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HUNTERIAN LECTURED.

VOL. II.

London :

Printed by A. Spottiswoode,
New.. Street- Square.

LECTURES

ON THE

COMPARATIVE ANATOMY AND PHYSIOLOGY

OF THE

VERTEBRATE ANIMALS,

DELIVERED AT

THE ROYAL COLLEGE OF SURGEONS OF ENGLAND,
IN 1844 AND 1846.

I5Y

RICHARD OWEN, F.R.S.

HUNTERIAN PROFESSOR, AND CONSERVATOR OF THE MUSEUM
OF THE COLLEGE.

LL. Rl'.C.

PART L — FISHES.

ILLUSTRATED BY NUMEROUS WOODCUTS.

LONDON :

FKINTED FOR

LONGMAN, BROWN, GREEN, AND LONGMANS,

PATERNOSTER-ROW,

1846.

“ But ask now the beasts, and they shall teach thee ; and the fowls of the
air, and they shall tell thee :

“ Or speak to the earth, and it shall teach thee ; and the fishes of the sea shall
declare unto thee.

“ Whoknoweth not in all these that the hand of the Lord hath wrought this?”

Job, xii. 7, 8, 9.

ADVERTISEMENT.

The increasing professional avocations of my friend Mr. W.
White Cooper having prevented his rendering the kind aid
which led to the publication of the “ Lectures on the Inverte-
brata” so speedily after their delivery, a longer delay has oc-
curred in the preparation for the press of those on the Ver-
tebrate Animals than was originally contemplated. Such notes
of these Lectures as Mr. Cooper had leisure to take he has
kindly placed at my disposal, and they have served to recal
characteristic expressions and ideas which suggested themselves
in the course of the oral demonstrations. The desire to verify
some of the propositions then enunciated, by repeating the ob-
servations on which they were founded, has led to many new
dissections and examinations of numerous specimens, and re-
ference is made to all those that form part of the Hunterian
Museum. I have, also, reconsulted most of the original
authorities from which the great bulk of the information im-
parted in the Lecture-room had been derived : and a list is
given of the Works referred to in the text.

The utility of the present Volume has been further regarded,
by ingrafting into the text some remarkable discoveries with

A 3

VI

ADVERTISEMENT.

which the Science of Comparative Anatomy has been enriched
since 1844, and by adding details which the time allotted to
the Hunterian course compelled me to omit in the theatre :
but I have been careful to preserve the scope and opinions of
the original Lectures, and, as far as possible, the very words in
which they were delivered.

The Volume concluding the Course will, I hope, appear in
the earlier half of the ensuing year.

London, 1846.

CONTENTS.

LECTURE I.

Introductory. Advantages and Applications of Anatomical Science, p. 2. Ge-
neral Characters of Vertebrate Animals, p. 5. Characters of the Class Pisces, p.
11. ; of the Class Re/)/!7!a,p. 13.; of the Class Aces, p. 16. ; of the Class Mammalia,
p. 17.

LECTURE II.

General Characters of the Skeleton, p. 20. Endo-skeleton and Exo-skeleton con-
trasted, p. 21. Splanchno-skeleton defined, p. 24. Bone; its chemical Com-
position in Fishes, p. 25. ; in Reptiles, p. 25. ; in Mammals, p. 25. ; in Birds, p.
26. Development of osseous Tissue, p. 27. Plasmatic System, p. 28. Texture
of the Bones in different Classes, p. 30. Growth of Bone, 31. Experiments of
Du Hamel and Hunter, p. 32. Structure of the Bones in Reptiles, p. 33. ; in
Mammals, p. 34. ; in Birds, p. 34. Definition of a Bone ; its difficulty, p. 36.
Classification of Bones, according to their Form, their Position, and Mode of
Development, p. 40. Homology, general, serial, and special, defined, p. 40.

LECTURE III.

General Type of the vertebrate Endo-skeleton, p.41. Definition of a Vertebra,
p. 42.; its Elements and their Synonyms, p. 42. Typical Vertebra exemplified,
p. 43. Number of Vertebrae governed by the nervous System, p. 44. Develop-
ment of vertebral Column ; permanent Arrests of its Stages exemplified in
Fishes, p. 45. Characters of the Vertebrae in different vertebrate Classes, p. 46.
Classification of Fishes, p. 47. Vertebral Column of Myxines, p. 51.; of Lam-
preys, p. 52. ; of Sturgeons, p. 53 ; of Chimeera-, p. 54. ; of Plagiostomes, p. 54. ; <

©f osseous Fishes, p. 57. Intercalations of Parts of Exo-skeleton to form median
Fins, 66. Caudal Fin, Characters of homocercal and heterocercal Fishes ; An-
tiquity of the latter, and their Predominance in the earlier fossiliferous Deposits,
p. 67. Characters of Malacopterygians, and Acanthopterygians, p. 68. Modi-
fication of dorsal Spines as Weapons, p. 69. Ichthyodorulites ; Lock-and- Trig-
ger Spine of Balistes, p. 69. ; dentigerous Spines of Siluroids, p. 70.

vm

CONTENTS.

LECTURE IV.

The Skull of Fishes. Cranium not distinct from spinal Column in Lancelet. De-
velopment of Skull in Fishes, p. 71. Permanent Arrests of its Stages exemplified
in the Dermopteri, p. 72. ; in the Plagiostomes, p. 73. ; and Lepidosiren, p. 78,
which is the Key to the Complexities of the Skull of Osseous Fishes. Pisoine
Characters of Skeleton of Lepidosiren, p. S3.

LECTURE V.

Skull of osseous Fishes. Its general Form, p. 84, and manifold Functions, p. 85. ;
its Cavities, p. 85. ; its Ridges and Depressions for muscular Attachments, p. 85.
Classification of its Bones, p. 86. ; Arrangement of those of the Endo-skeleton in
vertebral Segments, p. 87. The Segments defined, p. 88. Primary Segments of
Brain, which govern the vertebral Segments of Skull, p. 89. Neural Arches,
p. 89. Sense-capsules, p. 101. Haemal Arches, and their Appendages, p. 104.
Pal ato -maxillary Arch, p. 105. Tympano-mandlbular Arch, p. 110. Hyoidean
Arch, p. 114. The splanchnic branchial Arches, p. 116. Scapular Arch, p.
117. Modifications of the pectoral Fins, p. 120.; their special Homology
with Wings, Fore-limbs, and Arms, p. 124. ; their general Homology, p. 125.
Structure and Homologies of the ventral Fins, p. 126. Ichthyological Abbrevi-
ations and Formulae of the Fin-rays explained, p. 126. Linnaean Characters, from
ventral Fins, of the ‘ abdominal,’ ‘ thoracic,’ ‘jugular,’ and ‘ apodal’ Orders, p. 1 27.
Fins of Plagiostomes, p. 128.

LECTURE VI.

Dermal cranial Bones elucidated by the Skull of the Sturgeon, p. 130. ; and
Lepidosiren, p. 134. Relations of dermal Bones to mucous Ducts, p. 136.
Homologies of the opercular Bones, p. 137. Dermal Bones of the Trunk, p. 141.

‘ Lateral Line,’ what, p. 141. Structure, Homology, and Development of Scales
of Fishes, p. 141. ; their kinds defined, p. 142. Fishes with cycloid and ctenoid
Scales comparatively modern, p. 142. High Antiquity of Ganoids and Placoids,
p. 143. Embryonic Characters of primreval Fishes, p. 144. Development of
Fins, p. 144, ; permanent Arrests of its Stages in extinct Fishes, p. 145.
Teleology of the Skeleton of Fishes, p. 145. Adaptation of the gristly Skeleton
of the Shark, p. 147, and Sturgeon, p. 148, to their respective Habits. Final
Purpose of the large Head of Fishes, p. 149. Continued Growth of Cranium,
adjusted to restricted Growth of Brain, by modifications of arachnoid Tissue,
p. 150. Conditions of the Size, Mobility, and Complexity of the inferior Arches
of the Skull, p. 151. Advantages of the Absence of a Sacrum, and of the
restricted Development of the Homologues of Arms and Legs, p. 153. Ex-
periments showing the Uses of the different Fins, p. 156. Synonyms of the
Bones of the Head of Fishes, according to their special Homologies, p. 1 58.
Synonyms of the Bones of the Head of Fishes, according to their general
Homologies, p. 161.

COKTICNTS.

IX

LECTURE VII.

Myology of Fishes, p. 163. General Disposition of their muscular System seg-
mental, corresponding with the Vertebrae, p. 163 Special Description of the
segments, or ‘ Myocommata,’ p. 164. Modified Myocommata of the Head,
p. 165. Muscles of Torpedo, p. 167. Muscles of the Pectoral Fins, p. 167. ;
of the Ventral Fins, p. 168. ; of the Vertebral Fins, p. 168. Characters of the
Myonine in Fishes, p. 169. ; Crimping, p. 169. Action of the Muscles of
Fishes in swimming, leaping, flying, and wielding their various Weapons, p. 170.

LECTURE VIII.

Neurology of Fishes, p. 171. Simple neural axis of Lancelet, p. 171. Natural
Division of neural axis into ‘ Brain’ and ‘ Myelon’ in other Fishes, p. 172. Cha-
racters of Myelon or ‘ Medulla Spinalis,’ p. 172. Myelonal Ganglia and Canal,
p. 173. ‘ Macromyelon’ or Medulla Oblongata, p. 174. Cerebellum, p. 175.

Mesencephalon, p. 177 Optic Lobes, p. 177. Hypoaria, p. 178. Hypophysis,
p. 179. Conarium, p. 179. Prosencephalon, p. 180. Rhinencephalon, p. 182.
Distinction between Rhinencephalic Crura and Olfactory Nerves, p. 183. Ho-
mology of Prosencephalon, p. 184. Physiology of the Vagal Lobes, p. 185.;
of the Cerebellum, p. 186. ; of the Optic Lobes, p. 187. ; of the Prosence-
phalon, p. 188. Membranes of the Neural Axis, p. 188. ; Olfactory Nerves,
p. 189. Optic Nerves, p. 190. Oculo-Motorius, p. 191. Trochlearis, p. 193.
Abducent, p. 193. Trigeminal, p. 193. Facial, p. 195. Acoustic, p. 195.
Vagus, p. 195. Spinal Nerves, p. 197. Sympathetic, p. 198. Organs of
Smell, p. 199. Organ of Sight, p. 202. Organ of Hearing, p. 207. Its Con-
nection with the Air-Bladder, p. 210. Electric Organs in Torpedo, p. 212.; in
Gymnotus, p. 213. Experiments on, by Matteucci, p. 215. ; and Faraday, p. 216.
Baron Humboldt’s Account of the capture of Gymnoti, p. 216. Analogies of
Action of Electric Organs to that of voluntary Muscle, p. 217. Muciferous
Nerves, p. 218. Follicular Nerves, p. 218.

LECTURE IX.

Digestive System of Fishes, p. 219. The Teeth, p. 219. : their Number, p. 219.;
Form, p. 219. ; Situation, p. 221. ; Attachment, p. 222. ; Substance, p. 224. ;
Chemical Composition, p. 225. ; Structure, p. 226. ; Development, and Re-
production, p. 227. The Mouth, p. 228. ; anterior and posterior Jaws,
p. 229. Quasi-Salivary Glands, p. 230. ; Irritable Palate of Cyprinoids, p.
230. (Esophagus, p. 232. Stomach, p. 233. Regurgitation and Rumination
of Fishes, p. 236. Peritoneum, its outlets, p. 231. ; Intestines, small, p. 237. ;
large, p. 238. Spiral Valve, p. 239. ; its final purpose in Sharks, p. 240.
Relative position of Anus characteristic of Fishes, p. 240. Mesogastry and
Mesentery, p. 241. Variable Situation of Cloacal Outlet, p. 241. ‘ Cop-

rolites,’ p. 241. Liver, p. 241. Gall-bladder, p. 243. Gall-ducts, p. 244.
Pancreas, p. 244. In what Fishes it is absent, and why, p. 2-14. ; its progressive
Development in Fishes, p. 245.

X

CONTENTS.

LECTURE X.

Vascular System of Fishes, p. 246. Absorbents, Lacteals, p. 247. ; Lymphatics,
p. 248. Lymphatic Heart, p. 248. Veins, vertebral, p. 250. ; Visceral, p. 251.
Portal System, p. 252. Portal Heart of Myxines, p. 252. Hepatic Venous
Sinuses, p. 252. Genesis of Blood-discs, p. 253. The Heart, p. 253. Acar-
diac Vascular System of Lancelot, p. 254. Pericardium, p. 255. ; its Outlets,
p. 255. Homology and Analogy of the Fish’s Heart, p. 255. Auricle, p. 256.
Ventricle, p. 257. Bulbus arteriosus, p. 257. Heart of Lepidosiren, p. 258.
Essential Character of a second Auricle, p. 258. Branchial Artery, p. 258.
Comparison of normal Gills of Fishes with Gill-sacs of Myxinoids and Lam-
preys, p. 259. Branchial Apertures in Lancelot, Myxine, Bdellostome, Lam-
prey, Plagiostomes, and Osseous Fishes, p. 259. Branchi* liberse and Branchice
fixse, p. 259. What kills a Fish when out of Water, 260. Modifications of
Gill-chamber enabling a Fish to live out of Water, p. 260. Functions of Gills,
p. 260. Gills plicated, tufted, pectinated, p. 261. ; uniserial and biserial, p. 26). ;
variable Number in bony Fishes, p. 261. Defensive Valves and Processes of Gill-
arches, p. 262. Branchial Circulation, p. 263. Development of Gills, p. 264.
Hyoid uniserial Gill, p. 265. Retentions of embryonic branchial Structures,
p. 266. Deciduous external Gills in Plagiostomes, p. 267. Accessory branchial
Organs in the Labyrinthibranchii, in Heterobranchus, in Amphipnous, p. 267. ; in
Saccobranchus, p. 268. Arteries, p. 268. Pseudobranchiae, p. 268. Question
of their Relations to thyroid Glands discussed, p. 269. Plexus mirabiles in
Lamna and Thynnus, p. 271. Spleen, p. 271.

LECTURE XL

Pneumatic and Renal Organs. Air-bladder, p. 272. ; its Structure, p. 272. ; and
gradual Metamorphosis into a Lung, p. 273. Inconstant Character of the ru-
dimental Air-breathing Organ, and of the Ductus pneumaticus, p. 273. ; Vas-
cularity of Air-bladder, its Diversities, p. 274. Unipolar Retia mirabilia,
p. 275. Bipolar Retia mirabilia, p. 275. ‘ Air-gland’ present in some Fishes

that have the Air-duct, p. 276. Magnus’s Discovery of free Gases in Blood,
p. 276. Chemical Analysis of Contents of Air-bladders, p. 276. Primary
Function of Air-bladder in Locomotion of Fish'es, p. 276. ; Objection from its
Absence in Sharks obviated, p. 277. Adaptation of Gills and Air-bladder of
Lepidosiren to its Habits, p. 278. ; Homology and Analogy of Air-bladder dis-
cussed, p. 278. Renal System of Fishes, p. 282. Kidneys of Dermopteri,
p. 282. ; of Osseous Fishes, p. 282. Urinary Bladder, p. 282. Renal System
of Lepidosiren and Plagiostomes, p. 283. Relations of Kidneys of Fishes to
the primordial Kidneys of higher Vertebrates, pp. 282. 285. Supra-renal
Bodies, p. 285.

LECTURE XII.

Generative System, p. 286. ; its enormous Development and extensive Range of
Varieties in Fishes, p. 286. These represent progressively arrested Stages of
its Development, p. 286. ; Parallelism in this respect between Male and Female

CONTENTS.

XI

Organs, p. 292. The Testis, where single, p. 286. ; where double, p. 287. ; where
provided with a Duct, p. 287. ; Varieties of the Vas deferens, p. 287. ; its Ter-
mination, p. 287. Further Complexities by an Epididymis, p. 288. ; by a cel-
lular Receptacle, or ‘ Vesicula,’ p. 288. ; by a rudimental Penis, p. 288. ; and
Claspers, p. 288. Female Organs, p. 288. ; show corresponding arrests of de-
velopmental stages, p. 289. ; the Ovarium, p. 289. ; at first without Oviduct,
p. 289. ; various Conditions and Termination of Oviduct, p. 290. ‘ Stroma

Ovarii,’ p. 289. Modification of Ovary in Fishes, with ovarian Gestation, p. 289.
Ovarian Scrotum, p. 289. Stages in development of the ‘ Morsus Diaboli,’
p. 289. Fallopian, glandular, and uterine Divisions of Oviducts in Plagios-
tomes, p. 290. Uterine Cotyledons, p. 291. Marsupial Pouches, p. 291. De-
velopment of Fishes, its Seven Stages, p. 291. Semination, p. 292. Sperma-
tozoa, p. 292. Germination, p. 293. Ovarian Ovum, p. 293. Fecundation,
p. 293. Sexual Characters and migratory Instincts, p. 294. Combats of
Males, p. 294. Spawning, p. 294. Foetation, p. 295. First Changes in the
Ovum, Rusconi’s Observations, p. 295. ; compared with the Development of the
Entozoon, p. 296. Rotation of Embryo in ovo, p. 296. Vertebral and visceral
germinal Layers, p. 296. ‘ Laminae dorsales ’ and ‘ Laminae ventrales,’ p. 296.

Succession of vertebral Parts, p. 297. Development of alimentary Canal, p. 297. ;
of Vessels, p. 297. ; of the Heart, p. 298. ; of the branchial Arches and Vessels,
p. 298. ; of the Brain, p. 298. ; of the Liver, the Kidneys, and generative
Organs, p. 298. ; of the Air-bladder and Duct, p. 299. ; of the Rostrum and
Jaws, p. 299. Embryonic Position of Mouth retained in Plagiostomes, and
embryonic Form of Head in all the ‘ Old Red ’ Fishes, p. 299. External and
internal Yolk, p. 299. External Branch i®, p. 300. Singular Forms of Eggs
in oviparous Plagiostomes, p. 301. Ovoviviparous and viviparous Plagiostomes,
p. 301. Essential Distinction of latter from Mammals, p. 301. Growth of
Fishes, especially of the Salmon, its Metamorphoses and Migrations, p. 302.
Incubation of Fishes, p. 303. ; in marsupial Pouches of the Male, p. 303.
Nests and parental Instincts of certain Fishes, p. 303.

HUNTERIAN LECTURES,

1844.

INTRODUCTORY LECTURE..

CHARACTERS OF THE CLzVSSES OF VERTEBRATE ANIMALS.

Mr. President and Gentlemen,

In appearing before you on the present occasion, again honoured by
the Council with the arduous and responsible duties of the Hunterian
Professorship, it might be expected that time, and the repetition of
their performance, would have abated much of that anxiety and diffi-
dence which naturally oppress whoever undertakes to expound from
this place, and before this audience, the principles of Comparative
Anatomy and Physiology. Seven successive annual deliveries of the
Hunterian Lectures have, indeed, in some measure familiarised me
with this department of the expository labours of the Museum ;
but they have also tended to impress me with the necessity for
increased exertion in order to their successful fulfilment. And
now, more than on any previous occasion, Avhen we have assembled
in the Theatre of the College under the auspices of a new Charter,
honoured, for the second time, by a special mark of the Royal
condescension and favour*, it more especially behoves us, each in
his respective sphere, and according to his capacity, to redouble our
efforts to maintain, and, if possible, to raise, the high character of
British Surgery.

Called by the fruitful principle of the division of labour to the
duties of the conservation, extension, and exposition of the pre-
parations which enrich the Museum, — impressed by a sense
of the intimate connection of the present estimation of Surgical
Science with the labours in Comparative Anatomy of that immortal
Physiologist by whom the Museum was founded, — convinced that
what has before reflected lustre on the name of Surgeon must
continue to have the same influence, — I have felt it e.specially

* The present Charter of tli3 Royal College of Surgeons was granted September
4th, 1843.

VOL. II.

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HUNTERIAN LECTURES,

1844.

INTRODUCTORY LECTURE.,

CnAKACTERS OF THE CLASSES OF VERTEBRATE ANIMALS.

Mr. President and Gentlemen,

In appearing before you on the present occasion, again honoured by
the Council with the arduous and responsible duties of the Hunterian
Professorship, it might be expected that time, and the repetition of
their performance, would have abated much of that anxiety and diffi-
dence which naturally ojipress whoever undertakes to expound from
this place, and before this audience, the principles of Comparative
Anatomy and Physiology. Seven successive annual deliveries of the
Hunterian Lectures have, indeed, in some measure familiai’ised me
with this department of the expository labours of the Museum ;
but they have also tended to impress me with the necessity for
increased exertion in order to their successful fulfilment. And
now, more than on any previous occasion, when we have assembled
in the Theatre of the College under the auspices of a new Charter,
honoured, for the second time, by a special mark of the Royal
condescension and favour *, it more especially behoves us, each in
his respective sphere, and according to his capacity, to redouble our
efforts to maintain, and, if possible, to raise, the high character of
British Surgery.

