the four
pairs, counted from before backward, are respectively, the
( episternals ' (es), ' hyosternals ' (hs,) ( hyposternals ' (ps), and
( xiphisternals ' (xs).

In all the Chelonians, save the coriaceous (Sphargis) and soft
turtles ( Trionycidcs), the outer surface of the carapace is impressed
by the horny scutes, commonly called ( tortoise-shell ; ' and these
epidermal productions have received definite names in Zoological
Treatises, their modifications being found of great use in charac-
terising species. In fig. 52, v\ is placed on the first c vertebral
scute ' close to its union with the first and second ( costal scutes ; '
and v 2 to v 5 indicate the succeeding vertebral scutes, the outer
angles of which are similarly wedged between the adjoining pairs
of ( costal scutes : ' beyond the costal scutes are a series of ( mar-

ANATOMY OF VERTEBRATES.

63

53

ginal scutes,' supported by the marginal plates, and crossing their
sutures.

In the Trionycidce the exterior surface of the carapace and
plastron is remarkable for its rough vermicular or punctate
sculpturing.

The median bony pieces of the carapace, fig. 52, ch, s i to s 11,
have been regarded as lateral expansions of the summits of the
neural spines ; the medio-lateral pieces, ib. pi i to pi 8, as similar
developements of the ribs ; and the marginal pieces ib. m\ to m 13,
as the homologues of the sternal ribs. But the developement of
the carapace shows that ossification begins independently in a
fibro-cartilagmous matrix of the corium in the first, ch, and some
of the last, s 9 to s 11, median plates,
and extends from the summits of the
neural spines into only eight of the in-
tervening plates, s i to s 8 : ossification
also extends into the contiguous lateral
plates, pi i to pi 8, in some Chelonia,
not from the corresponding part of the
subjacent ribs, but from points alter-
nately nearer and farther from their
heads,1 showing that such extension of
ossification into the corium is not a
developement of the tubercle of the
rib, as has been supposed. Ossification
commences independently in the corium
for all the marginal plates, in i to py ; these never coalesce with the
bones uniting the sternum with the vertebral ribs, are often more
numerous, sometimes less numerous, than those ribs, and in a few
species are wanting. Whence it is to be inferred that the ex-
panded bones of the carapace, which are supported and impressed
by the thick epidermal scutes called 'tortoise-shell,' are dermal
ossifications, homologous with those which support the nuchal and
dorsal epidermal scutes in the crocodile. Along the under surface
of the costal plate the slender or proper portion of the rib may
be traced, of its ordinary breadth to near the head, which liberates
itself from the costal plate, as at I, fig. 51, to articulate to the in-
terspace of the two contiguous vertebra, to the posterior of which
such rib properly belongs.

In the ' plastron,' fig. 53, the entosternal, s, answers to the
sternum in the crocodile : the parial pieces are ( haemapophyses ' or

Plastron of Cfielone caouanna

1 CLXII. p. 163, pi. xiii. fig. 4.

64 ANATOMY OF VERTEBRATES.

sternal ribs, connate in a more or less complete degree with dermal
bony plates. There were five pairs in the extinct Pleurosternon.

In the marine Chelonians the dermal ossifications, fig. 52, pi i to
8, do not cover the whole of the intercostal spaces ; the slender
ribs project beyond them. In the fresh-water and land kinds
they extend to the marginal plates and complete the bony roof, as
in fiir. 51. There is a similar difference in the decree of ossification

O tJ

of the ( plastron ' between the genus Chelone and the genera Emys
and Testudo.

In the Chelonia the true centrum of the atlas does not coalesce,
as an ' odontoid ' process, with that of the axis, and usually supports
its own neural arch : the hypapophysis is proportionally reduced. 1
All the eight cervical vertebra, fig. 51, E, are free, movable, and
ribless : the fourth of these vertebras has a much elongated centrum,
which is convex at both ends : the eighth is short and broad, with
the anterior surface of the body divided into two transversely
elongated convexities, and the posterior part of the body forming
a sino-le convex surface divided into two lateral facets : the under

o

part of the centrum is carinate ; the neural arch, which is
anchylosed to this centrum, is short, broad, obtuse, and overarched
by the broad expanded nuchal plate. The first dorsal vertebra
is also short and broad, with two short and thick pleurapophyses,
articulated by one end to the expanded anterior part of the
centrum, and united by suture at the other end to the succeeding
pair of ribs. The head of each rib of the second pair is supported
upon a strong trihedral neck, and articulated to the interspace of
the first and second dorsal vertebras : it is connate, at the part
corresponding to the tubercle, with the first broad costal plate,
which articulates by suture to the lateral margin of the first
neural plate, and to portions of the nuchal and third neural
plates : the connate rib, which is almost lost in the substance of
the costal plate, is continued with it to the anterior and outer part
of the carapace, where it resumes its subcylindrical form, and
articulates with the second and third marginal pieces of the cara-
pace. The neural arch of the second dorsal vertebra is shifted
forwards to the interspace between its own centrum and that of
the first dorsal vertebra. A similar disposition of the neural
arch and of the ribs prevails in the third to the ninth dorsal
vertebras inclusive. The bony floor of the great abdominal box,
or ( plastron,' is formed by the hasmapophyses and sternum connate
with dermal osseous plates, forming, as in the turtle, nine pieces,

1 CLXVII p. 435, pi. xiii.

ANATOMY OF VERTEBRATES. 65

but they are more ossified, and the hyo- and hypo-sternals unite
suturally with the fourth, fifth, and sixth marginal plates, forming
the side-walls of the bony chamber cut through in fig. 51. The
junction between the hyo- and hypo-sternals admits of some
yielding movement. The iliac bones abut against the pleurapo-
physes of the tenth, eleventh, and twelfth vertebras, counting from
the first dorsal vertebra. These three vertebra form the sacrum :
their pleurapophyses are unanchylosed, converge, and unite at
their distal extremities to form the articular surface for the ilium.
Beyond these the caudal vertebrae, ib. H, thirty-five in number in
Testudo elephantopus, are free, with short, straight, and thick
pleurapophyses, articulated to the sides of the anterior expanded
portions of the centrums. They diminish to mere tubercles in the
tenth caudal vertebra, and disappear in the remainder. The neural
arches of the caudal vertebra? are flat above, and without spines.

§ 24. Vertebral column of Crocodilia. - - In this order free
pleurapophyses are developed from all the cervical vertebras ; that
of the atlas, fig. 54, #, is attached to the hypapophysis ; the neur-
apophyses rest, in part upon this element, in part upon the proper
centrum, which coalesces with that of the axis : the neural spine
of the atlas remains distinct, like that of the occiput, and is broad
and flat. The centrum of the axis is flat in front, and convex
behind : the neural arch, as in the succeeding vertebra, is com-
pleted by the connate spine. The pleurapophysis, ib. b, has a
bifurcate head. "\Vith the exception of the two sacral vertebras,
which are flat at one end and concave at the other, and of the first
caudal vertebra, which is convex at both ends, the bodies of
all the vertebras beyond the axis are concave in front and convex

»/

behind. The procoslian centrum of the third cervical is shorter
but broader than the second ; a parapophysis is developed from
the side of the centrum, and a diapophysis from the base of the
neural arch ; the pleurapophysis is shorter, its fixed extremity is
bifid, articulating to the two above-named processes ; its free
extremity expands, and its anterior angle is directed forward to
abut against the inner surface of the extremity of the rib of both
the axis and atlas, whilst its posterior prolongation overlaps the rib
of the fourth vertebra. The same general characters and imbri-
cated coadaptation of the ribs, not given in the diagram, 54,
characterize the succeeding cervical vertebras to the seventh
inclusive, fig. 57, p, the hypapophysis progressively though slightly
increasing in size. In the eighth cervical the rib, h, becomes
elongated and slender ; the anterior angle is almost or quite
suppressed, and the posterior one more developed and produced

VOL. I. F

66

ANATOMY OF VERTEBRATES.

54

more downward, so as to form the body of the rib, which termi-
nates, however, in a free point. In the ninth cervical, the rib, ?',
is increased in length, but is still what would be termed a ' false '
or l floating rib ' in anthropotomy.

In the succeeding vertebra the pleurapophysis, fig. 54, k,

articulates with a hrcmapophysis, and
the haemal arch is completed by a
haemal spine ; by which completion
of the typical segment we distinguish
the commencement of the series of
dorsal vertebras. With regard to the
so-called ' perforation of the transverse
process ' this equally exists in the pre-
sent vertebra, as in the cervicals ; on
the other hand, the cervical vertebras
equally show surfaces for the articu-
lation of ribs. The typical characters
of the segment, due to the completion
of both neural and haemal arches, are
continued in some species of Crocodilia
to the sixteenth, in some (Crocodilus
acutus) to the eighteenth vertebra. In
the Crocodilus acutus and the Alligator
lucius the hremapophysis of the eighth
dorsal rib (seventeenth segment from
the head) joins that of the antecedent
vertebra. The pleurapophyses project
freely outward, and become * floating
ribs ' in the eighteenth, fig. 55, b,
nineteenth, ib. c, and twentieth, ib. d,
vertebrae, in which they become rapidly
shorter, and in the last appear as mere
appendages to the end of the long and
broad diapophyses : but the haemapo-
physes by no means disappear after
the solution of their union with their
pleurapophyses ; they are essentially
independent elements of the segment, and are accordingly con-
tinued, in pairs, fig. 55, 3, 4, 5, 6, 7, and 56, along the ventral sur-
face of the abdomen of the Crocodilia, as far as their modified
homotypes the pubic bones, ib. 8. They are more or less ossified,
and are generally divided into two or three pieces. A short carti-
laginous piece, an unossified part of the pleurapophysis, intervenes

Diagram of anterior vertebras,
Crocodile, cc.

ANATOMY OF VERTEBRATES.

67

between it and the hasmapophysis. A small cartilaginous appen-
dage is attached to some of the ribs.

The lumbar vertebrae are those in which the diapophyses cease
to support moveable pleurapophyses, although they are elongated
by the coalesced rudiments of such, ib. e, f, y, h, which are distinct
in the young Crocodile. The length and persistent individuality
of more or fewer of these rudiniental ribs determines the number
of the dorsal and lumbar vertebrae respectively, and exemplifies
the purely artificial character of the distinction. The number of
vertebras between the skull and the sacrum is twenty-four. In
the skeleton of a Gavial, I have seen thirteen dorsal and two
lumbar; in that of a Crocodilus cataphractus twelve dorsal and
three lumbar ; in those of a Crocodilus acutus and Alligator lucius,
eleven dorsal and four lumbar, fig. 57, which is the most com-
mon number. Cuvier assigns five lumbar vertebrae to Croc.

55

Diagram of posterior trunk-vertebra, Crocodile, cc.

biporcatus. But these varieties in the developement or coales-
cence of the stunted pleurapophysis are of no essential moment.
The coalescence of the rib with the diapophysis obliterates of
course the character of the ' costal articular surface,' which we
have seen to be common to both dorsal and cervical vertebrae.
The lumbar zygapophyses have their articular surfaces almost
horizontal, and the diapophyses, if not longer, have their antero-
posterior extent somewhat increased ; they are much depressed,
or flattened horizontally.

The sacral vertebras, fig. 57, s, are very distinctly marked by
the flatness of the coadapted ends of their centrums ; there are
never more than two such vertebras in the Crocodilia, recent or
extinct : in the first the anterior surface of the centrum is concave,
in the second the posterior surface; the zygapophyses are not
obliterated in either of these sacral vertebras, so that the aspects of

F 2

68

ANATOMY OF VERTEBRATES.

56

their articular surface — upward in the anterior pair, downward
in the posterior pair — determines at once the corresponding ex-
tremity of a detached sacral vertebra. The thick and strong
transverse processes form another characteristic of these vertebra? ;

for a long period the suture
near their base remains to show
how large a proportion is formed
by the pleurapophysis. This
element, fig. 55, z, articulates
more with the centrum than
with the diapophysis developed
from the neural arch ; it ter-
minates by a rough, truncate, ex-
panded extremity, which almost
or quite joins that of the similarly
but more expanded rib, ib. k,
of the other sacral vertebra.
Against these extremities is ap-
plied a supplementary costal
piece, serially homologous with
the fibrous tract indicated by
the dotted lines between h and
7, (/ and 6, fig. 55 ; but ossified,
expanded, and interposing it-
self between the pleurapophyses
and ha3inapophyses of both sacral
vertebras, not of one only.
This intermediate pleurapophy-
sial part is called the ' ilium '
fig. 57, 62 : it is short, thick,
very broad, and subtriangular,
the lower truncated apex form-
ing with the connected extrem-

o

ity of the haamapophysis an arti-
cular cavity for the diverging
appendage, called the ( hind leg.'
The hasmapophysis of the anterior sacral vertebra is called ' pubis,'
fig. 55, 8, fig. 56, 5 ; it is moderately long and slender, but expanded
and flattened at its lower extremity, which is directed forward
toward that of its fellow, and joined to it through the intermedium
of a broad, cartilaginous, hrcmal spine, ib. 10 and 11, completing the
haemal canal. The hremapophysis of the second sacral, fig. 55, 9,
fig. 56, 4, is broader, subdepressed, and subtriangular, expanding

Diagram of the hremal arches of the trunk,
viewed from above. Crocodile, cc.

ANATOMY OF VERTEBRATES. 69

as it approaches its fellow to complete the second pelvic hremal
arch. The size of these elements of the hsemal arch, and their
distinctive shapes, have obtained for them, in anthropotomy , special
names : their diverging appendage being developed into a potent
locomotive member. The crocodile yields a clear view of the serial
homolosnes of the haemal elements alons; the trunk. In fio-. 56,

O O o '

they are sketched as seen from the dorsal aspect. The haemapo-
physes extend from h i, 2, 3, to h 6, 5, 4 : the haemal spines, mostly
confluent, are co-extensive from hs to 10, where they expand as a
cartilage between 6 and 5. The pair of hsemapophyses, h i, are
called ' coracoids,' and bear the special number 5 2: the pair, 5, are
the ( pubic bones ' ; the pair, 4, the e ischia.' The haemal spine, hs,
is called ( episternum,' the succeeding more or less confluent spines,
9, form the ' sternum ' : in Man their abdominal continuation, not
quitting the fibrous tissue-state, is called f linea alba ' ; it be-
comes cartilage in the Crocodilia, ib. 10, and partly bony in old
specimens. The abdominal haemapophyses, represented by the
6 intersectiones tenclineae musculi recti abdominis ' of anthropotomy,
are commonly ossified, each from two centres, in old Crocodilia.

The pleurapophysis is reduced to a transverse process in the
first caudal vertebra, fig. 55, / ; which, besides being biconvex,
has no articular surface for the haemapophyses : these elements
reappear in the succeeding segments, detached, as in the lumbar
series, from their pleurapophyses, but articulated to the centrum
directly, fig. 7, with a backward displacement, to the interspace
between their own and the succeeding vertebra, fig. 57, //. After
the fourteenth caudal vertebra the transverse processes disappear,
the centrum becomes compressed, and the neural and haemal
spines give adequate vertical extent to the long and strong nata-
tory tail, to near its pointed termination.

The characters of the trunk-vertebras of existing Crocodilia,
especially their proccolian type, are those which their predecessors
presented throughout all the tertiary series of deposits,1 and by
some species from cretaceous beds.2 But in all the secondary
series below the chalk, the Crocodilia present flattened or sub-con-
cave vertebral surfaces; or, if the cup-and-ball structure be
present, it shows reverse positions to the procoelian type, e. g. in
the anterior trunk-vertebrae of the genus of oolitic Crocodilian,
thence termed 4 Streptospondylus? A similar e opisthocoelian '
modification is presented by the cervical and anterior dorsal
vertebrae of the more gigantic Cetiosaurus ; and, in a minor degree,

i. p, 117, pis. 1 D, 3, 3 A.

• » ^? O r» » » O /IT ~V T TT V\ Q Q O

1 CLXIII., part iii. p, 117, pis. 1 D, 3, 5

2 Crocodilus basifissus, CLXtv. p. 380.

70

ANATOMY OF VERTEBRATES.

,5,

N

57 by some of the great reptiles, with

limbs more adapted for terrestrial pro-
gression, called ' Dinosauria' ; favour-
ing in these the flexibility of the neck,
as the same ball-and-socket structure
does in the large herbivorous quadru-
peds of the present day. 1 The neural
arch in the dorsal region of Dinosauria^
was enlarged and strengthened by a
bony platform, with supporting ridges :
the sacrum included from four to six
vertebras, having the neural arch
shifted so as to rest upon two cen-
trums and bind them together.

§ 25. Vertebral column of Ptero-
sauria. - - In tracing the modifications
of the skeleton from the earliest forms
of extinct species, the procoelian type of
vertebra appears first in the extinct
group of Reptiles (Pterosaurid) adap-
ted for flight ; the Pterodactyles of the
Lias show it, with a confluent neural
arch and a pneumatic foramen on each
side of the vertebra.2 The cervical ver-
tebrae of Pterodactyles, fig. Ill, are the
largest, seven or eight in number, of
which the first two coalesce. The atlas
has a very short discoid centrum and
two slender neurapophyses. The dorsal
vertebrae become smaller to the pelvis ;
they may be fifteen in number, fol-
lowed by two lumbar, from three to
seven sacral, and a variable number
of caudal vertebras. One family of
Pterodactyles had a long and stiff tail ;
the rest, as in fig. Ill, a short tail.
The anterior free ribs have bifurcate
heads ; and, as this structure is asso-
ciated in modern Reptilia, with a
four-chambered heart, that organ had
probably reached the same stage of
skeleton of Alligator perfection in the flying Reptiles, the

1 CLXIII. parts v. and vi. ; xxx. p. 285. 2 CLII. p. 161, pi. x.

ANATOMY OF VERTEBRATES. 7!

huge terrestrial Dinosaurs, and other extinct groups with the same
costal structure. The existing Reptilia are but a remnant of a
once extensive and varied class of cold-blooded vertebrates, which,
since the mesozoic epoch has been on the wane.1

§ 26. Developement of the skull. — In reviewing the modifications
of this part of the vertebral column in the H&matocrya, we
retrace our steps to the lowest water-breathing forms, and
recommence with the Dermopterous subclass.

Passing from the trunk to the head, we find in the Lancelet
(Branchiostoma), fig. 23, that the cranium is not indicated by
difference of size or structure of the rudimental vertebral column,
but consists of the gradually contracting anterior termination of
the neural canal, which retains its primitive fibro-membranous wall,
71, ob, without any superaddition of parts, and is supported by the
tapering end of the notochord, ib. ch. This part extends farther
forward than the cranial end of the neural canal, indicating the

7 o

iion-developement of the prosencephalon and corresponding part
of the cranial cavity. In fact, there is no ganglionic cerebral
expansion whatever in this vermiform fish : the epencephalon or
medulla oblongata is indicated by the origin of the trigeminal
nerve, ib. ob, in advance of which the mesencephalic segment sends
off the short optic nerve to the dark ocellus, op, and there terminates,
somewhat obtusely, beneath what Dr. KoLLiKEE,2 has described
as a ciliated olfactory capsule, ib. ol. The cranium of the Lancelet,
therefore, may be said to be composed of the notochord and its
membranous capsule, without the superaddition of cartilaginous
or osseous coverings. But, as an appendage to the skull, may be
described the jointed, cartilaginous, hannal arch, ib. h, which
extends from below the cranial end of the chorda dorsalis, down-
ward and backward on each side of the orifice of the pharynx ;
this represents the labial arch of higher Myxinoids, and supports
several pairs of the jointed slender oral filaments. It is the sole
chondrified part of the skeleton in the Branchiostoma.

The cartilaginous tissue is superinduced upon the fibrous brain-
sac in osseous fishes, in the following manner. The notochord
advances as far as the pituitary sac, or f hypophysis cerebri,' where
it terminates in a point ; cartilage is developed on each side,
forming a thick f occipito-sphenoidal ' 3 mass, which extends out-
ward, and forms the earball or acoustic capsule. The cartilage
rises a little way upon the lateral walls of the cranium, and is
there insensibly lost in the primitive cranial membrane. At the

1 CLXXX. p. 320. 2 xxxii. p. 32.

3 Plaque nuchale, Vogt ; Knocherne basis cranii, Miiller, xxi.

Muller

72 ANATOMY OF VERTEBRATES.

end of the notochord the basal cartilages, developed in continua-
tions of its capsule, diverge, surround the pituitary vesicle, and
meet in front of it, forming the f sphenoidal arches/ l which join,
or expand into the ' vomerine plate.' 2

The immature Lamprey, called Sand-lance (Ammocoetes}, retains
a like condition of the skull, fig. 58, to the second or third year.
The occipital cartilages extend from the sides of the pointed end
of the notochord, ib. ch, and expand into the acoustic
capsules, ib. 16: the sphenoidal arches, ib. 5, encom-
pass the pituitary or hypophysial space, Ay, now closed
by a membrane-cartilaginous plate, and unite anteriorly
to form a small vomerine plate, ib. is, in front of
which is the single undivided nasal capsule, ib. 19.
The now expanded cerebral end of the neural canal,
fig. 59, ft, is still defended by fibrous membrane only;
but is divided from the vomerine plate, ib. 13, by a

Base of skull, t • i i

backward extension of the nasal sac, ib. 19, to the
pituitary vesicle.
In the Myxine the acoustic capsules are approximated at the
base of the skull ; the sphenoidal arches are longer, and unite with
the palatine plate and arches, from which are sent off the labial
cartilaginous processes supporting the buccal tentacles homologous
with those in the Lancelet. In the long hypophysial interspace of

the sphenoidal arches a more or less firm
cartilaginous plate is developed, from which
a slender median process is continued for-
ward to the vomerine or palatine plate,
which supports the nasal capsule ; another
side view of stun, Ammocete, process extends backward to the occipital

Miiller 1

cartilage. Other processes are also sent

off from the sides, which form a complex system of peculiarly
Myxinoid cartilages.3

In the mature Lamprey (Petromyzoii)., fig. 60, the occipital
cartilage is continued backward, in the form of two slender
processes, <?, upon the under part of the notochord, ch, into the
cervical region. The hypophysial space, liy, in front of the
occipital cartilage, remains permanently open, but has been con-
verted into the posterior aperture of the naso-palatiue canal. The
sphenoidal arches, 5, are very short, approximated towards the
middle line ; and the vomerine cartilage, 13, is brought back
closer to the sphenoidal arches. TAVO cartilaginous arches, 24,

1 Anses laterales, Vogt ; Fliigel-forsatze basis cranii, Miiller.

2 Plaque faciale, Vogt ; Gaumcnplatte, Miiller. 3 xxi.

ANATOMY OF VERTEBRATES.

73

circumscribe elliptical spaces outside the presphenokl plate : these
appear to represent the pterygoid arches, fig. 61, z, but, as in the
embryo of higher fishes, are not separated from the base of the skull
by distinct joints. The basal cartilages, after forming
the ear-capsules, ib. g, extend upon the sides of the cra-
nium, ib. h, arch over its back part, and leave only its
upper and middle part membranous, as in the human
embryo when ossification of the cranium commences.
The cranium is continued below the olfactory capsule,
ib. k, into the ' rostral plate,' /. Behind the pterygoid
arch, z, the process representing the stylo-hyal, ib. i'9
i" ', passes down, and expands to give attachment to
the muscles of the tongue ; the f basihyal ' supports,
by its forward f glossohyal ' extension, the large den-
tigerous tongue, and by its backward ' urohyal ' growth, s, adds to
the surface of insertion of the muscles. The cartilage descending

o &

from the side of the fore part of the cranium to join the pterygoid
arch, i, may represent a ' tympanic ' pedicle : it mainly supports,
as in the Sturgeon, fig. 62, ?8, and Shark, the membrane, fig. 61, x,
and cartilages, forming the roof and margin of the mouth ; in which

Gl

Base of skull,
Lamprey.

XXI.

Skull of Sea Lamprey (Tctromyzon marinus). xxi.

n may be compared to the ' palatine,' and o to the maxillary, while
p seems to be a special labial cartilage in this suctorial fish : q and r
are processes for the muscles working this peculiar apparatus ;
and in addition to these is the cartilaginous basket before de-
scribed, fig. 24, 45, which supports the modified and perforated
homologue of the large respiratory pharynx, fig. 23, a, in the
Branchiostome.

Thus, in the Dermopterous fishes, the developement of the skull
is arrested at more or less early embryonic stages ; whence it

74

ANATOMY OF VERTEBRATES.

proceeds in a special direction, to stamp the species with its own
distinctive and peculiar character : in the Branchiostoma by the
articulated cartilaginous labial arch and its numerous filaments ;
and in the proper Myxinoids and Lampreys by the formation of
the complex system of lateral and labial cartilages ; or by the
modification of the palatine, maxillary, and hyoid rudiments, in
relation to the suctorial function of the mouth.

In the Sturgeon (Acipenser) fig. 62, the growth of cartilage has
inclosed the whole of the brain-case, f, y, and blended with its
walls the ear-capsules : in advance of this it developes protective
cavities for the now well-developed eyes and double nasal sacs : the
orbit, i, being divided from the nostril, k, by the ridge, 2, and
both supported by a ' vomerine ' basis, cf" : beyond which the
cranium is continued forward as a long pointed rostrum. The
cartilaginous pedicle suspending the palato-maxillary apparatus is

Fore part of endoskeleton, Sturgeon

divided into three pieces ; the epitympanic, ib. m, the mesotym-
panic, ib. n, and the hypotympanic, ib. 26. The latter supports
the palatine vault, 20, with which the pterygoids, se, are confluent ;
the maxillary, 21, the premaxillary bone, 22, the labial cartilage,
74, and the mandible, 32. All these parts of the edentulous
suctorial mouth are very small in proportion to the size of the
head and entire fish ; and they are the only ossified parts of
the endoskeleton. The premaxillary is a subtriaugular plate,
joined by ligament to its fellow, trenchant anteriorly, and
extending in an arched form to the mandible. The mandible, 32,
articulates by a concavity to the pterygoid and premaxillary, and
consists of a single piece, united to its fellow by a ligamentous
symphysis.

The mouth of the Sturgeon opens upon the under surface
of the head, and is protruded and retracted chiefly by the move-

ANATOMY OF VERTEBRATES. 75

ments of the tympanic pedicle, which swings, like a pendulum,
from its point of suspension to the post-orbital process, fig. 29, y" .
The hyoid arch is also small and simple in the Sturgeon. The
epi-hyal is short, and attached to near the upper end of the hypo-
tympanic. The cerato-hyal, fig. 62, 40, of thrice the length, is
expanded above, and is attached by ligament extending from that
part to near the joint of the loAver jaw. The basi-hyal is a short
stibcubical piece : it gives attachment anteriorly to cerato-hyals,
and posteriorly to the anterior basi-braiichial and hypo-branchial
cartilages.

The three first branchial arches consist of hypo-branchials,
progressively decreasing in size, of cerato-branchials, epi-bran-
chials, and pharyngo-branchials : the fourth arch consists of
cerato-branchials and epi-branchials : the fifth arch of cerato-
branchials only. The branchial cavity is closed by an opercular
dermal scale, d, 35, supported by the expanded tympanic cartilage,
m, fig. 62.

The cartilaginous representative of the par-occipital projects
backward from each angle of the occiput. A triangular supra-
scapular cartilage, fig. 62, so, has the angles of its base slightly
produced, one being articulated to the end of the par-occipital,
the other to the ex-occipital region. To the apex is attached
the scapulo-coracoid arch, ib. 51, 52. The coracoid cartilage
expands as it descends, sends inward and forward a broad
wedge-shaped plate, and presents a large perforation at its thick
posterior part, answering probably to the perforated ulna of
osseous Fishes, here confluent with the arch. The pectoral fin
is articulated to the under part of this perforated projection : the
coracoid terminates by a broad thin plate beneath the pericardium,
where it is joined by strong aponeurosis to that of the opposite
coracoid.

Special developement proceeds further in the skull of the
singular Acipenseroid, called ( paddle-fish ' (Planirostra Spatula).
It is remarkable for the rostral prolongation of the nasal and
vomerine bones, the rostrum being flattened horizontally and
expanded like the mandibles of a Spoonbill. The sides of the
rostrum are strengthened by a reticulate disposition of bony
matter in the form of stars, the rays of which anastomose. The
upper part of the cranium is less perfectly chondrified than in
the Sturgeon. There is a long vacuity between the frontal,
parietal, postfrontal and mastoid bones : the tympanic pedicle is a
simple elongated piece of bone expanded at both ends. The
mandibular and hyoidean arches are suspended by a short cartilage

76 ANATOMY OF VERTEBRATES.

to the end of the tympanic bone : the palatines are extremely small.
The premaxillary and maxillary bones seem to have coalesced ;
they expand as they extend backward to become attached to the
cartilage supporting the mandibular arch. The slightly ossified
pterygoids run parallel with them along the inner sides to the same
part. The articular and dentary pieces of the lower jaw have coa-
lesced, but there is a trace of a slender splenial piece on the inner
side of the mandible. All the bones of the mouth are edentulous,
but the membrane covering the extremities of the upper and
lower jaw is roughened by extremely minute denticles in the
recent fish. The ceratohyals are partially ossified : the rest of
the hyoidean arch is cartilaginous. A branchiostegal appendage
in the form of an irregular elongated flattened bone, resolved
posteriorly into osseous fibres, extends from each side of the
commencement of the hyoidean arch. A similar but larger oper-
cular appendage extends backward from the extremity of the
tympanic pedicle.

§ 27. Skull of Plagiostomi.- -The more or less cartilaginous skull
of the Plagiostomous fishes might be histologically regarded as the
transitional step from the Cyclostomous to the Osseous fishes ; but,
morphologically, it offers a different, apparently simpler type ; and
one which, through the progress of developement in the direct
vertebrate route, more nearly approximates to the cranial organi-
sation in the Batrachia. The Monk-fish ( Squatina, — an interme-
diate form between the Sharks and Rays,) affords a good and typical
example of the essential characters of the plagiostomous skull.
The cranial end of the notochord and its capsule are converted
into firm granular cartilage ; extending forward so as to constitute
an oblong flattened plate forming the whole basis cranii. The
posterior margin of this 6 occipito-sphenoidal ' plate supports two
convex condyles, for articulation with the body and parapophyses
of the axis. The body of the atlas has coalesced with the basi-
occipital, as is indicated by its slender but separate neural arch.
The lateral margins of the basal cartilage have two notches, the
intervening prominence representing the primitive sphenoidal
arch, here filled up and sending off a rudimental pterygoid process
outwards. Just anterior to the median ridge there is a small
fossa, (in the young Squatina a foramen,) the last trace of the
pituitary canal : the basal cartilage then expands to form the
lower border of the groove which receives the palatine process or
point of suspension of the palato-maxillary arch, in front of which
it contracts to form the vomerine base of the cranium. The cra-
nial cavity is not moulded on the brain, but is of larger size ; it

ANATOMY OF VERTEBRATES. 77

communicates by means of the nervous and vascular foramina
with the acoustic chamber in the thick lateral wall : this insulation
of the labyrinth is common to the Plagiostomes. The cranial
cavity is closed by membrane anteriorly. The foramina for the
fifth pair of nerves mark the ' alisphenoidal ' portion of the enclo-
cartilage : those for the optic nerves the ' orbitosphenoidal ' part:
the e prefrontal' portion is marked by the olfactory foramina, and
their articulation with the palatine part of the maxillary arch.

The exterior of the skull is variously and singularly modified in
different Sharks and Rays, the developement proceeding from the
advanced cartilaginous stage just described, to establish peculiar
plagiostomous characters, and to adapt the individual to its special
sphere of existence.

The same general confluence of cartilage, which pervades the
protecting walls of the brain-case, characterises the appended
arches of the cranium. A single strong suspensory pedicle, fig.
30, c, articulated to the side of the skull beneath the posterior
angular (mastoid) process, has the hyoidean, and partly the man-
dibular,1 arches attached to its lower end, the former, d, by a close
joint, the latter by two ligaments. The maxillary arch, in Squa-
tina, is suspended by a ligament from its ascending or palatal
process, to the notch between the vomerine and the anterior
supracranial cartilaginous plate. From this point the jaw is con-
tinued in one direction forward and inward, completing the arch,
ib. e, by meeting its fellow, to which it has a close ligamentous
junction ; and in the opposite direction, backward and outward, as
a coalesced diverging appendage to the outer side of the tympanic
pedicle, where it forms the more immediate articulation for the
lower jaw, like the hypotympanic continuation of the upper
maxillary bone in the Batrachia, fig. 71, e. Each lateral half or
ramus of the mandible, fig. 30, d, consists of a single cartilage,
the two being united together at the symphysis by ligament.

Two slender labial cartilages, ib. /, are developed on each
side the maxillary, and one, g, on each side the mandibular
arch ; which complete the sides of the mouth. These cartilages
Cuvier regarded as rudiments, respectively, of the maxillary
and dentary bones, the dentigerous maxillary arch as the palatine
bones, and the mandibular arch as the articular piece of the
lower jaw : but both palatines and articulars co-exist with
labial cartilages, like those of Squatina, in a Brazilian Torpedo

1 Throughout this work the term 'mandible' is applied to the lower jaw, and the
inverted cranial arch which that jaw completes is called ' mandibular : ' the arch
formed by the upper jaw is called 'maxillary.'

78

ANATOMY OF VERTEBRATES.

63

(Narcine), and at the same time with distinct pterygoid

cartilages.1

Four or five short cartilaginous rays diverge from the posterior

margin of the tympanic pedicle, ib. c, and support a membrane

answering to the opercular flap in Osseous fishes ; in their ultimate

homology these rays are the skeleton of the diverging appendage

or limb of the tympano-mandibular arch.

The hyoid arch in Squatina, as in most other Plagiostomes,

consists of tAVO long and strong cerato-hyals, and a median flat-
tened symmetrical piece,
the basi-hyal. Six short
cartilaginous rays extend
outwards from the back
part of the cornua, support-
ing the outer membranous
wall of the branchial sac :
these answer to the bran-
chiostegal rays in osseous
fishes, and support the di-
verging appendage or limb
of the hyoidean arch. But
the fold of integument in

o

which they project is not
liberated, and is continuous
with that supported by the
opercular rays from the
tympanic pedicle. Five
branchial arches, fig. 30,
i, 2, 3, 4, 5, succeed the
hyoidean ; but are sus-
pended, as in the Lam-
prey, from the sides of the
anterior vertebra? of the
trunk. In the Sea-hound
(Scymnus /zWzzV),fig. 6 3, the
ceratobranchials, /, /, and
basibranchials, e, e, are
shown, with the frame-
work of the gills, q, i. Be-

Skullwith branchial and scapular arches, Scymnus. xini. j7

hind these arches is the sca-

pulo-coracoid arc, 52, united by cartilaginous confluence at the
mid-line, not by ligament as in the Sturgeon.

1 xxi. 1835, pi. v. figs. 3 & 4. It may be questioned whether the detached plate,
called palatine by Di\ Henle, be not rather the entopterygoid.

ANATOMY OF VERTEBRATES. 79

The Cestracion, so interesting from its early introduction into
the seas of this planet, is not so far advanced in cranial de-
velopement as is the more modern Squatina. In the existing
species of the Australian seas {Cestracion Phillipi), the cartilagi-
nous basioccipital retains a deep conical excavation,, adapted to a
corresponding one in the atlas, which cavity is consolidated by
cartilage in the Squatina ; the original place of the extended ante-
rior end of the chorda, along the middle of the posterior half of
the basicranial cartilage, continues membranous, and the pitui-
tary perforation is permanently closed by membrane only ; the
basal cartilage expands anterior to this, and comes into close
connection with the maxillary arch, and is thence continued
forward, contracting to a point between the nasal capsules, which
meet at the middle line above the symphysis of the upper jaw.
The proper cranial cartilage is thinner than in the Squatina;
the anterior or pineal fontanelle forms an extended membranous
tract on the upper part of the cranium ; the vertical ridges, which
rise from the sides of this tract, extend forward and outward to
support the nasal sacs, and are continued backward, interrupted
by a notch filled by membrane, to the posterior angular processes,
which overhang the joint of the maxillo-hyoidean pedicle. The
maxillary and mandibular arches are as simple as in Squatina,
but much stronger, since they support a series of massive grinding
teeth, as well as pointed ones, or laniaries. The rami of the lower
jaw are confluent at the symphysis.

The Skates and Rays have the skull movably articulated, as in
Squatina, by two basilar condyles and an intervening space, to
the axis. The skull is flat and broad ; the upper wall mem-
branous for a greater or less extent, fig. 64, except in Narcine,
where it is closed by cartilage. The anterior or vomerine part
forms a long pyramidal rostrum, to which are usually articulated
cartilages connecting its extremities with the anterior angles of
the enormously developed pectoral fin, ib. 12 : in the space
between the skull and those fins, the Torpedo carries its electric
batteries. The tympanic pedicles, are short and thick ; the
maxillary and mandibular arches long and wide, stretching trans-
versely across the under part of the head.

In the ordinary Sharks the forward prolongation of the cranial
cavity gives a quite anterior position, and almost vertical plane,
to the fontanelle : three columnar rostral cartilages are produced,
two from above, and one from between the nasal cavities, which
processes converge and coalesce to form the framework of a kind of
cut-water, at the fore-part of the skull. In the place of articular

80

ANATOMY OF VEHTEBEATES.

condyles, processes extend backward from each side of the occi-
pital foramen and clasp, as it were, the bodies of three or four
anterior vertebras of the trunk. The pterygoidean arches extend
outward, in Carcharias, from the base of the cranium, but, as in
embryo osseous fishes, are confluent therewith at both ends. The
maxillary arch, suspended near its closed anterior extremity to

64

28

Skate (_Eaia bat is)

the vomerine part of the base of the skull, is thence extended
backward to the articulation of the lower jaw. A simple carti-
laginous pedicle forms the upper part (pleurapophysis) of the
mandibular arch, which is completed below by the lower jaw. A
few cartilaginous rays diverge outward and backward from the
pedicle, and support a small opercular flap or fin. The hyoid

ANATOMY OF VERTEBRATES.

81

65

arch consists of a basihyoid and two simple ceratohyoid carti-
lages ; the stylohyal is ligamentous, as in the Squatina. Short
cartilaginous rays diverge from the ceratohyal to support the
branchiostegal membrane, or hyoid fin. The scapular arch,
which we shall find normally articulated with the occiput in
osseous fishes, is attached thereto, at a little distance behind the
head, by ligament and muscles in the Sharks, fig. 30, 51 : from
this arch, also, cartilaginous rays, ib. k, I, immediately diverge for
the support of a radiated appendage or fin — the homotype of the
tympanic or opercular fin.

The capsules of the special organs of sense are all cartilaginous :
that of the ear is involved in the lateral
walls of the cranium ; that of the eye is
articulated by a cartilaginous pedicle with
the orbit ; and that of the nose, figs. 30 and
63, b, is overarched by the nasal processes
of the epicranial cartilage, ib. «, and is
completed below by membrane. At the
summit of the occiput in Carcharias and
some other sharks may be seen two closely
approximated oval ' fenestrte,' which lead
to the acoustic labyrinth, and are covered
by skin in the recent fish.

Amongst the stranger forms in which
special developement radiates, in diverging
from that stage of the common vertebrate
route attained by the Plagiostomes, may
be noticed the lateral transverse elonga-
tions of the orbital processes, supporting
the eyeballs at their extremity, and giv-
ing the peculiar form to the skull of
certain Sharks, thence called ' Hammer-
headed' (Zyyana). In the 'Saw-fish'
(Pnstis), the rostrum, fig. 65, is produced
into a long, flat, plate, having a row of
tootlv-like bodies implanted in sockets along
each margin. The walls of these sockets
and the midpart of the rostrum are ossified.
The proper jaws and teeth a have the usual inferior position in the
Sharks. In the Eagle-ray (Myliobates) a cartilage is attached to
the anterior prolonged angle of the great pectoral fin, and con-
nects it with the fore part of the cranial (internasal) cartilage ;
it supports a number of branched and jointed cartilaginous rays,

VOL. I. a

Motith and rostrum of Saw-fish
(Pristia).

82 ANATOMY OF VERTEBRATES.

which project forward, and are connected at the middle line
with a like series from the opposite side of the head ; they may
be regarded as partial dismemberments of the great pectorals ;
and in Rhinoptera Braziliensis their supporting cartilage is
directly continued from that of the pectoral fins, though it is
closely attached to the fore part of the head. These form what
Miillcr has termed 'cranial fins;' but the parts more properly
meriting that name are the opercular and braiichiostegal appen-
dages of the tympanic and hyoidean arches.

§ 28. Skull of Protopteri. - -Thus far we have seen that the base
of the skull is first formed by the anterior prolongation of the
notochord and the expansion therefrom of its capsule ; and that the
cranial cavity results from the extension of the outer layer of that
membrane over the anterior end of the nervous axis. We saw
next the superaddition of special capsules for the organs of sense ;
and the cartilaginous tissue developed in the notochordal sheath
at the base and sides of the cranium, according to a pattern
common to the lowest and to the embryos of the higher vertebrata.
We saw the cartilaginous tissue acquiring a firmer texture, hard-
ened by superficial osseous grains, or tesserae, mounting higher
upon the lateral and upper walls of the cranium, and at length
entirely defending it : and we then also recognised the maxillary,
mandibular, and hyoidean arches, established in a firm cartilaginous
material, and on a recognisable ichthyic type.

We have now to trace the course and the forms under which
the osseous material is superadded to, or substituted for, the
primitive cartilaginous material of the skull ; and the remarkable
Lepidosiren, whose organisation was first made known as in the
generic form called Protopterus,1 offers a transitional step, in the
shape and structure of its skull, between the gristly and the bony
cold-blooded vertebrates.

In the Lepidosiren, ossification of the cranial end of the noto-
chord extends along the under and lateral part of its sheath,
backward to beneath the atlas, fig. 41, i, the posterior slightly
expanded end of this ossified part supporting, as in Squatina,
the neurapophyses of the atlas, fig. 66, ?i, the bases of which
expand and meet above the notochord and below the spinal
canal. Ossification of the notochordal sheath commencing at
its under part, ib. b, ascends upon the sides of the notochord as
it advances forward, and encloses it above, where it supports the
medulla oblongata, and the lateral bony plates (neurapophyses)

1 XXXIII.

ANATOMY OF VERTEBRATES. 83

called exoccipitals, ib. 2 ; leaving behind a wide oblique conca-
vity lodging the anterior unossified end of the
notochord, which does not extend further upon the
basis cranii. The exoccipitals, ib. 2, 2, expand as
they ascend and converge to meet above the ( fora-
men magnum' which they complete. A small mass

n .-. i . -, . -i -i Atlas and

ot cartilage connects their upper ends with each occipital vertebra,
other, and with the overhanging backwardly pro-
jecting point of the frontoccipital spine, ib. 3. This cartila-
ginous mass answers to the base of the superoccipital in better
ossified fishes : a similar cartilage connects the exoccipitals with
the occipital spine in the Tetrodon.

We clearly perceive in the Lepidosiren that ossification, ad-
vancing on the common cartilaginous mould of the piscine skull,
has marked out the neurapophyses and centrum of the posterior
cranial vertebra. The occipital pleurapophyses, called ( scapulae,'
fig. 41, 51, appear as strong, bony, styliform appendages, articu-
lated by a synovial capsule and joint, one on each side, to the ex-
and basi-occipitals. To the pleurapophyses are attached the upper
extremities of the hceinapophyses (coracoids, fig. 41, 52) which
unite together below, and thus complete the hasmal arch of the
occipital vertebra, here unusually developed in relation to its
office of protecting the heart and pericardium. The coracoids
belong to the same category of vertebral elements as the sternal
ribs which protect the heart in higher Yertebrata. The hasmal
arch of the occipital vertebra of the Lepidosiren supports a filiform
appendage, ib. 57 ; it is the key to the homology of the anterior
or upper limbs of the higher Vertebrata.

In the second (parietal) and third (frontal) cranial vertebras,
ossification extends along the basal and along the spinal elements,
but not into the neurapophysial or lateral elements ; these remain
cartilaginous in continuation with the cartilage surrounding the
internal ear. The basal ossification, representing at its posterior
end the body of the atlas, then the basioccipital, expands as
it advances along the base of the skull in the situation of the
sphenoids, constituting the floor of the cerebral chamber, sup-
porting the medulla oblongata, the hypophysis, the crura and
lobes of the cerebrum, and terminating a little in advance of the
olfactory lobes by a broad transverse margin, bounding a triangular
space left between it and the converging palatine arches, which
space is filled by the persistent ( vomerine ' cartilage. The sides
of the basicranial plate bend down to abut against the bases of
the pterygoid plates. In this expansion of the basisphenoid the

G 2

84 ANATOMY OF VERTEBRATES.

Lepidosiren resembles the Plagiostomes. Two ridges rise from the
upper surface of the basioccipito-sphenoidal plate, near its outer
margin, and support the cartilaginous lateral walls of the cranium.
The cranial cavity is defended above by a longitudinal bony roof,
fig. 67, 11, nearly coextensive with the bony floor beneath: the
roof commences behind by the spine or point which overhangs the
exoccipitals, gradually expands as it advances, resting upon the
cartilaginous walls of the cranium, is then suddenly contracted, and
is united anteriorly by fibrous ligament to the ascending process of
the palato-maxillary arch, 20, and to the base of the naso-premax-
illary plate, 15. A strong sharp crest or spine rises from above the
whole of the middle line of the cranial roof-bone, which may be
regarded as representing the mid-frontal, the parietal, and super-
occipital bones, or, in more general terms, the neural spines of the
three cranial vertebras : but this supracranial bone not only covers
the medulla oblongata, cerebellum, optic lobes, pineal sac, and
cerebral hemispheres, but also the olfactory lobes. The lateral
cartilaginous walls of the cranium are continued forward from the

o

acoustic capsule between the basal and superior osseous plates :
the part perforated by the fifth pair of nerves, and protecting
the side of the optic lobes, represents the 'alisphenoid': the
next portion in advance, protecting the sides of the cerebral
hemispheres and perforated by the optic nerve, answers to the
orbitosphenoid : and the cartilage terminates by a ( prefrontal' part
which is perforated by the olfactory nerve, and which abuts laterally
against the ascending or palatine process of the maxillary arch.

The extension of the lateral cartilages of the cranium forward
and downward to form the articulation for the lower jaw, is like
that in the Chimera and batrachian larva, fig. 6 9 A, e ; but ossifica-
tion has co-extended along two tracts, which con-

67

verge as they descend, one, fig. 41, 28, from above
and behind to the outer, the other, ib. 23, from before
to the inner, side of the cartilaginous mandibular
cranial spmes and Joint» whicn tnese bon7 Plates strengthen and sup-
Uppe2sl-m Lcpir Port like the backs of a book. The posterior of these
is the tympanic, the anterior one the pterygoid,
which is confluent with the palato-maxillary bone, the dentigerous
part of which extends outward, downward, and backward, fig* 67,
21, but does not reach, as in the Sharks and Rays, the mandibular
joint, From the upper part of the palato-maxillary a compressed
sharp process, ib. 20, ascends obliquely backward, and terminates
in a point : the inner side of this process is closely attached by
ligament to the fore and outer part of the frontal portion of the

ANATOMY OF VERTEBRATES. 85

epicranial bone, ib. 11 ; the outer side of the process is excavated
for the reception of the outer and anterior process of the super-
temporal bone. This bone, fig. 41, 12, in connection with the
ascending process of the maxillary, ib. 20, forms the upper part
of the orbit, and behind this connection it sends out the post-
orbital process, beyond which it extends backward, freely over-
hanging the fronto-occipital, and gradually decreasing to a point,
and giving; attachment to the anterior end of the great dorse-lateral

o o ~

muscles of the trunk. This bone is flat above like a scale, and
from its superficial position might be classed with the dermal
skeleton: the strong temporal muscle is attached to the two
surfaces, divided by the ridge on its inferior part : it is movable
up and down upon its anterior ligamentous union. It represents
the postorbital and supratemporal bones in Ganocephala.

Each ramus of the lower jaw is composed of an articular, ib. 29,
and a dentary, ib. 32, piece, the latter anchylosed together at the
symphysis, and completing the tympano-mandibular arch. The
articular piece is a simple slender plate, strengthening the outer
part of the articular concavity of the jaw, and closing the outer
groove of the dentary, along which it is continued forward to near
the symphysis, where it ends in a point. The articular trochlea is
formed by the persistent cartilage. The dentary piece has the
notched and trenchant dentinal plate anchylosed to it, and sends
up a strong coronoid process. Serial homology guides in the
determination of the special one of the part of the upper jaw to
which the dentary is opposed. Behind the tympanic is the pre-
opercular, fig. 41, 34. The ceratohyal, 40, is suspended to the
petrosal cartilage close behind the tympanic pedicle ; it joins its
fellow below without the intervention of a basihyal : it supports a
branchiostegal ray, 37.

In the Ganocephala the head was connected by ligament, as in
the Protopteri, to the vertebral column of the trunk, and chiefly
by the basioccipital part. The temporal vacuities were more
completely roofed over by bone, including the postorbital and
supertemporal ossifications.

§ 29. Skull of Batrachia. — In modern members of this order
the ossification of the skull, like its chondrification in Plagiostomi^
is simplified, or so continuous as to indicate but obscurely its essen-
tially segmental character: and this condition will be noticed
before entering upon the description of the complex and instruc-
tive osteology of the head in the more specially developed and
divergent cold-blooded Vertebrates, called ( bony fishes.'

In Batrachia the plagiostomous articulation of the head to the

86 ANATOMY OF VERTEBRATES.

trunk by a pair of condyles, fig. 72, <?, e, is resumed. The chief steps
in the development of the batrachian skull will be premised before
entering upon the various modifications. In the larva of the frog,
fig. 42, the outer layer of the notochordal capsule expands at the
fore part of that vertebral basis to enclose the brain, and its appen-
dages, the sense-organs. The cartilage therein developed, fig. 68,
as the head expands, forms an occipito-petrosal mass, fig. 42,
16, including laterally the ear-capsules ; it bifurcates anteriorly
into the ' sphenoidal arches,' which reunite in front of an oblong
hypophysial space to form a broad prefronto-vomerine mass. The
occipito-petrosal cartilage sends out on each side a thick s masto-
tympanic ' process, which bifurcates ; the division directed for-
ward and inward fig. 42, 26, is the ( pterygoid ; ' that passing
forward and downward is the ' hypo tympanic/ To the back part
is attached the hyoid cartilage, ib. 40 : to the end is attached the
' mandibular ' cartilage, ib. so, fig. 6 9 A, d, also called ' Meckel's
process.' The subsequent ossification begins partly in the carti-
lage, partly in the persistent notochordal membrane : the first
may be called ( chondrogenous,' the second ( sclerogenous ' bones :
some are disposed to regard the first only as ( endoskeletal,' the
latter as ( exoskeletal.'

To the first category belong the neurapophyses of the occiput,
exoccipitals, figs. 43 and 68, 2 ; each of which developes a ( zygapo-

physis ' or condyle, fig. 73, e, for the atlas, fig, 43, a :
any petrosal ossification upon the ear-capsule is a
growth from the exoccipital and from the alisphe-
noid, ib. 6 : the expanded disc of the ( columella ' or

-1

' stapes ' is a distinct ossicle, between 2 and 25,
fig. 43 ; as is also the f hypo tympanic ' articulation,
ib. 29, for the mandible, so, 32. The neurapophyses
of the third segment, ' orbitosphenoid,' fio^s. 42 and

Incipient ossification „ 11,1 • • r> -i

of the skuii. Larva 43, 10, perforated by the optic nerves, are ossmed
in the cartilaginous basis, as are those of the
fourth segment (prefrontals), figs. 42, 44, 68, u, perforated by
the olfactory nerves ; whilst those of the second segment, 6 ali-
sphenoids,' ib. 6, perforated by the trigeminal, longer remain
gristly. All the chondrogenous elements are thick bones.

From the membranous basis of the skull are developed the
following bones, which are more or less lamelliform. The basi-
occipito-sphenoidal plate, fig. 73, m, forms the base of the skull
from the condyles to the vomerine cartilage. The mastotym-
panic, fig. 43, 25, fig. 44, s, 25, fig. 68, 8, extends from the
mastoid cartilage, where it is broadest, to the outside of the

ANATOMY OF VERTEBRATES.

87

69

69A

Hyo-branckial frame, skull, Tadpole, cxxxix.

hypotympanic, fig. 43, 29. The parietals, ib., 44 and 68, 7, and

afterwards the frontals, ib. ib., 11, progressively cover the 'fon-

tanelle ' above, as the basioccipito-sphenoid covers the hypophysial

vacuity below. An antorbital plate, fig. 72, b, extends from the

frontal to the maxillary. The premaxillaries, at first beak-shaped,

figs. 42, 22, and 6 9 A, n, expand transversely as the month widens

to form its fore-part, fig. 71,

n : external to the premaxillary

pedicles begins the ossification of

the turbinals. The tfpterygoid

plate,' fig. 43, 24, extends to the

inner side of the hypotympanic,

29, and forward to the ( palatine '

bone, and the bifid dentigerous

6 vomerine ' plate, fig. 73, Z, /.

From the membrane covering

( MeckePs cartilage,' figs. 69A and 70, d, are exclusively developed

the mandibular elements, the ( angular,' fig. 43, so, and f dentary,'

ib. 32, being the chief; there is also a ' splenial,' which in some

perennibranchiate Batrachia supports teeth. As the mandible,

fig. 71, d, lengthens, the tympanic, ib. e, shortens and becomes

more vertical, and the hyoid arch, ib. a, shifts its attachment to

the petrosal, close behind, but distinct from, the tympanic.

In the Lepidosiren the ali- and orbito-sphenoids and the hypo-
tympanic remain cartilaginous ;
premaxillaries are represented
by their ascending or facial
parts coalesced into a single
plate, supporting the twTo pre-
hensile teeth. The postorbito-
supertemporals, fig. 41, 12, are
6 dermal ' or scleral bones, over-
lapping the fronto-parietals.
They are not present in modern Batrachia.

In the Axolotl (Axolotes marmoratus), the basioccipital is repre-
sented by the posterior part of the common broad and flat basi-
cranial bone. The exoccipitals are separated below by this process,
and above by a cartilaginous representative of the superoccipital.
Each exoccipital developes a small, almost flattened coiidyle,
anterior to which it is perforated by the eighth pair of nerves ; it
articulates above with the parietal and mastotympanic, and is
separated from the alisphenoid by the large cartilaginous petrosal,
to which a small discoid representative of the stapes is attached,

71

Hyo-braucliial fi-ame, skull, older Tadpole, cxxxi

88 ANATOMY OF VERTEBRATES.

closing the homolosfue of the * fenestra ovalis.' The basi-

o o

sphenoidal portion of the basicranial plate sends out an angular
process on each side, which supports the alisphenoid. The
surfaces of the alisphenoid are directed forward and backward,
instead of from side to side, and it constitutes chiefly the anterior
parietes of the otocrane ; the inner and anterior border is
notched by the great trigeminal nerve. The parietals are long
and broad, divided by the sagittal suture, and impressed at the
posterior and outer angle by the anterior attachment of the great
dorsal trunk-muscles. The masto-tympanic is articulated to this
part of the parietal and to the exoccipital ; it includes all the
divisions of the pedicle save the lowest, ( hypotympanic,' which
affords the articulation to the mandible. The orbitosphenoids
are divided by an unossified tract of some extent from the ali-
sphenoids, and articulate above with the extremity of the parietal,
the frontal and prefrontal bones. There are neither paroccipitals
nor postfrontals. The vomerine portion of the basicranial plate
is chiefly cartilaginous. The turbinals are very small, and
separated from each other by the junction of the premaxillaries
with the frontals. The bone extending from the frontal to the
maxillary in front of the orbit may be termed ( antorbital ; ' the
ossification which extends therefrom, in higher Batrachians, takes
the situation of the facial plate of the prefrontal, of the nasal, and
of the lacrymal. The pedicles (tf apophyse montante,' Cuvier,)
of the premaxillaries are long and narrow. The small maxillary is
attached to the antorbital, to the palatine, and to the premaxil-
lary ; the end of the bone extends freely backward as in the
Menopome, fig. 43, 21. The alveolar border of both premaxillaries
and maxillaries supports a single row of small equal and sharp-
pointed denticles. Two bones attached to the anterior and outer
part of the basicranial bone, and which may be regarded either as
' vomerine or palatal, support each a narrow rasp-like group of
minute denticles, which are continued backAvard upon the be-
ginning of the pterygoids ; the pterygoids continued from these
bones and from the sides of the basicranial bone expand as they
extend backward and apply themselves to the inner side of the
tympanic pedicle. The nasal meatus has its posterior termination
between the beginning of the pterygoid and the end of the
maxillary bones. Besides the ordinary row of denticles upon the
clentary piece of the lower jaw, there is a second shorter series
upon the splenial piece.

In theMeiiobranch(^/eft0Z»/Ymc/«/s later alls) the occipital condyles
are transversely oblong, convex vertically, concave transversely,

ANATOMY OF VERTEBRATES.

89

developed from the exoccipitals, which are separated above and
below, as in the Axolotl : each exoccipital forms the posterior half of
the otocrane, is perforated by the nervus vagus, and articulates
above with the parietal and masto-tynipanic. The basisphenoid is
very broad and flat : the alisphenoids bound the fore part of the
otocrane, transmit the trigeminal nerve, and abut against the tym-
panic pedicle in its course backward to the rnastoid. The parietals
are divided by the sagittal suture and develope a small ridge there
posteriorly : each parietal sends down a process in front of the ali-
sphenoid which rests upon the pterygoid, representing the so-called
'columella' in Lizards. There are no maxillary bones. The alveolar
border of the premaxillaries, which support a single row of long
and slender teeth, ten in number in each bone, terminates in a
point projecting freely outward and backward. The vomero-pala-
tine bones unite together anteriorly, but diverge posteriorly, where
they give attachment by their outer margin to the pterygoids.

The two foregoing are examples of the Ichthyomorphs which
retain the gills, and thence are termed ( perennibranchiate.' The
Menopome, figs. 43, 72, and 73, represents a later phase of larval

72

Upper view of skull of the Menopome. cxxxis.

Under view of the skull.

life, the gills being absorbed and only the branchial slits re-
maining. In fig. 72, e e are exoccipitals, each developing a
condyle ; c, c, parietals ; g, g mastotympanics ; h hypotympanic ;
a, a, frontals, b, b, antorbitals ; d, d, nasals ; n, orbitosphenoid ;
k, k, premaxillaries ; i, i, maxillaries ; f, f, pterygoids. In fig.
73, m is the basioccipito-sphenoidal ; e, e, exoccipitals ; g, g,
mastotympanics ; A, h, hypotympanics ; /, /, pterygoids ; /, /,
vomers ; k, k, premaxillaries.

In the Frog (Rana) when the metamorphosis is complete, the

90 ANATOMY OF VERTEBRATES.

exoccipitals have coalesced with the superoccipital above, and with
the basioccipito-sphenoidal plate below ; this latter, fig. 98 A, sends
out on each side a process to form the floor of the otocrane, and its
forward extension is long and narrow : the tympanic developes a
frame for the large ear-drum, fig. 44, N : the stapes, now colu-
melliform, stretches from that membrane to the foramen of the
labyrinth. ( Meckel's cartilage,' figs. 69 and 71, d, contributes
nothing to the bony conductor of sonorous vibrations which
becomes subdivided into a chain of ossicles in Mammalia. The
hypotympanic, fig. 44, 28, sends forward a process to the end of
the maxillary, thus articulating, as in the Plagiostomes, with both
upper and lower jaws. The essential or neurapophysial parts of
the prefrontals encompass the prosencephalon, and coalesce to
form a ring of bone, like the exoccipitals : it is the ' os en
ceinture ' of Cuvier,1 part of which appears at the upper surface
of the cranium, fig. 44, u, between the frontals and antorbitals,
ib. is, which here, and still more in the Toad, assume the
character of nasals connate with lacrymals. Between these and
the premaxillaries are the small bony parts of the olfactory sacs,
usually described as ' nasal bones.' The orbital and temporal
fossae form one wide common vacuity on each side the cranium :
it is divided from the nostril by the junction of the maxillary,
ib. 21, with the naso-lacrymal bone : the premaxillaries, ib. 22,
are small bones, with a well-marked facial and buccal portion.
The palatines, fig. 98, A, are transversely extended : the divided
vomer is dentigerous : the pterygoid, ib. 24, sends out three rays
for the sphenoidal, tympanic, and palato-maxillary connections re-
spectively. The mandible is edentulous. The hyoid arch with
its branchial appendages has changed its connections as well as
shape. In the tadpole, with the fully-developed gills, the carti-
lage representing the stylo- and cerato-hyals, figs. 69 and 6 9 A, a, is
short and thick, and attached to the back of the tympanic pedicle,
ib. e, to the end of which is articulated the mandible, ib. d. The
ceratohyals are connected below to a median piece, ib. Z>, which may
represent both the basihyal and basibranchial : it directly supports
the hypobranchials c, c, to which the ceratobranchials, or branchial
arches are attached. As the gills wither, the stylo-ceratohyals, figs.
70 and 71, a, lengthen, attenuate, and acquire an independent
attachment to the petrosal ; the basi- and hypo-branchial s, fig.
74, c, c, coalesce into a single cartilaginous plate, with the
6 basihyal,' ib. b ; and the ceratobranchials are reduced to a single
pair, which represent the so-called e posterior cornua ' of the hyoid.

1 cxxxix. torn V. pt. 2, p. 389, pis. xxiv. — xxvii., well illustrate the osteology of
the Batrachia.

ANATOMY OF VERTEBRATES.

91

74

Hyobrancliial frame, Rana paradoxa. cxxxix.

The scapular arch, fig. 42, so, 51, retrogrades, like the hyoid, from
its primitive position in the larva.

Cuvier, at thexonclusion of his description of the batrachian skull,
remarks, ' This skull does
not accord with the theory
of the three, four, or seven
vertebrae, or even of one
(cranial) vertebra, any more
than it does with that of the
identity in the number of
bones ' (in different animals). l

At the same time he de-
termines the special homo-
logy of the twenty-six bones,
exclusive of the mandible and hyoid apparatus, and assigns to them
the same names, --and as regards the majority, correctly, — which
those bones bear in the rest of the vertebrate province. We have
been led, therefore, to look for some higher law within which that
of the special conformity may be included.

In many instances of trunk-vertebra?, the neurapophyses meet
below, as well as above the neural axis, their bases being extended
towards each other so as to interpose between that axis and the
vertebral centrum. This condition is repeated by the exoccipitals
which form the neural arch of the epencephalon, and encompass it,
in Batrachia, giving passage to its chief pair of nerves and de-
veloping articular processes for the succeeding vertebra. The two
pairs of neurapophyses in advance, retain the more ordinary rela-
tions of these elements, the more expanded mes- and pros-encephala
having their bony ring or arch completed by a centrum below and
a spine above. One neurapophysis (alisphenoid) transmits the
trigeminal nerve, the other (orbitosphenoid) the optic nerve : the
fourth or anterior neural arch (f os en ceinture ' and ( ethmoide '
of Cuvier) encompasses the foremost segment of the brain
as the exoccipitals do the hindmost ; and they give passage
to the olfactory nerves. Ossification of this ring of bone begins
in its lateral halves : the essential relations and functions being
those which characterise the bones which in bony fishes will be
described as ( prefrontals.' Beneath, and supporting them, is a
pair of bones which may be regarded as a mesially divided
' centrum ' (vomer) : and above is a pair of bones which may be

1 cxxxix. ' Ce crane ne s'accorde pas plus avec la theorie des trois, des quatre, ou
des sept vertebres, meme avec celle d'une vertebre, qu'avec celle de 1'identite de
nombre des os,' vol. v. pt. ii. p. 391.

92 ANATOMY OF VERTEBRATES.

regarded as a mesially divided neural spine (nasal). Thus may be
discerned four cranial segments having the essential characters and
relations of the neural arch of the type vertebra. The upper, 22,
and lower, so, jaws, the hyoid, 40, and scapulocoracoid, 50-52, fig. 42,
constitute four inverted arches ; but their vertebral relations will
be better understood in the composition of the skull in bony fishes.
§ 30. Skull of Osseous Fishes. — The head is larger in proportion
to the trunk in fishes than in other vertebrate classes ; it is usually
in form of a cone, figs. 34, 38, whose base is vertical, directed back-
ward, and joined at once to the trunk, and whose sides are three in
number, one superior, and two lateral and inferior. The cone is
shorter or longer, more or less compressed or squeezed from side
to side, more or less depressed or flattened from above downward,
with a sharper or blunter apex, in different species. The base of
the skull is perforated by the hole, called ( foramen magnum,' for
the exit of the spinal marrow ; the apex is more or less widely and
deeply cleft transversely by the aperture of the mouth ; the eye-
sockets or 'orbits,' ib. 17, are lateral, large, and usually with a
free and wide intercommunication in the skeleton ; the two
vertical fissures behind are called ( gill-slits,' or branchial or oper-
cular apertures ; and there is a mechanism like a door, ib., 35, 36,
37, for opening and closing them. The mouth receives not only
the food, but also the streams of water for respiration, which
escape by the gill-slits. The head contains not only the brain and
organs of sense, but likewise the heart and breathing organs.
The inferior or ' hasmal ' arches are greatly developed accordingly,
and their diverging appendages support membranes that can act
upon the surrounding fluid, and are more or less employed in
locomotion : one pair of these appendages, ib. P, 55, 56, answers,
in fact, to the fore-limbs in higher animals ; and their sustaining
arch, ib. 51, 52, in many fishes, also supports the homologues of
the hind-limbs, v, :o. Thus brain and sense-organs, jaws and
tongue, heart and gills, arms and legs, may all belong to the head ;
and the disproportionate size of the skull, and its firm attachment
to the trunk, required by these functions, are precisely the
conditions most favourable for facilitating the course of the fish
through its native element.

o

It may well be conceived, then, that more bones enter into the
formation of the skull in fishes than in any other animals ; and the
composition of this skull has been rightly deemed the most
difficult problem in Comparative Anatomy. c It is truly remark-
able,' writes the gifted Oken, to whom we owe the first clue to its
solution, ( what it costs to solve any one problem in Philosophical

ANATOMY OF VERTEBRATES.

93

Anatomy. Without knowing the what, the how, and the u'hy,
one may stand, not for hours or days, but weeks, before a fish's
skull, and our contemplation will be little more than a vacant
stare at its complex stalactitic form.'

To show what the bones are that enter into the composition of
the skull of the fish ; how, or according to what law, they are there
arranged ; and why, or to what end, they are modified, so as to
deviate from that law or archetype, will next be our aim. These
points, rightly understood, yield the key to the composition of the
skull in all vertebrata, and they cannot be omitted without detri-
ment to the main end of the most elementary essay on the
skeletons of animals. The comprehension of the description will
be facilitated by reference to figs. 75 — 85 ; and still more if the
reader have at hand the skull of any large fish.

In the Cod(Gadus morrhua, L. fig. 75), e. g., it may be observed,
in the first place, that most of the bones are, more or less, like

15

Skull of Cod (Morrliua vulgaris), Cuv.

large scales; have what, in anatomy, is called the e squamous' cha-
racter and mode of union, being flattened, thinned off at the edge,
and overlapping one another ; and one sees that, though the skull,
as a whole, has less freedom of movement on the trunk, more of
the component bones enjoy independent movements. Before we
proceed to pull apart the bones, it may be well to remark, that the
principal cavities, formed by their coadaptation, are the ( cranium,

94

ANATOMY OF VERTEBRATES.

76

lodging the brain and the organs of hearing; the c orbital,' and f nasal'
chambers ; the ( buccal ' and f branchial ' canals. Some of these
cavities are not well defined. The exterior of the skull is traversed
by five longitudinal crests, intercepting four channels which lodge
the beginnings of the great muscles of the upper half of the trunk.
The median crest is developed from the superoccipital, figs. 75, 76, 3,
and sometimes also from the frontal, fig. 75, n : the lateral crest is
formed by the parietal, fig. 76, 7, and paroccipital, ib. 4: the

external crest by the postfrontal, ib. 12,
and mastoid, ib. 8. The lower border
of the orbit, fig. 75, g, g, projects freely
downward. The hind border of the
operculum is produced into spines in
some species, fig. 82.

In the analysis of the fish's skull
it is best to begin at the back part ;
for the segments of the skeleton de-
viate most from the archetype as they
recede in position toward the two ex-
tremes of the body. After a little
practice one succeeds in detaching the
bones which form the back part or
base of the conical skull, and which
immediately precede and join those of
the trunk ; we thus obtain a ' segment '
or 6 vertebra ' of the skull. If we
next proceed to separate a little the
bones composing this segment, we
find those that were most closely in-
terlocked to be in number and ar-
rangement as follows : — Two single and symmetrical bones,
and two pairs of unsymmetrical bones, forming a circle ; or, if
the lower symmetrical bone, which is the largest, be regarded as
the base, the other five form an arch supported by it, of which
the upper symmetrical bone is the key-stone, fig. 77. This
answers to the f neural ' arch of the typical vertebra : the base-
bone is the ( centrum,' i ; the pair of bones, which articulated with
its upper surface and protected the hind division of the brain,
form the ( neurapophyses,' 2 ; the smaller pair of bones, projecting
outward, like transverse processes, are the ( diapophyses,' 4 ; the
symmetrical bone completing the arch, and terminating above in a
long crest or spine, is the f neural spine,' 3. It will be observed
that the centrum is concave at that surface which articulates with

Upper surface of cranium, Perch
(Perca fluviatilis)

ANATOMY OF VERTEBRATES.

95

Disarticulated epencephalic arch,

viewed from behind : Cod

(Morrhua vulgar is)

the centrum of the first vertebra of the trunk : the opposite
surface is also concave, but expanded and very irregular, in order
to effect a much firmer union with the centrum of the next cranial
segment in advance — great strength and

O O O

fixity being required in this part of the
skeleton, instead of the mobility and elas-
ticity which is needed in the vertebral
column of the trunk. It may be also
observed that the ( neurapophyses ' are per-
forated, like most of those in the trunk,
for the passage of nerves ; that the diapo-
physes give attachment to the bones which
form the great inferior or hremal arch ; and
that the neural spine retains much of the
shape of the parts so called in the trunk.
Nevertheless, the elements of the neural
arch of this hindmost segment of the skull
have undergone so much developement and modification of shape,
that they have received special names, and have been enumerated
as so many distinct and particular bones. The centrum, i, is
called ' basioccipital ; ' the neurapophyses, 2, e exoccipitals ; ' the
neural spine, 3, ' superoccipital ; ' the diapophyses, 4, ' parocci-
pitals.' In the human skeleton all those parts are blended together
into a mass, which is called the ' occipital bone.' In Philosophical
Anatomy it is the ' epencephalic arch,' because it surrounds the
hindmost segment of the brain called ( epencephalon.'

The entire segment, here disarticulated, is called the ( occipital
vertebra,' and in it we have next to notice the widely-expanded
inferior or hnamal arch, fig. 81, 50, H. This consists of three
pairs of bones. The first pair are bifurcate, and have two points
of attachment to the neural arch, the lower prong, answering to
what is called the ' head of the rib,' abutting upon the neura-
pophysis ; the upper prong, answering to the ( tubercle of the
rib,' articulating to the diapophysis. The second pair of bones
are long and slender, and represent the body of the rib. The
first and second piece together answer to the element called
( pleurapophysis ; ' the third pair of bones are the ' haemapophyses ; '
these support diverging appendages consisting of many bones
and rays. The special names of the above elements of the
haemal arch of the occipital vertebra are, from above downwards,
e suprascapula,' so ; ( scapula,' 51 ; ( coracoid,' 52. The inverted arch,
so formed, encompasses, supports, and protects the heart or centre
of the haemal system ; it is called the ( scapular arch.' There

96 ANATOMY OF VERTEBRATES.

are cold-blooded animals — the gymnothorax and slow- worm,
e. g.- -in which this arch supports no appendage ; there are others
-Lepidosiren and Protopterus, fig. 41, 52 — in which it supports
an appendage in the form of a single many-jointed ray, ib. 57.
In other fishes, the number of rays progressively increase, until,
in those called ( rays ' par excellence, fig. 64, they exceed a hundred
in number, and are of great length, forming the chief and most
conspicuous parts of the fish. The more common condition of
the appendage in question is that exhibited in the Cod, fig. 34,
So developed, it is called in Ichthyology the f pectoral fin,' ib. P :
otherwise and variously modified in higher animals, the same part
becomes a fore-leg, a wing, an arm and hand.

Proceeding to the next segment, in advance, in the Cod-fish's

o ~ * *

skull, we find that the bone which articulated with the centrum
of the occipital segment is continued forward beneath a great pro-
portion of the skull. In quadrupeds, however, the corresponding
part of the base of the skull is occupied by two bones ; and if the
single long bone in the fish be sawn across at the part where the
natural suture exists in the beast, we have then little difficulty in
disarticulating and bringing away with it a series of bones similar
in number and arrangement to those of the occipital segment.

In the skeletons of most animals the centrums of two or more
segments become, in certain parts of the body, confluent, or they
may be connate ; they form, in fact, one bone, like that, e. g.,
which human anatomists call ( sacrum.' By the term ( confluent '
is meant the cohesion or blending together of two bones which
were originally separate ; by ( connate,' that the ossification of
the common fibrous or cartilaginous bases of two bones proceeds
from one point or centre, and so converts such bases into one
bone : this is the case, e. g., in the radius and ulna of the frog,
and in its tibia and fibula. In both instances they are to the eye
a single bone ; but the mind, transcending the senses, recognises
such single bone as being essentially two. In like manner it
recognises the ( occipital bone ' of man as essentially four bones ;
but these have become ' confluent,' and were not ' connate.' The
centrums of the two middle segments of the fish's skull are con-
nate, and the little violence above recommended is requisite to
detach the penultimate segment of the skull. When detached,
the bones of it are seen to be so arranged as to form a neural and
a hremal arch. In the neural arch, fig. 78, the centrum, neura-
pophyses, diapophyses, and neural spine are distinct: moreover,
the neural spine in the Cod, and many other fishes, is bifid, or
split at the median line. The centrum is called ' basiphenoid,' 5 ;

ANATOMY OF VERTEBRATES.

97

the neurapophysis, f alisphenoid,' 6 ; the neural spine, f parietal,'
7 ; and the diapophysis, ' mastoid,' 8. The alisphenoids protect
the sides of the optic lobes, and the
rest of the penultimate segment of
the brain called ( mesencephalon ; '
the mastoids project outward and
backward as strong transverse pro-
cesses, and give attachment to the
piers of the great inverted haemal
arch. Before noticing its struc-
ture, I may remark that, in the
recent Cod-fish, the case, partly

gristly, partly bony, which Contains Disarticulated mesencephalic arch, viewed
0 f, i . . -, from behind ; Cod (Morrhua vulgaris)

the organ of hearing, is wedged

between the last and penultimate neural arches of the skull.
The extent to which the ear-case is ossified varies in different
fishes, but the bone is always developed in the outer-wall of the
case. In the Cod it is unusually large, and is called ' petrosal,'
fig. 81, IG; in the Perch, fig. 84, 16, and Carp, fig. 83, 16, it is
smaller : it forms no part of the segmented neuroskeleton. In the
acoustic organ which it contributes to enclose, there is a body as
hard as shell, like half a split almond : it is the ( otolite,' fig.

81, 16.

The haemal arch consists of a pleurapophysis and a haemapo-
physis on each side, and a haemal spine ; the pleurapophysis is in
two parts, the upper one called ( stylohyal,' ib. 38 ; the lower one
called f eplhyal,' ib. 39 ; the haemapophysis is called ' ceratohyal,'
ib. 40. The haemal spine is subdivided into four stumpy bones,
called collectively 'basihyal,' ib. 4i ; and which, in most fishes,
support a bone directed forward, entering the substance of the
tongue, called f glossohyal,' ib. 42 ; and another bone directed
backward, called ' urohyal,' ib. 43.

The ceratohyal part of the haemapophysis supports an appendage,
or rudimental limb, called ' branchiostegal,' fig. 81, 44, answering
to the pectoral fin diverging from the haemal arch, in the adjoining
occipital segment.

The penultimate segment of the skull above described is called
the f parietal vertebra ; ' the neural arch is called ( mesencephalic ; '
and the hamial arch is called ' hyoidean ' in reference to its sup-
porting and subserving the movements of the tongue.

The next segment, or the second of the skull, counting back-
ward, can be detached from the foremost segment without dividing
any bone. It is then seen to consist, like the third and fourth

VOL. I. H

98

ANATOMY OF VERTEBRATES.

Disarticulated prosencephalic arch, Cod
(Morrhua vulgaris)

segments, of two arches and a common centre ; but the consti-
tuent bones have been subject to more extreme modifications.
The centrum, called ( presphenoid,' fig. 79, 9, is produced far
forward, slightly expanding ; the neurapophyses, called ( orbito-

sphenoids,' ib. 10, are small semi-
oval plates, protecting the sides of
the cerebrum ; the neural spine, or
key-bone of the arch, called f frontal,'
ib. 11, is enormously expanded, but
in the Cod is single ; the diapophyses,
called ( post-frontals,' ib. 12, project
outward from the hinder angles of
the frontal, and give attachment to
the piers of the inverted haemal arch.
The first bone of this arch is com-
mon in Fishes to it and to that of the
last described vertebra, being the
bone called ( epitympanic,' fig. 81, 25 ;
this modification is called for by the
necessity of consentaneous move-
ments of the two inverted arches, in
connection with the deglutition and course of the streams of

O

water required for the branchial respiration. The haemal arch
of the present segment --enormously developed — is plainly
divided primarily on each side into a pleurapophysis and hgema-
pophysis ; for these elements are joined together by a movable
articulation, whilst the bones into which they are subdivided
are suturally interlocked together. The pleurapophysis is so
subdivided into four pieces ; the upper one, articulating with
the postfrontal and mastoid — the diapophyses of the tAVO middle
segments of the skull- -is called ' epitympanic,' ib. 25; the hind-
most of the two middle pieces is the ' mesotympanic,' ib. 26 : the
foremost of the two middle pieces is the ' pretympanic,' ib. 27 ;
the lower piece is the hypotympanic, ib. 28 ; this presents a joint-
surface, convex in one way, concave in the other, called a ( gingly-
moid condyle,' for the hagmapophysis, or lower division of the
arch. In most air-breathing vertebrates- -the Serpent, fig. 97,
e.g. --the pleurapophysis resumes its normal simplicity, and is a
single bone, 28, which is called the ( tympanic ; ' in the eel-tribe, as
in the Batrachia, figs. 43, 72,^, h, it is in two pieces. The greater
subdivision, in more actively breathing Fishes, of the tympanic
pedicle, gives it additional elasticity, and by their overlapping,
interlocking junction, greater resistance against fracture ; and

ANATOMY OF VERTEBRATES. 99

these qualities seem to have been required in consequence of the
presence of a complex and largely developed diverging appendage,
which forms the framework of the principal flap or door, called
( operculum,' figs. 81, 84, 34-37, that opens and closes the branchial
fissures on each side. The appendage in question consists of four
bones ; the one articulated to the tympanic pedicle is called ( pre-
opercular,' ib. 34 ; the other three are, counting downward, the
' opercular,' ib. 35 ; the f subopercular,' ib. 36 ; the interopercular,'
ib. 37. The hremapophysis is subdivided into two, three, or more
pieces, in different fishes, suturally interlocked together ; the most
common division is into two subequal parts, one presenting the
concavo-convex joint to the pleurapophysis, and called ( articular,'
ib. 29 ; the other, bifurcated behind to receive the point of 29, and
joining its fellow at the opposite end, to complete the haemal arch :
it supports a number of the hard bodies called ' teeth,' and hence
it has been termed the ( dentary,' ib. 32. In the Cod there is a
small separate bone, below the joint of the articular, forming an
angle there, and called the e angular piece,' fig. 75, 30.

In consequence of this extreme modification, in relation to the
offices of seizing and acting upon the food, the pair of ha3ma-
pophyses of the present segment of the skull have received the
name of ( lower jaw,' or ( mandible ' (mandibula). The haemal
arch is, hence, called ' mandibular : ' the neural arch ( prosen-
cephalic : ' the entire segment is called the ' frontal vertebra.'

The first segment, forming the anterior extremity of the neuro-
skeleton, like most peripheral parts, is that which has undergone
the most extreme modifications. The
obvious arrangement, nevertheless, of its
constituent bones, when viewed from be-
hind, after its detachment from the second
segment, affords one of the most conclu-
sive proofs of the principle of adherence
to common type which governs all the
segments of the neuroskeleton, whatever

Offices they may be modified tO fulfil. Disarticulated rhinencephalic arch,
„, -I 1 r» i • i • Cod (Morrhua vulgarly

Hie neural arch, ng. 80, is plainly mani-
fested, but is now reduced to its essential elements — viz., the
centrum, the neurapophyses, and the neural spine. The centrum
is expanded anteriorly, where it usually supports some teeth on
its under surface in fishes; it is called the ' vomer,' ib. 13. The
neurapophyses are notched (in the Cod), or perforated (in the
Sword-fish), by the crura or prolongations of the brain, which
expand into its anterior division, called rhinencephalon, or

H 2

100

ANATOMY OF VERTEBRATES.

( olfactory lobes' ; the special name of such neurapophysis is ( pre-
frontal,' ib. 14. The neural spine is usually single, sometimes
cleft alon£ the middle ; it is the 'nasal.' ib. 15.

o

The haemal arch, fig. 81, 20-^2, H, is drawn forward, so that its
apex, as well as its piers, are joined to the centrum (vomer), and
usually also to the neural spine (nasal), closing up anteriorly the
neural canal. The pleurapophyses are simple, short, sending
backward an expanded plate ; they are called ' palatines,' ib. and
fig. 84, 20. The haemapophyses are simple, and their essential
part, intervening between the pleurapophysis and haemal spine, is

81

.TTl

Side view of cranial vertebrae and sense-capsules ; the liamial arches, H H, in outline, Cod (Morrhua vulgaris)

short and thick ; but they send a long process backward ; this
element is called ' maxillary,' ib. 21. The haemal spine, cleft
at the middle line, sends one process upward of varying length
in different fishes, and a second downward and backward, and
its under surface is beset with teeth in most fishes : it is called
( premaxillary,' ib. 22. Each pleurapophysis supports a f diverg-
ing appendage,' consisting commonly of two bones : the outer
one, which fixes the present ha3inal arch to the succeeding one,
is called f pterygoid,' figs. 75, 81, 24; the inner one is the ' ento-
pterygoid,' ib. 23. The entire segment is called the f nasal vertebra ;'
its neural arch is the e rhinencephalic ; ' its haemal arch, forming
what is termed the upper jaw (maxilla), is called the f maxillary '
arch and appendages.

On reviewing the arrangement of the bones of the foreo'oinoj

O o O O

segments, one cannot but be struck by the strength of the arches
which protect and encompass the brain, and by the efficiency of that

ANATOMY OF VERTEBRATES.

101

arrangement which provides such an arch for each primary divi-
sion of the brain ; and a sentiment of admiration naturally arises
on examinino; the firm interlocking of the extended sutural sur-

o o

faces, and especially of those uniting the proper elements of the
arch with the buttresses wedged in between the piers and key-
stone, and to which buttresses (diapophyses) the larger hremal
arches are suspended.

In addition to the parts of the neuroskeleton, the bones of the
head include the ossified part of the ear-capsule, ( petrosal,' fig.
81, 16, already mentioned; an ossified part of the eye-capsule,
commonly in two pieces, ' sclerotals,' ib. 17 ; and an ossified part
of the capsule of the organ of smell, ' turbinal,' ib. 19. Another
assemblage of splaiichnoskeletal bones support the gills, and are
in the form of slender bony hoops, called ' branchial arches,'
fig. 85, 48, 49. They are partly supported by the hyoidean arch.
Amongst the bones of the muco-dermal system, may be noticed
those that circumscribe the lower part of the orbit, fig. 75, g, g ;
of which the anterior, ib. 73, is pretty constant in the vertebrate
series, and is called ' lacrymal.' In fishes they are called ' subor-
bitals,' and are occasionally present in great numbers, as, e. g., in
the Tunny, or developed to enormous size as in the Gurnard,
fio\ 82, and allied fishes, thence called f mail-cheeked.' A similar

o *

82

Fore part of the skeleton of the Gurnard (Trigla Lyra)

series of bones called ' supertemporals ' sometimes overarches the
temporal fossa.

At the outset of the study of Osteology it is essential to know
well the numerous bones in the head of a fish, and to fix in the
memory their arrangement and names. The latter, as we have

102 ANATOMY OF VERTEBRATES.

seen, are of two kinds, as regards the bones of the neuroskeleton :
the one kind is ( general,' indicative of the relation of the skull-
bones to the typical segment, and which names they bear in
common with the same elements in the segments of the trunk ;
the other kind is ( special,' and bestowed on account of the par-
ticular developement and shape of such elements, as they are
modified in the head for particular functions. A great proportion
of the bones in the head of a fish exist in a very similar state of
connection and arrangement in the heads of other vertebrates, up
to and including man himself. No method could be less con-

o

ducive to a true and philosophical comprehension of the vertebrate
skeleton than the beginning its study in man — the most modified
of all vertebrate forms, and that which recedes furthest from the
common pattern. Through an inevitable ignorance of that pattern,
the bones in Anthropotomy are indicated only by special names
more or less relating to the particular forms these bones happen
to bear in man ; such names, when applied to the tallying bones
in lower animals, losing that significance, and becoming arbitrary
signs. Owing to the frequent modification by confluence of the
human bones, collections of them, so united, have received a
single name, as, e. g. ( occipital,' ( temporal,' &c. ; whilst their
constituents, which are usually distinct vertebral elements, have
received no names, or are defined as processes, e. g. ' condyloid
process of the occipital bone,' ' styloid process of the temporal
bone,' i petrous portion of the temporal bone,' &c. The classifi-
cation, moreover, of the bones of the head in Human Anatomy,
viz. into those of the cranium and those of the face, is artificial or
special, and consequently defective. Many bones which essentially
belong to the skull are wholly omitted in such classification.

In regard to the archetype skeleton, fishes, which were the first
forms of vertebrate life introduced into this planet, deviate the
least therefrom ; and according to the foregoing analysis of the
bones of the head, it follows that such bones are primarily divisible
into those of-

The Neuroskeleton ;
The Splanchnoskeleton ;
The Dermoskeletoii.

The neuroskeletal bones are arranged in four segments, called

The Occipital vertebra ;
The Parietal vertebra ;
The Frontal vertebra ;
The Nasal vertebra.

ANATOMY OF VERTEBRATES. 103

Each segment consists of a 'neural' and a 'hsemal' arch.
(Fig. 81, N, H.) The neural arches are-

N I. Epencephalic arch (bones Nos. i, 2, 3, 4) ;
N II. Mesencephalic arch (5, 6, 7, s) ;
N in. Prosencephalic arch (9, 10, 11, 12);
N iv. Rhinencephalic arch (13, u, is).

The haemal arches are —

H i. Scapular arch (50-52) ;

H II. Hyoidean arch (33-43) ;

H in. Mandibular arch (28-32) ;

H iv. Maxillary arch (20-22).

The diverging appendages of the haemal arches are —

1. The Pectoral (54-57) ;

2. The Branchiostegal (44) ;

3. The Opercular (34-37);

4. The Pterygoid (23-24).

The bones or parts of the splanchnoskeleton which are inter-
calated with or attached to the arches of the true vertebral
segments, are-

The Petrosal (IG) or ear-capsule, with the otolite, is";
The Sclerotal(i7) or eye-capsule;
The Turbinal (19) or nose-capsule ;
The Branchial arches (45-49) ;
The Teeth.

The bones of the dermoskeleton are-

The Supratemporals (74) ;
The Postorbitals (72) ;
The Superorbitals (71);
The Suborbitals (73);

The Labials (75), and others which will be pointed out in
certain ganoid fishes.

Such appears to be the natural classification of the parts which
constitute the complex skull of Osseous Fishes.

104 ANATOMY OF VERTEBRATES.

The term f cranium ' might well be applied to the four neural
arches collectively, figs. 76, 83 ; but would exclude some bones
called ' cranial,' and include some called ( facial,' in Human
Anatomy. In a side view of the naturally connected bones of
those arches, such as is shown in the Carp, fig. 83, the upper
part of the cranium is formed by the neural spines called super-
occipital 3, parietal 7, frontal 11, and nasal is; the lower part
by the centrums called basioccipital i, basisphenoid 5, presphe-
noid 9, and vomer 1 3 : the side-walls by the neurapophyses called
exoccipital 2, alisphenoid 6, orbitosphenoid 10, and prefrontal 14.
Between 2 and 6 is intercalated the petrosal 16 : between the
fore part of 9 and 10 is the ( inter orbital is,' which is an inconstant
ossification in fishes. The outstanding or transverse processes
are the paroccipital 4, the mastoid 8, and the postfrontal 12.

83

Cranium of a Carp.

In the Carp the parietals meet and unite upon the vertex by a
' sagittal ' suture : in most osseous fishes, as in the Cod and Perch,
figs. 76, 77, they are separated by the junction of the superocci-
pital, 3, with the very large frontals, 11,11. At the base of the
skull may be seen, in the Perch, fig. 84, the basioccipital i, the
articular processes of the exoccipitals 2, and the spine-shaped end
of the superoccipital 3. The paroccipital 4, is separated below
from the exoccipital by the petrosal 16. The basi-presphenoid, 5
and 9, carries forward the bodies of the vertebra? to the vomer 13*,
which is expanded and dentigerous anteriorly, as the bodies of
the cervical vertebras support teeth in the Deirodon (p. 57). The
alisphenoids 6, the orbitosphenoids 10, and the prefrontals 14, are
attached to the sides of the basal elements ; more externally are
seen the frontal 11, postfrontal 12, mastoid 8, and paroccipital 4.
On the left side are shown the palatine 20, the entopterygoid

ANATOMY OF VERTEBRATES.

105

23, and external to it the pterygoid abutting upon the hypotym-
panic, 28 d : between this and the epitympanic, 28, are the
mesotympanic, 38, and the pretympanic b. The preopercular, 34,
runs parallel with, strengthens, and connects together the divisions

12

11

Base of the skull with left side of mandibular arch and its orercular appendage, Perch (Perc a fluviatilis)

of the tympanic pedicle : it supports the opercular, 35, the sub-
opercular, 36, and the interopercular, 37. In the mandibular
ramus the articular is marked 29, and the dentary 32. The free
end of the maxillary is seen at 21.

In fig. 85 the maxillary and mandibular arches and appendages
are removed, the stylohyal, 38, having been detached from the
epitympanic. It resumes its normal attachment to its segment
when the special branchial apparatus becomes abrogated, as in
the advanced batrachian, fig. 71, in which we saw the change of
position, as contrasted with the earlier piscine condition of the
larva, fig. 69 A. In the complex and ossified hyoidean arch of

106

ANATOMY OF VERTEBRATES.

fishes we find, after the stylohyal 33, the epihyal 39, the cerato-
hyal 40, and basihyal 41 ; to which may be articulated a glosso-
hyal 42, and a urohyal 43 : this is a large compressed lamelli-
form bone in the Perch. Seven branchiostegal rays, 44, are
articulated to the epi- and cerato-hyals. Four branchial arches
are attached to the base of the cranium. The first consists of the
ceratobranchial, 47, and epibranchial, 48, elements : both of which
support a series of processes, 63, directed towards the cavity of
the mouth and defending the entry to the branchial fissures. The
second and third arches are connected above by the pharyngo-

85

50

Hyobranchial and scapular arches, Perch (Perca fluviatilis)

branchial elements, 49, to the cranium ; and these elements usually
support teeth. The gills are attached to grooves on the outer
side of the epi- and cerato-branchials ; the arches being closed
below by the c basibranchials ' which are attached to the hyoid.
The suprascapula, so, is attached by its lower branch to the basi-
occipital, and by its upper one to the paroccipital, 4. The
scapula, 51, supports the coracoid, 52, to which the clavicle, 58, is
attached, the relative position of which to the coracoid becomes
changed as the scapular arch is detached from its natural con-

ANATOMY OF VERTEBRATES. 107

nection and displaced backward. The humeral segment of the
fore limb is rarely developed in fishes ; the radius, 54, and ulna, 55,
are directly articulated with the coracoid, and are commonly much
more broad than lonsr.

o

Some of the special characters and modifications of the bones
of the head will next be briefly noticed.

The articular cup for the atlas varies from the deep conical
excavation seen, fig. 77, i, in the Cod, to the almost flat surface
in the Halibut ; it is rare to find, as in the Pipe-fish (Fistularia),
the basioccipital presenting a convex surface for articulation with
the body of the atlas ; or to find this centrum confluent with the
basioccipital, as in Polypterus. In many fishes the under part
of the basioccipital is expanded and excavated; in the Carp,
the under part is produced into a broad triangular plate, fig. 83, i,
which supports the large upper pharyngeal grinding tooth ; in
the ganoid Lepidosteus, the basioccipital developes two plates
from its upper and outer angles, which complete the foramen
magnum and support the exoccipitals above. The exoccipitals,
fig. 77, 2, are perforated for the passage of the nervi vagi, some-
times for the first spinal or hypoglossal nerve ; the foramina being
unusually large in the Carp tribe, fig. 83, 2, where they relate
also to the connection of the air-bladder with the organ of hearing,
by means of the ossicles, «, b, c, d, and e.

In some fishes, e.g. Perca, fig. 84, 2, the exoccipitals send
backward articular processes modified to allow a slight move-
ment upon the anterior articular processes of the atlas. Like
the neurapophyses of the trunk in some fishes (e.g. Lepidosiren,
Thynnus, Xipliias), the bases of the exoccipitals expand, and
meet upon the upper surface of the basioccipital, and immediately
support the medulla oblongata.

The superoccipital, fig. 77, 3, usually sends upward and back-
ward a strong compressed spine from the whole extent of the
middle line, and a transverse ( superoccipital ' ridge outwards
from each side of the base of the spine, to the external angles of
the bone. In most fishes this bone advances forward and joins
the frontal, pushing aside, as it were, the parietals, as in fig. 76,
3 ; in Balistes the produced part of the superoccipital is even
wedged into the hinder half of the frontal suture. In the Carp,
on the contrary, the anterior angle of the superoccipital is trun-
cated, forming the base of the triangle, and is articulated by a
lamboidal suture to the parietal bones, fig. 83, 7, which here meet
at the mid-line of the skull, and the upper part of the occipital
spine is low and flattened. The superoccipital is also separated

108 ANATOMY OF VERTEBRATES.

from the frontal by the parietals, in the Salmonoid, Clupeoid,
Mursenoid, and most ganoid fishes ; and is itself divided, in Amia
and Lepidosteus, by a median suture ; these modifications tell
strongly against extending the homology of the superoccipital with
the supernumerary ' interparietal' bone of Mammals, beyond the
anteriorly produced interparietal portion ; which, however, is not
developed from a separate centre in Fishes.

When the skull is much compressed the occipital spine is
usually very lofty, as in the Opah-fish sm&Argyreiosus, fig. 38 : in
the Light-horseman fish (Epliippus) it expands above its origin into
a thick crest of bone, giving the skull the appearance of a helmet ;
but in low flattened skulls the spine is much reduced, projecting
merely backward, as in the Pike and Salmon, and being some-
times obsolete, as in the Remora. In a few instances, the broad
posterior part of the superoccipital articulates with the neural
arch and spine of the atlas, and sometimes, on the other hand, e.g.
in the Halibut, the entire bone is pushed by the paroccipitals
upon the upper surface of the skull, where it manifests the loss of
symmetry by the absence of the expanded plate on the left side of
the spine.

In broad and depressed skulls the par occipital,1 fig. 76, 4, forms
a strong crest, and exceeds the exoccipital in size ; in narrow and
deep skulls the proportions of these bones are commonly reversed,
and the paroccipitals sometimes disappear. In the Shad, the
paroccipitals unite with the mastoids almost as in the Chelonia ;
and in Polyprion they are connate with the exoccipitals as in
batrachian and crocodilian Reptiles. In Synodus, Callichthys,
and Hcterobranclius., the paroccipital is visible only at the back
part, not at the upper part, of the skull. The inner surface of
the paroccipital, like that of the exoccipital, is excavated for the
lodgment of part of the posterior and external semicircular canal
of the enormous internal oro-an of hearing in Fishes. The outer

o ~

projecting process supports the upper fork of the first piece of
the scapular arch ; sometimes, as in Ephippus, by a distinct arti-
cular cavity. The neural parts of the occipital vertebra are those
which are commonly in Fishes the most completely ossified at the
expense of their primitive cartilaginous bases ; and, in Polypterus,
they become anchylosed into one piece, like the occipital bone
of Anthropotoiriy, the superoccipital being as little developed as
in Protopterus.

1 The paroccipitals are not to be confounded with the dermal bone called ' epiotic '
by Professor Huxley, in his reproduction of Miiller's figure of the head of Polt/pterus,
in the Government Publication, (CLXVIII.) p. 22, fig. 16.

ANATOMY OF VERTEBRATES. 109

The basisphenoid (figs. 78 and 84, 5) is usually bifurcate poste-
riorly, and more or less expanded beneath the cranial cavity ; it
is then continued forward (sometimes after sending out a pair of
lateral processes, as in the Perch, more commonly without such
processes) along the base of the interorbital space to near the
fore part of the roof of the mouth : its posterior extremity is
joined by a squamose suture, as in Diodon, to the basioccipital ;
or, more commonly, as in the Cod, is firmly wedged by a kind of
double gomphosis into the basioccipital ; its expanded part sup-
ports the petrosals and alisphenoids : the presphenoidal prolono-a-
tion (figs. 83 and 84, 9) articulates with the orbitosphenoids and
the ethmoid, is, when this is ossified; and it terminates forward
by a cavity receiving the pointed end of the vomer, fig. 84, is.
It is this portion of the basi-pre-sphenoid which manifests the loss
of symmetry in the flat fishes (Pleuronectidce*), being twisted up
to one side of the skull. The basi-pre-sphenoid varies in form
with that of the head in general, being longest and narrowest in
long and narrow skulls, and the converse. The whole of its
upper surface is commonly rough for articulation with the petrosals
and alisphenoids ; rarely does any portion enter into the direct
formation of the cranial cavity, and then, e. g. in the Cod, a small
surface may support the pituitary sac. When it enters more
largely into the formation of the floor of the cranial cavity, it
usually sends upward a little process on each side ; or, as in Fis-
tularia, a transverse ridge. The basisphenoid is smooth below,
where it is usually flattened or convex, but sometimes is pro-
duced downward in the form of a median ridge, and sometimes is
perforated for the lodgment of certain muscles of the eyeball.
In the Polypterus both ali- and orbito-sphenoids are aiichylosed to
the basi-pre-sphenoid, and the result is a bone that answers to the
major part of the ' os sphenoides' of Anthropotomy. As two large
and important hremal arches of the head are suspended from the
parapophyses of the second and third cranial vertebrae, this seems
to be the condition of the fixation and coalescence of the bodies of
those vertebras in all Fishes.

In some, e. g. Perch and Carp, the base of each alisphenoid
rises above the basisphenoid, and then sends inward a horizontal
plate, which, meeting that of the opposite alisphenoid, forms the
immediate support of the mesencephalon, and at the same time the
roof of a canal, excavated in the basisphenoid, and which
traverses the base of the skull, below the cranial cavity, from
before backwards, opening behind at the under part of the basi-
occipital ; this subcranial canal exists in the Salmonoids, Sparoids,

110 ANATOMY OF VERTEBRATES.

Scomberoids, and is very remarkable in most fishes with lofty
compressed skulls, as the Epliippus. In them it resembles, but is
not homologous with, the posterior prolongation of the nasal pas-
sao-es in the Crocodiles, and it lodges some of the muscles of the

O ^

eyeball. The form of the alisphenoids is influenced by that of the
skull ; when this is low and flat, their antero-posterior exceeds their
vertical extent ; in deep and compressed skulls they are narrow and
higli plates ; in ordinary shaped skulls they present either a sub-
circular form, and are perforated, as in the Carp, fig. 83, 6, or are
reniform, the anterior border being deeply notched, as in the Cod,
fig. 81, G; they form a more definite and fixed proportion of the
lateral parietes of the skull than do the petrosals, ib. IG, which
are interposed between them and the exoccipitals ; and they have
their essential function in sustaining and protecting the sides of
the mesencephalon, and in affording exit to the second and third
divisions of the fifth pair of nerves. The alisphenoid articulates
in the Cod with the petrosal posteriorly, with the orbitosphenoid
anteriorly, and with the mastoid and postfrontal above. Where
the alisphenoids have a greater relative size, as in the Perch, and
where the less constant petrosal decreases or disappears, their
connections are more extensive ; they then reach the exoccipitals,
and sometimes even join a small part of the basioccipital. In
the incompletely ossified skulls of some fishes, e. g. the Pike and
the Salmon tribe, the basal and lateral cranial bones are lined by
cartilage, which forms the medium of union between them,
especially the lateral ones : in better ossified fishes, e. g. the Cod,
the union of the alisphenoids is by suture, partly dentated, partly
squamous. In the Cod the second and third divisions of the tri-
geminal nerve pass out of the cranium by the anterior notch ; in
some other fishes they escape by foramina in the alisphenoid : a
part of the vestibule and the anterior semicircular canal of the
acoustic labyrinth usually encroach upon its inner concavity,
whence some have deemed it to be the petrous bone. The chief
variety in the parietals, figs. 76 and 83 7, has been noted in con-
nection with the superoccipital, ib. 3.

In some fishes the parietal is perforated by the ( nervus
lateralis,' which supplies the vertical fins. The left parietal is
broader than the right in the Halibut and some other flat fishes
(Pleuronectidcz).

The process for the attachment of the great trunk-muscles is
developed from the outer margin of the mastoid, figs. 83, 85, s ;
the inner side of this bone is expanded, and enters slightly into
the formation of the walls of the cranial, or rather of the acoustic

ANATOMY OF VERTEBRATES. Ill

cavity ; its inner, usually cartilaginous, surface lodging part of
one of the semicircular canals. It is wedged into the interspace
of the ex- and par-occipitals, the petrosal, the alisphenoid, the
parietal, the frontal, and postfrontal bones. The projecting pro-
cess lodges above the chief mucous canal of the head, and below
affords attachment to the epitympanic, or upper piece of the
bony pedicle from which the mandibular, hyoid, and opercular
bones are suspended.

The orbitosphenoids, figs. 83, 85, 10, are osseous plates usually
of a square shape, sometimes semicircular or semielliptic, as in
the Cod; larger in the Malacopteri, fig. 83, 10 ; very small in
most Acantlwpteri ; and sometimes represented by a descending
plate of the frontal, as in the Garpike, or by unossified cartilage,
as in mail-cheeked fishes. In the Carp their bases meet, like those
of the alisphenoids, above the sphenoid : when osseous matter is
developed in the interorbital septum the orbitosphenoids are
articulated by their under and anterior part to that bone or
bones, fig. 83, lo.1 The olfactory nerves pass forward by the
superior interspace of the orbitosphenoids and the optic nerves
escape by their inferior interspace, or by a direct perforation ; and
the essential functions of the orbitosphenoids relate to the pro-
tection of the sides of the cerebrum or prosencephalon, and to
the transmission of the optic nerves. The orbitosphenoids
frequently bound or complete the foramen ovale.

Although the frontal always enters into the formation of the
cranial cavity, its major part forms the roof of the orbits, which
accessory function is the chief condition of the great expanse of
this neural spine in fishes. Single, and sending up a median crest
in the Cod, the Ephippus, and some other fishes, the frontal is
more commonly divided along the median line, the divisions
having the form of long and broad subtriangular plates, fig. 76,
11, 1 1 ; narrower in the lofty compressed skulls, smaller in those
with large orbits, and becoming greatly expanded in the fishes
with small and deep-set eyes. Each frontal sends up its own crest
in the Tunny,2 the interspace leading to a foramen, penetrating the
cranial cavity in front of the single occipital spine : a larger
fontanelle exists in the Cobitis and some Siluroids between the
frontal and parietal bones. In the Salamandroid fishes (e. g.
Polypterus) each frontal sends down a vertical longitudinal plate,

1 The specially developed interorbital septum, or 'cranial aethmoid' of Cuvier in
the Bream and Carp, misled Bojanus into the belief that it was the body of the
prosencephalic vertebra (vertebra optica). — Isis, 1818, p. 502.

2 Reminding one of the double spine of the neural arch of the atlas in Tetrodon.

112 ANATOMY OF VERTEBRATES.

which rests directly upon the presphenoid, and intercepts a
canal along which the olfactory c crura ' arc continued forward
to the prefrontals : the lateral parietes of this canal thus form
not only a complete, but a double bony partition between the
orbits. In the Shad a corresponding descending plate takes
the place of the orbitosphenoid. In most Acanthopteri an olfac-
tory groove is formed by short vertical descending plates from
the under surface of the frontal. The midfrontal is single in
the PleuronectidcB, but has undergone more modification than
any of the preceding bones in connection with the general distor-
tion and loss of symmetry of the head : in the Halibut the right
posterior angle is truncated, and the rest of that side scooped out,
as it were, to form the lar^e orbit of the risjlit side : the left side

? o o

of the bone retains its normal form : a median crest, a continuation
of that upon the superoccipital, divides the two sides.

The postfrontals, figs. 75, 76, 83, 12, 12, obviously belong to the
same category of vertebral pieces as the mastoids, whose promi-
nent crest they partly underlie and complete, lending their aid in
the formation of the single (e. g. Cod, Salmon), or double, (e. g.
Pike) articular cavities for the tympanic pedicle : like the mastoids
they are ossified in and from the primitive cranial cartilage ; and
their inner surface is expanded, but this less frequently enters
into the formation of the cranial cavity : they form the posterior
boundary of the orbit ; are articulated below to the orbitosphenoid
and alisphenoid, above to the frontal, and by their posterior and
upper surfaces to the mastoid.

The vomer, figs. 83, 84, 1.3, is wedged into the under part of
the presphenoid ; its antero-lateral angles are articulated to the
prefrontals; its upper surface supports the nasal bone, sometimes
immediately, sometimes by an intervening ethmoidal cartilage.
The palatine bones abut against the expanded anterior part of
the vomer, the under side of which commonly supports teeth.
The left ala of the anterior end of the vomer is chiefly developed
in the Halibut and other flat fishes. In the Lepidosteus, the
vomer is divided into two, as in Batrachia, by a median cleft.
Although its posterior end joins obliquely to the under part of
the presphenoid, it is not, therefore, less a continuation of the
basicranial series than is the postsphenoid, which joins in a
similar manner with the basioccipital.

The prefrontals defend and support the olfactory prolongations
of the cerebral axis, give passage to these so-called ( olfactory
nerves,' bound the orbits anteriorly, form the surface of attachment
or suspension for the palatine bones, and through these for the

ANATOMY OF VERTEBRATES. 113

palato-maxillary arch : they rest below upon the presphenoid and
vomer, support above the fore part of the frontal and the back
part of the nasal bones, and, by their outer or facial extension,
give attachment to the large antorbital or lacrymal bone. They
are ossified in and from pre-existing cranial cartilage.

Such are the essential characters of the bones which Cuvier has
called e frontaux anterieures ' l in Fishes, and to which I apply the
name of ' prefrontal ' in all classes of Vertebrate animals. In the
Cyprinoids, and most Halecoids, the prefrontals form part of an
interorbital septum. When anchylosis begins to prevail in the
cranial bones of Fishes, the prefrontals manifest their essential
relationship to the vomerine and nasal bones by becoming confluent
with them : thus we recognise the prefrontals in the confluent
parts of the nasal vertebra of the Conger, by the external groove
conducting the olfactory nerves to the nasal capsules, and by the
inferior process from which the palatine bone is suspended.2 In
the Mur&nce, also, the prefrontals are plainly confluent with the
nasal, is, bone, and form the well marked articular surfaces for the
palato-maxillary bone. In some fishes a process of the prefrontal
circumscribes the foramen by which the olfactory ' crus ' finally
emerges from the anterior prolongation of the cranio-vertebral
canal. In the Carp this part of the brain traverses a deep notch
on the inner side of the prefrontal, fig. 83, u. In the Cod the
palatine arch is chiefly but not wholly suspended to the prefron-
tals. The right prefrontal is the smallest in the unsymmetrical
skulls of the flat-fishes.

The nasal bone is usually single, and terminates forward in a
thick obtuse extremity. The anterior end of the nasal is deepest
in those Fishes which have a small maxillary arch suspended from
the cranial axis by vertical palatines, and which have a large

1 ' Deux frontaux anterieures, qui donnent passage aux nerfs olfactifs, ferment les
orbites en avant, s'appuyent sur le sphenoide et le vomer, et donnent attache par une
facette de leur horde inferieitre aux palatins.' — Legons a" Anat. Comp. ii. 1837, p. 606.
Compare this enunciation of the essential characters of the anterior frontals with
Cuvier's descriptions of the bones to which he applies that name in other classes, and
with the variable determinations of the same bones by other anatomists — le lacrymal,
Geoffroy and Spix ; lamina cribrosa ossis ethmoidei of Bojanus ; seitliche re'ichbeine,
Meckel, Wagner. Without at present entering into the respective merits or demerits
of these determinations, I shall only state that the prefrontals, under whatever names
they are described, are essentially the neurapophyses of the nasal vertebra, and that
the failure in the attempt to determine the special homologies of these bones may, in
every case, be traced to the non- appreciation of their true general homology.

2 In the Conger, Cuvier l recognises the prefrontals as persistent cartilages.

1 Op. cit. (xui.), ii. p- 235,
VOL. I. I

114 ANATOMY OF VERTEBRATES.

basicranial canal. In some fishes, as the Salmonida, the nasal is
broad but not deep : in Istiophorus it is long and narrow : in the
Discoboles and Lophobranchii it is a short vertical compressed
plate : it is altogether absent in the Lophius, or is represented
here, as in the Diodon, by a fibrous membrane, retaining the
primitive histological condition of the skeleton. In the Flying
Gurnard the nasal has no immediate connection with the vomer ;
but this is a rare exception. In most fishes the nasal cavity is
more completely divided by the nasal bone into two distinct lateral
fossa) than in any other class of Vertebrates.

In Amia, Lepidosteus, Polypterus, and many extinct ganoid
Fishes the nasal is divided at the median line. The horn-like pro-
jection from the fore part of the skull of the Naseus unicornis is
formed chiefly by a process of the frontal bone, to the under part
of which a small nasal is articulated.

The turbinals, or osseous capsules of the nose, are situated at the
sides or above the nasal : the premaxillary and the maxillary
bones are usually attached to its extremity through the medium of
a symmetrical cartilage which is articulated with the fore part of
the nasal bone, and extends forward to the interspace of the upper
ends of the premaxillaries. This ( prenasal ' cartilage often forms
a septum between the two ' ossa turbinata : ' it is partially ossified
in the Carp.

The sense-capsules are so intercalated with the neural arches,
which are modified to form cavities for their reception, that the
demonstration of the skull will be best facilitated by describing
them before we proceed to the hrcmal arches of the cranial verte-
bras.

Acoustic capsule, or petrosal, figs. 81, 83, 85, 16.

We have seen that the first developed cartilage upon the
primitive membranous wall of the skull forms a special protecting
envelope for the labyrinth, which alone constitutes the organ of
hearing in Fishes (Ammocetes, fig. 58, ie). In the progressive
accumulation of cartilaginous tissue upon the base and sides of
the cranium, the ear-capsule loses its individuality, and becomes
buried in the common thick basilateral parietes of the cranium.
It is blended with that persistent cartilaginous part of the skull in
the Lepidosiren ; but, in the better ossified Fishes, when the
osseous centres of the neurapophyses of the cranial vertebra?
begin to be established in that cartilaginous basis, a distinct bone
is likewise, in most cases, developed for the more express defence
of the labyrinth. Since, however, functions are less specialised,
less confined to the particular organ ultimately destined for their

ANATOMY OE VERTEBRATES. 115

performance in the lower than in the higher classes, we find in
Fishes several bones taking part with the special acoustic capsule
in the lodgment of the labyrinth ; and it is only in the higher
Vertebrates that the capsule, under the name of the f petrous
bone,' entirely and exclusively envelopes the labyrinth. Its
ossification commences later than that of the cranial neurapo-
physes, in the series of Osseous Fishes : there are species (e. g.
Pike) in which, after the exoccipitals, alisphenoids, and orbito-
sphenoids have received their destined amount of ossification, the
petrosal still remains in the cartilaginous state : it is small in the
Carp, fig. 83, 16, and Bream; in the Perch, figs. 84, 85, 16, it is
more developed ; it is somewhat larger in the flat-fish (e. g.
Halibut); and in the Cod, fig. 81, 16, attains an equal size with
the alisphenoid, ib. 6, which it resembles in form, except that the
notched margin is posterior. Here it forms the posterior lateral
wall of the cranium ; articulates below with the basioccipital i, and
basisphenoid, above with the mastoid 8, and paroccipital 4, behind
with the exoccipital 2, and before with the alisphenoid 6 : it sup-
ports the cochlear division of the labyrinth containing the otolites.
The cavity called ' otocrane ' lodging the petrosal with the rest
of the ear-capsule, is formed, on each side, by the exoccipital,
paroccipital 4, alisphenoid 6, mastoid 8, and postfrontal 4 : it is some-
times closed externally, but opens widely into the cranial cavity.

The optic capsule, or sclerotal, fig. 81, 17, like the acoustic cap-
sule, is cartilaginous in Plagiostomes, and also in the semi-osseous
fishes, as in most Ganoids, the Lepidosiren, the Lophius, the
Lophobranchs and Plectognathes. In better ossified fishes it is
bony, and commonly consists of two hollow hemispheroid pieces,
each with two opposite emarginations ; the inner ones circum-
scribing the hole, (analogous to the meatus internus of the
petrosal), for the entry of the nerves and vessels to the essential
parts of the organ of vision ; and the outer or anterior emargina-
tions supporting the cornea. As this part of the skeleton of the
head retains its primitive fibro-membranous condition in Man, it
is called f the sclerotic coat of the eye ; ' and the osseous plates
developed in it in Birds, many Reptiles, and Fishes, are termed
( sclerotic bones.' It bears, however, the same essential relation
to the vascular and nervous parts of the organ of sight, which the
petrous bone does to those parts of the organ of hearing, and
which the turbinal bones do to the organ of smell : the per-
sistent independence of the eye-capsule, which has led to its being
commonly overlooked as part of the skeleton, relates to the
requisite mobility and free suspension of the organ of vision. In

I 2

116 ANATOMY OF VERTEBRATES.

the Cartilaginous Fishes, however, it is articulated by means of a
pedicle with the orbitosphenoid. The osseous cavity or ( orbit '
lodging the eyeball is formed by the presphenoid, orbitosphenoid,
frontal 11, postfrontal 4, prefrontal u, and palatine 20, bones : it
opens widely outwards, where it is, often, further circumscribed
by the chain of suborbital scale-bones below, and, but less fre-
quently, by a superorbital bone above. The bony orbits in most
fishes communicate freely together, or rather with that narrow
prolongation of the cranial cavity lodging the olfactory crura :
but, in many Malacopteri, e. g. the Shads and Erythrinus, the
Citharinus and Hydrocyon, the Synbranchus, and the genus
Cyprinus, fig. 83, an osseous septum, is, divides the orbits. In
the Amia, Lepidosteus and Polypterus the orbits are divided
by a double septum, forming the proper walls of the olfactory
prolongation of the cranium, as is the case in the Batrachia.

The olfactory capsules, or turlinals, fig. 81, 19, are lodged in a
cavity called ( nasal,' bounded by a variable number of bones, of
which the vomer, ib. 13, the prefrontals, ib. u, and the nasals, ib.
15, are the most constant : in many bony fishes the nasal chamber
is closed behind by cartilage, which partly forms the interorbital
septum ; but in which, in some species, a slender symmetrical
bifurcate (Perch) or subquadrate ossicle is developed ; in the
Cyprinoid (fig. 83, is) and Siluroid Fishes, it articulates below to
the presphenoid, behind and above to the orbitosphenoids, and
above and before to the frontals and prefrontals, forming the chief
part of the interorbital septum. The capsules of the terminal
pituitary expansion of the organ of smell are cartilaginous in the
Plagiostomes, Chimreroids, in most Ganoids, and in the Lepido-
siren. They form a single tube, with interrupted cartilaginous
parietes, like a trachea, in several of the Cyclostomes. The tur-
binals are developed for the more immediate support of each ol-
factory capsule, in osseous fishes ; they are generally thin, more or
less elongated, and coiled scales ; situated at the sides of the nasal
bone and of the ascending processes of the premaxillaries ; usually
free, but in the Gurnards articulated with the prefrontals and
nasal, and in the Cock-fish (Argyreiosus) suspended above the nasal
bone, from the anterior prominence of the frontal spine.

The palato-maxillary arch, fig. 81, 20, 21, 22, H, presents a simple
and intelligible condition in the Lepidosiren and Plagiostomous
fishes ; in all it is completed or closed at one point only, viz., where
the premaxillaries meet or coalesce, fig. 67, 22. The palatine bones
are the piers of this inverted arch, and their points of suspension
are their attachments to the prefrontals, the vomerine, and the

ANATOMY OF VERTEBRATES. 117

nasal bones. The arch is completed by the maxillary and pre-
maxillary bones, the symphysis of the latter forming its apex ;
and it is inclined forward, nearly or quite parallel with the base
of the skull ; which, in most fishes, extends to the apex of the
arch, and in some far beyond it, being usually more or less closely
attached to it. In air-breathing Vertebrates the arch is more de-
pendent, circumscribing below the nasal or respiratory canal. The
pterygoid bones project backward and outward as the appendages
of the palato-maxillary arch, ib. 23. Both maxillary and intermax-
illary bones tend by their peculiar developement and independent
movement in bony fishes to project freely outward, downward, and
backward. We find, at least, that the general form, position, and
attachments of the single and simple palato-maxillary arch, in the
Lepidosiren or Cestracion, are represented in most osseous fishes,
by their several detached bones, the names of which have been
just mentioned.

The palatine (pleurapophysis of nasal vertebra, figs. 81, 84, 20) is
an inequilateral triangular bone, thick and strong at its upper
part, which sends off two processes : one is the essential point of
suspension of the palato-maxillary arch, and articulates with the
prefrontal and vomer at their point of union ; the other is convex,
and passes forward to be articulated to a concavity in the superior
maxillary, to which, in all Fishes, it affords a more or less moveable
joint. In the Parrot-fishes and Diodons the articulation is quite
analogous to that of the mandible below with the tympanic pedicle.
In the Lepidosteus, Amia, and most Ganoids, it is by a suture. In
the Shad the palatine articulates with the premaxillary as well as
the maxillary. In the Mormyrus the palatines meet, and unite
together at the median line. The posterior border is joined to
the entopterygoid, fig. 84, 23, and its outer angle to the pterygoid.
The palatine contributes to form the floor of the orbit and the
roof of the mouth ; in many fishes it supports teeth, but is eden-
tulous in the Cod. It varies much in form in different species ; is
slender and elongated in the wide-mouthed voracious fishes as

o

the Pike, and is short and broad in the broad-headed, small-
mouthed fishes.

The maxillary (haemapophysis of nasal vertebra, fig. 81, 21) is
usually a small edentulous bone,1 concealed in a fold of the skin
between the palatine and premaxillary : it lies, in the Cod, fig.
75, 21, posterior to and parallel with the premaxillary, 22, which it
resembles in form, but is longer and thinner in most osseous fishes :

1 The Os mystaceum of ichthyotomists.

118 ANATOMY OF VERTEBRATES.

the upper, usually bifurcate, end of the maxillary, forms a socket
on which the ascending or nasal process of the premaxillary
glides ; a posterior tubercle at this end is attached to the palatine,
and ligaments connect the same expanded end to the nasal, the
turbinal, the vomer, and the premaxillary : the lower and hinder
expanded end of the bone is attached by strong elastic ligament,
in which a labial gristle is commonly developed, to the lower jaw.
In the Salmon and Herring tribe, the Sudis, fig. 86, 21, Amia,
and most Ganoids, the maxillary supports teeth. In the Plecto-

gnathi (Globe-fish and File-fish), the
maxillaries coalesce wholly or in part
with the premaxillaries. In the Lepi-
dosteus the contrary condition prevails :
the premaxillary and maxillary bones
constitute, indeed, a single dentigerous
arch or border of the upper jaw, as in
» Disarticulated bo.es of paiato- % 86, but are subdivided into many

maxillary arch (Arapaimagigas) bony pieces, a Condition which SCCmS tO

have prevailed in some of the ancient extinct ganoid fishes. In
the Polypterus the maxillary is large and undivided on each side ;
it supports teeth, and sends inward a palatine plate to join the
vomer and the palatine bone ; thus acquiring a fixed position and
all the normal features of the bone in higher animals. The
maxillary bone is very diminutive in the Siluroid fishes, and
appears, with the premaxillary, to be entirely wanting in certain
Eels (MurcenidcB).

The premaxillary (haemal spine of nasal vertebra, figs. 75, 81, 22),
one of a symmetrical pair in the Cod and most other osseous fishes,
is moderately long and slender, slightly curved, expanded and
notched at both extremities : the anterior end is bent upward,
forming the nasal process, and is attached by lax ligaments to the
nasal bone and prenasal cartilage, to the palatine, and to the
anterior ends of the maxillary bones. The premaxillaries are
movably connected to each other by their anterior ends ; the nasal
processes are separated by the prenasal cartilage, the lower or
outer branches project freely downward and outward, fig. 75, 22 :
the labial border of each premaxillary is beset with teeth, whilst
the maxillary bone is quite edentulous in most osseous fishes, as
in the Cod, ib. 21. In Dioclon the premaxillaries and their
lamellated dental apparatus coalesce and constitute a single sym-
metrical beak-shaped bone : the premaxillary is also single in
Mormyrus. The confluent premaxillaries constitute the sword-
like anterior prolongation of the snout in Xiphias, and are firmly

ANATOMY OF VERTEBRATES. 119

and immovably articulated with the prenasal and maxillary bones,
in both the Sword-fish and the Garpike. The premaxillaries are
commonly more extended in the transverse than in the vertical
direction ; but there are many examples in Fishes where their de-
velopement is equal in both directions. The vertical extension,
which forms the nasal branch of the premaxillary, is of unusual
length in the fishes with protractile snouts, as, for example, in the
Picarels (Menidce), the Dories (Zeus), and in certain Wrasses, as
Coricus, and especially the Epibulus, or Sparus insidiator of
Pallas, fig. 87, 22. In this fish the nasal branch of the inter-
maxillary, ib. 22', plays in a groove

on the upper surface of the skull, and -^^ S7

reaches as far back as the occiput when
the mouth is retracted. The descend-
ing or maxillary branch is attached
by a ligament, ib. 22 ", longer than
itself, to the lower end of the maxil-
lary bone, ib. 21, and consequently
draws forward that bone, together with

the lower jaW, tO which the Same end Mechanism of protraction and retraction
„ .,, • 111 T °^ tne moutn (Epibulus insidiator)

oi the maxillary is attached by liga-
ment, when the long nasal branch of the premaxillary glides
forward out of the epicranial groove. The protractile action is
further favoured by a peculiar modification of the hypotympanic,
ib. 28, which, by its great length and movable articulation at
both ends, cooperates with the long premaxillary in the sudden
projection of the mouth, by which this fish seizes the small, agile,
aquatic insects that constitute its prey. In the Lopltius the nasal
processes of the premaxillaries enter a groove in the frontal :
in the Uranoscopus they also reach the frontal, playing upon the
small nasal bone and pressing it down, as it were, upon the
vomer. In the Dactylopterus they penetrate between the nasal
and the vomer, and play in the cavity of the rhinencephalic arch.
The diverging appendage of the palato-maxillary arch consists,
in Fishes, of the pterygoid and entopterygoid bones, which, as
they are the least important parts of the arch, so are they the
least constant : they are wanting, for example, in the Synodon,
Platystacus, Hydrocyon, and Lophius ; are connate with, or
indistinguishable from, the palatine in most Salmonoids and Eels ;
whilst in the Muraena a single bone, the pterygoid, exists, but is
disconnected with the maxillary arch. Most Fishes, however,
present, as in the Cod, the two bones above named. The ento-
pterygoid is edentulous in the Perch, fig. 84, 23, Cod, and most

120 ANATOMY OF VERTEBRATES.

other fishes, but is richly beset with teeth in the Arapaima gigas.
It principally constitutes the floor of the orbit, its breadth de-
pending much upon the depth of that cavity ; it sometimes is
joined by its median margin to the vomer and presphenoid, as in
•the Cod-tribe, Carp-tribe, and Flat-fishes ; and to the basisphenoid
in Lepidosteus, Erythrinus, and Pofypterus, and then divides the
orbit from the mouth ; but more commonly a vacuity here exists
in the bony skull, filled up only by mucous membrane in the
recent fish ; in Upeneus, Polyprion, and Cheilinis, for example,
the entopterygoid does not join the basisphenoid.

The pterygoid forms in the Cod, fig. 75, 24, an inequilateral
triangular plate, but more elongated than the palatine, with which
it is dovetailed anteriorly ; it becomes thicker towards its pos-
terior end, which is truncated and firmly ingrained with the
anterior border of the hypotympanic ; its lower border is smooth,
thickened, and concave ; edentulous in the Cod, but more fre-
quently supporting teeth, as in the Perch. The pterygoid and
palatine appear to form one bone in the great Sudis, (Arapaima
gigas, fig. 86, 20, 24): and they are confluent in the Eel tribe.

The ten bones of which the palato-maxillary arch is composed
in Osseous fishes are, in the Cod and most other species, so dis-
posed, in relation to the peculiar movements of the mouth, as to
appear like three parallel and independent arches, successively
attached behind one another, by their keystones, to the fore part
of the axis of the skull, and with their piers or crura suspended
freely downward and outward, fig. 75, 22, 21, except those of the
last or pterygo-palatine arch, ib. 23, 24, which abut against the
tympanic pedicles. The simplification or confluence of the two
first of these spurious arches is eifected in the Salmonoid Fishes,
Sudis, fig. 86, &c., by the shortening of the premaxillary, and by
the mode of its attachment to the maxillary, which now forms
the larger part of the border of the mouth and supports teeth :
the maxillaries are brought into close articulation with the pala-
tines in the Plectoo-nathes, and the consolidation of the whole

O '

series into its normal unity is effected in the Lepidosiren. The
palatines form the true bases of the inverted arch at their points
of attachment to the prefrontals ; the premaxillaries constitute the
true apex, at their mutual junction or symphysis ; the approxi-
mation of which to the anterior end of the axis of the skull is
rendered possible in fishes, by the absence of any air-passage or
nasal canal ; the pterygoids are the diverging appendages of the
arch ; but are attached posteriorly to strengthen the pedicle sup-
porting the lower jaw, and combine its movements with those of

ANATOMY OF VERTEBRATES. 121

the upper jaw ; just as the bony appendages of one costal arch in
Birds associate its movements with those of the next.

Tympano-mandibular arch, fig. 81, H, 25 — 32. — This presents
its true inverted or haemal character ; its apex or key-stone formed
by the symphysial junction of the lower jaw hanging downwards
freely, below the vertebral axis of the skull. The piers, or points of
suspension, of the arch, are formed by the epitympanics : each epi-
tympanic is articulated to both the postfrontal, 12, and the mastoid,
8, and is divided artificially in fig. 81 ; its articular surface is formed
in the Cod by a single elongated condyle, fig. 75, 28 ; in many
other fishes by a double condyle, one for each of the above-named
cranial parapophyses, fig. 84, 28. In the Diodon the upper border
of the epitympanic is articulated by a deeply indented suture to
the frontal, the postfrontal and mastoid bones : its posterior
margin supports, as in many other fishes, a circular articular sur-
face for the opercular bone, fig. 84, 35. Below the condyle, the
epitympanic in the Cod, fig. 75, becomes compressed laterally,
but is much expanded from before backward. The almost con-
stant bifurcation of both ends of the epitympanic in osseous
fishes, for articulation with two cranial parapophyses above, and
suspending two inverted arches below, make it appear like a
coalescence of the uppermost pieces of both those arches. In
most fishes the lower end is bifid, and supports both the man-
clibular and the hyoidean arches; the stylohyoid, fig. 81,38, being
attached near the junction of the epitympanic with the meso-
tympanic. The contiguous ribs of the Chelonia are immovably
connected together to ensure fixity and strength to the carapace :
the bulky apparatus suspended from the parietal and frontal ver-
tebra of osseous fishes demanded the additional strength in the
supporting axis which is gained by the confluence of their bodies,
and also by that of the proximal pieces of the pleurapophyses by
which the two haemal arches are suspended from those vertebra.
The anterior division of the epitympanic piece articulates with
the preopercular, fig. 75, 34, the mesotynipanic, fig. 81, 26, and
pretympanic, ib. 27 ; the posterior division is again bifurcate in
the Cod, supporting part of the preopercular and part of the
opercular bone. A strong crest projects from its outer surface in
this and many other fishes. The epitympanic is simple at both
ends in the Carp tribe.

The mesotympanic, figs. 81, 26, 84, 38, is a slender, compressed,
slightly curved, elongated bone, articulated by its upper part or
base to the epitympanic and preopercular ; by its lower end to the
inner side of the hypotympanic, reaching almost to the mandibular

122 ANATOMY OF VERTEBKATES.

trochlea; and by its anterior border to the pretympanic. ib. b. The
mesotympanic is confluent with the epitympanic in the Siluroid, the
Mursenoid, and some other fishes ; but does not join the epitympanic
in the Lepidosteus, being in that fish supported by the preopercular.

The pretympanic, figs. 81, 27, 84, Z», is an oblong bony scale,
with the posterior margin thickened and grooved for the reception
of the fore part of the mesotympanic and the upper and fore part
of the hypotympanic. It is confluent with the hypotympanic in
the Conger and Mursena : it does not join either this or the meso-
tympanic in the Lepidosteus.

The hypotympanic, figs. 81, 28, 75 and 84, 2$d, is a triangular
plate of bone, like the epitympanic reversed, bearing the articular
convex trochlea for the lower jaw upon its inferior apex and with
a straight base. The posterior margin of the hypotympanic is
grooved for the reception of part of the preopercular, ib. 34,
its inner side is excavated for the insertion of the pointed end
of the mesotympanic, and the anterior angle is wedged between
the pretympanic and the pterygoid, 24, and is firmly united to
the latter ; the trochlea is slightly concave transversely, convex
in a greater degree from before backwards. The Sly-bream
(Epibulus, Cuv,), presents the most remarkable modification of
the hypotympanic, fig. 87, 28 ; it is much elongated and slender,
carrying the lower jaw at an unusual distance from the base of the
skull, and it is itself movably connected at its upper end with the
mesotympanic. Thus, in the extensive protractile and retractile
movements of the mouth, the under jaw swings backward and for-
ward on its long pedicle, as on a pendulum ; the lower jaw being
further supported or steadied in those movements by a long ligament,
extending from the preoperculum to its angular piece, ib. /, so.

By the confluence of the meso- and epi-tympanics, and of the
pre- and hypo-tympanics, in the Eel tribe, the suspensory pedicle
of the lower jaw is reduced to two pieces, as in Batrachia. In
the Lepidosiren it is represented, as we have seen, by a single
osseous piece ; but this I regard as the homologue of only the
lower half of the pedicle in the MurcencB) viz. the confluent pre-
and hypo-tympanic pieces. This progressive simplification, or
diminution of the multiplied centres of ossification of the tympanic
pedicle of Fishes, even within the limits of the class, has mainly
weighed with me in rejecting the Cuvierian view of its special
homologies ; according to which, not only the squamotemporal
bone and the malar bone of higher animals, but also the ( syrnplectic '
— a peculiar ichthyic bone --are superadded to the 'tympanic'
or quadrate bone of Reptiles and Birds, in the formation of the

ANATOMY OF VERTEBRATES. 123

suspensory pedicle of the under jaw of Fishes. Ascending to the
higher generalisations of homology, we see in the tympanic pedicle
a serial repetition of the palatine bone ; and, in both, the ribs or
pleurapophyses of contiguous vertebras specially modified for the
masticatory functions of the arches they support.

The mandible, figs. 81, 84, 29, 32, is the lower portion of the
arch, being articulated to the hypotympanics above, and closed by
a ligamentous union or bony symphysis with its fellow at its lower
end. The term f ramus ' is applied in Anthropotomy to each half
of the mandible, and each ramus consists of two, three, or more
pieces in different fishes. Most commonly it consists of two
pieces, one (hremapophysis proper, 29,) articulated to the suspensory
pedicle, and edentulous, analogous to the maxillary ; and the other
(haemal spine, 32,) completing the arch, and commonly supporting
teeth, like the premaxillary. In the Cod, and some other fishes,
a third small piece is superadded, at the angle of the posterior
piece, fig. 75, so. The dentary, 32, is deeply excavated, and
receives a cylindrical cartilage, the remnant of the embryonal
haemal arch, fig. 69 A, d, and the vessels and nerves of the teeth.
The Sudis, fig. 88, the Polypterus, and Amia, have the splint-
like plate along; the inner

OO

surface of the ramus, called
e splenial : ' it supports teeth
and developes a coronoid pro-
cess. In both Sudis and Le-
pidosteus there is superadded a Lower jaw' (Arapaima gi(ja*

small bony piece, ib. 29 a, answering to the surangular in Reptiles.

The Diverging Appendage of the tympano-mandibular arch
consists of the bones which support the gill-cover, a kind of short
and broad fin, the movements of which regulate the passage of
the currents through the branchial cavity, opening and closing the
branchial aperture on each side of the head. The first of these
'opercular' bones is the preopercular, fig. 75, 34, which is usually
the longest in the vertical direction. In the Gurnards, or ' mailed-
cheeked' Fishes, fig. 82, the preopercular is articulated with the
enormously developed suborbital scale bone, 73.

Three bones usually constitute the second series of this
appendage : the upper one is commonly the largest and of a
triangular form, thin and with radiated lines like a scale : it is
the opercular, figs. 75, 84, 35 : in the Cod it is principally connected
with the posterior margin of the preopercular, and below with the
subopercular, ib. 36 ; but it has usually, also, a partial attachment
to the outer angle of the epitympanic, fig. 84 ; and is some-

124 ANATOMY OF VERTEBRATES.

times (Diodon, Lopliius, Anguilla) exclusively suspended therefrom.
In the Lophius piscatorius the opercular is a long and strong bone
suspended vertically from the convex epitympanic condyle, and
with a long and slender fin-ray proceeding from the back part of
that joint. The subopercular forms the chief part of the opercular
fin by its long backwardly produced lower angle. The sub-
opercular bone in the Conger is soon reduced to a mere ray,
which curves backwards and upwards like one of the branchio-
stegals. The opercular itself, though shorter and retaining more
of its laminated form, also shows plainly, by its length and curva-
ture in the Eels, its essential nature as a metamorphosed ray of
the tympanic fin. We have seen that all the framework of this
fin had the form of rays in the Plagiostomes. In Muraena the
small opercular bones articulate only to the under half of the
tympanic pedicle. The subopercular is wanting in the Shad.
The lowermost bone, called the interopercular, figs. 75, 84, 37, is
articulated to the preopercular above, to the subopercular behind,
and usually to the back part of the mandible ; it is attached, also,
in the Cod, by ligament to the ceratohyoid in front. The inter-
opercular and preopercular are the parts of the appendage which
are most elongated in the peculiarly lengthened head of the
Fistularia.

The third inverted arch of the skull is the chyoidean,'fig. 81, 38-4 1,
and is suspended, in Osseous Fishes, through the medium of the epi-
tympanic bone, 25, to the mastoid, s ; showing it to be the ha3mal arch
of the parietal vertebra. The first portion of the arch, stylohyal, fig.
85, 38, is a slender styliform bone, which is attached at the upper
end by ligament to the inner side of the epitympanic, close to its
junction with the mesotympanic, and at the lower end to the
apex of a triangular plate of bone, which forms the upper portion
of the ( great cornu.' I apply to this second piece, which is pretty
constant in fishes, the name of epihyal, ib. 39 : the third longer
and stronger piece is the ceratohyal, ib. 40. The keystone or
body of the inverted hyoid arch is formed by two small subcubical
bones on each side, the basihyals, ib. 41. These complete the
bony arch in some fishes : in most others there is a median
styliform ossicle, extended forward from the basihyal symphysis
into the substance of the tongue, called the glosso-hyal, ib. 42 ; and
another symmetrical, but usually triangular, compressed bone,
which expands as it extends backwards, in the middle line, from
the basihyals ; this is the urohyal, ib. and fig. 75, 43. It is connected
with the symphysis of the coracoids, which closes below the fourth
of the cranial inverted arches, and it thus forms the isthmus which

ANATOMY OF VERTEBRATES. 125

separates below the two branchial apertures. In the Conger the
hyoidean arch is simplified by the persistent ligamentous state of
the stylohyal, and by the confluence of the basihyals with the
ceratohyals ; a long glossohyal is articulated to the upper part of
the ligamentous symphysis, and a long compressed urohyal to the
under part of the same junction of the hyoid arch. The glosso-
hyal is wanting in the Mur&nophis.

The Diverging Appendage of the hyoidean arch retains the form
of simple, elongated, slender, slightly curved rays, articulated to
depressions in the outer and posterior margins of the epi- and
cerato-hyals : they are called ( branchiostegals,' or gill-cover rays,
fig. 85, 44, because they support the membrane which closes
externally the branchial chamber. The number of these rays
varies, and their presence is not constant even in the bony Fishes :
there are but three broad and flat rays in the Carp ; whilst the
clupeoid Elops has more than thirty rays in each gill-cover : the
most common number is seven, as in the Cod, fig. 75, 44. They
are of enormous length in the Angler, and serve to support the
membrane which is developed to form a great receptacle on each
side of the head of that singular fish.

The fourth cranial inverted arch, fig. 81, so — 52, H, is that
which is attached to the paroccipital ; or to the paroccipital and
mastoid ; or, as in the Cod, to the paroccipital and petrosal ; or
as in the Perch, fig. 85, so, and Shad, to the paroccipital and
basioccipital : thus either wholly or in part to the parapophysis
of the occipital vertebra, of which it is essentially the haemal
arch ; it is usually termed the ( scapular arch.' In the Eel tribe,
where it is very feebly developed, and sometimes devoid of any
diverging appendage, it is loosely suspended behind the skull ;
and in the Plagiostomes, fig. 30, si, 52, it is not directly
attached to its proper vertebra, the occiput, but is removed
further back, where we shall usually find it displaced in higher
Vertebrates, in order to allow of greater freedom to the move-
ments of the head.

The superior piece of the arch, f supra-scapular,' figs. 81, 85,
50, is bifurcate in the Cod, or consists of two short columnar
bones, attached anteriorly, the one to the paroccipital, the other
and shorter piece to the petrosal, and coalescing posteriorly at an
acute angle, to form a slightly expanded disk, from which the
second piece of the arch is suspended vertically. This piece,
called ' scapula,' ib. 51, is a slender, straight bone, terminating in
a point below, and mortised into a groove on the upper and outer
side of the lower and principal bone of the scapular arch. The

126 ANATOMY OF VERTEBRATES.

supraseapula and scapula together represent the rib or pleur-
apophysis of the occipital vertebra ; they are always confluent in
the Siluroicls. The lower bone ' coracoid,' ib. 52, completes the
arch. In the Cod its pointed upper extremity projects behind
the scapula ; the middle part developes backward a broad plate
giving attachment to the radiated appendage of the arch : the
lower end bends inward and forward gradually decreasing to a
point,, which is usually connected to that of the opposite coracoid
by ligament, and also to the urohyal. In the Siluridas the
coracoids expand below, and are united together by a dentated
suture. In all Fishes they support and defend the heart, and form
the frame or ' sill ' against which the opercular and branchiostegal
doors shut in closing the branchial cavity : they also give attach-
ment to the aponeurotic diaphragm dividing the pericardial from
the abdominal cavity.

The bones of the head being in completest number, de-
parting least from the vertebral pattern, and susceptible of the
most intelligible definitions in the class of Fishes, afford the best
basis for determining their homologies and fixing their nomencla-
ture in the higher vertebrate series.

§ 31. Skull of Chelonia. If the back part of the skull of a

Turtle (Chelone, fig. 89) be compared with
that of a Cod, fig. 77, it will be seen that the
lowest bone, i, offers an articular surface
for the centrum of the atlas, passes for-
ward, expanding, to articulate with the
basisphenoid, supports the ' medulla ob-
longata,' and is suturally articulated above
to the pair of bones, fig. 89, 2, 2, which pro-
tect the sides of the epencephalon. These,

Back view of cranium, Tin-tie • , , i i ^ -t

moreover, transmit the nypogiossal and

vagal nerves, develope each an articulation for the neurapophyses
of the atlas, and converge above to support the keystone of the
arch, 3. We have, thus, unmistakeable characters of the basi-
ex- and super-occipitals ; there is also a bone, 4, wedged between
the ex- 2, and super- 3, occipitals mesially, and joined laterally
to the mastoid, 8 : excavated on its inner surface by the postero-
external semicircular canal, and produced on its outer surface for
the insertion of the ( biventer cervicis ' and ' complexus ' ; it is the
homologue of the paroccipital (' occipitale externe,' Cuvier), and
bears the same general relation to the hindmost vertebral segment
of the skull which the mastoid, 8, does to the next segment in
advance.

ANATOMY OF VERTEBRATES.

127

In fig. 90, the centrum i, neurapophyses 2, and neural spine
3, of the epencephalic arch, are seen from their inner or cranial
surface : with the increasing bulk of the brain, the spine, 3,
begins to expand laterally, and take a greater share in roofing
over the hinder part or epencephalon : the parapophysis, 4, is
excluded in this view. The gristly capsule of the ear-organ fills
up the otocrane formed by the bones, 2, 3, 5, and 6 ; and extends
outward and backward to enter the basal cavity of 4, the par-

90

Section of cranium, Turtle (diclone mydas)

occipital : were ossification to extend into the acoustic capsule,
either from an independent centre, like 16, figs. 81, 83, 84, or
by continuous growth from any of the otocranial bones, the true
homologue of the ( petrosal ' or ' petrous portion of the temporal
bone ' of Anthropotomy would be established. In some Emydians
there is a small autogenous bony plate in the acoustic cartilage,
close to the foramen caroticum.

The basisphenoid, 5, continues forward the series of cranial
centrums, expands beneath the cranial cavity, articulates on each
side with the alisphenoid, 6, and sends out from its under and
lateral surface a plate to articulate with the pterygoids, fig. 98 B, 24,
and, in the Emys, with the petrosal. The alisphenoid, 6, fig. 90,
protects the side of the mesencephalon (optic lobe), is widely
notched anteriorly by the emerging divisions (2nd and 3rd) of the
trigeminal nerve, is perforated posteriorly by a filament of the
acoustic nerve, where it joins the cartilaginous petrosal ; it
articulates above with the mastoid, 8, and parietal, 7, and in
front with the orbitosphenoid, 11. The anterior semicircular
canal is partly lodged in the cavity of the otocrane contributed

128

ANATOMY OF VERTEBHATES.

by the alisphenoid. Thus in the bone 6, we have all the characters
of that so numbered in figs. 81, 83, and 85, and called 'ali-
sphenoid ' in the fish. The chief modification is due to the greater
developement of 3, fig. 90, in Chelonia, which overlaps 6 as well
as 2.

The parietals, figs. 90, 91, are united, as in Cyprinoid and
Ganoid fishes, by the sagittal suture, and are much expanded both
transversely and longitudinally, overlapping, in the Turtle, the

91

18

Skull of Turtle (Chelone mydas)

superoccipital, fig. 90, 3, and articulated with it and the mastoids,
fig. 91, 8, behind; and with the frontals, ib. n, before. Each
parietal, also, sends down a long vertical plate, 7', fig. 90, which
unites with the alisphenoid, 6, and orbitosphenoid, 10, this ossifica-
tion taking the place and function of the latter neurapophyses in
fishes.

The bone, figs. 89, 91,8, which articulates with the paroccipital
4, parietal 7, and postfrontal 12, which aifords the surface of attach-
ment to the upper end of the tympanic 28, enters into the for-
mation of the acoustic chamber in some Emydians, and projects
outward and backward to give insertion to the latissimus colli
and trachelomastoideus, repeats the chief and essential characters
of the bone so numbered, and called ' mastoid ' in Fishes, figs. 75,
76, 83, 85,8: and forms the transverse process of the parietal
vertebra.

The forward continuation of the vertebral bodies from 5 remains
cartilaginous : the lower half of the sides of the prosencephalon

ANATOMY OF VERTEBRATES. 129

are defended partly by fibre-cartilage, partly by the exogenous
descending lamellae, 7', of the parietals : there are no separate ossifi-
cations answering to 9 and 10 in fishes.1 The frontals, fio;s. 90. 91,

O O •'

11, are supported like an arch between the parietals 7 and pre-
frontals, 1 4 : and each sends down a longitudinal lamella, bound-
ing the sides of the narrow anterior continuation of the brain-

o

chamber, as in Polypterus ; but continued by an unossified plate to
the cartilaginous presphenoid and vomer below. The postfrontal,
fig. 91, 12, extends from its connections with the frontal n, and
parietal 7, downward and backward to unite with the mastoid, 8,
in the Turtle, and with the malar, 2fi, and squamosal, 27, in all
Chelonia. It forms the posterior boundary of the orbit, but does
not contribute any share to the proper cranial walls.

The median symmetrical bone, fig. 90, 13, which, like a hypa-
pophysis, is developed in the lower part or production of the
notochordal capsule, which underlaps the anterior end of the
basi-pre-sphenoid, 5, by its narrow hinder part, - - expanding as it
advances to articulate with the prefrontals, 14, — having the pala-
tine bones, ib. 20, abutting against the broad anterior part, and
entering by its under surface into the formation of the roof of the
mouth, fig. 98 B, n, repeats the essential characters of the bone so
numbered and termed f vomer ' in Fishes, figs. 81, 83, 84, 85, 13 ;
and, like it, represents the centrum of the foremost segment of the
vertebral series. The vomer is single in Chelonia, as in most fishes.

The bones, fig. 90, 14, in neurapophysial relation with the vomer,
protecting the sides of the rhinencephalon or olfactory bulbs,
entering into the antero-superior boundary of the orbit, forming
part of the surface of attachment of the palatines, supporting
the fore part of the frontals, and connected, but more commonly
connate, with the nasals, ib. is, fig. 91, 14, repeat the essential
characters of the prefrontals of Fishes, figs. 83, 85, 1 4. Connate, as
in Chelonia they usually are, with the nasals, their outer expanded
plate unites with the maxillary, fig. 91, 21, and completes the
upper border of the nostril, is.

The palatines, figs. 90, 98 B, 20, form the sides of the roof of the
mouth, articulating medially with the vomer, is, n, and laterally
with the maxillary, 21, and pterygoid, 24. The maxillary, figs.
90, 91, 21, presents a palatal, facial, and orbital plate. The palatal
plate, fig. 98 B, 21, developes a masticatory ridge parallel with the
sharp alveolar border. The facial plate, fig. 91, 21, shows the con-
nections with the prefronto-nasal, u, the premaxillary, 2-2, and the
malar, 26 ; the orbital plate is usually perforated by the lacrymal

1 xxxviir. ; Tab. xxi. fig. 89, 1, r.
VOL. I. K

130 ANATOMY OF VERTEBRATES.

canal, the bone so called being ossified continuously, as a process,
from the maxillary. The premaxillaries, figs. 90, 91, 22, closing the
arch anteriorly, are very small in all Chelonia, and the sutures
marking them oft' from the maxillaries are wanting in some
Mud-turtles (Tetronyx longicollis, Fitz. Trionyx Bibroni):1 the
premaxillary part of the facial profile is vertical in many Chelonia,
as in fig. 91 : but in Tetronyx it extends from the nostril down-
ward and backward — the reverse of prognathism.

The pterygoid, fig. 90, 24, diverges from the vomer and pala-
tine, or from the palatine and maxillary, fig. 98 B, backward and
outward : uniting, in Chelone, with its fellow below the basi-
sphenoid, fig. 90, 5, and diverging outward and backward to abut,
at «, against the tympanic, 28. In some Soft-turtles, e.g., Trionyx
( Gymnopus) indicus, the vomer is directly continued from the basi-
pre-sphenoid, and divides the pterygoids from each other.

A second outer bar of bone, fixing the maxillary arch to the
tympanic, is present in all Chelonia, and divided into two pieces.
The proximal piece, fig. 91, 26, is articulated with the maxillary,
21, enters into the lower and back part of the orbital border, unites
superiorly with the postfrontal, 12, and posteriorly with the second
piece, 27. To the bone, 26, the term 'malar' is given; to the
bone, 27, the name ( scjuamosal.' The latter, resembling a vertical
scale or plate, articulates above with the postfrontal, 12, and
mastoid, 8 ; and behind with the tympanic, 28. It completes the
arch called ( zygomatic,' bounding externally the temporal fossa,
which is roofed over by bone in the Turtles (figs. 89 and 91), and
a few Emyds ; but is widely open above in other Chelonia.

The tympanic pedicle is a single bone, fig. 91,28, expanded above,
with a more or less circular border for the insertion of the mem-
brana tympani ; excavated internally by the tympanic air-cells ;
notched behind for the reception of the colurnellar stapes, as in
the Turtles, fig. 91 ; with a narrower cleft in Tetronyx, and with
the borders uniting in the Tortoises and some other Chelonia.

O *

reducing the stapedial passage to a foramen or canal, fig. 92, 28.
The lower end of the tympanic supports a transversely extended
condyle with an undulated or nearly flattened surface. The tym-
panic articulates above with the paroccipital, fig. 89, 4, in some
species with the alisphenoid, in others with the superoccipital, as
well as with the mastoid, ib. and fig. 91, 8.

The mandible consists of an 'articular' element, small, but dis-
tinct in the Turtle, fig. 91, ao; connate in Emys with the f suran-

1 XLIV. No. 954, p. 185.

ANATOMY OF VERTEBRATES.

131

gular,' fig. 92, 29 ; of an ( angular ' continued into a f splenial,' ib. so ;
of a ' coronoid,' ib. 29' ; and of a f dentary,' ib. 32. All Chelonia
are edentulous : the alveolar borders of both upper and lower
jaws are sheathed with horn : but in a few species, especially the
soft turtles ( Trionyx, Tetronyx} these borders are notched or pro-
duced into tooth-like processes. The dentary elements coalesce
at the symphysis ; which, in the Snappers, especially Chelydra
( Chelonura) Temminckii, is produced into a sharp hook.

The hyoid arch consists of a basihyal, fig. 92, 41, a pair of short

92

ii

Side view of cranial vertebras, Emys

processes, ib. e, giving attachment to the genio- and hyo-glossi
muscles : of a pair of long ceratohyals, 40, by which the arch is
suspended to the mastoids ; and of a pair of hyobranchials, 47. To
complete the series of skull-bones homologous with those of the
fish, represented in fig. 81, it is necessary to bring forward the
scapular arch which had receded a short distance from its vertebra
in the Batrachia, fig. 42, 52, from a more remote position in the
Chelonia : we then find that 51, fig. 92, answers to the scapula,
fig. 81, 51 ; and that 52, fig. 92, answers to the coracoid, fig. 81, 52 :
the diverging series of many-jointed rays in the fish, fig. 81, are
now developed into the fore-limb, fig. 92, 53 — 58.

K 2

132 ANATOMY OF VERTEBRATES.

In this figure the several bones of the head of the European
Box-terrapene (Emys EuropcBa, Wgl.) are represented, disarti-
culated, in a side view of their vertebral relations. Beneath the
Roman figure, I, are the centrum, i. neurapophysis, 2, neural
spine, 3, and parapophysis 4, forming the neural (epencephalic)
arch ; with the pleurapophysis, 51, and haemapophysis, 52, forming
the haemal (scapular) arch, with its appendage, of the occipital
vertebra. Beneath n are the centrum, 5, the neurapophysis,
6, the neural spine, 7, the parapophysis, 8, forming the neural
(mesencephalic) arch : from 8 is suspended by an unossified
pleurapophysis the hremapophysis, 40, the haemal spine, 41, with
the appendage, 47, of the haemal (hyoidean) arch of the parietal
vertebra. Under in are the neurapophysis, 10, neural spine, n,
and parapophysis, 12, forming the neural (prosencephalic) arch ;
with the pleurapophysis, 28, and composite haemapophysis, 29 — 32,
forming the haemal (mandibular) arch of the frontal vertebra, of
which the centrum is not an independent ossification. Beneath
IV are, the centrum, 13, the connate neurapophyses and neural
spines, 14, forming the neural (rhinencephalic) arch ; with the
pleurapophysis, 20, haemapophysis, 21, and haemal spine, 22,
forming the haemal (maxillary) arch of the nasal vertebra. The
diverging appendages, for the fixation of this haemal arch are
more developed than in Fishes, where it retains more of its
typical mobility. Besides the appendage, 24, of the pleurapo-
physis, there is now another, extending in two successive
segments, 26 and 27, from the haemapophysis. The splanchnic
ossicle, 16', is part of the acoustic organ : the circle of bones, 17,
belong to the visual organ. Such are the ' general homologies '
of the bones of the chelonian head, in reference to the vertebrate
archetype, fig. 21. Compared with bones of the piscine head,
fig. 81, previously named and characterised, those of fig. 92 are : —

1. Basioccipital.

2. Exoccipital.

3. Superoccipital.

4. Paroccipital.

5. Basisphenoid.

6. Alisphenoid.

7. Parietal.

8. Mastoid.

9. Presphenoid (unossified).

10. Orbitosphenoid (in great part cartilaginous),
n. Frontal.
12. Postfrontal.

ANATOMY OF VERTEBRATES. 133

is. Vomer.

u. Prefrontal (with, is, nasal, distinct in some Clielonia).

16. (Petrosal, unossified from an independent centre); 16', a
superadded ossicle, s stapes,' ( columella ' ; with a gristly represen-
tative of ( malleus; ' in special relation to an organ of hearing affected
by vibrations of air : superadded to all the bones developed in and
from the embryonic haemal arch called ( Meckel's process.'

17. Sclerotals.

19. Turbinal (unossified).

20. Palatine.

21. Maxillary.

22. Premaxillary.

24. Pterygoid, with ossification extending into the seat of 23,
ento-pterygoid.

26. Malar (not answering to the bone so numbered in fig. 81).

27. Squamosal (ib. these bones do not exist in Fishes).

28. Tympanic (here a single bone ; its subdivisions are 25 — 28
in fig. 81).

29. Articular with Surangular.
29'. Coronal.

so. Angular with Splenial.

32. Dentary.

40. Ceratohyal.

41. Basihyal.

47. Cerato-branchial, (or ( thyrohyal ' in reference to the
larynx of air-breathers, a new developement upon the vestige
of the branchial apparatus of fishes).

50. Suprascapula (unossified).

51. Scapula.

52. Coracoid.

52'. Acromial process of scapula.

53. Humerus (rarely a separate ossification in Fishes).

54. Ulna.

55. Radius.

56. Carpus.

57. 58. Digital rays.

The chief differences in regard to the presence and absence of
bones between the Tortoise and the Fish are seen in those
belonging to the category of ( diverging appendages : ' thus the
< branchiostegals,' 43, and ' operculars,' 34 — 37, fig. 81, are sup-
pressed in the Reptile ; while the ' malar,' 26, and squamosal,
27, are not developed in the fish. Some minor, but interesting,
modifications of cranial structure present themselves within the

134 ANATOMY OF VERTEBRATES.

limits of the Chclonian order. Figs. 90 and 91 exemplify that
which prevails in the marine species (Chelone}. In them the head
is proportionally larger ; and, being incapable of retraction within
the carapace, is additionally protected by extension of bone into
the fascia covering the temporal muscles, so as to form a complete
osseus vaulted roof over the temporal fossae, due to exogenous
growths from the postfrontals, fig. 91, 12, the parietals, 7, and the
mastoids, 8.

In the almost sole instance in which such accessory defence is
afforded to a non-marine species — the Brazilian Pipitu (Podo-
cnemis expansa] - - the temporal roof is chiefly formed by the
parietals, and is completed laterally by a larger proportion of the
squamosal than of the postfrontal, which does not exceed its
relative size in other Terrapenes. The present species further
differs from the marine Turtles in the non-ossification of the
vomer and the consequent absence of a septum in the posterior
nostrils ; in the greater breadth of the pterygoids, which send
out a compressed rounded process into the temporal depressions :
the orbits also are much smaller, and are bounded behind by
orbital processes of the postfrontal and malar bones : the mastoids
and paroccipitals are more produced backward, and the entire
skull is more depressed than in the Turtles. In other freshwater
Tortoises (Emys, &c.), the parietal crista is continued into the
occipital one without being extended over the temporal fossa? ;
the fascia covering the muscular masses in these fossae undergoing
no ossification. The bony hoop for the membrana tympani is
incomplete behind, and the columelliform stapes passes through a
notch instead of a foramen to attain the tympanic membrane.
The mastoid is excavated to form a tympanic air-cell.

In the true Tortoises the temporal depressions are exposed, as in
the Terrapenes : the head is proportionally small and can be
withdrawn beneath the protective roof of the carapace. The skull
is rounder and less depressed than in the Terrapenes. The
tympanic hoop is notched behind, but the columelliform stapes
passes through a small foramen. The palatine processes of the
maxillaries are on a plane much below that of the continuation of
the basis cranii formed by the vomer and palatines.

In the soft-turtles ( Trionicidce), the skull is long, depressed,
triangular, the muzzle forming the obtuse apex, and the base
remarkable for its four backward prolongations. The inferior of
these is the shortest, and terminates in the occipital condyle ; the
superior is the longest, and is formed by the superoccipital spine :
the two lateral processes are developed from the paroccipitals and

ANATOMY OF VERTEBRATES.

135

mastoids. The premaxillary is either wanting,, or it is very small,
and represented by its alveolar border only ; the maxillaries
meeting above it. The alveolar borders of both upper and lower
jaws show a regular series of vascular pits or foramina, indica-
tive of the primitive separate matrices, like those of teeth, winch
laid the foundation in the young animal of the continuous horny
coverings of the jaws.

Temminck's Snapper (Chelonura Temminckii) is remarkable for
the upper convexity and enormous expanse of the cranium, chiefly
due to the temporal fossae, contrasted with the short and narrow
face. In a fossil chelonian from the Portland stone ( Ch. planiceps)
and in another from the Chalk ( Ch. pulcliriceps) the nasals were
distinct from the prefrontals, which is a rare exception in existing
species.

93

Nnr

Side view of cranial vertebra and sense-capsules, Crocodile

§ 32. Skull of Crocodilia.— Passing next to the skull of the
Crocodile, we find the first difference in the less complex condition
of the epencephalic arch, fig. 93, N i, which consists of four, instead
of, as in the Fish and Turtle, six bones. The basioccipital, figs. 93
and 94, i, presents, like the centrums of the trunk, a convexity at
its posterior articular surface ; but its anterior one, like the hind-
most centrum of the sacrum, unites with the next centrum in ad-
vance, ib. 5, by a flat rough sutural surface. Like most of the cen-
trums in the neck and beginning of the back, that of the occiput
developes a hypapophysis, but this descending process is longer and
larger. The exoccipitals, ib. 2, articulate suturally, like the neur-
apophyses of the trunk, with the upper and lateral parts of their

136 ANATOMY OF VERTEBRATES.

centrum; are concave mesially, fig. 94, 2, towards the brain-segment
which they protect, meeting above it to support the neural spine, 3 ;
they develope a petrosal plate, which meets a corresponding one
from the alisphenoid ; they give exit to the vagal and hypo-
glossal nerves, and send outward a strong process, fig. 93, 4,
which articulates with the mastoid and tympanic. The anterior
and inner part of the base of this process is excavated by part
of the acoustic cavity : its outer extremity is rough for the attach-
ment of muscles : it thus repeats the essential characters of the ' par-
occipital ' in the Fish and Turtle ; but it is ossified, as an exogenous
transverse process, from the neurapophysis (exoccipital, 2). The
superoccipital, figs. 93 and 94, 3, is broad and flat, like the
similarly detached neural spine of the atlas ; it advances a little
forward, beyond its sustaining neurapophyses, to protect the upper
surface of the cerebellum ; it is traversed by tympanic air-cells,
and assists with the ex- and par-occipitals, 2, 4, in the formation of
the ear-chamber.

Proceeding with the neural arches of the Crocodile's skull, if we
dislocate the segment in advance of the occiput, fig. 93, N 2, we
bring away, in connection with the long base-bone, 5, the bone, 9.
The two connate cranial centrums must be artificially divided, in
order to obtain the segments distinct to which they belong. The
hinder portion, 5, of the great base-bone, which is the centrum of
the parietal vertebra, is the basisphenoid. It supports that part
of the ( mesencephalon,' which is formed by the lobe of the third
ventricle, and its upper surface is excavated for the pituitary
prolongation of that cavity. The basisphenoid developes from its
under surface a ( hypapophysis,' which is suturally united with the
fore part of that of the basioccipital, but extends further down, and is
similarly united in front to the ' pterygoids,' fig. 94, 24. These rough
sutural surfaces of the long descending process of the basisphenoid
are very characteristic of that centrum, when detached, in a fossil
state. The neurapophyses of the parietal vertebra, 6, 6, the ali-
sphenoids, protect the sides of the mesencephalon, and are notched
at their anterior margin, for a conjugational foramen transmitting
the trigeminal nerve. As accessory functions they contribute, like
the corresponding bones in fishes, to the formation of the ear-
chamber. They have, however, a little retrograded in position,
resting below in part upon the occipital centrum, and supporting
more of the spine of that segment, 3, than of their own, 7. The
spine of the parietal vertebra (parietal, figs. 93, 94, 95, 7), is a single,
depressed bone, like that of the occipital vertebra ; it completes
the mesencephalic arch, as its crown or key-bone ; it is partially

ANATOMY OF VERTEBRATES. 137

excavated by the tympanic air-cells, and overlaps the superoccipital.
The bones, ib. 8, 8, wedged between 6 and 7, are developed from
independent centres, and preserve their individuality, as in Fishes.
They form no part of the inner walls of the cranium, but are
partially excavated by the tympanic cavity, and send outward and
backward a strong transverse process for muscular attachment.
They afford a ligamentous attachment to the haemal (hyoid, fig.
93, H 2, 40) arch of their own segment, and articulate largely with
the pleurapophyses, (tympanic, ib. 2s), of the antecedent hremal
arch, whose more backward displacement, in comparison with its
position in the fish's skull, is well illustrated in the metamorphosis
of the Frog, figs. 69 A and 71.

On removing the neural arch of the parietal vertebra, after the
section of its confluent centrum, the elements of the corresponding
arch of the frontal vertebra, fig. 93, N in, are seen to present the
same arrangement. The compressed produced centrum (presphe-
noid, ib. 9) has its form modified like that of the vertebral centrums
at the opposite extreme of the body in many birds. The neurapo-
physes (orbitosphenoids, ib. 10) articulate with the upper part of
9 ; they are expanded, and smoothly excavated on their inner surface
to support the sides of the large prosencephalon, showing more
plainly their archetypal character than in Chelonia ; they dismiss
the optic nerves by a notch. They show the same tendency to a
retrograde change of position as the neighbouring neurapophyses,
6 ; for though they support a greater proportion of their proper
spine, 11, they also support part of the parietal spine, 7, and rest,
in part, below upon the parietal centrum, 5. The neural spine, n,
of the frontal vertebra retains its normal character as a single
symmetrical bone, like the parietal spine which it partly overlaps ;
it also completes the neural arch of its own segment, but is remark-
ably extended forward, where it is much thickened, and assists in
forming the cavities for the eyeballs; it is the ( frontal' bone.

In contemplating in the skull itself, or such side view as is
given in fig. 94, the relative position of the frontal, n, to the
parietal, 7, and of this to the superoccipital, 3, which is overlapped
by the parietal, just as itself overlaps the flattened spine of the
atlas, we gain a conviction which cannot be shaken by any
difference in their mode of ossification, by their median bipartition,
or by their extreme expansion in other animals, that the above-named
single, median, imbricated bones, each completing its neural arch,
and permanently distinct from the piers of such arch, must repeat
the same element in those successive arches --in other words,
must be ' homotypes,' or serially homologous. In like manner the

138 ANATOMY OF VERTEBRATES.

serial homology of those piers, called e neurapophyses,' viz., the
lamina; of the atlas, the exoccipitals, the alisphenoids, and the
orbitosphenoids, is equally unmistakable. Nor can we shut out of
view the same serial relationship of the paroccipitals, fig. 95, 4, as
coalesced diapophyses of the occipital vertebra, with the mastoids, ib.
8, and the postfrontals, 12, as par- or di-apophyses of their respective
vertebra?. All stand out from the sides of the cranium, as tranverse
processes for muscular attachment ; all are alike autogenous in the
Turtles ; and all of them, in Fishes, offer articular surfaces for the
ribs of their respective vertebrae ; and these characters are retained
in the postfrontals as well as in the mastoids of the Crocodiles.

The frontal diapophysis, figs. 93, 95, 12, is wedged between the
back part of the spine, 11, and the neurapophysis, 10; its out-
wardly projecting process extends backward, and joins that of
the succeeding diapophysis, 8 ; but, notwithstanding the retro -
gradation of the inferior arch, it still articulates with part of its
own pleurapophysial element, 28, which forms the proximal element
of that arch.

There finally remain in the cranium of the Crocodile, after the
successive detachment of the foregoing arches, the bones termi-
nating the fore part of the skull, 1ST 4, fig. 93 ; but, notwithstand-
ing the extreme degree of modification to which their extreme
position subjects them, we can still trace in their arrangement
a correspondence with the vertebrate type.

A long and slender symmetrical grooved bone, fig. 93, 13, is con-
tinued forward from the coalesced pterygoids, 24, and stands in the
relation of a centrum to the vertical plates of bone, 14, which expand
as they rise into a broad, thick, triangular plate, with an exposed
horizontal superior surface. These bones, the prefrontals 14, stand
in the relation of neurapophyses to the rhinencephalic prolonga-
tions of the brain commonly called ' olfactory nerves ; ' and they
form the piers or haunches of a neural arch, which is completed
above by a pair of symmetrical bones, is, called ' nasals,' which I
regard as a divided or bifid neural spine ; the independent basal
ossification, answering to the vomer in Fishes, figs. 81, 84, 13, and
Chelonians fig. 98 B, n, is in advance of its proper segment, and
divided in the middle line as in Ganoid Fishes and Batrachia. In
some Alligators (All. niger) the divided vomer extends far for-
ward, expands anteriorly, and appears upon the bony palate.

Almost all the other bones of the head of the Crocodile are
adjusted so as to constitute four inverted arches. These are the
haemal arches of the four segments or vertebras, of which the
neural arches have been just described. But they have been the

ANATOMY OF VERTEBRATES. 139

seat of much greater modifications, by which they are made sub-
servient to a variety of functions unknown in the haemal arches of
the rest of the body. Thus the two anterior hremal arches of the
head perform the office of seizing and bruising the food ; are
armed for that purpose with teeth : and, whilst one arch is firmly
fixed, the other works upon it like the hammer upon the anvil.
The elements of the fixed arch, called f maxillary arch,' fig. 93, H,
iv, have accordino-lv undergone the greatest amount of change, in

o *> o o o

order to adapt that arch to its share in mastication, as well as for
forming part of the passage for the respiratory medium which
traverses it. Almost the whole of the upper surface of the max-
illary arch is firmly united to contiguous parts of the skull by
rough or sutural surfaces, and its strength is increased by bony

94

Section of cranium, Crocodile

appendages, which diverge from it to abut against other parts of
the skull. Comparative Anatomy teaches that, of the numerous
places of attachment, the one which connects the maxillary arch by
its element, 20, with the centrum, is, and with the descending plates
of the neurapophyses, u, of the nasal segment, is the normal or
the most constant point of its suspension ; the bone, 20, being the
pleurapophysial element of the maxillary arch : it is called the
' palatine,' because the under surface forms a portion of the bony
roof of the mouth, called the ' palate,' as in fig. 98 c, 20. It is
articulated at its fore part with the bone, 21, which is the haema-
pophysial element of the arch. This bone is called the ' maxil-
lary,' and is greatly developed both in length and breadth, fig.
95, 21 : it is connected with 20, figs. 94, 98 C, behind and
with 22 in front, which are parts of the same arch, and with
the diverging appendages of the arch, viz., fig. 95, 26, the malar
bone, and fig. 98 c, 25, the ectopterygoid : the maxillary is also
united with the nasals, is, and the lacrymal, 73, as well as
with its fellow of the opposite side. The smooth, expanded

140 ANATOMY OF VERTEBRATES.

horizontal plate, which effects the latter junction, is called
the palatal plate of the maxillary, fig. 98 c, 21 ; the thickened
external border, where this plate meets the external rough surface
of the bone, and which is perforated for the lodgment of the
teeth, is the ( alveolar border.' The haemal spine or key-bone of
the arch, 22, is bifid, and the arch is completed by the symphysial
junction of the two symmetrical halves ; these halves are called
f premaxillary bones : ' these bones, like the maxillaries, have a
rough facial plate, fig. 95, 22, and a smooth palatal plate, fig. 98 c,
22, with the connecting alveolar border. The median symphysis
is perforated vertically through both plates ; the outer or upper
hole being the external nostril, fig. 95, 22, the under or palatal
one being the premaxillary aperture, fig. 98 C, p.

Both the palatine and the maxillary bones send outward and
backward parts or processes which diverge from the line of the
haemal arch, and give attachment to distinct bones, which form
the ' diverging appendages ' of the arch, and serve to attach it, as
do the diverging appendages of the thoracic haemal arches in the
bird, to the succeeding arch.

The appendage, 24, called ' pterygoid,' effects a more extensive
attachment, and is peculiarly developed in the Crocodilia, As it
extends backward it expands, unites with its fellow both below
and above the nasal canal, encompassing it so as to form the hinder
or palatal nostril, fig. 98 C, n ; the coalesced pterygoids articulate
anteriorly with the divided vomer, the palatines, and the basi-
pre-sphenoid : posteriorly each broad wing, extending outward,
gives attachment to a second bone, ib. 25, called l ectopterygoid,'
"which is firmly connected with the maxillary, 21, the malar, 26,
and the postfrontal, 12. The second diverging ray of the maxil-
lary arch is of great strength ; it extends from the maxillary, fig. 95,
21, to the tympanic, 28, and is divided into two pieces, the malar,
26, and the squamosal, 27 ; both of which begin to assume more
lengthened and slender proportions than in the Turtle (compare
fig. 95 with 91). Such are the chief Crocodilian modifications of
the hamial arch and appendages of the anterior or nasal vertebra
of the skull.

The hamial arch of the frontal vertebra, fig. 92, H, iii, is
someAvhat less metamorphosed, and has no diverging appendage.
It is slightly displaced backward, and is articulated by only a
small proportion of its pleurapophysis, 28, to the parapophysis, 12,
of its own segment ; the major part of that short and strong rib
articulating with the parapophysis, 8, of the succeeding segment.
The bone, fig. 95, 2$, called 'tympanic,' because it serves to support

ANATOMY OF VERTEBRATES. 141

the c drum of the ear ' in air-breathing vertebrates, is short, strong,
and immovably wedged, in the Crocodilia, between the paroccipital,
4, mastoid, 8, postfrontal, 12, and squamosal, 27 ; and the conditions
of this fixation of the pleurapophysis are exemplified in the great
developement of the hasmapophysis (mandible), which is here
unusually long, supports numerous teeth, and requires, therefore,
a firm point of suspension, in the violent actions to which the jaws
are put in retaining and overcoming the struggles of a powerful
living prey. The movable articulation between the tympanic, 28,
and the rest of the haemal arch is analogous to that which we find
between the thoracic pleurapophysis and haamapophysis in birds.
But the haamapophysis of the mandibular arch in the Crocodiles
is subdivided into several pieces, in order to combine the greatest
elasticity and strength with a not excessive weight of bone. The
different pieces of this adaptively subdivided element have received
definite names. That numbered 29, fig. 93, which offers the articular
concavity to the convex condyle of the tympanic, 28, is called the
6 articular ' piece ; that beneath it, so, which developes the angle
of the jaw, when this projects, is the 'angular' piece; the piece
above, 29, and e, fig. 95, is the ' surangular ;' the thin, broad, flat
piece, 31, fig. 93, applied, like a splint, to the inner side of the
other parts of the mandible, is the ( splenial ; ' the small accessory
ossicle, 31', is the f coronoid,' because it developes the process, so
called, in lizards ; the anterior piece, 32, which supports the teeth,
is called the ( dentary.' The purport of this subdivision of the
lower jaw-bone has been well explained by Conybeare1 and
Buckland,2 by the analogy of its structure to that adopted in
binding together several parallel plates of elastic wood or steel to
make a crossbow, and also in setting together thin plates of steel
in the springs of carriages. Dr. Buckland adds — ' Those who
have witnessed the shock given to the head of a crocodile by the act
of snapping together its thin long jaws, must have seen how liable
to fracture the lower jaw would be, were it composed of one bone
only on each side.' The same reasoning applies to the composite
structure of the long tympanic pedicle in fishes. In each case the
splicing and bracing together of thin flat bones of unequal length
and of varying thickness, affords compensation for the weakness
and risk of fracture that would otherwise have attended the
elongation of the parts. In the abdomen of the crocodile the
analogous subdivision of the haamapophyses, there called abdo-
minal ribs, allows of a slight change of their length, in the
expansion and contraction of the walls of that cavity ; and since

1 'Geol. Trans.' 1821, p. 565. - 'Bridgewater Treatise,' 1836, vol. i. p. 176.

142 ANATOMY OF VERTEBRATES.

amphibious reptiles, when on land, rest the whole weight of the
abdomen directly upon the ground, the necessity of the modifi-
cation diminishing liability to fracture further appears. These
analogies are important, as demonstrating that the general homo-
logy of the elements of a natural segment of the skeleton is not
affected or obscured by their subdivision for a special end.
The purposive modification of the hrcmapophyses of the frontal
vertebra is but a repetition of that which affects the same
elements in the abdominal vertebrae.

Passing next to the haemal arch of the parietal vertebra, fig.
93, ir, ii, we are first struck by its small relative size. Its
restricted functions have not required it to grow in proportion
with the other arches, and it consequently retains much of its
embryonal dimensions. It consists of a ligamentous ' stylohyal,'
retaining the same primitive histological condition which obstructs
the ordinary recognition of the pleural element of the lumbar haamal
arches ; of a cartilaginous ( epihyal,' 39, intervening between this
and the ossified hamiapophysis, or ceratohyal, 40 ; and of the haemal
spine, 4J, which retains its cartilaginous state, like its homotypes,
in the abdomen : there they get the special name of l abdominal
sternum,' here of f basihyal.' The basihyal has, however, coalesced
with the thyrohyals to form a broad cartilaginous plate, the anterior
border rising like a valve to close the fauces, and the posterior
angles extending beyond and sustaining the thyroid and other
parts of the larynx. The long bony ( ceratohyal ' and the com-
monly cartilaginous ' epihyal ' are suspended by the ligamentous
f stylohyal ' to the back part of the tympanic at its junction with
the paroccipital process ; the whole arch having, like the man-
dibular one, retrograded from the connection it presents in Fishes.

This retrogradation is still more considerable in the succeeding
haemal arch, fig 92, H i ; fig. 57, 51. In comparing the occipital
segment of the Crocodile's skeleton with that of the Fish, fig. 81,
the chief modification that distinguishes that segment in the Cro-
codile is the apparent absence of its haemal arch. We recognise,
however, the special homologues of the constituents of that arch
of the Fish's skeleton, fig. 34, in the bones 51 and 52 of the Cro-
codile's skeleton, fig. 57 ; but the upper or suprascapular piece, 50,
fig. 92, retains, in connection with the loss of its proximal or cranial
articulations, its cartilaginous state : the scapula, 51, is ossified, as
is likewise the coracoid, 52, the lower end of which is separated
from its fellow by the interposition of a median, symmetrical,
partially ossified piece called ' episternum.' The power of recog-
nising the special homologies of 50, 51, and 52 in the Crocodile,

ANATOMY OF VERTEBRATES. 143

with, the similarly numbered constituents of the same arch in
Fishes — though masked, not only by modifications of form and
proportion, but even of very substance, as in the case of 50 —
depends upon the circumstance of these bones constituting the
same essential element of the archetypal skeleton, viz. the fourth
haemal arch, numbered pi, 52, in fig. 17. For although in the pre-
sent instance there is superadded to the adaptive modifications
above cited the rarer one of altered connections, Cuvier does not
hesitate to give the same names, f suprascapulaire' to 50, and
f scapulaire' to 51, in both Fish and Crocodile ; but he did not per-
ceive or admit that the narrower relations of special homology
were a result of, and necessarily included in, the wider law of
general homology. According to the latter law, we discern in fig.
93, 50 and 51, a compound ' pleurapophysis,' in 52 a ( haemapophy sis,'
and in hs, the ( haemal spine,' completing the haemal arch.1

The scapulo-coracoid arch, both elements, 51, 5-2, of which
retain the form of strong and thick vertebral and sternal ribs in
the Crocodile, is applied in the skeleton of that animal over the
anterior thoracic haemal arches. Viewed as a more robust hamial
arch, it is obviously out of place in reference to the rest of its
vertebral segment. If we seek to determine that segment by the
mode in which we restore to their centrums the less displaced
neural arches of the antecedent vertebras of the cranium or in the
sacrum of the bird,2 we proceed to examine the vertebra before
and behind the displaced arch, with the view to discover the one
which needs it, in order to be made typically complete. Finding
no centrum and neural arch without its pleurapophyses from the

1 The author of No. CLXXI, in criticising this conclusion, omits consideration of
the cartilaginous element, fig. 93, so : as it exists and required due attention, I
was led to regard it as the homologue of the ossified element, figs. 81, 85, 50, in
Fishes, and as being part, one might say, half, of the pleurapophysis. No anatomist has
impugned such determination of the special homology of the ' lame cartilagineuse
du bord spinal de Pomoplate ' of the Crocodile, with the ' partie spinal del'omoplate '
of the Frog, and with the ' os surscapulaire ' of the Fish. Now the latter is the
homotype of the proximal half of the compound pleurapophysis of the pelvic arch,
of which the part called ' ilium ' answers to the part called ' scapula.' There remains,
therefore, for Dr. Humphrey's consideration, the serial and general homologies of the

* suprascapula ; ' in the omission of which lurks the fallacy of his criticism. CLXXI,
pp. 27, 28. The alleged difference of developement, at most one of direction of growth,
is futile.

A ' haemal arch ' having been defined as including the ' pleurapophysis ' as well as

* hremapophysis,' by altering the meaning of the term and restricting the ' haemal parts
of the vertebra ' to the ' ha?mapophyses and hasmal spine,' Dr. Humphrey makes
ground for pronouncing the part of the hcemal arch, 50 and 51, in figs. 81 and 92,
as being the hasm- not the pleur-apophysis.

2 See 'On the Archetype and Homologies of the Vertebrate Skeleton,' pp. 117
and 159.

144 ANATOMY OF VERTEBRATES.

scapula to the pelvis, we give up our search in that direction ;
and in the opposite direction we find no vertebra without its ribs,
until we reach the occiput ; there we have centrum and neural
arch,, with connate parapophyses, but without the haemal arch,
which arch can only be supplied by a restoration of the bones
50-52 to the place which they naturally occupy in the skeleton of
the fish. And since the bones 50-52 in the Crocodile, fig. 57, are
specially homologous with those so numbered in the Fish, fig. 34,
we must conclude that they are likewise homologous in a
higher sense ; that in the Fish the scapula-coracoid arch is in its
natural or typical position, whereas in the Crocodile it has been
displaced for a special purpose. Thus, agreeably with a general
principle, we perceive that, as the lower vertebrate animal illus-
trates the closer adhesion to the archetype1 by the natural articu-
lation of the scapulo-coracoid arch to the occiput, so the higher
vertebrate manifests the superior influence of the antagonizing
power of adaptive modification by the removal of that arch from
its proper segment.

The anthropotomist, by his mode of counting and defining the
dorsal vertebrae and ribs, admits, unconsciously perhaps, the
important principle in general homology which is here exemplified ;
and which, pursued to its legitimate consequences, and further
applied, demonstrates that the suprascapula and scapula are the
modified rib of that centrum and neural arch, which he calls the
f occipital bone ; ' and that the change of place which chiefly masks
that relation (for a very elementary acquaintance with Compara-
tive Anatomy shows how little mere form and proportion affect
the homological characters of bones), differs only in extent, and
not in kind, from the modification which makes a minor amount
of comparative observation requisite, in order to determine the
relation of the shifted dorsal rib to its proper centrum in the
human skeleton.

With reference, therefore, to the occipital vertebra of the Cro-
codile, if the comparatively well-developed and permanently
distinct ribs of all the cervical vertebrae prove the scapular arch
to belong to none of those segments,2 and if that haamal arch be
required to complete the occipital segment, which it actually does
complete in fishes, then the same conclusion must apply to the
same arch in other animals, up to man himself.

1 The term ' simple primary form ' appears to Dr. Humphrey, CLXXI, p. 34, to
be more correct than the word ' archetype.'

2 Close the eyes to the fact of the suprascapular element in the Crocodile, and you
then may, with Dr. Humphrey, see its representative in one of the cervical pleur-
apophyses. Comp. ib. p. 28, and note, p. 144, of the present work.

ANATOMY OF VERTEBRATES.

145

The locomotive extremity, fig. 92, 53-57, is the diverging ap-
pendage of the arch, under one of its numerous modes and grades
of developement.

Coadjusted as the above-defined vertebral elements are in the
skull of the Crocodile, they compose such a whole as is represented
in fig. 95. Each temporal fossa is circumscribed externally by
two horizontal bony arches ; the upper one formed by the post-
frontal, 12, and mastoid, 8 ; the lower one by the malar, 26, and
squamosal, 27 : the tympanic, 28, and mastoid, 8, bound the
fossa behind : the coarticulated processes from the postfrontal and
malar form a partial division between the fossa and the orbit in

95

Skull of Crocodile

front. The orbit is circumscribed by these bones, with the frontal,
11, prefrontal, u, and lacrymal, b. A superorbital or palpebral
derm-ossicle strengthens the upper eyelid. The external nostril,
single and advanced in Crocodilia, is surrounded sometimes, as in
Gavials, by the premaxillaries, 22 ; sometimes, as in fig. 95, admit-
ting also the points of the nasals, is. The internal nostril opens far
back, beneath the occiput, fig. 98 c, n, and is exclusively surrounded
by the pterygoids, 24 : its plane is horizontal in Gavials and some
Alligators ; but is more or less oblique, looking backward, in
Crocodiles. Behind and above it are the median and lateral
Eustachian bony outlets, from which the membranous continua-
tions of the tubes converge and unite in the single valvular aper-
ture on the soft palate. L The vast extent of the bony roof of the

1 CLXXII., pi. xii. fig. 5. This paper may be referred to for other cranial foramina,
and for the details of the complex bony structure of the median and lateral
VOL. I. L

146 ANATOMY OF VERTEBRATES.

mouth is interrupted by the large ' ptery go-maxillary ' vacuities,
ib. //, bounded externally by the maxillaries and ectopterygoids :
at the fore part is the small ( prepalatine ' opening, ib. p. In the
Gavials each pterygoid expands at its outer and fore border into a
large oval bulla. The palatines and maxillaries are excavated by
sinuses communicating with the nasal passages. The form of the
maxillo-premaxillary palatine suture helps by its variation to the
distinction of species.1 The anterior expanded parts of the divided
vomer appear upon the bony palate in some Alligators.2

The otic capsule remains in great part cartilaginous : towards
the cranial cavity it is defended by the thin otocranial plates of
the alisphenoid, superoccipital and paroccipital, with occasionally a
small scale, representing a rudimental petrosal. The eye-capsule
is not defended by bony plates, as in Chelonia. The turbinals
remain cartilaginous.

o

The cranial cavity is miserably small in these huge cold-blooded
Carnivora; its main part, shown in section, fig. 94, 2, o, 10, may
be filled by a man's thumb in a skull of three feet in length. The
proper brain-chamber is, however, continued along the groove
beneath the interorbital platform to the second slight expansion
between the prefrontals, 14, where the rhinencephalic (olfactory)
lobes send forward the true olfactory nerves.

If the foregoing statement of the grounds for determining the
homologies, general and special, of the skull-bones of the Crocodilia
may have seemed tedious or unnecessary, I excuse myself by the
importance attached to the subject by Cuvier, who, in the last
lecture which he delivered, stated : l If we were agreed as to the
Crocodile's head, we should be so as to that of other animals ; be-
cause the Crocodile is intermediate between mammals, birds, and
fishes.' Admitting, with some latitude, the reason, a sense of the
importance of a determination of the bones answerable to those
previously defined in Chelonia and Fishes, has influenced me in
the foregoing description of the skull of the Crocodilia.

§ 33. Skull of Opliidia.- -The skull in Lacertians and Ophi-
dians departs from the vertebral pattern by a greater degree of
confluence and a minor extent of neurapophysial ossification,
than in Crocodilia : and that of Serpents manifests more strongly
the principle of adaptive developement.

Eustachian canals in Crocodilia. See also the preparations, XLIV., Nos. 706, 727, 728,
750, pp. 154—164.

1 Ib. XLIV., p. 1 63, where that characteristic of Crocodilus rhombifer is specified.

2 Ib. No. 764, p. 166.

ANATOMY OF VERTEBRATES. 147

In the Python, figs. 96 and 97, the basioccipital, i, is subhex-
agonal, broadest anteriorly, smooth and concave above, suturally
rough on each side, with a recurved pointed hypapophysis : the
hinder facet forms the lower half of the occipital condyle, on each

96

Section of the Skitil of a Python

side of which is a small sharp process. The basioccipital unites
above with the exoccipital, 2, and alispheiioid, 6 ; and in front
with the basisphenoid, 5. The exoccipitals (2, 2) are each pro-
duced backward into a peduncular process supporting a moiety
of the upper half of the occipital condyle : at the outer side of
the base of the peduncle is an obtuse process, forming the
upper part of the ridge continued upon the basioccipital. The
outer and fore part of the exoccipital expands, and is perforated
by a slit for the eighth pair of nerves, articulates below with
the basioccipital, is excavated in front to lodge the petrosal
cartilage where it articulates with the alisphenoid, and unites
above with the superoccipital, 3. This is of a subrhomboidal
form, sends a spine from its upper and hinder surface, expands
laterally into oblong processes, is notched anteriorly and sends
down two thin plates from its under surface, bounding on the
mesial side the surface for the cerebellum, and by the outer
side forming the inner and upper parts of the acoustic cavities.
The superoccipital articulates below with the exoccipitals and
alisphenoids, and in front with the parietal, by which it is over-
lapped in its whole extent. The occipital vertebra is as if it were
sheathed in the expanded posterior outlet of the parietal one, the
centrum resting on the oblique surface of that in front, and the
anterior base of the neural spine entering a cavity in and being
overlapped by that of the preceding neural spine : the analogy of
this kind of ' emboitement ' of the occipital in the parietal vertebra
with the firm interlocking of the ordinary vertebra? of the trunk is

L 2

148

ANATOMY OF VERTEBRATES.

very interesting : the end gained seems to be, in grovelling
reptiles liable to have the head bruised, an extra protection of
the epencephalon- -the most important segment to life of all the
primary divisions of the cerebrospinal axis. The thickness of
its immediately protecting walls (formed by the basi-, ex-, and
super-occipitals) is equal to that of the same vertebral elements
in the human skull ; but they are moreover composed of very
firm and dense tissue throughout, having no diploe : the epen-
cephalon also derives a further and equally thick bony covering
from the basisphenoid and the parietals, the latter being partly
overlapped by the mastoids, fig. 97, 8, which form here a third layer
of the cranial Avail.

The basisphenoid, fig. 96, 5, and presphenoid, 9, form a single

97

•2-2

Skull of a Python

bone, and the chief keel of the cranial superstructure. The
posterior articular surface looks obliquely upward and backward,
and supports that of the vertebral centrum behind, as the posterior
ball of the ordinary vertebrae supports the oblique cup of the
succeeding one : here, however, all motion is abrogated between
the two vertebrae, and the co-adapted surfaces are rough and
sutural. The basisphenoid presents a smooth cerebral channel
above for the mesencephalon, in front of which a deep depression
(sella) sinks abruptly into the expanded part of the bone, and

there bifurcates, each fork forming a short cul-de-sac in the sub-

~

stance of the bone. The transverse processes from the under
and lateral surfaces are well marked, strong, but short, much
thicker in the Python than in the Boa. The alisphenoids, 6, form
the anterior half of the fenestra ovalis, which is completed by
the exoccipitals ; and in their two large perforations for the
posterior divisions of the fifth pair of nerves, as well as in their

ANATOMY OF VERTEBRATES. 149

relative size and position, the alisphenoids agree with those of the
Frog. Each alisphenoid is a thick suboval piece, with a tuber-
cular process on its under and lateral part : it rests upon the
basisphenoid and basioccipital, supports the posterior part of the
parietal and a portion of the mastoid, 8, and unites anteriorly with
the descending lateral plate of the parietal bone.

The parietal, 7, is a large and long, symmetrical roof-shaped
bone, with a median longitudinal crest along its upper surface,
where the two originally distinct moieties have coalesced. It is
narrowest posteriorly, where it overlaps the superoccipital, and is
itself overlapped by the mastoid : it is convex at its middle part on
each side the sagittal spine, and is continued downward and in-
ward to rest immediately upon the basisphenoid, 5. This part of
the parietal seems to be formed by an extension of ossification
along a membranous space, like that which permanently remains
so in the Frog, between the alisphenoid and orbitosphenoid : the
mesencephalon and the chief part of the cerebral lobes are protected
by this unusually developed spine of the mesencephalic vertebra.
The optic foramina are conjugational ones, between the anterior
border of the lateral plate of the parietal and the posterior border
of the corresponding plate of the frontal.

The frontals, n, rest by descending lateral plates, representing
connate orbitosphenoids, upon the presphenoidal prolongation of
the basisphenoid : the upper surface of each frontal is flat, sub-
quadrate, broader than long in the Boa, and the reverse in the
Python, where the roof of the orbit is continued outward by a
detached superorbital bone : there is a distinct, oval, articular sur-
face near the anterior median angle of each frontal to which the pre-
frontal, 14, is attached : the angle itself is slightly produced to form
the articular process for the nasal bones. The smooth orbitosphe-
noidal plate of the frontal joins the outer margin of the upper surface
of the frontal at an acute ano-le ; the inner side of each frontal is

o *

deeply excavated for the prolongation of the cerebral lobes, and
the cavity is converted into a canal by a median vertical plate of
bone at the inner and anterior end of the frontal. The frontals join
the parietals and postfrontals behind, and, by the connate orbito-
sphenoid plates, the presphenoid below, the prefrontals and nasals
before, and the superorbitals at their lateral margins. The orbito-
sphenoidal plates have their bases extended inward, and meet below
the prosencephalon and above the presphenoid, as the neurapo-
physes of the atlas meet each other above the centrum. The anterior
third part of such inwardly produced base is met by a downward
production of the mesial margin of the frontal, forming a septum

150 ANATOMY OF VERTEBRATES.

between the olfactory prolongations of the brain, but is not con-
fluent with the frontal septum : the outer portion of the orbitosphe-
noidal plate is smooth externally, and deeply notched posteriorly
for the optic foramen.

The post-frontal, fig. 97, 4, is a moderately long trihedral bone,
articulated by its expanded cranial end to the frontal and parietal,
and bent down to rest upon the outer and fore angle of the ecto-
pterygoid, 25. It does not reach that bone in the Boa, nor in
poisonous Serpents. In both the Boa and Python it receives the
anterior sharp angle of the parietal in a notch.

The natural segment which terminates the cranium anteriorly,
and is formed by the vomerine, prefrontal and nasal bones, is very
distinct in the Ophidians.

The vomer is divided, as in some ganoid Fishes and Batrachians,
but is edentulous : each half is a long, narrow plate, smooth and
convex below, concave above, with the inner margin slightly
raised : pointed anteriorly, and with two processes and an inter-
vening notch above the base of the pointed end. The prefrontals,
14, are connate with the lacrymals. The two bones which inter-
vene between the vomerine and nasal bones are the turbinals, fig.
96, d, they are bent longitudinally outwards in the form of a
semicylinder about the termination of the olfactory nerves.

The spine of the nasal vertebra is divided symmetrically as in
the Frog, forming the nasal bones, fig. 97, 15 ; they are elongated,
bent plates, with the shorter upper part arching outward and
downward, completing the olfactory canal above ; and with a longer
median plate forming a vertical wall, applied closely to its fellow,
except in front, where the nasal process of the premaxillary is
received in the interspace of the nasals.

The acoustic capsule remains in great part cartilaginous : there
is no detached centre of ossification in it : to whatever extent this
capsule is ossified, it is by a continuous extension from the alisphe-
noid. The long stapes, fig. 97, 16, extends from the ' fenestra vesti-
buli ' to the subcutaneous ear-drum attached to the tympanic bone,
28. The sclerotic capsule of the eye is chiefly fibrous, with a thin
inner layer of cartilage ; the olfactory capsule is in a great measure
ossified, as above described.

Maxillary arch.- -The palatine, fig. 96, 20, or first piece of this
arch is a strong, oblong bone, having the inner side of its obtuse
anterior end applied to the sides of the prefrontals and turbinals,
and, near its posterior end, sending a short, thick process upward
and inward for ligamentous attachment to the lacrymal, and a
second similar process outward as the point of suspension of the

ANATOMY OF VERTEBRATES. 151

maxillary bone : between these processes the palatine is perforated,
and behind them it terminates in a point. The chief part of the
maxillary bone, 21, is continued forward from its point of suspen-
sion, increasing in depth, and terminating obtusely : a shorter
process is also, as usual, continued backward. The point of
suspension of the maxillary forms a short, narrow, palatine process :
the dental branch of the supramaxillary nerve penetrates the
upper and fore part of this process, and its chief division escapes
by a foramen on the outer and fore part of the maxillary. A space
occupied by elastic ligament intervenes between the maxillary and
the premaxillary, 22, which is single and symmetrical, and firmly
wedged into the nasal interspace : the anterior expanded part of
this small triangular bone supports two teeth. Thus the bony
maxillary arch is interrupted by two ligamentous intervals at the
sides of the premaxillary key-bone, in functional relation to the
peculiar independent movements of the maxillary and palatine
bones required by Serpents during the act of engulfing their
usually large prey.

Two bones extend backward as appendages to the maxillary
arch ; one is the ( pterygoid,' 24, from the palatine, the other the
ectopterygoid, 25, from the maxillary. The pterygoid is continued
from the posterior extremity of the palatine to abut against the
end of the tympanic pedicle : the under part of its anterior half
is beset with teeth, fig. 96, 24. The ectopterygoid, 25, overlaps
the posterior end of the maxillary, and is articulated by its posterior
obliquely cut end to the outer surface of the middle expanded part
of the pterygoid.

Mandibular arch.- -The tympanic bone, 28, is a strong, trihedral
pedicle, articulated by an oblique upper surface to the end of the
mastoid, 8, and expanded transversely below to form the antero-
posteriorly convex, transversely concave, condyle for the lower jaw.
This consists chiefly of an articular 31, and a dentary 32, with a
small coronoid and splenial piece. The articular piece, 31, including
the angular and suranffular elements of the Crocodile, ends ob-

o ~

tusely, immediately behind the condyle : it is a little contracted in
front of it, and gradually expands to its middle part, sends up two
short processes, then suddenly contracts and terminates in a point
wedged into the posterior and outer notch of the dentary piece. The
articular is deeply grooved above, and produced into a ridge below.
The coronoid is a short compressed plate : the splenial is a longer
plate applied to the inner side of the articular and dentary. The
outer side of the dentary has a single perforation near its anterior
end : this is united to that of the opposite ramus by elastic ligament.

152 ANATOMY OF VERTEBRATES.

The skull of the Boa Constrictor differs from that of the
Python, not only in the greater breadth of the frontals, but in
that of the nasals ; in the absence of the superorbital, in the
more slender and cylindrical form of the ectopterygoid, and in
the larger and higher internal border of the coronoid. But the
mechanism of the jaws is the same. By the elastic matter join-
ing together the extremities of the maxillary and mandibnlar
bones, those on the right side can be drawn apart from those on
the left, and the mouth can be opened not only vertically, as in
other vertebrate animals, but also transversely, as in insects.
Viewing the bones of the mouth that support teeth in the great
constricting serpents, they offer the appearance of six jaws --four
above and two below ; the inner pair of jaws above are formed by
the palatine and pterygoid bones, fig. 96, 20-24, the outer pair by
the maxillaries, ib. 21, the under pair by the mandibles, or ' rami,'
as they are termed, of the lower jaw, fig. 97, 31-32.

Each of these six jaws, moreover, besides the movements ver-
tically and laterally, can be protruded and retracted, independently
of the other : by these movements the Boa is enabled to retain
and slowly engulf its prey, which may be much larger than its
own body. At the first seizure the head of the prey is held
firmly by the long and sharp recurved teeth of all the jaws,
whilst the body is crushed by the overlapping coils of the serpent ;
the death-struggles having ceased, the Constrictor slowly uncoils,
and the head of the prey is bedewed wTith an abundant slimy
mucus : one jaw is then unfixed, and its teeth withdrawn by
being pushed forward, when they are again infixed, further back
upon the prey ; the next jaw is then unfixed, protruded, and
reattached ; and so with the rest in succession- -this movement of
protraction being almost the only one of which they are susceptible
whilst stretched apart to the utmost by the bulk of the animal
encompassed by them : thus, by their successive movements, the
prey is slowly and spirally introduced into the wide gullet.

In comparing the skull of a poisonous with that of a constrict-
ing Serpent, the differential characters consist, in the Rattlesnake
(^Crotalus) e.g., chiefly in the modification of form and attach-
ments of the maxillary, which is movably articulated to the
palatine, ectopterygoid, and lacrymal bones ; but chiefly supported
by the latter, which presents the form of a short, strong, three-
sided pedicle, extending from the anterior external angle of the
frontal to the anterior and upper part of the maxillary. The
articular surface of the maxillary is slightly concave, of an oval
shape : the surface articulating with the ectopterygoid on the poste-

ANATOMY OF VERTEBRATES. 153

rior and upper part of the maxillary is smaller and convex. The
maxillary bone is pushed forward and rotated upon the lacrymal
joint by the advance of the ectopterygoid, which is associated with
the movements of the tympanic pedicle of the lower jaw by means
of the true pterygoid bone. The premaxillary is edentulous. A
long, perforated poison-fang is anchylosed to the maxillary. The
palatine bone has four or five, and the pterygoid from eight to ten,
small, imperforate, pointed, and recurved teeth. The frontal bones
are broader than they are long : there are no superorbitals. A strong
ridge is developed from the under surface of the basisphenoid, and
a long and strong recurved spine from that of the basioccipital ;
these give insertion to the powerful e longi colli ' muscles, by which
the downward stroke of the head is performed in the infliction of
the wound by the poison-fangs.

The skull of the typical Ophidian reptiles most resembles that
of Lizards, but lacks the outer diverging appendage, formed by the
malar and squamosal, of the maxillary arch. It differs from that
of Batrachians in the distinct basi- and superoccipitals ; in the
superoccipital forming part of the ear-chamber ; in the basioc-
cipital combining with the exoccipital to form a single articular
condyle for the atlas ; in the ossification of the membranous space
between the elongated parietals and the sphenoid ; in the constant
coalescence of the parietals with one another ; in the connation of
the orbitosphenoids with the frontals, and in the meeting of the
orbitosphenoids below the prosencephalon upon the upper sur-
face of the presphenoid ; in the presence of distinct postfrontals,
and the attachment thereto of the ectopterygoids, whereby they
form an anterior point of suspension of the lower jaw, through the
medium of the pterygoid and tympanic bones ; in the connation
of the prefrontals and lacrymals.

In the AmphisbcEna fulifjinosa coalescence still further simplifies
the cranial structure : the parts of the epencephalic arch con-
stitute a single occipital bone ; the superoccipital crest extends
forward into a sagittal one ; a small foramen marks the boundary :
the premaxillary is single, and, with the rest of the upper jaw, is
fixed ; the tympanic is short, compared with that of true Serpents,
and extends almost horizontally forward, in a line with the lower
jaw which it supports ; the coronoid is more developed. The
nostrils, divided by the premaxillary, are terminal ; or even, as
in Lepidosternon, may open behind the fore end of the skull : in
this A mphisb amian the maxillaries overlap the nasals to join the
premaxillary. l

1 CLXXIII., pi. 15, figS. 8, 11.

154 ANATOMY OF VERTEBRATES.

§ 34. Skull of Lacertilia.- -Lizards, like Serpents, have the cra-
nial bones, especially those of the haemal arches and appendages,
more elongated, slender, and liberated than in Crocodiles and Che-
lonians; the temporal vacuities and orbits are large, and the external
nostrils are apart. Lizards retain the malo-squamosal bar connect-
ing the maxillary with the tympanic ; and some of them develope,
as in the Crocodile, the upper zygomatic arch formed by the post-
frontal and mastoid. The neurapophysial walls of the parietal and
frontal segments retain much of their fibro-cartilairinous tissue ; and

O O

the cranial roof is there sustained by a bony pillar on each side
(f columella ' of Cuvier), which has its base implanted in a fossa
of the pterygoid, and underprops the parietal near its outer border.
The homologies of the cranial bones of the Python, figs. 96 and
97, with those of the Crocodile, figs. 93, 94, and 95, being recog-
nised, those of any Lizard will be readily understood.

In a New Zealand Gecko (liliynclioceplialus !) the occipital con-
dyle is unusually elongated transversely, and presents the form of
a crescentic, convex bar, bent upward. The basisphenoid sends
down two short processes to abut against the pterygoids. The
parietal bone is perforated by a small median fontanelle close to
the sagittal suture : its upper surface presents two strong curved
and approximated temporal crests, divided by a median, angular,
longitudinal furrow : the crests are continued outward upon the
posterior bifurcated part of the parietal to be continuous with that
forming the upper border of the mastoid : the frontal is divided
by a median suture, as is the parietal in the common Gecko.
The posterior frontal supports a strong, obtuse ridge forming the
back part of the frame of the orbit, and unites below \vith the
malar and behind with the mastoid. The premaxillary bones are
divided by a median suture, and their dentigerous border projects
below the level of that of the maxillary bones. The vomer is
likewise divided by a median suture. The palatal apertures of
the nostrils are bounded behind by the vomer and palatal plate of
the maxillary : this plate is of unusual breadth, as compared with
the Lizards generally, and presents the unusual peculiarity of a
dentigerous ridge parallel with the posterior half of the alveolar
border. It is situated close to the inner side of this border, leav-
ing only space sufficient for the reception of the teeth of the
under jaw. The teeth are confluent with the summits of the
proper and accessory alveolar ridges. The palatine bones are
united together along the anterior halves. The rami of the lower
jaw are not anchylosed at the symphysis. The alveolar border is

1 CLVIII.

ANATOMY OF VERTEBRATES. 155

serrated by a single row of anchylosed teeth. The coronoid piece
is triangular, rises into a point, and presents a smooth articular
surface on its inner side, adapted to the anterior lateral projection
of the pterygoid.

In the skull of the black Scink ( Cyclodus nic/cr-), the frontal and
parietal bones are thick and expanded ; the parietal is bifurcated
behind, and articulated with the mastoids and paroccipitals. The
postfrontals are separated from the malars by the squamosals,
which extend between the malars and the mastoids to form the
strong lateral bony arch resting anteriorly upon the malar and the
maxillary, and posteriorly on the parietal and tympanic. Con-
comitantly with the strong osseous roof of the cranium, there is
an arrest of osseous developement in the fibro-membranous
neurapophysial walls of the cranium : two lateral processes
extend downward into these walls from the parietal and for-
ward from the exoccipitals ; but the protective office of the
alisphenoids is solely performed by the columnar { columellas,'
which extend from the interspaces of the processes above
mentioned, to rest upon the upper groove of the pterygoids.
The orbitosphenoids are represented by still more slender bony
styles, which circumscribe the outlets for the optic nerves, and
form the anterior boundary of the prosencephalic division of the
cranium. The lacrymal bones are large and divided on each side,
as in most Lizards. The premaxillaries are confluent, and their
nasal process separates the external nostrils from each other.
Each pterygoid presents a rough surface towards the palate, but
does not support teeth. There is a small ossicle between the
pterygoid processes of the sphenoid and the true pterygoid bones.
The columelliform stapes is extremely long and slender.

In the Iguana the parietal supports a single median crest : the
posterior margin of the frontal is notched by the fronto-parietal
fontanelle : both lacrymal and postfrontal are subdivided into two
pieces ; the lacrymal foramen is a e conjugational ' one between the
two pieces. The upper portion of the lacrymal represents the
facial part of the prefrontal ; it does not send down a neurapo-
physial plate to join the vomer or palatines, nor forms any part of
the lateral walls of the rhinencephalic cavity, or of the foramen
for the transmission of the olfactory nerves. The palatine nostrils,
fig. 98, D, n, are very long, and notch the large palatines, 20; the
pterygoids, 24, each support a row of small teeth.

In the skull of the Monitor Lizard ( Varanus niloticus) the
basioccipital sends down a pair of short, obtuse hypapophyses :
those of the basisphenoid are larger and abut against the ptery-

loG ANATOMY OF VERTEBRATES.

goicls : these bones are applied to the back part of the tympanic,
and the slender e columella' rests upon the middle of their upper
surface. The parietal is perforated near its anterior border.
The postfrontal has a descending postorbital process. The pre-
frontal developes a partial post-lateral wall for the rhinencephalic
chamber ; externally it supports an antorbital dermal bone : the
small perforated lacrymal is a distinct bone. The nasal and pre-
maxillary are both single bones, as in most Lacertians. The
malar, wedged anteriorly between the maxillary, palatine, lacrymal
and ectopterygoid, curves backward as a slender style terminating
in a point, leaving the orbit uncircled by bone behind : the
squamosal, wedged behind between the mastoid and tympanic,
curves forward to a point beneath the postfrontal.

In the American Monitor ( Tejus nicjropunctatus) the nasals are
divided: the malar articulates behind with the postorbital- -a dis-
memberment of the postfrontal, which continues the zygomatic
arch with the squamosal : there is no ' foramen parietale.'

In the Chameleon the teeth are short, and so confluent with the
jaws that these appear to have simply a serrated margin. The
external nostrils perforate the maxillary bone ; a long, compressed,
serrated crest arches upward and backward from the superoccipital
and parietal bones, and joins the processes of bone continued from
the mastoids. In the Chameleo bifurcus the anterior fork-like
productions are formed by the maxillary and prefrontal bones.
The premaxillary at the bottom of the cleft is very small.

In Draco volans there is merely the rudiment of a spine or
ridge from the superoccipital ; an arched transverse ridge separates
the occipital from the parietal region of the skull. The post-
frontal, mastoid, and paroccipital project successively from their
respective cranial segments, and well manifest their character as
the transverse processes of these.

The vacuities in the bony palate are many, and show much
variety in the cold-blooded, especially the reptilian, series, in
regard to their number, kind, and relative size. The most con-
stant are those which are more or less circumscribed by the max-
illary and pterygoid, and constitute a pair. They are present in
Polypterus and most Ganoids, bounded outwardly by the maxil-
lary, medially by the palatine, and behind by the pterygoid.
In the Menopome the vomer, fig. 73, /, forms the median and
the pterygoid,/, the posterior boundary. In the Frog, fig. 98,
A, the pterygo-maxillary vacuities, ?/, are divided from each
other by the basispheiioid ; whilst the palatine forms the front
boundary and separates them from the nasal apertures, n. In

ANATOMY OF VERTEBRATES.

157

Lizards, ib. D, the palatine 20, and pterygoid 24, form the median
boundary, the maxillary, 21, and ectopterygoid the outer one oft/.
In the Crocodiles, ib. C, the palatine 20 forms the median, the
ectopterygoid 25 the outer, the maxillary 21 the fore, and the ptery-
goid 24 with the ectopterygoid the hind, boundary. In the Che-
Ionia there is no ectopterygoid to divide the pterygo-maxillary
vacuity from the lower opening of the temporal fossa. The next
openings in point of constancy are the palatal, or posterior,
or internal nostrils — ( palatonares ; ' but they are variously formed
and situated. In the Menopome, fig. 73, there is no palatine bone
to divide them from the pterygo-maxillary vacuity ; in fig. 98 A,
the Frog, the transverse palatine forms the posterior boundary
of the palatonares, n, the vomer the inner, and the maxillary the
outer, boundary; they are similarly encompassed in the Lizards,

98

B

Frog.

Tortoise. Crocodile.

Palatal apertures, Eeptilia.

Iguana.

ib. D, n. In the Crocodiles, the palatonares, ib. C, n, form a single
aperture surrounded by the pterygoids, and situated far back.
There is also a single premaxillary foramen, ib. C, p, at the fore
part of the bony palate. This is sometimes divided into two by the
premaxillary, like the external nostrils, as in the Iguana, ib. D, p.
In most Lizards there is a more or less elongate ( interpterygoid'
vacuity, ib. D, s, bounded behind by the hypapophyses of the
basisphenoid, laterally by the pterygoids, and usually extending
some way between the palatines. In the Mosasaurus the inter-
pterygoid fissure does not extend far back between the pterygoids,
but is bounded in a greater proportion by the palatines. Some-
times there is a distinct small ( interpalatine ' vacuity, ib. m, in

158 ANATOMY OF VERTEBRATES.

advance of the interpterygoid ; and more rarely there occurs an
( intervomerine ' vacuity still more in advance.

Thus there are definable and iiameable, in the bony palate of
reptiles, the f pterygo-maxillary,' ( palatonarial,' f premaxillary,'
6 interpterygoid,' 'interpalatal,' and ' intervomerine ' vacuities or
foramina- - more or less valuable as characters of recent and
extinct species.

§ 35. Skull of Ichthyopterygia. — Amongst the illustrations of
extreme varieties in the reptilian skull which Palaeontology has
brought to light, may be cited the Ichthyosaurus, the Dicynodon,
and the Pterodactylus.

That of the first combines in a peculiar manner some piscine
with reptilian characters. It differs from all existing Reptilia in
the great size of the premaxillary, fig. 105, 22, and small size of
the maxillary, 21 ; in the lateral aspects and antorbital position of
the nostrils ; in the immense size of the orbits, and in the large and
numerous sclerotic plates, which latter structures give to the skull
of the Ichthyosaurus its most striking features.

The two supplemental bones of the skull, which have no homo-
logues in existing Crocodilians, are the postorbital and super-
squamosal ; both, however, are developed in Archecjosaurus and
the Labyrinthodonts. The postorbital is the homologue of the
inferior division of the postfrontal in those Lacertians — e. g.,
Iguana, Tejus, Ophisaurus, Anguis, in which that bone is said to
be divided ; but in Ichthyosaurus it more resembles a dismember-
ment of the malar, 26. Its thin obtuse scale-like lower end over-
laps and joins by a squamous suture the hind end of the malar :
the postorbital expands as it ascends to the middle of the back of
the orbit, then gradually contracts to a point as it curves upward
and forward, articulating with the supersquamosal and post-
frontal, 12. The supersquamosal may be in like manner regarded
as a dismemberment of the squamosal, 27 ; were it confluent there-
with, the resemblance which the bone would present to the zygo-
rnatic and squamosal parts of the mammalian temporal bone would
be very close ; save that the squamous part w^ould be removed
from the inner to the outer wall of the temporal fossa. The nostril
is bounded by the lacrymal, 73, nasal, 15, maxillary, 21, and pre-
maxillary, 22, bones. It is distant from the orbit about half its own
long diameter. Like the orbit, the plane of its outlet is vertical.

The pterygo-maxillary vacuities are very long and narrow,
broadest behind, where they are bounded, as in Lizards, by the
anterior concavities of the basisphenoid, and gradually narrowing
to a point close to the palatine nostrils. These are smaller than

ANATOMY OF VERTEBRATES. 159

in most Lizards, and are circumscribed by the palatines, ecto-
pterygoid, maxillary, and premaxillary. The pterygomalar fis-
sures are the lower outlets of the temporal fossa? ; their sudden
posterior breadth, due to the emargination of the pterygoid, relates
to the passage of the muscles for attachment to the lower jaw.
The parietal foramen is bounded by both parietals and frontals,
11 ; its presence is a mark of labyrinthodont and lacertian affini-
ties ; its formation is like that in Iguana and Rhynchocephalus.
The occipitoparietal vacuities are larger than in Crocodilia, smaller
than in Lacertilia ; they are bounded internally by the basi-, ex-,
and super-occipitals, externally by the parietal and mastoid. The
auditory apertures are bounded by the tympanic and squa-
mosal : the tympanic, 28, takes a greater share in the formation
of the ' meatus auditorius' in Lizards ; in Crocodiles the bone 28
is restricted to that which it takes in Ichthyosaurus.1

In comparing the jaws of the Ichthyosaurus tenuirostris with
those of the gangetic Gharrial, an equal degree of strength and
of alveolar border for teeth result from two very different propor-
tions in which the maxillary and premaxillary bones are combined

V •/

together to form the upper jaw. The prolongation of the snout
is the same : the difference of structure relates to the collective
tendency of the affinities of the Ichthyosaurus to an antecedent
hrcmatocryal type of structure still partly shown by Lizards.
The backward or antorbital position of the nostrils, like that in
whales, is related to the marine existence of the Ichthyosaurs.
But in the Labyrinthodonts, in which the nostrils are nearer the
fore part of the head, their anterior boundaries are formed by
the premaxillaries, as in modern Lizards : it appears, therefore,
to be in conformity with these affinities that the premaxillaries
of the Ichthyosaur sjiould enter into the same relation with the
nostrils, although this involves an extent of anterior develope-
ment proportionate to the length of the jaws, the forward pro-
duction of which sharp-toothed instruments fitted the Ichthyosaur,
like the modern Dolphin for the prehension of agile fishes.

§ 36. Skull of Dicynodontia. — The skull of the Dicynodon^
fig. 99, is articulated with the atlas by a single condyle, formed by
the basi- and ex-occipitals in equal proportions : the latter have
coalesced, as in the Crocodiles, wTith the paroccipitals. The parie-
tals form one bone, perforated by a small ( foramen parietale ' close
to the coronal suture. The frontals, n, contribute a share to the
superorbital border ; their median suture is distinct, as is that

1 CXLVII. p. 388.

1GO

ANATOMY OF VERTEBRATES.

between the nasals, 15. The prefrontal, 14, extends to the nostril, n.
The lacrymal, is, forms the rest of the fore part of the orbit, ex-
tending forward upon the face. The sides of the premaxillary, 22,
bend abruptly down in front of the nostrils, to join the maxillary,
20, 21 ; this forms the lower boundary of the nostril, n, and joins
above and behind with the prefrontal, lacrymal, and nasal bones :
the maxillary projects below the orbit, like a forward continuation
of the zygoma, becomes more prominent as it advances, and soon
forms the outer angle of the three-sided socket of the canine tusk, c.
There is a single but strong zygomatic arch formed by the malar,
26, and squamosal, 27, abutting against the upper end of the tym-

99

Skull of Dicynodon

panic pedicle, 28. The rami of the lower jaw augment in depth
from the angle to the symphysis, where they are confluent. The
angle projects a very little way beyond the articulation. The
articular surface is moderately concave, and looks obliquely up-
ward and backward. The elements of the posterior half of the
ramus answer to the articular, angular, 26, and surangular, 25. A
thin vertical splenial plate, on the inner side of the ramus, begins
about an inch in advance of the angle, and extends forward to the
symphysis, at the back part of which it appears to become con-
fluent with its fellow. The part answering to the angular diverges
from the surangular, and forms the hind boundary of an oblong
vacuity at the middle of the side of the ramus, the fore part of
which vacuity is formed by a bifurcation of the dentary element,
23. This is thickened and strengthened by a ridge, subsiding at
the vertical channel upon the side of the symphysis, receiving the

ANATOMY OF VERTEBEATES. 1<>1

tusk, s, when the mouth is closed. The symphysis of the man-
dible is peculiarly massive — broad, high, and thick. Anteriorly
it is convex in every direction ; it is bent or produced upward,
terminating in a broad trenchant margin, like the fore part of the
lower mandible of a macaw. The modification of the back part
of the cranium, especially the great expansion due exclusively to
the developement of ridges for augmenting the surface of attach-
ment of muscles (for the brain of the cold-blooded reptile would
need but a small spot of the centre of the occipital plates for its
protection), indicates the power that was brought to bear upon
the head as the framework in which were strongly fixed the two
large tusks. The strength or resistance of the cavities receiving

O O *— '

the deeply implanted bases of the tusks was increased by the
ridges developed from the outer part of their bony wall.

Only the Crocodiles now show a like extent of ossification of the
occiput, and only the Chelonians the trenchant toothless mandible ;
but in both the outer nostril is single and median : the Lizards
repeat the divided apertures for respiring air : in Mammals alone
do we find a developement of canine tusks like that in the
Dicynodonts.

§ 37. Skull of Pterosauria. — The skull of the Pferodactyle,
fig. Ill, was as remarkable for its light and delicate structure as
that of the Dicynodont for its compact massiveness. It had a
single occipital condyle : a post-fronto-mastoid arch and a malo-
squamosal arch on each side ; the latter abutting against the end
of the tympanic pedicle. The orbit was large, and the eyeball
defended by sclerotic plates. The external nostrils were divided,
and placed about midway between the orbits and the muzzle.
There was a large vacuity between the orbits, o, and nostrils, n.
The jaws varied much in length in different species.

§ 38. Scapular arch and appendage. — Parts which project
from the body to act on the surrounding medium commence as
a bud or fold of skin, within which is formed the framework, in
texture and structure according to the work to be done. The
reaction of the medium, whether air, water, or earth, calls for the
due resistance usually afforded by junction of the projecting part
with a segment of the endoskeleton. Thus, in Fishes, the frame
of the opercular flap articulates with the tympano-mandibular
arch : that of the branchiostegal (gill-covering) flap with the
hremal arch of the parietal vertebra : that of the pectoral flap or
limb with the same arch of the occipital vertebra. The frame
of the caudal flap or fin is attached to the terminal vertebrae of
the body : those of the dorsal and anal fins are less firmly inter-

VOL. I. M

162

ANATOMY OF VERTEBRATES.

locked with the neural and haemal spines of more advanced
vertebra?.

All these various supports of flaps, fins, or limbs belong to the
same natural genetic group of skeletal parts : their peripheral rays
are not f dermal bones ; ' they are developed between folds, not in
the substance, of the integument ; although in some instances
they press away the skin and become coated by a ganoid conver-
sion or calcification of its outer layer.

The most simple condition of the parial (pectoral and pelvic)
limbs is manifested by the Lepidosiren, fig. 100. A filamentary
appendage is sustained by a single many-jointed cartilaginous ray,
fig. 101 A, a. In one species there are attached at right angles
to the pectoral ray fine filaments sustaining the narrow fold
of membrane continued from its posterior side. A similar series
of finer rays supports the membrane continued from the dorsal
detached dermoneurals of Polyptcrus.

Protoptcrus (Lepidosiren} annectens. xxxm.

The arch sustaining the pectoral limbs of Lepidosiren is also
simple, departing least from its archetypal condition. A long
straight cylindrical bone, fig. 101, A, 51, pi, is attached by a short
ligamentous mass to the epencephalic arch, ib. n, of which it is
the rib, or ' pleurapophysis,' assuming in ulterior developements
the special name of ' scapula.' With each scapula is articulated a
larger and more flattened bone, ib. 52 : the two converge and
meet at their lower ends, .completing, as hremapophyses, a widely
expanded hremal arch. The entire segment, A, conforms to the
thoracic modification of the Archetype vertebra, fig. 19 ; and, simi-
larly, is expanded in order to encompass and protect the heart : but
it is simplified by the absence of the hamial spine in Protopterus,
as the neural spine is sometimes wanting in a neural arch. The
hremapophysis, h, in ascending the vertebrate scale, assumes special
forms, signified by the term f coracoid,' with the number 52. In

ANATOMY OF VERTEBRATES.

163

JProtopteri, as in more piscine Hcematocrya, the coracoid ex-
clusively supports the appendage or limb.

From the condition exemplified in fig. 101, A, the developement

101

Elementary limbs, A, c, Lepidosiren ; B, D, Ampliiuma, CXL.

of the pectoral member diverges in two directions : one by multi-
plication of many-jointed rays, the other by simplification as to
number of rays and joints, with special modification and differen-
tiation of the latter.

§ 39. Pectoral limb of Fishes. — The first series of modifications
is now confined to Fishes : but, before describing the appendage,

1 • f x* J? xl 1 • • •.

a briei notice ot the arch is requisite.

In most Osseous Fishes the pleurapophysis of the occipital, like
that of the two antecedent cranial vertebras, is in more than one
piece ; but the divisions do not exceed two. The upper piece
(suprascapula) is commonly bifurcate, as in the Cod, figs. 34, 75,
81, 50, the lower prong answering to the ( head,' the upper one to
the ' tubercle ' of the thoracic rib in the Crocodile : the latter
articulates with the transverse process (jparoccipitaT). The lower
piece (scapulci), ib. 51, is a slender straight bone, pointed below,
and mortised into a groove of the coracoid, ib. 52. The two parts
of the scapula are confluent in the Siluroid Fishes. In the
Murasnoids the suprascapula is ligamentous, and loosely appends
the scapular arch to the skull. In the Playiostomi the arch is
detached from its vertebra, and has receded in position, to allow,
as it seems, for the great expanse of the appended fin.

The hrcmapophysis, or 'coracoid,' figs. 34, 38, 39, 75, 85, 52, is
longer and usually broader than the scapula. In the Cod-tribe,

M 2

164 ANATOMY OF VERTEBRATES.

its pointed upper extremity projects behind that bone and almost
touches the suprascapula ; a broad angular plate of the coracoid
projects backward and gives attachment to the radiated appendage,
below which it bends inward and forward, gradually decreasing
to a point, which is connected by ligament to its fellow, and to
the urohyal bone, fig. 43. The inner side of the coracoid is ex-
cavated, and its anterior margin folded inward and backward,
lodging the origin of the great lateral muscle of the trunk.

In most fishes the lower end of the arch is completed, as in the
Cod, by the ligamentous symphysis of the coracoids ; but in the
Siluri and Platycephali the coracoids expand below, and are firmly
joined together by a dentated suture. In all Fishes they support
and defend the heart, and form the frame, or sill, against which
the opercular and branchiostegal doors shut in closing the great
branchial cavity ; they also give attachment to the aponeurotic
diaphragm, dividing the pericardial from the abdominal cavity.

To the inner side of the upper end of the coracoid there is
attached, in the Cod and Carp, a bony appendage in the form of
a single styliform rib ; but in other Fishes this is more frequently
composed of two pieces, as in the Perch. This single or double
bone, figs. 34, 38, 85, 58, is slightly expanded at its upper end in
the Cod-tribe, where it is attached by ligament to the inner side
of the angular process of the coracoid : its slender pointed portion
extends downward and backward, and terminates freely in the
lateral mass of muscles. In the Batrachus its upper extremity
rises above the coracoid, and is directly attached to the spinous
process of the atlas. In some Fishes, as the Snipe-fish ( Centriscus
Scolopax), the Cock-fish (Aryyreiosus Vomer), the Lancet-fish
(Sf'yanus), it is joined by the lower end to the corresponding
bone of the opposite side, thus completing an independent in-
verted arch, behind the scapular one. There is some reason,
therefore, for viewing the bone 58 as representing the ha3inal
arch of the atlas, or its hasmapophysial portion.

The usually free lower extremities of these ha3inapophyses, to-
gether with their taking no share in the direct support of the pec-
toral fins, and their inconstant existence, oppose the view of their
special homology with the coracoids of higher Vertebrates.
To that with the ( clavicles' of higher classes it has been
objected that these bones are always situated in those classes in
advance of the coracoids ; but this inverted position may be a
consequence of the backward displacement of the scapula and
coracoid in the air-breathing Vertebrates.

The appendage of the scapular arch, in most Osseous Fishes,

ANATOMY OF VERTEBRATES. 165

is composed of three segments : the first, of two, rarely of three,
bones immediately articulated with the coracoid ; the next, of a
series of from two to six smaller bones ; which, lastly, support a
series of spines or jointed rays. These rays serially repeat the
branchiostegal rays in the hyoidean appendage, and the opercular
rays in the tympanic appendage. The vegetative repetition of
digits and joints, and the vegetative sameness of form in those
multiplied peripheral parts of the fins of Fishes, accord with the
characters of all other organs on their first introduction into the
animal series. The single row of fewer ossicles, figs. 34 and
81, 56, supporting the rays, 57, obviously represents the double
carpal series in Mammals ; and the bones of the brachium and
antibrachium seem in like manner to be reduced to a single series,
54, 55. In the ventral fin, fig. 34, v, no segment is developed
between the arch, 63, and the digital rays, 70 : it is in this respect
like the branchiostegal fin, 40, 44.

The pectoral fin is directed backward, and being applied,
prone, to the lateral surface of the trunk, the ray or digit answer-
ing to the thumb is toward the ventral surface. The lowest of

o

the bones supporting the carpus should, therefore, be regarded as
the radius (figs. 34 and 81, 54), holding the position which that
bone unquestionably does in the similarly disposed pectoral fin of
the Plesiosaur, fig. 45, 54, and Cetacea. The upper bone, which
commonly affords support to a smaller proportion of the carpal
row, may be compared to the ulna (ib. 55). As a third small
bone is articulated to the coracoid, in some Osseous Fishes,
at least in their immature state, the name of humerus may be
confined to that bone : but in these it is generally above and on
the inner side of the ulna, and seems to be rather a dismember-
ment of it. In the Salmonida, it is more distinctly developed;
it is articulated in the Bull-trout (S. eriox}1 to the middle of the
back part of the coracoid by a transversely elongated extremity ;
and is expanded at its distal end, where it articulates by cartilage
with the radius and ulna. In the Cod, Haddock, and most other
Fishes there is no separate representative of the humerus : in
these the ulna is a short and broad plate of bone, deeply emargi-
nate anteriorly, attached by suture to the coracoid, and by the
opposite expanded end to the radius, and to one or two of the
carpal ossicles, and directly to the upper or ulnar ray of the fin.

In the Bull-head and Sea-scorpion (Cottus), the radius and
ulna are widely separated, and two of the large square carpal

1 XLIV. p. 18, No. 46.

166

ANATOMY OF VERTEBRATES.

plates in their interspace articulate directly with the coracoid. A
similar arrangement obtains in the Gurnards and the Wolf-fish ;
but the carpals in the interspace of the radius and ulna are sepa-
rated from the coracoids by a space occupied by clear cartilage ;
and in the Wolf-fish the intermediate carpals are almost divided
by two opposite notches. The ulna is perforated in all these
fishes. The radius is of enormous size in the Opah (Lampris), the
Cock-fish, fig. 38, and the Flying -fish ; it is anchylosed with the
coracoid in the Silurus, to give firmer support to the strong
serrated pectoral spine. Both radius and ulna are connate with
the coracoid in the Angler (Lophius, fig. 102, 54, 55).

The ossicles called carpals are usually four or five in number,

102

Coracoid aiid bones of pectoral fin, Angler (Lophiits)

as in the Cod tribe, fig. 81, 56; they progressively increase in
length from the ulnar to the radial side of the carpus, especially
in the Parrot-fish (Scarus^) and the Mullets (MugiT). They are
three in number and elongated in the Polypterus, fig. 103, 56,
but are reduced to two in number, and more elongated in the
Lophius, fig. 102, se) ; thus they retain in this species and in the
Sharks, fig. 104, their primitive form of ( rays ;' but change to broad
flat bones in the Wolf-fish, just as the rays of the opercular fin
exchange that form in the Plagiostomes for broad and flat plates
in ordinary Osseous Fishes.

The rays representing the metacarpal and phalangial bones are,
in the Cod, twenty in number, and all soft, jointed, and sometimes
bifurcate at the distal end. Their proximal ends are slightly
expanded and overlap each other, but are so articulated as to
permit an oblique divarication of the rays to the extent permitted
by the uniting fin-membrane, the combined effect being a move-
ment of the fin, like that called the ' feathering of an oar.' Each

ANATOMY OF VERTEBRATES. 167

soft and jointed ray splits easily into two halves as far as its base,
and appears to be essentially a conjoined pair.

In the series of Osseous Fishes the rays of the pectoral and
ventral fins offer the same modifications as those of the median
fins, on which have been founded the division into ' Malacoptery-
6 gians ' and ( Acanthopterygians : ' in the former, the last or ulnar
fin-ray, is usually thicker than the rest ; in the latter it is always
a hard, unjointed spine : in some Fishes it forms a strong pointed
or serrated weapon (Silurus). In the Gurnards, fig. 82, the three
lowest rays are detached and free, like true fingers ; and are soft,
multi-articulated, and larger than the rest ; they are supplied by
special nerves, which come from the peculiar ganglionic enlarge-
ments of the spinal chord, and are organs of exploration and of
subaqueous reptation.1 In all the Gurnards the natatory part of
the pectoral member is of large size ; but in one species (Dactylo-
pterus) it presents an unusual expanse, and is able by its stroke to
raise and sustain for a brief period the body of the fish in the air.
The pectoral fins present a still greater developement in the true
Flying-fish (Exoccetus).

In some Malacopteri and Ganoidei a segment analogous to a
metacarpus may be distinguished by modification of structure
from the phalangeal portion of the fin rays : in the Polypterus
there are seventeen simple cylindrical metacarpal bones, fig. 103,
57, the middle ones being the longest : they sustain thirty -five
digital rays, and are supported by 103

carpal bones, ib. 103, 56, of which

two are almost as remarkable for _< 41

their length as in the Lophius ; the
third, shorter and broader, is wedged
into the interspace of the two longer
ones, but does not directly join the Bones of Pectoral
metacarpus. The carpus is supported by a small radius, 55, and
ulna, 54, which articulate directly with the coracoid. A further
approach to the higher conditions of the pectoral member is made
by the same Fish in the carpal portion projecting freely from the
side of the body, as in the Lophioid Fishes. In the Salmon,
where eleven such metacarpals support thirteen or fourteen fin-
rays, the carpus is short and consists of four bones.

In the Plagiostomes the scapular arch is detached from the oc-
ciput, the conditions of its displacement being the more varied and
vigorous use, or the enormous expanse, of the pectoral fin ; per-

1 CLIX. p. 46.

168

ANATOMY OF VERTEBRATES.

haps, also, the more posterior position of the heart in these Fishes.
In the Sharks and Chimaerae the arch is loosely suspended by
ligaments from the vertebral column : in the Rays the point of re-
sistance of their enormous pectoral fins has a firmer, but somewhat
anomalous attachment, by the medium of the coalesced upper ends
of the suprascapular pieces to the summits of the spines of the
confluent anterior portion of the thoracic abdominal vertebra?. In
the Sharks the scapular arch consists chiefly of the coracoid por-
tions, fig. 104, 52, which are confluent together beneath the peri-
cardium which they support and defend ; the scapular ends of the
arch, connected to the coracoids by ligament, project freely upward,
backward, and outward. To a posterior prominence of the cora-
coid cartilage corresponding with the anchylosed radius and ulna,
ib. 54, 55, in the Lophius, there are attached, in the Dog-fish and
most other Sharks, three sub- compressed,, sub-elongated carpal

104

Cartilages of the pectoral fin and arch of the Dog-fish (Spinax acanthias)

cartilages, the uppermost, ib. 56, the smallest, and styliform ; it
supports the upper or outer phalangeal ray. The next bone, ib. se',
is the largest and triangular, attached by its apex to the arch, and
supporting by its base the majority of the phalanges. The third
carpal, ib. 56", is a smaller but triangular cartilage, and supports
six of the lower or radial phalanges. Three joints (metacarpal
and digital) complete each cartilaginous ray or representative
of the finger, ib. 57 ; and into the outer surface of the last are
inserted the fine horny rays or filaments, ib. 57/x, the homologues
of the claws and nails of higher Vertebrata, but which on their first
appearance, in the present highly organised class of Fishes, mani-

ANATOMY OF VERTEBRATES. 169

fest, like other newly introduced organs, the principle of vegetative
repetition, there being three or four horny filaments to each carti-
laginous ungual phalanx.

On the fore part of the coracoid arch, near to the prominence
supporting the fin, there are developed a vertical series of small
bony cylindrical nuclei in the substance of the cartilage in most
Sharks. In the Rays the coraco-scapular arch forms an entire
circle or girdle attached to the dorsal spines : it consists of one
continuous cartilage in the Rhinobates, but in other Rays is divided
into coracoid, scapular, and suprascapular portions, the latter
united together by ligament. The scapula and coracoid expand
at their outer ends, where they join each other by three points, to
each of which a cartilage is articulated homologous to the three
above described in the Shark, and which immediately sustain the
fin-rays. The posterior cartilage answering to the upper one in
the Shark curves backward and reaches the ventral fin : the an-
terior cartilage curves forward, and its extremity is joined by the
antorbital process as it proceeds to be attached to the end of the
rostral cartilage ; the middle proximal cartilage is comparatively
short and crescentic, and sustains about a sixth part of the fin-rays,
which are the longest, the rest being supported by the anterior
and posterior carpals, and gradually diminishing in length as they
approach the ends of those cartilages.

Developement by irrelative repetition of parts reaches a maximum
in the present plagiostomous group. In the common Ray, fig. 64,
there are upwards of a hundred many-jointed fingers in each pectoral
limb : but all are bound up in a common function of the simplest
kind.

§ 40. Pectoral limb of Reptiles. — The other route of develope-
ment from the prototypal condition exemplified in fig. 101, A and
C, leads to a differentiation of the several divisions and parts of the
limb, and their adaptation to particular functions or parts of com-
bined and varied mechanical actions.

The first step, as manifested in the Amphimne, ib. B, c, is the
formation of a Ions; inflexible segment, as a lever of greater resist-

o o o

ance, 53 and 65 ; this is followed by a pair of similar, but shorter
cylindrical bones, each sustaining a ray of few joints. The
proximal bone assumes through ulterior developements the special
name f humerus,' or arm-bone, with the symbol 53, in the fore
limb; and of 'femur,' or thigh-bone, with the symbol 65, in the hind
limb. The two bones of the next segment become, in the fore
limb, f radius,' 54, and ' ulna,' 55 — collectively, antibrachium or
6 fore-arm;' in the hind limb, tibia, 66, fibula, 67 — collectively,

170

ANATOMY OF VERTEBRATES.

105

the cnemion or leg. The mass of fibro-cartilage, in which
more or fewer ossicles are subsequently developed, interposed

between the antibrachium and terminal
rays, is the 6 carpus,' 56 : the corre-
sponding mass in the hind limb is the
tarsus, 68. The terminal rays are the
digits, called f hand,' and ( fingers,' 69,
in the fore limb ; ( foot ' and ' toes ' in
the hind limb. The proximal joints of
these rays, being bound together in a
sheath of integument, are differentiated
as c metacarpals ' in the hand, and ( meta-
tarsals ' in the foot. The other joints
are the ( phalanges,' ultimately distin-
guished as ( proximal,' ( middle,' ( distal '
or ' ungual,' as usually supporting a claw
or nail.

In the extinct Ganocephala, and in the
few surviving ichthyomorphous or per-
ennibranchiate Batrachia, the simple
type of limb, as in fig. 101, B, is re-
tained; only that the digital rays in-
crease in number from the tf two ' in
Amphiuma, to ( three ' in Proteus, and
to f four ' in Menopoma, fig. 43, 57, and
Axolotes.

In the extinct Ichthyopterygia the digits
may be seven, eight, or nine in number,
and consist of numerous short joints —
a significant mark of piscine affinity :
they are bound together, but converge
towards a point : the joints are of a flat-
tened angular form, and interlock with

a '

those of the contiguous digit, the whole
forming a continuous, broad, slightly
flexible basis of support to the fin. The
essential distinction from the fin of the
fish is shown by the well developed
6 humerus,' 53, and by the complex sca-
pular arch. The two antibrachial bones
retain the piscine shortness and breadth ;
skeleton of ichthyosaurus, with and the metacarpal series is less distinctly

cast of spiral intestine. CLXIII. defined than ill SOlllC fishes.

ANATOMY OF VERTEBRATES. 171

The scapula, 51, is short and straight, displaced backward from
the occiput, and contributing to form the shoulder-joint, as in the
Batrachia and higher air-breathers : but it shows a certain breadth
and flatness. The coracoid, 52, is still broader, not cartilaginous
as in most perennibranchs, but well ossified, and united below
with its fellow, and with a small ' episternum ' of a triradiate
form, one ray of which is wedged into the fore part of the
intercoracoid fissure. There is also a pair of bones, so, long and
slender, articulated with the fore border of the scapula and the
transverse rays of the episternum : they are the clavicles. A
supplementary flattened bone, the ' epicoracoid,' is wedged between
the scapula, clavicle, and coracoid. The above complex and
powerful scapular arch would enable the fore-paddles to act upon
the land with sufficient power to effect a shuffling forward move-
ment of the body, as in the Turtle ( Chelone) and Seal tribe : but
the main office of the fore-limb in the Ichthyosaur was that of a
pectoral fin.

In the Plesiosaurus, fig. 45, the limbs acquired a developement
more closely accordant with that in Chelone. The scapula, 51,
developes an acromial process representing the clavicle. The
coracoid, 52, is unusually extended in the trunk's axis, and is united
with its fellow by a long symphysis interposed between the an-
terior abdominal rib and the episternum ; it articulates at its fore
part with the episternum and clavicular process, and, further back,
with the lower end of the scapula to form the humeral joint.

The humerus is proportionally longer than in Ichthyosaurus ;
the radius is better developed, and slightly expanded at both ends ;
the ulna retains a flattened reniform shape. The carpal series is
distinct, in a double row of ossicles, the largest at the radial side
of the wrist, the opposite side retaining more unossified material.
The digits are five in number, with the proximal and more elongated
joints representing a metacarpus. The phalanges are shorter, and
decrease in size to the tips of the digits, which converge. The
first or radial digit has generally 3 phalanges, the second from 5
to 7, the third 8 or 9, the fourth 8, the fifth 5 or 6 : all are flattened
and included in a common sheath of integument like those of the
Turtle ; but the paddle had no claws.

The scapular arch retains the same essential simplicity in the
Chelonian as in the Sauropterygian order, only the acromial or
clavicular process is relatively longer, more like a collar bone ; it
extends from near the articular part of the scapula toward the
median line, in advance of the coracoid, fig. 51, O, with the
medial end ligamentously attached to the episternal. In the

172

ANATOMY OF VERTEBRATES.

106

Tortoise (Testudo) it is shorter, in Chelys, fig. 106, b, it is longer
than the scapula, a. This bone in all Chelonians is a strong, straight
columnar one, with the upper end connected by ligament with the
inner surface of the first costal plate, fig. 51, N; it descends almost
vertically to the shoulder-joint, of which it forms, in common with
the coracoid, the 'glenoid' cavity, fig. 106, //. The coracoid,
suturally united at that end with the scapula, passes inward and
backward, fig. 51, o, expanding and becoming flattened at its
median end, which does not meet its fellow nor articulate with
the sternum. The coracoid is broad and short in the Tortoise ;

long and slender in Chelone and
Emys, fig. 51, o, of intermediate
proportions in Trionyx and Chelys,
fig. 106, c. The scapular arch
and proximal part of the limb being
included in the thoracic abdominal
box, the humerus is peculiarly
bent and twisted in the terres-
trial species in order to emerge
from the front fissure, and plant
the foot on the ground, fig. 51,
p. In the Tortoise the ordinary
position of the fore-limb is that
of extreme pronation, with the
olecranon forward and outward,
and the radial side of the hand
downward. The capsule of the
shoulder-joint includes a consider-
able part of the neck of the
humerus. The hemispheroid 'head projects unusually from the
back part of the bone, which looks upward : the tuberosities
are large and bent toward the palmar aspect : that which is
internal in most animals is here ' postero-superior ; ' that called
' external ' is 6 postero-internal ' in position ; from the former is
continued the ' deltoid crest.' The distal end is expanded and
rather flattened from before backward. In the Turtle the humeral
shaft and its lower end is compressed laterally : and the bone
is almost straight in those marine species ; in all Chelonia it is
solid throughout. The ulna is shorter, and in the Turtle, fig.
107, b, the olecranon is less developed than in the Tortoise, fig. 108,
by 55. The contrast between the marchers and the swimmers is
most striking in the proportions of the toes. In the Turtle,
fig. 107, the pollex, /, is short and has two phalanges after the

Scapular arch, Chehjs. CLI.

ANATOMY OF VERTEBRATES.

173

107

metacarpal : the last phalanx supporting a claw. The three
middle digits, it, Hi, iv, have each three long phalanges, the
last being flattened and without a claw ; the fifth has two pha-
langes. All these are connected together by a web. In the
Tortoise, fig. 108, all the toes are very short and subequal ; and
each has one metacarpal and two phalanges, the last supporting a
claw ; the few species in which the fifth has but one phalanx
and no claw form the genus Homopus, Dum. and Bib. In
Emys europ&a, fig. 51, T, u, the first and fifth digits have each a
metacarpal and two phalanges ; the others have three phalanges ;
the last bears a claw in each digit. In the Soft or Mud-turtles.

C5

the pollex has two phalanges, the
second with a claw ; the three middle
digits have each three phalanges,
but only the index and meclius have
the claw; the fifth digit has two

o

phalanges and no claw, whence
the generic name Triomjx, proposed
for these frequenters of the muddy
estuary.

In the Crocodilia the scapular arch
consists of a simple scapula, fig. 57,
51, and coracoid, ib. 52, and fig. 54,
8 : these compressed, narrow, mode-
rately long plates of bone, are
thickest where they are united to-
gether to form the glenoid cavity
for the humerus. In each, the bone
contracts beyond the articular ex-
pansion, becomes sub-cylindrical,
but soon again flattens and expands
to its opposite end ; that of the sca-
pula is free, that of the coracoid
joins the lateral border of the ster-
num. There is no trace of clavicle,
no acromial projection from the sca-
pula.

The humerus, fig. 51, 53, presents two curves : the articular head
is a transversely elongated, sub-oval convexity ; it is continued
upon the short, obtuse, angular prominence, answering to the inner
or ulnar tuberosity. The radial crest begins to project from the
shaft at some distance from the head of the bone. There is a
longitudinal ridge on the anconal surface close to the radial border.

Bones of fore-arm and paddle, Chelone. CLI.

174

ANATOMY OF VERTEBRATES.

108

I II III IV V

Laud Tortoise. CLI.

The distal end is transversely extended and divided anteriorly

into two condyles. The shaft has a medullary
cavity smaller than in land lizards. The radius,
fig. 57) t, fig. 109, Z>, 54, has an oval head, an
almost cylindrical and straight shaft, with an
oblong and subcompressed distal end. The ulna,
fig. 57, s, fig. 109, #, 55, articulates with the
outer condyle of the humerus by an oval facet,
the thick convex border of which swells out be-
hind like the beginning of an ' olecranon ; ' the

O O

shaft of the ulna is compressed transversely and
curves slightly outward ; the distal end is less
than the proximal one, and articulates with the
second and third bones of the carpus. The first
metacarpal supports two phalanges, I, the second three, n, the
third and fourth, each four, the fifth, V, three phalanges which
109 are very slender ; but the proportions are shown

in the cut ; only the toes, I, n, and in, have the
claw. All are basally united by a short web,
but the fore-foot is chiefly used in movements
upon land.

In the Monitor ( Varanus niloticus) the supra-
scapula is a broad semiossified plate : the
scapula is short and broad, and appears to
have coalesced with the coracoid. This bone
is much expanded, and has two deep notches
anteriorly, and a perforation near the humeral
articulation. In some Lizards it sends for-
ward an acromial process. The coracoid is
shorter and broader than in the Crocodile,
abuts against the upper margin of the rhorn-
boidal sternum, and sends off two processes
from its anterior border, the one next the sca-
pula abutting against the transverse branch of
the episternum ; the other against the sub-
ossified epicoracoid : this element overlaps that
of the opposite side. In the Monitor, as in
most Lizards, there are distinct clavicles : usu-
ally long and slender bones, with more or less
expanded extremities, extending from the body
of the episternum and accompanying the trans-
verse branch to abut against the scapula ; and sometimes also
reaching the outer process of the coracoid. In Lacerta, Cuv.

Bonos of fore-arm and
foot, Crocodile. CLI.

ANATOMY OF VERTEBRATE S.

175

110

and Scincus, the clavicle expands at its medial half, which has a

large vacuity or perforation occupied by membrane. In the

Chameleon the scapular arch is

as simple as in the Crocodile,

but the coracoid is shorter and

broader.

The humerus in Lacertians is
usually larger and straighter, fig.
50, Draco volans, than in the
Crocodiles, with a more compact
wall and wider medullary cavity.
The radius, ib. and fig. 110, b,
54, is almost straight, and slender,
with an oval proximal articular
concavity, and a distal surface
partly convex, partly concave.
The ulna, fig. 110, a, 55, shows
the olecranon better developed
than in the Crocodile : its dis-
tal articular surface is convex.
The dibits are five in number,

o *

the phalanges are 2, 3, 4, 5 and 3,
counting from the metacarpal of
the first to that of the fifth digit :
each has a claw supported on
a moderately long, compressed,

curved, and pointed phalanx. The Chameleon offers an exception
to the numerical rule, the phalanges being 2, 3, 4, 4, 3 ; and the
direction of the digits modified for the scansorial function in these
arboreal Lacertians : I, n, and in, enveloped by the skin as far
as the claws, are directed forward ; iv, and v, similarly sheathed,
are directed backward : and the joints are shorter and broader than
in Land-lizards,

The fore limbs in Draco volans accord with the usual lacertian
type, and take no share in the support of the parachute. But
in the extinct order of truly volant Reptiles (Pterosauria) they
were modified for the exclusive support and service of the wings.
The scapula, fig. Ill, 51, long, narrow, flattened, and slightly
expanded, lay more parallel with the spine than in land and sea
Reptiles. The coracoid, strong and straight, and combining, as
usual, with the scapula to form the glenoid cavity, articulated at
the opposite end with a groove at the fore-part of a discoid
sternum, which part is produced and keeled. The humerus, ib.

Bonds of fore-arm and foot, Chameleon. CLI.

176

ANATOMY OF VERTEBRATES.

53, is more expanded at its proximal end than in the Crocodile or
Lizard ; the inner (ulnar) tuberosity is more prominent, the radial
crest much more developed : with a base coextensive with one
fifth of the shaft of the bone, it extends in a greater proportion
from the shaft, affording a powerful lever to the muscles inserted
into it. The articular head is reniform. The shaft is cylindrical :

ill

Skeleton of Pterodactylus crassirostris. A. Restoration of Pterodactyle. CLXXX.

the walls thin and compact, the cavity large, and was filled with
air as in birds of flio-ht.1

o

The e pneumatic foramen,' or that by which the air passed from
a contiguous air-cell into the bone, is situated on the fore (palmar)
side, a little below the radial end of the head of the bone. The
radius, ib. 54, and ulna, ib. 55, are very long, straight, and closely
connected together. The digits show the lacertian number of

1 CXLIX. p. 16. CLXVI. p. 451. This discovery breaks down the following
distinction : ' Au rcste, on distingue toujours 1'humerus d'un lezard do celui d'un
oiseau, parceque le premier n'est pas creux ni percc de trous pour Fentree de Fair
dans son intc-ricur.' CLI. v. pt. 2, p. 296.

ANATOMY OF VERTEBRATES. 177

phalanges from the first to the fourth, and slightly increase in
length: each terminated by a deep compressed,, curved and
pointed ungual phalanx. The modification converting the limb
into a wing is confined to and concentrated upon the fifth digit, ib.
5 : its metacarpal presents almost the thickness of an antibrachial
bone: the proximal phalanx, of equal thickness, has more than
twice the length, and at the proximal joint shows a process like
an olecranon. This is usually followed, as in Pterodactylus
crassirostris, by three similarly elongated phalanges, of which the
last gradually tapers to a point. The fore limb thus exceeds in
length the whole body, and is presumed to have supported a
membranous wing, as in the sketch A, fig. 111.

Such are the chief modifications by which the fore-limb, in the
Reptilian series of cold-blooded air-breathers is or has been
adapted for aquatic, amphibious, terrestrial, arboreal, and aerial
life. Before, however, quitting this subject, it may facilitate the
comprehension of the homologies of the carpal series of ossicles,
by concluding with a separate and serial review of them in the
Reptilian group.

In the Toad (Bufo) the carpus includes eight bones : the two
principal are the ' lunare,' fig. 44, c, /, and ( cuneiforme,' ib. c,
respectively articulating with the radial and ulnar divisions of the
antibrachial bone, ib. 54, 55 ; the scaphoid, c, s, presents its ( inter-
medial' position between the lunare and the four ossicles on the
radial side of the distal series : these consist of the trapezium t,
trapezoides tr, magnum m, and the divisions of the unciform u for
the fourth and fifth digits; that for the fifth being the largest
of the five bones. The thumb, I, is represented by its metacarpal
only ; the index, fig. 44, A, n, and medius, in, have each a
metacarpal with two phalanges ; the digits IV and v have each
three phalanges.

In the Tortoise ( Testudo, fig. 108), the antibrachium articulates
with three carpals forming the proximal row ; the first or radial
bone, ib. «, answers to the ( scaphoid ' with the ' intermedium ' e ;
the second ib. c, to the lunare ; the third, ib. d, to the cunei-
forme ; the lunare being interposed between the ends of the radius
and ulna. In the Emys, fig. 5 1 , s, the carpus has a similar struc-
ture ; but in some species there is a distinct pisiforme. In the
Turtle ( Chelone), the scaphoid is reduced in size, and represents
only the intermedium, fig. 107, <?; it is separated by the lunare
c, from the radius «, and is pushed into a position analogous to
that which its homotype the 4 naviculare ' holds in the mammalian
tarsus. Without the light from the testudinate modification,

VOL. I. N

178 ANATOMY OF VERTEBRATES.

fig. 108, the bone c, fig. 107, might be taken for a connate
6 scapholunar.' In both tortoise, terrapcne, and turtle, the distal
row of carpals consists, as in the Toad, of five bones, one to each
of the five metacarpals. About their homology there is no diffi-
culty ; the bone, fig. 107, i, which supports the pollex, i, is the
trapezium ; the next 2, the trapezoides ; the third 3, the magnum ;
and the fourth and fifth are the two parts showing the type-state
of the connate bones, called f unciform ' in mammals. A bone
analogous to a ' pisiform, f, fig. 107, is attached to the ulnar
division, 5, of the unciform, and, usually, also articulates with the
cuneiform in the Turtle. In Chdys and Trionyx, the bone
answering to a, e, fig. 108, is divided ; the part, e, answering to
the ' intermedium ; ' Trionyx has also a ( pisiform.' The carpus
in most Lacertians, e.g. in Varanus niloticus1, has the scaphoid
reduced, as in Chelone, to the intermedia! portion ; but the trape-
zium unites directly with the lunare, and this articulates exclu-
sively with the radius, simulating the scaphoid in position ; it
has, however, on its ulnar side, the ( cuneiform ' articulating with
the ulna, and a ( pisiform ' terminates the proximal row. The
distal row consists of five distinct bones ; the unciform being
divided, as in Chelonians. In the Chameleon, fig. 110, the
proximal carpal series consists of the bones c and d, answering to
the two respectively articulating with the radius and ulna in
Varanus, and with those marked c and d in figs. 107 and 108.
The second carpal row has received two interpretations. In one
they are represented by the five subelongate bones having the
distal joints of metacarpals ; in the other they have coalesced into
the single bone c, which otherwise would be merely an enlarged
6 intermedium.' We shall afterwards see IIOAV the principle of
' serial homology ' helps in the solution of such problems. The
five bones radiating from the bone c are metacarpals ; the first
supports two, the second three, the third four phalanges, as in other
Lacertians ; and the equality of length in the opposing pair of
digits, iv and v, is preserved by the deduction of a phalanx from
the lacertian number.

The correspondence of the Chameleon's scapular arch with that
of the Crocodile has been adverted to ; and, similarly, the distal
row of carpals is reduced to a single bone, fig. 109, f, in the
Crocodile, supporting the medius, in, annularis, iv, and minimus,
v, digits ; and answering to the magnum and unciforme connate.
The proximal row includes three bones answering to the lunare,
c, and cuneiforme, d, in Chelone, fig. 107, and Chameleo, fig. 110 ;

1 CLI. pi. XVII, fig. 45.

ANATOMY OF VERTEBRATES.

179

112

to which is added a pisiforine, fig. 109, e, in the usual position.
The peculiarity of the bones c and d in Crocodilia, is their unusual
length, showing a constricted shaft between the expanded ends,
thus simulating metacarpals in shape, for which, when found as
detached fossils, they have been mistaken.

The digits in the class Reptilia are generally characterised by
a progressive increase in the number of their joints, from the first
or innermost to the third or fourth ; the Chelonia being the chief
exceptions. In Testudo, fig. 108, each digit has one metacarpal
and two phalanges ; in Test, tabulata the fifth digit has but one
phalanx.1

§ 41. Pelvic arch and limb of Fishes.- -Some cold-blooded verte-
brates, e. g. Muramoids and Ophidians, have neither fore nor hind
limbs. In a few, e. g. AnguillidcB, Gymnoti,
Xiphias, Siren, the scapular arch and limbs
are present, but not the pelvic arch and limbs.
In most fishes the latter exist, but less deve-
loped than the pectoral ones, and less fixed in
position.

Only the hsemapophysial portion of the
pelvic arch is developed in connection with
the diverging appendages, termed in Fishes the
( ventral fins.' Their rays in osseous fishes,
fig. 112, 68, are directly supported by the bones,
68, which, uniting together, near the point of
attachment of the fins without an intervening
bone, resemble their homotypcs, the coracoids ;
by virtue of which ( serial homology,' we infer
their special one with the iscliia of higher
animals. Each bone is a subtriangular plate, supporting the
fin by its expanded end ; and, either suspended in the flesh,
as in the Salmon and Sturgeon, fig. 29, v, or attached by the
narrower end to the coracoid, 52, as in the Cod, fig. 36, 63. The
representatives of tarsal, tibial, and femoral bones, are wanting in
all Fishes. In Acanthopterans one or more of the anterior rays
of the ventral fin may be hard unjointed spines, as in the other
fins ; in Malacopterans all the ventral rays are soft, multiarti-
culate, and bifurcate.

In no fish is this incomplete pelvic arch directly attached to the
vertebral column. If we may judge from the position in which
the ventral fin appears in the developement of the embryo fish, as

1 XLIV. p. 205, No. 1079 : see also pp. 206, 207, Nos. 1079, 1083, 1087, 1091,
1093, for further details of the bony structure of the fore foot in Chelonia,

N 2

Pi-lvic arch and limbs,
Trout (Salmo)

180 ANATOMY OF VERTEBRATES.

a little bud attached to the skin of the belly, and from the fact
that all the fishes in the geological formations anterior to the
chalk are abdominal, that is, have the ventral fins near the pos-
terior end of the abdomen, as in the Sturgeon, fig. 29, v, we may
conclude that the supporting bones are, essentially, the haemapo-
physes of the last rib-bearing (or pelvic) abdominal vertebra.
Being suspended more or less freely from the under or ventral part
of the body, these fins are subject to great diversity of position in
relation to the two extremes of the abdomen. On these differences
Linna3us based his primary classification of Fishes ; he united
together, for example, those fishes which have the pelvic or
ventral fins near the anus, fig. 29, to form the order called ' Pisces
Abdominales ; ' those with the ventral fins beneath the pectorals,
fig. 38, into an order called ' Pisces Thoracici ; ' and those with
the ventrals in advance of the pectorals, fig. 34, v, into an order
called ' Pisces Jugulares ; ' lastly, those fishes in which the ventral
fins were absent formed the order called ' Pisces Apodes] indicating
his recognition of the homology of such fins with the hinder or
lower limbs of higher animals.

In the Salmonidce (S. Eriox, fig. 112, c) the ischia, 63, are
united by a cartilaginous symphysis at the medial line, and
underlie the last six abdominal vertebrae. Each supports a
ventral fin of nine rays, 68. In the Angler (Lophius piscatorius)
the ischium is attached by one end to the coracoid, and expands
at the opposite end to join its fellow, and support the six rays of
the ventral. It also sends up a vertical process, simulating an
ilium. The ( thoracic ' character depends on the greater length of
the ischia, as compared with that in the ' jugular' fishes. In the
Lepidosiren, fig. 41, as in the Sturgeon, fig. 29, and other
' ventral fishes,' the ischia, 64, are suspended beneath their proper
vertebra. They support in Lepidosiren a single-jointed ray, 66.
In Lepidopus, in the Blennies, the Forked Hake (Phycis), the
Forked Beard (Raniceps), and some other fishes, the ventral fins
are likewise mere filamentary feelers. In the Lump-suckers
( Cyclopterus), the ventrals unite together, and combine with part
of the pectorals to form a sucking disc or organ of adhesion,
below the head, just as the opercular and branchiostegal fins are
united together to form the gill-cover. The ventral fin is better
developed in the Plagiostomes than in other fishes. The support-
ing arch consists indeed of the same simple elements, hasmapo-
physial, cartilaginous, confluent at the middle line, and loosely
suspended in the abdominal walls ; but they do not immediately
support the fin-rays. Two intermediate cartilages are articulated
to the expanded outer ends of the inverted arch ; the anterior is

ANATOMY OF VERTEBRATES. 181

•

the shortest in the Dog-fish, and supports three or four rays ; the
posterior one is much longer, and supports the remainder of the
rays, fifteen or sixteen in number. To the end of this cartilage
likewise is attached, in the male Plagiostomes, the peculiar ac-
cessory generative organ or clasper. In the Torpedo the arch
sends forward two processes, and these are of greater length in
the extinct Cyclobates oligodactylus, XL. p. 225, pi. 5. In the
Chimeroids the short narrow processes which extend above
the place of articulation of the ventral fins simulate iliac bones :
the expanded portions which meet below represent the ischia ;
they are each of them perforated by a large round aperture, filled
by membrane. The cartilage, answering to the tibia, supports
the rays of the ventral fin and the clasper.

§ 42. Pelvic arch and limb of Reptiles. - - Passing from the
Protopterus, fig. 101, c, to the Proteus, ib. D, we find the
pair of cartilages answering to the piscine f ischia' aided by
a second pair, 62, called ' ilia,' in supporting the diverging
appendage ; and this pair is attached to the riblets of the last
abdominal or ' sacral ' vertebra. The appendage or ( limb ' now
consists of definable segments, which are specialised through sub-
sequent developements : the first, as the ' femur ; ' the second — a
pair of shorter and smaller joints — respectively as ( tibia ' and
( fibula ; ' these being followed, with the intervention of a cartila-
ginous f tarsal ' mass, by a pair of many-jointed rays or ( digits.'

A closer correspondence, however, with the piscine type was,
in some respects, retained by the extinct Ichthyosauri, fig. 105.

Although the iliac element, 62, was joined with the ischial, 63,
in supporting the fin, such sustaining arch remained freely sus-
pended, as in the ( ventral fishes ' of Linnaeus. A second hrema-
pophysial arch, 64, was likewise present, in advance of the ischial
one, answering to the ( pubis ; ' this afforded the extent of origin
required by the muscles of the better developed fin. The next step
in progress is exemplified by the single long and inferiorly flattened
and expanded bone, 65, answering to the ' femur,' and through
which, as on a pedicle, the fin could be more freely rotated, and
moved to and fro. To the end of the femur were ligamentously
articulated the two short flattened bones representing the tibia
and fibula ; followed by the series of multiarticulate digits, joined
together to form the common basis of the fin, which, like the
pectoral one, tapered to a point.1

With the increased length, and progressive differentiation of the
several segments of the fin, as in Plesiosaurus, fig. 45, the pubic

No twist, real or imaginary, of humcrus or femur obscures or is needed to
explain the homotypes in the pectoral and pelvic members. CLX.

182 ANATOMY OF VERTEBRATES.

basis, 64, for muscular attachments, became co-expanded ; the
ischia also, 63, assumed the form of flattened triangular plates ;
ami the ilia, though still 'long bones,' were stronger, and attached
by ligament to the riblets of one or two vertebrae ; and these, in
Nothosaurus, became expanded for more effective fixation of the
pelvic arch. A f tarsus,' 68, and ' metatarsus,' are now definable ;
and the ( digits,' with fewer joints, do not exceed five in number.
All the bones are solid in both Ichthyo- and Sauro-pterygia.

From the Sauropterygian type of pelvic arch and limb, the
transition is easiest to that in the marine Chelonia of the present
day. But the course of developement from the Proteus will be
here resumed and traced to the saltatory grade which the hind-
limb acquires in the Batrachian order.

Amphiuma tridaetylum, with proportionally shorter hind-limbs
than in Proteus (fig. 101, D), has them terminated by three toes.
Mcnobranchus shows four toes : and Menopoma five, which is the
number usual in the hind-limbs of Newts and Salamanders. In
Menopoma, fig. 43, the sacral vertebra, s, has a longer and
stronger transverse process, t, and riblet, pi, than the vertebras
before and behind ; and pi is united to the cartilaginous elements,
63 and 64, closing the inverted arch by the rib-like continuation, 62.
To the lower end of this simple ( ilium ' and conjoined part of the
( ischio-pubic ' cartilage is ligamentously attached the short and
simple femur. To this succeeds a shorter tibia and fibula - - the
latter reminding us of the plesiosaurian fibula, by its outward
curve. The tarsus is cartilaginous in Menopoma ; the metatarsals
support 1, 2, 3, 3, 2 phalanges, respectively, from the innermost, I,
to the fifth, v. The toes are webbed to near the last joint. Every
joint in the limb is syndesmotic, and the ossification of the bones is
limited to an outer crust, covering persistent solid cartilage. In
the decomposing body this dissolves away ; and if the ossified
parts become petrified, the fossil bone appears to have had a large
medullary cavity.

In the Land-salamander the broad ischio-pubic plate, fig. 113,

becomes ossified at b, but remains cartila-
ginous at the angles c, and the symphysis ;
whence it extends forward, and bifurcates,
as at d, representing the last pair of abdo-
minal ribs in higher reptiles. There is a
vascular perforation in each pubic part of
the plate. The ilium, a, retains its simple

Pelvic, Salaninnder. *l Tl 1

rib-like character.
The Tadpole, fig. 42, affords a significant example of the trans-

ANATOMY OF VERTEBRATES.

183

mutation of a natatory to a saltatory type of hind-limb, irre-
spective of efforts and exercises through successive generations
producing and accumulating small changes,, and independently of
any selection by nature of such generations as were enabled,
through the accidental variety of a slightly lengthened hind-limb,
to conquer in the battle of life, and to transmit the tendency
towards such disproportion to their posterity.

If the law by winch so much of the change of structure adapted
to terrestrial life takes place in the active independent aquatic
animal be a mystery, and seeming exception, it does not the less
impress the believer in the derivative origin of species with the idea
of unseen and undiscovered powers, that may operate in produc-
ing such result, ( according to a natural Law or Secondary Cause.' 1

The hind-limb of the Frog (Rana) closely accords at first with
that of the Menopome ; a rib-like continuation, fig. 42, 62, of the
pleurapophysis, pi, of the last abdominal vertebra, gives attachment
to a short femur, 65 ; ossification of the shorter tibia, 56, and fibula, 57,
speedily unites them proximally ; five subequal digits bud out of
the primitive fin-like projection from the integument; and a simple
cartilaginous tarsus, 68, at first intervenes between the toes and
the leg. The due length and power of the hind-limb is produced
by elongation of all its elements, including the iliac parts of the
sustaining arch. In the Toad (Bufo) the sacral process, or anchy-
losed riblets, transmitting thereby the weight
of the trunk upon the legs, are depressed and
expanded at their extremities ; in Pipa,
fig. 44, B, s, remarkably so, and resting upon
the anterior halves of the ilia. In the Toad
the femur is shorter than the ilium, and the
tibia is shorter than the femur. In the Frog,
fig. 44, contrary proportions prevail. The im-
pulse of the hind-limbs is applied, in all tail-
less Batrachia, to the hindmost part of the
body, beyond the lengthened coccygeal style,
fig. 114, A, (/, by the remarkable backward
production of the ilia, ib. A, 62, which expand
and unite, forming a symphysis, above the
acetabula ; thence they transmit the impulse
of the limbs to the short and strong trans-
verse processes of the sacrum, a. A. pair
of commonly anchylosed semicircular bony Front
plates, f ischia,' 63, unite with the iliac sym-
physis to form the lower half of the joints for the femora, 65,

1 CXLI. p. 86.

114

B

of tlie

184 ANATOMY OF VERTEBRATES.

The femur in the Frog, fig. 44, 65, is a long slender bone, with
a slight double bend; the head is expanded, convex, and ter-
minal ; the back part of the upper fourth of the shaft shows a
longitudinal ridge ; the distal end is expanded and truncate.
Both ends of the femur are usually in the state of epiphyses.
The tibia and fibula are confluent longitudinally, but preserve
their respective medullary canals, and indicate their transcend-
ental distinction by an anterior and posterior longitudinal furrow
at the expanded ends of the seeming single bone ; usually, also,
by a perforation from before backward. A single epiphysis con-
stitutes each articular end. The astragalus «, and calcaneum cl,
are much elongated. The former is slightly bent. They com-
monly coalesce at their proximal and distal extremities ; at the
former, by means of an epiphysis ; at the latter, with the connate
representatives of the naviculare, s, and cuboides, b. Two cunei-
form bones remain distinct and support the three inner toes, i, ii,
Hi : a third expanded bone projects, like a supplemental digit, ci,
from the inner (tibial) side of the tarsus ; it may represent the
( entocuneiform.' One (Rand) or two (Pipa) sesamoid bones are
developed in the extensor tendons behind the tibio-tarsal joint:
their function is that of the lever part of the calcaneum. The
first metatarsal supports two phalanges, I ; the second, two ; the
third, three ; the fourth, four ; and the fifth, three.

In Bufo agua I found a semiossified tubercle upon the proximal
end of each ilium. In Pipa, the confluent calcaneum and cuboid
form a long three-sided bone with the angles sharp : the long
astragalus presents a similar form.

To the student of Comparative Anatomy entering upon the
vast domain of that science with ideas of the bones derived from
those of the human skeleton, and associating the special shapes
and proportions they there present with the names that have been
learnt from Anthropotomy, few parts are more perplexing or de-
ceptive than the pelvis in the Chelonian reptiles. Viewing, for
example, that of the Trionyx, as it is represented in fig. 116, he
would conclude h to be the iliac bones, and i the pubic bones,
separated at the symphysis ; or as answering to the parts so called
in the single ( os innominatum ' of man. The rectification of the
error affords a valuable lesson of the unimportance of size and
shape in determining special homology, and of the necessity of
knowing the foetal as well as the adult conditions of the human
pelvis. He would learn, first, that the threefold nature of the
( innominate ' bone, which is transitory in man, is permanent
in the reptile ; next, that the bone which is largest and

ANATOMY OF VERTEBRATES. 185

broadest in the human foetal pelvis is the least and slenderest
in that of the Turtle. To comprehend the nature of the Chelo-
nian pelvis, the connections and relative positions of its bones
must be studied in the entire skeleton.

The two bones that articulate with the transverse processes
of vertebra3 and, extending l haemad ' (downward or forward),
combine at the opposite end with the other bones forming the
acetabulum, are those alone which show the essential characters
of the ilia in air-breathing vertebrates. In the figure of the
pelvis of the Turtle viewed from below or from the haemal aspect,
fig. 115, that surface of the sacrum is figured to illustrate the

115

Pelvis of Chelone (from below). CLX.

above character of connection. Two stunted pleurapophyses
converge from the two centrums, and afford a close ligamentous
attachment to the proximal or upper ends of the ilia, «, a. These
bones are also attached to the contiguous costal plates of the cara-
pace, which they support as stout strong pillars. They slightly
expand at their acetabular ends, where each unites with two other
bones. The bone c descends and meets its fellow at the mid
line, as does likewise the bone b: c c being posterior in position
answer to the ischia of the human foatus ; b b to the pubics.
These are remarkably expanded, and, besides forming an exten-
sive symphysis between b, b, each developes a broad angular
process or tuberosity which is ligamentously attached to the
plastron, forming the foundation for the support of the pillar, a,
that underprops the carapace.

186

ANATOMY OF VERTEBRATES.

A slight modification is presented by Trionyx, in which a view
of the pelvis is given from the dorsal aspect, the sacrum being
removed, in fig. 116 : here i shows the end of the ilium, 62, which
was attached to that part of the vertebral column : a is the ex-
panded acetabular end of these short, straight, columnar bones.

116

62

Pelvis of Trionyx, (from above, without the sacrum). CLI.

The ischia, c, c, develope tuberosities/,/, and unite at the ischial
symphysis, 64, d. The pubics b, b, articulate by a broader tube-
rosity, h, with the plastron, and have a greater transverse extent.
The ' outlet ' of the pelvis is not, as might be supposed, between e
and 64, but between i and/. The wider space answers to the ob-
turatorial one in Man ; and, were ossification to be extended from
the ischial, 64, to the pubic, e ', symphysis, it would be divided into
the two vacuities called ( foramina ovalia seu obturatoria ' in the
human pelvis. Such division does actually take place in the
Tortoises (Testudo) and Terrapenes, as shown at v, fig. 51, in
Emys Europcea.

In the Tortoise (Testudo) the iliac bones are vertical and
columnar, like the scapula, but are shorter and more compressed.
The pubis expands to join its fellow at the median symphysis and
the ischium posteriorly : it sends outward and downward a long
thick obtuse process from its anterior margin. The ischia, in like
manner, expand where they unite together to prolong the sym-
physis backward. The ' foramen ovale seu thyroideum ' is nearly
circular on each side. In Hydraspis the ilia articulate directly by
part of their under surface to the xiphisternals, and the pubis
becomes confluent with the same parts of the plastron by the
tuberous process.

The femur is shorter than the humerus in the Turtles : the head
is round, surmounted by a broad, thick, short trochanter : the

ANATOMY OF VERTEBFvATES.

187

117

shaft is almost straight, slightly expanded at the distal end, at the
back part of which the condyles are feebly indicated. In Terra-
penes, fig. 51, w, and Tortoises, the femur equals or exceeds the
humerus in length : its shaft is more bent : the troehanter is divided
into two processes, most distinct in Trionyx. In no Chelonian is
there a medullary cavity : ossification extends throughout the bone :
the two bones of the leg, ib. x, T, are nearly straight ; the tibia is the
largest, with the proximal end almost semi-
circular, and the distal one less expanded
and subconcave, with a slightly-developed
malleolus in Testudo and Emys. The fibula,
fig. 117, 67, is a little bent, enlarging the
interosseous space in Trionyx: it presents
a convexity to the tarsus. There is no bony
patella in any Chelonian. In Testudo
tabulata I found a synovial joint between
its fibrous representative and the femur,
distinct from the proper capsule of the knee-
joint. The proximal row of the tarsus con-
sists of two bones, astragalus, «, and cal-
caneum, which in most Tortoises become
confluent. The distal row consists of five
bones, four of which support the four nor-
mal toes, and the fifth a rudiment of the
metatarsal of the fifth toe, u; the fourth
and fifth of the second row of tarsals
answer to the os cuboides of higher ani-
mals ; the other three bones to the three
ossa cuneiforrnia. The astragalar part of
the single proximal bone includes also the naviculare.

In the Trionyx, fig. 117, the proximal row consists of a single
bone, «, answering to the astragalus and naviculare : the distal
row consists of five bones, of which the three cuneiformia are very
small : the two divisions of the cuboides, bf, c, are very large ;
the first may include the articular part of the calcaneum ; the
outermost is dilated and angular. In Chelone and Chelys the
calcaneum is distinct from both the cuboid and the astragalo-navi-

o

cular bones. The digits are moderately long, rather flattened and
divaricated, supporting the hind webbed foot ; the metatarsal sup-
ports two phalanges in the first toe ; in the other toes it supports
three, the last having a claw.

In Trionyx the fifth digit, fig. 117, v, has two small phalanges
and no claw. In Emys and Cistudo the digits decrease in strength

Bones of leg and foot,
Trionyx. CLI.

188

ANATOMY OF VERTEBRATES.

118

from the first to the fifth, and in length from the second to the
fifth. In the Land tortoises,, the fifth toe is reduced to a metatarsal

rudiment: the others are short and thick, fig.
118, each with two phalanges, the second sup-
porting a claw, and adapted, like those of the fore
foot, for burrowing. The two extremes of modi-
fication of the hind foot in the chelonian series
are presented by the Turtle and Tortoise : the
great comparative weight and bulk of the body
to be supported on dry land involve a form of
limb and foot resembling that in the Elephant ;
whence the largest kind of Land-tortoise has been
termed ( Testudo elepliantopus?

The general homology of the pelvic bones of
the Crocodile has been previously discussed,
pp. 67-69, and illustrated, figs. 55, 56, 57. The
serial homology of the two hasmapophysial elements derives satis-
factory elucidation from their crocodilian condition. Of those of the
scapular arch, called clavicle' and f coracoid,' in the vertebrates pos-
sessing both, the anterior very rarely enters into the formation of the
joint for the appendage ; whilst the posterior invariably does so.

119

Bones of leg and
foot, Test udo

62

Left pelvic bones Crocodile. CLI.

In the foetal mammal, before the coalescence of the stunted cora-
coid, this relation may be seen. So in the Crocodile, the posterior
haemapophysis, fig. 119, 63, combines with the ilium, 62, to the
exclusion of the pubis, 64, in the formation of the acetabulum,
repeating the articular characters of the coracoid; whilst the
more slender pubis placed anterior to the joint, and abutting by its
mesial end against the abdominal sternum, figs. 5, 6, 10, repeats

ANATOMY OF VERTEBRATES. 189

those characters of the clavicle of lizards. Accordingly in the
progressive reduction of the pelvic arch to a single hsemapophysial
element sustaining the appendage, as in Osseous Fishes, we may
discern the characters of the ' ischium ' in that element, rather
than of the pubis.

The ilium of the Crocodile is twice as broad as long, produced
beyond the two vertebra to which it is articulated : it descends
vertically to the acetabulum, of which it forms the upper half.
The anterior production or tuberosity, «, is the thickest, the pos-
terior is the longest. The ischium developes a strong bent process
from the fore part of the acetabular end, to which the pubis is
articulated : as it descends and inclines inward, it becomes flat-
tened and expanded, b, and joins its fellow by a moderately
extended ischial symphysis. The pubis is directed more forward,
and though smaller and more slender, resembles the ischium by
the expanse of the medial end. As ossification is not extended
along the mid-line from the ischial symphysis to the pubis, no
' obturator foramina ' are defined, but a wide vacuity intervenes, as
in Chelone and Trionyx.

The femur, fig. 57, v, is bent in curves opposite to those of the
humerus : the head is convex, subcompressed laterally, flattened
externally : the chief process is from the inner side, at the upper
third of the shaft : there is a ridge external and above this process :
the distal end expands transversely, and developes backward two
condyles ; the outermost receives part of the head of the fibula. It
is longer than the humerus, but in a less degree in modern than in
mesozoic crocodiles. The tibia, figs. 57 and 120, 66, presents a
large triangular head to the femur, the division of the back part of
which into two condyles is feebly indicated : it offers a smaller
convex crescentic surface to the tarsus. The fibula, ib. 67, is
slender and subcylindrical ; much compressed above, more ex-
panded and triangular below. Each of the foregoing long bones
has a medullary cavity. There is no patella ; but there is a fibro-
cartilaginous 4 fabella,' with granular bone, in old crocodiles,
behind the outer condyle.

The principal tarsal bone, fig. 120, c, represents the astragalus,
naviculare, and entocuneiform, connate, of the human series;
articulating with the distal end of the tibia and a small part of the
fibula above, with the calcaneum and cuboid externally, and with
the first and second metatarsals and the ectocuneiform below.
The calcaneum, d, intervenes between the fibula and cuboid, and
has a short but thick posterior tuberosity, y, fig. 57. The cuboid,
fig. 120^ e, supports the fifth, v, fourth, iv, and part of the third,

190

ANATOMY OF VERTEBRATES.

120

Hi, metatarsals. The cctocuneiform, /, is wedged between the
bases of the second and third metatarsals. These, by the oblique
overlapping arrangement of their expanded bases, resemble the

articulations of the ventral fin-
rays in most fishes. The fifth
is flattened and expanded to sup-
port the broad scale from the
outer side of the foot, but is
curtailed in length and supports
no toe.

The four normal metatarsals
are much larger than the corres-

o

ponding metacarpals. That of
the first toe, z, is the shortest
and strongest; it supports two
phalanges : the other three are
of nearly equal length, but lose
thickness from the second, ii, to
the fourth, Hi: the second sup-
ports three phalanges ; the third,
four ; the fourth, also four, the
claw and its phalanx being ab-
sent in this toe : ii, Hi, and w,
are webbed in true Crocodiles,
but semipalmate in Alligators.
In most Lacertiaiis two verte-
brae are modified for articulation
with the iliac bones, as in the Mo-
nitor ( Varanus, fig. 121, a) : but
in the Chameleon there are three
sacrals. In the great Monitor
the ilium, b, extends backward
beyond the junction, terminat-
ing obtusely, and bends down
as it passes forward with a short
process above the acetabulum.
Both ischium and pubis com-
bine with the ilium in forming this cavity. The ischium, c,
is usually most expanded at its symphysial border, which is pro-
duced backward. The pubis, /, appears as a more direct con-
tinuation of the ilium, and is perforated near its acetabular end,
anterior to which it developes a process. The symphysial car-
tilage is continued from the ischium to the pubis, dividing the

Bones of leg and foot,

ANATOMY OF VERTEBRATES. 191

interspace into the ( obturator foramina,' and becoming ossified in

old Monitors. The femur resembles that of

the Crocodile, but with the inner trochanter

better developed, with a larger medullary cavity,

and with a more marked depression on the outer

condyle for the fibular articulation. The division

of the back part of the head of the tibia is usually

more marked. The head of the fibula, fig. 122,

67, b, rises higher than in the Crocodile.

In Varanus niloticus,1 the elongated iliac Feu-is of the Monitor
bone abuts against the transverse processes of
the two sacral vertebrae, the first on the right side and the second
on the left side being applied on a plane higher than the
opposite processes: that of the first caudal vertebra also abuts
against the ilium on the left side. The ilium sends off a tuber-
osity in front of the sacro-iliac syndesmosis, and it joins the pubis
and ischium by a broad suture. The trochanter arises from the
inner and back part of the proximal end of the shaft of the
femur. There are two ossified patellae in the tendon of the great
extensor of the leg. The tarsus differs from that of the Crpcodile
chiefly in there being a ' mesocuneiform ' supporting the second
metatarsal, fig. 122, ii: but this is wanting in many lacertians.
The bone a' is as composite as in the crocodile. The fifth meta-
tarsal is flattened, and articulated farther back than the rest,
extending along the outer side of the cuboid, c, to the calca-
neum, l)\ it supports an unguiculate toe of four phalanges,
fig. 122, v : the number of phalanges in the other toes progres-
sively increases from two in the first, i, to five in the fourth, iv,
with proportionate increase of length.

The chief modification of the hind limb of Lacertians is found
in the Chameleon, fig. 123. The ilium is a simple elongate,
subcompressed bone descending vertically from the converging
ends of the sacral processes to the acetabulum. The fibula,
fig. 123, b, 67, is bent outward. In the tarsus may be seen a
stunted homologue of the astragalo-navicular bone, of, receiving
the end of the tibia ; and a larger calcaneurn, b' , in like relation
with the fibula : these form a cavity for the spheroid f cuneiform,'
d, by which the prehensile foot rotates on the leg ; and there is a
cuboid, c3 exclusively supporting the fifth metatarsal, v. This
determination of the homologies of the tarsal bones with those of
the ambulatory lizards, shows the nature of the five short but
metatarsially shaped bones supporting the toes, and settles the

1 XLIT. p. 149, No. 678,

192

ANATOMY OF VERTEBRATES.

122

homology of their homotypes in the fore-foot, fig. J 10. The first
metatarsal supports two phalanges, fig. 123, i ; the second, three ;
the third and fourthj each four phalanges ; and the fifth, three. The

first and second toes are opposed
to the other three in the hind foot,
contrariwise to the arrangement in
the fore foot.

In the Pterodactylea fig. Ill,
the hind limb adhered closely to
the lacertian type ; the metatarsals
were distinct; the phalanges in-
creased in number from the first
to the fourth toe, but retained
more equality of length than in
lizards : all the five toes were
unguiculate, the claw phalanx com-
pressed and deep. Although in
some species there were four or
five sacral vertebra?, the hind-
limbs were too feeble to sustain
the body, as in Birds : they more
probably served to suspend it, as
in Bats, with a concomitant
strengthening of the claws.

The reptilian hind-limbs, with
their arch, acquired the most com-
plex structure in the great extinct
Dicynodont l and Dinosaurian 2
orders. In Dicynodon tigriceps
ossification extended over the
whole of the interspace between
the ischium and pubis, obliterat-

m

ing altogether the obturatorial

Bones of leg and foot, Monitor

foramina: and both iliac and
ischial bones articulated, as in
edentate mammals with a long
sacrum. In the Iguanodon six
vertebras were modified with interlocking centrums and neural

C3

arches, the latter resting on, and suturally joined to, the
contiguous halves of two centrums. The femur exhibited an
upper and external ( great trochaiiter,' besides the inner tro-

1 CJLV.

CXLVI. (1841), pp. 114, 130.

ANATOMY OF VERTEBRATES.

io;

123

chanter better developed than in modern lizards : examples of

this bone four feet in length have been discovered. In the

~

almost equally colossal Sclelidosaur the toes
of the hind foot were reduced to four in num-
ber by suppression, as in the Crocodile, of
the fifth. In the Iguanodon they were re-
duced to three by the suppression also of the
first toe ; the retained toes were short and
broad, with phalanges in number respectively
three, four, and five ; but the latter so much
shorter as to reduce the outer to the same
length as the inner toe, and with the middle
one both longer and larger ; showing in the
great herbivorous Saurian an interesting ana-
logy to the hind limb of the Rhinoceros.1

§ 43. Derrnoskeleton of Fishes.- -The scales
of fishes may be regarded, from their seat and
mode of developement, as parts of the dermo-
skeleton : and in the palaeo- and meso-zoic
species they were ossified, in the form of
granules, tubercles, plates, or imbricated
scales. Bony fishes, with scales so soft and
soluble as to leave no trace in fossilization,
seem not to have existed before the creta-
ceous period : for even the exoskeleton of the
Leptolejridce of the lower and middle oolites
has been preserved to us through the thin coating of petrifiable
ganoine with which their minute and delicate scales were covered.
Tubercular integument, like the ( shagreen ' of sharks and dog-
fishes, has come down to us from a period as remote as the
Silurian. In skates and rays the skin is studded by bone in larger
masses; sometimes, as in the ' Thornback,' developing a small
bent spine.

The hard-rays in the fin of the Perch and other Acanthopteri,
the larger and fewer spear-like weapons of the Sticklebacks
( Gasterostei), Sheat-fishes ( Siluridce), Trigger-fishes (Balistes), and
some Snipe-fishes ( Centriscus), are all parts of the dermoskeleton.

In Balistes capriscus - - a rare British fish - - the anterior dorsal
is preceded by a strong erectile spine : its base is expanded and
perforated, and a bony bolt from the supporting plate passes freely
through it : when the spine is raised, a hollow at the back part of

Bones of the leg and foot,
Chameleon. CLI.

VOL. I.

1 CLIV.

O

194 ANATOMY OF VERTEBRATES.

the base receives a prominence from the next bony ray, which
fixes the spine in the erect position, as the hammer of a gun-lock
acts at full cock ; and the spine cannot be forced down till the
small spine or ' hammer ' has been depressed, as by pulling the
trigger. This mechanism may also be compared to the fixing
and unfixing of a bayonet. When the spine is unfixed and bent
down it is received into a groove on the supporting plate, and
offers no impediment to the progress of the fish through the water.
The generic name (Batistes) and the common Italian name of the
fish (Pesce balestra), refer to this structure : the spine is rough-
ened by ganoid grains, whence our English name of * File-fish.1
The hind border of the analogous weapon of the Centriscus
humerosus and of most Sheat-fish is denticulated, so that they
inflict a ragged wound. In all such weaponed osseous fishes, the
base of the spine is modified for articulation with another bone.
In gristly fishes so armed the base of the spine is simple, smooth,
hollow, implanted deeply in the flesh and attached to ligament
and muscle.

The great majority of such weapons found in a fossil state,
called ' ichthyodorulites,' show by their basal structure that they
come from Plagiostomous fishes, and exemplify in a remarkable
manner the efficiency, beauty, and variety, of the ancient armoury
of that order. In some, the marginal serrations were themselves
denticulate (Edestes).1 Certain Rays (Trygoii) have spines with
both margins serrate.2

The series of side-scales perforated by the mucous duct in the
modern soft-scaled fishes are usually more or less ossified. In the
Eel tribe the lateral mucous ossicles are tubular and concealed by
the epiderm. In the Sole and Plaice the mucous scale bones of
the lateral line are quite superficial. There are many circular
radiated ossicles scattered over the dark or upper side of the skin
of the Turbot. A row of small chevron-shaped dermal bones
extends along the median line of the belly of the Herring, and the
extremity of each lateral process, fig. 37, dh, is connected with
that of the long and slender vertebral rib, completing the inferior
arch, like a sternum and sternal ribs. The Dory has two rows of
thick osseous plates along the under part of the abdomen ; but
their superficial position indicates their essentially dermal charac-
ter. Parts analogous to a sternum are thus supplied from the
exoskeleton as they are from the splanchnoskeleton in the Lam-
prey, fig. 1 1 ; but the true homologues of the sternum are first

1 CLXXX. p. 124,. fig. 38. 2 Ib. 123.

ANATOMY OF VERTEBRATES.

195

seen in the endoskeleton of the Batrachia. In the Trunk-fishes
(Ostracion), and Pipe-fishes (Syngnathus), the dermal scale bones
form a continuous coat of mail, like a tessellated quincuncial pave-
ment, over the entire body, as shown in the transverse section,
fig. 16, d n, dp, d h, and the endoskeleton is but little ossified.
The like is seen in the Hippocamps. Thus, in Pegasus draco,
fig. 124, with the exception of the small premaxillaries d, and
mandible £, all the visible hard parts of the head are due to the
dermoskeleton : such, e.g., as the rostrum, «; the plates in which
the eyes are placed, b ; the gill-covers, h ; the median plate, g,

124

Dermoskeleton of the Flying Hippocamp (Pegasus)

supporting the hyobranchial arches ; the zone, i, sustaining the
large pectoral fins ; and the hard case of the incubating pouch,
o, q.

In the Ganoidei, parts of the exoskeleton coalesce with endo-
skeletal bones of the skull, especially the sclerogenous ones, while
others overlie the true cranial bones. Thus, in the Sturgeon,
the ganoid plate, marked d 3, fig. 125, simulates a superocci-
pital ; l but its hornologue in Polypterus and Lepidosteus is subdi-
vided : and as the cartilaginous homologue of the epencephalic arch

1 CXLV. (1846) p. 134.
O 2

19G

ANATOMY OF VERTEBRATES.

underlies the plate d 3, in Acipenser Sturio, so also do the ossified
ex- and super-occipitals underlie in Potypterus the three dermal
plates corresponding in position with d 3 in Ac. Sturio. The true par-
occipital is equally distinct from the plate marked d 8, in Ac. Sturio
and its representative subdivisions in Polypterus. The dermal
plates in advance of these coalesce with the true parietals, frontal s,
postfroiitals, and part of the mastoids. But the varieties in the
dermal plates within the limits of a genus, as exemplified by the

-^J^-i <=cx-o-5cx-=3jx3^r^r^'

Fore part of eiido- and exo-skeleton of Sturgeon

126

ft

single interfrontal in Acipenser Sturio, by the three interfrontals
in Ac. Scypha, by the divided superoccipital plate in Ac. breviros-
tris, &c., sufficiently warn against the confusion arising from
applying to dermal plates the names of the true cranial bones in
recent and extinct ganoid and placoganoid fishes. The median
cranial ganoid plates in the Sturgeons are plainly a continuation
forward of the dermal plates, (ib. d s, fig. 125), of the mid-line of

the back ; and examples of a like re-
petition occur amongst the Osseous
Fishes in the dermal epicranial spines,
for example, of the Angler (Lophius),
which support the long fishing-fila-
ments upon the head, or in those
modified ones forming the sucking disk
on the head of the Remora.

In certain fishes of the Devonian or
Old Red Sandstone period the head and part of the trunk were
encased by coarticulated ganoid bony plates. Fig. 127 shows the
proportions in which the exo- and endo-skeleton entered into the
conservable framework of one of these ancient fishes, termed
Coccosteus (kokkos berry, osteon bone), in reference to the tuber-
cular enamelling of the exterior of the combined helmet and

Scales of Aniblyptcrus striatus

ANATOMY OF VERTEBRATES,

197

cuirass. In the composition of this
sutures, not mucous grooves, may be
discerned the following plates : 5,
median ; 6, lateral ; 7, premedian ; 8,
prelateral; 9, rostral:, 12, dorsomedian\
14, postdorsomedian ; is, sublateral\ 20,
postventrolateral') 22, preventrolateral ;
24, suborbital.

The blank space between the neu-
ral, n, and haemal, A, spines of the
fossil endoskeleton indicates the posi-
tion of the soft f notochorcl,' c, which
has been dissolved away.

In the Pterichthys of the same geo-
logical formation, the helmet was
moveably articulated with the trunk-
buckler.

In Cephalaspis the armour of the
head was shield-shaped, with the pos-
terior angles produced backward in a
pointed form.

The fishes with enamelled dermal
bones in the form of plates, whether
coarticulated, fig. 127, or detached as in
the Sheat-fishes and Sturgeons, fig. 125,
d p, d s, are called f placoganoid : '
those in which they have the size,
form, and overlapping arrangement of
scales, fig. 126, are called 'lepidoganoid.'
The genera Polypterus and Lepidosteus
exceptionally exemplify the latter con-
dition of the dermoskeleton at the
present day : it was the rule with the
fishes of the mesozoic period, and
with those of the paleozoic which
were not ' placoid ' or ' placoganoid.'

In fig. 126, a indicates the outer
surface of parts of two series of the
rhomboidal ganoid scales of the extinct
Arriblypterus : and b the inner surface
of two scales, showing the ridge pro-
duced at one end into a projecting
peg, which fits into a notch of the next

armour, as defined by

127

J ^^ O ^-A r

» V'". a- f L,

as.

at*.

&

^ afe"

':a>

*r*.

JR.

u%

Endo-and exo-skeleton, Coccosteus. CLVI.

198 ANATOMY OF VERTEBRATES.

scale, in the way that tiles are pegged together in the roof of a
house.

In the Porcupine-fishes (Diodon) the spines are supported by
triradiate interlocking dermal bones.

§ 44. Dermoskeleton of Reptiles. --In the Scincoid family of the
Lacertians, the scales are more or less ossified ; least so in the
smooth-scaled genera (Scincus, Tiliqua) ; but in Cyclodus resembling
scutes, and giving a knobby character to the surface. In Cyclura,
Lophura, and Xiphosurus velifer, dermal bones in the form of
spines project or raise the skin above the dorsal or caudal vertebrae.
The horizontal plates connate with the neural spines, and with
the ribs, are dermal ossifications, as are the neural plates and
marginal plates which remain distinct from the endoskeleton,
in the composition of the carapace of the Chelonia. The plastron
is also formed by dermal plates, connate with the sternum and
sternal ribs.

In existing Crocodilia the upper surface of the trunk is de-
fended by bony scutes, usually quadrate in form, smooth on the
inner surface, sculptured and longitudinally ridged on the outer ;
arranged in transverse series, more or less apart, of twos or
fours, upon the neck ; but six or eight in a transverse line and
close set, so as to have a longitudinal as well as transverse
arrangement along the back. The numbers and patterns of these
scutes are noted in zoological comparisons and characters of
genera and species.1 The Alligators are defended by a ventral
as well as dorsal cuirass, separated, as Natterer observed in
Champsa palpebrosa, Ch. trigonata, Ch. gibbiceps, only by a
narrow and soft longitudinal groove along the sides of the neck
and trunk.2 But the most remarkable anatomical modifications
are presented by the extinct and especially the mesozoic Cro-
codilia.

The presence of a ventral as well as a dorsal series of scutes
and their distinctive characters were first noted in the Teleosauri.
The dorsal scutes are in close-set sub-imbricate transverse rows,
the posterior margin overlapping the anterior one of the next
row. I counted twenty such rows in a specimen of the Whitby
Teleosaur, of which sixteen covered the vertebrae between the
last cervical and first caudal. In the ventral shield or plastron,
only the two scutes in each row are on the same transverse parallel
which border the mid-line of the abdomen ; the others have an
alternate interlocking arrangement. These ventral scutes are

1 CLI. torn. v. pp. 79, 80, pi. ir. 2 CLVH. torn. n. (1840) p. 320.

ANATOMY OF VERTEBRATES. 199

not carinate ; and such is the case likewise with the dorsal scutes
of certain species l of Teleosaur. In a Wealden Crocodile ( Gonio-
pholis), the angles of the oblong quadrilateral dorsal scutes are
well marked, and from one of them was continued a peg-like
process, which fitted a depression on the under surface of the con-
tiguous angle of the next scute, thus serving to bind together the

o ~ o o

scutes in the way in which the enamelled scales were united in
many extinct ganoid fishes, fig. 125. The outer surface was
impressed by numerous deep, round, or oblong pits ; but a larger
proportion of the fore part of this surface was overlapped by the
antecedent scute than in Teleosaurus, and this part is smooth and
thinner than the rest of the scute. Associated with the quadrate
toothed scutes, ascribed to the back of Goniopholis, and irregu-
larly scattered in the matrix, I have observed others of a hexa-
gonal form, with a similarly pitted outer surface, but without the
peg, and with thick sutural margins. They indicate a similar
alternate arrangement and interlocking of the ventral scutes, as

o o

in Teleosaurus.

The dermal armour of Hyl&osaurus and Scelidosaurus appears to
have consisted of series of detached scutes of an elliptical or circular
form, without sutural or smoothly overlapping margins : of great
thickness, with the outer surface, in most, pyramidal, or rising to
a longitudinal ridged summit. In Hylceosaurus certain scutes
situated above the dorsal spines were of a very long and narrow
triangular form with the base oblique ; and seem to have
formed a defensive fringe of strong spines along the back, as in
Xiphosurus. In Scelidosaurus the surface was defended by several

longitudinal series of massive unconnected bones : those in the

&

middle of the dorsal surface being in pairs upon the nape, and
single along the tail, where three are coextensive with from five

O o

to seven subjacent vertebrae : a corresponding medial series of
rather smaller and less vertically developed scutes defended the
under surface of the tail ; and there were one or more lateral
series of a more depressed and fuller ovate form, in that region.2

1 CXLVI. p. 79. The volume of the Serial containing Natterer's memoir, though
bearing the date 1840, had not reached this country when I communicated the second
part of my ' Report on Fossil Reptiles ' to the British Association.

2 cxciii.

200

CHAPTER III.

128

MUSCULAR SYSTEM OF H2EMATOCRYA.

§ 45. Structure of Muscle. — Muscular tissue is fibrous, and resol-
vable into fine threads inclosed in a delicate sheath, called 4 elemen-
tary fibres.' These, in Vertebrates, are of two kinds ; in one the
fibre is crossed by close parallel lines ; in the other it is smooth.
The transversely striped character is too fine to be seen without the
aid of the microscope ; but may be indicated to the naked eye by
the iridescence of the surface in certain lights.1 All the muscles
subject to the influence of the will, or cerebral action, have striped
fibres. Most of the involuntary muscles have unstriped fibres ;
those of the heart and gullet are among the exceptions ; and, on
the other hand, the muscles performing the rhythmical movements
of the gill-covers in fishes, like those of the thoracic walls in

higher air-breathers, have the
striped fibre. But besides the close
cross parallel lines, longitudinal
ones, darker, wider apart, and of
varying extent, often present them-
selves on the elementary fibre of
voluntary muscle, as in fig. 128,
A a.~

The fibre, though termed l ele-
mentary ' may, by manipulation
and chemical agency, be resolved
into parts of different forms.3 It

Portions of striped elementary fibres, showing

a cleavage in opposite directions, magnified 8661118 lllOSt prone to Split llltO lon-
300 diam. CLXXXV. , . , i • i i i

gitudmal tracts, which nave been

termed ' fibrils,' fig. 128, A, b and c, and these have a show
of segments equalling in length the breadth of the transverse
striae. Sometimes such segments appear by alternate dark and
light parts of a continuous rectilinear fibril, as in the upper por-
tion at c, fig. 128. Sometimes the segments are marked off by

1 xx. vol. i. p. 10. 2 CLXXXV. p. 508.

Ib.

STRUCTURE OF MUSCLE. 201

constrictions, giving a scolloped border and beaded character to
the fibril, as in the lower portion, at c. Sometimes the striped
fibre cleaves into transverse portions or discs, fig. 128, B, a, b,
corresponding in breadth to the cross-stripes, and to the seeming
segments of the fibrils.

The following is the average diameter of the striped fibre, of
different classes, in fractions of an inch : -

Fishes . . . from y^- to -^g-
Reptiles

» 1000 » 100

"Birds i _J_

JLJ1J.V.IO . . . . • <<TT-

1500 350

Mammals . . . „ yiVo « rii"'1

Thus, among vertebrates, fishes, and in fishes the Skates (Rctia),
have the thickest elementary striped muscular fibre ; and its
elastic tunic, the f sarcolemma,' can be best demonstrated in them.
When the fibre is broken across, as in fig. 129, the sarcolemma a
may remain, connecting the severed portions, b, b.

The characteristic vital property of muscular fibre is to alter,

129

Portions of a bi-oken elementary striped muscular fibre b, held together
l>y the imtorn twisted sarcolemma «. liuia bati.i. CLXXXV.

under stimulus, its relative dimensions of length and breadth.
When it becomes shorter and thicker it is said ' to contract ; ' and
by these contractions the movements of the body, and of its parts,
are produced.

In the contraction of a smooth elementary muscular fibre it has
been seen to grow thicker at a part, and shorter, without falling
out of the straight line.2 In the contraction of a striped elemen-
tary fibre it has been seen to grow thicker at successive parts, by
approximation of the cross stripes, as in fig. 130, at a, a, a, along
one side ; or engaging the whole thickness of the fibre, as at &,&,#;
and these successive partial thickenings, with concomitant shorten-
ing of the fibre, have been termed ( waves of contraction.'3

~ *

On the cessation of the act, the fibre may fall into zig-zag folds
1 CLXXXV. p. 510. - xciv. Editor's note, p. 261. (1837). 3 CLXXXV. p. 525,

202

ANATOMY OF VERTEBRATES.

130

on resuming its length ; but it is commonly drawn out straight, as
before the contraction, by ( antagonistic ' muscles, in the living

animal. The uncontracted state of mus-
cular fibre is sometimes termed ' relaxa-
tion,' but is more properly a state of
quiescence or equipollency.

Muscles consist of series or bundles of
the elementary fibres, with their vessels
and nerves, connected together by areolar
tissue : either in lengthened or flattened
masses, fixed at the two extremities, called
f solid muscles ; ' or disposed around cavities
or canals, and called ' hollow muscles.'

The non-contractile fibrous parts by
which the ' solid muscles ' are attached to
the endo- sclero- and exo-skeletons, are
called ' tendons ' when long and slender, and
s aponeuroses ' when broad and flat.
§ 46. Myology of Fishes.- The modification of the active organs
of motion, and their deviation from the fundamental vertebrate
type, proceed concomitantly with the metamorphosis of the passive
organs, as Vertebrates rise in the scale and gain higher and more
varied endowments : therefore, as the segments of the skeleton

131

Stages of contraction seen in an
elementary fibre of the Skate. The
uppermost state is that previous to
the commencement of contraction.

CLXXXV.

Muscular system, Perca fluviutills

preserve the greatest amount of uniformity in the lowest class, so
does the principle of vegetative repetition most prevail in the
corresponding segments of the muscular system.

The chief masses of this system in ordinary Osseous Fishes are
disposed on each side of the trunk, in a series of vertical flakes or

MYOLOGY OF FISHES. 203

segments, corresponding in number with the vertebrae. Each
lateral flake (myocomma, fig. 131, a, b, c) 1 is attached by its inner
border to the osseous and fibrous parts of the corresponding
vertically extended segment of the endoskeleton, by its outer
border to the skin, and by its fore and hind surfaces to an aponeu-
rotic septum common to it and the contiguous myocommas. The
gelatinous tissue of these septa is dissolved by boiling, and the
muscular segments or flakes are then easily separated, as we find
in carving a fish at table. The vegetative similarity of the myo-
cornmas of the trunk has led to their being described as parts of
one f great side-muscle,' extending from the occiput and scapular
arch to the bases of the caudal fin-rays. The modifications of the
cranial vertebrae impress corresponding changes on their muscular
segments, and special names have been conveniently applied to
their constituent, and in fact often separated and independently
acting, fasciculi.

The fibres of each myocomnia of the trunk run straight and
nearly horizontally from one septum to the next ; but they are
peculiarly grouped, so as usually to form semi-conical masses, of
which the upper, a, and lower, 5, have their apices turned back-
ward ; whilst a middle cone, c, formed by the contiguous parts of
the preceding, has its apex directed forward ; this fits into the
interspace between the antecedent upper and lower cones, the
apices of which reciprocally enter the depressions in the succeed-
ing segment, whereby all the segments are firmly locked together,
their general direction being from without obliquely inward and
backward, and their peripheral borders describing the zig-zag-
course represented in fig. 131, in which one myocomma is repre-
sented partly detached, and others quite removed from the side of
the abdomen. Thus, guided by the fundamental segmental type
of the vertebrate structure, we come to recognise the ( grand
muscle laterale,' of Cuvier, as a group of essentially distinct
vertical masses or segments. A superficial view of these seg-
ments, or an artificial analysis, has led to their being regarded as
forming a series of horizontal muscles, extending* lengthwise from

O O CJ

the head to the tail : the upper portions, «, of the myocommas
being grouped together, and described as a dorsal longitudinal

1 Professor Goodsir proposes (CLXXVIII.) to alter this term to ' myotome,' and to
substitute for 'vertebra' or 'osteocomma' (CXLI, 1849, p. 88) the term ' sclerotome,'
&c. : but this form of compound has been pre-engaged, for their -special cutting
instruments, by the sclerotomists, neurotomists, lithotomists, and other classes of
operating surgeons and their instrument-makers. If the itch of change be uncontrol-
lable, I would suggest 'osteomere,' ' scleromere,' ' neuromere,' &c. (Gr. ^pos, part
instead of Kcfyt/ua, segment.

204

ANATOMY OF VERTEBRATES.

muscle, with tendinous intersections directed downward and back-
ward - - the lower portions, b, as a ventral longitudinal muscle,
with tendinous intersections directed downward and forward,
whilst the margins of the middle portions of the myocommas, c,
being curved, and usually bisected by the lateral mucous line, have
been taken as indications of two intermediate longitudinal muscles.
In the Sharks, instead of a curve the margins of the middle
portions of the myocommas form an angle with the apex turned
forward, fig. 132 ; and in the Rays the dorsal portions have

132

Muscles of fore part of Shark (Squalus glaucus). XLIII.

actually become insulated from the middle ones, and metamor-
phosed into a continuous longitudinal muscle, fig. 139, «, the
133 change being essentially the same with that which the
bony segments themselves undergo, when by anchy-
losis the sacral or cranial vertebrae are blended into a
continuous longitudinal piece. In many bony fishes
the middle fibres of the caudal myocommas are dis-
posed in two cones ; a transverse section of the tail
caudal section of as in fig. 133, shows the two concentric series of cut
Mackarei. segments of the sheathed cones, on each side of the

o

spine. The portions of the myocommas above the lateral line
become grouped, in fish-like Batrachia and in Ophidia, into three
longitudinal muscles, comparable respectively to the ' spinalis
dorsi,' ' longissimus dorsi,' and f sacrolumbalis,' the portions below
the line responding to certain intercostals and the ( rectus abdo-
minis,' of higher vertebrates.