Called by the fruitful pidnciple of the division of labour to the
duties of the conservation, extension, and exposition of the pre-
parations which enrich the Museum, — impressed by a sense
of the intimate connection of the present estimation of Surgical
Science with the labours in Comparative Anatomy of that immortal
Physiologist by whom the Museum was founded, — convinced that
what has before reflected lustre on the name of Surgeon must
continue to have the same influence, — I have felt it especially

* The present Charter of the Royal College of Surgeons was granted September
4th, 1843.

YOU. II.

r.

2

INTRODUCTORY LECTURE.

incumbent on me to labour in the acquisition of that knowledge of
the science of Animal Organisation, and of its varied and daily
extending applications, which may enable me so to discharge my
present duties that the valuable time, which you are not unwilling to
spare for attendance on these Lectures, may be not unprofitably
bestowed.

And, first, permit me to dwell a little on the inestimable privilege
which we enjoy, in entering upon our Professional studies by the
portal of Anatomy.

How vast and diversified a field of knowledge opens out before us
as we gaze from that portal ! Consider what it is that forms the
subject of our essential introductory study ; nothing less than the
organic mechanism of the last and highest created product which has
been introduced into this planet. Contrast this, which both Sage and
Poet have called the “ noblest study of mankind,” with the dry and
unattractive preliminary exercises of the Lawyer or the Divine.

Every new term which the Anatomical student has to commit to
memory is associated with a recognisable object, with some part
which may be vibrating, contracting, or pulsating, in his own frame.

First, we enter upon the study of Human Anatomy that we may
know with what we have to deal as Operative Surgeons ; and, as Phy-
sicians, may recognise the seat of disease. Then, that we may learn,
by the structure and connections of the parts of the Human body,
their office in the vital economy. We next test the physiological ideas,
so acquired, by experiments on the lower animals, which we are thus
led to dissect in order to find the amount of resemblance with the
Human structure which must guide the operation, influence the
judgment as to the I’esult, and indicate the conditions for new expe-
riments.

We cannot advance far into the lower region of Anatomy without
appreciating the same admirable adjustment of means to ends which
pervades the Human frame : thus the field of Physiology expands
before us, and we are enabled to bear a part with a Ray or a
Paley in illustrating the doctrine of final causes, and demonstrating
the “ Wisdom of God in the Creation.”

In extending our Anatomical comparisons, we cannot fail to be
struck with the close general resemblance of the structure of the
lower animals with that of Man : almost every part of the Human
frame has its homologue in some inferior animal ; and we at length
begin to perceive that Man’s organisation is a special modification
of a more general type. From analysis, the philosophic mind
is irresistibly led on to comparison and synthetic combination
of the multitude of particulars observed. In grasping the abstract idea
of the general type, we appreciate the precise nature of the charac-

INTRODUCTORY LECTURE.

3

:eristlc modifications of the Human frame ; and then only can we be
said to know properly our own structure, and, from Anthropo-
tomists, to become Anatomists in the true sense of the word.

As such we begin to feel ourselves in possession of an instrument
which can be brought to operate successfully in the solution of
deep and difficult problems of more general interest in the common-
wealth of knowledge, and which renders us indispensable auxiliaries
in the advancement of Sciences whieh might at first appear to have
but a remote relationship with Anatomy. I need not expatiate on
the light which Anatomy lends to the Zoologist, in threading the in-
tricate mazes of the natural affinities of animals : it is, by universal
consent, admitted to be the essential basis of a sound system of classi-
fication. I need not dwell on the importance of the Comparative Ana-
tomy of the minute and low organised Invertebrata in establishing
true theories, and eradicating false notions, of the origin of living
species ; of which different hypothetical secondary causes have been
from time to time offered for the acceptance or speculation of the
tliinking public.

But I would allude to the power wdiich the appreciation of the co-
relations and interdependencies of the several parts of each organic
machine gives us to interpret the nature of the whole from the ob-
servation of a part.

By this principle its discoverer, the immortal Cuvier, and his
successors in this application of Anatomj’, have been enabled to re-
store and reconstruct many species that have been blotted out of the
book of life. By this we determine from fossil bones or fragments,
submitted to us by the Geologist, the speeies which are charac-
teristie of different strata. By physiological deductions we can prove
that such species, now extinct, have lived and died, generation after
generation, through the pei'iod when those additions were made to
the earth’s crust which their remains charaeterise.

Thus, and thus only, can we obtain a clear idea of the lapse of
time in which these formations have taken plaee. The order of
superposition of strata indicates, indeed, their successive formation,
but the determination of their organic remains proves that each
formation ivas gradual and progressive.

One of the results of this application of Anatomy has been no less
than the discovery of the law of succession of animal life on this
planet, or the determination of the relative periods at which the dif-
ferent classes were successively called into being.

Another result may be expected, and is in progress, as a corollary
of the preceding, viz. the determination of the true Chronology of
the Earth.

B ‘2

4

INTRODUCTOKY LECTURE.

We know that it has pleased God to grant us faculties, by the
right use of which we may obtain a true knowledge of His works ;
and it seems part of His providence to permit certain parcels of
knowledge to be thus introduced from time to time, to the dissipation
of the erroneous notions which previously prevailed. By the exer-
cise of these faculties, the true shape of our Spheroid was determined,
and, after some opposition*, accepted : next, its true relation to the
sun, as respects its motion. It has been reserved for the present
generation to acquire more just ideas of the age of the world, and
Anatomy has been, and must be, the chief and most essential means
of establishing this important element in the earth’s history.

But Anatomy aids not only the Geologist, but the Geographer : by
comparing the local distribution of restored extinct species from
coeval geological strata over all the earth, with the geographical dis-
tribution of existing animals, we obtain an insight into the past con-
ditions of continents and islands ; we determine that our own island,
for example, once formed part of the continent, and obtain data for
tracing out much greater mutations and alternations of land and
sea.f

Thus, upon Anatomy depends the safe and successful practice of
Medicine and Surgery: the knowledge of the uses of parts, and of
their essential nature in Man, viewed as modifications of a general
type. Anatomy is the basis of right classification and philosophical
Zoology : it unfolds the law of the introduction of animal life on this
planet ; it is essential to the right progress of Geology, and gives
an insight into the true chronology and ancient geography of the
globe.

Almost every day brings some new proof of the importance of the
knowledge of Animal Organisation, which bids fair to take rank as the
first of all sciences ; and it is to Anatomy, thal we have the high
privilege to be introduced at the very outset of our professional
studies.

More might be said, and better, in praise of our peculiar science ;
but when I reflect on that department which I propose to treat of
in the present Lectures, viz. the Comparative Anatomy of the Ver-
tebrate Classes of Animals, its great extent, and the diversity of
details which it embraces, I feel it incumbent to enter, without fur-
ther preface, upon the proper subject of this Course.

• See Laetaiitius, Instit. lib. iii. c. 24, against the earth’s rotundity ; and Angus-
tine, De Civil. Dei, lib. xvi. c. 9. against Antipodes.

f Report of British Association for the Advancement of Science, 1844; and
“ History of British Fossil Mammalia,” 8vo. 1845, pp. xxvii. xlvi.

CUARACTEKS OF VERTEBRATE ANIMALS.

5

In the numerous classes of animals which constituted that inferior,
more extensive, and diversified group, linked together by the single
negative character of the absence of a vertebral column, and thence
termed “ Invertebrata,” we saw that, as the several series became ele-
vated in the scale of organisation, they diverged from one another by
reason of the preponderating development of some particular class of
organs, and culminated in species, inferior either in their general form,
or their powers of motion and perception, to some of the antecedent
forms, through which the series had passed.* The spider and the crab
are not the kinds of animals in which one should have anticipated
that the type of organisation, so richly varied in the Insect class, would
have ended, had that class been a step in the dii’ect progress to the
vertebrate series. The loss of wings, and the abrogation of the power
of flight, would indicate a retrograde course of development. In the in-
sect, the animal organs, more particularly those of locomotion, prepon-
derate over the vegetative or plastic organs, and in the attempt, as it
were, to restore the balance, by establishing, as in the Crustacea and
Arachnida, a better defined system of circulation, and a more vigorous
and concentrated heart, the general plan of the articulate structure
appears not to be such as to bear this adjustment without a sacrifice
of some of the faculties enjoyed by Insects. So likewise the route of
organisation traceable through the molluscous type seems, on the
other hand, to lead to an extreme subordination of the motive and
sensitive to the vegetative systems. And in those species which make
the nearest approach to the Vertebrata, we find the viscera of organic
life occupying so large a propoi’tion of the body, that no room is left\
for the development of nervous or muscular organs, except by what
seems an undue expansion and overloading of the head, as, for ex-
ample, in the Cephalopoda. In fact, the nervous system, the essence
and prime distinction of the animal, had not, so to speak, any proper
or defined abode in the bodies of the invertebrated animals. Its
centres were sometimes dispersed irregularly through the general
cavity of the body, sometimes aggregated around the gullet, some-
times arranged with more symmetry along the abdomen ; yet seldom
better cared for or protected than the neighbouring viscera.

The grand modification, by which a higher type of organisation is
established, and one which becomes finally equal to all the contin-
gencies, powers, and otfices of animated beings, in relation to this
planet, is the allocation of the mysterious albuminous electric pulp in
a special -cylindrical cavity, of which the firm walls rest upon a basal

* Hunterian Lectures, Invertebratii, 8vo. 18-L5.

B

6

INTRODUCTORY LECTURE.

axis, forming the centre of support to the whole frame, and from
which all the motive powers radiate, and this axial cylinder {Jig> 1. v)
is called the “Vertebral Column ; ” vertebral, as consisting of seg-
ments of the skeleton, which turn one upon the other, and as being
the centre on which the whole body can bend and rotate ; from the
Latin “ verto, vertere^' to turn.

Ideal section of a Vertebrate (Mammalian) animal.

The vertebrated animals have the nervous matter concentrated in
this vertebral case, which expands at certain parts, where the
lai’gest currents of sensation enter, and those of volition go out ; and
more especially at the anterior or upper extremity, where the impres-
sions to be appreciated by the nervous centre are the most varied
and the most distinct. The expanded mass of nervous matter, at this
part, is called the brain {fig. 1. b), the rest of the nervous axis, the
spmal chord, {ch, cJi) ; whence the highest primary group of animals
is called “ Myelencephala,” from the Greek words signifying brain
and spinal marrow. The prolongations and ramifications from these
centres, forming the internuntiate channels of sensation and the will,
are the nerves.

There are five special modifications of sensation in the vertebrated
animals, three of which have special nerves, viz. smell {ol), sight (o/>),
and hearing {au). Taste (t) appears to be less generally enjoyed
by the Vertebrata, and its nerve is a large branch of an ordinary
nerve, the fifth pair. Feeling, which, in its more exquisite degree,
constitutes touch, seems a common property of all those nervous fila-
ments, which, passing into the posterior columns of the central axis,
are continued to the brain. Speaking generally, such are the attri-
butes of the recipient or sensitive portion of the nervous axis in the
Vertebrated animals. They can take cognisance of all the impressing
powers which surround tliem ; as the character and resistance of tlie
surface which supports tliem, the flavour and fitness of the substances
Avhich nourish them, the purity of the atmosphere which they breathe,

CIIARACTliUS OF VERTEBRATE ANI3EVLS.

7

the delicate vibrations of that atmosphere which follow the mutual
contact or percussion of sonorous bodies, and the finer vibrations of
a more subtle aether, the appreciation of which produces the sense
of sight.

With these means of perceiving, knowing, and investigating the
world around them, the Vertebratcd animals possess a proportionate
power of acting upon and subduing it. Not any species is fixed to
the earth ; all can move, and every variety and power of animal
locomotion is manifested in the vertebrated sub-kingdom. Yet some
permanently retain the worm-like figure, which all primarily manifest
in common with the embryos of the articulate series ; but always
with the grand difference of the dorsal nervous column. Such
vermiform species glide by undulatory inflections of the entire
body through the waters, or on the surface of the ground. But in
most Vertebrata special instruments of locomotion are developed ;
some single from the median line, some in pairs ; the latter never ex-
ceed four in number, two before or above, called arms, or pectoral
extremities (P), and two below or behind, called legs, or pelvic extre-
mities ( V) : thus, the vertebrated type is essentially tetrapodak* The
solid mechanical supporting and resisting axis, framework, or lever-
age (s/{) of these members is internal, vascular, and commonly ossi-
fied. It is covered, and, as it were, clothed by the muscles (?«), which
are attached to its outer surface. The elementary contractile fibre of
tlie voluntary muscular system is transversely sti'iated.

The internal position of the skeleton seems to be the chief con-
dition of the attainment, by certain Vertebrata, of a bulk far surpass-
ing that of the largest of the Invertebrata : and the division of the
skeleton into numerous pieces diversely articulated, gives great variety
and precision to the movements of the Vertebrate animals.

The forms and proportions of the Vertebrata are as vai’ied as their
kinds of locomotion, and the elements in Avhich these are exercised.
With very few exceptions the body is laterally symmetrical, the right
and left sides corresponding. We may likewise discern a general
characteristic of the Vertebrata in the tendency to a symmetrical
development, or a repetition of parts in the vertical direction ;
that is, in the dorsal and ventral regions. Each vertebral segment
of the internal skeleton, for example, forms typically a dorsal and a
ventral arch ; the one protecting the neiwous axis, the other the vas-
cular trunks and organs of plastic life. The nervous trunk itself

* The homologues of these special instruments of locomotion may exist in
greater numbers, more or less developed and modified, in suhserviency to other
functions ; as, for example, the opercular and hranchiostegal flaps of fishes, the
simple appendages of the ribs in fishes and in birds. The arms and legs commence
in Lepidosiren, for example, as simple unbranehed filamentary appendages diverging
from inferior vertebral aiches.

8

INTRODUCTORY LECTURE.

consists of dorsal and ventral columns. Whilst the Invertebrata
manifest a general tendency to development in breadth, the Ver-
tebrata rather gain in height by this doubling or repetition of
parts in the vertical or dorso-ventral direction ; and in this we may
discern the tendency to rise above the surface of the earth, until in
man the entire body is uplifted ; and what is below and above in all
other Vertebrata, in him becomes before and behind.

The general external integument in the Vertebrata is rarely bur-
thened and clogged by large and massive calcareous plates, but is
usually defended by light, and sometimes exquisitely organised and
singularly complex developments of the epidermal covering ; modified
according to the spheres of existence, the habitual temperature and
movements, and therefore eminently characteristic of the different
classes of Vertebrated animals.

The actions of the unusually developed nervous element, — whether
the vibrating filament conveys to the sentient centre impressions
from without, or, obedient to the inward intelligence, imparts from
within the stimulus of volition to the moving fibre, — are essentially
productive of change. It is most probable that the same nervous
fibre is not equally fit for two successive actions ; but needs, after
each, a certain amount of restoration. The same may be predicated
of the action of the muscular fibre ; viz., that some change, no matter
how small, but to that extent unfitting it for the due repetition of
the act, is the consequence of its stimulated contraction : and thus
the continued existence of the living animal requires the presence of
organs of renewal and repair in intimate, but harmonious combination,
with those of sensation and motion.

The raw material of this restoration is derived from without : the
alimentary canal, in which the conversion and animalisation of the
food take place, is provided, in the Vertebrata, with two apertures,
an entry or mouth (os), and an excremental outlet {as). The jaws
(y ) are two in number, and placed one below or behind" the other,
working vertically or in the axis of trunk ; the principal part of
the alimentary canal is contained in an abdominal cavity, and is sup-
ported by a reflection of the serous membrane upon the walls of that
cavity; and the canal is divided into oesophagus (ce), stomach (y),
and intestine (^). All Vertebrata have a liver (Z) which is usually
a very complicated gland, with a speciixl venous or portal system of
vessels ; and the biliary secretion is conveyed into the commence-
ment of the intestine. The pancreas (p), which in most Vertebrata
presents the form of a compact and conglomerate gland, adds its se-
cretion to the bile in the duodenum. The spleen (s), a cellulo-
vascular ganglion, or gland without a duct, makes its first appeai’ance
coincidently with that of the portal vein, and manifests a progressive

CHARACTERS OF VERTEBRATE ANIMALS. ^

9

development closely corresponding with that of the pancreas. Lac-
teal vessels convey the nutrient fluid to the veins, and thus it reaches
the heart.

The central organ of circulation, always present, and of a compact
muscular character, always below or anterior in position to the ali-
mentary tube and nervous axis, is situated towards the fore-part of
the body, most commonly in a compartment distinct from the abdo-
men, where it is suspended in a special bag or pericardium {fig- 1.
li). The blood is red in all the Vertebrated animals, and the colouring
matter is contained in microscopic discoid cells, of an oval or circular
form {fig. 4.). The whole or part of the circulating fluid is trans-
mitted directly from the heart to the respiratory organ {fig- 1. /</)•
The respiratory medium, whether air or water, is admitted to the
respiratory organ by the mouth. From this organ the arterial blood
is sent, sometimes directly, sometimes after a second return to the
heart, or in both ways, to the rest of the system ; but the breathing
organs are never developed, as we saw in many of the Invertebrata,
from the returning venous channels.

The venous blood in the lower Vertebrata is submitted to the
depurating influence of the kidneys; but in the higher Vertebrata
these de-azotising glands {li) are supplied exclusively by arteries.
A part of the venous blood in all Vertebrata circulates through the
liver, as through a second and subordinate lung, before it finally
reaches the heart.

The system for perpetuating the species is not complete in any
Vertebrated animal ; that is, the generative organs are divided be-
tween two individuals, there being no natural Hermaphrodite in this
sub-kingdom. Every Vertebrate embryo soon takes on its special
and determinate sexual character, and ends a perfect male or per-
fect female — a fertiliser or a producer.

'T'he instinctive sense of dependence upon another, manifested by the
im|mlse to seek out a mate, — which impulse, even in fishes, is some-
times so irresistible that they throw themselves on shore in the pur-
suit,— this first step in the supercession of the lower and more general
law of individual or self preservation, although not fii’st introduced
at the Vertebrate stage of the animal series, is never departed from
after that stage has been gained. To this sexual relation is next
added a self-sacrificing impulse of a higher kind, viz. the parental
instinct. As we rise in the survey of Vertebrate phenomena, we see
the entire devotion of self to offspring in the patient incubation of
the bird, in the unwearied exertions of the Swift or the Hawk to
obtain food for their callow brood when hatched ; in the bold de-
monstration Avhich the lien, at other times so timid, will malcc to
repel threatened attacks against her cowering young.

10

INTRODUCTORY LECTURE.

Still closer becomes the link between the parent and offspring in
the Mammalian class, by the substitution, for the exclusion of a pas-
sive irresponsive ovum, of the birth of a living young, making
instinctive irresistible appeal, as soon as boim, to maternal sympathy ;
deriving nutriment immediately from the parent’s body, and both
giving and receiving pleasure by that act.

These beautiful foreshadowings of higher attributes are, however,
transitory in the brute creation, and the relations cease, as soon as
the young quadruped can provide for itself. Preservation of off-
spring has been superinduced on self-preservation, but there is as
yet no self-improvement : this is the peculiar attribute of mankind.
The human species is characterised by the prolonged dependence of
a slowly maturing offspring on parental cares and affections, in which
are laid the foundations of the social system, and time given for in-
stilling those principles on which Man’s best wisdom and truest hap-
piness are based, and by which he is prepared for another and a
higher sphere of existence. In this destination alone may we dis-
cern an adequate end and purpose in the great organic scheme deve-
loped upon our planet.

In ascending to Man, we trace a very extensive and varied, but
progressive course of development, through the great Vertebrated
Series, which commences at a very low point.

It might, perhaps, be imagined that the lowest Vertebrated form
began where the highest Invertebrated form ended, and made a direct
step in advance in the scale of Animal Organisation. Such, indeed,
ought necessarily to follow on the hypothesis of the development of
species by progressive transmutation, and of the arrangement of
animal life in a single and uninterrupted chain of being.

But truer views of the nature and direction of Zoological affinities,
and a deeper insight into the laws of Development and of Unity of
Organisation in the Animal Kingdom, concur to disprove those once
favourite and recently-revived hypotheses. We have seen that the
Invertebrata resemble each other only at the earliest and most tran-
sitory periods of their development, diverging thence, in special
directions, to the manifestation of very distinct types of animal struc-
ture. So likewise we must look to the very beginning of the de-
velopment of the Vertebrate animal before we shall discover that
amount of concordance which will justify us in predicating “Unity
of Organisation” between it and any of the Invertebrated forms.
And when, with infinite care and minutest scrutiny, availing our-
selves of all the aids and appliances of optical art, we have arrived
at clear and satisfactory demonstration of the greatest amount of re-
semblance, in constitution and properties, between the Vertebrate

CnARACTERS OF VERTEBRATE ANIMALS.