The myocommas of one side are separated from those of the
opposite side of the body by the vertebrae, by the interneural
and interhaemal aponeuroses, and by the abdominal cavity and its
proper walls, fig. 131, h, p. The ventral portions recede from each
other to give passage to the ventral fins, v, as in fig. 135, a : and

MYOLOGY OF FISHES.

205

the ventral and lateral tracts separate to give passage to the pec-
toral fins, as at «, h, fig. 134.

From this part forward, portions of the myocommas undergo
that change, analogous to anchylosis, which justifies their being
regarded as distinct longitudinal muscles : here the separated
ventral tract, fig. 135, a, derives a firmer origin from the clavicle,
and, in consequence of the forward curve of the coracoid, it is
not only expanded but lengthened out, in order to be inserted
there. But the serial homoloo-y of this fasciculus with the more

o»/

normal ventral portions of the succeeding myocommas, the hrenia-
pophysial attachments of which have not risen above the aponeu-
rotic state, is unmistak cable. The lateral portion of the anterior
myocomma, fig. 134, h,y, is attached to the upper end of the coracoid
and to the scapula ; the dorsal portion, f, to the suprascapula, par-
occipital and superoccipital. We recognise the dorsal portion of
the posterior cranial myocomma in the fasciculus called ' protractor
scapulas,' fig. 134, e, the middle portion in that which is exposed
by the removal of the operculum, and which extends from the
scapula to the mastoid, fig. 137, 20; the ventral portions in the
fasciculi continued from the coracoid forward to the hyoid, c, cy

134

Side muscles of head, Perch, xxxin.

fig. 135 : the corresponding portions of the more anterior cephalic
muscular segments may be recognised in d and 27, fig. 135.

'206

ANATOMY OF VERTEBRATES.

Other dismemberments of the cranial myocommas are specialised
to act upon the branchiostegal appendages, the branchiae, the
upper and lower jaws, &c. ; and the chief of these, under their
special denominations will next be noticed.

The upper and lower jaws are so connected together in Osseous
Fishes that one cannot be moved without affecting the other, and

C5

both are alike moveable. Protrusion and retraction affect them
equally, and usually to a greater extent than divarication and ap-
proximation, or the opening and shutting of the mouth : in a
minor degree, also, the two halves of both maxillary and mandibu-
lar arches have transverse movements, varying the angle at which
they severally meet at the premaxillaryor premandibular symphysis.
The most important retractor, which tends in that action also to close
the mouth, is the large subquadrate muscle, retractor oris, fig. 134,
20, 20, which arises from the tympanic pedicle and anterior border
of the preoperculum, and is inserted by the upper fasciculus into
the maxillary ; by a lower fasciculus into the mandible behind the
coronoid process ; and by an aponeurosis into the membrane uniting
the two jaws near the angle of the mouth. The muscle which
tends to open the mouth by depressing the mandible, on which it

135

Lower muscles of head and fins, Perch, xxxin.

exclusively acts, is that marked 27 in fig. 135 ; it arises from the
ceratohyal, and is inserted into the back part of the dentary, near
the symphysis. Cuvier deems it the homologue of the geniohy-
oideus. Above the insertions of the geniohyoid pair is a muscle,
the intermandibularis, fig. 135, 21, which passes transversely from
one dentary to the other, approximating the halves of the man-

MYOLOGY OF FISHES.

207

dible after they may have been divaricated. The latter movement
depends upon the drawing upward and outward of the tympanic
pedicle. This action is performed chiefly by the muscle, levator
tympani, figs. 134 and 137, 24, which arises from the postfrontal
and expands to be inserted into the epi- and pre-tympanics and
into the ectopterygoid. In raising or drawing outward the tym-
panic pedicle and attached part of the pterygoid, this muscle tends
to dilate the branchial cavity and the back part of the mouth. It
is antagonised by the muscle, depressor tympani, fig. 136, 22, 22,
which arises from the basi- and ali-sphenoids, and expands with
diverging fibres to be inserted into the epi- and pre-tympanics and
into the entopterygoid. It depresses the tympanic, or approximates
it to the opposite pedicle, and contracts the branchial cavity.

The movements of the opercular appendage are like those of its
supporting arch, and are performed by muscles placed behind
those of that arch. The levator operculi, figs. 134 and 136, 25,
arises from the niastoid crest, and is inserted into the upper and
outer part of the opercular bone. The depressor operculi, fig. 136,

136

Muscles of hyoid and operculum, Perch, xxxm.

26, arises from the alisphenoid and petrosal, and is inserted into
the inner ridge of the opercular bone. The retractor liyoidei,
fig. 137, i d, fig. 135, c, c, extends from the coracoid to the iiro-
and basi-hyals, but is chiefly implanted into the sides of the

208

ANATOMY OF VERTEBRATES.

former, and becomes through the medium of 27, a retractor of the
mandible. When the retractor hyoidei relaxes and the mandible
is the fixed point, the genio-hyoidei, fig. 135, 27, become pro-
tractors of the hyoid arch. In some fishes a transverse muscle,
repeating the characters of 21, fig. 135, passes from one ceratohyal
to the other. The branchiostegal appendage has muscles for rais-
ing and depressing, divaricating and approximating the rays. The
levator branchiostegorum, figs. 135 and 136, 28, arises from the
inner surface of the hinder half of the opercular bone and from
a contiguous part of the subopercular, and is continued from ray
to ray to the lowest, being loosely attached to their inner surface.
It forms a kind of muscular capsule of the branchial chamber.
The depressor branchiosteyorum., fig. 135, d, arises from the lower
end of the ceratohyal and passes obliquely backward, crossing
its fellow, to be inserted into the inferior branchiostegal ray.
These muscles regulate the capacity of the branchial chamber,

137

Muscles of fins and gills, Perch, xxxnr.

and mainly act upon the water it contains : they show accord-
ingly much diversity, especially 23, in relation to the respiratory
characteristics and connected peculiarities in different fishes. In

MYOLOGY OF FISHES. 209

the Angler (Lophius) the levator is enormous, forming the wall
of the capacious reservoir on each side and behind the gills, and
uniting extensively with its fellow at and beyond the urohyal :
each long branchiostegal ray has, likewise, its peculiar muscles,
originating from the supporting arch. In the AnguillidcR the
isthmal union or raphe of the levatores reaches from the basi-
and uro-hyals to the coracoid.

The branclu'al arches are supplied with muscles attaching them
to surrounding parts, or passing from one part to another of the
arch itself.

The branchi-levatores, fig. 137, 3, arise from the alisphenoid and
divide into four fasciculi, respectively inserted into the epibran-
chial of its own arch. The masto-branchialis, ib. 26, arises from
the extremity of the mastoid, and divides into two fasciculi, one
inserted into the fourth epibranchial, the other into the third
pharyngobranchial and the contiguous part of the pharynx.

The branchi-retr actor es consist of two fasciculi, one superior,
fig. 137, 37, which arises from the upper half of the coracoid,
passing horizontally to its insertion : the other inferior, ib. 32,
passing from the lower part of the coracoid obliquely upward :
they retract and partly depress the branchial arches.

The branchi-depressor, fig. 137, 35, arises from the basihyal and
ascends obliquely backward to its insertion into the cerato-
branchials : it is the more direct antagonist of the levatores.

CJ

The protractor scapula, fig. 134, e, arises from the back part of
the masto-parietal ridge, and is inserted into the coarticulated
parts of the suprascapula and scapula. The middle portion of the
great lateral muscle, ib. g, h, serves, by its insertion, as a retractor
scapulce. The corresponding insertion of the lower portion of the
great muscle into the coracoid retracts that part of the scapulo-
coracoid arch, and is so modified as to have received the name
subcoracoidcus, ib. «, fig. 131, f.

The muscles of the pectoral fin form a pair, in two layers, on
both the outer and inner sides of its antibrachio-carpal base : and
the fibres of one layer run obliquely in a different direction from
those of the other layer in both pairs of muscles. The outer pair
abducts or protracts the fin, the inner pair adducts or retracts it,
sweeping it back into contact with the flank : the first movement
might be called 'extension,' the second, ( flexion.' The superficial
abductor, fig. 134, 14, arises from the upper and outer part of the
coracoid ; it tends to elevate as well as extend the pectoral : the
deep abductor, fig. 137, is, comes from the outer border of the
lower part of the coracoid ; it depresses as well as extends the fin.

VOL. i. p

210 ANATOMY OF VERTEBRATES.

The lower portions of both muscles are shown in fig. 135, 14, 15.
Of the inner pair of muscles, a portion of the deeper layer, dis-
posed so as to raise as well as adduct the pectoral fin, is shown at
16, fig. 137. Each muscle is inserted into the bases of the fin-rays,
resolving itself into fasciculi and short tendons corresponding in
number with those rays : by different combinations of action these
fasciculi divaricate or approximate the rays.

The ischial basis of the ventral fins in abdominal fishes may be
moved a little forward or backward by the action of the ' infra-
carinales ' according as they lie in front or behind the pelvis.
The latter, ' retractor ischii? fig. 131, iv, pass backward to the
vent, inclose it, and are continued to the base of the anal fin. The
protractor ischii, fig. 135, is, passes forward to be attached to the
lower end of the coracoid. The protractors are short in thoracic
fishes, e. g., the Perch, and less distinct from the lower parts of
the myocommas than in ventral fishes, e. g., the Salmon. In
fishes, e. g., the Lophius, where the ischia are wide apart, there
is a transverse muscle to draw them together, and antagonise
the portions of the side muscles that tend to draw them further
apart. The muscles which act upon the ventral rays, like those
of the pectoral ones, form a pair, or two layers of slightly decus-
sating fibres, on both the outer and inner sides of the base of the

O •*

fin. The outer or inferior muscles, fig. 135, 10, 17, depress or
extend the ventral fins ; the opposite muscles raise or flex them.
The portion of the deeper depressor shown at 17, fig. 135, serves
to expand or dilate the ventrals.

The movements of the rays of the median fins are effected
by three or four pairs of small muscles attached to each ray.
The superficial ones, fig. 131, x, arising from the skin, are
inserted into the sides of the base of the dermoneural or dermo-
hremal spine. The deep ones, ib. ?/, arise from the interneural
or interhremal spine, and are inserted into the base of the
dermoneural or dermohrcmal spine : the anterior of these, fig.
137, 3, erects the spine ; the posterior, ib. 4, depresses it. The
myocommas answering to the neural and ha3mal spines of the
coalesced or suppressed centres of the terminal caudal vertebras,
change their direction like those spines, slightly diverging from
the axis of the trunk to be inserted into them : these modified ter-
minal segments, by their connection with the interlocked myo-
commas of the great lateral masses, concentrate the chief force
of those muscles upon the caudal fin. The rays of this im-
portant fin are moved by three series of muscles, the one super-
ficial, the second deep-seated, the third interspiiious. The

MYOLOGY OF FISHES. 211

superficial muscle, arising from the terminal aponeurosis of the
'lateral muscle,' expands and separates fan-wise, fig. 131, z9 to its
insertion into the bases of the caudal rays. The deeper-seated
fascicles are exposed by the removal of the foregoing and their
aponeurotic origin, and arise from the coalesced terminal centrums
of the caudal vertebra, to be inserted further from the basal joints
of the rays, and more advantageously for effecting the movements
which alter the spread of the tail-fin. Slender longitudinal mus-
cles, suj)ra-carinales, extend along the mid-line of the back from
the occiput to the first dorsal, and along the interspaces of the
dorsal fins in the Cod : similar muscles, fig. 131, u, extend from
the last dorsal to the caudal fin in the Perch ; and infra-cari-
nales, ib. v, extend from the anal to the caudal along the keel of
the tail. In the Gymnotus the supra-carinales form a single pair,
which extends from the occiput to the end of the tail. The modi-
fied cranio-dermal spines, which constitute the oval sucking-disc
of the Remora, have a complex series of minute muscles, which
raise or depress the transverse lattice-work ; and thus become the
means of giving the little feeble fish all the advantage of the rapid
course of the whale or the ship to which it may have attached
itself. The muscular and membranous webs of the coalesced pec-
torals and ventrals of the Lump-fish, form a sucker on the oppo-
site surface of the body, by which it may safely anchor itself to the
rock, in the midst of the turbulent surf or storm-tossed breaker.

There are many modifications of the muscular system in the
orders at the two extremes of the class.

The segmental disposition of the muscular masses is most
simple, most distinct, most like the annulose type, in the Cyclo-
stomi : yet it is considerably specialised for the due working of
the suctorial apparatus. In the Lamprey, fig. 138, slips are con-
tinued or derived from the anterior part of the myocommas, for
draAving back, bending in different directions, and expanding the
mouth. Of these, the superior, e, is inserted into the cartilage,
fig. 24, 20 ; raises and fixes it, giving a fulcrum and favourable
direction for the muscle, fig. 138, I, which directly retracts and
raises the sucker, a: the inferior slip,/, is inserted into the pro-
cess, fig. 24, q, and into the lower border of the gristly base of the
sucker, ib. 22 : it retracts and depresses the sucker. An interme-
diate lateral slip, inserted a little higher upon the margin of q, fig.
24, retracts and draws outward the sucker. All these retractors,
co-operating, serve to expand the sucker ; or, if duly antagonised
by the sphincter or is, pull back the object seized by the sucker, or
draw the body of the fish towards it, according to the fixed point.

p 2

212

ANATOMY OF VERTEBRATES.

138

Muscles of head and sucker; Launnvy,

XLIII.

Shorter muscles arise, above, from the cranial cartilage, fig. 24, d,
and below, from the hyoid cartilage, to act upon parts of the sucker ;
the latter, g, h, diverge to their insertions. Part of the deep-
seated longitudinal expansor oris, more directly antagonising the
circular sphincter or is, a, is seen at m, fig. 136.

Details of the myology of the Myxinoids with a comparison of
the muscular system of Fishes with that of higher Vertebrates, will
be found in xxi. pp. 179-249.

In the Trunk-fish ( Ostracion) flexion of the trunk is abrogated

by the case of ganoid armour, fig. 16,
dn, dh, inclosing the body, and which
leaves only the jaws and fins free.
The myocommas are accordingly re-
duced to a thin layer of longitudinal
fibres, modified posteriorly for inser-
tion into the moveable part of the
tail and its fin.

In another plectognath, the odd-
shaped Sun-fish (Orthagoriscus) the
muscles of the continuous vertical fins
take the place of the ordinary myocom-
mas : those of the lofty dorsal com-
mencing behind the occiput ; those of the deep anal behind the
short abdomen : the dermoneurales arise from the integument,
especially the fibrous septum of the lateral line ; the deeper-seated
interneurales from the neural and interneural spines. Each series
is more or less blended together, conformably with the degree of
confluence of the interneurals, upon the expanded ends of which
the spines of the dorsal fin move as one body, the anal fin having
a similar structure. Nevertheless, towards their insertion, the
fasciculi of the fin-rays become, like them, distinct ; each one
behind being sheathed by the one in front, and their long tendons
passing through lubricated grooves or sheaths to their insertions.
On the sides of the abdomen the muscles are reduced to two fas-
ciculi, expanding, the one from the clavicle, the other from the
coracoid, upon the peritoneum.1

Amongst the Plar/iostomi, the Sharks are the most active and
powerful, and in them the muscular system is most developed, and
in certain parts most specialised. The more acute angles formed
by the intermyocommal septa have already been noticed, fig. 132.
A fasciculus continued from the upper portion is inserted, by a
strong aponeurosis into the upper part of the cranium, ib. a, a.

1 XLVI. and CXCVIT.

MYOLOGY OF FISHES.

213

139

The muscles of the jaws are very powerful, as might be expected
in these fierce and predatory fishes. One, analogous to the ( tem-
poral,' fig. 132, m, arises from the lateral and posterior ridge of
the cranium, and its fibres converge as they pass obliquely down-
ward and forward to their insertion into the mandible. They are
covered in great part by the stronger muscle ib. /, analogous to
the ' masseter,' which arises from the under part of the postfrontal
ridge, passes over the maxillo-mandibular joint, as over a pulley,
and expands to its insertion in the lower side and ridge of the
hinder two-thirds of the mandible. Smaller muscles, f maxillo-
mandibulareSf ib. g, pass from the upper to the lower jaw, and
directly close the mouth. The openers are chiefly the mus-
cles, p, which have their chief fulcrum in the coracoids,
and expand to be inserted into the symphysis mandibulae.
The gill-apertures are contracted by the muscles, q, q, and di-
lated by others passing obliquely from above to their front boun-
daries. The muscular invest-
ment of the branchial chamber
of the Torpedo fig. 139, r, re-
ceives a fasciculus from the
scapula, and sends another,
ib. o, forwards to the cra-
nium, from which the con-
strictor of the electric bat-
tery, E, is continued. The
protractor scapulce in the
Skate and Torpedo is of con-
siderable length, in conse-
quence of the backward dis-
placement of the scapular
arch, and is of great strength,
by reason of the enormous
pectoral appendage which
the arch sustains. The myo-
commas of the trunk are
fused into four great longitu-
dinal masses. The neuro-
medial mass, fig. 139, a,
arises from the scapula, s, and by strong carneous fasciculi
from the vertebra behind the scapular attachment : above the
pelvis they divide into tendinous slips, which pass backward
in separate sheaths, to be successively inserted into each vertebra
as far as the end of the tail. The neuro-lateral mass or muscle,

Muscles and electric batteries of the Torpedo.
XLIII.

214 ANATOMY OF VERTEBRATES.

ib. c, arising from the outer part of the scapula and from the
parapophyses of succeeding vertebras, is inserted by similarly
disposed, but more slender tendons. At their termination, each
tendon bifurcates, allowing that appropriated to the succeeding
vertebra to pass through it, so that all, save the last, are both
perforati and perforantes. The protractor scapulce, ib. z, be-
comes, when antagonised by the two foregoing muscles, the
chief elevator of the head. Of the two muscles of the ros-
trum in the Ray, the superior, levator rostri, arises from the
scapula by a short fleshy belly ending in a slender round tendon
which runs above the branchiae in a sy no vial sheath to the rostral
cartilage, which it serves to raise : the inferior, depressor rostri,
arises from the lower part of the coalesced anterior vertebra?, runs
obliquely outward, and then curves inward to its insertion into the
lower part of the base of the rostrum. The muscles of the jaws
in the Kays include, with maxillo-mandibulares, those answering
to / and ?n in the Shark, fig. 132. The depressor mandibuli is a
large oblong mass of parallel longitudinal fibres, arising from the
lower (coracoid) part of the scapular cincture, and passing forward
to be inserted into the mid part of the mandible. Two small mus-
cles, one on each side, contribute to depress the mandible : they
are attached in front near the commissure of the lips, and, running
inward, almost cross each other beneath the great depressor. A
third muscle has its fibres remarkably interlaced, but divisible into
three chief fascicles, two of which are anterior and one posterior :
this is derived from the end of the upper jaw and joins the hinder
margin of the second mass. The first portion is situated in front
and above the maxilla, near its commissure, and runs obliquely to
join the outer edge of the second fascicle : all co-operate in firmly
closing the mouth. The protractor oris forms a pair of long and
slender muscles passing from the rostrum between the cranial base
and the palate to be inserted into the maxilla. The muscles of
the vast pectoral fins form two thick fleshy layers, covering its car-
tilages above, fig. 139, t, and below, and dividing into as many
fasciculi as there are fin-rays, into which they are inserted. A
similar arrangement obtains in the muscles of the ventral fins, ib. v.

The muscles, in Fishes, of the eye-ball, the air-bladder, and of
some other special organs, will be described with the parts they
move.

The muscular tissue (myonine) of fishes is usually colourless,
often opaline, or yellowish ; white when boiled : the muscles of
the pectoral fins of the Sturgeon and Shark are, however, deeper
coloured than the others ; and most of the muscles of the Tunny

MYOLOGY OF REPTILES. 215

are red, like those of the warm-blooded classes. The want of
colour relates to the comparatively small proportion of red blood
circulated through the muscular system,1 and the smaller propor-
tion of red-particles in the blood of fishes : the exceptions cited
seem to depend on increased circulation with great energy of
action ; and, in the Bonito and Tunny, with a greater quantity of
blood and a higher temperature2 than in other fishes. The deep
orange colour of the flesh of the Salmon and Char depends on a
peculiar oil diffused through the cellular sheaths of the fibres.
The muscular fasciculi of Fishes are usually short and simple :
and very rarely converge to be inserted by tendinous chords.3 The
proportion of myonine is greater in Fishes than in other Verte-
brata ; the irritability of its fibres is considerable, and is long re-
tained. Fishermen take advantage of this property, and induce
rigid muscular contraction, long after the usual signs of life have
disappeared, by transverse cuts and immersion of the muscles in
cold water : this operation, by which the firmness and specific
gravity of the muscular tissue are increased, is called ( crimping.'

§ 47. Myology of Reptiles.- The myonine of the air-breathing
Haematocrya is always pale in colour, and the fibres are tenacious
of their irritability : the energy of the muscular contraction is in
some instances, and on some occasions, great ; but cannot be ex-
cited in frequent succession, such power being soon exhausted.

In the ichthyomorphous Batrachia the recent myonine presents
a pearly clearness, as in some fishes, and the chief bulk of the
tissue is arranged in transverse segments, of which, however, the
progress of massing into longitudinal groups is greater than in the
Sharks. In the Salamander, figs. 140, 141, the neural or upper
halves of the myocommas, separated at the midline of the back by
a furrow lodging cutaneous follicles, have a tendency to group
themselves into distinct longitudinal tracts, as they advance for-
ward : just as their homologue — the common ' erector spina? ' in
man - - subdivides into the longitudinal masses called ( sacro-lum-
balis,' ( longissimus dorsi,' and ( spinalis dorsi,' &c., in its corres-
ponding course. The median portion, fig. 140,5 a, in Salamandra,
representing the spinalis dorsi in the trunk, has its anterior
insertions in the neural arches and spines of the cervical and occi-
pital vertebra ; and there answers to the ( spinalis ' and ' semispi-
nalis ' colli, and to the f bi venter cervicis ' and ( complexus.' The
lateral portion, answering to the longissimus dorsi and sacro-lum-
balis in the trunk, represents, by its insertions, the ( transversalis
colli ' and trachelo-mastoideus, fig. 140, 5, in the neck. The haemal

1 XLVIII. pp. 4, 16. 2 L. 3 XLIX. p. 3.

216

ANATOMY OF VERTEBRATES.

W

I

or lower half of the myocommas in the
trunk, fig. 140, 6, has been held to represent
the oljliquus externus abdominis ; but, as it
is segmented by aponeurotic prolongations of
the short pleurapophyses, both in the abdo-
minal and caudal regions, it is more like a
series of intercostals. The broad, thin, car-
neotendinous sheets, called 6 external ' and
( internal oblique ' muscles in Mammals, hav-
ing their fibres running in opposite directions,
may, indeed, be referred to the same system
of segmental trunk-muscles ; but this grade
of differentiation is not reached in Fishes
and fish-like Batrachians. The medial parts
of the haemal myocommas are more distinct,
and show more of the character of a longi-
tudinal muscle with tendinous intersections,
like the ' lineae transverse ' of the human
6 rectus abdominis ;' and this muscle is one
of the determinable homologues of a recog-
nisable tract of the myocommas of the fish
and newt. In the Salamander, however,
the tract, fig. 141, s, is as superficial as that
part of the sheath of the ' rectus abdominis '
in Mammals ; and it forms a corresponding
part of the sheath of a deeper-seated longi-
tudinal muscle, fig. 141, 7. Both 7 and 8
are specialisations of the lowest haemal por-
tions of the myocommas : they are anteriorly
resolved, or continued, as in Fishes, into
muscles acting upon the scapular, hyoidean,
and mandibular arches. The pubohyoideus,

7, arises from the pubis and outer part of
the gristly heemapophysis, or Y-shaped
cartilage, fig. 113, d\ it runs forward
in a sheath, analogous to that formed
by the aponeurosis of the external and in-
ternal oblique muscles of Mammals, and is
inserted into the ceratohyal. The muscle,

8, called rectus abdominis, by Funk,1 has its
attachment to the pubis through the medium
of the Y-shaped cartilage, which represents
the marsupial bones and tendinous f pillars
of the abdominal ring ' in Mammals : it is

Muscles of Salamandra Icrrestris.

CLXXXVII.

CLXXXV1I.

MYOLOGY OF REPTILES. 217

attached anteriorly in part to the triangular short sternum, ex-
tending beyond it to the transverse part of the episternum, and
is thence continued (as in fig. 135, 27), to the symphysis mandi-
bulae, representing the geniohyoideus. A small fasciculus, fig. 141,
10, is also sent to the coraco-scapular joint.

The upper jaw is fixed. The muscle which, by its insertion
into the lower jaw, acts as a temporalis, is divided into two
fasciculi ; one, fig. 140, 2, has the normal origin from the side of the
cranium; the other, ib. i, atlanto-mandibularis, acts with greater
force by deriving its origin from the neural arch and spine of the
atlas. The masseter, ib. 3, arises from the mastoid and epitym-
panic, and is inserted into the outer surface of the hinder half of
the mandible. The occipito-mandibularis, or digastricus, ib. 4,
arises from the paroccipital and back part of the epitympanic,
and is inserted into the angular element behind the tympano-
mandibular joint Avhereby it opens the mouth. In this action it
is aided by the strip, ib. 13, which passes from the angle of the
jaw upward to the skin. Some amount of lateral movement of
the mandible is effected by a pterygoid muscle. The retraction of
the mandible is provided by the muscle, ib. 13, although it seems
lost in the skin, as it passes backward from the angular process.
A mylohyoideus, fig. 141, 11, passes from one ramus to the other,
external to the geniohyoideus, ib. 8/, and to the following
muscles of the hyoid arch. The genio-ceratoideus, ib. u, arises
from near the symphysis mandibula?, and is inserted into the cera-
tohyal. The hyolranchialis, ib. is, passes from the base of the
ceratohyal to the hyobranchial cornu.

With the growth and specialisation of the segments of the
limbs the muscles became larger, more numerous, and more dis-
tinct. The pectoralis, fig. 141, 16«, 16, has its origin extended from
the fore part of the coracoid and episternum to the linea alba, or
aponeurotic continuation of the sternum, half an inch beyond the
coracoid ; the fibres converge to their insertion into the pectoral
ridge of the humerus ; but so that the coracoid portion is almost
a distinct muscle. This muscle suspends the fore part of the
trunk upon the fore-legs, and besides depressing the humerus,
rotates it in the plane of the body's axis as different portions of
the muscle come into action.

A muscle, fig. 140, n, arising from scattered fibres by a longi-
tudinal tract of the aponeurosis, covering the loncjissimus and
spinalis dorsi, collects those fibres and contracts as it descends
over the hind part of the scapula to be inserted into the back part
of the pectoral ridge. An anterior part, ib. 22, of the same

218

Muscles of Salamandni

ANATOMY OF VERTEBRATES.

Ml

system of converging fibres

takes its origin from the
scapula itself, and converges
to an insertion close to that
of the preceding. The entire
mass of the muscles 22 and
11 antagonise that, 16, lea,
below ; one raises, the other
\ depresses, and both rotate,
the humerus to and fro. As
the fore-limb gains size and
pOAver in higher air-breathers,
the muscle n seeks a more
extended origin, covers a
greater proportion of the seg-
meiital system of trunk-
muscles, acquires the name
of latissimus dor si, and, in
Anthropotomy, is classed
amongst the f first layer of
the muscles of the back.' The
muscle 22, becomes deve-
loped into f supra- ' and ( in-
fra-spinatus? and, perhaps,
also deltoides. The pro-
tractor scapula, arising, as in
Fishes, from the paroccipital,
noAV also derives fibres from
the transverse processes of the
first and second trunk-verte-
brae, and divides into two dis-
tinct fasciculi; one, fig. 140,

19, is inserted into the base
of the scapula ; the other, ib.

20, into the humeral end of
that bone. A small strip, is,
which tends more directly
to raise the scapula, arises
from the transverse proces-
ses of the third vertebra ; but
the muscle, 19, is that which
best answers to the levator
scapulce of Mammals. Two

CLXXXVII.

MYOLOGY OF REPTILES. 219

strips from the second and third cervical diapophyses, inserted
into the under part of the scapula, indicate the commencement of
the serratus magnus anticus, fig. 141, 21. The mass of muscle,
figs. 140, 141, 23, which protracts or 'flexes' the fore-arm, aris-
ing from the fore and inner part of the glenoid cavity and from
the fore part of the hnmerus, represents the biceps and brachialis
internus. The retractor or extensor mass, ib. 24, answers to
the divisions of the triceps. On the antibrachiiim the flexor of
the wrist is divided into a ( radial,' fig. 141, 25, and culnar,'
fig. 140, 20, portion ; as is likewise the extensor, of which, 27,
fig. 141, represents the extensor carpi ulnaris, and 28 the extensor
carpi radialis : 29 is the flexor digitorum communis, and 30 the
extensor digitorum communis.

The pectoralis, fig. 141, 16, is represented in the pelvic limb
by the muscle, ib. 36, which arises from the ischiopubic sym-
physis, and is inserted into the front and inner part of the
head of the tibia. This mass in higher reptiles becomes dif-
ferentiated into the pectineus, the adductors, and the gracilis ;
it depresses and adducts the pelvic limb. Its chief antagonist
is marked 36 in fig. 140. It rises from the ilium, and is inserted
into the lower and outer part of the femur, and also into the
outer part of the head of the tibia ; it corresponds by its origin
with 22 in the fore limb, and becomes developed into glutens
externus and ( tensor fascia femoris' in Mammals. The fasciculi
which correspond with 11, in the fore-limb are 37 and 32, fig. 140;
they arise from fascia connected with the transverse processes of
the third and fourth caudal vertebra?, and are inserted into the
middle and back part of the femur. The muscle, 31, which arises
from the fore part of the ilium, and is inserted into the upper
third of the femur, repeats the anterior fibres of 22 in the scapular
limb. The chief difference is that the protractors, 31, and retrac-
tors, 32 and 37, of the thigh are more distinct from the abductor
and levator, 36 ; and that this has a more advantageous insertion
for its office by being extended to the second segment of the
limb. The retractors, 32, 37, act like the latissimus dorsi 11 : their
origin is in connection with the vertebral or axial system : they
become developed in the pelvic limb of higher animals into parts
of the ' glutei ' and ' pyriformis.'

The protractors or flexors of the thigh, 34, 35, which answer to
those of the arm, 23, arise from the fore and under part of the
ilium, and are inserted into the fore and upper end of the tibia.
The muscle, fig. 141, 35, which passes to the inner side of the head
of the tibia, answers best to the sartorius ; the larger mass on its

220 ANATOMY OF VERTEBRATES.

outer side, 34, to the triceps extensor cruris, and more especially
to the rectus femoris, as having its chief origin from the ilium ;
whilst its tendon expands over the fore part of the knee joint, as
that of 23 passes over the fore part of the elbow joint ; and both
without having any sesamoid lever developed therein.

The retractors or extensors of the thigh and leg, ib. 33, answer-
ing to the retractors of the arm and fore-arm, 24, arise from the
hinder and outer part of the ilium, and are inserted partly into the
femur, partly into the outer part of the head of the tibia. A
muscle, fig. 141, 38 (sacro-plantaris}, forming part of this system,
has a special extent and disposition, favouring the effective back-
ward stroke of the foot in swimming : it arises from the sacral rib
and is inserted into the plantar fascia. It is a ' flexor ' of the leg,
like the ' biceps flexor cruris :' it is an ( extensor ' of the foot, like
the ' plantaris.' And here a few remarks may be offered on the
terms ( flexion ' and ' extension,' as applied to the ( fore-arm ' and
6 leg; ' in higher air-breathing Vertebrates and in Man.

C? ~ ~

The fore and hind limbs of the Salamander are figured extended
in corresponding positions, in fig. 140, as those of the Plesiosaurus
are represented in fig. 45. The ulna is external or posterior in the
arm, the fibula in the leg. If, in the dead newt, the fore-arm be
moved upon the arm to and fro, in the direction of the trunk's axis,
it can be bent at an angle with the arm either way ; and the like
would most probably be the case in the Plesiosaur : there is
no bony configuration of the elbow-joint to prevent this in either
reptile ; only the ligaments favour the forward bend more

than the hinder one, in the batrachian. In the hind limb the les;

o

can be bent at an angle with the thigh, both forward and back-
ward; but the ligaments of the joint offer more resistance to the
forward than to the backward bend. As we ascend the verte-
brate scale in the comparison of limbs, a bone of the fore-arm
sends a process across the back part of the elbow-joint which
fits into a cavity in the bone above the joint when the two are

brought into the same line ; and the fore-arm cannot be bent

~ *

back at an angle with the arm without fracture of the inter-
locking bar or ' olecranon.' In the leg the contrary bend, at an
angle forward upon the thigh, is prevented by configuration of
the knee-joint, with interarticular cartilages and ligaments.

Thus the forward bend is favoured in the fore-limb ; the back-
ward bend in the hind limb.

In quadrupeds the limbs are habitually retained with the first
and second segments more or less bent in the directions favoured
by the configuration of the elbow-joint and knee-joint respec-

MYOLOGY OF REPTILES. 221

tively, to which the muscles conform in relative size and posi-
tion. These opposite bends are shown in the skeleton of the
Crocodile, fig. 57.

When the leg, 66, is brought forward (protracted), widening the
angle between it and the thigh, v, and when the fore-arm, 55, is
brought forward, contracting the angle between it and the arm,
53, the motions are the same, or homologous in both limbs. But
in one case such motion is called s flexion ;' in the other f exten-
sion :' these terms relating not to the absolute line or direction of
motion of the limb, but to the resulting relative position of one
segment of the limb to another. The protractor muscles draw-
ing forward the second segment of the limb to an angle with
the first, are called ' flexors ;' those drawing forward the second
segment from an angle with the first, are called ' extensors.' The
same distinction is made with the ' retractors,' according as, in
drawing back the second segment, they rotate it from an angle
to a straight line with the first segment, or from a straight line to
an angle. Thus the homologous movements are signified by dif-
ferent terms, and the homotypy of the muscles has been masked
by the same artificial verbal distinctions. The ' flexors ' of the
fore-arm answer to the ( extensors ' of the leo; in serial homoloo-y.

O O«/

The ( biceps flexor cubiti,' with the e brachialis anticus,' is the
homotype of the f triceps extensor cruris,' not of the ( biceps flexor
cruris ;' while this muscle, with the semitendinosus, is the homotype
of the e triceps extensor cubiti.' Much of the difficulty of com-
prehending the true serial homology of the parts of the fore and
hind limb has arisen from regarding the flexors in the one limb to
be the homotypes of the flexors of the other, and vice versa. The
pertinacity with which the idea of the patella being the homotype
of the olecranon is maintained, depends in a great degree upon the
error of supposing the 6 triceps extensor cubiti ' and the ( biceps
extensor cruris ' to be homotypes or serial homologues.1

Returning to the Newts, we find the chief retractor or extensor,

o

fio;. 141, 39, of the foot answering to the retractors or flexors of

* O

the carpus, 25 and 26. But, as regards the toes, since their joints
are so arranged as to allow them to be most easily and extensively

1 Some anatomists assuming this to be a matter determined and unquestionable,
make it the basis for impugning the opinion that the patella answers serially to the
tendon of the biceps brachii, and especially to the sesamoid sometimes developed
therein. " Unless we are entirely to disregard the guidance of muscular relations
in determining homology, we must admit that the ossicle upon the olecranon is the
homotype of the patella," &c. CLXXI. p. 21, and CLX. passim. The muscular
concur with the osseous relations in showing that the ossicle upon the olecranon is
the homotype of that upon the peronecranon, or produced head of the fibula in
certain marsupial and other mammals. CLXI. pi. 1, fig. 16.

222 ANATOMY OF VERTEBRATES.

moved in the direction of ( retraction.' as the limbs hano; in fiV 140,

O O

flic l flexors ' of the fingers have their homotypes in the hind limb
called ( flexors of the toes,' and the muscles effecting the opposite
movements of the dibits are termed ' extensors ' in both fore and

o

hind limbs. The muscle, 40, arising from the fascia of the knee,
becomes by its insertion the extensor longus digitorum pedis.
The muscle, 41, is the flexor longus digitorum pedis. A sliort
extensor arises from the fore part of the tarsus ; its tendons
unite with those of the long extensor. A sliort flexor from the
opposite side of the tarsus divides, to be inserted by fleshy fibres
into the tendons of the flexor longus. The hallux has a special
extensor and abductor : the fifth toe has also an abductor : these
combining in action, enlarge the breadth of the foot.

In the higher reptiles, of the order Crocodilia, chiefly affecting
the watery element, and with frame and limbs proportioned
for natation, the primitive segmental structure continues to
be shown by the vertical aponeuroses passing outward from each
successive vertebra, especially from the di- and pleur-apophyses ;
they divide the mass of muscles answering to the caudal myo-
commas of Fishes and fish-like Batrachia in the tail ; to the
spinalis dorsi, longissimus dorsi, and sacrolumbalis of higher Ver-
tebrates in the back ; and to the cervicalis ascendens, splenius capitis,
and transversalis colli in the neck. The posterior attachment of
the sacrolumbalis is to the fore part of the ilium by a slender ten-
don : that of the longissimus dorsi is to the sacral ribs. External
to the longissimus dorsi is the trachelomastoideus, originating
behind from the diapophyses of the, second or third dorsal vertebra,
passing forward between the di- and zyg-apophyses of the cer-
vical vertebras, deriving slips therefrom, and inserted into the
mastoid. The complexus rises from the sides of the neural spines
of the middle cervical vertebrae, and is inserted into the parocci-
pital. The splenius capitis arises from the neural spines of the
anterior dorsals, and is partly a continuation of the spinalis dorsi :
it is inserted into the superoccipital, and shows traces of the seg-
mental structure. The powerful muscles of the tail are more
decidedly divided by aponeurotic septa into segments, correspond-
ing with the vertebras ; but they are grouped together, by Cuvier,
into three pairs of longitudinal muscles. The first is neural in
position, and chiefly a backward prolongation of the spinalis dorsi ;
the myocommal septa form an angle directed forward. The
second is lateral, and begins by a strong tendon from the upper and
back part of the ilium, and by a second tendon from the ischium :
it is also connected with fleshy flattened fasciculi from the pubis

MYOLOGY OF REPTILES. 223

and abdominal ribs : its myocommal septa describe an acute angle
directed backward. At the base of the tail it descends to the
lower border, and covers part of the third muscular column.
This derives a tendinous origin from the inner trochanterian ridge
of the femur, and from a ligament thence extending to the femoro-

~ o

fibular articulation : from these attachments the muscle passes
backward to the haemal arches and spines related thereto by
alternating origins and insertions, and there assumes the myocom-
mal character of the lowest or hremal tract in the tail of the Newt
and Fish. By its anterior attachments in the Crocodile, this series
of muscles- -\\\Qfemoro-peroneo-coccygius of Cuvier-- closely asso-
ciates the pelvic limbs with the tail in the natatory actions and
evolutions of the amphibious carnivore.

The mandibular muscles are strongly developed in the Cro-
codile in comparison

with other Saurians ; 142

although they seem,
after a comparison witli

.1 r •

those 01 carnivorous
mammals, small in pro-
portion to the length
and massiveness of the
jaws. The temporal
is represented by two

niUSCleS, One Of Which, Mandnmlnr muscles, Crocodile

the pretemporalis, fig.

142, e, has its origin extended forward into the orbit from
beneath the postfrontal, whence its fibres pass obliquely back-
ward : the larger temporalis, ib. f, is attached to the parietal,
the mastoid, and tympanic, and its fibres pass vertically external
to those of the pretemporal, to be inserted into the coronoid and
surangular. The pteryyoidei are larger muscles than the tem-
porales ; the one from the ectopterygoid, fig. 142, h, receives
an accession of fibres from the long pterygoid bone, and,
passing obliquely backward, swells out into almost a hemi-
spheric prominence at its insertion into the outer side of the
angular elements at h. The apertor oris, or digastric, ib. g, arising
from the back part of the prominent mastoid, descends obliquely
backward to the projecting angular process behind the tympano-
mandibular joint. When the mandible rests on the bank, as at
a, a, supporting the head of the crocodile, and makes its angles,
ib. 29, the fixed point, the digastrici, g, acting upon the lever of the
mastoid, 8, open the mouth by rotating the cranium and upper

224

ANATOMY OF VERTEBRATES.

143

A

jaw from b to c, upon the tympano-mandibular joints, t. Obser-
vation of this action engendered the notion that the upper jaw
was moveable, and that this was a peculiarity of the Crocodile ;
but it moves only as part of the entire cranium.

As the muscles of the limbs reach their maximum of number
and variety in the Chclonia and saltatory Batrachia, they will be
specified in those groups ; and the myology of the trunk will be
resumed, as it is seen in the Opkidia.

In these reptiles, as might be expected from the functions of
the spinal column, specialisation of the muscles of the vertebra?
and ribs reaches its maximum. The coalescence of the upper or
neuromcsial and neurolateral parts of the myocommas into longi-
tudinal tracts is more complete and distinct than in the fish-like

Batrachia, or the Crocodilia ;
the primitive distinction or
segmentation being pre-
served only at the points of
attachment.

In the neuromesial tract,
fig. 143, A, those which
may be called ( origins ' are
in two series, one from the
bases of the neural spines,
the other by short tendons
from the diapophyses : the
fleshy fibres from each ori-
gin converge and coalesce
as they pass forward, and
terminate in a lono; slender

o

tendon : these tendons are
attached to the summits
of the neural spines. We
have here the characters
of semispinalis and spinalis
dorsi. The column external
to the preceding answers to
the lonyissimus dorsi ; it
arises by a series of fleshy
origins from the transverse
processes, and by tendons
from the contiguous parts
of the ribs ; the fleshy fibres
pass forward and outward partly to the fascia covering the

Muscles of the vertebra and ribs. Python, cxci.

MYOLOGY OF REPTILES. 225

semispinalis dorsi, and partly to its insertions into the neural
spines ; its foremost attachment is to the siiperoccipital. The
third (neurolateral) tract derives fibres from the tendinous origins
of the lono-issirnus dorsi, and detaches from its outer side thin

o •*

slips, each inserted by a slender tendon into a rib ; it represents
the sacrolumbalis. A muscle deriving slips of origin from the
zygapophyses of four or six anterior vertebra passes forward to be
inserted into the mastoid, fig. 145, r, and represents the trachelo-
mastoideus. On the under part of the vertebral centrum are a
series of oblique fasciculi, extending and converging in pairs from
the diapophysis of one vertebra to the hypapophysis of the second
or third vertebra in advance. The lone/us colli at the fore
or upper part of the spinal column in Mammals and Man is a
repetition of this series ; the greater extent and developement of
which in Ophidians is indicated by the number and length of the
hypapophyses, hy, figs. 46, 47 : and of the subdiapophyses, d! ',
fig. 47 a ; and these are maximised in Crotalus and Naia ; the
co-related muscle, having its foremost insertion into the occipital
hypapophysis, fig. 146, p, brings down the head in the blow
inflicted by the venom-fangs with proportionate force.

On removing the semispinalis dorsi, muscles appear which pass
obliquely between the transverse and spinous processes, like the
series called multifidus spina in Man. Beneath these are inter-
spinales and intertransver sales. External to the multifidus spinae
is a series of levatores costarum breviores, fig. 143, B, arising
from the diapophyses, and respectively inserted into the rib of
the succeeding vertebra. At their insertion arise the pretra-
hentes costarum, ib. C, which run more obliquely backward,
and terminate each in the eighth (Naia) rib beyond that
from which it arose ; being attached also to the intermediate
ribs and intercostal fascite. In Python they are continued on
to the tenth or twelfth rib, fig. 143, D, and these continua-
tions have been described as a distinct series. Beneath them
is a shorter series, the pretrahentes breviores, ib. E. The retra-
hentes costarum, fig. 144, C, arise from the lower part of the
diapophysis, and pass obliquely forward and outward along the
internal surface of the ribs to be inserted into the fourth rib in
advance. Where these muscles terminate, the transversals abdo-
minis, ib. D, takes its serrated origin ; its fibres descend obliquely
forward and terminate, with those of the opposite side, in the
raphe, or medial tendinous line ; which closely adheres to that
part of the inserted border of the ventral scutes. The retrahentes
inferiores, ib. B, interdigitate at their origins (in Python) with

VOL. I. Q

22G

ANATOMY OF VERTEBRATES.

144

those of the transversalis abdominis, and pass forward to be
inserted at the end of the bony part of the fourth rib in advance.
The muscle answering to the rectus abdominis, ib. A, has the
short rib-cartilages for its intersections, instead of the fibrous
6 linear transversse,' as in Man.

The inter costales, fig. 143, r, have their usual position and
decussating arrangement in two planes. The squamo-costales,
figs. 143, 144, I, i, arise from the ribs near the insertions of the
leuatores costarum, B : these origins have been detached and the
muscles reflected ; in the figures they pass obliquely backward,

and are inserted into
the skin near the outer
margins of the ventral
scutes,

The scuto-costales. fio*.

' C5

143, H H, rise from the
fore part of the end of
the rib, and are inserted
into the edge of the
scute.

The inter scutales, figs.
143, 144, F, G, K, are
in two layers, which
decussate each other,
and cooperate with the
scuto-costales in alter-
nately erecting and de-
pressing the scutes.1
The fixed point of one
series is the ' linea alba,'
ib. E ; of the other, the
line of insertion of the
squamo-costales, ib. I.
The co-ordinate effects

of the foregoing; mus-

o o

cles of the ribs and

Muscles of the ribs and scutes, Python, cxci. scutes produce deter-

minate movements, to

and fro, of the ribs, with alternate erection and depression of the
broad transverse ventral scutes.

The tympano-mandibular arch has unusual mobility in Ser-

xx. vol. i. pp. G9-72.

MYOLOGY OF EEPTILES.

227

pents : the long tympanic bone, fig. 97, 28, is suspended by its
extremity from that of the outstanding mastoid ; and besides the
movements of swinging to and fro to the extent allowed by the
loose articulations of the upper jaw, it is affected by the muscles
tendino- to divaricate the mandibular rami, as well as by a

O •'

muscle directly drawing its lower end outward. This latter re-
peats the levator tympanici of Fishes, fig. 134, 24 : but, with the
retrograde course of the ophidian tympanic, its levator has a
more posterior origin, viz. from the end of the mastoid, and is
inserted into the lower, instead of the upper, end of the tympanic.
To counteract these movements, we find a muscle answering
to the ( depressor tympani' of Fishes, fig. 136, 22, which arises
from the basi-occipito-sphenoid, fig. 146, m, and passes trans-
versely outward and backward to the lower end of the tym-
panic and co-articulated end of the mandible : it depresses the
tympanic and draws it and the articular part of the mandible
inwards.

Of the muscles which close the mouth, one, like the muscle /,
fig. 132, of the Shark, bears analogy to the masseter\ in the
absence of a zygoma, it arises from the post-frontal and contiguous
part of the ectopterygoid, fig. 145, e, passes backward, winding
round the tympano-mandibular joint, and is inserted into the
surangular and angular, as far forward as the dentary. In
venomous snakes its fascial origin spreads over the poison-bag,
ib. a. The temporalis,
ib. z, arises from the
side and spine of the
parietal, and descends
almost vertically, partly
covered by the mas-
seter, to be inserted into
the coronoid plate. The
post-temp or alls, ib. f,
arises from the fore part
of the mastoid and con-
tiguous part of the pa-
rietal, and descending
in front of the tympa-
nic is inserted into the coronoid ridge nearer to the joint of the
lower jaw.

The ( tympano-mandibular is? ib. g, which is analogous to the
digastricus, or its hinder belly in Mammals, arises from the back
part of the tympanic, and is inserted into that of the angular

Q 2

145

Muscles of the jaws, Crotalus. cs.cn.

228

ANAT01MY OF VERTEBRATES.

process of the mandible. From fascia attached to the neural
spines of some of the anterior vertebrae there extends a flattened
muscle, Heuro-inandibidaris, fig. 145, t, which unites with a smaller
strip from fascia connected with the ribs of those vertebrae,
costo-mandibularis, figs. 145, 147, ?/, to be inserted into the lower
border of the mandible. These muscles depress and retract the
lower jaw.

A powerful muscle, ectopteryyoideus, fig. 146, 7i, which in its
mandibular relations resembles the external pterygoid, advances

146

Muscles of the pterygo-palatine apparatus of the Crotalns. cxcu.

forward to the fore part of the ectopterygoid, and to the back part
of the maxillary in Python. In Crotalus it expands into a fascia,
spread over the pouch lodging the venom-fangs, preserving a
tract of tendinous strength for insertion into the lower part of the
hinder process of the maxillary. It cooperates with the erector
of the fang in fixing the moveable maxilla during the blow, and
retracts the fang on the relaxation of the erector. When its fore
part is the fixed point, the ectopterygoideus spreading its man-

MYOLOGY OF REPTILES.

229

147

dibular attachment over the articular capsule to the back part of
the angular process, protracts the lower jaw.

The entopterygoideus, fig. 145, k, is attached anteriorly to the
pterygoid bone, ib. 4, whence its fibres pass outward and back-
ward to the inner surface of the angular and surangular elements,
covered by the ectopterygoideus. It retracts and divaricates the
palato-pterygoid jaws, protracts and approximates the back parts
of the mandibular rami. The fore parts of those bones which,
through their loose elastic symphysial connection, yield laterally to
the pressure of the prey when seized, are brought together, after
it is swallowed, by an in-
termandibularis, answering
to 21, fig. 137, in fishes:
it is shown in fig. 147,
passing from the end of
one ramus to that of the
other, at v, v, with a me-
dian raphe, as in the my-
lohyoideus ; and sending a
slip v from each attach-
ment, which expands upon
the intermandibular inte-
gument, restoring and cor-

rugating it after its great
occasional stretching. In
this it is aided by a thin
layer of fibres internal to
and in close connection
with the insertion of the
costomandibularis exposed
by the outward reflection
of that muscle at fig.
147, a.

In Fishes the fore part
of the levator tympani, fig.
136, 22, is inserted into the

pterygoid. : berpents Mus,.k,s,lf th(. thlWitoftljertaul,,,uake.

the origin of the answer-
able part, presphenopteryyoidcus., is advanced forward to the pre-
sphenoid, whence its fibres, fig. 146, /, pass outward and backward
to their insertion into the pterygoid, 4, and ectopterygoid, 3, at
their junction. In protracting the pterygoid it pushes forward
the maxillary, rotating it outward in the Constrictors ; but, by

230 ANATOMY OF VERTEBRATES.

the modification of the bones peculiar to venomous serpents, as
shown at 3 and 2, fig. 146, the muscle rotates the short maxillary
vertically through the ectopterygoid, so as to bring the venom-
fang from the recumbent to the vertical position ready for the
blow.

The presphcnopalatine muscle arises from the side of the fore
part of the presphenoid and passes outward to its insertion along
the inner surface of the palatine. From the side of the pre-
sphenoid rises the small prespheno-vomerine muscle, fig. 146, v9
which sends forward a slender tendon to the half of the divided
vomer, and through that bone depresses and retracts the pre-
maxillary, ib. i, after the displacement of all the bones of the
mouth caused by the engulphing of the prey.

The hyoid arch is reduced to a pair of slender cartilaginous
ceratohyals, running forward, almost parallel, fig. 147, B, beneath
the sheath of the filamentary tongue, before their anterior mem-
branous union. The raphe of the muscles v and u, fig. 147, is so
far attached to the hyoid and lingual sheath, that by their con-
traction they raise the tongue after it has been pushed down : the
fibres of the costomandibularis, u, attached to the foremost part of
the mandible, through the same medial attachment protract the
lingual sheath; the posterior part of the costomandibularis can
retract the lingual sheath, and these actions are analogous to those
of the ' sternohyoid ' and ( geniohyoid ' muscles in higher verte-
brates. On reflecting the costomandibularis from the raphe out-
ward, the genioglossi are exposed : their antero-median attachment,
fig. 147, z', z' ', is to the raphe of the intermandibularis, v ; their
antero-lateral attachment, .z", is to the fore end of the mandibular
ramus. The muscle formed by their union, z, extends backward
along the lingual sheath to its extremity : it is the chief pro-
truder of the tongue. The retractors, answering to hyoglossi,
ib. A, arise from the hinder ends of the ceratohyals, run forward,
enter the lingual sheath, and seem to coalesce in forming the
main substance of the cylindrical tongue ; but they again separate
to terminate in its forked extremity. The fore part of the trachea
is closely connected with the lingual sheath, and advances so far
forward to terminate in the mouth, as to be subject to the stretch-
ings and displacements of the elastic floor of that cavity. A
special muscle, geniotrachealis, fig. 147, y, arises from the fore
end of the mandibular ramus, and passes inward and backward
to expand upon the sides of the fore part of the trachea. The
pair draw forward the glottis ; its retraction is effected through
the medium of the lingual sheath and its muscles.

MYOLOGY OF REPTILES. 231

There are small modifications of the muscles of the long anterior
outstretched ribs of the Cobra, fig. 46, pi, which sustain the
peculiar folds of integument forming the conspicuous ' hood ' of
that poisonous snake. These ribs are protracted or raised by the
levatores breviores, and by two sets of pretrahentes, one passing
over two ribs to the third behind, the others passing over one
rib to the second, and by the intercostales externi. The muscles
passing from the hood-ribs to the skin come off about four lines
from the head by a short tendon, the fleshy band extending
between one and two inches, outward and backward to its inser-
tion into the skin.

The muscular system of the trunk reaches, in Reptiles, its
maximum in Serpents ; it is reduced to a minimum in Tortoises :
yet, where it has to act on the only moveable part of the verte-
bral column of these slow and heavy house-bearers, it is specially
and in some parts largely developed.

Homology can seldom be determined or discerned, save in a
general way, in the fleshy parts of Chelonia ; as, e. g., that the
muscles upon or about the trunk-vertebra? answer to those so situ-
ated in lower or higher Vertebrates ; and that the primitive seg-
mental character of such muscles is still indicated by distinct and
successive attachments to a consecutive series of bony segments, as
is shown, e. g., in fig. 148, 37, 39, fig. 149, 27. Where a more
special determination has been attempted it has usually rested on
a similarity of attachment of one end of a muscle, with acknowledged
discrepancy at the other end ; as when Cuvier * compares 27, fig.
148, to the sacrolumbalis and lonyissimus dor si ; and when Bojanus2
gives the latter name to the portions of myocommas at the opposite
side of the back-bone, fig. 148, or calls the muscle, fig. 152, 91,
which arises from the pubis, the iliacus internus. It will be
understood, therefore, that in applying to the muscles of the Box-
tortoise (Emys Europaa), the names assigned to them by the
author of the exemplary and beautiful monograph3 from which
the illustrations, figs. 148 — 159, have been copied, they are to be
taken more or less in an arbitrary sense, and that the characters
of the muscles mainly exemplify the greater degree in which the
adaptive principle prevails over the archetypal one in the soft than
in the hard parts of the frame.

On the dorsal aspect of the vertebra? of the back, the muscular
system is restricted to the ( spinalis dorsi,' fig. 148, 39 ; it rises
from the neural and beginning of the costal plates, neural arch

1 xiii. i. p. 292. 2 xxxviii. 3 Ib.

232

ANATOMY OF VERTEBRATES.

148

and rib of the seventh to the third dorsal vertebra inclusive,
occupying the interspaces between those parts ; it is inserted
into the neural arch of the last cervical, and into the post-
zygapophysis of the next vertebra in advance.

The series of muscles called 'longus colli,' ib. 28, 28, com-
mences by the broad origin from the under part of the first and
second costal plates, and is continued by eight narrower slips
from the hypapophyses of the first dorsal, and seven antecedent
cervical vertebra. These fasciculi incline forward and inward,

overlapping each other, to
be inserted successively
into the parapophyses of
the eighth and lower part
of the centrum of the ante-
cedent cervicals, with in-
terposed sesamoids at the
sixth, fifth, and fourth ver-
tebrae ; the foremost inser-
tion being into the basi-
occipital.

Six or seven lateral por-
tions of cervical myocom-
mas, called inter transver-
sarii colli ; ib. 36, pass from
the diapophyses of the
eighth to the second cervi-
cals, and are inserted along
with the corresponding in-
sertions of the longus colli
from the sixth to the cen-
trum of the atlas, or odon-
toid. The intertransversarii
obliqui, figs. 148, 149, 37,
are four strips from the
diapophyses of the sixth,
fifth, fourth, and third vertebras, which pass forward and down-
ward to the parapophyses of the fourth, third, second, and first
cervicals respectively. There are interspinales between the
neural spines of the first three cervicals.

The transversalis cervicis, fig. 151, 33, arises from the post-
zygapophysis of the fifth, fourth, and third cervicals ; these blend
outwardly, and detach inwardly insertions to the postzygapo-
physes of the fourth, third, and second cervicals, and into the

Muscles of the dorsal, cervical, and occipital vertebra,
Etnys_Europa2a. xxxvin.

MYOLOGY OF REPTILES.

233

diapophysis of the atlas : the tendon so inserted is shown at 33,
fig. 148.

The complexus, fig. 148, 23, arises from the diapophyses of the
first three cervicals, and is inserted into the paroccipital : in
fig. 150, the hindmost origin of this muscle is marked 25.

The rectus capitis anticus lone/us, fig. 148, 29, arises from the
hypapophyses of the third and second cervicals, and is inserted
into the side of the basioccipital. The rectus capitis anticus
brevis, fig. 152, 30, arises from the atlantal hypapophysis, and is
inserted into the basioccipital. The rectus capitis posticus major,
fig. 148, 31, arises from the neural spines of the axis and atlas,
and is inserted into the paroccipital. The rectus capitis posticus
minor, ib. 31, arises from the neural arch and diapophysis of
the atlas, and is inserted into the base of the exoccipital.

The largest and most remarkable portions of muscular segments
of the trunk are those which are combined to effect the retraction
beneath the carapace of the head and neck. The retrahens

149

9 10

view iif trunk-muscles and deei'CT seated limlj-muscle?, L'mys Ewropcea. xxxvm.

capitis collique, figs. 149, 150, 27, arises by six fieshy fasciculi
from the neural arches and spines of the eighth to the fifth
dorsals inclusive ; these pass forward, blending together, and then
detach four tendinous insertions : of these, the anterior and
longest, as well as strongest, is into the basioccipital fossa ; the
other three are into the diapophyses of the fourth, fifth, and sixth
cervicals. It is not difficult to sever the part of the great re-
tractor connected with the cervical insertions, as a distinct muscle
from that inserted into the occiput. The biventer cervicis, figs.
150, 151, 24, arises from the neural spines of the fifth, fourth, and

234

ANATOMY OF VERTEBRATES.

third cervicals3 and is inserted into the same part of the occipital
vertebra.

The traclielomastoideus., fig. 150, 26, arises from the hypapophyses
of the third and second cervicals, and ascends obliquely to be
inserted into the mastoid.

The scalenus, fig. 150, 34, arises from the inner border of the
lower three-fourths of the scapula ; its fibres emerge as it
advances, and deliver strips of insertion to the diapophyses of the
eighth to the second cervical inclusive.

150

Side view of muscles of the trunk, head, and limbs, Emys Europcea. xxxvui.

The sternomastoideus , fig. 150, 22, arises from the middle of the
inner surface of the entosternum, and is inserted into the mastoid.

The diaphragmaticus, figs. 148, 149, 150, 42, 42, arises by three
sheets from the bodies of the fifth and fourth dorsals, and from
the rib of the third dorsal ; the two posterior unite to apply them-
selves and adhere to the mesial surface of the lung ; the third
sweeps over to the outer surface, 42, fig. 150, and 42, fig. 151, and
is reflected from its lower border upon the peritoneum.

The transversalis abdominis, figs. 150, 151, 41, arises along a
curved line on the inner surface of the fourth, fifth, sixth, and
seventh costal plates, extending from the end of the fourth to the
beginning of the seventh ; also by a separate fasciculus from the
eighth rib ; and by three slender tendons from near the cardinal
border of the hyposternal ; it is inserted by a broad tendinous
sheet into the mesial border of the same plastral element, which
is the homologue of the abdominal hremapophyses and spine
receiving the same insertion.

The obliquus externus, fig. 151, 40, arises from the inner side
of the. extremities of the last four costal plates, and adherent

MYOLOGY OF REPTILES.

235

marginal ones ; it is inserted along a sigmoid line extending from
the postero-external angle of the hyposternal to the middle of the
xiphisternal and by a special fasciculus and tendon into the lateral
process of the pubis.

The latissimus colli, figs. 151, 152, 21, consists of two parts ;
both are attached, above, to aponeuroses connecting them with
the cervical diapophyses ; the fibres of the posterior division,
fig. 149, 21 a, pass down and rather backward, over the muscles of
the base of the neck, and are inserted into the midline of the

151

ifli,

Side view of superficial muscles of trunk, head and limbs, Emys Europa'a. xxxvin.

epi- and ento-sternals : the fibres of the longer anterior portion
sweep transversely across the lateral and lower parts of the neck,
fig. 152, 21.

The extensor caudce, fig. 151, 47, includes the neural portions of
the myocominas of this region from its base, where the foremost
has a sacral origin, to near the tip. The flexor caudce, lateralis,
ib. 48, consists of the lateral parts of the same muscular seg-
ments. The flexor caudce inferior is shown at ib. 49 : \\\e flexor
caudce lumbalis in fig. 150, 50: the flexor caudce obturatorius in
figs. 151 and 156, 51.

The following are muscles of the tympano-mandibular arch.

The temporalis, figs. 151, 152, i, arises from the parietal and
superoccipital spines, and is inserted into the coronoid part of the
mandible. The pteryy 'oideus, figs. 148, 149, 152, 4, arises from
the outer surface of the pterygoid, and is inserted into the internal
tuberosity of the articular element of the mandible. The apertor
oris, or digastricus, figs. 150, 153, 3, arises from the mastoid, and
is inserted into the angular process of the mandible. The dilatator

236

ANATOMY OF VERTEBRATES.

, figs. 148, 149, 4, arises from the mastoid, and is inserted
into the postero-inferior angle of the tympanic and into the begin-
ning: of the eustachian tube.

o

The following arc muscles of the hyoidean arch and appen-
dages. The mylohyoideus3fLg. 153, 13, extends transversely between
the mandibular raini, and is attached to the hyoid by its median

lf>2

Muscles and viscera in situ, from Lelow, Emys Europcca. XXXVIII.

raphe. The omohyoideus, figs. 150, 152, 14, arises from the
coracoid, and is inserted into the basi-, cerato-, and thyro-hyals.
The geniohyoideus, figs. 150, 152, 15, 16, arises from the back part
of the symphysis mandibulse ; is united to its fellow as far back
as the basihyal, and there diverges to its insertion into the cera-
tohyal. The liijomaxillaris, fig. 150, IG, arises from the articular
element and is inserted into the ceratohyal. The geniofjlossus.

MYOLOGY OF REPTILES.

237

fig. 152, 17, arises from the dentary and is inserted into the outer
angle of the basihyal and into its triangular appendage. The
hyoglossus, fig. 151, 18, passes from the basihyal and its appendage
to the ceratohyal, which it covers on the left side of fig. 152.
The proper muscles of the scapular arch are very few3 by

153

•

Muscles of trunk and limbs, from below, Emys Europcea. xxxviri.

reason of its fixity, although it gives origin to many which act
upon other more moveable parts.

The subclavius, fig. 148, 59, arises from the under part of the
first costal plate, and is inserted into the suprascapula and con-
tiguous part of the scapula. The serratus maynus, fig. 152, 75,

238 ANATOMY OF VERTEBRATES.

fig. 153, 57, arises from part of the outer margins of the first and
second costal plates and from the same margin of the cardinal
process of the hyosternal and contiguous part of the hyposternal :
it is inserted into the upper surface of the coracoid. The latis-
simus dor si, fig. 152, 58, arises from the inner surface of the first
costal plate, and is inserted into the neck of the humerus. The
deltoides, fig. 153, GO, arises by three heads ; one, ib. GO a, from the
inner surface of the ento- and epi-sternals ; another, ib. GO b, from
the clavicular process of the scapula; and the third from the
angle between that process and the body of the scapula : it is
inserted into the lesser tuberosity of the humerus. The claviculo-
brachialis, fig. 152, 61, arises from the clavicle, and is inserted into
the outer tuberosity of the humerus. The subcoracoideus, fig. 153,
62, arises from the under surface of the coracoid, and is inserted
into the inner tuberosity of the humerus. The super cor acoideus,
figs. 151, 152, 64, arises from the upper surface of the coracoid,
and is inserted into the outer tuberosity of the humerus. The
teres minor., fig. 152, 65, arises from the posterior border of the
coracoid and is inserted into the pit between the humeral tuberosi-
ties, with an attachment to the capsule of the shoulder-joint.
The triceps brachii, figs. 152, 153, 65 a c, arises from above the
glenoid margin of the scapula, 65 a, and from the humerus, 65 c :
it is inserted into the olecranon. The biceps brachii, fig. 153, 66,
arises from the back part of the coracoid, ee" : it is inserted,
with the brachialis internus, into the ulna, and by a slender tendon,
66 «, into the radius. The brachialis internus, fig. 152, 67,
arises from the inner tuberosity and concave surface of the
humerus and is inserted into the proximal ends of both the radius
and ulna. The palmaris, figs. 150, 153, 68, arises from the outer
condyle of the humerus, and is inserted into the palmar apoiieu-
rosis. The flexor sublimis, figs. 151, 153, 69, arises from the outer
condyle of the humerus and is inserted into the metacarpal of the
fifth digit and into the tendon of the ulnaris internus. The flexor
profundus, figs. 150, 151, 70, arises from the concave side of the
ulna, and is inserted into an aponeurosis splitting into five tendons
for the last phalanges of the five digits. The pronator teres arises
from the outer condyle of the humerus : its insertion, shown in
fig. 154, 71, is into the radial side of the carpus, with that of the
pronator quadratics , ib. 72. The ulnaris internus, figs. 151, 153,

73, arises from the tubercle above the outer angle of the humerus,
and is inserted into the ulnar side of the carpus and contiguous
end of the fifth metacarpal. The ulnaris externus, figs. 151, 152,

74, arises from the tubercle above the inner condyle of the

MYOLOGY OF REPTILES.

239

154

Muscles of fore foot, Emys
Enropcea. XXXYIII.

humerus, and is inserted into the carpus near the ulna. The
radialis interims, fig. 154, 75, arises from the tuberosity above the
outer condyle of the humerus, and is inserted into the distal end
of the radius. The radialis externus lone/us,
fig. 152, 76, arises from the tuberosity above
the internal humeral condyle, and is inserted
into the radial margin of the carpus ; the
muscle converging towards 76, in the same
figure, is the radialis interims. The radialis
externus brevis, fig. 150, 77, arises from the
tuberosity above the internal humeral condyle,
and is inserted into the back of the carpus.
The supinator lone/us, figs. 152, 153, 78, arises
above the internal humeral condyle, and is in-
serted into the radial side of the carpus and
the same border of the radius. The supinator
brevis, fig. 152, 79, arises from the tubercle
above the inner humeral condyle, and is in-
serted into the back of the radius. The extensor
communis digitorum, fig. 151, so, arises from the
tuberosity above the inner humeral condyle, and is inserted into
the five metacarpals. The extensor proprius pollicis, fig. 150, 8J,
arises from the ulna, and is inserted into the metacarpal of the
pollex. The extensor proprius diyiti minimi., fig. 152, 82, arises
from the ulnar side of the carpus and is inserted into the meta-
carpal and first phalanx of the fifth digit. The extensores breves
diyitorum, figs. 151, 153, 83, arise from the back of the carpus
and metacarpus, and are inserted into the distal phalanges. The
abductor pollicis, fig. 153, 84, arises from the
inner side of the carpus, and is inserted into
the first phalanx of the pollex. The fiexores
breves digitorum, fig. 153, 88, arise from the
palmar sesamoids and fascia, and are inserted
into the phalanges. There are also, interossei,
both external and internal ; the latter are shown
at 90, figs. 154 and 155. The adductores digi-
torum, fig. 155, 86, are limited to the first,
second, and third fingers, to the metacarpals of
which the muscles incline, radiad, from the
second row of carpals.

The following are the muscles of the pelvic
arch and limb : -

The attr aliens pelvim, figs. 150, 153, 43, arises from contiguous

155

Muscles of fore-foot,
Emys Europcea. xxxvm.

240

ANATOMY OF VERTEBRATES.

156

Muscles of pelvis, Emys Europaa. xxxvm.

parts of the hypo- and xiphi-sternals, and is inserted into the
outer process of the; pubis. The retro lie us pdvim, ib. 44, arises
from the posterior half of the xiphisternal, and has a similar in-
sertion. More direct retractors of
the pelvis are the muscle called
flexor caudce obturator ius, which
arises from the caudal haemapo-
physes, and is inserted into the
front border of the obturator
foramen ; and the flexor cauda>
ischiadicus, ib. 52, with a similar
origin, but inserted into the ischial
symphysis. The pectineus (iliacus
interims, Boj.}, figs. 150, 152, 153, 91, arises from the upper surface
and outer process of the pubis, and is inserted into the inner tro-
chanter of the femur. Its insertion receives also a small fasciculus
from the ninth dorsal centrum, and the tenth pleurapophysis, which
may represent the psoas. A glutens, figs. 150, 151, 93, arises from
the ninth and tenth pleurapophyses, and from the ilium. A second
glutaus, figs. 150, 151, 152, 94, arises from the sacral and anterior
caudal pleurapophyses. Both are inserted into the outer trochanter,
together with a fasciculus, representing an obturator ius, from the
inner surface of the obturator fascia, and from the ischial symphysis.
The triceps adductor, figs. 152, 153, 97, arises from the inferior sur-
face of the pubis, and is inserted into the inner trochanter, crossed
by the ischio-pubic ligament. The quadratu$, fig. 152, 98, arises
from the tuber ischii, and is inserted into the back interspace of
the trochanters. The rectus femoris, fig. 151, 99, arises by a bifid
tendon from the upper end of the ilium, and is inserted, with the
vastus externus, fig. 150, TOU, vastus internus, fig. 151, 101, crurceus,
fig. 152, 102, and sartorius, fig. 153, 106, into the fore-part of the
head of the tibia. The semitendinosus, figs. 150, 152, 104, has
three origins, one from the back part of the upper end of the
ilium and contiguous part of the sacrum, a second from the tuber
ischia, a third from the back part of the ischial symphysis ; they
join a common tendon which passes behind the knee-joint, and
then bifurcates to be inserted into the outer proximal tuberosity
of the tibia, and into the gastrocnemius, 1 1 4 b. The semimem-
branosus, fig. 153, 105, has two origins, one, 105 «, from the first
caudal vertebra ; the other, 105 b, from the tuber ischii and ischio-
pubic ligament. It is inserted into the upper part of the tibia.
The yracilis, fig. 153, 107, arises from the middle of ischiopubic
ligament, and is inserted into the upper and outer part of the
tibia. The extensor communis dicjitorum, fig. 151, 108, arises from

MYOLOGY OF REPTILES. 241

the ridge anterior to the outer femoral condyle, and is inserted
into the distal phalanx of the hallux and into the proximal phalanges
of the other toes. The tibialis anticus, figs. 150, 153, 109, arises
from the antero-internal margin of the tibia, and is inserted into
the tibial side of the tarsus and first metatarsal. The peroneus,
fig. 151, 10, arises from the fore part of the fibula, and is inserted
into the cuboid, and fourth and fifth rnetatarsals. The digit-
extensor es breves, figs. 149, 151, in, arise from the dorsal aspect
of the second row of tarsals, metatarsals, and proximal phalanges,
and are inserted into the ungual phalanges. The extensor proprius
hallucis, figs. 152, 153, 112, arises from the lower end of the
fibula, and is inserted by a bifurcate tendon into the sides of the
first phalanx of the hallux. The abductor hallucis arises from the
tendon of the tibialis anticus, and from the first metatarsal, and is
inserted into the base of the proximal phalanx of the hallux.
The f/astrocnemius, figs. 151, 153, iu, has two heads, one, 114#,
from the outer femoral condyle; the other, iuZ», from the outer
margin of the tibia, and this receives also the tendon from the
semitendinosus : it is inserted into the calcaneum and expanded
metatarsal of the fifth digit, and is continued into the plantar
fascia. The plantaris, fig. 153, 115, arises above the outer femoral
condyle, and coalesces with the soleus, fig. 152, lie, and the digiti-
flexor longus, 117, to terminate in a common aponeurosis, attached
to both sides of the tarsus, and dividing, as in fig. 157, 117, to be
inserted into the ungual phalanges. The digitiflexores breves.,
fig. 157, us, are four in number, arise from the tarsus, and are

157

Muscles of hind-foot, Emys Europcea. xxxvin.

inserted into the sides of the middle phalanx, and by a slender
tendon into the ungual phalanx, of the four outer toes. The
tibialis posticus, figs. 152, 158, 119, arises from the inner and back
part of the fibula, and expands into an aponeurosis, including a
sesamoid, which divides to be inserted into the second row of
tarsals, and the metatarsals of the hallux and fifth digits. The
YOL. i. R

242 ANATOMY OF VERTEBRATES

Interosseus cruris, fig. 158, 120, extends obliquely between the
opposite margins of the leg-bones. The interossei diyitorum

158

Muscles of hind-foot, Emys Europcea. xxxvin.

dor sales, are shown at 122, and those of the plantar surface at 123,
fig. 158.

The highest faculty of terrestrial locomotion in the reptilian
class, is manifested by the saltatory batrachians.

In the hind limb of the froaj there is a muscle which extends

o

from the diapophysis of the third vertebra to the ilium, which it
tends to protract, and acting from which it may slightly bend the
back. The ectogluteus receives an accessory strip from the
coccygeal style. The mesogluteus is a strong muscle. The ento-
gluteus and iliacus are united. The obturator externus has a semi-
circular form. The quadratus femoris is in two strata. There
are two pectinei and four adductores femoris. The extensor cruris
consists of a vastus interims and a vastus externus with a coalesced
crurcBus ; there is no rectus femoris. The flexor cruris has but
one head or origin from the lower and back part of the ilium.
The semitendinosus has two heads, one from the fore part, the
other from the back part of the ischio-pubic symphysis. The
semimembranosus and gracilis have the usual attachments. The
sartorius resembles the rectus in its position and course in front of
the thigh : it is united to the tensor fascice lat(E. The gastro-
cnemius is represented by its external moiety, which is so large as
to give the appearance of a f calf ' to the leg: its tendon glides
behind the tibio-tarsal joint, and expands as it descends along
the tarsal segment into a plantar fascia. The tibialis anticus
arises by a strong tendon from the femur, and divides at the
middle of the tibia into a fascicle inserted into the astragalus, and

O '

a second inserted into the calcaneum ; in both at the proximal
. end. A cruro-tibialis rises from the lower end of the femur, and

LOCOMOTION OF FISHES. 243

is inserted into the fore part of the lower three-fourths of the
tibia. The tibialis posticus, with the usual origin, is inserted into
the astragalus, fig. 44, a. A peroneus arises from the outer
femoral condyle, and from the outer side of the leg-bone ; its
tendon bifurcates, one part being attached to the outer malleolus,
the other to the base of the calcaneum, ib. d. An extensor lonyits
digitorum arises from the outer malleolus, passes between the two
portions of the tibialis anticus, and, after sending an insertion to
the astragalus, is continued to the three middle toes. The
extensor brevis arises from the whole length of the calcaneum, and
divides into six parts, an external to the metatarsal of the hallux,
an internal to that of the minimus, and the intermediate four to
the phalanges of the four outer toes ; these unite with the tendons
of interossei externi, to which might be referred the extensor of the
hallux. Both this toe and the outermost have their abductors
for spreading the web. There is also an abductor of the ento-
cuneiform, fig. 44, ci, which resembles a small accessory digit.
The plantar aponeurosis, which receives a fleshy fascicle from the
tibio-tarsal capsule, gives origin to a muscle inserted into the
whole length of the astragalus, divides into six fascicles, which
form sheaths for the flexor tendons, two of which belong to the

o

fourth toe ; and, finally, is resolved into three tendons, of which
two go to the fifth toe, and one to the fourth. Thejlexor longus
digitorum arises from the tibio-tarsal capsule, and is expended
upon the three outer toes. The several insertions of the fore-
going digital flexors give one tendon for the lingual phalanx, and
two for the other phalanges.

§ 48. Locomotion of Fishes.- -Hitherto the osteology and myo-
logy of the cold-blooded Vertebrates have been considered chiefly
from a homological point of view. I have aimed at relieving the
dryness of descriptive detail, and at connecting the multifarious
particulars of this difficult part of Comparative Anatomy in
natural order, so as to be easily retained in the memory, by
referring to the relations which the bones and muscles of Fishes
and Reptiles bear to the general plan of vertebrate organisation,
and by indicating their analogies to transitory states of structure
in the embryo of higher animals, and to those answerable con-
ditions of the mature skeleton which, in longer lapse of time,
have successively prevailed and passed away in the generations
of species that have left recognisable remains in the superimposed
strata of the earth's crust.

To determine the parts of the vertebrate structure which are
most constant - - to trace their general, serial, and special homo-

R 2

244 ANATOMY OF VERTEBRATES.

logics, under all the various modifications by which they are
adapted to the several modes and spheres and grades of existence
of the different species- -should be the great aim of anatomical
science ; as being that which reduces its facts to the most natural
order, and their exposition to the simplest expressions.

It is impossible, in pursuing the requisite comparison upward
through the higher organised classes, not to recognise resemblances
between the ultimate states and forms of ichthyic organs, and the
transitory condition of the same parts, in the higher species.
But these resemblances have been sometimes overstated, or pre-
sented under unqualified metaphorical expressions, calculated to
mislead the student and to obstruct the attainment of complete
conceptions of their nature. We should lose most valuable fruits
of anatomical study were we to limit the application of its facts
to the elucidation of the unity of the vertebrate type of organi-
sation, or if we were to rest satisfied with the detection of the
analogies between the embryos of higher and the adults of lower
species in the scale of being. We must go further, and in a
different direction, to gain a view of the fruitful physiological
principle of the relation of each adaptation to its appropriate
function, if we would avoid the danger of resting in speculations
on the mode of operation of derivative secondary causes, and of
blinding the mental vision to the manifestations of Design which

O o

the various forms of the Animal Creation offer to our contem-
plation.

To revert, then, to the skeleton of Fishes, with a view to the
teleological application of the facts determined by the study of
this complex modification of the animal framework. No doubt
there is analogy between the cartilaginous state of the endo-
skeleton of Cuvier's Chondropterygians, and that of the same
part in the embryos of air-breathing Vertebrates ; but why the
gristly skeleton should be, as it commonly has been pronounced to
be, absolutely or teleologically inferior to the bony one is not so
obvious. The ordinary course of age, decrepitude, and decay of
the living body is associated with a progressive accumulation of
earthy and inorganic particles, gradually impeding and stiffening
the movements, and finally stopping the play of the vital machine.
And I know not why a flexible vascular animal substance should
be supposed to be raised in the histological scale because it has
become impregnated, and as it were petrified, by the abundant
intus-susception of earthy salts in its areolar tissue. It is perfectly
intelligible that this accelerated progress to the inorganic state
may be requisite for some special office of such calcified parts in

LOCOMOTION OF FISHES. 245

the individual economy ; but not, therefore, that it is an absolute
elevation of such parts in the series of animal tissues.

It has been deemed no mean result of Comparative Anatomy
to have pointed out the analogy between the shark's skeleton and
that of the human embryo, in their histological conditions ; and
no doubt it is a very interesting one. But the perception of
such analogy is not incompatible with the endeavour to gain
insight into the purpose of the Creator, in so arresting the ordi-
nary course of osteogeny in the highly organised fish. Xo law of
human intelligence condemns it to restrict its cognizance of the

o o

phenomenon, as solely those of an unfinished, incomplete stage of
an hypothetical serial developement of organic forms.

The predaceous Sharks are the most active and vigorous of
fishes ; like birds of prey, they soar, as it were, in the upper
regions of their atmosphere, and, without any aid from a modified
respiratory apparatus, devoid of an air-bladder, they habitually
maintain themselves near the surface of the sea, by the action of
their large and muscular fins. The gristly skeleton is in pro-
spective harmony with this mode and sphere of life, and we shall
subsequently find as well-marked modifications of the digestive
and other systems of the shark, by which the body is rendered as
light, and the space which encroaches on the muscular system as
small, as might be compatible with those actions. Besides, light-
ness, toughness, and elasticity are the qualities of the skeleton
most essential to the shark : to yield to the contraction of the
lateral inflectors, and aid in the recoil, are the functions which the
spine is mainly required to fulfil in the act of locomotion, and to
which its alternating elastic balls of fluid, and semi-ossified bi-
concave vertebras, so admirably adapt it. To have had their entire
skeleton consolidated and loaded with earthy matter would have
proved an encumbrance altogether at variance with the offices
which the Sharks are appointed to fulfil in the economy of the
great deep.

I suspect that those who see in a modification of the skeleton,
so beautifully adapted to the exigencies of the highest organised
of fishes, nothing more than a foreshowing of the cartilaginous

' o o o

condition of the reptilian embryo in an enormous tadpole, arrested
at an incomplete stage of typical developement, have been misled
by the common name given to the Plagiostomous fishes. The
animal basis of the shark's skeleton is not cartilage ; it is not that
consolidated jelly which forms the basis of the bones of higher
Vertebrates: it has more resemblance to mucus; it requires 1000
times its weight of boiling water for its solution, and is neither

246 ANATOMY OF VERTEBRATES.

precipitated by infusion of galls, nor yields any gelatine upon
evaporation.

In like manner the modifications of the dermal skeleton of
fishes have been viewed too exclusively in a retrospective relation
with the prevalent character of the skeleton of the Invertebrate
animals. Doubtless it is in the lowest class of Vertebrata that
the examples of great and exclusive developement of the exo-
skeleton are most numerous ; but some anatomists, in their zeal
to trace the serial progression of animal forms, seem to have lost
sight of all the vertebrate instances of the bony dermal skeleton,
except those presented by the ganoid and placoid fishes. He
must have sunk to the low conception that nature had been
limited to a certain allowance of the salts of lime in the formation
of each animal's skeleton, who could affirm that in the higher
Vertebrata ' the internal articulated skeleton takes all the earthy
matter for its consolidation,' l forgetting that the bulky Glyptodon,
and its diminutive congeners the Armadillos, have their internal
skeleton as fully developed and as completely ossified as in any
other mammal. The organising energies which perfect and
strengthen the osseous internal skeleton do not destroy nor in
any degree diminish the tendency to calcareous depositions on the
surface, when the habits and sphere of life of the warm-blooded
quadruped require a strong defensive covering from that source.
Neither do we find in the cold-blooded series that the endo-
skeleton of the alligator or scelidosaur was consolidated by a
minor amount of earthy matter than that of the naked frog or
horn-scaled lizard.

The moment that the observations of the naturalist bring to
light the mode of life of any of those fishes which are said to
retain an unusual proportion of the external shell of the Inverte-
brata, we are in a condition to appreciate the adaptation of that
external defensive covering to such mode of life. The Sturgeons,
ti.r example, were designed to be the scavengers of the great
rivers ; they swim low, grovel along the bottom, feeding, in
shoals, on the decomposing animal and vegetable substances
which are hurried down with the debris of the continents drained
by those rapid currents ; thus they are ever busied reconverting
the substances, which otherwise would tend to corrupt the ocean,
into living organised matter. These fishes are, therefore, duly
weighted by a ballast of dense dermal osseous plates, not scattered
at random over their surface, but regularly arranged, as the
seaman knows how ballast should be, in orderly series along the

1 xxvn. p. 527.

LOCOMOTION OF FISHES. -247

middle and at the sides of the body. The protection against the
water-logged timber and stones hurried along their feeding
grounds, which the sturgeons derive from their scale-armour,
renders needless the ossification of the cartilaginous case of the
brain or other parts of the endoskeleton ; and the weight of the
armour requires that endoskeleton to be kept as light as may be
compatible with its elastic property and other functions. The
sturgeons are further adjusted to their place in the liquid element,
and endowed with the power of changing their position and rising
to the surface, by a large air-bladder.

These teleological interpretations of the dermal bony plates
may give some insight into the habits and conditions of existence
of those Ganoid and heavily-protected Placoid Fishes which so
predominated in the earlier periods of animal life in our planet,
which Ganoids and Placoids have hitherto been viewed almost
exclusively by the light of the analogy of an embryonic f Age of
Fishes,' or explained as arrested stages in the transmutation of
Crustacea. I long ago demonstrated that both placoid plates and
ganoid scales, in the extinct (Lepidotus1^) as well as existing
(Lepidosteus) fishes, differed from the superficial shells of the
Invertebrata2 in presenting the same organisation for growth and
repair, the same essential microscopic structure, as the ossified
parts of the endoskeleton which they serve to protect.

The Coccosteus, fig. 127, of the Old Red Sandstone, like the
Pimelodus of the Ganges, had a half suit of such organised

^j C- }

armour ; and, as Hugh Miller 3 suggests, the habits of the modern
sheat-fish may have been foreshown in primeval times by the
placoganoid, burying the undefended part of its body in the mud,
and exposing only its helm and cuirass, to arrest, as they passed,
the smaller animals on which it preyed.

Nevertheless, the degree in which the exoskeleton predominates
over the endoskeleton as we penetrate into past time, descending
into the fossiliferous strata of the earth for evidence of ancient
life, is highly interesting and suggestive.

At the present day only two lepidoganoid genera of fishes are
known- -the Lepidosteus of North America, and the Polypterus of
Africa- -both restricted to fresh waters. Other existing fishes of
cognate organisation (Amia, Sudis, e. g.) have soluble and flexible
scales. As we descend to the older tertiary beds the number of
Lepidoganoids increases, their geographical relations expand, and
their sphere of life embraces the salt waters of the ocean. At
the present day the placoganoid and placoid, or plagiostomous,

1 v. p. 14. 2 xxvn. p. 337. 3 cxcvi. p. 288.

248 ANATOMY OF VERTEBRATES.

fishes, form a small minority of the class. In the chalk forma-
tions the number of the species of Placoids and Ganoids rapidly
increases, and soon preponderates ; in all the older fossiliferous
strata they exclusively represent the class of Fishes. The pre-
dominance of osseous matter deposited in the tegumentary system
in these ancient extinct Fishes is not unfrequently accompanied
by indications of a semi-cartilaginous state of the endoskeleton,
like that in the Lepidosiren of the present day ; the total absence
of any trace of vertebral centres, and the vacant tract, where they
should have been, between the bases of the neur- and hgem-
apophyses which have been little disturbed, as in fig. 127, show
plainly enough that the primitive gelatinous notochord has been
persistent.1 In not one of the extinct Fishes of the Devonian
and Silurian systems has a vertebral centrum been discovered ;
but the enamelled dermal osseous scales and plates are richly
developed, and most remarkable for their beautiful and varied
external sculpturing, and often for their great size.

In the mesozoic strata ganoid species exhibit a progressive
expanse and downward growth of the neurapophyses, converting
the notochordal capsule into distinct bony segments ; the terminal
cups of bone are subsequently added, and the centrum is completed.

At the present day the Lepidosiren repeats the notochordal con-
dition of the endoskeleton, but without the compensating ganoid or
placoid developements of the skin; and the Sheat-fishes {Siluridce}
combine the large tuberculated osseous dermal plates with a well
ossified internal skeleton. The existing sturgeons alone manifest
contrasted conditions of the endo- and exo-skeletons, like those in
the ancient placoganoids ; but what is now a rare and exceptional
instance of analogy to the testaceous and crustaceous Inverte-
brates was the rule in the first-born fishes of our globe.
Those fishes, which from the determination of the ossifying
energies to the endoskeleton have been termed Teleostei, consti-
tute the bulk of the tertiary and existing species of this class.
But gradations of endoskeletal ossification are still indicated.
A great proportion of the primitive cartilage is retained in the
skull of many of the Teleostei, the Salmon and Pike, for example ;
and the greater proportion of the animal to the earthy matter in
all the bones, their coarse texture, the radiating fibres of the flat
cranial bones, and the general absence of dentated sutures, are
characters in all Osseous Fishes, which remind the Anthropotomist

of transitional ones in the human foetus ; but the liijht of teleo-

7 ~

1 See also the beautiful illustration of this fact in the Microdus radiatus, No. 626,
of the Hunterian Series of Fossil Fishes in the Museum of the London College of
Surgeons; cxcm. p. 155.

LOCOMOTION OF FISHES. 249

logy demonstrates the perfection of such conditions, in relation to
the atmosphere and movements of the Fish. It is generally in
fresh-water abdominal Fishes that the semi-osseous condition of
the skull is found, and the diminution of the quantity of heavy
earthy particles may be connected with the less dense quality of
their medium, as compared with sea-water, and with the usually
more posterior position of the ventral fins.

In the form of a fish, the head is disproportionately large, as it
is in the mammalian embryo. But the head of a fish must needs be
large to meet and overcome the resistance of the fluid, in the
mode most favourable for rapid progression : it must therefore
grow with the growth of the fish. Hence the large cranial bones
always show the radiating osseous spiculas in their clear circum-
ference, which is the active seat of growth ; hence the number of
overlapping squamous sutures, which least oppose the progressive
extension of the bones. The cranial cavity expands with the
expansion of the head : the absorbents remove from within as the
arteries build up from without ; but the brain undergoes no cor-
responding increase ; it lies at the bottom of its capacious chamber,
which is principally occupied by a loose cellular tissue, situated,
like the arachnoid, between the pia mater and the dura mater, and
having its cells filled with an oily fluid, or sometimes, as in the
Sturgeon, by a compact fat,1 Now, this condition of the en-
velopes of the brain is not only, like the fibrous tissue and
squamous sutures of the ever-growing cranial bones, related to
the requisite proportions of the fore-part of the fish for facilita-
ting its progressive motion, but it is one which no embryo of a
higher animal ever presents : it is as peculiarly piscine, as it is
expressly adapted to the exigencies of the fish.

It has been held that confluence of distinct bones is a consequence
of high circulating and respiratory energies ; yet the anchyloses
of the superoccipital, parietal, and frontal above the cranium, and
of the basi-occipital, basi-sphenoid, and pre-sphenoid below the
cranium, in Lepidosiren, and the constant confluence of the basi-
and pre-sphenoids in all bony fishes, disprove the constancy of the
supposed relationship, and lead us to look for other explanations
of such coalescence of primitively or essentially distinct bones.
We shall find a final cause for the rapid consolidation and union
of the elongated bodies of the two middle cranial vertebra? of

o

Fishes in the necessity for strength in the basis of that part of
the skull, from the sides of which the large and heavy mandibular
and hyoid arches and their appendages are to be suspended, and

1 XXIIL t. i. p. 309.

250 ANATOMY OF VERTEBRATES.

to swing freely to and fro. The posterior and anterior sphenoids
continue distinct bones in all Mammals during a period of life at
which they form one continuous bone in Fishes.

The loose connections of most of the bones of the face may
likewise remind the homologist of their condition in the im-
perfectly developed skull of the embryos of higher animals ; but
this condition is especially subservient to the peculiar and ex-
tensive movements of the jaws, and of the bones connected with
the hyoid and branchial apparatus.

Not any of the limbs, properly so called, of Fishes, are pre-
hensile ; the mouth may be propelled and guided by them to the
food, but the act of seizing must be performed by the jaws.
Hence in many fishes both upper and lower maxillary bones enjoy
movements of protraction and retraction, as well as of opening
and shutting. The firm connections of the upper jaw, and wedged
fixity of the bone suspending the under jaw, which characterise
the higher Reptiles and Mammals, would be imperfections in the
Fish ; in which, therefore, such characters are not only absent,
but special developement in the opposite direction not unfre-
quently goes so far as to produce the most admirable mechanical
adjustments of the maxillary apparatus, compensating for the
absence of hands and arms, like those which have been exemplified
in the instance of the Epibulus insidiator.1 We must guard our-
selves, however, from inferring absolute superiority of structure
from apparent complexity. The lower jaw of fishes might at first
view seem more complex than that of man, because it consists of
a greater number of pieces, each ramus being composed of two or
three, and sometimes more separate bones. But, by parity of
reasoning, the dental system of that jaw might be regarded as
more complex, because it supports often three times, or ten times,
perhaps fifty times, the number of teeth which are found in the
human jaw. We here perceive, however, only an illustration of
the law of vegetative repetition as the character of inferior organ-
isms ; and we may view in the same light the multiplication of
pieces of which the supporting pedicle of the jaw is composed in
Fishes. But the great size and the double gleiioid or trochlear
articulation of that pedicle, are developemeiits beyond, and in
advance of the condition of the bones supporting the lower jaw
in Mammals, and relate both to the increase of the capacity of the
mouth in Fishes for the lodgment of the great hyoid and branchial
apparatus, and to the support of the opercula or doors which open
and close the branchial chambers. The division of the long

1 p. 119, fig. 87.

LOCOMOTION OF FISHES. 251

tympanic pedicle of Osseous Fishes into several partly overlapping
pieces adds to its strength, and by permitting a slight elastic
bending of the whole diminishes the liability to fracture. The
enormous size, moreover, of the tynipano-mandibular arch, and of
its diverging appendages, contributes to ensure that proportion of
the head to the trunk which is best adapted for the progressive
motion of the fish through the water. But without the admission
and appreciation of these pre-ordained adaptations to special exi-
gencies in the skeleton of Fishes, the superior strength and
complex developement of the tympanic pedicle and its appendages
would be inexplicable and unintelligible in this lowest and first
created class of Vertebrate animals.

All writers on Animal Mechanics have shown how admirably
the whole form of the fish is adapted to the element in which it
lives and moves : the viscera are packed in a small compass, in a
cavity brought forwards close to the head ; and whilst the conse-
quent abrogation of the neck gives the advantage of a more fixed
and resisting connection of the head to the trunk, a greater pro-
portion of the trunk behind is left free for the developement and
allocation of the muscular masses which are to move the tail. In
the caudal, which is usually the longest, portion of the trunk,
transverse processes cease to be developed, whilst dermal and
intercalary spines shoot out from the middle line above and below,
and give the vertically extended, compressed form, most efficient
for the lateral strokes, by the rapid alternation of which the fish
is propelled forwards in the diagonal, between the direction of
those forces. The advantage of the bi-concave form of vertebra
with intervening elastic capsules of gelatinous fluid, in effecting a
combination of the resilient with the muscular power, is still more
obvious in the Bony Fishes than in the Shark.

The normal character of Ichthyic myology shows itself in the
vast proportion of the vegetatively-repeated myocomnias, corre-
sponding with the vertebral segments, as compared with the
superadded system of muscles subservient to the action of their
diverging appendages : but this condition, which, inasmuch as it
deviates so little from the fundamental type, throws so much light
upon the essential nature and homologies of the muscles of the
Vertebrata, is not less admirably and expressly adapted to the
habits and medium of existence of the Fish. The interlocked
myocommas of the trunk constitute, physiologically, two great
lateral muscular masses, adapted by their attachments, and
especially by those of the anterior and posterior ends, to bend
vigorously from side to side, with the whole force of their alter-

252 ANATOMY OF VERTEBRATES,

nating antagonistic contractions, the caudal moiety of the trunk,
producing that double lash of the tail by which the fish darts
forwards with such velocity. When the lateral muscles are more
violently contracted, so as to bend the whole trunk, the recoil
may even raise and propel the fish some distance from its native
element : thus the salmon overleaps the roaring cataract wThich
opposes its migration to the shallow sources whither an irresistible
instinct impels it to the business of spawning ; and thus the
flying-fish, in the extremity of danger, baffles its pursuer by
springing aloft, and prolongs its oblique course through the air
by the aid of its outspread pectorals. When the anterior por-
tions of the great lateral masses act from the trunk as a fixed
point upon the head, they move it rapidly and forcibly from side
to side : in this way the Siluri deal severe blows with their out-
stretched serrated pectoral spines ; thus the Percoid and Cottoid
Fishes strike with their opercular spines ; and so likewise may
the Saw-fish (Pristis) and Sword-fish (Xiphias) wield their for-
midable weapons, although their deadly cut or thrust is commonly
delivered with the whole impetus of the onward course, the head
being rigidly fixed upon the trunk.

The supracarinales, combining with the dorsal portions of the
myocommata, give tension to the region of the back, slightly
raise the tail, and depress the dorsal fins. The infracarinales, in
combination with the retractores pubis, tend to compress the
abdomen, to constrict the anus, and to depress the tail.

The muscles of the pectoral fins, though, compared with those
of the homologous members in higher Vertebrates, they are very
small, few, and simple, yet suffice for all the requisite movements
of the fins ; elevating, depressing, advancing, and again laying
them prone and flat, by an oblique stroke, upon the sides of the
body. The rays or digits of both pectorals and ventrals, as well
as those of the median fins, can be divaricated and approximated,
the intervening webs spread out or folded up, and the extent of
surface required to react upon the ambient medium in each change
and degree of motion, can be duly regulated at pleasure.

In the ordinary forward movement the tail first bends from the
vertebral axis, which is the axis of motion, fig. 159, f, d, to a.
During this action the centre of gravity, c, slightly recedes.
From a the tail is next forcibly bent by the muscles on the
opposite side, in the direction of the line a i. The force of the
action upon the water in a i is translated to the body in i a,
causing the centre of gravity, c, to move obliquely forward, in
the direction of c h, parallel to i a. The tail, continuing its

LOCOMOTION OF FISHES.

253

159

Diagram of locomotive act,
Fish, cxxxi.

flexion in e o, acts backward, in the direction of o e ; having
reached the point o, it is again forcibly bent in the line o e,
causing an impulse on the centre of gravity in c b, parallel to o e ;
if the two forces c h and c b acted simul-
taneously, we should obtain the resultant
c f\ but, as they do not, the point c will
not move exactly in the line cf, but in a
curved line, evenly between d c f and a line
drawn parallel to it through h. The fish
being in motion, the tail describes the arc
of an ellipse ; whereas, if it were station-
ary, it would describe the arc of a circle.
The power of varying the position and ex-
panse of the tail-fin during the side-strokes
complicates the problem ; its plane may be
perpendicular to the stroke's direction, and
its expansion greatest at the beginning of
the stroke, as in a i ; and it may be oblique
to the direction of the rest of the stroke,
as in e o, with contraction of the surface. It
must, further, be considered that the water
having been set in motion by flexion in one direction, produces,
when meeting the tail moving in the opposite direction, a resis-
tance proportional to the sum of the squares of the two velocities.
The shape of the caudal fin varies much in fishes, according
to the kind and degree of motion required : in the imprisoned
embryo, or newly-hatched fry, in the long and slender undulating
eel, in the sluggish Lepidosiren, the vertebras continue to the end
of the body in a straight line, distinct, and decreasing to a point ;
and the tail is bordered above and below by a vertical fold of
skin; terminating either in a point, as in fig. 100, or obtusely.
Such fold or fin is symmetrical, but not f homocercal.' l The
vertical folds deepen ; at first, in some Plagiostomes, e. g.,
equably, forming a terminal lobe ; then excessively, in the lower
or haemal fold, with the developement therein of rays, and with an
upward or neural inclination of the supporting vertebra. Shorter
rays are developed in the shallower neural fold, which terminates
at the pointed end of the vertebral series. The anterior rays of
the hasmal fold, which are the longest, form a second point. The
tail-fin is thus bifurcate, but unsymmetrical ; and this stage of

1 By this latter term M. Agassiz signifies a subsequent grade of modification and
developement, and a grave fallacy lurks in its misapplication to the common embryonal
condition of the tail-fia in Fishes, as by the Author of cxcvm.

254 ANATOMY OF VERTEBRATES.

developement is termed the ' hcterocercal ' one. It is shown by
the Sturgeon, fig. 29, and by the Chimaeras and Sharks of the
present day. It was the fashion of tail (fig. 127) which prevailed
in Fishes throughout the palreozoic and triassic periods.

In some oolitic fishes first is observed such a lengthening of
the dermoneurals of the tail, with such a shortening and running
together of the terminal vertebras, and such a proportion of the
dermohrcmals, as leads to an equal-lobed caudal fin, which has
been termed ( homocercal ; ' but as it is only symmetrical in
contour, and remains more or less unsymmetrical in its frame-
work, I term it 4 homocercoid.' The ganoid fishes of the mesozoic
periods manifest several interesting gradations of this transitional
state from the hetero- to the true homo-cereal form, each step
being a permanent character of the extinct species presenting it.
The embryos and young of Sahnonidcs, of most Malacopteri, and
of many Acanthopteri, go through closely analogous stages to
those which were permanent in extinct fishes ; and the slight
upward twist of the coalesced terminal caudals, and the inequality
of its upper and lower lobes, indicate the fact in the symmetrically-
shaped ( homocercoid ' tail-fin of the adults.1 In the Anacantliini.,
fio;. 34, and Scomleroids. fio*. 33, the terminal tail-vertebra3 shrink

o 3 * ~ J

and coalesce in the line of the trunk's axis ; the dermoneural and
dermohsemal rays are equally developed, and a truly symmetrical
or f homocercal ' caudal fin is the result ; and this is the latest
and greatest modification of the organ. The majority of existing
species of bony fishes indicate, in the course of their acquisition of
the symmetrical tail-fin, the heterocercal stages at which it is seve-
rally arrested in different older extinct species, doubtless in close
relation with the power and kind of swimming required by each.
The heterocercal tail helps the fish to vary its onward course.
The Shark wheels about in pursuit of prey, and rotates the trunk,
to bring the inferiorly-opening mouth to bear upon the victim.
The Sturgeon maintains its body in the oblique position while
upturning the muddy bottom of the strongly-running stream, and
avoids, by deftly bending to right or left, the drift bodies that are
hurried down the river. The homocercal tail is a more effective
form for a straight forward rush. When it is truncate and tri-
angular, the apex being the centre of motion, the centre of force
is three-fourths the distance of its base from the axis of oscillation,
and the muscles of the tail act at a corresponding disadvantage.
When the tail is forked, as in fig;. 33, the area is in the inverse

' o

1 See the persistent " trace of the embryonal heterocercal form of the tail " in the
Sea-perch (Centropristis gigas, Owen), No. 191, p. 51, XLIV.

LOCOMOTION OF FISHES. 255

ratio of the distance from the centre of gravity, and the centre of
force is one-half the distance from the centre of motion ; conse-
quently the fishes so endowed have the greatest velocity. It is
such in the Sword-fish as to enable it to drive its rostral weapon
through a ship's timbers with the force of a cannon ball- -for
example, through fourteen inches of oak, after penetrating the
copper sheathing, four inches of deal, and a layer of felt.1

As most fishes require to sustain themselves above the bed or
bottom of their rivers, lakes, or seas, and as their specific gravity
is greater than that of water, they are commonly provided with
an air-bladder, situated immediately under the spine, and above
the centre of gravity, and usually accompanied with powers of
renewing, expelling, compressing, and dilating its gaseous contents.
This hydrostatic apparatus thus becomes an important auxiliary
organ of locomotion.

The Diodons and Tetrodons fill an immense expansion of the
oesophagus by swallowing air ; and as this lies below the centre of
gravity, the body, so inflated, rolls over, and they are drifted,
passively, back downward, by the winds and currents.

The air-bladder is absent in Dermopteri^ Plagiostomi, Pleuro-
mcticlce ; and such fishes, unless endowed with compensating
powers and proportions of body and fins, as in the Sharks,
habitually grovel at the bottom, and exhibit flattened forms of
body, as in the Rays and Flounders.

With the exception of the above-described modifications of a
few terminal vertebras, those of the trunk remain throughout life

o

distinct from one another in Fishes, as they originally are in the
embryos of all higher Vertebrates. The confluence of vertebras
at the base of the tail would have been a hindrance to the
required movements of such part of the spine in creatures which
progress by alternate vigorous inflections of a muscular tail. A
sacrum is a consolidation of a greater or less proportion of the
vertebral axis for the transference of more or less of the weight

o

of the body upon limbs organised for its support on dry land ;
such a modification would have been useless to the fish, and not
only useless, but a defect.

The pectoral fins — those curtailed prototypes of the fore-limbs
of other Yertebrata, with the last segment, or hand, alone pro-
jecting freely from the trunk, and swathed in a common undivided
tegumeutary sheath- -present a condition analogous to that of
the embryo buds of the homologous members in the higher Ver-

1 See the specimen in the Museum of the Royal College of Surgeons, London,
described in cxcv. p. 5.

256 ANATOMY OF VERTEBRATES.

tebrata. But what would have been the effect if both arm and
fore-arm had also extended freely from the side of the fish, and
dangled as a long flexible many-jointed appendage in the water !
This higher developement, as it is termed, in relation to the pre-
hensile limb of the denizen of dry land, would have been an im-
perfection in the structure of the creature which is to cleave the
liquid element : in it, therefore, the fore limb is reduced to the
smallest proportions consistent with its required functions : the
brachial and antibrachial segments are abrogated, or hidden in the
trunk : the hand alone projects and can be applied, when the fish
darts forward, prone and flat, by flexion of the wrist, to the side
of the trunk ; or it may be extended at right angles, with its flat
surfaces turned forward and backward, so as to check and arrest
more or less suddenly, according to its degree of extension, the
progress of the fish ; its breadth may also be diminished or
increased by approximating or divaricating the rays. In the act
of flexion, the fin slightly rotates and gives an oblique stroke
to the water. If one of the pectorals be extended, it will turn
the fish in a curve towards that side : if the other only, it
will turn it on the opposite side : they thus act as a rudder. For
these functions, however, the hand requires as much extra
developement in breadth, as reduction in length and thickness ;
and this is gained by the addition of ten, twenty, or it may be
even a hundred digital rays, beyond the number to which the
fingers are restricted, in the hand of the higher classes of Verte-
brata. We find, moreover, as numerous and strikino; modifi-

' y O

cations of the pectoral fins, in adjustment to the peculiar habits
of the species in Fishes, as we do of the fore limbs in any of the
higher classes. This fin may wield a formidable and special
weapon of offence, as in many Siluroid fishes. But the modified
hands have a more constant secondary office, that of touch, and
are applied to ascertain the nature of surrounding objects, and
particularly the character of the bottom of the water in which the
fish may live. The tactile action of the pectoral fins may be
witnessed when gold fish are transferred to a strange vessel ; they
compress their air-bladder, and allow themselves to sink near the
bottom, which they sweep as it were, by rapid and delicate vibra-
tions of the pectoral fins, apparently ascertaining that no sharp
stone or stick projects upwards, which might injure them in their
rapid movements round their prison. If the pectorals are to
perform a special office of exploration, certain digits are liberated
from the Aveb, and are specially endowed with nervous power for
a finer sense of touch, as we see in the Gurnards, fig. 82 ; in

LOCOMOTION OF FISHES. 257

which they also serve as limbs to creep along the bottom, when
the fish is exploring the sand with its mailed mouth.

Some Gobioids (Periopthalmus) can use their muscular pecto-
rals to shuffle along the shore, or hunt for insects in humid places.1
Certain Lophioids living on sand-banks that are left dry at low
water are enabled to hop after the retreating tide by a special
prolongation of the carpal joint of the pectoral fin, fig. 102 ; which
fin in these ( frog-fishes' projects like the limb of a terrestrial
quadruped, and presents two distinct segments clear of the trunk.

The sharks, whose form of body and strength of tail enable
them to swim near the surface of the ocean, are further adapted
for this sphere of activity and compensated for the absence of an
air-bladder by the large proportional size and strength of their
pectoral fins, figs. 30, 104, which take a greater share in their
active and varied evolutions than they can do in ordinary fishes.

The flat-bodied Rays, equally devoid of an air-bladder, and
with a long and slender tail, deprived of its ordinary propelling
powers, grovel at the bottom ; but have a still greater develope-
ment of the hands, fig. 64, 12, 12, which surpass in breadth the
whole trunk, and react with greater force upon it in raising it
from the bottom, by virtue of a special modification of the scapular
arch, which is directly attached to the dorsal vertebrae.

Xor is the pectoral member restricted in length where its
office, in subserviency to the special exigencies of the fish,
demands a developement in that direction ; the fingers of the
Exoccetus and Dactylopterus, are as long, and the web which they
sustain as broad, as in the expanded wing of the flying mammal.
Everywhere, whatever resemblance or analogy we may perceive
in the ichthyic modifications of the Vertebrate skeleton to the
lower forms or the embryos of the higher classes, we shall find
such analogies to be the result of special adaptations for the pur-
pose or function for which that part of the fish is designed.

The ventral fins or homologues of the hind-legs are still more
rudimental — still more embryonic, having in view the comparison
with the stages of developement in a land animal- -than the pec-
toral fins ; and their small proportional size reminds the homoJogist
of the later appearance of the hind limbs, in the developement of
the land Vertebrate. But the hind limbs more immediately relate
to the support and progression of an animal on dry land than the
fore limbs : the legs are the sole terrestrial locomotive organ's in
Birds, whose fore limbs are exclusively modified, as wings, for
motion in another element. The legs are the sole organ of sup*

1 CLXXIV. vol. iii. p. 97.
VOL. I. S

258 ANATOMY OF VERTEBRATES.

port and progression in Man, whose pectoral members or arms
are liberated from that office, and made entirely subservient to
the varied purposes to which an inventive faculty and an intel-
ligent will would apply them. To what purpose, then, encumber
a creature, always floating in a medium of nearly the same specific
gravity as itself, with hind limbs ? They could be of no use :
nay, to creatures that can only attain their prey, or escape their
enemy, by vigorous alternate strokes of the hind part of the
trunk, the attachment there of Ions; flexible limbs would be a

J O

grievous hindrance, a very monstrosity. So, therefore, we find
the developement and connections of the hind limbs of Fishes,
figs. 29, 34, 38, 64, v, restricted to the dimensions and form
which, whilst suited to the limited functions they are capable of
in this class, would prevent their interfering with the action of
more important parts of the locomotive machinery.

The plane of each ventral fin being horizontal, at right angles
to that of the caudal fin, their action serves to balance the body,
to incline it on either side when one fin only acts, and to elevate
or depress the fish by their joint effort.

In most fishes the ventral fins merely combine with the pectoral
fins in raising the body, and in preventing, as outriggers, the roll-
ing movement : but some interesting modifications in relation to

o o

particular habits of certain species have previously been pointed
out (p. 180). In the long-bodied and small-headed abdominal
fishes, the ventrals are situated near the anus, where they best
subserve the office of accessory balancers ; in the large-headed
thoracic and jugular fishes, the loose suspension of these fins, and
the absence of any connection with a sacral part of the vertebral
column, permits their transference forward, to aid the pectoral
fins in raising the head.

The planes of the dorsal, figs. 24, 39? D, and anal, ib. A, fins
are in that of the mesial longitudinal section, and their movements
are usually restricted to elevation and depression. They accord-
ingly increase or diminish the lateral surfaces of the fish, cor-
recting any tendency to oscillate laterally, or to turn upside
down, as the body would do without some muscular effort, since
in the ordinary posture, back upward, the centre of gravity lies
above the centre of figure. When the fins collapse and the mus-
cular action ceases, as in death, the fish floats belly upward.
However, in some singular exceptions, e. g. the Sun-fish, the dorsal
and anal fins are unusually extended, and take a more direct share,
by lateral undulating movements, in the locomotion of the fish.

In ordinary shaped Osseous Fishes, if the dorsal and anal fins be

LOCOMOTION OF SERPENTS. 259

.cut off, tlie fish reels to tlie right and left. If the pectorals be cut
off in a Perch or other big-headed fish, the head sinks ; if one
pectoral be cut off, the fish leans to that side ; if the ventral of
the same side be also removed, the fish loses its equilibrium ;
if the tail be cut off, the locomotive power is abrogated.

§ 49. Locomotion of Serpents. — The sole locomotive organs in
serpents are the vertebral column, with its muscles, and the large
stiff erectile epidermal scutes crossing the under surface of the body.

Although the vertebrae have synovial cup-and-ball terminal joints,
their reciprocal movements are greatly restricted by the ' tenon-
and-mortice ' articulations of the double zygapophyses at each end,
of which the inferior have flat horizontal surfaces, the superior
slightly oblique planes. But as a single segment of the back-
bone may be but -3-^ part of the length of the body, the sum of
the small movements between two vertebras becomes considerable
in a certain extent of the Ions; trunk.

o

A serpent may, however, be seen to progress without any
inflections, gliding sloAvly, with a ghost-like movement, in a
straight line. If the observer have the nerve to lay his hand flat

C3 **

in the reptile's course, he will feel, as the body glides over the
palm, the surface pressed, as it were, by the edges of a close-set
series of paper-knives, successively falling flat after such applica-
tion. The skin of the hand has been seized, so to speak, by the
edges of the stiff, short, but broad, transverse, horny, ventral
scutes, erected or made vertical for that purpose, and folding flat
upon the body when the effect of the resistance has been gained.
Each scute having secured a fulcrum in the plane of motion, the
ribs connected with it rotate, and transmit the movement upon
the trunk ; it is, in fact, a step whose length depends on the arc
through which the pair of ribs may oscillate and on the distances of
the scutes from the axes of motion. As both these are small, and
the motion has to be transmitted by the succession of short scutal
steps through the whole length of the body, this first kind of
progression is slow and gliding.

A second and swifter mode of locomotion on land is by succes-
sively bending and straightening portions of the body. Extension
will carry the straightened part forward in the direction of least
resistance. If most resistance be made by the point of the
tail, fig. 160, e, or by the application to the ground of the edges
of the erect scutes, between d and e, the extension of a c will
carry the head to h, the smooth overlapping unerected scutes
between a and d favouring the forward movement ; and this being
effected, and the ground grasped by the erection of the scutes

8 2

260 ANATOMY OF VERTEBRATES.

between a and c, flexion of the rest of the body will draw forward
the tail, as from I to e. As the extent of the flexion of, say a
fourth part of the body, exceeds the space through which a single
scute is moved in erection, so does this mode of motion greatly
exceed in swiftness the preceding. And this swiftness is accele-
rated when the serpent raises the body, in arched curves, from the
ground, increasing their span, and progressing in a vertically,
instead of a horizontally, undulating course ; when, by augmented
vigour of the muscular actions, the whole trunk may be raised
into a single arc, and the movement acquire the character of a
leap. Thus the body being bent, whilst the neck-scutes fix the
head, as at Z>, the tail will advance from a to e, fig. 161 ; when,
being fixed there by the subcaudal scutes, extension will carry
the head forward to d, and the serpent will have advanced by the
two actions of flexion and extension through a space equal to a e
or I h. But, if the act of extension be vigorous and sudden,
and an equivalent fulcrum be afforded by the tail, the whole body
may be carried forward, as by a leap, farther than its own length.
For the saltatory motion, however, the mechanism of a spiral
spring is commonly simulated ; the whole body is bent into a
series of close-set coils, the sudden extension of which, reacting
upon the point of earth against which the tail presses, throws the
serpent obliquely forward into the air. In all these movements
the curve is essentially lateral ; the amount of rotation between
the smaller vertebrae, at the two extremes of the body, permits
the flexion of the intermediate joints to assume, as in fig. 161, the
vertical position. There is no natural undulation of the body
upward and downward - - it can take place only from side to side.
So closely and compactly do the ten pairs of joints between each
of the two hundred or three hundred vertebra) fit together, that

O

even in the relaxed and dead state the body cannot be twisted.
If the attempt at rotation be made at the end of the tail 011 a
dead snake outstretched, the part grasped may be half-twisted ;
but the rest of the trunk will turn over, rigid, like a stick.

Serpents derive the same advantage from their lungs in water
as eels from their swim-bladder, the air-receptacles in both being
much alike, and placed above the centre of gravity. They pro-
gress by a similar series of successive lateral undulations, gene-
rating a surplus force in the moving body equal to the difference
between the force of the locomotive organs and the resistance
of the medium. In water-snakes this resistance is made more
effective by the lateral flattening or compression of the tail, which
can be drawn forward edgewise, and flapped back breadthwise.

LOCOMOTION OF SERPENTS.

261

160

i

Serpents climb trees by the same mechanism and actions as in
the first kind of locomotion ; the edges of the erected scutes
laying hold of the bark in succession, as the body glides spirally up
the bough. The tail has a prehensile faculty, especially exercised
by the great Constrictors while waiting for their prey.
They instinctively select a tree at the part of the
stream easiest of access to the thirsty mammals of
the forest, and suspend themselves, like a parasitic
creeper, from an overhanging branch, the head and
fore-part of the body being floated by the bladder-
like lungs upon the stream.

Serpents are too commonly looked down upon as
animals degraded from a higher type ; but their
whole organisation, and especially their bony struc-
ture, demonstrate that their parts are as exquisitely
adjusted to the form of their whole, and to their
habits and sphere of life, as is the organisation of
any animal which we call superior to them. It
is true that the serpent has no limbs, yet it can
outclimb the monkey, outswim the fish, outleap the
jerboa, and, suddenly loosing the close coils of its
crouching spiral, it can spring into the air and seize
the bird upon the wing : all these creatures have
been observed to fall its prey. The serpent has
neither hands nor talons, yet it can outwrestle the
athlete, and crush the tiger in the embrace of its
ponderous overlapping folds. Instead of licking up
its food as it glides along, the serpent uplifts its
crushed prey, and presents it, grasped in the death-
coil as in a hand, to its slimy gaping mouth.

It is truly wonderful to see the work of hands, feet, and

161

/

Motion of serpent

by undulations of

trunk. CG'iv.

a

Motion of serpent by arching the trunk . cciv.

fins, performed by a modification of the vertebral column

-by

262 ANATOMY OF VERTEBRATES.

a multiplication of its segments with mobility of its ribs But the
vertebra? are specially modified, to compensate, by the strength of
their numerous articulations, for the weakness of their manifold
repetition, and the consequent elongation of the slender column.
As serpents move chiefly on the surface of the earth, their danger
is greatest from pressure and blows from above ; all the joints are
fashioned accordingly to resist yielding, and sustain pressure in a
vertical direction.

§ ,:0. Locomotion of limbed Reptiles.- The fish-like Batrachia
move in water by means of the lateral inflections of the hinder-
half of the trunk, which is compressed and extended vertically
by a marginal tegumentary fin. The parial limbs are small and
feeble : they are limited, in the amphibious Siren, to the pectoral
region, and to the function of raising the head and fore-part of
the trunk upon the bank or shore. In the rest of the order
both pairs are present : in the Amphiume they are too feeble to
suggest any particular locomotive function ; but they subserve,
when somewhat more developed, a slow and awkward reptation,
as in the Menopome and Newt. In the Land- Salamander, fig.
140, they acquire the due strength for terrestrial progression, and
the tail is shortened and rounded. In the Toads and Fro«;s the

~

tail is absorbed, and the legs lengthened and strengthened, espe-
cially the hinder pair ; but with an outward direction from the
body, and a position too horizontal to enable them to raise or
support it above the ground.

The Frog, in repose, assumes a sitting posture, the thighs
turned outward and forward, the legs bent backward, and the
lengthened tarsi and feet directed forward. The fore-part of
the trunk is propped up by the fore limbs, at an angle of 45°,
with the base between the hind limbs, which, in their state of
flexion, are ready on the least alarm to project the body forward
by their sudden extension. The shoulder-joints of the limbs
that receive the shock on alighting from the leap are strength-
ened by an interarticular ligament. The great Bull-Frog may
clear six feet at a leap, and repeat them so rapidly as to escape a
pursuer, unless chased at a great distance from the water. Both
fore and liincl feet are webbed for swimming, which is chiefly
effected by strokes of the strong hind limbs. The large Indian
frog (Rana tigrina) is said to be able to run along the surface of
the water for a short distance.

The Tree-Frogs (Hyla) have a concave disc at the end of
each toe, for climbing and adhering to the bark and leaves of
trees.

LOCOMOTION OF LIMBED REPTILES.

263

162

Toads, with semipalmate feet, have an awkward, but not always
slow, progression on land by alternate movements of the limbs.
Some species are enabled, by peculiar tubercles or projections
from the palm or sole, to clamber up old Avails.

But the most remarkable climbers in the reptilian class are
certain lizards, especially those called f Geckos.' Each foot has
five toes, which are spread wide apart, expanded at the ends, and
terminated by a slencler sharp claw. The flattened under surface
of the toe-pad, fig. 162, is traversed by a series of
transverse folds, with deep interspaces ; the
margins of the folds, when applied to a smooth
surface, adhere thereto by atmospheric pressure,
through the vacuum caused by muscular erec-
tion of the folds, with concomitant expansion of
the interspaces ; thus the animal, alternately
applying and releasing its suckers, climbs a
vertical wall or plate of glass, or proceeds along
a ceiling with its back downward.

o

For climbing trees the adjustment of the toes
in opposition to each other, in equal or sub-
equal groups, as already described in the Cha-
meleon, pp. 175, 193, figs. 119, 123, is an
effective modification. In this reptile the limbs
are short and strong, and a prehensile tail is
added to the scansorial feet.

Ordinary lizards, by the great length of the trunk in proportion
to its breadth, and by the outward extension of the humerus and
femur, are under unfavourable mechanical conditions for rapid
course upon land. Yet such is the energy of the muscular con-
tractions in some species, under the stimulus of solar heat, that
they are deservedly called 4 agile,' and ' dart ' out of view in the
first rush from a pursuer. They have not, however, the power of
maintaining the exertion, and are soon overtaken, if they happen
to be far from their retreat. The swiftest runners, e. g. the Tachy-
dr 07722, have the fore and hind limbs least differing in length, and
consequently the vertebral column most parallel with the plane of
motion.

In the Crocodiles the fore limbs are shorter than the hind ones,
in which the foot is longer and more expanded, so as to present a
larger surface for striking the water in swimming. But the chief

O " o

natatory organ in these large amphibious reptiles is the long,
compressed tail. In the act of swimming, the fore limbs are
applied flat to the sides of the body, and the hind ones chiefly

Toe of Gecko, rnagn.
ecru.

2G4

ANATOMY OF VERTEBRATES.

used in modifying the course through the water. The fore limbs
were shorter, and the hind limbs longer in the extinct CrocodiUa
of marine habits. The stiffness of the neck, produced by the
overlapping of the expanded cervical ribs, adds to the power of
the head in overcoming the resistance of the water ; but detracts,

163

Flylug lizard (Draco volans), LINX. cciv.

with the almost inflexible cuirassed trunk, from the capacity to
capture prey on land, which is seldom overtaken, except by a

LOCOMOTION OF LIMBED REPTILES. 265

straight-forward rush : this, for a short extent, is dangerously
rapid ; hut the Crocodiles are most formidable and agile in their
habitual element the water.

The little Draco volans has a body which rarely exceeds
110 grains in weight; the delicate tegumentary parachute, sustained
by the long slender ribs, fig. 163, like the nervures of the insect's
wing, measures about five square inches - - its area being as great
in proportion to the weight of the animal as that of the Avings in
many birds. But the muscular apparatus, «, a, subserves only
the expansion and folding up of the membrane, which would
seem, therefore, to act, if the animal ever leaps into air or darts
through that element, merely as a sustaining parachute to break
the fall.

The Reptilia in which the fore limb was developed and modified,
in order to work membranous expansions with sufficient force to
raise and move the body in air, ceased to exist, apparently, during
the deposition of the cretaceous beds, prior to the tertiary epoch
in Geology. TTe learn from the fossilized remains of Ptero-
dactyles, that the weight of the body, compared to the area of
their outspread wings, must have been very small, fig. Ill, A;
that the bones were light, of a thin but compact osseous texture,
permeated by air. The digit, so enormously developed for
sustaining the main part of the wing, fig. Ill, 5, was restricted,
like the aiitibrachium in birds, to movements of abduction and
adduction, lying along the ulnar side of the fore-arm, and reaching
beyond the sacrum, when the wing was folded. The proportion
of the area of the outstretched wings to the body was greater in
Pterodactyles than in most birds, and equalled that in the bats ;
like which, the Pterodactyles would alter the alar area by alternate
abduction and adduction of the sustaining digit, combined with

~ O '

flexion and extension of the arm and fore-arm.

The large head and strong neck of the Pterodactyle seem to
have called for that extension and forward direction of the anti-
brachium, which would cause the centres of gravity and magnitude
to be more in advance than in either bird or bat. Their pelvic
limbs were little more developed than in Bats - - must have been
unequal to sustain the body- -may have concurred with the short
unguiculate digits of the fore limb, fig. Ill, i, 2, 3, 4, in a crawling
progress along the ground - - and, being terminated by toes of
equal length, probably served, as in bats, to suspend the body,
head downward, during sleep.

266 ANATOMY OF VERTEBRATES.

CHAPTER IV.

NERVOUS SYSTEM OF H2EMATOCRYA.

§ 51. Nervous tissues.- Nervous substance,, like muscular,
ranks with the most complex of animal tissues in chemical con-
stitution, and possesses the greatest atomic weight : but the albu-
minous form of proteine here prevails. Nervous tissue presents
two formal characters ; one vesicular and grey in colour, the
other fibrous and white : but the neurine inclosed by neurilemma
being softer than myonine, and less definite in arrangement after
death, the nerve-fibre usually appears as a tube with white contents.

Nervous substance has two principal dispositions ; one in
masses, called ' centres,' the other in threads, called l nerves.'
The centres in Vertebrate animals constitute, according to their
relative size or position, the spinal chord (myelon), the brain
(encephalon), and ganglions. In these the vesicular, grey, or
dynamic form of tissue is associated with the fibrous, white, or
conductive form. Most nerves consist of the white fibres, and all
are interimncial in office, establishing a communication between
the centres and the various parts of the body.

The centres, and their grey or vesicular constituent more
especially, appear to originate the nervous force : certain nerves
conduct it to the tissues, principally muscular, on which it acts
by producing contraction ; other nerves carry the impressions
received at their distal ends to the centres : the first are termed
' motory,' from the function they excite, and ( efferent,' from the
direction of conduction : the second are termed ' sensory ' and
f afferent.' Sensation, or the appreciation of the impression by the
individual, seems to follow only when the ' afferent' nerve conveys
its impressions to the brain ; when it stops short in the myelon,
or ends in a ganglion, it may excite a corresponding or connected
' efferent ' nerve to produce motion, or a e reflex ' action, which
may then take place without sensation or volition.

The myelon, the encephalon, and their nerves, constitute the
( myelencephalous ' or f cerebro-spinal ' system, to which belong
the ganglions on the sensory roots of the spinal and trigeminal
nerves, and those in the glosso-pharyngeal and vagal nerves.

NERVOUS TISSUES.

267

164

A chain of ganglions is situated on each side, near the vertebral
foramina, through which the cerebro-spinal nerves issue. These
ganglions radiate many nerves, connecting them one with another
and with the cerebro-spinal nerves, and ramifying in a plexiform
way upon the viscera and coats of the blood-vessels : they con-
stitute the 'sympathetic' or f ganglionic' system in Vertebrates.

In the cerebro-spinal nerves the primitive fibre consists of a
transparent elastic homogeneous tubular
membrane (neurilemma), fig. 164, a; its
contents are pulpy, homogeneous in the
living or recently dead state, and may be
pressed out of the sheath ; when treated
with water, as in fig. 164, «, or with alco-
hol, they condense into a white layer,
giving that colour to the tube : within the
white substance Remak defines a ( flattened
band,' and Purkinje an ( axis-cylinder.'
When treated with ether, oil-globules co-
alesce in the interior, and accumulate around
the exterior of the tube, fig. 164, b.

The delicacy of the neurilemma, and
mobility of its contents, lead, in many cases,
to partial dilatations of the tube, of a < van- Nerve tlll)C3 altercd by re.ageuts.
cose ' character, probably due to post-mortem

influences : in the living or natural state, the primitive nerve-
tube or fibre appears to be perfectly cylindrical.

The following are results of Todd's admeasurements of their
diameter, in the different vertebrate classes : -

Fishes (Eel) T~OTJ °^ an incn-

Reptiles (Frog) y-jVo" t° aijV'o °f an nicn«

Birds 2~oVo *° ToW °f an

Mammals y^W

an

Primitive nerve-fibres do not divide or branch; they are
associated together, in simple juxtaposition, supported by fine
layers of areolar tissue, which condense at the periphery into a
common sheath, to which the term ' neurilemma ' is commonly.

*/ -•

but not properly, given : it answers to the sheath which surrounds
a muscle, similarly binding the constituent fibres of the nerve
together, and supporting their nutrient capillaries. These are the
smallest in the body ; they run chiefly parallel with the nerve-
fibres, forming oblong meshes, completed at intervals by cross-
vessels. Sometimes the nerve-fibres have a wavy course within
the general sheath, fig. 165. In a few instances they have been

1 ccv. p. 593.

268

ANATOMY OF VERTEBRATES

165

observed to decussate, as in fig. 166, changing their relative

position within the sheath.

The termination of efferent nerves on
sentient surfaces of the skin appears to
be plexiform : but they have been seen
to enter the bases of the tactile papillae
in the form of loops. The looped termi-
nation has been distinctly seen by Henle upon the membrana
nictitans of the frog, and by Valentin on parts of the formative
matrix of teeth, fig. 167.

1G6

j

Wavy course of nerve fibres, within
the common sheath, ccv.

167

Diagram to show the clecussation of the primitive fibres within
the trunk of a nerve, ccv. ccvi.

Amongst the nerve-fibres of the sympathetic system are some
of a grey colour, sometimes called ' soft fibres,' which are flattened,

homogeneous, more minute than the
primitive fibres of the cerebro-spinal
system, and characterised by small
multimicleate bodies upon their sur-
face, fig. 168.

§ 52. My elencephalon of Fishes. — In
the cold-blooded Vertebrates the pro-
portion of the mass-form, or centres, to
the thread-form, or conductors, of the
nervous system is less than in the
warm-blooded classes.

In the Lancelet (Branchiostoma),
fig. 169, the neural axis, m d, shows
no distinction between brain and
myelon ; it is a slender tract of nu-
cleated cells, inclosed in a delicate
pia mater, constituting a continuous
chord, of opaline sub -transparency,
ductile and elastic. It is depressed
or band-like along its middle third,

Terminal nerves on the sac of the second i*i*i>ii 11

molar tooth of the lower jaw in the WlllCll IS Slightly grOOVCQ along tllC
sheep, showing the arrangement in TIT £ ^.1 1 1 f

loops, ccvi. medial line or the dorsal surface,

MYELENCEPHALON OF FISHES.

269

and tapering to both ends, but more gradually to the hinder
one, the fore-end being less acute. A streak of pigment-
cells marks the middle of the upper surface : darker cells mark
the origins of the nerves. These number from fifty to sixty

168

B

a

Xvrvous fibres from a soft or grey nerve in the Calf. ccvu.
A, fibre resolving itself into fibrilhe. B, a fibre doubled on itself,
showing the tlnttmed character. C, Two (Hires lying in juxtaposi-
tion, a, a, a, nuclei, c, a nuclear fibre (Kernfaser). d, a llbrilla.

pairs, and appear to come off as simple chords, fig. 170. They
perforate the membranous neural canal, and accompany the inter-
muscular septa, dividing into two principal branches - - one to the
neural or dorsal, the other to the haemal or ventral, muscular

169

"f

Diagram of Anatomy of the Lancelet, Brcmchiostoma

segments. The first pair of nerves, fig. 170, b, which Professor
Goodsir * thinks might correspond to the f trifacinl,' passes to the
membranous parts above the mouth : it may be the homologue of
that, which, when a part of such membrane becomes specialised
as an olfactory sac, becomes the olfactory nerve, as, e. g., in the

270

ANATOMY OF VERTEBRATES.

Lamprey. The second pair is much larger ; it passes out of the
neural canal, anterior to the first myocomma, and sends a branch,
170 c, fig. 170, upward and backward toward the front

edge of that segment, which communicates with
the dorsal branches of several successive nerves of
its own side, like the branch from the combined
trifacial and vagal nerves, marked i in fig. 204 :
the main trunk of the second nerve curves
downward and backward, d, fig. 170, communi-
cating with the corresponding parts of the suc-
ceeding nerves of its own side, to some way
beyond the vent, fig. 169, a s : this portion answers
to the branches 3 and 4 of the ' nervus lateralis '
in fig. 204. From the principal function of the
second (conspicuous) pair of nerves in the Lancelet,
as a ' nerve of association,' it probably answers to
both the trigeminal and vagal, which in most
higher fishes combine to form the ( lateral nerve,'
with the same relations to the spinal nerves and
median fins as the nerves c and d, fig. 170, show
in the Lancelet.

Costa1 describes and figures f la macchia bruna
degli occhi' (p. 14), ' Fopacita corrispoiidente
sopra e dietro degli occhi' (ib.),2 and 'talvota i
gangli olfattori ' (Tab. i., fig. 2, gy). Retzius3 re-
discovers the ocellus ; and Kolliker4 has more
particularly described the sub-terminal ciliated
depression, described as an f olfactory sac,' and
indicated in the diagram, fig. 169, of. According
to those observations, olfactory and optic nerve-
filaments may be inferred ; and the fore part of
the neural axis, including the trigemino-vagal
nerves, c b, fig. 169, will answer to the brain.
/$==- The succeeding nerves divide, soon after emerg-

ing, into dorsal and ventral branches, as in higher
fishes, corresponding in number with the muscular
segments. The nerves consist of the primitive
cylindrical fibres.

This is the most simple persistent condition of
the central organs of the nervous system known

Tlie nervous sys-
tem of Branchio-
stmna lanceolatum.

X.Q.

XXX.

Query, can this opake spot be an acoustic sac?

XXXII.

MYELON OF FISHES. 271

in the vertebrate subkingdom. In all other Fishes the fore part
of the neural axis receives the vagal, trigeminal, and special sense
nerves, and developes and supports ganglionic masses, principally
disposed in a linear series parallel with the axis : this part is the
4 brain ' (encephalon) ; the rest of the axis retaining its columnar
or chord-like character is the ' myelon,' and being lodged in the
canal of the spinal column., it is usually denned as the medulla
spinalis (spinal marrow, or spinal chord).

In the Lamprey the myelon is flattened, opaline, ductile, and
elastic, as in the Lancelet and other Dcrmopteri : in typical
Fishes it is inelastic and opaque, cylindrical or sub-depressed ;
of nearly uniform diameter, gradually tapering in the caudal
region to a point in heterocercal Fishes, but swelling into a small
terminal ganglion1 in most homocercal Fishes.

The Hunterian preparation of the skate (Raia Batisf shows
a slight (brachial or pectoral) enlargement of the myelon, where
the numerous large nerves are sent off to the great pectoral fins :
a feebler brachial enlargement may be noticed in the Sharks.
I have not recognised it in Osseous Fishes, not even in those with
enormous pectorals adapted for flight, e. g. Exoc&tus and Dae-
tylopterus : in the latter the small ganglionic risings upon the
dorsal columns of the cervical region of the myelon receive nerves
of sensation from the free soft rays of the pectorals, and the
homologous ganglions are more marked in other Gurnards

which have from three to five and sometimes six pairs3,
e. g. in Triyla Adriatica. Similar myelonal cervical ganglions
are present, also, in Potynemus. In the heterocercal Sturgeon
there is a feeble expansion of the myelon at the beginning of the
caudal region, whence it is continued, gradually diminishing to a
point along the neural canal in the upper lobe of the tail. In
some bony fishes (Trout, Blenuy) the caudal ganglion is not quite
terminal, and is less marked than in the Cod or Bream, in which
it is of a hard texture, but receives the last pair of spinal nerves.
The absence of this a-anorlion in the Shark shows that it relates

o ~

not to the strength of the tail but to its form, as depending on
the concentration and coalescence of the terminal vertebras ;
except, indeed, where such metamorphosis is extreme, as, e. g. in
Ortliagoriscus mola, and where it affects the entire condition of
the myelon, which has shrunk into a short, conical, and, according

1 LIU. p. 6; LIV. p. 2G (in the Cod).

2 xx. vol. iii. p. 40, prep. No. 1347.

3 LV. pi. 2, fig. 4, p. 106; and LIII. p, 6, pi. 2, fig. 24, 25.

272

ANATOMY OF VERTEBRATES.

171

to Arsaki (LIII. tab. iii. fig. 10), gangliated appendage to the
encephalon. A like singular modification, but without the
ganglionic structure, obtains in Tetrodon and Diodon, in a species
of which latter genus I found the myelon, fig. 171, M, only four
lines long, in a fish of seven inches in length and mea-
surinff three inches across the head. The neural canal

o

in these Plectognathic fishes is chiefly occupied by
a long l cauda equina,' ib. c e. But, insignificant as
the myelon here seems, it is something more than
merely unresolved nerve-fibres : transverse white
stria3 are discernible in it, with grey matter, showing
it to be a centre of nervous force, not a mere con-
ductor. In the Lophius a long cauda equina partly
conceals a short myelon, which terminates in a point
at about the twelfth vertebra. In other fishes the
myelon is very nearly or quite co-extensive with
the neural canal, and there is no cauda equina, or
bundle of nerve-roots, in the canal : a tendinous
thread sometimes ties the terminal o;anoiioii to the

O O

end of the canal.

A shallow longitudinal fissure divides the ventral

~

surface, and a deeper one the dorsal surface, of
the myelon, into equal moieties : a feeble longi-
tudinal lateral impression (Sturgeon) subdivides
these into dorsal and ventral columns ; in other fishes
(Cod, Herring) these are separated by a lateral tract, and six
columns or chords may be distinguished in the myelon - - two
dorsal or sensory, two ventral or motory, and two lateral or
restiform tracts. A minute cylindrical canal extends from the
fourth ventricle, beneath (ventrad of) the bottom of the dorsal
fissure, along the entire myelon ; this canal is not exposed in the
recent fish by merely divaricating the dorsal columns. Both
lateral halves of the myelon have grey matter in their interior,
and white transverse stria?. Although many fishes (Bream,
Dorsk) show a slight enlargement at each junction of the nerve-
roots with the myelon, the anatomical student will look in vain in
the recent Eel, or Lump-fish, for that ganglionic structure of the
myelon which the descriptions of Cuvier1 might lead him to
expect.

As the myelon approaches the encephalon, it expands ; and the
following changes may be here observed in the Cod and Shark :-

Brain and mye-
lon, Dtodcm,
natural size

1 xxiii , i p. 323 ; xm. iii. p.

176.

ENCEPHALON OF FISHES. 273

in the ventral columns a short longitudinal groove divides a
narrower median f pre-pyramidal' tract, fig. 172, a, from a broader
lateral ' olivary ' tract, ib. b : in the dorsal columns a median
' funicular ' tract, ib. <?, is similarly marked off from a lateral
' post-pyramidal ' tract, d : this is now, also, distinguished by a
deeper fissure from the true lateral or c restiform ' tract, c, at the
inferior part of which a distinct slender portion is
also sometimes defined. The post-pyramidal tracts 172

diverge, expand and blend anteriorly with the
similarly bulging restiform tracts, forming the side-
walls of a triangular or rhomboidal cavity, called the
' fourth ventricle,' fig. 173, y : the pre-pyramidal and
olivary tracts, forming the floor of the ventricle, are
covered below by a thin superficial layer of trans-
verse 'arciform fibres'1 ib. m, concealing their Section of medulla
boundary fissures. At the bottom of the ventricle <>^^,ca,-cha-
the myelonal canal is exposed, and its sides swell
and rise as rounded or ' teretial ' tracts,2 ib. f, from the floor of
the ventricle, diverging slightly as they advance, and exposing an
intermediate ' nodular ' tract ; this structure is well seen in the
basking shark ( Selache) : two lateral prominent ( vagal ' columns
also project inwards into the ventricle, from the conjoined resti-
form and post- pyramidal tracts; these vagal columns present a
series of nodules, fig. 173, f, corresponding with the fasciculi of
the roots of the great vagal nerve in Selacke.3

o o

In the Cyprinoid Fishes the median inferior tract rises into the
ventricle, and is developed into a smooth hemispheric mass, the
( nodulus,' fig. 178, k: the conjoined post-pyramidal and restiform
walls swell outwards, and form lateral 'vagal' lobes, large and

' o o

nodulated in the Carp, fig. 178, h, which is so tenacious of life. The
vagal lobes are enormously developed in the Torpedo ; they join the
trigeminal lobes, and present a yellowish colour in the recent fish :
many non-nucleated cells are present in their substance ; they give
origin to the nerves of the electric organs, and have been called
' lobi electrici ; ' but the vagal lobes are scarcely less remarkable
for their size in the Gymnotus, where they have no direct con-
nection with any of the nerves of the electric organs. In the
Cod the vagal ganglions are obsolete, and the nodulus slightly
swells above, and obliterates the ( calamus scriptorius.' In the
Lucioperca the vagal lobes are not very distinct, but they mark

1 Homologous with the ' filament! arciformi ' of Rolando, LVIII. p 170, t. i. fig. 2.

2 These are called ' vordere pyramiden ' by Dr. Stanuius. LVI. p. 43.

3 xx. vol.. in. p. 22; Prep. DO. 131 lA.

VOL. I. T

274

ANATOMY OF VERTEBRATES.

173

R

the commencement, and form the broadest part, of the very long
medulla oblongata, the restiform tracts diminishing in size as they
advance. In no other Vertebrates save Fishes are the vagal lobes
and the nodulus present.

The posterior pyramids, which are the anterior continuation of
the posterior myelonal columns, diverging as they are pushed
aside by the deeper-seated tracts that form the floor of the fourth
ventricle, and combining with the lateral columns to form the
corpus restiforme and the basis of the vagal lobes, again quit
those columns, converge, ascend, and unite together above the

cj -* Cv

anterior opening of the fourth ventricle : they there form either
a simple bridge or commissure, fig. 173, c, or are developed
upwards and backwards into a ganglionic mass, overarching the
ventricle ; this mass is the ( cerebellum,' figs. 174- -179, C. It is

formed chiefly by the post-pyramidal columns,
but doubtless derives some share of the proper
lateral or restiform fibres, as the result of the
previous confluence of these with the post-
pyramids.

The cerebellum retains its earliest embryonic
form of a simple commissural bridge or fold in the
parasitic suctorial Cyclostomes, in the heavily-
laden Sturgeon, fig. 173, C, and Polypterus,1
and in the almost fiiiless Lepidosiren,2 fig. 186,
C : it attains its highest developement, in the
cf present class, in the Sharks, where it not only
covers the fourth ventricle, but advances over
the optic lobes, and in the Saw-fish extends
beyond them to rest upon the cerebrum ; its
surface is further extended in these active
predaceous fishes by numerous transverse
folds, fig. 187, C. Inmost Osseous Fishes the
cerebellum is a smooth convex body, hemispheroid, fig. 175, C, or
transversely subelliptic (Eel, fig. 176, c), or longitudinally subel-
liptic (Lepidosteus), fig. 174, c ; but it may be an oblong body
(Diodon), fig. 171, C, or be depressed and tongue-shaped (Cod,
fig. 183, jf), or oval, or pyramidal (Perch, fig. 182, «) ; it is very
rarely found extending forward, as in Echeneis and Amblyopsis, fig.
175, C, over any part of the optic lobes ; but often backward
over the whole fourth ventricle, as in the Cod, fig. 183,/*, and the
Diodon, fig. 171, c ; or over the major part of the ventricle, as in the

1 xxv. p. 24, pi. ii. figs. 5, 7. 2 xxxm. p. 339, pi. 27.

Brain ; Sturgeon, cxcix.

ENCEPHALON OF FISHES.

275

Herring, fig. 184, c ; but sometimes covering only a small portion, as
in the Chub, fig. 177, c, the Lump-fish, and the Lepidosteus, fig.
174, c. The relative size of the cerebellum, accordingly, varies

175

176

Brain ;
Lepidosteus

Brain ; AmWyopsis
magnified

Brain; Eel. ecu.

177

greatly in different bony fishes ; it is very small in the lazy Lump-
fish, and extremely large in the active and warm-blooded Tunny,
where, also, its surface shows transverse groovings.
The cerebellum is unsymmetrically placed in the
Pike and some Flat-fish (Pleuronectidce), and is
unsymmetrically shaped in the Sharks : it presents
a longitudinal groove in the Diodon, and a pos-
terior notch in the Herring : a transverse notch di-
vides it into an anterior and posterior lobe in the
Lophius : it bears a crucial depression in the Skate.
The cerebellum presents in many fishes a small
cavity or fossa at its under part, continued from
the fourth ventricle, fig. 178, c: it is solid in the
Tench, the Garpike, and the common Eel : some
grey matter is usually found in its interior, with
feeble indications of white strias ; but there is no Bram and portion of
e arbor vitaa,' except in the Tunny and Sharks.

The posterior ( crura cerebelli ' are formed by
the posterior pyramids, fig. 172, d, with part of the restiform
tracts, ib. c ; vertical fibres from the sides of the cerebellum
continue to attach it to the

sides of the restiform or tri^e-

~

miual lobes, and some of these
are continued as arciform fila-
ments upon the under surface
of the medulla oblongata : they Section of Brain' Carp

answer to the ( crura cerebelli ad pontem ' of Mammalia ; but, as

T 2

spinal marrow
Chub (Leuciscus)

of

27G

ANATOMY OF VERTEBRATES.

179

there are no lateral lobes in the cerebellum in Fishes, these crura
are rudimentary, and the ' pons ' is absent. In the Shark they
connect the sides of the base of the cerebellum with the ( restiform
commissure,' figs. 172 & 187, /. In most Fishes two fasciculi of
medullary fibres proceed, as 6 anterior crura,' from the under and
fore part of the cerebellum, or converge from the lateral and fore-
part forward, to form the inner wall or septum, fig. 184, r, of the
optic lobes : these answer to the ' processus a cerebello ad testes '
of the human brain : they are connected below their origin at the
under part of the cerebellum by one or two transverse fasciculi of
white fibres, forming the ( commissura ansulata,' which crosses the
pre-pyrainids just behind the 'hypoaria,' fig. 185, n. The inferior
white surface of the cerebellum, which forms the roof of the fourth
ventricle, is called ' discus cerebelli,' and from this part small tuber-
cles project in a few fishes (e. g. Blennius and Sturio, fig. 173, c).
The restiform columns, quitting the post-pyramidal crura of
the cerebellum, and having effected by their previous confluence

therewith some interchange of filaments, swell
out at the anterior lateral parts of the medulla
oblongata, and give origin to the great trigeminal
nerve. They here form considerable ( trigeminal
lobes' in the Loach and Herring, fig. 184, i, and
are folded or ( fimbriate ' in Chimcera,fig. 179, del,
and most Plagiostomes, where they are closely
connected with a thick vascular mass of pia
mater and arachnoid. The trigeminal lobes are
convolute in the Skate ; enormous and blended
with the vagal lobes in the Torpedo ; but in most
Osseous Fishes (Lepidosteus, Cod) they are not
developed so as to merit the name of lobes. In
the Cod the inner surfaces of the restiform bodies
project into the fourth ventricle, and obliterate
the fore part of the calamus by meeting above
it ; this commissure, which is beneath the cere-
bellum, is the ( commissura restiformis,' fig. 182.
It is remarkably developed in Carcharias, where
it seems to form a small supplemental cerebellum
beneath the laro-e normal one : in fio-. 172

~ o

the medulla oblongata is cut across, the fourth
ventricle exposed from behind, and the restiform commissure, /, is
raised : it has an anterior and posterior median notch.

The primary division of the brain, which consists of the medulla
oblongata with the cerebellum and other less constant appendages

p — ,

o

cttC-

Bralu of Cli imtera mon-
strotsa. cxcix.

ENCEPHALON OF FISHES. 277

in Fishes, is called the ' epencephalon,' fig. 179, /, c, fig. 178, g, c ;
it is relatively larger, occupies a greater proportion of the cranium,
and is more complex and diversified in this than in any of the
higher classes of Vertebrata.

The next succeeding primary division of the brain is called the
( mesencephalon,' figs. 180 & 18 J, Z», e, f: it is usually the largest
division in Osseous Fishes, and con-
sists of two upper spheroidal bodies, ISO
called 'optic lobes,'1 figs. 176, 177,
180, b (in most of the figures, o),
of two loAver subspherical bodies,
called ( hypoaria,' 2 figs. 178, 185, n,
fig. 181, <?, with intervening con-
necting walls enclosing a cavity,

~ <? . ^ y Brain of Perch, upper surface, xxiu.

called the 'third ventricle, which

is prolonged downward into the pedicle of the f hypophysis,' or
pituitary gland, fig. 185, p, and upward into that of the f cona-
rium' or pineal gland, fig. 175, ic. The prepyramidal columns
are continued forwards, along the floor of the fourth ventricle,
where they are covered by a thin layer of medullary fibres, to the
hypoaria and prosencephalon : some fibres blending with the wall
of the third ventricle and the base of the optic lobes. The
transverse 'ansulate' commissure,3 which unites or crosses the pre-
pyramids before they penetrate the hypoaria, may be regarded as
the most anterior of the arciform fila-
ments, which feebly represent the
pons Varolii in Fishes. The restiforai
columns are expended chiefly in form-
ing the walls of the third ventricle and
the base and exterior walls of the optic

11 11 11' Brain of Perch, under surface, xxiu.

lobes, a small part only being con-
tinued forwards to the cerebrum in most Osseous Fishes. The
anterior cerebellar crura are chiefly lost in the inner walls or
septum of the optic lobes.

These lobes are commonly of a subspherical figure, and larger
than the cerebral lobes, as in figs. 177, 180, b, 171, 184, O; they are
often larger than the cerebellum, ib. ib. ; but of nearly equal size
with the cerebellum in the Eel, fig. 176; they are smaller than
the cerebral lobes, but larger than the cerebellum, in the Polypterus
and Lepidosiren, fig. 186, o; they are smaller than either the
cerebrum or cerebellum in the Amblyopsis spelceus, fig. 175, o, in

1 ' Lobes creux,' Cuvier. 2 ' Lobes inferieurs,' Ib. 3 LVII. pi. iv., fig. 7, /.

278

ANATOMY OF VERTEBRATES.

a.

the Chimaera, fig. 179, o, and in the Sharks, fig. 187, o. In
tlie latter they bear the same proportion to the optic nerves
and eyes as in other fishes, their small relative size depending
on the advanced developemcnt of both cerebellum and cere-
brum : in the blind Amblyops of the subterraneous waters,
the diminution of the optic lobes relates to the almost total
abrogation of the visual organ ; but since • both in the Amblyops
and the equally blind Myxine these lobes are present, they
cannot be exclusively the central ganglion of the optic nerve, nor
their sole function that of receiving the impressions of the sense
of sight, and making them perceptible as ideas by the animal.

The optic lobes are hollow in most Fishes, fig. 182, b. The

exterior surface shows blended grey and white matter, the white

182 fibres usually converging to the optic

nerves ; some of the fibres unite with
the anterior crura of the cerebellum
to form the septum of the optic lobes,
fig. 184, r, which consists of two or
four medullary fasciculi, decreasing in
the Tench, increasing in the Cod, as
they pass forward. On divaricating
the optic lobes from above, as in fig.
182, or by a horizontal section, as in fig. 183, their cavity, d, or
ventricle, is exposed : it communicates with the expanded myelen-
cephalous canal, called ( third ' and ( fourth ' ventricles, as shown
by the bristle, q. Its floor is variously configurated in different
fishes. There are one or two small white tubercles, 'tuberculi
optici,' figs. 182, 183, e, on each side of the back part of the septum;
the Cod, Salmon, Pike, and Perch, show four of these bodies; the
Carp and Herring, fig. 184, t, two: in the Carp they are oblong,
juxtaposed, and were called 'tuberculum cordiforme' by Haller;1
they are not present in the Polypterus, Lepidosiren, Sturgeon, or
Plaodostome fishes. External to these tubercles the floor of the

o

ventricle usually rises into a curved eminence, with its convexity
outwards; this is the ( torus semicircularis ' of Haller,2 fig. 184, w.
It is not homologous with either the ' thalamus opticus ' or the
' corpus striatum ' of the mammal's brain. In the Carp, where
the great physiologist first described and named them, the f tori '
are large, and much curved; in general they describe only a

1 In Salmo Umbla Haller calls them ' corpora quadrigemina,' as does Cuvier, in
Perca fluviatilis : they are analogous in form to the parts so named, in Mammals;
but are not homologous therewith.