11

embryo and the Invertebrate adult, — it is not with any of the higher
forms of Invertebrata, — with neither the Cephalopod, the Arachni-
dan, nor the Insect, — tliat such organic correspondence is found to
exist ; but it is with the lowest forms and simplest beginnings of
animal life, — with the infusorial monads. Only, in fact, during that
period of the ovum-life of the Vertebrated being, in which the mys-
terious properties of the impregnated germ- vesicle are diffused and
distributed by fissiparous multiplication amongst countless nucleated
cells — the progeny of the primary germinal vesicle and coheirs of

Ova of the Rabbit, at four early stages of development (Barry).

the seminal virtue — do we find such a form and such properties of
the Vertebrated animal as justify us in affirming that there is “ Unity
of Organisation” between it and an Invertebrate animal. (Compare
Jiff. 2. with cui 14., p. 24., Lectures on Invertebrata.)

The next step in the development of the ovum — and it is so speedy
a one, that those which precede it long escaped observation — im-
presses upon the nascent being its Vertebrated type. Cei'tain nu-
cleated cells lose their individuality and powers of propagation ; they
coalesce and fill the fine tubes so foi’med with albumen, as the final
act of their assimilative power, and thus become converted into
nervous tissue, in the form of a double chord 3. c/i), which, from
its first beginning, marks the dorsal aspect of the
embryonic trace : other nucleated cells lay the
foundation of the vertebral column (u) around the
spinal chord ; others again change into the softer
tissues, and the rest, circulating with the nutrient
fluid, as blood discs, through channels which
sketch out the sanguiferous system, maintain life,
and furnish materials by their powers of assimi-
lation and spontaneous fission to the growing
body. *

All vertebrated animals, during a greater or less extent of these
developmental processes, float in a liquid of similar specific gravity
to themselves. A vast proportion, constituting the lowest and fun-

* “The blood [damo, Hebr.'\ is the life.” — Dcut. xii. 23. ai/xa . . . ev tovtc^
yap €(TTi 7; \livxv-" — Josephus, Antiq. I. 3. 8. “ Empedocles,” says Plutarch, “con-

siders the soul to be the blood poured into the heart.” Homer (Odyssey, xi. 36.
97. 147.) says, “ The shades thirst after blood, for by its influence they escape from
Erebus, and regain speech.” See also Sprengel, “ Beitrage zur Gcscbichte der
Medizin,” i. 3. for the belief by the ancients in the vitality of the blood.

12

INTRODUCTORY LECTURE.

damental group of Vertebrated animals, are never destined to quit the
watery medium ; these constitute the class of Fishes. A few species
retain the primitive vermiform type, and have no distinct locomotive
members ; and these members, in the rest of the Piscine class, are
small and simple, rarely adapted for any other function than the pro-
pulsion or guidance of the body through the water. The form of the
body is, for the most part, such as mechanical principles teach to be
best adapted for moving with least resistance through a liquid
medium. The surface of the body is either smooth and lubricous,
or is covered by closely imbricated scales, rarely defended by bony
plates or roughened by hard tubercles ; still more rarely armed with
spines.

The central axis of the nervous system presents but one partial
enlargement, and that of comparatively small size, at its anterior ex-
tremity, forming the brain, which consists of a succession of simple
ganglionic masses (^fig. 46.), most of them exclusively appropriated
to the function of a nerve of special Sense. The power of touch can
be but feebly developed in fishes. The organ of taste is a very in-
conspicuous one, the chief function of the framework supporting it,
or the hyoidean apparatus, relating to the mechanism of swallowing
and breathing.

Of the organ of hearing there is no outward sign ; but the essential
part, the acoustic labyrinth, is present, and the semicircular canals
largely developed within. The labyrinth is without cochlea, and is
rarely provided with a special chamber, but is lodged, in common
with the brain, in the cranial cavity. The eyes are usually large,
but are seldom defended by eyelids, and never served by a lachrymal
organ. The alimentary canal is commonly short and simple, with its
divisions not always clearly marked, the short and wide gullet being
hardly distinguishable from the stomach. The pancreas, for the most
part, retains its primitive condition of separate cajcal appendages to
the duodenum. The heart consists essentially of one auricle and one
ventricle, receiving the venous blood, and propelling it to the gills ;
whence the circulation is continued over the entire body in vessels
only, which are aided by the contraction of the surrounding muscular
fibres.

The blood of fishes is cold ; its temperature being rarely elevated
above that of the surrounding medium. The coloured discs are
sometimes subcircular {fg. 4. g\ sometimes subelliptical (Ji) or ellip-
tic : comparatively large, but not the largest amongst vertebrate
animals.

The primordial elongated renal glands are persistent, and secrete
the urine from venous blood.

CHARACTERS OF THE CLASSES OP VERTEBRATE ANIMALS. 13

Procreation is rarely attended with a coitus or intromission, the
requisite accessory organs being wanting in the majority of the class ;
and the product still more rarely receives, after exclusion, any pa-
rental attention or care.

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

Frog ; /, Siren ; Cod-fish ; A, Skate,

In many respects Fishes typify the embryonic stages of develop-
ment of the higher animals : they were the first created Myelence-
phala ; and, througli a series of vast geological periods, as the Siluidan,
Devonian, and, perhaps, the Carboniferous, the sole representatives
of the Vertebrated sub-kingdom in this planet.

The second class of Vertebrated animals, called Reptilia, by no
means presents so uniform a type as that of Fishes, lleptiles have
more varied spheres of action. Some retain the form and breathe
the element of fishes, living and moving in water during the whole or
a part of their existence. The transition, indeed, from Fishes to
these lowest Amphibian or Batrachian forms is so close and gra-
dual, that whilst some true Reptiles* have passed for Fishes, the
higher Fishes f have been classed with Amphibia, and even at the
present day, a true Fish — the Protopterus or Lepidosiren — has been
described, and by some naturalists is still regarded, as a Reptile.
But no Reptile has dorsal parapophyses or the scapular arch articu-
lated to the occiput, and every Reptile has two auricles to the heai’t,
and the nasal canal communicating with the mouth. The Tortoises
i^Chelonia) and Lizards {Sauria) have locomotive members adapted
for progression on dry land ; hut they can only raise the body a little
way, if at all, above the ground, and creep rather than walk : the
Serpents (Ophidia) have no visible members, but move by the
reaction of the entire trunk upon the ground, and so drag their
belly through the dust of the earth: whence the name Reptilia"
(repo, to creep), given to this class of Vertebrate animals.

* Larvae of liana Paradoxa, called Frog-fish.

. f Sharks and Hays, called “ Amphibia nantes ” by Linnaeus.

14

INTRODUCTOKY LECTURE.

Reptiles are cold-blooded, like Fishes ; but all of them possess
lungs, or organs for breathing atmospheric air. Most of the class
exercise the function of these organs ; but some, retaining gills,
chiefly breathe water ; and those with lungs alone are less dependent
on respiration than the higher Vertebrata. Hence the Reptiles were
defined by Linnmus as “ arbitrary breathers,” — “ Pulmones spirantes
arbitrarie” — and were called by him Amphibia^ The blood is
remarkable for the large relative size and constant elliptical form of
its red particles 4. d, e), which, as in Fishes, have a distinct
granular nucleus. And, what is more remarkable, the size increases
in the ratio of the persistence of the branchial organs. You may, for
example, discern the blood-discs with the naked eye in the Siren
lacertina {fig. 4.y). The typical condition of the heart in Reptiles
is three-chambered ; having two auricles and one ventricle ; one
auricle receives the venous blood from the general system, the other
that which has undergone chemical change in the lungs : both kinds
of blood are mixed in the ventricle, and distributed in that state,
partly to the lungs again, partly to the general system. The breath-
ing apparatus is so far inferior to that of fishes, as that the whole
mass of circulating fluid is not distributed through it ; but this appa-
rently retrograde step in development seems as if preparatory to the
establishment of a more perfect respiratory system, adapted to the
exigencies of higher classes of animals. Always, however, in using
or hearing this metaphorical language, it is to be borne in mind, that
each condition, which represents a step in progress as regards the
series of species, is complete and perfect in relation to the particulai
species in which it is manifested.

The nervous system of Reptiles presents an advance in the
larger proportional size of the cerebral lobes ; but the whole brain
is still a mere linear series of smooth ganglionic masses, and
the cerebellum is often inferior, in size and complexity, to that in
Fishes.

The eyes are smaller than in Fishes, but generally more perfect
and defended by eyelids : the ears are provided with a vibratory
membrane and chamber, called the “ tympanum but the most
characteristic feature of Reptiles in contrast with Fishes, which
the organs of the senses present, is the establishment of a communi-
cation from the eye, the ear, and the nose respectively, with the
respiratory tract or mouth ; the eye by the lachrymal duct, the ear
by the Eustachian tube, and the nose by its prolongation into
a meatus, with a posterior opening into the mouth, or fauces.
This latter character the Siren manifests, but not the Lepidosiren,
nor any true Fish. The sense of touch must be enjoyed by the naked

CHARACTERS OF THE CLASSES OF VERTEBRATE ANIMALS. 15

Batracliians and the thin-skinned Lizards in a degree much superior
to any of the scaly class of Fishes : but the integument in many of
the Reptilia is covered or studded with horny or bony scutes.

The generation of Reptiles has certain analogies with that of Fishes.
It is still effected in some species, as the Frogs and Toads, without
intromission, and in the same species we perceive a simultaneous
development of very numerous ova ; but the Batrachia form the
exception instead of the rule. The intromittent organ which exists
in the great majority of the class is also double in most of these, as in
Serpents and many Lizards. There are in the Reptilia both viviparous
and oviparous species ; but the foetus in the former has no attach-
ment to the womb, and the eggs in the latter are hatched by ex-
traneous warmth : the young, after exclusion, receive no parental
care or tuition in any species of the class.

In investigating the various strata of the Earth, which form, as it
were, the grave-yards of as many successive generations of species
and classes, we meet with the earliest. remains of air-breathing
Vertebrate animals in the triassic or Permian series, subsequent to
the deposition of the coal*, and we consequently infer that the date of
their existence, in this planet, is much later than that of Fishes.
But the Reptilian class seems soon to have acquired a vast extension,
and to have flourished under a variety of forms, developed also to
an enormous bulk, with powers for the acquisition and assimilation
of both animal and vegetable substances, of which the present state
of the class can afford no adequate idea. The deposition of the
chalk-formation seems to have been the date of the decline of the
Reptilia, when they gave way to as varied and colossal forms of
animals of a higher type of organisation. Amongst the numerous
species, genera, and even orders of the Reptilia, which at that jicriod
became extinct, was one in which the anterior members of the
animal were developed into wings : these veritable “ Flying-Dragons,”
the “ Pterodactyles,” as they are termed, seem to have perished when
true winged Birds made their appearance.

The present is scarcely a suitable occasion for speculating, even if
time permitted, on the probable changes in the atmosphere of our
planet which accompanied those undoubted revolutions in its crust,
by the investigation of which we obtain the evidence of this suc-
cessive introduction of organic forms ; otherwise we might discuss
the reasonableness of the surmise that the atmosphere was unfit to be
breathed by lungs during that vast lapse of time when fishes reigned
supreme upon earth ; or we might enquire if the atmosphere of the

* The less conclusive evidence of foot-prinis would carry hack the dateof tlie Sala-
mandroid Cheirotheria to the coal formation. — Lyell, in Silliman's Journal, vol. ii. p. 25.

16

INTRODUCTORY LECTURE.

later secondary periods was so dank and dense, and overloaded witli
irrespirable elements, as to need the precipitation of so much carbon
as has been consolidated in our coal-fields and chalk-hills, before it
was fitted for the full development and vital enjoyment of the warm-
blooded and quick-breathing classes ? But these and other consi-
derations suggested by the successive introduction of water-breathing
and slow air-breathing Vertebrates, would lead us too far away from
the proper subject of the present elementary discourse. Sufiice it to
say, that the oviparous class of animals which next makes its ap-
pearance in the order of Creation, is remarkably characterised hy the
energy of the circulating and respiratory functions, and by the high
temperature of the body. I allude to the class Aves, characterised
as accurately, as briefly, by the name of “ feathered bipeds : ” bipeds,
because the anterior members are exclusively organised for flight ;
feathered, because the body which is to soar in air must be lightly
clad, and yet warmly clad, — must be covered by most efficient non-
conductors, so as to retain that elevated temperature which is the
necessary consequence of the organic combustion of so much mus-
cular and nervous fibre in the energetic actions of flight. But Birds
enjoy almost every kind of locomotion : a few (Apteryx) burrow in
the earth : some (Ostrich, Rhea) traverse its surface as swiftly as the
most rapid courser : many climb trees : an entire Order is aquatic,
swimming or diving with facility. The legs and feet of Birds are
accordingly variously modified for these different powers, and furnish
the Naturalist with excellent characters for the primary divisions of
the class. The lungs are now divided into very minute cells, pro-
ducing a vast extent of the vascular respiratory membrane ; they also
communicate with larger cells, forming capacious reservoirs of air,
which are continued through every part of the body, even into the
substance and cavities of the bones. The heart is divided into four
chambers, two muscular ventricles and two aurieles ; a single artery
arises from each ventricle, and a eomplete double circulation is es-
tablished,— the left auricle and ventricle circulating the arterial blood,
the right auricle and ventriele the venous, transmitting to the lungs
the entire mass of the carbonized blood. The blood is of a deep but
bright vermilion red, and richly laden with the discoid cells, which
are elliptical, but smaller than in the Reptilia {Jig. 4. c).

The jaws of Birds are always edentulous and sheathed with horn,
of divers configurations, adapted to their different modes of life and
kinds of food. The head is small, and supported upon a long neck ;
the mandibles performing most of those purposes for which the
anterior members, by their conversion into wings, are unfitted ; so
that the beak combines the functions of hand and mouth. The

CHARACTERS OF THE CLASSES OF VERTEBRATE ANIMALS. 17

gullet, being co-extensive with the neck, is of great length ; tlic
stomach is always divided into two cavities, the first glandular, the
second muscular ; and the distinction between small and large in-
testines is usually marked by the presence of two cceca. The in-
testine terminates, as in the Reptiles, in a common cloaca.

The cerebral hemispheres have acquired a large proportional size in
Birds as compared with Reptiles, and the cerebellum is complicated by
many transverse folds : but Birds are peculiarly distinguished by the
inferior and lateral position of the optic lobes ; and the whole brain
presents a more compact form and larger size, in proportion to the
spinal cord and nerves, than in Reptiles. The partial enlargements of
the spinal marrow, corresponding to the brachial and lumbar nervous
plexuses, are more marked than in Reptiles, and the lumbar en-
largement is distinguished by a ventricle. The sense of sight is
peculiarly keen and perfect in the class of Birds, and the eye has
some structures which are not found in other Vertebrata. The
organisation of the ear has likewise advanced, a cochlea, though of
simple form, being added to the semicircular canals. A circle of
feathers radiates from the outer aperture of the ear, forming a con-
cave disc or conch, to catch and concentrate the vibrations of sound ;
and such an advance is in harmony with the varied power of ex-
pressing the feelings and the passions with wliich Birds are gifted.
We may still, indeed, hear in the aquatic members of the class the
hiss of the serpent or the croak of the frog ; but as Birds rise in the
scale their vocal powers rapidly develope : the cock “ with shrill
clarion sounds the silent hours,” and the nightingale, bursting forth
in song, fills all the grove with her varied melody. With regard to
the sense of smell we estimate its improvement by observing the
more extensive and complex tui’binated cartilages in the present
Class. But taste must still be dull ; there is no true gustatory nerve,
and the tongue is commonly sheathed with horn. The beak is in
some birds modified to communicate a delicate faculty of touch, but
elsewhere this sense is very limited, the general surface of the body
being defended by the dense, imbricated, insensible plumage.

All birds are oviparous : only the aquatic birds enjoy intromission.
The female constructs a nest and incubates her eggs, and, after ex-
clusion, cherishes, feeds, and educates her young.

The class Mammalia, which crowns the vertebrated series and the
animal kingdom, is characterised by a double circulation, a quick
respiration by lungs subdivided into minute cells, warm blood, and,
with few exceptions, a covering of hair. But the lungs are not fixed
in the interspaces of the ribs, as in birds ; nor do they communicate
with abdominal air-cells ; but are confined, with the heart, and freely

VOL. TI. c

18

INTRODUCTORY LECTURE.

suspended in a particular compartment of the general cavity of the
body, called “ thorax,” which is partitioned off from the abdomen by
a transverse vaulted muscular floor, called the “diaphragm,” {fig. 1.
d). Neither the circulation nor the respiration are quite so active,
nor is the animal heat so high, as in the class of Birds ; few, indeed,
of the Mammalia enjoy the power of flight : most of the class are
quadrupeds, as they are commonly called par excellence, and support
themselves and move by the action of four feet upon the ground.
Some burrow : most can swim, and a few are exclusively adapted for
living in water, and have the form of fishes ; in these the hinder
limbs are wanting, and the anterior ones present the shape of fins :
but all Mammalia breathe the air directly. The colouring particles
of the blood are more minute than in birds, and for the most part of
a circular form, {fig. 4, a, b).

With a few exceptions the jaws of the Mammalia are armed
with teeth, variously modified in subserviency to the habits and
food of the different species. In like manner the stomach is sim-
ple or complex, in relation to the amount of change to be effected
in the assimilation of the food : the small intestine is usually divided
from the large by the presence of a single ccecum, and the rec-
tum, with very few exceptions, has its outlet distinct from that
of the genital and urinary systems. The kidneys are supplied with
blood from the renal arteries exclusively ; but the liver continues
to receive the superadded system of the vena portae. The secretion
of the kidneys is always conveyed to a urinary bladder {fig. 1. u), and
the penis is traversed by the urethral canal.

All Mammalia intromit in fecundation, and all are viviparous : in
most the ovum, after quitting the ovary, becomes a second time at-
tached to the parent, through a variously modified cellulo-vascular
organ called “ placenta.” The young are nourished after birth by the
secretion of glands, called mammary — whence the name of the class.
Perhaps the peculiar and constant existence of a well-developed
epiglottis, which Aristotle in one of his surprising generalisations
states to be present in all hairy viviparous quadrupeds, may have its
true relation of physiological co-existence with the mammary glands,
being most essential as a defence of the glottis during the act of
sucking.

The bodies of the vertebrm are united to each other by concen-
tric ligaments, attached commonly to flattened surfaces, forming the
intervertebral substance. The cervical vertebra are seven, not varying
in number according to the length or shortness of the neck. Hair
is the charactei-istic clothing of the body ; but almost all the modifi-
cations of the epidermal system which we meet with in the inferior
vertebrated classes are repeated in the present : thus we have quills

CHARACTERS OF THE CLASSES OF VERTEBRATE ANIMALS. 19

in the “ fretful porcupine,” spines in the hedgehog, scales an the
luanis, bony scutes in the armadillo ; whilst a few species at the two
extremes of the series are naked, for example, the whale and the
man.

Thus far the review of the general anatomical characteristics of
the Mammalian class seems not to indicate a very marked superiority :
in the energetic contraction of the muscular fibre, in the rapidity of
the actions of the heart and lungs, Mammals are surpassed by Birds :
but the functions which attain their highest development in the
Mammalian class are of far nobler character than those which are
more immediately connected with the maintenance of animal life.
The progressive expansion of the brain is greatest, and the final pre-
dominance of reason over instinct is achieved, in the present class ;
sensation is its characteristic rather than muscular energy or irrita-
bility ; the instincts become more varied, they are also less mechanical
and more educable. In Mammalia we first find the cerebral hemi-
spheres acquiring an additional extent of the grey and vascular
surface by convolutions, which increase in number and depth as the
species approximate Man : a fornix first, and then a corpus callosum,
are introduced into the Mammalian brain, to bring into mutual com-
munication the various parts of the hemispheres. A new cranial
bone, the squamosal, developed from the proximal piece of the man-
dibular arch, now, for the first time, takes a shai’e in the forma-
tion of the walls of the cranial cavity. The organs of the senses
attain their most complex structures in the present class. The ear
has a perfect spiral cochlea, and the distinct appendage called outer
ear. No bony plates are ever developed in the sclerotic coat of the eye.
The turbinated bones and pituitary membrane of the nose present in
most Mammalia a great, and in some a prodigious extent of surface.
The tongue is large, soft, and papillose, and is supplied with a gusta-
toiy as well as a motor and respiratory nerve.

We see the locomotive extremities progressively endowed with more
varied and complicated powers. At first retaining, in the Cetacea for
example, their primitive embryonic form of simple flattened fins ;
they next, with ampler proportions, acquire the full development of
the normal joints and segments, and have their extremities enveloped
in dense hoofs : next we find the digits liberated, and armed with
claws confined to the upper surface, leaving the under surface of
the toes free for the exercise of touch : then we have certain digits
endowed with special offices, and, by a particular position, enabled to
oppose the others, so as to seize, retain, and grasp : lastly, in Man,
the offices of support and locomotion are assigned to a single pair of
members, so organised as to sustain the body erect ; leaving the

20

LECTTJKE II,

anterior, and now the upper, limbs free to execute the various pur-
poses of the will, and terminated by a hand, which, in the matchless
harmony and adjustment of its organisation, is made the suitable
instrument of a rational intelligence.

LECTURE II.

THE SKELETON.

Descriptive Anatomy usually commences with the bones, and the
consideration of the passive organs of motion before the active ones
is conformable to the sequence of development, since the fixed points
are formed before the muscular fibres.

The branch of anatomy which treats of the Skeleton of Vertebrate
animals is designated “ Osteology,” because in anthropotomy it re-
lates exclusively to the bones and teeth. But the skeleton, according
to its etymological signification of hard and dry parts, might apply to
the hair and nails, and, indeed, the entire epidermal system. When,
also, in a general survey of the Vertebrata, we see the spinal column
gristly in some fishes, and the tendons bony in some birds ; and when
we call to mind such homological relations as that of the fibro-mem-
branous sclerotic of the human eye with the cartilaginous sclerotic of
the turtle and the osseous sclerotic of the cod-fish, it will be obvious
that the present branch of anatomy ought naturally to embrace the
aponeuroses, ligaments, and cartilages, since these are so many ar-
rested stages in the histological development of the internal skeleton.

In the Invertebrata we saw that the skeleton, or parts analogous *
to the bones of the Vertebrata, commonly consisted of large, strong,
thick, often unjointed plates, developed in or upon the skin, hardened
principally by carbonate of lime, protecting the whole body, and
having the muscles attached to the inner surface.

In the Vertebrata the skeleton chiefly consists of diversely con-
figurated, but most commonly cylindrical and articulated pieces,
hardened chiefly by phosphate of lime, developed from fibrous and
cartilaginous tissue in the interior of the body, of which it forms the
internal framework, giving attachment to the muscles by the outer
surface, and subserving their action as levers and fulcra.

The exterior calcified shells and crusts of the Invertebrata are un-

* For the sense in which the terms homologous and analogous are used in the
present Lectures, see the Glossary appended to the “ Lectures on Invertebrata,”
8vo. 1843.

THE SKELETON.

21

vascular ; they grow by the addition of layers to their circumference,
or they may be cast off when too small for the growing body, and be
reproduced of a more conformable size ; but they have no inherent
power of repair.

The internal bones of the Vertebrata are vascular ; they grow by
internal molecular addition and change, and have the power of repair-
ing fracture or other injury.

Such are the broad and obvious distinctive characters of the
skeletons of the Invertebrate and Vertebrate animals ; the contrasts
having relation chiefly to the difference in the development of the
nervous system. Thus, when the powers of discerning and avoiding
lethal or hurtful agencies are dull and contracted, the entire animal
is protected by a hard insensible dermal armour, or exo-skeleton ;
but, as those powers become expanded and quickened, the body is
disencumbered of its coat of mail, the skeleton is put inside, and made
subservient to the activities, and the skin becomes proportionally
more susceptible of outward impressions of pleasure and pain.

Some estimable anatomists, who have more especially devoted their
attention to the detection of the corresponding parts in different ani-
mals, have supposed that these different functions were performed by
modifications of essentially the same or homologous parts of the
skeleton

Observing that a segment of the outer skeleton of an articulate
animal, the thoracic ring of a lobster for example 5.), formed
a small canal (e s) for the nervous trunks, and a larger one (/?) for
the vascular trunks and plastic organs ; and that a thoracic segment
of the skeleton of a Vertebrate animal {fig. 6.) also formed a small
protecting canal for the spinal chord (c, ns\ and a larger hoop (c, hs)
about the vascular and other viscera of that cavity, — they have con-
cluded that both were modifications of the same elements or primary
segment of the skeleton. Cams, for instance (No. i. p. 73.), calls
both I’ings “vertebrae;” and Geoffrey St. Hilaire (ii. p. 119. pi. 7.)
thought it needed but to reverse the position of the Ci-ustacean, — to
turn what had been wrongly deemed the belly upwards, — in order

Segment of exo-skeleton, A$tacu5>

Segment of endo-skeleton, Mammal.

22

LECTURE II.

to demonstrate the unity of organisation between the Articulate and
Vertebrate animal. But the position of the brain is thereby reversed,
and the alimentary canal still intervenes in the Invertebrate between
the aortic trunk and the neural canal.

The outer and the inner skeletons do agree in certain relations :
neither of them are primitive parts of the organism, but are modifi-
cations or metamorphoses of other pre-existing systems : both serve
as fixed points of attachment to the muscles, aid their action as levers,
and determine the kind of movements by particular joints : both are
organs of protection and support.

But, besides the differences of tissue, mode of growth and vital
properties, already noticed, the exo- and the endo-skeletons differ in
the one being developed from the skin, the other from the internal
cellular and fibrous systems. The exo-skeleton defends or surrounds
the periphery of the animal ; the endo-skeleton the internal parts.
The exo-skeleton is related to the muscles by its inner surface, the
endo-skeleton by its outer surface. The exo-skeleton is the reflex of
the circumambient medium and relations of the animal : the endo-
skeleton is the index of its motive energies and its intelligence.

Even the neural canal itself is differently constructed in the
segments of the exo- and endo-skeletons selected for comparison : in
the Vertebrate it is an arch developed from a central column {c,fig. ff.),
which, in like manner, gives origin to the opposite or haemal arch ;
in the Articulate the neural canal is formed by processes, apodemata,
or entapophyses {e,fig. 5.) sent off from the great peripheral arch.
Moreover, the development of these processes relates rather to that
of the muscular than of the nervous systems. "We saw* how greatly
the ganglions vary in number and position upon the abdominal nerve-
trunks of insects. Now, if the entapophyses of the dermo-skeleton —
the secondary vertebrae of Carus — were developed, like the neural
arches of the vertebrae of the endo-skeleton, in special relation to the
protection of the nervous centres, and conformable in number with
the pairs of nerves thence sent offf, we ought to find them go-
verned by the existence and position of the ganglions ; but it is not
so. In the Myriapoda, as Von Baer well objects (m.), entapophyses
are entirely absent ; and in winged insects they are confined to the
thorax or locomotive segment, although there may be two, three, or four
ganglions in the abdomen. And, what is further to be remarked, the
thoracic entapophyses are not developed over the thoracic ganglions,
but over the inter-communicating chords. In fact, their relation to

* Lectures on Invertebrata, 8vo, 1 843, p. 205.

f “ Numerus veitebrarum semper cum numero nervorum spinalium intime co-
ha;ret.” — Otto Hcer, Be Ossium Concretione normali, &c., 4to. 1836, p. 6.

THE SKELETON.

23

the nerve-trunks seems to be accidental, depending upon the position
of the muscular masses to which they give attachment, and which
office is the essential condition of their existenee. For this purpose
the processes of the exo-skeleton of Insecta and Crustacea must go in-
wards, and thus they happen to protect certain parts of the nervous
system.

Only the highest of the Mollusca possess a true homologue of the
endo-skeleton, developed in relation to the defence of the nervous
centres : but it is a feeble cartilaginous rudiment in the best organised
Cephalopods ; and, in the cuttle-fish, is far outweighed by the calca-
reous dorsal plate which still represents the exo-skeleton of the tes-
taceous mollusks. Thus a cartilaginous cranial vertebra co-exists in
the highest Invertebrata with a calcareous dermal skeleton ; and
there is no abrupt contrast in passing tlience to the consideration of
the skeleton in the Vertebrata.

The exo-skeleton is by no means indeed dispensed with in th& Ver-
tebrate series, although the endo-skeleton is constant, and here attains
its full development. In the lowest class, most fishes, for example, pre-
sent an imbricated outer covering of scales, developed like shells,
between the derm and epiderm : other fishes have hard osseous plates
or spines scattered over their exterior, or are entirely surrounded
by a connected armour of dense enamelled bony scales, as in the
Lepidosteus and the Ostracion, which latter fish offers an instructive
example of the co-existence of an exo- with an endo-skeleton, and
a convincing refutation of the idea of the homology of the annular
segment of the crust of the lobster with a true typical vertebra. In
the subjoined diagram, {fig. 7.) n is the cartilaginous neural canal;

pi, the membranous pleurapophysial wall of
the abdomen ; h, the arterial and venous
trunks of the abdomen ; dn, dp, dh, the der-
mal ganoid plates. The ossified scutes of the
Crocodiles and the tesselated armour of the
Armadillos are examples of the exo-skeleton
co-existing with a well-developed and ossified
endo-skeleton ; and wherever the exo-skeleton
Segment ofendo- and exo- of a Vertebrate animal is calcified, it presents

skeletons, Ostracion. , •in,. i

the same organised vascular structure and
vital properties as the bones within. Most commonly the exo-
skeleton of the air-breathing Vertebrata is epidermal, as where it
forms the scales of the serpent or lizard, the large plates of the
tortoise, the imbricated pointed scales of the manis, the spines of the
hedgehog, the quills of the porcupine, the feathers of the bird, or the
hair of the ordinary mammal.

C 4

24

LECTURE II.

The skeleton is not entirely externa.1 or dermal in the Invertebrata.
Independently of the true cartilaginous endo-skeleton of the Cepha-
lopods, and of the entapophyses, sometimes also cartilaginous, of the
annular segments of the exo-skeleton of Insects and Crustacea, there
are parts, as the calcified framework supporting the gastric teeth,
and giving attachment to the muscles which work them, in the
lobster, and the calcareous gastric plates of the Bulla, which relate
more particularly to the functions of the internal organs, or contained
viscera ; and we find a corresponding group of parts of the general
skeleton in most Vertebrate animals. The cartilages or bones of the
larynx, trachea, and bronchia of the air-breathing Vertebrates, the
bones and cartilages supporting the branchiae in fishes and batra-
chians, the bones in the hearts of certain birds and mammals, are
examples of the visceral series of hard parts, or the “ splanchno
skeleton,” as it has been termed by Cams ; and very nearly and
naturally connected with this primary division of hard and dry parts
are those bones and gristles which form capsules, or support the
appendages of the special organs of the senses ; as, for example, the
sclerotic osseous cups or plates of the eye, the petrous capsule of the
labyrinth, the ossicles and cartilages of the tympanum and external
ear, the turbinate bones and gristles of the nose. But some of these
“ sense capsules ” are connected and intercalated with the true bones
of the endo-skeleton, and subservient to similar functions, besides
their own special uses, so that they are generally described as ordi-
nary bones of the skull. As in all arrangements of natural objects,
where nature is followed in selecting their characters, so in classi-
fying the parts of the general skeleton of the Vertebrata, the primary
groups blend into one another at their extremes, and make it difficult
to draw a well-defined boundary line between them. Thus the
hyoid and branchial arches closely resemble each other in fishes.
Bones of the dermo-skeleton combine with those of the endo-skeleton
to form the opercular and the single median fins. But we must not
on that account abandon the advantage of arrangement and classi-
fication in acquiring an intelligible and tenable knowledge of a
complex system of organs, when typical characters clearly indicate
the general primary groups. Clearly appreciating the existence of
such characters in the very numerous and diversified parts of the
general skeleton of the Vertebrate animals, I, therefore, adopt the
primary division of those parts into endo-skeleton, exo-skeleton, and
splanchno-skeleton.

The endo-skeleton may present itself to our observation under
three histological conditions, the fibrous, the cartilaginous, and the

THE SKELETON.

25

osseous : the exo- and splanchno-skeletons may offer also another,
or fourth condition, viz. the albuminous, or epidermal.

The most common tissue of the endo-skeleton of the Vertebrata is
that called “ bone,” and it is peculiar to this primary division of the
Animal Kingdom.

Bone consists of animal, chiefly gelatinous, matter, hardened by a
general but regulated diffusion of earthy molecules ; the proportion
of organic to inorganic matter varies in different classes. Fishes
have the least. Birds the largest proportion of earthy matter ; and of
the two, in this respect, intermediate classes, the Mammalia, espe-
cially the active predatory species, have more earth, or harder bones,
than Keptiles. This difference depends chiefly upon the quantity of
fluid, or evaporable matter, in the cells and tubes of the animal basis,
but not wholly, as some have supposed ; at least the apparently
exact, certainly most carefully and scientifically conducted experi-
ments of M. Bibra (iv.) on thoroughly di'ied portions of bone, show
the following differences : —

PROPOETIONS OF EARTHY AND ANIMAL MATTER IN THE BONES OP
VERTEBRATE ANIMALS.

FISHES.

Salmon.

Carp.

Cod.

Sulmo Salar.

Cyprinus Carpio.

Gadus Morrhua.

Organic

60-62

40-40

34-30

Inorganic

39-38

59-60

65-70

-- -

100-00

100-00

100-00

REPTILES.

Frog.

Snake.

Lizard.

Rana esculenta.

Coluber Natrix,

Lacerta agilis.

Organic

35-50

31-04

46-67

Inorganic

64-50

68-96

53-33

100 00

100-00

100-00

MAMMALS.

1.

Dolphin.

Ox. Wilu-Cat.

Man.

Delphinus

Bos Taurus. Felis Catus.

Homo.

De/phis.

(Femur.) (Femur.)

(Femur.)

Organic -

35-90

31-00 27-77

31-03

Inorganic -

64-10

69-00 72-23

68-97

100-00

100-00 100-00

100-00

26

LECTURE n.

BIRDS.

Organic

Inorganic

Goose.

Anser (femur.)

32-91

67-09

Turkey.

GaUopavo (femur.)

30-49

69-51

Hawk.

Falco Gallinarius.

26-72

73-28

100-00

100-00

100-00

In the above table it will be observed that the bones of the fresh-
water fishes are lighter and retain more animal matter than those of
the fish which swims in the denser sea, and that the Mammalian
marine species, Delphinus, differs little from the sea-fish in this
respect. The Batrachian Reptile has more animal matter in its bones
than the Ophidian or Saurian, and thus more resembles the Fish.
Serpents almost approach Birds in the great proportion of the
earthy salts, and hence the density and ivory-like whiteness of
their bones. The typical bones of Birds are the whitest and most
compact of all hones, by reason of their large proportion of earthy
matter, and also of the absence of marrow from their capacious
pneumatic cavities, on which their lightness depends : in those hones
of Birds from which air is excluded, the oily marrow deadens the
whiteness of the tissue, and it is often difiicult to get rid of the greasy
surface in skeletons.

The nature of the inorganic or hardening particles, and of the
organic basis, according to the analysis by Bibra of completely dried
portions of bone, is exemplified in the subjoined table, including a
species of each of the four classes of Vertehrata.

CHEJnCAL COMPOSITION OF BONES.

Hawk.

Man.

Tortoise.

Cod.

Phosphate of Lime, with trace

of Fluat - - -

64-39

59-63

52-66

57-29

Carbonate of Lime

7-03

7-33

12-53

4-90

Phosphate of Magnesia
Sulphate, Carbonate, and Chlo-

0-94

1-32

0-82

2-40

rate of Soda ...

0-92

0-69

0-90

1-10

Glutin 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

In addition to the differences already noted in the proportions of
earthy and animal matter, it is interesting to observe that the pi'opor-

THE SKELETON.

27

tion of soluble salts to the less soluble phosphates of lime is greatest
in the fish, and that there is most carbonate of lime in the bones of
the tortoise. The quantity of evaporable fluid is greatest in the
bones of Fishes, especially in those of the semi-osseous sharks and
rays, in the skeletons of which also the salts of soda are in larger
proportion than in the osseous fishes. The animal part of the
shark’s skeleton differs from the glutin of ordinary bones, and from
the ossifiable cartilage of higher animals; it has more analogy
with mucus, requiring 1000 times its weight of boiling water for
its solution ; and this is neither precipitated by infusion of galls, nor
yields any gelatine upon evaporation. In the entirely unossified
skeleton of the lamprey Bibra found only 1|- per cent, of earthy
salts.

How, we may next ask, are the inorganic earthy particles diffused
through the animal basis, and whence are they obtained ? Bones are
not a primitive formation, but the result of a transmutation of pre-
existing tissues. The inorganic salts defined in the foregoing tables
pre-exist in the albumen of the egg, in the milk which nourishes the
new-born mammal, in the plasma or “ liquor sanguinis ” of the circu-
lating fluids.

The blastema or primitive basis of bone is not originally cartilage,
but more resembles mucus in its chemical characters : it appears at
first to be a sub-transparent glairy fluid, but contains a multitude of
minute corpuscles. Its assumption of the cartilaginous character and
consistency is attended with the appearance in it of numerous small, sub-
elliptic, nucleated cells. As the cartilage hardens, these cells increase in
number and size, and begin to accumulate, and to be arranged in
linear series at the part where ossification is about to commence.
These series in the cartilage of long bones are usually vertical to its
ends, and in flat bones are vertical to the peripheral edge ; i. e.
they are parallel to the axis of the long bone, and are radiated in the
flat one, but not with mathematical exactness.

The nucleated cells are the instruments by which the earthy par-
ticles are arranged in order ; and, in bone, as in tooth, there may
be discerned in this predetermined arrangement, the same relation
to the acquisition of strength and power of resistance, with the
greatest economy of the building material, as in the disposition
of the beams and columns of a work of human architecture, (v.
p. vi.)

The power of the cells so to operate upon the salts of the plasma,
which percolates the intervening tissue, seems to reside chiefly in the
repellent property of their nuclei : I have been led by observation of

28

LECTURE II.

some of the phenomena of osteogeny to surmise that the walls and the
nucleus of the cell were in opposite electric or magnetic states, one
attracting, the other repelling, the surrounding earthy particles.

Certain of the columnar series of nucleated cells become more
aggregated or pressed together ; their nuclei become more concen-
trated, and, according to Miescher and Gerber, they coalesce and be-
come dissolved, leaving a cylindrical tube, parallel with the long
axis of the future bone. First, a reddish lymph, and then a capillary
vessel is prolonged into each of these cylinders, which is converted
into a “ Haversian,” or vascular canal : before, however, the direct
influence of the circulation has penetrated so far, the nucleated carti-
laginous cells have arranged or propagated themselves in concentric
series round the cylinder, and the intervening layers of the mole-
cular blastema begin to be impregnated with the hardening salts,
which, being repelled by the nuclei of the cells, are forced into the
concentric laminated arrangement around the Haversian canal. The
establishment of the capillary circulation in these canals accelerates
the progress of ossification by the rapid import of new material : the
resisting nuclei of the surrounding concentric cells, pressed on all
sides, undergo a remarkable change, and the nucleolar matter is
forced out in rays, but chiefly in the direction where the resistance
is least, viz. towards the Haversian canal. The remaining central
nuclear matter and that of the diverging rays finally become dis-
solved, and establish permanent bone-cells and minute tubes, which
tubes, traversing the concentric lamellee, open into the Haversian
canal, and receive the transuded plasma from the blood- capillary.
The tubes branch and anastomose, and form the medium of the trans-
mission of the plasma through the densest osseous tissue. This sys-
tem of cells and tubes, in fact, perform the same important function
in the nutrition of the osseous tissue, which I ascribed in 1838 to
the corresponding cells and tubes of the cemental tissue of the teeth
of the Megatherium (vi. p. 104.) : and they might be appropriately
termed the “ Plasmatic system.” They correspond with one of the
series of the “ vasa lymphatica” of the older physiologists ; the first
kind, for example, specified in Noquez’s edition of Kiel, quoted by
Hunter : “ Les premiers naissent des extremites arterielles ; on les
nomme ‘ arteres lymphatiques,’ qui peut-etre ne sont autre chose que
les conduits excretoires d’une lymphe tres subtile, ou de la matiere
qui transpire” (vn. vol. ii. p. 1 1.). The dentinal tubes of teeth and the
pl9,smatic tubes of bone are not, indeed, prolonged from attenuated
ends of arterial capillaries, but they receive the plasma transuded or
transpired from the parietal pores of the capillary system, and thus

THE SKELETON.

29

they agree in their main physiological relations with the first class of
Noquez’s Lymphatics : and the solid tissues of tooth and bone
manifest under the microscope a system of nutrient vessels, which
were only hypothetically known to the older physiologists. I have
detected a similar system of plasmatic tubes in tendon ; and they
probably exist, under characteristic modifications, in all tissues, con-
stituting the essential nutritive system of such.

The remains of the metamorphosed cartilaginous cells in bone
were first discovered by Purkinje and Deutsch, (viii.), arranged
in concentric series around the Haversian canals : they be-

lieved them to be solid, and called them “ corpuscula ossea.” Tre-
viranus (ix.) first described them as cavities or “ lacunae,” in the
intervals of the concentric ossified lamellte, and he believed them
to be filled with fluid. Professor Muller (x.) was led by the
whiteness of the radiated corpuscles when viewed by reflected light,
and by its disappearance, accompanied with evolution of gas, when
acted upon by dilute acid, to regard them as containing, either in
their parietes or cavity, calcareous salts. Serres and Doyere and
others have reproduced the idea of Treviranus, which is true to a
certain extent, but have erred in denying that the radiated cells
contain any calcareous salts, and have objected to the term “ calci-
gerous” applied to those cells. But the effects of reaction of dilute
acid in removing the opacity of the cell when viewed by transmitted
light, and in removing its whiteness when viewed by reflected light,
show that these optical phenomena are not due to the mere depth of
empty cells : aggregated particles of the earthy salts become depo-
sited after the solution of the resisting nuclear matter upon their
parietes ; but the cavities are preserved by the slow but constant
percolation of the plasmatic fluids. Thus bone, like dentine, “ pre-
sents a two-fold arrangement of its hardening particles, which are
either blended with the animal matter of the interspaces and parietes
of the tubes and cells, or are contained in a minute and irregular
granular state in their cavities;” and “the density of bone, as of
dentine, arises principally from the proportion of earth in the first of
these states of combination.” (v. p. iii.)