2 LIX. t. iii. p. 201.

Brain of Perch, with the optic lobes laid
open, and the cerebellum turned to the
right side. xxm.

ENCEPHALON OF FISHES.

183

small portion of a circle, fig. 182, h ; and in some bony fish, as tho
Garpike, Loach, and Lumpfish, they are scarcely raised above
the level of the floor of the ventricle. They are not deve-
loped in the Polypterus, the Lepidosiren,
or the higher Plagiostomes ; and both tori
and tuberculi are peculiar ichthyic develope-
ments in the ventricles of the optic lobes.
The bottom of the optic ventricle, fig. 184, v,
anterior and external to the 'tori,' is grey, and
usually prominent, with white fibres radiating
through it to rise and expand upon the walls
of the lobes. The optic lobes have almost
coalesced in the Sturgeon, fig. 274, o, Poly-
pterus, Lepidosiren, Amblyopsis, and Loach
(Cobitis). Where they are quite distinct
externally, as in most Osseous Fishes, they
are brought into mutual communication by one
or two commissures ; the anterior ' commissura
transversa ' is the most constant ; it is shown
in the Perch, fig. 182, and in the Herring,
fig. 184, s; it passes in front of the entry to
the third ventricle.

In the Myxine and Lepidosiren the prepyramidal fibres curve
suddenly forward and upward before expanding into the
floor and sides of the third ventricle, and they thus form a
small protuberance beneath the basis of the optic lobes, fig.
186, n. In the Shark the same columns swell out laterally,
and form two small protuberances, fig. 187, ?z, separated below
by the vascular (hypophysial) floor of the third ventricle. In
most Osseous Fishes the corres-
ponding fibres of the prepyrami-
dal tracts swell out suddenly, be-
neath the optic lobes, into two
protuberant well - defined oval
ganglions (chypoaria,' fig. 185, n,
fig. 181, e) : their bulk is increased
by added grey matter, which
variegates their outer surface ;
they are well developed in the
common Cod, in which, as in some
other fishes, they contain a cavity (hypoarian ventricle). In some
SalmonidcB their surface is striated ; in some Cyprinida (Tench)
they are confluent : but commonly they are distinct, and have in

Bruin and portion of niyelon
Cod. CCXVT.

184

185

Optic ventricles ;
Herring

Base of train ; Cod

280 ANATOMY OF VERTEBRATES.

their inferior interspace a vascular medullary depressed sac (the
f haematosac,' fig. 185, o), usually oblong, as in the Cod, rarely
bifid or cordiform, as in the Lumpfish. These prominences from
the floor of the mesencephalon, posterior to the infundibulum and
hypophysis, ib.p, are peculiar to the brain of fishes, and, in their full
developemeiit, are restricted to the typical osseous member of the
class ; they are absent in the lowest, and disappear in the highest
orders ; they are mere rudiments, or are wanting, in the Poly-
pterus, as in the still more amphibioid Lepidosiren.

The true vasculo-membranous infundibular downward pro-
longation of the third ventricle exists in all Osseous Fishes, and

O

extends from the anterior angle of the hypoaria, where these
exist : the infundibulum is commonly short and thick, so that the
hypophysis is almost sessile, as in the Cod ; but in the Lophius,
the infundibulum is longer than the entire brain, and the hypo-
physis lies at the fore-part of the cranial cavity, far in advance of
the cerebral lobes.1 In the Cod the hypophysis, fig. 185,7?, *s a
subspherical mass, with an irregular or slightly nodulated surface,
almost half the size of the human, so called, l pituitary gland,'
and illustrating the vast proportional size of this constant
appendage to the brain of Fishes. In the Lepidosiren the infun-
dibulum is wide, and the hypophysis a white flattened discoid
body, fig. 186, o.2 In all Fishes it is richly supplied with vessels,
and is closely attached to the floor of the cranium ; but, although
its early de /elopement checks or modifies that of the cranial
vertebra?, it is not provided with a special chamber or ( sella.'
The prolongations of the fibres from the mesencephalon which
expand into the prosencephalic or proper cerebral lobes rarely
show any preliminary developement of ' thalami ; ' but the parts
homologous with those recruiting ganglia are constantly indicated
by the attachment of the conarium, or upper prolongation of the
third ventricle.

The conarium, figs. 175, 186, 187, w} is as constant an append-
age of the encephalon in Fishes as the hypophysis ; but it is com-
monly only a vasculo-membranous pyramidal sac continued from
the third ventricle, the base expanding from between the anterior
interspace of the optic lobes, and the apex directed forward and
attached to the roof of the cranium. Some medullary matter
mingles with the membranous walls of the conarium in the
Clupeoid and Cyprinoid Fishes : in some Fishes there is grey
matter in the conarium : in most it is membranous only, as in the

1 i,x. p. 50, t. ii. fig. 1.

2 The hypophysis is marked g in xxxiii. pi. 27, fig. 4; and is called ' maramillary
body' in Lepidosiren annectens, ib. p. 361.

ENCEPHALON OF FISHES. 281

Lepidosiren, Sturgeon, and Shark : in all it is highly vascular.
In the Bream the conarium shows an analogous peculiarity to
that of the hypophysis in the Angler, viz. in the length and
tenuity of its attachment ; but this consists of two distinct crura.
The value of the constancy of the hypophysis and conarium con-
sists chiefly in their marking the boundary line between the mes-
and pros-encephala, although they belong to the mesencephalon,
and are both essentially vertical prolongations of the third ven-
tricle through an interspace produced by the divarication of the
main lateral columns of the encephalon.

The fasciculi continued forward from the parietes of the third
ventricle or mesencephalic basis, are principally those which may
be traced back through the epencephalon to the anterior and
lateral myelonal tracts, augmented by fibres from the grey centres
or lobes through which they have passed, and retaining a small
admixture. of post-pyramidal fibres from the optic septum,
fig. 184, r. In Osseous Fishes the two cerebral crura, so con-
stituted, rarely undergo any enlargement, homologous with the
6 thalami,' where they form the anterior boundary of the third
ventricle ; but after a very brief course, as ( crura cerebri,' fig. 178,
x, radiate into two small subspherical f prosencephalic ' masses of
grey matter, ib. P, situated anterior to the optic lobes, and there
in great part terminate. A few of the medullary fibres extend
along the base of the prosencephalon, receive a small tract of its
grey matter, converge to the anterior interspace of its lobes, and
either expand there into ' rhinencephala,' figs. 174, 175, 186, R,
or are continued forward and outward, as ( rhinencephalic crura,,'
figs. 178, 187, z} to form the olfactory lobes or ganglia, ib. R,
at some distance from the brain. Although the prosencephalic
lobes are commonly in contact with the optic lobes, yet something
analogous to the displacement of the rhinencephalon may be seen
in the prosencephalon of the Chimaera, in which the cerebral
crura, fig. 179, b, advance some way before they expand into the
prosencephala, P : in the Plagiostomes, also, the prosencephalic
crura, fig. 187, x} have a short independent tract in advance of
the optic lobes.

The prosencephala, figs. 177, a, 180 and 182, c, 183, a, b, in
other figs. P, are distinguished from the optic lobes by their
grey pinkish exterior, and, generally, also by their fissured
or nodulated surface. The first of these characters must be
looked for in recent fish: the second is more permanent.1 With

1 xx. vol. iii. it may be seen in preparations of the brain of the Eel (Anguilla acuti-
rostris, No. 1309, B); of the Lump-fish (Cyclopterus, No. 1309, C'); of the Gurnard
(Trigla hjra, No. 1309, D'); and especially in this specimen of the brain of the Cod

282 ANATOMY OF VERTEBRATES.

regard to the f cerebrum ' of the Cod. a median tract or con-

c5

volution is marked off by a longitudinal fissure, Avhich extends
along the back of each prosencephalon, defining a posterior and
inferior convolution ; the median convolution is vertically fissured
on its inner side. In the Amblyopsis, fig. 175, P, it is cleft
anteriorly ; and here, as in most fishes, the median longitudinal
tract is the most constant subdivision of the prosencephalic
superficies.

The large elongated prosencephala are smooth in Chimrcra,

fig. 179, P, Polypterus, and Lepidosiren, fig. 186, P, and in the

186 still more developed confluent mass

in the Sharks, fig. 187, P ; the
prosencephala are, also, smooth in
the Myxines, where they are rela-
tively smallest. The comparative

Brain of Lepidosiren . , , p .-. ,

anatomists, who have failed to

recognise the true homology of the prosencephalon in Osseous
Fishes, appear to have been misled chiefly by its small proportional
size, which is commonly that exhibited in the brain of the Cod,
the Carp, and the Globe-fish ; in some species the prosencephalon
is even smaller, as in the Gar-fish, the Herring, or the Lump-fish.
The prosencephalon equals the cerebellum in size, but is less than
the optic lobes in the Perch and Bream ; it equals the optic lobes,
but is less than the cerebellum, in the Eel ; in the Stickleback
and Gurnard the prosencephalon exceeds the cerebellum, still
more so in the Lepidosteus, but is less than the optic lobes ; in the
Lucioperca, the Amblyopsis, the Chimaera, and the Skate, neither
the cerebellum nor the optic lobes are so large as the prosence-
phalon ; in the large Sharks their united size scarcely equals that
of the prosencephalon ; and in the Salamandroid Polypterus and
the Lepidosiren the prosencephalic lobes surpass all the rest of
the brain, and vindicate their true cerebral character and impor-
tance. In the Amblyopsis the relative magnitude of the prosen-
cephalon is due to the diminution of the optic lobes in that blind
fish ; in the Plagiostomes it is due to absolute developement ; as it
is, also, in the Polypterus and Lepidosiren, where the prosence-
phalon presents the closest similarity in form and structure to that
division of the brain in the Batrachian Reptiles : each lobe, for

(No. 1309), which Hunter truly, though briefly, describes as follows : — "The cerebrum
fissured; the cerebellum a long projecting body, also fissured in a less degree; the
nates two projecting bodies: the optic nerves decussate one another." This is the
earliest recognition of the homology of the optic lobes with the anterior of the bigcini-
nal bodies of the human brain.

ENCEPHALON OF FISHES.

283

187

g a

Brain of Shark, Carcharias

example, is elongated in the axis of the skull, and is of a sub-
compressed oval form, and has a large ' lateral ventricle ' in its
interior in the Lepidosiren, fig. 186, I v. In the Skate, the pros-
encephala coalesce into a subdepressed transversely elongated
mass, their essential distinction being indicated by a mere super-
ficial median fissure ; in Carcharias, fig. 187, the prosencephalon
forms an almost globular mass, with scarcely a trace of a median
fissure. Among bony fishes the
prosencephalic lobes are more
or less confluent in Lucioperca
sandra, Tracliinus draco, Sar-
f/us, Mullus, Scomber trachinus,
Belone, Clupea harengus, and
Clupea sprattus ; they appear
distinct symmetrical spheroids
in most other fishes, their union
being reduced to a small trans-
verse medullary band (prosencephalic commissure).1 The sym-
metrical character of the prosencephala, as of the optic lobes, is
wanting in most Pleuronectidce.

The grey vascular neurine forms the greatest part of the pros-
encephalon inmost Osseous Fishes; the white fibres radiate through
this, and rarely appear on any part of the exterior surface ; the
white substance, however, predominates in the Plagiostomes and
Lepidosiren. As a rule, the prosencephalic lobes are solid ; but
the brain of Carcharias 2 shows a deep ventricular fissure at the
anterior and under part of the prosencephalon, with a vascular
fold of membrane or ' choroid plexus ' penetrating the fissure,
which is continued forward into the cms of the olfactory lobe.
The lateral ventricle is more extensive in the Lepidosiren, and is
continued directly into the olfactory lobe.

The ( rhinencephalon ' figs. 173 — 176, R, consists of two always
distinct lobes of grey matter, which receive the prolongations
of chiefly white fibres from the prosencephalon and its crura, and
give off the nerves to the olfactory capsule, whence they are
termed 4 olfactory lobes,' ' ttibera,' or ( ganglia.' The rhinence-
phala are solid bodies, always distinct, wide apart from each other
when remote from, and in mutual contact when near to, the rest
of the brain, but never united by a commissure. The rhinence-

1 Cams well recognises the homology of this commissure with that of the corptis
striatum, called * anterior commissure ' in the human brain, i. p. 24.
3 (No. 1310, A), xx. vol. iii.

284 ANATOMY OF VERTEBRATES.

phalic crura, figs. 171, 175, 178, 187, z, vary exceedingly in length.
In the Lepidosiren, fig. 186, they are feebly indicated by a con-
tinuous indentation circumscribing the base of the rhinenccphalon,
R, and defining it from the anterior end of each prosencephalic
lobe, P ; in Polypterus and Lepidosteus the indentation is deeper,
and the attachment of the base of the now pyriform rhinence-
phalon, fig. 174, R, sinks to the prolonged cms or basis of the pros-
encephalon. From this substratum the rhinencephalic crura are
prolonged in all Osseous Fishes : in some they are so short that the
rhinencephala are partly overlapped by the prosencephala ( Trie/la),
or rise into view immediately in front of them (Amblyopsis,
Anc/uilla, fig. 176, R, Coitus, Cyclopterus) ; but in many fishes the
rhinencephala are developed far in advance of the rest of the
brain, and their crura are prolonged close to the olfactory cap-
sules. This has led to a denial of the existence of olfactory lobes
in such fishes ; but the rhinencephala are truly present in both
the Cod and Carp, fig. 178, R ; they are merely removed to juxta-
position with the olfactory capsules, with a concomitant pro-
longation of their crura. These crura, so prolonged, ib. z, have
been called ' olfactory nerves ' by those who, failing to appreciate
the true homology of the remote ' rhinencephala,' have described
them as ganglionic swellings of the ends of the olfactory nerves.1
These ganglions, wherever situated, consist of proper nervous
matter over and above the mere radiation or expansion of the
fibres of the so-called ( olfactory nerves.' The true olfactory
nerve quits the rhinencephalon as a plexiform chord, or as a group
of distinct fibres. If the thick olfactory nerve of the Gurnard be
compared with the thick rhinencephalic crus of the Skate, or if the
long olfactory nerve of the Eel be compared with the long rhin-
encephalic crus of the Chub, fig. 177, k, their respective difference
of structure will be readily appreciated. The crus is a compact tract
of medullary with a small proportion of grey matter ; the nerve
is a bundle of nerve filaments : the medullary tract of the crus
is fibrous, but the fibres are as fine as in the crus cerebri, and
much more numerous and less easily separable than in the true
olfactory nerve. In this there is no grey tract : it consists wholly
of comparatively large and readily separable white fibres, which
radiate at once upon the olfactory capsule ; the divergence and
radiation of the true end of the olfactory nerve is well seen in
the Lepidosiren, fig. 186, i, ol. In Sharks a ventricle is continued
to each rhinencephalon along its crus from the prosencephalon. The

1 Camper, LXI. p. 95; Cuvier, xxur. p. 321.

ENCEPHALON OF FISHES. 285

olfactory nerve never forms a ganglion before spreading upon
the olfactory capsule ; the rhinencephalic crus, when prolonged
to the capsule, always expands into a ' tuberculum olfactorium,'
or rhinencephalon, before it transmits the true olfactory nerves to
the capsule. In other words, the olfactory nerve conveys im-
pressions to a proper centre or lobe, which, in Fishes, may be
situated close to the capsule, or close to the rest of the brain,
and the length of its crus will be inversely as that of the nerve.
The olfactory lobes or rhinencephala are serially homologous with
the optic lobes. As to the prosencephalon, since this does not
immediately receive or transmit any nerve, it resembles in this
important character the cerebellum, and proceeds, even in the
present class, to be developed to a degree beyond the ganglions
of any special nerves or organs of sense.

The more special homology of the prosencephalic lobes,
under their normal proportions and solid structure in Osseous
Fishes, with the parts of the complex and fully developed prosen-
cephalon in Mammals, will be made manifest as we trace the
progress of that complication synthetically. Cuvier had already,
by the opposite course of analysis, reduced the hemispheres
in birds to the e corpora striata,' with their commissures and a
thin supraventricular covering. ' Le corps cannele,' he says,
s forme a lui seul presque tout 1'hemisphere.' l But he failed
to recognise the homology of the prosencephala in Fishes.
Since Arsaki's time 2 their homology with the cerebral lobes of
Reptiles, Birds, and Mammals has been generally recog-
nised. Girgensohn3 says they may well be compared with
the ' corpora striata ; ' but he notes the important difference,
that, whereas these ( transmission ganglia ' (durchf/angsknoten)
give passage to the radiating fibres of the cerebral crura in
their course to other parts of the cerebrum in Mammals, those
fibres terminate in the solid prosencephala of Fishes. The
establishment of the lateral ventricles in the prosencephala of the
Plagiostomes and Lepidosiren also show them to be something
more than ( corpora striata.'

It now becomes important to note the mode of establishment
of these cerebral ventricles : they are not formed by the super-
addition of a layer or film of neurine overlapping parts answerable
to the solid hemispheres in other Fishes, but are either central
excavations, as in the elongated prosencephala of the Lepi-
dosiren, fig. 186, Iv. or they are deep fissures towards the under
part, as in the coalesced hemispheres of the Shark ; whence I

1 CC. t. ii. 1799, p. 162. 2 LIII. 1813. 3 LXIII. p. 155.

286 ANATOMY OF VERTEBRATES.

conclude that the solid prosencephalon of Osseous Fishes is not
u mere representative of a basal ganglion forming the floor of the
ventricle of the hemispheres in the higher Vertebrates, where such
ganglion is a medium of transmission or source of accession to
the cerebral fibres ; but that the fish's prosencephalon is the seat
of the terminal expansion of the radiating medullary fibres of the
cerebral crura. Dissection of the recent brain shows, as in
fig. 178, P, that these fibres, besides being blended with grey
matter, as in the corpora striata, are thickly covered with a
layer of the same grey and highly vascular neurine, of which the
hemispheric convolutions in Mammals are chiefly formed ; and it is
interesting to perceive on the superficies of the solid prosence-
phalon in many fishes the foreshadowing of the convolutions,
which are not fully established until an advanced Mammalian
grade is attained. The prosencephalon of the fish is far from
being a miniature model, but it may be regarded as the potential
representative, of the complex cerebral hemispheres of man.

The average proportional weight of the brain to the rest of
the body in Fishes is as 1 to 3000. In a chub (Leuciscus Cy-
prinus) weighing 842 scruples, the brain, exclusive of the olfactory
lobes, weighed one scruple ; in a carp ( Cyprinus Carpio), weigh-
ing 11,280 grains, the brain weighed 14 grains ; in a lamprey
weighing 750 grains, the brain weighed half a grain. A certain size
seems to be essential to the performance of its functions, as a
recipient of the impressions from the organs of sense ; and it
does not, therefore, vary in different species so as to accord pre-
cisely with the general bulk of the body. The size of the optic
lobes, e.g. has a more constant and direct relation to that of the
eyes, which soon acquire their full developement. We find the
entire brain proportionally greater in young than in old fishes :
it acquires its full size long before the termination of the
growth of the fish, if this has a fixed period. But as the
head must grow with the growth of the fish, under the con-
ditions of its progressive motion, provision for occupying the
increasing capacity of the cranium is made by a concomitant
developement of the light cellular arachnoid, which has the
further advantage of regulating the specific gravity of the head.

As the branchial respiration is a peculiarly active and im-
portant function in Fishes, and has an extraordinary apparatus of
bony or gristly arches with their muscles, we may associate there-
with the peculiar developement and complexity of the medulla
oblongata, as the centre of the vagal or respiratory nerves. The
Carp and other Cypriuoid Fishes, which have not the mechanical

ENCEPIIALON OF FISHES. 287

modifications for retaining water in contact with the gills, so
characteristic of the Apodal, the Lophioid, and Labyrinthi-branch
fishes, are remarkable, nevertheless, for their tenacity of life out
of water ; and the peculiarly developed vagal lobes may relate to
this maintenance of the power of the respiratory organs during a
suspension of their natural actions.

The extensive gradation of the cerebellum between the ex-

c?

tremes of structure presented by the Myxine and the Shark,
as might be expected, throws more direct light upon its function.
With regard to this, two views have been taken. According to

O •* O

one it is the organ of amativeness ; according to the other it is
the seat of the muscular sense, or the regulator of voluntary
motion. Many experiments in which the cerebellum has been
mutilated or removed in warm-blooded animals support the idea
of its intimate relation with the locomotive powers. But to the
conclusions from these experiments has been objected the pos-
sibility of the convulsive muscular phenomena having arisen from
the stimulus on the remaining centres, occasioned by the mutilation
or destruction of the one in question ; and it may well be doubted
whether Nature ever answers so truly when put to the torture,
as she does when speaking voluntarily through her own experi-
ments, if we may so call the ablation and addition of parts which
comparative anatomy offers to our contemplation.

If, in reference to the sexual hypothesis of the cerebellum, we
contrast the Lamprey with the Shark, we shall be led, by the
much larger proportional size of the generative organs in the
lower cartilaginous Fish, and from the observed fact of the male
and female Lampreys entwining or wreathing themselves entirely
about each other, mutually aiding in the expulsion of their
respective generative products, and so absorbed in the passion as
to permit themselves to be taken out of the water and replaced
there, without interruption of the act, to expect a larger cere-
bellum in the Lamprey than in the Shark. But the very re-
verse of this is the fact : the Lamprey has the smallest, and
the Shark the largest, cerebellum in the class of Fishes. If,
on the other hand, we compare the Cyclostome and Plagio-
stome Cartilaginous Fishes, in reference to their modes and
powers of locomotion, we shall find a contrast which directly
accords with that in their cerebellar developement. The Myxine
commonly passes its life as the internal parasite of some higher
organised fish : the Lamprey adheres by its suctorial mouth
to a stone, and seldom moves far from its place : neither fish
possesses pectoral or ventral fins. The Shark, on the contrary,

288 ANATOMY OF VERTEBRATES.

unaided by an air-bladder, sustains itself at the surface of the
sea, by vigorous muscular exertion of well-developed pectoral
and caudal fins, soars, as it were, in the upper regions of its
atmosphere, is proverbial for the rapidity of its course, and sub-
sists, like the Eagle, by pursuing and devouring a living prey :
it is the fish in which the instruments of voluntary motion are
best developed, and in which the cerebellum presents its largest
size and most complex structure. And this structure cannot be
the mere concomitant of a general advance of the organisation to
a higher type, for the sluggish Rays, that grovel at the bottom,
though they copulate, and have in most other respects the same grade
and type of structure as the more active Squaloid Plagiostomes,
yet have a much smaller cerebellum, with a mere crucial in-
dentation instead of transverse lamina?. A more decisive instance
of the relation of the cerebellum to the power of locomotion is
given by the Lepidosiren in which, with a more marked general
advance of organisation than in the Ray or Shark, the cerebellum
has not risen above the simple commissural condition which it
presents in the Lamprey ; the generative system, however, of the
Lepidosiren is as complex as in the Plagiostomes, and is more
extensive : but the fins are reduced to mere filaments, and the
fish is known to pass half the year in a state of torpid inactivity.
The cerebellum is large in the Chima3ra, fig. 179, c. In the heavy
laden ganoid fishes, the cerebellum is smaller than in the ordinary
Osseous Fishes : the imbricated armour of dense enamelled bony
scales must limit the lateral inflections of the tail ; so we find in
Polypterus the cerebellum hardly more developed than in Lepido-
siren, whilst in the somewhat more active and predaceous Lepi-
dosteus it is the smallest of all the segments of the brain. In
the grovelling Sturgeons the cerebellum offers a grade of develope-
ment above that in the Lepidosiren. Finally, amongst the normal
Osseous Fishes, the largest and highest organised cerebellum has
been found in the Tunny, whose muscular system approaches, in
some of its physical characters, most nearly to that of the warm-
blooded classes.

If we could enter the sensorium of the fish, and experience
the kind of sensations and ideas derived from the inlet of their
peculiarly developed and enormous eyes, we might be enabled to
understand the office of the peculiar complexities of their
large optic lobes : without such experience, we can at best
only indulge in vague conjecture from the analogy of our own
sensations. We find, when Nature reduces the organs of
sight to such minute specks as can give but a feeble idea of

ENCEPHALON OF FISHES. 289

the presence of light, sufficient, perhaps, to warn the Ambly-
opsis to retreat to the darker recesses of its subterranean
abode, that the optic lobes are not reduced in the same proportion,
but retain a form and size, which, as compared with their homo-
logues in other animals, are sufficiently remarkable to suggest a
function over and above that of receiving the impressions of
visual spectra, and forming the ideas consequent thereon.

The anatomical condition of the prosencephalon, and its
homology with the hemispheres of the bird's brain, experimented
on by Flourens,1 would lead to the belief that it was in this
division of the fish's brain that impressions become sensations, and
that here was the seat of distinct and tenable ideas : of such, for
example, as teach the fish its safest lurking-places, and give it that
degree of caution and discernment which requires the skill of the
practised angler to overmatch. If different parts of the prosence-
phalonwere special seats or organs of different psychical phenomena,
such phenomena are sufficiently diversified in the class of Fishes,
and are so energetically and exclusively manifested, as to justify the
expectation, on that physiological hypothesis, of corresponding
modifications in the form and developement of the homologues of
the cerebral hemispheres. Some species, as, for example, the
Shark and Pike, are predatory and ferocious : some, as the Angler
and the Skate, are crafty : some, as the Sword-fish and Stickle-
back, are combative : some, as the Carp and Barbel, are peaceful,
timid browsers : many fishes are social, especially at the season
of oviposition : a few are monogamous and copulate ; still fewer
nidificate and incubate their ova.

Now, if we compare the prosencephala of the Shark and Pike,
fishes equally sanguinary and insatiable, alike unsociable, the
tyrants respectively of the sea and lake, we find that those parts
of the brain differ more in shape, in relative size, and in struc-
ture, than in any two fishes. The prosencephalon of the Pike
is less than the cerebellum, much less than the optic lobes ; in
the Shark it exceeds in size all the rest of the brain : in the Pike,
the prosencephalon consists of two distinct lobes brought into
communication only by a slender transverse commissure ; in the
Shark, the hemispheres are indistinguishably blended into one
large subglobular mass. If we compare the prosencephala of the
Pike with those of the Carp, we find them narrow in the de-
vourer, broad in the prey.

The Lophius lurks at the bottom, hidden in the sand, waiting,
like the Skate, for its prey to come within the reach of its jaws :

1 LXIV.

VOL. I. U

290 ANATOMY OF VERTEBRATES.

the difference in the shape, size, and structure of their prosence-
pliala is hardly less than that between the Shark and Pike. The
combative Stickleback has longer and narrower prosencephala
than the cowardly Gudgeon. The nidificative and philo-pro-
genitive Callichthys has neither the antero-lateral nor the posterior
regions of the cerebrum more developed than in bony fishes
generally.

§ 53. Myelencephalon of Reptiles. — The perennibranchiate Bn-
trachia lead sluggish lives in swamps and pools ; their senses are
as little developed as those of the Lepidosiren, and their mus-
cular movements are perhaps even more restricted : hence, if the
cerebral lobes seem to preponderate, in proportion to other parts
of the brain, over the prosencephalon of Osseous Fishes, it is
rather by contrast with the rudimentary condition of the mes- and
ep-encephala than in the relative size of the prosencephalon to the
entire body.

In a Newt, weighing 39 grains, the brain weighs one-seventh
of a grain : and in the large Sirens, Amphiumes, and Menopomes,
the proportion of the brain to the body is less than in the
Newts.

The medulla oblongata slightly expands; the post-pyramidal
and restiform tracts diverge and expose a long and simple ' fourth
ventricle,' with a median fissure : the convergence and confluence
of the borders at the fore part of the ( calamus ' offer a feeble
rudiment of cerebellum. The optic lobe in the Axolotl is a long
elliptical body, two-thirds the breadth of the epencephalon. A
slight swelling below gives off the small optic nerves, and is
produced anteriorly into a vascular f hypophysis ' : a larger pineal
body extends from before the optic lobe upon the posterior inter-
space of the cerebral lobes, completing the mesencephalon, which
is the smallest of the primary divisions of the brain. The
cerebral hemispheres, twice the length and breadth of the optic
lobe, are smooth and hollow, like those of Lepidosiren. The
olfactory lobes are pyriform, with the base sessile on the fore
and outer part of the hemispheres ; the nerve is shorter than in
Lepidosiren. The cerebral ventricles are continued into the
olfactory lobes.

The small and simple brain may be wholly removed from a
torpid batrachian in the winter season, the medulla oblongata
included, by section of the myelon in front of the roots of the
second pair of cervical nerves ; and, nevertheless the animal
survives many weeks, preserving the reflex actions of the myelon
and nerves, the contractility of the muscular fibre, and the

ENCEPHALON OF REPTILES.

291

188

functions of organic life. In the active state of the summer
season, such mutilation is followed by death in one or two hours,

rarely more.1

In serpents, the cerebellum, fig. 188, c, expands into a depressed
semicircular lobe directed backward from the confluence of the
restiform crura and overlapping the major part of the fourth
ventricle, which appears as a short median fissure. The optic
lobes, ib. b, now expanded
to the breadth of the cere-
bellum, show both a longi-
tudinal and a transverse
fissure, the latter crossing
near the hinder border, and
giving to this part of the
brain a close resemblance
to its homologue the ' bige-
minal bodies * in Mammals.
The optic lobes are hollow :
the cerebral crura show
slight enlargements, like
optic thalami, anterior to
the optic lobes, before ex-
panding into the hemi-
spheres. These are pressed
into close contact medially,
and compose a prosence-
phalon nearly as broad as

Ion":, and double the

o7 •

breadth and length of the
mesencephalon. The outer
surface of the hemispheres
is smooth, composed of a
thin layer of vascular or
grey iieurine* Into their
cavity or ventricle a ( cor-
pus striatum' projects from
the under and outer side ; beneath or mesiad of which is a minor
prominence. The septum, formed by the thin mesial wall of
each hemisphere, is perforated for the passage of a ' chorokl
plexus.' The ventricles are continued forward into the olfactory
lobes, fig* 188, i ; each is marked off by an oblique fissure from
the fore part of the hemisphere, which it equals in breadth ;

1 cci.

u 2

ffl

Braiii aiid Xerves of the Boa Constrictor. LIT.

292

ANATOMY OF VERTEBRATES.

189

and alter a short curve, resolves itself into a close fasciculus of

olfactory nerves.

In the Lacertilia, the eyes being relatively larger
and more active in function than in Serpents, the
optic lobes, fig. 189, &, show corresponding increase
of proportional size to other parts of the brain. The
cerebellum, ib. c, is still smooth, depressed, semi-
circular, and leaves more of the fourth ventricle, e,
exposed than in Pytlwn. The optic lobes cease to
show the transverse fissure, and form a pair of hemi-
spherical hollow bodies. The cerebral hemispheres,
ib. a, form an elongate oval body, more contracted
anteriorly than in Python. The olfactory lobes, ib. g,

Lizard (Lacerta are contracted at their junction with the hemispheres

view!s)CcxvTr into the resemblance of ( crura rhinencephali.'

191

190

Brain of Tortoise, base view,
ceviii.

y

Bniiu of Turtle (Chelone), upper view.
CCXYI.

In the base view of the brain of the Tortoise, given in fig. 190,
the absence of ' pons Varolii ' and of olivary or pyramidal "bodies

ENCEFIIALON OF REPTILES. 293

is shown in the medulla oblongata, which is indicated by a slight
tumefaction giving off the fifth, 3, 4, 5, 6, seventh, 7, eighth, 8, and
ninth pairs of cerebral nerves : the tract is bounded anteriorly
by the hypophysis covering the origin of the optic nerves.
The continuation of the basal fibres of the hemispheres, P,
into the rhinencephalon, R, is shown.

In a side view, the several primary divisions of the cheloniaii
brain present the shapes and proportions shown in fig. 192, in which
c is the epencephalon, o, the mesencephalon, p the prosence-
phalon ; R, the rhinencephalon. The epencephalon includes the
medulla oblongata, with the cerebellum,

192

h
Brain of a Turtle (Oielone), side view. ecu.

In the turtle (Chelone, fig. 191) the cerebellum, c, is slightly
raised by the bristle, o, to expose the fourth ventricle, h, in which
the sides of the calamus rise into 6 teretial tracts.' The cere-
bellum is subelongate in its form, consisting of an arched layer
of neurine, smooth externally, of equal thickness throughout,
which spreads over a portion of the ventricle. The remainder
of that cavity is covered by a vascular plexus, derived from
the sides of the medulla oblongata, which forms a sort of valve,
and by becoming united to the margin of the cerebellum, com-
pletes the roof of the fourth ventricle, which is large and pro-
longed very far back. The optic lobes, o, are smooth, sphe-
roidal bodies, on a plane inferior to the cerebellum and cere-
brum. Each lobe has its ventricle, c*, which communicates, as
shown by the bristle, m, with the fourth ventricle, and likewise
with the third ; the ( iter ' to which may be seen by divaricating
the optic lobes, covered by pia mater reflected down the interspace,
and by a very thin layer of neurine. From the third ventricle a
canal, or ( infundibulum,' is continued down to the hypophysis, and
another upward to the ( pineal ' body, which is pyriform, hollow,
and highly vascular: it occupies the interspace between the
optic, o, and cerebral lobes, P. These form the largest of the

294 ANATOMY OF VERTEBRATES.

primary divisions of the brain,, but retain the form and character
of simple smooth nodules. Each lobe has its ventricle, fig. 191,
r, containing a ' corpus striatum,' fig. 193, i, in which
the ' crus cerebri,' fig. 194, i, principally expands ; also a
smaller oblong eminence connected with the e thalami optici,'
fig. 193, 2; and a transverse body extending anteriorly to the
mesencephalon from the base of one lateral ventricle to the
other. The choroid plexus is shown in the left ventricle of
fig. 193. The olfactory lobes, of a pyramidal form, have their
base defined by a fissure from the hemispheres ; each has
its ventricle, fig. 191, k, which communicates with the 'lateral'

one, r.

The myelonal canal, fig. 191, g, is continued along all the
encephalic masses, in which it expands, and assumes the name
of 'ventricles,' the narrower intercommunicating canal being
the 'iter.' The 'fourth' or epencephalic ventricle is single : the
hypoarian ventricles, in fishes, form a pair ; as do, likewise,
the mesencephalic, prosencephalic, and rhinencephalic ventricles.
The ' iter ' or common passage between the ep- mes- and pros-
encephalic ventricles, includes the cavity called ( third ventricle '
in Anthropotomy : to which cavity the mesencephalic ven-
tricles are reduced by the consolidation of the optic lobes in

Mammals. l

The epencephalic or 'fourth ' ventricle, exposed in figs. 193, and
194, c, shows the 'teretial' columns bounding the 'calamus' or
median fissure : external to these are ( funicular ' and ' pre-
pyramidal tracts : the restiform columns, forming the sides and,
anteriorly, the roof of the ventricle show grey and white striae
on their inner surface ; the cerebellum is removed from their
anterior union at s, fig. 194. The mesencephalic base which

1 The influence of the nomenclature of human anatomy, reflected downward upon
the dawning structures of the lower animals which culminate in Man, is nowhere more
obstructive to a plain and true indication of the nature of parts than in regard to those
of the brain. The ventricles, for example, were indicated by numbers, or by position.
But four of the primary ventricles, viz., the mesencephalic or optic pair, and the
rhinencephalic or olfactory pair, which are present in the majority of vertebrates, are
obliterated in Man ; whilst the interspace of commissural lamelke, exceptionally deve-
loped in the complex cerebrum of Man, and some higher Mammals, is made a 'fifth
ventricle,' as if it were a structure of correlative significance and importance with the
ventricles properly so called. Those cavities moreover in the human prosencephalon
are specialized as ' lateral, ' being the only ventricles retaining the parial state which
is shown by the mcs- ancl rhin-encephalic ventricles in all oviparous Vertebrates.
Whoever will carry out the application of neat substantive names to the homologous
parts and structures of the encephalon, as they may be ascensively determined, will
perform a good work in true Anatomy.

MYELON OF EEPTILES.

295

supports the optic lobes, is exposed from above, by their removal,
in fio;. 194, 2, showing the continua-

J -s \— '

193

194

195

tion of the ventricular cavity through
that segment of the brain. The base
of the excised ' corpus striatum ' into
which the ( crus cerebri ' expands, is
shown at i, fig. 194. The prolonga-
tion of the optic lobe crosses the
cerebral crus, externally, in its way
to the optic tract, fig. 195, d\ a por-
tion has been removed in this figure
to expose the crus cerebri in its ascent
to the hemisphere. Three tracts of
neurine may be traced from the pros-
encephalon to the rhinencephalon, of

Which the inferior One is the mOSt DissectionB of the b^nofa Turtle,

distinct, fig. 190.1

In the brain of the Crocodile a marked advance is seen in the
relative size of the cerebral lobes, especially in regard to their
breadth and height posteriorly, giving a pyriform shape to the
prosencephalon ; the optic lobes, also, are
not inferior in bulk to the cerebellum, and
this body shows a transverse fissure on its
exterior. The olfactory lobes, which are
situated near the hemispheres in the newly
hatched Crocodile, recede therefrom, and
advance, with a proportional prolongation
of the rhinencephalic crura. The optic
lobe shows a convex body projecting into
the ventricle from its posterior wall, which
body is serially homologous with the '• cor-
pus striatum ' in the ventricle of the cere-
bral hemisphere. In other respects the
brain of the Crocodile closely conforms with that of the Turtle.

With the exception of the anourus Batrachia, the myelon
(spinal chord) is continued into the tail, gradually decreasing to a
point, and is not resolved into a ' cauda equina.' Such, indeed,
is its condition in the tadpole state of the frogs and toads ; but,
with the acquisition of the mature form, the myelon shrinks in
leno*th, and terminates midway between the fore and hind limbs,
beino* resolved in the frog, into the three pairs of nerves which

Dissections of the brain of a
Turtle (Clielone). LIT.

1 xx. vol. iii. p. 22, No. 1312.

296 ANATOMY OF VERTEBRATES.

form the sciatic, and into a few filaments passing on to the
sacrum, fig. 208, f.

In all Reptiles there is an anterior and a posterior longitudinal
fissure and a central canal dilating into the epencephalic ventricle.
The myelonal canal is surrounded by a thin layer of grey
neurine, and, in Lacertians and Crocodilians, it extends as far as
the first caudal vertebra : in Ophidians, which have the longest
spinal chord, the canal is continued to near the end, which
goes as far as the penultimate caudal. The enlargements
giving origin to the nerves of the limbs are best marked
in Chelonia, owing to the relative slenderness of the myelon
in the trunk. In the Lizards and Crocodiles with nearly
equally developed limbs, the more muscular trunk and tail
demand a myelonal mass which renders the brachial and iliac
enlargements less conspicuous. There are no partial enlargements
of the myelon in Serpents ; the nerves, as numerous as the
vertebras, are given off at short and regular distances, as in

' O O '

fig. 188, m.

§ 54. Membranes of the Myelencephalon in Hcematocrya. — Both
brain and myelon are immediately invested by a thin but firm and
vascular membrane, the outer surface of which, in most Fishes and
many Reptiles, bears a stratum of pigment-cells belonging properly
to the central layer of the arachnoid, which has here coalesced
with the pia mater. This vascular membrane seems, therefore, to
be coloured with dark points, and sometimes to be minutely
speckled upon a silvery ground ; and the pigmental stratum often
accompanies the processes of the pia mater into the ventricles of
the brain. There is commonly a remarkable developement of the
vascular and pigmental membrane over the fourth, or epencephalic
ventricle ; it is largely developed in the Sturgeon, and conceals
the rudimental cerebellum in the Lepidosiren. In the Axolotl
calcareous particles are superadded to this covering of the epen-
cephalon. In Osseous Fishes the commonly considerable space
between the brain and cranial walls is occupied by a peculiar loose
cellular structure, filled by gelatinous or albuminous fluid, and by
oily matter : in the Perch and Bream it seems to consist of an
aggregate of minute spherical cells filled with fine colourless
oil, the mass being traversed by blood-vessels. Cuvier * found
the cells, which he compares to a kind of arachnoid, filled by a
compact adipose matter in the Tunny and Sturgeon. This modified
arachnoid exists, but in less quantity, in the spinal canal, and

1 XXTII, i. p. 309.

NERVES OF FISHES. 207

even accompanies the cerebral nerves in their exit from the skull
in some fishes with large nerve-foramina. There is much cellular
arachnoid above the cerebral lobes in the Lepiclosiren. A large
arachnoid is abundantly interposed between the dura mater and
pia mater in the Turtle ( Chelone), where two ligaments converge
from the arachnoid at the sides of the epencephalon to be attached
to a cartilaginous tubercle on the basioccipital. A number of
filamentary processes pass from the space between the cerebral
and optic lobes to the arachnoid above, like a rudimentary
' falx.'

The primitive fibrous capsule of the neural axis, the unossified
or unchrondrified remains of which, or of its inner layer, form
the so-called ' dura mater,' is most distinct in the low-organised

* o

Dermopteri ; in the Playiostomi it is reduced to a few thin shining
aponeurotic bands closely adherent to the inner surface of the
cartilaginous walls of the cranium and spinal canal ; such traces
of dura mater are more feeble and indistinct in Osseous Fishes,
in which no proper continuous fibrous membrane can be dis-
tinguished from the inner periosteum of the walls of the cerebro-
spinal cavity : no curtains of dura mater divide the cerebral from
the acoustic compartments of the cranium in the Osseous Fishes.
The dura mater, as a distinct fibrous membrane, lines the cavity
of the skull and spinal column in Reptiles.

§ 55. Nerves of Fishes. — First pair or Olfactory nerves. — The
head is short and obtuse in the embryo fish ; the ganglionic
centres of the olfactory nerves are always originally developed
in close contiguity with the proseiicephalon ; they are protected,
primarily, by the rhineiicephalic arch ; and, as this advances
in the elongation of the skull, and recedes from the prosence-
phalic arch, two modes of growth take place in the contained
nervous axis : either the brain is co-elongated, the rhinence-
phaloii retaining its primitive relation with its vertebra, and the
prolonged crura occupying the narrow interorbital tract of the
cranial cavity, or the rhinencephalon retains its primitive juxta-
position with the prosencephalon, and the olfactory nerves, figs.
180 — 182, o, 203, o, are prolonged through the interorbital space,
perforate or traverse a notch in the prefrontals, and expand, as a
resolved plexus, upon the pituitary plicated sac.

The rhinencephalon accompanies its vertebra and recedes from
the rest of the brain in Salmo, Cyprinus proper, Brama, Tinea,
Gadus, Lota, Hippoglossus, Clupea, Belone, Lucioperca, Cobitis,
Plectognathi, and Plagiostomi ; it retains its primitive contiguity
with the prosencephalon in Perca, Scomber, Esox, Pleuronectes,

298

ANATOMY OF VERTEBRATES.

1'JG

Blennius, Anyuillu, Cyclopterus, Gasterosteus, Eperlanus, Cot-

tus, Triyla, Amblyopsis,
EcheneiSy the Ganoidd,
and Lepidosiren*

As the eras of the
rhinencephalon is formed
not only of fibres con-
tinued from the proseii-
cephalon, but also, and
in some fishes chiefly, of
distinct white and grey
tracts, traceable along the

o

base of the mesencepha-
lon, in part as far back as
the prepyramidal bodies,
so the origin of the olfac-
tory nerve has been de-
scribed as characterised
by this complexity and
extent ; and it is true
that in some instances
(e. g. in the Perch),
where the rhinence-
phalon, figs. 180—182,
i, is in contact with the
prosencephalon, ib. c, a
small portion of the true
olfactory nerve may be
distinctly traced back-
ward as far as the mesen-
cephalon : just as we find
in some fishes (e. g.
Sturgeon) a portion of
the optic nerve traceable
as far back as the cere-
bellum, and in the Eel
to the hypoaria, and not
exclusively terminating
in the optic lobe. Most
of the characteristics of

Brain and cerebral nerves of Cod-fish (Gadus morrhua). LIV. . . T

origin and course attn-

o

buled in works of Comparative Anatomy to the olfactory nerves
are to be understood of the ' crura rhinencephali.' In the

NERVES OF FISHES.

299

Lancelet the little ciliated olfactory sac is brought into close
contact with the rhinencephalic extremity of the neural axis.
When the olfactory lobe or ganglion, in other Fishes, is near
the organ of smell, as in the Cod, fig. 196, o, it sends off the
nerves by numerous very short fasciculi. This multiplicity of
virtual origins of the proper nerve is less conspicuous where
the rhinencephalon is near the rest of the brain ; but a careful
analysis of the long olfactory nerve in the Eel, fig. 176, will
show that it is a fasciculus of filaments distinct from their

origin.

The optic nerves, like the eyes, are of large relative size in most
fishes ; but where the organs of sight are small, the nerves are
slender, as in the Silurus : they are still more slender in the
Myxinoids, and they are scarcely discernible filaments in the

197

193

a

Brain of Skate (Eaia}, base
view. ecu.

Brain of a Halibut (Hippoglossus), A upper, B under
view. ecu.

Amblyopsis, fig. 175, 2. In the Plagiostomes, fig. 197, Holoce-
phali, Ganoidei, and Protopteri, the optic nerves, ib. a, a, arise in
part from the optic lobes, ib. d, in part from the hypoaria, ib. c, c,
closely adhering to the fore part of the base of the mesencephalon,
and are there connected together by a transverse commissure, ib. b,
or close interblending of substance : they do not freely cross each
other. In ordinary Osseous Fishes, figs. 181, 185, the exterior white
fibres of the optic lobes converge to their under and anterior part,
to form the chief part of the origin of the optic nerves ; but a portion
of the origin may be traced through the septum opticum to the
cerebellum ; and in the Eel, the Garpike, and the Lump-fish, a
portion may be traced to the hypoaria : in the Cod, fig. 185, and

300

ANATOMY OF VERTEBRATES.

Hake some fibres of the optic nerve, ib. 2, are derived from both
the hypoaria, ib. n and fig. 199, d, and from the wall of the third
ventricle. The relation of the hypoaria to the nerves of sight is
illustrated in the fishes with unsymmetrical heads and eyes, e. g.
Pleuronectida ; in fig. 198, the optic lobe, e, and hypoarion, y,
giving origin to the larger optic nerve, c, are larger than the optic
lobe,y, and hypoarion,^, giving origin to the smaller optic nerve, d.
The nerves cross one another without interchange of fibres ; some-
times the right nerve in its passage to the left eye passes under,
fig. 199, &,#, fig. 201, sometimes over, figs. 185, 19 8, the left nerve:1
rarely does one nerve perforate the other, as, e. g. in the Herring.
The nerves are flattened where they decussate. In most Osseous
Fishes the structure of the optic nerve is peculiar ; it consists of
a folded plate of membrane and neurine, fig. 200, a, which usually
prevails throughout the length of the nerve, from its cerebral

attachment to the eyeball :
in some instances the inner
surface of the optic lobe is
also folded : and, in all, the
plaits may be observed to
be faintly continued upon
the retina, which is formed
by the unfolding of the
nerve. The optic nerve escapes, in Osseous Fishes, either through
the anterior fibrous wall of the cranium beneath the orbito-

sphenoid, or through a notch or a foramen
in that bone. In the Pleuronectida one optic
nerve is usually shorter, as well as smaller,
than the other, fig. 198. In the Eel the
nerves form, after decussation, a very acute
angle in the axis of the body, fig. 176, a: in the
Lump-fish they form an obtuse open angle.

Since there are no muscles of the eyeball
in the Lancelet, the Myxinoids, the Am-
blyopsis, and the Lepidosiren, there are no

Plaited optic nerve of a Mullet. m/vfniMr TIPWPCJ nf flip nvVn't Tn flip
a, optic nerve deprived of its HlOtOry HeiVCS Lt.

a

Brain of a Hake (Merluccius) with the base upward, ecu.

200

a sma11 ^^ lierve ancl a fourth nerve, which

of the eye through winch the are closely connected where they quit the

nerve is passing ; c, retina, •> •>

in which the nerve termi- cranium, again separate, the one to supply

nates. ecu. _ , _ . _

the rectus superior and rectus internus, the
other the obliquus superior ; the filaments supplying the other

1 The writer has seen both varieties in different individuals of Gadus morrhua.

NERVES OF FISHES.

301

muscles of the eyeball cannot be separated from the fifth pair. In
all other fishes the sixth or abducent nerve, fig. 185, 6, has its proper
origin, as well as the fourth and third. The third, or oculomo-
torius, ib. 3, rises from the base of the mesencephalon, behind the
hypoaria, ib. ?i, or from the commissura ansulata ; it escapes through
the orbito-sphenoid (Carp), or the unossified membrane beneath it
(Cod, fig. 196, 3), and is distributed constantly to the recti superior,
inferior, and internus, and to the obliquus inferior ; it also sends
filaments into the eyeball : the ciliary stem, or a branch of it,
usually unites with a branch of the fifth nerve, and sometimes,
as in the Mackerel, Gar-pike, and Lump-fish, developes a small
ciliary ganglion at the point of communication.

The fourth nerve, or trochlearis, fig. 196, 4, rises from the back
of the base of the optic lobes, between these and the cerebellum ;

201

Brain and origins of the fifth nerves of the Cod. ccvm.

it escapes either through the orbito-sphenoid (Carp), or the con-
tiguous membrane (Cod), and is constantly and exclusively dis-
tributed to the superior oblique eye-muscle, ib. g.

The sixth, or abducent, nerve, figs. 185, 196, 6, rises from the
prepyramidal tracts of the medulla oblongata, fig. 185, «, beneath
the fifth, and, in most Osseous Fishes, by two roots, as in the Cod,
ib. 6. It usually closely adheres to the ganglionic origin of the
fifth. In the Carp and Lump-fish it receives a filament from the
sympathetic, before its final distribution to the rectus externus,

302

ANATOMY OF VERTEBRATES.

fig. 196, 1) : it escapes by the foramen or anterior notch of the
alisphenoid, in advance of the fifth nerve.

This nerve, the trigeminal, enormous in all Fishes, from the
Lancelet to the Lepidosiren, rises, often by two or more roots, from
the restiform, or from the anterior angle between the olivary and
restiform tracts ; in some fishes from a special ganglion or enlarge-
ment of that part of the medulla oblongata, as in the Herring, fig.
184, i: in a few (Conger, Lump-fish) by a smaller origin resolved
into several roots. The trigeminus shows well its spinal (myelonal)
character in Fishes, only its double root is more deeply buried in
the medulla oblongata. In the Cod, fig. 201, the non-ganglionic
portion is shown at i, the roots of the ganglionic portion at 2, 2.
On the left side the non-ganglionic portion is separated and turned
back : on the right side its divisions are seen accompanying the
first, «, second, b, and third, c, branches of the trigeminal. The
fourth branch, d, is also composed of both portions of the nerve :
the fifth branch, e, is exclusively from the ganglionic portion.
The trigeminal is in close contact with the acoustic nerve, at their

202

Brain and fifth nerves of the Ray. co'vilt.

origins. In Coitus, Blennius, Cobitis, and Leudscus, the ganglionic
or dorsal roots recede from the ventral ones, as they penetrate the
medullary substance. The non-ganglionic roots in the Blenny
join the facial and glossopharyngeal. Of the five roots of the
trio-eminal in the Sturgeon, the first, second, and fourth form a

NERVES OF FISHES. 203

ganglion (Gasserianum). In the Skate (Raici) the roots of the
two ganglionic portions, fig. 202, a, b, of the trigeminal, arise from
the restiform tract : the non-ganglionic part, c, from the folded or
fimbriate part of the tract. A pin is passed between the second
ganglionic and the non-ganglionic portion ; the latter, c, being re-
flected back on the left side of the figure ; on the right side the
non-ganglionic branches, e, f, are left, accompanying the corre-
sponding branches of the ganglionic portion, a, e, f. The acoustic
nerve, 7, comes off as a branch of the second ganglionic part of
the trigeminal.

In Osseous Fishes the hindmost branch of the fifth nerve divides,
one part descending to the ( opercular ' nerve, fig. 203, t, the other
ascending to the f lateral ' nerve, ib. m ; but both receiving an acces-
sion from other sources to form those nerves respectively. A branch
of the vagus, fig. 202, t, ascends forward to join the fifth in
forming the dorsal division of the ' nervus lateralis,' ib. m, which
escapes by a foramen in the parietal bone ; the rest of the fifth
emerges from the skull by a hole (Carp), or a notch (Cod), of the
alisphenoid. The lateral nerve in the Cod is formed chiefly by
the fifth, fig. 196, 5, and receives only a slender filament of the
vagus. In the Carp the vagus chiefly forms the lateral nerve.
In the Cod, fig. 205, the lateral nerve first sends off a branch, ib. i,
which runs along the sides of the interneural spines, receiving
branches from all the spinal nerves ; it then curves down along
the scapular arch, gives branches to the pectoral, ib. p, and ven-
tral, ib. v, fins, supplies the great lateral muscular masses, ib.. 2,
and the mucous canal, ib. 3, and sends a nerve, ib. 4, to the inter-
La3mal spines, which communicates with filaments from the corre-
sponding spinal nerves : both interneural and interhaemal branches
terminate in the plexus supplying the caudal fin : thus all the
locomotive members are associated in action by means of the
nervi laterales. The mandibular division of the fifth (ramus man-
dibularis, seu maxillaris inferior) consists chiefly of motory filaments
which supply the muscles of the hyoid and mandibular arches,
and the 6 rarnus opercularis seufacialis,' fig. 202, t, to those of the
gill-cover ; the sensory filaments go to the teguments of the sides
of the head, ib. r, and under jaw, enter the dental canal, supply
the teeth, and, in the Cod, the symphysial tentacle.1 The maxil-
lary division (r. maxillaris) bifurcates behind the orbit, one branch
passes outward to supply the suborbital mucous canals and integu-
ments on the sides of the head ; the other, after sending a branch
obliquely outward, curves forward along the floor of the orbit,

1 ccxxvi. p. 45, tig. 2.

304

ANATOMY OF VERTEBRATES.

ib. v, gives off a palatine nerve (r. pterygo-palatinus), and supplies
the integuments, mucous tubes, and teeth of the upper jaw. The
super-orbital division, ib. e, gives off the two ciliary nerves, one

203

Cerebral nerves, Perch, xxm.

of which joins the ciliary branch of the third ; it supplies the
olfactory sacs, and the integuments of the upper and fore part of
the head.

In the Skate the large sensory branches of the fifth, sent to the
integuments, and to the singularly developed mucous canals, have
ganglionic enlargements near their origins, fig. 202, a, b, where
they leave the main trunk. The first electric nerve is given off
by the fifth in the Torpedo, fig. 139, 5, and many of the terminal
filaments of the tegumentary branches of the fifth are connected
with the peculiar muco-ganglionic corpuscles, described at p. 324,
fig. 215.1 In the Sturgeon the snout and its tentacula are sup-
plied by branches of the infra-orbital, not from the supra-orbital,
division of the fifth ; the opercular or facial branch supplies, in
addition to the gill-cover, the integuments and lips of the pro-
tractile mouth, and the pseudobranchia : it communicates with
the glosso-pharyngeal.

In the Lancelet the fifth nerve, fig. 169, ob, distributes many
filaments to the expanded sensitive integument which represents

1 LXXVII.

NERVES OF FISHES. 305

the head, and forms the sides of the wide oval opening ; it also
supplies the oral tentacula. In the Myxinoids the same nerve
supplies both the muscles and the integuments of the head, the
tentacula, the nasal tube, the mucous membrane of the mouth
and tongue, the hyoid and palatal teeth, and the pharynx. The
trigeminus supplies the same parts in the Lamprey, but in a more
compact manner, i. e. by fewer primary branches : that which
sends filaments to the rectus externus and rectus inferior of the
eyeball is continued forward beneath the skin and resolves itself
into a rich plexus, which supplies the thick cirrate border of the
suctorial lip : the nerves to the muscular parts of the jaws and
tongue arise distinct from the fifth, and their trunk may be
regarded as a ( facial' nerve ; one of the filaments of this joins a
branch of the vagus to form a short ( nervus lateralis.'

Thus in reference to the motor filaments of the trigeminus or
great spinal nerve of the head, those that form the portio dura or
facial nerve in higher Yertebrata are not distinct from the rest of

o

the trigeminus at its apparent origin, except in the Lamprey ; in
which, on the other hand, the motory filaments of the rectus
externus, forming the sixth nerve of higher Fishes and Vertebrates,
retain an associated origin with the trigeniinal. The ( facial ' part
of the operculo-lateral division of the fifth, in the Perch,1 is that
which supplies the mandibular, opercular, and branchiostegal
muscles. In the extended medulla oblongata of the Sander
(Lucioperca) the facial nerve has a distinct origin between the
trigeniinal and acoustic.

The acoustic nerve appears to be a primary branch of the fifth,
in the Skate, fig. 201, 7: its distribution on the labyrinth is beau-
tifully shown by Swan in Liv. pi. x. fig. 2. It communicates on
the great otolithic sac with a motor branch from the vagus, which,
after giving filaments to the posterior semicircular canal, passes
out to supply the first and the adjacent surface of the second gill,
and the faucial membrane. Swan calls this branch the ' glosso-
pharyngeal,' and says, ' this nerve, on being touched near its
origin in a recently-dead animal, immediately produces a contrac-
tion of the muscular appendages of the gills ' (ib. p. 41). In the
Cod the acoustic nerve, fig. 185, 7, which here as in all fishes
above the Dermopteri is of large size, rises close behind, but
distinct from, the fifth pair, ib. 5, between it and the vagus, ib. 8 :
the acoustic nerve receives a filament from the vagus, extends in

O . 7

a crescentic form, fig. 196, s, upon the labyrinth, expands upon

1 xxiii. torn. i. p. 325, pi. vi, fig. v. /u.
VOL. I. X

306 ANATOMY OF VERTEBRATES.

the large sac of the otolite, ib. i, and sends filaments to the
ampulliform ends of the semicircular canals. In other Osseous
Fishes (Pike, Blemiy) the acoustic blends at its origin with the
back part of that of the fifth : it sometimes communicates with
the opercular branch of the fifth, as well as with the glosso-
pharyngeal of the vagus. Its division on the acoustic sac is
shown, in the Perch, at s, s, fig. 203.

The nervus vagus., ib. £, has a developement proportional to
the extent and complexity of the branchial apparatus in Fishes,
and is usually larger than the trigeminal : it rises, fig. 185, 8, from
the restiform tract forming the side of the medulla oblongata, and
commonly from a specially developed lobe ; and is distributed to
the branchial apparatus, the pharynx and pharyngeal arches, the
oesophagus and stomach ; it sends filaments to the heart, and to
the air-bladder when this exists ; and it forms, or helps to form,
the ( nervus lateralis.' In the Lamprey a portion of the vagus
combines with branches of the facial and hypoglossal nerves to
form a short side-nerve extending to the middle third part of the
body. In Salmo, Clupea, Acipenser, the ( nervus lateralis' is formed
exclusively by the vagus : in the latter, as in Chimcera, Balistes,
Diodon, Cyclopterus, this nerve is a single longitudinal one : in
most bony fishes there are two which run parallel or nearly so.
In all these fishes it is continued very far back along the lateral
or latero-dorsal region of the body ; sometimes lodged deeply in
the lateral mass of muscles, e. g. Belone, Clupea, and Scomber,1
but more commonly the nerve or a main branch lies just under
the skin, and in the course of the lateral mucous line, as in the
Salmon and Sturgeon ; in the Flat-fish and Bull-heads it has both
a deep-seated and a superficial branch. In Upeneus the super-
ficial branch is sent off, dorsad, at an open angle from the main
trunk, to the lateral line, above which it runs in the Belone> the
superficial branch descends to gain the lateral line. In the
Carp and Herring the vagal ( ramus lateralis ' sends off a strong
branch to the dorsal fin ; in the Garpike it sends, as in the Cod,
branches to the pectoral and ventral fins ; it distributes other
branches to the skin and mucous ducts ; and some of these, in
most fishes, anastomose with branches of the spinal nerves, fig.
205. In the Perch there are two 'nervi laterales' on each side;
the dorsal one, fig. 203, m, above described, and the proper lateral
nerve, ib. /: this is formed exclusively by the vagus, and divides
into a superficial branch, supplying the lateral line, and a deep-

1 xx. vol. iii. p. 49, prep. no. 1384 (mackerel).

NERVES OF FISHES. 307

seated branch, communicating with the spinal nerves, and sup-
plying the myocommatal aponeuroses and the skin.1 Whether
the vagus forms the whole or a part of the e nervus lateralis,' this
does not arise like the ( nervus accessorius ' of higher Vertebrates,
from a motory tract of the myelon, but from a ganglionic part of
the vagus. The ( nervus lateralis ' chiefly supplies the skin,
mucous line, intermuscular septa, and vertical fins, most of them
peculiarly ichthyic parts, either by their preponderating develope-
ment, or their very existence.

The vagus sends supra-temporal branches to the head, and
opercular branches to the gill-covers. The usually double roots of
the nervus vagus pass out, in most Fishes, by a single foramen in
the exoccipital bone. The fore part of the root is the largest, and
is ganglionic : it is the true pneumo-gastric, supplying the gills,
pharynx, heart, and stomach, and sending filaments to the sep-
tum dividing the branchial from the abdominal cavity. In the
Tunny the branchial nerves are remarkable for their size and
their radical ganglions. The hinder second origin is the source of
the glosso-pharyngeal and lateral nerves. The former, which
has a distinct ganglion in the Herring and some other fishes,
supplies the first gill and contiguous parts, and thence passes
forward to the tongue. Some filaments rising behind the vagus
have been traced to the parts surrounding the brain within the
cranial cavity.'2 Each vagal nerve of the Sturgeon equals the
spinal chord in size, and rises by numerous roots. The nerve
has a like extensive tract of origin in the Sharks ; in which a
posterior fasciculus, fig. 187, 8, representing the ( nervus acces-
sorius,' can be best demonstrated.

There is no ' nervus lateralis ' in the Myxinoids, but the gastric
branches of the vagus are continued, united as a single nerve,
along the intestine to the anus. The vagus is represented in the
Branchiostoma by a branch sent from the fifth to the pharynx.
In the Myxine its origin is close to that of the fifth. The
erectile palatal organ of the Cyprinoids is wholly, and the electric
organs of the Torpedo are, in great part, supplied by this remark-
able vagal nerve. The proportion of grey to white filaments
in the vagus of Fishes is great er than in that nerve in higher

O O O

Vertebrates, which illustrates the progressive differentiation of
the great sympathetic.3

The first spinal, or myelonal, nerve rises usually by two roots,
the dorsal one having a ganglion, rarely by non-ganglionic roots
exclusively from the prepyramidal tracts : it usually emerges

1 xxni. torn. i. pp. 325-27. ~ ccxxvn. 3 ccxn.

x 2

303

ANATOMY OF VERTEBRATES.

between the ex-occipital and the atlas, and divides into a small
dorsal and a larger ventral branch : this communicates with the
ventral branch of the next spinal nerve, and supplies the pectoral
fin-muscles, the subcoradoideus, i, the retractor hyoidei, c, and
geniohyoidei, 27, fig. 135. It is called ' hypoglossal nerve ' by
some Ichthyotomists ; but this name more properly applies to a
nerve which, in some fishes, arises from the medulla oblongata
behind the vagus, is distributed to the muscles between the scapular
and hyoid arches, and unites with the first spinal nerve.

Each of the spinal nerves has a dorsal or sensory, and a ventral
or motory origin ; sometimes each rises singly ; sometimes, as in
the Cod, by two or more filaments, fig. 196. Both sensory and
motory roots are long in most fishes : the sensory root is the
largest, arises by more filaments, and further back than the
motory roots, in the Sturgeon.

In most Osseous Fishes one dorsal root goes to form the dorsal
branch of the spinal nerve, and the other dorsal root joins the
ventral branch of the same nerve : sometimes the ganglion is
formed on the dorsal root of the dorsal branch, as in the Cod ;
more commonly upon the whole sensory origin of the nerve,
where it emerges from the neural canal. In some fishes (Bream
and Garpike) the ganglions on the dorsal root are situated in the
spinal canal : more commonly (as in the Cod, the Ling, the

Sander) the ganglions are external to the spinal
canal. In both cases the nerve is increased in size
beyond the ganglion and the union of the ventral
root. This is well seen in the Skate, in which the
ganglions are situated beyond the holes of emer-
gence, and the junction of the two roots takes
place quite exterior to the neural canal.

The connection of the roots with the myelon
is weaker in Fishes than in air-breathing animals :
it is so easily broken in the Dermopteri as to have
led to a denial of its existence.1 The peculiar
combination of the dorsal and ventral roots of the
spinal nerves in Osseous Fishes is well seen in the
Cod.2 The dorsal root sends a filament, fig. 204, a,
and lateral nerves, upward, which joins a ventral filament, b. from

Cod. LIV. J

the preceding nerve, and forms the ramus dor-
salis, d\ the dorsal root sends two filaments, c, downward, which
unite together, and with a ventral filament, e, of the same nerve

204

Connections of spinal

1 LXXIX. ii. p. 479.

2 LIV. pi. x.

NERVES OF REPTILES.

309

to form the f ramus ventralis,' v. The filament of the ventral
root sent to the ramus dorsalis of the succeeding nerve perforates
the lower division of the dorsal root of its own nerve.

Thus each spinal nerve forms a ( ramus dorsalis,' fig. 205, 10,
and a ( ramus ventralis,' ib. 8 ; the ramus dorsalis includes a
sensory filament of its own nerve, and a motory filament of the
antecedent nerve : the ( ramus ventralis ' is formed by a motory

205

Lateral nerve and branches, Cod. LIY.

and a sensory filament of its own nerve ; both rami f ventrales '
and f dorsales ' are associated together, and with the vagal and
trigeminal nerves through the medium of the great f nervus
lateralis,' fig. 205, i, 8.

The dorsal roots of the nerves distributed to the free, explora-
tory, pectoral rays of the Gurnards, rise from special ganglionic
swellings of the cervical portion of the dorsal myelonal columns.

§ 56. Nerves of Reptiles.- The olfactory nerves are continued
in Reptiles, for a greater or less extent, from the rhinencephalon,
figs. 188, 191, to the olfactory sacs; the white and grey tracts
beneath the prosencephalon, fig. 1 90, p, described as roots of this
nerve, belong to the rhinencephalic crura: the true olfactory
nerves are less distinct from their centres than in other Ver-
tebrates. In the Python, fig. 188, the nerves, i, of equal
diameter with their centres, gradually expand, by resolution of
their fibres, as they approach the olfactory sacs, ib. d, and are
joined by part of the first division of the ' fifth.' The olfactory

310

ANATOMY OF VERTEBRATES,

nerves progressively increase in length in the Turtle, Iguana, and
Crocodile. The distribution of their fibres upon the vascular
pituitary membrane, supported by the turbinal cartilage, is well
displayed in a Himterian preparation of the Turtle.1

The optic nerves, corresponding in size with that of the eyes,

200

Cerebral, anterior spinal, and sympathetic nerves, Python. LIV.

are smallest in the fish-like Batrachians. They arise from the
optic lobes, fig. 192, o, thalami, and optic tracts, ib. d, and blend,
by a few decussating lamina;, into a chiasma, ib. />, before diverg-
ing to the visual organ : their course is shown, in the Python, at
2, fig. 188. The position of the 'third' or oculo-motor nerve is

1 xx. vol. iii. p. 89, rios. 1532. 1533.

NERVES OF REPTILES. 311

shown at 3, fig. 188. The course of the ' fourth' to the upper
oblique muscle is shown at 4, fig. 188. This nerve does not
exist, separately, in the fish-like Batrachians.

The fifth or trigeminal nerve shows its double (ganglionic and
non-ganglionic) origins in all Reptiles, and its threefold primary
division very distinctly, in all above the Perennibranchiates. In
the Serpent the first division is shown at 5, fig. 188, extending
forward beneath the 'fourth' nerve and upper oblique muscle,
and above the olfactory nerve and capsule. The second division,
fig. 188, 6, fig. 206, 4, after communicating with the sympathetic
nerve, divides : one branch supplies the membrane of the mouth
and palate ; the other passes out by canals in the upper jaw, and
terminates on the follicles and substance of the upper lip. The
third division, fig. 188, 7, fig. 206, 5, sends branches of its non-
ganglionic part to the muscles of the jaws ; a large branch enters
the dental canal of the mandible, supplies the tooth-capsules, and
emerges by three or more divisions : two of these, emerging at
the lower part of the mandible, communicate with branches of the
e eio'hth ' and ( ninth ' nerves, to be distributed to the muscles and

O '

parts beneath the mandibular arch : another gives filaments to the
membrane of the mouth as far as the sheath of the tongue ; the
main continuation, emerging at a foramen near the symphysis,
supplies the lower lip.

In the Turtle the first or ophthalmic division of the fifth
advances some way in the substance of the dura mater before
entering the orbit ; it sends a filament to combine with one of the

O '

third, to supply the ciliary nerves, without forming a ganglion : it
supplies the lacrymal and harderian glands, and is continued to
the olfactory fossa. The second or maxillary division quits the
third on entering the floor of the orbit, along which it curves,
sending from its concavity filaments to the lacrymal glands, and
dividing into two chief branches ; the internal branch, answering
to the spheno-palatine and suborbital, supplies the palate and floor
of the nasal cavity, and emerging at the fore-part of the orbit, it
spreads upon the maxillary tegument : the external branch passes
along the floor of the orbit, and emerges upon the face. The
third or ( mandibular ' division descends at the back-part of the
orbit, in front of the tympanic bone, supplies the temporal and
pterygoid muscles, enters the mandibular canal, and distributes
branches inwardly to the tongue and floor of the mouth, outwardly
to the mandibular follicles and tegument.

In the Frog the maxillary and mandibular divisions of the
trigeminal, arising distinctly from the ganglion, diverge to their

312 ANATOMY OF VERTEBRATES.

respective destinations at the middle of the floor of the orbit:
the hindmost branch, continuous with a filament from the
acoustic nerve, unites with a branch of the vagus, and is distributed
like the ( portio dura ' of the ' seventh ' nerve. The distinct
origin of this nerve, between the ( fifth ' and acoustic, is shown
in the Python, fig. 188, s; it communicates, fig. 206,6, with
the ganglion, ib. i, of the sympathetic, then passes through the
6 apertor oris,' to which it gives a branch ; communicates with
the first spinal nerve, and terminates on the ( costo-mandibularis '
muscle. The acoustic nerve, fig. 188, 9, soon divides, and enters
the labyrinth by two or more foramina. The glosso-pharyngeal,
fig. 188, 10, is distinct at its origin in Serpents and higher Reptiles.
In Batrachia it issues from the ganglion of the vagus. In the
Python the glosso-pharyngeal passes chiefly to the ganglion,
fig. 206, i, of the sympathetic. The 'nervus vagus,' fig. 188, 11,
arises by several filaments, and in the Chelonian and Crocodilian
reptiles is recruited by an ( accessorius,' arising from the tract of
the first and second spinal nerves. In the Python, fig. 206, 8,
the vagus communicates with the sympathetic, and then receives
the continuation of the glosso-pharyngeal from the ganglion, i.
It sends a branch to communicate with the ' ninth,' and to be
distributed to the muscles and membrane of the fauces. The
trunk is then continued down or back, close to the trachea and
jugular vein: on the left side it also accompanies the carotid
artery : it sends filaments along the large vessels to the heart, and
others behind each aorta, similar to the recurrent nerves, to be
distributed upon the trachea and esophagus : each trunk for a
short space accompanies the corresponding pulmonary artery to
the lung. Before reaching the liver it passes ventrad of the
lung for a short distance, and joins its fellow to form a single
nerve. This is continued under the capsule of the liver supplying
that organ, the lungs, and oesophagus. Near the end of the liver
the vagus sends a large branch, which communicates freely with
the sympathetic, to the left surface of the stomach, and this also
gives filaments to the contiguous part of the lung. The trunk,
on the right of the stomach, communicating with the sympathetic,
and with the division on the left, is continued a short way on the
membrane connecting the viscera, gives branches to the right side
of the stomach, and terminates on the beginning of the intestine,
at the pancreas.

In the Chelonia and Crocodilia the vagus quits the skull by two
or three of its roots, which unite outside to form the trunk of the
nerve ; its communication with the glosso-pharyngeal, the ninth,

NERVES OF REPTILES. 313

and the sympathetic, together with its ultimate distribution, are
in the main like those in Ophidia ; it exclusively supplies the
heart. In the Amphisb&na the accessorius is partially blended
with the vagus, and separates from it to be distributed to the
cervical muscles, joining branches of the first two spinal nerves.
In Chelonia and Crocodilia the accessorius blends with the o-an-

o

glion of the vagus : its continuation may be recognised in the
posterior branch sent by the vagus to the nuchal muscles.

The ' ninth' or hypoglossal nerve, fig. 188, 12, arises from the
motory tract, behind the vagus, from the trunk of which it receives
a branch ; it receives a smaller branch from the facial nerve ; com-
municates with the anterior cervical nerves ; and is distributed to
the muscles of the pharynx and tongue, to the forked end of which
the lingual branch may be traced. It sends a communicating
branch to those of the mandibular nerve, which are distributed to
the muscular floor of the mouth. In the Tortoise the hypoglossal
escapes by two precondyloid foramina ; after the union of these
origins the trunk communicates, as in Ophidia, with the vagal
and glosso-pharyngeal nerves : it sends a branch to the hyoid
muscles, a branch forward to the tongue, and a third downward
to the omohyoideus : the latter accompanies the vagus as far as
the fifth cervical.

The vagus enters in a larger proportion into the formation of
the nerve, or rather plexus, distributing branches to the parts to
which the source of nervous supply is ascribed to the hypo-
glossal ; but this nerve has a distinct origin by two roots in the
Turtle.

The first and second spinal nerves arise, in Chelone, like the
hypoglossal, by motory roots only ; the sensory or dorsal roots in
the other cervicals are smaller than the motory ones. The skin
of the neck is not very sensitive : the muscles are large and
numerous. In the back, where muscles are few and small, the
sensory roots of the spinal nerves exceed the motory ones in size.

The nerve which emerges between the first and second trunk-

O

vertebra? in Batrachia supplies the muscles and integuments of
the subjacent part of the throat, and sends a few filaments to
those of the scapula. Four of the succeeding spinal nerves
combine in the Salamander to form the brachial plexus : two only
form that plexus in the Frog, that emerging between the second
and third vertebrae being the largest. In the Crocodile the sixth
and seventh cervical nerves, with the two following, combine to
form the brachial plexus. In the Turtle the sixth, seventh,
eighth, and ninth spinal nerves constitute the brachial plexus.

314 ANATOMY OF VEKTEBPvATES.

This distributes a c circumflex ' or axillary, an ulnar, a radial or
( musculo-spiral,' and a median nerve. The circumflex supplies
the latissimus dorsi, claviculo-braehialis, supercoracoideus and
teres minor, and terminates on the integument at the back of the
arm. The ulnar nerve divides at the upper third of the humerus
into a branch supplying the extensor communis digitorum, ex-
tensor proprius pollicis, and ulnaris externus, a branch for the
triceps brachii, and a superficial cutaneous nerve distributed to
the integument on the back of the fore-arm and hand. The
radial nerve passes to the outer side of the humerus, distributing
muscular branches in its course, winds to the inner side, descends
in front of the elbow-joint, and terminates in muscular and
cutaneous branches. The median nerve passes along the back-
part of the scapula, giving branches to the pectoralis major, to
the shoulder-joint and surrounding skin : passes between the
humeral tuberosities, supplying the triceps brachii and brachialis
internus : then divides into an external branch, passing between
the pronator teres and radialis interims, and supplying the flexors
of the digits, and into an internal branch, gliding between the
radius and ulna, and ultimately forming the volar arch.

In the Frog the axillary nerve sends a branch to the muscles
and skin above the scapula : it is continued into the brachial,
which bifurcates. One branch winds round the humerus, like the
6 musculo-spiral,' sends a branch to the extensor cubiti, and passing
in front of the elbow-joint penetrates the mass of flexor muscles,
and reappears at the outer side of the fore-arm : it sends one
branch to the skin, and another to the back of the hand, which
divides to supply the same aspect of the digits. The other
division of the brachial nerve represents the ' median ; ' it divides
into a larger branch, running along the interosseous furrow of the
ulno-radial bone, which supplies the palm and palmar surface of
the digits, and into a smaller branch, which supplies the flexor
muscles of the digits.

The spinal nerves of the Serpent differ from those of the Eel
in the more distinct ganglion on the posterior root, and this rises
closer to the anterior root, which is rather larger. Each spinal
nerve communicates with the sympathetic, and accompanies
the rib, to be distributed to the vertebral muscles and integu-
ment, fig. 206.

In the Tortoise, nerves, analogous to the phrenic, are sent from
the first three dorsal pairs to the sheets of the diaphragmaticus,
fig. 150, 42. Succeeding dorsal nerves communicate with the
sympathetic, and send filaments into the substance of the carapace,

NERVES OF REPTILES. 315

most of which pass through, and terminate in the vascnlar beds of
the horny scutes.

The seventh and eighth dorsal nerves, and the three consecutive
pairs, contribute to the formation of the crural plexus. The
sciatic nerve is formed by the last dorsal and the first two sacral
nerves. In the Crocodiles and Lizards the sciatic is formed by
but two spinal nerves : in the Frogs and Toads by three,
figs. 207, 208.

The crural plexus in the Tortoise sends filaments to the trans-
versalis, fig. 150, 41, and obliquus abdominis, fig. 151, 40 ; to some
of the pelvic muscles and the glutaei ; it is then continued into the
limb as the ( crural nerve.' The obturator nerve is a direct branch
of the last dorsal. The sciatic nerve gives a filament to the
second glutaeus and to the obturatorius, and continues, as a
large trunk, to behind the knee-joint, where it divides into
the tibial and peroneal nerves. The tibial subdivides into a
popliteal branch, supplying the muscles at the back of the leg
and the sole or plantar side of the foot, and into an external
branch to the external muscles and integument. In the Turtle
(Chelone),1 one division of the sciatic gives branches to the
muscles of the thigh, and is continued to the plantar surface
of the foot, dividing into digital nerves, terminating on

* O O •* o

the skin ; the other division, after giving off some muscular
branches, passes to the skin on the dorsal surface of the fin.

In Lizards the crural nerve is formed by the two lumbar nerves,
and is distributed to the muscles on the fore-part of the thigh ;
the sciatic nerve is formed by the last lumbar, the two sacral
nerves, is continued along the inner side of the thigh, supplying
the muscles as far as the digits, and branching to accompany them.

In the Frog a pearly vesicle, with calcareous molecules, covers
each spinal nerve where it comes out of the spinal canal. Of the
four pairs of nerves which proceed from the termination of the
short myelon, three constitute on each side the ' sciatic plexus,'
which unites into a single large nerve opposite the acetabulum.
The sciatic nerve enters the muscles at the back-part of the thigh,
supplies them, and divides near the knee-joint into an external
and internal branch, distributed to the muscles, digits, and skin of
the hind-leg and foot.

The tenacity of vital force in Hcematocrya9 and the seemingly
peculiar susceptibility to the voltaic current in the Frog, have
made that animal the usual subject of the experiments exemplifying

1 LTV, pi. xvi.

316

ANATOMY OF VERTEBRATES.

207

relations between the electrical, nervous, and muscular forces. It
may be convenient, therefore, to some readers to find here, in con-
nection with the nervous
system of the Batrachia,
an account of the chief
modes of preparing it
for the purpose of such
experiments. Galvani
removed the skin from
the hinder part and limbs
of the frog, exposed the
lumbar plexus, leaving
it in connection with the
part of the spine from
which the nerves issued,
and cut away all the
parts save the trunks of
the sciatic nerves, be-
tween the spine, s, and
the hind limbs, A & B,
fig. 207. So prepared,
it is usually called ( Gal-
vani's frog.'

The ' galvanoscopic leg,' fig. 207, c, is prepared by skinning it,
dissecting out the sciatic nerve from among the muscles at the
posterior part of the thigh, then amputating the leg just above
the knee-joint, leaving the nerve connected with the leg, c.

If the nerve of c be laid upon the muscles of either leg of
Galvani's frog, A or B, and if these muscles are excited to contrac-
tion, by pricking the myelon in s, the muscles of the galvanoscopic
leg, C, will be simultaneously contracted. If a second galvano-
scopic leg be prepared, and the nerve be laid upon the muscles of
the first, and a third be placed in the same relation with the
second, contractions will take place in all three legs, when the
thigh-muscles of the Galvani's frog, A & B, are excited to contract.
This ( induced contraction ' cannot be extended to a fourth gal-
vanoscopic leg.

If the nerve of the galvanoscopic leg be left in connection with
the rest of the frog's body, and the nerve be laid across the thighs
of a ( Galvani's frog,' as in fig. 208 ; these being excited to con-
tract, not only the galvanoscopic leg, c, but the opposite leg, F,
contract; the one by direct stimulus of the sciatic nerve, the
other by stimulus of the myelon from the inferent or e sensitive '

Galvani's frog, and the galvanoscopic leg. ccv.

NERVES OF REPTILES.

317

fibres of the nerve, c, reflected upon the limb, F. In short, that
muscle will contract when the stimulating current has its origin
in a source external to that body.

208

Galvanoscopic leg, c, in connection with the rest of the frog, F, laid across a ' Galvanf s frog.' ccv.

Immerse each leg of a ( Galvani's frog' in a cup of water,
the positive wire, P, of a voltaic battery being placed in one
cup, the negative wire, N, in the other, as in fig. 209. In

209

Frog, as prepared by Galvani. p, positive wire : N, negative wire : of the battery 5 o, connecting wire of

the two vessels.

the limb A the current runs in the reverse direction of that
of the volitional nervous force : in the limb B it runs in the
same direction. After the voltaic current has passed a short
time through the nerves, contractions occur in the limb B, not in

318 ANATOMY OF VERTEBRATES.

the limb A, in e making ' the current, or completing the circuit ;
whilst contractions occur in the limb A in ' breaking ' the current,
as by removing one of the wires : the limb in which the current
is direct contracts on making the current ; the limb in which the
current is inverse contracts on breaking the current. It needs
only to leave one wire in the water, and to remove or introduce
the other, in order to ( break ' or f make ' the current. If the two
vessels be further connected by a conductor of copper wire, as at
O, fig. 209, contractions of both limbs take place on both making
and breaking the connection.

C5

Neuricity l is not electricity, any more than is myonicity ;
both are peculiar modes of polar force. Any point of the surface
of a nerve is positive in relation to any point of the transverse
section of the same nerve, just as any point of the surface of
a muscle is positive in relation to any point of the transverse
section of the same muscle.2 Ligature of a nerve arrests the
nervous current, not the electric current ; a divided nerve con-
nected by an electric conductor transmits the electric current ;
but the nervous current excited by stimulus above the section
is arrested by the electric conductor. Neuricity is convertible
into myonicity and into other forms of polar force, just as
myonicity or the muscular force may be disposed of by conver-
sion into heat,3 electricity,4 and chemicity, the latter shown by the
evolution of carbonic acid.5 Molecular change, in nervous and in
muscular fibre, attends the exercise of their respective forces.

§ 57. Sympathetic system.- -This consists of one or more ganglia,
usually a series of such arranged on each side of the vertebral
centres from near the occiput to the opposite end of the abdominal
cavity, or to the anterior caudal vertebrae. Where the ganglia are
numerous they are connected in each lateral series by a band of
nervous fibres, and resemble a pair of gangliated cords. These
communicate with the contiguous spinal nerves, and with the
cranial nerves, usually through small ganglia in different parts of
the head, fig. 206. At the caudal end the two sympathetic cords
usually unite with a single ganglion in the under or fore part of
the body of the anterior caudal vertebra.

A sympathetic ganglion is a body connected with bundles of
nerve-fibres, the chief proceeding to or from it in the direction of
its axis, the smaller nerves diverging more or less transversely.

1 'Vis nervosa,' 'Nervous force,' 'Nervous fluid;' it is in relation to the latter name,
expressive of an exploded idea, that the term 'current' is still used in reference to the
course of the polar force, whether nervous, magnetic, or electric.

2 ccxi. 3 ccix. 4 Ib. 5 Ib.

SYMPATHETIC SYSTEM.

319

210

It consists of ; ganglionic corpuscles/ or ganglion-vesicles, fig. 210.
«, b, c, and nerve-fibres,, imbedded in a nucleated fibrous tissue.

The ganglion vesicle may be
circumscribed, or be continued
into a nerve-fibre, or into two
nerve-fibres from opposite poles
of the vesicle ; it is termed ac-
cordingly fapolar,' { unipolar,' and
( bi-polar : ' the last is the most
common form, the first probably
a genetic stao;e. When a g-an-

c? o o

glion-cell is connected by more
than two processes with nerves,
it is a ' multipolar cell : ' these

are most common in the ganglia From the sympathetic (gastric) ganglion of the Kay.

211

of the main cord of the sympa-
thetic ; the bipolar cells prevail in the ganglia of the posterior
roots of the spinal nerves, fig.
201. The nerve-fibres in ganglions
consist of the ' white * or broader
kind, and of the ' grey 'or finer kind;
there are also still more minute
but solid or homogeneous fibres,
surrounding and connecting the
true nervous constituents of the
ganglion. A nerve on entering
a ganglion breaks up into its
component fibres, which interlace
about the ganglion-cells, some-
times winding round them, with
plexiform interchanges of fibres
from other entering nerves and
from the cells.

Bidder and Volkman1 give the
subjoined magnified view, fio-.
212, of the 'intercommunicating'
nerve-fibres between a sympathetic
ganglion and a spinal nerve in the
Frog. H P is the sympathetic, H
showing the part next the head;
C P is the spinal nerve, c showino-
the part next the myelon ; a is a portion of the communicating

1 ccxn.

A. Spinal ganglion of the Ray, 40 diameters.
B. Portion of the same, dissected, ccxxn.

320

ANATOMY OF VERTEBRATES.

branch passing to the myelon ; b, a portion passing to the peri-
phery ; c, fibres of the communicating nerve passing in the
sympathetic towards the head ; d, similar fibres passing towards

212

fl

Communication between the sympathetic and third spinal nerve in the Frog. ccxn.

the pelvis ; g, g, are ganglion-cells ; h, specks of pigment, which
mark the ganglions in the Frog.

§ 58. Sympathetic of Fishes.- - This system, as being an off-
shoot or subordinate element of the general myelencephalous
series of nerve-organs, is differentiated by progressive steps. In
the Myxinoid Fishes it is represented by the intestinal branch
continued from the confluence of the two nervi vagi. In Osseous
Fishes the visceral plexuses are continued into or connected with
slender nerves, accompanying the aorta along the haemal canal,
and representing the trunks of the sympathetic in higher Verte-
brates. The first or anterior communication of this nerve, in the
Cod, is with a branch of the fifth, and a filament is sent forward
to the ciliary ganglion : in the Carp a filament joins the abducent
nerve, to which Cuvier thought he had also traced a filament of

o

the sympathetic in the Cod ; the sympathetic next communicates
with that anterior portion of the vagus (the glosso-pharyngeal)
which joins part of the acoustic nerve, and supplies the first par-
tition of the gills ; the sympathetic trunks also receive accessions
from the trunks of the vagus, and, converging, intercommunicate

SYMPATHETIC OF EEPTILES. 321

by a cross branch : they then send nerves which join the gastric
branches of the vagi, in order to form or join a splanchnic ganglion
and plexus on the mesenteric artery, from which plexus branches
are sent to the intestines, pancreas, and spleen. The sympathetic
trunks are continued on each side of the aorta, along the back of
the abdomen, into the hremal canal ; communicate, in their course,
with the ventral branches of each of the spinal nerves ; supply by
filaments, usually accompanying the arteries, the kidneys, the
generative glands, and the urinary bladder, where this exists ;
and often, finally, blend together into a common trunk beneath
the tail. Ganglions are sometimes found at the junction of the
sympathetic with the fifth, as well as at that with the glosso-
pharyngeal and with the vagus, before the great splanchnic is
formed : small ganglions are more rarely discernible at the junction
of the sympathetic with the spinal nerves.

The splanchnic ganglion of the Skate is a large fusiform body,
of an ash-red colour; the succeeding ganglia on the trunks of
the sympathetic are larger and more constant than in Osseous
Fishes ; but the intervening chords are semi-transparent.

§ 59. Sympathetic of Reptiles.- -The trunks of the sympathetic
appear, in the Frog, to be formed in a great proportion by con-
tributions from or communications with the spinal nerves ; there
are, however, slight enlargements at the points of connection,
often marked by pigment-cells, in which true ganglion-cells
occur, as shown in fig. 212, h.

In Ophidia the trunks of the sympathetic, conspicuous at the
anterior part of the trunk-cavity, on each side the vertebra,
bodies, show as little any enlargements where they receive the
communicating branches of the spinal nerves as in Batrachia.
They slightly diverge as they approach the basis cranii, and are
reflected outwards to the vagus, forming a conspicuous ganglion
at the junction. From this ganglion the sympathetic is continued
forward in a canal of the basisphenoid, and forms a small ganglion
with a branch of the second division of the fifth ; it sends fila-
ments to the membrane covering the posterior part of the mouth
and palate, one of which communicates again with the maxillary
nerve. From the last ganglion there proceeds ' another branch
forward to form another ganglionic union ' (spheno-palatine) 6 with
a branch of the second trunk of the fifth, and from this a branch
is sent to the posterior part of the nose, to ramify on the schnei-
derian membrane ; other branches are given to the membrane
covering the mouth and palate, and one passes forward and com-
municates again with a branch of the second trunk of the fifth,

VOL. I. Y

322 ANATOMY OF VERTEBRATES.

and is distributed on the membrane covering the anterior part of
the mouth and palate. It is worthy of remark that the nerves
distributed on the membrane of the mouth and nose communicate
so many times with branches of the second trunk of the fifth, and
their connection is so much greater than in the Turtle ; but in
this creature the palate is horny, and not so extensive in propor-
tion to the size of the head. 3, prolongation of the sympathetic
connected with the trunk of the par vagum, but not directly with
the ganglion of the sympathetic ; it communicates with the ninth
nerve, then passes down the spine, and communicates with the
eleven superior spinal nerves ; it emerges on each side at the
place the superior branches of the vertebral artery enter to dis-
tribute branches in the intercostal spaces ; it is continued down-
wards in a very fine plexiform prolongation with the vertebral
artery, as far as the origin from the right aorta ; it then branches
to each side beneath the membrane connecting the viscera with
the ribs and spine, and communicates with filaments of the par
vagum ; it is afterwards continued downwards, receiving a fila-
ment from each spinal nerve ; in its course it is a very fine nerve,
and has not any more ganglia than the first, and those communi-
cating with the second trunk of the fifth ; but at different points
from which the nerves pass to the viscera, there is an appearance
of a delicate plexus : this plexiform structure varies in different
parts, and becomes much greater about the beginning of the
intestine, where it resembles that corresponding with the semi-
lunar ganglion in the Turtle : near the kidney it assumes the
form of a nervous membrane or retina, before it is distributed on
the urinary and generative organs. Branches pass from the
plexuses with the arteries to the different viscera.' l

Bojanus describes the sympathetic nerve of the Emys JEuropcea
as accompanying the carotid artery into the cranium, and uniting
with the vidian and the facial nerves. On issuing from the
cranium it is closely connected with the vagus and with the
glosso-pharyngeal nerves, so that it is difficult to say whether a
superior cervical ganglion exists or not ; and as the cervical
vertebra are ribless, there is no ' vertebral canal,' and the nerve
is closely connected with the vagus throughout the whole length
of the neck. Below the sixth cervical vertebra the sympathetic
nerve separates itself from the sheath of the vagus, and becomes
connected with a middle cervical «;ano;lion, whence issue filaments

O O '

that are distributed to the aorta, the cardiac plexus, and the creliac
plexus. Between the seventh and eighth cervical vertebras is
situated the inferior cervical ganglion, like an elongated swelling

1 XLIV. p. 66.

APPENDAGES OF THE NERVES. 323

of the nerve ; subsequently two dorsal ganglia occur, and further
down, towards the middle of the back, there occurs a third and last
ganglion, which furnishes the splanchnic nerve : the remainder of
the sympathetic is made up of one or two cords, which, in the
sacral region, give off a great number of branches, the divisions of

O " O ~ *

which form the renal, hypogastric, and sacral plexuses.

In the Turtle ( Chelone) the cervical portion of the sympathetic
has the same exposed position, and communications, with the vagus
above and the axillary plexus below, sending off filaments also to
the arteries. The branch accompanying a division of the carotid
in a canal at the base of the skull gives a filament to the portio
dura, and communicates with the maxillary part of the fifth, to
terminate on the back part of the palate. Another branch enters
with another division of the carotid into the reticular sinus close
to the auditory meatus, and communicates with the portio dura,
glossopharyngeal, and ninth nerves. In the trunk-cavity, the
sympathetic passes from ganglion to ganglion as two cords, a thick
and a fine one, neither of which passes behind the neck of the
rib ; the intercommunicating branches with the spinal nerves are
perforated by an anterior branch of the intercostal artery. The
chief nerves given off from the sympathetic form two plexuses, in
the place of the ( semilunar ganglia ' of mammals : the smaller
plexus sends filaments along the coeliac artery to the stomach, the
larger plexus along the mesenteric artery to the intestines. Other
branches pass to the kidneys, and the communications with the
spinal nerves mark out the delicate prolongation of the sympa-
thetic to behind the rectum.

In the Crocodile the cervical part of the sympathetic lies in
the ( vertebral canal,' or between the neck and tubercle of the rib,
and the ganglions are more distinct where the communications
with the spinal nerves occur, from the cervical to the lumbar
region. The interganglionic longitudinal trunks are two, one
passing behind the neck of the rib where it exists, at the fore-part
of the chest. The longitudinal trunks converge, and unite upon
the beginning of the caudal artery. There is much pigmental
matter upon the sheaths of the ganglions and nerves.

§ 60. Appendages of the Nervous System. - - Certain nerves, as
those of the palm and sole in Man, and those of the mesentery in
other mammals, have peculiar corpuscles appended to them, called
'pacinian,' after their discoverer. Fig. 213 shows one of the nerves
of the palm with the corpuscles appended, of the natural size.
Those in the mesentery of the cat are numerous, conspicuous, and
favourable subjects for microscopical investigation. They show

Y 2

324

ANATOMY OF VERTEBRATES.

Nerve of the palm,
with Pacinian cor-
puscles, Human,
ccxxvin.

214

a pedicle and capsule, with a canal and central cavity. A single
213 nervous fibre, fig. 214, n, leaves its fasciculus with

a portion of the nerve-sheath, ib. b, and proceeds
to the centre of a series of concentric capsules,
of a nucleated fibrous tissue. The nerve, n, on
entering the central cavity, loses its white sub-
stance, and, at the opposite end of the axial cavity,
terminates by a tubercular enlargement. An
arterial twig, a, accompanies the nerve-fibre along
the pedicle, and divides into capillaries, which form
loops in some of the intercapsular spaces. The
central cavity contains a clear fluid : it varies much
in shape.

Analogous bodies were discovered by Savi,
arranged in linear series, bordering the anterior
part of the mouth and nostrils, and extending
over the surface of the fore-part of the elec-
trical organs in the Torpedo; they are appended
to and appear to be terminal developements of the filaments of

the fifth pair of nerves. Each
follicle, fig. 215, is formed of two
larger capsules, f and g, which
adhere together near the fibrous
band, c, c, supporting and fixing
the organ ; it contains a granular
substance, e, on which lies the
nerve- twig, b, d, transmitted from
the nerve, a. This twig commonly
receives a smaller anastomosing
filament, k, from a contiguous
follicle. Sometimes two nerve-
twigs pass from the main branch
to the same follicle, in which case
it contains two distinct granular
masses. These follicles are de-
veloped from ganglionic or sensory
branches of the fifth nerve. No
proper pacinian corpuscles have
been observed in connection with
this nerve, nor with the glosso-
pharyngeal, the portio dura, or
any purely motor nerve.

Pacinian corpuscle, on mesentericnerre of -cat. Besides the Savian COrpUSCleS

Magu. cuxxix.

ORGAN OF TOUCH IN FISHES.

325

215

One of the follicular nervous organs of the Torpedo.
Magn. LXXVII.

the Torpedo has a system of mucousxorgans in intimate connec-
tion with nerves of sensation : but this is common to it with other
Plagiostomes. The system
commences, in the Torpedo,
by groups of globular vesicles,
fig. 139, M, arranged sym-
metricallv, outside the elec-

»/ •*

trical organs, from which
tubes are continued in parallel
bundles until they separate
themselves to perforate the
skin, and terminate by ori-
fices, some at the dorsal, some
at the ventral surface of the
head. A branch of the gang-
lionic part of the fifth expands
upon the ampulliform com-
mencement of each of the muciferous tubes. Similar organs

o

exist in Sharks. Hunter placed first in the series of specimens
of organs of touch in Fishes the snout of the Spotted Dog-fish
(Scyllium), ( to show the manner of the nerves ramifying, as also
their apparent termination in this part, each ultimate nerve
appearing to terminate in the bottom of a tube or duct, the sides
of which secrete and convey a thick mucus to the skin.'1
Jacobson compares them to the whiskers in the Cat. Besides the
rostrum, these iiervo-mucous organs are situated upon the sides
and under part of the head, and on the fore part of the trunk ;
they are crowded between the masseter, fig. 132, /, and the
branchial openings, ib. q, where they separate into two groups,
one diverging downward, forward, and backward, to beneath the
pectoral fin ; the other directed upward, forward, and backward, to
the occiput.

§ 61. Organ of Touch in H&matocrya.- -In the Dermopteri,
the AnguillidcB, Siluroids, and a few other Fishes, with the in-
tegument wholly or in part scaleless, or with very minute and
delicate scales, lubricated with mucus, the whole or major part of
the external surface may be susceptible of impressions from the
surface of extraneous bodies coming in contact therewith. But
in the majority of the class the exercise of any faculty of touch
must be limited to the lips, to parts of certain fins, or to the
specially developed organs called ( barbules.'

1 xx. vol. iii. p. 55, prep. no. 1395.

326 ANATOMY OF VERTEBRATES.

Such an organisation of a fold of skin bordering the mouth as
implies the tactile faculty is rare in Fishes ; the Cyprinoids
exemplify it, and more especially many of the Indian species :
also the marine family of Labroids. In the Sturgeon the lip has
numerous papillae, and more minute papilla? occur on the lips of
many fresh-water fishes. In the Eels the upper lip is richly
supplied by the fifth nerve, and the upper lip of the Lepidosiren
is papillose. The soft skin of the sucking-lip of the Lamprey is
well supplied with a reticulate arrangement of sensitive filaments
from the fifth ; its margin is papillose, fig. 277. The associated
pectoral and ventral fins, forming the sucker in the Lump-fishes,
have a texture of the applied surface, which seems adapted to
receive impressions from the part it touches, whereby the fish
may ascertain its fitness or otherwise for the application of the
anchoring organ.

The pectoral fins seem to be applied occasionally to explore the
nature of the bed of the water inhabited by the fish ; and in the
Gurnards ( Triglidce) three soft flexible rays are detached from the
fin, like fingers, fig. 82, and the large nerves supplying them have
ffano-lionic enlargements at their origins. The filiform radial

o ~ o o

appendages of the Polynemidce., and the prolonged ventral fins of
Osphromenus, Trichogaster, and other Labyrinthibranchs, and of
the Ophidiidas, enter into the present class of organs. The
barbules are long, slender, pointed processes of the skin, either
median or in pairs : the former are limited to the under jaw, as in
the Cod ; the latter may be developed from both jaws, and are
called, according to their position, ( premaxillary,' ( angular,'
1 nasal,' &c. They are commonly found in the grovelling fishes,
such as the Sheat-fishes, Loaches, Barbels, Sturgeons, fig. 123,5,
or in the parasitic Myxines, fig. 248. The nerves supplying the
barbules are large and derived from ganglionic divisions of the
fifth pair. A Cod, blind by absence or destruction of both
eyeballs, has been captured in good condition ; and it may be
supposed to have found its food by exploring with the symphysial
barbule, as well as by the sense of smell.1 The sublingual fila-
ment of many UranoscopincB, and the rostral tentacle of Malthe
and Halieutaa? may also exercise a tactile faculty. The limbs
of Lepidosiren, fig. 100, have the general form rather of organs
of exploration than of locomotion.

The scaleless condition of the skin in Batrachia makes it more

1 XCVITT. p. 72.

2 CLXXIV. iii. p. 204. The homologous organs in Lophius seem to act as bait, to
attract small fishes.

ORGAN OF TASTE IN EEPTILES. 327

susceptible of impressions than in higher Reptilia ; the discoid
expansions of the toe-ends in Hyla, and the filamentary appen-
dages of the toes in Pipa, may have more sense of feeling than
other parts, but seem not to be applied in active touch. The
labial papillae of larval Frogs are so placed and supplied by nerves
as to suggest a tactile function. Certain Ophidians, e.g. Herpeton
tentaculatum, have a pair of tentacular appendages upon the
snout: but the long, extensile, forked, filiform tongue seems to
be used rather as an organ of exploration than of taste in most
Serpents, and in the slender-tongued Lizards. The expanded
toes of Geckos, fig. 162, the short, thick, scansorially-opposed
digits in Chameleons, and the concave surface of their prehensile
tail, although mainly modifications for locomotive purposes, may
well be supposed to have a surface more sensitive than other
parts of the body. The snout-like production of the upper lip
in TrionychidcR and Chelys, with the subsidiary tegumentary pro-
ductions of the head in the latter, are probably more direct and
active instruments of tactile exploration in these soft-skinned,
mud-haunting, and chiefly nocturnal Chelonia. Some nocturnal
Tree- Snakes (Dryophys, Passeritci) have a prolonged snout.

§ 62. Organ of Taste in Reptiles.- -The glosso-hyal, fig. 85, 42,
does not support, in Fishes, an organisation of soft parts for a
special sense of taste : and the description of the tongue and other
projections and structures in the interior of the mouth will be
given in connection with the preparatory digestive organs. A
tongue, as a gustatory organ, is as little developed in the perenni-
branchial Reptiles, and is absent in the marsupial Toads (Pipa).
There is as little trace of tongue during most of the larval period
in other Anura ; but, about the time when the fore limbs are in
bud, the membrane covering the basihyal begins to develope vas-
cular fungiform papillae, with looped capillaries and muscular fibre :
the whole mass growing and extending from before backward, and
constituting the retroflexed tongue, by the time the tail is atrophied.
The free part is usually bifid or bilobed. It is mainly an organ
of prehension, and will be described as such, together with the
tongue of the Chameleon, in connection with the organs of nutri-
tion. In the thick-tongued Lizards, e. g. Iguana tuber citlata, the
dorsum and sides of the tongue are minutely papillose ; in Tiliqua
scincoides they are coarsely papillose : both the food and the teeth of
these Sauria indicate a certain amount of mastication, with which
the sense of taste is correlated. In most Reptilia the food is bolted
entire. In the Tortoise ( Testudo indica) the tongue is beset with
numerous elongated and pointed papillae: in the Turtle (Chelone

328 ANATOMY OF VERTEBRATES.

mydas) the tongue is wrinkled and devoid of papillae. In the
Crocodiles the tongue has no projecting extremity, and is but
slightly raised above the level of the membrane which attaches its
circumference to the mandible : but its dorsum is marked by a
group of follicles and increased vascularity of that part of its
surface.

§ 63. Organ of Smell in H&matocrya.- -The essential character
of the organ of smell, in Fishes, is the pituitary membrane lining
a sac with one or more apertures upon the external surface ; and
that, in the few exceptions in which it is extended into a canal
communicating with the mouth or fauces, such naso-palatine canal
is never traversed by the respiratory medium in its course to the
respiratory organs.

The extremities of the olfactory nerves, fig. 203, o, expand
upon the pituitary membrane, which is highly vascular, and is
covered by ciliated epithelium : its extensive surface is packed
into the small compass of the olfactory capsule by numerous folds.
The capsule is formed by a fibrous membrane, which is sometimes
supported by a cartilaginous, and more frequently by an osseous,
basis, called the ' turbinal bone,' fig. 81, 19.1

In the Dermopteri the olfactory organ is single : Kolliker 2
regards as such a small, blind, tegumentary depression, fig. 169, o/,
beset with vibratile cilia, and connected with the anterior end of
the quasi-brain of the Branchiostoma. The more obvious and
satisfactorily determined olfactory organ of the Ammocete is in the
median line, opening above the mouth in front of the brain-sac,
fig. 59, 19, whence a narrow canal is produced backward from the
bottom of the sac to the base of the skull. In the Myxine the
parietes of the olfactory canal are similarly situated, lined by a
longitudinally-plicated pituitary membrane, and are strengthened
by cartilaginous rings, like a trachea. The naso-palatine tube
opens backward upon the roof of the mouth, and this opening is
provided with a valve. In the Lamprey the flask-shaped nasal
sac, fig. 61, k, opens upon the top of the head : a simple mem-
branous tube is continued from the expanded bottom of the sac,
which dilates as it descends, but terminates in a blind end at the
hypophysial vacuity, fig. 60, hi/, of the base of the skull, where
the mucous membrane of the palate passes over it entire and
imperforate.3

In all Fishes, save the Dermopteri) the olfactory organs are
double, and they have no communication with the mouth. In

1 LIV. 2 xxxn. p. 32, pi. ii. fig. 5, A. 3 xxi. pi. 43, figs. ii. & iv.

ORGAN OF SMELL IN FISHES. 329

Osseous Fishes they are situated on the sides of the snout, iu a
cavity formed by the nasal, fig. 75, 15, the prefrontal, 14, the
lacrymal, 73, the premaxillary, 22, and the vomer. The capsules
are covered externally by the skin, which is usually pierced by
two openings for each sac : the Chromides, and all the Wrasses
with ctenoid scales, have a single opening for each nose-sac ;
where there are two nostrils the posterior is usually open, the
anterior closed, as by a sphincter or a valve : the anterior aperture
is often produced into a tubular process, as in the Loach, which
acts, either by muscular power or by some modification of form,
as a valve. Both apertures in some Lophioid Fishes are bell-
shaped and pedunculate. In some Siluri a tentacle is continued
from the external nasal tube. When the nasal sac is round, the
pituitary plica? radiate from its centre : when the sac is elongated,
it is usually traversed by an axial partition with a row of folds on
each side ; and there are transitional arrangements, as in the
Perch, figs. 131, o /, & 134. In a few Fishes these folds are
further complicated by secondary processes. The Sturgeon pre-
sents the radiated type of the olfactory organ with secondary folds,
fig. 125, 19, but, like the Polypterus and Lepidosteus, each nasal
sac has a double aperture : the Lepidosiren has an elongated nasal
sac, with the biserial arrangement of pituitary folds, and with two
apertures, fig. 186, ol, upon the under part of the thick upper lip,
but neither of these communicate witli the mouth. In some
Osseous Fishes the olfactory sac is divided into a plicated and a
smooth part : the former exercising the sense-function, the latter
that of a reservoir. In the Mackerel this extends down to the
palate : in the Wolf-fish the reservoir passes backward, expanding,
as far as the back part of the palate, w^here it ends blindly. The
prolongation of the single nasal cavity in the Lamprey is analogous
to this.

In the Plagiostomes the nasal cavities are situated beneath the
snout, in the Sharks, figs. 30 & 63, b : beneath the fore part of
the head, behind the base of the rostrum, in the Saw-fish (Pristis),
fig. 65 : or near the angles of the mouth, as in the Chimera and
the Rays, where a groove extends to the mouth. Each olfactory
cavity has a single and commonly wide opening, defended by
valvular processes, supported by peculiar cartilages more or less
intimately connected with the proper olfactory cartilaginous sacs,
and representing the superadded cartilages of the ( alse nasi ' in
higher Yertebrata.1 They have their proper muscles : whence we
must conclude that these Fishes scent as well as smell, i. e. actively

1 See the description of these 'nasenfliigelknorpel' in xxi. p. 171.

330 ANATOMY OF VERTEBRATES.

search for odoriferous impressions by rapidly changing the current
of water through the olfactory sac.1

The Protopteri show no outward signs of olfactory organs : the
thick upper lip must be raised to bring the plicated sac, with its
two remote orifices, into view. In Amphiuma the external nostrils
are minute, approximate, and near the end of the snout. In the
Siren and Axolotl the external nostril is conspicuous on each
side the snout: the internal one opens outside the series of
pterygo-vomerine teeth. In the Siren the maxillary does not
extend back so as to divide the internal nostril from the inner or
under part of the lip : in the Axolotl it is so extended, and the
opening is situated between the maxillary and palatine series of
teeth. In these, as in the Proteus, the olfactory membrane is
plicated at right angles to a longitudinal seam. In the Newts
and Salamanders the olfactory membrane is smooth, and lines an
oval cavity with an external nostril and a palatal one, the former
defended by a little fold of skin.

In tailless Batrachia the external nostril has an inferior flap,
endowed with a slight movement : the palatal is widely open,
between the palatine and maxillary bones, near the fore part of
the mouth. The olfactory membrane is not augmented by any
folds or prominences. In the Pipa it presents a cylindrical form,
and its outer opening is much nearer that of the opposite side
than in other Anoura. In Ophidia the external nostrils are
double ; the internal nostril is single and median : the bone and
gristle supporting the olfactory sac make some prominences in it ;
the pituitary membrane is almost black in some Colubers. In
Anguis, and other snake-like Lacertians, the palatal nostrils open
separately.

In the Iguana a single broad turbinal cartilage extends into the

O O C2

olfactory cavity from the outer side, terminating below in two
tuberosities. The meatus extends at first longitudinally back-
ward, then bends downward to open upon the palate between the
anterior maxillary and the pterygoid teeth. The turbinal projects,
with slight modifications of proportion and form in the nasal
cavity of other Lacertians. The external nostrils offer varieties
of relative size, shape, and position, seldom receding far from the
muzzle in existing species. In the extinct Saurians of marine
habits, Ichthyosaurus and Plesiosaurus, the external nostrils
opened near the orbits, at a distance from the muzzle. In Chelonia

1 'Is the mode of smelling in Fishes similar to tasting in other animals? Or is
the air contained in water impregnated with the odoriferous parts, and is it this air
which the fish smells? '--John Hunter, in xx. vol. iii. p. 88.

ORGAN OF SIGHT IN FISHES. 331

and Crocodilia, the external opening to the nasal organ in the skull
is single and median, situated at or near the end of the muzzle.
But in the Chelonia the nostrils are distinct, although approximate,
on the integument : in Trionyx and Chelys they are tubular, con-
tinued along a short proboscidiform production of the integument.
The septum narium is gristly. In the Turtle ( Chelone) the nasal
cavity suddenly expands to contain the turbinal cartilage. The
periosteum of the cavity and the pituitary membrane are both
coloured by dark pigment, and the latter is thick and vascular.
The palatal orifice is median and single, towards the fore part of
the roof of the mouth. In the Crocodilia the tegumentary nostril,
like the osseous one, is single, crescentic, with the concavity
backward, and closed by the fleshy posterior valvular lobe : in the
Gavial the tegument surrounding the nostril is thick, abundant,
and can be raised from the bone, or erected, to bring the orifice to
the surface of the water without exposure of other parts of the
head. The nasal cavity is of oreat leno-th, commencino; at the

«/ O O

fore part of the muzzle, and terminating beneath the occiput, also
by a single aperture, close to which the nasal septum terminates.
The anterior third part of the meatus is most expanded : the
pituitary membrane is extended upon a bilobed turbinal, partly
bony and partly gristly : the meatus also communicates with
large cells or sinuses.

§ 64. Ore/an of Sight in Fishes. — The organ of sight makes its
appearance in the lowest of Fishes, e. g. the Lancelet and Myxine,
under as simple a form as in the Leech : a minute tegumentary
follicle is coated by dark pigment, which receives the end of a
special cerebral nerve. This simple eyespeck, the first mechanism
for the appreciation of light, is repeated in the Amblyopsis spelceus,
fig. 175, n. Rudimental eyeballs covered by the skin exist in the
Aptericlithy s ccecus : the small, but more complex, eyes of the
Lepidosiren, with crystalline and vitreous humours, choroid and
sclerotic tunics, are also covered by the skin, but this becomes
transparent where it passes over them, and, adhering to the
sclerotic, forms a f cornea.' The eyes of the Eel tribe and the
Siluroid Fishes are small : they are of moderate size in the
Plagiostomes and Ganoids ; but in most Osseous Fishes the eyes
are remarkable for their large size, which becomes enormous in
some, e. g. Orthac/oriscus, Myripristis, Priacanthus. The eyes
are usually placed in orbital cavities, one on each side of the
head ; only in the unsymmetrical Flat-fish are they both placed
on the same side : in the Stargazer ( Uranoscopus) the eyes are
approximated on the upper surface of a nearly cubical head, and

ANATOMY OF VERTEBRATES.

216

_, '' f n «/.

•Kssssf-/ -t-\%=

Eye of Sword-fish ; one- third
natural size.

are directed towards the heavens : in the Hammer-headed Sharks
they are supported on long outward -projecting pedicles.

The optic nerve, fig. 216, «, usually perforates the eyeball
obliquely out of its axis, but sometimes directly in its axis. In

Osseous Fishes it is compressed where it
passes through the sclerotic and choroid,
and then forms the retina by unfolding
itself, like a fan spread out and bent into
the form of a cone, leaving a fissure, 5, where
the free lateral borders meet after lining
about two-thirds of the hollow globe. This
fissure extends from the entry of the nerve
to the anterior margin of the retina, and
through it a fold of the innermost layer of
the choroid passes into the vitreous humour,
sometimes accompanied by the dark pig-
mental Ruyschian layer.1 The fold of the vascular choroid,
whether accompanied by the pigmental layer or not, is called the
6 falciform process,' c ; it carries before it a fold of the proper
tunic of the vitreous humour ({ membrana hyaloidea'), and usually
extends to the capsule of the lens, d, to which it is attached by
means of a clear but firm substance, called the ' campanula
Halleri.'

The posterior or outer layer of the retina consists of the cel-
lular basis, supporting the stratum of cylindricules, standing
vertically upon its concave surface, with the interblended twin-
fusiform corpuscles, both of which microscopic structures are more
easily demonstrated in the present than in the higher classes of
Vertebrata. Each twin-corpuscle is surrounded by a circle of
cylindricules. The primitive nerve-fibres radiate over the cylin-
dricules, without anastomosing, and terminate in free ends, not by
loops, at the basis of the ciliary zone. A delicate but well-
defined raised rim or f bead' runs along both the anterior margins
of the retina, and along those which form the falciform slit.

The crystalline lens (d) is spherical, or nearly so, large, firm,
with a dense nucleus : it is almost buried in the vitreous humour,
where it is steadied by the attachment of the falciform ligament
to its thin capsule : the fore part projects through the pupil
against the flat cornea, and so nearly fills the anterior chamber,
that but a very small space is left for ' aqueous humour.' In the
cod and other Gadidce the fibres of the lens converge, like the

1 xx. vol. iii. p. 144; eye of the Bonito, prep. no. 1651.

ORGAN OF SIGHT IN FISHES.

333

217

meridians of a globe, to two opposite points or poles of the sphe-
roid : in the Salmonidce and Shark, they converge to a linear tract
or septum at each pole, as in fig
218. In the fibres of the lens
of a cod Brewster discovered
the marginal teeth, like those of
rack-work, by which the fibres
are interlocked together, as in
fig. 217.

This acute observer computes
five millions of fibres and sixty-
two thousand five hundred mil-
lions of teeth in the lens of a cod :
yet in the living and fresh state
this organ is transparent.

The radiating fibres and elong-
ated cells of the hyaloid tissue,1
with the interstitial ( vitreous

hlimOUr,' present a firmer COn- Fibres of lens, highly magnified, showing inter-
. ,1 • ,1 locking of their toothed margins, ccxm

sistency than in the human eye,

and show their intimate structure and arrangement more clearly

under the microscope than in Mammalia.

The membranes situated between the retina and sclerotica,
called collectively ( choroid
tunic,' are three in num-
ber : the external layer in
Osseous Fishes, called ( mem-
Irana aryenteaj fig. 216, e, is
composed chiefly of micro-
scopical acicular crystals
reflecting a silvery, or some •
times a golden lustre, with a
delicate cellular basis, which
assumes more firmness where
it is continued upon the iris.
The second or middle layer
is the ( membrana vasculosaj
sen ' Halleriy ib. jf, and, as
its name implies, is the chief

. . Arrangement of fibres of leiis, Salmon, ccxiu.

seat of the ramifications of

the choroid vessels : it also supports the ciliary nerves. The

218

1 LXY.

334 ANATOMY OF VERTEBRATES.

innermost layer is the f membrana pictaj sen ' RuyschianaJ g}
also called ( uvea,' which is composed of hexagonal pigment-cells,
usually of a deep brown or black colour. In the Grey Shark
(Galeus), the silvery layer is laid upon the central surface, not
the periphery of the choroid.1

The formation of the iris, A, by the production of all these mem-
branes is well shown in the eye of the Sword-fish Xiphias, fig. 216,
where its thick base or ( ciliary ligament ' h overlaps the con-
vex border of the bony sclerotic.2 The membrana argentea upon
the front of the iris gives great brilliancy to the eye, in many
fishes. The pupil, z, is large and usually round : in many Pla-
giostomes it is elliptic ; in Galeus it is quadrangular ; in the flat-
bodied Skates and Pleuroiiectida?, that grovel at the bottom and
receive the rays of light from above, a fringed process descends
from the upper margin of the pupil, and regulates the quantities
of admitted light by being let down or drawn up like a blind.

The muscular structure of the iris is very feebly developed in
most fishes : it is best seen in the pupillary curtain of the Skate,
the plicated anterior border of the uvea forms the so-called
( ciliary zone, or processes,' k : they are the most complicated in
the great Shark (Sclache) where each process ( consists of two or
three minute folds, which, as they run forward, unite into one,
and terminate in a point at the circumference of the iris :'3 but
they do not, as yet, project freely inward and forward from the
surface of the uvea.

The subordinate and accessory character of the sclerotic cap-
sule, fig. 216, /, Z, fig. 219,t/,jf, is illustrated in most Osseous Fishes
by its deviation from the sub-spherical form of the true eyeball
which it protects, and by the great quantity of cellular, and often
also of adipose tissue, fig. 216, which fills the wide interspace be-
tween the sclerotic and the choroid. In the fibrous tissue of the
sclerotic are usually developed the two cartilaginous or osseous
hemispheroid cups already described (p. 115, fig. 81, 17); but in
place of these, in the Orthagoriscus, as in the Plagiostomes, the
capsule is strengthened by a single hollow, cartilaginous, perforated
spheroid. This varies in thickness at different parts, being usually
thickest behind, and particularly so in the Sturgeon. The ante-
rior aperture is closed by the cornea ?z, which is essentially a
modified portion of the corium o, adhering to, as it passes over,
the usually thickened borders of that aperture. In the eye of the
may be traced an accession to the cornea from the outer

1 xx. vol. iii. p. 147, prep. no. 1669. 2 Ib. prep. no. 1661.

3 Ib. prep. no. 1670, A. 4 Ib. prep. no. 1661.

OKGAN OF SIGHT IN PISHES. 335

fibrous layer of the sclerotic, which undergoes the same change
of tissue, and forms the posterior layer of the cornea. This
transparent window of the eye-capsule is quite flat : its laminated
structure is well displayed in the cornea of the Orthagoriscus*
and a dark-brown pigment here stains the soft integument or
6 conjunctive membrane' (0), continued from the periphery of the
cornea, In the eye of the same fish,2 a very delicate layer or
lining membrane is reflected from the posterior surface of the
cornea, answering to the ' membrane of the aqueous humour ' of
land animals : this humour exists in very small quantity, just
enough to lubricate the iris in the eyes of Fishes : the medium
through which the rays of light reach the eye needs no refractive
aid from an aqueous fluid interposed before the lens in the globe
itself.

Amongst the most characteristic peculiarities of the eye in
the typical or Osseous Fishes is the so-called ' choroid gland '
fig. 216, o, fig. 219, /a; this is of the class of bodies called f vaso-
ganglions : ' it usually presents a dark red colour, and lies between
the ' silvery' and ( vascular ' layers of the choroid, more or less
encompassing, in the shape of a horse-shoe or bent magnet, the
entry of the optic nerve. Dr. Albers3 discovered the rich marginal
plexuses of vessels, i the roots of which have their origin in this
body,' and the body itself he believed to consist also of a convolu-
tion of blood-vessels. Ordinary dissection, however, shows its
compact substance to be arranged in parallel straight lines running
between the convex and concave borders, and it has been called a
( muscle ; ' but the supposed ' fibres consisted, in reality, of minute,
parallel, and closely-disposed vessels, both arteries and veins.'4
Professor Miiller has detected a relation of coexistence between
the choroid vaso-gangiion and the pseudo-branchia, to which the
Sturgeon, Lepidosiren, and the Plagiostomes are amongst the
exceptions, having the pseudo-branchia? but not the vaso-ganglia ;
Silurus, Pimelodus , Synodon, Cobitis, and all the Eel-tribe, have
neither pseudo- branchiae nor choroid vaso-ganglia.

The most remarkable exception in the structure of the eye in
the present class is presented by the Anableps, the cornea of
which is bisected by an opaque horizontal line, and the iris per-
forated by two pupils.

The general form of the eyeball, or rather its capsule, in Fishes,
is a spheroid, flattened anteriorly, around which part the integu-
ments commonly form a circular fold, yielding to the movements

1 xx. vol. iii. p. 147, prep. no. 1665. 2 Ib. prep. no. 1649.

3 LXXV/. 4 xx. vol. iii. (1836); p. 145, prep. 1656; and LXVII.

/

336

ANATOMY OF VERTEBRATES.

219

3

of the globe. In Orthac/oriscus the circular palpebral fold is
deeper, and is provided with a sphincter : in most Scomberoid and
Clupeoid Fishes there is an anterior and a posterior vertical trans-
parent fold or eyelid. In the eye of the tope and blue Shark,
there is a nictitating membrane superadded to a well-developed
circular palpebral fold of the skin, A conjunctive membrane is

reflected from the circular eyelid over the
third eyelid,, which is placed at the nasal side
of the orbit, and then passes over the anterior
half of the eyeball. A strong ( nictitator ' mus-
cle rises from the temporal side of the orbit, and
passing through a muscular and ligamentous
loop, descends obliquely to be inserted into the
lower margin of the third lid. The trochlear
muscle has an insertion into the upper part of
the circular lid, and depresses that part simul-
taneously with the raising of the third lid. 1 The
proper muscles of the eyeball exist in all fishes
except the Myxinoids and Lepidosiren, and
consist of the four recti, fig. 219,1,2,3,4, and two
obliqui, ib. a, b : the latter rise from the nasal
side of the orbit, and are inserted most favour-
ably for effecting the rotatory movements of
the eyeball : but the superior oblique, #, has
not its direction changed by a trochlea in the
present class. In the Galeus there is a special
protuberance of the upper part of the carti-
laginous sclerotic for the common insertion of
the rectus superior and obliquus superior ;
and a second protuberance below for the common insertion of
the obliquus inferior and rectus inferior. The recti muscles
rise in many Osseous Fishes from the sub-cranial canal ; 2
the origin of the rectus externus being prolonged furthest back.
But the recti muscles are most remarkable for their leno-th

o

in the Hammer-headed Sharks, since they rise from the basis
cranii, and extend along the lateral processes or peduncles, at the

1 The family of Sharks, including Galeus, Carcharias, with this grade of palpebral
structure, are called ' nictitantes ; ' they are amongst the most active and formidable
of these great predatory Fishes.

2 If, therefore, we regard this canal as part of the orbits, we must add the alisphenoid,
basisphenoid, and even the basioccipital, to the bones enumerated at p. 116, as forming
the chambers for the eyeballs and their appendages in Fishes; and this multiplicity of
orbital bones interestingly repeats or parallels the characteristic formation of the
otocranes or ear-chambers in the present class.

Coats of the eye of the Perch

XXIII.

ORGANS OF SIGHT IN REPTILES. 337

free extremities of which the eyeballs are situated. In all
Plagiostomes the eyeball is supported on a cartilaginous peduncle :
this is short and broad in the Rays ; longer and cylindrical in the
Sharks ; in Selache it is articulated by a ball and socket synovia!
joint to a tubercle above, and external to the entry of the optic
nerve.1 A fibrous ligament attaches the sclerotic to the wall of

O

the orbit in the Sturgeon and the Salmon.

The space between the eyeball and the orbit contains a soft bed
of gelatinous and adipose substance : but there is no lacrymal
gland in Fishes. An apparatus to moisten the cornea was, of
course, unnecessary in animals perpetually moving in a liquid
medium. The cornea, which in most fishes is always exposed to
that medium, is flat ; it is, therefore, less liable to injury in the
rapid movements of the fish, and being level with the side of the
head, offers no impediment to those movements. This form of
cornea diminishes the capacity of the aqueous chamber ; but the
aqueous humour is needed only to float the free border of the iris ;
and to make up for the small quantity of that humour, the refrac-
tive power of the lens is maximised by its spherical form. To
compensate for the deviation from the spherical form of the eye-
ball, produced by the flattening of its fore-part, and the consequent
loss of power to resist external pressure, the sclerotic capsule is
cartilaginous or bony.

§ 65. Organs of Sic/lit in Reptiles.- The eyes are very small,
of simple structure, and concealed by the skin, which passes
smoothly over them with little other change than subtransparency
of texture, in both the ichthyo- and ophio-morphous Batrachia.
The sclerotic, in Proteus, is lined by some dark pigment, and
contains a minute spherical lens. It may serve to warn the
animal, wandering into light, to retreat to the safe darkness of its
native subterranean waters. The Axolotl has the eyeball better
developed, and provided with muscles ; but devoid of lids. In
the Newts there is a horizontal fold of integument over each eye-
ball : the retina is thick, although the optic nerve is small : the
choroid shows pigment : the pupil is transverse ; the lens is
spherical. The cornea is convex in the Land Salamander. In
Newts the eyeballs are retracted in water, and are less prominent
than in air ; for this purpose there is a kind of choauoid muscle,
besides the ordinary recti and obliqui. The eyeball is very small
in Pipa, and has no eyelid. In the Frog, the eyeball is propor-
tionally large, and is prominent ; the globe is spherical ; the
sclerotic of subcartilaginous hardness anteriorly ; elsewhere it

1 xx. vol. iii. p. 175, prep. no. 1762.
VOL. I. Z

ANATOMY OF VERTEBRATES.

allows the colour of the choroid to be seen through it : the cornea
is very convex. The choroid has an argentine or nacreous layer
externally, and a dark pigment internally ; the former gives the
bright colour to the iris in both Frogs and Toads. The pupil is
subrhomboidal. A slightly plicated ciliary circle adheres to the
capsule of the lens. The retina is thick, and is continued to the
capsule of the crystalline, which forms a small spheroid lens.
Besides the usual muscles of the eyeball, there is a choanoid
muscle ; the eyes are strongly retracted when the Frog dives.
The chief nictitating lid is the lower one ; the upper eyelid merely
follows the movements of the eyeball when it is turned down. A
small muscle arising from the lower and back part of the eyeball sends
two tendons through the choanoid, which wind over the sides of
the ball to a pulley at each angle of the orbit, through which they
pass to be attached to the angles of the lower lid : this is transparent.
The eyes are small in Serpents : the sclerotic is fibre-carti-
laginous, but thin : the choroid resembles that in the Frog, but

220

with less brilliancy of the argentine
layer: the ciliary plica? are small and
feeble : there is a delicate falciform pro-
cess, without pigment : the lens is more
spheroid than in Lizards : the pupil is
round in most Serpents ; but is a ver-
tical slit in venomous Snakes, in Boidce,
and in the nocturnal species of Dipsa-
didce ; and is horizontal in most species
of Dryophis, especially those which have

Dingrammatic section of the eye of a the muzzle pointed and prolonged. Bllt

Viper, magu. ccxiv.

the chief peculiarity in the ophidian
organ of vision is in its defensive part, fig. 220. The integu-
ment, c, is continued from the surrounding circles of scales,
d, directly over the eye : it consists of a layer of transparent
epiderm, and a thin layer of chorium, which adheres to the outer
part of the conjunctive sac,/. At the exuviating period, the epi-
derm, c, becomes opake, and is shed in connection with that of the
head and body. The conjunctiva covers a great proportion of the
eyeball, a, before it is reflected, as at e, e, forward to line the
antocular tegument, c. The cavity,/, is large, and receives the
lacrymal secretion. In the Pythons and Colubers, a pore at the
lower and forepart of the cavity, very minute in many species,
but admitting a bristle in Python, leads to a slender membranous
duct, which dilates into a pouch communicating with the mouth
behind the premaxillary. In the Viper and other venomous
Serpents, the lacrymal canal opens into the nasal mcatus. The

ORGANS OF SIGHT IN REPTILES.

339

221

Section of eye,
Monitor

ccxxx.

lacrymal gland is large, especially in the Constrictors, and con-
tributes its secretion to that of other sources of lubrication of the
mouth during the long and difficult act of deglutition.

It is interesting to note the correspondence of condition between
the eye and ear, in regard to the fore court of each organ, which Ser-
pents exclusively exemplify, among air-breathing Vertebrates. The
tympanic chamber parallels the conjunctive chamber; both are closed
externally, — the one by the ear-drum, the other by the antocular
membrane : the lacrymal canal is the homotype of the eustachian.

In Lizards, fig. 221, the eyeball is less globular, more flattened
anteriorly than in Serpents, and the sclerotic is strengthened near
the cornea by a circle of small sub-imbricate osseous
plates, cL The lens, ib. i3 is more convex behind than
in front ; a ' falciform process,1 ib. p, is connected
with its capsule ; and in the Iguanas and Monitors
it has a delicate layer of pigment-cells. The
ciliary folds are more marked than in Serpents.
In the Geckos the pupil is vertically oval : the
retina shows a spot in the axis of vision. In the
Chameleon the cornea is small ; an antocular fold of skin is con-
tinued in front of the globe, but it is opake and perforated in the
middle : it moves with the eyeball ; the conjunctiva attaching it
to the fore-part of the ball, and the integument at its junction
with the skin of the head, being very thin, yielding, and wrinkled.
The sclerotic is so thin that the dark colour of the choroid appears
through it : it becomes thicker anteriorly, especially at the inser-
tion of the cornea. The retina shows the ' macula centralis,' or
e foramen Socmmerringi,' on the nasal side and a little above the
termination of the optic nerve, fig. 221, o.1 The pupil is round ;
the lens is very small and almost spherical. The muscles have the
usual disposition and number ; but each eye enjoys an independent
motion. The great extinct marine Lizards (Ichthyosaurus) had very
large eyes, fig. 105, with the sclerotic plates developed even in
greater proportion than in mo-
dern Lizards.

In the fresh-water Tortoise
(Emys, fig. 222, b\ the chief
part of the eyeball is oblately
spheroid, with the segment of a

Smaller Sphere at the fore-part ; «, Lacrymal and nanlerian t'land* : 6, eye-hall

-i /> i ,• i c, Sclerotic plates. Emys Europica. xx \viir

a circle oi sclerotic plates, c,

being imbedded at the junction, and sustaining the cornea.

1 CCxr. pp. 1. 104; xx. torn. iii. p. 156.
Z 2

340

ANATOMY OF VERTEBRATES.

223

In the Turtle the sclerotic is cartilaginous, thickest behind,
and thicker at the temporal than at the nasal side of the globe.
The cornea is flatter than in the Emys or Land-Tortoise.

r-m ^ 1 • *^

J optic nerve penetrates the sclerotic, as in other reptiles, exter-
nally to the axis of vision, fig. 222, b, and makes a conical projection

in the interior of the eyeball, from which
the thick retina expands and extends to the
ciliary circle, fig. 223 : there is no falciform
ligament. The choroid is thick, and
coloured by a deep-brown pigment. The
ciliary plica? are neatly defined, but do not
project freely from the surface. The pupil
is round ; the crystalline is more convex in
the Turtle than in the fresh-water or land-
Tortoises. The short ciliary arteries form a
plexus round the optic nerve in Chelone.
The cornea is more convex in the Tortoise,

fig. 222, than in the Turtle. The lacrymal glands are two, fig. 222,
a ; the smaller (harderian) one is internal and inferior in position ;
the larger is external, applied to the eyeball, fig. 224, and sending
its ducts to a deep fossa in the outer angle of the eyelids. These,
fig. 225, are thick, opake, covered by polygonal epidermic scales ;
the lower lid is largest, most moveable, and has fewest scales

Section of the eye-ball of the
xxxvm.

224

225

Eye-ball of Emi/* Enropcra : shewing the external
l.-icrynial gland, xxxvm.

Eye-lids of Eniii*
Earopcsa. xxxvm.

upon it in Chelone : there is also a nictitant membrane situated
vertically at the inner canthtis, and having a horizontal motion.
The duct of the harderian gland opens on its internal surface
near the line of reflection of the conjunctive membrane upon it ;
and the secretion subserves the movements of the third lid. Be-
sides the four recti and two obliqui muscles of the eyeball, there
is a choanoid or retractor muscle divided into four fasciculi.

In the Crocodile, the sclerotic plates are not developed : the
membrane, fig. 226, .1-, n, is of a firm fibre-cartilaginous tissue,
allowing the dark hue of the choroid to appear through it : the
cornea, t, is large and convex. The choroid is thinner and with

ORGANS OF SIGHT IN REPTILES.

341

226

Au extcninl view of tlie eye, eyelid?, muscles,
&c. of a Crocodile. XX.

a blacker pigment than in other Reptiles, and the ciliary plica? are
longer and more distinct, extending beyond the origin of the iris.
This is anteriorly of a pale yellow colour ; the pupil is vertical.

The eye of the Crocodile is chiefly peculiar for the massive and
complex character of its appendages, fig. 226, to which the eye-
ball itself, x, u9 t, bears but a small
proportion. No other or higher
animal offers such a structure : it
was one of the discoveries of
Hunter, who left a drawing of it,
which was engraved, and3 with his
preparation, no. 1770, described in
xx. vol. iii. In the copy of this
drawing, fig. 226, the upper, e, and
lower, b, eyelids are severed at the
outer canthus, and drawn apart to
show the third or nictitant eyelid, h,
and the extent of the conjunctiva. Of
this membrane e is the free surface of
the part which lines the ordinary
eyelids, whence it is reflected over
the nictitant lid at y, h, k ; and then
upon the cornea at the line marked e , upon the part of the
circumference next the outer canthus. The free margins of
the upper and loAver lids are marked c ; they are devoid of cilia, as
in all H&matocrya : h is the free margin of the third lid. The
glands sending their secretion to the conjunctival space are the
proper lacrymal and the harderian ; the duct of the latter termi-
nates on the inner surface of the base of the nictitant lid, at k.
From the conjunctival chamber the secretion of both glands is
conveyed by the two puncta lacrymalia, f, to the duct termin-
ating in the nasal cavity. The muscles are divisible into those of
the eyelids and those of the eyeball. The nictitator, fig. 226, z,
arises from the inner and upper part of the ball, proceeds outward
and downward, winding round the optic nerve and choanoid muscle
(which protects the nerve from the pressure of the nictitator in
action), and is inserted into the inferior angle of the third lid.
Whilst the muscle draws this outward over the eyeball, it at the
same time rotates the ball inward beneath the third lid, being
attached to movable points at both extremities. The upper eyelid
has a levator muscle, m, chiefly inserted into the palpebral ossicle,
but also sending a few fibres, n, to be attached to the palpebral
conjunctiva near its angle of reflection. The under lid has a

342 ANATOMY OF VERTEBRATES.

depressor muscle, o. Of the muscles of the eyeball, p marks the
rectus superior ; q the rcctus inferior ; r the rectus externus ; a
the obliquus inferior : the rectus interims and obliquus superior
are likewise present. The letter x marks the insertion of the
choanoid muscle or retractor of the eyeball, which consists of four
portions surrounding the optic nerve, v. Counting these with the
other muscles of the eyeball and lids, there are not fewer than
thirteen ; and the eye of the Crocodile has its special skeleton as
well as muscles, represented by the super-palpebral ossicle.

In both lieptiles and Fishes the range of gradations of dioptric
structures is very great ; and the number of species in which the
eye is a mere passive recipient of the stimulus of light, and unfit
for sight, or the discernment of outward objects, is greater in the
air-breathing than in the water-breathing Hcematocrya.

§66. Organ of Hearing in Fishes*- -The cartilaginous capsules
of the acoustic organs are precociously developed in all Fishes : in
the Myxinoids and Ammocetes they retain their primitive exterior
position at the sides of the base of the proper cranium, fig. 58, 16;
they are less conspicuous in the Lamprey, fig. 60, 16 ; they
become involved in the thick cartilaginous walls of the cranium in
the Plagiostomes ; and, in Osseous Fishes, are walled up exter-
nally either by the surrounding cranial bones, or by a special

227

Otocrane and labyrinth of Perch, xxiu.

ossification of the exterior part of the capsule itself, forming an
6 os petrosum/ as e. g. in the Carp, fig. 83, 16, and Perch, figs.
85, 84, 16. In the dry skull the ear-chamber appears as a large
lateral compartment of the cranial cavity, fig. 227, o ; and is
formed as described in p. 115.

In the Myxinoids the membranous labyrinth is a simple annular
tube, lined by vibratile cilia, filled with fluid, and supporting
the ramifications of the acoustic nerve. In the Ammocete and
Lamprey the labyrinth is specially attached to its cartilaginous
capsule, and consists of a ( vestibule ' and two ' semicircular canals,'

ORGAN OF HEARING IN FISHES. 343

each of which dilates,, at its origin, into an f ampulla/ which has
some processes from its inner surface. The two canals again
communicate with the vestibule, where they cross each other : the
two divisions of the acoustic nerve first surround the ampullae
before they spread over the rest of the labyrinth. The acoustic
communicates with the cranial cavity by two openings : the inferior
and larger is oval and closed by membrane : the superior gives
passage to the acoustic nerve.

In all other Fishes the membranous labyrinth, fig. 229, «, o,
consists of a vestibule, ib. «, and three semicircular canals, o ; the
vestibule dilating into one or more ( sacculi,' separated by a con-
striction, or by a narrow canal, from the f alveus communis,' and
containing, besides the fluid called ' endolymph,' two or more
masses of carbonate of lime, called ( otolites.' 1 These are compact
and crystalline in Osseous Fishes. The largest, fig. 81, IG", is an
oval or round flattened body, striated and indented at the margins ;
convex, and sometimes grooved (Ephippus), on one side, more or
less excavated on the other. The smaller otolite is less regular in
its shape : there are often two of these. Each semicircular canal
rises by an ampulliform end, fig. 229, e, f, g, from the 'alveus
communis,' «, and communicates, by the opposite end, either with
another canal, or with the vestibule separately, without previous
dilatation : two of the canals are subvertical in their course, and
are anterior, e9 and posterior, </, in relative position : the third
canal, f, is external and horizontal. A septum is continued across
the ampulla from the line where the division of the acoustic nerve
enters : a large proportion of the nerve expands upon the sac of
the otolites. In some fishes this communicates with the vestibule
by a narrow canal. All the parts of the labyrinth are of large
size ; yet the compartments of the otocrane which the semicircular
canals, fig. 229, e,f} g, traverse, ( are much too wide for them,
and they are supported in these passages by a very fine cellular
membrane.'2 In the Pike (JEsox Indus') a pyriform membranous
sac, lodged in the commencement of the spinal canal, opens into
the vestibule near the entrance of the posterior semicircular canal.
The Plectognaths, Lophobranchs, Holocephali, and Sturgeons
resemble the bony fishes in the form and position of the labyrinth ;
but the otolites are represented by cretaceous particles ; and in
the Chimaera the communication between the cranium and otocrane
begins to contract. The otolites are a hard chalky substance in

1 Figures of these bodies will be found in xx. vol. iii. pi. 35; in LXVIIL, LXXI.; and
in LXXII., with microscopic figures of the crystals.

2 Hunter, vn. iii. p. 101.

344

ANATOMY OF VERTEBRATES.

228

the Lepidosiren, in which, as well as in the Plagiostomes, the
whole labyrinth is buried in the thick basi-lateral walls of the
cranium. In Plagiostomes the capsule conforms more closely in

size and configuration to the membranous

o

labyrinth ; its passages and compartments
are lined by a delicate perichondrium, from
which filaments are detached to support
the semicircular canal. The vestibule is
divided in the Skate and Tope into three
compartments, — the ( alveus communis,'
fig. 228, a ; the sac, ib. b, and the cysticule,
ib. c ; and it has also a small crecal append-
age, called the ( utricule,' ib. d : the otolitic
contents are like soft chalk, and are dis-
posed in two masses ; one very large, occu-

Organ of hearing, Skate. LXVIII. . , -i ,, i , • i , i , i

pymg the sac and the cysticule, the other

small, and lodged in the utricule. A canal extends in Sharks
from the vestibular capsule to a foramen at the upper part of
the occiput, which is closed by the skin. In the Rays, besides
this ( fcnestra capsuloe,' ib. v, a membranous canal, ib. o, p, is pro-
duced from the vestibule itself, and, as Hunter well describes,
s from the union of the two perpendicular canals, fig. 228, p ;
which is the case with all the Ray kind, the external orifice
being small, and placed on the upper flat surface of the head.'
So minute and approximated are these ( outer ears,' 1 that Scarpa
may be pardoned for overlooking them, though scarcely for
the warmth with which he repudiates their existence.2 The
"' meatus vestibuli' is provided at its bent extremity, fig. 228, o,
with a special muscle, ib. w.

A true tympanic cavity and membrane, together with a cochlea,
are absent in all Fishes. But in many osseous species a com-
munication is established, either by tubular prolongations, or by
chains of ossicles, between the acoustic labyrinth and the air-
bladder. Weber3 discovered the latter interesting structure in
the Carp, Loach, and Sheat-fish. A canal is sent from the sac of
each vestibule, fig. 229, &, to a common ( sinus impar,' ib. //, in
the substance of the basi-occipital : this communicates on each

1 xcu. p. 296. Hunter's original memoir 'On the Organ of Hearing in Fishes ' was
printed in the volume of the Philosophical Transactions for 1782, not, as Breschet
states, in the year 1786. (LVIII. p. 53.)

2 'Hunterum autcm atque Monroum vehementer super hue re sibi hallucinates
fuisse.' (LX. pp. 1,2.)

LXXHI.

ORGAN OF HEARING IN FISHES.

345

229

side by a small orifice with two subspherical ( atria/ on the body
of the atlas, close to the
foramen magnum, which
6 atria ' are supported ex-
ternally by the ossicles /
and m, and, by means of
the large ossicle o, are
brought into communica-
tion with the fore part of
the air-bladder, p. Both
the atria and common
sinus are filled by the
endolymph, and from the
fore part of the sinus a
6 canalis furcatus,' ib. ?',
is produced, the blind
ends of which penetrate
the alisphenoids. In the
grovelling Loach ( Colitis
barbatulii), the air-bladder
would seem to exist
chiefly in subserviency
to the oro-an of hearing;.

~ o

It is so small as to be
wholly included within
the singularly modified
parapophyses of the se-
cond and third cervical
vertebras, which are ex-
panded and coalesced so
as to form a large f bulla
ossea ' beneath their cen-
trums.1 The three ossicles
on each side, which brino-

o

the air-bladder into com-
munication with the ( atria'
of the labyrinth, are also
concealed by the fore part
of the parapophysial bul-
Ia3 : it is plain, therefore,
that they are not dis-
memberments Of those Ol'ean of Hearing in situ, with air-bladder and ossicles, Carp.

LXXIII.

1 xxxix. i. p. 380.

346 ANATOMY OF VERTEBRATES.

lateral or transverse apophyses of the vertebra; ; and, with regard
to their relation to the ' ossicula auditus ' of the tympanic cavity
in Mammalia,, Weber mistook a relation of analogy for one of
homology, when he called them ( malleus/ ' incus,' and ' stapes.'
They belong, like the capsules of the special organs of sense, to
the ' splanchiioskeleton.' And since the vestibule is prolonged
by the ' atria ' into the neural canal of the atlas, this vertebra
must be added, in the Cyprinoid and Siluroid Fishes, to the
parts of the cranial vertebra) enumerated at p. 115, as entering
into the formation of the chamber of the acoustic organ. In the
Herring a tubular prolongation of the fore part of the air-bladder
advances to the basioccipital, and bifurcates ; each branch pene-
trates the side of the base of the skull, again bifurcates, and
terminates in two blind sacs, which are in contact with similar
cascal processes of the labyrinth. In the Holocentrum and
Sargus, crccal processes of the swim-bladder also diverge, to
attach themselves to the membrane closing the part of the oto-
crane containing the sac of the great otolite.

o o

In Osseous Fishes the sonorous vibrations of their liquid element
is communicated by the medium of the solid parts of their body,
and in some species, also, through the vibrations of the air in the
air-bladder, to the liquid contents of the labyrinth. In the Plagio-
stomous Fishes the resonance in the walls of their cartilaginous
cranium is less than in the bony skull of ordinary fishes ; but the
labyrinth is wholly inclosed in the cartilage ; and a further com-
pensation is made by the prolongation of its chamber to the surface
of the body in some, and by a similar prolongation of the mem-
branous labyrinth itself in others. The position of the external
orifices on the top of the head in the Skate tribe, may relate to
the commonly prone position of these flat fishes at the bottom of
the sea. Professor Miiller concludes, from his experiments, e that
the air-bladder in fishes, in addition to other uses, serves the
purpose of increasing by resonance the intensity of the sonorous
undulations communicated from water to the body of the fish.'1
The vibrations thus communicated to the peri- and endo-lymph of
the labyrinth are doubtless made to beat more strongly upon the
delicate extremities of the acoustic nerve, in Osseous Fishes, by
their effect upon the suspended otolites : and it will be observed,
that the chief portions of the nerve expand upon those chambers
of the vestibule, which contain the otolites. The large size of the
organ of hearing, and especially that of the hard otolites, also relate
to the medium through which the sonorous vibrations are propagated

1 LXXllI. p. 1245.

ORGAN OF HEARING IN REPTILES. 347

to the fish, and to the mode in which they are transmitted to the
organ ; in like manner as the eyeballs are expanded, in order to
take in the utmost possible amount of light. The contracted
encephalon harmonises with and suffices for the sensations and
volitions, and the simple series of ideas daily repeated in the
monotonous existence of the scaled inhabitants of the waters.

§ 67. Organ of Hearing in Reptiles. — The otocrane is large in
proportion to the cranium, in the Perennibranchs, but is distinct
from it : it is chiefly excavated in the alisphenoid and exoccipital.
It includes a vestibule, three semicircular canals (Proteus, Axelotes),
and the otolithic sac containing a cretaceous matter, which has
more shape and consistency in the Axolotl than in the Newts and
Salamanders. The external orifice of the acoustic capsule can
now be recognised as a ( vestibular ' one, or ( fenestra ovalis,' and
it is closed by a cartilaginous plate representing the base of the
stapes, connected with a slender ossicle in the Axolotl : but as yet
there is no trace of tympanic cavity. The analogy of the ear to
the eye, by the absence of the tympanic and conjunctivo-lacrymal
forecourts in the respective organs of Fishes, is still kept up in the
fish-like Reptilia.

The tympanic adjunct to the organ of hearing makes its first
appearance, simultaneously with the developement of eyelids and
lacrymal organs, in the Batrachia which have quitted their aquatic
for an aerial existence. Beyond the vestibular foramen is
continued a short but wide passage outward, or ( meatus,' closed
from the external air by a thin transparent vibratile membrane-
the ' tympanum ' or ear-drum. From the gristly plate closing
the vestibular foramen a slender bony style is continued across
the ( tympanic cavity ' to a drum, to which it is attached by a
capitular or spatulate cartilage, in which a small muscle is inserter !.
A wide vertical passage from the tympanic cavity to the fauces
preserves the equilibrium between the air in that cavity and the
atmosphere outside : it is called ' eustachian tube.' This tube
will be found to bear relation to the size and exposed condition of
the ear-drum, and perhaps, also, to its form, which, in the Frog
and other air-breathing Ovipara, is convex externally. In the
Pipa the bony meatus is long and tubular in shape, the eustachian
tubes terminate by a single median and minute orifice on the

«/ O

palate : the ear-drum is concealed by a partial covering of skin.
It is less conspicuous externally in all Toads than in Frogs : a small
muscle acts on the cartilage connected with the ear-drum, and a
second longer muscle is attached to the discoid piece closing the
vestibular orifice. The labyrinth consists of alveus communis,

S4S ANATOMY OF VERTEBRATES.

three semicircular canals, and otolithic sacculus containing a semi-
fluid cretaceous substance : it is proportionally smallest in Pipa.

All serpents have the internal organ of hearing, similar in the
main to the above : the base of the stapes closing the foramen
vestibuli, is connected, in most serpents, by a long slender bony
style, fig. 97, 16, through the medium of a cartilage and liga-
mentous fibres to the skin, which shows no sign of ear-drum or
external meatus. No air is admitted by an eustachian canal to
the cellular substance traversed by the tympanic ossicle ; and of
this there is no trace in Tythlops and Rhinophis.

In Lacertians, the modification of part of the integument for
the special reception of sonorous vibrations is resumed. In the
Iguana, the ear-drum is partially protected by its oblique position
and by a rising or fold of the skin at the back part of its circum-
ference. It consists of the proper fibrous tissue of the tympanic
membrane, covered externally by a thin layer of epithelium, and
internally by the lining membrane of the tympanic cavity. The
communication between the membrana vestibuli and membrana
tympani is by the stapedial disc, the columelliform ossicle and the
terminal or ' malleal ' cartilage. The eustachian canal is rela-
tively narrower, and its course more oblique than in the Frog : the
otolite is a lenticular calcareous body, firmer than in the Frog.

In the Chelonia the ear-drum is again masked by unmodified
integument ; in the Turtle ( Chelone mydas) it is covered by the
second scale counting upward from the articulation of the lower
jaw. The membrana tympani is, however, distinctly formed,
thicker and more opake than in Batrachia or Lacertia, and con-
vex outwardly. The long columelliform ossicle fig. 92, ie', is
connected with it by a discoid cartilage, and, at the opposite end,
penetrates and closes the vestibular orifice by a sub-cartilaginous
plate. The tympanic cavity is divided into two parts by a bony
septum, intercommunicating at the columellar canal : the inner
or antevestibular part also communicates with cells on the mastoid.
The eustachian canal is narrow, and descends behind the arti-
culation of the mandible ; its palatal opening is more remote from
that of the opposite ear than in other Reptilia. The proper cap-
sule of the labyrinth is cartilaginous : besides the three semi-
circular canals and the otolithic capsule, there now buds from the
vestibule a beginning of a cochlea, with a corresponding small
opening into the tympanic cavity.

These approximations to the higher structure of the internal
ear are more conspicuous in Crocodilia. The cochlear process is
conical, with the apex, fig. 230, a, slightly bent; its cavity is

ORGAN OF HEARING IN REPTILES.