The primitive arrangement of the osseous tissue, so composed, is
lamellar, the lamellte being arranged either concentrically around the
Haversian canal, or around the entire circumference of the bone, or in
interrupted plates connecting together the Haversian cylinders, and
those with the generally surrounding peripheral lamellae.

The Haversian canals usually contain, in addition to the capillary
vessel, some oil, and this is the seat of the green colour in the bones
of the Belone and Lepidosiren.

30

LECTURE II.

In most osseous fishes the nucleus of the cartilage-cell quite dis-
appears in the process of ossification, and only the tubular prolon-
gations of the nuclear matter leave permanent traces, as plasmatic
tubes, which traverse the osseous lamellse in the intervals of the vas-
cular canal, and freely open into the latter, which are unusually
numerous. In the bones of Reptiles there is more diversity in the
number of the Haversian canals, which is less in Ophidians and
Saurians than in the fish-like Batrachian. The radiated cells are
always present, but are less regular in form and rather larger than in
Mammals ; they are rounder in Birds, with less conspicuous radiating
plasmatic tubes ; they are usually more elliptic and compressed in
Mammals, in the osseous tissue of which class the more appreciable
difference in microscopic structure obtains in the relative size of the
Haversian canals to the plasmatic, calcigerous, radiated cells.

These cells vary little in diameter in different Mammalia ; but the
Haversian canals which average of ^’loh in diameter in the

mouse are g^^^th of an inch in diameter in the ox, and of an

inch in the human subject.

The Haversian canals are fewer in the dense osseous tissue of
Birds than in that of Mammals : in the bones of Chelonia and
Batrachia they are more numerous, larger, and more reticularly dis-
posed ; the radiated cells are also larger.

In my treatise on the teeth (v. pp. xvi — xxii.), I have shown that
the osseous tissue corresponds in microscopic structure with that of
the dentine in many fishes. In no class is the structure of the teeth
more varied, and in none do we find such extreme modifications in
that of the bones.

Throughout a great part of the skeleton of the pike the osseous,
like the dental, tissue is characterised by “a reticulo-medullary
tubular structure : ” the meshes or interspaces being traversed by the
rich series of plasmatic tubes communicating with the vascular or
Haversian canals ; and there are few central dilatations radiating
plasmatic tubes, in other words, few purkingian cells.

In this section of the lower jaw of a Mursena (Prep. 2560 a.) we per-
ceive, on the contrary, an abundance of radiated cells, but no Haversian
canals. The cells, divided lengthwise, present a long, thin ellipse, with
the ends prolonged into plasmatic tubes, larger than those which radiate
from the sides ; and, as the terminal prolongations communicate with
each other, a series of cells may often be traced resembling a monili-
form or alternately dilated and contracted canal. In a section of a
jaw of the common eel, large, irregular vascular canals are seen,
combined with radiated cells like those in the Mursena. In a section
taken from the second thin longitudinal crest of the cranium of an

THE SKELETON.

31

Ephippus, tliere are no radiated cells ; the dense tissue is traversed
by parallel undulating plasmatic tubes, which here and there present
slight dilatations, divide, and give off minuter tubes which anastomose
in their interspaces. The medullary canals, from which the tube
derive their plasma, are few and large.

Almost endless are the minor modifications of the structure of the
osseous tissue of the Vertebrate animals, chiefly produced by varieties
in size, course, and number of the vascular canals and the radiated
cells and tubes : both vascular canals and radiated cells may be ab-
sent in the portion of bone examined ; but the plasmatic tubes are
always present. In the dermal bone-plates of the sturgeon, they
become, in the dense exterior layer, as minute as in the so-called
enamel of the shark’s teeth.*

The growth of bone presents some modiflcations in the different
classes of Vertebrate animals.

In Fishes the bones continue to increase in dimension almost
throughout life : this is best seen in the cranium, where the periphery
of the bones, both of those which overlap by squamous sutures, and
those which interlock by broad dentated surfaces, is cartilaginous,
and, in the thin bones, sub-transparent. Here the development,
serial arrangement and metamorphoses of the cartilaginous cells, in
other words, the growth of temporary cartilage, are always to be
seen in progress.

I The long bones of most Reptiles retain a layer of ossifying cartilage
beneath the terminal articulating cartilage, and growth continues at
their extremities throughout life. Few of the long bones of Birds have
separate terminal pieces or epiphyses : the distal epiphysis of the tibia
is an exception to this rule ; but the distinct single piece which forms
the upper end of the ankle-bone in the young bird represents the tarsal
segment, and rests, not on a single diaphysis, but on the still separate
proximal ends of the three metatarsals. In tail-less Batrachians and
in most of the Mammalian class, the ends of the long cylindrical bones,
which support the articular cartilages, are distinct in the growing
bone from the shaft, and are termed “ epiphyses,” the shaft being the
“ diaphysis : ” the seat of the active growth of the bone is in a carti-
I laginous crust at the ends of the diaphysis. When the epiphyses
finally coalesce with the diaphysis, growth in the direction of the
bone’s axis is at an end : but in the Mammalian bones, as in those of
Birds and Reptiles, there is a slower growth going on over the entire
periphery of the bone, which is covered by the periosteum : the

* The work of Bibra (iv.) contains good observations and illustrations of the
comparative microscopic anatomy of the osseous tissue in the different classes of
Vertebrata.

32

LECTURE II.

periosteum is that membrane in which the vascular system of a bone
undergoes the amount of subdivision which reduces its capillaries to
the dimensions suited for penetrating the pores leading to the vascular
and Haversian canals.

These preparations of the bones of young pigs fed with madder j
(Nos. 190 — 201. Phys. Series), and those of young birds, showing '
artificial perforations (Nos. 188, 189.), illustrate some experiments j
by Hunter on the growth of bone. j

The strong affinity of phosphate of lime for the colouring matter j

of the Rubia tinctorum, which, when taken as food, passes into the j

plasma of the circulating fluids and combines with the phosphates of
lime with which that fluid comes in contact, has been supposed to
throw some clear light upon the growth of bone. All the phosphate i
of lime which is deposited in tooth or bone, whilst the madder is in i
the system, is deeply tinged by it, and Hunter found that the exterior !
layers of the growing bone of a young pig which had been fed a
fortnight on madder were most strongly coloured. But he observed
also in another young pig similarly fed, but killed a fortnight after
the madder had been omitted from its food, that “ the exterior of the
bones was of the natural colour, but the interior red.” (xi. p. 75.)
The inference deduced was, that a new layer of bone, during the
absence of madder from the circulating system, had been formed,
uncoloured, on the exterior surface.

Mr. Gribson endeavoured to invalidate the conclusion, by hinting
that the colouring matter might have been removed from the pre-
viously stained bone by the serum of the blood, which fluid he be-
lieved to have a greater affinity for the dye than phosphate of lime
had; but Mr. Paget has proved by experiment that the phos-
phates have actually the stronger affinity for the dye.

The well-known fact that the phosphates on every internal or
external surface of the bone, which is exposed to the current of the
dye-charged plasma, attract the dye, by no means invalidates the con-
clusions from the ingenious experiments of Hunter ; for the quantity
of colour so imbibed by the previously and completely formed bone
is always much less than that which the growing bone receives from
the phosphates deposited during the presence of madder in the cir-
culating system.

Hunter’s experiments, therefore, coincide with those of Du Hamel,
made by encompassing shafts of growing bones with rings of wire,
in proving that the increase in circumference is due to growth at the
periphery beneath the periosteum, such rings having been found,
after a certain period of growth, in the cavity of the enlarged bone.
The growth in length is, however, much more active ; and this, in

THE SKELETON.

33

the long bones of Mammalia, takes place chiefly at the cartilaginous
ends beneath the epiphyses. This is proved by boring holes, or intro-
ducing shots, at definite distances in the diaphyses of growing bones,
and examining the perforations a week or a fortnight after the ex-
periments. The interval between the holes next the ends of the
bone is found much increased, whilst that between those nearer the
middle is but little, if at all, changed. All these experiments concur
to prove that the growth of a bone is not by uniform and general
extension, but by accelerated increase at particular parts.

But extension of parts is not the sole process which takes place in
the growth of bone : to adapt the bone to its specific oflice changes
are wrought in it by the absorption of parts previously formed, espe-
cially in the higher classes of Vertebrata. In fishes we observe a
simple unmodified increase ; but in some species, ossification com-
mences at the periphery of the animal mould or basis, and is always
limited to a thin outer crust of the bone, the rest remaining carti-
laginous or gelatinous. In some of the higher cartilaginous fishes,
for example, an osseous crust is formed upon the periphery of certain
cartilages, in the form of prisms, which contain oval calcigerous cells,
but without conspicuous radiated tubes. Such bones in a dried or
fossil state seem to have had large internal or medullary cavities ; but
they were filled by the unossified animal basis. To whatever extent
the bone of a fish is originally ossified, such it remains, and con-
sequently most of the bones of fishes are solid or spongy in their
interior.

The bones of the Chelonia are likewise solid ; a coarse diploe fills
the interior of the long bones of the extremities ; and we find a
similar structure in the bones of the Cetacea and of the Seal trihe.
Among terrestrial mammals the inactive Sloths and their great
extinct congeners, the Megatherium and Mylodon (xii. p. 83.),
have the long bones of the extremities solid ; whilst the agile Ru-
minant shows each diaphysis in the condition of the hollow column,
both the strength and lightness of the bones being increased by the
progressive absorption of the first-formed substance, as new bone is de-
posited from without. The condition which is illustrated by this section
of the femur of the Nilghau (Prep. 856 c), is common, in fact, to the
long bones of all land mammals, except the Tardigrades above specified.
The Saurian and most of the Batrachian reptiles have likewise the
cavity in each long bone, called “ medullary,” from its containing a
cellular tissue filled by a fine, light, oily matter or marrow. Even
the ribs of the large Ophidians have their medullary cavities : and
the bodies of the vertebrae of some lizards and of the great extinct
Poikilopleuron are similarly excavated. The medullary cavities of the

VOL. n. D

34

LECTURE II.

long bones of the extremities of the colossal Iguanodons and Megalo-
saurs are as capacious as in any mammalian quadruped, and the white
crystallised spar with which these petrified bones are often filled, is
called, not unaptly, “ fossil marrow ” by the quarry-men. In the ordi-
nary marrow -bones of quadrupeds the walls of the cavity are thickest
and strongest at the middle, and become thin towards the ends, where
the peripheral concentric lamellae are separated by wider interspaces,
and are broken up into a fine lattice or lace work. All the cavity and
the cells are lined by a delicate membrane, less vascular than the exter-
nal periosteum, which secretes and immediately contains the marrow ;
this fine oily fluid diminishes the brittleness of the bones. A special
artery called the “ medullary,” supplies the lining membrane of the
medullary cavity ; and the foramen and canal have the same relative
position and course in most Mammalia as in Man ; to wit, the canal
in the humerus and tibia inclines distad, in the femur and anti-
brachial bones proximad, as it approaches the medullary cavity : the
true Ruminants, however, present an exception as regards the femur,
in which the medullary artery, instead of penetrating the back part of
the shaft and running upwards, enters the fore part of the shaft at its
upper third, and inclines downwards.

The flat bones of Mammalia, e. g. those of the cranium, the sca-
pulas, and ilia, have a spongy texture, called diploe, included between
two compact plates ; the internal one in the cranial bones is called
the “ vitreous table” from its density and brittleness. But the most
compact example of the osseous tissue is the bone containing the
organ of hearing, thence called “ petrous,” which, with the tympanic
bone, reaches the maximum of density in the Cetacea.

The bones of birds, especially those of flight, present the opposite ex-
treme of lightness ; not but that the osseous tissue itself is more com-
pact than in most Mammalia, but its quantity in any given bone is much
less, the most admirable economy being traceable throughout the skele-
ton of birds in the advantageous arrangement of the weighty material
for the office it is destined to perform. Thus, in the long bones, the ca-
vities, analogous to the medullary in mammals, are more extensive, and
the solid walls of the bone much thinner ; a large aperture called the
“ foramen pneumaticum,” near one or both ends 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 the
bone, instead of being occupied by a spongy diploe, present a light
open network, slender columns shooting across in different di-
rections from wall to wall, and these columns are likewise hollow.
The vastly expanded beak, with its hornlike process, in the Hornbill

THE SKELETON.

35

forms one great air-cell, -with thin bony parietes ; and in this bird, in
the Swifts, and the Humming-birds, every. bone of the skeleton, down
to the phalanges of the claws, is pneumatic.

The extent to which the skeleton is permeated by aii', varies in
diflferent birds, in relation chiefly to their different kinds and powers
of flight. The opposite extreme to the Swift is met with in the
terrestrial Apteryx and aquatic Penguin, in which not any bone of the
skeleton receives air.

In the mammalian class the air-cells of bone are confined to the
head, and are filled from the nasal or tympanic cavities, never from
the lungs. The frontal, sphenoidal, and maxillary sinuses, and the
mastoid cells, are examples of pneumatic bones in the human subject.
The frontal sinuses extend backwards over the calvarium in most
Ruminants, and penetrate the cores of the horns in oxen, sheep, and
a few antilopes.

The whole diploe of the upper, back, and side w^alls of the cranium
was inflated, as it were, with air in the great extinct Sloths ; the
outer table was raised considerably above the vitreous, and the brain
thus seemingly defended by a double skull; the advantage of which
modification to these leaf-devouring animals, in the event of blows
from the falling trees which they uprooted, is well displayed in the
healed fractures of the skull of the Mylodon, in the museum of the
College (xii. p. 157.). The outer table of the entire epicranium is
similarly raised above the inner one by intervening large air-cells,
and their sinuous septa, in the Gii’affe ; the short horns are solid, but
are sustained by the vaulted roof of the skull; and, as the animal
can deal heavy blows with these simple weapons, the concussion is
diminished by the interposition of these air-chambers between the
outer table and the immediate covering of the brain.

The most remarkable development of air-cells in the mammalian
class is, however, presented by the Elephant ; the intellectual phy-
siognomy of this great Pachyderm being caused, as in the Owl, not
by actual capacity of the brain-case, but by the enormous extent of
the pneumatic cellular diploe between the two tables of the skull.

In each of these modifications the vacuities of the osseous tissue,
whether mere cancelli as in the Tortoise, or small medullary cavities
as in the Crocodile, or larger medullary cavities as in Mammals, or
pneumatic cavities and sinuses, are the result of secondary changes
by absorption, and not of the primitive constitution of the bones.
These are in all air-breathing animals solid at their first commence-
ment, and the vacuities are formed by the removal of osseous matter
previously formed, whilst fresh bone is added to the exterior surface.

n 2

36

LECTURE II.

The thinnest-walled and hollowest pneumatic bone of the bird of
flight was first solid, next a marrow-bone, and Anally the case of an
air-cell. The solid bones of the Penguin, and the medullary femur
of the Apteryx and Dinornis, are arrested stages of that course of
development through which the pneumatic wing-bone of the soaring
Eagle had previously passed.

In proceeding after the foregoing survey of the general nature,
chemical constitution, development, growth, and structure of the
osseous system, to the description of the skeleton in the vertebrate
animals, there next remains to define a bone; and the endeavour to
do this has not been the least difficult part of my task, with re-
ference to the applicability of the definition to the vertebrate series
in general.

To the human anatomist the question — what is a bone? — may ap-
pear a very simple, if not a needless one : he will most probably reply
that a bone is any single piece of osseous matter entering into the
composition of the adult sheleton ; and, agreeably with this definition,
he will enumerate about 260 bones in the human skeleton.

Soemmering, who includes the thirty -two teeth in his enumeration,
reckons from 259 to 264 bones ; but he counts the os spheno-occipitale
as a single bone, and also regards, with previous anthropotomists, the
os temporis, the os sacrum, and the os innominatum, as individual
bones ; the sternum, he says, may include two or three bones, &c.
(xiii. p. 6.) : but, in Birds, the os occipitale is not only anchylosed to
the sphenoid, but these early coalesce with the parietals and frontals ;
and, in short, the entire cranium proper consists, according to the
above definition, of a single bone. Blumenbach, however, applying
the human standard, describes it as composed of the proper bones of
the cranium consolidated, as it were, into a single piece (xrv. p. 56.).
And in the same spirit most modern anthropotomists, influenced by
the comparatively late period at which the sphenoid becomes anchy-
losed to the occipital in Man, regard them as two essentially distinct
bones. In directing our survey downwards in the mammalian scale,
we speedily meet with examples of persistent divisions of bones which
are single in Man. Thus it is rare to find the basi-occipital confluent
with the basi-sphenoid in mammalian quadrupeds ; and before we quit
that class we meet with adults in some of the marsupial and monotre-
matous ^species, for example, in which the supra-occipital, “ pars
occipitalis proprie sic dicta,” of Soemmering, is distinct from the con-
dyloid parts, and these from the basilar or cuneiform process of the os
occipitis : in short, the single occipital bone in Man is four bones in
the Opossum or Echidna; and just as the human cranial bones lose
their individuality in the Bird, so do those of the Marsupial lose their

THE SKELETON.

37

individuality in the ordinary mammalian and human skull. In many
Mammalia we find the pterygoid processes of anthropotomy per-
manently distinct bones ; even in Birds, where the progress of ossific
confluence is so general and rapid, the pterygoids and tympanies,
which are subordinate processes in Man, are always independent
bones.

In many Mammalia the styloid, the auditory, the petrous, and the
mastoid processes remain distinct from the squamous or main part of
the temporal, throughout life ; and some of these claim the more to be
regarded as distinct bones, since they obviously belong to different
natural groups of bones in the skeleton ; as the styloid process, for
example, to the series of bones forming the hyoidean arch.

The artificial character of that view of the os sacrum, in which this
obviously more or less confluent congeries of modified vertebrae is
counted as a single component bone of the skeleton, is sufficiently
obvious. The os innominatum is represented throughout life in most
reptiles by three distinct bones, answering to the iliac, ischial, and
pubic portions in anthropotomy. The sternum in most quadrupeds
consists of one more bone than the number of pairs of ribs which join
it ; thus it includes as many as thirteen distinct bones in the Bradypus
didactylus.

The arbitrary character of the above cited definition of a bone,
and the essentially complex nature of many of the single bones and
independency of the processes of bone in anthropotomy, are taught
by anatomy, properly so called, which reveals the true natural groups
of bones, and the modifications of these which peculiarly characterise
the human subject.

It will occur to those who have studied human osteogeny, that
the parts of the single bones of anthropotomy which have been
adduced as continuing permanently distinct in lower animals, are
originally distinct in the human foetus : the occipital bone, for
example, is ossified from four separate centres ; the pterygoid pro-
cesses have distinct centres of ossification ; the styloid, and the
mastoid processes, and the tympanic ring, are separate parts in the
foetus. The constituent vertebrae of the sacrum remain longer dis-
tinct ; and the ilium, ischium, and pubes are still later in anchy-
losing together, to form the ‘ nameless bone.’

These and the like correspondencies between the points of ossifica-
tion of the human foetal skeleton, and the separate bones of the adult
skeletons of inferior animals, are pregnant with interest, and rank
among the most striking illustrations of unity of plan in the verte-
brate organisation.

Cuvier, commenting on the arbitrary character of some of the

38

LECTURE II.

definitions of single bones in antbropotomy, goes so far as to state
that, in order to ascertain the true number of bones in each species,
we must descend to the primitive osseous centres as they are mani-
fested in the foetus.*

According to this rule we ought to count the humerus as three bones,
and the femur as four bones instead of one ; for the ossification of the
latter begins at four distinct points, one for the shaft, one for the
head, one for the great trochanter, and one for the distal condyles.
But who will be induced to regard these parts and processes as dis-
tinct bones ? No such distinction is kept up in any of the lower
classes. In both Birds and Reptiles the femur is developed from a
single centre.

The rule laid down by the great French anatomist fails in its ap-
plication to the difficult point under consideration, because he did not
distinguish between those centres of ossification that have homological
relations, and those that have only teleological ones : i. e. between
the separate points of ossification of a human bone which typify per-
manently distinct bones in the lower animals, and the separate
points which, without such signification, facilitate ossification, and
have for their final cause the well-being of the growing animal.
The young lamb or foal, for example, can stand on its four legs
as soon as it is born ; it lifts its body well above the ground, and
quickly begins to run and bourtd. The shock to the limbs themselves
is broken and diminished at this tender age, by the divisions of the
supporting long bones, — by the interposition of the cushions of
cartilage between the diaphyses and the epiphyses. And the jar
that might affect the pulpy and largely developed brain of the im-
mature animal is further diffused and intercepted by the epiphysial
articular extremities of the bodies of the vertebrae.