349

230

'"IP

IA^

Organ of hearing, Crocodile.

divided into two compartments by a double cartilaginous septum,
ib. b, except at the apex, where they communicate ; whilst, at the
base, one compartment, f scala vestibuli,' communicates with the
vestibule, the other, e scala tympani,'
by a small orifice (foramen cochlea?,
sen rotundum), with the tympanic
cavity, in the dry skull, but closed
by membrane in the living animal.
The cochlear division of the acoustic
nerve is shown at v, fig. 230. The
semicircular canals are small com-
pared with those of fishes : c is the
anterior perpendicular, d the pos-
terior perpendicular, and e the ex-
ternal or horizontal, canal which
curves over the ( foramen ovale,' f.
The membrana tympani, ^7, is lodged
at the bottom of a deep fissure,
and is protected by an opercular flap of the integument,
h, fitting to a smaller fold below, i, and accurately closing the
passage. This is the sole approach to an external ear known
in existing Reptilia. The ear-drum is inclined downward and
outward, adapted to the reception of sound from above, and also
to the position of the overhanging flap. The gristly represen-
tation of the malleus, k, is well-marked, and the ear-drum is
thickened at its place of attachment : the columellar part of the
stapes, /, extends obliquely downward to the foramen ovale, sen
vestibuli, f. The tympanic cavity, m, is singularly extended
by air-cells, not only developed in the mastoid, but in the
basi-, par-, and super-occipitals, fig. 94, 3, in the alisphenoid and
parietal, ib. 7, bones. The communications between the tympanic
cavity and fauces are more complex than in other animals,1
although the eustachian faucial opening, n, is single, median, and
common to both ears. It is situated a short way behind the pos-
terior nostril ; and from it is continued a median, o, and two lateral,
p, canals. The median canal rises and enters a bony canal between
the basioccipital and basisphenoid, which bifurcates, one branch, q,
inclining forward into the basisphenoid, the other, r, continued ver-
tically into the basioccipital, both in the medial plane. Each of
these branches again bifurcates, transversely, one to the right,
the other to the left, opening upon the floor of the tympanic cavity.

1 CI.XXII.

350 ANATOMY OF VERTEBRATES.

The lateral membranous canals, p9 p, from the eustacnian outlet,
diverge to the orifices of corresponding lateral bony canals, which
ascend between the basioccipital and basisphcnoid, and communi-
cate each with the transverse subdivision, s, of the posterior or
occipital branch of the median eustachian canal: a small rhomboidal
sinus is formed at the point of union, from which a short canal,
t, is continued to the tympanic cavity. The common inferior
outlet, situated on a prominence, is partly closed by a valve, ??,

reducing its area to a crescentic form.1

^j

§ G8. Electric Organs of Fishes.- -Besides the modifications and
appendages of the peripheral extremities of the nerves consti-
tuting organs of special sense, and those of which the function is
still conjectural, there are nerves in fishes subject to more extra-
ordinary combinations, and forming instruments, unknown in the
higher vertebrate classes, having the property of accumulating
and concentrating the subtle mode of force applicable to the com-
munication of electric shocks. The faculty is limited to few
genera, the most remarkable being Torpedo and Gymnotus, the
species of which possess the electric organs in the highest state of
developement. In a minor degree the organs and power exist in
J\Ialapterurus electricus, Mai. Beninensiss Mormyrus longipinniSy
JMor. oxyrhynchus, Mor. dorsalis, Trichiurus electricus, Gymnarchus
niloticus, and Tetraodon electricus.

In the Torpedo Galvanii the organs are two in number, are
large, flattened, reniform bodies, lodged on each side of the head
and gills, and encompassed by these and by the anterior borders
of the pectoral fins (fig. 139, E) : they consist of a mass of ver-
tical, for the most part hexagonal, prisms, the ends of which are
covered by the dorsal and ventral integuments. Beneath these
the organs are immediately coated by a thin glistening aponeu-
rosis, which sends down partitions forming the chambers of the
prismatic columns. Each column, when insulated in the recent
fish, seems like a mass of clear trembling jelly; but consists of a
series of delicate membranous plates inclosed by, or adherent by
their margins to, a proper capsule, and separated from each other
by a small quantity of a limpid albuminous fluid. Each flattened
cell thus formed is lined by an epithelium of nucleated cells :
the fibrous tissue of the plates and common capsule presents the
microscopic characters of elastic tissue ; between it and the epi-
thelium is a clear unorganised layer, the seat of the ultimate
ramifications of the vessels and nerves. The proper capsule
adheres to the aponeurotic partition-walls which support the

1 CLXXII. p. 521, pi?, xl. xli. xlii.

ELECTRIC ORGANS OF FISHES.

351

columns and the larger branches of the nerves and vessels of the
organ. Some of the vertical columns do not extend through the
entire thickness of the organ ; but are interrupted where the
deep-seated nerves traverse the substance of the battery, fig. 231,
A, D. The transverse plates of the vertical columns are shown

231

The right electrical organ, divided horizontally, at the place where the nerves cuter, Torpedo. LXXXI.

at E. Hunter, who counted 470 columns in each organ, describes
the partitions as being very vascular : — ' The arteries,' he says,
f are brandies from the vessels of the gills, which convey the
blood that has received the influence of respiration.'1 But the

1 LXXXI.

352

ANATOMY OF VERTEBRATES.

most characteristic feature of the organisation of the electric
battery is its enormous supply of nervous matter. Each organ
derives this supply from one branch of the trigcminal, fig. 231, A,
and from four branches of the vagal nerves, ib., B, C, D ; the four
anterior nerves are each as thick as the spinal cord : the last
nerve is a feeble branch of the vagus. The trigemiiial and
vagal enlargements of the olivary and restiform tracts coalesce on
each side, forming the so-called ' electric lobes ' of the medulla
oblongata. The electric branch of the fifth nerve may be defined
even at its origin, from the true ganglionic part of that nerve ;
and both this and the vagal branches consist entirely of the pri-
mitive nerve-fibres of animal life, as in fig. 164. The nerve-
trunks are distributed by successive resolution into smaller and
smaller fasciculi, until they finally penetrate the septa of the
columns, and terminate thereon by meshes formed by loops, or by
the return and anastomosis of the primitive nerve-fibres.1

In the eel-like Gymnotus the electric organs are four in
number, and are situated two on each side the body, extending
from behind the pectoral fins to near the end of the tail, fig. 232,

232

Right electrical organs, Gymnotus (rechiced). ccxvii.

/{, L They occupy and almost constitute the whole lower half of
the trunk, fig. 233 ; the upper organ, ib. h, being much larger than
the lower one, ib. z, from which it is separated by a thin muscular
and aponeurotic stratum. The organs of one side are separated
from those of the other, above by the vertebral column and its
muscles, ib. c, then by the air-bladder, ib. d, and below this by
an aponeurotic septum, ib. k. From this septum, and from that
covering the air-bladder, there extend outward, to be attached to
the skin, a series of horizontal, or nearly horizontal, membranes,
arranged in the longitudinal axis of the body nearly parallel to
one another ; they are of great but varying length, some being
co-extensive with the whole organ, fig. 232, k : their breadth is
almost that of the semidiameter of the plane of the body in

1 LXXVI.

ELECTRIC ORGANS OF FISHES.

353

which they are situated, fig. 233, h. These membranes are about
half a line apart at their outer borders ; but, as they pass from
the skin towards their inner attachments, they approach one

233

Vertical transverse section, Gymnotus, natural size. ccxv.

another. They are intersected transversely by more delicate
vertical plates, extending from the skin to the median aponeu-
rosis, and coextensive in length with the breadth of the septa
between which they are placed. Hunter counted about 240 of
these plates in a single inch of length of the horizontal mem-
brane.1 He compares those stronger membranes to the aponeu-
rotic walls of the prisms of the Torpedo, and the inter-
secting delicate plates to the partitions of the prisms : and if
we admit the analogy of these plates, and of those of the Tor-
pedo, to the plates of the voltaic pile, we perceive that, in the

VOL. I.

LXXX.

A A

354 ANATOMY OF VERTEBRATES.

Gymnotus, the batteries are horizontal and the plates vertical,
fig. 233, A, whilst in the Torpedo the batteries are vertical and
their plates horizontal, fig. 231, E. The situation of the organs
is also very different in the two fishes ; they extend from before
the pectoral fins to the anterior part of the head in the one,
fig. 139, E, and from behind the pectoral fins to near the end of
the tail in the other, fig. 232, k. But a more important difference
exists in the condition of the interspaces between the delicate
transverse plates. In the Torpedo they simply contain a fluid.
In the Gymnotus two strata of pyramidal cells diverge from a
common basis traversing each interspace, and terminate freely,
the one towards one plate, the other towards the opposite plate,
and divide the fluid into a ( pre-cellular ' and ( post-cellular '
portion. The cellular basis is ( positive,' the post-cellular fluid
and the partition-plate is negative, constituting the e voltaic
couple ; ' whilst the pre-cellular fluid is the conducting element
between one ( couple ' or plate and the next : the whole represents
the ternary type of the voltaic pile. The Torpedo's structure is
according to the binary type. Another remarkable difference
is in the source of the nervous supply. In the Gymnotus the
electric organs are supplied by the s rami ventrales' of all the
spinal nerves, about 200 pairs, that issue in the course of
their extent; some of the filaments ramify upon the horizontal
membranes from their cutaneous margins ; but the greater part of
the nerves come from the deeper-seated branches which descend
upon the median aponeurotic partition-wall, and spread upon the
septa of the organ from within outwards. Yet the nervus late-
ralis, which is derived from the same cerebral nerves as those
which, in the Torpedo, supply the electric batteries, and which is
formed by similar proportions of the trigeminal and vagus, ex-
tends the whole length of the electric organs in the Gymnotus
without rendering them a filament; it is situated nearer the
spine, and is of larger size than usual, but Hunter was not
able to trace any nerves going from it to join those of the
medulla spinalis, which run to the organ.1 The quantity of
nervous matter supplied to the batteries of the Gymnotus is
less than in the Torpedo : but more substance enters into their
composition.

The proportional size of the electric organs is also much
greater in the Gymnotus than in the Torpedo : indeed, the proper
body of the Gymnotus is, as it were, a mere appendage tacked on

1 LXXXI.

ELECTRIC ORGANS OF FISHES.

355

234

Section of Malapterurus electrlcus. ccxix.

to the fore part of the enormous batteries ; for the digestive and
generative viscera, with the respiratory and circulating organs,
the brain and organs of sense, —
all, in fact, that constitute the
proper animal, — are confined to
that small segment of the entire
body which is anterior to the elec-
trical apparatus, fig. 232, b. The
vent even opens beneath the head,
in advance of the pectoral fins.

The electric organs of the Ma-
lapterurus electricus1 form a layer
fig. 234, A, immediately beneath
the skin, enveloping the whole
body except the head and fins, and separated from the muscles,
ib. G, by a fascia with vessels and nerves, ib. B, and by a layer
of adipose tissue, ib. E. The electric organ is divided by fine
decussating membranes into minute lozenge-shaped cells, about a
third of a line in diameter, fig. 235, B. It is supplied by a large
nerve issuing from the beginning of the myelon and arising from
a mass, in its substance, of ganglion-cells, like those in the electric
lobes of the Torpedo. A considerable ganglion is also formed upon
the nerve beyond its origin, from which the trunk is continued
along the side of the body, like a ( nervus lateralis,' and distributes
branches to the diffused organ. The structure of the organ is such
that the electric currents run in all directions, and
a discharge would take place from any point of
its surface, whence, perhaps, the necessity for a
layer of nonconducting substance, E, between
the proper body of the fish and the organ. The
shock delivered, wanting the concentration re-
sulting from the structure in the Torpedo, is
comparatively feeble, but suffices for defence;
the fish being protected by its electrifying coat,
as is the hedgehog by its spines.

In the Mormyrus longipinnis the electric organ
consists of four series of membranous septa
placed longitudinally on the tail, two on each
side. Each series consists of about 150 septa
with intervals of g^th of a line, filled by albu-

235

Section of electric organ,
Malapterurus, ccxviu.
A, skin ; B, electric cells
c, fascia ; D, cellular tis-
sue, with a, artery, v,

vein, n, nerve ; E, adi-

minous fluid. The septa are stronger than pose tissue.
those in the hexagonal columns of the Torpedo.2

1 xcn. and ccxix.

ccxx.

A A 2

356 ANATOMY OF VERTEBRATES.

An animal must be in communication with the Torpedo by
two distinct points, in order to receive the shock.1 If an insulated
frog's leg, fig. 207, C, touches the Torpedo by the end of the nerve
only, no muscular contractions ensue on the discharge of the bat-
tery; but a second contact by a portion of muscle, or any other
part of the leg, immediately produces them.2

The dorsal surface of the electric organ is positive, the ven-
tral surface negative. The Torpedo has no power of otherwise
directing the electric currents ; but Matteucci found that wound-
ing the electric lobes of the brain sometimes reversed the direc-

o

tion.3 These currents, besides their effects on the living body,
exercise all the other known powers of electricity ; they render
the needle magnetic,4 decompose chemical compounds, and emit
the spark.5 The discharge of strong currents is usually accom-
panied by visible contraction of parts of the body, usually by a
retraction of the eyes of the Torpedo, and one muscle, fig. 139,
o, is arranged so as to constrict part of the circumference of each
battery ; but such consentaneous muscular action, though it may
add to the force of the discharge, is not essential to its produc-
tion. The benumbing effect seems to be produced by the rapid
succession of shocks delivered by the recent and vigorous fish.
Matteucci ascertained that, during the discharge, the nerves of
the organ were not traversed by any electric current. Pacini,6
from a minute comparison of the organs, deduces that the elec-
tricity in the Torpedo is produced by the dynamical conflict
between the two polarities inherent in two sorts or different
degrees of innervation, as it is evolved in the thermo-electric pile
by the conflict of two polarities inherent in two different degrees
of temperature ; whilst in the Gymnotus it is produced, as in
the voltaic pile, by the chemical conflict between the materials
of the elements excited by the nervous influence.

Humboldt has given a lively narrative of the mode of capture

1 When the Neapolitan fishermen pull their nets to shore, their first act usually is
to wash the captured fishes by dashing over them bucketfuls of sea-water ; and if ;i
Torpedo be amongst them it makes its presence instantly felt by the shock transmitted
to the arm discharging the bucket. If the fish be handled, the shock is too strong
and painful to he willingly encountered a second time, and the arm continues long be-
numbed. Each repetition of the discharge, however, enfeebles its force, and the
surface of the fish capable of communicating the shock progressively contracts, as
life departs, to the region of the organs themselves. When the fisherman dashes
the stream of water over the Torpedo, the electric current passes up from the
dorsal surface of the batteries against the stream to the man's hand, and the circle
is completed by the earth extending from the man's feet to the ventral surface of the
prone fish.

2 I.XXVII. p. 148. 3 Ib. 4 LXXX1I. 5 LXXVII. 6 CCXVIII.

ELECTRIC ORGANS OF FISHES. 357

of the Gymnoti, employed by the Indians of South America,1 and
all its circumstances establish the close general analogy between the
Gymnotus and Torpedo in the vital phenomena attending the ex-
ercise of their extraordinary means of offence. It is voluntary and
exhaustive of the nervous energy ; like voluntary muscular effort,
it needs repose and nourishment to produce a fresh accumulation.
In the experiments performed by Professor Faraday on a large
living Gymnotus,2 the most powerful shocks were received when
one hand grasped the head and the other hand the tail, of which
I had painful experience ; especially at the wrists, the elbows,
and across the back. But the nearer the hands were together
within certain limits, the less powerful was the shock. It was
demonstrated by the galvanometer that the direction of the elec-
tric current was from the anterior parts of the animal to the pos-
terior parts, and that the person touching the fish with both hands
received only the discharge of the parts of the organs included
between the points of contact. Needles were converted into
magnets : iodine was obtained by polar decomposition of iodide
of potassium ; and, availing himself of this test, Faraday showed
that any given part of the organ is negative to other parts before
it, and positive to such as are behind it. Finally, heat was
evolved, and the electric spark obtained. The delicate plates

1 They rouse the Gymnoti by driving horses and mules into the ponds which those
fish inhabit, and harpoon them when they have exhausted their electricity upon the
unhappy quadrupeds; ' I wished,' says Humboldt, 'that a clever artist could have
depicted the most animated period of the attack: the groups of Indians surrounding
the pond, the horses with their manes erect arid eyeballs wild with pain and fright,
striving to escape from the electric storm which they had roused, and driven back by
the shouts and long whips of the excited Indians : the livid yellow eels, like great
water-snakes, swimming near the surface and pursuing their enemy: all these objects
presented a most picturesque and exciting ensemble. In less than five minutes two
horses were killed. The eel, being more than five feet in length, glides beneath the
body of the horse, and discharges the whole length of its electric organ. It attacks,
at the same time, the heart, the digestive viscera, and, above all, the gastric plexus of
nerves. I thought the scene would have a tragic termination, and expected to see
most of the quadrupeds killed; but the Indians assured me the fishing would soon be
finished, and that only the first attack of the Gymnoti was really formidable. In fact,
after the conflict had lasted a quarter of an hour, the mules and horses appeared less
alarmed ; they no longer erected their manes, and their eyes expressed less pain and
terror. One no longer saw them struck down in the water; and the eels, instead of
swimming to the attack, retreated from their assailants, and approached the shore.'
The Indians now began to use their missiles; and, by means of the long cord attached
to the harpoon, jerked the fish out of the water, without receiving any shock so long
as the cord was dry; but a less cautious assailant, who had climbed an overhanging
bongh, was brought down into the water, amidst the laughter of his companions, by
the shock sent upwards from the wounded Gymnotus, along the wetted cord attached
to the harpoon, cvn. p. 55.

2 LXXXIII.

358 ANATOMY OF VERTEBRATES.

sustaining the terminal meshes of the nerves and vessels are hori-
zontal in the Torpedo ; the course of the electric current is
from above downwards. The corresponding plates in the Gym-
notus are vertical ; the direction of the electric current is from
before backwards : i. e. it is vertical to the planes of the plates in
both cases.

The row of compressed cells constituting the electric prism of
the Torpedo offers some analogy to the row of microscopic discs
of which the elementary muscular filament appears to consist,
fig. 128,, B. The looped termination of the exciting nerve is
common to muscular tissue and that of the electric organ. The
electric, like the motory nerves, rise from the anterior myelonal
tracts ; and, though they have a special lobe at their origin, beyond
that origin, in the Torpedo, they have no ganglion. An impression
on any part of the body of the Torpedo is carried by the sensory
nerves either directly, or through the posterior myelonal tracts, to
the brain, excites there the act of volition, which is conveyed
along the electric nerves to the organs, and produces the shock :
in muscular contraction, the impression and volition take the same
course to the muscular fibres. If the electric nerves are divided
at their origin from the brain, the course of the stimulus is inter-
rupted, and no irritant to the body has any effect on the electric
organs any more than it would have under the like circumstances
on the muscles. But, if the ends of the nerves in connection
with the organ be irritated, the discharge of electricity takes place,
just as irritating the end of the divided motor nerve in connection
with the muscle would induce its contraction. If part of the
electric nerves be left in connection with the brain, the stimulus
of volition cannot, through these, excite the discharge of the
whole organ, but only of that part of the organ to which the
undivided nerves are distributed. So, likewise, the irritation of
the end of a divided nerve in connection with the electric appa-
ratus, excites the discharge of only that part to which such nerve
is distributed. We have seen that the power of exciting the
electric action, like that of exciting the muscular contraction, is
exhausted by exercise and recovered by repose : it is also augmented
by energetic circulation and respiration ; and what is more signi-
ficative of their close analogy, both powers are exalted by the
direct action, on the nervous centres, of the drug ( strychnine : '
its application causes simultaneously a tetanic state of the muscles
of the fish, and a rapid succession of involuntary electric dis-
charges. '

1 LXXVII. p. 162.

359

CHAPTEE V.

DIGESTIVE SYSTEM OF H^EMATOCRYA.

§ 69. Dental Tissues.- - A tooth is a hard body attached to the
mouth or commencement of the alimentary canal, partially exposed,
when developed. Calcified teeth are peculiar to the Vertebrates, and
may be defined as bodies primarily, if not permanently, distinct from
the skeleton, consisting of a cellular and tubular basis of animal
matter containing earthy particles, a fluid, and a vascular pulp.

In general, the earth is present in such quantity as to render
the tooth harder than bone, in which case the animal basis is gela-
tinous, as in other hard parts where a great proportion of earth is
combined with animal matter. In a very few instances, among the
vertebrate animals, the hardening material exists in a much
smaller proportion, and the animal basis is albuminous ; the teeth
here agree, in both chemical and physical qualities, with horn.

True teeth consist commonly of two or more tissues, character-
ised by the proportions of their earthy and animal constituents,
and by the size, form, and direction of the cavities in the animal
basis which contain the earth, the fluid, or the vascular pulp.

The tissue which forms the body of the tooth is called ' dentine,'
(dentinum, Lat. ; zahnbein, zahnsubstanz, Germ. ; T*woire, Fr.,
fig. 236, d).

The tissue which forms the outer crust of the tooth is called
' cement ' (ccementum, crusta petrosa^ Lat., ib. e).

The third tissue, when present, is situated between the dentine
and cement, and is called ' enamel' (encaustum, adamas, Lat., ib. e).

6 Dentine ' consists of an organised animal basis and of earthy
particles : the basis is disposed in the form of compartments or
cells, fig. 237, b, and extremely minute tubes, ib. a : the earthy
particles have a twofold arrangement, being either blended with
the animal matter of the interspaces and parietes of the tubes, or
contained in a minute granular state in their cavities. The density
of the dentine arises principally from the proportion of earth in
the first of these states of combination. The tubes contain, near the
formative pulp, filamentary processes of that part l ; and convey a

1 CCXLVI. vol. iv. p. 929.

ANATOMY OF VERTEBRATES.

colourless fluid, probably transuded 'plasma': they thus relate
not only to the mechanical conditions of the tooth, but to the
vitality and nutrition of the dentine. This tissue has few or no
canals large enough to admit capillary vessels with the red
236 particles of blood, and it has been

therefore called ' imvascular dentine.'
' Cement ' always closely corres-
ponds in texture with the osseous tissue
of the same animal ; and wherever
it occurs of sufficient thickness, as
upon the teeth of the horse, sloth, or
ruminant, it is also traversed, like
bone, by vascular canals, fig. 236, c>
When the osseous tissue is excavated,
as in dentigerous Vertebrates above
fishes, by minute radiated cells, form-
ing with their contents the ' cor-
puscles of Purkinje,' fig. 15, these are
likewise present, of similar size and
form, in the ( cement,' and are its
chief characteristic as a constituent of
the tooth. The hardening material
of the cement is partly segregated
and combined with the parietes of the
radiated cells and canals, and is partly
contained in disgregated granules in
the cells, which are thus rendered
white and opaque, viewed by reflected
light. The relative density of the
dentine and cement varies according
to the proportion of the earthy material, and chiefly of that part
which is combined with the animal matter in the walls of the
cavities, as compared with the size and number of the cavities
themselves. In the complex grinders of the elephant, the masked
boar, and the capybara, the cement, which forms nearly half the
mass of the tooth, wears down sooner than the dentine.

The ' enamel,' fig. 235, e, is the hardest constituent of a tooth,
and, consequently, the hardest of animal tissues ; but it consists,
like the other dental substances, of earthy matter arranged by
organic forces in an animal matrix. Here, however, the earth is
mainly contained in the canals of the animal membrane ; and, in
mammals and reptiles, completely fills those canals, which are com-
paratively wide, whilst their parietes are of extreme tenuity. The

Magnified section of incisor, Horse ;
c cement, d dentine, e enamel, v.

DENTAL TISSUES.

361

237

4iS^'Mi i' J^{ ^MKA'

hardening salts of the enamel are not only present in far greater
proportion than in the other dental tissues ; but., in some animals,
are peculiarly distinguished by the presence of fluate of lime.

Teeth vary in number, size, form, structure, modifications of
tissue, position, and mode of attach-
ment, in different animals. They
are principally adapted for seizing,
tearing, dividing, pounding, or grind-
ing the food ; in some they are
modified to serve as weapons of
offence and defence ; in others, as
aids in locomotion, means of anchor-
age, instruments for uprooting or
cutting down trees, or for transport
and working of building materials ;
they are characteristic of age and
sex ; and in man they have secondary relations subservient to
beauty and to speech.

Teeth are always most intimately related to the food and habits
of the animal, and are therefore highly interesting to the physiol-
ogist. They form for the same reason most important guides to
the naturalist in the classification of animals ; and their value, as
zoological characters, is enhanced by the facility with which, from
their position, they can be examined in living or recent animals.
The durability cf their tissues renders them not less available to

—b

—a

Section of tusk of Dugong, niagn. v.

238

^v

^

**"&

^^.^ -^-^" ^ -. £Ss^£u£^3S2Sii%i;

:-*

Magnified section of molar, Megatherium ; v vasodentine, f dentine, c cement, vi.

the palaeontologist in the determination of the nature and affini-
ties of extinct species, of whose organisation they are often the
sole remains discoverable in the deposits of former periods of the
earth's history.

The simplest modification of dentine is that in which capillary
tracts of the primitive vascular pulp remain uncalcified, and per-

3G2

ANATOMY OF VERTEBRATES.

239

' \

!*•»« • I/,")™: •< >"n»\w\y\?,\\

Section of tooth of Cachalot, half natural
size. v.

manently carry red blood into the
substance of the tissue. These
so-called 6 medullary ' or ' vascu-
lar' canals present various dis-
positions in the dentine which
they modify, and which is called
6 vaso-dentine.' It is often com-
bined with true dentine in the
same tooth ; e.g. in the scalpri-
form incisors of certain Rodents,1
the tusks of the Elephant,2 the
molars of the extinct Megathe-
rium, fig. 238, v.

A third kind of dentine is
where the cellular basis is ar-
ranged in concentric layers around
the vascular canals, and contains
( radiated cells ' like those of the
osseous tissue : it is called ( osteo-
dentine,' fig. 239, o. The transi-
tion from dentine to vaso-dentine,
and from this to osteo-dentine, is
gradual, and the resemblance of
osteo-dentine to true bone is very
close.

The chemical composition of
teeth is exemplified in the sub-
joined analyses of those organs
and their tissues from species of
the different vertebrate classes : —

M«

LION

ox

CROCODILE

PIKE

1
43

. — i

o

"oJ

a

Jj

r— I
<D

a

•P

_§

-P

g

fH

d

c3

r*

c3

d

cS

r*

a

0) O cS

O>

a

03

d

o>

^

Q}

s

hf)'"~t "n

ft

ft

w

ft

w

O

ft

o

'- 4-1
CS O

h-)

Phosphate of lime, with a trace
of fluate of lime

66-72

89-82

60-03

83-33

59-57

81-86

58-73

53-69

53-39

63-98

Carbonate of lime

3-36

4-37

3-00

2-94

7-00

9-33

7-22

6-30

6-29

2-54

Phosphate of magnesia

1-08

1-34

4-21

3-70

0-99

1-20

0-99

10-22

9-90

0-73

Salts

0-83

0-8S

0-77

0-64

0-91

0-93

0-82

1-34

1-42

0-97

Chondrine

27-61

3-39

31-57

9-39

30-71

6-66

31-31

27-66

28-15

30-60

Fat .

0-40

0-20

0-42

a trace

0-82

0-02

0-93

0-79

0-76

1-18

100-00

100-00

100-00

100-00

100-00

100-00

100-00

100-00

100-00

100-00

1 v. p. 405.

v. p. 643.

DENTAL TISSUES.

363

240

Section of pharjngeal tooth of Lahrus,
magnified, v.

The examples are extremely few, and peculiar to the class
Pisces, of calcified teeth which consist of a single tissue, and this is
always a modification of dentine. The large pharyngeal teeth of
the Wrasse (Labrus} consist of
a very hard kind of unvascular
dentine. Fig. 240 shows a ver-
tical section of one of these teeth,
supported upon the vascular
osseous tissue of the pharyngeal
bone : p is the pulp cavity.

The next stage of complexity
is where a portion of the dentine
is modified by vascular canals.
Teeth, thus composed of dentine
and vaso-dentine, are very com-
mon in fishes. The hard dentine
is always external, and holds the
place, and performs the office, of
enamel in the teeth of higher
animals ; but it is only analogous
to enamel, not the same tissue.
Fig. 241 exemplifies this struc-
ture in a longitudinal section of the tooth of a Shark (Lamna).

The molars of the Dugong (Halicore) are composed of dentine
and cement . the latter substance forming a thick outer layer,
fig. 242, c.

In the teeth of the Cachalot (Physeter) the pulp-cavity of the
growing tooth becomes filled up by osteodentine, the result of a
modified calcification of the dentinal pulp ; when the tooth presents
three tissues, as shown in fig. 239, in which c is the thick external
cement, d the hard dentine, and o the osteodentine ; sometimes
developed in loose stalactitic-shaped nodules.

In the teeth of the Sloth, and its great extinct congener, the
Megatherium, the hard dentine is reduced to a thin laver. fig-. 238,

v O

t, and the chief bulk of the tooth is made up of a central body of
vaso-dentine, ib. v., and a thick external crust of cement, ib. c.

Besides the number of constituent tissues teeth become 'complex'
in structure by the proportion and disposition, chiefly inflection,
of more or fewer of those tissues.

Certain fishes and the extinct ( Labyrinthodont ' reptiles ex-
hibit this complexity in a remarkable degree. In fig. 243, the
tooth of the Labyrinthodon salamandro'ides feebly indicates its
singular structure by the longitudinal striae. But every streak is

364

ANATOMY OF VERTEBRATES.

211

a fissure, into which a thin outer layer of cement, fig. 244, c, is
reflected into the body of the tooth, following the sinuous wavings

of the lobes of dentine, d, which
diverge from the central pulp-cavity, a.
The inflected fold of cement, c, runs
straight for about half a line, and then
becomes wavy, the waves rapidly in-
creasing in breadth as they recede from
the periphery of the tooth ; the first two,
three, or four undulations are simple ;
then their contour itself becomes
broken by smaller or secondary waves
these become stronger as the fold ap-
proaches the centre of the tooth, when
it increases in thickness, and finally
terminates by a slight dilatation or
loop close to the pulp-cavity, from
which the free margin of the inflected
fold of cement is separated by an
extremely thin layer of dentine. The
number of the inflected conver<nno;

o O

folds of dentine is about fifty at the
middle of the crown of the tooth
figured, but is greater at the base.
All the inflected folds of cement at
the base of the tooth have the same
section of tooth of a shark (Lamna\ complicated disposition with increased

magn. ; v vaso-dentine, d gano-dentine. v. l

extent ; but, as they approach their ter-
mination towards the upper part of the tooth, they also gradually
diminish in breadth, and consequently penetrate to a less distance
into the substance of the tooth. Hence, in such a section as is
delineated, fig. 244, it will be observed that some of the convo-
luted folds, as those marked c, extend near to the centre of the
tooth ; others, as those marked c1 ', reach only about half way to
the centre ; and those folds, c", which, to use a geological ex-
pression, are ' cropping out,' penetrate to a very short distance
into the dentine, and resemble, in their extent and simplicity, the
conver«;m(T folds of cement in the fangs of the tooth of the

o O o

Ichthyosaurus and Lepidosteus.

The disposition of the dentine is still more complicated than
that of the cement, It consists of a slender, central, conical
column, excavated by a conical pulp-cavity for a certain distance
from the base of the tooth ; and this column sends radiating out-

DENTAL TISSUES.

365

wards, from its circumference, a series of vertical plates, which
divide into two once or twice before they terminate at the
periphery of the tooth.

Each of these diverging and dichotomising plates gives off
throughout its course smaller processes, which stand at right

242

f-

Section of tooth of Dugong ; A, natural size; B, magnified ; d, dentine ; c, cement. V.

angles, or nearly so, to the main plate ; they are generally oppo-
site, but sometimes alternate ; many of the secondary plates or
processes, which are given off near the centre of the tooth, also
divide into two before they terminate ; and their contour is seen,
in the transverse section, to partake of all the undulations of the
folds of cement which invest and divide the dentinal plates and
processes from each other.

The dental pulp-cavity is reduced to a mere line about the
upper third of the tooth, but throughout its whole extent fissures
radiate from it, corresponding in number with the radiating plates
of dentine. Each fissure is continued along the middle of each
plate, dividing where this divides, and extending along the middle
of each bifurcation and process to within a short distance of the
line of cement. The pulp-fissure commonly dilates into a canal

366

ANATOMY OF VERTEBRATES.

243

at the origin of the lateral processes of the radiating plates, before
it divides to accompany and penetrate those processes.

The main fissures or radiations
of the pulp- cavity extend to with-
in a line or half a line of the
periphery of the tooth, and sud-
denly dilate at their terminations
into spaces, which, in transverse
section, are subcircular, oval, or
pyriform, p : the branches of the
radiating lines, which are conti-
nued into the lateral secondary
plates or processes of the dentinal
Iamella3, likewise dilate into simi-
lar, and generally smaller spaces.
All these spaces, or canals, in the
living tooth, must have been oc-
cupied by corresponding processes
of the vascular pulp : they consti-
tute as many centres of radiation
of the fine tubes, which, with
their uniting clear substance,
constitute the dentine. l

An analogous complexity is
produced by numerous fissures,
radiating from a central mass of
vasodentine, which more or less
fills up the pulp cavity of the
seemingly simple conical teeth,
fig. 245, of the extinct ' Dendro-
dont ' fishes.

A portion of the transverse section, a, fig. 245, magnified,
fig. 246, shows the fissures diverging from the pulp-cavity, p, and
its reticulate extensions, and sending small branches into the den-
tinal lamellae.

These lateral offsets subdivide into a few short ramifications,
like the branches of a shrub, and terminate in irregular and
somewhat angular dilatations, simulating leaves, but which resolve
themselves into radiating fasciculi of dentinal tubes. There are

o

from fifteen to twenty-five or thirty-six of these short and small
lateral branches on each side of the main rays.

Tooth of a Labyrinthodon, natural size ; a line of
section, v.

v. pp. 195—217, pi. 64A, 64B.

DENTAL TISSUES.

367

244

d

A third kind of complication is produced by an aggregation of
many simple teeth into a single mass, fig. 247.

The examples of these
truly compound teeth are
most common in the class
of Fishes, but the illustra-
tion here selected is from
the Mammalian class.
Each tooth of the Cape
Ant-eater ( Orycteropus)
presents a simple form, is
deeply set in the jaw,
but without dividing into
fangs ; its broad and flat
base is porous, like the
section of a common cane.
The canals to which these
pores lead contain pro-
cesses of a vascular pulp,

Portion of transverse section of tooth of Labyrinthodon,
magn. v.

245

and are the centres of ra-
diation of as many independent series of dentinal tubules. Each
tooth consists of a congeries of long and slender prismatic
columns of dentine, cemented together by their ossified capsules.
Fig. 247 is part of a transverse section of such compound tooth,
showing c the cement, d the dentine, p the
pulp-cavity of the denticles, and df a section
of one of the denticles just beyond its bifur-
cation.

In the series of tissues, ( cement ' and
f dentine,' under its diverse modifications,
rank with osteine. Enamel is a tissue per
se : it might be compared to calcified epi-
derm ; but, in the teeth of Fishes, there are
intermediate gradations of structure which
link enamel to dentine, and this to bone.

Tooth of a Dendrodus, natural

The general form of the matrix or forma- size. v.

tive organ of teeth, and the relative position of the dentinal pulp
to its product, bear a close resemblance to the formative organ
of hair and bristle. In these, however, the papilla or pulp is
developed from the skin, in teeth from the mucous membrane.

Teeth further agree with the extravascular appendages of the
skin in being shed and reproduced, sometimes once, sometimes
frequently, during the lifetime of the individual. In some

a

368

ANATOMY OF VERTEBRATES.

instances, as with certain dermal appendages, the reproduction of
the tooth is uninterrupted, or continuous. A tooth, when fully
formed, is subject to decay, but has no inherent power of
reparation.

246

Portion of transverse section of tooth of a Dendrodus, magn. v.

Thus teeth are analogous to epidermal and horny parts in their
mode of developement, in their shedding and reproduction, and
in their exposure to outward influences ; but the antlers of deer
are similarly exposed, and are likewise shed and renewed, yet,
like the teeth and horn-cores of the ox, they are classed with
the osseous tissues.

§ 70. Teeth of Fishes. — In this class of Vertebrates the teeth,
whether we study them in regard to their number, form, substance,
structure, situation, or mode of attachment, offer a greater and
more striking series of varieties than do those of any other class
of Animals.

As to number, they range from zero to countless quantities.
The Lancelet, the Ammocete, the Sturgeon, fig. 125, 22, 32, the
Paddle- fish, and the whole order of Lophobranchii, are edentulous.
The Myxinoids, fig. 248, have a single pointed tooth, a, on the
roof of the mouth, and two serrated dental plates, b, on the
tongue. The Tench has a single grmdinor-tooth on the occiput,

O O O ~ •!•

TEETH OF FISHES.

3G9

247

d-

fig. 250, c, opposed to two dentigerous pharyngeal jaws, d, d,
below. In the Lepidosiren a single maxillary dental plate,
fig. 251, a, is opposed to a single mandibular one, b, and there are
two small denticles on the nasal bone, c. In the extinct Sharks
with crushing teeth, called Ceratodus and Ctenodus, the jaws were
armed with four teeth, two above and
two below.1 In the Chimaerae two
mandibular teeth are opposed to four
maxillary teeth.2 From this low point
the number in different Fishes is pro-
gressively multiplied until, in the
Pike, the Siluroids, fig. 252, and many
other fishes, the mouth becomes
crowded with innumerable teeth.

With respect to form, I may pre-
mise that as organised beings with-
draw themselves more and more, in
their ascent in the scale of life, from
the influence of common physical
agents, so their parts progressively
deviate from geometrical figures : it
is. only, therefore, in the lowest ver-
tebrated class that we find teeth in the
form of perfect cubes, and of prisms
or plates with three sides (Myletes), four sides ( Scarus), five, or six
sides (Myliobates, fig. 249). The cone is the most common form in
Fishes : such teeth may be slender, sharp-
pointed, and so minute, numerous, and closely
aggregated, as to resemble the plush or pile
of velvet ; these are called ' villiform teeth '
(denies villiformes, dents en velours*^); all the
teeth of the Perch are of this kind : when the
teeth are equally fine and numerous, but
longer, they are called ( ciliiform ' (denies
ciliiformes) : when the teeth are similar to, but
rather stronger than these, they are called ( setiform ' (denies seti-
formes, dents en brosse) : conical teeth, as close set and sharp
pointed as the villiform teeth, but of larger size, are called ' rasp-
teeth ' (denies raduliformes, dents en rape or en cardes, fio\ 252) ;
the Pike presents such teeth on the back part of the vomer : the
teeth of the Sheat-fish (Silurus glanis) present all the gradations

1 v. pi. 22. 2 v. pi. 28.

3 The French terms are those used by Cuvier in xxni. passim.

VOL. I. BE

Transverse section of tooth of
nmgn. v.

248

Teeth of Myxine. xxx.

370

ANATOMY OF VERTEBRATES.

2-19

jaws and teeth

250

between the villiform and radulifonn types. Setiform teeth
are common in the Fishes thence called Chaetodonts ;! in the

genus Citharina they bifurcate at
their free extremities ; in the genus
Platax they end there in three di-
verging points, and the cone here
merges into the long and slender
cylinder, fig. 253.

Sometimes the cone is compressed
into a trenchant blade : and this may
be pointed and recurved, as in the
Murcena ; or barbed, as in Trichiurus,
and some other Scomberoids ; or it
may be bent upon itself, like a tenterhook, as in the fishes thence
called Goniodonts.2 In the Bonito may be perceived a progressive

thickening of the base of
the conical teeth : and this
being combined in other
predatory fishes with in-
creased size and recurved
direction, they then resem-
ble the laniary or canine
teeth of carnivorous quad-
rupeds, as we see in the
large teeth of the Pike, in
the Lophius, fig. 260, and
in certain sharks, fig. 263.
The anterior diverging
grappling teeth of the wolf-
fish form stronger cones ;

and by progressive blunting, flattening, and expansion of the

apex, observable in different fishes, the
cone gradually changes to the thick and
short cylinder, such as is seen in the back
teeth of the wolf-fish, and in similar grind-
ing and crushing teeth in other genera,
whether feeders on sea-weeds or on crusta-
ceous and testaceous animals. The grind-
ing surface of these short cylindrical teeth
may be convex, as in the Sheep's-head
fish (Sart/us)', or flattened, as in the
pharyngeal teeth of the Wrasse (Labrus, fig. 254). Sometimes
the hemispheric teeth are so numerous, and spread over so broad a

Teeth of Tench, v.

251

Teeth of Lepidosiren. xxxm.

, a bristle ; uSovs, n tooth.

ia, an angle ; oSouy, a tooth.

TEETH OF FISHES.

371

252

surface, as to resemble a pavement, as in the pharyngeal bones of
the Wrasse or Rock-fish (Labrus, fig. 254) ; or they may be
so small, as well as numerous (denies graniformes}, as to give a
granulated surface to the part of the mouth
to which they are attached (premaxillaries
of Cossyphus).1 A progressive increase of
the transverse over the vertical diameter may
be traced in the molar teeth of different
fishes, and sometimes in those of the same
individual, as in .Labrus, until the cylindrical
form is exchanged for that of the depressed
plate. Such dental plates (denies lamelli-
formes) may be found, not only circular,
but elliptical, oval, semilunar, sigmoid, ob-
long, or even square, hexagonal, pentagonal,
or triangular ; and the grinding surface may
present various and beautiful kinds of sculp-
turing. The broadest and thinnest lamelli-
form teeth are those that form the complex
grinding tubercle of the Diodon, fig. 257,
b. The front teeth of the Flounder and Sargus
present the form of compressed plates, at

Palatine bone and teeth
(Silurus). v.

least in the crown, and are denies incisivi. Numerous

*

shaped dental plates (denies cuneati) are set vertically in the
253 251

Mandibnlar teeth,,
magnified (Platax). v.

Inferior pharyngeal bone and teeth (Labrus). v.

upper pharyngeal bone of the Parrot-fish (Scarus, fig. 255).
A thin lamella, slightly curved like a finger-nail, is the singular
form of tooth in an extinct genus of fishes, thence called
Petalodus. Sometimes the incisive form of tooth is notched
in the middle of the cutting edge, as in Sargus unimacitlatus.
Sometimes the edge of the crown is trilobate (Aplodactylus,
fig. 256). Sometimes it is made quinquelobate by a double

1 v pi. 45, fig 1.
B B 2

37-2

ANATOMY OF VERTEBRATES.

255

notch on each side of the large middle lobe (Hoops'). In the
formidable Sea-pike (Sphyr&na Barracuda^) the crown of each
tooth, large and small, is produced into a compressed and sharp

point, and resembles a lancet. Sometimes
the edges of such lancet-shaped teeth are
finely serrated, as in Priodon, and the great
Sharks of the genus Carcharias, the fossil
teeth of which indicate a species ( Carch.
Mcgalodon) sixty or seventy feet in length.
The lancetted form is exchanged for the
stronger spear-shaped tooth in the Sharks
of the genus Lamna, fig. 260 ; and in the
allied great extinct Otodus, as in the small
Porbeagle, similarly shaped, but stronger,
piercing and cutting teeth were complicated
by one or more accessory compressed cusps on
each side of their base, like the Malay crease.
With respect to situation, the teeth, in
Sharks and Rays, are limited to the bones
(maxillary and maiidibular), which form the
anterior aperture of the mouth : in the
Carp and other Cyprinoids the teeth are confined to the bones
(pharyngeal and basioccipital) which circumscribe the posterior
aperture of the mouth. The Wrasses (Labrus) and
the Parrot-fishes ( Scarus) have teeth on the pre-max-
illary and pre-inandibular, as well as on the upper
and lower pharyngeals ; both the anterior and
posterior apertures of the mouth being thus pro-

Superior pliiir.vu.ireal bones and
teeth (Scams). T.

256

Front teeth of A
daetyhis. v.

vided with instruments for seizing, dividing, or com-
minuting the food, the grinders being situated at
the pharynx. In most fishes teeth are developed
also in the intermediate parts of the oral cavity,
as on the palatines, the vomer, the hyoid bones,
the branchial arches ; and, though less commonly, on the pte-

rygoids, the entopterygoids and
the sphenoids. It is very rare to
find teeth developed on the true
superior maxillary bones ; but the
Herring and Salmon tribes, some
of the Ganoid Fishes, and the
great Sudis, fig. 86, 21, are ex-
amples of this approach to the
hio-her Vertebrates. Among the

Section of the jaw and teeth of the Globe-fish •, ... /» ,,*"

anomalous positions ol teeth may

TEETH OF FISHES.

373

258

be cited, besides the nasal teeth of the Lepidosiren, fig. 251, c,
and the occipital alveolus of the Carp and Tench, fig. 250, the
marginal alveoli of the prolonged, depressed, well ossified rostrum
of the Saw-fish (Pristis, fig. 65). In the Lampreys, fig. 138, and
in Helostomus (an osseous fish), most of the teeth are attached to
the lips. Lastly, it is peculiar to the class Pisces, amongst Verte-
brates, to offer examples
of teeth developed in the
median line of the mouth,
as in the palate of the
Myxines, fig. 248, a ;
or crossing the symphy-
sis of the jaw, as in
Notidanus, Scymnus, and
Myliobates, fig. 249.

Xor is the mode less
varied than the place of
attachment. The teeth
of Lophius, Pceciliit,
Anableps, are always
moveable. In most
fislies they are anchy-
losed to the jaws by con-
tinuous ossification from
the base of the dental
pulp. Sometimes we

i Beak of Parrot-fish (Scams muricatus). v.

find, not the base, but

one side, of the tooth anchylosed to the alveolar border of the

259

Section of the jaw of the Parrot-fish, showing the progress of dentition, v.

jaw ; and the teeth oppose each other by their sides instead

£74

ANATOMY OF VERTEBRATES.

2GO

Portion of the jaw of Lophius piscatorius, showing the liga-
meutous attachment of the teeth, v.

of their summits (Scams, fig. 259); in Pimelodus, however,
where the teeth are thus attached, the crown is bent down
in the upper teeth, and bent up in the lower ones, at right angles

to the fang, so that they
oppose each other by the
normal surfaces. Certain
teeth of recent and fossil
cartilaginous fishes have
their base divided into
processes like fangs, but
these serve for the attach-
ment of ligaments, and
are not set in bony sockets
like the true fano;s or

O

roots of the teeth of Mam-
mals.

The base of anchylosed
teeth is, at first, attached
to the jawbone by liga-
ment; and in the Cod-fish, Wolf-fish, and some other spe-
cies, as calcification of the tooth progresses towards its base,
the subjacent portion of the jawbone receives a stimulus, and

developes a process corres-
ponding in size and form
with the base of the tooth :
for some time a thin layer
of ligamentous substance
intervenes, but anchylosis
usually takes place to a
greater or less extent before
the tooth is shed. Most of
the teeth of the Lophius re-
tain the primitive connection ; the ligaments, fig. 260, d, of the large
internal or posterior teeth of the upper and lower jaws, radiate on
the corresponding sides of the bone, the base of the tooth resting
on a conformable alveolar process. The ligaments do not permit
the tooth to be bent outward beyond the vertical position, but
yield to pressure in the contrary direction, by which the point of
the tooth may be directed towards the back of the mouth, as at c;
the instant, however, that the pressure is remitted, the tooth
returns through the elasticity of the bent ligaments, as by the
action of a spring, into its usual erect position, b ; the deglutition
of the prey of this voracious fish is thus facilitated, and its escape

261

>c /

Teeth of the "Wrasse (Crenilabrus'). V.

TEETH OF FISHES. 375

prevented. The broad and generally bifurcate bony base of the
teeth of Sharks is attached by ligament to the semiossified crust
of the cartilaginous jaws, fig. 263 ; but they have no power of
erecting or depressing the teeth at will. The small and closely
crowded teeth of Rays are also connected by ligaments to the
subjacent maxillary and mandibular membranes. The broad tes-
selated teeth of the Myliobates have their attached surface longi-
tudinally grooved to afford them better hold-fast, and the sides of
the contiguous teeth are articulated together by serrated or finely
undulating sutures, a structure unique in dental organisation.
The teeth of the Sphyr&na are examples of the ordinary im-
plantation in sockets, with the addition of a slight anchylosis of the
base of the fully-formed tooth with the alveolar parietes ; and the
compressed rostral teeth of the Saw-fish, fig. 65, are deeply
implanted in sockets. In the latter the hind margin of their base
is grooved, and a corresponding ridge from the back part of the
socket fits into the groove, and gives additional fixation to the
tooth. Some implanted teeth in the present class have their
hollow base further supported, like the claws of the feline tribe,
upon a bony process arising from the base of the socket ; the in-
cisors of the Balistes, e.g. afford an example of this double or
reciprocal gomphosis.1 In fact, the whole of this part of the
organisation of fishes is replete with beautiful instances of design
and instructive illustrations of animal mechanics. The vertical
section of a pharyngeal jaw and teeth of the Wrasse (Labrus)
would afford the architect a model of a dome of unusual strength,
and so supported as to relieve from pressure the floor of a vaulted
chamber beneath. The base of the dome-shaped tooth, fig. 240,
p9 is slightly contracted, and is implanted in a shallow circular
cavity ; the rounded margin of which is adapted to a circular
groove in the contracted part of the base ; the margin of the
tooth which immediately transmits the pressure of the bone, is
strengthened by an inwardly projecting convex ridge. The
masonry of this inner buttress, and of the dome itself, is composed
of hollow columns, every one of which is placed so as best to
resist or transmit in the due direction the external pressure.
The floor of the alveolus is thus relieved from the office of sus-
taining the tooth : it forms, in fact, the roof of a lower vault, in
which the germ of a successional tooth, fig. 261, b, is in course of
developement. The superincumbent pressure is exclusively
sustained by the border of the alveolus, whence it is transferred to

1 V. p. 82, pi. 40.

37G ANATOMY OF VERTEBRATES.

the walls dividing the vaulted cavities containing; the c^rms of the

o o

new teeth ; the roofs of these cavities yield to the absorbent
process consequent on the growth of the new teeth without
materially weakening the attachment of the old teeth, and without
the new teeth being subjected to any pressure until their growth
is sufficiently advanced to enable them to bear it with safety ; by
this time the sustaining borders of the old alveolus are under-
mined, and the old worn-down tooth is shed.

The dental system of the Wolf-fish (Anarrliiclias Lupus), is
adapted for feeding on hard Crustacea and testacea. But, in
order to secure the capture of the shell-fish, the teeth of the
Wolf-fish are not all crushers ; some present the lam'ary type,
with the apices more or less recurved and blunted by use,
and consist of strong cones spread abroad, like grappling-hooks,
at the anterior part of the mouth.1

The premaxillary teeth are conical, and arranged in two rows.

v O

There are three large, strong, diverging laniaries at the anterior
end of each premandibular bone, and immediately behind these

an irregular number of shorter and smaller conical teeth, which

~

gradually exchange this form for that of large obtuse tubercles ;
these extend backward, in a double alternate series, along a great
part of the alveolar border of the bone. Each palatine bone
supports a double row of teeth, the outer ones being conical and
straight, and from four to six in number ; the inner ones two,
three, or four in number, and tuberculate. The lower surface of
the vomer is covered by a double irregularly alternate series of
the same kind of large crushing teeth as those at the middle of
the premandibular. All the teeth are anchylosed to more or less
developed alveolar eminences, like the anterior teeth of the
Lophius.

From the enormous developement of the muscles of the jaws,
and the strength of the shells of the whelks and other testacea
which are cracked and crushed by the teeth, their fracture and
displacement must obviously be no unfrequent occurrence ; and
most specimens of the jaws of the Wolf-fish exhibit some of the
teeth separated at the line of anchylosis, or broken off above the
base.

With regard to the substance of the teeth of Fishes, the
modifications of dentine, called vaso-dentine and osteo-dentine,
predominate much more than in the higher Vertebrates, and they
thus more closely resemble the bones which support them. The

1 v. pi. GO, 61.

TEETH OF FISHES, 377

teeth of most of the Chsetodonts are flexible, elastic., and composed
of a yellowish subtransparent albuminous tissue ; such, likewise,
are the labial teeth of the Helostome, the premaxillary and
mandibular teeth of the Goniodonts, and of the percoid genus
Trichodon. In the Cyclostomes the teeth consist of a denser
albuminous substance. The upper pharyngeal molar of the Carp
consists of a peculiar brown and semitransparent tissue, hardened
by salts of lime and magnesia. The teeth of the Flying-fish
(Exoc&tus) and Sucking-fish (Remora) consist of osteo-dentine.
In many Fishes, e. g. the Acanthurus, Sphyrcena, and certain
Sharks (Lemma, fig. 241), a base, or body of osteo-dentine, is
coated by a layer of true dentine, d, but of unusual hardness, like
enamel : in Prionodon this hard tissue predominates. In the
Labrus the pharyngeal crushing teeth consist wholly of hard or
unvascular dentine, fig. 240. In most Pycnodonts and Cestra-
cionts, and many other Fishes, the body of the tooth consists of
ordinary unvascular dentine, covered by a modification of gano-
dentine. In Sargus and Balistes the body of the tooth consists
of true dentine, and the crown is covered by a thick layer of a
denser tissue, differing from the f enamel ' of Mammalia only in
the more complicated and organised mode of deposition of the
earthy salts. The ossification of the capsule of the complex
matrix of these teeth covers the enamel with a thin coating of

o

' cement.' In the pharyngeal teeth of the Scar us a fourth sub-
stance is added by the ossification of the base of the pulp after
its summit and periphery have been converted into hard dentine ;
and the teeth, fig. 262, thus composed of cement, c, enamel, e,
dentine, d, and osteo-dentine, are the most complex in regard to
their substance that have yet been discovered in the animal
kingdom.

o

The tubes which convey the capillary vessels through the
substance of the osteo- and vase-dentine of the teeth of Fishes
were early recognised, on account of their comparatively large
size ; as by Andre, e. g. in the teeth of Acanthurus^ and by
Cuvier and Von Born in the teeth of the wolf-fish and other
species. Leeuwenhoek had also detected the much finer tubes
of the peripheral dentine of the teeth of the haddock.2 These
' dentinal tubuli ' are given off from the parietes of the vascular
canals, and bend, divide, and subdivide rapidly in the hard basis-
tissue of the interspaces of those canals in osteo-dentine ; the
dentinal tubuli alone are found in true dentine, and they have a

1 CCXLVII. 2 CCXLYIIL, p. 1003.

378 ANATOMY OF VERTEBRATES.

straightcr and more parallel course, usually at right angles to the
outer surface of the dentine. Those conical teeth which, when
fully formed, consist wholly or in great part of osteo-dentine or
vaso-dentine, always first appear with an apex of hard or true
dentine. In some Fishes the simple central basal pulp-cavity of
such teeth, instead of breaking up into irregular or parallel
canals, sends out a series of vertical plates from its periphery,
which, when calcified, give a fluted character to the base of the
tooth, e. g. in Lepidosteus oxyurus.1 This is the first step in the
pattern of complication which attains its maximum in Labyrinth-
odonts and Dendrodonts, figs. 244, 246.

Thus, with reference to the main tissue of tooth, we find not
fewer than six leading modifications in Fishes : hard or true
dentine (Sparoids, Labroids, Lophius, Balistes, Pycuodonts,
Prionodon, Sphyrcena, Megalichthys, Rhizodus, Diodon, Scants),
osteo-dentine ( Cestracion, Acrodus, Lepidosiren, Ctenodus, Hybodus,
Percoids, Scicenoids, Cottoids, Gobioids, and many others), vaso-
dentine (Psammodus, Chim&roids, Pristis, Myliobates), plici-dentine
(Lophius, Holopty chius, Lepidosteus oxyurus, at the base of the
teeth), labyrintho-dentine (Lepidosteus platyrhinus, Bothriolepis),
and dendro- dentine (Dendrodus) ; besides the compound teeth of
the Scarus and Diodon.

One structural modification may prevail in some teeth, another
in other teeth, of the same fish ; and two or more modifications
may be present in the same tooth, arising from changes in the
process of calcification and a persistency of portions or processes
of the primitive vascular pulp or matrix of the dentine.

The dense covering of the beak-like jaws of the Parrot-fishes
(Scarus, figs. 258, 259) consists of a stratum of prismatic denticles,
standing almost vertically to the external surface of the jaw-bone.
It is peculiarly adapted to the habits and exigences of a tribe of
Fishes which browse upon the lithophytes that clothe, as with a
richly tinted carpet, the bottom of the sea, just as the Ruminant
quadrupeds crop the herbage of the dry land.

The irritable bodies of the gelatinous polypes which constitute
the food of these Fishes retract, when touched, into their star-
shaped stony shells, and the Scari consequently require a dental
apparatus strong enough to break off or scoop out these calcareous
recesses. The jaws are, therefore, prominent, short, and stout,
and the exposed portions of the premaxillaries and premandibulars

' Wyman, American Journal of Natural Sciences, Oct. 1843. Cuvier has given
an accurate view of the plaited structure of the base of the Wolf-rish's teeth in pi. 32,
fig. 7, of his Lemons d' Anatomic Comparee, 1805.

TEETH Or FISHES. 379

are encased by the above-described complicated dental covering.
The polypes and their cells are reduced to a pulp by the action of
the pharyngeal jaws and teeth, that close the posterior aperture of
the mouth. The superior dentigerous pharyngeals, fig. 255,, present
the form of an elongated, vertical, inequilateral, triangular plate ;
the upper and anterior margin forms a thickened articular surface,
convex from side to side, and playing in a corresponding groove or
concavity upon the base of the skull ; the inferior boundary of the
triangle is the longest, and also the broadest ; it is convex in the
antero-posterior direction, and flat from side to side. On this
surface the teeth are implanted, and in most species they form
two rows : the outer one consisting of very small, the inner one
of large, dental plates, which are set nearly transversely across
the lower surface of the upper pharyngeal bones and teeth,
in close apposition, one behind the other : their internal angles
are produced beyond the margin of the bone, and interlock with
those of the adjoining bone when the pharyngeals are in
their natural position ; the smaller denticles of the outer row
are set in the external interspaces of those of the inner row.
The single inferior pharyngeal bone consists principally of an
oblong dentigerous plate,1 supported by a strong, slightly curved.,
transverse, osseous bar, the extremities of which expand into thick
obtuse processes for the implantation of the triturating muscles*
A longitudinal row of small oval teeth alternating with the
large lamelliform teeth, like those of the superior pharyngeals.,
bounds the dentigerous plate on each side ; the intermediate space
is occupied exclusively by the larger wedge-shaped teeth, set
vertically in the bone, and arranged transversely in alternate and
pretty close-set series.

The dental plates are developed in wide and deep cavities in
the substance of the posterior part of the lower, and of the ante-
rior part of the upper pharyngeal bones. The teeth exhibit
progressive stages of formation as they approach those in use ; and,
as their formation advances to completion they become soldered
together by ossification of their respective capsules into one com-
pound tooth, which soon becomes anchylosed by ossification of the
dentinal pulp to the pharyngeal bone itself.

In the dentine of the pharyngeal teeth of the Scarus the
dentinal tubes average a diameter of 2 0 * O-Q of an inch, and are
separated by interspaces equal to twice their own diameter. The
course of these tubes is shown in fig. 262, d, in which they are

1 v. pi. 51, fig. 3.

380

ANATOMY OF VERTEBRATES.

exposed by a vertical section through the middle of two of
the superior denticles. Each tube is minutely undulated :
it dichotomises three or four times near its termination,, sends
off many fine lateral branches into the clear uniting sub-
stance, and finally terminates in a series of minute cells and
inosculating loops at the line of junction with the enamel.
This substance, fig. 262, e, is as thick as the dentine, and
consists of a similar combination of minute tubes and a clear
connecting substance. The tubes may be described as com-
mencing from the peripheral surface of the tooth to which they

262

Two of the upper phuryngeal teeth i Scaras -, nuign. r.

stand at right angles, and, having proceeded parallel to each other
halfway towards the dentine, they then begin to divide and sub-
divide, the branches crossing each other obliquely, and finally
terminating in the cellular boundary between the enamel and
dentine.

In the progress of attrition, the thin coat of cement resulting
from the ossification of the capsule is first removed from the apex
of the tooth, then the enamel constituting that apex, next the
dentine, and, finally, the coarse central cellular bone, supporting
the hollow tooth : and thus is produced a triturating surface of
four substances of different degrees of density. The enamel,

TEETH OF FISHES. 381

being the hardest element, appears in the form of elliptical trans-
verse ridges, inclosing the dentine and central bone : and external

O ' O

to the enamel is the cement, c, which binds together the different
denticles.

There is a close analogy between the dental mass of the Scarus
and the complicated grinders of the Elephant, both in form,
structure, and in the reproduction of the component denticles in
horizontal succession. But in the fish the complexity of the
triturating surface is greater than in the mammal, since, from the

O ~

mode in which, the wedge-shaped denticles of the Scarus are
implanted upon, and anchylosecl to, the processes of the supporting
bone, this likewise enters into the formation of the masticatory
surface when the tooth is worn down to a certain point.

The proof of the efficacy of the complex masticatory apparatus
above described is afforded by the contents of the alimentary
canal of the Scari. The intestines are usually laden with a chalky
pulp, to which the coral dwellings have been reduced.

Dev elopement.- As might be supposed, by the above-defined
varied and predominating vascular organisation in the teeth of
Fishes, and the passage from non-vascular dentine to vascular
dentine in the same tooth, the developement of dentine by centri-
petal metamorphosis and calcification of the pulp was determined
by observations made on the developement of the teeth in the
present class.1

It is interesting to observe in it the process arrested at each of
the well-marked stages through which the developement of a
Mammalian tooth passes. In all Fishes the first step is the simple
production of a soft vascular papilla from the free surface of the
buccal membrane : in Sharks and Rays these papillae, fig. 382, c,
do not proceed to sink into the substance of the gum, but are
covered by caps of an opposite free fold of the buccal membrane :
these caps do not contract any organic connection with the papilli-
form matrix, but, as this is converted into dental tissue, ib. b, the
tooth is gradually withdrawn from the extraneous protecting cap,
to take its place and assume the erect position on the margin of
the jaw, fig. 263, a. Here, therefore, is represented the first and
transitory ' papillary ' stage of dental developement in Mammals :
and the simple crescentic cartilaginous maxillary plate, d, with
the open groove behind containing the germinal papillae of the
teeth, offers in the Shark a magnified representation of the earliest
condition of the jaws and teeth in the human embryo.

In manv Fishes, e. s:. Lophius. Esox, the dental papillae become

v O J. J. 1

1 LXXXIX. p. 784.

382

ANATOMY OF VERTEBRATES.

203

buried in the membrane from which they rise, and the surface
to which their basis is attached becomes the bottom of a

closed sac : but this sac
does not become inclosed in
the substance of the jaw ;
so that teeth at different
stages of growth are
brought away with the
thick and soft gum, when
it is stripped from the
jaw-bone. The final fixa-
tion of teeth, so formed,
is effected by the develope-
ment of ligamentous fibres

o

in the submucous tissue be-
tween the jaw and the base
of the tooth, which fibres
become the medium of con-
nection between those parts,
either as elastic ligaments
or by continuous ossifica-
tion. Here, therefore, is
represented the f follicular '
stage of the developement
of a Mammalian tooth :
but the ( eruptive ' stage
takes place without pre-
vious inclosure of the follicle and matrix in the substance of the
jaw-bone.

In Batistes, Scarus, Spliyrcena, the Sparoids, and many other
Fishes, the formation of the teeth presents all the usual stages
which have been observed to succeed each other in the dentition
of the higher Vertebrates : the papilla sinks into a follicle, becomes
surrounded by a capsule, and is then included within a closed
alveolus of the growing jaw, figs. 259, 261, c, where the develope-
ment of the tooth takes place and is followed by the usual eruptive
stages. A distinct enamel-pulp is developed from the inner
surface of the capsule in Batistes, Scarus, Saryus, and Cliryso-
2>lirys.

In the formidable Barracuda (Spkyr<zna} the loss or fracture of
the lancet-shaped teeth, in the conflict with a struggling prey, is
repaired by an uninterrupted succession of new pulps and teeth.
The existence of these is indicated by the foramina, which are

Vertical section of ja\v and teeth (Lanma). v.

TEETH OF FISHES. 383

situated immediately posterior to, or on the inner margin of, the
sockets of the teeth in place : these foramina lead to alveoli of
reserve, in which the crowns of the new teeth, in diiferent stages
of developement, are loosely embedded. It is in this position of
the germs of the teeth that the Sphyraenoid fishes, both recent
and fossil, mainly differ, as to their dental characters, from the rest
of the Scomberoid family.

It is interesting to observe that the alternate teeth are, in
general, contemporaneously shed : so that the maxillary armour is
thus preserved in an effective state. The relative position of
the new teeth to their predecessors, and their influence upon
them, resembles, in the Sphyrcena, some of the phenomena which
will be described in the dentition of the Crocodilian Reptiles.
To the Crocodiles the present voracious Fish also approximates in

the alveolar lodgement of the teeth : but it manifests its ichthvic

~ •/

character in the anchylosis of the fully-developed teeth to their
sockets, and still more strikingly in the intimate structure of the
teeth.

In all Fishes the teeth are shed and renewed, not once only, as
in Mammals, but frequently, during the whole course of their
lives. The maxillary dental plates of Lepidosiren, the cylindrical
dental masses of the Chimceroid and Edaphodont Fishes, and the
rostral teeth of Pristis (if these modified dermal spines may be so
called), are, perhaps, the sole examples of ( permanent teeth ' to
be met with in the whole class.

When the teeth are developed in alveolar cavities, they are
usually succeeded by others in the vertical direction, as in the
pharyngeal bones of the Labroids, fig. 261 : but sometimes
they follow one after the other, side by side, as in the Scaroids,
fig. 259, c. In Reptiles and Mammals the successional teeth
owe the origin of their matrix to the budding out from the cap-
sule of their predecessors of a caecal process, in which the
papillary rudiment of the dentinal pulp is developed; but, in
the great majority of Fishes, the germs of the new teeth are
developed, like those of the old, from the free surface of the
buccal membrane throughout the entire period of succession :
a circumstance peculiar to the present class. The Angler, the
Pike, and most of our common Fishes, illustrate this mode of
dental reproduction ; it is very conspicuous in the cartilaginous
Fishes, figs. 263 and 264, in which the whole phalanx of their
numerous teeth is ever marching slowly forwards in rotatory
•orooress over the alveolar border of the iaw, the teeth beiii£

JL O <J O

successively cast off as they reach the outer margin, and new

384

ANATOMY OF VERTEBRATES.

teeth rising from the mucuous membrane behind the rear rank of
the phalanx.

This endless succession and decadence of the teeth, together
with the vast numbers in which they often coexist in the same

26i

Skull and jaws of Port Jackson Shark (Cestracion Phtlippii), showing the forms and arrangement of

the teeth, v.

Fish, illustrate the law of Vegetative or Irrelative Repetition,1 as
it manifests itself on the first introduction of new organs in the

o

Animal Kingdom, under which light we must view the above-
described organised and calcified preparatory instruments of
digestion in the lowest class of the vertebrate series.

o

At the extreme limit of the class of Fishes, and connecting
that class with the Reptiles, stands the very remarkable genus,
the dental system of which is figured in cut 251. This consists
of two small, slender, conical, sharp-pointed, and slightly recurved
teeth, which project downward from the nasal bone, <?, and of
strong trenchant dental plates, anchylosed with the alveolar border
of the upper, «, and lower, I, jaws, in each of which the plate
is divided at the middle, or symphysial line, so as to form two
distinct lateral teeth. The office of the two laniariform teeth is
to pierce and retain the nutritive substance or prey which is

1 CCXLIX.

TEETH OF REPTILES. 385

afterwards divided and comminuted by the strong maxillary
dental plates.

§ 71. Teeth of Reptiles. — If we compare the dental system
of Lepidosiren with that in Batrachia, it is to the larval state
of the Anouraiis that an analogy may be found : the tadpole of
the Frog having its maxilla and mandibula each sheathed with a
continuous horny trenchant covering. Were this sheath actually
dentmal in tissue and united to the jaw-bone, the resemblance to
the Lepidosiren would be closer : but it is never calcified, and is
shed during the progress of the metamorphosis.1 The Siren
alone, among the perennibranchiates, retains the sheath upon
the extremity of the upper and lower jaws ; it consists of a firm
albuminous tissue, and becomes harder than horn. But these
trenchant mandibles, which play upon one another like the blades
of a pair of curved scissors, are associated with numerous small
but distinct true teeth, which are grouped together to form a
rasp-like surface on each half of the divided vomer, and which
beset the alveolar border of the splenial element of the mandible
below.

The whole order of Chelonia is edentulous, as well as the family
of Toads (Bufonidce) in the order Batrachia; certain extinct
genera of Saurians were likewise edentulous, e. g. Rliyncliosaurus
and Oudenodon*

In the Tortoises and Turtles the jaws are covered by a sheath
of horn, which in some species is very dense ; its working surface
is trenchant in the carnivorous species, but is thick, variously
sculptured, and adapted for both cutting and bruising in the
vegetable feeders. The developement of the continuous horny
maxillary sheath commences, as in the Parrot tribe, from a
series of distinct papilla?, which sink into alveolar cavities,
regularly arranged (in Trionyx) along the margins of the upper
and lower jaw-bones : these alveoli are indicated by the persist-
ence of vascular canals long after the originally separate tooth-
like cones have become confluent, and the horny sheath com-
pleted.

The teeth of the dentigerous Saurian, Ophidian, and Batrachian
Reptiles are, for the most part, simple and adapted for seizing
and holding, but not for dividing or masticating, their food. The
Siren alone combines true teeth with a horny maxillary trenchant
sheath, like that of the Chelonian Reptiles.

1 The large dental plates of Lepidosiren have their nearest homologues in those of
the extinct fish called Ceratodus (v. pi. 22, fig. 2).

2 ccxxm. p. 54, pi. I. fig. 1.

VOL. I. C C

386 ANATOMY OF VERTEBRATES.

With respect to number -, in no existing Reptile are the teeth
reduced so low as in certain Mammals and Fishes ; nor, on the
other hand, are they ever so multiplied as in many of the latter
class. Myolmtrachus paradoxus, an Australian Frog, has but two
teeth in the premaxillary bones. The extinct Dicynodont Reptiles
of South Africa had two long tusks implanted in the upper jaw,
fig. 27 1.1 Some species of Ampkisbcena (A. alba), with fifteen
teeth in the upper jaw and fourteen in the lower jaw, and certain
Monitors ( Varanus), with sixteen teeth in the upper and fourteen
in the lower jaw exemplify a low number of teeth amongst
existing Reptiles ; and certain Batrachians, with teeth ( en cardes '
at the roof of the mouth, or which have upwards of eighty teeth
in each lateral maxillary series, present the opposite extreme.
Rarely, however, is the number of the teeth so fixed and
determinate in any Reptile as to be characteristic of the
species, and still more rarely have the individual teeth such cha-
racters as to be determined homologically from one species to
another.

With respect to situation, the teeth may be present on the jaws
only, i. e. the maxillary, the premaxillary, and mandibular bones,
as in the Crocodiles, fig. 95, and many Lizards : or upon the jaws
and roof of the mouth : and here either upon the pterygoid bones,
as in the Iguana, fig. 98, D, 24, and Mosasaur ; or upon both
palatine and pterygoid bones, as in most Serpents, fig. 266, 20, 24 ;
or upon the vomer, as in most Batrachians, fig. 265, /; or upon both
vomerine and pterygoid bones, as in the Axolotl ; or upon the
vomerine and sphenoid bones, as in Salamandra glutinosa. With
respect to the marginal or jaw teeth, these may be absent in the
premaxillary bones, as in many Serpents, fig. 266, 22 : or they
may be present in the upper and not in the lower jaw, as in most
Frogs : or in both upper and lower jaws, as in the tailed
Batrachians : and among these they may be supported, upon the
lower jaw, by the premandibular or dentary piece, as in the
Salamanders, Menopome, Amphiume, Proteus : or upon the
splenial piece, as in the Siren : or upon both splenial and pre-
mandibular bones, as in the Axolotl. The palatine and pterygoid
teeth may, in the Batrachians, be arranged in several rows, like
the ' dents en cardes ' of Fishes. The sphenoid and splenial teeth
are always so arranged in the few species that possess them. The
intermaxillary, maxillary, and premandibular teeth are uniserial,
or in one row, with the exception of the Crecilia and the extinct

1 CLVIII. vol. vii. p. 59.

TEETH OF REPTILES. 387

Labyrinthodonts, which have a double row of teeth at the anterior
part of the lower jaw.

The teeth of Reptiles, with few exceptions, present a simple
conical form, with the crown more or less curved, and the apex
more or less acute. The cone varies in length and thickness ; its
transverse section is sometimes circular, but more commonly
elliptical or oval : and this modification of the cone may be traced
through every gradation, from the thick, round, canine-like tooth
of the Crocodile to the sabre-shaped fang of the Varanus, the
Megalosaur, and the Cladeiodon.1 Sometimes, as in the fully
formed teeth of the Megalosaur, one of the margins of the com-
pressed crown of the tooth is trenchant, sometimes both are so ;
and these may be simply sharp-edged, as in the Varanus of Timor,
or finely serrated, as in the great Varanus, the Cladeiodon, and
the Megalosaur.2

The outer surface of the crown of the tooth is usually smooth ;
it may be polished, as in the Leiodon, or impressed with fine
lines, as in the Labyrinthodon, fig. 243, or raised into many
narrow ridges, as in the Pleiosaur and Polyptychodon, or
broken by a few broad ridges, as in the Iguanodon, fig. 273, or
grooved by a single longitudinal furrow, as in some Serpents,
fig. 269, c.3

The cone is longest and its summit sharpest in the Serpents :
from these may be traced, chiefly in the Lizard tribe, a pro-
gressive shortening, expansion of the base, and blunting of
the apex of the tooth, until the cone is reduced to a hemi-
spherical tubercle, or plate, as in Ct/clodus, fig. 272, and, in a more
remarkable degree, in the extinct shellfish-eating Saurian, called
Placodus.4

In the Pleiosaur the dental cone is three-sided, with one of the
angles rounded off. The posterior subcompressed teeth of the
Alligator, fig. 275, present a new modification of form ; here they
terminate in a mammillate summit, supported by a slightly con-
stricted neck. In the tooth of the Hylreosaur the expanded
summit is flattened, bent, and spear-shaped, with the edges
blunted. But the expansion of the crown is greatest in the
subcompressed teeth of the extinct Cardiodon and the existing
Iguanas, the teeth of which are farther complicated by having
the margins notched. The great Iguanodon had the crown of
the tooth expanded both in length and breadth, and combining

1 v. pi. 62 A, fig. 4. 3 Ib. pi. 65. CCL. vol. iv. figs. 209, 210.

2 Ib. fig. Gc. 4 CXLIII. p. 169.

c c 2

388 ANATOMY OF VERTEBRATES.

marginal dentations with longitudinal ridges: this tooth, fig. 273,
presents the most complicated external form as yet discovered in
the class of Reptiles.

In no Reptile does the base of the tooth ever branch into fangs.

Attachment. - - As a general rule, the teeth of Reptiles are
anchylosed to the bone which supports them. When they con-
tinue distinct, they may be lodged either in a continuous groove,
as in the Ichthyosaur,1 or in separate sockets, as in the Plesiosaur
and Crocodilians, fig. 275. The base of the tooth is anchylosed
to the wall of a moderately deep socket in the extinct Megalosaur
and Thecodon. In the Labyrinthodonts and Csecilise, among the
Batrachians, in most Ophidians, and in the Geckos, Agamians,
and Yaranians, among the Saurians, the base of the tooth is
imbedded in a shallow socket, and is confluent therewith.

In the Sciiicoids, the Safeguards ( Tejus\ in most Iguaniaiis, in
the Chameleons and many Lacertian reptiles, the tooth is anchy-
losed by an oblique surface extending from the base more or less
upon the outer side of the crown to an external alveolar plate of
bone,2 the inner alveolar plate not being developed. In the Frogs
the teeth are similarly but less firmly attached to an external
parapet of bone. The Lizards which have their teeth thus
attached to the side of the jaw are termed ' Pleurodonts.' In a
few Iguanians, as the Istiures and Rhynchocephalus, the teeth are
soldered to the margins of the jaws ; and in some large extinct
Lacertians, e. g. the Mosasaur and Leiodon, each tooth is fixed
upon a conical process of the alveolar border : these Sauria are
termed f Acrodonts.'

Such modifications of the attachment of the teeth of Reptiles
are adapted to the habits and food of the species ; and they likewise
offer an analogy to some of the transitory conditions of the human
teeth. There is a period, for example, when the primitive dental
papilla? are not defended by either an outer or an inner alveolar
process, any more than their calcified homologues, which are con-
fluent with the margin of the jaw in the Rhynchocephalus.3
There is another stage in which the groove containing the dental
germs is defended by a single external cartilaginous alveolar
ridge ; this condition is permanently typified in the Cyclodus.,
fig. 272, and most existing Lizards. Next there is developed in
the human embryo an internal alveolar plate, and the sacs and
pulps of the teeth sink into a deep but continuous groove, in
which traces of transverse partitions soon make their appear-

1 v. pi. 13, fig. 9. 2 v. pi. 67.

3 CLVIII. pt. 2, pi. 6, figs. 5 & 6, p. 83.

TEETH OF EEPTILES. 389

ance ; in the ancient Ichthyosaur the relation of the jaws to
the teeth never advanced beyond this stage. Finally, the dental
groove is divided by complete partitions, and a separate socket is
formed for each tooth ; and this stage of developement is attained
in the highest-organised Reptiles, e. g. the Crocodiles, figs. 95,
275.

Substance.- This may be four-fold, and a single tooth may be
composed of dentine, cement, enamel, and bone : but the dentine
and cement are present in the teeth of all Reptiles.

In the Batrachians and Ophidians a thin layer of cement
invests the central body of dentine, and, as usual, follows any
inflections or sinuosities that may characterise its surface. Be-
sides the outer coat of cement, which is thickest at the base, a
generally thin coat of enamel defends the crown of the tooth in
most Saurians, and the last remains of the pulp are not unfre-
quently converted into a coarse bone, both in the teeth which
are anchylosed to the jaw, and in some teeth, as those of the
Ichthyosaur, winch remain free. The modification called ( vaso-
dentine ' is peculiar in the present class to the teeth of the
Iguanodon.1

Structure. — The varieties of dental structure are few in the
Reptiles as compared with Fishes or Mammals, and its most com-
plicated condition arises from interblending of the dentinal and
other substances rather than from modifications of the tissues
themselves. In the teeth of most Reptiles the intimate structure
of the dentine is of the hard or unvascular kind, presenting only
plasmatic or dentinal tubes, diverging from the pulp cavity, at
right angles to the external surface of the tooth. Such dentine
may be folded inwardly upon itself, so as to produce a deep longi-
tudinal indentation on one side of the tooth ; it is the expansion of
the bottom of such a longitudinal deep fold that forms the central
canal of the venom-fang of the Serpent : but its structure remains
unaltered ; and although the pulp-cavity, fig. 270, p, is reduced
to the form of a crescentic fissure, the dentinal tubes continue to
radiate from it according to the usual law. By a similar inflection
of many vertical longitudinal folds of the cement and external
surface of the tooth at regular intervals around the entire cir-
cumference of the tooth, and by a corresponding extension of
radiated processes of the pulp-cavity and dentine into the inter-
spaces of such inflected and converging folds, a modification of
dental structure is established in certain extinct Reptiles, which,

1 v. pi. 71, Iguanodon.

300

ANATOMY OF VERTEBRATES.

Teeth of Menopoiue ; fc premaxillary, I vonierine,
x maxillary

by the various sinuosities of the interblended folds of cement and
processes of dentine, with the partial dilatations of the radiated
pulp-cavity, produces the complicated structure which is described
at p. 365, and figured in cut 244.

Developement- -The teeth of Reptiles are never completed at the

first or papillary stage ; the pulp
sinks into a follicle, and becomes
inclosed by a capsule ; and in
certain reptiles this becomes
more or less surrounded by bone ;
but the ' eruptive ' stage, in the
sense in which this is usually
understood, as signifying the ex-
trication of the young tooth from
a closed alveolus, is not exem-

plified in recent Reptiles, and
was rare in extinct ones.1

The completion of a tooth,
with the exception of the Dicy-
nodont Reptiles, is soon fol-
lowed by preparation for its
removal and succession ; the faculty of developing new tooth-
germs seems to be unlimited in the present class, and the phe-
nomena of dental decadence and replacement are manifested at
every period of life ; the number of teeth is generally the same in
each successive series, and the difference of size presented by the
teeth of different and distant series in the same individual is
considerable.

The new germ is always developed, in the first instance, at
the side of the base of the old tooth, never in the cavity
of the base ; the crocodiles form no exception to this rule.
The poison-fangs of serpents succeed each other from behind
forwards ; in almost every other instance the germ of the succes-
sional tooth is developed at the inner side of the base of its
predecessor. In the Frog the dental germ makes its appear-
ance in the form of a papilla developed from the bottom and
towards the outer side of a small fissure in the mucous membrane
or gum that fills up the shallow groove at the inner side of the
alveolar parapet and its adherent teeth : the papilla is soon
enveloped by a capsular process of the surrounding membrane.
As the tooth acquires hardness and size, it presses against the

1 CXLIII. p. 178, pi. ix., fig. 4, a'.

TEETH OF REPTILES. 391

base of the contiguous attached tooth, causes a progressive
absorption of that part, and finally undermines, displaces, and
replaces its predecessor. The number of nascent matrices of the
successional teeth is so great in the Frog, and they are crowded so
close together, that it is not unusual to find the capsules of con-
tiguous tooth-germs becoming adherent together, as their ossifi-
cation proceeds. After a brief maceration, the soft gum may be
stripped from the shallow alveolar depression, and the younger
tooth-germs in different stages of growth are brought away
with it.

The mode of development of the teeth of serpents does not
differ essentially from that of the teeth of the Batrachian above
described, except in the relation of the papilla? of the suc-
cessional poison-fangs to the branch of the poison-duct that
traverses the cavity of the loose mucous gum in which they are
developed.

Some of the peculiarities of the dentition of the Batrachians
have already been noticed, as in the comparison of the Siren
with the Lepidosiren, in which the true amphibian was shown
to have numerous teeth on the palate and lower jaw.1 The
piscine character of rasp-like teeth aggregated in numerous
series, is manifested also in the Axolotl,2 upon the palatal region
of the mouth, and upon the splenial or opercular element of the
lower jaw ; but the superior maxillary bones are here developed,
and also support teeth. The premandibular and the premaxillary
bones, instead of preserving the larval condition of the horny
sheath, have their alveolar border armed with a single row of

7 o

small, equal, fine and sharp-pointed denticles, which are continued
above, along the maxillaries ; thus establishing the commence-
ment of the ordinary Batrachian condition of the marginal teeth
of the buccal cavity. The dentigerous bones of the palate consist
of two plates on each side, as in the Siren ; the anterior pair, or
vomerine bones, converge and meet at their anterior extremities ;
the minute denticles which they support are arranged quincun-
cially ; the posterior pair of bones are continued backwards
according to the usual disposition of the pterygoids, to abut
against the tympanic bones ; the denticles are confined to the
anterior part of their oral surface, and resemble in their arrange-
ment and anchylosed attachment those of the vomerine series, of
which they form the posterior termination.

In the Menopome, fig. 265, the teeth are small, pointed, in a

1 V; pi. 62, figs. 5 & 6. 2 Ib. pi. 62, fig. 4.

392 ANATOMY OF VERTEBRATES.

single row, in each bone ; describing a semicircle, upon the pre-
maxillary, k, and maxillary, x, bones : a shorter parallel series is
supported on the vomerine bones, Z.1 The mandibular series is
received into the interspace of the two rows in the upper jaw.

The Frogs (Rana)'i have 110 teeth on the lower jaw ; but in
some species the alveolar edge of this bone is finely notched or
dentated, as in the horned Frogs ( Ceratophrys). Dactylethra has
maxillary teeth only ; Myobatrachus has but two horizontal pre-
maxillary teeth. Both premaxillary and maxillary bones usually
support a long, close-set, single series of small, conical, hollow
teeth, of which the apices only project beyond the external alveo-
lar ridge to which they are attached. A short transverse row of
similar but smaller teeth extends along the posterior border of each
vomer. Other dispositions of the vomerine teeth help to charac-
terise the genera of Ranida, in a few of which they are wanting ;
as, e.g., in Uperoleia, in the slender-armed Frogs (Leptobrachiuni),
in Oxyglossus, and in some of the Tree Frogs (e.g. Eucnemis}, in
which the roof of the mouth is edentulous.

Amongst the most extraordinary examples of extinct reptiles
are those which are characterised by the labyrinthic modification
of the dental structure above described, and which, with some
affinities to Saurians, combine characters which are essentially
those of the order Batrachia. In Labyrintlwdon leptognatlius., the
upper jaw contains a single row of small teeth, about sixty in
number, anterior to which are three or four large conical tusks.
The apical two thirds of each tooth is smooth, but the basal third is
fluted and anchylosed to the outer wall of the socket. The osseous
roof of the mouth is principally composed of a pair of broad and
fiat bones, homologous with the divided vomer in Batrachia, but of
much greater relative extent. Each bone supports anteriorly three
median small teeth and two outer larger ones, from which a longi-
tudinal row of small and equal-sized teeth is continued backward
alono; the exterior margin of the vomer. The whole of this series

o o

of vomerine teeth is nearly concentric with the maxillary teeth.

In Lacertine reptiles the examples of a row of palatal teeth are
rare, and, when present, it is short, and situated upon the ptery-
goid bones, as in the Iguana and Mosasaur. In Batrachians the
most common disposition of the palatal teeth is a transverse row
placed at the anterior part of the divided vomer, as in Frogs, and the
Menopome. In the Amphiume, the vomerine teeth form a nearly
longitudinal series along the outer margin of the palatine bones.

1 v. pi. 62, fig. 10. 2 Ib. pi. 62, fig. 10.

TEETH OF REPTILES. 393

The Labyrinthodon combines both these dispositions of the palatal
teeth. The lower jaw, like the upper, contains a series of small
teeth, with a few larger tusks anterior to them. The sockets of
the teeth are shallower than in the upper jaw ; the outer wall is
more developed than the inner, and the anchylosed bases of the
teeth more nearly resemble, in their oblique position, those of
existing Batrachia. Between the apex and the part where the
inflected vertical folds of the cement commence, the tooth of the
Labyrinthodon resembles, in the simplicity of its intimate struc-
ture, that of the entire tooth of ordinary Batrachia and most
reptiles ; and in the lower or basal half of the tooth the labyrinthic
structure above described commences, and gradually increases in
complexity.

In the genus Deirodon,1 the teeth of the ordinary bones of the
mouth are so small as to be scarcely perceptible ; and they appear
to be soon lost. An acquaintance with the habits and food of this
species has shown how admirably this apparent defect is adapted
to its well-being. Its business is to restrain the undue increase of
the smaller birds by devouring their eggs. Now if the teeth had
existed of the ordinary form and proportions in the maxillary and
palatal regions, the egg would have been broken as soon as it was
seized, and much of the nutritious contents would have escaped
from the lipless mouth of the snake in the act of deglutition ; but,
owing to the almost edentulous state of the jaws, the egg glides
along the expanded opening unbroken ; and it is not until it has
reached the gullet, and the closed mouth prevents any escape of
the nutritious matter, that the egg becomes exposed to instru-
ments adapted for its perforation. These instruments consist of
the hypapophyses of the seven or eight posterior cervical vertebras,
the extremities of which are capped by a layer of hard cement,
and penetrate the dorsal parietes of the O2sophagus.2 They may
be readily seen, even in very small subjects, in the interior of that
tube, in which their points are directed backwards. The shell
being sawed open longitudinally by these vertebral teeth, the
egg is crushed by the contractions of the gullet, and is carried to
the stomach, where the shell is no doubt soon dissolved by the
acid gastric juice.

In the Boa and Pythons, fig. 266, the teeth are slender, conical,
bent backward and inward above their base of attachment. The
premaxillary bone in some, ib. 22, is edentulous ; in most it
supports four small teeth; each maxillary bone, ib. 21, has a row

1 The Coluber scaber of Linnagus ; an arboreal serpent of South Africa.

2 Jourdan, in CCXLII. t. vi. p. 160.

394

ANATOMY OF VERTEBRATES.

of larger ones, which gradually decrease in size as they are placed
further back. There are teeth of similar size and proportions in
each premandibular bone. These teeth are separated by intervals,

266

267

Dentition, upper jaw, Python. CCL.

from which other teeth, similar to those in place, have been
detached. The base of each is anchylosed to a shallow alveolus,
extending obliquely across the alveolar groove, of which the outer

is higher than the inner wall.

~

The palatine teeth, ib. 20, are as large as the maxillary, and

are similarly attached. The
pterygoid teeth, ib. 24,
which complete the inter-
nal dental series on the
roof of the mouth, are of
smaller size, and gradually
diminish as they recede
backward. In the inter-
spaces of the fixed teeth
in both of these bones, the
places of attachment of the
shed teeth are always visi-
ble ; so that the dental for-
mula, if it included the
vacated with the occupied
sockets, would express a
greater number of teeth
than are ever in place and
use at the same time.

The smaller non-veno-
mous serpents, Colubridce,
e. g. have two rows of teeth

Roof of the mouth of the Rattlesnake, showing the poison- . -i c £ ±\ j_ i

fangs, 10, 11, and pterygoid teeth, 9. CCL. OU the TOOI OI tllC HlOUtll,

TEETH OF REPTILES.

395

extending along the palatines and pterygoids. The genus Oli-
yodon appears to form the sole exception to this rule. In the
Dryinus nasutus, a few small teeth are present on the ecto-
pteiygoid as well as on the pterygoid.

In Dryophis, Dipsas, and Bucephalus, in which the maxillary
teeth increase in size towards the posterior part of the bone, the
large terminal teeth of the series are traversed along their anterior
and convex side by a longitudinal groove. In the Bucephalus
capensis, the two or three posterior maxillary teeth present this
structure, and are much larger than the anterior teeth, or those of
the palatine and premandibular series. They add materially,
therefore, to the power of retaining the prey, and may conduct into
the wounds which they inflict an acrid saliva ; but they are not
in connection with the duct of an express poison-gland. The
long grooved fangs are either firmly fixed to the maxillary bones,
or are slightly moveable, according to their period of growth.
They are concealed by a sheath of thick and soft gum, and their
points are directed backward. The sheath always contains loose
recumbent grooved teeth, ready to succeed those in place.

In most of the Colubri, each maxillary and premandibular bone
includes from twenty to twenty-five teeth. They are less numerous
in the genera Tortrix and Homalopsis, and are reduced to a still
smaller number in the poisonous serpents, in the typical genera
of which the short maxillary
bone supports only a single
perforated fang.

The maxillary, fig. 268, e,
diminishes in length with the
decreasing number of teeth
which it supports : the ecto-
pterygoid, d, elongates in the
same ratio, so as to retain its
position as an abutment against
the shortened maxillary ; and
the muscles implanted into
the ectopterygoid communicate through it to the maxillary
bone the hinge-like movements backward and forward upon the
ginglymoid articulations connecting that bone with the prefrontal
and palatine bones. As the fully developed poison-fangs are
attached by the same firm basal anchylosis to maxillary sockets,
which forms the characteristic mode of attachment of the simple
or solid teeth, they necessarily follow all the movements of the
superior maxillary bone. When the external pterygoid is re-

268

•Structure of the poison-teeth of the Rattle-snake

396 ANATOMY OF VERTEBRATES.

traded, the superior maxillary rotates backward, and the poison-
fang is concealed in the lax mucous gum, with its point turned
backward, fig. 267, 10. When the muscles draw forward the
external pterygoid, the maxillary bone is pushed forward, and the
recumbent fang withdrawn from its concealment and erected.

In this power of changing the direction of a large tooth, so that
it may not impede the passage of food through the mouth, we may
perceive an analogy between the viper and the Lophius ; but in
the fish the movement is confined to the tooth alone, and is de-
pendent on the mere physical property of the elastic medium of
attachment ; in the serpent the tooth has no independent motion,
but rotates with the jaw, whose movements are governed by
muscular actions. In the fish the great teeth are erect, except
when pressed down by some extraneous force. In the serpent
the habitual position of the fang is the recumbent one, and its
erection takes place only when the envenomed blow is to be
struck.

A true idea of the structure of a poison-fang will be formed
by supposing the crown of a simple tooth, as that of a boa, to
be pressed flat, and its edges to be then bent towards each other,
and soldered together so as to form a hollow cylinder, or rather
cone, open at both ends. The flattening of the fang and its
inflection around the poison-duct commences immediately above
the base, and the suture of the inflected margins runs alono; the

O O

anterior and convex side of the recurved fang, as shown in
fig. 269, A : the poison-canal is thus in front of the pulp-cavity, as
shown in the longitudinal section of the fang, fig. 268, ?/, and
fig. 269, B. The basal aperture of the poison- canal, ib. v, is oblique,
and its opposite outlet v' is still more so, presenting the form of a
narrow elliptical longitudinal fissure, terminating at a short dis-
tance from the apex of the fang. In fig. 268, a fine hair is repre-
sented as passing through the poison-canal by the duct of the fang.

The secretion of the poison-gland is conveyed to the basal aperture
of the poison-canal of the fang. We may suppose, that as the
analogous lacrymal and salivary glands in other animals are most
active during particular emotions, so the rage which stimulates the
venom-snake to use its deadly weapon must be accompanied with
an increased secretion and great distension of the poison-glands ;
and as the action of the compressing muscles is contemporaneous
with the blow by which the serpent inflicts the wound, the poison
is at the same moment injected with force into the wound from
the apical outlet of the perforated fang.

The duct which conveys the poison, although it runs through

TEETH OF KEPTILES.

397

Poison-fangs of A, Viper ; B, Cobra (in section) ;
c, Hydrophis. v.

the centre of a great part of the tooth, is really on the outside of
the tooth, the canal in which it is lodged and protected being
formed by a longitudinal inflection of the deiitinal parietes of the
pulp-cavity, fig. 270, c. This 269

inflection commences a little A

beyond the base of the tooth,
where its nature is readily
appreciated, as the poison-
duct there rests in a slight
groove or longitudinal inden-
tation on the convex side of
the fang, fig. 269, A, B, v ;
as it proceeds it sinks deeper
into the substance of the
tooth, and the sides of the
groove meet and seem to
coalesce, so that the trace of
the inflected fold ceases, in
some species, to be percepti-
ble to the naked eye ; and the fang appears, as it is commonly
described, to be perforated by the duct of the poison-gland. In
the Hydrophis the groove remains permanently open, as in fig.
269, c.

From the position of the poison-canal it follows that the
transverse section of the
tooth varies in form in dif-
ferent parts of the tooth : at
the base it is oblong, with a
large pulp-cavity of a cor-
responding form, with an
entering notch at the ante-
rior surface, fig. 268, c;
farther on, the transverse
section presents the form of
a horseshoe, and the pulp-
cavity that of a crescent, the
horns of which extend into
the sides of the deep cavity
of the poison-fang : a little
beyond this part the sec-
tion of the tooth itself is
crescentic, with the horns obtuse and in contact, so as to circum-
scribe the poison-canal ; and along the whole of the middle four

270

Section of poison-fang of Cobra, rnagn. v.

398 ANATOMY OF VERTEBRATES.

sixths of the tooth, the section, of which a magnified view is given
in fig. 270, shows the dentine of the fang inclosing the poison-
canal, and having its own centre or pulp-canal, p, p, in the form
of a crescentic fissure, situated close to the concave border of the
inflected surface of the tooth. The pulp-cavity disappears, and
the poison-canal again resumes the form of a groove near the apex
of the fang, fig. 269, A, B, v' , and terminates on the anterior surface
in an elongated fissure.

The venom-fangs of the viper, rattle-snake, and the Fer-de-
lance are coated only with a thin layer of a subtransparent and
minutely cellular cement. The disposition of the dentinal tubes
is obedient to the general law of verticality to the external
surface of the tooth ; it is represented as seen in the trans-
verse section from the middle of the fang in fig. 270. Since
the inflected surface of the tooth can be exposed to no other
pressure than that of the turgescent duct with which it is
in contact, the tubes which proceed to the central surface,
while maintaining their normal relation of the ri«;ht ano;le to

C3 C? O

it, are extremely short ; and the layer of dentine separating the
poison-tube from the pulp-cavity is proportionally thin. The
dentinal tubes that radiate from the opposite side of the pulp-
cavity to the exposed surface b of the tooth are disproportionately
long.

The teeth of Ophidians are developed and completed in that
part which forms the original seat of the tooth-germs in all
animals ; viz. the mucous membrane or gum covering the alveolar
border of the dentigerous bones. The primitive dental papilla in
the common harmless snake very soon sinks into the substance of
the gum, and becomes enclosed by a capsule. As soon as the
deposition of the calcareous salts commences in the apex of the
papilla, the capsule covering that part becomes ossified and
adherent to the dentine, and the tooth begins to pierce and
emerge from the gum before its mould, the pulp, is half com-
pleted. Fresh layers of cells are successively added to the base
of the pulp, and converted, by their confluence and calcification,
into the tubular dentine, until the full size of the tooth is
attained, when its situation in the gum is gradually changed,
and its base becomes anchylosed to the shallow cavity of the
alveolar surface of the bone. In the posterior part of the large
mucous sheath of the poison-fang, the successors of this tooth
are always to be found in different stages of developement ;
the pulp is at first a simple papilla, and when it has sunk into
the gum the succeeding portion presents a depression along its

TEETH OF EEPTILES.

399

inferior surface, as it lies horizontally, with the apex directed
backward ; the capsule adheres to this inflected surface of the
pulp ; and the base of the groove of the loose growing poison-
fano; is brought into the same relation with the duct of the

o o

poison gland as the displaced fang, which has been severed from
the duct.

The existing species of Lizards differ from those of Crocodiles
in the anchylosed condition of the teeth, which present few modi-
fications of importance : those that yield most fruit to physiology,
and which have most expanded our ideas of the extent of the

271

Skull of Dicynodon lacerticeps, one third natural size

resources of Nature and the exceptional deviations from what
was deemed the rule of structure in the Saurian dentition,
have been discovered by the study of the fossil teeth of extinct
forms of the order. Amongst these the most extraordinary are
those called e Dicynodonts,'1 from their dentition being reduced
to one long and large canine tooth on each side of the upper
jaw. These teeth recall, at first sight, the character which the
long poison-fangs give, when erected, to the upper jaw of
the Rattle snake. The alveolar border of the lower jaw and of
the premaxillary part of the upper jaw is trenchant, and seems
to have been sheathed with horn. The maxillary, fig. 271,
21, is excavated by a wide and deep alveolus, with a circular
area, and lodges a long and strong, slightly curved, and sharp-
pointed tusk, which projects about two thirds of its length from

1 From Sis, two, and Kvv6Sous, the name given by Hippocrates to the canine teeth,
and signifying the same idea as their common English denomination.

400 ANATOMY OF VERTEBRATES.

the open extremity of the socket ; the two converging, as they
descend along the outer side of the compressed symphysis of
the lower jaw. The tusk is principally composed of a body of
compact unvascular dentine. The base is excavated by a wide
conical pulp-cavity with the apex extending to about one half
of the implanted part of the tusk, and a linear tract is continued
along the centre of the solid part of the tusk.

The enamel is thinner than in the teeth of the Crocodile.
There is a trace of cement on the exterior of the sections of the
implanted base of the tusks. In the lower jaw, ib. 25, 23, the
alveolar border of the dentary element presents a smooth and even
edge, which seems to have played like a scissor-blade upon the
inner side of the corresponding edentulous border of the upper
jaw. In some Dicynodonts (Ptyclioynatlius) the symphysis was
singularly produced upward.

Until the discovery of the Rliynclwsaurus1 and Oudenodon, this
edentulous and horn-sheathed condition of the jaws was supposed
to be peculiar to the Chelonian order among reptiles.2 In the
Saurian Dicynodon we find, superadded to the horn-clad man-
dibles of the Tortoise, a pair of tusks, borrowed as it were from
the mammalian class, or rather foreshadowing a structure which,
in the actual creation, is peculiar to certain members of the
highest-organised warm-blooded animals.

In the other Reptilia, recent or extinct, which most nearly
approach the Mammalia in the structure of their teeth, the dif-
ference characteristic of the inferior and cold-blooded class is
manifested in the shape, and in the system of shedding and suc-
cession, of the teeth: the base of the implanted tooth seldom
becomes consolidated, never contracted to a point, as in the
fangs of most mammalian teeth ; and at all periods of growth
one or more germs of teeth are formed within or near the base
of the tooth in use, prepared to succeed it, and progressing
towards its displacement. The dental armature of the jaws is
kept in serviceable order by uninterrupted change and succes-
sion ; but the matrix of the individual tooth is soon exhausted,
and the life of the tooth itself may be said to be comparatively
short.

The Dicynodonts not only manifest the higher type of free
implantation of the base of the tooth in a deep and complete
socket, common to Crocodilians, Megalosaurs, and Thecodonts,
but make an additional step towards the mammalian type of

1 Transactions of the Cambridge Philosophical Society, vol. vii. part iii. 2 CLVIII.

TEETH OF REPTILES. 401

dentition, by maintaining the serviceable state of the tusk by
virtue of constant renovation of the substance of one and the
same matrix, according to the principle manifested in the long-
lived and ever-growing tusks of the Walrus, and the scalpriform
incisors of the Rodentia.

Naturalists have availed themselves of characteristics of the
dental system to arrange the genera of the squamate Lacertians.
In the first group, the teeth are solid, or without any perma-
nent internal cavity, and are anchylosed by their base to the
alveolar groove. The species which present this character are
called ' Pleodonts.' In the second group, the teeth are excavated,
or retain the pulp-cavity, and are less firmly fixed to the jaws,
being applied vertically, like piles or buttresses, against the outer
alveolar parapet, but not adhering by their base. This group is
called ' Crelodonts.'

The Monitor of South America (Tupinambis teyuixiii) is
an example of the Pleodont group, in which the premaxillary
teeth are ten in number. The maxillary teeth vary from ten
to fifteen on each side, and increase in size as they are placed
farther back : the hindmost teeth are tricuspid in young indi-
viduals, and present the form of simple tubercles in the old
Monitors. The mandibular teeth, fifteen to eighteen in number
in each ramus, correspond in size and form with those above.
In the Coelodont group, the ' Swift lizards ' ( Tachydromus) have
the pterygoid bones armed with minute teeth. The teeth on both
upper and lower jaws are of larger size, and the hinder ones are
tricuspid. The true Lizards (Lacertci) have two kinds of teeth
quoad form ; the anterior small, conical, and recurved : the pos-
terior larger, and bi- or tri-cuspid. Some species have also
pterygoid teeth ; as the common Lacerta agilis.

In the gigantic fossil Sea-monitor of Maestricht (Mosasaurus)
the teeth combine the ' Pleodont ' with the f Acrodont ' characters.
All the teeth are slightly recurved, and their peripheral surface
is smooth : the crown is pyramidal, with the outer side nearly
plane, or slightly convex, and separated by two sharp ridges from
the remaining surface, which forms a half-cone. The larger teeth
are implanted upon the premaxillary, maxillary, and premandibular
bones ; a series of similarly shaped but much smaller teeth are
placed upon the pterygoid bones.

Most of the smooth-scaled Lizards have small mouths and
slender sharp teeth, fitted best for insect food : they are usually
confined to the upper and lower jaws ; but the medicinal Scink of
ancient pharmacy ( Scincus officinalis) has four or five small obtuse

VOL. i. D r>

402 ANATOMY OF VERTEBRATES.

teeth upon each pterygoid bone. The chief exception to the
typical dentition of the present family is made by the large
scincoid lizards of Australia, which, on that account, have received
the generic name of Cyclodus. The dentition of the Cyclodus
nigroluteus is exemplified in the lower jaw, fig. 272. In the upper
jaw, the single premaxillary bone has depressions for twelve teeth,

272

Lower jaw and teeth of Cyclodus nigroluteus. v.

of which only the alternate ones are usually in place ; they are of
very small size, with the fang compressed laterally, and the crown
antero-posteriorly, so as to resemble a true incisor in form, the
summit sloping to an edge from behind forwards, with the middle
of the cutting surface a little produced. Each superior maxillary
bone has depressions for fourteen teeth ; they quickly increase in
size, and exchange their conical for a sub-hemispherical crown ;
the eighth to the thirteenth inclusive are the largest teeth ; they
are set obliquely, and pretty close together. In the lower jaw
there are two small incisors, at the anterior part of each pre-
mandibular bone corresponding with those of the premaxillary ;
these are succeeded by five or six conical teeth, and the rest
correspond in size and form with the tuberculate molars of the
upper jaw. All the teeth are attached, after the Pleurodont type,
by their base and outer margin to shallow depressions on the
outer side of the external alveolar parapet. The germs of the
successional teeth, c, fig. 272, are developed at the inner side of the
base of their predecessors, «, which they excavate, undermine,
and displace in the usual manner.

Certain genera of the Iguanian family of Lizards, e. g. Istiurus,
Lophyrus, Calotes, and Otocryptis, have the teeth soldered, like
those of Mosasaiirus, to the summit of the alveolar ridge, and
thence are called ( Acrodonts : ' in all these lizards the maxillary
and mandibular teeth may be divided into anterior laniary and
posterior molary teeth. In other Iguanians the teeth are lodged
in a common shallow oblique alveolar groove, and are soldered
to excavations on the inner surface of the outer wall of the
groove : these are called ( Pleurodonts.' Most of them possess
pterygoid as well as maxillary teeth : but the following genera,

TEETH OF REPTILES. 403

Hyperanodon, Tropidolepis, Phrynosoma, and Cattisaurus, are

exceptions.

In the Pleurodont Iguanians, the teeth never present the true
laniary form ; and, if simply conical, as at the extremes of the
maxillary series, the cone is more or less obtuse ; but, in general,
it is expanded, more or less trilobate, or dentated along the margin
of the crown. The Amblyrliynclius, a genus remarkable for the
marine habits of at least one of the species (Ambtyrhynchus ater),
whose diet is sea-weed, has the tricuspid structure well developed
in the posterior teeth. The typical genus of the present family
of Saurians (Iguana tuberculata) is characterised by the crenate
or dentated margin of the crown of the maxillary and premandi-
bular teeth, a few of the anterior small ones excepted. The ptery-

teeth are arranged in two or three irregular rows, resembling

o o o o

somewhat the f dents en cardes ' of Fishes. In the full-grown
Iguana tuberculata there are from forty-seven to forty-nine teeth
in both upper and lower jaws. The number is less in young
subjects. The two rows of pterygoid teeth are in close order
on each side. In the horned Iguana (Metopoceros cornutus) there
is a single row of small teeth implanted in each pterygoid bone,
fig. 98, D, 24.

The teeth of the Iguanodon, though resembling those of the
Iguana, do not present an exact magnified image of them, but
differ in the greater relative thickness of the crown, its more
complicated external surface, and in a modification of the internal
structure, by which this huge herbivorous extinct lizard deviates
from every other known reptile.

As in the Iguana, the base of the tooth is elongated, contracted,
and subcylindrical ; the crown expanded, and smoothly
convex on the inner side. When first formed, it is
acuminate, compressed, its sloping sides serrate, and
its external surface traversed by a median longitu-
dinal ridge, and coated by a layer of enamel ; but,
beyond this point, the description of the tooth of the
Iguanodon indicates characters peculiar to that genus.
Three longitudinal ridges, fig. 273, traverse the outer
surface of the crown, one on each side of the median
primitive ridge ; these are separated from each other,
and from the serrated margins of the crown, by four
wide and smooth longitudinal grooves. In the upper jaw the
teeth are less curved, and are thicker transversely to the jaw :
the primary ridge is much more prominent. The marginal ser-
rations present, under a low magnifying power, the form of

I) D 2

404 ANATOMY OF VERTEBRATES.

transverse ridges, themselves notched, so as to resemble the mam-
mil lated margins of the unworn plates of the elephant's grinder.
These ridges or dentations do not extend beyond the expanded
part of the crown : the longitudinal ridges are continued farther
down, especially the median ones, which do not subside till the
fang of the tooth begins to assume its subcylindrical form.

At the earlier stages of abrasion, a sharp edge is maintained at
the external part of the tootli by means of the enamel which
covers, and is restricted to, that surface of the crown. The
prominent ridges upon that surface give a sinuous contour to the
middle of the cutting edge, whilst its sides are jagged by the
lateral serrations. The dentine next the enamel is harder than
the vaso-dentine of the opposite half of the crown. When the
crown is worn away beyond the enamel, it presents a broad and
nearly horizontal grinding surface, and another dental substance
is brought into use to give an inequality to that surface ; this
is the ossified remnant of the pulp, which, being firmer than
the surrounding dentine, forms a slight transverse ridge in the
middle of the grinding surface. The tooth in this stage has
exchanged the functions of an incisor for that of a molar, and is
prepared to give the final compression, or comminution, to the
coarsely divided vegetable matters, such as might be afforded by
the Clathrarice and similar fossil plants, which are found buried
with the lomanodon.

O

In the Crocodilian Monitor ( Varanus bivittatus) the large fixed
compressed teeth, of which there may be about seven in each
upper maxillary bone and six in each premandibular, are anchy-
losed by the whole of their base and by an oblique surface leading
upwards on the outer side of the tooth to a slight depression on
the alveolar surface. The base of the tooth is finely striated, the
lines being produced by inflected folds of the external cement, as
in the Ichthyosaur and Labyrinthodon, but they are short and
straight, as in those of the former genus. The great Varanus,
like the variegated species, manifests its affinity to the Crocodilians
in the number of successive teeth which are in progress of growth
to replace each other ; but, from the position in which the germs
of the successional teeth are developed, the more advanced teeth
iri this species, as in the Varanus variegatus, do not exhibit the
excavations that characterise the same parts of the teeth of the
Enaliosaurs and Crocodiles.

In some extinct Saurians, which, in other parts of their organi-
sation, adhere to the Lacertine division of the order, the teeth were
implanted in sockets, either loosely or confluent with the bony walls

TEETH OF REPTILES. 405

of the cavity : these are termed the ' Thecodoiit ' Lacertians : their
dental character is seen in the oldest known of all Saurians, viz. the
(Protorosaurus of the Thuringian copper-slates), and the PalcRo-
saurus of the dolomitic conglomerates near Bristol. The com-
pressed Varanian form of tooth, with trenchant and finely dentated
margins, which characterised these ancient Lizards, is continued
in the comparatively more recent and gigantic species called Mega-
losaurus. In this terrestrial carnivorous Reptile the teeth, when
first protruded above the gum, presented a double cutting edge of
serrated enamel; the position and line of action were nearly vertical,
and, like the two-edged point of a sabre, the teeth cut equally on
each side. As the tooth advanced in growth it became curved
backward, in the form of a pruning-knife, and the edge of serrated
enamel was continued downward to the base of the inner and
cutting side of the tooth, whilst on the outer side a similar edge
descended but a short distance from the point, and the convex
portion of the tooth became blunt and thick, as the back of a
knife is made thick for the purpose of producing strength. The
strength of the tooth was further increased by the expansion of
its side. ( In a tooth thus formed for cutting along its concave
edgQ, each movement of the jaw combined the power of the knife
and saw : whilst the apex, in making the first incision, acted like
the two-edged point of a sabre. The backward curvature of the
full-grown teeth enabled them to retain, like barbs, the prey
which they had penetrated. In these adaptations we see con-
trivances which human ingenuity has also adopted in the prepara-
tion of various instruments of art.'1

The teeth of the Meyalosaur consist of a central body of
dentine, with an investment of enamel upon the crown, and of
cement over all, but thickest upon the fang. The marginal
serrations are formed almost entirely by the enamel. The remains
of the dentinal pulp are converted into a coarse bone in the com-
pletely formed tooth.

In most Pterodactyles the teeth are of one kind, few and far
apart, fig. Ill, with long, slender, compressed, slightly recurved,
pointed crowns ; but some, from the more ancient secondary
deposits, show, behind a few teeth of the above prehensile
character, a close-set row of small lancet-shaped teeth : such
modification characterises the genus Dimorphodon.

The teeth of the Ichthyosaur have a simple more or less
acutely conical form, with a long and, usually, expanded or

1 Buckland, Bridgewater Treatise, vol. i. p. 237.

1

406 ANATOMY OF VERTEBRATES.

ventricose base, or implanted fang. They are confined to the
premaxillary, maxillary, and premandibular bones, in which they
are arranged in close series, and of nearly equal size. They
consist of a body of unvascular dentine, invested at the base by a
thick layer of cement, and at the crown by a layer of enamel,
which is itself covered by a very thin coat of cement ; the pulp-
cavity is more or less occupied in fully formed teeth by a coarse
bone. The external surface of the tooth is marked by the longi-
tudinal impressions and ridges, but the teeth vary both as to
outward sculpturing and general form in the different species.1
The chief peculiarity of the dental system of the Ichthyosaur
is the mode of the implantation of the teeth : instead of being
anchylosed to the bottom and side of a continuous shallow groove,
as in most Lacertians, or implanted in distinct sockets, as in the
Thecodon, Megalosaur, or Pterodactyle, they are lodged loosely
in a long and deep continuous furrow, and retained by slight
ridges between the teeth, along the sides and bottom of the
furrow, and by the gum and organised membranes continued into
the groove and upon the base of the teeth. The germs of the
new teeth are developed at the inner side of the base of the
old ones.

The best and most readily recognisable characters by which
the existing Crocodilians are grouped in appropriate genera are
derived from modifications of the dental system.

In the Caimans (genus Alligator) the teeth vary in number

18—18 22—22
trom — - to - : the fourth tooth 01 the lower jaw, or

18 — 18 22 — 22

canine, is received into a cavity of the palatal surface of the upper
jaw, where it is concealed when the mouth is shut. In old
individuals the upper jaw is perforated by these large inferior
canines, and the fossa? are converted into foramina.

In the Crocodiles (genus Crocodilus) the first tooth in the lower
jaw perforates the palatal process of the premaxillary bone when
the mouth is closed ; the fourth tooth in the lower jaw is received
into a notch excavated in the side of the alveolar border of the
upper jaw, and is visible externally when the mouth is closed.

In the two preceding genera the alveolar borders of the jaw
have an uneven or wavy contour, and the teeth are of an unequal
size.

In the Gavials (genus Gavialis} the teeth are nearly equal in
size and similar in form in both jaws, and the first as well as the

1 v. pi. 73.

TEETH OF REPTILES.

407

fourth tooth in the lower jaw passes into a groove in the margin
of the upper jaw when the mouth is closed.

In the Alligators and Crocodiles the teeth are more unequal in
size, and less regular in arrangement, and more diversified in
form, than in the Gavials : witness the strong thick conical
laniary teeth as contrasted with the blunt mammillate summits of
the posterior teeth in the Alligator, fig. 275. The teeth of the
Gavial are subequal, most of them present the form of a crown,
shown in fig. 274, long, slender, pointed, subcompressed from
before backward, with a trenchant edge on the right and left
sides, between which a few faint longitudinal ridges traverse the
basal part of the enamelled crown.

In the black Alligator of Guiana the first fourteen teeth
of the lower jaw are implanted in distinct sockets, the re-
maining posterior teeth are lodged close to-
gether in a continuous groove, in which the
divisions for sockets are faintly indicated by
vertical ridges, as in the jaws of the Ichthyo-
saurs. A thin compact floor of bone separates
this groove, and the sockets anterior to it, from
the large cavity of the ramus of the jaw ; it is
pierced by bloodvessels for the supply of the
pulps of the growing teeth and the vascular
dentiparous membrane which lines the alveolar
cavities.

The tooth-germ is developed from the mem-
brane covering; the angle between the floor and

O O

the inner wall of the socket. It becomes in
this situation completely enveloped by its cap-
sule, and an enamel-organ is formed at the
inner surface of the capsule before the young
tooth penetrates the interior of the pulp-cavity
of its predecessor.

The matrix of the young growing tooth Teetll ln clifferent stages of
affects, by its pressure, the inner wall of the
socket, as shown in fig. 275, and forms for itself
a shallow recess : at the same time it attacks
the side of the base of the contained tooth ;
then, gaining a more extensive attachment by
its basis and increased size, it penetrates the large pulp-cavity
of the previously formed tooth, either by a circular or semi-
circular perforation. The size of the calcified part of the
tooth-matrix which has produced the corresponding absorption of

*°™*J!0 £e

^e base partly absorbed

by the pressure of b, the

succession^ tooth ;beiow

which is figured c, the

serm of the next tooth

to follow, v.

408

ANATOMY OF VERTEBRATES.

275

Section of lower jaw, with four alveoli arid teeth, of the black
Alligator, v.

the previously formed tooth on the one side, and of the alveolar

process on the other, is
represented in the ex-
posed alveolus of fig.
275, the tooth a hav-
ing been displaced and
turned round to show
the effects of the stimu-
lus of the pressure. The
size of the perforation
in the tooth, and of the
depression in the jaw,
proves them to have
been,, in great part,
caused by the soft ma-
trix, which must have
produced its effect not
by mere mechanical
force. The resistance
of the wall of the pulp-
cavity having been thus overcome, the growing tooth and its
matrix recede from the temporary alveolar depression, and sink
into the substance of the pulp contained in the cavity of the
fully formed tooth. As the new tooth, ib. c, grows, the pulp of the
old one is removed ; the old tooth itself is next attacked, and,
the crown being undermined by the absorption of the inner sur-
face of its base, may be broken off by a slight external force,
when the point of the new tooth is exposed. The frail remains
of the old tooth are sometimes lifted off the socket upon the
crown of the new one, as in fig. 275, I, when they are speedily
removed by the action of the jaws.

No sooner has the young tooth penetrated the interior of the
old one than another germ begins to be developed from the angle
between the base of the young tooth and the inner alveolar
process, or in the same relative position as that in which its
immediate predecessor began to rise, and the processes of succes-
sion and displacement are carried on, uninterruptedly, throughout
the long life of these cold-blooded carnivorous Reptiles.

From the period of exclusion from the egg, the teeth of the
Crocodile succeed each other in the vertical direction ; none are
added from behind forward, like the true molars in Mammalia.
It follows, therefore, that the number of the teeth of the Croco-
dile is as great when it first sees the light as when it has acquired

ALIMENTARY CANAL OF FISHES. 409

its full size ; and, owing to the rapidity of the succession,, the

cavity at the base of the fully formed tooth is never consolidated.

The fossil jaws of the extinct Crocodilians demonstrate that the

same law regulated the succession of the teeth at the ancient

o

epochs when those highly organised Reptiles prevailed in greatest
numbers, and under the most varied generic and specific modifica-
tions. Of these the most remarkable, in reference to the dental
system, is the Galeosaurus, in which the well-marked differences
of size and shape permit the division of the teeth, in both upper
and lower jaws, into incisors, canines, and molars. This is the
nearest approach to a mammalian type of dentition hitherto ob-
served in the Reptilian class.1

§ 72. Alimentary canal of Fishes. — The cavity, commonly
termed ' abdominal,' which lodges the main part of the alimentary
canal and its appendages, seems to occupy a smaller proportion of
the trunk in Fishes, fig. 276, I, h, i, than in Reptiles, fig. 292,
d> iv, by reason of the slight and gradual contraction of the body
beyond the vent to form the muscular organ of the tail-fin : the
greater and more abrupt contraction of the answerable part in
Reptiles distinguishes it more plainly as the ' tail ' ; the f trunk '
is usually a longer segment of the body than in Fishes. In these,
however, the abdominal cavity commences immediately behind the
head : in most Reptiles a ( neck ' intervenes. In Fishes a thoracic
or pericardial cavity, fig. 276, o, is partitioned off from the fore-
part of the proper abdominal one : and there are in this class
exceptional examples of the shortest abdominal cavity in pro-
portion to the length of the body known in the Vertebrate
province, as e. g. in Gymnotus, fig. 232, in which the abdomen does
not extend into the compartment, b, much beyond the vent,
which is seen near the angle of the cut integument, beneath the
mandible.

The cavity containing the beginning of the alimentary canal is
called the ' mouth.' This, in Fishes, is the common entry and
vestibule to both the digestive, fig. 276, d to g, and the respi-
ratory, ib. t, u, organs ; it is, therefore, of great capacity : and, as
the transmission of the food to the stomach and of the respiratory
currents to the gills is performed by similar acts of deglutition,
the bony arches which surround the mouth are not only large,
but are complicated by a mechanism for regulating the transit
of the nutritious and oxygenating media, each to its respective
locality. The branchial slits, in most Fishes, are provided with

! ccxxm. p. 58, pi. u.

410

ANATOMY OF VERTEBRATES.

denticles and sieve-like plates or processes, fig. 85, 63, to prevent
the entry of food into the interspaces of the gills, and the branchial

276

Digestive organs in situ, Flanirostra.

outlets are guarded by valves which reciprocally prevent the
regurgitation of the respiratory streams back into the mouth.

The necessary cooperation of the jaws with the hyoid arch in
the rhythmical movements of respiration is incompatible with
protracted maxillary mastication ; and, accordingly, the branchial
apparatus renders a compensatory return by giving up, as it were,
the last pair of its arches to the completion of the work which the
proper or anterior jaws were compelled by their services to re-
spiration to leave unfinished : and thus the mouth of typical Fishes
is closed at both ends by dentigerous jaws.1

The first portal to the alimentary tract is usually formed by the
upper and lower jaws, fig. 276, a, b, and their teeth: the Gym-
nodonts are so called on account of their conspicuous manifestation
of this character, fig. 258. In most Fishes the jaws are covered
by the skin, which, in passing into the mouth, takes on the
character of the mucous membrane. In some Fishes the inteffu-

o

ment is folded before passing over the jaws, and the arched
and fortified barrier is preceded by a fosse inclosed by fleshy lips.
The Wrasses (Labridce), Mullets {MugilidcE), and the Carp-tribe
{Cyprinidce) exemplify this character. In Crenilabrus, Chcerops,
and JuliSy the lips are plicated. In Muyil labeosus the thick upper
lip has a transverse fold. In some Cyprinidoz the labial organs
are developed to excess, as, for example, in the genus thence
termed Labeobarbus, in which the lips are not only unusually thick
and fleshy, but the lower one is produced downward like a pointed
beard : it forms a long cone in Monnyrus Petersii. The labiated
Fishes have not, however, so distinct a ' sphincter oris ' as

1 The Mullets ' take in a quantity of sand and mud, and after having worked it
for some time between the pharyngeal bones, they eject the roughest and indigestible
portion of it.' CLXXIV. iii. p. 411.

ALIMENTAHY CANAL OF FISHES. 411

Mammals : nor does the skin, continued from the lip over the jaw,
show so well the character of the ( gum.' Many Fishes, especially
those of the Cyprinoid, Mugiloid, and Siluroid families, have
fleshy and sensitive labial barbs or cirri ; those of the Siluroids
being supported by bony or gristly stems. Tentacles depend
from the rostral prolongation of the Sturgeon, and from the man-
dibular symphysis of the Cod. The Lepidosiren and Cod have
fringed processes or filaments between the teeth and lips, which
seem designed to assist in testing and selecting the food.1 The
lips of most Sharks and Rays are partially supported by labial
cartilages.

The edentulous Sturgeon is compensated by a produced cartila-
ginous snout, with which it upturns the mud in quest of food at
the bottom of the rivers it frequents. The allied Spatularia, in
which a minutely shagreened surface on the jaws represents the
whole dental system, has had the force of dev elopement of subsi-
diary organs of alimentation expended in the production of the
still more remarkable rostrum, fig. 276, ?/, which is broad and flat,
like the mandible of a spoonbill, and is more than half the length
of the entire body. Other modifications and actions of the mouth
Ijave been noticed in the description of the jaws.

The conical lip of the suctorial Myxinoids, fig. 248, sends off
from its anterior expanded border six or eight long tentacula : this
border is fringed by numerous cirri in the Lamprey, fig. 277, the
inner surface of the lips is beset with short branched tentacles in
the Ammocete : the Lancelet has more simple, but highly vascular
intra-buccal processes, fig. 169, </, g, and the vertically fissured
aperture of its mouth is provided on each side with a series of
long slender jointed and ciliated tentacula, ib.y,y, which mainly
tend, by the perpetual vortex they cause in the surrounding
water, to bring the animalcular nutriment within the grasp of the
pharynx, ph, the orifice of which is also surrounded by vibratile
cilia. There is no tongue in this rudimentary fish : that organ is
often absent or very small in the typical members of the Class ;
its basis, the glossohyal, when it projects at all into the mouth, as
in fig. 276, c, is rarely covered by integuments so organised as to
suggest their being endowed with the sense of taste. In Anguil-
lidce the lingual membrane is raised by some adipose and muscular

1 Mr. Couch narrates an instance of a large Cod, in good condition, taken on a
line at Polperro, Cornwall, in which the orbits contained no eyeballs, but were covered
with an opake reticulated skin. So that he felt convinced that ' eyes never had
existed ;' yet the fish was in good condition, and must have depended on the tactile
organs about the mouth for the discovery of its food. xcvm. p. 72.

412

ANATOMY OF VERTEBRATES.

tissue. But the surface of the prominent tongue is generally
callous,, and either smooth and devoid of papillae, or, if the repre-

277

Vertical section of mouth, Lamprey, v.

sentatives of these be present, they are calcified and the tongue is
beset with teeth. It, then, seizes and passes the food on to the
gullet; but the supporting arch of the tongue, fig. 85, 38-40, works
chiefly for respiratory purposes. In the Lamprey, the tongue, fig.
277, d, is more exclusively related to the digestive function than
in higher Fishes : it can be protruded and retracted, like a piston,
when the sucker is attached to the prey ; and it is armed by small
serrate teeth for tearing the flesh. In a few Fishes the integu-
ment of the palate presents that degree of vascularity and supply
of nerves which indicates some selective sense, analogous to taste.
In the Cyprinoids the palate is cushioned with a thick soft
vascular substance, exuding mucus by numerous minute pores,
but more remarkable for its irritable erectile or contractile
property : l if any part of this be pricked in a live Carp, the part
rises immediately into a cone, which slowly subsides ; this peculiar
tissue is richly supplied by branches of the glosso-pharyngeal
nerves : it may assist in the requisite movements of the vegetable
food, as well as add to it an animalising and solvent mucus, whilst
it is undergoing mastication by the pharyngeal teeth. In the
Gymnotus there are four series of branched fleshy processes in the
mouth, one upon the dorsum of the tongue, a second depending
from the palate, and one along each side of the mouth.

The only representatives of a salivary system in Fishes are the
mucous follicles that communicate with the mouth.2 The chief of

1 XCIX.

2 The reddish vascular body, discovered by Retzius (cxxi.) between the basi-

ALIMENTARY CANAL OF FISHES. 413

these, in the Lamprey, open into a pair of membranous pouches,
which discharge the secretion each by a small orifice below the
side of the tongue.1

There are neither tonsils nor velum palati in Fishes : the folds
of membrane behind the upper and lower jaws, of which ( internal
lips' the Sword-fish and Dory afford good examples, seem intended
to prevent the reflux of the respiratory streams of water rather
than the escape of food from the mouth. In the Lepidosiren these
folds or inner lips are papillose and glandular. That of the
upper jaw in the Ray has a marginal fringe.

In the aberrant Dermopteri and Plagiostomi, at the two extremes
of the class, in which there are numerous branchial apertures on
each side, and the respiratory streams do not necessarily enter by
the mouth, the last pair of branchial arches are not metamorphosed
into pharyngeal jaws, and the entry to the gullet is simply con-
stricted by a sphincter ; in the Lepidosiren it is further defended
by a soft valvular fold like an epiglottis.2

The alimentary canal is usually short, simple, but capacious, in
Fishes ; in a few instances, e.g. Branchiostoma (fig. 169, ph, as),
Myxinoids,3 Exocetus, Lepidosiren* it extends in almost a straight
line from the pharynx to the anus : but it is generally disposed in
folds and sometimes in numerous convolutions. In Dermopteri
the stomach is hardly defined : in the rest of the class the alimen-
tary canal is primarily divided into a gastric and an intestinal
portion by the constriction called ( pylorus,' fig. 28 1, c. The gastric
portion is subdivided into ' oesophagus,' ib. a, and stomach, ib. Z>,
the boundary line being more commonly indicated by a change of
structure of the lining membrane than by a cardiac constriction :
the intestinal portion is subdivided into a ( small ' and a 6 large
intestine ; ' the latter usually answering to the ( intestinum
rectum,' and the boundary, when well defined, being a constric-
tion and an internal valvular fold ; but very rarely marked by
an external caecum. From the oesophagus the alimentary canal is
situated wholly or in part in the abdominal cavity, to the walls of
which it is usually suspended by mesogastric and mesenteric
duplicatures of the peritoneal lining membrane of the abdomen.
When not wholly so situated, the part extends beyond the peri-
toneal region into the muscular mass of the tail ; a portion of the

branchials and the sterno-kyoid muscles in Cartilaginous Fishes, and which exists also
in Gadus, Salmo, and some other Osseous Fishes, has been compared to a sublingual
salivary gland: but it is a " vaso-ganglion " like the thyroid.

1 ccxxiv. 2 xxxiu. p. 342, fig. j, d.

3 xxi. Neurologie, tab. iii. fig. 6. 4 xxxm. pi. 25.

414 ANATOMY OF VERTEBRATES.

intestine, for example, lies between the right myocommata and
the haemal spines in the Sole. The peritoneal serous membrane,
which defines the abdominal cavity, extends anteriorly to the
pericardium, from which it is separated by a double apoiieurotic
septum, fig. 276, o : it is continued along the back over the ventral
surface of the kidneys and the air-bladder, when this exists, a little
way beyond the anus, and is reflected upon the alimentary canal,
ib. d, i, the liver, /, /, the spleen, n, the pancreas, k, or its caecal
substitutes, the ovaria or testes, and the urinary bladder, if this be
present. In many Fishes the peritoneum does not form a shut
sac, but communicates with the external surface, by one orifice
(Branchiostoma, fig. 169, od, Lepidosiren, xxxin. pi. 25, fig. 1,
a), or two (Lamprey, Eel, Salmon, Sturgeon, Planirostra,
Chimaera, and Plagiostomes, fig. 352, p, p), situated, except
in the Lancelet, in or near the cloaca : the membrane in the
neighbourhood of these orifices is beset with vibratile cilia.1

o

The peritoneal orifices give exit to the generative products
(milt or roe) in the Lancelet, Myxinoids, Lampreys, Murasnidae,
and Salmonidre, but not in the Lepidosiren and Plagiostomes.
In the Myxinoids, Ammocetes, Sturgeons, Chimaerae and Pla-
giostomes, the peritoneum communicates also with the peri-
cardium.2

The jaws and mouth are subservient in most Fishes to the
respiratory as well as the digestive functions : in the Lancelet,
this community of offices extends through a great part of the
alimentary canal, which is dilated into a capacious sac, and is
richly provided with branchial vessels and vibratile cilia arranged
along transverse linear clefts, by which the water escapes into a
surrounding cavity : (the arrow a extends from the pharynx into
the intestine in fig. 169 :) the oesophageal portion of the alimen-
tary canal is here seen to be longer than the whole gastric and
intestinal portions. In the Cyclostomes lateral diverticula are
derived from the oesophagus and metamorphosed into special
respiratory sacs, communicating by narrow canals both with the
O2sophagus and with the external surface, fig. 315,/", m, h: in other
Fishes the respiratory apparatus is more concentrated and brought
more forward, so as to communicate with the pharynx, and to
leave the ossophagus free for the exclusive transmission of food to
the stomach.

The oesophagus, fig. 279, d, is usually a short and wide funnel-
shaped canal with a thick muscular coat and a smooth epithelial

1 ccxxxiv. p. 360. 2 LXIX. pi. 8.

ALIMENTARY CANAL OF FISHES. 415

lining, more or less longitudinally folded to admit of increased
capacity for the deglutition of the often unmasticated or undivided
food. The muscular fibres are arranged in different fasciculi, the
outer ones being usually circular, the inner ones longitudinal.
Some fasciculi from the abdominal vertebrae are attached to the
oesophagus in the Coitus scorpius.1 The cardiac half of the
oesophagus is characterised by increasing width in most Cyprin-
idce, and by a more vascular or otherwise modified texture in
the Pharyngognathiy Lophobranchii, the Gobioids, Blennies,
Flying-fish, Garfish, and some others. The inner surface of the
oesophagus sends off short processes, papilliform in Box and Ccesio,
obtuse in Acipenser? hard and almost tooth-like in Rhombus xan-
thurus, StromatcBus Jiatola, and Tetragonurus. The inner surface
of the gullet presents longitudinal papillose ridges in Planirostra.
But the most striking peculiarities of the oesophagus are met with
in the Plagiostomes. A layer of grey parenchymatous substance
is interposed between the muscular and inner coats at the cardiac
half of the oesophagus in the Torpedo. Numerous pyramidal
retroverted processes, jagged or fringed at their extremity, project
from the inner surface of the oesophagus in the Dog-fish (Spinax
acanthias),3 and some other Sharks, fig. 278, a. In the great Basking
Shark (Selache) the homologous processes near the cardia acquire
unusual length, dividing and subdividing as they extend inwards,
so that the cardiac opening is surrounded by ramified tufts directed
towards the stomach.4 This valvular mechanism, fig. 278, b, would
prevent the return of such fishes or mollusks as may have been
swallowed alive and uninjured by the small obtuse teeth of this
great Shark. In many Osseous Fishes we may, finally, notice
the communication of the ' ductus pneumaticus ' with the oeso-
phagus, usually by a small simple foramen ; but provided with
special muscles in the Lepidosteus, where it opens upon the
dorsal aspect of the oesophagus, and with a sphincter and cartilage
in the Polypterus, and Lepidosiren, where it communicates like a
true glottis with the ventral surface of the beginning of the
oesophagus. In the Globe-fishes (Diodon, Tetrodoii) the great
air-sac seems to be a more direct developement, as a cul de sac,
of the oesophagus.5 These singular fishes blow themselves up
by swallowing the air, which escapes through a large anterior
oblique orifice into the sac : and this again communicates with

1 xcix. 2 xx. vol. i. p. 126, prep. no. 463.

3 Ib. prep. no. 664. 4 Ib. prep. no. 464. A.

5 Ib. vol. iii. p. 271, pi. 47, preps, nos. 2093—2095.

416

ANATOMY OF VERTEBRATES.

the forepart of the oesophagus by a second orifice much smaller
than the first, and having a tumid valvular margin.

The cardiac orifice of the stomach is occasionally defined by a
constriction, as in the Planirostra and Mormyrus, fig. 280 : but
an increased expansion with increased vascularity and a more
delicate epithelial lining of the mucous membrane more usually
indicate, in Fishes, the beginning of the digestive cavity. The
stomach is a simple and commonly an ample cavity, with a
great disproportion in the diameters of the cardiac and pyloric
orifices ; in the Cornish Porbeagle- Shark, for example, the cardiac
entry will readily admit a child's head, whilst the pyloric outlet
will barely allow of the passage of a crow-quill.

There are two predominant forms of the stomach in Fishes, viz.
the ' siphonal ' and the f caecal.' In the first it presents the form of
a bent tube or canal, as in the Turbot, fig. 287, «, I, Flounder,
Sole, Cod, Haddock, Salmon, fig. 286, a,b, Carp, Tench, Ide, Lump-
fish, File-fish, Lepidosteus, Sturgeon, Paddle-fish, and most Plagio-

278

Alimentary canal of Shark. CCLXVI.

stomes, fio;. 278 : in the second form the cardiac division of the

" O

stomach terminates in a blind sac, and the short pyloric portion is
continued from its right side, as in the Perch, the Scorpaena, the
Gurnards, the Bull-heads, the Smelts, the Whiting, fig. 285, the
Angler, the Pike, the Lucioperca, the Sword-fish, fig. 282, the
Silurus, the Herring, the Sprat, fig. 288, the Pilchard, the
Conger, the Murrena, and the Polypterus, fig. 279. A transi-
tional form, in which the pyloric end is bent so abruptly upon

ALIMENTARY CANAL OF FISHES.

417

279

Stomach arid pan-
creas, Polyptcrun.

the cardiac as to make the coecal character of the latter doubtful,
is presented by the short and capacious stomach of the Burbot, the
Blenny, and the Gynmotus. In the Mormyrus
the stomach presents the rare form of a globular
sac, fig. 280, e. In the siphonal stomach of the
Cyprinida and Balistidcs the pylorus is little if at
all discernible, and the transition into intestine is
gradual. In the Salmon the intestine is indicated
by the pyloric appendages, fig. 286, c: in the
Sharks there is a true pylorus, and in Selache, fig.
278, an interposed pouch. Where the caacal cha-
racter of the stomach is well marked, the length of
the blind end of the cardia varies considerably.
In the Turbot it is wide and short, fig. 287, b :
in the Sand-lance (Ammodytes) it is very large : in
the Polypterus, fig. 279, <?, Conger, and Sword-
fish, fig. 282, it forms almost the whole of the
elongated stomach, the short pyloric portion, fig. 279,/, being
continued from near its commencement : in the equally elongated
stomach of the Pike, the pyloric portion is continued from the
cardiac sac at a little distance from its blind end ; the Herring,
Sprat, fig. 288, Whiting, fig. 285, Gurnard, and Scorprena show
an intermediate position of the pyloric portion, and this is usually
attended with a shorter and wider form of the cardiac caecum.
The pyloric portion is usually slender, fig. 278, c, or conical, figs.
285, 287 ; but it dilates into a wide sac in Saryus and Lophius ;
and forms a small oval pouch in Trachypterus.

In certain Fishes the stomach deviates from the typical forms
either into the extreme of simplicity or the
converse, without, however, attaining in any
species that degree of complexity which
characterises some of the higher-organised
Vertebrates. A proper gastric compartment of
the alimentary canal cannot be said to exist in
the Lancelet : the long caecum, fig. 169, hd, Z,
continued from it just beyond the cardia,
appears to be a simple form of liver. In the higher Dermopteri,
as the Sand-prides, the Myxines, and the Lampreys, as also
in Cobitis and Lepidosiren, the stomach is continued straight
from the o?sophagus to the intestine. I have found the capa-
cious cardiac division of the stomach of the Lophius partially
divided into two sacs ; the unusually wide and short pyloric
portion forming a third sac : there may also be observed a few

VOL. I. E E

280

Stomach and pancreas,
Mormyrus.

418 ANATOMY OF VERTEBRATES.

obtuse processes from the inner side of the cardia in this fish. In
the Gillaroo Trout the ascending or pyloric half of the bent or
siphonal stomach has its muscular parietes unusually thickened,
by which it is enabled to bruivse the shells of the small fluviatile
testaceans that abound in the streams to which this variety of
trout is peculiar.1 The pyloric portion of the stomach is very
muscular in the Indian Whiting (Johnius), and in some species of
Scomber : but the modification which gives the stomach the true
character of a gizzard is best seen in the Mullets (Mugil). The
cardiac portion here forms a long cul de sac ; the pyloric part is
continued from the cardiac end of this at right angles, and is of a
conical figure externally ; but the cavity within is reduced almost
to a linear fissure by the great developement of the muscular
parietes, which are an inch thick at the base of the cone ; and this
part is lined by a thick horny epithelium.2 In the Herring the ductus
pneumaticus of the swim-bladder is continued from the attenuated
extremity of the cardiac end of the stomach, fig. 281, b. In the
Basking-shark the contracted pyloric division of the stomach, figs.
278, c, and 284, fy communicates by a narrow aperture with a
second small rounded cavity, fig. 284, f, which opens by a narrow
pylorus into the short and capacious duodenum, fig. 278, f, 284, g.

Such are the observed extremes of the modifications of the
stomach in Fishes, which it will be seen, therefore, are far from
according with or paralleling those of the dental system. There
is often, indeed, no essential difference of form in the stomach of
a fish with exclusively laniary teeth, e. g. the carnivorous Salmon,
and in that of one with exclusively molar teeth, e. g. the herbi-
vorous Carp. The ./Etobates, whose teeth form a crushing
pavement, has a stomach similar in shape and size to that in the
common Ray, in which every tooth is conical and sharp-pointed.

The inner surface of the stomach presents few modifications in
Fishes : it is usually smooth ; rarely reticulate, as in the Gym-
notus ; still more rarely papillose. The lining membrane is
thrown into wavy longitudinal rugas in the cardiac portion of
the stomach of most Sharks, fig. 278. The gastric follicles are
conspicuous, especially in the pyloric portion of the stomach in
many Fishes, as, e. g., the Gurnards, Blennies, and Lump-suckers.
The circular pyloric valve is commonly well developed, and has
sometimes a fimbriated margin. The solvent power of the gastric
secretion is conspicuously exemplified in Fishes : if a voracious
species be captured after having swallowed its prey, the part lodged
in the stomach is usually found more or less dissolved, whilst

1 xcn. p. 126. 2 xx, vol. i. p. 141. prep. no. 502.

ALIMENTARY CANAL OF FISHES. 419

that which is in the oesophagus may be entire ; and, in specimens
dissected some hours after death, one may observe what Hunter
so well describes, ( the digesting part of the stomach itself reduced
to the same dissolved state as the digested part of the food.'1

The muscular action of a fish's stomach consists of vermicular
contractions, creeping slowly in continuous succession from the
cardia to the pylorus ; and impressing a twofold gyratory motion
on the contents : so that, while some portions are proceeding to
the pylorus, other portions are returning towards the cardia,
More direct constrictive and dilative movements occur, with in-
tervals of repose, at both the orifices, the vital contraction being
antagonised by pressure from within. The pylorus has the power,
very evidently, of controlling that pressure, and only portions of
completely comminuted and digested food (chyme) are permitted
to pass into the intestine. The cardiac orifice appears to have less
control over the contents of the stomach ; coarser portions of the
food from time to time return into the oesophagus, and are brought
again within the sphere of the pharyngeal jaws, and subjected to
their masticatory and comminuting operations. The Fishes which
afford the best evidence of this ruminating action are the Cy-
prinoids, (Carp, Tench, Bream,) caught after they have fed
voraciously on the ground-bait previously laid in their feeding
haunts to insure the angler good sport. A Carp in this predica-
ment, laid open, shows well and long the peristaltic movements
of the alimentary canal ; and the successive regurgitations of the
gastric contents produce actions of the pharyngeal jaws as the
half-bruised grains come into contact with them, and excite the
singular tumefaction and subsidence of the irritable palate, as
portions of the regurgitated food are pressed upon it. The
shortness and width of the oesophagus, the masticatory me-
chanism at its commencement, and its direct terminal con-
tinuation with the cardiac portion of the stomach, relate to the
combination of an act analogous to rumination, with the ordinary
processes of digestion, in all Fishes possessing those concatenated
and peculiar structures. Sometimes the Fishes, as, for example,
the Sturgeon, the Paddle-fish, the Dog-fish, and the Selache,
whose oesophagus is best organised to prevent regurgitation from
the stomach, are devoid of the pharyngeal jaws and teeth.

Fishes disgorge the shells and other indigestible parts of their
food : and when hooked or netted, sometimes empty their stomach
by an instinctive act of fear, or to facilitate escape by lightening
their load.

1 xcii. p. 120.

E E 2

420

ANATOMY OF VERTEBRATES.

The intestinal canal is shorter in Fishes generally than in the
higher Vertebrates: in the Dermopteri,Plagiostomes, Holocephali,
Sturioniclae, Paddle-fish, fig, 276, / to z, the Lepidosiren,1 the
Flying-fish, the Loach, the Garpike, the Wolf-fish, the Salmon,

281

Abdominal viscera, Herring, cxvi.

282

the Herring, fig. 281, and the apodal fishes, it is shorter than the
body itself: in some of the above-cited examples the intestine
extends in a straight line from the pylorus to the anus, fig. 281,
<?, e, f; in most fishes it presents two or three folds ; the Sun-fish
( Orthagoriscus) shows about six longitudinal ones : the intestine
is sinuous in the Sword-fish, fig. 282, et f\ concentrically and
subspirally wound in the Mullet, in which the convolutions are
numerous and form a triangular mass ; and it is in this fucivorous
fish, in the Chaetodonts, and the Carp-tribe, that the intestinal
canal attains its greatest length in the present class.

With a few exceptions, of which the
Dermopteri and the Lepidosiren are
examples, the intestines are divided
into ( small,' and ( large.' The begin-

* ~ o

ning of the small intestine, to which is
arbitrarily given the name of f duode-
num,' fig. 278, i, fig. 281, c, e, is usually
wider than the rest of that division
of the canal : it receives the ducts of
the liver and pancreas ; and, in most
Osseous Fishes, that of the creca, fig.
281, d, which are usually termed, from
their communication with, or develope-
ment from, the commencement of the
small intestine, f appendices pyloricae.'
The termination of the small intestine
is commonly marked by a circular
valve. In the Bogue- bream (Box

1 xxxm. pi. 25. figs. 1 and 2.

Diagram of digestive organs, .V///7<mx.
xxvi n.

ALIMENTARY CANAL OF FISHES. 421

vulgaris) and the Flounder, there is a small crecal process at
the commencement of the large intestine ; there are two short
caeca at the same part in Box Salpa.1 The large intestine is
usually short and straight in Fishes, answering to the rectum
of higher animals,, fig. 282, f,y. In some Fishes, e. g., Salmo,
Clupea, Esox, Anableps, Anarrhichas, and the Gymnodonts, it
preserves the same diameter as the small intestine, and the
term ( large ' becomes arbitrary : in Gasterosteus, Centriscus, Ostra-
cion, Balistes, and Syngnathus, it is even narrower than the
( small intestine ; ' but most commonly it is wider, as in the
Percoid family, the Gurnards (Triylidce), the Breams (Sparidae),
Scicena, Scomber, Coitus, Labrus, Pleuronectes, Gadus, Lophius,
Cyclopterus, the Siluridce, the Plagiostomi, and the Planirostra,
fig. 276, h.

The tunics of the intestinal canal consist in Fishes, as in other
Vertebrates, of the peritoneal or serous, the muscular, and the
mucous coats, with their intervening cellular connecting layers,
and the epithelial lining; the muscular and mucous coats are
commonly thicker and of a coarser character than in the warm-
blooded classes ; pigmental cells are not unfrequently developed
in the serous coat; the epithelial scales of the intestine of the
Lancelet support vibratile cilia.

The muscular fibres are arranged in a thin outer longitudinal and

O CJ

a thick inner circular stratum (Sturgeon) ; 2 the elementary fibres
in general present the smooth character of those of the involun-
tary system ; but Reichert 3 has detected the transversely striated
fibre in the muscular tunic of the whole tract of the intestine
in the Tench.

The mucous membrane presents numerous modifications, some
of them more complex and remarkable than in any of the higher
Vertebrates. It is commonly thick and glandular, and always
highly vascular. In the small intestines it presents, in some
Fishes (Cod), 4 a smooth and even surface ; in some it is
produced into obliquely longitudinal or wavy folds ; 5 in the
Herring it presents feeble transverse rugae ; in many Fishes it is
reticulate, as in the Wolf-fish 6 and Murcena ; 7 this character is
present in the peculiarly thick and parenchymatoid mucous tunic
of the small intestine of the Sturgeon, where the larger meshes
include irregular spaces, subdivided into smaller cells.8 In a few
Fishes the mucous membrane is coarsely villose or papillose. In

1 xxxm. t. vi. pp. 624, 270. 2 xx. vol. i. p. 200, preps, nos. 637, 639. 3 xcm. p. 26.
4 xx. vol. i. p. 199, prep. no. 633. 5 Ib. Turbot, prep. no. 634, Salmon, prep. no. 635.
6 Ib. prep. no. 630. 7 Ib. prep. no. 631. 8 Ib. prep. no. 638.

422 ANATOMY OF VERTEBRATES.

Orthagoriscus it is both reticulate and villous, the villi being1

o * o

longest at the beginning; of the canal. There is often a well-

O CJ CJ

marked difference in the character of the lining membrane of the
small and large intestines : thus, in the Salmon, the rugre become
fewer, larger, and less oblique as they approach the rectum ; the
commencement of this intestine is marked by a large transverse
fold or circular valve, which is succeeded by several others less
produced, and resembling the valvulas conniventes in the human
jejunum.1 The straight ' large intestine,' which is relatively
longer in the Amia, Polypterus, Paddle-fish, fig. 276,/i, z, Sturgeon,
and Chima3ra3, is characterised by the continuity of such transverse
folds as those in the Salmon, producing an uninterrupted spiral
valve of the mucous membrane. In the Lepidosiren the entire
tract of the straight and short intestine is traversed by this pecu-
liarly piscine extension of the inner coat.2 The spiral valve
characterises the large intestine, fig. 278, k, in all the Plagiostomes,
and establishes the essential difference between the short and
apparently simple intestinal canal of these cartilaginous fishes, and
that of the low-organised Myxiiioid species.

The true homologue of the small intestine is extremely short in
the Plagiostomes ; it is narrow in the Rays, expanded and some-
times sacciform, fig. 284, g, in the Sharks, where it seems to form
the commencement of the suddenly expanded large intestine :
this is straight, and though constituting the chief extent of the
intestinal canal, it is very short in proportion to the body ; not
exceeding, for example, one eighth of the entire length of the
body in the Alopias or Fox-shark. The economy of space in
the abdominal cavity is, however, effected at the expense of the
serous and muscular coats, not of the mucous membrane. The
required extent of secreting and absorbing superficies is gained
by raising or drawing inwards, from the intestinal parietes, the
mucous membrane in a broad fold at the beginning of the large
intestine, and continuing it in spiral volutions to near the anus.
The coils may be either longitudinal and wound vertically about
the axis of the intestinal cylinder, or they may be transverse to
that axis. In the first case, when the gut is slit open lengthwise,
the whole extent of the fold may be uncoiled and spread out as a
broad sheet ; and, if the gut be divided transversely, the cut
edges of the valve present a spiral disposition, as in fig. 283.
The longitudinal form of the spiral valve may be seen in the
squaloid genera Carcharias, Scoliodon, Galeocerdo, Thalassorliinus,

1 xx. vol. i. p. 199, prep. no. 635. 2 xxxm. p. 343, pi. 25, fig. 2.

ALIMENTARY CANAL OF FISHES.

423

283

284

and Zygcena.1 In the second and more common modification, the
fold of mucous membrane is disposed in close
transverse coils, as shown in the longitudinal
section of the Selache's gut, fig. 284, h ; and a
transverse section exposes only the flat surface of
one of the coils. In the Fox-shark (Alopias
Vulpes) ; the valve describes thirty-four circuni- spiral vaive,
gyrations within seven inches' extent of the
intestine ; the mucous membrane is minutely honeycombed : a
few scattered fibres of elastic or involuntary muscular tissue may
be traced in the vasculo-cellular
layer included within the mucous
fold, and they form a slender band
within the free border of the valve,
retaining much elasticity in the dead
intestine, and drawing that border
into festoons. Besides Selache, fig.
284, h, and Alopias, the spiral valve
is transverse in Galeus, Lamna, and
all the Dog-fishes (ScylliidcR and
Spinacida). The trunk of the ' arteria
meseraica intestinalis,' and that of
the corresponding veins of the longi-
tudinally convoluted valve, run along
its free thickened border, and the
vein quits its commencement to join
the vena portae : 2 the arterial and venous trunks of the trans-
versely spiral valve are external to the gut.

One may connect the peculiarity of the spiral valve with the
necessity for reducing the mass and weight of the abdominal
contents in the active high-swimming Sharks, which have no
swim-bladder : the essential part of an intestine being its secern-
ing and absorbing surface, we see in them the requisite extent of
the vasculo-mucous membrane packed in the smallest compass, and
associated with the least possible quantity of accessory muscular
and serous tunics, by the modifications above described. Analogous
ones exist, however, in other Plagiostomes, and in the Lamprey,
to which the above physiological explanation will not apply ; and
the spiral valve is associated with the air-bladder in some of the
highly organised Ganoids, and in the Lepidosiren. Nevertheless,

1 XL vi. t. iv. p. 314 ; t. xcvi. p. 277, pi. 2 and 3. See also, xx. prep. no. 645 ;
probably from Scoliodon.

2 Duvernoy, xcvm. p. 274, pi. 10.

Spiral valve, Selache. CCLXVI.