We thus readily discern a final purpose in the distinct centres of
ossification of the vertebral bodies, long bones, and the limbs of mam-
mals, which would not apply to the condition of the crawling reptiles.
The diminutive brain in these low and slow cold-blooded animals
does not demand such protection against concussion ; neither does the
mode of locomotion in the quadruped reptiles render such concussion
likely ; their limbs sprawl outwards, and push along the body, which
commonly trails upon the ground ; therefore we find no epiphyses
with interposed cartilage at the ends of a distinct shaft in the long
bones of Saurians and Tortoises. But when the reptile moves by leaps,
then the principle of ossifying the long bone by distinct centres again

*■ “ Mals ces distinctions sont arbitraires, et pour avoir le veritable nombre des os
de chaque espece, il faut remonter jusqu’ aux premiers noyaux osseux tels qu’ils se
montrcnt dans le foetus.” (xiii. tom. i. p. 120.)

THE SKELETON.

39

prevails, and the extremities of the humeri and femora long remain
epiphyses in the frog.

A final purpose is no doubt, also, subserved in most of the separate
centres of ossification which relate homologically to permanently dis-
tinct bones in the general vertebrate series ; it has long been re-
cognised in relation to facilitating birth in the human foetus ; but
some facts will occur to the human osteogenist, of which no teleolo-
gical explanation can be given.

One sees not, for example, why the process of the scapula which
gives attachment to the pectoralis minor, the coraco-brachialis, and
the short head of the biceps should not be developed by continuous
ossification from the body of the blade-bone, like that which forms
the spinous process of the same bone. It is a well-known fact, how-
ever, that not only in Man, but in all Mammalia, the coracoid process
is ossified from a separate centre. In the Monotremes it is not only a
distinct, but is as large a bone as in Birds and Keptiles, in which
it continues a distinct bone throughout life. Here, then, we have
the homological, without a teleological explanation of the separate
centre for the coracoid process in the ossification of the human blade-
bone.

This distinction in the nature and relations of such centres, which
is indispensable in the right application of the facts of osteogeny to
the determination of the number of essentially distinct bones in any
given skeleton, has never been considered, so far as I know, in that
application. Some homologists (n. xiv.) have gone beyond Cuvier,
and still more beyond nature, in arguing the number of individual
bones, as indicated by the number of separate centres of ossification
in the embryo, to be the same in all vertebrate animals ; and that they
afterwards differed, or seemed to differ, only by reason of the greater
or less rapidity or extent of the confluence of those ossific centres or
essentially distinct bones.

This primitive conformity of separate osseous pieces in the verte-
brate series holds good, however, only in regard to the separate
centres of ossification of those bones of higher animals which have
homological relations to the permanently distinct bones of lower spe-
cies ; it by no means applies to those which have merely teleological
relations to the species in which they exist.

But, besides the epiphyses of the long bones of Mammalia, which
enter into the latter category, and cannot, therefore, be properly
viewed in the light of distinct bones ; what are we to say to the
intercalated, inconstant “ ossa wormiana,” or to the ossified tendons
of birds, or to those developed in the tendons of the vertebral muscles
of the musk-deer? Are these to be reckoned equally distinct and in-

40

LECTURE II.

dividual bones of the skeleton, with the occipital and parietal bones,
with tjhe dorsal vertebrae, or the tibiae ?

In considering this and other questions previously discussed, you
will begin to appreciate the difficulties in defining or determining
what shall be considered a distinct and an individual bone in the
skeleton.

If we apply to each species the anthropotomical definition of a
bone, as “ any single osseous piece of which the skeleton of the ma-
ture animal is composed,” we must qualify it by subordinate de-
finitions of the different natures of such separate pieces of the skeleton.
Hitherto bones have been primarily classified according to their
form, as long and cylindrical, broad and flat, thick and squab,
symmetrical, or unsymmetrical (xm. xi. pp. 9, 10.) ; or, according to
their position, into median * and lateral (xvi. p. xviii.), or into endo-
skeletal, exo-skeletal, and splanchno -skeletal bones (i. p. 113. 115.).
But, besides these, the above discussed deeper and more essential
differences of the bones require that they should be divided into
simple, as being developed from a single centre, and compound, as
developed from separate centres ; and the compound bones, in the
human subject, for example, may be subdivided into the teleologically
compound, as the ossa cylindrica, which are originally developed
from separate centres in relation to a spinal final purpose ; and the
homologically compound, as most of the ossa lata (occiput, scapula),
and many ossa mixta (vertebrae, sacrum), which are developed from
separate centres, representing permanently distinct simple bones in
other Vertebrata.

The teleologically compound bones have their relations limited to
the particular exigencies of particular classes, but the homologically
compound bones have relations extending over the whole vertebrate
series.

The great aim of the philosophical osteologist is to determine,
by natural characters, the natural groups of bones of which a verte-
brate skeleton typically consists ; and, next, the relations of individual
simple bones to each other in those primary groups, and to define the
general, serial, and special homologies of each bone throughout the
vertebrate series.

By general homology I mean the relation in which a bone stands to
the primary segment of the skeleton of which it is a part ; thus, when
the basi-occipital bone (basilar process of the os occipitis in anthropo-

* These are mostly symmetrical ; but the youngest anthropotomist must have
met with instances of a curved vomer, and an unsymmetrical sternum ; and, on the
other hand, most of the phalanges among the ossa paria, sen lateralia, are sym-
metrical.

THE SKELETON.

41

tomy) is said to be the centrum or body of the occipital or posterior
cranial vertebra, its general homology is enunciated. When it is said
to repeat in its vertebra, or to answer to the basi -sphenoid in the parie-
tal vertebra, or to the body or centrum in the atlas, dentata, or any other
of the vertebral segments of the skeleton, its serial homology is indi-
cated : when the essential correspondence of the basilar process of the
occipital bone in Man with the distinct bone called “ basi-occipital ”
in a Crocodile or Fish is shown, its special homology is determined.

LECTURE III.

THE VERTEBRA, AND VERTEBRAL COLUMN IN FISHES.

To understand the fundamental type of the vertebrate skeleton its
study must be commenced, not in the highest species, — not in that
skeleton where irrelative repetition is least, and where modification
of each part in mutual subserviency to another is greatest, — but in
the lowest Class where, conformably with the law enunciated in the
previous Course *, vegetative uniformity most prevails, and the pri-
mitive type is least obscured by teleological adaptations.

Such conditions are best displayed in the skeletons of fishes : fishes
form, however, but one branch of the vertebrate stem, which, like
other primary branches, ramifies in diverging from the common
trunk. We should miss our aim, therefore, and be led astray from
the detection of the true general type of the vertebrate skeleton,
were we to confine our observations to fishes only. A comparison of
their skeletons with those of the higher classes teaches that the na-
tural arrangements of the parts of the endo-skeleton in Vertebrata,
like that of the exo-skeleton in Articulata, is in a series of segments
succeeding each other in the axis of the body. I do not find these
successive segments composed of precisely the same number of bones
in all Vertebrata ; rarely, indeed, in the same animal. Yet certain
constituent parts of each segment do preserve such constancy in their
existence, relative position, and offices throughout the body, as to
enforce a conviction that they are homologous parts, both in the con-
secutive series of the same individual skeleton, and throughout the
entire series of vertebrate animals.

* Lectures on Invcrtebrata, 8vo. 1843, p. 364.

42

LECTURE III.

To each of these primary segments of the skeleton I shall, with
Geoffroy St. Hilaire (xiv. ii.), apply the term “ vertebra ” : the
word may seem to the anthropotomist to be used in a different or
more extended sense than it is usually understood ; yet he is
himself, unconsciously perhaps, in the habit of including in certain
vertebrae of the human body, elements which he excludes from the
idea in other natural segments of the same kind ; influenced by dif-
ferences of proportion and coalescence, which are the most variable
characters of a bone. Thus the rib of a cervical vertebra is the “ pro-
cessus transversus perforatus,” or the “ radix anticus processus trans-
versi vertebrae colli : ” whilst in the chest, it is “ costa,” or “ pars ossea
costae.” (xiii. 239. 250.) But the ulna is not the less an ulna in the
horse, because it is small and anchylosed to the radius.

The osteology of Man, therefore, cannot be fully or- rightly under-
stood until the type of which it is a modiflcation is known, and the
first step to this knowledge is the determination of the vertebral
segments, or natural groups of bones, of which the myelencephalous
skeleton consists.

I define a vertebra, as one of those segments of the endo-skeleton
tvhich constitute the axis of the body, and the protecting canals of the
nervous and vascular trunks : such a segment may also support di-
verging appendages. Exclusive of these, it consists in its typical
completeness, of the following parts or elements : —

c. A body or centrum. *
n. Two neurapophyses. f
p. Two parapophyses. J
pi. Two pleurapophyses. §
h. Two hcemapophyses. ||
ns, A neural spine. %
hs. A haemal spine. .**

zygapophysis ,-.j
diapophysis,..^
parapophysis

Mhaemapophysis
II haemal spine

neural spine

neurapophysis

pleurapophysis

Ideal typical vertebra.

* Greek, kentron, centre. Syn. Corpus verteirce'. Corps de vertebre, Cuvier;
Tertiar-wirbel, Curus ; Wirhel-h'drper, GexmStt^^Cycleal, Geoffrey; Cyclo-vertehral
dement. Grant.

f Gr. neuron, nerve ; and apophysis, a process of bone. Syn. Arcus posterior
vertebra, seu radices arcus posterioris. Dechplatten and Grundplatten, Cams. Bogen-.
stiicke des Riickenwirbels, Carus. Obere Wirbelbogen, Germ. Partie annulaire, Cuv.
Ferial, Geof. Peri-vertebral elements, Grant.

Gr. para, trans, across ; and apophysis. Syn. Radix prior seu antica processus.

' The Latin synonyms are from Soemmerring’s Classical Anthropotomy, “ De
corporis human! fabrica,” 1794.

* The German synonyms are those of John Muller, Wagner, and niost German
Zootomists, unless otherwise specified.

THE VERTEBRA IN FISHES.

43

These, being usually developed from distinct and independent
centres, I have termed “autogenous” elements (xix. p. 518.). Other
parts, more properly called processes, which shoot out as continu-
ations from some of the preceding elements, are termed “ exogenous : ”
e. g. (<) the diapophyses, or upper “ transverse processes,” * and (z)
the zygapophyses, or the “ oblique ” or “ articular processes ” f of
human anatomy.

The autogenous processes generally circumscribe holes about the
centrum, which, in the chain of vertebrae, form canals. The
most constant and extensive canal is that 8. n) :j: formed

above the centrum, for the lodgment of the trunk of the ner-
vous system (neural axis) by the parts thence termed “ neurapo-
physes.” The second canal (^fig. 8. K) |;j:, below the centrum, is in its
entire extent more irregular and interrupted ; it lodges the central
organ and large trunks of the vascular system (haemal axis), and is
usually formed by the laminae, thence termed “ haemapophyses.” At
the sides of the centrum, most commonly in the cervical region, a
canal (y?y. 9. v) is circumscribed by the pleurapophysis or costal
process (ib. pZ), and by the diapophysis or upper transverse process
(ib. <), which canal includes a vessel, and often also a nerve.

Thus a typical or perfect vertebra, with all its elements, presents
four canals or perforations about a common centre ; such a vertebra
we find in the thorax of man, and most of the higher classes of Ver-
tebrata {^fig- 6.), also in the neck of many birds. In the example
from the latter class (yfig. 9.), the haemapophyses (4, s) are anchy-

iransversi vertebrcB ; Querforsatz, Carus ; Uniere Querforsatz, Germ. ; Apophyse trans-
verse, Cuv. ; Paraal, Geof. ; Para-vertebral elements. Grant.

§ Gr. pleura, a ribj and apophysis, Syn. Processus transversus vertebrce cervicalis,
Costa seu, pars vertebralis, seu ossea, costce. Puchentheil and Ober-sternal-theil des
Urwirbelhogens, Carus ; Cdtes vertebrates, Cuv. ; Paraal, Geof. ; Cata-vertebral ele-
ments, Grant.

II By Syncope for haematoapophyses, from Gr. haima, blood ; and apophysis.
Syn. Cartilago costce, seu pars sternalis costce : in the abdomen, inscriptiones tendinece
musculi recti ; Vnter-sternal-theil des Urwirbelbogens, Carus; Pogenstiicke des Bauch-
wirbel, Carus; Untere IVirbelbogen, Ger. ; CStes sternaJes, Cuv.; Os ploy £ en chevron,
Cuv. ; Cataal, Geof. ; Cata-vertebral elements. Grant.

Syn. Processus spinosus vertebrce. Its base is the Oberer Tertiar-wirbel, Carus ;
its apex is the Oberer Dorn-forsatz, Carus ; Apophyse epineuse, Cuv. ; Epial, Geof. ;
Epi-vertebral elements. Grant

*• Syn. Ossa sterni et processus cnsiformis ; in the abAomei\,^‘linea alba.” Sternal-
wirbel Kbrper, Carus ; Unterer Dorn-forsatz, Carus.

* Diapophysis, from Gr. dia, trans, across ; and apophysis. Syn. Radix posticus
processus transversi vertebrce, and processus transversus. Queforsatz, Carus ; Obere
Querforsatz, Germ. ; Apophyse transverse, Cuv.

f Zygapophysis, from Gr. zugos, junction ; and apophysis. Syn. Processus obliquus
vertebrce,; Seitlicher Tertiar-wirbel, Carus; Gelenk-forsatz, Germ.; Apophyse articu-
laire, Cuvier.

i Ruckenmarhs-kanal, Carus.

Aortenkanal, Carus.

T

44 LECTURE III.

losed to the under part of the centrum, to which part they are
moveably articulated in the tails of most reptiles and mammals ; space
being needed only for the protection of the ca-
rotids in the one case, and for the caudal artery
and vein in the other. In the chest, where the
central organ of circulation is to be lodged, an
expansion of the haemal arch takes place, analo-
gous to that which the neural arches of the
cranial vertebrae present for the lodgment of the
brain. Accordingly in the thorax, the pleura-
pophyses {Jig. 6. pi) are much elongated, and
the hasmapophyses {Jig. 6. Ji) are removed from
the centrum, and are articulated to the distant ends of the pleura-
pophyses ; the bony hoop being completed by the intercalation of
the haemal spine {Jig. 6. hs) between the ends of the h^mapo-
physes. And this spine is here sometimes as widely expanded (in
the thorax of Birds and Chelonians, for example) as is the neural
spine (parietal bone or bones) of the middle cranial vertebra in
Mammals. In both cases, also, it may be developed from two lateral
halves, and a bony intermuscular crust may be extended from the
mid-line, as in the skull of the Hyaena, and the breast bone of the
Hawk.

The vertebrae of the trunk present essentially their most simple,
though often apparently the most complete, condition in Fishes, in
which class a typical vertebra can only be obtained from the head ;
in the rest of the column, the hamapophyses, for example, are always
absent or unossified. It is by no means true that the several elements
of a vertebra are found most isolated and distinct in the lowest classes ;
the neurapophyses are commonly anchylosed to the centrum in fishes,
but commonly remain isolated and distinct in reptiles ; the haemal
canal is formed by modified parapophyses in fishes, but by isolated
and distinct haemapophyses co-existing with transverse processes
in reptiles and mammals.

The number of vertebrae, or at least of neural arches, is governed
by the number of segments of the cerebro-spinal axis. These
segments in the spinal chord are chiefiy indicated by the pairs of |
spinal nerves. In the brain, the centres are more definitely indi- ,
cated by the ganglionic form under which they first make their
appearance ; but here, by the superaddition of fasciculi of nerve- |
fibres for the special functions of the brain, the origins of essentially t
single nerves become separated, and the motor roots divided from the ;
sensitive, as we see in the nerves of the eyeball. Hence, the cranial i
vertebrae do not correspond with the number of seemingly distinct *

THE VERTEBUjE IN FISHES.

45

cranial nerves ; and they undergo, in their neural arches, as extreme
modifications as we perceive in the ha;mal portions of those vertebrie
that protect the great centres of the vascular system. We may
learn how much the development of the neurapophyses and vertebral
bodies depends, in the trunk, upon the conjunction of nerves with the
spinal chord, by the fact that, in the regenerated tails of lizards, the
vertebral axis remains continuous and unjointed, because there is no
co-extensive spinal chord giving off pairs of nerves.

An extremely delicate fibrous band, with successively accumulated
gelatinous cells, compacted in the form of a cylindrical column, and
inclosed by a membranous sheath, is the primitive basis, called
‘ chorda dorsalis,’ in and around which are developed the cartila-
ginous or osseous elements, by which the vertebral column is estab-
lished in every class of Myelencephala (iii. p. 340.).

The earlier stages of vertebral development are permanently re-
presented, with individual peculiarities superinduced, in the lower
forms of the class of fishes. In the anencephalous Lancelot {Bran-
chiostoma) the lowest of all, the entire vertebral column consists of
the gelatino-cellular chord and its membranous sheath. In the
Lamprey cartilaginous arches and spines are added above the chorda
dorsalis, in the membranous wall of the neural canal, and in the tail,
also beneath it. In the Sturgeon and Chimsera, the bases of the
cartilaginous arches inclose the ‘ chorda.’ In the Lepidosiren the
neural and haemal arches and their spines are ossified, but the
centrums are still confluent as a dorsal membrano-gelatinous chord.
In many Sharks and Rays the ‘ chorda ’ is encroached upon by
osseous or cartilaginous convergent laminae, and by concentric,
successively shorter, centripetally developed cylinders, and is thus
reduced to a string of gelatinous beads, each bead occupying
the interspace between the opposed concave surfaces of the ver-
tebral bodies. This moniliform state of the chorda dorsalis is
persistent in most osseous fishes, the biconcave bodies of the ver-
tebrae being perforated in the centre ; whilst, in some other osseous
fishes, the gelatinous biconical segments of the ‘ chorda ’ are insulated
by the completed centripetal progress of ossification ; and in one ex-
ception {Lepidosteus), they are converted into osseous balls, fixed to
the fore part of each vertebral body, which plays in the concavity or
cup of the next vertebra in advance.

The neural and haemal arches and spines are bony in all osseous
fishes ; and in all fishes chondrification and ossification of the ver-
tebral column commences in these arches. In reptiles, birds, and
mammals, the vertebrae are bony throughout.

Development diverges from the membrano-gelatinous stage, so as

46

LECTURE 111.

to establish three types of vertebrae, which may be characterised by
the form of the articular ends of the centrum, as the “ biconcave,”
the “ concavo-convex,” and the “ flattened” types, respectively dis-
tinguishing, as a general rule. Fishes, air-breathing Ovipara, and
Mammals.

The least perfect form of a vertebra is that in fishes, though it
often seems the most complex, from the intercalation of bones of the
dermal system, and Geoflroy (ii. p. 119.)* was unfortunate in
taking a fish’s vertebra, with this extrinsic complication, as the
perfect type of that primary segment of the myelencephalous ske-
leton. Two of the autogenous elements, the “ hsemapophyses,” for
example, are not developed tiU we reach the Eeptilia : in fishes they
are represented by the “ parapophyses ” or lower transverse pro-
cesses.

Before entering, however, upon the special osteology of the class
Pisces, it wiU be necessary to explain the sense in which the terms of
groups or divisions of the class are used in these Lectures, in reference
to their anatomical characters. Cuvier (xxiv. ii. p. 128.) primarily
divides the class, according to the nature of their endo-skeleton, into
Pisces asset, and Pisces cartilaginei ; but the latter group includes
species of widely difierent grades of organisation, and in the “ Tables
of Classification” exhibited in my first course of Lectures in this
Theatre in 1837, 1 separated the Lampreys, Myxinoids, and Lancelets,
under the name “ Z^emop^eri,” from the rest of the Chondropterygii
of Cuvier, making these the highest, and those the lowest order of
fishes, f

M. Agassiz, with views enlarged by a survey of the extinct
members of the class, divided the Pisces, by characters taken from
the exo-skeleton, into four primary groups ; viz. Placoidei, Ganoidei,
Cycloidei, and Ctenoidei.

The fishes of the Placoid order are characterised by having the
skin covered irregularly with plates of hard osseous matter, some-
times of large size, and sometimes reduced to small points, as where
they form the shagreen on the skin of many sharks and the prickly
tubercles on the skin of most rays. This order comprehends all the

* This ingenious anatomist was thus driven to as arbitrary assumptions of mu-
tations of placa, and to as far-fetched analogies, in reference to the supposed ele-
mentary parts of the vertebra, as in his attempt to exemplify the homologies of the
cephalic division of the endo-skeleton of the higher Vertebrata, by the combined
bones of the exo- and endo-skeleton, which constitute the complex skull in
Fishes,

t The distinguished naturalist, C. L. Bonaparte, Prince of Canino, has also
founded a distinct order for the Cyclostomous Chondropterygians of Cuvier, under
the name of “ Marsipo-branchii,” which well applies to the Lampreys and Myxi-
noids.— Selachorum Tnbula Analytica, 1838.

THE VERTEBKiE IN FISHES.

47

cartilaginous fishes of Cuvier, except the Sturgeons and Chimerae
(Sturioniens). It is as necessary, however, for the expression of
general anatomical propositions, to separate the Dermopferi from the
Placoidei of Agassiz as from the Chondropterygii of Cuvier ; and
it is with this restriction that the Placoids will be referred to
in these Lectures, as answering namely to the Plagiostomes of
Cuvier.

The Ganoid fishes are defended by plates or scales covered with a
thick coat of enamel ; some of considerable dimensions and irregular
form, as in the Sturgeon ; more commonly angular and imbricated, as
in the Bony Pike {Lepidosteus). Most of the species and genera of
this order have become extinct. The recent species included in it
by Agassiz differ materially in their anatomical characters.

The Ctenoid fishes have scales formed of laminae of horn, or of un-
enamelled bone, with the posterior margin pectinated, like a comb ;
e. g., the Perch, and most of the Acanthopterygii of Cuvier.

The Cycloid fishes have their scales composed of laminae of horn
or unenamelled bone, of a rounded form, with smooth and simple
margins. The Carp, the Salmon, the Herring, and many other Ma-
lacopterygii of Cuvier, are examples of this order.

Linnaeus divided the bony fishes into the orders Jugulares, Tho-
racici, Abdominales, and Apodes, according to the position or the
absence of the ventral fins. Cuvier divided the bony fishes, ac-
cording to the structure of the fins, into Acanthopterygii and
Malacopterygii. Not many general anatomical propositions, how-
ever, can be expressed with regard to these orders. A more natu-
ral arrangement has been founded upon a consideration of both
external and internal anatomical characters by Prof. J. Muller
(xxv.), which, with some modifications, I here adopt ; arranging the
class of Fishes, as follows, in the ascending series : —

Classis PISCES.

Ordo I. Dermopteri.

Endo-skeleton unossified; exo-skeleton and vertical fins muco-
dermoid ; vermiform, or abrachial and apodal ; no pancreas ; no air-
bladder.

Suborder I. Pharyngobranchii, seu Cirrhostomi.

Gills free, pharyngeal, inoperculate ; no heart.

Fam. Amphioxidce. Example *, Lancelet.

* These are cited under their common English names, where such exists.

48

LECTURE III.

Suborder 2. Marsipobranchii {Cyclostomi, Guvier).

Gills fixed, bursiform, inoperculate, receiving the respiratory-
streams by apertures usually numerous and lateral, distinct from the
mouth ; a heart.

Fam. Myxinoidei, Examples, Myxine, or Hag.

Petromyzontidce, Lamprey.

Ordo II. Malacopteri {Physostomi, Muller).

Endo-skeleton ossified ; exo-skeleton, in most, as cycloid, in a few
as ganoid, scales ; fins supported by rays, all, save the first sometimes
in the dorsal and pectoral, soft or jointed ; abdominal or apodal ; gills
free, operculate ; a swim-bladder and air-duct.

Suborder 1. Apodes.

Fam. Symhranchidm, Example, Cuchia.

MurcBnidce, Eel.

GymnotidcB, Gymnotus.

Suborder 2. Abdominales.

Fam. Heteropygii, Example, Amblyopsis.

ClupeidcB,

Herring.

SalmonidcB,

Salmon.

Scopelidce,

Saurus.

Characini,

Myletes.

GalaxidcB,

Galaxias.

Esocidce,

Pikei^

Mormyrida,

Mormyrus.

CyprinodontidcB,

Umber.

CyprinidcB,

Carp.

Siluridce,

Sheat-fish.

Ordo HI. Phartngognathi (Muller).

Endo-skeleton ossified ; exo-skeleton in some as cycloid, in others
as ctenoid, scales ; inferior pharyngeal bones coalesced ; swim-bladder
without duct.

Suborder 1. Malacopterygii.

Fam. Scomber-esocidcB, Example, Saury-pike.

Suborder 2. Acanthopterygh.

Fam. ChromidcB, Example, Chromis.
Cyclo-Labridce, Wrasse.

Cteno-Labridcp, Pomacentrus.

CLASSIFICATION OF FISHES.

49

Orclo IV. Anacantiiini (Muller).

Endo-skeleton ossified ; exo-skeleton in some as cycloid, in others as
ctenoid scales ; fins supported by flexible or jointed rays ; ventrals
beneath the pectorals, or none ; swim-bladder without air-duct.

Suborder 1. Apodes.

Fam. Ophididw, Example, Ophidium.

Suborder 2. Thoracici.

Fam. Gadidce, Example, Cod,

Pleur07iectidcB, Plaice.

Ordo V. Acanthopteri (Muller).

Endo-skeleton ossified ; exo-skeleton 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 ; swim-bladder with-
out air-duct.

Fam. PercidcB,

SclerogenidcE,

ScicBuidce,

Labyrinthihranchii,

Mugilidee,

Notacanthidm.,

ScomberidcB,

Squamipennes,

Tanioidei,

Theutyidcc,

Fistularidce,

Gobiidcc,

Blenniidce,

Lophiidee,

Example, Perch.

Gurnard.

Maigre.

Anabas.

Mullet.

Notacanth. >.

Mackerel.

Chietodon.

Riband-fish.

Acanthurus, or Lancet-fish,
Pipe-mouth- and Snipe-fish.
Goby, Remora, and Lumpfish.
Blenny and Wolf-fish.

Angler.

Ordo VI. — Plectognathi ( Cuvier V

Endo-skeleton partially ossified ; exo-skeleton as ganoid scales or
spines ; maxillaries and pre-maxillaries fixed together ; swim-bladder
without air-duct.

Fam. BalistincE, Example, File-fish,

Ostraciones, Trunk-fish.

Gymnodontes, Globe-fish.

VOL. II.

e

50

LECTURE III.

Ordo VII. — Lophobranchii (Cuvier).

Endo-skeleton partially ossified ; exo-skeleton ganoid ; gills tufted,
opercular aperture small ; swim-bladder without air-duct.

Fam. HippocampidcE, Example, Sea-horse.

Syngnathidce, Pipe-fish.

Ordo VIII. — Ganoidei.*

Endo-skeleton in some osseous, in some cartilaginous, in some partly
osseous partly cartilaginous ; exo-skeleton ganoid ; fins usually with
the first ray a strong spine ; a swim-bladder and air-duct.

Earn. Salamandroidei,

Pycnodontidce,

Lepidoidei,

Sturionidce,

Acanthodei^

DipteridcE,

Cephalaspidce,

Example,

I Polypterus.
Pycnodus.
Dapedius.
Sturgeon.
Paddle-fish.
Acanthodes.
Dipterus.
Cephalaspis.

Ordo IX. — Protopteri.

Endo-skeleton partly osseous partly cartilaginous ; exo-skeleton as
cycloid scales ; pectorals and ventrals as flexible filaments ; gills
filamentary, free ; no pancreas ; swim-bladder as a double lung, with
an air-duct ; intestine with a spiral valve.

Fam. Sirenoidei, Example, Lepidosiren.

Ordo X. — Holocephali.

Endo-skeleton cartilaginous ; exo-skeleton as placoid granules ;
most of the fins with a strong spine for the first ray, ventrals abdo-
minal ; gills laminated, attached by their margins ; a single external
gill aperture ; no swim-bladder ; intestine with spiral valve. Co-
pula gaudent.

* I use this ordinal term of M. Agassiz in the sense in which it is restricted
by Professor J. Miiller.

VERTEBRAL COLUMN OF FISHES.

51

Fara. Chimceroidei,

Example, Chimaira.

Edaphodontidce,

r Edaphodon.
X Passalodon.

Ordo XI.

— Plagiostomi.

Endo-skeleton cartilaginous

or partially ossified ; exo-skeleton ida-

coid ; gills fixed with five or more gill-apertures ; no swim-bladder ;
scapular arch detached from the head ; ventrals abdf^iinal ; intestine
with spiral valve. Copula gaudent.

Fam. Hybodontidce,

Example, Hybodus.

CestraciontidcB,

Cestracion.

Notodanidce,

Gray-shark.

SpinacidcB,

Piked Dog-fish.

Scylliidce,

Spotted Dog-fish.

Nictitantes,

Tope.

LamnidcB,

Porbeagle.

AlopeciidcE,

Fox-shark.

Scymniida;,

Greenland-shark.

SquatincB,

Monk-fish.

Zygcenidce,

Hammerhead-shark.

Pristidce,

Saw-fish.

RhinohatidcB,

Rhinobates.

Torpedinidce,

Electric-ray.

Raiidce,

Ray or Skate.

TrygonidcB,

Sting-ray or Fireflaire.

Myliobatidce,

Eagle-ray.

CephalopteridcB,

Cephaloptera.

Adipose substance.'-^

Neural canal.

Inner layer— ^

Fibrous band,

Outer layer— IS
of fibrous capsule.

or basis of
Gelatinous chorda.

Transverse vertical section of vertebral column of Myxine.

In the Myxinoid fishes the neural and hcemal canals are formed
by a separation of the layers of the outer division of the fibro-mem-
branous sheath of the gelatinous chorda (yfy. 10.) ; the neural canal
extending the whole length of the upper part of the chorda, the
hasmal canal being confined to the caudal region, where it contains the
prolongation of the aorta and the vena cava (xjci. p. 25.). In the
Lamprey {Petromyzon) cartilaginous laminai ^fig- 11. n) are de-
veloped in the fibrous sheath (^), and give the first indication of neural
arches. We should hardly expect to find the unity of the vertebral

E 2

52

LECTURE III.

type to be further exemplified at this low step in the series, but rather
be prepared for a divergence into individual peculiarities ; and this
is illustrated by the complex development of the visceral arches for
the support of the heart and gills, which are homologous to the
branchial arches in higher fishes. Yet the analogy of these parts in
the Lamprey, which Muller has termed the cartilaginous basket of
the branchim (xxi. p. 254.) to the modifications of the pleurapophyses,
hsemapophyses and their spines, constituting the ribs and sternum in
the air-breathing Vertebrates, is so close that we may be justified in
describing them in connexion with the vertebral column.

Seven cartilaginous processes, analogous to pleurapophyses, but
homologous with epibranchials 11. 48, 48), came off from a car-
tilaginous tract on both sides of the chorda dorsalis, one below each al-
ternate neurapophysis (ib. w) : after a short course outwards and down-
wards the process divides into three branches, one passing forwards,
one backwards, and the intermediate process (cerato-branchial, 47), or
continuation of the quasi-rib, downwards : the anterior and posterior
processes of contiguous ribs coalesce and form arches above the
branchial apertures (i, 2, to 7), which are circumscribed by similar
arches, formed below by analogous branches there given off from the
cerato-branchial ; this then descends, bends inwards, dilates, and is
perforated ; then contracts and joins a broad and long cartilaginous
hypo-branchial (45), or quasi-sternum, typifying by its double row
of perforations that complex bone in birds. The anterior branches
of the first cerato-branchial unite to form a vertical arch, convex for-
wards ; the posterior pair (47') expand and unite to form the per-
forated cartilaginous case, lined by the pericardium, which contains
the heart : pursuing the analogy of this complex cartilaginous
branchial and cardiac skeleton with the thorax of higher Vertebrata,
we might regard the posterior processes of the ribs as foreshadowing
the costal appendages of birds. Homologically, the entire apparatus
answers to the branchial skeleton of higher fishes, a part which
Geoffroy St. Hilaire regards as a repetition of the thorax of air-
breathing Vertebrata, but which the metamorphoses of the Batrachia
prove to be a development of the visceral skeleton in immediate con-
nexion with the hyoidean arch.

VERTEBRAL COLUMN OF PISHES.

53

Returning, then, to what may be ealled the high road of vertebral
development, we find in the Sturgeons (Sturio, Polyodon), that the
inner layer of the fibrous eapsule of the gelatinous ‘chorda’ has in-
creased in thickness, and assumed the texture of tough hyaline car-
tilage. In the outer layer are developed distinct, firm, and opaque
cartilages, the neurapophyses, which, in the young sturgeon 12.),
are two superimposed pieces on each side, the basal portion bounding
the neural canal, the apical portion the parallel canal filled by fibrous
elastic ligament and adipose tissue * ; above this is the single car-
tilaginous neural spine. The parapophyses are now distinctly de-
veloped, and joined together by a continuous expanded base, forming
an inverted arch beneath the ‘ chorda ’ for the vascular trunks, even in

Fibro-adipose
canal.

Neural canal.
Gelatinous chorda..

'

Inner layer"
of fiVirous capsule
as h} aline cartilage.

Neural spine.

1 — -/ Neurapophysis.

Interncural cartilage.

j^^^^Pleurapophysis.

■Parapophysis-
- Interhajraal cartilage.

^ Haemal canal.
Abdominal vertebra, Sturgeon.

the abdomen. Short and simple pleurapophyses are articulated by
ligament to the ends of the laterally projecting parapophyses in the
first twelve or twenty abdominal vertebrae ; the parapophyses them-
selves gradually disappear, or bend down to form haemal arches in the
tail, at the end of which we find haemal cartilaginous spines cor-
responding to the neural spines above. The first five or six neural
arches are confluent with each other in the sturgeon, and, with the
parapophyses, enclose the fore part of the ‘chorda’ in a firm, con-
tinuous, cartilaginous sheath, perforated for the exit of the nerves.
The tapering anterior end of the ‘ chorda ’ is continued forwards
into the basal elements of the cranial vertebrae.

Vegetative repetition of perivertebral parts not only manifests
itself in the double neurapophysis on each side, but in a small
accessary (interneural) cartilage, at the fore and back part of the
base of the neurapophysis ; and by a similar (interhtemal) one at the
fore and back part of most of the parapophyses. The peripheral
cartilages are more feebly developed in the Polyodon. j"

* I long ago pointed out, in a preparation of Hunter’s (No. S.Sd. ), the “ space above
the canal of the spinal chord formed by the divarication of the cartilaginous pieces
which constitute the support of the spinous processes of the vertebras. This is filled
by fibro-cartllaginous substance, connecting the processes in question.” (xx. vol. i. )
t Cuvier, Memoires du Museum, tom. i. 1815, p. 130.

E 3

54

LECTURE III.

In the southern Chimiera ( Callorhynchus) a greater proportion of
the chorda dorsalis is composed of the dense fibrous capsule, but it
shows no trace of annular structure. In the northern Chimsera,
according to Muller (xxi. p. 68.), another stage towards the forma-
tion of vertebral bodies begins to manifest itself by slender sub-
ossified rings in the cartilaginous sheath of the chorda dorsalis,
which, however, are more numerous than the neural arches. The
neurapophyses and the bases of the transverse processes of about ten
of the anterior vertebrae coalesce, in all the Chimaerae, to form a
continuous accessary covering of the fore part of the chorda ; and
the confluent neural spines here form a broad and high compressed
cartilaginous plate. In the remainder of the vertebral column the
neural arches are distinct from the transverse processes (parapophyses),
and from the haemal arches, which these constitute in the tail.
Between each neurapophysis an accessary cartilaginous interneura-
pophysis* is wedged.

Amongst the Sharks {Squalidce) a beautiful progression in the
further development of a vertebra has been traced out, chiefly
by J. Muller (xxi. p. 64.). \n Heptanchus {Squalus cinereus) the
vertebral centres are still feebly and vegetatively marked out by
numerous slender rings of hard cartilage in the capsule, the number
of vertebra being more definitively indicated by the neurapophyses
and parapophyses ; but these remain cartilaginous. Interneural
pieces are wedged between the neural arches, and close them above ;
the pleurapophyses are similarly wedged into the interspaces of the
parapophyses, and articulate directly with the vertebral bodies, f In
the Piked Dog-fish (Acanthias) the vertebral centres coincide in
number with the neural arches, and are defined by a thin layer of
bone, which forms the conical cavity at each end, but the rest of the
vertebra remains cartilaginous. In the Spotted Dog-fish (Scyllium)
the whole exterior of the centrum is covered by soft cartilage, except
at the concave ends, where the two thin funnel-shaped plates of os-
seous matter coalesce at their perforated apices, and form a basis of the
vertebral body like an hour-glass ; the series of these centrums
protecting a continuous moniliform chorda dorsalis. In the great
Basking Shark ( Selache) the vertebral bodies are chiefly established
by the terminal bony cones, the thick margins of which give
attachment to the elastic capsules containing the fluid remains
of the gelatinous chorda, which now tensely fills the interver-

* “ Ossa intercalaria crurum,'’ “ Lamince intercrurales"

f Traces of the vegetative repetition of vertebral elements may be seen in the
higher animals : the interparietal bone of the Rodents is the ‘ os intercalate spinale ’
of the second cranial vertebra, and the ossa Wormiana are ‘ ossa intercalaria,’ as
John Midler has well remarked in his memoir on Myxinoids, p. 92.

VERTEBRAL COLUMN OF FISHES.

55

tebral biconical spaces.* The rest of the centrum is strengtliened by
a beautiful arrangement of osseous plates, with intervening layers
of cartilage (yfig. 13.). Four sub-compressed conical cavities ex-
tend, two from the bases of the neura-
pophyses (w, n), and two from those of the
parapophyses (p, p) towards the centre of
the vertebral body, contracting as they 2>e-
netrate it. These cavities always remain
filled by a clear cartilage : the central two-
thirds of the vertebral body contain con-
centric and minutely perforated rings or

cylinders of bone, interrupted by the four

Vertical transverse section of i i . n

ceatrum os seiachc maxima. depressions: the peripheral third contains
longitudinal bony lamina, which radiate, perpendicularly to the
plane of the outermost cylinder, toward the periphery of the ver-
tebra : these outer laminae lie, therefore, parallel with the axis of
the vertebra, and the intervening fissures, like those between the
concentric cylinders within, are filled by clear cartilage, which shrinks
and leaves them open in the dry vertebra. There is a transition from
the cylindrical to the longitudinal lamellar structure ; the outer
cylinder being broken up, and sending out processes which join the
irregular inner edges of the outer lamellae.

There are few examples in the animal economy in which the
smallest possible quantity of earthy matter is arranged according to
such beautiful and clearly manifested mechanical principles, for
affording the greatest amount of strength, and that degree of resistance
which the necessarily light, semi-ossified vertebra of a gigantic Shark,
maintaining itself near the surface by muscular exertion, without
help from a swim-bladder, must have to sustain during the vigorous
inflexions of the vertebral column, producing the violent compressions
of their interposed elastic balls.

I have been induced to enter into the details of the condition of
the vertebral of the Selache, both on account of the large scale on which
the beautiful structure is shown, and because of the meagre notice of it
in Home’s “ Anatomy of the Basking Shsirk {Squalus maximusi),” of
which John Miiller justly complains. Muller’s inference that the
vertebrm of Selache resemble those of Lamna is correct : but in
Lamna cornubica the outer longitudinal plates are fewer, and are
bent so as to intercept long elliptical spaces filled with cartilage.

* Mr. Clift found, on piercing the capsule with a knife, that the contained fluid
was spirted out to a considerable distance, by the contraction or recoil of the tensely
filled elastic bag. See Prep. Nos. 237 a. and 237 b. and xx. vol. i. 18,32.

f Phil. Trans. 1809, p- 177.

E 4

56

LECTURE III.

Cuvier appears to have overlooked the peripheral longitudinal
lamellae : he says, “ dans certains grands squales, le maximus, par ex-
emple, ce sont des lames cylindriques, toutes concentriques, toutes
separees par des couches d’un cartilage tendre,” &c. {Legons d' Anat.
Comp. 1835, i. p. 127.) Our compilers have copied this description,
and, as usual, have applied it to the vertebrae of Fishes in general.
In the Squatina, the part of the vertebral body included by the ter-
minal cones is, indeed, composed of concentric layers, decreasing in
breadth as they approach the centre ; but, in the Cestracion, there
are no concentric layers, but only longitudinal lamell®, radiating
from the centre to the circumference, and giving off short lateral
plates as they diverge : the most common disposition of the osseous
matter in the vertebral bodies of the Plagiostomes is a combination
of longitudinal and cylindrical plates, as in the Selache.

In the Tope ( Galeus communis), as well as in most Sharks which
possess the nictitating eyelid, may be seen the highest stage of ver-
tebral ossification in the Chondropterygian Fishes : the external
surface, as well as the terminal eoncavities, of the centrum, are
covered by a smooth osseous crust, except at the openings of the
four conical cavities, which, as in Selache, correspond with the
bases of the neur- and par-apophyses. In most Sharks the principle
of vegetative repetition is manifested in the numerous centres of os-
sification in the cartilaginous neural and haemal arches : four stellate
points, for example, represent the neurapophysis in Galeus, and as
many smaller points the neural spine : in most other Squalian genera
the centrum supports two osseous pieces on each side of the spinal
eanal : one of these, by its position above the neural canal of the
centrum, claims to be regarded as the neurapophysis ; the other by
its position, usually over the intervertebral space, and by its shape
as an inverted cone, indicates an intercalary interneural piece. It is
worthy of remark that the nerve-foramen is usually not a “ trou de
conjugaison” between these cartilages, but a direct perforation of
either the neurapophysis, or of both this and the interneurapophysis,
when both roots of the spinal nerve escape separately. The ribs
(pleurapophyses) are short and simple semi-osseous styles attached to
the ends of the parapophyses, in this skeleton of the Tope, [Prep.
369.] along the twenty-six anterior vertebrae, decreasing in length
posteriorly. In the Piked Dog-fish the ribs are quite cartilaginous,
and I have counted forty pairs : in a few Sharks, as in Carcharias,
Heptanchus, and Alopias, the ribs are connected to the centrum at
the base of the parapophyses.