424 ANATOMY OF VERTEBRATES.

it is to be remarked that the intestinal canal is shortest, and
the spiral valve most complex and extensive, in the Sharks.
In both these and the Rays, the valve subsides at a short distance
from the anus ; and into the back part of this terminal portion of
the rectum an elongated crccal process with a glandular inner
surface opens fig. 352, i. The anus itself communicates with the
fore part of a large cloacal cavity in the Plagiostomes. In other
Fishes, where it opens distinctly upon or near the external surface,
it is anterior in position to the orifices of oviducts, or sperm-
ducts, fig. 281, f, and of the uterus or urinary bladder; the
Lepidosiren has the peculiarly ichthyic arrangement of the anal,
genital, and urinal outlets.1

In the Dermopteri the intestinal canal is rather closely attached
to the back of the abdomen, though the primitively continuous
mesenteric fold becomes reduced in the Lampreys to filamentary
processes accompanying the mesenteric vessels. A similar reduc-
tion of the mesentery to detached membranous bands occurs in
the Syngnathi and Cyprinidse. The mesentery is entire in the
Lepidosiren, the Plagiostomes, and many other Fishes : it is
usually single and continuous from the stomach to the end of the
intestine : there are two parallel mesogastries in the Eel, and a
kind of omental accumulation of adipose matter is sometimes
found alons; the ventral surface of the intestines : a second mesen-

o

tery is continued from this part of the intestine to the ventral
parietes of the abdomen in the Murrena.

The position of the cloacal outlet varies much in Fishes : in
some of the jugular species it follows the ventral fins to the
region of the throat ; and in the apodal Gymnotus, fig. 232, it is
placed so far forward as to remind us of the position of the
excretory outlet in the Cephalopods. It is beneath the pectorals
in the Amblyopsis spel&us : but the more normal posterior position
of the vent obtains in most abdominal and all cartilaginous
Fishes.

Petrified faeces or ( coprolites ' give some insight into the struc-
ture of the intestinal canal in extinct species of Fishes : some
that have been found in the skeleton of the abdomen of the
great Macropoma of the Kentish Chalk, and detached coprolites
associated with the scales and bones of the more ancient
Megalichthys, indicate by their exterior spiral grooves that these

1 xxxin. pi. 25, fig. 1, m, n, o, I. The Branchiostoma offers no exception to this
rule ; the opening by which the ova and semen are expelled is a common peritoneal
outlet.

LIVER OF FISHES. 425

ancient Ganoids, like their modern representative, the Poh/pterus,
possessed the spiral valve.

§ 73. Liver of Fishes.- -The liver makes its first appearance
in the lowest vertebrated, as in the lowest articulated, species,
under the form of a simple ca3cal production from the common
alimentary canal. Commencing in the Laucelet, fig. 169, lid,
a little beyond the orifi.ce py, the hepatic caecum, /, extends
forward from its place of communication with the canal ii, and
terminates in a blind end. In the Myxinoids the liver, as in
all higher Fishes, fig. 282, a, is a well-defined conglomerate, or
acinous, parenchymatoid organ, with a portal and an arterial
circulation, with hepatic ducts, and generally a gall-bladder and
cystic duct, ib. c, by which the bile is conveyed to the duodenum,
from which the stomach is divided by a pyloric valvular ori-
fice. l

The texture of the liver is soft and lacerable ; its colour usually
lighter than in higher Vertebrates, being whitish in the Lophius,
and in many other Fishes of a yellowish grey or yellowish brown:
it is, however, reddish in the Bream, of a bright red in the
Holocentrum orientale, orange in Holocentrum hastatum, yellow in
Atherina presbyter, green in Petromyzon marinus, reddish brown
in the Tunny, dark brown in the Lepidosiren, almost black in
the Paddle-fish. In the Siluridce a portion of the liver, usually
forming a middle lobe, thinner than the rest and of a lighter
colour, has been described as the ' pancreas : ' it has a distinct
duct, opening near that of the ductus choledochus. In most Fishes
the liver is remarkable for the quantity of fine oil in its substance,
under which form almost the whole of the adipose matter is there
concentrated in the Cod tribe, the Rays, and the Sharks.2 Fishes
which, like the Salmon and Wolf-fish, have oil more diffused
through the body, have comparatively little oil in the liver.

The liver is generally of large proportional size : it is attached at
the fore-part of the abdomen to the aponeurotic wall partitioning
off the pericardium, fig. 276, I, o, and extends backward, with a
few exceptions, further on the left than on the right side : in the
Carp, the Bream, and the Stickleback, the right lobe is longest.
Its shape varies with that of the body or of the abdominal cavity ;
it is broadest, for example, in the Rays, longest in the Eels ; not,

1 The Bream is the only fish in which I have found the cystic duct terminating
directly in the stomach.

The myriads of Dog-fish captured and commonly rejected on our coasts show
that the fishermen have not yet taken full advantage of this anatomical fact, which
exposes to them an abundant source of a pure and valuable oil.

426 ANATOMY OF VERTEBRATES.

however, elongated in the Gymnotus, in which apodal fish, by
reason of the peculiar aggregation of the organs of vegetative
life in the region of the head, the liver is divided into two short

o

and broad lobes connected by a transverse lobule. The liver
consists of one lobe in most Salmonoid and Lucioid Fishes, in
the Gymnodonts and Lophobranchs, in the Mullets, Loaches,
and Bullheads. It is long and simple in the Lamprey and
Lepidosiren ; long and bilobed in the Conger. The Lump-fish
has a lobulus besides the chief lobe, which is round and flat.
There is a short thick convex lobe to the right of the long left
lobe in the Lophius. In many Fishes the two lobes are subequal :
they are rarely quite distinct, as in the Myxinoids ; but commonly
confluent at their base, as in the Wolf-fish, or connected by a
short transverse portion, as in most Sharks, the Siluroids, the
Polypterus, the Dory, the Coryphene, the Chastodonts, and the
Cod tribe. In the Whiting the two chief lobes extend the whole
length of the abdomen ; in the Shark about half the length,
fig. 352, b (in which the left lobe is cut away). The liver is
trilobed in the Corvina, the Clupeoid, and the Cyprinoid Fishes :
in many of the latter family it almost conceals the convoluted
intestinal canal. The broad and flat liver of the Raiida3 is tri-
lobed. The liver is much subdivided in the Sandlaiice and in
the Tunny, in which latter fish it presents remarkable modifica-
tions of the vascular system.1 There are few well-established
exceptions to the general rule of the presence of a gall-bladder
in the class of Fishes. My dissections confirm the statement of
its absence in the Lump-fish by Cuvier2 and Wagner.3 Cuvier
did not detect a gall-bladder in Lates niloticus, Holocentrum Sogho,
Sphyrcena Barracuda, Trigla lyra, Trigla cuculus, Corvina dentex,
Glyphisodon saxatilis, Lepidopus argenteus, Labrus turdus, Ammo-
dytes, and Echineis remora. The gall-bladder is wanting in the
Ammocete and Lamprey, but exists in the Myxinoids ; it is absent
in Pristis, Zygcena, and Selache, but is present in Galeus, and
others of the Shark tribe. The rich series of observations
recorded by Cuvier4 and his able Editors5 on the gall-bladder
and gall-ducts in Fishes have not afforded a clue to the law of
the developement of the special receptacle of the biliary secretion
in Fishes. The pouch in which the aggregated hepatic ducts
terminate in the Selache maxima may compensate for the absence
of the gall-bladder in that Shark ; these ducts are enclosed in a
broad flat band of dense cellular tissue, fig. 284, /, which passes

1 cm. 2 xii. t. iv. p. 551. 3 XLVII.

4 xxin. passim. 5 xii. t. iv. pt. ii. p. 559-569.

LIVER OF FISHES. 427

obliquely down in front of the stomach as far as the duodenum,
when each of the ducts opens by a separate oblique orifice into a
common cavity, ib. m, of an oval form, communicating with the
duodenum by a single opening.

The gall-bladder is usually situated towards the fore-part of
the liver, and attached to the right lobe when this exists, as in
fig. 276, m. In some Cyprinoids and Rays, and in the Sturgeon,
it is imbedded in the substance of the liver. In many Chsetodonts
and Salmonoids, in the Sword-fish, fig. 282, c, in the Eel and the
Muraena, it hangs freely at some distance from the liver. I found
the gall-bladder three inches from the liver in a Lophius of two
feet in length. The size of the gall-bladder varies in different
Fishes ; it is very small in most Rays : in Osseous Fishes it
usually bears a direct relation to that of the liver itself. It is
pyriform in the Lophius, Mullet, Sea-perch (Sebastes), Pike,
Sturgeon, Planirostra, and most other Fishes : it is subspherical
in the Grey-shark ( Galeus), and in the Wolf-fish : it is like a
long-necked flask in Polypterus ; is bent like a retort in Xiphias,
ib. c : and is remarkably long and slender in Scicena, Upeneus,
Lates nobilis, and in the Bonito, the Tunny, and other Scombridce.
The bile is sometimes conveyed to the gall-bladder, fig. 291, c, by
hepato-cystic ducts, ib. d, d, and thence by a cystic duct, ib. e, into
the duodenum (Wolf-fish, Erythrinus, Lepidosiren) : or it passes at
once to the intestine by a single hepatic duct, formed by the union
of several branches from the liver (Zi/ace?ia, where the duct is very
long) : or by two hepatic ducts opening separately into the intestine,
as in Pristis : or an hepatic duct from the left lobe joins a cystic duct
from the bladder, receiving the gall from the right lobe, and the
secretion is conveyed by a ' ductus comniunis choledochus ' into the
duodenum, as in Pimelodus : or the bile is conveyed to the duode-
num partly by a cystic duct and partly by a distinct hepatic^duct,
as in the Salmon, in which the latter dilates before it terminates.
In the Lophius three hepatic ducts join the very long cystic, which
duct sometimes dilates where it receives them. In the Sword-
fish three or four hepatic ducts communicate with the cystic,
to form the ductus communis, fig. 282, b. In the Turbot there
are more numerous hepatic ducts, some of which communicate
with different parts of the cystic duct, and four open into the
dilated termination of the ductus communis.1 In the Galeus the
cystic duct runs some way through the substance of the liver, and
sometimes between the tunics of the pyloric canal of the stomach,

1 xx. vol. i. prep. no. 811 A.

423

ANATOMY OF VERTEBRATES.

285

before it enters the commencement of the wide intestine, near the
beginning of the spiral valve. The gall-duct in the Sturgeon and
Planirostra terminates at a greater distance above the valvular
intestine. The ordinary position of the entry of the bile into the
alimentary canal in Osseous Fishes is at the commencement of the
small intestine near the pylorus. The terminal part of the gall-
duct is usually slightly expanded, fig. 291, e, and its orifice is often
supported on a papilla, as in the Sturgeon, the Skate, and the
Labrax lupus.

§ 74. Pyloric Appendages and Pancreas of Fishes. - - In most

Osseous Fishes the intestine
buds out at its commencement
into long and slender pouches,
or ca3ca, fig. 281, d, into which
it appears that the food does
not enter, and which, there-
fore, increase the direct secre-
ting surface of the alimentary
tract, over and above the ex-
tent of the mechanism for
pounding and propelling the
chyme, or of the vascular sur-
face which selects and absorbs
the chyle. By a very gradual
series of changes of these caecal
processes, within the limits of
the class of Fishes, they be-
come massed into a body, fig.
282, d, like the conglomerate
gland, called ' pancreas' in Man.
The secretion of the rudimen-
tal representatives of this gland
is so like the fluid which the
ordinary mucous surface of the
intestine eliminates and sets
free from its capillary system,
that conditions of the ordinary
alimentary tract exist in some
Fishes which render needless

Alimentary canal of the Whiting (Merlanrjusvulgaris), {he deVelopemCnt of tll6 Sp6-
showiug the pile of casca around the pylorus, ccxxxi. . ™,

cial accessory surfaces. JLne

Dermopteri show no trace of pancreas ; their whole digestive
canal is simple : the organisation for which that canal is the

PYLORIC APPENDAGES OF FISHES.

429

commissariat is the most simple in the Piscine class. The
Lamprey, at the head of the Dermopterous order, derives from
the slight spiral extension of its intestinal mucous coat the

286

Portion of the alimentary canal of the Salmon (Salrno salar), showing one double row of caecal
appendages and portions of the other, ccxxxi.

required concomitant complexity of the digestive canal. In
several Osseous Fishes, either the inactive nature of the species,
or the extent or special modifications (the long intestine and
glandular palate of the Carp, the thickened mucous membrane

430

ANATOMY OF VERTEBRATES.

287

of the duodenum of the Eel, for example) of the ordinary tract
of the alimentary canal, render unnecessary the presence of a

pancreas. Thus there is
no caecal production of the
duodenum in the Ambas-
sis, Wolf-fish, Warty Agrio-
pe, nor in most Labroids,
Cyprinoids, Lucioids, Silur-
oids, nor in the apodal Mala-
copteri, nor in the Lopho-
branchs and Plectognats ; nor
in the genera Antennarius,
Malth&us, and Batrachus.
The pancreas is represented
by a single pyloric caecum
in the Sandlance and Poly-
pterus, fig. 279, k: by two
caeca in most Labyrinthi-
branchs, in many species of
Amphiprion, in the Lophius,
the Turbot, fig. 287, and
the Mormyrus, fig. 280, k :

Pyloric caeca of the Turbot (Rhombus maximus). ccxxxi. , , . '

by three caeca in the Perch,

the percoid Popes (Acerina), the Asprodes, and Diploprions : of
from four to nine caeca in the genus Cottus : of from five to nine

caeca in the ffenus Trinla :

288 « •

of six caeca and upwards in

Scorjxzna and Holocentrum :
of nine caeca in the Sprat,
fig. 288 : and so on, increas-
ing to a numerous group of
pendent pyloric pouches, as
we find in the Scomberoids,
Chaetodonts, Gadoids, fig.
285, Halecoids, fig. 286,
Cyclopterus, and Lepidos-
teus. There is a difference,
however, worthy of note, in
the mode and extent of at-
tachment of these numerous
caeca: in the Salmon, fig. 286, Herring, fig. 281, d, Sprat, fig.
288, and Haddock, they rank almost in a line along the whole
duodenum : in the Gymnotus, Lump-fish, and Whiting, fig.

Pyloric cseca of the Sprat (Clupea sprattus)

PYLORIC APPENDAGES OF FISHES. 431

285, they form a circular cluster around the distal side of the
pylorus. Even in the longitudinally arranged caaca the principle
of concentration dawns ; thus the fifty pan- 289

creatic caeca of the Pilchard communicate
with the duodenum by thirty orifices : but
the fifty attenuated terminal blind sacs in
the pancreas of the Lump-fish unite, reunite,
and discharge their secretion bv a circle

O «/ One of the four bunches of

of six orifices around the duodenal side of pyloric appendages of the

. Whiting, isolated; showing

the pyionc valve. In the Tunny a more their union and reunion to

,,..,,, , n . form a single tube, ccxxxi.

subdivided bunch ot pancreatic caeca empty

themselves by five orifices : in the Whiting about one hundred
and twenty peripheral caeca progressively unite into four groups
or bunches, fig. 289, communicating, each by a single duct, with
the duodenum : in the Sword-fish, fig. 282, J, a more compact
gland-like mass pours its secretion into the gut by two orifices, e :
and, finally, in the Sturgeon and Paddle-fish, fig. 276, k, by a
single opening of what now becomes the short and wide duct of
the gland. The interposition of cellular tissue binding together
longer, more slender, and more ramified caeca, with a concomitant
increase of the vascular supply, and a common covering or
capsule, finally converts the accessory intestinal growths into a
parenchymatous conglomerate gland, as we see in the Sword-fish,
Sturgeon, Holocephali, and Plagiostomes ; the papilliform ter-
mination of the duct of such a pancreas is shown in the Selache,
at fig. 284, i. It sometimes exceeds the liver in weight.

The existence of this developed form of secreting organ, over
and above the spiral intestinal valve, may relate to the high
organisation of these Cartilaginous Fishes, and to the great
developement of the organs of locomotion, occasioning the neces-
sity for rapid and complete digestion. But if we compare the
few existing species of heavily laden Ganoid fishes, we shall
again find good evidence of the compensation for a pancreas by
the extension of the intestinal mucous membrane within the
canal, the circumstances calling for a more complete developement
of the digestive system in the predatory Sharks and large-
finned Rays not being present. Thus the Polypterus, which has
a spiral intestinal valve, has only one short pyloric caecum,
fig. 279, A; whilst the Lepidosteus, which has no spiral valve,
has a compact group of above a hundred small caeca, which unite
and reunite to communicate by a few apertures with the com-
mencement of the duodenum.

The inner or mucous surface of the pyloric caeca is laminated

432

ANATOMY OF VERTEBRATES.

in some Fishes : in others it is villous, with orifices of crypts at the
basal intervals of the flattened villi : in the Herring, fig. 290, the
surface is minutely honeycombed ; the cells or crypts being about
Y^-Q of an inch in diameter, and each is filled with a mass of
epithelial cells, as seen in the section B, fig. 290. The basis of

290

291

Crypts of pyloric cseca, Herring, ccxxxi.

Pancreas (/) of a Flounder, ccxxxn.

the crypts is fibrous and projects between and often beyond the
level of their openings. The masses of epithelium resemble one
of the stages of the contents of the ultimate follicles of the
pancreatic acinus of a Mammal. The relation, however, of the
pyloric appendages of the Fish to that of the pancreatic gland of
the higher Vertebrates may be but one of analogy.

There is a minute, but more constant glandular body present
both in fishes which possess {Salmo, Gadus, Perca) and those
that do not possess (Platessa, Belone, Brama, e.g.) the pyloric
creca. It is too small, fig. 2 9 l,f, for the performance of the pan-
creatic function in digestion ; but the contiguity of the terminal
dilatation of the duct, ib. g, with that of the ductus choledochus,
ib. e, and of their respective openings into the duodenum, suggests
that this glandule may be the rudimental homologue of the
pancreas of air-breathing Vertebrates.

In the Lepidosiren the body imbedded between the muscular
and serous coats of the stomach, and referred to as probably
' splenic ' incxLV. p. 271, sends its secretion by ducts converging
to one canal which opens beyond the pylorus, close to the orifice
of the hepatic duct.1

1 According to ccxxxni. p. 10.

ALIMENTARY CANAL OF REPTILES.

433

292

§ 75. Alimentary canal of Reptiles.- -The cavity containing, as
in Fishes, the alimentary
canal, with the kidney sand
principal organs of gene-
ration, also lodges in Rep-
tiles, fig. 292, the heart, «,
b, c, and kings, h, i. In
most the whole cavity is
lined by the peritoneum,
which is reflected upon the
several viscera. In the
transverse section of the
cavity, fig. 293, the thick
line diagrammatically
shows the peritoneum re-
flected from the vertebral
centrum upon the aortal
and caval trunks, h, the
spleen, I, and stomach, a,
whence it is continued to
form the omeiital fold, e, c :
from the ventral surface
the peritoneum is reflected
at one small part upon the
remains of the umbilical
vein, forming the so-called
6 falciform,' g, and ' round,'
d, ligaments of the liver.
In the Crocodilia the peri-
toneum does not extend forward beyond the stomach and liver,
but is reflected upon the posterior (sacral) surface 293

of both organs,1 circumscribing a smaller ' abdo-
minal' cavity, and including fewer viscera, than in
Mammals.

In female Reptiles, the serous membrane of
the abdomen is continuous with the mucous mem-
brane of the oviducts ; the subhexagonal or poly-
gonal flattened cells of its epithelium giving place
to the ciliated epithelial cells at the margin of the
oviducal aperture. In both male and female
Chelonia, the peritoneum is continued, as an in- Transverse section of
fundibular canal, into the ' corpus cavernosum'

Abdominal cavity and viscera, Draco volans. CCL.

the abdominal cavity,
Lizard, ccxxxv.

VOL. I.

1 ccxxxvi. vol. ii. p. 336.
F F

434

ANATOMY OF VERTEBRATES.

294

of the penis ! and clitoris : in the Crocodilia, besides com-
municating with that structure, the peritoneal canals open out-
wardly upon papillae, situated on each side of the base of the
penis 2 and clitoris. These are the exceptions, in the reptilian
class, to the typical character of the peritoneum as a closed
( serous ' sac. In most Reptiles pigmental cells are blended with
or supersede the ordinary tessellated lining of epithelial cells in
certain parts of the peritoneal surface.

The mouth in Reptiles gives passage to respiratory currents
as well as to the food in the Perennibranchiates, and in all
the air-breathers along that extent of the cavity which is poste-
rior to the palato-nares, fig. 294, B, h : the Crocodilia alone
having the nasal distinct from the oral passage.

In Chelonia, the jaws
with their horny covering
form, as in Gymnodont
fishes, the first portal to
the alimentary canal : in
many Batrachia the in-
tegument passes evenly
over the alveolar margins
of the jaws, as in fig. 294,
a, a : in Ophidia, Sauria,
and Crocodilia., a narrow
tract of soft and vascular
integument intervenes be-

o

tween the scale-clad border
of the mouth and the jaws ;
sinking into a more or less
shallow groove, which de-
fines the lips and receives the secretion of a row of mucous
crypts : but such lips are hard and inflexible : in certain Frogs and
Toads they are of softer texture : but in none are produced or
prehensile.

The walls of the mouth expand into pouches in certain
Reptiles, as e. g. at the sides of the face in male Frogs, below the
tongue in Hyla, and produced from the same part into a conspicu-
ous gular bag, as in the Draco volans, fig. 303, d. But these
pouches receive air, not, as in some higher Vertebrates, food ; and
usually relate to the powers of voice.

The bony walls of the mouth have been already described ; the

1 xx. vol. iv. p. 62, preps, nos. 2448 — 2451.

2 Ib. vol. iv. p. 60, prep. no. 2439 ; and ccxxxvn. p. 153.

Ciliated surface of the mouth and gullet, Triton.

CCXXXVIIl.

ALIMENT AKY CANAL OF REPTILES.

435

295

lining membrane retains the ciliated epithelium in most Batrachia.
In fig. 294, B shows the roof of the mouth of a Newt, of the
natural size and magnified : A shows the floor of the mouth with
the oesophagus, d, laid open from above, the stomach, e, and lungs,
f, f. a is the lower jaw, b the tongue, c the glottis. The currents
produced by the vibratile cilia are made visible by powdered
charcoal, and their course is indicated by the arrows, beginning at
the symphysis and extending to the cardiac end of the oesophagus.
The ciliary movement ( is remarkably vivid in the mouth of the
Serpent ; and in the Tortoise it endures for several days after death,
not ceasing till the parts are destroyed by putrefaction.' 1 Fig.
295 gives a magnified view of some of the ordinary nucleated
epithelial scales, a, b, c, and of some ciliated scales, d, e, f, g,
from the mouth of the Frog.

The tongue, as an organ of taste in
Reptiles, has been noticed, p. 327. In
Newts it is usually small, as at b, fig.
294. In most tailless Batrachians it is
large: attached to the floor of the mouth,

o

a little behind the symphysis of the

mandible, with its free border directed

backward.2 This part can be raised

and thrown out of the mouth by a

rotatory movement, as on a hinge, with

a certain elongation, equaling in some

Toads two thirds or more of the length

of the body. A glutinous saliva is

spread over the surface : both the pro-

trusile and retractile movements are executed with extreme

velocity, and thus the insect is seized and swallowed more

quickly than the eye can follow, when the Batrachian has

brought its mouth within the distance at which the tongue can

O O

reach the fly.

The hyoid being raised and the mandible depressed, the genio-
glossi, having their fixed point at the symphysis, raise and jerk
forward the free part of the tongue ; at the same instant the
tongue is narrowed and lengthened by the action of transverse
fibres in its substance : the return movements are due to the
hyoglossi, acting from the hyoid arch, while this is at the same
time depressed and retracted. In most Frogs the back part of
the tongue is bifurcate, fig. 350, «, or bilobecl (Polypedates) : in

1 ccxxxvm. vol. i. p. 631

« -w -wr . 7 . *

Nucleated and ciliated epithelial scales
mouth of Frog

2 In

txxviu. vol. i. p. 631.

Heteroglossus the tongue is attached by a central pedicle.

F F 2

43(> ANATOMY OF VERTEBRATES.

Oxyglossus it is rounded, as in Toads and some Hylida>, e. g.
JElosia ; but here the whole margin adheres : the rarest form, in
anourous Batrachians, is that of Rhinoplirynus, in which the fore
part of the tongue is free.1 In Serpents the tongue takes no other
share in the prehension of food than by the degree in which it may
assist in the act of drinking ; it is very long, slender, cylindrical,
protractile, consisting of a pair of muscular cylinders, in close
connection along the basal two thirds, but liberated from each
other, and tapering each to a point at the anterior third : these
are in constant vibration when the tongue is protruded, and are in
great part withdrawn, with the undivided body of the tongue, into
a sheath when the organ is retracted. This act is performed by
the ( glossohyoidei,' fig. 147, A ; protrusion is effected by the genio-
hyoidei, ib. z, z' . The orifice of the sheath is strengthened by a
pair of cartilaginous plates, on which other muscles act.2 The
ununited symphysis of the mandible leaves a passage for the
tongue without the need of ( opening * the mouth : and the acts
of protrusion and retraction are usually seen to be frequently
repeated. The Amphisbcenid(B and Anguidce have short, thick,
hardly protractile, and sub-bifurcate tongues.

The arboreal Chameleons, clinging on all fours to their tree
branch, depend wholly on their singularly extensile tongue for
the prehension of their volatile insect food. The movements of
this organ are as instantaneous as in the Toad and Frog, and

296

Tongue of the Chameleon partially extended. CCL.

are due to combined muscular and elastic forces, acting within
the tongue and upon its supporting bones, with concomitant
modifications of the hyoid arch. The glosso-hyal is produced
into a long and cylindrical, fibro-cartilaginous style ; it penetrates
a fibrous sheath in the substance of the tongue, which, when

1 It affords the character of Dr. Giinther's section Proteroglossa, CLXXV.

2 CCXLI. p. 368, pi. 46, fig. 15.

ALIMENTARY CANAL OF REPTILES.

437

retracted, fig. 297, A and c, is almost wholly supported thereby,
and, when withdrawn, the cavity of the sheath is occupied by
a ductile cellulosity. The bulbous end of the tongue, fig. 296,
and fig. 297, A, B, is divided by a transverse curved groove into
a shorter upper, ib. a, and a longer lower lobe, ib. d, resembling the
prehensile part of the Elephant's proboscis ; the surface is finely
rugous, and bedewed by adhesive secretion. Between the bulb
and the base the glossohyal sheath is immediately surrounded by
fibrous, degenerating into lax elastic, tissue, covered by the lingual
skin, which is thrown into circular rugae or rings, in the contracted
state (as in fig. 297, A, I, and in c, where this part of the tongue
is exposed by divaricating the geniohyoid muscles, c). The tissue
of the glossohyal sheath consists chiefly of unstriped muscular fibres,
arranged transversely. The longitudinal fibres are those of a pair
of ( glossohyoidei,' extending along the sides of the annular exten-
sile part, and spreading out at the bulbous part, of the tongue.
The circular fibres, strongly contracting, diminish the thickness,
increase the length, and, squeezing the smooth supporting style, slip
off the elongated part of the tongue from its fore part with a certain

297

B

Ui.

Tongue of the Chameleon. CCXL.

jerk. But with this action is associated a more powerful propeller
of the weighted bulbous end of the tongue, exercised by the
muscles of its bony support. The geniohyoidei, fig. C, c, and A, e,

438 ANATOMY OF VERTEBRATES.

draw forward the basihyal upon the ends of the ceratohyals, k,
which are steadied by the slender muscles ' ceratomandibularis,'/,
and ' ceratosternalis,' h : so that the inverted bony arch, from
being vertical, as at A, k, is made horizontal, as at B, k ; the basi-
hyal being brought forward about an inch, and with a force and
precision, due to the fixation of the ceratohyal tips, by their guy-
rope-like muscles, f and h, which adds greatly to the propelling
force. This force, added to, and acting consentaneously with, the
elongation of the annulose part of the tongue, b, A and B, jerks
out the swollen prehensile end of the tongue to the full extent
allowed by its elastic yielding tissue, which, on the cessation of
the muscular actions and their momentum, retracts the bulb ; and
the drawing back of the tongue is effected by the contraction of
the glossohyoidei, and of the elastic cellular tissue, readjusting
the sheath upon the glossohyal : also by the retraction of the hyoid,
through the sternohyoidei muscles, fig. 297, A, C, y. These are
assisted by the omohyoidei, ib. A, i ; and the actions of e and g are
made more effective by the cooperation of /"^ind h, in steadying
the points of the inverted arch upon which the swinging move-
ments to and fro of the basi- and glosso-hyals take place. The
mechanism and forces of the extension and contraction of the
Chameleon's tongue are essentially the same as those of the
tongue in Toads and Geckos, among which those species can
most elongate the organ, when the hyoid muscles jerk it out of
the mouth, which have the greatest proportion of ( linguales ' fibres
arranged so as to contract its breadth.1

The styliform glossohyal, besides supporting the retracted
tongue and increasing the force of the constricting ( linguales '
fibres, enables aim to be taken at the object to be reached. The
Chameleon, having discerned its prey, brings its head into position,
opens the mouth to the extent required for the tongue's passage :
then, steadying the apparatus f by a sort of tremulous rigid
movement,' shoots out the tongue, and retracts it with the fly,
the velocity of the action being such as to ( startle one afresh
every time it is witnessed.'2

The tongue of the Crocodile, fig. 298, c, is slightly raised by
its fleshy portion above the level of the membranous floor of the

1 The explanation above given agrees in essentials with that proposed by Hunter
(xx. vol. iii. p. 68), and Cnvier (xii. ed. 1, torn. iii. p. 273) ; other hypotheses are
cited in ccxxxix. torn. vi. p. 76, and CCXL. vol. iv. p. 1147.

2 CCXL. p. 1150. The whole of Dr. Salter's excellent article is well worth careful
study. A previous dissection of a Gecko's tongue, after maceration, as the Chame-
leon's ought to be, in alcohol, facilitates the recognition of the circular arrangement
of non-striped ' linguales ' fibres, described by Hunter and Cuvier.

ALIMENTARY CANAL OF REPTILES.

439

mouth, but is not prolonged freely beyond it; its back part

appears to rise,, but this is due to the 298

continuation of the membrane from the

base of the tongue over a transverse

cartilaginous plate, formed by the basi-

hyal, which, abutting against the velum

palati, ib. d, can close the back part

of the mouth. So that, when the

Crocodile holds submerged a drowning

prey, the water traversing the mouth

has no access to the glottis.1

The membrane covering the dorsurn
of the tongue is beset by mucous
crypts ; the 6 ceratoglossi ' divide into
fasciculi, which decussate across the
median line.

A salivary apparatus is as little
specialised in Batrachians as in Fishes.
Mucous crypts upon the tongue or
palate subserve the need of lubricating
the quickly swallowed and unmasti-
cated food. In Lizards a series of
orifices of mucous crypts extend
along the lip-groove of both jaws. In
the Crocodile, besides the lingual fol-

•* o

licles, there are groups of more com-
plex ones on each side, behind the
palato-nares, opening into the meshes
of the plicated faucial membrane. In
Chelonians there are groups of mucous
follicles below the tongue, representing
the sublingual glands of Mammals.
The labial glands are abundantly de-
veloped in Ophidians. The secretion
of the lacrymal glands is added to the
lubricating fluid of the mouth. The
poison-gland of venomous Serpents
may be regarded as a specially de-
veloped parotid, but will be described
in another section. In all Reptiles
the secretions entering the mouth are
rather mucous and mechanical in func- Mouth, guiiet,and stomach, crocodile.

1 xx. vol. iii. p. 72, prep. no. 1466,

440

ANATOMY OF VERTEBRATES.

299

tion than truly salivary, as exercising any alterant influence on
the nature of the food.

A l velum palati ' is developed only in the Crocodilia : an
epiglottis is not present in any Reptile : the basihyal valve of the
Crocodiles is analogous to one, and some lizards show a rudiment of
epiglottis. The sides of the pharynx are cleft by the gill-slits in the
perennibranchiate Batrachia ; and one slit on each side remains
open in some of the caducibranehiate species, as, e. g., in Menopoma.
In the Siren there are three clefts on each side, defended by inter-
locking pointed processes, closely resembling the narrower of the
five lateral branchial clefts in the Lepidosiren, fig. 316, i, 3, 4, 5.
The oesophagus is short and wide in Batrachia, fig. 294, d, c,

long and wide in Ophidia, fig. 300, d,
e, f, of moderate length and width in
Chelonia, narrower in Crocodilia., fig.
298, e, and still more so in insecti-
vorous Lacertilia, fig. 303, e. It is
remarkably dilatable and thin-coated
in Snakes, as at fig. 300, /, in which
its intrinsic propelling power is sup-
plemented by the constriction of the
surrounding trunk-muscles during
the deglutition of bulky prey. The
other chief peculiarities in the struc-
ture of this part of the alimentary
canal of Reptiles are, the perforation
of its walls by certain elongated and
enameled hypapophyses in Deirodon,1 ante, p. 393, and the produc-
tion of the lining membrane into pointed processes, directed to the
stonmch, and covered by thick epithelium in the Turtles ( Chelone}?
These aid in the deglutition of the long slippery seaweeds on
which the Turtle feeds ; in carnivorous Chelonia they are not
present; the lining membrane in Testudo indica, e. g., is thrown
into longitudinal rugse when undistended, and presents a fine
reticular and porous surface. The ciliated epithelium is con-
tinued along; the gullet in Triton, fi^. 294, d, and in the larvae of

O G •* O

Toads and Frogs.3 The muscular tunic of the gullet is strongest
in the Turtles.

The stomach presents, in Reptiles, its most simple form in the
Ophidian and Batrachian orders, especially in the ichthyo- and

1 Jourdan, in CCXLII. torn. vi. p. 160.

2 xx. torn. i. p. 126, preps, nos. 460, 461; XLIII. pt. iv. pi. v. fig 7.

3 crxi.ni. torn. i. p. 191.

Retro-verted processes in oesophagus of
Turtle (Chelone). CCL.

ALIMENTARY CANAL OF REPTILES.

441

300

tr

ophio-morphous kinds of the latter. The transition from the
gullet to the stomach is scarcely indicated externally. On the
inner surface it is shown, in the Python, by the more vascular
and rugous character of the longitudinal folds continued into it
from the oesophagus, the interspaces of the folds being reticulate.
The stomach, which is straight, as in the Rattlesnake, fig. 300, g,
contracts at first gradually, then quickly, to the
pylorus, whence a narrow canal, of about an inch
in length in a Python of ten feet long,1 conducts
to the suddenly expanded intestine. In the
Proteus, Siren, and Amphiuma the stomach is
long, cylindrical, and nearly straight ; there is
no intervening canal between pylorus and in-
testine. The stomach is distinguished from the
oesophagus by the thickness of its coats, and by
the spongy and vascular character of the lining
membrane. In the Siren and Triton, fig. 294,
the pyloric end bends a little to the right ; this
bend is more marked in Salamandra. In the
Frog, the stomach, fig. 305, «, c, is pyriform,
placed on the left side of the abdomen, with a
slight curve to the right side. In the Lizard the
stomach, fig. 301, «, is fusiform, with a similar
position : but, in curving to the right, it ad-
vances from behind forward. In the Flying
Lizard (Draco volans), fig. 303, f, and the
Iguana, the stomach is rather pyriform, but the
shape varies with the state of the contents.

In the Chelonia the stomach so far accords
with the broad and flattened form of trunk that
it is placed more transversely, bending as it passes
from the left to the right side. In fig. 302 the
gradual passage from the oesophagus, T, to the
stomach, K, is shown in the fresh-water Tortoise,
Emys europcea, in which the stomach is cylin-
drical and elongated, curving behind, and in a
deep oToove of the left lobe of the liver, I, to

, P, , , . ' * Viscera, in fore part of

the right, where the pyloric portion of the the abdomen, of the

1/1 i , i • i • Rattlesnake. CCL.

stomach, K , becomes narrower and thicker in its

coats. The muscular fibres of the layer radiate from an

aponeurotic part on each side, at the chief bend. The mucous

I!

1 xx. vol. i. p. 1 43, no. 504 A.

442

ANATOMY OF VERTEBRATES.

301

membrane is disposed in longitudinal rugae, most marked at the
cardiac half; the orifices of gastric follicles are numerous at the
pyloric portion. Here Hunter noticed ' a glandular part on one
side, a little way from the pylorus, with many orifices.' l In the
Turtle ( Chelone) the muscular tunic of the stomach becomes, in
the adult, remarkably thick, for due compression of the vegetable
contents ; in the young animal the coats are as thin as in Emys?
In this genus, and other carnivorous Clielojiia, the cardiac orifice
is very wide compared with the pyloric.

The Crocodilia present the most complex stomach known in

existing members of the Reptilian
class. The principal cavity is of a
rather flattened sub-circular or full
oval shape ; there is a tendon, fig.
298, ?', at the middle of each side,
better defined than in Chelonia, and
the muscular fibres radiate therefrom,
ib. f9 f. It communicates by a wide
aperture with the oesophagus, and by
a very narrow one with the pyloric
portion, ib. ^7, which is a small sub-
spherical pouch with a still smaller
oblique aperture into the intestine,
ib. k. The analogy to the gizzard of
the bird is further shown by the fre-
quent occurrence of stones in the
stomach of the Crocodile.3 In all
carnivorous Reptiles the prey is swal-
lowed whole, and its entry into the
stomach is easy : but nothing is per-
mitted to pass out into the intestine
except the chyme and other fluids.
In herbivorous Reptiles the pylorus gives passage to vegetable
matters whose digestion is completed in the colon.

In the disposition and attachment of the intestinal canal, the

1 ccxxxvi. vol. ii. p. 357.

2 xx. toin. i. p. 146, preps, nos. 514-516.

3 xx. vol. i. p. 146, prep. no. 518 A. In the stomach of a Crocodilus acutus, from
Jamaica, Hunter ' found the whole of the feathers of a bird, with a few of the bones,
which had lost all their earth, exactly similar to a bone which has been steeped in an
acid.... There were stones in the stomach of considerable size, larger, e. g. than the
end of a man's thumb.' ccxxxvi. vol. ii. p. 337. Dr. Jones (CCXLV. p. 94) found in
the stomach of an Alligator ' the bones, teeth, hoofs, and hair of a pig ; the flesh had
been entirely digested.'

Abdominal viscera of a Lizard, ccxxxv.

ALIMENTARY CANAL OF REPTILES.

443

Crocodilia again offer the chief exception to Reptiles in general ;
in these the mesogaster, fig. 301, h, is directly and broadly con-
tinued into the mesentery, as this is into a mesocolon ; they
are nominal distinctions of the same simple duplicature of the
peritoneal membrane. In the Crocodile the intestine, after

302

Viscera of the Female Tortoise (Emys europcea} seen from behind ; the lungs have been removed.

XXXVIII.

forming the duodenal loops, passes back to cross the spine to the
left, in close connection thereto : and, descending, again becomes
loose, and defines a 'root ' or beginning of a distinct ( mesentery';
in no Reptile is there a separate mesocolon. Thus, it is only
in Crocodilia that a ( duodenal ' portion of the intestine can be

444 ANATOMY OF VERTEBRATES.

distinctly defined; in other Reptiles it is indicated by its relation
to the pancreas and to the ducts of this gland and the liver, as at
e, /, fig. 301 (Lacerta), fig. 306, c, d(Rana), and fig. 305 ( Chelone).
The large intestine is definitely marked off in all Reptiles, but is
short and, in most, simple, straight, and without cascal production
at its beginning.

In no Reptile is the intestine so short and straight, or so
long and convoluted, as in certain Fishes ; as a general rule,
it is shorter in proportion to the trunk than in warm-blooded
Vertebrates.

In the Siren and Amphiume the intestine makes a few short
turns in its longitudinal course, and expands into a straight and
wide colon or rectum.1 In the Menopome2 the convolutions are
more numerous, and the rectum is relatively wider. In Ccecilia
the intestine is continued in a slightly convoluted manner to the
short rectum which opens near the hinder extremity of the snake-
like body. The Newts and Salamanders have short intestines,
with few coils ; so likewise have the Toads and Frogs ; but, in
the larval state of the latter, the intestine is very long, and forms
a double series of spiral coils, fig. 42, i ; and the modification by
absorption of this herbivorous type of gut to the carnivorous one is
not among the least of the marvellous changes which the anourous
Batrachian undergoes in passing to its adult condition. In most
Serpents the short intestinal folds are packed closely together in a
long mass by connecting cellular tissue. In Sea-snakes (Hydi-ophis)
the convolutions are more free. In Lizards the intestinal con-
volutions are commonly few, fig. 301, i, fig. 303, y, and free. In
the Chelonia, fi«;s. 302 and 304, the convolutions of the small grit

J O O

are larger and more numerous ; they are also well marked in
the Crocodilta.

The muscular tissue of the intestine shows an external layer of
longitudinal fibres, and an internal layer of circular ones ; the
latter is remarkably thick in Chelone. In gilled and tailed
Batrachia the mucous membrane presents fine undulatory longi-
tudinal rugae, not parallel, but often uniting. In Toads the rugaa
are transverse at the jejunum : in Frogs the rugas are zigzag.
The mucous membrane of the intestine presents, in the Python,
small, flattened, scale-like processes ; in some Serpents they are
longitudinally extended, and fringed at the margin ; the appearance
of circular or ' connivent ' valves is due to the close coils of the
gut within a common peritoneal sheath. In the Chama3leon the
intestinal rugae are rhomboidal, and their free border is minutely

1 xx. vol. i. p. 122, prep. no. 444. 2 Ib. p. 203, prep. no. 654.

ALIMENTARY CANAL OF REPTILES.

445

303

fimbriate. In a Tortoise ( Testudo indica) the inner surface of the
small intestine is reticulate : in Testudo tabulata and in the Emys
europ&a it is disposed in small and numerous longitudinal rugae :
in Chelone imbricata and Chelone Midas the principal rugae have a
wavy and slightly zigzag disposition. In the Crocodile the lining
membrane of the jejunum is finely reticulate :
in the ileum it rises into longitudinal folds : in
the colon it again becomes minutely reticulate,
and is thrown into irregular rugae.

The intestinal tube usually somewhat dimi-
nishes in diameter as it approaches the colon.
The Batrachia have no caecum ; the small in-
testine, in the Frog, makes a sudden bend, to
terminate obliquely in the short and wide colon.1
The more oblique entry of the ileum into the
colon of the Crocodile gives the appearance of a
short pouch on one side : some of the circular
fibres of the muscular tunic enter the ileo-colic
valve.2

In the Python the large intestine begins by
a subelongate, pointed caecum, marked off from
the colon by a plaited valvular fold ; 3 a succes-
sion of such folds occurs in the rest of the laro;e

C5

gut. Iii some land and fresh-water Tortoises
( Testudo tabulata, Testudo yrceca, Emys europaa)
the ileum opens obliquely into the side of the
beginning of the colon, leaving a short and
simple tf caecal ' summit of that gut ; 4 the mar-
gins of the ileo-caacal orifice are puckered into
folds, two of which, in Testudo yr&ca, are continued into the
colon, the intervening groove extending for a short distance
along the curve of the colon. The colon is longer and wider
in the herbivorous Tortoises, and usually contains grass, leaves,
or other vegetable substances, the small intestines being
empty. In some species of Agama {Ardiscosoma), Galiotes,
SteUio, Monitor, and in the Draco volans, fig. 303, k, there is a
small caecum at the beginning of the colon, ib. i: and this gut,
when distended, seems distinguishable from the narrower rectum.
But the most complex large intestine has been met with in the
herbivorous Iguanas.5 The ileum terminates by a slit on a ridge

Alimentary canal,
Draco volans. CCL.

1 xx. vol. i. p. 204, no. 669. 2 Ib. no 670. 3 Ib. no. 671 A.

3 xx. vol. i. p. 206, no. 671 B.

1 Ib. no. 671.

446

ANATOMY OF VERTEBRATES.

projecting into the caecum, which is continued beyond, spirally,
and contracting to open into the colon by a rounded puckered
aperture, at the end of a conical valvular prominence. Valvular
folds of the mucous membrane project into the colon from its
concave side, decreasing in breadth as they descend. The coats
of the intestine make smaller indentations from the convex side,
opposite the intervals of the larger folds. Beyond these folds the
colon diminishes in diameter, and makes a sudden turn upon
itself before becoming the ' rectum.' The ca3cum is, here, not a
mere ( caput coli,' but a distinct segment of the alimentary canal,
having an orifice for ingress, and a second for egress, of contents,
analogous to the carclia and pylorus of the stomach, with parietes
more muscular than either of the intestines with which it com-
municates.1

It would seem, from petrified contents or excretions of the
intestine, that some part, probably the terminal one, of this canal
had been provided, in the extinct Ichthyosaur, with a spiral valve,
fig. 105 ('coprolite' figured below the pelvis).

The rectum does not open directly upon the exterior of the
body in any Reptile, but into a cavity, or ' cloaca,' common to it

1 The following Table (CCXLV. p. 92) gives the weight of the body, in grains, and
the lengths of the alimentary canal, in inches, in various Reptiles.

Length

"Weight of

Length of

of body

the body

the canal

inches

grains

inches

Menopoma attegkaniensis .....

24

Rana Catesbiana (Bullfrog) ....

9,800

34

Heterodon niger (Black viper) ....

32

4,620

26

Psammophis jlagelliformis (Coachwhip snake)

68

5,141

42

Coluber guttatus (Corn snake) ....

54

9, 600

54

Coluber constrictor (Black snake) ....

54

5, 100

36

Crotalus adamanteus (Rattlesnake)

48

6, 180

42

Alligator mississippiensis (Alligator)

211, 940

147

Chelone caretta (Loggerhead turtle)

36,985

102

Chelydra serpentina (Snapping turtle) .

16,235

46

Emys reticulata (Chicken terrapin)

8,400

38

Emys serrata (Yellow-bellied terrapin) .

27, 172

66

Testudo Polyphemus (Gopher) ....

45, 500

78

Trionyx ferox (Soft turtle) .....

48

Length

Length of

Length

of the

small in-

of large

sto-

testine

intes-

mach

tines

inches

inches

inches

Menopoma alleghaniensis .....

3|

16

6

Rana Catesbiana .......

4

30

Chelydra serpentina . . ...

4

32

10

Testudo Polyphemus. ......

8

24

46

ALIMENTARY CANAL OF REPTILES. 447

with the urinary, genital, and allantoic orifices, when the latter
bladder persists in any degree.

In the Batracliia l the allantois opens into the fore part of the
cloaca, or, as it seems, into that part of the rectum ; behind the
rectal outlet are the orifices of the two sperm-ducts or oviducts :
behind these are the orifices of the ureters ; the genital and
urinary outlets are usually prominent. The rectal orifice is less
distinct and constricted, and the cloaca seems more a continuation
of the gut than in higher Reptiles. In the male Triton the
rectum forms a valvular projection into the cloaca, after it has
received the orifices of the vasa deferentia.

In true Ophidia there is no remnant of allantois opening into
the fore part of the rectum or cloaca ; in Anguis a small bladder
remains in that connection,2 which expands, in limbed Lizards, to
larger proportions. In Coluber, as in other Serpents, the terminal
orifice of the rectum is well marked ; behind it is a semilunar
fissure, receiving the outlets of the oviducts, and behind that is
the bilobed prominence on which the ureters open.3 The cloaca
in Lizards shows the valvular fold between the intestinal orifice
and those of the genital and renal conduits, together with the
orifice of the allantois at the fore part of the rectum. In the
Chelonia the allantois, fig. 302, u', opens into the fore part of the
cloaca, below or beyond the rectal orifice : this has a distinct
sphincter ; 4 the compartment of the cloaca receiving the terminal
orifices of the genital and urinary canal, and of the allautois, is also
divided by a projecting border, like a distinct orifice, from the
outer compartment, in which the clitoris, fig. 302, H, or penis lies :
the former is termed the ( urogenital,' the latter the ( vestibular,'
part of the cloaca ; the urogenital orifice is transverse or semi-lunar.
In Chclydra serpentina the oviducal orifices are immediately behind
the rectal one : the allantoic orifice is in front of it ; behind the
oviducts are the terminations of the ureters, and behind these,
within the vestibule, are the wide orifices of two cloacal sacculi,5
each of which exceeds the allantois in size. In Emys europcea,
fig. 302, u, u, they equal the allantoic bladder, u'. The allantois
in the Crocodilia is reduced to a urinary bladder-like dilatation of
the fore part of the cloaca, into which the rectum opens obliquely,
and by a valvular protrusion ; the genital orifices are behind this,

1 Siren, xx. vol. iv. no. 2695 ; Amphiuma, ib. no. 2397; Menopoma, ib. no. 239 ; Tor-
toise, ib. nos. 2401, 2699; Salamandra, ib. no. 2407; Rana, ib. nos. 2409, 2702; Pipa,
ib, no. 2707.

2 xx. vol. iv. p. 57, no. 2422. 3 Ib. no. 2708. 4 Ib. vol. i. no. 751.

5 'Anal sacculi,' xx. vol. iv. (1838) p. 147, no. 2722 B. 'Vessies auxiliares,'
CCXLIV. (1839), p. 456. 'Vessies lombaires,' ccxxxix. torn. vi. p. 363.

448 ANATOMY OF VERTEBRATES.

and then come those of the ureters.1 The urogenital compart-
ment opens into the vestibule by a narrow fissure, the lower part
of which is continued into the groove of the penis or clitoris

lyino; in the vestibule.

«/ ~

The cloacal outlet, commonly termed the ( anus,' varies in shape
in Rcptilia, but is more constant in position than in Pisces ; it is
never so far forward as in some of that class. In tailed Batrachia
it is a longitudinal slit in the axis of the trunk ; in anourous

o '

larvae it is protected by folds of membrane, which unite to form
the lower border of the tail-fin ; during the progress of absorption
of this natatory organ the anus is somewhat advanced, and assumes
a rounded form with a sphincter. In the Sea-snake (Pelamys}
the anus is longitudinally bilabiate, but the anterior part of the
fissure is crossed by a semilunar fold or ridge. In Lizards the
corresponding fold, with its scaly covering, is larger, covers more
of the orifice, and gives it a transverse semilunar shape. It has a
similar form in the Turtle. In Emys it is a puckered aperture,
with a tunical border beneath the base of the tail ; in Trionyx it
is a longitudinal orifice, and nearer the end of the short tail. In
the Iguana the posterior valve of the cloacal opening is approxi-
mated, and applied to the anterior one by a muscle which arises
from each angle of the fissure or fold between the tail and the
thighs. The dilatation of the orifice is produced by two pairs of
muscles, attached, the one to the femoro-caudal fold, the other to
the lower surface of the tail.

§ 76. The Liver of Reptiles.— This organ is proportionally
large in all Reptiles : its form is mainly governed by that of the
body. In Serpents, fig. 300, 0, it is unilobate, long, and slender ;
in Tortoises, fig. 302, i, it is short and broad, chiefly composed of
two subequal lobes; in Lizards, fig. 292, k, it offers an inter-
mediate form.

In the Lepidosiren the liver consists of one long lobe, with a
transverse notch on the left side, lodging the gall-bladder. In
the Siren the liver presents a similar form, with the addition of a
small left lobe at the anterior end. In the Amphiume the long
and slender subtrihedral liver extends through nearly two thirds
of the abdominal cavity, and the gall-bladder is an inch distant
from the lower end. In the Menopome the liver is shorter and
broader, with the gall-bladder lodged in a fissure which makes
the posterior end bifurcate. In the Newt the liver has a similar
terminal notch into which a peritoneal fold enters. In the Frog

1 xx. vol. i. no. 747, vol. iv. no. 2438.

LIVER OF REPTILES.

449

the liver is divided into a right and left lobe,, with subdivisions of
the latter. In the Pipa the right and left divisions are quite
distinct, and each is subdivided. In Ccecilia the elongated liver
is divided into several small flattened lobes. The liver, in the
Chameleon, consists of one lobe ; in the Gecko (Platydactylus
guttatus) and the Draco volans, fig. 292, k, it is triangular: the

304

Viscera of the Female Tortoise (Emys europcea). xxxvin.

anterior angle accompanies the vena cava towards the heart : a
second angle, m, m, enters the curve of the stomach : the third is
directed backward, along the right side : the gall-bladder lies in a
notch between the last two angles. In some other Lizards this
notch is deeper, and the increased size of the left process gives the
liver a bilobed character ; the vena portre enters the fissure, the
vena cava enters the longer right lobe. In the Iguana the liver
extends from right to left, with a convexity forward, and with a
VOL. i. G G

450

ANATOMY OF VEKTEBRATES.

slender prolongation along the right side, into the apex of which
the postcaval vein enters. It has a narrow l falciform ' ligament.

In the Crocodile the liver is divided into a right and left lobe,
anteriorly, by the heart, which almost wholly enters the fissure.
The right lobe is the largest, with the gall-bladder on its concave
side. The liver is more equally divided in Chelonia, fig. 304, I, I,
and chiefly also by the heart, ib. A', B'. The stomach, ib. K,
deeply impresses the left lobe, and is buried in it in some species
(Emys serrata). In many there is a process, like the ' lobulus
Spigelii,' entering the curve of the stomach. In the higher
Reptiles the liver is contained in a peritoneal pouch ; in Chelonia
and Crocodilia each lobe has its pouch more or less distinct. In
the Crocodile the capsule becomes aponeurotic, whence it is con-
tinued from the sterno-sacral border of the gland to the abdominal
parietes, to be connected, like a diaphragm, with the transversus
abdominis muscle.1

The lobes of the liver are subdivided into numerous and minute
lobules, compactly united by interlobular cellular tissue. The
lobules themselves are composed of corpuscles, or ( acini,' occupy-
ing the meshes of the vascular network pervading the lobule ;
these ' acini ' are larger in Reptiles than in Fishes. Their
secretion finds its way into biliary canals, distinguishable as
such, with proper walls, on the exterior of the lobule ; these
ducts anastomose in the interlobular spaces, and form larger
canals, accompanying the hepatic vessels,, and, after repeated
unions, issuing, as the ( hepatic ducts,' from the portal fissure.
The walls of the ducts have no follicular glandules. The hepatic
tissue in Reptiles is usually softer than in warm-blooded Verte-

1 Dr. Jones, CCXLV. p. 113, ascertained the weight of the body and of the liver in the
following Reptilia, and gives the relative weight of the latter in the subjoined form.

Number of

Weight of

times the

the body

weight of

its liver

in grains.

Rana Catesbiana (Bullfrog)

9,800

55

Heterodon niger (Black viper)

4,620

26

Psammophisflagelliformis (Coachwhip snake)

5, 141

71

Coluber guttatus (Corn-snake) .

9,600

64

Coluber constrictor (Black snake)

5, 100

57

Crotalus adamanteus (Rattlesnake) " .

6, 180

55

Alligator mississippiensis (Alligator) .

76, 507

73

Chelone caretta (Loggerhead Turtle) .

36,985

47

CheJydra serpentina (Snapping turtle)

16,985

42

Emys terrapin (Salt-water terrapin)

11,937

53

Emys reticulata (Chicken terrapin)

8,400

18

Emys serrata (Yellow-bellied terrapin)

23, 100

48

Testudo Polyphemus (Gopher)

45, 500

50

LIVER OF REPTILES. 451

brates, and firmer than in Fishes. It never contains so large a
proportion of oil as in plagiostomous and some other Fishes.

A gall-bladder exists in all Reptiles. It lies in a notch on the
left side of the elongated liver in the Lepidosiren, Siren, Proteus,
and Amphiume, and in a notch at the hind end of the liver in
Menopoma, Triton, and Salamandra. In Anourous Batrachia the
gall-bladder is imbedded in the right lobe. In the Chameleon
the gall-bladder is at the hind border of the liver; in Draco
volans, fig. 292, m, it lies in the notch between the left and hinder
angle ; in the Cyclodus and Iguana in the notch between the two
hinder divisions of the liver. The gall-bladder is deeply im-
bedded in the substance of the right lobe of the liver in Testudo :
it adheres by about one third of its length to the right lobe in
Chelone : it has a similar attachment in Crocodilus, but is less
closely connected, and sometimes quite detached, in Alligator and
Gavialis. In true Ophidia the gall-bladder, fig. 300, p, is removed
beyond the liver to the side of the narrow canal connecting the
stomach with the intestine. In the snake-like Lizards (Anguis,
Amphisbcemi) the gall-bladder is in contact with the liver.

In Lepidosiren, Siren, and Amphiuma, the hepatic ducts com-
municate with the cystic, or with the gall-bladder (Siren), and
the bile is conveyed directly by the cystic duct to the beginning
of the intestine. In the Iguana there is a distinct hepatic duct
which enters the duodenum about an inch from the pylorus,
a cyst-hepatic duct which enters the side of the gall-bladder, and
cystic ducts which leave the globose bladder abruptly. In Che-
Ionia the hepatic ducts unite with the cystic : but sometimes one
is continued directly to the intestine ( Testudo grceca). In Chelone
Midas a long hepatic duct from the left lobe unites with a shorter
one from the right lobe, and the trunk joins the cystic near its
entrance into the duodenum. The cystic is very short and wide,
and runs obliquely through the thick walls of the duodenum.
In the Crocodile the hepatic duct sends a branch to the gall-
bladder, and goes to terminate in the duodenum, distinct from the
cystic. This arises from the apex of the bladder, and is long and
straight. In Ophidia the hepatic duct is of great length, and
unites with the cystic in the substance of the pancreas, near
the termination of the common duct, In some species (Dispho-
lidus) it previously sends a branch directly to the gall-bladder.
The cystic duct in Python, single at its commencement, divides
into numerous branches, which penetrate the pancreas, and re-
unite with each other and the hepatic before terminating in the
duodenum. The advantage of this modification of the biliary

G G 2

452 ANATOMY OF VERTEBRATES.

receptacle and ducts is obvious. Had the gall-bladder been
attached to the liver, as in insectivorous Anguidce and Lizards,
it would have been compressed by the prey, which in true
Serpents is usually of large bulk when introduced into the
stomach. The stimulus of such pressure would have led to the
expulsion of the contents of the gall-bladder into the intestine
before the chyme had been prepared, and passed on into the
gut : the relative position of the liver to the stomach subjects
the ofland to such stimulus to secrete whilst the contents of the

o

distended stomach are undergoing digestion. The bile is con-
veyed away by the long hepatic duct, but is reflected along
the branching cystic ducts to the gall-bladder, which has been
transferred to a position beyond the pressure of the stomach. It
is so placed, however, as to be affected by the distension of the
narrow canal which conveys the chyme to the duodenum, and is
thus stimulated to render up the bile to the gut, just at the time
when it is wanted for the separation of the chyle from the chyme.
This fact in comparative anatomy is significant of the share taken
by the biliary secretion in the act of chylification.

The gall-bladder is not, however, a simple reservoir ; its vascular
and secreting inner surface can operate upon the bile by both
subtraction and addition : the more watery part may be diminished
by absorption : the cylindrical epithelial cells which form the
innermost layer of the mucous membrane may be shed into the
liquid, with the contents of mucous follicles which are more or
less developed in that membrane. The mucous surface is
augmented by minute furrows in the Crocodile : in the Testudo
elephantopus it is nearly smooth.

The bile in Chelonia and most Reptiles is green : Hunter
notices its pale yellow colour in the f Water-snake,' and its want
of bitter taste in the Chameleon.1 Chemical researches on the
nature of bile have been almost exclusively confined to that of
Mammals, in connection with which class the chief results will
be noted. The glycocholic acid is wanting in the bile of the
Boa, as in that of the Dog. As might be supposed, from the
prevalent colour of the bile in Reptiles, the fbiliverdine' primarily
exists in it, not as a transformation of ( cholepyrrhine,' which is
the primary colouring principle in most Mammals. The propor-
tion of taurocholate of soda in the bile of a Python is estimated
at 8 -46 in 100, and in that of a Boa to 6*2 in 100 ; a trace of the
same principle has been detected in the bile of a Tortoise. In

1 ccxxxvi. vol. ii. pp. 373, 378.

PANCEEAS OF REPTILES.

453

305

all Reptiles the bile is poured into the gut near to, sometimes
close to, the pylorus.1

§ 77. Pancreas of Reptiles. — The pancreas in Reptiles is a
light grey or yellowish, sometimes pinkish, coloured gland, con-
sisting of numerous ' acini,' giving origin each to a duct, the
acini being united by them, like the short stalks of grapes, in
bunches, about a larger duct;
such aggregates or ( lobules'
further uniting into l lobes,'
and their ducts into a com-
mon canal, which terminates
either with, or close to, the
biliary duct in the intestine.
The lobes are separate in
Python, of a subcircular
flattened form, suspended
cluster-wise by ducts of from
six to twelve lines in length,
before uniting into the com-
mon canal.

The pancreas has a close
texture in herbivorous Che-
Ionia, forming a thin layer,
spread out in the duodenal
mesentery, fig. 305, where
it branches into numerous
lobes. In most Ophidians
and in many Lizards it pre-
sents a more compact form, fig. 301, f. There are intermediate
conditions of structure in the present class. The pancreas is
ramified in Menobranchus : it is more circumscribed in Menopoma,
where it forms a long, slender, yellow gland. It is rather broader
in Amphiuma and Triton. In the Frog, fig. 306,^?, it is flattened,
elongate, narrowest at the emergence of the duct (opposite c), and
sending a process, which surrounds the gall-duct, as far as the gall-
bladder. In the Salamander it is long and narrow. It is thick and
pyramidal in Ccecilia albiventer; straight, elongate, and slightly
forked in Ccecilia interrupta : it is ovoid in most Colubridce ; of a

1 The relative size of the liver in Reptilia does not relate to, or throw light on, its
probable accessory function as an elaborator of the albumen and disc-cells of the
blood, or as helping to maintain animal temperature by the formation of grape-sugar
out of the nitrogenized elements. Dr. Jones, however, detected the presence of grape-
sugar in the liver of cold-blooded Animals at all periods of starvation.

Paucreas

. CCXXXI

454

ANATOMY OF VERTEBRATES.

306

compact triangular form in the Rattlesnake,1 where it is closely
attached to the commencement of the intestine, and is perforated by
the biliary ducts. The pancreas is small and flattened in Lizards,
usually dividing as it recedes from the attachment by the duct to

the duodenum into a portion accompanying
the biliary duct, and another extending to
or towards the spleen. It is very small in
the Iguana. In the Crocodile the pan-
creas is divided into two elongated lobes,
and sometimes sends its secretion into the
duodenum by two ducts. In Chelydra
serpentina the pancreas extends from the
pylorus some inches along the duodenum,
dividing and again uniting, forming a loop,
and giving off a process which extends to
the spleen. In the Turtle ( Chelone Midas)
the pancreatic duct terminates on a pa-
pilla, which projects into the terminal ex-
pansion, or ' ampulla,' of the bile-duct.

The pancreas in carnivorous Terrapins (Emys) is more bulky
and compact in form than in the fucivorous Turtles ( Chelone).

Thus in the vegetable-feeding Gopher the pancreas is -g-g-Vo" of
the total weight of the animal : whilst in the carnivorous Snapper
it is -g-i-y- of the total weight of the animal. As the proportion
of fat consumed by Carnivora must be greater than that by
Herbivora, the results of the above comparative observations
accord with the view of the use of the pancreas in preparing
fatty matters for absorption.2

1 xx. vol. i. p. 235, no. 778.

2 Dr. Jones, CCXLV. p. 107, ascertained the weight of the body and of the pancreas
in several American Reptilia, and gives the relative weight of the latter in the sub-
joined form.

Liver, pancreas, and spleen of
the Frog (Sana), ccxxxi.

Rana Catesbiana (Bull-frog)
Heterodon niger (Black viper)
Psammophis flagelliformis (Coachwhip snak
Coluber guttatus (Corn snake) .
Coluber constrictor (Black snake)
Crotalus durissus (Banded rattlesnake)
Chelone caretta (Loggerhead turtle) .
Chelydra serpentina (Snapping turtle)
Emys terrapin (Salt-water terrapin) .
Emys reticulata (Chicken terrapin)
Emys serrata (Yellow-bellied terrapin)
Testudo Polyphemus (male Gopher) .

»

e)

Number of times
the weight
of its pancreas.

1088
537
1353
1371
472
965
518
630
994
763
1067
3500

455

CHAPTER VI.

ABSOKBENT SYSTEM OF H^MATOCRYA.

§ 78. ALL the definite structures of soft parts — acini and
simpler gland-follicles,, their prolonged outlets or ' ducts/- -com-
pacted sheets or strata called ( skin ' and ' membranes/ mucous or
serous,, — bladders, sinuses, and tubes, arterial or venous, — threads
or fibres, muscular, ligamentous, or nervous — are covered, coated,
or lined, by a loose or soft elastic substance, which, as it con-
nects the better-defined structures together, and fills up their
interspaces, is termed e connective tissue ' (tela conjunctiva, tela
cellulosa). It is dispersed in irregular plates, with intervals, cells, or
6 lacuna?,' and the plates consist of delicate and extremely minute
fibrils. The intervals contain a fluid called ( serous,' varying
in: quantity, and also in quality, according to circumstances :
and they intercommunicate freely. These cavities are the seat
of a transudation from ( vessels ' and other more definite fluid-
holding structures during life : and reciprocally the ' serosity ' is
resumed by the beginnings or pores of sinuses and canals.

The serosity of the cavities of the connective tissue usually
consists of-

Water

Albumen ...
Extractive matters and fat
Mixed salts

975*20
5'42
0'76
15-621

But it is subject to varieties from many causes, mechanical and
chemical, operating both within and out of the body.

The vessels or canals which seem to be most closely connected
with, or to be most directly traceable from, the connective
tissue and its lacunae are those called lymphatics, lacteals, and
absorbent vessels. This system exists as a separate organic
vascular apparatus only in the Vertebrate subkingdom : it was
first observed in Mammalia,2 was discovered by John Hunter in

1 CCLIT.

2 In the dog, by Aselli, in 1622 : at least the part of the absorbent system called

' lacteals,' in the mesentery of the animal. CCLIII.

456 ANATOMY OF VERTEBRATES.

Birds1 and Reptiles,2 and afterwards described by Mr. Hewson
and Dr. Monro in Fishes. The most systematic and detailed
descriptions of the absorbent system of the Oviparous Animals,
published in the last century, are those of Hewson.3

§79. Absorbents of Fishes.- The lacteal system in Fishes
commences by a reticulate or plexiform layer of vessels attached
to the connective tissue on the outer or cellular side of the mucous
coat of the stomach and intestines : in the Skate4 the network is so
coarse that, when inflated, dried, and cut open, it appears like a
subdivided cellular or areolar receptacle. The chyle is conveyed
thence in all Fishes by more vasiform lacteals, situated immediately
beneath the serous covering of the intestines, to large reticulate re-
ceptacles, one in the mesenteric angle along the junction of the small
and large intestines, the other extending along the duodenum, its
pancreatic appendages, and the pyloric part of the stomach, and
often also surrounding the spleen. The presence of the mesentery
in the Myxinoids, and its absence in the Lampreys, involve corre-
sponding differences in their lacteal systems : in the Myxinoids
the lacteals are supported and conveyed by the mesentery to the
dorsal region of the abdomen, and empty themselves into a
receptacle above the aorta and the cardinal veins, between these
and the vertebral chord : in the Lamprey the lacteals pass
forward, and enter the abdominal cavernous sinus beneath the
aorta.

The lymphatic system is best demonstrated by injecting the
large absorbent trunk which runs upon the inner surface of the

1 ' It is but doing justice to the ingenious Mr. John Hunter to mention here, that
these lymphatics in the necks of fowls were first discovered by him many years ago.'
(Hewson, civ. 1768, p. 220.)

2 Hunter's account of this discovery is as follows: — ' In the beginning of the winter
1764-5, I got a crocodile, which had been in a show for several years in London
before it died. It was, at the time of its death, perhaps the largest ever seen in this
country, having grown, to my knowledge, above three feet in length, and was above
five feet long when it died. I sent to Mr. Hewson, and, before I opened it, I read over
to him my former descriptions of the dissections of this animal relative to the ' absorbing
system,' both of some of the larger lymphatics and of the lacteals, with a view to see
how far these descriptions would agree with the appearances in the animal now before
us; and, on comparing them, they exactly corresponded. This was the crocodile
from which Mr. Hewson took his observations of the colour of the chyle.' Hunter
here alludes to the note appended to Mr. Hewson's paper on the 'Lymphatic System
in Amphibious Animals,' Philosophical Transactions, vol. lix. 1769, p. 199 a: 'In
a crocodile which I lately saw by favour of Mr. John Hunter, the chyle was
white.'

3 civ. 1768, 1769.

4 In this and other Plagiostomes the gastric lacteals are confined chiefly to the
contracted pyloric canal.

ABSORBENTS OF FISHES. 457

ventral parietes of the abdomen, along the median line from the
vent forward to the interspace of the pectoral fins, where the
size of the vessel best favours the insertion of the injectiug-pipe.
It receives the lymphatics of the pectorals, and (in thoracic and
jugular Fishes) of the ventral fins : then, advancing forward
through the coracoid arch, it spreads out into a rich network,
which almost surrounds the pericardium. The lymphatic plexus
which covers the heart of the Sturgeon and Paddle-fish presents
a spongy and almost glandular appearance wThen uninjected : the
tissue between the muscular and mucous coats of the gullet in
the Rays,1 the gland-like mass in the orbit and palate of the
Chima3ra3, and that lodged in a peritoneal fold of certain Sharks,
may likewise be appendages to the lymphatic system.2 Large
lymphatic trunks from the upper (dorsal) part of the circum-
cardial plexus receive the lymphatics of the myocommata by a
deep-seated trunk which runs along the ribs, and the lymphatics
of the mucous ducts and integuments by a superficial trunk which
extends along the lateral line, and gets a penniform character by
the regular mode in which its tributary lymphatics join it.

In the Wolf-fish (Anarrhichas} the lacteals commence in pro-
cesses of the edges of the mucous folds by cells or blind ends,
from which the vessels proceed to form a close plexus on the
outer surface of the intestine, and accompany in a plexiform
manner the bloodvessels. In the Turbot there are similar
plexiform surroundings of the bloodvessels of the stomach : and
in Silurus glanis the lacteal network covers all the stomach.3

In the Eel the gastro-enteric absorbent plexus communicates
with a cavernous sinus upon the lower surface of the stomach,
and with a larger one which accompanies the intestinal canal,
whence other plexuses pass to the great subvertebral lymphatic
trunks. Along the free border of the intestinal spiral valve, in
Plagiostomes, there is a varicose lacteal reservoir, from which
proceed the vessels forming the reticulate layer beneath the
mucous membrane. The lymphatics of the head form minor
plexuses at the bases of the orbits, and in the Carp they extend
into the basi-cranial canal ; those from the cellular arachnoid pass
through the occipital foramen to join the lymphatics of the spinal
canal, and terminate in the cervical and sub-occipital trunks,
which receive the lymphatics from the upper extremities of the
gills : these, with the deep-seated lymphatics from the kidneys,
join the single or double trunks at the under part of the vertebral

1 xx. vol. i. p. 126, no. 462. 2 CCLXI. p. 269.

3 cv. pp. 27, 30, pi. 6, figs. 1 and 2 ; pi. 7, figs. 3 and 4.

458 ANATOMY OF VERTEBRATES.

column, which combine with the lacteal plexiform trunks con-
tinued forward along each side of the stomach and rcsophagus,
to form a large, short, common lacteo-lymphatic trunk on each
side, which terminates in the jugular vein near its junction with
the short precaval vein. Fohman. l describes other and minor com-
munications between the absorbent and venous systems of Fishes,
as, e. g., in the gastric and intestinal plexuses in the Sheat-fish
and Turbot. The lymphatic system of the caudal portion of the
body is chiefly received by two caudal sinuses, intercommunicating
by a transverse canal, which sometimes perforates the base of the
anchylosed compressed terminal tail-vertebra.

The lymphatics of Fishes consist generally of a single tunic :
a most delicate epithelial lining may be distinguished in the
larger trunks. The only situations where valves have been seen
in these vessels are at the terminations of the trunks in the
caudal and the jugular veins. There are no lymphatic glands :
these are represented by the large and numerous plexuses, and
possibly by the gland-like layers or substances above-mentioned.
The chyle as well as the lymph of Fishes is colourless and
transparent: the plasmic corpuscles or lymph-cells are few in
number.2 The analysis of the lymph in Fishes is still a
desideratum.

§ 80. Absorbents of Reptiles.- -In the intestines of the Frog
and Salamander the lacteals form a network of large canals,
with minute or close meshes coextensive with the mucous
membrane ; the vessels continued therefrom accompany the
mesenteric arteries, sometimes forming a pair, running along
opposite sides, with occasional connecting cross-branches ; more
commonly having these so numerous as to constitute a continuous
reticulate sheath about the artery, the cavity of which sheath
seems, in some parts, to be only partially divided by cross
threads.3 These lacteals, or intestinal lymphatics, open into a
receptacle at the dorsal line of reflection of the mesentery, of
large size in the Frog, but contracted and assuming rather the

1 cv.

1 In CXLV. these lymph-corpuscles are described as ' centres of assimilative force,
manifesting inherent power of developement and change, some being granular, others
with a capsule and in the condition of nucleated cells,' p. 249 (1846). Prof. Kolliker
testifies to the fissiparous multiplication of the lymph-corpuscles in the lacteals of the
dog, cat, and rabbit. The corpuscle, in the condition of the nucleated cell, elongates,
the nucleus divides into two ; between which the cell contracts and finally divides
(CCLXII. p. 639). In Fishes the nucleus undergoes further subdivision before the
fission of the cells takes place.

3 CCLVI. p. 249.

ABSORBENTS OF REPTILES. 459

form of a ( thoracic duct ' in the Newt ; it proceeds along the aorta
in both, communicating with lymphatic canals near the liver, and
dividing anteriorly, to accompany the right and left aortic arches,
and to receive the lymphatic conduits from the head and fore-limbs,
before terminating in the subclavian veins. Some of the vessels,
both arteries and veins, of the trunk have a similar lymphatic
sheath, but the principal conduits of the lymph, in the Batrachia,
have the form of irregular sinuses or lacunae, of great capacity
between the skin and flesh, and of smaller size in the inter-
muscular spaces of the limbs.1 Air or liquid introduced into
these lymph-receptacles finds its way into the veins by the above,
and perhaps other, communications. The lymphatics of the
hind-part of the body and limbs communicate with a pair of
subcutaneous receptacles, with contractile walls, behind each
femoral joint ; there is a similar pair in front of the scapulas.2
These receptacles have a subrhythmical action, not synchronous
with one another, or with the pulsations of the heart, or with
any of the movements of respiration, which in Batrachia are
degiutitioual chiefly. The muscular fibres of these ( lymph-
hearts ' are of the striped kind.3 The cervical pair transmit
their lymph into the jugular veins, and distend them at each
systole. The pelvic lymph-hearts have been seen to pulsate
sixty times in the minute in a frog.4 In the large Ceratoplirys
cornuta two pairs of ischiadic lymph-hearts have been found.5

In the Tortoise the pelvic lymph-hearts are two, of a more
circumscribed rounded form, situated on each side of the bodies
of the vertebras, between the femoral joints and the hind-border
of the carapace ; the valves at the inlets and outlets of the
lymph conduits, impressing the course of motion of the fluid,
are here readily seen.6 In Lizards and Crocodiles the pelvic
lymph-hearts are situated near or upon the diapophyses of the
first caudal vertebra. In Pseudopus Pallasii they lie between
the muscles upon the sacral diapophyses, receiving the lymph
each by a single conduit from the great abdominal sinus, and
transmitting it to the umbilical veins ; they pulsate about fifty
times in the minute.7 In true Serpents (Python, e. g.) the
lymph-hearts are elongate, and situated behind the last pair of
ribs and upon the rib-like diapophyses of the anterior caudal
vertebras ; they receive the lymph by three orifices at one end,
and transmit it by two opposite orifices, to conduits com-

1 CCLVII. p. 28. ~ CCLV. p. 89. 3 CCLVIII. p. 58.

4 LXXIV. 5 Ib. 6 CCLV. pi. 1. 7 CCLIX. p. 25, pi. 3.

4GO ANATOMY OF VERTEBRATES.

municating with the caudal vein. The three tunics of these
hearts, of which the middle one is muscular, with the inferent
and afferent valvular structures, are well displayed in the
Python.1

The intestinal lymphatics, in Serpents, open into a large
receptacle, extending along the root of the mesentery, beginning
near the vent where it is narrow, receiving the lymphatics of
the tail, and extending forward, greatly expanded, as far as the
stomach, where it forms a cul-de-sac. This receptacle is reflected
about the aorta, which seems included in it, and receives the
lymphatics of the genital organs, kidneys, and intestines. Before
reaching the stomach, it sends off a plexiform conduit, which
receives the lymphatics of the pancreas, spleen, stomach, and
liver, the latter gland being more or less completely sheathed by
the lymphatic receptacle ; this then contracts into an irregular
canal as it approaches the pericardium, where it terminates in a
cul-de-sac, but transmits the lymph by several lateral vessels to
a large plexus near the great vessels of the heart. The above
continuation of the abdominal receptacle has been called the
f right ' or ' inferior ' thoracic duct. The ' left ' or ' superior ' or
' dorsal ' thoracic duct leaves the great receptacle nearer its
anterior extremity, by three or four conduits, and advances along
the oesophagus to the pericardium, anastomosing with the right
duct, by transverse channels. On reaching the pericardium, the
left duct divides into two channels, which reunite in front of
the pericardium, and join the lymphatic plexus about the great
vessels, from which the lymph is conducted by two or three
terminal trunks to the two great precaval veins.2

In Chdonia the chyle is absorbed into a stratum of intestinal
lymphatics, which, in the form of a close network, lies between
the muscular and mucous coats ; 3 from this the conduits pierce
the muscular tunic, and affect a longitudinal course on the
exterior of the gut until they quit it, accompanying the me-
senteric bloodvessels to the great chyle- and lymph-receptacle,
fig. 307, C, c, which extends from the middle of the dorsal part
of the abdomen backward to between the vertebras and rectum.
Here it receives the lymphatics of the hinder limbs and tail, and,
in succession forwards, those of the cloaca and its appendages, ib.
u, u, of the kidneys, ib. O, of the genital organs, ib. H, and intes-
tines, ib. v ; it presents the same quasi-capsular relation to the

1 CCLX. p. 538, pi. 13, figs. 7, 8, 9. 2 CCLVII. p. 15.

3 xx. vol. ii. p. 17, nos. 850-858.

ABSORBENTS OF REPTILES.

4G1

aorta as in Batrachia, and bifurcates anteriorly, the divisions
inclosing the right and left pulmonary arteries and aorta?, and

'rHPC..? • ;'W£S==^- s -ss f^-^s Y1 fa*

?^t>V^$-iiB|^^S ^- -E = "T^^ " J--**i

'

Viscera in situ, seen from behind, with the lymph-receptacle (Emys europcea). XXXYIII.

terminating at the beginning of the two precaval veins, by
elliptical orifices guarded by valves. The lymphatic system of
the trunk and limbs affects the form of irregular plexuses and
dilatations.

The lymphatic system in Lacertilia resembles in the main
that of Ophidia and Chelonia. In Crocodilia there are several
signs of advance. Hunter 1 noted the white colour of the chyle :
the ' receptaculum ' is more circumscribed ; its anterior divisions
are more vasiform, more like i thoracic ducts ; ' there is a compact
gland-like plexus of lacteals at the root of the mesentery. At
the base of the tail the lymphatics surround the artery and vein

1 ccxxvi. vol. ii. p. 335.

462 ANATOMY OF VERTEBRATES.

by a Large plexus, filling up the haemal canal ; they present also
a plexiform character at the axilla? and base of the neck, about
the jugular veins ; but the vasiform character is generally better
marked in the lymphatics of the Crocodile than in lower Reptiles,
and the valves occur more frequently.

The lymph-corpuscles are very few, and rarely visible in the
lymphatics of the tail of the Tadpole, but were numerous in the
lymphatic canals near the liver in Salamandra. By carefully
puncturing the large subcutaneous lymph-reservoirs of the Frog,
at the upper part of the thigh, the pure fluid may be obtained
from the living animal : but analysis of lymph has chiefly been
performed on the larger quantities discharged from artificial
fistula? of the thoracic duct in the Horse and Cow, and its results
will be given in connection with the Mammalian class.

463

CHAPTER VII.

CIRCULATING AND RESPIRATORY SYSTEMS OF H2EMATOCRYA.

§ 81. Blood of Pishes.- -The red blood of Vertebrates owes
its colour to the albuminoid substance called ( haematosine,
existing in the discoid corpuscles called f blood-globules,' ' blood-
cells/ or ( blood-discs.' These float in the light straw-coloured
fluid called ( plasma,' which consists of water holding in solution
proteine principles, hydrocarbonates of the fatty nature, saccharine,
and saline matters. The watery solvent predominates in the
blood of Fishes and Batrachians. The f proteine' basis exists
under the combinations termed ' albumen ' and ( fibrin.'

The blood-discs in Fishes are commonly of a full elliptic shape,
as in the Cod, fig. 8, y, and Skate, fig. 8, A, p. 4 : but in the
Lamprey and Ammocete they are nearly circular. In the Myxine,
however, they are elliptic, and some are fusiform. They present
the largest size in the Sharks, but are smaller in them in proportion
to the body, or mass of blood, than in Batrachia.1 Besides the red
discs there are the larger white corpuscles in the blood of Fishes as
in that of higher Vertebrates, but in less proportion than in Sau-
rians, Birds, or Mammals.

The comparison of main physiological importance between the
blood in different groups of Vertebrates, is that which relates to
the proportion of the organic matters contained in the water.

Prevost and Dumas expressed the general results of this com-
parison of the blood of the cold-blooded classes in the following

TABLE OF THE PROPORTION OF WATER, CLOT (BLOOD-DISCS AND FIBRIN),

ALBUMEN, AND SALTS.

H^IIATOCRYA

Water

Clot

Albumen
and Salts

Rana esculenta (Frog) .......

884

69

46

Sal/no Jario (Trout) .......

864

64

72

Lota molva (Burbot) .......

886

48

66

Anguilla latirostris (Eel) ......

846

94

60 -

1 See ccxxxix. torn. i. p. 89, for the dimensions, in fractions of a millemeter, of the
blood-discs of Fishes.

2 CCLXV. p. 64.

464

ANATOMY OF VERTEBRATES.

Dr. Joseph Jones l has pushed this kind of analysis further, as
shown by the subjoined table.

MOIST BLOOD-DISCS

PLASMA

Total
Weight

"Water

Solid
Matters

Total
Weight

Water

Solid
Matters

Zygana malleus (Hammer-shark)

293-44

220-08

73-36

706-56

641-06

65-50

Lcpidosteus osscus (Gar-fish) .

229-00

17175

57-25

771-00

714-95

56-05

Salmo fario (Trout).

275-20

206-40

68-80

•

Lota molva (Burbot)

192-40

144-30

48-10

Anguilla latirostris (Eel) .

240-00

180-00

60-00

§ 82. Veins of Fishes. — As the blood moves in a circle, it
signifies little at what point we commence the description of the
parts in which it flows. But as, in tracing the progress of the
nutriment through the organs concerned in its chylification and
sanguification, we were led by the lymphatics to the veins, we
begin with them the account of the circulating system in the
present class.

The tunics of the veins of Fishes are unusually thin, and their
valves few : though commonly in the form of tubes, yet they more
frequently dilate into sinuses than in the higher classes, and traces
of the diffused condition of the venous receptacles, so common in
the Invertebrates, are not wanting in Fishes ; as, for example, in
the fissures of the renal organs, where the veins seem to lose their
proper tunics, or to blend them with the common cellular tissue
of the part ; and in the great cavernous sinus beneath the abdo-
minal aorta, receiving the renal and genital veins in the Lamprey.
The jugular veins of Osseous Fishes and the hepatic veins of the
Rays form remarkable sinuses. The very delicate fibres of the
proper venous tunic affect a longitudinal disposition : and in many
of the veins of Fishes the walls show pigment, usually in the form
of stellate cells.

The veins of Fishes constitute two well-defined systems ; viz.
the f vertebral ' and the ' visceral,' answering to the division of the
nerves and muscles into those of f animal ' and ( organic ' life : the

o

portal system is a subdivison of the visceral one, but also fre-
quently includes part of the vertebral system of veins, especially
in the Myxines, in which the portal sinus forms a common meeting-
point between portions of both systems.2

The capillary system of vessels consists in Fishes, as in other
Vertebrates, of minute but similar-sized tubules, capable of carrying

1 CCXLV. p. 27.

2 Retzius, iu xxi. * Gefiisssystem,' 1841, p. 16.

VEINS OF FISHES.

465

308

a single file of blood-discs, and connecting the termination of the
arteries with the commencement of the veins, figs. 328, 329.

The vertebral system of veins commences by a series of capil-
lary roots in the integuments and muscles, which unite to form
branches corresponding with the muscular and osseous segments
of the body : these f segmental ' veins consist, in the tail, of upper
or neural, and lower or haemal
branches; in the abdomen, of
upper and lateral branches ; in
the head, where the vertebral
segments are more modified, the
veins manifest a less -regular

o

and appreciable correspondence
with these segments. The ce-
phalic veins, returning the blood
from the cranial vertebras, their
appendages and surrounding
soft parts, from the brain, the
organs of special sense and their
orbits or proper cavities, from
the mouth and pharynx, and,
receiving also the whole or part
of the ' venae mitritiae ' from the
branchial arches, unite together
on each side to form a pair of
( jugular ' veins, fig. 308, v*9 each
of which usually dilates into a
larger simis, and again contracts
and resumes the vasiform cha-
racter, as it descends to beneath
the parapophyses of the atlas
and axis, in order to join the
corresponding trunk of the ver-
tebral veins of the body.1 This
great trunk, called ' vena cardi-
nalis,' 2 fig. 308, v, commences

at the base Of the tail-fin, Circulation of the Mood in the Fish. CCLXVL

where it receives blood, and some affirm also lymph, from the pul-
sating sac there present in the Eel-tribe. The vein-trunk is

1 In the Lamprey the corresponding jugular trunks lie above the aponeurotic repre-
sentatives of the vertebral parapophyses.

2 'La veine cave' of Cuvier; but it is not homologous with either the ' inferior' or
* superior venae cavce ' of Man.

VOL. I.

H

466 ANATOMY OF VERTEBRATES.

double, there being one for each side of the body, and both right
and left ( vcnic cardinales ' extend forward, in close contact, along
the haemal canal in the tail, then through the abdomen, and in both
regions immediately beneath the aorta and vertebral bodies, to near
the first vertebra, where each trunk diverges and descends to join
its corresponding ( vena jugularis,' fig. 308, v, forming the short
' precaval ' vein,1 ib. v, which empties itself in the great auricular
sinus between the aponeurotic layers of the pericardial and abdo-
minal septum. In the Lamprey the vena cardinalis is single along
the tail, but it bifurcates on entering the abdomen into two veins,
each of which is six times as large as the aorta. The left cardinal
vein is larger than the right in the Myxinoids : but the symme-
trical disposition of the vertebral venous system is more disturbed
in many Osseous Fishes, at the expense of the right side ; the right
cardinal vein, after some transverse connecting channels with the
left, finally terminating or losing itself therein anteriorly : part of
the right jugular vein, also, in this case enters the left or common
cardinal vein.2 In the Tunny the two c vena? jugulares ' unite and
form a common trunk, which enters the auricular sinus indepen-
dently.3 The Shad, the Pike, and the Lucioperca are examples
where the jugular veins are symmetrical, and terminate distinctly
in the precaval veins. With regard to the vertebro-venal system
of the trunk, not all the segmental branches terminate in the
( vena cardinalis ; ' the neural twigs form with the myelonal veins
a trunk which runs parallel with the cardinal veins, but above
the vertebral bodies in the neural canal. This trunk, the ( vena
neuralis,' communicates by short lateral and vertical canals with
the venre cardinales, and in the region of the abdomen these short
aiiastomising veins perforate the substance of the kidneys, and
receive the l renal veins ' before terminating in the abdominal

o

cardinal veins. The neural vein gradually exhausts itself by
these descending branches, and does not extend to or terminate
anteriorly in the precaval trunk. Jacobson, observing that the
abdominal anastomotic branches of the neural vein, in transferring
its contents to the cardinal veins, perforated the kidneys, thought

1 Ductus Cuvieri, Rathke; quervenenstcimme, Miiller. The precaval veins are the
homologues of the two ' superior cavse ' in Reptiles and Birds, which receive the so-
called 'azygos' veins or reduced homologues of the ' vense cardinales' of Fishes: in
the higher Mammals and in Man they are concentrated into a single ' superior vena
cava,' receiving the 'venae cardinales ' by a common trunk, thence called 'azygos ' in
Anthropotomy. The anatomical student is usually introduced to the cardinal veins,
as represented by their single homologue in the human subject, where their normal
symmetrical character becomes masked by an extreme modification, and where the
name ' azygos ' is applicable only to so exceptional a condition.

2 xxi. p. 38. a Ib. p. 37.

VEINS OF FISHES. 467

that those branches ramified in the renal tissue, like the portal
veins in the liver ; but my observations concur with those of
Meckel and Cuvier,1 in showing that they rather receive or com-
municate with the renal veins in transitu in Osseous Fishes. In
the Lamprey the renal vein assumes the form of a cellular or
cavernous sinus, of a very dark colour, extending alone- the
mesial margin of the kidney, uniting with its fellow posteriorly,
and communicating by small orifices with the contiguous cardinal
vein.

The visceral system of veins commences in Osseous Fishes by
the capillaries of the stomach and intestines, of the pancreatic
casca and spleen, of the generative organs and air-bladcler : these
by progressive union and reunion, constitute either a single trunk
which forms the portal arterial vein, fig. 308, L, of the liver ; or,
as in the Perch, a second trunk, the true homologue of the ( in-

' O

ferior vena cava ' which returns the blood from the genital organs

O O

and air-bladder to the auricular sinus, without previous ramifica-
tion in the liver ; the portal trunk being formed only by the veins
of the alimentary canal and its appendages. The portal trunk is
single in the Ling, the Burbot, the Pope, the Eel, the Lamprey,
and the Plagiostomes ; but, in the Carp, where the lobes of the
liver interlace with the convolutions of the intestine, the veins of
this canal pass directly into the liver by several small branches,
which ramify therein without forming a portal trunk.

In the Plagiostomes with the longitudinal spiral valve the main
root of the portal vein is concealed in the free, thickened, muscu-
lar margin of that valve : 2 the trunk of the intestinal vein is

O

lodged also in an internal fold of the mucous coat in the Lamprey :
in the Plagiostomes and Ganoids with transverse coils of the spiral
valve, the venous blood is collected into an external intestinal vein.
In the Paddle-fish this vein joins the vein of the spleen (fig. 276,
ft), and then, with the duodenal, pancreatic, and gastric veins,
forms the portal trunk.

Professors Eschricht and Miiller 3 found, in the Tunny, that
the veins of the stomach, intestine, pyloric appendages, and
spleen, respectively subdivided into numerous minute venules,
which interlaced with corresponding ( retia mirabilia ' of the
arterial branches sent from the coeliac axis to the same viscera,
and formed pyriform masses of vessels before entering the liver.

In a few Osseous Fishes, as the Shad, some of the caudal
branches of the vertebral system of veins anastomose with the

. p. 381. 2 xcvni. p. 274. 3 em.

H H 2

4G8

ANATOMY OF VERTEBRATES.

veins of the rectum, and thus form part of the roots of the portal
system. But the most interesting modification of the portal
system of Fishes is that discovered by Ketzius in the Glutinous
Hag. In this and also in other Myxinoids, the genital and intes-
tinal veins form a common trunk aloni>; the line of attachment of

o

the mesentery : all the gastric veins that do not empty themselves
into the cardinal vein also join the great mesenteric vein. This
vein advances to the space between the pericardium and the right
suprarenal body, receives the anterior vein of that body (its posterior
one joining the cardinal vein), and dilates into an elongated sinus,
which is said to contract, as if it were a portal heart. The ante-
rior part of this sinus receives a vein from the right anterior
parietes of the body, which is formed by the union of all those
of the muscular parts there which do not join the right jugular
vein : the portal arterial vein is sent off from the posterior end of
the pulsating sac, near the entry of the mesenteric vein, and goes
backward to beneath the two livers, and there divides, enters, and
ramifies in each. The hepatic vein of the hinder and larger liver
enters the common trunk or sinus formed by the union of the two
cardinal veins with the left jugular : the hepatic vein of the smaller
liver joins the termination of the left jugular vein, and they toge-
ther end in the opposite side of the same common sinus.

In the Plagiostomes the right jugular and cardinal veins unite,
and, receiving the vein of the pectoral fin (brachial vein), and a
superficial vein from the head (external jugular), form a short
transverse ' precaval ' trunk. A corresponding precaval trunk is
formed in the same way on the left side, and the great auricular
sinus is constituted by these and by the wide hepatic veins, which
contract before they terminate. In many Osseous Fishes, as
Salmo, SiluruSy Belone, Anyuilla., Ammodytes, and Accipenser,

the hepatic veins terminate in the
common sinus by a single trunk ;
in others, as Tliynnus, Gadus,
JEsox, and Pleuronectes, by two
trunks ; and in a few Fishes, as
Clupea, Coitus, and certain Cy-
prinoids, by three or more trunks.
The pulsatile sac in the Eel,
309, is situated near the
beginning of the cardinal vein
on the ha3mal side of the caudal
vertebras at the end of the tail.
It is of a yellowish colour,

309

fig.

Caudal venous heart of Eel

CCLXIV.

niagn. 20 diam.

VEINS OF FISHES. 469

checquered more or less with stellate pigment ; in shape fusiform,
fig. 309, A, or pyriform, ib. B ; at the distal end it is connected
with a small vein, c9 which collects the blood from the capillaries
of the tail, d, d' : at its proximal end it is connected with the
commencement of the cardinal vein, I). The blood, which is deep
red, appears to flow into the sac in a continuous stream from c ; it
is forced out at each contraction in an interrupted current, quickly,
in successive portions, into b, where the movement soon subsides
into a continuous stream. During the systole the veins c and b
are lengthened, being drawn out ; in the diastole they resume
their size, and assist in elongating the sac ; which, both by
its contents and connections, is to be regarded as a f venous
heart.' 1

Thus in Fishes the chyle, having already begun to manifest its
independent life by the developement of distinct microscopic
granular corpuscles, as primitive centres of assimilative force,
before it enters the lacteals, undergoes in those vessels and their
receptacles a further stage of conversion into blood by the reaction
and, as it were, impregnation of the lymph, and by the interchange
of properties therewith : the vitalising stimulus of which inter-
change and reaction is manifested by the repeated spontaneous
fission of the corpuscles, many of which now acquire a capsule,
and thus become nuclei of cells. Then the mixed chyle and
chyme enter the veins, where a further interchange of properties
with the venous blood and a new course of action and reaction
takes place. The primitive pale chyle-corpuscles are here few in
number ; they have a capsule, and the granular character of their
contents shows them to be in the course of change. The venous
blood undergoes some change, probably, in its passage through the
kidneys, by virtue of the anastomoses of the renal vascular
system : it undergoes further change in its circulation through
the liver, in so far as the bile, a fluid highly charged with
carbon and hydrogen, is eliminated from it : that in some fishes
(JShjxine., Bdellostoma) a contractile receptacle accelerates its
course through the portal circulation. The venous blood now
shows a marked accession of coloured corpuscles ; and it has
finally to be submitted to the influence of the atmosphere, and
especially to the reaction of the oxygenous element ; and for this,
the most important and efficient cause of its conversion into
arterial blood, a contractile cavity, with strong muscular walls, is
provided, in order to impel the blood to the organs especially des-
tined to effect its decarbonisation and oxygenation.

1 CSLV. p. 253 (1846).

470 ANATOMY OF VERTEBRATES.

§ 83. Heart of Fishes.- -The propelling organ is called the
' heart,' fig. 308, n ; the respiratory organs the ( gills ' or branchiae,
ib. B, b ; fig. 312, i, 6 ; fig. 323, 2, 3, 4, 5 ; they submit the blood
to the influence of the air through the medium of the water in
which it is suspended or dissolved.

There is only one known fish, viz. the Lancelet, in which a
venous or branchial heart is not developed as a compact and pre-
dominant muscular organ of circulation : a great vein answering
to the ' vena cardinalis ' extends forward along the caudal region,
beneath the chorda dorsalis, above the kidney, fig. 169, h ; and as
it extends along the branchial ossophageal sac gives vessels to or
receives them from the ciliated vertical bands or divisions of that
sac, which vessels communicate with a vascular trunk along the
inferior part of that sac. This trunk at its posterior end dilates
into a small sinus, ov, which pulsates rhythmically, and represents
rudimentally the branchial heart of the Myxinoids : the cardinal
vein, ba, divides anteriorly, and supplies the short vascular pro-
cesses, gg, which project above the pharyngeal orifice, ph, into the
wide buccal cavity : the blood oxygenized in these processes is
transmitted to the cerebral portion of the neural axis, to the
organs of sense, especially the sensitive integument of the head,
and to the jointed labial tentacula, f, f, whence it returns to the
pharynx by the labial vessels which there unite together, and with
the inferior trunk of the vascular system, or arches, of the branchial
pharynx.

In the Myxinoids a heart consisting of an auricle and a ven-
tricle is situated, like the pulsating tube or sinus of the Lancelet,
far back from the head, in the beginning of the abdomen, where
it is inclosed by a fold or duplicature of the peritoneum, extending
between the cardiac end of the oesophagus above, and the anterior
liver below, and forming the homologue of the pericardium, which
sac communicates freely by a wide opening with the common
peritoneal cavity. The auricle is much longer than the ventricle :
it receives the blood from the common sinus by an orifice defended
by a double valve. The auricle communicates with the left side
of the rounded ventricle, the { ostium venosum ' having also a double
valve. There are no e columnar earner ' or ( chordae tendinese.' The
artery, single here as in all Fishes, rises from the fore-part of the
ventricle with a pair of semilunar valves at the ' ostium arteriosum '
behind its origin, beyond which it slightly dilates, but has no
muscular parietes constituting a ' bulbus arteriosus.' In a large
Myxinoid (Bdellostoma cirratum, Dum.) the vessel from the heart
divides at once into two branchial trunks, reminding one of the

HEART OF FISHES.

471

310

separate branchial arteries of the Cephalopoda.1 In other species
of Bdettostoma the artery extends beyond two or three pairs of
gills before it bifurcates; and Miiller2 saw one instance in the
Mijxine glutinosa, where the branchial artery
continued single as far as the anterior gills.

The pericardium of the Ammocete com-
municates by one wide orifice with the peri-
toneum : that of the Lamprey is a shut sac,
and is supported by a perforated case of
cartilage, formed by the last modified pair of
branchial arches, fig. 310, m. Not any of the
Dermopteri possess the < bulbus arteriosus : '
this is present, and forms, as it were, a
third compartment of the heart, 311, B,
beyond the ventricle, ib. A, and auricle, ib.
C, in all other Fishes : nay, if we include
the great ( sinus communis,' ib. D, as part of
the heart, then we may reckon four cham-
bers in that of Fishes; but these succeed L-
each other in a linear series, like the centres
of the brain, and their valves are so disposed
as to impress one course upon the same cur-
rent of blood from behind forward, driving
it exclusively into the branchial artery and
its ramifications. This is very different
from the arrangement and relations of the
four compartments of the human heart.
Physiologically the heart of Fishes answers
to the venous or pulmonary division, viz.
the rischt auricle and ventricle of the mammalian heart, and

O '

its quadripartite structure in Fishes illustrates the law of vege-
tative repetition, rather than that of true physiological compli-
cation. The auricle and the ventricle are, however, alone proper
to the heart itself: the sinus is a developement of the termination
of the venous system, as the muscular bulb is a superaddition to
the commencement of the arterial trunk. The heart of Fishes
with the muscular branchial artery is the ' homologue ' of the left
auricle, ventricle, and aorta in higher Vertebrates ; but it performs
a function ( analogous ' to that of the pulnionic auricle and ventricle
in them.

Some of the higher organised Fishes, which present the normal
structure of the heart, have, like the Myxinoids, a perforated

Heart and gills, Lamprey
(Petromyzon). cxx.

1 xx. vol. ii. p. 78, prep. no. 1018.

xxi. p. 9.

472

ANATOMY OF VERTEBRATES.

pericardium. In the Sturgeon the communication with the peri-
toneum is by a single elongated canal extending along the ventral
surface of the oesophagus. In the Planirostra and Chimaeroids
the pericardio-peritoneal canal is also single. In the Plagiostomcs

311

Heart and gill-arches, Perch, xxm.

it bifurcates,, after leaving the pericardium, into two canals, which
diverge and open into the peritoneum, opposite the end of the
esophagus : no ciliary movements have been noticed on the
surface of these remarkable conduits. The serous layer of the
pericardium is defended by an outer aponeurotic coat in Osseous
Fishes and Plagiostomes, which adheres to the surrounding parts.
In the Sturgeon, Wolf-fish, Loach and Murrena, short fibrous
bands supporting vessels pass from different parts of the peri-
cardium to the surface of the heart : in most other fishes the heart
hangs freely except at the two opposite poles, viz. where the
sinus communicates with the auricle, and where the bulbus
arteriosus is continued into the branchial artery.

In the Plagiostomes the sinus itself is situated within the peri-
cardium ; but in Osseous Fishes between the layers of the posterior
aponeurotic partition between it and the abdomen. The heart is sit-
uated below the hind-part of the gills, and, as these are more concen-
trated in the head in all Fishes above the Dermopteri,so the position
of the heart is more advanced, fig. 308, H. In the Plagiostomes, the
Sturgeons, and many Osseous Fishes, e.g. the Perch, the Angler
(Lophius), and the Sun-fish ( Orthagoriscus),the orifice by which the
great sinus communicates with the auricle is guarded by two semilunar
valves ; but these are far from being constant in the Teleostomi.
The auricle, when distended, is larger in proportion to the ventricle

HEART OF FISHES. 473

in Fishes than in higher Vertebrates. Its relative position to the
ventricle varies in different species, and permanently represents as
many similar variations displayed temporarily during the course of
the heart's developement in birds and mammals ; thus in the heart
of Scorp&na scrofa., as in the Myxinoids, the auricle is posterior to
and in the same longitudinal line with the ventricle : in the
Perch, fig. 311, c, Carp, Sole, and Eel, it has advanced to the
same transverse line, on the dorsal and left side of the ventricle :
in the Sturionidje and other Ganoids it extends more forward,
dorsad of both ventricle and bulbus arteriosus, and the heart,
including the venous sinus, is now bent into a sigmoid form. The
walls of the auricle are membranous, with thin muscular fasciculi
decussating and forming an open network ; but these are closer
and stronger in the Sun-fish, Sturgeons, and Plagiostonies. The
cavity is simple, but its inner surface is much fasciculated in the

Sun-fish and Sturgeon, where the ends of the valves of the sinus

~ 3

are attached to the strongest muscular bands. Only in the
Lepidosiren is there any vestige of a septum, and this is reticu-
late. The auricle communicates by a single orifice, commonly
with the dorsal or the anterior part of the ventricle : this is
guarded usually by two free semilunar valves ; but in the
Sturgeon, their margins and their surface next the ventricle are

O O

attached to numerous ( chords tendinea?.' In the Orthagoriscus
the auricular aperture is guarded by four semilunar valves, the
two smaller ones being placed at right angles with and on the
auricular side of the two larger and normal valves : their margins
are free.

The ventricle, fig. 311, A, usually presents the form of a four-
sided pyramid, one side dorsad toward the auricle ; one angle
ventrad, and the base forward. In the Lepidosteus and Poly-
pterus, however, it is pyriform : in the Pike it is lozenge-shaped :
in the Lophius, as in the Myxinoids and Lampreys, it is oval : in
most Plao;iostomes its transverse diameter is the longest, as if

O CD

preparatory to a division. Its cavity is, however, simple in all
fishes. The parietes of the ventricle are very muscular, and the
fibres are redder than those of any other part of the muscular
system ; but the colour is less deep in the ground-fishes than in
those that swim nearer the surface, and enjoy more active loco-
motion and respiration. The exterior muscular fibres decussate
and interlace together irregularly and inextricably ; but the
deeper-seated ones form more regular layers, the innermost being
transverse and circular, and separating readily by slight decom-
position from the outer and more longitudinal layers. Some of

474 ANATOMY OF VEUTEBTCATES.

the internal fasciculi send off the ' chorda? tendineae ' above men-
tioned in the Sturgeon; but in almost all other fishes those
f chords ' are absent, and the auricular valve is free. In most
Osseous Fishes the orifice at the base of the bulbus arteriosus is
provided with a pair of semilunar valves : the Sun-fish ( Orthayo-
77'scM.s) has four such valves there.1 But the Ganoids, Holocephali,
and Plao'iostomcs have two or more transverse rows of semilunar

o

valves attached to the inner surface of their long and muscular
bulbus arteriosus. There are two rows of three valves in the
Grey Shark (Galeus), in the Blue Shark (Carcharias), in the
Dog-fish (Scyllium), and in the Chimaeroids : the Amia has two
rows of six valves : in the genera Sphyrna, Mustelus, Acanthias,
Alopias, Lamna, Rhinobatus, Torpedo, and Accipenser, there are
three rows of valves: the Sturgeon's heart2 shows five valves in
the anterior row, and four valves in each of the other rows ; and
the free margins of the valves are connected by short ( chordae
tendineaa ' to the parietes of the bulb. The genera Hexanthus,
Heptanchus., Centrophorus, and Trygon have four rows of valves.
The heart of the Raia Batis3 shows five rows, the valves
increasing;; in size to the last row, which is at the termination of

o

the bulb. Scymnus, Squatina, and Myliobat's have also five
rows of valves. In Cephaloptera the large bulbus arteriosus 4
presents internally three longitudinal angular ridges, at the sides
of which are small valves disposed in pairs, and in four or five
rows : besides these there are three larger valves at the begin-
ning, and three at the end of the bulb. The valves are still more
numerous in lepidoganoid fishes, and are arranged in longitudinal
rather than in transverse rows : the Polypterus shows three such
rows of nine or ten larger semilunar valves alternating with as
many rows of smaller valves. The Lepidosteus has five longi-
tudinal rows of sub-equal valves : those at the end of the bulb
being always the largest and most efficient. In the Lepidosiren
the place of valves is supplied in its long and twisted bulbus
arteriosus by two longitudinal ridges, fig. 312, c ; 5 the interesting
stages, which we have been tracing through the highly organised
Ganoids and Plagiostomes, in the partition of the bulb into
distinct arterial trunks for the systemic and pulmonic circulation,
being most advanced in this amphibious fish.

The auricle in the Lepidosiren annectens, ib. «, is essentially
single, but has two ear-like appendages.6 The venous sinus

1 xx. ii. p. 37, prep. no. 905. 2 Ib. p. 38, prep. no. 908. 3 Ib. p. 38, prep. no. 909.
1 I found its cavity more capacious than that of the contracted ventricle.
5 xxxm. p. 343. p. pi. xxvi. fig. 2. c. G Ib. p. 345.

GILLS OF FISHES.

475

312

communicates with it without any intervening valve ; the auricle

receives the vein from the air-bladder by a distinct aperture, close

to the opening into the ventricle ; regurgitation into the vein

being prevented by a hard valvular

tubercle, which also projects into the

ventricle. The ventricle (fig. &) is

single, like the auricle ; its inner

parietes are very irregular : a ' tra-

becula ' projects from the lower

part of the cavity, like a rudimental

septum : a smaller transverse ( tra-

becula' arches over and acts as a

valve to the single auriculo-ventri-

o

cular opening, but there are no
proper membranous semiluuar
valves.

The muscular parietes of the
'bulbus arteriosus' are distinct in
all fishes from those of the ventricle ;
they may be overlapped by these,
but an aponeurotic septum inter-
venes between the origin of the bulb

i?

and the overlapping ventricular
fibres.1

§ 84. GUIs of Fishes.- -The primary division of the branchial
artery in the Myxinoids has been already described. Each gill-
sac receives, either from the trunk or its bifurcations, its proper
artery. The leading condition of the gills in other fishes may be
understood by supposing each compressed sac of a Myxine, fig.

CircuIatJr.'-r cind respiratory organs,
Lepidosireu

313

314

Two gil1- •: r=, L'JcUo-
stoiiia

Two gill-sacs, Lamprey

313, m, to be split through its plane, and each half to be glued by
its outer smooth side to an intermediate septum, which would then
support the opposite halves of two distinct sacs, and expose their
vascular mucous surface to view. If the septum be attached by

1 xx. vol. ii. p. 39, prep. no. 910.

476

ANATOMY OF VERTEBRATES.

its entire margin, the condition of the plagiostomous gill is effected.
If the septum be liberated at the outer part of its circumference
and the vascular surfaces are produced into pectinated lamelli-
gerous processes, tufts, or filaments, proceeding from the free arch,
the gill of an ordinary osseous or teleostomous fish is formed.
Such a gill is the homologue, not of a single gill-sac, but of the
contiguous halves of two distinct gill-sacs, in the Myxines.
Already, in the Lampreys, the first stage of this bi-partition may
be seen, fig. 314, m, and the next stage in the Sharks and Rays:
consequently in these fishes, a different artery goes to the anterior
branchial surface of each sac or fissure from that which supplies
the posterior branchial surface of the same fissure ; whilst one
branchial artery is appropriated to each supporting septum or
arch between the fissures, as it is to the liberated septum or
branchial arch in the Teleostomi.1 Before describing the branchial

o

vessels it will be necessary to describe the organs upon which

they ramify.

In the Lampreys and Plagiostomes each supporting septum of

the two (anterior and posterior) branchial mucous surfaces is

attached to the pharyngeal and dermal integu-
ments by its entire peripheral margin, and the
streams of water flow out by as many fissures
in the skin, ib. k, as those by which they enter
from the pharynx, ib./: these are called ( fixed
gills,' and the species possessing them are cha-
racterised as 'pisces branchiis fixis.' In the
Teleostomi = Osseous, Plectognathic, Lopho-
branchiate, Ganoid, and Holocephalous fishes,
the outer border of the supporting branchial
arch is unattached to the skin, and plays freely
backward and forward, with its gill-surfaces,
in a common gill-cavity which has a single
outlet, usually in the form of a vertical fissure :

the species with this structure are called ( pisces branchiis

liberis.'

In the Myxine the outlets of the six lateral branchial sacs, fig.
315, m, on each side are produced into short tubes, which open
into a longitudinal canal, k, directed backward, and discharging

1 CXLV. p. 258. Prof. Milne Edwards has exemplified this homc-lo^y by the sub-
joined formula -.—

Osseous Fishes B . ac . B 1 B2 B.3 B4

315

Branchial organs,
Myxiue

Plagiostomous Fishes

b.b

b b

B 1 B2

b b

B2

b b

b.

B4 B 5

GILLS OF FISHES.

477

116

the branchial stream by an orifice, h} near the middle line of the
ventral surface : between the two outlets of these lateral lono-i-

o

tudinal canals, but nearer the left one, is a third larger opening,
i, which communicates by a short duct with the end of the long
oesophagus^ /, and admits the water, which passes from that tube
by the lateral orifices, f} leading into the branchial sacs. This is
the first step in developement beyond that simpler condition which
prevails in the Lancelet, where the whole parietes of a much
dilated oesophagus, fig. 169, rr, are organised for respiration ; and
besides the pharyngeal opening, ph, the sac communicates by a
short and wide ( ductus cesophago-cutaneus,' ib. od, with the
external surface, and also with the peritoneal cavity. The
common respiratory surface of the oesophagus is ciliated in the
Lancelet. The sacs developed from the oesophagus, and specially
set apart for respiration in the Myxinoids, have a highly vascular,
but not a ciliated mucous surface : this is disposed in radiated
folds, and is further increased by secondary plicae. The seven
branchial sacs on each side of the oesophagus
have short external ducts, fig. 313, k, which
open by as many distinct orifices in the skin
in a species of Bdellostoma hence called hep-
tatrema : the internal branchial ducts com-
municate by as many openings, ib. f9 with
the oesophagus. In the Lampreys there are,
also, seven stigmata on each side ; but another
stage in the separation of the respiratory from
the digestive tract is here seen, for each in-
ternal duct communicates with a median
canal, fig. 310, d, beneath and distinct from
the oesophagus, terminating in a blind end
behind, and communicating anteriorly with
the fauces by an opening guarded by a double
membranous valve.

In all higher fishes the inlets to the branchial
interspaces are situated on each side the
fauces, and are equal in number with those
interspaces, fig. 316, i — 5. The outlets are,
with the exception of the Plagiostomes, single
on each side : they vary much in size ; are
relatively largest in the Herring and Mackerel
families, smallest in the Eels and Lophioid
fishes ; in some of the small Frog-fishes,
Antennarius, the circular branchial pore is produced into a

Branchial slits and lungs,
Lepidosiren. xxxm.

478 ANATOMY OF VERTEBRATES.

short tube above each pectoral fin. The power of existing
long out of water depends chiefly on these mechanical modi-
fications for detaining a quantity of that element in the
branchial sacs ; for fishes perish when taken out of water, chiefly
by the cohesion and desiccation of their fine vascular branchial
processes, through which the blood is thereby prevented from
passing.1 If sufficient water can be retained to keep the gill-
plates floating, the oxygen which is consumed by the capillary
branchial circulation is supplied to the water retained in the
branchial sac directly from the air. In some of the Eel tribe the
small branchial outlets are closely approximated below, as in
Sphagebranclius ; and they are blended into a single orifice in
Si/mbranchus, analogous to that in the Myxine. In some Ganoids,
many Plagiostomes, fig. 137, br, and all Sturgeons, a canal leads
from the fore part of each side of the branchial chamber to the
top of the head ; the outlets are called ' spiracles,' the canals
6 spiracular.' The nasal sac communicates in the Lamprey with
the single homologous canal, the inner or faucial aperture of
which is shown at c, fig. 277.

The branchial chamber is largest in the fishes which have the
smallest outlets, as, e.g., in the Eel tribe, the Uranoscopi, the
Blennies, and especially the Lophioids : extending backward in the
Angler (Lophius piscatorius) towards the hind part of the abdomen,
with a proportional elongation of the branchiostegal rays ; and
still further back in Halieutea. The opercular flaps forming the
outer wall of the gill- chambers are described at pp. 123, 124,
fig. 84 ; the branchial arches at p. 106, fig. 85. The basi-
branchials are usually present only in the two or three anterior
arches, the others joining below directly, or by the medium of a
gristly plate ( Trigla) to the last basibranchial ; or terminating
loosely, as in Murenophis. The hypobranchials are usually
present only in the first or second arches : the most constant
elements, both as to existence and shape, are the ceratobranchials,
fig. 85, 47, and epibranchials, ib. 48. The pharyngo-branchials,
ib. 49, vary in shape and tissue ; they attach the arches to the
base of the skull, and develope, with the anterior epibranchials,
fig. 325, the complex labyrinthic appendages of the branchial
apparatus in the Climbing Perch (Anabas) and its allies. In
Lophius and Diodon there are only three pairs of branchial arches.
The fissures between the arches become shorter as they recede in
position, the last being commonly a mere foramen : their vertical
extent shows an agreement with that of the outer gill-slit : they

1 cvi. p. 124.

GILLS OE FISHES.

479

317

A branchial leaf, with the respiratory capillaries on side,
Cod. CCLXVIII.

are long, e.g. in the Mackerel ; short in the Eel : in the Lopho-
branchs they are one-third the length of the arches : in the
Plectogonaths they are half that length ; in the Carp-tribe they
are nearly as long, in the Salmon-tribe quite as long, as the
branchial arches themselves.

The main purpose of the gills of fishes being to expose the
venous blood in a state of minute subdivision to streams of water,
the branchial arteries rapidly divide and subdivide until they
resolve themselves into mi-
croscopic capillaries. These
constitute a network in one
plane or layer, fig. 317,
supported by an elastic
plate, and covered by a
tessellated and non-ciliated
epithelium. This covering
and the tunics of the capil-
laries are so thin as to
allow the chemical inter-
change and decomposition
to take place between the carbonated blood and the oxygenated
water. The requisite extent of the respiratory field of capillaries is
gained by various modes of multiplying the surface
within a limited space. In the Marsipolranchii
and Plagiostomi, for example, by folds of mem-
brane on plane surfaces : in the Lopholranchii by
clavate processes grouped into tufts : in the Pro-
topteri, by double or single fringes of filaments :
in the rest of the class by the production of the
capillary-supporting plates from each side of long,
compressed, slender, pointed processes, extending,
like the teeth of a comb, but in a double row, fig.
3 1 8, d, d, from the convex side of each branchial arch,
fig. 311, b.

Each pair of processes has its fiat sides turned
toward contiguous pairs, and the two processes of
each pair stand edgeways toward each other,, and
are commonly united for a greater or less extent
from their base : hence Cuvier describes each pair
as a single bifurcated plate, ( feuillet.' ]

In the Swordfish (Xiphias), the processes of the
same pair stand quite free from each other ; whence

318

Aristotle described this fish as having double the

1 xxin. i. p. 379.

Diagram of the cir-
culation of the blood
through the bran-
chial leaflets. Fish.

XXIII.

480 ANATOMY OF VERTEBRATES.

usual number of gills.1 But to compensate for tins independ-
ence, and to prevent the inconvenience of mutual pressure,, the
processes of the same series are united together by little vascular
lamella;, so that the surface of the gill is reticulate rather than
pectinate. In the Orthayoriscus the processes of each series are
not opposite, but alternate. In a few species the processes of
each pair are joined together to near their apices, as in the
Sturgeon, in which the musculo-membranous medium of union
extends from pair to pair throughout the entire gill, forming a
true ' septum branchiale,' and presenting a transition to the more
complete septum which divides the respiratory vascular surfaces
in the Plagiostomes.

In fig. 318, the course of the blood through a pair of branchial
processes is diagrammatically shown : a is a section of the
branchial artery ; d is the branch sent along the outer margin of
the process ; e is the vessel receiving the blood from the capil-
laries after the respiratory change has been effected, and returning
it, along the inner border of the process, to the branchial vein, the
sectional area of which is shown at c. In fig. 319 are shown the
vascular plates or lamellae, b, of the branchial processes, A7, in the
Cod (Morrliua vulgaris), in which they are confined to the inner
half or two-thirds of the process. Fig. 317, representing a trans-
verse section of the process, shows the degree and form in which
the plates extend from it on each side : the arrows indicate the
course of the blood from the outer to the inner border of the
plate-bearing process. Fig. 320 represents the frame-work
supporting the vascular structure of the gill : a is a section of the
branchial arch ; b is the base of the branchial process attached to
but distinct from the arch : c its outer obtuse border ; d its inner
border, from which are continued the elastic cords, f, extending
along the outer margin of the lamellae, fig. 317, i, and maintaining
them outstretched.2 The number of plates on one process has been
estimated at 55 in the Gudgeon, 96 in the Tench, 106 in the
Barbel, 135 in the Carp, 700 in the Eel, 1000 in the Cod,
1400 in the Salmon, 1600 in the Sturgeon.

In some Osseous Fishes certain of the branchial arches support
only one series of processes ; such are called e um'serial,' or ' half
gills ; but, as a general rule, they support ' biserial,' or ( whole '
gills. Most of the Labroids, the genera Coitus, Scorpcsna,
Selastes, Apistes, Zeus, Antennarius, Polypterus, Goliesox,

1 xxni. t. yiii. p. 192.

2 For the histology of these structures, see Dr. Williams's minute description in
CCLXVIII. pp. 288-290.

GILLS OF FISHES.

481

Lepadoy aster, and the Cyclopterus liparis have three biserial gills
and one uniserial gill ; the genera LopJiius, Batrachus, Diodon,
Tetrodon, Monopterus, Cotylis, have three biserial gills ; Malth&a
and Lepidosiren have two biserial gills and one uniserial gill ; the

319

320

Section of branchial arch with a pair of processes, Section of branchial arch, a, with supporting frarae-
A', supporting the branchial plates, b, Cod. work of the plate-bearing processes, Cod.

CCLXVIII. CCLXVIII.

Cuchia {Amphipnous) has only two gills. The above enumeration
refers to the branchial organs of one side ; they are symmetrical
in all fishes, and the uniserial opercular gill is not counted, as not
being attached to a proper branchial arch.

The branchial processes are bony, at least along the outer and
thicker border, in most Osseous Fishes (e.g. Salmo, Alosa, Gadus).
They are gristly, like the arches which support them, in the
Sturgeon, where they break up into delicate branched fringes,
along their outer margin. Small ( interbranchial ' muscles extend,
through the uniting septum, between the bases of the processes,
for effecting slight reciprocal movements.1

VOL. I.

1 CXII. CXIII.

II

482 ANATOMY OF VERTEBRATES.

The concave borders of the branchial arches are usually beset
with defensive processes, fringes, or tubercles, and these sometimes
support small teeth which aid in deglutition ; but the chief office
of these appendages, which project inward toward the mouth, is to
prevent the passage of any particles to the interspaces of the gills,
which might injure or irritate their delicate texture. In the
edentulous Sturgeon and Paddlefish each arch supports a close-set
series of such retroverted slender tapering filaments, fig. 276,
Avhich are longer than the opposite branchial processes, ib. u :
they are developed even from the fifth or pharyngeal arch, which
has no gill. Similar fringes of extreme delicacy defend the
branchial slit in the Gray Mullet. Frequently such a fringe is
developed only from the first branchial arch, Mackarel, Perch,
fig. 85, 63, the rest supporting dentated tubercles, fig. 321, and
the last or pharyngeal arch being beset with teeth only. In the
Remora and many other Fishes, the defensive tubercles on
opposite sides of the same branchial fissure interlock, like the
teeth of a cog-wheel. In the Lepidosiren annectens, fig. 316,
short valvular processes are developed from the sides of those
branchial fissures only which lead to the gills, the first and second
arches having no gills. In the Confer, all the branchial arches

O o O y

are devoid of defensive fringes or tubercles.1

~

The immediate force of the heart's contraction is applied by a
short and rapidly divided arterial trunk, fig. 308, B, upon the
branchial circulation. Only in a few fishes is the heart removed
backward from the close proximity of the gills, and then the
branchial artery is proportionally elongated ; as in the Eel tribe,
especially the SynbranchidcB : the artery is long in the Planirostra,
fig. 276, s. The primary branches are always opposite and sym-
metrical, but vary in number in different species. Very commonly,
as in the Perch, they are three in number on each side ; the first
branch dividing, as in fig. 308, B B, to supply the fourth and third
gills, the second going to the second, and the third to the first
gill, ib. b, be. In the Polypterus and Skate there are only two
primary branches on each side : the first supplies the three poste-
rior gills ; the second, formed by a terminal bifurcation of the
branchial trunk, supplies the anterior gill in the Polypterus, and
in the Skate bifurcates to supply also the uniserial, opercular, or
hyoid gill. The Fox-Shark (Alopias) and the Lepidosteus give
examples of four pairs of primary branches from the branchial

1 Sec prep. 1038. (Conger), and its description, xx. 1834, p. 83.

GILLS OF FISHES.

483

321

trunk. In the Shark the first pair come off close together from
the dorsal part of the trunk : the arteries of the last pair quickly
bifurcate, and thus each of the five branchial fissures receives its
artery. The Myxinoids offer the exceptional instances of the
bifurcation of the branchial trunk by a vertical division into two
lateral forks, extended in one species to near its base : the
Lepidosteus presents the still rarer example of the trunk being
cleft horizontally into an upper and lower primary division ; the
upper or dorsal division sends off two branches on each side, the
posterior dividing to supply the fourth, fig. 323, 5, and third,
ib. 4, gills, the anterior going to the second gill, ib. 3 : the lower
division sends off the pair of arteries to the first pair of gills,
ib. 2, then extends forward and bifurcates to supply the uniserial
opercular gills, ib. i, which are present in this ganoid genus, as
in the Sturgeon.1 In the Cod
and other Osseous Fishes the
vessels on each side, which are
analogous to the pulmonary
veins in man, unite to form the
6 aortic circle,' fig. 321, a, which
encompasses the basisphenoid,H.
The current of arterialised blood
fl:>ws forward at the fore-part of
this circle into the hyo-oper-
cular, of, and orbito-nasal, I,
arteries ; but the main streams
are directed backward, and con-
verge in the direction of the
arrows to the aortic trunk. The carotids, c, the homologues of the
subclavians, d, sent to the pectoral fins, and sometimes the coro-
nary vessels of the heart, are sent off from the aortic circle. But
no systemic heart or rudiment of a propelling receptacle is de-
veloped in any fish at the point of confluence of the branchial
veins.

Small vessels are sent off from th3 marginal branchial venules
by short trunks, which ramify beneath the branchial membrane,
and become the ' arterias nutritiae ' of the gills : their capillaries
are collected into venous trunks, which quit the gills commonly
at both their extremities, those from the dorsal ends joining
the jugular veins, those from the ventral ends emptying

Commencement of Systemic Circulation, Dorse
(Gadus Callarias). xxv.

1 XXV.

i i 2

484

ANATOMY OF VERTEBRATES.

themselves into the proscavals, or directly into the great auricular
sinus.1

Such is the outline of the general structure of the beautiful
and complex mechanism of the normal or pectinated gills of fishes.
Of this there are many minor modifications ; some of which receive
explanation from known phenomena in the dcvelopement of the
gills ; 2 others, tclcogically, from the habits of the species.

Five branchial arches and arteries, or vascular hoops, are
developed on each side in the embryo of all fishes above the Der-
mopteri, as a general rule.3 At first the trunk of the branchial
arteries simply bifurcates, the divisions passing round the pharynx

and reuniting on its dor-
sal surface, to form the
aorta. Behind this pri-
mary circle, which cor-
responds with the fold
developing the hyoid and
mandibular arches, four
additional arterial hoops
are sent off, fig. 322, ?/,
which traverse, without
further ramifications, the
convex side of the four
anterior simple branchial arches, and reunite above in the aortic
trunk, ib. m. If a sixth arterial arch be developed, correspond-
ing with the fifth branchial arch, as its presence in the Lepi-
dosiren would indicate, it has not been observed, and must
soon disappear in most Osseous Fishes. In these the gills make
their appearance as leaflets budding out from the convexity of
the four anterior branchial arches, each leaflet supporting a
corresponding loop of the branchial artery ; and, as the bifur-
cation and extension of the primary leaflets and the pullulation
of secondary laminae and loops proceed, the vascular arch begins to
separate itself lengthwise into two channels, traversed by opposite
currents, and thereby establishing an arterial, fig. 318, d, and a
venous, ib. e, trunk in relation to the loops and their vascular
developements on the branchial processes. In Osseous Fishes

1 These ' vena? nutritisD' are unusually large in the Carp; but are not, as Du Verney
supposed (cvm.), directly continued from the true ' venas branchiales;' and they do
not, therefore, divert any of the stream of arterialised blood from the aorta to pour it
directly into the venous sinus. See Muller, XXT, 1841, p. 28.

2 cxi. cxn. cxi ii.

3 The six-gilled Shark (Hexanchus) and the seven-gilled Shark (Heptanchii*} are
among the few exceptions.

Embryo Osseous Fish

GILLS OF FISHES.

4S5

323

Branchiae mid pseudo-branchia,
Lcpidoftcus. xxn.

324

the primary arterial arch, corresponding with the anterior or
hyoid one, developes either a simple
(uniserial) gill, or a plexiform, plu-
mose, rudiment of a gill, or both, or
neither. In the Lepidosteus this arch
retains its primitive connection with
the extremity of the branchi-arterial
trunk, and developes on each side a
small uniserial pectinated gill, fig. 323,
i, from the membrane clothing the
inner surface of the cerato-hyoid and
preopercular bones : the vein or effe-
rent vessel, e, of this gill goes to a smaller
pectinated organ, ib. K, consisting like-
wise of one series of vascular filaments, which agrees with the
( pseudobranchia ' of other fishes in being supplied with arterial
blood. In the Sturgeon, the Lepidosiren, and the Plagiostomes the
representative of the primary vascular arch has become, by partial
bifurcation of the branchi-arterial
trunk, a secondary branch, sent off
by the artery of the first branchial
arch: but it nevertheless developes
a simple gill, of one series of filaments
in the Lepidosiren, fig. 324, i, and of
the anterior series of lamella? in the first
gill-bag of the Plagiostomes : and this
series is attached, like the opercular
gill of the Lepidosteus and Sturgeon,
to the membrane supported by the
hyoid arch.

In most Osseous Fishes we recognise
the reduced homologue of the anterior
primary vascular arch in that vessel,
fig. 321, e, which is continued from the
venous or refluent division of the
second primary vascular arch ; not, as
in the foregoing fishes, from the ar-
terial division of that arch, or from
the branchial trunk. The vessel in
question carries, therefore, arterial
blood : it manifests its primitive
character by returning into the circulus aorticus, as at e , fig.
321, but now receives blood from it, and is called ( arteria

Respiratory and circulatory organs,
Lepidosiren cniiiccten?-. xxxni.

486 ANATOMY OF VERTEBRATES.

hyo-opercularis : ' the pseudo-brancllia, when present, as at
fig. 321, R, is developed from it.

In Osseous Fishes the four normal biscrial pectinated gills are
developed only from the four anterior branchial arches ; the fifth
and last arch has no gill developed from it, but is converted, as we
have seen, into a pair of accessory jaws. In the Lepidosiren, as
in Hexanchus, the fifth arch supports a uniscrial gill, fig. 324, 6.
In the Planirostra, although the branchial pecten is not developed
from it, yet the same kind of long slender filamentary processes
project inwards from its concavity, as from that of each of the
anterior four pairs of branchial arches. The five interspaces
between the hyoid arch and the five branchial arches are originally
exposed on the sides of the head of the embryo osseous fish ; the
opercular and branchiostegal appendages are later developements,
and the single branchial outlet is the result of the formation of the

o

gill-cover. Thus the numerous branchial apertures in the carti-
laginous fishes, like the substance of their skeleton, are retentions

o y *

of embryonic structures. Very interesting arrests of developement
are also found in bony fishes. We have seen that the primary vas-
cular hoops sweep over their respective arches without sending off
any branches, the (subsequently) branchial veins being, in the
embryo, direct continuations of the branchial arteries. This
primitive condition is persistent in the fourth branchial arch of
certain Muraenoid fishes of the Ganges, Monopterus, Syrribranchus; l
it is persistent in the first and second branchial arches of the eel-
like Lepidosiren, fig. 324. 2, 3. Such arches are, therefore, gill-
less, and a certain proportion only of the blood transmitted from
the heart is aerated in the gills : about one fourth, e. g. in Mono-
pterus., goes directly to the aorta in its venous state ; a larger
quantity would pass into the roots of the aorta, fig. 312, o, o, and
mix with the general circulation in the Lepidosiren, were no part
of the current diverted by the vessels /, I', into the lung-like
modification of its air-bladder.

A tuft of filaments, supporting each a single vascular loop, and
covered with non~ciliate epithelium, extends from each branchial
plate, protruding from the outer slit, in the embryo of the Plagio-
stomes ; 2 and a similar tuft also extends from the spiracle in those
species which possess it, e. g. Mustelus and Acanthias ; but
these preliminary branchial organs soon disappear.4 Three seem-
ingly analogous filaments are retained on each side, for a longer
period, in the Lepidosiren annectens ; but lose that vascular and

1 cxix. : xx, vol. v. p. 72. 3 LXIX. p. 88, pi. 14.

4 LXXXII. cxxv. cxm. p. 97.

GILLS OF FISHES. 487

respiratory character before they are absorbed. Accessory
respiratory organs, acting chiefly as a reservoir or filter of
water,1 are developed from the upper part of the pharynx
in the Climbing Perch (Anabas scandens) and allied fishes of
amphibious habits ; they are complex folds of slightly vascular
membrane supported on sinuous plates developed from the
pharyngo- and epi-branchials of the ante- 325

rior branchial arches, fig. 325, 48 ; whence
this family of fishes is called Labyrinthi-
branchii. An accessory branchial ramified
vascular or°'an is similarly situated in the

~ •>

genus thence called Heterobranchus. It re-
sembles a miniature tree of red coral, is
hollow and muscular, and serves not only for
respiration, but, as Cuvier suggests, to aid in

propelling the arterialised blood intO the Branchial arches and labyrin-

.1 r* ^ • ft 7 • \ tbic reservoir, Anabas. xxiri.

aorta. In the Lucnia (Amp/upnous), a

finless snake-like fish, which lurks in holes in the marshes of
Bengal, the second branchial arch supports a few long fibrils, and
the third a simple lamina fringed at its edge ; the first and fourth
arches have not even the rudiment of a gill. The branchial
function is transferred to a receptacle on each side of the head,
above the branchial arches, covered by the upper part of the oper-
cular membrane ; these receptacles have a cellular and highly
vascular internal surface ; the cavity communicates with the
mouth by an opening between the hyoid and first branchial arch,
and receives its blood from the terminal bifurcation of the
branchial artery, and also from the efferent vessels of the rudi-
mental gills. Those from the supplemental lung-like vascular
sacs are collected into two trunks, which unite with the posterior
unbranched branchial arteries to form the aorta. Thus about one
half of the volume of blood transmitted from the heart is con-
veyed to the aorta without being exposed to the action of the air.
This amphibious fish is, as might be expected, of a sluggish and
torpid nature, and remarkable for its tenacity of life. The homo-
logues of the superior branchial sacs extend in a Gangetic Siluroid
fish, the Singio, beyond the cranium, backward beneath the dorsal
myocommata upon the neural arches of the vertebra? to near the
end of the tail, where they terminate in blind ends. The inner
tunic of the sacs is a delicate vascular membrane, supplied by a
continuation of the posterior branchial artery. The position of
the palatal opening of the sac, in relation to the lamina? of the

1 CLXXIV, vol. iii. p. 372.

4b8 ANATOMY OF VERTEBRATES.

second and third arches, is such that water can with difficulty
penetrate them, and they are usually found to contain air. They
are not, however, the homologues of the air-bladder or of lungs,
though they arc analogous to the latter in function. By this
extreme modification of the opercular gill the Singio (Sacco-
branchus, Cuv.) is enabled to travel on land to a great distance
from its native rivers or marshes, and, like the Cuchia, is remark-
able for surviving the infliction of severe wounds.1 In most fishes
a rich developement of follicles on the walls of the gill-chamber
supplies the branchial machinery with a lubricating mucus.

The mechanism of branchial respiration differs from that of
swallowing, only in the streams of water being prevented from
entering the gullet, and being diverted to the branchial slits on
each side the pharynx.

The mouth opens by the retraction of the premaxillary and the
depression of the mandible. Almost simultaneously the mandi-
bular rami are divaricated behind by the action of the f levatores
tympani,' fig. 134, 24, upon their pedicles; the opercular flaps are
drawn outward by the ( levatores operculi,' ib. 25 ; the branchio-
stegal membrane is dilated by divarication of the rays, the ( leva-
tores branchiostegarum,' fig. 135, 28, opposing the ( depressores,'
ib. d, in this action ; the branchial arches are successively drawn
forward and outward by the ( branchi-levatores,' fig. 137, 3, and
6 mastobranchiales,' ib. 26 ; and the branchial chamber being thus
expanded, the water rushes in through the sieve-like inner slits,
and fills the chambers, floating apart the gills and filtering
between every branchial process and fold. The inner slits are,
then, closed by the protraction of the hyoid and depression of the
branchial arches, the ' geniohyoidei,' fig. 135, cooperating with
the f branchi-depressores,' fig. 137, ?5, in this action ; the branchial
processes are approximated and divaricated by special muscles,
and elastic parts. The respiratory currents are driven out by the
contraction of the branchiostegal membranes and the depression
and adduction of the opercular flaps, which, on the expulsion of
the currents, close like a door upon the f sill ' formed by the
scapular arch. In the Plagiostomes the branchial currents are
moved and directed by muscles, combined with elastic structures,
more immediately acting on the inner and outer slits and the
intermediate chambers.

§ 85. Arteries of Fishes.- -The first structure to be noticed in
connection with the arterial system, is the vascular body already
alluded to under the name of ' pseudobranchia.' Mormyrus, Tinea,

1 CXVII.

ARTERIES OF FISHES. 489

Cobitis, Nandus, Silurus, Batrachus, Gymnotus, Murcenophis, and
Mur&na are examples of genera in which it has not been detected.
In almost all other Osseous Fishes it is present, situated on each side
of the head, in advance of the dorsal end of the first biserial gill,

o *

under the form either of a small exposed row of vascular filaments,
like a uniserial gill (as in all Sciaenoids and many other Acantlw-
pteri, the Pleuronectidce, and the Lepidosteus, fig. 323, n) ; or, like
a vaso-ganglionic body, composed of parallel vascular lobes, and
covered by the membrane of the branchial chamber (as in Esox,
Cyprinus, Gadus, fig. 321, E,). In both cases the vein or efferent
vessel of the psetidobranchia becomes the ophthalmic artery, ib. k,
and the choroid ( vaso-ganglion,' when present, is developed from
it. The Sturgeon, like the Lepidosteus and Lepidosiren, has a
uniserial opercular gill, the homologue of the first so-called ' half-
gill ' of the Plagiostomes ; and, on the anterior wall of the ' spira-
cular canal,' a small vascular lamellate body receives arterialised
blood by a vessel sent off from the vein of the first biserial gill ;
which blood, after being subdivided amongst innumerable pinna-
tifid capillaries is collected again into the efferent vessel of that
body, and divides into the artery for the brain (encephalic), and
that for the eye (ophthalmic). The pseudobranchia is thus a kind
of f rete mirabile ' for both the cerebral and ophthalmic circulation
in the Sturgeon ] : in Osseous Fishes it stands in that relation to the
eye only, and is most generally associated with the more immediate
ophthalmic ' rete mirabile,' called f choroid gland,' fig. 216, o.
The pseudobranchia, in the Plagiostomes that have the spiracula, is
developed, as in the Sturgeon, on the anterior wall of each of those
temporal outlets from the branchial cavity : its ( vena arteriosa '
supplies the eyes and part of the brain : it coexists in the Plagio-
stomes, Chima3roids, Sturgeons, and some Osseous Fishes, with
the vaso-ganglion supplied by vessels from the anterior branchial
veins, which lies bet ween the anterior basi-branchials and the sterno-
hyoid muscles. Besides the small nasal and orbital arteries, and
the hyo-opercular, from which the proper ophthalmic artery is
derived, the carotids are usually sent off from the ' circulus
aorticus.' In the Chimosra the carotids are transmitted directly
from the anterior branchial veins ; and, in the Pike, the artery of
the pectoral fins (brachial) is transmitted from the common trunk
of the two anterior branchial veins. In the Myxines an anterior,
as well as a posterior, aorta is continued from the common conflu-
ence of the branchial veins. In all higher fishes the posterior
aorta is the only systemic trunk so formed.

1 xxi. pp. 41-67, 75.

490 ANATOMY OF VERTEBRATES.

This aorta extends beneath the bodies of the vertebra? along the
abdomen and through the homial canal to the end of the tail. In
many Cyprinoid fishes it dilates beneath eaeh abdominal vertebra
into a sinus. It gives off intercostal arteries, which in many
adult fishes become fewer in number than the intercostal spaces ;
it supplies numerous small branches to the kidneys. In the
Syngnathi the aorta grooves the kidney in its course, and in the
Anchovy sinks into the renal substance. The first principal
visceral branch is the ' co3liac ; ' which sometimes, as in the
Burbot, is sent off from the posterior part of the ( circulus
aorticus,' and in some Sharks by two trunks from the same part.
The next branch is a posterior mesenteric, which varies in size
according to the extent of the intestinal canal supplied by the
cocliac. Between these, in some fishes, the brachial arteries are
sent off from the abdominal aorta : these vessels in the large-
firmed Torpedos and Chimserae have a partial investment of
muscular fibres, like secondary bulbs, but without any valvular
structure to give effect in onward flow to their action.1

In the Porbeagle Shark (Lamna cornubica) the two coeliac
arteries each split into a bundle of small arterioles, which inter-
lace with a similar resolution of the hepatic veins to form a mixed
fasciculate ( plexus mirabilis ' between the pericardial septum and
the liver. The arterial blood is collected again into a trunk on
the outer side of each plexus ; and is distributed by the ramifi-
cations of those trunks in the ordinary way to the stomach and
intestines.2 The arterial branches to the spiral valve in the Fox
Shark are remarkable for the rich bundles of twigs by which they
distribute the blood to that production. In the Mediterranean
Tunnies ( Thynnus and Auxis) the branches of the ca3liaco-mesen-
teric artery sent to the stomach, the pancreas and the intestines,
severally split up into similar fasciculate plexuses, which are
interlaced with corresponding plexuses of the veins from those
viscera prior to the formation of the portal trunk.

But the most common modification of the visceral vascular
system is the sudden division and termination of a branch, usually
of the gastric artery, in a small body chiefly composed of the
cellular beginnings of the returning veins, forming the vaso-
ganglion so constant in all higher Vertebrates, and called the
e spleen,' fig. 276, n ; fig. 281,^. It is not present in the Lancelet ;
and the gland-like bodies near the cardia in the Cyclostomes, and
near the pylorus in the Lepidosiren, which some have called
e spleen,' are more like the recognised remnants of the vitellicle in
Osseous Fishes, where a true spleen is actually present. The

1 xcvni. 2 xxi. p. 99, pi. 5.

AIR-BLADDER OF FISHES. 491

vein of the spleen always contributes to form the ( vena portae ; '
but it is important to note that it is not essential to the formation
of that vessel. The absence of the spleen in fishes is concomitant
with the absence of the pancreas ; and the increased size and
complexity of the spleen is associated in some fishes with a cor-
responding developement of the pancreas. Thus there is an
accessory spleen in the Sturgeon ; and the spleen is divided into
numerous distinct lobules in Lamna, Selache, fig. 278, d, and
some other highly organised Plagiostomes. In most Osseous
Fishes the spleen is appended by its vessels, and a meso-splenic
fold of peritoneum to the hinder end or bend of the stomach, or
to the beginning of the intestine : it is of variable but commonly
triangular shape ; of a deep red or brown-red colour, and soft
and spongy : the venous cells of which it is chiefly composed are
filled with granular corpuscles.

§ 86. Air-bladder of Fishes.- -The organ so denominated is found,
in most Osseous Fishes, in the form of an elongated bladder, tensely
filled by air, extending along the back of the abdomen, between the
kidneys and the chylopoietic viscera, fig. 281, k, and sometimes
(^Gymnotus, fig. 233, d, Ophiocephalus, Coins) beneath the caudal
Vertebrae to near the end of the tail. It is sometimes bifurcate (as
we see it in most Scomberoids and Carangoids,1 in some species. of
Diodon, Tetrodon, of Dactylopterus, Pimelodus, Prionotus) ; seldom
divided lengthwise into two bladders {Arms, Gayora, Polypterus,
Lepidosiren, fig. 324, p, p) : more often divided crosswise into
two compartments, which intercommunicate by a contracted
orifice (Cyprinidce, fig. 229, p g, CliaracinidcB), or are quite
separate (^Bayrus Jilamentosus , Gymnotus equilabiatus]. In the
Siluroid genus Pangasius the air-bladder is divided into four
longitudinally succeeding portions. In the Triyla hirundo the
swim-bladder is notched anteriorly by one indent, and posteriorly
by two indents, from which notches septa project inwards : some-
times the air-bladder is divided partially, both lengthwise and
crosswise (Cobitis fossilis, Auclienipterus furcatus, some species of
Pimelodus). Sometimes the bladder sends forward two blind
processes from its forepart (Sphyrcena barracuda, Triyla cuculus,
Conodon antillanus, some species of Micropoyon and Otolithus) ;
sometimes from its hind part (Cantharis vulyaris, Lethrinus
atlanticus, Heliases insolatus, some species of Sillayo, Mcena, and
Smaris) ; sometimes from both ends (Dules maculatus, Pimelipterus

1 Dr. Giinther tells mo that all the species of these families with a short and
elevated body, with a short abdominal cavity, and with strong first htemal and inter-
haMual spines, have the air-bladder bifurcate behind, extending backward between the
muscles of the tail, to or beyond the middle of its length.

492

ANATOMY OF VERTEBRATES.

32G

is, Lactarius delicatulus). Comma trispinosa, fig. 326, has
two slender crecal processes from each side of its air-bladder ; the

Bearded Umbrina has three such processes; the
allied ( Maigre ' and other species of Sciccutt,
with most of the Corvince, have very numerous
lateral pneumatic crcca, which, as in Johnius
lolatus, fig. 327, are more or less ramified.1 In
some species of Chcilonemus and Gadus blind
processes are continued from both the sides and
ends of the air-bladder (see the anterior ones
in Gadus callarias, fig. 321, A, p). In Gadus
Navavac/a the lateral productions expand, and
line corresponding expansions or excavations of
the abdominal parapophyses, thus foreshadow-
ing the pneumatic bones of birds. In Kurtus the
air-bladder is encircled by expanded ribs, curving
and meeting below it.'2

The proper walls of the air-bladder of ordi-
nary Osseous Fishes consist of a shining silvery
fibrous tunic, the fibres being arranged for the
most part transversely or circularly, and in two
layers fig. 229, q r; they are contractile and elastic; but
the walls of the anterior compartment of the air-bladder of

Cyprinoids, ib. p, are much more elastic than
those of the posterior one. The air-bladder

is lined by a delicate mucous membrane, with a

.
' plaster epithelium ; ' it is more or less covered

by the peritoneum. Its cavity is commonly
simple ; in the Sheat-fish it is divided by a
vertical longitudinal septum along three-fourths
of its posterior part.3 The lateral compart-
ments are subdivided by transverse septa in
many other Siluroids (e. g. genus Bagrus) : the
large air-bladder of some species of Erythrinus
(e. g. E. salmis, E. tcsniatus) is partially subdi-
vided into smaller cells. The cellular subdivi-
sion is such in the air-bladder of the Amia, that
Cuvier compared it to the lung of a reptile 4 ;
an<l th e transition from the air or swim-bladder

Air-bladder, Corvina

trispinosa,

327

1 xxxix. i. p. 94, after Cuvier and Valenciennes, xxm. pi. 13S, 139. The most
complex form is that described by Giinthcr (CLXXIV, vol. ii. p. 313) in Cullichthys
lucida, where the air-bladder forms a second investment of the abdominal viscera,
within the peritoneum.

• CLXXIV. vol. ii. p. 10. 3 ex vi. vol. ii. p. 33, pi. 6, fig. 4. 4 xxiv. vol. ii. p. 377.

AIR-BLADDER OE EISHES. 493

to the lung is completed in the Lepidosiren, in which the
cellular subdivision and multiplication of the vascular surface are
combined with a complete bilateral partition of the bladder into
two elongated sacs, with a supply of venous blood from a true
pulmonary artery, and with the communication of the ductus
pneumaticus, as in the Polypterus, with the ventral surface of the
oesophagus.

At the first introduction into the Animal Kingdom of a true
lung, or air-breathing organ communicating with the pharynx or
oesophagus, much variety of form and structure, much inconstancy
even as to existence, might be expected, especially in that class in
which the normal function of the new organ could be so seldom in
any degree exercised, and in which, therefore, different accessory
or subordinate offices predominate in such rudimental represen-
tative of the pulmonary organ. There is no swim-bladder, for
example, in the orders Dermopteri, Holocephali, and Plagiostomi ;
it is present in one of the families ( Gadidce) of the thoracic sub-
order of Anacanthini, and not in the other family (Pleuronectidai) ;
here we can associate its absence with the peculiar flattened
form and grovelling habits of the species. In like manner we may
account for the absence of the air-bladder in the Angler (Lophius),
which habitually keeps the sea-bottom : but the mechanical expla-
nation of the absence or rudimental condition of the swim-bladder
is not so obvious in regard to the Acanthopterous genera Percis,
Percophis, Eleginus, Auxis, Tracliypterus, and Gymnetrus. A
large and often complex air-bladder exists in most of the Siluroid
fishes ; but the genera Loricaria, Rliinelepis, and Hypostoma are
exceptions in that family, having no air-bladder. What is more
inexplicable is, that while some species of the same genus,
Puli/nemus and Scomber for example, have a large swim-bladder,
others want it, or have it of extremely small size.

The variation in respect to the presence or absence of an air-
duct (ductus pueumaticus) is expressed in the characters of the
orders in the Classification of Fishes, pp. 10- -12. The duct,
which is shown by its place of communication with the beginning
of the oesophagus, and by the rudimental larynx, in Polypterus
and Lepidosiren, fig. 316, e, to be the homologue of the trachea
of air-breathing Vertebrates, is a simple and delicate membranous
tube ; but it presents considerable variation in its length, diameter,
and place of communication with the alimentary tract. In the
Herring the ductus pneumaticus is produced from the posterior
attenuated end of the cardiac division of the stomach, fig. 281, i,
and opens into the fusiform air-bladder at the junction of the

494 ANATOMY OF VERTEBRATES.

middle and posterior thirds of that organ.1 The long, narrow,
and flexuous ductus pneumaticus is continued from the forepart
of the posterior division of the air-bladder in the Cyprinoids, and
opens into the dorsal part of the oesophagus, fig. 229, su : the
short, straight, and wide ductus pneumaticus, in the Lcpidosteus,
opens also into the dorsal part of the oesophagus, the orifice being
served by a sphincter : in the Erythrinus the air-duct commu-
nicates with the side of the oesophagus ; in Polypterus, as in
Lepidosiren., with the under or ventral part of the beginning of
the rcsophagus. 2

The principal seat of the vascular ramifications in the air-
bladder, like that in a true lung, is the mucous lining membrane ;
but the modes of ramification in the primitive piscine form of the
air-breathing organ are as variable as any of its other properties.
The arteries of the air-bladder are derived sometimes directly
from the abdominal aorta, sometimes from the coeliac artery,
sometimes from the last branchial vein ; and in the Lepidosiren
they are continued from the aortic termination of the two non-
ramified branchial arteries, fig. 312, I', and therefore convey
venous blood to the cellular, lung-like, double air-bladder. The
veins of the air-bladder return, in some fishes, to the portal vein ;
in some, to the hepatic vein ; in some, to the great cardinal vein ;
and, in the Lepidosiren, ib. //, they penetrate, by a common
trunk, the great post-caval vein, ib. e, formed by the confluence
of the visceral and vertebral veins of the trunk ; but instead of
terminating there, the pulmonary venous trunk passes forward,
through the sinus and auricle, to the entry into the ventricle, and
there terminates above the valvular cartilaginous tubercle. Thus

o

the aerated blood from the lungs enters the ventricle directly,
instead of being previously mixed with the venous blood in the
auricle.

The vascular system of the lung-like air-bladders of the
Protopterous and Ganoid Fishes forms no ' retia mirabilia ' or
vaso-ganglions, but resolves itself into a generally diffused
reticular capillary system, which is much richer and closer in
the more subdivided and thicker cellular structure of the anterior
than of the posterior parts of the bladders in the Lepidosiren.

In the Osseous Fishes the principal forms of the terminal
divisions of the arteries of the air-bladder are as follows:- -1. A
resolution of the smaller ramifications into fan-like tufts of
capillaries over almost every part of the inner surface (Carp).
2. The formation of similar, but larger and more localised,

CJ

1 cxiv. vol. ii. pi. viii. fig. 1. 2 xxi. 1841, p. 194.

AIR-BLADDER OF FISHES.

495

328

radiating tufts (Pike) ; in both without any special aggregation
of the capillaries to form a ' vaso-ganglion.' 3. The conversion
of the tufts by rapid subdivision into capillaries aggregated so as
to form red gland-like bodies ; the capillaries reuniting into larger
vessels, which again ramify richly round the border of the gland-
like body ; the rest of the inner surface of the air-bladder having
the ordinary simple capillary system (Perch and Cod). In the
Cod-fish, a large artery, a branch of the coeliac, and a still larger
vein, which empties itself into the mesenteric, perforate together
the fibrous tunic of the swim-bladder. Before they reach the
inner surface, they divide into some branches, which then radiate
and subdivide upon the mucous membrane : the arterioles
frequently anastomose together, and the venules as frequently
anastomose with each other : both are inextricably interwoven,
and form the basis of the so-called ' air-gland,' which is essentially
a large ( bipolar rete mirabile,' or vaso-ganglion. The ultimate
vessels of this body form loops,
where the arteries return into
veins, fig. 328, and these loops
are covered by a layer of vessels
and epithelium, a, a. This organ,
however, is further composed of
a number of peculiarly arranged,
elongated corpuscles, which de-
pend in two rows from each
vascular branch, and are bound
together by a loose cellular
tissue : the corpuscles are beset

With fine villiform processes. Superficial and looped vessels of the vaso-ganglion
mi ITT f .1 air-bladder, Cod. CCLXVIII.

Ihe blood returns from the vaso-

ganglions by small veins which rarely accompany, more commonly
cross, the arteries. 4. The two chief ' retia mirabilia,' or vaso-
ganglions, in the air-bladder of the Eel and Conger, which are
situated at the sides of the opening of the air-duct, are also
6 bipolar,' and consist of both arterioles and venules : they consist
of straight parallel capillaries, as in fig. 329 : their efferent trunks
do not ramify in the immediate margin of the vaso-sanoiion from

" O O c5

which they issue, as in the vaso-ganglions of the Cod, Burbot,
Acerine, and Perch, but run for some distance before they
again branch to form the common capillary system of the lining
membrane of the air-bladder.

Eathke l failed to detect the opening of the air-duct with the
1 cxi. 'Ueber die Schwimm-blase einiger Fische,' p. 98.

496 ANATOMY OF VERTEBRATES.

oesophagus in the Eel ; but De La Roche had well described the
oblique aperture,,1 and accurately cites the whole family of the
Eels as fishes having both the so-called f air-gland ' and the

o o

pneumatic duct. It had been supposed that the vascular 4 air-
gland ' was present only in those fishes which could not derive
the gaseous contents of their swim-bladder from without; and
unquestionably in those fishes which have the shortest and
widest ducts (Sturgeon, Amia, Erythrinus, Lepidosteus, Lepido-
siren, Polyptcrus) the supposed air-secreting vaso-ganglions are
not developed. Since Professor Magnus has determined the

existence of free carbonic
acid gas, of oxygen, and of
azote in the blood, and dis-
solved in different propor-
tions in the venous and the

Parallel vessels of the vase-ganglion of the air-bladder, arterial blood, it may be
Eel. CCLXVIII. -,.-, n i .-,

readily conceived that the

venules of the vaso-ganglions may withdraw carbonic acid gas
from the arterioles, and that these may reach the inner surface of
the air-bladder richer in oxygen and poorer in carbonic acid than
when they penetrated the vaso-ganglions.2

The air-duct may allow the gas to escape under certain circum-
stances ; and the small size and obliquity of its orifice in many
Osseous Fishes (Carp, Eel) seem only to adapt it to act as a
safety-valve against sudden expansion of the gas when the fish
rises to the surface : 3 but in the higher organised species above-
cited, with short and wide air-ducts, these may, likewise, convey
air to the bladder.

The contents of the air-bladder consist, in most freshwater-
fishes, of nitrogen, and a very small quantity of oxygen, with a

trace of carbonic acid «;as : but in the air-bladder of sea-fishes,

~ '

and especially of those which frequent great depths, oxygen
predominates.4

In the genera Auvhenipterus, Synodon, Malapterurm , and some
other Siluroids, the axis vertebra sends out on each side a slender

1 cxvn. p. 201. 2 xxi. 1841, p. 98. See also Dr. J. Davy, in Phil. Trans. 1838.

5 Neither the air-duct nor the elasticity of the air-bladder are equal to prevent the
consequences of a too rapid removal from the enormous pressure which fishes sustain
at great depths in the sea; those that are drawn up quickly by the hook are often
found to have the air-bladder ruptured, and sometimes the stomach is protruded from
the mouth by the pressure of the suddenly extricated and expanded gas.

4 Humboldt found the gas in the air-bladder of the electric Gymnotus to consist of
96° of nitrogen and 4° of oxygen. Blot found 87° of oxygen in some of the deep-
sea Mediterranean fishes, the rest nitrogen, with a trace of carbonic acid. No hydro-
gen has ever been detected in the air-bladders of fishes.

AIR-BLADDER OF FISHES. 497

process, which expands at its end into a large round plate : this is
applied to the side of the air-bladder, and can be made to press
upon it, and expel the air through the duct by the action of a
small muscle arising from ftie skull. In some species of Gadus
muscular fibres extend from the vertebral column upon the air-
bladder. The nerves of the air-bladder are derived from the vagus
after it has received organic fibres from the sympathetic, fig. 229, t.

Viewing the general modifications and relations of the air-
bladder throughout the class of Fishes, we cannot but discern and
admit, notwithstanding some seeming capricious varieties, that its
chief and most general function is a mechanical one, serving to
regulate the specific gravity of the fish, to aid it in maintaining a
particular level in its element, and in rising or sinking as occa-
sion may serve. The general law of its absence in the parasitic and
suctorial Dermopteri, and in all ground-fishes, as the Pleuronectida
and Ray-tribe, supports the above conclusion. Borelli1 found
that those fishes whose air-bladders were burst sank to the bottom
and were unable to rise. Nor does the absence of the air-bladder
in the surface-swimming Sharks militate against this view of its
physical function : for though the air-bladder serves, it also
enslaves. It opposes, for example, those Fishes that possess it in
their endeavours to turn on one side, and it demands a constant
action of the balancing fins to prevent that complete upsetting of
the body which it occasions from the weight of the superimposed
vertebral column and muscles when life and action are extinct.
The Sharks require, by the position of their mouth and in their
common pursuit of living prey, freedom in turning and great
variety as well as power of locomotion : if they are not aided
by a swim-bladder, neither are their muscular exertions impeded
by one ; whilst their swimming organs acquire that degree of
developement and force which suffices for all the evolutions they
are called upon to perform. TTith regard to the accessory offices
of the air-bladder in relation to the sense of hearing, the chief of
these remarkable modifications by which it is brought into com-
munication with the acoustic labyrinth have been already described,
p. 344. In a few genera (Triyla), the air-bladder and its duct
are subservient to the production of sounds.

Under all its diversities of structure and function the homology
of the swim-bladder with the lungs is clearly traceable ; and
finally, in those orders of Fishes which lead more directly to the
Reptilia, as, for example, the salamandroid Ganoidei and Protopteri,
those further modifications are superinduced upon the air-bladder,

1 cxxxi. cap. 23.
YOL. I. K K

498 ANATOMY OF VERTEBRATES.

by which it becomes also analogous in function to the lungs of
the air-breathing Amphibia.

The Lepidosiren annectens l inhabits a part of the river Gambia,
which in the rainy season overflow! extensive tracts, that are
again left dry in the dry season. Those which do not follow the
retreating waters escape from the scorching rays of the African
sun by burrowing in the mud, which is soon baked hard above
them ; but they maintain a communication with the air by a
small aperture, and, coiling themselves up in their cool chamber,
clothe themselves by a layer of thick mucous secretion, and
await, in a torpid state, the return of the rains and the over-
flowing of the mud-banks. The advent of their proper element
wakes them into activity : they then emerge from the softened
mud, swim briskly about, feed voraciously, and propagate.

The peculiar modifications of the gills and air-bladder of the
Lepidosiren are precisely those which adapt them to the peculiar
conditions of their existence. In the inactive state into which
they are thrown by their false position as terrestrial animals, the
circulation, which would have been liable to be stopped had all
the branchial arteries developed gills, as in normal fishes, is
carried on through the two persistent primitive vascular channels,
fig. 312, 2 and 3. Whatever amount of respiration was requisite
to maintain life during the dry months is effected in the pulmonary
air-bladders ; its short and wide duct or trachea, the resophageal
orifice of which is kept open by a laryngeal cartilage, fig. 316, jf,
introduces the air directly into the bladders : the blood transmitted
through the branchial arches to the pulmonary arteries, fig. 312, /',
is distributed by their ramifications over the cellular surface of
the air-bladders,' and is returned arterialised by the pulmonary
veins, ib. p, p' '. A mixed venous and arterial blood is thence
distributed to the system, and again to the air-bladders. True
arterial blood exists only in the pulmonary veins, and unmixed
venous blood only in the system of the venae cava3 ; whence the
necessity, apparently, for that peculiar arrangement by which the
arterial blood is conveyed directly to the ventricle by the pul-
monary vein. When the Lepidosiren resumes its true position as
a fish, the branchial circulation is vigorously resumed, a larger
proportion of arterialised blood enters the aorta, and both the
nervous and muscular systems receive the additional stimulus and
support requisite for the maintenance of their energetic actions.

Anatomists and physiologists have expressed different views as
to the hornologies and analogies of the respiratory organs of

1 XXXIII.

AIR-BLADDER OF FISHES. 499

fishes. Indeed the essential distinction of those relations has
seldom been clearly kept in view. When we read in the
latest edition of the Comparative Anatomy of Cuvier : e the
gills are the lungs of animals absolutely aquatic ; ' 1 and, with
regard to the cartilaginous or osseous supports of the gills,
( they are in our opinion, to the gills of fishes, what the carti-
laginous or osseous tracheal rings are to the lungs of the three
superior classes : ' 2 we are left in doubt whether it is meant
that the gills and their mechanical supports merely perform the
same function in Fishes which the lungs and windpipe do in
Mammals, or whether they are not also actually the same parts
differently modified in relation to the different respiratory media
of the two classes. Geoffrey St. Hilaire leaves no doubt as to
his meaning where he argues that the branchial arches of fishes
are the modified tracheal rings of the air-breathing classes ; we
perceive that he is enunciating his belief in a relation of homo-
logy. The truth of his proposition will be best tested by first
considering the homologies of the air-bladder of fishes. In the

o o

Lepidosiren the notochord, the parapophyses, the attachment of
the scapulae to the occiput, the branchiostegal covering of the
permanent gills, the opercular bones, the presence of a spiral in-
testinal valve, the relative position of the anus, the extra-oral
nasal sacs, the scaly integuments, the mucous tubes on the head,
the f lateral line,' in short, the totality of the organisation of
the Lepidosiren, exemplify its fundamental ichthyic nature. It
is extremely interesting to find the Ganoid Polypterus, which
of all osseous fishes most closely resembles the Lepidosiren in its
spiral intestinal valve, in the bipartition of the long air-bladder,
the origin of the arteries of that part, and the place and laryngeal
mode of communication of the short and wide air-duct or wind-
pipe, also presenting the closest agreement with the Lepidosiren
in the important character of the form of the brain. The common
objection to the view of the air-bladder of fishes being the rudi-
mental homologue of the lunsrs of air-breathing Vertebrates has

o o o

been, that the artery of the air-bladder carries arterial blood, that
of the lungs venous blood. But in the Polypterus and Lepido-
siren, in reference to this character, the arteries of air-bladders
are derived from the returning dorsal portions of the branchial
vascular arches before their union to form the aorta. In the

1 'Les branchies sont les poumons des animaux absolument aquatiques.' (xm.
t. yii. p. 164.)

- * Elles sont, a notre avis, aux branchies des poisson?, ce que les cerceaux carti-
lagineux ou osseux des voies aeriennes sont aux poumous des trois classes supe-
rieures.' (Ib. p. 177.)

K K 2

500 ANATOMY OF VERTEBRATES.

Polypterus the artery of each air-sac is formed by the union of
the efferent vessels of the last gill : the blood is, therefore,
arterialised before entering the artery of the air-sac. In the
Lepidosiren, by reason of the non-developement of gills on two
of the branchial arches, the blood transmitted to the air-sac is
venous. But this difference relates only to the presence or
absence of a particular developement of the branchial vascular
arches, from which the air-bladders of the two species are supplied
with blood : it is a difference which modifies the function without
at all chanrnno; the essential nature of the air-bladders themselves :

o o

the relative position of these vascular sacs, their form and size,
their mode of communication with the oesophagus, — in short,
every character by which relations of homology are determined,
— are the same in both Polypterus and Lepidosiren.1 The lungs
of the Lepidosiren being, then, unequivocally the homologues of
the air-bladder of the Polypterus, it follows that they must be
homologous with the air-bladders of other fishes, whatever be the

O '

modifications of form or function of such air-bladders. Between
the completely divided air-bladder of the Polypterus and the un-
divided air-bladder of the Lepidosteus there are numerous degrees
of bifurcation in the series of fishes : it is to the undivided state
of the air-bladder in the Lepidosteus that its more strictly dorsal
position, and its communication with that aspect of the oesophagus,
are due : these modifications, however, do not affect its relation
of homology with the divided air-bladder of the allied genus
Polypterus, any more than with the divided air-bladders of the
Colitis larbatula or Arius gag or a, in which the divisions are con-
fined to the fore part of the abdomen, and are inclosed in osseous
cups developed from anterior trunk- vertebrae. Thus, the series
of transitions traceable in the air-bladders of fishes proves those
of the Lepidosiren to be the homologous organs ; whilst the
developement, relative position, and connection of the lungs of
the Batrachia equally prove those lungs to be the homologues of
the air-bladders of the Lepidosiren. Consequently, the air-
bladder of the Fish is homologous with the lungs of the Batrachian
and of all air-breathing Vertebrates ; although the air-bladder of
the fish does not perform the function of a lung, but is analo-
gous to the air-chambers in the Nautilus shell.

§ 87. Blood of Reptiles.- -The blood of Reptiles has red cor-
puscles of a flattened sub-biconvex elliptical shape ; proportionally
smallest in Ophidia, roundest in Chelonia, and largest in Batrachia :

1 Compare xxxui. pi. xxvii. figs. 3 and 4, with xxv. pl.ii. figs. 5 and 6, and fig. 54,
xxxni. p. 182, with xxv. pi. ii. fig 7.

BLOOD OF REPTILES. 501

In these the size is greater in the ratio of the persistence of the
branchial apparatus ; and the perennibranchiates present the
biggest blood-discs absolutely,, as well as in proportion to the size
of the body, of all vertebrate animals. The two extremes in the
relative size of the blood-discs in piilmonated Hcematocrya are
shown in those of a Crocodile, which was twenty feet in length,
p. 4, fig. 8, e, and in those of a Siren lacertina, which was two
feet in length, ib. f. The latter, which are just visible to the
naked eye, serve to demonstrate the highly refractive divisions of
the nucleus, and the nuclear capsule.1

There is less blood in cold-blooded than in warm-blooded
animals, and more blood in some fishes, the Tunny, e. g., than in
any reptile. Dr. Joseph Jones 2 estimates the average quantity
of blood to be :—

In Serpents . . . ^ to ^ of the weight of the body.

Emys terrapin ^ to ^ „ „

Emys serrata . . ^ to ^ „ ,,

Testudo polyphemus • TI^° TT » »

Blood drawn from a living Batrachian is of a purplish red
colour, and coagulates into a clot including the discs, floating in
clear serum. The clot is firmer than that of fishes, but less firm
than in allantoic reptiles ; in a few hours the clot dissolves and
liberates the discs. In the recently drawn blood of Chelonia
most of the discs settle at the bottom of the vessel, and are not
included in the clear clot which forms above them. The fibrin in
this clot speedily passes into albumen. The colour of the serum
in most reptiles, e. g. Batrachia, Ophidia, Crocodilia, and some
Chelonia ( Testudo polyphemus), is a light yellow : in many carni-
vorous Chelonia (Emys serrata, E. reticulata, E. terrapin), it is of
a golden colour. When treated with a drop of sulphuric acid,
and gently heated, the peculiar smell of the species, due, e. g. in
the Alligator, to the musk-glands, and in the Rattlesnake to the
anal glands, is plainly developed.

The blood of Ophidia contains the greatest proportion of solid
constituents, in the cold-blooded Vertebrates.3

§ 88. Veins of Reptiles.- -The capillary blood-vessels having a
calibre proportionate to the diameter of the blood-discs which
flow along them in single file, are largest in the Batrachia, in
which class the best examples are afforded for demonstrating to

1 CCLXXIII. and CCLXXIV. 2 CCXLV.

3 Dr. Joseph Jones, from whose excellent and original work (CCXLV.) most of the
above particulars are taken, suggests that the richness of the ophidian blood may be
due to the fact of serpents seldom, if ever, drinking. The comparatively unimportant
details of the diameters of reptilian blood-discs may be seen in ccxxxix, tome i»
p. 89.

502

ANATOMY OF VERTEBRATES.

330

Capillaries with blood-discs of the web of the foot,
Frog, niagru CCLXVII.

331

the eye the circulatory motion of the blood, flowing constantly
from the arteries to the veins, as seen, e.g. by transmitted light

in a membranous part of
the frog's or newt's struc-
ture, under the micro-
scope, fig. 330.

The venous system of
Batrachians resembles that
of Fishes in the degree in
which the species retain
the piscine character. The
cardinal veins, essentially
those which return the
blood from the osseous and
muscular segments of the
trunk, are largest in the
Perennibranchs, and de-
crease, as the hind-limbs
acquire more size and
power, in the Newts and
Land -Salamanders, until,
in the tail-less and long-
le^ed Fro^s and Toads,

SO CD

the primitive venous trunk
of the body is reduced
to the condition of the
'azygos' vein in Mammals,
and the great bulk of the
blood is submitted to the
influence of the kidneys
and liver before it is re-
turned to the heart.

In the Frog, fig. 331, the
blood being collected from
each hind-limb into an is-
chiadic and iliac vein, these
unite into a common iliac
vein, which divides. One
branch joins that of the
opposite iliac, and receives
the vein of the great allan-
toic bladder, to form thu
f umbilical vein,' fig. 331, u: the other branch, K, goes to the

Circulation in the Pros'. CCLXVII.

VEINS OF REPTILES. 503

kidney of its own side. It inclines to the outer border of the
gland, and divides into two branches, which ramify in the renal
tissue. The vein of the genital glands and conduits, and a vein
from the lumbo-dorsal segments, also enter and ramify in the
kidneys. The blood of this ( reni-portal ' system is collected into
a sinus at the inner border of each gland, and is conveyed
by the vein, k, into the postcaval trunk, v. The umbilical vein
ascends along the ventral aspect of the abdomen, attached to the
mid-line of the muscular walls of the cavity : as it approaches
the liver it sends branches which penetrate directly the hepatic
tissue, and a branch which receives the veins of the intestines,
spleen, and stomach ; but, before completing the portal system, L,
it sends a small vein directly to the postcaval, near the auricle.
The hepatic vein, /, joins the postcaval trunk, v. The blood
from the head and fore-limbs is collected into a right and left
jugular and axillary trunk, which unite to form a precaval vein,
o, on each side. The postcaval vein, in the Perennibranchs, after
receiving the renal veins, is suspended by a duplicature of peri-
toneum to the back of the abdomen, the fold being continued
from the vein to the mesentery : it enters a groove or canal in the
liver, and receives the hepatic veins and the left precaval, before
terminating in the auricular sinus. There are a few valves in

o

the venous trunks of Batrachia ; but their chief characteristic is
the presence of ( striped fibre ' in the muscular coat.1 This is
associated with the faculty of rhythmical pulsation in the post-
caval, axillary, and iliac trunks, independently of the pulsations
of the heart.2 The abdominal venous trunks traverse wide lymph-
reservoirs ; and their exterior is here and there roughened by
little vascular loops, floating in the lymph, but communicating
exclusively with the mother- vein.3

In Oj)Mdia the cutaneous veins of the trunk and intercostal
veins communicate with a large abdominal vein which runs along
the under part of the abdominal walls, and answers to the umbi-
lical vein in Batrachia. The caudal vein bifurcates on entering
the abdomen, each division after receiving blood from the genital
ducts and contiguous intestine, attaches itself to the kidney, and
ramifies upon its several overlapping lobes : the efferent renal
veins unite to form a trunk, which, on emerging from the inner
and fore-part of the kidney, joins its fellow to form the postcaval
vein. The veins of the intestinal canal, genital glands, and fatty
appendages, which have not contributed to the reni-portal system,
unite with those of the pancreas and spleen to form the hepato-

1 CCLXXVII. 2 CCLXX. 3 CCLXXVII.

504

ANATOMY OF VEKTEBRATES.

332

portal vein : this dilates and describes a spiral curve on entering
the liver, and has a valvular structure ensuring the onward flow
of blood to the elongated gland, during the compression exercised
in the contortions of the Snake. The hepatic veins enter the

postcaval, and this large trunk
terminates in the hind end of
the long auricular sinus.

The blood from the head and
fore-part of the body is re-
turned to the fore-part of the
sinus by a jugular vein and an
inferior azygos vein, each of
which has a pair of valves at
its termination : and by a su-
perior azygos vein, which has
three valves at its termination:
there is a fourth vein, answer-
ing to the left precaval, which
passes behind the left auricle
to terminate in the right sinus
auriculae near the postcaval
orifice: it receives the coronary
vein before its termination.

In Lacertians the blood
from the hind limbs is partly
conveyed by a reni-portal
vein, fig. 332, K, to the kid-
neys, and partly by a trunk,
which communicates with the
caudal vein to an umbilical
or sub-abdominal vein, L : this,
as it advances, collects blood
from the ventral walls of the
trunk, and receives a recur-
rent thoracic vein : it then
communicates with the trunk
of the gastrointestinal^ pan-

Circulation in a Lizard (Lacerta ocellata). CCLXVII. oreitic and SDldlic VCDIS

to form the great portal vein which penetrates the liver. The
renal veins, k, unite to form the postcaval, v, which afterwards
receives the hepatic veins, and proceeds to the auricular sinus.
A small cardinal or azygos vein, returning part of the blood
from the tail, advances along the back part of the abdominal

VEINS OF REPTILES. 505

cavity, receiving the segmental or vertebral veins, and terminates
in the left precaval vein. The jugular and the axillary trunks
unite to form a precaval vein, fig. 332, v*, on each side, the left of
which as usual passes behind the auricles to the postcaval orifice
of the sinus.

In the Chelonia the blood from the tail and hind limbs is
conveyed along the plastron by a pair of ' umbilical ' or sub-
abdominal trunks, which receive the veins of the large allantoic
bladders, and the meseraic veins, to form the great portal trunk.
A small derivative branch from the posterior part of each umbi-
lical communicates with lumbo -dorsal vertebral veins, and with
some veins from the genital organs to form the reni-portal veins.
The renal veins unite with the ovarian or testicular veins to form
the postcaval, which traverses the liver and receives there the
hepatic veins : the wide and short trunk, fig. 336, v, then termi-
nates in the auricular sinus. The blood is returned from the
head and fore-limbs by the jugulars, figs. 302 and 304, i, i, and
from the axillary veins, ib. h, h. Each axillary unites with the
jugular of its own side to form a precaval vein : the right and left
precavals enter separately the auricular sinus, the left precaval
opening near the postcaval vein.

In the Crocodile, the caudal vein, on entering the abdomen,
divides into two trunks : each unites with the ischial and iliac
veins of its own side and advances towards the kidney. Here
the trunk sends off a reni-portal vein, and is then continued
towards the hepato-portal system. The renal veins from the inner
side of the kidneys unite to form the postcaval, fig. 339, Y,
which receives the left precaval, fig. 340, v**, at its entry into the
auricular sinus, ib. S : the hepatic veins open separately into the
contiguous end of the sinus, fis;. 339, S. The blood from the head

O O •/

and forelimbs is conveyed to the heart, as in other Reptiles, by a
pair of precavals, of which the right, ib. v, terminates in the fore-
part of the sinus, and the left traverses the back part of the heart,
receiving the coronary veins, to join the postcaval or to terminate
near its auricular orifice.

§ 89. Heart of Reptiles. — In Lepidosiren the vein from the lung-
like air-bladders traverses the auricle and opens directly into the
ventricle. In Siren the pulmonary vein dilates, before commu-
nicating with the ventricle, into a small auricle, which is not
outwardly distinct from the much larger auricle receiving the
veins of the body.1 This is remarkable for its large size, thin
walls, and hollow, fimbriated processes, which overlap and almost

1 XXXIII.

506 ANATOMY OF VERTEBRATES.

conceal the ventricle. The two precavals and the postcaval
terminate in a sinus, which the pulmonary venal trunk seems to
enter, but to the inner surface of which it adheres in its course to
its proper auricular chamber. The ventricle is obtuse and some-
times sub-bifid at the apex : it is connected to the pericardium by
the usual reflection of the serous layer upon the bulbus-arteriosus,
and also by a fold reflected from the apex upon the coronary vein,
which is thence continued to the venous sinus. The muscular
parietes of the ventricle are about a line in thickness, and loosely
fasciculate. The cavity is partially divided by an incomplete
septum, terminating by a concave border opposite the orifice of
the artery, on each side of which are the valves closing the two
auriculo-ventricular orifices. The aorta, narrow, and with thin
walls at its commencement, after a short subspiral course, thickens
into an elongate f bulbus arteriosus,' which includes a longitudinal
valvular prominence, grooved at its fore-part in correspondence
with the origins of the branchial arteries. There is a pair of
valves at the origin of the aorta, and a second pair near the
beginning of the bulb. The distinction of the pulmonary from
the systemic auricle, first observed in Siren, has been since deter-
mined in Menobranchus1, Axolotes*, Amphiuma, and Menopoma*
In Proteus, in which some of the blood of the puny lungs is con-
veyed to systemic veins, the auricular septum is not complete,
according to Hyrtl.4 In Amphiuma the auricle is smaller and
less fimbriated than in Siren. The ventricle is similarly connected
to the pericardium by the apex, as well as by the artery. This
forms a half spiral turn at its origin, and dilates into a broader
and shorter bulb than in Siren.

In Menopoma the auricles are still more reduced in size, and lie,
as in Salamandra, fig. 333, «, when undistended, to the left of the
ventricle : their outer surface, as in Menolranchus, is entire. The
ventricle is of a flattened triangular form : its cavity is occupied
by the loose fasciculate muscular structure through which the
blood filters, as through a sponge, from the small contiguous
auricular apertures, each of which has a simple valve, to the
( ostium arteriosum.' The artery inclines, with a slight twist, to
the left, and swells into a subspherical bulb. The valves are
confined to the narrower part, and are in two transverse rows,
four in each row, each valve of a conical shape, pointing forward.5
The first row is just above the ostium : the second is halfway
between this and the bulb.

1 CCLXXVIII. p. 73. 2 CCLXXIX. p. 45. 3 CCLXIX. p. 215.

4 CCLXXX, p. 258. 5 xx, ii. p. 45, pi. xxiii. fig. 2.

HEART OF REPTILES.

507

333

The pulmonic auricle augments in size with the more exclusive
share taken by the lungs in respiration : but the auricular part
of the heart shows hardly any outward sign of its division in
Batrachians. It is small, smooth, and
situated to the left and in advance
of the ventricle, in Newts and Sala-
manders, fig. 333, a. In Frogs and
Toads the auricle is applied to the base
of the ventricle, and to the back and
side of the aorta and its bulb. The
ventricle, usually of a more rounded
form than in fig. 331, H, is occupied
by the muscular fasciculi, except at a
small part between the auriculo-ven-
tricular and aortal orifices. The bulbus
arteriosus is incompletely divided by
opposite longitudinal folds,the margins
of which meet, but remain free.

In Serpents the heart agrees with

Other Organs in itS elongate form. The Heart, vascular arches, and hyo-branchial

auricles are in advance of the ventricle, apparatus' Salamailder

their lower obtuse ends slightly overlapping its base : they are sepa-
rated anteriorly by the co-elongate intrapericardial origins of the
arteries called f conus arteriosus,' answering to the bulbous part in
Batrachia ; a slight ( auricular ' production of the right auricle is
tied down to the arteries by the serous layer of the pericardium.

The right auricle consists of a sinus and auricle proper. The
sinus receives three veins at its fore part ; the orifice of the right
jugular and of the inferior azygos is guarded by a pair of valves :
in the orifice of the superior azygos I found three semilunar
valves ; two veins open at the back or hind part of the sinus, the
largest being the postcaval, the smaller one the left precaval.
The aperture of communication with the auricle is longitudinal,
near the middle of the sinus, of a full elliptical shape, guarded by
a pair of membranous valves, situated within the proper auricle.
The sinus has the structure of the large veins, with the serous
layer of the pericardium reflected over it. The auricle has a
finely fasciculate muscular wall, thickest at its lower and fore
part. The auriculo-ventricular aperture is a semilunar slit,
opening into the base of the ventricle, near the origin of the
pulmonary artery, and defended by a short membranous valve,
having one or two chordas tendinea3 attached to its free margin.
The left auricle is shorter than the right, but of equal breadth

508

ANATOMY OF VERTEBRATES.

334

when distended, and without a sinus. The pulmonary veins
form a common trunk, about half the size of the postcaval,
which advances, in contact with and to the left of the post-
caval, to open into the hind end of the left auricle, without
any valvular structure. The auriculo-ventricular orifice, shaped
like that of the right auricle, is close to the termination of
the pulmonary vein : it is guarded by a short valve, at the
back of the base of the ventricle, to which chords tendinerc are
attached.

The ventricle is conical, with, an obtuse apex. More than half
the cavity, including the apical part, is occupied by a fasciculate
decussating muscular structure, from which rises an incomplete
septum, supporting that between the origins of the pulmonary
artery and left aorta. The upper or fore part of the ventricular
cavity is formed by a flat sort of platform or roof, supporting the
auricular septum, and having the curved auriculo-ventricular slits
and valves on each side, with the concavities opposite each other,
giving the roof a circular shape.

The incomplete septum divides the anterior or sternal (pulmonic)

cavity, whence the pulmonary artery
arises, from that at the posterior or
dorsal part leading to the orifice of
the left aorta, and receiving the blood
from the auricles : this ventricular
cavity does not extend so near to the
apex as the pulmonic cavity does.
The part of the ventricle whence the
rio-ht aorta rises is a still smaller

o

space. A pair of semilunar valves
guards the origin of each artery.

The heart in Lacertilia essentially
resembles that in Ophidia, but is
shorter in proportion to its breadth.
The right auricle, fig. 334, h'f is
divided by a bivalved orifice from the
sinus ; the left auricle, ib. h, has no sinus : it is smaller than the
right. Each auriculo-ventricular orifice or slit is guarded by a single
valve. The pulmonic cavity of the ventricle, fig. 334, H, p, is
divided from the aortic cavity, H', by a partial septum, indicated
by the dotted outline. The cavity i-i' receives, as in Ophidia, the
blood from the auricles, and gives off the left aorta, A, the right
aorta, A', rising from its back part.

In Chelonia the heart, following, as in Ophidia, the general

Heart of Laccrta otellata. CCLXVII.

HEART OF REPTILES.

500

335

Heart of Testudo grccca

shape of the body, shows its greatest breadth, figs. 304, A, 335.
The two auricles, when distended, are of nearly equal size, and
of a subquadrate form, fig. 336, M, o. The bivalved orifice
between the sinus and the auricle, ib.
v, o, is a transverse slit. The white
arrow, o, shows the course of the blood
from the right auricle, past the valve
supported by the base of the auricu-
lar septum, into the aortic cavity of
the ventricle. In fig. 337 a bristle
passes through the orifice left by the
incomplete septum between the aortic
and pulmonic cavities into the latter,
which is the largest in Emys, as in
Ophidia and Lacertilia : the bivalved
orifice of the pulmonary artery, p, is
shown. In fig. 338 that of the left aorta,
A, is similarly exposed, and the in-
complete septum is cut through : the
root of the right aorta, A', is behind
that of the left. The relative position
of the origins of the three arteries from the chelonian ventricle
is shown in fig. 336, where P is the pulmonary, A the left aorta,
A' the right aorta, the most posterior, or dorsal, of the three
arteries. The ventricle is almost wholly occupied by a spongy
muscular structure, and the cavities
are smaller in Testudo than in Emys.
The left auricle, fig. 336, M, receives
the arterial blood from the lungs by
a single vein, the common trunk of the
pulmonary veins, ib. /, / : it opens into
the back part of the auricle near the
septum, and is guarded by a single
oblique membranous fold, ib. M. Each
auriculo-ventricular orifice is guarded
by a fold which extends across it from
either side of the base of the inter-
auricular septum ; to that of the left
auricle a small part of the muscular
structure is attached by chordae tendinea3. Opposite to the right
valve a semilunar ridge projects, in Testudo indica, which is the
rudiment of the second auriculo-ventricular valve in the Cro-
codile, and of the fleshy valve of that orifice in the right ventricle

336

Structure of auricles : heart of CTiclys

fimbriata

510

ANATOMY OF VERTEBRATES.

of Birds.1 The apex of the ventricle is attached by a short fold
of the serous membrane to the pericardium, fig. 336, t.

337 338

A'

339

a

a

Structure of ventricle, Emys europcea. xxxvm.

In all the foregoing modifications of the reptilian heart the
venous blood from the general system and the arterialised blood
from the lungs are transmitted by distinct auricular reservoirs

into the ventricle, where,
through the spongy character
of the receptacle, and the free
intercommunication between
the basal spaces into which
the auricles open and from
which the arteries proceed, the
blood is transmitted, in a more
or less mixed state, to the
lungs and to the general sys-
tem.

In the Crocodilian order a
marked advance is made in the
structure of the heart. The
blood from the general system
is poured by the veins into a
sinus, fig. 339, s, whence it
passes into a right auricle, ib.
o, by the usual bivalved aper-
ture. The auricle has a more
distinct t appendix,' and its mus-
cular walls are thicker than in
lower reptiles. The auriculo-

l.'i 'lit auricle and ventricle, Crocodilus acutua Ventricular Orifice ig defended

1 xx. vol. ii. p. 48, prep. no. 920.

HEART OF REPTILES.

511

340

not only by tlie ordinary valve on its left side, which is attached
to the base of the auricular septum, but by a similar though
smaller fold on the opposite or right side : this fold becomes the
fleshy auriculo-ventricular valve in birds. To the junction of the
two valves at their lower angle a fleshy column is attached. The
ventricular cavity, ib. R, which receives the venous blood, propels
it to the left aorta, A, and to the pulmonary artery, P : the origin
of each is guarded by a pair of semilunar valves. Immediately
above the larger of those of the left aorta is an orifice leading
into the right aorta: in fig. 339, a bristle is passed from
the left aorta through this
orifice into the right axil-
lary branch, «, of the right
or brachio-cephalic aorta.
In the figure, the valve is
drawn down to show the
orifice ; in its natural state,
it conceals and would cover
the orifice as the blood
flowed from the ventricle
into the left aorta. Some
openings lead from the pul-
monic cavity of the ventri-
cle into a spongy structure,
which has been defined as
a particular cavity (spatium
inter ventriculare) of the
ventricle ; but it is essenti-
ally a part of the pulmonic
chamber : bristles are passed
through the orifices or in-
tercolumnar spaces, leading
from R to this structure, in
fig. 339. The left auricle,
fig. 340, M, when distended, is smaller than the right, and of a more
transverse form : its muscular part is produced into an appendage,
which almost meets that of the right auricle in front of the f conus
arteriosus,' embracing the ( sulcus coronalis ' of the heart. There
is a small pulmonary sinus receiving the short trunks of the
pulmonary veins, fig. 340, /, /. The left auriculo-ventricular
aperture is defended by a broad membranous fold continued into
the ventricle from the middle of the base of the inter auricular
septum : to its margin are attached a few chorda) tendinea3 : the

Left auricle and ventricle, Crocodilus acntus

512 ANATOMY OF VERTEBRATES.

cavity into which it opens, fig. 340, L, is distinct from the
pulmonic cavity, the septum being complete : its walls are smooth,
or less broken by c columns earners ' than in other Reptiles ; and
the free walls of this ventricle are more compactly muscular. The
ventricle is produced in a subconical form, from its base to the
origin of the right or brachiocephalic aorta : the auriculo-ventri-
cular valve is slit, in fig. 340, to show the course of the ventricle
to the origin of that aorta : this has a pair of semilunar valves,
above which is the intercommunicating orifice with the left
aorta.

Thus the heart, in Crocodilia, consists of two auricles and two
ventricles, corresponding to the ( right ' and ' left ' auricles and
ventricles of Mammals. But, through the origin of an aorta from
the right as well as from the left ventricle, and their intercom-

o

munication, it follows that whenever, from an impeded state of the
pulmonary circulation, the right ventricle and its arteries become
over-distended, the venous blood flows through the inter-aortic
orifice into the arterial trunk, which, after supplying the head
and fore-limbs, bends, at A' ', over the right bronchus and effects
an union at A", fig. 339, with the left aorta, A, h. Such a state of
the circulation coincides with and facilitates the long submersion
of the Crocodile. When the animal is on land and breathing the
air directly, the arterialized blood flows freely into the ventricle, fig.
340, L, and the synchronous currents from this and the opposite
ventricle throw forward the valves at the respective origins of the
two aorta3 and close the interaortal orifice. The arterial and venous
streams flow on unmixed ; the former to the brain and other parts
of the head and fore-limbs ; the latter, by the branch, h, fig. 339,
chiefly to the liver and contiguous viscera ; a small part mixing
with the arterial blood in A', to be transmitted by A" to the other
abdominal viscera, hind limbs, and tail. To convert the heart of
the Crocodile into that of the bird, it needs only to obliterate the
left aorta; fig. 339, R, to appropriate the right or pulmonic ven-
tricle, exclusively to the service of the pulmonary artery ; and the
( left ' or systemic ventricle to the service of the aorta, which in
Hcematotherma is the exclusive distributor of arterial blood, in an
unmixed state, to the general system.

§ 90. Gills of Batracliia. --The blood is conveyed in all Reptiles
from the ventricular part of the heart, really or apparently by a
single trunk, which, in the one case, is called the ( bulbus arte-
riosus,' in the other the 6 conus arteriosus.' The interior develope-
ments by which the c bulbus ' is converted into the ' conus,' are
interestingly gradational, and the insulation of the pulmonary

GILLS OF BATRACHIA.

513

341

External gills, larva of Frog, ccxxxvm

artery to its ventricular origin is not effected until the batrachian
type is passed.

In the lower or perennibranchiate members of the order, the
single artery from the ventricle sends, as in Fishes, the whole of
the blood primarily to branchial organs, throughout life, and, in
all Batrachia, at the earlier aquatic period of existence ; a
description of the gills, permanent or deciduous, will, therefore,
be premised. At page 87 are described and figured, fig. 69, the
hyo-branchial arch and appendages of the larva of the Frog.
The basihyal, b, suspended by cera-
tohyals, a, to the tympanic pedicle,
e, supports a pair of cerato-branchials,
c, which each send off four branchial
arches. All these parts are cartilage.
The heart distributes the blood by a
short trunk through four pairs of vas-
cular arches, which, bending round
the gullet, reunite behind to form the
aorta. Before the larva quits the egg,
a tegumentary tubercle buds out in
front of the branchial cleft, and soon
shoots into a trifid appendage, fig. 341,
A and B, each process lengthening and bifurcating after the larva
is extricated. These filaments, of cylindrical shape, ib. c, each
support a single capillary

loop, pushed out from the 312

primitive vascular arch, and
are covered by ciliated epi-
thelium, producing the cur-
rents indicated by the arrows
in c. The branchial cavity
communicates at first, as in
Branchiostoma, with the
abdominal one, as well as
with the outer surface by
the branchial clefts. About
the fourth day these simple
outer gills begin to shrink ;
they are absorbed by the

seventh day. The cartilaginous arches, also beginning to shrink,
become more internal by the progressive growth of the head.

In the Newt (Triton, fig. 342), three pairs of external gills are
developed, at first as simple filaments, each with its capillary

Head and branchial appendages of the larva of a Xewt
(Triton) niagn. CCLXVIII.

YOL. I.

L L

514

ANATOMY OF VERTEBRATES.

343

One of the gills of the Newt, raagn. CCLXVIII.

344

loop, but speedily expanding, lengthening and branching into
lateral processes with corresponding looplets ; these blood-channels
intercommunicating by a capillary network, as at d, fig. 343. The

gill is covered by ciliated
scales, ib. e, which change
into nonciliated epithe-
lium, f, shortly before the
gills are absorbed.

The size of the gills is as
the proximity of their cleve-
loping vascular arch to the

propelling organ of the
blood. In the Proteus
anguinus three pairs only
of branchial and vascular arches are developed, corresponding
with the number of external gills. In Siren lacertina, as in
caducibranchiate Batrachians, there are four pairs of branchial
arches ; the first and fourth being fixed, the second and third free :

their contiguous borders on the
concave side are provided with
small interlocking processes. The
gills are in three pairs, increasing
in size, according to the above-
stated dynamic condition, from
the first to the third, which is
attached to both the third and
fourth arches : the upper or outer
surface is entire and covered by
ordinary integument ; the under
or inner surface is produced into
piniiatifid fringes, supporting the
capillary branchial vessels and
covered by thin epithelium. Each
gill is attached by its base an-
terior to and above the gill-slit,
which it overhangs. In the Axolotl,
fig. 344, the fringes of the gills are

longer and more slender. In the

&

Menobranclms they resemble those
of the Triton. In the Siren, Pro-
teus, and Menobranclms the outer
gills are persistent, and, perhaps,
also in Axolotes. In each of these

Circulating and respiratory organs, Axolotl,
Axolotes mexicanus. CCLXVII.

GILLS OF BATRACHIA. 515

( perennibranchiate ' Batrachians, arteries are developed from the
last pair of branchial vascular arches, as at p, fig. 344, to convey
blood to the luno-s.

o

In Menopoma and Amphiuma the gill-opening persists on each
side ; but of the original four pairs of vascular arches only the
second and third accompany remains of branchial arches, circum-
scribe the gullet, and reunite behind to form the beginning of
the aortic trunk. The extent of the ossification of the hyo-
branchial framework in some measure corresponds with the degree
in which the branchial organs of respiration are retained. In
Proteus the ceratohyals, urohyal, two pairs of basibraiichials, and
three pairs of ceratobranchials become bony. In the Siren the
ceratohyals, urohyal, one pair of basibranchials, and two pairs of
ceratobranchials are bony. The Menopome and Cryptobranchus
agree with the Newts and Salamanders (fig. 333), in having the
basihyal, w, the ceratohyals, x, x, and two pairs of cerato-
branchials, y and z ; but the latter pair is proportionally longer
and shows two elements of the arch, on each side, ossified. In
the Anourous Batrachians the branchial arches are reduced to the
basal portions of a single pair of ceratobranchials (p. 91, fig. 74),
which persist, in most higher Vertebrates, as the ' posterior
cornua ' of the f hyoid bone.'

The parts of the branchial framework in immediate relation
with the support of the deciduous gills never pass beyond the
cartilaginous stage ; and a histological test is thus afforded of the
temporary or permanent character of the branchia? in a Batrachiari
presenting them. The deciduous gills offer many modifications
in the larvae of the caducibranchiate species. In a tropical South
American Frog ( Opisthodelphy s ovifera), e. g., the external gills
are formed before the larva is excluded, and expand into a broad
membranous disc at their extremity.

But whatever the form or structure of the external gills, they
are fitted only to their office as such : that being discharged, they
turn to no other use, but lose their ciliated and vascular structure,
and disappear. The Tadpole, meanwhile, being subject to a
series of changes in every system of organs concerned in the daily
needs of the coming aerial and terrestrial existence, still passes
more or less time in water, and supplements the early attempts
at pulmonary respiration by pullulating loops and looplets of capil-
laries, fig. 345, «, from the branchial vessel, b, e, supported by the
cartilaginous arch, c, and coated by delicate non-ciliated epithe-
lium : the terminal processes of these ( internal gills ' support a
single capillary loop, d. They resemble the commencing gills of

LL 2

516

ANATOMY OF VERTEBRATES.

Teleostomous Fishes, especially of the Lophobranchs ; and the
analogy to the piscine respiratory structures is enhanced by the
growth of an opercular fold of membrane, protecting the branchial

chamber; but this, by pro-
gressive adhesion of its
posterior border to the cer-
vical integument, reduces
the lateral fissures to one
inferior foramen. In the
Newts, the side-slits are
longer retained. The
young of CcBcilia show a
branchial pore on each
side, with traces of bran-
chial fringes. The embryo
Salamander shows exter-
nal gills while in the
womb ; and, when these
disappear, the branchial
arches adhere to the oper-
cular fold of skin, the
external outlet being an
inferior transverse slit.

In Newts, Salamanders, Cflecilire, and Anourans, the branchial
orifices become obliterated after the absorption of the internal
gills. The gigantic Newt of Japan (Cryptobranchus) equally
differs from Mcnopoma and Amphiuma in the closure of those
orifices. Their retention in these large American Newts, with
the superadded persistency of the branchiae themselves in Meno-
branchus, Siren, and Proteus, are amongst the most significant
evidences of the manifestation of generic characters through

The internal branchios of the Tadpole of the Frog, magn.

CCLXV1II.

stages

of

one

general

course of transmutatioual

arrested
developement.

§ 91. Arteries of Reptiles.- -In the Axolotl, fig. 344, the three
anterior pairs of vascular arches rise distinctly from the ( bulbus,'
A ; the fourth pair blend their origins with those of the third :
the three anterior pairs are, functionally, branchial arteries, ib. B,
course along the corresponding branchial arches to the sides of
the neck, and then quit them to enter the base of the pendent
gill, running along the antero-inferior border : they there send off
a double series of branches, which penetrate and ramify in the
branchial fringes, and constitute at their end and margin a capil-
lary net-work, like that in fig. 343. From this the returning

ARTERIES OF REPTILES. 517

channels converge to form the 'branchial veins,' ib. b. which

O '

re-enter the neck,, course along the dorsal walls of the pharynx,
and unite to form the ri«;ht and left aortas, or roots of the common

o

median arterial trunk, ib. A. From the first or foremost branchial
vein is given off the carotid or cephalic artery, a*. The fourth
pair of vascular arches pass outward and backward, and each
divides, the larger portion, P, going to the lungs, the smaller
division pursuing its course to the back of the oesophagus, where it
unites with the third ( branchial vein,' and adds a small proportion
of unrespired blood to the contents of the aorta.

In the Proteus the bulbus arteriosus divides into a pair of
vessels, each of which, as it diverges, again divides ; the anterior
division supplies the anterior gill : the posterior division bifurcates,
to supply the second and third gills. But, before distributing
the branchial capillaries, each artery communicates by a direct
anastomosing channel with the branchial vein ; in other words,
only a portion of each primary vascular arch is appropriated to
the gills, and a certain proportion of the blood goes from the
heart to the aortic trunk without being submitted to the respira-
tory process. The small artery to the slender simple pulmonary
sac is sent off from the hindmost branchial vein. The cephalic
arteries arise from the foremost branchial veins, and consequently
supply the brain with purer arterial blood than that which goes
to the body.

The changes in the vascular arches, consequent on absorption
of the gills, are chiefly due to the enlargement of anastomosing
channels, between the inferent and efferent branchial trunks, like
those in Proteus. The course of these changes reduces the
arterial system in Menopoma to the condition of which Hunter
left the illustrations published in xx. vol. ii. The bulbus is
shortened, and the origins of the primary vascular arches
approximated : those of the third and fourth are blended together.
The foremost arch is smaller than the second or third : it sends off
an artery to the intermandibular space, a second to the side of the
head, a third to the pharynx, beyond which it bends abruptly
back, to enter the aortal root. The second and third vascular
arches are of equal size, wind round the wide pharynx, anterior
to the branchial opening, and unite on reaching its back part to
form the aortal root : this sends forward a small artery to the side
of the mouth, and, a little further on, the main carotid artery,
beyond which the roots converge backward, and unite to form
the aortic trunk. The hindmost vascular arch is the smallest,
and courses round the oesophagus, below or behind the branchial

518 ANATOMY OF VERTEBRATES,

opening, behind which it sends off the pulmonary artery, and
returns, at an acute angle, to join the third vascular arch near its
termination in the aortic root ; or, the pulmonary artery may be
said to be formed by a small branch from the third arch, in con-
junction with the fourth arch. The branchial arteries are sent off
from the aortic trunk, about an inch beyond its origin.

In the Newt the small anastomosing vessel at the base of each
gill, between the ingoing and outcoming trunks, enlarges as the
flow of blood is checked by the stunting of the gill in the course
of its absorption ; so that, when this is complete, the blood flows
from the ( bulbus ' round to the aorta in a continuous unchecked
stream, fig. 333, as at its first appearance.

In the Frog this course of change issues in the following per-
sistent disposition of the primitive vascular arches :- -The anterior,
originally the fourth, pair, which have their origins brought back
so as to seem to rise from the pair preceding, are sometimes called
its ( carotid branches : ' they diverge outward, as in their primitive
course, have a partial enlargement, and send off the 'lingual.'

J. CD CJ •*

pharyngeal, and entocarotid arteries. The next pair of vascular
arches, answering to the third of the primitive pairs, sends off
the laryngeal and brachial arteries, also a tributary to the sub-
cutaneous cervical, and are continued backward and inward,
supplying the oesophagus in this course, to form by their union
the aorta, A. The first pair, answering to the second and first
of the primitive pairs, send off the second root of the artery
Avhich ramifies on the subcutaneous cervical gland, and the
pulmonary artery ; the dorsal part of the second primitive arch
now appears as the accessory root of the subcutaneous cervical
artery given off from the aortic root, as above mentioned.

The brachial artery sends off an external thoracic, distributed
to the muscles of the fore-part of the abdomen, a subscapular
branch, a circumflex artery, supplying the muscles of the shoulder,
and is then continued to the fore-arm, where it becomes * radial,'
sends off a recurrent branch, and divides near the wrist into a
dorso-carpal and palmar branch, which terminates in the digital
arteries and the intervening web of capillaries.

The aortic trunk gives off the gastro-mesenteric artery, dividing
into ( cosliac ' and mesenteric branches ; then the suprarenal and
renal arteries, the lumbar, and the genital arteries (spermatic or
ovarian), and bifurcates to form the common iliacs. From each
of these are sent off a vesico-epigastric artery continued from the
allantoic bladder forward upon the abdominal walls, the external
and internal circumflex arteries, and the femoral, which, on reaching

ARTERIES OF REPTILES. 519

the leg, divides into posterior and anterior tibial, terminating in the
digital arteries and capillaries of the webs.

In Ophidian, Lacertian, and Chelonian Keptiles the ( bulbus '
of the embryo heart becomes divided into three distinct tabes,
which remain closely united together by their outer fibrous tissue,
and covered anteriorly by the reflected serous layer of the peri-
cardium. The extent of this union,, or length of the ( conus
vasculosus,' is greatest in the Serpents. In the Python it may
exceed two inches in length ; and, when the serous and fibrous
tunics are dissected away, the origin of the pulmonary artery is
seen to the left, next to it is the origin of the left aorta, and to
the right of this, about an inch above the ventricle, the trunk of

o

the right aorta appears, which, as it diverges from the left, sends
off the single carotid artery. This artery is the remnant of the
anterior of three primitive vascular arches. The right aortic
arch and the left aortic arch, which unite behind and beyond the
pericardium to form the abdominal aorta, are the proceeds of the
middle primitive arches : the pulmonary artery is the issue of the
changes of the posterior or first pair of vascular arches.

In the Lacertilia the extent of modification is somewhat less.
Looking on the sternal surface of the heart, the pulmonary trunk
is the foremost, the left aorta is the next, the right aorta is the
hindmost. The left and right aortic arches converge, and unite or
intercommunicate, behind and usually below or beyond the heart,
to form the abdominal aorta. In Lacerta ocellata, fig. 334, P
marks the origin of the pulmonary artery, which ascends and
divides : the left branch, P, passing in front of the left descending
aorta, with which it is connected by a ductus arteriosus, D, before
proceeding to the left lung, p, fig. 332 ; the right pulmonary
artery, fig. 334, p', passes behind the ' arterial cone,' and in front
of the right descending aorta, A', with which it communicates,
or is connected, by a ductus arteriosus before proceeding to the
right lung. These ' ductus arteriosi ' exist in the Python, are
shown in the Tortoise, fig. 335, D, D, and in the Crocodile,
fig. 340, D, r/. The third primitive arterial trunk, called ( right
aorta,' divides into the right arch (below A' in fig. 334), and
into the common trunk of the two cephalic or carotid arteries,
ib. a, «*, describing the upper arches : the common trunk of
the brachial arteries is usually given off from the right aortic
arch. In Psammosaurus griseus the common trunk of the carotid
does not bifurcate until it has ascended the neck as far as the
origin of the bronchial tubes : and not until after the right aorta
has arched over the right bronchus does it send off, at an acute

520 ANATOMY OF VERTEBRATES.

angle, the common trunk of the right and left brachials. The
left aortic arch, in Psammosaurus, sends off a gastric and mesen-
teric artery before it joins the right aortic arch ; and this is the
case also in the Tortoise, fig. 335, I, and Crocodile, fig. 339, h,
the left aorta being then so reduced in size as to resemble a
' ductus arteriosus.'

In the Tortoise the right aorta, soon after its origin, sends off
a common trunk, which quickly subdivides into the carotids,
fig. 335, a*, a*, and brachials, ib. «, a ; and the same is the case
with Enujs, in which the four arteries are seen cut short near their
origins, between A' and A, figs. 337 and 338.

In the Crocodile the two ( arteriaa innominate,' figs. 339, 340, b,b,
are longer before they divide into the brachial, «, and carotid, a' :
both innominata3 arise by a short common trunk from the right
aorta, which divides, soon after its origin, into that trunk and the
right aortic arch, ib. A'. This arch winds over the right pul-
monary artery, fig. 339, p', with which it is connected by a
' ductus arteriosus ' (the arch is reflected upward and the ' ductus '
D', severed from the pulmonary artery, p', in fig. 340). The
origin of the right or brachi-cephalic aorta is hidden by that
of the left aorta, fig. 339, A, which is anterior, or on the sternal
side of it. The left aorta, as it winds over the left pulmonary
artery, is attached to it by a ' ductus arteriosus,' the remnant of
the channel by which the first vascular arch originally com-
municated with the second, to aid in forming the aorta, before its
current of blood was diverted to the uses of the well-developed
lung, after exclusion. The continuation of the main part of the
left aorta into the great visceral artery, fig. 339, A, reduces its
original union with the right aortic arch, A', A" ', to a small anas-
tomotic channel.

The following particulars are notable with regard to the dis-
tribution of arterial blood by the right aorta in Reptiles. The
anterior vascular arch, in Ophidia, is converted into a pair of
cephalic or carotid arteries in the young Snake, and this structure
is retained in the common Snake ( Coluber natrix) ; in Python
tic/ris I found the right carotid much reduced in size ; in the
Viper ( V. verus\ and some other Serpents, the cervical part of
the right carotid is obliterated : but the cephalic portion remains,
and receives blood by the anastomosis of one of its branches
with the left carotid.1 In the Viper, and some other venomous
Serpents, the internal maxillary branch of the carotid forms a
rete mirabile behind the poison-gland.2 The right aortic arch,

1 CCLXXXl. 2 CCLXXXII. p. 260.

LUNGS OF REPTILES.

521

346

soon after it has curved over the right pulmonary artery, sends off
the trunk of the vertebral and anterior intercostal arteries : in its
origin and position, this trunk resembles the common brachial
trunk in Lizards.

The relation of the origin of the right aorta to the ventricular
compartment, first receiving the arterialised blood from the
pulmonary auricle, and the distribution of the branches of the
right aorta, are such, that the head, neck, and fore-limbs receive
chiefly arterialised blood, and the abdominal viscera, the trunk,
hind-limbs, and tail, are supplied with mixed venous and arterial
blood. But this localised distribution of the two kinds of blood
is more completely effected in the Cro-
codiles, through the modification of the
' ~

heart and arteries before described.

§ 92. Lungs of Reptiles. - - An opening
on the midline of the ventral side of the
pharynx, fig. 346, c, receives air introduced
into the mouth, and conveys it to the
receptacles which, in Reptiles and all
higher Vertebrates, are called f lungs,' ib.
fy f. The opening, usually a short longi-
tudinal slit, leads, in the Newt and Pro-
teus, to a small crescentic membranous
sac, from the angles of which are pro-
duced the long slender pulmonic bags. In
the Axolotl a short tube, strengthened by
a few feeble subannular cartilages, con-
ducts the air to the lungs, which com-
mence just beyond the heart : in the Siren and Land- Salamander
a similar trachea divides into two branches, one to each lung.1 In
all these tailed Batracliia the pulmonary bags have simple or even
walls. The artery, formed as above described, from the hindmost
vascular arch, joined by a branch from the next arch, runs along
one side or border, and the vein returns along the opposite border
of the lung. The branches proceed from the artery, fig. 348,
a, transversely, with regular intervals, midway in which the
venules are formed which course half-round the cylinder to open
into the longitudinal vein : fibres of elastic tissue accompany the
arterioles and venules. The intervening capillaries constitute a
regular network, uniformly over the pulmonary surface ; they
seem to be mere channels for the passage of the blood discs, fig.
347, with intervals or islets of compacted cells, containing nuclei

xciv. p. 395.

Respiratory organs, Xewt.

CCXXXV1II.

522

ANATOMY OF VERTEBRATES.

and granules^ ib. a. This vascular surface is covered by a delicate
carpet of epithelial cells, fig. 348 , certain linear tracts of which,

347

Respiratory surface, lung.of Newt, magnified, with the epithelium
out of focus. CCLXVIII.

ib. by b9 are ciliated. The exterior of the lung is covered by
delicate peritoneal nonciliated scales.

348

surface, lung of Newt, magnified, with the epithelial covering

ill fOCUS. CCLXVIII.

In the Siren the lungs are narrow bags, coextensive with the

LUNGS OF REPTILES.

523

349

long trunk ; and the ciliated tracts upon the inner surface begin
to be raised therefrom, and to mark out shallow depressions 011
the vascular surface, at least along the anterior half of the sac.
In the Axolotl, in which the lungs terminate at the hinder third
of the abdomen, the alveolar depressions or cells are more marked.
In the Amphiume the lungs are narrow, and terminate in a point,
within a short distance of the anus : on the inner surface elastic
bands are developed in the inter-alveolar partitions, and the alveoli
begin to be subdivided into smaller cells. In the Menopome the
lungs have a similar structure, but are proportionally smaller, and
with larger alveolar depressions.

The lungs of the Frog, fig. 349, are wider in proportion to
their length, and extend along the
dorsal part of the abdominal cavity,
with the vertebral bodies and vascu-
lar trunks intervening. They are
continued by short bronchia? or bron-
chial apertures, fig. 350, f, directly
from the larynx. The proper tissue
of the bag is composed of very elastic
fibre, covered by peritoneal epithe-
lium, and lined by the capillary net-
Avork and its epithelial covering ;
the pulmonary artery takes its course
beneath the peritoneal layer, the pul-
monary vein runs beneath the inter-
nal epithelium ; the one on the fore
and outer part, the other nearer the
inner or mesial side of the lung. The
whole inner surface is honeycombed,
and the alveoli are subdivided into
smaller cells. The arterioles run
along the attached borders of the septa, the venules along the
free borders. The ciliary epithelium is limited to the margins
of the alveoli supporting the larger venules: the capillary net-
work, covered by non-ciliated delicate epithelial scales, is
disposed upon the sides and bottom of the ultimate cells, the
septa having a layer of the capillary network on each side.
Thus the lungs of the tailless Batrachia, and more especially of
the Pipa, in which they are very broad and the bronchial tubes
long, have a more extensive respiratory surface in proportion to
their size than in the tailed species.

But the pulmonary artery is not exclusively distributed to the

Heart and lungs, Frog. CCLXTIII.

524 ANATOMY OF VERTEBRATES.

lung : it sends a branch to the f rete mirabile ' of the parotoid, or
group of subcutaneous cervical glands, and, in the Frog, the
branch from the pulmonary artery joins one from the aorta to
form a large subcutaneous artery, more extensively distributed
upon the skin, which exercises a respiratory office in these
naked Batrachia. In the Siren, Menopome, and Amphiume,
the pulmonary artery distributes some small twigs to the oeso-
phagus.

In the poisonous, colubrine, and marine Snakes the lung is,
functionally, single, one only being developed, but of great length,
for the respiratory purpose, the other becoming aborted into a
small or scarcely discernible rudiment. The trachea, fig. 300, a,
has numerous and entire cartilaginous rings along a certain pro-
portion of its course, and the lung, ib. B, seems to be formed by
a dilatation of the membranous part of the trachea! tube, after
the rings become incomplete : but these may be traced supporting
a narrow and shallow kind of air-canal to the hind end of the
lung in Pelamis bicolor.1 A similar structure has been observed
in Vipers (Echidna arietans), and, for a shorter extent, in Rattle-
snakes, in which the trachea is shorter than in non-venomous
Snakes. The expanded membranous part of the lung is honey-
combed, with subdivisions of the alveoli at the fore-part of the
lung, for a varying thickness and extent in different species. The
rudiment of the atrophied lung is often indicated by an orifice in
the trachea, at or near its entry into the functional lung, leading
to a small pouch. This adheres to the terminal whole-rings of
the trachea in Coluber natrix and Naja tripudians. In the great
constricting Serpents both lungs are functionally but unequally
developed. In Python tigris the left lung is nearly half as long
as the right : but, by its structure, it takes almost an equal share
in the respiratory function, the vascular and honeycombed parietes
being of nearly the same extent as in the right lung. So much
of this as is prolonged beyond the left lung has thin, simple, and
comparatively unvascular walls, performing the office of a reservoir
of air, which may be useful during the period, when the delicate
windpipe is squeezed flat by a large prey in progress of slow
deglutition.2 The proper parietes of the lungs almost every-
where adheres, by lax cellular tissue, to the contiguous organs.
In the Slow-worm (Anguis fragilis) the lungs are relatively
shorter than in true Ophidia, but the left is only half the length
of the right lung. A similar difference is presented by the lungs

1 xx. vol. ii. p. 93, prep. no. 1089. 2 Ib. p. 94; prep, no, 1093 A.

LUNGS OF EEPTILES. 525

of Bipes lepidopus. In Pseudopus Pallasii the lungs are of nearly
equal length.

In most Lacertian Reptiles the lungs are equal, are broader
in proportion to their length, and the short bronchus terminates
abruptly in the single pulmonary cavity. The parietes are honey-
combed and vascular, but in a less degree as they extend from the
heart : in Geckos and Agamas the alveoli are deepest on the
mesial side of the lungs. In the Iguana the pulmonary cavity is
divided by a few deep partitions into primary lodges, the parietes
of which are honeycombed by secondary and tertiary cells.1 In
a Monitor (JRegenia ocellata) the bronchus is continued some way
alone- the interior of the lung;.2 The lungs of the Chameleon are

o o o

remarkable for their great extent, for the delicacy of their
parietes, and the number of ca^cal processes continued from their
anterior and inferior margins. Each lung is partially divided
longitudinally at its fore part into two cavities, which have their
vascular surface increased by subdivision into cellular alveoli ;
the posterior appendiculated part of the lung is of a simpler
and less vascular structure, and may serve as a reservoir of
air. Marginal caecal productions of the pulmonary bag exist also
in the Geckos (e. g. Ptyodactylus jimbriatus) and in Polychrus
marmoratus. In Geckos and Scinks the trachea terminates in
the lungs without dividing into bronchi.

In the Chelonia the lungs present a further stage of complica-
tion, and are adherent to the surrounding parts. In those of
Chelydra serpentina, e.g. the general cavity of each lung is divided
into eight compartments, the walls of which are honeycombed
and vascular, especially at their fore part. The bronchial tube
extends to the hindmost compartment of the lung,3 communi-
cating by special orifices with the anterior ones, and sending
continuations of its fibrous structure along the free border of
the septa.

In the Sea-Turtles ( Chelone) the lungs extend over the back
part of the abdomen to the pelvis, and must act as an air-bladder
durino; their swimming : 4 the bronchial tubes are continued.

O O '

gradually decreasing, to near the end of the lungs, and retaining
cartilaginous rings or half-rings along three-fourths of their
course. They communicate with numerous primary divisions of
the pulmonary cavity, each of which is divided into cells, which
are subdivided to the third or fourth degree, with proportionate
extension of the vascular respiratory surface. The ultimate cells

1 xx. ib. p. 96. 2 cccxxi. p. 525.

3 Ib. p. 96, prep. no. 1109 A. * Ibid. p. 96, prep. no. 1110.

526

ANATOMY OF VERTEBRATES.

* the outer margin of tlie luncc are the largest and their

c O *~? tJ

parictes tlie least vascular.

Subjoined is a tabular view l of the capacity of the lungs in
examples of different families of the Chelonian order, ' obtained
by pumping out the air of the lungs, then pumping in water,
then pumping out the water again and measuring its amount in
cubic inches.' 2 This table shows that aquatic Chelonia require
less air in their lungs, in proportion to the weight of the body,
than land Chelouia ; and that in mud-dwellers and the soft-turtles
( Trionycida) other parts are auxiliary to the lungs in the act of
breathing. Thus the more permeable texture and minor thick-
ness of the epiderm in the Trionycida suggest the aptness of the
skin for respiratory influence on the blood, analogous to that of a
gill. The integument of the under side of the body in these
estuary turtles, which seldom leave the water except to lay their
eggs, is highly vascular.

Dr. Sager found f arranged along the surface of the tongue of
Trionyx, and somewhat in rows, as well as on the fauces and
about the rima glottidis, and also over the edges of the cornua
hyoidea, a number of delicate fringes, resembling, especially on
the hyoid arches, the fimbriated gills of the Menobranchus.' 3
Professor Agassiz remarks that, f after seeing this Turtle remain-
inn; under water for half-an-hour without showing the least si<m

O O O

of oppression, it seems plausible to assume that these fringes may
be similar to the internal gills of Tadpoles, not only in their
shape but also in their function.' 4

In the Crocodile ( Crocodilus acutus) the bronchial tube enters
the middle of the lung and is continued for a short distance into
its substance before losing the cartilaginous annular structure,

1 TABLE SHOWING THE CAPACITY OF THE LUNGS COMPARED WITH THE WEIGHT

OF THE BODY. CCC. p. 283.

Species

Mode of Life

Weight of
body

Capacity of
the lungs

Length of
Cai'apace

Testudo polyphemus, fcem.

On dry ground and

ounces

cubic inches

inches

in sand holes

95

35

ioi

Cistudo triunguis, foem. .

In dry woods, under

a

leaves

19

17f

6f

Ptychemys rugosa, fcem. .

In water and on land

62

22A

*±

11

Cinosternon pennsylvanicum,

&

foem.

In water and mud

8

1

4.1

Chelydra serpentina, mas.

In water and mud

65

2

7

10

Trionyx ferox, foem

In water and mud

76

41

^ 0

13

CCC. vol. i. p. 284.

3 cccn. quoted in ccc. pp. 277, 284.
4 Ibid. p. 284.

LARYNX OF REPTILES.

527

sending off lateral branches : it then abruptly terminates in a
dilated elongated passage, similar to those in which the side-
branches open. These passages correspond with the primary
divisions of the pulmonary cavity in the . Turtle, and the air
passes from them by numerous round apertures into the smaller
subdivisions forming the cellular structure of the luno;.1

o

§93. Larynx of Reptiles. — In perennibranchial and tailed
Batrachia the glottis is a simple longitudinal fissure, fig. 346, «,
in the middle of the ventral walls of the pharynx, each side of
which is commonly strengthened by a slender portion of fibro-
cartilage (Amphiuma), or so divided as to represent an ( arytenoid '
and a ' laryngo-tracheal ' cartilage (Proteus). The slit opens
into a small membranous cavity, usually kept patent by lateral
cartilages, from which the lungs diverge directly in Proteus,
Ampliiuma, and Triton, and with a short trachea intervening in
Siren, Axolotes, Menopoma, and Salamandra, the trachea being
either membranous or with feeble rudiments of cartilaginous rino-s.

O C5

In tailless Batrachia the larynx is well developed, especially
in the males. There is, in most, an annular thyrocricoid cartilage,
which supports in all a pair of large arytenoids, of a triangular
shape, the apex forming the upper and lateral boundary of the
larynx, fig. 351, a : the chords vocales
stretch transversely from one end of the
base to the other, and are wanting only in
Pipa and Dactylethra. Above and below
the vocal chords, fig. 350, c, there is a
mucous pouch ; and between the chords
there is, in some species, a cartilage. The
muscles are a ( dilator ' and a ' constrictor
rima3 glottidis,' and a ' compressor glottidis,'
arising from the cerato-branchials, fig. 74,
p. 91, and inserted into the posterior angle
of the arytenoid : by bending this angle
outward, it stretches the vocal chords, and,
both muscles acting, they compress the
larynx. This is an influential muscle in
regard to the voice or croak, and varies with
its quality in different species ; it is want-
ins; in the mute Pipa. In Bombinator iqneus TTg^ie' laiJnx' and lungs'

-* y male Frog, Sana temporaria.

and Hyla verrucosa the arytenoids are ob- cccxx-

tuse-angled and nearly equilateral triangles. In Bufo cinereus

1 xx. vol. ii. p. 97, prep. no. 1118.

350

-c

528

ANATOMY OF VERTEBRATES.

351

they are more acute-angled and directed backward. In the Toad

(Bnfo) the chordae vocales are thin
elastic membranes, and in two pairs, fig.
351, a and b : the sacculi are seen to be
lodged in the large arytenoid cartilages.
The males of the common and edible
Frogs (Rana) have two submandibular
sacs, the male Tree-Frog (Hyla) has
one such sac, opening by a straight canal
into the larynx, and susceptible of con-
siderable distension by air during the
croak. All these diversities of laryngeal
structure affect the loudness, deepness,
or sharpness of the peculiar vocal notes
of Frogs and Toads. The air passes

Larynx aud lungs (c, d) Toad, Bufo. tO the lungS, fig. 350, (/, 351, C, d, by

short bronchi, fig. 350, f, save in the

Pipa, in which the bronchial tubes are long, especially in the
female.

The glottis in Serpents can be drawn forward and protruded
from the mouth by the action of the geniotrachedles muscles,
fig. 147, y, p. 229. In marine serpents the glottis is situated
very near the forepart of the mouth, and the air can be inspired
at the surface without exposure of the jaws. The upper rings
of the trachea coalesce to form a cricothyroid cartilage, sending
forward two processes which represent the arytenoids in many
Ophidia ; but which are freely articulated therewith in the great
constrictors. The ' processus epiglotticus ' is subquadrate in
Boa. True ( chordae vocales ' are absent ; and the voice is
reduced to a hissing sound produced by the action of the expired
air upon the margins of the glottis. The rings of the trachea
are entire, and the trachea varies in length in different ser-
pents before it reaches the lung. Along this it continues, of
decreasing breadth, with portions of the rings, as if incrusted in
the pulmonary parietes, for an extent varying in different
serpents.

In Lacertians a cricothyroid cartilage supports a pair of
arytenoid cartilages : in most there is a cartilaginous or osseous
' processus epiglotticus,' which, in a few, coexists with an incom-
plete epiglottis. The mucous membrane of the glottis is reflected
over the arytenoids, forming a depression beneath them, and folds
with free margins : these ' vocal chords ' are broad in the Chame-
leon and Gecko, and stretch from the base of the arytenoid to the

LARYNX OF REPTILES. 529

inner surface of the cricothyroid. In Lacerta and Ascalabotes
the corresponding fold is very narrow, and the chirping call-note
of the Gecko may depend rather on the vibration of the margins
of the glottis than on the vocal folds, which cannot be brought
into contact or be made tense. In the Chameleon, the lining
membrane of the larynx is produced between the cricothyroid and
first tracheal ring into a pouch. In the Stellio of the Levant the
tracheal rings are osseous : in most Lizards they are cartilaginous.
The trachea is remarkable for its width in Platydactylus yuttatus,
but the diameter is reduced to one half in Platydactylus vittatus.
In the Chameleon and most other Lacertians it is still narrower.
Amongst the Chelonia the Hawksbill Turtle ( Chelone imbricata)
shows a glottis undefended by retroverted papilla?, or by an epi-
glottis, but capable of being accurately closed by its constrictors.
The thyroid cartilage in all Chelonia is distinct from the cricoid :
the arytenoids are triangular, and their inner facet is large in
Emijs and Testudo. The ordinary sound produced by the larynx
of the Chelonia is a sort of hiss. The European fresh-water Tor-
toise emits a low piping note, and Agassiz records the same fact in
regard to some North American Emy dians. * In Chelone my das the
f rima glottidis ' supports on each side a mucous fold, which serves
to produce a low grunt or bark at certain seasons. In some Tor-
toises ( Testudo tabulata, T. elephantopus) a triangular membrane
ascends from the base of the larynx to the ( rima,' dividing it into
two parts. The rings of the trachea are entire and cartilaginous :
in some species the trachea bifurcates half way towards the
lungs, the bronchi being of great length, and one of them usually
describing a large curve : in Testudo gr&ca the left bronchus is
three fourths longer than the tracheal trunk ; but in Testudo
coue'i the trachea is one fourth longer than the bronchi. The

o

production of the snout in the Trionycidce enables the terminal
nostrils to be raised above the surface of the water, to respire,
without exposure of the animal.

In the Nilotic Crocodile the mucous membrane is produced into
a fold on each side the ( rima glottidis : ' the folds deepen as they
extend backward, and are produced into a pair of pointed pro-
cesses above the arytenoids* The broad cartilaginous plate of
the basihyal rises in front of the glottis like an epiglottis. On
divaricating the rimal folds they are seen to bound a wide pouch
anterior to and above the true ( aditus larynstis,' which is much

«/ o

shorter than the ( rima,' The thyroid and cricoid coalesce to form
one annular cartilage supporting the pair of arytenoids. The

1 CCC. vol. i. p. 284,
VOL. I. Bl M

530 ANATOMY OF VERTEBRATES.

membrane covering these forms a wide depression anterior to and
below them, before being continued as chordae vocales, along the
posterior half of each side the ' aditus laryngis.' These ' chordae '
operate in producing the f bellow ' of the Crocodile, a loud sound,
between barking and roaring.

The trachea in the Nilotic and some other kinds of Crocodile
forms a bend or loop before dividing into the bronchi : this loop
is not found in the Alligator or Gavial. The erectile structure of
the single tegumentary nostril in the Gavial, serves, like the short
proboscis of the Trionyx, to enable the aquatic reptile to breathe
the air with more safety.

§ 94. Respiratory actions of Reptiles. — The lungs in Batrachia
being suspended in a common thoracic-abdominal cavity, without
the costal or diaphragmatic mechanism of expansion, are filled
with air by acts of deglutition.

The hyoid, fig. 350, b, is depressed ; the pharynx, ib. <?, is
dilated: the air enters by the nostrils, and its return is prevented
by their internal valvular folds, and by the application of the
tongue, ib. a, against their palatal openings. The contraction of
the throat-muscles and retraction of the eyeballs send the air
backward, the gullet contracts, the glottis opens, and the air is
driven through the bronchi, f, into the lungs, g. If the mouth of
a Frog be kept forcibly open it is soon asphyxiated, the essential
respiratory acts being prevented : if a breach be made in the
abdominal walls, and the act of deglutition can be performed, the
lungs are inflated. Expiration is performed by the elasticity of
the pulmonary parietes, which is such as to quite empty the lung
and reduce it to the size of a small pea, the abdomen being
opened.

The lungs of Chelonia being lodged in a cavity, the capacity of
which is only aifected by the retraction and protrusion of the
limbs and tail, appear, also, to be filled with air, chiefly by acts
of deglutition. These are so habitual that ( the working of the

o o

throat ' continues when the Turtle is immersed in water ; and
Hunter was led by observing this circumstance, to relinquish the
idea of its being a respiratory act. It is, in fact, in the Chelonia
in which the plastron remains unfixed by bone to the carapace
( Chelone, Trionyx) that respiratory acts due to movements of the
thoracic-abdominal walls are most conspicuous. ' If a Turtle be
thrown upon its back, and makes an inspiration, we may observe
that its four fins are, as it were, erected ; the breast-bone is pushed
forward, and the cavity swells out wherever the parts are soft. All
this is done, I conceive, by the muscles of the extremities moving

RESPIRATORY ACTIONS OF REPTILES. 531

their respective bones in an inverted order : instead of their
moving the extremity, the extremity becomes the fixed point :
the bones answering to the clavicles are moved forward, and the

O '

bones of the pelvis at the lower part are pushed against the inside
of the breast-bone, so that the whole bone is pushed out. They
appear to draw in their breath but once in twenty minutes or
half-an-hour, and often at a much longer interval.' l

It is probable that such respiratory actions could not be per-
formed by the animal when swimming and diving ; and it is
certain that such actions of the limb-muscles could not effect
any motion of the breast-bone in the great proportion of the
Chelonian order, in which the plastron is fixed. The capacity
of the thoracic-abdominal cavity may be slightly affected by the
movements of the limbs acting on the soft walls at its fore and
and back parts, fig. 149, p. 233 ; the diaphragmatic muscles,
figs. 150, 151, 42, may cooperate; but respiration goes on when
the limbs are motionless, and apparently by acts of deglutition, as
indicated by the ( working of the throat.'

In Ophidia, Lacertilia, and Crocodilia, respiration is performed
by the expansion and contraction of the more movable parts of
the parietes of the cavity containing the lungs : for this being
dilated the air rushes in by the only available passage, viz. the
glottis and windpipe, to the lungs. The articulations of the ribs
in serpents allow of their rotation forward and backward, and
even of a slight divarication of the two ribs of each pair. This
mechanism and the muscles concerned in working it are described,
pp. 55, 56, 224, figs. 143, 144. To whatever degree the visceral
cavity may be so expanded, the air enters by the nostrils or
glottis, if they be open and free ; and a general expansile or
inspiratory movement may then be noticed.2 But the great
length of the thoracic-abdominal cavity and the numbers of pairs
of moveable ribs - -in some serpents three hundred pairs — are
associated with partial enlargements and contractions of the
cavity, effecting corresponding changes in the long pulmonary
bao- without affecting the total volume of air in it, if the «iottis

O •* *~> O

be not in communication with the outward air, either directly or
through the medium of the nostrils. Schlegel has observed about
thirty such partial dilatations of the trunk and lung between two
inspirations.3 When the Constrictors swallow their prey the
glottis is protruded from the mouth : this may be a consequence of
the pressure exercised on the parietes of the greatly distended
mouth, and may not relate to the necessity of directly receiving

1 ccxxxvi. vol. ii. p. 348. 2 CCLXXXV. 3 ccxxxiv. torn. i. p. 53.

M M 2

532 ANATOMY OF VERTEBRATES.

air during the period occupied by the rotatory transit of the prey
to the gullet : it is more probable that at this time the trachea is
squeezed flat, and the air in the hinder reservoir of the largest
lung may serve to keep up the small amount of respiration needed
during the passage of the prey to the stomach, the snake being
then at rest and almost torpid.

In Lizards and Crocodiles certain pairs of vertebral ribs
(pleurapophyses) at the forepart of the thoracic-abdominal cavity
articulate with sternal ribs (ha3mapophyses), the bony arches being
completed by the sternum below. The pleurapophysis, fig. 49, 4/*
(p. 57), forms an angle directed backward at the joint with the
hcemapophysis, ib. 6, the muscles raising or drawing outward and
forward the upper rib open the angle between it and the lower
one; and the head of the rib being fixed to the vertebra, the
sternum yields, is depressed, and both the vertical and transverse
diameters of the cavity containing the lungs are increased.
Consequently the air enters the pulmonary cavities. By the
contrary actions, the thoracic-abdominal cavity is contracted, and,
the elasticity of the pulmonary parietes aiding, the air is expelled.

In the Crocodile the increase in the number of the complete
sterno-costal arches, fig. 56, i, 2, 3, &c. (p. 68), gives greater effect
to their respiratory movements : and the muscular fibres attached
to the midriff-like sheets expanded upon the hepatic lobes, may aid
in making the general expansion of the thoracic-abdominal cavity
tell more directly upon the lungs.

Almost all the Lacertilia and Batrachia have the peculiarity
of inflating their lungs, when they are under the influence of fear
or of some other excitement : in the Chameleon, as well as in
Polychrus and many other Iguanoids/the expansion of the trunk
consequent thereon aids in producing the remarkable change of
colours to which we shall recur in the chapter on the integu-
ments.

533

CHAPTER VIII.

URINARY SYSTEM OF H^EMATOCRYA.

§ 95. Kidneys of Fishes. — In all Vertebrates an excretory
organ is very early developed in the form of a tube, extending
from each side of the cloaca forward, along the dorsal region of

* <~> o

the abdomen, close to the spine, where it communicates with a
number of slender blind tubes placed at right angles to it ; the
longitudinal trunk-tube serving as the excretory duct of the
shorter transverse secerning crcca. These glands are transitory in
the air-breathing Vertebrates and are called, from their discoverer,
( corpora Wolffiana ; ' they are persistent in fishes l and are
called ( kidneys,' fig. 352, n: in both they are renal organs and
secrete urine.

A slightly opaque, slender, elongated glandular body, in the
situation marked h in fig. 169, may represent the renal organ in
Branchiostoma. The structure of this organ is more obvious in
the Myxinoids : it is double : each long duct, fig. 353, i, «, as it
extends from the cloaca through the abdominal cavity, sends off,
at regular but distant intervals from its outer side, a short wide
tube, ib. by which communicates by a narrow opening with a blind
sac, ib. d. At the bottom of this sac or caecum there is a small
vaso-ganglion, fig. 353, 2, D, free on all sides save that by which
the vessels, ib. «, enter, and ib. Z>,2 quit it : there are no urini-
ferous tubes in this vaso-ganglion : the contents of the caecum
must react through its thin parietes and those of the capillaries
with which it is in contact upon the blood in those capillaries, and
extract therefrom the azotised uric principle. Analogous vascu-
lar bodies, formed chiefly by convoluted tufts of arterial capilla-
ries, are present in the Wolffian bodies of Mammals, and in the
persistent renal organs of all Vertebrates. They are called, after
their discoverer, 6 Malpighian corpuscles,' and the uriniferous
tubes take their rise by a sacciform blind beginning applied over
the vascular tuft or ganglion.3

The combined secerning casca and vaso-ganglia form in the

1 cxxx. ii. p. 314. 2 xxi. p. 13. 3 cxxxvn.

534

ANATOMY OF VERTEBRATES.

352

Lampreys * a continuous narrow elongated gland, which extends in
their young or Ammocete condition throughout the abdomen, but in
the full-grown fish (PetromyzoTi) along the posterior two thirds : in

both being confined to the
dorsal part of the cavity,
fig. 354, g. The ureters,
ib. c, open into the short
canal leading to the pa-
pillary production of the
peritoneal outlets close
to the anus.2

In most Osseous Fishes
the kidneys are long and
narrow, and extend
through the whole or a

o

great part of the dorsal
region of the abdomen,

o

firmly attached to the
vertebral column ; they
are usually broadest and
thickest anteriorly , where
they sometimes present
a lobulated surface ; they
contract, approximate,
and frequently blend to-
gether as they extend
backwards ( Cyclopterus) ;
sometimes penetrating
the haemal canal in the
tail. In the Gymnotus
the kidneys are distinct
and thickest at their pos-
terior ends, as they are
in the Gurnard, fig. 379,
k, and in most Sharks.
The kidneys have not
a well-defined capsule
in Osseous Fishes, but
their ventral surface is immediately covered by an aponeurotic
membrane, against which the peritoneum, and the air-bladder
when present, are applied. The renal tissue is soft and spongy,

1 In Petromyzon marinus the diameter of the tubuli urinifcri is n-^th of an inch, that
of the capillaries of the kidneys being j^th of an inch. 2 xx. iv. pi. 56, fig. 1, e.

Viscera of male Shark, showing kidneys, n, in situ

KIDNEYS OF FISHES.

535

firmest at the fore-part of the gland ; usually of a reddish-brown
colour ; sometimes soaked, as it were, with dark pigment.1 It is
supplied by numerous small arteries from the abdominal aorta,2
which form Malpighian corpuscles ; but these are fewer in
number and less complex than in the true kidneys of higher
Vertebrates. The primary branches of the tubuli uriniferi, given
off from the long ureter, are extremely numerous ; their divisions
in the renal substance are comparatively few ; they are in most
fishes convoluted and of equal
diameter, extending through the
whole renal substance, which
shoAvs no distinction of cortical
and medullary parts, and has
neither ' pelvis ' nor ( mammil-
la} : ' they are lined by a ciliated
epithelium. Sometimes a single
common ureter quits the coa-
lesced hinder ends of the kid-
neys, as in the Pike, and termi-
nates in a urinary bladder. More
frequently the essentially duplex
nature of the kidneys is mani-
fested by the emergence of two
ureters from the ventral surface
of their posterior ends when these
have coalesced : in some fishes the

in .1. The anterior extremity of the kidney, Bdcllo-

ureters unite together alter quit- stoma. xxi. 2. Man-i^hum body ana its bioud-

, . .. , . , vessels, Bdellostoma. XXI.

ting the kidneys, and terminate by

a common gradually widening canal in the urinary bladder ; some-
times they enter the urinary bladder separately, as in the Wolf-
fish, where they both terminate on its left side, half an inch above
the cervix : rarely are any smaller accessory ureters seen, as e. g.
in the Stickleback, to terminate also, separately, in the bladder.
This, in aquatic animals apparently needless, receptacle of a fluid
excretion is5 nevertheless, rarely absent in Osseous Fishes ; the
Pilchard, the Herring, and the Loach are among the few instances
where it is not developed. In the Loach a very short, in the
Herring a long, common ureter terminates behind the anus. In
the Gymnotus the common ureter is so wide as to serve as a
receptacle, and it is directed forward to reach its termination
immediately behind the advanced vent.

The urinary bladder is sometimes round, fig. 379, b, sometimes

1 As in Lepidosiren, xxxm. p. 349. 2 Hunter, vn. vol. ii. p. 112.

536

ANATOMY OF VERTEBRATES.

354

oval or pyriform, often bifid at its fundus, or two-horned ; it is
largest in those fishes, as the Pleuronectida, Lophius, Orthagoriscus,
and Cyclopterus, in which the air-bladder is absent. In Catty ony-
mus the bifid urinary bladder extends the whole length of the
abdomen. It always lies behind the rectum, generally receives
the ureter or ureters nearer its fundus than its cervix, and the latter
is prolonged usually into a prominent papilla behind the vent.
The lono- cervix vesicoe in the Salmon is surrounded by a venous

plexus. In the Sturgeon the wide
ureters extend along the outer
borders of the kidneys, and re-
ceive the vasa defer entia or the
oviducts in their course towards
the cloaca, where they unite into
a short duct which forms the com-
mon outlet of the urinary and
generative products.

The kidneys are long, narrow,
but distinct from each other in
all the Ganoid Fishes and in the
Lepidosiren. In the Lophius the
kidneys present a more compact
form, and are situated wide apart,
far forwards in the abdomen, in
depressions on either side of the
origins of the ' retractores palati.'
The kidneys of the Plagiostomes
are also of a more compact form
than in Osseous Fishes, and are
always distinct, and generally
show a cerebriform convoluted or
lobulated exterior : the primary
branches of the uriniferous tubes are fewer, and their dichotomous
ramifications more numerous i1 the ureteric trunk becomes superficial
along the inner and fore-part of the hinder half of each kidney ;
after quitting which it dilates in the Grey Shark (^Galeus) into a
kind of receptacle, fig. 352, m, behind each oviduct or vas deferens,
and communicating with its fellow near the cloaca, terminates by
a single urethral canal upon a kind of penis or clitoris, ib. o,
at the back of the anus, within a large common cloaca. In the
Torpedo, the ureters terminate on the cloacal papilla by two dis-

1 In the Ray, the diameter of the terminal branches of the tubuli uriniferi are
of an inch, that of the capillary renal arteries being y^th of an inch.

Cj

Kidney and generative organs, Lamprey (Pctro-
myzon mariutts). xx.

KIDNEYS OF REPTILES. 537

tinct orifices.1 In the Skate and Thornback each ureter terminates
in the neck of a short bifid bladder : these open by a common urethra
upon the cloacal papilla. The Lepidosiren has a small urinary
bladder situated behind the rectum and in front of the oviducts : the
ureters do not communicate directly with it, but terminate sepa-
rately on small papilla? in the oviducal compartment of the cloaca.2

With regard to the circulation in the kidney of those Fishes, as
e. g. the Plagiostomes, the Lophius, and the Lepidosiren, in which
the organ is best defined, the vein on the outer side of the kidney
which receives blood from the tail, the abdominal parietes, and the
generative organs has so far the aspect of a ( portal ' or inferent
vessel, that a second and larger vein, whose roots take their rise
in part from the renal substance, extends from the inner and fore-
part of the kidney to convey its blood to the postcaval vein. The
exterior vein is not, however, completely expended in the kidney,
but is also continued forward from the anterior end to join the
veins from the anterior abdominal parietes, and sometimes those
from the pectoral fins. In all Fishes the kidneys maintain the same
relations with the cardinal veins that their transitory homologues
the ' Wolffian bodies ' do in the embryo of higher Vertebrates.

§ 96. Kidneys of Reptiles. — In this class the kidneys are always
a distinct pair, and are more circumscribed in form, and more
compact in structure than in Fishes ; but, as in them, the renal
tissue is uniform, not divided into ( cortical ' and ' medullary ' parts.

In the Siren each kidney is a long, oval, subcompressed body,
tapering anteriorly to a point situated in the hind part of the
abdomen, dorsad of the rectum, with an entire investment of
peritoneum reflected upon their inner edges, where they receive
small arteries. The ureters enter the back part of the cloaca, from
the fore part of which is developed a small allantoid or urinary blad-
der. The kidneys of Amphiuma resemble those of Siren. In the
Menopoma the kidneys are relatively longer, extending nearly the
whole leno-th of the abdomen on each side of the vertebral bodies.

O

In the Newt the kidneys are less elongate, and their forepart
becomes so thin and transparent that it lends itself favourably to
microscopical examination. The ciliated epithelium continued
from the uriniferous tubule, terminates abruptly shortly after
entering the Malpighian capsule, fig 355, ep : the basilemma
of the capsule, b?n, beyond the termination of the ciliated
epithelium, appears to be unclothed : it is a homogenous, trans-
parent, structureless substance, perforated by the inferent and
efferent vessels, and not reflected over them. The inferent

1 cxxxvi. 2 xxxiu. pi. 27.

538

ANATOMY OF VERTEBRATES.

355

Malpighiau body, Newt. CCLXXXVI.

356

vessel dilates on entering, forms a few coils, again contracts, and

becomes the efferent vessel.1 In the
Frog the kidneys present a more
compact form ; they are flattened,
subelongate, with a convex outer
border and a nearly straight inner
one, fig. 331, K, k. They are situated
at the pelvic end of the abdominal
cavity behind the rectum and allantoid
bladder : the peritoneum covering
only their sternal surface. The renal
capillaries, derived from the reniportal
vein, ib. K, ramify through the gland to
reach the Malpighian capsule, fig. 356,
f: in the specimen figured, by Bowman,2
under the magnifying power of 320 dia-
meters, the part where the capillaries enter (near t) is obscured by

an uriniferous tube. On enter-
ing, the capillary enlarges and
forms a few coils, m, which lie
bare in the capsular cavity. The
lemma begins to receive an epi-
thelial lining at f, f, which
increases in thickness to the neck
of the tubule, d, d, and is covered
by cilia : these may maintain
their motions hours after the
death of the Frog. The urini-
ferous tubules form by succes-
sive unions the ureter, which
opens into the urogenital com-
partment of the cloaca, opposite
the orifice of the large bifid al-
lantoid bladder, the contents of
which are mainly water.

In Serpents the kidneys, fig.
357, t, t, partake of the usual
elongated form of the viscera,
and are subdivided into numerous
flattened, overlapping lobes, so
as readily to accommodate them-
selves to the flexuosities of the

body, rrog. cxxxvn. l^rt of the trunk in which they

1 cxxxvir. 2 Ib.

KIDNEYS OF REPTILES.

539

35;

are lodged. In most Serpents they are unsymmetrically situated ;
the left in Coluber natrix, e.g., being one-fourth of its length
nearer the cloaca than the right kidney ; and they are loosely
attached to the dorsal abdominal walls. Each renal lobe is so
distinct that it may be regarded as a separate kidney or renule :
it is reniform in Python and Boa, and is principally composed of
the ramifications of the renal artery, the
reniportal and renal veins, and the urini-
ferous tubules with their initial (Malpi-
ghian) capsules. The artery of the renule,
entering at the notch or ( hilum,' repre-
senting the pelvis, distributes its branches
fanwise through the middle of the sub-
stance : each branch, fig. 358, a, sends
twigs to the Malpighian capsule which
form within it the dilated plexus, ana-
logous to that in fig. 356, whence the
blood is returned by the efferent vessel,
in the direction of the arrow, to the
branch of the reniportal vein, fig. 358,
p, v : these branches being distributed
fan-wise over both surfaces of the flat-
tened renule. In this course they com-
municate with, or help to form, a rich
venous plexus, ib. p, surrounding the
tubuli uriniferi, ib. t. and communicating

* o

with the branch of the renal or emulgent
vein, ib. e, v, which accompanies the
artery, in the mid-substance of the
renule.

The tubuli, ib. t, continued, as in fig.
356, from the capsule of the ( Malpighian
body,' after some convolutions, pass to the
surface next which the f body ' is placed,
and terminate in a branch of the ureter,
there situated : these superficial

nr

Kidneys and small organs, Rattle-
siiake (Crotalus). CCL.

branches are dispersed fan-wise, converg-
ing to the ( hilum,' and are often seen

o

injected, as it were, by the opake white pultaceous urinary
excretion. The Malpighian bodies diminish in size and the tubuli
in length, towards the thin edge of the renule.

Thus, on each superficies of the flattened renule are the radiatino-
ramuli of the ureters, ur} and reni-portal veins, pv ; whilst alono-

540

ANATOMY OF VEKTEBRATES.

the plane, midway between these surfaces, are the similarly
disposed branches of the renal artery, a, and renal vein, v. The
material of the urinary excretion thrown by the epithelial cells or
bags from the inner surface into the cavity of the uriniferous

tubules, t, is derived from
the rich venous plexus, p,
everywhere in contact with
their outer surface : the sero-
sity exuded from the dilated
arterial plexus in the Malpi-
ghian capsule, propelled by
the ciliary action, dilutes and
washes out the excretion
from the tubuli, whence it is
conveyed by the superficial
branches of the ureters to
the trunk, or ureter, com-
mon to the several renules,
and, by the ureters, is dis-
charged into the cloaca.1

o

There is no urinary or allan-
toid bladder in Serpents.

The kidneys in Lacertians,
fig. 301, k, fig. 332, are
shorter, broader, and less
subdivided than in Serpents ;
situated close to the verte-
bral bodies at the hinder part of the abdominal cavity ; they
are usually pointed at their forepart ( Cyclodus). In the Iguana
they are of an oblong, subdepressed form : their structure is
essentially that above described in the Boa. The ureter runs
superficially, as it collects its tributaries, along the free or ventral
surface of the kidney, and terminates in a slight eminence, papilla or
ridge, close to the genital orifice, in the urogenital compartment
of the cloaca, behind or dorsad of the anus. Anterior to, or sternad
of, the terminal orifice of the rectum, is that of the urinary or
allantoid bladder, of large size in the Iguana. In this reptile
Hunter found the bladder ( filled with a white fluid,' and ( there
were small calculi in it.' 2 In the same reptile he records the pre-
sence of e one brown calculus in each ureter, almost filling the
duct.'3

1 The ingenious and lucid explanation of the functions of the minute structures
given by their discoverer, Mr. Bowman, in cxxxvu.

UT

a

Plan of disposition of blood-vessels and tubuli in the
reuule of Boa. cxxxvu.

2 ccxxxvi. vol. ii. p. 3G7.

Ibid.

KIDNEYS OF REPTILES.

541

The fatty appendages which are attached to the kidneys or
urinary bladder in Batrachia, Ophidia, and Lacertilia, attain a
remarkable size in some members of the latter order ; in the
Iguana tuberculata they are attached by a narrow process to the
sides of the bladder, near its neck.1

In the Chelonia the kidneys present a more compact form,
and their surface is convoluted through the disposition of the
component lobes. They have the same low pelvic position as
in Lizards, but are smaller in proportion, and are outside the
peritoneum. In the Tortoise ( Testudo tabulata) they are oblong,
broad, thick, subtrihedral bodies : in the Turtle ( Chelone my das)
they are flattened anteriorly, or towards the abdominal cavity,
convex where they rest upon
the dorsal wall. In JEmys,
figs. 307 and 359, o, they are
semioval. The tubuli urini-
feri pass to the superficies of
the lobules and there form the
branches of the ureter, which
unite towards the mesial border
with the beginning of the main
duct, ib. N; this is short, and
terminates, with the spermduct,
c, in the male, in the uroge-

359

nital Cavity at F. The rectal Male organs of generation, and kidney of

J t europcea. xxxvm.

orifice intervenes between this

and the wide opening of the urinary bladder, ib. M, M". This
receptacle is proportionally smallest in the marine Chelonia
( Chelone, Trionyx) : in its contracted state it presents, in Chelone
mydas, thick muscular parietes and a corrugated internal surface.
In terrestrial and fresh-water Chelonia the bladder is relatively
much larger, and with thinner walls. In many it is bifid. In
Emydians, besides the ordinary bladder, fig. 304, u, a pair of
other bladders, ib. u', u", communicate by wide orifices, behind
the ureters, with the cloaca (p. 447).

In the Crocodilia the kidneys are of an oblong oval form ; the
forepart is thickest or largest, and is sternad of the psoas muscle,
the hind part extends into the side of the pelvis ; they are in
contact with each other at the mid-line. The surface is convo-
luted, like the brain, but with smaller and more numerous gyra3 ;
the colour of the kidney is usually a deep brown. The ureters
terminate in low papillae, in the urogenital compartment of the

1 xx. vol. iii. p. 221, prep. no. 1820 A.

542 ANATOMY OF VERTEBRATES.

cloaca behind the genital orifices ; the forepart of the cloaca
is slightly dilated, and the rectum opens therein by a valvular
protrusion.

The formation and disposition of the reniportal and renal or
emulgent veins have been previously described.

§ 97. Adrenals of H&matocrya.- -The bodies called ( suprarenal
capsules/ 'renes succenturiatas,' 'capsulae atrabiliariae,' &c., in Man,
may be represented in the lowest Vertebrates, e. g. the Myxinoids,
in the form of a pair of small oval lobulated bodies situated in
advance of the kidneys, and close or adherent to the portal sinus.
In the lamprey a glandular body lies between the aorta and car-
dinal vein, adhering to the coats of the latter ; but it has not the
characteristic structure of the adrenals in higher Vertebrates. In
ordinary Osseous Fishes the adrenals have been recognised as
roundish bodies of a light grey colour ; commonly two, rarely
three or more in number, situated sometimes near the middle,
oftener at the hinder ends of the kidneys, at or near the entry of
the haemal canal ; but in the Eel they are found where the two
kidneys unite. They are commonly symmetrical in position ;
but in the genus Scomber one adrenal is in advance of the other ;
and in Pleuronectidce they lie both on the same side of the body.
Sometimes they lie free, sometimes they are imbedded in the renal
tissue : they usually possess a proper capsule, and present a
minutely granular texture without distinction of cortical and
medullary parts. Their surface is smooth in some Fishes, irregular
in others ; in large and old Pike three adrenals have been seen ;
but in the young (e Jack,' one foot long), the kidney has been
found to be beset with a number of small adrenals.1 The yellow-
ish adrenals of the Sturgeon occur as numerous small glandular
bodies studding the dorsal surface of the kidney. Four or five
similar bodies are sometimes found in the Skate ; but more com-
monly in Plagiostomes, the adrenals are represented by a single
elongated narrow yellowish and lobulate body, situated behind the
kidney, and sometimes extending behind the dilated ureter.2 The
adrenal in Fishes, whether compacted or subdivided, consists of an
aggregate of lobules, with proper capsules, connected by looser
connective tissue : each lobule consists of cells of about TnWth of

i U (J O

an inch in diameter, containing nuclei, fat-globules, and molecular
particles, the latter being mostly aggregated about the nucleus.
Processes from the lobular capsule pass inward and insulate the
multinucleate cells. In the young Pike the molecular-clothed
nuclei acquire a cell-wall, become liberated, and converted into

1 CCLXXXVII. - cxxr.

ADRENALS OF H^MATOCRYA. 543

new mnlthmcleate cells. In old Pike this multiplication is
arrested : the connective tissue increases in quantity and density,
and the multinucleate cells are more separated from each other.
The connective tissue and the capsules which it forms for the
adrenal and its subdivisions, are richly supplied with blood-vessels.

The structure of the adrenals, however, is subject to great
variation within the limits of one and the same species in the
piscine class. The following modifications have been observed in
the Cod-fish l : 1. Very rarely the adrenals are entirely absent.
2. They are semifluid, very vascular, not encased in a capsule,
and without defined form ; the blood-corpuscles are extremely
numerous, aggregated in small lumps, and in various stages of
transmutation. 3. They possess a proper capsule, being more or
less vascular. 4. They are shrunk, with but a few, or without
any blood-vessels. 5. Not rarely a part of an adrenal is composed
of cells and lobules, whilst another part is a formless conglomera-
tion of molecular particles, fat-globules, &c.

Adrenals are entirely absent in the Herring and in the Launce
(Ammodytes Tobianus).

The fish-like Batrachia resemble some Fishes in the subdivided
condition of the adrenals ; twenty or more lobules, showing the
above-described structure, may be found partly imbedded in the
substance of the kidney, at its mesial border, partly between the
kidney and the renal and postcaval veins, surrounding the coats
of the efferent veins (Siren, Tritoii). In the Frog and Toad the
adrenals appear as a yellow streak on the sternal aspect of the
kidney, arching from about one line from the fore end to within
two lines of the hind end of the gland ; it shows a lobular struc-
ture, and surrounds the efferent emulgent veins, closely adhering
to or imbedded in the coats, as they leave the kidney to join or
form the postcaval vein. The lobules consist of groups of multi-
nuclear cells, containing a greater proportion of oil-globules than
in Fishes : but both the free nuclei and granules are present, the
former sometimes showing stages of developement into nucleate
cells. The blood is supplied chiefly by branches of the reniportal

vein.

In the Ophidia the adrenals are long, slender, lobulate bodies,
closely adherent to the coats of the emulgent veins, in advance of
the kidneys : in a Python of ten feet in length they measure
nearly one inch. The adrenals are rather less elongated in Anyuis
fragilis. The adrenals are supplied by minute branches from the

1 cccsxxi. ' Fische,' p. 258.

544 ANATOMY OF VERTEBRATES.

aorta, and more abundantly by vessels sent to them from the
plexus vcnosus of the neural canal ; both kind of vessels ramify
in their substance, forming a fine capillary network upon the
capsules of the niultinucleate cells. The blood is returned from
the right adrenal directly to the postcaval vein, and from the left
adrenal to the corresponding emulgent vein. In Lacerta ocellata,
each adrenal is about one sixth of an inch in length, and one-
eighth of an inch in breadth, adherent to the emulgent vein,
where it forms the postcaval : upon which the right and usually
the larger adrenal sometimes lies. In the male Lizard it is
situated between the vein and the vas deferens : in the female,
between the vein and the ovary. The adrenals are lobulated,
and well supplied with blood ; their minute structure is essentially
the same as that in Ophidia and Batrachia.

Hunter left preparations of two glandular bodies, with a con-
volute exterior surface, and a homogenous parenchyme, similarly
disposed, which he called ( supra-renal glands ' of a Tortoise ; J
and, in his ' Anatomy of a Land-Tortoise,' he writes, ( The
capsula renalis is large and flat, situated above the kidneys : it
looks like a pancreas, being conglomerated, but, when cut into,
appears to be all of the same substance.'2 Bojaiius regarded two
long bodies, situated at the inner margin of the kidneys of Emys
europcea as the adrenals ; but, according to Ecker, the adrenals
of Testudo grceca lie on the abdominal (sternal) surface of the
kidney, imbedded in its substance, extending almost the whole
length of the gland, as in the Frog.3 Under the microscope they
appeared as aggregates of yellow granules, each inclosed by a
proper capsule, and containing nuclei, oil-globules, and molecular
particles.

Hunter describes the adrenals in the Crocodile as ' two oblong

&

bodies, darker on their exterior surface than internally, and in
some places little yellow bodies are to be seen upon them, as in
the kidney ; and on the outer edge is a very small yellow thread
passing down, which is continued along the broad ligament its
whole length towards the anus.' 4 This might be the remnant of
the duct of the primordial kidney.

1 xx. vol. iii. p. 130, preps, nos. 1277, 1278. 2 ccxxxvr. vol. ii. p. 364.

8 CCLXXXVII. 4 ccxxxvi. vol. ii. p. 340.

54o

CHAPTER IX.

TEGUMENTARY SYSTEM OF ELEMATOCRYA.

§ 98. Composition of Tegument. — The tegumentary organs of
Vertebrates, where they do not happen, as in exceptional instances
or parts of the body, to blend with the periosteum of the endo-
skeleton, are defined from subjacent structures by loose or yielding
connective tissue : hence the facility with which Vertebrates of
all classes can be ( skinned.' The part so removed is the f tegu-
ment,' and constitutes the outermost of the organs differentiated
in the course of embryonal developemeut from what has been
termed the ( serous' or ' animal ' layer of the blastoderm.

Tegument mainly consists of an outer epithelial layer, called
( epiderm,' and an inner fibrous or areolar layer, called ' derm.'
The tissue of the derm includes 'white fibres' and ( yellow fibres.'
The white element forms bands of unequal thickness, striated
longitudinally, but irregularly, and breaking up into fibrils of
different width, the finest being too minute for micrometry. The
white bands interlace in various directions, with a wavy course,
frequently subdividing, and joining those near them. The yellow
fibres are solitary, very elastic, disposed to curl, branching at
intervals of variable length, and the branches, usually as large as
the trunk, uniting with contiguous ones. A drop of acetic acid,
which instantly swells the white bands and makes them trans-
parent, produces no change on the yellow filaments.1 Into the
derm enter bloodvessels, absorbents, and nerves : it never contains
fat. Epiderm consists of epithelial cells of every form — caudate,
tessellate, rarely ciliate — and in all stages of developement,
increasing in density, horizontality, and overlappingness as they
approach the outer surface of the skin, and blended with pigment-
cells and pigment-particles in proportion as they are near the derm :
but many other parts are specialised in the tegumentary area of the
blastoderm than those which, from their greater abundance and
constancy, give the character to the two best defined layers.

Bulbs or pulps of hairs and feathers, bony scutes, and fish-scales

1 ccxc. i. p. 491.
VOL. I. N N

546

ANATOMY OF VERTEBKATES.

-sebaceous, sudoriparous, and mucous follicles — may be developed
in or from the derm : the epiderm may be condensed into nails,
claws, hoofs, horns and horny scales. The warm-blooded are dis-
tinguished from the cold-blooded classes by the non-conducting or
heat-retaining nature of the superficial covering of the tegument.

360

Diagrammatic section of skin of flsh.

§ 99. Teguments of Fishes. — The skin in fishes is more tensely
stretched over the body, and often more closely united to the sub-
jacent fascia or flesh, than in other Vertebrates : consequently it
enjoys less mobility. The constituent fibres of the derm or
corium are so disposed as to give it a laminated structure, fig.
360, a ; the horizontal layers being connected by vertical sub-
elastic fibres,1 ib. b. The numerous papillae or processes from the
skin of the under part of the head of the Sole (Solea vulgaris)
give it a villous character : other instances where the derm deve-
lopes tactile papillae in fishes are indicated at pp. 326,411.

In the Lancelet the dermal fibres are minute, and compacted
into two planes, one nearly at right angles to the other. In the
Lamprey the derm consists of two layers of flattened fibres cross-
ing each other at right angles. The epiderm exhibits numerous
large stellate pigment-cells. In the Eel, the epiderm is soft and
thick, consisting of many layers of cells, caudate and tessellate,
those next the derm showing pigment in stellar masses : the

granular pigment-cells look like black
spots in the epiderm. On removing
this, narrow oblong scales, two lines
to three lines long, fig. 361, «, are seen
imbedded in depressions of the derm.
They consist of a finely reticulate car-
tilage, the long axis of the meshes,
which may be cells with confluent
walls, running nearly parallel to the
contour of the scale, as shown in the
magnified section taken at the line marked in fig. 361, a. In the
Blenny (Zoarces) the skin presents circular depressions which are

1 ' Arctuons bands ' of Clark (ccxcn, p. 148), who well distinguishes them from
the gland-ducts perforating the skin in certain fishes, e. g., murcena.

361

Scale of Ed : a, nnt. size, and portion
niagn. ccxcm.

TEGUMENTS OF FISHES.

547

362

Cycloid scale, xxn.

due to the presence of small round scales, about -^-j th in. diameter,
with concentric and radiating lines: they are set deep in the
derm. In the Sand-eel (Ammodytes), the
scales are proportionally larger, and one
margin rises from the derm and pushes out-
ward the portion of epiderm covering it : the
dermal depression is limited to the opposite
margin, and is deeper than in the Eel. The
free part of the scale retains the reticular
structure ; in the imbedded part the areolrc
are obliterated in the direction from the centre
to the circumference ; the radiating lines preserve their distance,
but, being united by cross fibres close set, the structure appears
to be laminated. The majority of flexible scales present the
same pattern of concentric and radiating lines : the concentric
lines are the finest, most numerous, and constant ; they repeat
the contour of the scale, and with most regularity at the anterior
imbedded and covered part, where growth chiefly takes place,
the stages of which are marked by these lines. The ( nucleus ' or
beginning of the scale is usually excentric, fig. 362, n. The ra-
diating lines, fig. 362 and 363, r, r, are larger and fewer : they
are most numerous in the Loach ( Cobitis), are sometimes confined
to the forepart of the scale, fig. 363, or may be absent {Salmo)i
they are furrows. The parts of the scale-margin between the
ends of the radiating lines usually project in different degrees
from a slight convexity, as in figs. 362, 363, to the form of pro-
cesses. The latter are most common at the anterior implanted
border of the scale (Esox) : in many fishes the opposite or free
border has numerous tooth-like processes, and
similar parts may project from the adjacent
periphery of the scale in two or more rows.
Such scales with a comb-like free border, fig.
363, t, characterise the fishes thence called
6 ctenoid : ' where the free border of the scale
is rounded or simply undulated, fig. 362, it
characterises the ( cycloid ' fishes of Agassiz. *
The seat of chief vascularity and greatest
activity and variety of developement is at the
periphery of the derm, between it and the
epiderm. Here are formed the scales, constituting an imbri-
cate covering of the body in most fishes ; but, in a few, contiguous
or scattered. According to their structure and shape, scales are

1 XXII.

N N -2

363

Ctenoid scale,

548

ANATOMY OF VERTEBRATES.

364

Ganoid scales, Amblypterus.

365

termed ( placoid,' fig. 365, < ganoid,' fig. 364, < cycloid,' fig. 362,
' ctenoid,' fig. 363. In the first and second kinds bone-earth predo-
minates, and the scales are as hard as teeth ; in the two latter kinds

the earth is in less quantity, so that
the scale is flexible : it is rarely want-
ing. The kinds of scale graduate
into each other. Most flexible scales
present two structures: one next the
derm is composed of gristly lamina?,
usually firm and elastic, fig. 360, c ;
the superficial portion, ib. d, is
laminated and hardened by interla-
mellar calcareous granules.1 In the posterior or exposed part
of the scale of a Carp there is a peripheral osseous layer, deve-
loping the outer markings or projections of the scale, fig. 360, d\ a

middle laminated layer, with
calcareous granules, ib. e ;
and the internal layer of
lamina? of structureless car-
tilage, ib. c.

In the Tunny ( Thynnus
vulgaris) the scales are com-
posed of fine, partially ossi-
fied, lamina?, between which
are elongated ( lacuna? ' or
bone-cells: the scale is cancel-
lous at its middle part.2 In Le-
pidosteus the scale is thicker,
is composed of very thin ossi-
fied layers, fig. 366,«, perfo-
rated by vertical tubes about
gljjjjjth in. diameter, and having
numerous lacuna? in their
interspaces,3 the radiating
canals of which communicate
with a more minute series of vertical branched tubules, called ( Le-
pidine ' by their describer.4 These, in most ganoid fishes, have a
less general distribution through the scale than the larger and less

o ~

branched series, which, from their analogy to dentinal tubes, I have
called ( plasmatic,' conceiving them to relate to the nutrition and
vitality of the scale, as doubtless also do the l lepidine ' tubules in

Placoid scale A, B, nat. size ; 0, magn. section,

1 ' Corpuscles of Mandl,' cccm. : 'Lenticular bodies' of Williamson, ccxcn.
2 ooxciii. vol. ii. p. 70. 3 v. p. 14. 4 ccxci. p. 439.

TEGUMENTS OF FISHES. 549

the parts of the scale to which they are limited. The peripheral
surface of the scale is coated by a layer of hard transparent lami-
nated substance, ib. bl (' email/ Ag. ; 'ganoin,' ' Wilk.'2). In Lepi-
dosteus and Potypterus the ganoin is usually confined to two-thirds
of the outer surface of the scale. In both existing Ganoids the
scale is perforated vertically by a few larger
tubes, analogous to the ' vascular canals ' of ___ s66
bone, and conveying blood from the derm to
the delicate layer of membrane extending from
the scale-pit, fig. 360, f, upon the ganoin.
In the scales of extinct Ganoidei a portion
of the deeper layer of ganoin traversed by
minute branching tubuli, and devoid of
lacuna), has received the name of e kosmin.'3 structure of ganoid scales.

CQXG.IU

This tissue constitutes the chief part of the

tooth-shaped bodies of the ' shagreen ' of the Dog-fish and many
other Placoids ; in which it cannot be histologically distin-
guished from hard dentine.4 In fig. 365 are given a side view, A,
and upper view, B, of one of the ( placoid scales,' or spiny tubercles
of the Thornback (Raia clavata) : C is a magnified section of the
scale. The substance of the spine consists of superimposed conical
lamellae, having, in the -Thornback, a widely open pulp-cavity,
ib. p, from which proceed vascular canals, resolving into plasmatic
tubes, radiating and ramifying through the substance as in ordi-
nary teeth. The base of the spine-bearing scale, ib. Z>, is imbedded
in the derm ; and, as the ' haversian canals ' of the jaw pass into
the ( medullary canals ' of the teeth thereto anchylosed, so do the
capillaries of the derm pass directly into the ( vascular ' canals
and pulp-cavity of the dermal dentine in all the various forms of
placoid scales, many of which have a coating of true e ganoin '
over the fine-tubed dentine or ' kosmin.' Other modifications of
the dermoskeleton, such as the placoganoid and acaiithoganoid,
are noticed at pp. 193-198, and illustrated in figs. 124-127.

The calcification of scales, as of teeth, fig. 242, and bone, fig.
15, takes place in layers of the organic basis successively formed:
but the primitive lamellate condition is most conspicuous in fish-
scales. The idea of excretion, or the throwing out of such layers
from a secreting surface, is, however, as inadequate to represent
the facts of the formation and structure of the exoskeleton as of
the endoskeleton of fishes.5

1 XXTI. vol. i. p. 74. - ccxci. p. 438. 3 Ib. p. 444. 4 v. p. 14.

5 The microscopical observations on the structures of recent and fossil teeth, with
incidental notices of corresponding organisation in ossified scales, communicated by

550 ANATOMY OF VERTEBRATES.

The varied and often brilliant colours of fishes are due to
pigment-cells at different depths of the skin, but chiefly in the
active or differentiating area : those of silvery and golden lustre
are mostly on the surface of the scales : the silvery pigment, called
s argentine,' is an article of commerce, used for the colouring of
factitious pearls, and offers a crystalline character under the
microscope. The blue, red, green, or other bright-coloured pig-
ment is usually associated with fine oil, and occupies areolie
favouring accumulation at, or retreat from, the superficies, and
thus effecting changes in the colours of the fish, harmonising
their exterior with the hue of the bottom of their haunt.1

The surface of the body is lubricated in most Fishes by
mucus, sometimes, as in the Eel and Burbot, forming a thick
layer. The skin of the Eel is perforated by numerous ducts
or follicles, which contribute to this excretion.2 In the Pike the
scattered ducts notch the border of the scales, near their termina-
tion : one series of follicles represents the lateral line, as in the
Eel. In most Fishes the follicles of the lateral row are connected
by a longitudinal canal, of which they appear to be branches ; more
particularly so in those species (Dory, Opah) in which the follicles
are produced into secondary tubes, and open at some distance
from, usually beneath, the lateral canal. In the Mugil cephalus
there are several lateral canals, giving off the follicles which
tunnel the scales in their outward course. The lateral canal
itself so marks the scales along which it runs, its follicular outlets
perforating them. The ' nervus lateralis ' sends a filament to
each scale-follicle or tunnel ; 3 the cephalic system of well-nerved
mucous canals excavates oddly superficial bones of the head in
many Teleostomi:* this system is noticed \n. Plagiostomi, at p. 225.
The nervous structure connected with the system of the lateral
line suo-ffests a stimulus to active excretion from emotional causes,

o~ *

as in the skin-glands of Batrachia.

§ 100. Teguments of Reptiles. — The derm in Batrachia presents

me to the meeting of the British Association in August 1838, and to the Academy of
Sciences, Institute of France, December 1839, established the 'conversion-theory,' and
compel any one attempting to revive the ' excretion theory ' to substitute a definition of
the process wholly different from that to which De Blainville and other supporters of the
theory held in 1838-9. Prof. Williamson, who has pursued microscopical investigations
into the scales of recent and fossil fishes with perseverance and success, affirms the facts
which he brought forward (ccxci. p. 437) 'to be, at least, sufficiently conclusive to
settle the question, by showing that, whilst the scales are formed, as originally stated
by M. Agassiz, by the apposition of successive layers, these layers are not generated
by any process of secretion, but by the calcification of an organised basis, resembling
that of bones and teeth, as asserted by Prof. Owen.'

1 ccxciv. p. 327. 2 ccxcu. 3 Lcydig (CCLXXVII. p. 203, fig. 108) describes
it as ending in a kind of ganglion. 4 ccciv. p. 171.

TEGUMENTS OF REPTILES.

551

367

a lamellate structure, fig. 368, g, like that of Fishes, but with the
direction of the fibres, in succeeding layers, more regularly alter-
nating. In most parts of the trunk of the Anoura the skin is
separated by wide lymphatic lacunae, fig. 367, F, from the subcuta-
neous fascia, ib. E. Marsupial pouches, one for each larvaa ib. B, c,
are temporarilydeveloped in
the skin of the back of the fe-
male Pipa : a common dorsal
pouch for eggs and larvae is
present in the female Noto-
trema jnarsupiatuw^ Gnth.,
and in Qpisthodelphys, The
epiderm in Perennibranchi-
ates resembles that of mu-
raenoid Fishes : in most A-
noura the constituent nucle-
ate cells are more condensed,
fig. 368, b : in many Toads
the epiderm is tuberculate ;
rarely are scales, and scutes
never, present in the exist-
ing Batrachia. In CcBcilia

o

the skin is ringed by trans-

verse rus;a3. In the Amen-

o

Female Pipa, or Surinam Toad.

can Newts, of the genus
Plestiodon, the small scales
present a reticulate struc-
ture. In Bufo tuberosus the epiderm forms on the dorsal tuber-
cles a horny spine in the centre, surrounded by a ring of
smaller spines: Bufo asper has conical spine-bearing tubercles
on the back and sides of the trunk : those on the upper eye-
lids of certain Toads have earned for them the generic name
Ceratophrys (Rana cornuta, Linn.). In Salamandra unguiculata,
and in Dactijlethra among the Toads, the epiderm is condensed
into a claw at the end of some of the digits : in D. fifulleri it
also forms a spur at the base of the first hind-toe. In Pipa the
skin is produced at the end of each fore-toe into a 3- or 4-forked
appendage, fig. 367. As a rule, the Batrachia are without claws.
Pigment-cells, fig. 368, «, are developed in various degrees, and
of diverse shades of colour, commonly of a dull and neutral or
mixed tint, but giving to parts of the skin of the land Salamander
a yellow or orange hue, and painting the surface of the Tree-
Frog (Hi/la) a bright polished green.

552

ANATOMY OF VERTEBRATES.

368

Mucous follicles abound in the skin of all the Batrachia : they
are found in linear rows in parts of the Siren : ! are more generally
diffused in the Axolotl.2 In the Frog they are spheroidal,3 fig.
368, d, or subdepresscd,4 situated in the superficies of the derm, c\
their ducts perforate the epiderm, b, and terminate by rounded5
or triradiate6 orifices, ib. B. Like the lateral canals of Fishes,
they usually contain a clear fluid, which they expel on irritation
of their nerve, ib. /.7 This fluid, in the Newts and Toads,

appears to possess an acid or
irritating property. A stork will
swallow a frog, but rejects a toad,
if picked up by mistake. The
cutaneous follicles are more local-
ised in the land Salamander,
and their secretion is whitish and
opake, of an acrid nature, and
poured out abundantly when the
animal is alarmed or irritated.
The cutaneous follicles are nu-
merous and close-set in the
American Newts of the genera
Ambystoma and Plethodon, in
which they exude a milky fluid.8
Special aggregates of cutane-
ous follicles occur in most
Batrachia. In the land Sala-
mander they form a porous
tubercle behind each eye. In
many Anoura the homologous
glandular tubercles (f parotoids '
of Giinther9) are conspicuous
above the tympanum (Alytidce, Bufonidci) : they are enormous in
Bufo agua, and are situated on each side of the neck in Uperoliidce.
In Bufo calamita, besides the ordinary parotoids, there is a similar
glandular tubercle on the upper side of the legs. The skin of
the back in Kalophrynus is thick and glandular, like a parotoid.
In Hylarana the skin has two glandular folds, one on each side of
the back, usually of a white colour. Platymantis plicifera has
several pairs of such longitudinal folds or ridges.10 In Polypedates

1 xx. vol. iii. p. 277, prop. no. 2108. 2 CCLXXIX. tav. ii. fig. 7. 3 ccxcv. taf.
ii. fig. 10. 4 Ib. fig. 7. 5 Ib. fig. 2. 6 Ib. fig. 3. 7 Ib. (6841), p. clvi.

8 ccxcvr. p. 281. ° Printed by mistake ' paratoid ' in his excellent Catalogue.

10 CLXXV. p. 96, pi. viii. fig. B.

Section of tegument and cutaneous glands of
the Frog, magnified, coxcv.

TEGUMENTS OF REPTILES , 553

a glandular fold curves from above the tympanum to the axilla or
shoulder.

The skin takes an important share in respiration in the
Anourous Batrachia,1 and there is a relation of ( supply and
demand ' between the cutaneous follicles and the large allantoic
bladder : the latter would seem to receive water directly by the
cloaca, when the Frog may be in that element, and to serve as a
reservoir for the supply of cutaneous transpiration when the
batrachian is on dry land.2

The epiderm is periodically shed in Batrachia. It comes away
in shreds in the aquatic kinds. In the Toad the old epiderm
splits along the middle line of both back and belly, and each
lateral half is wriggled off in folds towards the sides. It is then,
by contortions of the trunk and limbs, loosened from the hind-
limbs, and removed from them by the animal bringing first one and
then the other leg forward under the arm, when, by withdrawing
the hind-leg, its cuticle is left under the fore-leg. The two
portions are now pushed forward to the mouth, by the help of
which the anterior extremities are also divested of their cuticle.
The whole mass is finally pushed by the hands into the mouth,
and swallowed at a single gulp. The new cuticle is bright, soft,
and covered with a colourless mucus.3

In Serpents the epiderm is shed, usually entire, and the animal,
partially blindfolded by the opacity of the layer passing over the
cornea, fig. 220, c, seeks an obscure retreat ; but I have watched
the process of exuviation in a captive snake. It rubs the front
and sides of the mouth against its prison wall, thus detaching and
reflecting the cuticle from the oral margin, until it is turned back
from over the whole head : the snake then brings forward its tail

o

and coils it transversely round the head, and by pushing the head
through the coil turns the cuticle back upon the neck ; then
tightening the coil and renewing the forward movement, threading
the body, as it were, through the caudal ring, the cuticle is
pushed further and further back until the eversion has been
carried so near the end of the tail as prevents the further action
of the coil; the animal finally glides along dragging behind the
whole of the loosened epiderm, and a few wriggling actions of the
tail serve to completely detach it. Thus, the entire outer skin of
the snake may be found shed and turned inside out, the process of
exuviation being like the turning off a stocking from the leg and
foot. The whole of the exuviable epiderm in Ophidia has been
condensed into the form of scales : these are small and pretty
1 ccxcvn. 2 Ib. 3 ccxcvm. vol i. p. 102,

554 ANATOMY OF VERTEBRATES.

regular in size and shape along the back and sides of the body ;
but are large and transversely extended across the under part,
forming what are termed the c ventral scutes,' l scuta ventralia,'
the use of which in locomotion is explained at p. 259. All or
most of the scutes below the tail (' scuta sub-caudalia ') are single
in Crotalus, Bungarus, Boa ; in Python., the Colultridce, and most
other serpents they are f paired,' or divided along the middle line.
In most sea-snakes the abdomen is compressed and keeled below ;
in Pclamys the keel is bordered by two rows of scales ; in Hydro-
pliys it is formed by large bituberculate scales ; Platurus has the
venter scutate, with the caudal scales in pairs. Larger scales
occur in the head of most serpents, and serve as zoological cha-
racters, being denned as ( scuta marginalia labii superioris sen in-
ferioris,' 'scutum labiale medium,' ' scuta mentalia,' ( scuta ocularia,'
6 scuta frenalia,' ( scuta nasalia,' &c. The scales of serpents may
be smooth or carinate, they are rarely tuberculate (dorsal scales of
Xenodermus) ; and in their disposition they may be either ' con-
tiguous.' or ( imbricate.'

d J

The epiderm is condensed into claws or hooks (( calcaria ') upon
the rudiments of hind limbs that border the vent : these are best
seen in Boa, Python, Eryx, Tortrix ; it is developed into small
horns above the eyes in Vipera cerastes. In the Rattlesnake the
epiderm forms a series of hard moveable rings at the end of the
tail, twenty to thirty in number in full-grown specimens,
decreasing in size to the end of the series. The terminal (3 to 8)
caudal vertebrse coalesce into a long conical bone, covered by
thick, soft, vascular derm, divided by two deep annular grooves
into three transverse swellings : the basal ring of one joint grasps
the projecting second ring of the preceding joint, and this
incloses the third ring of the joint next but one in advance.
Since the second rounded annular portion of each joint is thus
securely grasped by the first rounded annular portion of the piece
behind it, and the third by the second, and yet all of them so
loosely as to leave room for motion, it has been supposed that
when the foremost piece has been completed, and a new piece in
advance is about to be formed, the skin which is to secrete it is so
modified that its first swelling, which secreted the first projection
of the former piece, assumes that shape and size which are
accommodated to the shape and size of the second projection of
the new piece, whilst the second swelling which secreted the
second projection of the piece takes the dimensions suited to
the third projection of the future new ring. The basal projections
of the successive rings are chiefly visible externally, only the first

TEGUMENTS OF REPTILES. 555

rino; has a vital connection with the derm : it is caused to vibrate

o

by the muscles of the tail, and its vibration communicates a
quivering motion, accompanied by a rattling noise, to the dry
horny pieces behind it.1

The pigment-cells are mostly combined with the epidermal
ones to form the deeper layers of the scales, and ornament the
skin of snakes with various and sometimes brilliant colours. The
poisonous serpents are mostly of a sombre hue. The periphery of
the derm is modelled according to the pattern, contiguous or im-
bricate, of the epiderm, the scales of which are evolved thereupon.
The blood-vessels form a beautiful and regular network, the area
corresponding with the shape of the scales, being lozenge-shaped,
e. g- in Coluber natrix? with the uniting angle at the centre of

C? ' DO

each scale.

The skin of the snout developes tentacular appendages in Her-
peton tentaculatum. The integument in the Cobras (Naja)
expands into a broad fold on each side the neck : the folds are
supported by correspondingly elongated ribs, p. 55, fig. 46, pi. ;
when these are drawn forward an oval disc of skin is caused, sur-
passing the head in breadth, and usually rendered more conspicuous
by well-defined tracts of pigment. The name of ( spectacle-
snake ' refers to the pair of circular spots connected by a curved
streak on the hood of the Naia tripudians.

The secreting follicles of the skin in Serpents are chiefly con-
fined to certain depressions or inverted folds of the derm. These
in Crotalus and Trigonoceplialus constitute a pit between the
nostril and eye on each side of the head. The hinder scutes of
the lower lip have pits in Python Schleyelii ; as have those of both
lips in Python amethystinus. In Amj)hisb(Ena alba and in Chirotes
there is a row of pores in front of the vent.

The skin in most Lacertians resembles that of Serpents : the
scales are thickened epiderm or horn ; in most imbricate, in a
few (Zonosaurus, V. der H.) verticillate ; usually smooth, but
in some carinate, and in some tuberculate or gibbous : in a few
they support a spine at certain parts of the body, as, e. g. the
caudal scales of Zonurus, both dorsal and caudal scales of Tr '-
bolonotus, the circumtynipanic scales of Agama, the occipital
scales of Phrynosoma, and scattered dorsal and lateral scales in
the Australian Lacerta muricata of White. Bone is developed
at the base of the scale forming part thereof, or combining scute
and scale, in Ophisaurus, Tribolonotus, Trachysaurus. In the
Chameleons the scales are small and thin, like grains. The

* o

1 ccxcix. p. 294, pi. xii. 2 xx. vol. Hi. p. 241.

556 ANATOMY OF VERTEBRATES.

pigmental system of the skin is remarkably developed in this
family : it is of various colours — red, blue, yellow, brown ; each
colour is lodged in contractile areolar spaces, and can be accu-
mulated near or withdrawn from the surface. When the Chame-
leon is kept long in a cold dark place all the pigment subsides
into the derm, the superficial pale grey colour of which appears
through the thin epiderm. When brought into the light and
warmth the pigments flow to the surface, in harmony with the
colour of that on which the animal rests, which usually in this
arboreal reptile is green. If, however, the Chameleon be irri-
tated, the colour may change to a vinous red, or deepen almost to
black : commonly the surface is more or less mottled, grey, yellow
and green. These phenomena, which have made a proverb of
the Chameleon, are manifested in a minor degree by some other
Reptiles, by most Fishes, and by Cephalopoda.

The integument, besides covering the surface of the body,
extends, in many Lacertians, from various parts, in different
forms and degrees. In Basiliscus and Histiurus calotes it forms a

o

compressed fold or crest along the midline of the back and tail.
In Crocodilurus the tail has a double crest above : in Phyllurus
platurus the lateral expansions of the skin of the short tail give it
a leaf-shape. In Hoplurus and Tropidurus cyclura the skin of the
throat is folded transversely : in Agama the transverse fold is asso-
ciated with a longitudinal fold beneath the under jaw. The jugular
fold is longitudinal and pendulous, like a dewlap, in Iguana,
Corythophanes, and Semioplwrus. In Cldamydosaurus a very
broad transverse fold of skin extends from above each tympanum
across the lower part of the neck : it is partly supported and
moved by much elongated cerato- and thyro-hyals, and can be
expanded and brought forward or erected, so as to give a formid-
able aspect to this Lizard, when it is attacked or alarmed.

In the small insectivorous Draco volans of Limiasus a broad
fold of skin, on each side of the body, fig. 163, is supported by
five pairs of slender elongated free ribs, fig. 50, by the movement
of which the folds can be expanded into a sort of parachute, as
explained at p. 265. The special modification of the tegument
of the toes in the Geckos is described at p. 263, fig. 162. In
the extinct Pterodactyles still more extensive duplicatures of skin
were supported on a much elongated digit, and constituted true
wings, as in the Bats, p. 265, fig. Ill, A. In many Lizards, on
the inside of the thigh, there is a row of tuberculate perforated
scales, beneath each of which lies a pedunculate gland, studded
with marginal follicles : the presence and position of these ( pori

TEGUMENTS OF REPTILES. 557

femorales ' afford generic characters. They are wanting in the
Chameleons. Certain male Geckos have both femoral and sub-
anal pores. In Pygopus lepidopodus the snbanal pores are dis-
posed in a single series, but in Lialis in pairs, on each side.

In the Crocodilia the conversion of parts of the integument into
bone is constant, and the osseous structure shows interlaced or
crossing fibres, like that of the derm in and from which the
scutes are developed. The arrangements and forms of these
scutes in different genera of recent and fossil Crocodilia are
described at pp. 198, 199. As in Fishes, the dermoskeleton was
most developed in the extinct secondary species. In modern
Crocodiles a serrated crest extends above the tail, which divides
at the base of that organ.

A section of the dorsal integument of Trionyx ferox shows a
thin epiderm, then a thicker layer of elastic fibres, next many
layers of fibres crossing each other regularly, and producing
seeming layers of the derm. In Sphargis a superficial portion of
the derm is ossified, so as to form a kind of girdle to the trunk,
beneath which is a felt of soft corinm, and under this the endo-
skeleton. In all other CJielonia the derm adheres to the periosteum
of certain neural spines and pairs of pleur- and haem-apophyses,
whence ossification extends in different degrees into the substance
of the derm. In most Clielonia a series of bones are developed
independently in the derm, at the circumference of the trunk,
and also above certain neural spines, with winch they may or
may not become anchylosed.1

The dermal bones connate with neural spines are those above
the nine dorsal vertebra), figs. 370, 371, ch, s\-ss : they are
termed ( neural plates.' The dermal bones connate with pleura-
pophyses are those which take ossification from near the heads of
the second to the ninth, inclusive of the dorsal ribs, ib. ph-j)Is.
The dermal bones connate with hremapophyses are those which
start from the sternal or abdominal ribs, or coalesced groups of
ribs, figs. 372, 373, called hyosternal, hs, hyposternal, ps, and
xiphisternal, xs. Occasionally, ossification extends into the skin
from the entosternal, s (Emyda ceylonensis), and from the epi-
sternals, es {Cryptopus Petersii). The dermal bones are least
developed in the Trionycidce, and are not covered by horny epi-
derm. f Neural ' and ( costal ' plates are present in all. One
pair of dermal bones is developed from the hyosternals in Trionyx
subplanus ; in Trionyx niloticus and some other species dermal
bones are developed from the hyo-, hypo- and xiphi-sternals, the

1 CLXII. p. 165.

558

ANATOMY OF VERTEBRATES.

hyo- and hypo-sternal plates on each side being naturally united
together ; in Erniida cei/lonensis dermal bones are developed from

O *^ *^ -.

the epi-, hypo- and xiphi-sternals, and from the entosternal or
sternum proper, forming seven pieces : the skin of the hinder
margin of the broad depressed trunk is strengthened in Emyda

369

f77/2

Inuer surface, Carapace, youug Tortoise.

Outer surface, Carapace, young Tortoise.

by a few dermal ossicles ; much of the skin of the trunk, where
not ossified, in TrionycidcB, has the dermal tissue of cartilaginous
hardness.

In the Turtles, or marine Chelonia, besides the eight connate
neural plates, fig. 52, 51-58 (p. 61), dermal bones are developed
•in advance of and behind them, and are commonly unattached
to the subjacent vertebrae. The anterior one, ib. ch, is the
6 nuchal ' plate : the posterior one, ib. py, is the ( pygal ' plate ;
the costal plates, ph-ph, articulate suturally with the neural
plates, but do not extend to the end of the ribs ; the marginal
plates, mi-m\2, are articulated with each other and with the
nuchal and pygal plates suturally, and eight on each side receive
the ends of the eight ribs supporting the costal plates. Two

TEGUMENTS OF REPTILES.

559

pairs of dermal bones are developed from the hyo- and hypo-
sternals, fig. 53, hs and ps: but these do not articulate with the
marginal series. In Freshwater and Land Tortoises the dermal

o

ossifications spread further, uniting all the parts of the plastron

371

372

Outer surface, plastron, young Tortoise.

Inner surface, plastron, young Tortoise.

into one more or less flat floor, and all the parts of the carapace
into one more or less convex roof, fig. 51 ; side-walls being like-
wise now formed by the union of the hyo- and hypo-sternals
with the coextensive marginal plates. In all Chelonia, save the
Trionycidte and Sphargis9 the epiderm of the trunk is condensed
into large horny scales, usually contiguous, more rarely imbricate,
and then only on the carapace. They may be keeled, or rugous,
or scabrous, but are commonly smooth and polished, or marked
only by concentric lines of growth. Their growing margins
indent the dermal bones supporting them, forming the triradiate
grooves, e. g. upon the beginnings of the costal plates in the
young Tortoise, fig. 370, 7^/1, and those marked 51-55 on the
neural and costal plates in the Turtle, fig. 52. The large epi-
dermal plates of the carapace and plastron are termed ( shields '
and ' tortoise-shell : ' most of them have special names in Zoology,
as they afford useful characters in the discrimination of genera
and species ; whilst the impressions they leave upon the subjacent
bones give similar light in the interpretation of fossil remains,

500 ANATOMY OF VERTEBRATES.

after the horny shields themselves have perished. The cpiderm
is disposed upon the head in various forms : in most freshwater
Chelonia it is a continuous thin hard layer on the top and sides of
the head : in marine and terrestrial Chelonia it is usually in the
form of large plates, leaving marginal impressions on the skull,
and distinguished by special names : they are more symmetrical in
Chelone than in Testudo. The skin of the neck and of the limbs
is covered by small contiguous scales : some of these are of
larger size on parts of the feet. The epiderm is thickened and
condensed into a beak in all Chelonia,, and into claws in most.
In Sphargis, however, the claws are replaced by small coriaceous
scales : in Chelone only one digit on each foot supports a claw :
in Caretta two digits, and in Trionycidce three digits, support
claws : in some Tortoises ( Testudo) there are four claws 011
each foot : in most Tortoises and Terrapins (Emys) there is an
additional claw on the fore-foot: in the heavy Land Tortoises
the claws assume the form of hoofs. The epiderm of the tail is
usually wrinkled, and covered only by small scales : in the
Snapper (Chelydra) it supports a row of hard compressed
tubercles ; in some Tortoises the end of the tail has a thick
epidermal sheath, which, in the male Cinosternon, is armed with a
pointed tip.

The large imbricate plates of the carapace of Chelone have their
fore border imbedded in a matrix of the derm, and here receive
their chief increase, the older parts moving backward, and being
worn off. The plates with contiguous borders receive increase
at their under surface and entire circumference ; the concentric
lines of growth may be marks of annual increment : * but these
usually show a greater ratio of growth at the front and sides than
at the back The old and dull superficial layer is worn away, or
thrown off from time to time, leaving the rest of the epidermal
shield of a bright colour : the smooth or scaly epiderm of the
limbs and neck is usually shed entire.

The skin of the neck developes fimbriate processes and
caruncles in Chelys fimbriata : that of the nose is produced into a
short snout in most TrionycidcB.

The deeper stratum of soft, usually imbricate, epithelial cells
of the epiderm are intermixed with pigmental cells, mostly dark
brown or black ; abundant pigment-particles are also suspended
in an oily fluid, occupying areolar spaces of the deep epiderm,
and usually of the brighter yellow, red, or green colours. Such

1 As conjectured by Agussiz, ccc. vol. i. pt. ii. p. 259.

TEGUMENTS OF KEPTILES. 561

pigmental cells are blended with the tissue of the shields and
scales, and may ornament the former with well-marked patterns,
e.g. in Testudo areolata, Emys ornata, Emys picta, &c.

Cutaneous glands or follicles open between the warts of the
skin in Chelydra, and probably occasion their musky odour : but
this, in other Chelonia, appears to be due to larger, more com-
pact, and more localised glands. Beneath the epiderm of the
skin of the under part of the body, in the Soft-Turtles, is an
extensive network of vessels, spreading into dendritic ramifica-
tions, too numerous and large for the mere nutritive purposes of
the skin or supply of epithelial cells, and therefore probably1
subservient to respiration.

Viewing the integuments in their relations to the external
influences from which they defend the body, and by which they
are themselves affected, we may remark that most of the house-
bearing Reptiles which have the surface of their abode habitually
in contact with air or water have the epiderm hard and thick,
whilst those living in ooze or mud have it soft and thin. In the
sea the horny scutes may be partially loosened, and grow over
one another : in the air they condense upon the surface with the
margins in contact : in the mud the skin is lubricous : the only
known scaleless species of marine habits {Sphargis coriacea) has
the tegument tough and leathery. In the most vagrant and widely
diffused Turtle (Chelone imlricata) the separation of the scales
takes place at a part of their circumference, which makes the
direction of imbrication the most favourable to their aquatic
movements. Growing and projecting from before backward, the
one in front overlapping the next behind, the polished shields
offer no resistance to the forward movement impressed upon the
body by the oar-shaped limbs ; whilst the scutal interspaces,
widening as the trunk tends to recede during the preparation for
the next stroke, oppose the backward slipping, and take hold, so
to speak, upon the wave, retaining the advantage of one stroke
until the next is played.

1 As conjectured by Agassiz, ccc. vol. i. pt. ii. p, 284.

VOL. I. 00

562

ANATOMY OF VERTEBRATES.

CHAPTER X.

PECULIAR AND DUCTLESS GLANDS.

§101. Scent-glands of Reptiles.- The Chelonia, like most
Reptiles, have scent-glands, with periodical access of activity,
enabling and exciting, as it seems, the sexes to find each other at
the pairing season. In Tortoises the gland, fig. 373, a, is situated
beneath the skin of the mentum ; its duct, Z», in a Testudo indica
of two feet long, opens about an inch and a half behind the
symphysis of the mandible, and about half an inch from the

373

Section of mandible showing the scent-gland. Testudo indica.

mesial line. In the Turtle the glands excrete at the base of the
neck ; in the Kinosternoii a gland is situated near the fore and
hind margins of the side-walls, uniting the carapace and plastron :
the duct perforates the bone, and opens by a fine slit in the wall.
In the Crocodilia a small sinus is formed by an inward fold of
integument near the inner side of the maiidibular ramus, into
which sinus opens the dilated duct of a gland, which is surrounded
by a muscle, detached from the back part of the pharynx, and
proceeding along the outer side of the ceratohyal to expand upon
the gland and reservoir.1 Cuvier2 describes its contents as being
unctuous, of a dark grey colour, with a strong musky odour.

1 xx. vol. iii. p. 272; prep. no. 2106.

xii. torn. v. p. 252 (1805).

POISON-GLANDS OF REPTILES. 563

The Crocodiles have glandular follicles, which open at the
anus. Hunter preserved ( a section of the skin of a Turtle
(Chelone), to show a gland situated near its anus.'1 There is a
glandular fossa which opens into the dorsal part of the cloaca.,
close to the termination of the rectum in most Emydians.

The anal bags in Serpents are two in number, of an elongate
form, fig. 357, in: they are lodged in the base of the tail, and
open into the back part of the cloaca : their excretion has a
strong, disagreeable, nauseating odour.

§ 102. Poison-glands of Reptiles.- -The gland which secretes
the poison in ordinary venomous Serpents is situated on each side
the head, anterior to the tympanic pedicle, inclosed in a strong
capsule, fig. 145, a (p. 227), and partly
covered by the muscle analogous to
the masseter, ib. e, some of the fibres
of which, fig. 374, «, are attached to
the capsule, ib. b. On reflecting these,
as in fig. 374, the gland, ib. c, is seen
composed of a series of elongated
narrow lobes, extending from the main
duct at the lower border of the gland

Upward and backward. Each lobe Poison apparatus of the Viper (Vipera

fY> • fiti i • i Berus). cxvi.

gives on a series ol lobules, which are

again subdivided into smaller creca. Their secretion is collected
into the dilated beginning of the duct which conveys it to the base
of the poison-fang, f\ the bristle e passes from the duct into the
poison-canal of the fang, the structure of which is described, pp.
396-398 : the gum-capsule, d, of the reserve-fangs, g, is laid open.
In Hydrophis the poison-gland is of smaller size, narrow, elongate,
broadest behind, and extended upon the maxillary and ecto-
pterygoid bones, in advance of the masseter : its capsule is
attached to the tendinous tract (p. 228) detached from the
digastricus and ectopterygoid : its duct enters the foremost of the
series of four to six small fangs attached to the maxillary. The
bite of these inferiorly endowed venomous Sea-Snakes has proved
fatal : they are said to occasionally climb along the hawser into
ships at anchor ; and as they may be drawn in, adhering to it by
their prehensile tail, or be caught in the fishing-net and hauled
on board, it is well that their dangerous property should be
known.

The secretion of the poison-gland is a tasteless fluid, drying
under exposure to air into small scales : it is soluble in water,

1 xx. vol. iii. p. 279, prep. no. 2130.
oo2

564

ANATOMY OF VERTEBRATES.

375

insoluble in alcohol, and slightly reddens litmus paper: it long
retains its noxious property. Against this the mucous surface of
the alimentary tract is proof: the poison, to take effect, must
enter the current of the blood. Here it is ordinarily introduced
by the puncture of the poison-fang, but it takes effect by applica-
tion to an abraded surface. The poison affects the nervous
system ; death is usually preceded by spasmodic convulsions, and
followed by speedy putrefaction.

§ 103. The Thyroid Body or Gland of H&matocrya.- - In the
Skate (Raia) the body which seems to have best claim to be

regarded as a thyroid is situated sternad
of the terminal division of the branchial
artery, of a reddish-grey colour and con-
glomerate exterior. It consists of nume-
rous, mostly subspherical, vesicles, of from
•g^- to Tj-T inch diameter, fig. 375, having
a structureless tunic, A, lined by a thick
stratum of epithelial substance, consist-
ing of nuclei and granular matter, B. Dr.
Handfield Jones, who has given the above
result of microscopical investigation of this
ductless gland, also found, in the Skate,
' at some distance behind it, just at the
junction of the branchial arches anteriorly,
a small light reddish mass, which was
covered by a thin fascia, and by mucous membrane.'1 It consisted
' of vesicles about ^-j-g to y^- inch diameter,' fig. 376, ' formed

by a structureless " limitary '
tunic, thickly lined by epithelial
substance, and containing abund-
ance of nuclei and granular matter,
with a few cells. The pseudo-
branchia, situated on the anterior
wall of the spiracular canal, is
manifestly of entirely different
structure to the organs described.
It consists of small plica? of mucous
membrane, covered by a kind of
pavement epithelium.'2
In the Menobranchus the thyroid is represented by two
symmetrical bodies, situated at the sides of the basibranchials.

1 CCLXXXIX. p. 1110. 2 Ib., and see CXLV. p. 270, with reference to the non-

thyroid nature of the pseudo-branchiae in other fishes.

Vesicle from thyroid of Skate.
CCLXXXIX.

376

rrfs-

Vesicle from accessory thyroid of Skate, diam.
In. CCLXXXIX.

THYMUS OF REPTILES. 5G5

In the Frog they lie on the carotids, also close to the basi-
branchials, or thyrohyals.

In a Python of ten feet in length the thyroid was an oval body,
ten lines by six lines in the two diameters, lodged in the fork
made by the divergence of the large and small carotids, and
having the smaller thymus bodies, one on each side.

In the true Lizards (Lacerta) the thyroid is single, but broader
than it is long ; in the Monitor it is double : it is single in Geckos,
Skincs, and Chameleons, but has a more advanced position in the
latter, where it is underlapped, or covered, by the laryngeal pouch.

In Chelonia the thyroid, as in Serpents, lies between the two
carotids, but is usually covered by the pericardia! part of the
thymus. The constituent vesicles are from -f-^ to -^ inch diameter,
closely aggregated : the epithelial lining contains a row of nuclei
imbedded in the granular substance, fig.
278. Among the contents of the vesicles

were found, in most, ( one to three yellow-

• i 11111

ish, coarsely granular globules, -g^ to

T oV o- inch diameter.' < A fine large octo- Portion of the wall of a veslclfrom
hedral crystal was also seen in one of the the thyroid of a Tortoise. CCLXXXIX

cavities.'1

§ 104. The Tlujmus Body or Gland of Reptiles. — The ductless
gland- like tubulo-vesicular body to which the name ' thymus '
can, with any homological probability, be given makes its first
appearance in the Vertebrate series with the establishment of
lungs as the main or exclusive respiratory organ.2 Thus in Siren
and Proteus the thymus is wanting, as in all Fishes : in tailed
Batrachia (Menopoma, Triton) it is represented by a pair of
bodies situated, one on each side, near the origin of the pulmonary
artery. They make their appearance near the same part, but
rather more in advance of the pericardium, in the larvae of
anourous Batrachia, and often degenerate into fat in the old Frog
or Toad. In most Ophidia the thymus lies on each side of the
carotid, of elongate form and unequal size : sometimes in two or
more distinct parts : usually associated with, and concealed by,
fatty matter. In a Python of ten feet in length I found the
thymus in two bodies, each about the size of a pea, of a yellowish
colour, one situated on the termination of the right jugular, the
other between the origin of the larger carotid and the left jugular.
Between the thymus bodies was the much larger single thyroid.
In the Psanimosaur and Iguana the thymus is broad and flat,
covers sternally the thyroid, extends along the common trunk of

1 CCLXXIX. p. 1100. 2 CXVIII.

5G6 ANATOMY OF VERTEBRATES.

the carotids, and divides to accompany them a short distance. In
the young Crocodile1 the thymns is relatively larger, thicker,
subtrihedral, extending backward upon the pericardium, as well
as forward along the carotids to the basis cranii. In young
Chclonia an elongate body, of a yellowish white colour, lies
between the carotid and axillary trunks on each side : it presents
lateral cavities, defined by limitary membrane, and containing
nuclei, oil-drops, and fine molecular matter. In older Cltelonia it
seems to degenerate into fat.

§ 105. Reproducible Parts in Hannatocrya.- -One effect of life
is the reproduction of the parts of the body as they pass away
through unfitness for the required actions : this mainly takes
place molecularly and invisibly ; but parts of the integument, hairs,
teeth, antlers, may be cast off en masse, and reproduced on a scale
which catches the ordinary attention as a new growth. Certain
animals have the faculty of reproducing organs and compound
parts of the body which may have been removed by violence :
amongst Vertebrates the property is greatest in the cold-blooded
series ; and here, so far as experiment yet shows, is most conspi-
cuous in the tailed species and larva? of the batrachian order. In
the Newt ( Triton) the tail, amputated at any distance from the
base, is reproduced : the same with respect to the fore-limb and
hind-limb, the reproduced member having the digits, but with
diminished power of movement. The same member has been, in
young Newts, removed and restored four times successively. In
the experiments recorded by Bonnet,2 it was found that warmth
promoted, and cold retarded, the regeneration of the part. An
eyeball of a Newt was extirpated, and, in the course of a year, it
was restored with the usual organisation. Dumeril cut off about
three-fourths of the head of a Triton marmoratus, and deposited
the animal at the bottom of a large vessel, having half an inch
depth of water, which was constantly renewed. The Newt con-
tinued to live, and to move slowly. The nostrils, the tongue, the
eyes, and the ears were gone, and the senses reduced to that of
touch. It crept slowly, and Dumeril imagines cautiously, about,
occasionally raising the neck to the surface, as if to breathe. The
process of cicatrisation at length completely closed the aperture of
respiration and deglutition ; and so it survived for three months
after the operation, when it died from accidental neglect. This
experiment exemplifies chiefly the power of endurance of mutila-
tion, and, collaterally, the respiratory function of the skin. In

1 I have not had an opportunity of examining this structure in a full-grown speci-
men of Crocodilian. 8 ccci. torn. xi. pp. 62-179.

REPRODUCIBLE PARTS IN REPTILES. 567

the young larvae of Rana temporaria and Bombinator igneus, Dr.
Giinther cut off the tail, and it was reproduced before the time
when its absorption normally commences : it was transparent and
colourless, a small quantity of pigment being deposited at its root
only. ( Larvae from fourteen to twenty days old did not survive
the loss of the entire tail, probably because they are disabled from
obtaining the requisite food ; but if only a portion of the tail be
cut off, it is more or less completely reproduced until its growth
is arrested by the commencement of the last stage of metamor-
phosis. If a hind limb be cut off when the larva is about two
lines long it is reproduced. No part of an Anourous Batrachian
is reproducible after completion of the metamorphosis, not even
the interdigital web.'1

In Reptilia the power of local reproduction has been exemplified
chiefly in respect of the tails of Lizards. Hunter's preparations,
nos. 2208-2223, are all from this order, and include species of
Ameiva, Gecko, and true Lacerta. No instance of the restored
tail shows ossified vertebrae, and some exemplify the tendency to
greater abnormality in the reproduced part. A structure of the
normal caudal vertebras, related apparently to this property, is
noticed at p. 59 : the caudal muscles, by their proportions and
interlocking arrangement, seem likewise to favour the rupture of
the tail. When it is cast off, it continues to writhe for some
time, and, when these motions have ceased, exemplifies the reflex
function on being pricked or otherwise irritated.

The degree in which the reproduction of parts is exemplified
in Fishes awaits the results of experiments. Van der Hoeven2
affirms that parts of the fins are restored after amputation, and
that the power is limited to this extent. Amputation of the
small adipose dorsal fin has, however, served to mark an individual
Salmon from its ' parr ' state to that of the f grilse ; ' } and it appears
that only the peripheral (dermoneural or dermohaemal) rays are
reproducible, and to this the hard ones in Acanthopterans form
an exception. ( The modified dermoneurals forming the cephalic
tentacles of Lophius and Antennarius are as frequently repro-
duced as they are injured, to meet the particular use which these
angling fishes make of them : they may be observed in every
stage of growth. Lost parts of fins appear to be more easily
reproduced in young than in old fishes.'^

«

1 MS. Notes by Dr. A. Giinther. 2 cccv. vol. ii. p. 52.

3 cccxxxiv. ' The wound caused by marking was covered with skin, and in some
a coating of scales had formed part.' Page 5. 4 MS. Notes by Dr. A. Giinther.

568 ANATOMY OF VERTEBRATES.

CHAPTER XL

GENERATIVE SYSTEM OF II^EMATOCllYA.

§ 106. Male Organs of Fishes. — All Fishes are dioecious, or of
distinct sex. The male parts of generation present a progressive
gradation of complexity from the essential gland, or testis, as a
single organ distinguishable only by microscopic examination of
its contents from an ovarium, to a more definite and concentrated
form of testis with complete bipartition ; then to the developement
of a proper duct or f vas deferens,' next of a vesicula seminalis
and prostate, afterwards of an intromittent organ, and finally of
superadded ( claspers,' or mechanical instruments for retention
of the female in coitu. In Petromyzon marinus the testis is a
long thin plate, disposed in the form of a series of folds, closely
attached by a duplicature of the peritoneum to the median line of
the back of the abdomen, between the kidneys ; the extension of
the overlapping oblique folds to the right and left of the line of
attachment feebly indicates the duplex character of the gland.1
Its tissue consists of small spherical cells filled with spermatozoa,
fig. 402. These escape, by dehiscence of the cells and rupture
of the peritoneal covering, into the abdominal cavity, and are
expelled by reciprocal pressure of the intertwined sexes from the
peritoneal outlets at the cloaca. The Eel closely resembles the
Lamprey in the general form and condition of the male organs ;
but the right and left sides of the plicated testis are more distinct,
and the spermatic cells are more numerous and minute.

The Sand-Eel {Ammodytes)* has a single testis, compacted into
an elongated triedral form, and impressed by a median longitudinal
fissure : it usually inclines a little to the right side. In the Perch
the single testis inclines to the left : in the Blenny and the Loach
it lies in the middle line. In these osseous fishes the glandular
part of the testis is inclosed in a proper fibrous capsule, which is
continued from the posterior end of the gland, with its serdus
covering, into a short and simple sperm-duct, or 6 vas deferens,'
which opens usually into, or receives, the urethral prolongation
of the urinary bladder. In the Gurnard the testes, fig. 378, a,

1 xx. vol. iv. p. 48, prop. no. 2373. 2 Ib. p. 49, prep. no. 2378.

MALE ORGANS OF FISHES.

5G9

379

are distinct from each other, but their e vasa deferentia ' almost
immediately unite into a common duct, e, which joins the urethra,
c, behind the rectum, h, and terminates at the
outlet, y. In the Salmon and the Herring the
6 vasa deferentia ' do not unite together until
near their termination in the urethra. In the
Cod and the Bull-head (Cottus) the common
portion of the efferent duct is much dilated :
it forms a saccular seminal reservoir in the
Sole. The canal common to the ureter and
vas deferens is of great length in the Sturgeon :
a valve prevents the regurgitation. of the urine
into the spermatic duct. The urethra is usually
produced into a papilla, Avhich projects con-
spicuously from the back part Of the Cloaca in Renal and male organs :

the viviparous Poecilia, Anableps, and Bleimy :

it is large also in the Lump-fish. The testes are almost

entirely extra-abdominal in the Flounder and some other Pleu-

ronectidcB, extending backward into a kind of concealed scrotum

between the integuments

and muscles on each side

above the anal fin. The

testes differ much in form

in different Osseous Fishes,

but are remarkable in all

for their enormous seasonal

increase : when fully deve-

loped, they are commonly
known as the f milt ' or ( soft
roe.' In Gymnotus they are
two oblong triedral bodies,
attenuated at both ends.
In the Pipe-fishes (Syn-
ynathi) they present the form
of two simple elongated
straight tubes, fig. 427 ,
g 3.1 In the Lump-fishes
(Cyclopterf) they are di-
vided by incisions into
lobes : in the Cod a vast

/» . -, -i Structure of the testis iu Clupea Alosa. cxxn.

extent ot the vascular sur-
face of the glandular substance is packed into a small com-

1 xx. vol. iv. p. 48, prep. no. 2375,

570

ANATOMY OF VERTEBRATES.

380

pass, by being disposed in convolutions upon the edge of the
' mesorchium.' The primitive spermatic cells, which are per-
sistent in the Cyclostomes, have coalesced into tubes (tubuli
seminiferi) in Osseous Fishes ; the tubes open at one end in the
wide and sometimes saccular commencement of the vas deferens,
and terminate at the other, either by blind free extremities or

by reticulate anastomoses.1 In the Herring, Shad,
and other Clupeoids, the secerning tubes ramify
and anastomose in the substance of the testicle,
and from this plexus, fig. 379, the initial casca
are prolonged to the surface of the gland, where
their obtuse blind ends give a granulated appear-
ance to the exterior.

In the Plagiostomes the testes, figs. 352, k,
380, «, are always distinct from one another, and
usually of a circumscribed compact form, situated
far forward in the abdominal cavity. They have
a proper capsule, or ' tunica albuginea,' and a
peritoneal covering ; the capsule sends many ( septa'
into the substance of the gland, and the lobes thus
formed consist chiefly of the tubuli testis, and
their expanded cell-like extremities, filled with
the spermatozoa : the convolutions of the f tubuli '
are plainly discernible in the portion of the testis
of the Basking Shark (Selache maxima) preserved
jn ^Q Hunteriaii Museum. London, prep. no.

t *•

2396, A.2 Numerous ( vasa efferentia' convey
the f semen ' to the beginning of the f vas deferens,' 3 which forms
a large ( epididymis,' fig. 380, b, by its manifold convolutions.
These gradually decrease as the duct, ib. e, approaches the cloaca,
when it becomes straight, and expands into an elongated reservoir,
ib. f, the mucous surface of which is commonly increased by
numerous transverse plica3, as in Spinax and Selache. Behind
the termination of the rectum the ' vasa deferentia ' suddenly
diminish, approximate, communicate with the ureters, and ter-
minate upon the cloacal penis, fig. 352, o. This is hardly visible,
and the testes are very small, except at the breeding season, in
the Piked Dog-fish (Spinax).

The claspers are present in the Chimaeroid Fishes as well as in
the Plagiostomes. They project backward, as appendages to the
bases of the anal fins, and are sometimes bent inward at their
free extremities, figs. 352, ^, 380, m. Near this part may be

1 cxxn. p. 105. ' xx. vol. iv. p. 52

organs, left side:

Spinax.

cxxxiv.

FEMALE ORGANS OF FISHES.

571

381

discerned a fissure, which is the outlet of a blind sac, extending
forward from the base of the clasper, beneath the muscles and
skin, at the sides of the cloaca. The inner surface of the cavity
is smooth, and lubricated by a fluid mucus : the attached vascular
surface is richly supplied with vessels, especially with veins : in
the Rays a glandular body adds its secretion to that of the surface
of the cavity.

§ 107. Female Organs of Fishes.- -The gradations of structure
of the female organs correspond very closely
with those of the male. In the young Lam-
prey the ovarium is a simple longitudinal mem-
branous plate, fig. 381, c, suspended by a fold
of the peritoneum ( mesoarium) along the under
part of the vertebral column : it increases in
breadth and thickness as the ova are developed
in it, and still more so in length, beins; accom-

' CD * ~

modated to its locality by numerous folds, fig.

382. But no superadditions are made to this

primitive structure : the ova, d, escape by

rupture of their capsules into the abdomen, Z>,

and are excluded by the peritoneal aperture,

ib. /. In all other Fishes in which vasa

deferentia are absent in the male, oviducts are

absent in the female. But it does not always

happen, where vasa deferentia are developed in the male, that

the homotypal ducts exist in the female : the Salmon is an

example in which the ova are discharged by dehiscence into the

abdominal cavity, and escape

by peritoneal outlets, as in

the Eel and Lamprey.

With this exception, the
parallelism of the male and
female organs is very close.

Thus the ovarium is sino;le

~

in those bony Fishes, as the
Perch, the Blenny, the
Loach, and the Ammodyte,1
in which the testis is sinoie :

o

the median cleft of the ovary

* A» ovnnan fold of the Lamprey.

of the Ammodyte is deeper

than that of the testis, but the continuity of the two seemingly
distinct glands is obvious at the upper and lower ends. In

1 xx. vol. iv. p. 133. prep. no. 2675, A.

Renal and female organs
1'ifi-omyzon. xx.

382

572

ANATOMY OF VERTEBRATES.

most Osseous Fishes the ovaria, fig. 383, A, form two elongated
sacs of mucous membrane, with a thin fibrous tunic and a perito-
neal covering, closed anteriorly, but produced posteriorly into a
short, straight, and commonly wide oviduct, terminating behind
the anus, and commonly before the urethra, fig. 281, i. In the

Pipe-fishes the oviducts con-
383 tinue distinct to the cloaca.

In most Fishes the oviducts
coalesce, after a brief course,
as in the Herring, or after a
longer course, into a single
tube before arriving at the
cloaca : the common terminal
portion becomes much dilated
in tfre Cod-fish, the Lump-fish,
aiid"~some others. The ( stroma,'
or cellular tissue, Avhich is the
seat of developement of the
ova, is interposed between the
mucous and fibrous tunics of
the ovarian sac : it sometimes,
though rarely, is coextensive
with the mucous membrane.
In the Lophius the two ovaria
are long and large plicated
tubes, flattened when empty,
cylindrical when inflated, with
the ovigerous stroma lining, as
it were, only the ventral half

of the walls of the cylinder, and terminating where the oviducal
portions of each sac unite together to form the common short
efferent canal. The inner surface of the { stroma ' is beset with
small tubercles, arranged in interrupted linear series, each tubercle
supporting four or five papilliform ovisacs. In the Pike the stroma
forms a longitudinal strip, in short transverse plaits, along the
median side of the long ovarian sacs : fig. 383, B, shows two of the
ovarian plaits, from which the developed ova hang in subpedun-1
culate ovisacs. In the Wolf-fish the stroma extends over the
whole of the internal surface of the ovary, into the cavity of
which it projects in the form of numerous oval compressed
processes. In general, its superficies is extended by being plaited
into numerous folds, which are transverse in the Cod and Salmon,
oblique in the Mackerel, and longitudinal in some other Fishes.

B

Ovaries and oviduct of an Osseous Fish.

FEMALE ORGANS OF FISHES.

573

In the Salmon the free surface of the stroma is exposed. In the
Osseous Fishes that retain and hatch their ova the stroma does
not extend to the posterior part of the ovarian sac, but this

384

Viscera of female Shark, xx.

serves as a kind of uterus, and contains an abundant albuminous
secretion at the season of the internal incubation. The viviparous

574 ANATOMY OF VERTEBRATES.

Blenny (Zoarces), the Anableps, tlie Poccilia, and Embiotoca1
arc examples of ovo-viviparous Osseous Fishes, and at the same
time manifest naturally, what occurs as a rare adnormality in
higher Vertebrates, viz. ovarian gestation. In the Plaice and
other Pleuronectidre the parallelism between the male and female
organs is so close that the ovaria also escape from the abdomen,
and become lodged in greater or less proportion in subcutaneous
scrota! cavities above the basis of the anal fin.2

In the Lamprey the short and narrow lateral infimdibuliform
passages behind the rectum, into which the ureters open, and
which terminate in the peritoneal outlets, fig. 381, <?, /, have been
compared to short oviducts. In the Sturgeon actual oviducts
are continued from the ureters forward, which open by wide
infundibular apertures, comparable to the 6 morsus diaboli ' of
anthropotomy, into the general peritoneal cavity, and receive the
ripe ova as they burst from the ovarium. The urine is prevented
from regurgitation into the serous cavity through the same
passage by a valve which only allows the passage of the ova
backward into the common urogenital duct.

The higher grade of the sexual organisation of the female
Plagiostome, as compared with the cartilaginous Ganoid fish, is
manifested chiefly by modification of the oviducts : they are
always two in number, fig. 384, q, r, and distinct from one end
to the other, but they are brought into close proximity, or
coalesce at both ends : they are always distinct from the ureters,
which terminate on the prominent urethral clitoris, ib. £, between
the oviducal outlets, ib. s, s. Different parts of the oviducts are
modified, moreover, for special functions, superadded to that of
effecting the safe transit of the generative product. The ovaria
of Plagiostomes, fig. 384, n, are relatively much smaller than in
other Fishes, of a more compact form, and confined to the fore
part of the abdominal cavity : they are sometimes blended into a
single body. The stroma is not spread over the walls of a cavity,
but is collected into a loose cellular mass, circumscribed by a
fibrous membrane, and suspended by a duplicature of peritoneum
to the dorsal parietes of the abdomen, at the sides of the
esophagus. The ova are much fewer in number than in the
( roe ' of Osseous Fishes, and are seen in different stages of
growth, being developed more consecutively. The approximate
or confluent abdominal apertures of the oviduct, ib. q, are anterior
to the ovarium, between the liver and the pericardial septum ;
they form together a heart-shaped opening, with entire margins,

1 CCCXXXV ~ XLIII. V. pi. 4, fig. 1.

FEMALE ORGANS OF FISHES. 575

attached by two diverging ligaments to the abdominal walls. If
a little powdered charcoal be sprinkled on the ovarian orifices and
ligaments exposed by opening the abdomen in a fresh caught
female Dog-fish, the particles will be seen to move towards and
enter the common oviducal aperture, indicative of a ciliated
epithelium in the serous membrane, which may aid in the
transport of the ova to that aperture. The oviducts, narrow,

and with thin tunics at their commencement, diverge from each

* ~

other, arching over the fore part of the ovaria, and then descend
along the ventral surface of the kidneys, to terminate at the
lateral and posterior parts of the cloaca, ib. s. A glandular body,
ib. o, is developed in their coats, after the first, fifth, or sixth part
of their extent, and their terminal half or third part, ib. r, is
dilated; the sizes of the glandular and of the uterine parts of
the oviduct are usually in inverse proportion : in the oviparous
Plagiostomes the gland is large, the uterus small, and the reverse
obtains in the viviparous species, fig. 384. The inner surface of
the Fallopian portion of the oviduct presents longitudinal or very
oblique folds of the delicate mucous membrane : but near the
aperture the folds resolve themselves into minute compressed villi.
The glandular part varies in structure as wrell as in size in different
species. In the viviparous Dog-fish {Spinax acanthias) it consists
of two elliptic flattened lobes, of laminated structure, the free
surface presenting minute transverse stria?, beset with pores, the
orifices of secerning tubes, the aggregate of which composes the
layer of glandular substance. In the oviparous Homelyn (Raia
maculatd) the lobes of the large rudimental glands are reniform,
and consist of close-set layers of secerning tubes. In the Tope
(Galeus) the lobes of the gland present the same essential
structure, but are conical, subspiral, and hollow. The uterine
part of the oviduct in the viviparous Dog-fish, fig. 384, r, has
the lining membrane produced into longitudinal folds, with wavy
margins, each of which contains a single vessel following its
sinuosities, and sending off branches to the parietes of the
oviduct : the folds gradually subside at the outlet of the oviduct.
In the oviparous Dog-fish (Scylliuni] the folds of the lining
membrane of the corresponding part of the oviduct are oblique,
and their vessels are derived from trunks in the walls of the
oviduct, and are distributed in minute and tortuous ramifi-
cations on the folds.1 The uterus of the Smooth Dog-fish
(Scoliodon, M. ; Emissole lisse, Cuv.) shows several uterine

1 xx. vol. iv. p. 136,

576 ANATOMY OF VERTEBRATES.

cotyledons developed from the internal surface of the dilated part
of the oviduct: corresponding foetal cotyledons are developed
from the vitellicle of the embryo.

Thus the various forms of the generative organs of Fishes
resolve themselves into four well-marked grades of complexity.
First, the essential gland, testis or ovarium, without excretory
canal. Second, the same, with a simple duct, continuous with
testis or ovarium. Third, a partial oviduct, not continuous with
the ovarium, and not separated from the ureter. Fourth, testis
or ovarium, of a more compact form, each with a long and
complex duct, distinct from the ureter ; the beginning of the
vas deferens convoluted into an epididymis, and its end dilated
into a seminal reservoir, with a plicated glandular inner surface ;
the oviduct not continuous with the ovarium, but with a nida-
mental gland near its commencement, and dilating into a
receptacle, with a plicated surface, at its terminal half. Besides
the ' claspers ' of the Plagiostomes, there are other accessory
organs of generation, viz. the subcaudal marsupial tegumentary
folds in the male of some species of Syngnathus, fig. 427, o,1 and
the subabdominal marsupial pouch in the male Hippocamps.2

§ 108. Male Organs of Batrachians.- -These consist of testes, their
ducts and appendages, the seminal reservoir, and the common ex-
cretory canal and terminal papilla : there is no intromittent organ.

The testes, though in some Batrachia subdivided, resemble in
their relative size and compactness of form and tissue those of the
Plagiostomes. In the Proteus anguinus the testis is long, cylin-
drical, with obtuse ends, slightly fissured lengthwise by the
insertion of the suspensory ligament : they sometimes show in-
equality of size, and the right is usually about three vertebra?
in advance of the left. In Amphiuma the testis is subcylin-
drical, and tapers at both extremities : adipose appendages project
from their free or ventral surface. In the Axolotl the ( mesor-
chium,' or suspensory duplicature of peritoneum, is broader, and
permits the vessels and ducts to be readily seen as they traverse
it transversely. The adipose appendages are branched In the
Menopome the testes are rather broader than in the Amphiume,
approaching the oval shape. This is likewise the case with
one or both testes of the great Japan Newt {Sieboldtia or
Cryptobranclius), which are suspended by a broad mesorchium
on each side of the aorta and narrow remnants of the Wolffian
bodies, between the ends of the lungs and the beginnings of the
kidneys.

1 xx. vol. v. ]>. 07, preps, nos. 3226-3228. - lb. p. 68, preps, nos. 3230 and 3231.

MALE ORGANS OF BATRACHIANS.

577

385

In most Newts the testis is divided into two lobes, fig. 387, «,
one, usually the larger, in advance of the other : I have observed
three detached lobes or testes on each side. In the Salamander
there may be one or two smaller lobes or accessory testes, besides
the two chief divisions of the gland.1

In tailless Batrachians the testes, in accordance with the shape
of the body, present a full oval form, compact and undivided : they
are situated, as shown in the Frog, fig. 3S5,/,/, on the ventral
side of the anterior half of the kidneys, g, g, having an entire
investment of peritoneum, often deeply or brightly coloured by
pigmental cells, which forms a broad and short mesorchium,
suspending them to the renal glands and supporting the blood-
vessels and efferent ducts. Processes of peritoneum, filled with
fat, ib. /, /, diverge from the fore part of both bodies.

In all Batrachians the testis consists of seminiferous caaca, more
elongated than the sperm-follicles of Fishes, shorter and straighter
than in higher Reptiles, having their blind ends next the capsule.
This consists of a fibrous or ( al-
bugineous ' tunic, beneath the
serous one : both have been re-
moved to show the tubuli testis
•in Swammerdam's accurate figure,
fig. 386. The semen is conveyed
by short transverse efferent ducts,
A, to a common longitudinal canal,
i. In the Menopome about ten
vasa efferentia quit the elong-
ated testes and enter the common
canal, which extends along the an-
terior three-fourths of the kidney,
and at its fore-end is connected
with the ligamentous remnant of
the duct of the Wolffian body : it
is thence reflected back along the

o

outer border of the kidney, receiv-
ing in its course toward the cloaca
the ureters, which are short
transverse or oblique tubes, from ten to twenty in number : the
urino-seminal canal, supported by a narrow fold of peritoneum,
forms a few slight bends, and gradually expands as it approaches its
termination at the back part of the cloaca. In Sieboldia maxima
the longitudinal canal which receives the short efferent ducts is

1 xx. vol. iv. p. 53.
VOL. I. p p

Generative organs of male Frog. CCLXX.

578

ANATOMY OF VERTEBRATES.

386

Testis of Frog. CCLXX.

387

continued forward to the Wolffian ligament, far in advance of
the testes, contracting to a point : in its backward course, between

the testis and remnant of the Wolffian
gland, it receives a few short transverse
ducts therefrom, which come from small
masses of convoluted tubes, still pervious
to mercurial injection in the male dissected
by Dr. J. Van der Hoeveii : continuing its
descent, the longitudinal duct gradually
expands, describing convolutions, and re-
ceiving in its course along the outer side
of the kidneys the excretory ducts, two or
three in number, of those glands. Each
urino-seminal canal expands into a simple
oblong reservoir, with thickened glandular coats, at the ter-
mination of the rectum, and communicates with the cloaca
by a papilliform orifice, a little in advance of the blind end of

the reservoir. The slender elongated
remnants of the Wolffian glands are direct
continuations from the fore part of the
kidneys.

In the Newt ( Triton t&niatus) from four
to five efferent tubes, fig. 387, c, c, quit
each of the two chief divisions of the testis,
ib. «, and terminate in the common longi-
tudinal canal, ib. d, which extends forward
to the Wolffian ligament, and backward to

o *

the anterior end of the kidney, ib. e : in this
course it sends off about ten short trans-
verse branches, which, after dilating and
convoluting, ib. i9 severally terminate in
the beginning and fore part of the urino-
seminal canal, ib. f. The small dilatation
and larger mass of convolutions on each of

CJ

the transverse branches of the longitudinal
duct are retentions of modified parts of the
Wolffian or primordial urogenital gland. The
urino-seminal duct, /, forms many close
coils, like an epididymis, as it approaches
the kidney : it receives directly one or two uriniferous tubes, ib. /,
and communicates, near its termination, with the orifices of a
series of modified ureters, ib. g, which receive the rest of

•m

Male organs, Newt. Triton
tieniatus. cccxxn.

MALE ORGANS OF REPTILES.

579

the urine as well as the semen. Each uriniferous duct dilates
into a long reservoir, describing a curve external to the kidney,
the first or anterior being the longest, the rest successively shorter :
they are connected together, eight to ten in number, so as to
form, in appearance, a flattened semi-oval ' vesicula seminalis,' and
terminate by a short wide canal, ib. m, common to them and the
vas deferens, in the back part of the cloaca.

In the Frog about six transverse efferent ducts, fig. 385, h.

o * ~ y *

enter the longitudinal one, g, extending along the inner (mesial)
side of the kidney, which is reflected round the fore end of that
gland to form the beginning of the urino-seminal canal, ib. z,
which courses along the outer (lateral) side of the kidney. This
canal does not describe convolutions : it enlarges as it progressively
receives the ureters, and suddenly expands beyond the kidney
into a semi-oval ( vesicula seminalis,' ib. k, the outer half of which
has folliculo-fflandular walls, the inner half being smooth and

o o

with the character of a reservoir. A short duct conveys the
contents of the vesicle to the back of the cloaca, ib. I ; at the
fore part is the orifice, c, of the allantoid bladder, e.

No Batrachian has the intromittent organ, or a vas deferens
distinct from an ureter: a stage in the substitution of kidneys
for Wolffian bodies is hereby obviously indicated.

§ 109. Male Organs of Reptiles.- -In the scaled Reptiles the
conduits from the kidney and the
testes are distinct to the cloaca, and
terminate there on separate papilla?.
The testes, fig. 389, b, are compara-
tively small and compact : they are
always abdominal, with a complete
investment of peritoneum, fre-
quently coloured by pigment-cells.
They have a strong albugineal
tunic, and consist of blind semini-
ferous tubes, fig. 388, much longer
and more slender than in Batra-
chians, and packed up in close
convolute folds, in ill-defined loculi

of the gland. From these tubes a Tubuli semlnlferi . testis of Lizard.
variable number of efferent canals

proceed, which are inclosed in a prolongation of the tunics of the
testis for a brief course, and then unite into a vas deferens.

In the Ophidia the testes, fig. 357, h, h, are of a more elongate

388

P P 2

580 ANATOMY OF VERTEBRATES.

form than in other Reptiles. In the common harmless Snake
( Coluber natrix) they are oblong, subcompressed, in advance of the
kidneys, the right about an inch more forward than the left,
corresponding to the difference in the relative position of the
kidneys. In the Rattlesnake the testes are more symmetrical
in position. The vas deferens, disposed in short undulations,
goes along the kidney to the cloaca, the papillae terminating near
the beginning of the urethral groove. The intromittent organs

o o o o

are two in number, and consist of invertible sheaths, or long
narrow bags, with a highly vascular papillose lining membrane,
bifurcate at their blind end, to which are attached the muscles,
fig. 357, /, for inverting and keeping them retracted and hidden
in the base of the tail. By tumefaction of the vascular portions
of the bags, and the action of the ( constrictor basis caudae ' and
6 sphincter cloacae,' they are everted. In the Rattlesnake the
blind end of each inverted pouch bifurcates, and the vascular
membrane is thickened and produced into many processes near
the bifurcation : when eversion with erectile tumefaction of the
parts takes place, each penis presents a papillose and bifurcate
glans, as in fig. 357, k. In Elaphis quadrilineatus the body of
the penis presents large retroverted papillae, and the glans is
beset with small flattened wrinkled processes.

In the Slow-worm (Anguis) the testes are situated a little
anterior to the dilated rectum, the right in advance of the left ;
the sperm-duct simulates a long epididymis by its initial convolu-
tions or transverse folds. The intromittent organs are invertible
and evertible pouches, as in Serpents, but are shorter.

In a Seine-lizard (Tiliquci) the right testis is more advanced
in position than the left. The body of the penial pouch, when
everted, shows transverse rugae, and the sub-bifurcate glans short
retroverted papillae. In Lacerta ocellata, as in Draco volans,
fig. 389, the testes, b, show a similar degree of unsymmetrical
position. The sperm-ducts form, by a series of short transverse
folds, a long body or band, like an epididymis : but there is no
structure properly so called consisting of the convolutions of
several efferent tubes prior to their union to form the vas
deferens, ib. c. In the interspace of the orifices of the ureters
a ridge is continued backward, on each side of which is the orifice
of the vas deferens, whence is continued the urethral groove
extending along the penial sheath to the papillose blind end or
glans.

The peritoneal covering of the testes shows in some Lizards

MALE ORGANS OF REPTILES.

581

389

stellate pigment-cells : in the Chameleon they give a black colour
to the gland.

The short and outwardly extended legs of Lizards serve for
progression, not for support, and the animal rests with its belly
on the ground, as in Serpents :
hence the necessity not only for
the internal position of the testes,
but for the mechanism by which
the intromittent organs can be
inverted, and safely lodged out
of sight, in the base of the tail,
when not in use.

In the Turtle (Chelone mi-
das) each testis is an elongate,
cylindrical, slightly bent body,
decreasing in size at the end next
the cloaca : the efferent tubes
leave it near the fore or upper
part of its concavity, and soon
join the vas defer ens, which
forms a large and compact body
by numerous convolutions, situ-
ated between the testis and
kidney. Each vas defer ens ter-
minates, with the ureter, in a
papilla, the spermatic orifice
being nearer the bladder. The penis is short, and is indicated,
in the unexcited state, chiefly by the urethra! groove ; only the
glans and the pointed end of the fibrocartilaginous body imme-
diately above it project from the cloacal surface, and these are
partly enclosed by a thick duplicature of the cloacal membrane,
representing a preputium : in the erection of the organ this fold
is everted and obliterated.

In the Emys europaa the testes, fig. 390, r/, and convoluted
sperm-duct, ib. c, are separated from the kidneys, ib. o, by the
peritoneum, which, after giving an entire investment to the testes,
is simply reflected over the contiguous surface of the kidney :
an artery, I, s, runs between the two glands. The testis presents
a full elliptic figure : its peritoneal covering is usually stained
with a dark pigment : x is the spermatic artery, z the spermatic
vein. The sperm-duct opens, close to the ureter, upon a papilla,
fig. 391, F, at the commencement of the urethra! groove, ib. G.
The penis, in both freshwater and land Chelonia, is longer and

Male organs, Draco volans.

582

ANATOMY OF VERTEBRATES.

390

T'

Male organs of Emys europcea. xxxvin.

391

larger than in the marine species : it is subcylindrical, with an
expanded terminal glans, ib. I, usually ending in a point. The

urethral groove, ib. G,
extends along the mid-
dle of the dorsal surface,
and becomes deeper as
it approaches the glans :
in erection the tumefac-
tion of its borders con-
verts the groove into a
temporary canal, and it
then appears to end by
an orifice, K, which is
usually divided by a
papillary eminence. The
penis consists of two ' corpora cavernosa,' ib. H, which are firm
fibrous bodies, cohering mesially and attached to the ventral surface

of the cloaca; and of two median
tracts, fig. 392, 4, of a more vas-
cular erectile tissue, forming the
walls of the mediangroove, 5, and
covered by a soft quasi-mucous
membrane. Each vascular tract
commences by an enlargement,
fig. 390, E, analogous to the bul-
bus urethrcB. The erectile tissue
is continued forward, thinly at
first, but afterwards increasing
in thickness, to the glans, figs.
391, I, and 392, which it chiefly
constitutes. On each side of
the mid-line of the penis is a
canal, fig. 392, f, which at one
end communicates with the
cavity of the peritoneum, and
by the other end is prolonged
into the substance of the glans,
where it terminates, blindly or
by a kind of reticulate sinus.1
The penis is provided with
two retractors, fig. 391, 55,
fig. 392, 55', arising from the

K

Penis of Emys euro pa a. xxxvi i r.

1 xx. vol. iv. p. 62, prep. no. 2450.

FEMALE ORGANS OF REPTILES.

583

392

SS'

Peritoneal canals of penis ;
eitropcea. xxxvm.

393

ischium, and extended along the under (ventral) surface of the
penis to the glans. This muscle folds up the penis in retracting it
within the cloaca, and at the same time closes thereby the orifice
of the rectum, fig. 390, A, and that of the
allaiitoic bladder, ib. M. Erection is fol-
lowed by eversion of the cloaca, effected
by its ( sphincter.' The developement of
the penis bears relation to the physical
impediments to coitus, caused by shape,
extent, and completeness of the shell, and
by the medium in which the act takes
place : thus the penis is least developed
in the marine species, with a flattened
carapace and incomplete plastron. The
glans penis is trilobate in Trionyx.

In the Crocodile the testes are longer
than in Che Ionia, and rather more in
advance of the kidneys. The penis is single, with a dorsal groove,
continued forward on a slender conical process.
It consists of a firm fibrous cavernous structure,
commencing by two crura, and becoming softer
towards the glans, which consist of vascular and
erectile tissue : this is prolonged beyond the apex
of the corpus cavernosum, so that two points are
thus seen, one above the other : these points are
united together on each side, and also in the middle,
by a vertical septum, which divides the interspace
between them into two culs-de-sac. The urethral
groove is continued as far as the extremity of the
upper point. The peritoneal canals do not pene-
trate the cavernous structure, but lead to and open
outwardly on papillae, situated on each side the
base of the penis, within the cloaca.

As Lizards are allied to Serpents by the
double extra-cloaca! penis, so Tortoises are allied
to Crocodiles by the single intra-cloacal penis :
the structure of this organ also presents two
types, respectively characterising the scaled and
scuted groups of Reptilia.

§ 110. Female Organs of Reptiles.- -In the Axolotl, fig.
393, and Sii'en lacertina, the ovaries, ib. f, are granular elongated
bodies, situated on each side of the root of the mesentery. They

Female organs; Axolotl.

584 ANATOMY OF VERTEBRATES.

consist of delicate folds of membrane, inclosing stroma studded
with ovisacs, of two grades of size, the larger with ova for the
present season, the smaller for the following one. In a Siren
with enlarged ovaries I observed them bearing impressions of
the intestinal convolutions. The oviducts, ib. i, are external to
the ovaria, and are attached to the sides of the spine, each by a
broad duplicature of peritoneum. They commence anteriorly by a
simple slit-like aperture, with entire borders, A, are attenuated at
their commencement, and soon begin to be disposed in short parallel
transverse folds, in the Axolotl about twelve, in the Siren twenty,
in number, which gradually diminish near the cloaca, where the
oviducts open behind the rectum upon small prominences. Above
the kidneys, g, a linear tract, k, indicates the remnant of the
Wolffian body.

The foregoing type of female organs is closely followed in
all the perennibraiichiate Batrachia. In the Newt the ovaries,
as they expand, assume a lobulated exterior and greater relative
breadth, especially at their hinder end, than in the Axolotl.
Each oviduct begins by a simple slit-shaped aperture, between
the pericardium and liver, and passes backward in a wavy course,
which becomes irregular as it approaches the kidneys : here the
oviducts diverge from each other, then approximate at the medial
line, and again diverge, describing a regular curve outward, and
again converge to their cloacal terminations.

In the Salamander (^Salamandra maculosa) the oviduct is more
definitely divided into an oviducal, or ' fallopian,' and a uterine
part : the former, fig. 394, a, is slender, and before impregnation
is convoluted to within a short distance of the cloaca, where it
suddenly expands into the uterine part, b : this part curves for-
ward and outward before terminating in the cloaca at c. The
young are developed in this expanded part of the oviduct, which
is much enlarged after impregnation, as in the figure.

In the tailless Batrachia the ovary, in its quiescent state, fig.
395, o, has the form of an irregularly plicated membranous sac,
with thin and transparent parietes. The initial aperture of the
oviduct, ib. «, is situated close to the base of the heart : the tube
is disposed in many, usually transverse, folds or coils, before its
termination in the dilatable terminal part, in which the ova to be
impregnated and discharged in the same season are accumulated,
as in fig. 395, b. In the cloaca the following outlets are seen:-
in front, that of the allantoic bladder, behind it that of the
rectum, then the oviducal outlets, ib. c, and lastly those of the
ureters.

FEMALE ORGANS OF REPTILES.

585

In scaled Reptiles there is a clitoris or some representative
trace of the intromittent organ of the other sex.

In Ophidia the ovaries, like the testes, are long, slender, and
disposed one, usually the right, in advance of the other, and
the ovisacs are developed for impregnation, in a single longitudinal
series in most species. The ovaries are connected with the begin-
ning of the oviducts by a broad fold of peritoneum. Each oviduct
commences by an expanded ostium, with a wide fissure, fig. 396,
a ; its tunics, at first delicate and transparent, increase in thickness
as the tube contracts : here its course is slightly wavy, but it soon
becomes straight, and, in the viviparous Serpents, expanded, ib. b :

394

395

Oviducts and uteri, Salamander.

Oviducts and uteri, Frog.

in the Rattlesnake the lining membrane of the oviduct, prior to
the expansion, is disposed in minute parallel longitudinal rugae.
The correspondence of the ostia of the oviducts, a, with the
ovaries in position renders the left shorter than the right, and
in viviparous Serpents it usually contains fewer ova or young, as
in fig;. 396. The cloacal terminations of the oviducts are in a

o

semilunar fissure, behind the orifice of the rectum.

In the Lacertians the ovaria usually manifest a slight want of
symmetry in position, the right being a little more advanced than

586

ANATOMY OF VERTEBRATES.

396

the left. In the Lacerta bUineata each ovary shows about a
dozen visible ovisacs : the oviducts are plicated throughout their
course. In Agama atra there are seven or eight equally developed
ovisacs in each ovary. In an Iguana the left ovary exceeded the

right in size, and the imma-
ture ovisacs appeared as
flattened discs overlapping
each other. The duplica-
ture of peritoneum which
connects the oviduct to the
side of the vertebra is con-
tinued beyond the canal,
and terminates in a free edge.
In the ovoviviparous Lizard
(Lacerta \_Zootoca/\ muralis\
the part of the oviduct in
which embryonal develope-
ment proceeds is very ex-
pansile, as in the Viper ; in
the specimen figured, fig.
397, the right oviduct con-
tained three ova, ib. <?, the
left two ova: the ovaria are
shown at a, the abdominal
aperture of the left oviduct
at c, the fallopian part of
the tube at d, the uterine
part at e, the terminal part
at f: the peritoneal fold,
attaching the oviduct to the
ovary and to the spine, is
marked b, the rectum g,
and the cloaca h.

In Chelonia the ovaries
are symmetrically disposed,
and placed far back in the
abdomen. The female or-
gans of the Turtle ( Chelone

Female organs impregnated, Vriper. cccvur. &

midas), in the quiescent

state, show the ovaries in the form of a broad, flattened, variously
folded substance, thickly studded with innumerable ovisacs, like
white specks : each ovary is attached by a peritoneal fold, ( meso-
arium,' to the sides of vertebrae, between the rectum and the

FEMALE ORGANS OF REPTILES.

587

397

Back view of female organs impregnated ;
Zootoca.

oviducts. The oviduct commences by a simple elongated slit,
opening upon the free margin of the
mesoary ; the duct soon contracts to
almost capillary tenuity, and gradually
expands as it approaches the cloaca,
contracting again before its termi-
nation.

In the Snapper (Chelydra) the ovi-
duct is disposed in short transverse
folds, between the layers of a broad
duplicature of peritoneum, gradually
diminishing in width, and increasing in
the thickness of its parietes as it ap-
proaches the cloaca. The inner sur-
face of the initial part of the duct
presents a series of oblique folds, which gradually become more
produced and more longitudinal. The oviducts terminate between
two diverging folds of the

398

lining membrane of the

o

cloaca, which folds gradu-
ally subside as they con-
verge to meet and termi-

o

nate in the sinus of the
6 glans clitoridis.' In the
European Freshwater Tor-
toise the inner surface of
the initial, narrow, and thiii-
walled part of the oviduct,
A", p, fig. 398, is disposed
in fine longitudinal folds,
and is lined by ciliate epi-
thelium : beyond these, for
a short space, ib. o, the walls
of the oviduct are glandu-
lar : in the expanded part
(containing an egg in the
example figured) the rugaa
of the lining membrane are
feeble and sinuous. Ex-
ternal to the mucous mem-
brane there is a stratum of
muscular fibres, by the con-
tractions of which the ovum is propelled along the oviduct:

Descent of the egg in the oviduct of Emys. One oviduct,
the cloaca and parts opening therein, xxxvm.

588 ANATOMY OF VERTEBRATES,

at the termination, F, where the egg-shell is secreted, the
membrane is vascular, and thrown into broad irregular rugae,
which are continued as far as its termination, n, in the cloaca.
The ureter, E, opens behind the oviduct, a : the allantoic bladder,
B, and rectum, m, in front.

In Crocodilia the ovaria are more advanced in position, and more
compact in form and structure, presenting, in the unexcited state,
a surface granulated by minute ovisacs. The abdominal orifice of
the oviduct has an entire margin; the duct maintains a more
uniform diameter, and sooner gets upon the edge of the supporting
fold of peritoneum than in Chelonia. The lining membrane of
the hind part of the oviduct is puckered up into close-set undu-
lating transverse rugae : but these subside gradually toward the
terminal shell-forming segment, where the membrane shows minute
longitudinal puckerings. The outlet projects into the cloaca.
The clitoris arises by two crura, and is impressed by a longitudinal
groove.

Of parts in female Reptiles accessory to generation, the most
remarkable are the temporary tegumentary pouches on the back
of the female Pipa, fig. 367, B, c, which, receiving the impregnated
ova, retain the young until the metamorphosis is complete. In
Nototrema and Opisthodelphys there is a large single pouch in
the middle of the back, with the entrance above the vent. It
serves for the reception of the ova, which are hatched therein.
This pouch is peculiar to the female, which attains nearly to its
full size before the pouch is developed. After the reception of
the ova, it extends nearly over the whole back of the animal,
whilst it is shrunk and scarcely visible when the season of pro-
pagation has passed.

589

CHAPTER XII.

GENERATIVE PRODUCTS AND DEVELOPEMENT OF

H^MATOCRYA.

THE functions of the above-described Generative Organs are
s semination/ ( ovulation,' ' fecundation,' and ( exclusion,' to which
is added, in some Haamatocrya, that of ' foetation.' Semination,
or the production of sperm-cells, is peculiar to the testis : ovula-
tion, or the production of germ-cells and vitellus, is peculiar to
the ovary : fecundation is the combined act of the male and
female. A part of the oviduct is usually modified to add
accessory parts to the ovum, or in subserviency to foetation in the
viviparous Hcematocrya : but, in a few instances, the protective
and portative functions are relegated to tegumentary wombs or
marsupia, whichmay be developed in either sex. Exclusion of the
male generative product is called ' emission,' that of the female
generative product ' oviposition : ' but if the ovum be arrested for
the process of foetation, the exclusion of the foetus is then termed
' birth.' Sometimes the male assists in the process of exclusion.

§ 111. Semination of Hcematocrya.- The product of the testis
in Fishes consists of ' sperm-cells,' 'spermatoa,' and ' spermatozoa,'
with very scanty fluid medium of suspension : the function is
seasonal, and attended by
rapid increase of the glands.
This is greatest in Osseous
Fishes, in the testes of which,
at the beginning of their
enlargement, the sperm-cells
(cysts or ( mother-cells') are
seen, fig. 399, «, containing
one or more spermatoa (f cells
of developement '), ib. b. These usually escape from the sperm-cell
as such, and then undergo some change of shape, through the deve-
lopement of the spermatozoa within them. The rupture of the
spermatoon gives issue to the extremely fine capillary appendage,
or ' tail,' the movements of which extricate the nuclear mass forming
the so-called ' body ' of the spermatozoon. In most Osseous

Sperm-cells with spermatoa, Bream. CCCYI.

/>90

ANATOMY OF VERTEBRATES.

Fishes the spermatozoa resemble those of the Perch, fig. 400 : but
in some, e. g. the Loach, there is a small swelling at the insertion
of the appendage, as in fig. 401. In a few the ' body ' is scarcely
indicated, e. g. in the river Lamprey, fig. 402 : in the Petromyzon
marinus the body expands into an egg-shape.

400 401 402

Spermatozoa of Perca
fliiviatilis. cccvi.

Spermatozoa of Cobitis
fossilis. cccvi.

Spermatozoon of Petromyzon
fluviatilis. cccvi.

The spermatozoa in the Plagiostomes are very long, with an
anterior cylindrical body. This is proportionally shortest in
Chimcera monstrosa, and is disposed in three spiral coils : in
Scyllium canicula it is about half the length of the spermatozoon,

403

404

405

A. Spermatozoa of
Scymnus nicceensis. cccvi.

B

B. Spermatozoon of
Torpedo Narce. cccvi.

Spermatozoa within the
sperm-cell (Torpedo Narce).
CCCVI.

is straight, and tapers at both ends : in Scymnus nic&ensis, fig.
403, it is spirally disposed. In Spinax acanthias, the Rays and
Torpedos, fig. 404, the spiral coils are rather closer, usually four
in number: in Raia oxyrhynclius the coils are more numerous,
but only affect the anterior half of the body.

In the Plagiostomes the spermatoa appear as one or more nuclei
within the sperm-cell, like those in fig. 399, b : but they are not,
as in Osseous Fishes, excluded in that state. * In each spermatoon

1 cccvi. vol. iv. p. 484.

SEMINATION OF H^MATOCRYA.

591

406

Bundle of Spermatozoa
•within the sperm-cell.
TorpedoNarce. cccrvi.

a spermatozoon is developed, which escapes by solution of the
spermatoal wall into the sperm-cell, as in fig. 405. l At this stage
the body does not show the spiral disposition.
If the sperm-cell has contained numerous
spermatoa, the resulting spermatozoa group
themselves into a bundle, as in fig. 406 : their
bodies are contiguous and acquire the spiral form
before escaping from the dilated sperm-cell.

The spermatozoa are developed in most
Batrachia as they are in the Plagiostomi ; a
sperm-cell may contain from ten to twenty
spermatoa, in each of which the spermatozoon
is developed, as in fig. 407, and through solu-
tion of the spermatoal membrane the sperma-
tozoa become free in the cavity of the sperm-
cell, where they usually aggregate into a bundle, pressing the sperm-
cell into a pear-shape, which bursts at its small end, and liberates
either the filamentary appendages, as in the Frog, or the spiral
bodies, as inPelobates : in either case the remains of the
sperm-cell continue recognisable, for some time, at the
non-liberated ends of the spermatozoa, as in fig. 408, a.

In the igneous Toad (Bombinator igneus) the
spermatozoa lie confusedly within the sperm-cell :
the remains of the spermatoon long adhere, like a
pectinate appendage, to the spermatozoon. When
fully developed and liberated, the spermatozoa show
a long cylindrical body, attenuated towards the head,
which is again slightly enlarged, and more gradually shrinking

408 409 410

407

Spermatoon
vrith its con-
tained sperma-
tozoon, from
the sperm-cell
of a Frog,
cccvn.

Bundle of Spermatozoa, c,
escaping from the sperm-
cell, «. Pelobates. ccovi.

Spermatozoa of Bombinator
igneus.

Part of Spermatozoon of
Triton.

into the filamentary tail, which is reflected and coiled in narrow
1 "Sometimes the entire nucleus becomes a cuil of fibre." — Barry, ovn. 1842, pis.

v. vi. xi.

592

ANATOMY OF VERTEBRATES.

spirals about the body, fig. 409. The spermatozoa of the
Salamander and Newt have a similar form and disposition, and the
coils of the reflected tail present the appearance of a crenate
fringe or ridge, as in fig. 410. The fully-developed spermatozoa
of Pelobates fuscus have a long spirally disposed body, gradually
attenuating into the filamentary appendage, fig. 411; the total
length is about -£$• of a line : the looser anterior end has a constant
vibratile motion.

In the Frog, fig. 412, the body of the spermatozoon is long,
cylindrical and straight, and is terminated by a straight capillary

411

412

413

414

Spermatozoa of Pelobates
fuscus.

Spermatozoon of
Eana tcmporaria.

Spermatozoa of Lacertn
agilis.

Sperm-cell, a, with
four spermatoa, b,
and their contained
spermatozoa, Tes-
tudo grated, cccvu.

appendage. In the Coluber natrix the body of the spermatozoon
is pointed anteriorly : in Lizards it is shorter and more obtuse,
fig. 413. The spermatoa rarely exceed eight in number in the
sperm-cell, from which they usually escape prior to the full
developement and extrication of the spermatozoa. The same
is the case also in Testudo grceca : but here the sperm-cell,
fig. 414, «, remains longer than in Lizards and Snakes, and
spermatoa, ib. b, with developed spermatozoa, may be observed
within it.

§ 112. Ovulation in Osseous Fishes and Botrachians.- -In
Cyclostomous and Teleostomous Fishes, and in Batrachians, the
ova are developed almost simultaneously at each breeding season :
whilst in Chimasroid and Plagiostomous Fishes, as in scaled

o

Reptiles, the ova are successively developed, or come to perfection
at longer or shorter intervals. In Osseous Fishes, however,
besides the ova of the present season, there are the germs of
those of the next, often studding the ovisacs of the former. In
the ovary of the Frog, before pairing-time, three sets of ova are

Ovarian Ovum

OVULATION IN OSSEOUS FISHES AND BATRACHIANS. 593

distinguished: those about to be discharged are large and dark-
coloured, those intended for the next season are also of uniform
size, but smaller, and partially coloured, and the rest are much
smaller, colourless, and varying in minuteness. In Plagiostomes
the ova are fewer in number than in the c roe-fish.' From four
to fourteen ova, for example, may be developed at one season in
the Torpedo ( T. marmoratct)^ whilst in the Herring
25,000 ova, in the Lump-fish 155,000 ova, in the
Holibut, 3,500,000 ova, have been estimated to fill
the enlarged ovarian sacs. In a Lump-fish, the
total weight of which was 9 Ibs. 8 ounces, or 66,500
grains, the ovaries weighed 3 Ibs. 3 ounces, or 22,300
grains : thus they were to the body as 1 to 3. Each
ovum weighed one-seventh of a grain.2

In all Fishes the ova are formed in chambers of the ovary,
called ( ovisacs.'3 In Osseous Fishes the ovisac consists of a
delicate membranous hollow sphere, fig. 415, «, lined by
epithelial nucleate cells, and surrounded by a thin layer of the
proper tissue, or f stroma,' b, of the ovary ; which, as it protrudes
with the growth of the ovum into the ovarian cavity, carries
before it a covering of the delicate mucous membrane lining

~ o

that cavity. This tunic is not present in Cyclostomes and Pla-
giostomes. The first-formed and essential part of the ovum
is the germ-cell, or f germinal vesicle,' c, which, in Osseous
Fishes, shows several nuclei, macula?, or ( germ-spots,' d, but in
Plagiostomes only a single nucleus. Around the germ-cell there
accumulates a collection of minute yolk-corpuscles and albuminous
granules, e, with oil-like globules,/, and in some species (Carp)
fiat angular corpuscles are added : all are suspended in a clear
gelatinous yolk-fluid, and are ultimately circumscribed by a delicate
yolk-membrane, g, devoid of visible structure. The increase of
the ova is due chiefly to the accumulation of the yolk, and its
colour to that which the oil-globules acquire as the ova approach
maturity. Finally is formed the external tunic, or ' ectosac.'4 At

1 CXXXII.

2 cccvin. p. 49. The periodical, but rapid and enormous increase of the hard and
soft roes in osseous fishes admits of no rigid cinctures, no unyielding bony hoops
around the abdominal cavity, such as would have resulted from a conversion of the
pleurapophyses, by their junction with hsemapophyses and a sternum, into * true ribs.'
We see, therefore, in the fecundity of fishes — in this compensation for their limited
intelligence and numerous foes— the physiological condition of their free or 'floating'
ribs. 3 xx. iv. 1838, p. 131.

4 As the homology of this tunic is not clearly dcterminable either with the vitellinc
membrane of the ovum of the Bird, or with the chorion of that of the Mammal, it is
indicated by the above term in the description of the ovum of the Osseous Fish.

VOL. I. Q Q

594 ANATOMY OF VERTEBRATES.

tins period the ova in Osseous Fishes escape into the cavity of
the ovarium, and the ectosac then receives its villi, or appendages
for adhesion, in the Fishes possessing them. The ovisac remains
behind, and coalesces with the stroma of the ovigerous layer, to
form, according to Barry, a f vesicle analogous to the Graaffian

O */ -1 O

vesicle of Mammals ; ' l but the evacuated ovisacs collapse and
speedily disappear, after the discharge of the ova, in the shrunken
ovarium of Dermopteri and in the collapsed ovarian bag of Osseous
Fishes : they are longer recognisable in the more compact and
solid ovaries of the Plagiostomes.

The earlier stages of the developement of the ovum within the
ovisac are illustrated in figs. 1 A-D (pp. 1 and 2), from Hansom's
observations on the Stickleback (Gasterosteus aculeatus). In 1 A
the ovisac, c, has a diameter of T^-^ inch : the germinal vesicle, d,
appears as a gelatinous spheroid, with few 'maculaa' and a scarcely
definite wall : a slightly turbid fluid, #, fills the space between
the vesicle and the ovisac, from the inner surface of which a few
delicate epithelial cells, b, project. In B, with a diameter of
-rri-Q- inch, the macula? have increased in number, and the germinal
vesicle in size : fine yolk-granules have begun to aggregate near
the periphery, but there is no vitelline membrane : on the exterior
of the ovisac are the nuclei of flattened cells. In c, with a
diameter of T^Q- inch, the macula? have become more numerous
and distinct : the yolk-granules more abundant and opake : the
yolk-mass is now more circumscribed, and a clear space intervenes
between it and the ovisac. In D, with a diameter of -~o inch,
the germinal vesicle has more macula?, but has ceased to grow :
the yolk-granules are much increased in number, and a clear
peripheral space indicates the beginning of the formation of the
external membrane, ch.

The ( roe,' or ova, of Osseous Fishes, being usually shed in or
on the sediment of shores, are subject to the action of the flow of
streams or break of waves upon their sandy or gravelly bed, and
these pellucid and seemingly delicate vesicular spherules are
accordingly provided with a very elastic and resisting outer coat,
constructed 011 a principle analogous to that by which a tooth
sustains and exerts its pressure. This coat is composed of a
close-set series of hollow columns, set perpendicularly to the sur-
face, fig. 416, h : the part of the outer surface turned into view, at
c, shows the pores, or ' lumina,' of the tubules. The yolk, «, with
its granules, granular and nucleated corpuscles, and oil-globules,
no w shows its delicate structureless membrane, which is partly

1 cix 1st Series, p. 814.

OVULATION IN OSSEOUS FISHES AND BATRACHIANS. 505

416

detached from the ectosac, as it becomes after impregnation.
Against the ectosac, h, are closely applied the flattened epithelial
cells, d, which line the ovisac and probably contribute to the
growth or thickening of the external membrane. In the Perch
the ectosaccal tubes have a
slightly spiral course., and
the peripheral end of each
is set in a small hexagonal
prism : this outer stratum
serves to connect the ex-
cluded ova in groups. The
ova of the Stickleback have
villi developed for this pur-
pose from one part of the
exterior, figs. 417 and 421.

The structure of the outer
coat of the ova of Fishes re-
lates not only to the accidents
of appulse, but to the act of
impregnation, which takes
place after exclusion and
exposure. Besides the pores,
or tubular orifices, of the

ectosac, there has been observed, in the ova of GasterosteusJ
Salmo,2 Blenniusf Esox, Triglaf a foramen homologous with the
micropyle of the invertebrate ovum. Dr. Ransom, its discoverer,
has observed the passage of the spermatozoa through this foramen
into the ovum. Fig. 417, A, gives a magnified view of a portion
of the surface of a mature ovarian ovum of the Stickleback,
showing the funnel-shaped depression leading to the aperture of
the micropyle, with a few of the flask-shaped villi of the outer
membrane : B represents diagrammatically a section of the ectosac
and funnel of the micropyle : C is a portion of the membrane
at the apex of the funnel, with the aperture of the micropyle
pressed flat, of the Trout's egg, magnified 500 diameters : D is
a similar portion, magnified 1,000 diameters, showing the f lumen'
of the ectosaccal tubules, and the hexagonal division of the spaces
between them.5

In the Batrachia (Frog) a greater proportion of the ovarian ova
show different states of developement, previous to sexual pairing,
than in Osseous Fishes, although all those destined for iinpreg-

1 CLXXVI. - cccviii. and cccix. p. (101). 3 cxxx. pt. li. p. 4.

4 cccx p. 376, fig. 6. 5 cccviii. p. (101),

Part of the ovarian ovum of the Salmon, cccviii.

Q Q 2

596

ANATOMY OF VERTEBRATES.

nation at the same season are simultaneously ripened. As soon
as the germ-cell is recognisable, it is contained in a delicate ovisac,
and speedily exhibits several nuclei, or macula, fig. 418, B, cj\ it is

417

413

»•****•••»?•«••• - - .
»«•«*•*» . V, ,.*•••*
«•••• •**•»»».,»*•»'

O 9 0 ® q> e
0 • O o

d Q O » •

le of the ovum in Osseous Pish, cccvm. Batracliian ovum in the ovisac,

inch diam. cccvm.

surrounded by a clear albuminous yolk fluid, vp, which gradually
becomes opake, and about which the yolk-granules accumulate,
among which is the opake or dark aggregate peculiar to Batrachia,
and called the yolk-nucleus, ib. vn. This body disappears as the
yolk-mass approaches its mature bulk, and acquires the larger
quadrilateral or quadrangular particles. -The smooth and well-

OVULATION IN CARTILAGINOUS FISHES. 597

defined periphery of the yolk-mass is in close contact with the
layer of nucleated cells lining the ovisac, ib. s : and at a later
stage of developement, when the pigment-cells have been applied
to the surface of the germinal portion of the yolk, a distinct
external membrane is present. In the month of February the
maculae of the germ-cell multiply and form aggregates, with
envelopes, representing cells with a granular nucleus, which
nucleus finally disappears, and the so-rendered clear cells escape
by solution of the coat of the germ-cell into the surrounding
yolk-substance, this rupture or disappearance of the germ-cell
preceding, as in some Osseous Fishes, the reception of the matter
of the spermatozoon. The ripe ovarian ovum of the Frog (Rana
temporarici) is from TV to TV inch diameter. The outer membrane
(ectosac) of the ovum, after quitting the ovarium, is surrounded
and defended, before exclusion, by the gelatinous secretion of the
oviduct : it does not show the structure of that of the Fish. If
a fmicropyle' exist prior to impregnation, as Prevost and Dumas
record,1 it has escaped the express research of some later observers.2
The full-sized ovum of the oviduct retains its spherical form, fig.
420, A. In the Newts the ectosac of the ovum is elliptical,
fig. 420, B, and a clear albuminous fluid intervenes between it
and the yolk. In Triton cristatus the yolk is bright yellow : in
Lissotriton punctatus it is ash-coloured : in the Land-Salamander
it is orange. In tailless Batrachia the colour is limited to the
surface of the yolk, which is grey beneath : in the Toad the
pigment is almost black, in the Frog it is dark brown : in both
it covers all the surface, save one small round spot; in Alytes
obstetricans it covers half the yolk : it stains vertically from -J-
to j1^ of the diameter of the yolk : in all it defines the germinal
part of the yolk.

§ 113. Ovulation in Cartilaginous Fishes and Scaled Reptiles.—
If the generative organs and products were exclusively to govern
the classification of Animals, the Chimaeroids and Plao-iostomes

D

would be separated from other Anallantoids, and be combined
with scaled Reptiles, with which they agree in the type and
grade of their generative organs, and in the more important
characters of the structure of the ovum. Its essential con-
stituent, the germ-cell, has a single nucleus, and it becomes
surrounded, while in the circumscribed ovary, with a large mass
of vitelline substance, consisting in great part of oily and
albuminous matter, inclosed in delicate vesicles. Besides these,
there is a small proportion of the yolk, consisting of minute
1 In the centre of the brown hemisphere, cccxi. p. 104. 2 cccxiu.

598

ANATOMY OF VERTEBRATES.

granules and granular corpuscles, more immediately surrounding
the germ-cell ; which, moving from the centre to the periphery
of the yolk, there forms the ( cicatricula,' the exclusive seat of
subsequent developement. In the cartilaginous Fishes the im-
pregnating influence is received before the ovum quits the ovarium,

or shortly after. In the
egg's passage through the
oviduct the yolk is sur-
rounded by fluid albumen,
and finally by a case of
the denser albuminous
secretion of the nida-
mental gland. The form
of the egg when thus
invested is remarkable,
and different in different

genera.

D

External form of ova of Oviparous Cartilaginous Fishes.

cccvin.

In the Skate, fig. 419,
A, it is an oblong quad-
rangular flattened case,
with the angles produced
forward and backward,
like those of a butcher's
tray. In the Spotted
Dog-fish, ib. B, the ova

O 3

are also quadrangular,
but longer, and the angles

o J o

are extended into filamen-
tary tendrils, which attach themselves to floating bodies, and thus
keep the ovum near the surface, where the influence of solar heat
and light is greatest. In Notidanus, with a similarly shaped cirri-
gerous egg, the anterior and posterior surfaces are crossed by
about twenty parallel transverse ridges.1 In Cestracion the egg
is pyriform, with a broad ridge, or plate, wound edge-wise round
it in five spiral volutions. The eggs of Callorhynchus resemble a
broad-leaved fucus, in the form of a long depressed ellipse, with
a plicated and fringed margin.2 The ovum of the Myxine
glutinosa, fig. 419. c, is a long ellipse, terminated at each end by
a tassel of slender tubular filaments, twenty-five to thirty in
number, expanding at their free end (opposite D) into a funnel-
shaped process.3

1 xx. vol. v. p. 70, preps, nos. 3245, 3246.

2 xx. vol. v. p. 69, preps, nos. 3235, A. and r..

3 cccvm. p. 51.

FECUNDATION IN FISHES.

589

420

The structure and formation of the ovum in scaled and scuted
Heptiles are essentially the same as in the cartilaginous Fishes.
The germ-cell, with a single nucleus, is first formed in a delicate
ovisac imbedded in the stroma of a solid ovarium. A yolk of
large size is added, of which
the greater part consists of
large non-nucleated oil-vesi-
cles, and the smaller part
of the vitelliiie granules and
cells with a granulated nu-
cleus ; these originally sur-
round the germ-cell, then
indicate its tract from the
centre to the periphery of
the yolk, and form with the
matter of the germ-cell the
cicatricula, or blastoderm.
This occupies a much smaller
extent of the surface of the
yolk than in the small-

Extcrnal forms of different eggs of Reptiles and Birds.

CCCVIII.

yolked eggs of Batrachians
and Osseous Fishes, and
segmentation is limited

thereto, the rest of the yolk being nutritive. The ovum, con-
sisting of the above parts, inclosed in a vitelliiie membrane, quits
the ovary and is received into the oviduct : here it acquires a
certain proportion of soft albumen, upon which is condensed a
thin tough layer, called ' chorion.' In the ovo-viviparous Snakes
( Viper CL) and Lizards ( Zootocci) this membrane is thin : in the
oviparous species it acquires a crust of calcareous matter before
exclusion. This crust is very thin and scanty in most Serpents
and Lizards, but is thicker in Chelonia and Crocodilia, forming a
shell. The egg is spherical in some Chelonia, spheroidal in others,
fig. 420, F, elliptical in Emys, fig. 399 : in the Crocodiles the egg
is a long ellipse, fig. 420, E. In no reptile does it show the
oval form which prevails in Birds, ib. C and D.

§ 114. Fecundation in Fishes.- -Certain changes and peculiar
phenomena attend the increase of size of the soft and hard roes
during these primary processes of generation. The colours of
the fish become more marked and brilliant: the different sexes
are often distinguished by peculiar tints, as the male Stickleback
by his bright red throat, for example. The cutaneous crest on
the head is developed in Scdarias and many other Blemiioids, e.g.,

GOO ANATOMY OF VERTEBIIATES.

in tlic male viviparous Blcnny, which, by cvcrsion of the
terminations of the sperm-canals, impregnates internally. The
claspers in the male Plagiostomes then acquire their full deve-
lopement and force : the basal glands in those of the Rays
enlarge. In Osseous Fishes the whole abdomen swells, and the
viscera are displaced by the prodigious bulk of the germinal and
seminal matter.

As the period of ( fecundation ' approaches, the female osseous
fish seeks a favourable situation for depositing her spawn, usually
in shoal water, where it can be most influenced by solar warmth
and light. The marine Herring, Mackerel, and Pilchard approach
the shore in shoals : the fluviatile Salmon quits the estuary to
ascend the river, overcoming, with astonishing perseverance and
force, the rapids or other mechanical difficulties ! that impede its
migration to the shallow sources, whither the sexual instinct

O '

impels it as the fit place for oviposition. The female fish is
closely pursued by the male, sometimes by two : in the Capelin
(Mallotus) these swim on each side of her, aiding by their
pressure in the expulsion of the spawn, and at the same time
impregnating it by diffusing over it the fluid of the milt : thus
absorbed in the sexual passion, they have been seen, on the
shores of Newfoundland, to rush on land in their spasmodic
course over the shallows, which they strew with the fecundated
ova. In some genera violent combats take place between the males.
Mr. Shaw,2 a close observer of the habits and developement of
the Salmon, states: — e On January 10, 1836, I observed a female
Salmon of about 16 Ibs., and two males of at least 25 Ibs., engaged
in depositing their spawn. The two males kept up an incessant
conflict during the Avhole day for possession of the female, and,
in the course of their struggles, frequently drove each other
almost ashore, and were repeatedly on the surface, displaying
their dorsal fins and lashing the water with their tails. The
female throws herself at intervals of a few minutes upon her side,
and, while in that position, by the rapid action of her tail, she
digs a receptacle for her ova, a portion of which she deposits,
and, again turning upon her side, she covers it up by the renewed
action of the tail, thus alternately digging, depositing, and covering
the ova, until the process is completed by the laying of the whole
mass, an operation which generally occupies three or four days.'

In the ovo-viviparous Osseous Fishes the well-developed cloacal
papilla, in which the sperm-ducts terminate, doubtless serves to

1 Save those erected by stupid cupidity to effectually bar the salmon's progress.

2 cxxiv. p. 551.

FECUNDATION IN FISHES.

(J01

421

ensure intromission. The superadcled claspers in the male Plagio-
stomes lend more effectual aid in the act of internal impregnation,
for in those species that are oviparous the ova are impregnated and
covered by a nidamental coat, or ' shell,' prior to exclusion.

In Osseous Fishes, where exclusion usually precedes impregna-
tion, the first change observed in the
ovum after entering the water is its im-
bibition, causing a separation of the outer
tunic from that of the yolk, fig. 421, A.
Dr. Kansom connects the phenomenon
with the passage of the spermatozoa
through the niicropyle, which he ob-
served in his experiments on the ova
of the Stickleback.1 In these ova,
about three minutes after impregnation,
the funnel of the micropyle, which had
descended into a depression on the
upper surface of the germinal part, fig.
421, B, began to be withdrawn by the
recession of the external membrane from
the surface of the yolk and the forma-
tion of the intervening clear space.
About ten minutes after impregnation
the clear respiratory space is more
marked : the germinal layer, with a few
large oil-globules, is distinguishable by
its opacity from the clearer part of
the yolk, ib. A. In the Perch it presents a greyish, in the Pike
a yellowish, tint. The germinal vesicle, which had previously
become filled and obscured by granules and granular corpuscles,
breaks up to form, or contribute to form, the germinal layer,
which now becomes more circumscribed and distinct : the process
of segmentation, which follows that of impregnation, is limited
to the germinal portion of the yolk, with which it is co-extensive.
In the Perch the ova assume a greenish tint shortly after impreg-
nation. There is reason to suppose that impregnation of the
Qo-crs of both Sharks and Rays takes place in the ovarium or the

OO " -1

contiguous part of the oviduct, for they become enveloped in the
dense albuminous secretion of the nidamental glands after having
passed that part, which covering would prevent the subsequent
influence of the spermatozoa.

§ 115. Developement of Fishes. — The germinal layer consists of

1 Cited in cccvm. p. 98.

Ovum of the Gasterosteus at the time
of impregnation.

G32 ANATOMY OF VERTEBRATES.

a minutely granular matter, with clear corpuscles, vitelline cells,
and oil-particles : it projects from the surface of the yolk, fig.
422, a, and becomes transparent : the vitelline and oil-globules,
aggregating at its base, buoy it up. The formation of two
hyaline centres is followed by the cleavage of the germinal layer
into two equal parts, ib. b, and these are next cleft at right angles
into four, ib. c. In the Tench this occurred about half an hour
after the rising of the germ-layer. Each of the four divisions
undergoes subdivision, but irregularly, ib. d: further sub-
division gives the surface a mulberry character, ib. £, and

finally the parts are broken up to
such a decree of minuteness that

O

the surface is ao-ain made smooth.

~

The hyaline principle, which is the
centre and cause of these successive
divisions, is thus diffused through,
or assimilated by, the whole germinal

First steps in the clevclopement of a Teuch. lay 61', which liaS thereby beCOme

the ' germ-mass.' It now subsides

to the form of a circular disc, separated by a layer of oil-globules
from the yolk. The process occupies about three days in the
Salmon, and from fifteen to twenty hours in the Pike : 1 before it
is completed in the latter fish the yolk rotates within the ectosac.2

A cavity is formed in the centre of the germ-mass, which, as
the mass subsides and extends over the yolk, is obliterated by the
contact of the outer and inner layers. It clothes half the yolk
by about the end of the third day, and when it covers two-thirds
or more, the rotation ceases. The margin of the germ-mass
encompassing the uninclosed part of the yolk is tumid. No
rotation takes place in the ovum of the Perch,3 and the germ-
mass incloses the whole vitellus, as in the Cyprinoids.

The peripheral layer in the Pike begins to rise from the tumid
margin of the germ-mass, as from a base, and extends, contracting,
towards the opposite pole : this tract of germ-substance is the f em-
bryonal ' or ' primitive trace.' It next sinks in along the median line,
forming a furrow, which stops short of the two ends of the trace :
that end opposite the point from which the germ began, swells into
the head, and the median furrow expands upon it ; the cephalic
borders are next united by a thin layer of epithelial cells above the
furrow, converting it into a cavity or ventricle, and the myelonal
furrow is similarly covered by a layer, uniting the lateral columns.
The embryonal trace becomes longer, narrower, and bends round
1 cccxix. p. 486. - CXXXT. 3 Ib. p. 512.

DEVELOPEMENT OF FISHES.

603

423

half the vitellus, fig. 422, f. A layer of epithelial cells forms a
net-work over the whole dorsal (upper) surface of the embryo.
In the germ-mass broadening from the primitive trace oblique
striaB appear, indicating its division into segments : these begin-
nings of aponeurotic septa probably accompany and support ner-
vous productions from the myelonal columns.

Two transverse constrictions begin to divide the cephalic
enlargement into three lobes, the second and third of which
expand into vesicles : an accumulation of cells at the sides of the
middle expansion appears to add greatly to its breadth, but forms
the basis of the eyes. A similar accumulation of darkish granular
matter on each side of the third enlargement lays the foundation
of the acoustic vesicles.

The differentiation and confluence of the cell-constituents of
the primitive trace have previously led to the formation of a
pair of albuminous chords along the sides of the median furrow,
forming the myelon proper ; the cells exterior* to and above them
are converted into muscle and fibrous septa, whilst beneath the
columns is the jelly-filled cylinder, with a transversely striate
sheath, pointed at both ends, forming the ( iiotochord,' fig. 423, ch :
its anterior point passes a little
in advance of the acoustic vesi-
cles, ib. f. Beneath the noto-
chord and surrounding blastema
is stretched the vegetative or
mucous layer of cells, in contact
with the yolk. Both head and
tail of the now cylindrical em-
bryo are liberated from the sur-
face of the yolk. A fold of
blastema, reflected from the under part of the head, sinks, like a
pouch, ib. /, into the yolk, and soon includes the rudiment of the
heart, like a bent cord, ib. k, which begins to oscillate about the
seventh day. From the mid-line of the inferior surface of the
embryo, or its mucous layer, two longitudinal plates descend,
diverging into the yolk-substance, and form the primitive intes-
tinal groove.

The ophthalmic vesicle, ib. g, elongates and curves outward, until
the two ends almost come into contact : between those ends and
beneath the delicate tegumentary layer connecting them the
crystalline lens, ib. b, is formed. About the same time, the
otolites appear in the acoustic vesicles, ib./*, and these have now
acquired a cartilaginous case. The cerebral lobes, r, begin to

Head of embryo Pike, cccxix.

G04 ANATOMY OF VERTEBRATES.

be formed by small folds, rising laterally, and overlapping the
fore-part of the second enlargement, ib. O, which has expanded to
greater breadth. The olfactory cavities appear as small cutaneous
depressions or follicles, ib. r.

The two myelonal columns, expanding between the ear-sacs,
and receding so as to show the notochord beneath, bend npward
and inward, and unite, to be continued into the back part of
the optic lobes, thus commencing the cerebellar bridge, ib. C,
across the epencephalic ventricle. The encephalic vacuities have
begun to be filled by the granular basis of the cerebral fibre or
substance. The intestinal groove begins to be converted into a
canal at its two ends, which are closed : beneath the anterior end,
and behind the heart, progressively accumulates the cellular basis
of the liver. The free caudal end of the embryo grows rapidly ;
muscular heavings of the body occur before the heart beats, and
pulsation begins before the cavity is visible in the cell-mass.
The heart appears first as a cylinder of cells, changing in its
movements from a straight to a bent fissure, fig. 423, h, and pro-
pelling only colourless plasma ; a canal is next seen, along which
the blood-particles traverse the cylinder, from the yolk below to
the head above : these blood-particles are spherical or polyhedral,
colourless and homogeneous, and are more minute than the
germinal cells. The cardiac cylinder is next divided by a con-
striction into an auricular and a ventricular compartment. The
blood, in which the discs soon acquire increased size and a pale
red colour,1 is propelled from the ventricle by channels encom-
passing the fore part of the alimentary canal into a dorsal trunk,
which, after a short course, bends down, and returns as a vein to
the vitellus, over which the blood at first courses in undeterminate
streams, but which converge to enter the auricular division of
the heart. As the abdominal cavity, intestine, and body elongate,
a succession of such vertical loops is formed, receding from the
first, with corresponding elongation of the aorta and postcaval, or
entero-vitelline, vein. The aorta soon sends off pairs of trans-
verse loops, corresponding with the vertebral segments, the
returning channels of which open into or constitute the cardinal
vein. The embryo now encompasses the yolk, as in fig. 422, g.

In the eye the crystalline, developed from the epithelial layer
uniting the two ends of the bent ophthalmic vesicles, sinks deeper

1 Lerebouillet observed in embryo-fishes raised in tanks from artificial impregna-
tion, that the blood-particles were later in formation, and more scanty than in the
embryos derived from the free streams : a remark worthy the attention of the breeder
of fish, cccxix. 580.

PEVELOPEMENT OF FISHES. G05

as those ends approximate each other. The choroid appears in the
form of an inner cylinder, applied to the sunk back-part of the
lens, and its extremities, approximating and uniting, produce the
choroidal fissure : the eye is now the most conspicuous part of
the embryo, especially in the ovum of the Salmoriida, and is a
useful sign to the pisciculturist of the impregnation and vitality
of the egg.

The hinder ca^cal part of the intestine rapidly elongates, from
behind forward, the yolk advancing in position. The anterior
caecum also elongates from before backward : the open part of
the intestine, which communicates with the vitelline sac, becomes
in the same measure constricted.

When the two divisions of the heart are bent upon one another,
the liver shows several small creca, which rapidly multiply, and
become opake : it is situated, fig. 424, /, behind the heart and
above the yolk, now becoming reduced to a globule of oil, which
is long retained in the young Perch.

The primordial kidneys appear as two parallel rows of rounded
cells, above the liver, their ducts uniting to form a tube, which
runs above the intestine, and dilates above the hinder crecal end
of the gut.

The pectoral fins begin to bud forth : the protocercal mem-
branous fin-fold commences at the middle of the back, borders
the tail, and returns along the belly as far as the vitellus. Large
pigment-cells are spread over the yolk-sac, which become stel-
late. Muscular fibres appear in the myocommata as transparent
cylinders, without the transverse stria3 : they move the tail
vigorously, and cause the embryo and its yolk-sac, in the Perch,
to rotate in the egg. This has increased in size by imbibition
of water, and its external coat is thinned by stretching ; it now
gives way, and the embryo is extricated, about the tenth day in
the Pike and the twelfth day in the Perch. The size and shape of
the yolk-sac, fig. 424, c, vary in different kinds of Osseous Fishes.1
The vitelline vascular network, ib. d, is the first respiratory organ
of the fish : its divisions carry the blood-discs only in single files.
The outer tunic covering the vascular one permits the interchange
of gases between the blood and the water outside. This respired
or arterial blood is mixed with the venous blood which is returned
to the heart by the cardinal veins, and is distributed, so mixed,
by the arteries. The vitelline capillaries gradually exchange a
reticulate for a parallel longitudinal course, with diminution of

1 In artificial hatching, young trout, and especially char, show a difficulty in extri-
cating the yolk-sac, and many perish from inability to liberate themselves.

GOG

ANATOMY OF VERTEBRATES.

numbers and increase of size : and as the fitness of the vascular
surface for respiration decreases, the developcment of the gills
progresses. The branchial arches appear, three in quick succes-
sion, from behind forward, and branchial tubercles bud from them
in like order. The mouth and the branchial slits being now
opened, the arches move rythmically, so as to produce branchial
currents : the blood is yellowish, and the discs begin to show the
flat oval shape. As the vitellicle decreases, its circulation is
changed, or merged into the portal hepatic system ; and now that
through the branchial buds begins. The change of the vitelline
for the branchial circulation relates, in a general way, to that
from the confined to the free state of the young fish : but no
such alterations of the circulating or breathing systems attend
the escape of the fish from the egg as mark extrication in the
Reptile and Bird, or birth in the Mammal. Vitelline respiration,
carried on in ovo by means of the imbibed water between the outer
and vitelline tunics, continues to operate for a longer or shorter
period after the little fish is free, according to the species, and also
according to the individual constitution in the same species.

Each branchial bud is at first a solid cell-mass, and is excavated
to receive the blood with blood-discs in single file : secondary
tubercles bud forth at right angles to the primary ones, through
which similar blood currents flow : the primary buds become the
stems of the leaflets into which the secondary ones are developed,
and the cartilaginous axis of the arch and stems next appears.
The pseudo-branchia also shows itself behind the eye, in the form
of flattened elongated folds, through which the blood courses at
first in a few vascular loops. In the Andbas, and probably other
Labyrinthibranchs, the
epibraiichial reservoir,
fio;. 325, retains a com-

o •*

parative degree of sim-
plicity until the fish is
full-grown.

The intestinal canal,
after the formation of the
mouth and vent, retains
its uniform diameter, ex-
cept where it is partly
surrounded by a mass of
the cells, in which the

liver, fig. 424, /, is developed : the gall-bladder appears to be a cajcal
production from the intestine, independently of the liver. Opposite

424

Fore Part of eml>ryo Osseous Fish.

DEVELOPEMENT OF FISHES . 607

the liver a tubercle of cells buds out, which elongates,, enlarges,
and then acquires a cavity : this is the beginning of the air-
bladder, ib. s. Many Fishes retain the tubular connection with
the alimentary canal, and those which ultimately lose the f ductus
pneumaticus ' usually retain for a longer or shorter period that
evidence of the place and mode of origin of the air-bladder.
The posterior compartment of the air-bladder is first developed
in the Cyprinoids, which accounts for the connection of the
air-duct with that part : the whole posterior compartment disap-
pears with the duct in the Loach. In the Herring the primitive
place of its connection with the alimentary canal is retained.

The ureter, </, developed from the intestine before the embryo
quits the ovum, communicates with the extremities of the trans-
verse parallel tubuli, p, formed by confluence of primitive cells in
the renal blastema. The cardinal veins traverse or groove the
renal organs, as they do the AYolffian bodies in the embryos of
higher Vertebrates ; and this primitive relation of the vascular to
the renal system is not changed in Fishes by the substitution of
true kidneys for the primordial renal organs. In many Fishes a
ca3cal process is developed from the fore, or ventral, surface of
the termination of the intestine, and extends forward, as a
bladder : its growth is arrested at various stages in different
species, and it is termed f urinary bladder,' but it is the homologue
or beginning of the allantois.

The intestinal wall is completed, and the fissure behind the
liver closed, by the time the yolk is consumed. The vent opens,
in the Pike, on the fourth day after extrication : in the Perch
coloured particles added to the water were seen to traverse the
intestine, and escape ' per anum ' on the sixth day.1 Previously
the mucous walls of the gut are in contact, although the peri-
staltic movements are active. About the eighth day the presence
of bile is indicated by the colour of the gall-bladder and ducts. The
stomach expands, and divides the oesophagus from the intestine.

After extrication the eye loses the choroidal fissure : the iris ac-
quires the silvery pigment. The ear-sacs assume a triangular form :
the two otolites grow unequally by additional calcareous layers.

The primary enlargements of the encephalon are connected,
respectively, with the acoustic, optic, and olfactory nerves : the
anterior one, fig. 424, r, becomes divided into prosencephalon and
rhiuencephalon ; the second, o, rapidly gains superior bulk in
connection with the large eyeballs, and its pineal and pituitary
appendages appear as vascular membranous canals. The cere-

1 CCCxix. p. 483.

G08 ANATOMY OF VERTEBRATES.

belltim is the last part which is formed by reflection upon the
upper and fore part of the epencephalon, A.

The mode of developement of the cartilaginous cranium is
described at pp. 71-74. In the Perch a layer of cartilage-cells
beneath the fore-part of the head is continued down on each side
into the front border of the inferior transverse mouth : a second
cartilaginous arch extends from the side of the cranium, behind
the eyes, and supports the hinder and more prominent border of
the mouth : a delicate cartilaginous filament from each side of the
occiput seeks an attachment with the basis of the rapidly vibrating
pectoral fin, and proceeds to curve beneath the cardiac chamber.
Between this basis of the scapular arch and the mandibular arch
are discernible several smaller arches, beneath the large ear-sacs,
of which three are conspicuous as f branchial arches,' but the
foremost acquires the most decided gristly structure, and is
proximally attached to the origins of the mandibular arch : it
becomes the hyoid arch. The first and second inferior or haemal
arches, called ' maxillary ' and e mandibular,' rotate forward upon
their piers, or points of attachment, and from being vertical
become more and more oblique, until the opening of the mouth is
brought to the fore-part of the head, and becomes terminal in
position : the third, or hyoid, arch, in a minor degree, takes the
same forward inclination : the arches between this and the
scapular one are monopolised by the branchial organs, which are
transitory or undeveloped in the higher Haematocrya. Ossifica-
tion in the proto-cranial cartilage begins in the four pairs of
neurapophyses, answering to the four hremal arches below, and to
the four primary divisions of the encephalon : the four vertebral
segments composing the head are as instructively illustrated by
the developement of the skull as by that of the brain.

The scales are formed late in all Osseous Fishes : their integu-
ments remain smooth and lubricous, as in the Dermopteri, some
time after the disappearance of the vitellus.

After the formation of the embryonal, continuous fin-fold
blastema accumulates in its dorsal, anal, and caudal regions ;
and, as the rays are here formed, the intervening membrane
begins to be absorbed. The fin-rays (dermo-neurals and -ha3inals)
commence near the free border, and elongate by approaching the
neural spines : they there meet the inter-neurals and -hremals,
which grow in the opposite direction. During the formation of
the caudal rays, the end of the notochord, in the Pike, Perch
and Salmon, bends upward, or c neurad : ' the heterocercal type
succeeds the protocercal one, and is followed by the resumption
of symmetry under the more advanced e homocercal ' condition.

DEVELOPEMENT OF FISHES.

609

415

This, as a rule,, is the form and structure acquired by the tail in
existing Teleostomous Fishes: but the 'heteroeercal' modification
does not intervene between the proto- and homo-cereal ones in
the Gadidce.

The pectoral fins are developed usually before extrication, and
are often of large relative size : in this respect, as well as in the
inferior position of the mouth, in the unsymmetrical form of the
tail, in the gristly skeleton, and uncovered gill-slits, the embryo
Salmon, Pike, Perch, &c., manifest transitory characters which
are permanent in Sharks.

The singular productions of the rostrum in most Plagiostomes,
like the elongation of the jaws in osseous species, are later
phenomena of developement. It is interesting to find the broad,
depressed, obtuse embryonic form of head common to many of the
Fishes of the old red-sandstone. M. Agassiz thus accounts for the
extreme rarity of the Ichthyolites of this formation presenting a
profile view of the head : it lies in most cases upon the upper or
the under surface of the body.

All the Plagiostomes have the external as well as the internal
division of the vitellicle, fig. 425 ;
the peduncle of the external one
d, is longer, in some species con-
siderably so, than in Osseous
Fishes, and it is beset with villi
in Carcharias and Zyg&na.1
The tegumentary covering of the
outer yolk, ib. if9 is denser and
more opake in Plagiostomes :
the inner yolk, ib. e, is co-
vered only by the proper vitel-
liiie tunic, which is thin and
transparent : it communicates
with the short tract of small
intestine which intervenes be-
tween the pylorus and the val-
vular straight gut, h : it receives
the external yolk, d' ', as this is
progressively squeezed into the abdomen by the contraction
and interstitial absorption of its tunics, cr : and, as no part of the
foetal abdominal appendage is cast off, nor the chord divided, there
is no cicatrix — no umbilicus. The arterial vessels of the yolk are
derived, not from the mesenteric vein as in Osseous Fishes, but

Embryo Cartilaginous fish, Scyllium.

VOL. I.

1 cxxin. tf. iii.
R R

CIO

ANATOMY OF VERTEBRATES.

426

from ramifications of a branch of the mesenteric artery, and the
blood is returned to the mesenteric vein. Hunter's preparations
of the embryo Carcharias (No. 1061), Sci/llium (No. 3250)5
Spinax (No. 3255), and Alopias (No. 3261) *, demonstrate another
foetal peculiarity which later researches 2 have shown to be pro-
bably common to all Plagiostomes, viz. the external fringe of
filaments developed from the branchial surfaces, b : a tuft extends
out of each aperture, and even from the spiracula, a, in the genera
with those accessory openings. Each filament contains a single ca-
pillary loop : 3 they disappear early, being removed by absorption.
The last remnants may be seen in the preparation of the foetal Saw-
fish (Pristis9 No. 3263),4 which is eight inches in length, including
the saw, and has the duct of the external vitellicle attached. In

the oviparous Sharks, the branchial filaments
react on the streams of water admitted into the
egg by the apertures, fig. 426, c. In the ovo-
viviparous Sharks the size and position of the
cloacal apertures of the uteri would seem adapted
to allow free ingress of sea-water; so that,
whilst the vitellicle, ib. b, administers to the nutri-
ment of the embryo, a, the external branchiae may
perform the respiratory function. In the smooth
Emissole (Mustelus levis\ vascular cotyledons are
developed from the vitelline (omphalo-mesen-
teric) capillaries, which are firmly connected to
the uterine cotyledons ; so that here the vitel-
licle, like a true placenta, may perform both the
nutrient and respiratory functions : the external
branchiaa disappear some time before the exclusion of the embryo
and the absorption of the yolk. In the Lepidosiren anncctcns 5
three small external branchial filaments project from the single
opercular aperture on each side, and are long retained.

Some of the Plagiostomous Fishes are oviparous, but not as in
the majority of Osseous Fishes ; a remarkable transposition in the
times of the processes of fecundation and exclusion marks the
distinction. In the oviparous Osseous Fishes the ova are first
excluded, then impregnated : in the oviparous Plagiostomes im-
pregnation is internal, and precedes oviposition. The eggs are
much fewer in number, but their impregnation is more certain
than in the scattered indiscriminate act of spawning of the
Osseous Fishes, where the countless numbers of the ova seem to

1 xx. vols. ii. and v.

2 Rudolphi, LXXVI. ; Rathkc, cxi. ; Leuckart, cxxv. ; J. Davy, LXXXII.

3

Ecrg raid Embryo ; Scyl-
One fourth uat.
size.

A. Thompson, cxi.

5 Jardine, cxxxv.; Peters,_cxxxvi.

GKOWTH AND NESTS OF FISHES. 611

compensate for the chances that may intervene to prevent the
contact of the milt.

§ 116. Growth and Nests of Fishes. — When developement has
stamped the Fish with its specific characters, growth proceeds at
various rates and to different degrees, according to the species
— viz., from the size of the Stickleback to that of the Shark
of thirty-five feet long (Selache maxima). Carp, Pike, and some
other Fishes, which may live in ponds or lakes under circum-
stances favourable for continuous observation of the same in-
dividual, show that growth is not definitely arrested as an adult
character ; few Fishes, perhaps, can be called ( full-grown ' in
the sense in which the term is applied to warm-blooded Verte-
brates : but, after attaining the average size characteristic of the
species, individuals under favourable circumstances continue to
increase, though very slowly, in size. Growth is accompanied in
many species by changes of colour, in some by a greater propor-
tional size of the head, or by elongation or curvature of the mandi-
ble, or by increased length of a rostral prolongation — sword or
saw : other special weapons, as the dorsal spines of Cestracionts,
File-fish, and Dog-fish, and both dorsal and pectoral spines of Sheat-
fish, acquire length and hardness, or dentate borders, in the course
of growth. External sexual characters are assumed, as shown in
the form and structure of the ventral fins in some Osseous Fishes1,
in the growth of the f claspers ' of Plagiostomes, and of the mar-
supial folds or pouches of Lophobranchs. In the Dolphin ( Cory-
ph&na), the cranial crest and fore-part of the dorsal fin gain so
much proportional height that young individuals of even two
feet in length were referred by Cuvier to a distinct genus
(Lampugus)?

In a few instances the changes accompanying growth amount to
a metamorphosis. The edentulous state of the young Lamprey,
and the semicircular form of the upper lip, are exchanged for the
suctorial multidentate mouth, shown in fio-. 277. The external

o

branchial apertures enlarge, and the furrow in which they at first
open disappears. The perfect form of the Lamprey is not attained
until the fourth year. During half or two thirds of that time, the
growing Petromyzon presents a form which passes as that of a
distinct genus of Cyclostomes (Ammoccetes),3 The Leptocephali
are probably larva? of some larger known fish : they have never
been observed with roe or milt : the same may prove to be the
case with Branchiostoma.

' In almost all the Teleostomes the body of the young is more

1 cccxxxvin. 2 CLXXIV. ii. p. 405. 3 cccxxvn. p. 323.

R R 2

G12 ANATOMY OF VERTEBRATES.

slender than that of the mature fish, or the height of the body is
less in comparison with its length. The eye ceases to grow long
before the individual has attained its full size ; so that old fishes
have comparatively smaller eyes than young ones. The form of
Fishes is altered by changes in the shape of fins, by the develope-
inent or by the loss of spines belonging to the opercular apparatus
or to the fins ; as in the following examples.

f a. Some of the fin-rays are prolonged with age into long
filaments : species of A?ithias) Pagrus, Ephippus, Callionymus.

6 b. Some of the fin-rays are prolonged in young individuals,
but the filaments are worn off with age : Lophius, Echeneis,
Tracliynotus.

6 c. Cephalacantlius is merely the young of Dactylopterus ;
the pectoral fins are short in the young, and become with
age so long as to serve for an organ of flying in the adult
(Dactylopterus).

( d. In some species of Tliyr sites and Gempylus the ventral fin
is reduced to a very small spine, which in the young is very
long, nearly half as long as the head. Sometimes the young
has ventral fins, whilst they are entirely absent in the adult:
Stromateus.

6 e. The young of almost all the Caranyidce have the pra3Oper-
culum armed, like a Percoid : this bone is entirely smooth in the
mature fishes. The same in Ldbrus.

6f. Some fish have no visible, or but a rudimentary, spinous
dorsal fin ; this fin is very distinct in the young : Brama, Platax,
Stromateus.

6 g. Large prominences of the skin are developed, which are
absent in the young : Cyclopterus.

' h. Many of the well-armed Siluroids have the osseous carapace
on the head and neck more or less covered with skin in early
age : the dorsal and pectoral spines are more feeble in the young
than in the old.' *

There are few fields of Natural History that return more mate-
rial reward for scientific labour than that relating to the sfeneratioii

~ o

and growth of Fishes. The mercantile value of the Salmon,
and the necessity for basing laws that are to operate in its
preservation upon a knowledge of its natural history, have led to
interesting observations on its growth and migrations.

Mr. Shaw,2 observing ova spawned on January 10th, no-
ticed dark eye-specks and some movement of the embryo in

1 For the above examples I am indebted to my colleague, Dr. A. Giinther.

2 cxxiv.

GROWTH AND NESTS OF FISHES. 613

the ovum on February 26th, that is, forty-eight days after being
deposited ; and on April 8th, or ninety days after impregnation of
the ova, the young were excluded. They measured |ths of an
inch in length ; the vitellicle beiii£ -|ths of an inch in length.

O ? O o O •*

oblong in form, and of a light red colour : the tail was margined
like that of the tadpole, with a continuous fin running from the
dorsal above to the anal beneath. The vitelline sac and its con-
tents were absorbed by May 30th, or in about fifty days, until
which time the young fish did not leave the gravel of the hatch-
ing-pond. This quiescent state in their place of concealment, from
the period of exclusion to the absorption of the yolk, seems to
be common to Osseous Fishes ; but the time varies in different
species : it is much shorter in the Tench, Perch, or Pike, for
example, than in the Salmon. When the young Salmon mea-
sures an inch in length, the vertical fin begins to divide itself into
the dorsal, adipose, caudal and anal fins ; and the transverse bars
on the sides of the body make their appearance. It is very active,
and continues in the shallows of its native stream till the fol-
lowing spring, when it has attained the length of from three to
four inches, and is called the ( May-parr.' In this state the
6 parr ' descend into deeper parts of the river, and are believed by
Mr. Shaw to remain there over the second winter. The weaker
ones do so, but the stronger fish proceed to the estuary at
once. In April, the caudal, pectoral, and dorsal fins assume a
dusky margin ; the lateral bars begin to be concealed by a silvery
pigment ; and the migratory dress, characteristic of the stage
called ' smolt,' is assumed. Such fish begin in April and May
to congregate in shoals and to migrate seaward : they return in
July and August, of a size proportionate to the length of
their stay in the estuary. A smolt may not exceed two ounces
in weight when it goes to sea : after a few months there it may
have grown to a f grilse ' of eight or ten pounds' weight : ' at
two years and eight months old it becomes a Salmon of from
twelve to fifteen pounds' weight.' 1 It may subsequently acquire
a bulk of forty pounds' weight, and upwards.

In the Syncjnatlms acus the sexes come together in the month
of April, and the ova pass from the female and are transferred
into the subcaudal pouch of the male, fig. 426, n, being fecundated
in transitu, and the valves of the pouch immediately close over
them. In the month of July the young, ib. 0, o, are hatched and
quit the pouch ; but they follow their father, and return for shelter

1 cccxxv. p. 120. Experiments on marked fish have proved this extraordinary
rate of growth, cccxxxiv. p. 57.

€14

ANATOMY OF VERTEBRATES.

427

93-

into their nursery when danger threatens.1 In Syngnathus
ophidian the male carries the eggs under the flat abdomen in cells

placed lengthwise in three rows.2 In the
male Hippocamp the rnarsupium is subcau-
dal, opening by a vertical fissure just below
the vent.3 In the Holconoti the young ac-
quire full developement, perfect gills, and a
size one third that of the parent, before
quitting the ovarian marsupium.4

Both Salmon and Trout excavate the
gravelly bed which they select for spawning ;
and the ova may be found from one to two
feet deep in this stony nest. The Stick-
leback ( Gasterosteus aculeatus) fabricates a
more artificial nest. Aristotle signalises the
Phycis, since recognised as a Mediterranean
species of Golius, as the only sea-fish that
makes a nest and deposits its spawn therein.
Olivi confirmed the statement, and describes
the nest as being composed of sea-weeds
(algae and zostera), adding that the male fish
guards the female during the act of oviposi-
tion, and the young fry during their deve-
lopement.5

Dr. Hancock has observed similar habits
in certain fresh-water Siluroid Fishes of De-
merara called ' Hassars,' which belong to the
genus Callichthys : the Round-headed Has-
sar forms its nest of grass ; the Flat-headed
Hassar of leaves. ' They are monogamous :
both male and female remain by the side of
the nest till the spawn is hatched, with as
much solicitude as a hen guards her eggs,
and they courageously attack any assailant.
Hence the negroes frequently take them
by putting their hands into the water close
to the nest ; on agitating which, the male
Hassar springs furiously at them, and is

Marsupial pouch of Syngnatlius tllUS Captured.

§117. Fecundation of Ecptiles. — Szlsi-
manders, Newts, Frogs, and Toads are generally apt for breeding

0-

1 Eckstroem (1831), quoted in xxxix. ii. p. 327.

2 xx vol. v. p. 67, prep. no. 322y.
{ xxni. t. xii. p. 6.

1 Ib. no. 3223.
6 CCCXXVT. p. 244.

4 cccxxxv.

FECUNDATION OF REPTILES. 615

when they have attained their third year. As the season of impreg-
nation approaches, the expansion of the abdomen, unfettered by
costal hoops, becomes enormous, especially in the females. The
nuptial tints are assumed, the yellows and pinks being brightest.
The males of certain Newts acquire the dorsal crest and a broader
tail-fin, aiding in the manoeuvres required for the internal impreg-
nation. The male of the large Warty-Newt ( Triton cristatus) in
the spring season seeks the female and pursues her, vibrating his
tail with a motion like that of cracking a whip, and, with a rapid
evolution the tumid labia of the cloaca in the two sexes are
brought into contact, and the spermatozoa get access to the
oviduct : the pair sink to the bottom. The Salamandra japonica
of Houttuyn (Sal. unguiculata, Schleg.) at this season has a claw
on each digit of the fore limb. The male Frog acquires the
dark-coloured swelling of the radial digit or thumb, by which
he is better able to retain the female in his grasp during the long
protracted business of impregnation. The larynx of the Toads,
and especially of the male Pipa, now gains its fullest develope-
ment and loudest power of croak. Lizards and Serpents exhibit
their brightest colours : in the male Constrictors the copulatory anal
hooks become conspicuous. The anal scent-glands are in active
function in both groups. The male Crocodile, like certain fishes,
fights for the female : the musky odour emitted by the submaxil-
lary glands pervades their haunts at this time. Many Chelonia
show sexual difference of form. In Land-Tortoises the plastron is
concave in the male and flat in the female. In the Cinosternoida
the fore part of the carapace is broader in the female, and the tail
is longer and stronger in the male, which has also a patch of
rough scales between the thigh and leg, not present in the female.
In the Trionycidoi the tail extends beyond the rim of the shell in
the males only : it is a mere stump in the females : besides this differ-
ence, the male of Trionyx (Aspidonectes spinifer) shows a slightly
oval form ; and the spines along the front margin, and the tubercles
behind them and on the hind part of the carapace, are less promi-
nent. In Trionyx (Platypeltis) ferox the latter character is reversed.
In the Emydians the body of the male is usually flatter and
longer than in the female. In copulation the male mounts on the
back of the female : Emys picta performs the act when seven
years of age ; the female does not begin to oviposit before her
eleventh year, Additional ova are developed in the ovary after
the first copulation, and a certain number of those already formed
begin to acquire a larger size, and ( go on growing for four successive
years before they are laid : ' thus the species is enabled to lay
annually from five to seven eggs after it has reached its eleventh

GIG ANATOMY OF VERTEBRATES.

year.' l Although the Emydians lay once every year, soon after the
period of copulation in the spring, the coitus is repeated a second
time every year in the autumn, shortly before the species return to
their winter quarters : and Agassiz concludes that in Emydians ' a
repetition of the act twice every year, for four successive years, is
necessary to determine the final developement of a new individual.

§ 118. Oviposition of Reptiles.- -\ do not know particulars of
this process in the Perennibranchiates. Some Newts (Triton
cristatus, e. g.) deposit the eggs upon aquatic plants (Polygonum.
Persicaria, e. g.), folding the leaf by means of the hind feet in
such a way that its under surface is turned inward, and the fold
made to stick by the adhesive coating of the egg which she inserts
in the fold. Our smaller Newt (Lissotriton punctatus, Bell) fre-
quently glues the egg in the axilla of the leaf.2

Oviposition of the Frog takes place during the sexual embrace
at the bottom of the water : as each egg is extruded, it is fertilised,
and, the chorion absorbing water, the egg acquires a diameter of
about three lines, the coloured vitellus appearing as a dot in the
middle of the transparent jelly : the ova adhere together in a
mass, and this is usually floated to the surface by disengagement
of gas in the substance of the glairy envelope.

The ova are excluded under similar circumstances in the Toad;
but in a long string of jelly, in which they are arranged alter-
nately in a double series ; the string may be a sixth of an inch in
diameter and from three to four feet in length. In the obstetric

o

Toad (Alytcs), the male impregnates in water, assists in the exclu-
sion of the eggs, causes them to adhere to his own hind legs by
small pedicles, and then seeks the land : only when embryonic
developement is sufficiently advanced does he leave his place of
concealment, and betake himself to the water with the young brood
with which he has charged himself. The male Pipa is asserted to
place the eggs upon the back of the female, which give the stimulus
to the formation of the cutaneous cells in which the whole course
of metamorphosis is completed, fig. 367. In Opistliodelpliys and
Nototrema, the ova are transferred to the common pouch of the
dorsal integument, described at p. 588.

The common Hinged Snake (Natrix torquata) excludes the eggs,
sixteen to twenty in number, connected together by a glutinous
coating, usually in some fermenting mass of decaying organic
matter, whereby they are often transported and spread abroad in
the manuring of fields and gardens. The Viper is not subject to
this ovipositing cause of dispersion, and the confinement to a limited
locality would seem to be the condition of the viviparity of most

1 ccc. Part iii. p. 491. 2 cccxvu.

OV1POSITION OF REPTILES. 617

or all poisonous serpents. It affects, however, the harmless Slow-
worm (Anguis fragilis) and nimble Lizard (Zootoca vivipara), both
of which usually produce their young alive. An American Boa
Constrictor brought forth living young, and also eggs, in the Zoolo-
gical Gardens of Amsterdam.1 The old world constricting serpents
would seem all to be oviparous ; but instead of excluding the eggs
where they would have the advantage of extraneous heat, they are
arranged by the female in a heap around which she coils herself
in a series of progressively decreasing spirals, constituting a
pyramid of which the head of the Python forms the apex.

The fact has been observed in respect to species of Python in
India : Col. Abbott, in a communication on this subject to the
London Zoological Society, states that the incubation lasted more
than three months.2 More exact observations have been made on
captive Pythons. In the Python bivittatus, in the ( Jardin des
Plantes,' at Paris, copulation took place on the 22nd of January,
and the act was often repeated until the end of February. On
the 5th of May, the female excluded fifteen eggs, between 6 A.M.
and 9*30 A.M. The eggs were all separate, of an elongate oval at
the moment of exclusion, with a flexible greyish-coloured shell :
they soon swelled into an elliptic shape, both ends becoming equal
in size, and the shell, as it dried, became hard and of a pure
white. The temperature of the female augments several degrees
above that of the surrounding atmosphere, and is very sensible to
the touch when she has disposed herself in incubating coils about
her eggs. Between the 3rd and 7th of July the eggs were
hatched. The mother did not eat during the incubating period,
but several times drank with avidity water which was offered
to her, indicative of a sort of febrile state. The heat of the body
gradually fell towards the end of incubation.3

A similar phenomenon in the case of a Python Sebce excited
the public curiosity at the Zoological Gardens of London in 1861 ;
the temperature of the body rose to 96° Fahr. between the incu-
bating coils.4

The Lacerta agilis lays her eggs, from twelve to fourteen in
number, in hollows which she prepares in the sand, and, having
deposited the eggs, covers them with sand, and leaves them to be
hatched by solar heat. The Iguana oviposits in the hollows of trees ;
the eggs, about forty in number, are oblong, about an inch in
length.5 Most of the Lacertilia are oviparous ; but the details as
to their oviposition are scanty : the shell is slightly calcareous.

All the Chelonians are oviparous, and the shell is calcified

1 cccxxxvii, p. 368. - Ib. p. 188. 3 cccxxiv.

4 cccxxxvii. p. 367. 5 cccxxxix.

618 ANATOMY OF VERTEBRATES.

almost as completely as in the bird, though in most retaining
some flexibility. In the Painted Terrapin (Emys picta) the ova-
rian e^Gfs do not show much difference in size until the seventh

OO

year, and oviposition does not begin before the eleventh year.
Agassiz is of opinion that all American Emydians begin to lay
eggs from the eleventh to the fourteenth year, when individual
growth is checked and proceeds more slowly. Each species
makes a single nest, and lays the eggs of that season at one time.1
Emys picta digs with the hind legs a perpendicular hole near the
stream she frequents, and may repeat the operation several times
before selecting one as fit for oviposition : in this she deposits
from five to seven eggs. The Snapper ( Chetydra serpentina) exca-
vates at first directly downward and then laterally, making the
widest part of the hole where the eggs are deposited on one side
of the external opening. When the eggs are laid, the female
tramples down and smooths over the earth, so that, when dry,
the place is hardly noticeable. She lays from twenty to forty,
about the size of a walnut. Cinosternon lays only from three to
five eggs. Nanemys guttata is usually limited to two or three
eggs. Land Tortoises rarely lay more than four or five eggs at a
season, and make the nidamental burrow in dry ground. The
Gopher (Testudo Carolina., L.) has a dwelling burrow, but forms a
separate cavity near its mouth for oviposition : in this the female
lays five eggs, then fills the nest up with earth, and flattens it
down smoothly by her own weight.

The Trionycid(R lay from twelve to twenty eggs, or more, of
the shape and size of a musket-ball, in a hole in the sand near the
water's edge. The shell is thick and brittle.

The Sea Turtles ( Chelone, Splmrc/is) are the most prolific of the
order. They oviposit in May or the beginning of June, in dry
sand, on the shore above high-water mark. The female selects a
still moonlight night, when her senses of hearing and seeing may
best avail her to detect an enemy. If satisfied, she proceeds to
scoop out the sand with her hind fins, using them alternately, and
when the sand has accumulated behind her, she scatters it abroad
by violent jerks of the paddles ; a hole being made between one
and two feet in depth, the eggs are dropped in one by one, and
disposed in regular layers to the number of from 150 to 200.
The period of the entire operation may be half an hour. When
concluded, the Turtle scrapes the loose sand back over the eggs,
and makes the surface level and smooth. She then retreats to the
water, and leaves the hatching of the e«;2;s to the heat of the sand.2

o oo

1 CCC. Part iii. p. 500. 2 Audubon, quoted in cccxvn. p. 4, and CCC. Part ii. p. 328.

DEVELOPEMENT OF BATRACHIA. 619

The Crocodilians, like the Chelonians, are all oviparous, and
the process of oviposition is very similar. The eggs, of an ellip-
tical form and with a firm calcareous shell, are buried on the
shore, and left to hatch by extraneous heat.

§ 119. Developement of Batrachia. — After impregnation of the
batrachian ovum the dark or germinal part of the yolk is always
uppermost, and its central point may be defined as the germinal
pole. Here begins, usually about three hours after impregnation
in the Frog, fig. 452, «, the process of segmentation,1 by a fissure
which passes in a determinate direction through the canal of the
yolk, dividing it into two ellipsoid masses, ib. b. About the fifth
hour a second cleft appears, near the point where the first com-
menced, crossing the first at right angles. If an ovum in this state
be frozen, it splits into four segments of a sphere. Fissures next
appear, which, in relation to the two foregoing, might be termed
6 equatorial,' but with varieties exemplified in e,f, g, fig. 452. New
( meridional ' furrows follow, ib. h, crossed again by other ( equa-
torial ' ones, until the surface of the yolk presents the form of a
blackberry. Further subdivision proceeds to such an extent as to
render the surface again apparently smooth. This series of pheno-
mena, resulting in the formation of the germ-mass, occupies about
twenty-four hours, or less, according to the temperature. The
fissures at their first appearance show minute lines at right angles,
indicative of the molecular movements causing them. After the
surface of the yolk has resumed its smoothness on the completion
of the germ-mass, peripheral cells become filled with dark pigment,
and constitute a general ' cambium' or outer investment, fig;. 428. a.

O J O '

At the point where the formation of this investment, as well as of
the germ-mass, began, an eminence appears by the developement
of new cells beneath the investment, which loses its colour at this
part, indicating the first rudiment of the embryo as an oval clear
spot, divided at its hinder end by a crescentic fissure from the
contiguous yolk, and with its anterior end sunk therein. The
embryonal cells, as they accumulate, assume a polyhedral figure,
and their different strata are seen by transverse sections. The
first superficial appearance of the embryo is an oblong rising,

1 The phenomenon of the division and subdivision of the yolk in animals was first
observed by Prevost and Dumas in the ovum of the Frog (Annales des Sciences
Nat. t. ii.., May 1824, p. 112). Franz Bauer, in the same year, delineated partially
the same important phenomenon, in the beautiful drawings which he prepared for
Sir Ev. Home (cccxvi. pis. v. and vi.); but his employer had no appreciation or
comprehension of what was thus shown him. Bergmann detected, in 1841, the
hyaline nucleus in the centre of each subdivision of the yolk ; and the combination
of the spermatised cell progeny of the germinal vesicle with other elements of the
yolk- substance appears to be a necessary prelude to segmentation.

G20

ANATOMY OF VERTEBRATES.

largest at one end, and impressed by a slight longitudinal fissure.
The rudiments of the neural axis are first recognisable in the two
parallel longitudinal elevations ('primitive trace' or 'laminae
dorsales,' ib. m, n) bordering the fissure. Beneath these is at the
same time forming the notochordal rudiment of the vertebral

O

column, ib. c. The albuminous principle is concentrated in
m, the gelatinous one in c : this chemical differentiation does
not affect n. The polyhedral cells extend the vertebral layer
oil each side of the e primitive trace,' which also increases
in length : the neural columns, at first flat and horizontal,

o '

rise at their outer margins, approximate, and ultimately unite
above, where they are covered by the peripheral cell-layer, a :
they are also defended by the nascent neurapophyses, ib. n.
Meanwhile the ( animal ' layer is extending laterally, ib. b, beneath

the investing membrane, a ; and the cephalic
end of the embryo enlarges and raises itself
from the yolk-bed. A section of the ovum
just prior to the coalescence of the e laminae
dorsales ' to form the neural axis, as in fig.
428, shows, a, the dark investing membrane,
or f cambium : ' b, the musculo-tegumentary
layer, inclosing the whole yolk, v ; m, the
myelonal columns ; c, the notochord ; n, the
blastema, in which cartilaginous rudiments
of the neurapophyses begin ; h, the cavity,
beneath the germ due to solution of the
yolk-substance. On the ventral aspect of the embryo layers of
cells have been forming two parallel ridges projecting into the
yolk ; and the intermediate space is converted by liquefaction of

cells into a primitive alimentary
groove. But all the systems and
organs for the support of the
embryo begin to be developed
after the main basis of the neural
and vertebral parts has been
established.

Figure 429, A, gives a view of
the embryo of the Frog from
the dorsal aspect, showing the
myelonal columns at the period

of their meeting above the myelonal canal and the commencing
encephalic expansion, the extension of the neuro-vertebral tracts
outward, and the indication of lucmal arches of the cephalic

Section of yolk arid embryo,
Frog, magn. LXXIV.

429

B

Embryo of the Frog, ccxxxvm.

DEVELOPEMENT OF BATRACHIA.

621

segments. In B, the cervical constriction begins to define the
head from the trunk : the complete coalescence of the myelonal
tracts obliterates the linear trace of the median furrow, and the
neurapophysial rudiments border the myelon. The embryo and
its supporting yolk-mass are separated from the chorion by a clear
fluid ; and in the above-figured stages of developenient the ciliated
epithelium begins to act upon the fluid in the direction indicated
by the arrows, proceeding backward and downward along the
sides : the currents are strongest on the haemal arches, from which
the branchiae are about to be developed. In the mass of em-
bryonal cells between the cephalic enlargement of the embryo
and the yolk, the heart, fig. 431, r, is formed, which becomes
hollow, and pulsates before the red blood appears ; when the
communication with the system of vessels is established, the
heart propels blood, at first pale and with spherical corpuscles,
in channels formed by liquefaction of cells in the blastema of
the second haemal arch ; and these primary vascular arches esta-
blish the communication with the longitudinal aortic trunk simi-

o

larly formed along the under part of the notochord. The blood
returns by venous channels along the yolk, now progressively
becoming inclosed by the lateral intestinal plates, and the simple
circulation is complete.

From the substance around the vascular arches are formed as
many branchial arches, as subordinate developements from the
second primary hasmal or visceral arch ;
and from the branchial arches are
budded the succession of vascular loops
and coextended ciliated integument,
constituting the outer oills on each

o o

side of the batrachian larva, fig. 430.

' O

In the magnified portion of the gill, c,
the arrows indicate the direction of the
ciliary currents. Soon after the ap-
pearance of the heart, and of the arches
which encompass the primitive bucco-
branchial cavity, a pericardium, lined
with epithelial cells, is formed around
the heart. Between the cephalic ha3inal arches interspaces are
opened, communicating with the bucco-branchial cavity, and from
one of these the budding gills begin to protrude.

The growth of the neuro vertebral axis is chiefly lengthwise,
and, as it proceeds, its two extremities lift themselves above the
level of the rest of the germinal basis ; the shorter and more

430

Larva of Frog ; A, nat. size. CCXXXYIII.

622

ANATOMY OF VERTEBRATES.

431

obtuse as the head, the more acute and longer free part as the
tail. In this growth the amphibian passes from a state in which
a longitudinal section would show it supported by a spherical
yolk, to that represented in fig. 431, in which the vitelline, or

( haemal,' portion pre-
sents a semioval section,
h v : it is inclosed, as in
fig. 428, by the ha3inal
prolongations of the or-
ganic layer forming the
abdominal parietes, a,
and lined by the fmu-

Longituclinal section, Embryo of Frog. LXXIV. •> i • -i

cous layer, i : this be-
comes differentiated as the tunics of the alimentary canal, inclosing
the vitellus as the primary contents of such canal in all Batrachia.
The canal now communicates with the bucco-branchial cavity ;
and this opens externally on the lower part of the head by a
vertical fissure, on each side of which a small protuberance buds
out, forming a special organ of adhesion — a pair of temporary
cephalic limbs. A pair of branchiae budding out from the gill-
aperture, the whole yolk being now closed in by both the in-
testinal and cutaneous layers, and the tail having gained its
muscular segments and cutaneous border-fin, the little tadpole,
by increasing vigour of its movements, bursts the egg-mem-
branes and comes forth. The external stimulus which most
influences this stage is warmth. In Italy, Rusconi observed
the eggs of the Frog to be hatched in four days ; Bauer
figures one extricating itself, in a warm spring, at Kew, after
the fifth day : * in a cold spring, it may be prolonged through
four weeks. In Alytes obstetricans, the developement of the
f mucous' layer proceeds to form a convoluted intestinal canal
before ( extrication.' In Rana esculenta, and probably other
Frogs, the vegetative organs are later in developement, and the
cavity, fig. 431, h v, has not assumed the intestinal form when
the embryo quits the egg : but in all Batrachia the whole yolk is
wanted for the formation of their long spirally wound larval gut.
Herein is a differential character between the Batrachian and the
Fish. In the latter, the supply for the mid-period of develope-
ment is received, primarily, from the vascular rather than from
the digestive system, and a part only of the yolk is required for
the formation of the straight and simple intestinal canal. Ac-
cordingly, the mucous layer, as in the diagram, fig. 432, ?', in

1 cccxvi. pi. vi., fig. 1 A.

DEVELOPEMENT OF BATPvACHIA. 623

forming the intestinal canal, h, excludes a portion of the yolk, v :

the tegumentary or ( serous' lay- 432

er, a, accompanies the ( mucous '

layer, i, in the process of severing

the vitelline from the intestinal

cavities, and an outer yolk, or ' vi-

tellicle,' results.

The embryo of the Frog is ex-
tricated at a less advanced stage

of developement than that of any x> ^, a

other vertebrate animal: the neu-
ral laminae have united along the i-ongitudinai section, Embryo of FI^. LXXIV.

trunk, and two of the haemal arches have become complete
below the head, but, in other parts, the neural and hrenial canals
are closed only by the corresponding laminae in a state of mem-
brane, the original investing membrane of the yolk being retained
over all.

After extrication, the tadpole rapidly grows, and the chief
change of form is witnessed in the gills : each of the two lateral
gills puts forth four plates, which have vascular and richly ciliated
surfaces, fig. 430, c : a short additional leaflet is sometimes deve-
loped from the base of the hinder gill. ( The current of the
blood poured in regular pulsations at each contraction of the
heart passes up each stem or main branch of the branchiae, and a
distinct stream is given off to each leaf; it is propelled to the
extremity, and then returns down the opposite sides in the most
regular manner, and the parts are so transparent that every
globule of blood is distinctly and beautifully visible.'1

The first cutaneous mouth is defined by epidermal jaws, in the
form of a very short transversely extended beak, fig. 433, 22, sur-
rounded by a lip armed with minute rasp-like denticles, and aided
by the pair of cephalic suckers projecting behind the mouth. The
wide pharynx, communicating also with the outer world by the
lateral branchial slits, is extended posteriorly by a short esophagus
to a simple gastric enlargement, beyond which an equally simple
intestinal sac, laden with the remnant of the vitellus, gives issue
to a short and straight rectum, which is continued to the long
tegumentary and transitory cloacal canal at the fore-part of the
subcaudal fin. The contained yolk, fig. 431, kv} is not, as in Fishes,
fio-. 432, v, a mere ( food-yolk :' it is part of the germ-mass, and
consists of the embryonal cells, with their nutritious oil-globules.
Whilst, therefore, it serves to nourish the growing embryo, it also

1 cccxvu. p. 101.

ANATOMY OF VERTEBRATES.

continues to be the seat of progressing developement, and coil
after coil of intestine is formed between the duodenum before,
and the rectum behind the primitive simple vitelline sac, the
coils being disposed in a close double spiral, fig. 433, 7. Thus,
the fully developed larva is provided with an alimentary canal,

433

434

Diagram of the anatomy of the Tadpole.

adapted, by its length and complexity, for the assimilation
of the decaying vegetable matters which chiefly constitute its
food. In the conversion of this digestive apparatus into that
of the purely carnivorous Frog, the horny cutaneous beak is
changed into a wide mouth formed by well-ossified jaws, the
lower one armed with sharp teeth. The branchial pharynx is
contracted and closed at the sides, except where it communicates

with the ears. The oesopha-
gus and stomach are elong-
ated ; the intestine is marvel-
lously shortened ; the rectum
contracts, and is found to
open, after the absorption of
the tail and cutaneous anal
fold, just in front of the
symphysis pubis, now com-
pleted by the developement
of the hind limbs. Whilst
-j the heart, as a bent tube, fig.
434,^, sends off the branchial
arteries from its fore part, it
is connected behind with ves-
sels ramifying on the vitel-
licle, ib., b : a portion of this
is soon seen to be marked

Tadpole of Toad, magn. cxxn.

off from the rest, as the
basis of the future liver and pancreas.

1 CCOXXVIII.

DEVELOPEMENT OF BATRACHIA. 625

The embryonal cells that lay the foundation of these glands,
fig, 434,, e, are situated in the angle between the intestinal yolk-
mass, ib. b, and the stomach, ib. c ; not behind it, as in Fishes,
fig. 435. They form a hollow gland or caecum with a wall of com-
pacted cells ; and, after a communication has been established with
the gut, other cavities or casca pullulate in the cell-blastema, and
the liver becomes conspicuous. l Nowhere,' says Reichert, l is the
new generation of cells within parent- cells so obvious as in the
blastema of the liver and pancreas.' * The primordial kidneys, or
de-azotising organs, have now begun to be developed between
the aorta and the intestinal plates, and the ducts of these,
together with the anal prolongation of the intestinal tube, open
upon the temporary tegumentary vent. In the Tadpole, as in a
Fish, the mouth is destitute of tongue, but at the entrance of the
mouth over the lips we find among the cartilaginous teeth at
that region numerous conical-shaped bodies. These labial papilla
consist of an external border of prismatic epithelial cells provided
with cilia. The tongue makes its appearance when the fore limbs,
fig. 433, 54, 55, are evolved. The habits now alter : the Tadpole
no longer feeds on decomposing substances, and cannot live long
immersed in water. As the tail of the Tadpole atrophies, the
fungiforni papillae appear upon the nascent tongue, increase in
size, and acquire the permanent complex form.

Soon after the external gills have reached their full develope-
ment, they begin to shrink, and finally disappear ; but the
branchial circulation is maintained some time longer upon the
internal gills (p. 516, fig. 345); these consist of numerous short
tuft-like processes from the membrane covering the cartilaginous
branchial arches, fig. 433, 47 : they are protected by the growth
of a membranous gill-cover, which, as the external branchiae are
absorbed, leaves only one small external orifice, by which the
branchial streams admitted by the mouth continue to be expelled.
This orifice may be very plainly seen like a crescentic cicatrix,
a little behind and below the left eye, in the larva of the Rana
paradoxa.2

The chief distinction between the fully developed branchial
circulation in the Batrachian larva and that of the Fish consists in
the presence of small anastomosing channels, between the branchial
artery and vein of each gill, proximad of the gill itself.

The part which these anastomoses play will be understood by
the following description and figures of the vascular transformation
as observed in the Newt. When the gills are in full developement

1 CCCXXTIII. 2 xx. vol. v. p, 77, preps, nos. 3286-3287, E.

VOL. I. S S

626

ANATOMY OF VERTEBRATES.

435

Branchial circulation ; larval Newt (Triton). CCLXXXII.

and .activity, the principal circulating vessels present the arraiio-c-
ment shown in fig. 435.

The vessel, ib. 4, originally distinct and large before the deve-
lopement of the gills, is now very small, and so close to the
origin of 3 as to appear to be its first branch : it anastomoses
with the branch 21 from the aortal root of its own side, and
proceeds to the nascent lung 19. The artery 3 supplies the hind-
most gill, and distri-
butes its branches to
the several branchial
leaflets, 5, where they are
resolved into the capil-

j.

lary network, fig. 343,
p. 514 ; the blood is re-
turned by the branchial
veins, fig. 435, 7, 8, to the
trunk 9, which at 16 joins
the corresponding vein of
the middle gill to form
the aortal root or arch of
that side : this receives
the anastomosing vessel 13, from the branchial vein of the first gill,
and then sends off the accessory origin, 21, of the pulmonary artery,
19. The third primary vascular arch, 2, is the branchial artery of
the middle gill : it effects a small anastomotic communication, 14,
with the vein of the gill before proceeding to expend itself upon the
branchial lamellae, 6 ; the returning trunk, 9, after receiving the
anastomotic twig, 14, joins the vein, 16, of the third gill to form
the aortic arch. The foremost primary vascular arch, i, before
going to the first gill, anastomoses by a small channel, 5, with the
vein, 9, of that gill ; which vein, after the above anastomosis.,
sends off the vessel 1 1 to the head : before the anastomosis it
passes back and divides into the vessel 13, joining the beginning
of the aortal arch, and the recurrent branch 12, which also conveys
arterialised blood to the head.

As absorption of the branchiae proceeds in the progressing
metamorphosis, the following changes are observed in the above
described vessels, fig. 436 : the anastomosing channel, r>, between
the roots of the artery and vein of the first gill, dilates as the cir-
culation through that gill is checked, and sends more blood into
the artery n, into the anastomotic channel 13, and into the artery
1 2. In like manner the blood of the second gill begins to be diverted
by the anastomotic channel as its base leading to 16, which assumes

DEVELOPEMENT OF BATRACHIA.

ear

436

Branchial circulation during absorption of gills; larval
Xf\vt (Triton). CCLXXXH.

a size that gives it the character of the aortic arch. The pul-
monary vessel, 4, now
equals in size the trunk,
3, of which it was a
branch ; and it exceeds
the tributary 21.

With the total disap-
pearance of the gills the
blood of the foremost
vascular arch is carried
into the two chief ar-
teries of the head, fig.
437,12,18; either directly,
or by the transformation
of the anastomotic channel into a recurrent origin of one of these :
it is thus converted into the carotid arteries. In higher Reptiles
the origins of i, i, are blended or produced into a common trunk
of the carotids.

The next vascular arch, 2, 2, is now transformed into the rio-ht

o

and left arch of the aorta, by the enlargement of the anastomotic
channel 14, fig. 435 ; with changes in length and position by which
it gives off the cutaneous artery of the neck, is. The tributary, 21,
to the pulmonary artery, 4-19, is now shortened, and transverse in
position : in higher Reptiles it is still more shortened, and finally
obliterated as the ' ductus arteriosus ' on each side. The orbital
artery, is, fig. 436, and n, fig. 437, continues to be sent off from
the aortic arch.

The first or hindmost of the primitive vascular arches is now
converted into the pulmonary artery,
and the blood which was transmitted
by 3, figs. 435 and 436, is now diverted
from the largest of the gills to the
lungs.

The blastema, which lays the foun-
dation of the lungs, is situated behind
and at the sides of the fore part of
the alimentary canal, where it enters
the bucco-branchial cavity. The
kinoes beo-in to be formed as soon as

O O

the intestine behind has taken on its
first sigmoid curvature. They are
not developed from the alimentary
canal, but communicate with it soon after the establishment

s s 2

437

Change sin branchial vessels after afosorp
tioTi of gills; Newt. CCLXXII.

6-28 ANATOMY OF VERTEBRATES.

of the respiratory cavity in their primitive and independent
blastema : their communicating duct advances with the elonga-
tion of the oesophagus, and at the point of its communication
therewith the larynx is ultimately developed. The lungs them-
selves extend, as simple elongated sacs slightly reticulated on the
inner surface, backward into the abdominal cavity. These recep-
tacles are no sooner formed than the larva rises to the surface
and swallows air, which passes into and expands the prepared
cavity. When the pulmonary respiration has regularly begun, the
fore-limbs are liberated from the branchial chamber, which now
begins rapidly to contract its dimensions, and .to be completely
partitioned off from the abdominal cavity with which it had pre-
viously communicated.

The changes in the hyo-branchial apparatus, accompanying
those of the breathing organs, are defined at p. 90, and illustrated
in figs. 69-71 and 74. The developement of the vertebra? is
attended with the conversion of biconcave into cup-and-ball
joints, by ossification of the substance of the cavities, a, fig. 433,
and its coalescence either with the fore (Pipa) or back (^Rana)
part of the centrum, c. The chief facts in the formation of the
skull are stated at p. 86, figs. 68-71.

About the middle period of aquatic life, the true or permanent
kidneys begin to be formed from and upon the primordial ones ;
and the basis of the ovaria, or testes, may now be discerned. The
oviduct is soon distinct from the ureter ; but the testes retain the
same excretory duct as the kidneys : their vasa deferentia com-
municate with retained casca of the primordial kidneys before
penetrating the later glands : the upper or anterior ends of the
first remain for some time behind the heart.

In the often-quoted experiments of Edwards,1 it is not clearly
shown that the Tadpoles of the Frogs were constantly supplied
with proper temperature and food, and therefore it is not satisfac-
torily proved that the arrest of the metamorphosis was due solely
to the absence of light. Mere absence or diminution of this
stimulus does not in all cases check the progress of the tadpole to
the Frog-state. Ova of a Frog, deposited on March 11, were
placed in a vessel covered with six or eight folds of black glazed
calico in a dark part of a room, but in a temperature of from 55° to
65° Fahrenheit, and supplied with proper food.2 The larvse were
hatched on March 20 ; attained the length of an inch on May 1, fig.
438 ; had pushed out their hind-legs, fig. 439, on May 10, and
their fore-legs, fig. 440, on May 16 : the tail began to be absorbed

1 CCXCVIL 2 CCCXVIII,

DEVELOPEMENT OF BATRACIIIA.

G29

at that date, was reduced to a stump, fig. 441, on the 18th, and was
removed by May 20 ; the metamorphosis being fully completed, as
in fig. 442, in all the tadpoles by May 22.

43S

440

Apodal Tadpole.

439

Quadrupedal Tadpole.
441 442

Bipedal Tadpole. Young Frogs.

Rana temporaria.

The figures 438 to 441 illustrate the chief outward changes which

O C5

accompany the batrachian metamorphosis, as exemplified in Rana.

In Bufo the tadpole is smaller and blacker in all the stages of

growth and metamorphosis. In both genera of Anourans the

growth is greatest at the phase figured in 439 ; with the subse-

£•> O -1 O '

quent phases the bulk of the body is diminished : and this is
remarkably the case in the Rana paradoxa.

In the Newts ( Triton) the gills are in three pairs, larger and
more complex than in the Frog : the fore-limbs are the first to
emerge, and the gills persist long after the hind-limbs are deve-
loped. If late hatched and in a cold season, the gills may be re-
tained through the ensuing winter : they are absorbed before the
next breeding season comes on.

Much ingenious conjecture has been expended on the influence
of external circumstances and internal volitions and efforts during
the struggles for existence in the origin of species by progressive
transmutation ; and their succession on this planet has been
speculatively assigned to such causes. In the metamorphoses of
the Batrachia we seem to have such process carried on before our
eyes to its extrernest extent. Not merely is one specific form
changed to another of the same genus ; not merely is one generic
modification of an order substituted for another ; the transmu-
tation is not even limited by passing from one order ( Urodela) to
another (Anoura) : it affects a transition from class to class. The
Fish becomes the Frog ; the aquatic animal changes to the terres-
trial one ; the water-breather becomes the air-breather ; an insect
diet is substituted for a vegetable one. And these changes, more-
over, proceed gradually, continuously, and without any interruption

630 ANATOMY OF VERTEBRATES.

of active life. The larva having started into independent ex-
istence as a fish, does not relapse into the passive torpor of the
ovum,, to leave the organising energies to complete their work
untroubled by the play of the parts they are to transmute, but
step by step each organ is modified, and the behaviour of the
animal and its life-sphere are the consequence, not the cause, of
the changes.

The external gills are not dried and shrivelled by exposure to
the air, nor does the larva gain its lungs by efforts to change its
element and inhale a new respiratory medium. The beak is
shed, the jaws and tongue are developed, and the gut shortened,
before the young Frog is in a condition to catch a single fly.
The embryo acquires the breathing and locomotive organs —
gills and compressed tail — while imprisoned in the ovum; and
the tadpole obtains its lungs and land-limbs while a denizen of
the pool : action and reaction between the germ and the gela-
tinous atmosphere of the yolk, or between the larva and its
aqueous atmosphere, have no part in these transmutations. The
Batrachian is compelled to a new sphere of life by antecedent
obliterations, absorptions, and developements, in which external
influences and internal efforts have no share.

The phenomena of batrachian metamorphosis, that each spring
are observable wherever there is a pool of water in a green field
of England, are amongst the most suggestive and instructive

~ * O DO

which the animal economy affords.

§ 120. Devclopement of Scaled Reptiles. — From the difference in
the structure of the ovum in the scaled and naked Reptiles, the pro-
portion of the food-yolk to the germ-yolk is much greater in the
former, and the formation of a germ-mass by the diffusive process
of successive fissions is restricted to a smaller proportion of the
ovum than in Fishes. The formation of the embryonic trace closely
resembles that in the Fish and Frog ; but, instead of rising above
the yolk-ball, the embryo sinks into it ; first by the head, which,
as it plunges in, gets covered by a fold or hood of the ( serous ' or
outer embryonal cell-layer, drawn progressively over the body
until it is sheathed to beyond the heart ; then the tail, bending
down, acquires a caudal sheath ; and the rest of the trunk sinking,
the margins of the serous bed are produced over it continuously
with the bodies of the cephalic and caudal sheaths, contracting
concentrically until the whole embryo is inclosed in a ( serous ' bag,
reflected, as it seems, from the umbilicus, and thus the ( amnios,'
fig. 445, a, is constituted. The embryo being imprisoned in the
scrum of this bag, branchine could not act, and are not developed ;

DEVELOPEMENT OF EEPTILIA. 631

but a temporary air-breathing organ is substituted to remove the
carbon as the organic machine becomes more complex, and its
actions more vigorous and various. From the fore-part of the
cloaca a vesicle is protruded which elongates, escapes by the um-
bilicus, and, carrying along with it blood-vessels, applies their
ramifications to the inner side of the shell : this is the ( allantois,'
figs. 445 and 450, b.

On the part of the yolk supporting the embryo blood-channels
appear which form a circular canal called ' vena termiualis ; ' it
bends towards the embryo at the part near the head, and passes
through the opening of the cephalic hood to a transverse canal,
6 vena aiferens,' behind the heart: this is now an obliquely bent tube,
which pulsates and sends the circulating fluid to a dorsal vessel,
which soon distributes vessels, ris;ht and left, in the abdominal

J O

region to the ( vena termiualis.' towards which numerous chan-

~ *

nels pass from the included space, fig. 450, c, the whole now
forming the ( area vasculosa ' upon the yolk. The fluid first
circulated in this system of channels is pale plasma with granules.1
The first circulation in an amniotic embryo may be described as
passing from the heart-tube by vascular arches to the ' dorsal
artery,' which supplies the parts of the embryo, and sends ( om-
phalo-meseraic ' branches to the e area vasculosa,' from the f vena
terminalis ' of which area the blood returns by the ( vena afFerens '
to the heart. The dorsal artery bifurcates posteriorly, and returns
along; the abdomen as the e veua3 cardinales : ' the arteries to the

o

head also return as ' precaval veins,' and all these terminate in
the fvena afFerens.' Dilatations of the heart-tube indicate a
ventricle, fig. 443, a, and a e bulbus arteriosus, ib. b : ' the latter is
more prominent at first. An auricular dilatation behind the ven-
tricle next appears. A protuberance in advance of the caudal
curvature is formed by what soon is recognisable as a hollow sac,
ib. d\ which, as it expands, carries with it branches from the
dorsal artery : these are the f umbilical ' or ( allantoic ' arteries,
fig. 450, i, which convey, as the bag protrudes and expands, part
of the circulation to receive the influence of the air through the
pores of the shell ; and, the blood returning by the ' umbilical ' or
' allantoic veins,' a subsidiary circulation to the vitelline, ib. c, is
established, analogous to the branchial one of Batrachians and
Fishes. The blood has now become red, and of shades indicating
its arterial and venous conditions. The blood-corpuscles, at first
globular, become slightly flattened, but the discs are circular be-
fore acquiring their elliptical form.2 The omphalo-mesenteric

1 Hunter, CCLXXX. (1794) p. 45, and xx. vol. v. p. xxiv.

2 When the heart begins to lose its tubular shape the blood-particles are minute

632 ANATOMY OF VERTEBRATES.

arteries diverge from a common trunk, and the venous channels
become more concentrated towards the heart. A venous sinus is
formed behind the auricle, and this is divided by a valvular struc-
ture from the ventricle, which now is larger than the bulbus.

The changes of the primitive vascular arches into the arterial
trunks arising from the adult heart are effected more speedily and
directly in allantoic Reptiles than in Batrachia, pp. 519, 520,
because no branchial organs and vessels are developed : such spe-
cial respiratory apparatus for a temporary aquatic existence is
interposed in the anallantoic species, and interrupts, so to speak,
the course of the transformation which is now to be described.

The primitive distribution of blood from the ( bulbus ' of the
embryonal heart in ( Vertebrates ' is by a series of symmetrical
arches on each side the alimentary canal, dorsad of which those
loops or arches unite to form or join the aortic trunk: they relate
to the primitive segmental character of the embryo, co-existing
with maxillary, mandibular, hyoidean, and scapular segments, all
of which at this period are unclosed arches on the sternal aspect
of the fore-part of the body.

The four or five primitive vascular arches have no essential
relation to gills, any more than the clefts or depressions between
the budding piers of the maxillary, fig. 444, a, mandibular, ib. b,
and hyoidean, ib. c, arches are necessarily the precursors of the
branchial openings. Both primary structures exist in the embryo
of those vertebrate classes that never possess the true branchial
organs : these are superadded developements upon the common
segmental type of pleurapophysial and pleurarterial parts, which
developements are peculiar to Fishes and Batrachians, persisting
in the first, and vanishing in most of the latter Vertebrates.
Of the three vascular arches on each side by which the blood
passed from the bulbus to the dorsal vessel, the hindmost are
progressively converted, with the growth of the lungs, into the
( pulmonary arteries,' each retaining a connection with the second
pair of vascular arches ; the third, or anterior pair, with the
developemeiit of the head and fore-limbs, in like manner become
diverted to their exclusive service, but for a time retain a con-
transparent globular cells, with a large granulated nucleus (mesoblast, Ag.), attached
to the wall. ' By the application of water the nucleus bursts and the whole granular
contents come out, but still retain their globular state and appear to have a membrane
about them. From this it would appear that the apparently granular contents of the
mesoblast constitute, in reality, an entoblast (nucleolus), which fills the mesoblast.'
The flat elliptic form is not attained until very late. The mesoblast is faint and
homogeneous to within a short time before extrication of the turtle: in the adult it
contains a darker entoblast. ccc. p. 617.

DEVELOPEMENT OF REPTILIA.

633

nection with the mid-pair, as shown in fig. 332, p. 504, at A.
The returning blood from the expanding lungs leads to the deve-
lopement of a distinct chamber in the auricle, which finally be-
comes the left auricle. Partitions in the bulbus arteriosus effect
a distinct communication of the pulmonary arteries with the
ventricle, and a division of what now becomes ( aorta ' into two
trunks. Of these one is appropriated to the left of the primitive
pair of middle arches ; the other becomes the trunk of the right
arch of that pair, and also of the anterior pair in course of change
into brachial and carotid arteries. The ' ductus arteriosi,' between
the anterior and middle arches (fig. 332, A), are usually absorbed
(as at D, fig. 334) : those between the posterior and middle arches
(D, fig. 335) are longer retained through the same course of change.
The trunk, which gives off the carotids either exclusively or in
common with the brachials, is posterior in Reptiles to the trunk
of the left aorta, and to that of the pulmonary artery. With the
developernent of septa in the bulbus, there proceeds a like change
in the ventricle itself, but it does not reach the condition of a
complete ( septum ventriculorum ' until the crocodilian type of
Hrematocrya is attained (figs. 339, 340).

The substitution of kidneys for Wolflfian bodies is preceded by
an enlargement of the latter, fig. 443, /, at their middle part,
with attenuation of their ends : the
true kidneys begin to be formed at
the upper medial part, and their uri-
niferous tubes are larger and more
convoluted. The genital organs
appear as a narrow white band upon
the ventral side of the Wolflfian body.

The developement of the brain
closely resembles that in the Fish
(pp. 604, 607), but it soon bends
down at a stronger anode with the

O CD

myelon. The cerebellar fold is first
distinguishable ; afterwards the de-
flected anterior part of the encepha-
lon becomes divided into mesen-
cephalon, cerebrum, and olfactory
lobes, and the cerebrum speedily

. .-i . . n i . , Embryo of Lacerta viridis.

attains the superiority oi size which

distinguishes the brain of the Reptile from that of the Fish. The
pineal gland shows a large proportional size in the embryo Turtle,
as does also the ' thalamus ' or lower lobe of the mesencephalon,

443

(534 ANATOMY OF VERTEBRATES.

in which the optic nerves chiefly originate : the ventricles are
large in each mass. The eye-ball is formed, as in Fishes, by the
bending of a sausage-like bag about the lens, and the coalescence
of the ends brought into contact. The cicatrix, shown in fig. 443,
soon disappears. The capsule is next differentiated from the lens
proper. The eye-ball is, at first, unprotected, as in Fishes ; but
the contiguous skin -border begins to encroach upon its fore part,
with modified growth, to form the eyelids.

After the developement of the labyrinth from the primitive
ear-capsule, a tympanic cavity is formed, in which the ( stapes '

appears as a short thick cartilaginous
cylinder in the Chelonia, in which the
( meatus auditorius ' broadens outwards
to a trumpet shape, which it retains. In
the Ophidia the ( stapes,' fig. 444, B, e, is
similarly developed, independently of the
tympanic and mandibular (or so-called
Meckel's) cartilage, ib. d, as shown by
Rathke, in Natrix torquata. The nostrils
appear as deep depressions at the fore end
of the head, the margins of which become
incurved, and the bottom of the sac is
produced into a canal communicating with

Hicmal arches of cranium ; embryo -f n o
Snake, cccxxx.

In and from the membrane of the

notochord, continued along the basis cranii, is developed the
cartilage of the basi-presphenoid, blending laterally with the
ear-capsules : the basal cartilage bifurcates anteriorly, and re-
unites surrounding the hypophysial fissure : it is then continued
singly forward, and expands anteriorly in connection with car-
tilaginous plates from which, in Chelonia and Ophidia, the
profronto-nasal bones are developed. In Lacertilia the large
' lacrymal' bones grow from the same embryonal cartilage.
Behind these foremost representatives of neurapophyses are
three pairs, more clearly showing the neurapophysial characters :
the pair resting on the bifurcated presphenoidal part of the
basal cartilage, in relation to the optic nerves, become ( orbito-
sphenoids ; ' 1 the next pair, in relation to the trigeminal nerves,
situated anterior to the ( ear-capsules,' become the f alisphe-
noids;'2 the pair behind the ear-capsules, resting on the
basioccipital, become the ex- and par-occipitals.3 Thus the

1 cccxxx. taf. vii. fig. 17,/, ' vorderer Keilbeinfliigcl.' 2 Ib. e, ' hinterer Keilbeinflugel.

3 Ib. 6, ' Scitcnthcil ties Hinterhauptbdnes.'

DEVELOPEMENT OF REPTILIA. 635

neural arches of four vertebral segments are plainly indicated in
the developement of the reptilian cranium. The haemal arches
make their first appearance as pairs of slender rib-like bones :
the foremost, fig. 444, a, becomes the palato- maxillary arch ; l the
next early shows more clearly its division into the pleur- and
haem-apophysial parts of the tyrnpano-mandibular arch, ib. b ; the
third, ib. c, is the hyoid arch : the fourth has no longer the
cephalic relation which it shows in Fishes ; and the four neura-
pophyses are matched below by only three heeniapophyses in the
reptilian cranium.

In the oviparous Snakes, Natrix torquata, e. g., a certain
progress in the developement of the embryo is found to have
been made when the egg is laid, and the rest is completed and
the young extricated in the course of about two months, sooner
or later, according to the surrounding temperature.

When developement has advanced to the formation of the
amnios about the embryo, the head is distinct, and shows the eye-
ball and ear-sac ; also the maxillary and mandibular processes and
the beginning of the hyoid, with the intervening depressions, mis-
called ( branchial clefts : ' the heart, as a sigmoidally bent tube,
fills the concavity between the frontal process and the chest:
the allantois has protruded, as a globular vesicle, about the size
of the head ; and beyond its emergence the tail forms a single
spiral coil : the vascular area on which the vitelline vessels ramify
covers half the food-yolk. The long trunk of the Serpent grows
in a series of decreasing spirals, and when five or six are formed,
the rudiment of the liver and the primordial kidneys are dis-
cernible. Fig. 444 shows the embryo at this period magnified
four times : a is the amnios, b

A \ *"

the allantois, d its tubular stem,
produced from the cloaca, or
( urachus : ' the front view of the «.

head shows the ( frontal process,'
0, and the bases, n, of the palato-
maxillary haemal arch. The pri-
mordial kidneys are remarkable
for their length : c indicates a
portion of the vitellicle. With
the dilatation of the fore-part of

\ . Embryo Snake (Matrix), cccxxx.

the alimentary canal indicating

the stomach, a small appendage, the pancreas, appears, marking

the beginning of the intestine. The lungs are next seen as a

1 cccxxx. taf. viu fig. 11, e, ' Oberkicfer.'

636

ANATOMY OF VERTEBKATES.

44G

symmetrical pair of longish simple sacs, extending from the
pharynx on each side of the oesophagus to the beginning of the
liver : the left division soon begins to exceed the right in length,
and then seems to monopolise the power of growth. The common
stem or neck of the pulmonary sacs elongates, contracts, and
begins to show traces of the transverse cartilages ; and at about
the latter third of the developemental period the right lung appears
as a mere appendage to the beginning of the left. The appear-
ance of malpighian bodies, as minute red points on part of the
surface of the primordial kidneys, is the first indication of the
developement therefrom of the kidneys : these grow between
the primordial kidneys and the vertebra at the hindmost end of
the abdominal cavity. The testis, or ovary, is differentiated from
the ventral surface of the fore-part of the primordial glands : at

one period of developement the primor-
dial ducts coexist with the sperm-duct
and ureters. Four or five ducts emerge
from the liver and unite into a com-
mon one before communicating with
the intestine ; a similar duct, proceed-
ing from the common one, expands at
its opposite end into the gall-bladder.
This remains near the pylorus : the
hepatic ducts elongate as the intestine
recedes on the growth of the snake.
The spleen first appears as an append-
age to the narrow end of the pancreas.
In the male embryo, the two bifurcate
penes project from the cloaca before
the period of extrication.

Figure 446 shows the posterior half
of the embryo of the Viper at a late
period of developement. The yolk
bag, «, is much reduced in size, but
is not yet taken into the abdominal
cavity ; b is the portion of the amnios
adherent to the vitellicle ; c is the
short pedicle, including part of d, the

ductus vitello-intestinalis, which as-
cends to terminate at e, between the

Foetus of Viper, xi.nr.

longitudinal lolds 01 the mucous mem-

G

brane of the small intestine, f. The continuation of the intestine to
the cloaca, /, is shown at y, li ; the ovaria at i, i ; the kidneys at k, ft.

DEVELOPEMENT OF REPTILIA.

637

447

yolk partially taken into the abdominal cavity. XLIII.

448

In figure 447, the vitel-
licle of a Viper, at a more
advanced period, shows part
of the food-yolk entering
the abdominal cavity, at a :
the ductus vitello-intesti-
nalis, d, is reduced to a
thread : g is the intestine,
and k the kidney.

Figure 448 shows the
body of a Viper just before

tlie periOQ OI extrication yitciiiclc of a Viper at a more advanced period, showing the

from the egg - coverings ;
the parietes of the abdomen
are partly removed to show
the vitellicle, b, which has
now become inclosed in
that cavity, with almost
complete obliteration of the
umbilical cicatrix : #, the
remains of amnios and al-
lantois : d, the much short-
ened ductus vitello-intesti-
ualis : g, the liver : ff, the
stomach : f. the duodenum :

t/ •*

?z, the small intestine : the
other letters indicate the
same parts as in the pre-
ceding figures.

The gravid Viper is more
than usually sluggish, and
loves to bask in the hot
sunshine, turning her belly
as if to court the aid of the
extraneous warmth in ac-
celerating the internal in-
cubation of her eggs.

Figure 449 shows the

o

egg and embryo of the
Monitor Lizard near the

period of extrication: a is Body of a Viper just before it is hatched. XLIII.

the remnant of the food-yolk : b the amnion laid open to show the
embryo, rf; its long trunk and tail are packed in spiral folds as

71

G38

ANATOMY OF VERTEBRATES.

449

in the embryo Serpent : e is the leathery and partially calcified
egg-shell. An embryo Lizard, at an earlier period of develope-
ment, is shown in fig. 443.

Hunter left the following preparations illustrative of the

developement of the Cro-
codile. No. 3364 shows the
calcareous outer crust of
the inner 'membrana puta-
minis' of the egg : No. 3365
shows the attachment of the
vascular allantoisto that shell
membrane in an embryo in
which part of the yolk has been
received within the abdomen.
In No. 3366 the hinder half
of the Crocodile is dissected
to show the condition of the
vitelline and allantoic sacs at
the close of foetal develope-
ment : the vitellicle presents
an irregular lobated form.

o

and its short and narrow
duct communicates with the
small intestine a little below
the duodenum : the aUantois
communicates with the lower
and fore part of the cloaca
by means of a long and slender duct homologous with the urachus :
but no part is dilated, as in certain Lizards, to form the urinary

bladder. In No. 3370 is shown the
vitellicle, after inclusion within the
abdominal walls ; it is much reduced
in size, and its contents are hard and
stringy.

The period of external incubation
by the action of the sun's rays upon
the sand-nest of the eggs of the
Turtle (Chelone Midas) has been
ascertained to be seven weeks.

Figure 450 shows the embryo
of a Snapping Turtle (Chelydra
serpentina) from an egg laid June 21st and opened September 21st
of the same year. The amnios is cut away : c shows the ' area vascu-

Egg and embryo of the Monitor Lizard. XLIII.

450

Embryo Tortoise, Chrlijdra n<.-rj» nbi i«. ccc.

DEVELOPEMEXT OF KEPTILTA.

639

451

losa,' with the omphalo-mesenteric vessels ; b is part of the allantois
with the allantoic or ' umbilical ' vessels, i. The outline of the cara-
pace is just marked on the back of the embryo, and the proportion
of the vertebral column not so modified appears to be greater, as
is its resemblance to the type-form of Eeptile, than in the adult.

The condition of the carapace and the outward form of a Fresh-
Water Tortoise (Emys) is shown in figure 451. The amnios, a, is
turned back to show the posi-
tion of the limbs and head in
the egg : b is the part of the
allantois ; c the remnant of the
yolk. The central opening of
the plastron, which is perma-
nent in the marine Chelonia,
is seen at this period in all the
order, but is quickly filled up
in the land and fresh-water
species. The chief speciality
in the developement of the
scaled Eeptiles, compared with
each other, relates to that of
the carapace and plastron of
the Chelonia : and this has
been explained at pp. 557-9,
and illustrated in figs. 369-72.

When the Turtle is hatched,
the bones of the head show
different degrees of ossification.
The premaxillary and preman-
dibular are most advanced for the purposes of feeding ; the maxil-
lary, the back part of the mandible, the prefronto-nasal, frontal,
and parietal come next in hardness. The superoccipital shows an
outer layer of bone, the rest being gristle ; the basioccipital and
basisphenoid begin to be ossified from the centre ; the alisphenoids
and exoccipitals are still cartilaginous.

The limbs begin to show the digital divisions soon after the
carapace is outlined, and the cartilages of the metacarpals and
metatarsals are first discernible ; the phalanges are composed of
compacted polygonal cells at near the term of incubation, which
then become ' cartilage cells,' widely divided by blastema. The
long bones of the limbs show a thin outer crust of bone inclosing
cartilage, which is progressively ossified, solidifying the shaft,
without subsequent excavation of any medullary cavity.

Embryo of an Emys.

VOL. I.

TT

G40

ANATOMY OP VERTEBRATES.

In the cold-blooded reptiles, hatched by external heat, indepen-
dently of incubation, the course of developement may be inter-
rupted for longer periods, without hurt to the embryo, than in the
warm-blooded Ovipara. Agassiz states that in Testudinata the
common period of hatching may be f postponed for months.'

In Snakes and Lizards a sharp tooth is developed in the pre-
maxillary of the embryo, towards the close of incubation, where-
with they cut through the tough egg-shell.1 The operation of this
transitory and purposive weapon has been observed by Weinland :2
it totally disappears in the adult of most Ophidia. For breaking
through the more brittle shell in Chelonia the embryo is provided
with a sort of horn or hard excrescence above the end of the upper
jaw : this afterwards disappears. In the Crocodilia the snout of
the nearly hatched young is sufficiently hard to break the egg-
shell ; but there is no distinct tubercle, nor any precociously
developed premaxillary tooth.3

1 cccxxxvr.

2 cccxxxvr. 3 crc. p. 288.

452

Initial steps of Vertol irate Developcmqpt. Gorm-3'olk of
Rana temporaria. " cccxxxvr.

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CLXXXII. OWEN. Fossil Reptilia of the Cretaceous Formations. 1851.
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CCXXXVIII. SHARPEY, W. Art. Cilia, Cyclopaedia of Anatomy, vol. i.
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CCXLVII. AXDRE. Description of the Teeth of Choetodon nigricans, Philoso-
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CCLV. MULLER, J. On the existence of four distinct Hearts, having regular
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CCL VI. RUSCONI. Observations sur les vaisseaux lymphatiques de la Sala-
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CCLXI. LEYDIG. Zur Anatomie und Histologie der Clim&ra monstrosa,
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CCLXII. KOLLIKER. Elemeus d'Histologie. 1860.
CCLXIII. HALL, Dr. Marshall. Essay on the Circulation. 8vo. 1831.
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CCLXVII. THOMSON, Allen. Art. Circulation, Cyclopaedia of Anatomy, vol. i.
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CCLXXI. SWAMMERDAM. Biblia Naturae. Eol.

CCLXXII. LAMBOTTE. Memoire sur les modifications que subissent les appareils
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CCLXXIII. OwrEN. On the Blood-disks of Siren lacertina, Microscopical Jour-
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CCLXXXII. HYRTL. Ueber einige Wundernetze bei Amphibien, Medizinische
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CCLXXXIV. SCHLEGEL. Physionomie des Serpents.
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CCLXXXVI. JOHNSON, Geo., M.D. Art. Ren., Cyclopaedia of Anatomy, vol. iv.
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CCXCII. CLARKE, A., M.D. Observations on the Anatomy of the Skin of a
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