In the Monk-fish ( Squatina), a transitional form between Rays
and Sharks, the vertebral bodies are very numerous, and manifest ex-

VEKTEBUAL COLUMN OF FISHES.

57

ternally a thin layer of hyaline cartilage, internally a thin layer of
bone, and, between these, two alternate layers of semi-osseous and
hyaline cartilages.

In the flat Plagiostomes (Skates, Rays, Torpedos) vegetative re-
petition manifests itself still more strongly in the multiplication of
vertebras, and especially of the central elements ; which, as indicated
by their rudimentary primary ossification in Chimcera and Heptan-
chus, are commonly more numerous than the more constant neural
arches ; nor are interneural and interhaemal pieces altogether wanting
in the Rays. Muller (xxi. p. 92.) rightly states that in Raia cla-
vata these ossa intercalaria constitute the chief part of the neural
arch, at the anterior part of the vertebral column ; whilst the neura-
pophyses resume their ordinary share in its formation at the posterior
part of the column. In the Zygcena we perceive, also, interspinal
cartilages. In Rhinobatus a single spine answers to two vertebral
bodies (xxi. p. 93.), and we may well suppose this multiplication of
central pieces to have been carried still farther in the primmval fossil
Ray (^Spinachorhinus) from the Dorsetshire Lias.*

In the anchylosed cervical vertebrae of the Skate the short cen-
trums are indicated by transverse bars along the middle of the under
part. The parapophyses in most Rays pass forwards, and are then bent
backwards, the angle of one fitting, like an articular process, into the
notch of the parapophysis in advance : they do not support pleura-
pophyses ; they gradually bend down behind the pelvic arch, and
complete the haemal canal about six vertebrae beyond it ; the haemal
spines become flattened in the tail of some Rays.

In the ‘ Pisces ossei ’ of the Cuvierian system, which include
the great majority and typical members of the class, it might be ex-
pected that ossification, of the vertebral axis at least, would be a
constant condition : yet I have already had occasion to allude to a
fish, viz. Lepidosiren, in which the embryonic state of the bodies of
the vertebrm, as a continuous chondro-gelatinous chord, remains ;
although the neur- and par-apophyses, many cranial bones, and the
maxillary, mandibular, hyoidean and scapular arches, are well ossi-
fied. The fact of many fossil Ganoid fishes showing the same parts
of the skeleton petrified and undisturbed, but without a trace of the
central elements of the vertebrae, shows that the transitional condition
of the Lepidosiren’s skeleton was not uncommon in the primaeval

* Squaloraia of Riley and Stutchbury (Geol. Trans, ad ser. vol. v. p. 83. pi. 4.),
regarded as a fossil reptile by Dr. Grant (Lecture.s, Lancet, Jan. 1834, p. 576.) ;
170 vertebral bodies are included in tbe abdominal part of tbe column ; and the
part extending beyond the pelvic arch, if equal to that in most Rays, probably did
not contain less than four times the above number of abdominal vertebroB.

58

LECTURE III.

members of the class. So far as the observations of M. Agassiz have
extended, not one of the fossil fishes hitherto discovered in the Silurian
and Devonian rocks, the most ancient in which remains of that class
have been found, manifest a vertebral centrum ; and not many have
shown neural and hsemal arches and spines.*

As a rule we find that the existing bony fishes have well ossified
vertebrae, but retain a greater proportion, than in higher classes, of
the primitive gelatinous basis, which fills up the deep concavity of
each articular end of the centrum 14. c). Only in the sala-
mandroid Lepidosteus, with its lung-like air-bladder, does ossification
encroach upon these cavities, so as to render the anterior end of the
centrum convex, the posterior end concave 15.), and thus unite

Scar US.

the vertebrae together by ball and socket joints, (xxvi. p. 59.)
In the rest of the class, the vertebral bodies are connected together
by a strong elastic capsule, attached to the border of the base of each
terminal hollow cone, and enclosing the gelatinous fluid, which tensely
fills the biconcave space and renders the entire column light and
elastic.

The vertebra of a bony fish consists essentially of a bicon-
cave body, of two neurapophyses ^fig- 16. n) completing the canal

Abdominal vertebrse, Mugil. Abdominal vertebrfe, Pike (Esox).

of the spinal chord, and usually supporting a spinous process (ns) ;
of two parapophyses (p) usually projecting from the lower part of the
sides of the body, or bent down to form the canal for the aorta (/ig- 20.) :

Agassiz, Poissons Fossiles du Systeme Devonien, 4to. p. xxvi.

VERTEBRAL COLUMN OF FISHES-

59

to which are added in the abdominal region of most fishes two pleura-
pophyses {pi), or vertebral floating ribs.

Ossification commences in the bases of the two neurapophyses and
the two parapophyses, and in the terminal concave plates of the cen-
trum ; the intermediate part of the centrum is sometimes completely
ossified, when it is filled by a coarse cancellous texture. More com-
monly a communicating aperture is left between the two terminal
concavities, (as indicated by the dotted line in Jig. 16.) ; and, in many
cases, the plates by which calcification attains the periphery of the
body leave interspaces permanently occupied by cartilage, forming
cavities in the dried vertebrae, especially at their under part, or giving
a reticulate surface to the sides of the centrum. The expanded bases
of the neur- and par-apophyses usually soon become confluent with the
bony centrum : sometimes first expanding so as wholly to enclose it,
as, for example, in the Tunny, where the line of demarcation may
always be seen at the border of the articular concavity, though it be
quite obliterated at the centre, as a section through that part demon-
strates.

In the Pike the neurapophyses seldom, in the Polypterus never,
coalesce with the centrum: the letter s shows the neurapophysial suture
in Jig. 17. In the Salmonida; the parapophyses remain, for some time,
distinct from the body of the vertebra as well as from the ribs. In the
anterior vertebrae of the Carp the neurapophyses remain distinct, as
they do in the atlas of many other fishes, and a suture is observable
between the parapophyses and centrum in embryo Cyprinoids.* In each
vertebra the summits of the two neurapophyses usually become an-
chylosed together, and to their spine ; but in the Lepidosiren {Jig. 27.)
the spine retains its character as a distinct element, and is always at-
tached by ligament to the tops of the neurapophyses, as it is in the
Sturgeon {Jig. 12.). In the anterior abdominal vertebrje of the Tetro-
don, 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, as might at first sight
be supposed, enormously developed oblique processes, for they gra-
dually approximate and blend together, to form the single normal
spine at the sixth abdominal vertebra : in the Barbel the neural
arches also support two spines, but one is placed behind the other.

The interspaces of the neural arches are occupied by a fibrous
aponeurosis — the remains of the primitive essential covering of the
neui’al axis : but in most fishes the arches are additionally con-
nected together by articular or oblique processes (zygapophyses),
which are developed from the base of each neurapophysis ; sometimes

First noticed by Von Baer.

60

LECTURE III.

four, two anterior, two posterior, as in the Mullet {Mugil,jig. 16. z) ;
sometimes two, as in the Perch, the posterior in this and most other
fishes being overlapped by the anterior articulating process of the
succeeding vertebra : commonly only the anterior zygapophysis is
developed {fig. 17. z), which touches, but rarely overlaps, as in the
Polypterus, the neural arch in advance. It is peculiar to fishes to
have articular processes developed from the parapophyses ; we have
noticed these already in the abdominal region in the Ray; in the
osseous fishes, when present, they are confined to the caudal vertebra
{fig.\%. z')\ they are particularly developed, sometimes branched.

forming a network about the hajmal canal in certain species of Tunny
( Thynnus, xxin. i. p. 265.). In Loricaria peculiar accessary pro-
cesses are sent out from the neural arch of the seven anterior ver-
tebrae which abut against the osseous lateral shields of the dermal
skeleton.

The parapophyses are very short in some fishes {Salmo, Cluped) :
they are longest and most expanded in the abdominal region of the
Cod tribe {fig. 19. p), where they support the air-bladder, which in-
timately adheres to their under surface, and, in one species of Gadus,
sends processes into expanded cavities of the parapophyses, thus fore-
showing the pneumatic bones of birds. They gradually bend down
near the tail, where they form, as in all fishes, the haemal canal.

The pleurapophyses of fishes correspond to what are usually 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. 23.), their distal ends are not connected with any bones
analogous to sternal ribs or sternum ; i. e. the abdomen is unclosed
below by the crura and spines completing the haemal arch. The
true homologues of sternal ribs or abdominal haemapophyses re-
tain the primitive aponeurotic tissue, and may be well seen in the
Bream, extending from the ends of the vertebral ribs. These elements.

VERTEBKAL COLUMN OF FISHES.

G1

or pleurapophyses 19. pi, pi) are usually appended to the

extremities of the parapophyses, the articulation frequently pres(int-
ing a reciprocal notch in each. But, in some bony fishes, as Platax,
the ribs articulate with the bodies of the vertebrae, in depressions
behind the parapophyses ; and in Polypterus beneath the para-

62

LECTURE III.

pophyses, as in the cai'tilaginous 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
to form the haemal canal and spine in the tail ; and we derive the
same striking evidence of the true nature of these inferior arches
from the skeleton of the Tunny, the Dory, and some other fishes. 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 {fig. 19. 58) which project from the inner
side of the scapulae, and which have been described as coracoids
(Cuvier) and sometimes as displaced iliac bones (Cams). By the mus-
cles attached to these styliform bones the succeeding ribs are drawn
forwards and the abdomen expanded in the Cyprinoids. Pleura-
pophyses are entirely absent in the Sun-fish, Globe-fish {Diodon),
the Tetrodon, the Pipe-fish {Fistularia and Syngnathus), the Lump-
fish and the Angler. This of all osseous, or rather semi-osseous,
fishes presents the simplest vertebral column : the abdominal ver-
tebrae are not only devoid of ribs, but have the feeblest rudiments
of parapophyses. The bodies of these vertebrae 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 repre-
sents the lower transverse process in other fishes : it is obsolete in
the anterior abdominal vertebr* ; begins to appear about the middle
ones ; shows its true character in the tenth ; and elongates, bending
downwards, backwards, and inwards, to coalesce with its fellow, and
form the h^mal arch at the twelfth or thirteenth vertebra, from
which the haemal spine is developed. The interlocking process of
the anterior vertebra disappears 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 vertebrae of the Tetrodon are more firmly clamped
together by the parapophyses than in the Angler.

A vegetative sameness of form prevails in Fishes throughout the
vertebral column of the trunk, which is made up of only two kinds
of vertebrae, characterised by the direction of the parapophyses :

* The gelatino-cartllaginous basis is progressively but continuously ossified
around these foramina, which form part of a vast series of exceptions to the so-
called “ loi de conjugaison” of M. Serres; who, by this phrase, expresses his notion
that every foramen is formed, like those that give passage to the spinal nerves in
Mammalia, by the approximation of two notches of two distinct bones or bony
elements.

VERTEBRAL COLUMN OF FISHES.

G3

Q

Endo- and exo-ske-
letal elements of a
caudal vertebra of
a Plaice (Pleuro-
ncctes).*

these in the abdominal region are lateral, usually
stand out and support ribs ; but in the caudal region
they bend down and coalesce at their extremities.
The caudal vertebrfe of some flat-fishes (^Pleuronectida,
Jig. 20.), the Polypterus and the Murasnm, would seem
to disprove this homology of the haemal arches, since
transverse processes from the sides of the body co-
exist with them, as they do in the Cetacea. But, if
we trace the vertebral modifications throughout the
entire column in any of these fishes, we shall find
that the h^mal arches are actually parts of the trans-
verse processes ; not independent elements, as in the
Cetacea ; but due to a progressive bifurcation : this,
in Murcena Helena, for example, begins at the end
of the transverse processes of about the twenty-fifth
vertebra, the forks diverging as the fissure deepens,
until, at about the seventy-third, the lower fork de-
scends at a right angle to the upper one (which re-
mains to represent the transverse process), and, meeting
its fellow, forms the htemal arch, and supports the
antero-posteriorly expanded haemal spine. In the Plaice
a small process is given off from the expanded base
of the descending parapophysis of the first caudal ver-
tebra, which increases in length in the second, rises
upon the side of the body in the third, becomes dis-
tinct from the parapophysis in the fourth, and gra-
dually diminishes to the ninth or tenth caudal vertebra,
when it disappears. These false transverse processes
never support ribs.

The atlas may usually be distinguished by some
slight modification of the anterior articular end of the
body, by the persistent suture of the neural arch, or
by the absence or detachment of its pleurapophyses :
but none of these characters are constant. Peculiar
processes are sometimes sent off from the under part
of the centrum : two very long and strong processes
from this part are articulated with the basi-occipital
in the great Sudis (^Arapaima gigas). The second
vertebra is never characterised by an odontoid pro-
cess ; but the absence of this is not to be accounted

Compare this figure with nature, and with the figures of a corresponding ver-
tebra in II. pi. 5., and in xxviii. p. 58. The names assigned by Geoffroy St. Hilaire

64

LECTURE III.

for by the characteristically well-developed body of the atlas in
fishes, since the atlas has a small centrum in crocodiles and birds,
where the odontoid process likewise exists.

The number of vertebra3 varies greatly in the different osseous
fishes : the Plectognathi {^Diodon, Tetrodon,) have the fewest and
largest : the apodal fishes (Eels, Gymnotes,) have the most and
smallest, in proportion to their size. It is not often easy to deter-
mine the precise number, on account of the coalescence of some of
the vertebrm, or at least of their central elements, in particular parts
of the column. Instances of anchylosis of some of the anterior ver-
tebra, analogous to that noticed in the cartilaginous Sturgeons,
Chimserm, Rhinobates, and some Sharks, occur also amongst the
osseous fishes, as in many Siluroid and Cyprinoid species ; in the
Loricaria and Fistularia : here is an example {Jig- 21.) of the four
singularly elongated anchylosed anterior abdominal ver-
tebra, in the Tobacco-pipe fish {Fistularia tabaccaria).
A coalescence of several vertebne is more constant at the
opposite end of the column in osseous fishes, in order to
form the base of the caudal fin. The bodies at least of the
vertebras situated here, at the part most remote from the
centre of life, do not emerge separately from the primitive
embryonic condition of the gelatinous ‘chorda,’ but are
continuously ossified to form a common, compressed, ver-
tically extended, and often bifurcated bony plate {fig- 18.
n'h'), from which the neural and haemal arches and their
spines radiate : from these elements alone can the number
of vertebrae of the caudal fin be estimated ; normal de-
velopment 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 vertebrae 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 ter-
minates the suddenly truncated body of this oddly shaped
fish. Our common Pike afibrds a simple and intelligible
view of this modified base of the tail-fin : in the Eels, the Polypterus,
the Lepidosiren, the Trichiurus, and Pipe-fishes, the vertebras always
remain distinct to the end ofHhe tail.

Cuvier, in the tables of the number of vertebrae in various species

to tlie several parts of this combined segment of endo- and exo-skeleton are oppo-
site the left hand of the reader; those applied to them in the present work are
placed opposite the right hand.

Anchylosed
anterior verte-
bra;, Pipe-fish
( Fistularia) .

VERTEBRAL COLUMN OP FISHES.

65

22

of fishes contained in the “ Legons d’ Anatomic Comparee,” * counts
the anchylosed vertebrie of the caudal fin as one, and so assigns seven-
teen vertebrie to the Sun-fish. I find but sixteen according
to the vertebral centres, eight abdominal, and eight caudal :
but if we count the neural spines, we have then twelve
caudal vertebrje ; the spines of the last five being driven, as
it were, by the extreme contraction of their anchylosed
bodies, to rest their bases upon the back part of the seventh
or last upright neural spine. In the Conger there are 162
vertebrae, in the Ophidium 204, and in the Gymnotus 236
vertebrae ; but even this number is surpassed by some of the
plagiostomous fishes. Nor are the extremities of the ver-
tebral column the only regions where anchylosis of the ver-
tebrae takes place. Hunter had preserved this specimen of
confluence of the first two vertebrae of the post-abdominal
or caudal region in a large flat-fish (probably Rhombus,
Jig. 22.), forming a true sacrum. In the Halibut {Ilippo-
glossus) the parapophyses of the corresponding vertebras,
with those of the last abdominal, are similarly united,
though the bodies remain distinct. In Loricaria both the
upper and lov/er arches of a considerable 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.

Although the vertebrae 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 the Spinachorhinus they are extremely
short ; in the Fistularia extremely long ; in the Tetrodon
they are much compressed ; in the Platycephalus they are

Anchylosed moi'c depressed ; in the tail of the Tunny the entire ver-
caudai ver- tcbra is cubical, with the ends hollowed as usual, but the
sacrum,’ of a foui' other sidcs flat, the upper and lower ones being formed,
in the connected series, by the neural and hsemal arcues ot
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 haemal
canals of their own, but of the succeeding, centrum.

The principle of vegetative repetition is manifested, in osseous
* Ed. 1836, tom. i. p. 229.

VOL. II. P

66

LECTURE III,

fishes, by the numerous centres of ossification, from which shoot out
bony rays affording additional strength to many of the intermuscular
aponeuroses : some of these supernumerary or intercalary ossicles
belong to the endo-skeleton, but most of them to the exo-skeleton.
In the former system of bones may be ranked those spines which are
attached to, or near to, the heads of the ribs, and extend upwards, out-
wards, and backwards, between the dorsal and lateral masses of muscles :
these are the ‘ diverging appendages ’ of the abdominal ribs
{fig. 17. ip, fig. 23. pi a), and may be termed ‘ epipleural spines ; ’
though they sometimes pass gradually, as the vertebrm approach
the tail, from the rib upon the parapophysis,
and even in the posterior abdominal vertebrae
(e. g. Holocentruni), upon the bodies and neural
arches. They are the “ obere rippe ” of
Meckel, and at the fore-part of the abdomen,
in Polypterus, the epipleural spines are stronger
than the ribs themselves. The spinous appen-
dages are remarkably developed in the Halecoid
fishes, (Salmon and Herring,) in the Mackerel-
tribe, and the Dolphin {Coryphcena). In our
common herring you will find them attached
not only to the ribs {fig. 23. pi, a), but also di-
verging from the parapophyses {pa), and the
neurapophyses {no), and the vertebra is further
complicated by dermal bones, those on the under surface of the
abdomen {dti) being connected, like the scutes of serpents, with the
lower ends of the ribs {'pl).

The very distinct histological condition of the endo- and exo-
skeleton of the Sturgeon {fig. 43.), shows clearly the nature of
those spines {fig- 19. dn, dn), which form, in osseous fishes, a second
row, of greater or less extent, above the true neural spines, and sup-
port the dorsal fins. Thus, in Accipenser Ratzburgii, twelve of the
hard enamelled calcareous plates (ganoid scales) along the mid-line of
the back, send upwards and backwards a moderately long spine : the
series is then continued in a cartilaginous state to support the dorsal fin.

In the Polypterus sixteen accessary bones, in the form of longer
and sharper spines, are extended over thrice as many vertebrm :
and each dermal spine supports a membrane, strengthened at its upper
part by four or five branched and jointed rays. From the base of
the dermal spines, other spines {fig. 19. in, in) usually shoot down-
wards, into the intervals of the neural spines : these inverted spines
may be the homologues of the wedge-shaped interneural pieees before
noticed in the vertebrm of Sharks, and may well retain that name in
the osseous fishes. Sometimes they are double, as in the Flat-fish

Abdominal vertebra,
Herring {Clwpea).

VERTEBRAL COLUMN OP FISHES.

67

(Plaice, Sole, he., fig. 20.), and in some parts of the vertebral column
of the Deep-fish, as the Dory, the Chsetodon, the Sun-fish, &c. But
whatever modifications these dermal and intercalary spines present
above, the same are usually repeated below, in connection with the
haemal arches and spines, for the support of the anal fin : and just as
in the framework of the dorsal fin we find interneural spines and der-
moneural spines, so in that of the anal fin we recognise interhaemal
spines {fig. 19. ih), and dermoha;mal spines (ib. dh), with the, some-
times, expanded base from which they diverge. Both interneural
and interlnemal spines are, in the osseous fishes, commonly shaped like
little daggers, plunged in the flesh up to the hilt, which is represented
by the part to which the true fin-ray (dermoneural or dermohaemal
spine) is attached. These parts of the dermal skeleton, developed in
the primitive continuous fold of skin which forms the groundwork of
the vertical fins in the embryo fish, manifest the vegetative character,
which is the usual concomitant of iieripheral position, by the partial
spontaneous fission which each ray has undergone in the progress of
its development ; this is shown by the longitudinal raphe or suture
along which each dermal spine or ray may commonly be divided
into two lateral moieties. The framework of the caudal fin is
composed of the same intercalary and dermal spines, sujieradded
to the proper neural and Inemal spines, of those caudal vertebral
which have coalesced and been shortened by absorption, in the pro-
gress of embryonic development, to form the base of the terminal fin
(fig. 18, 19. c, dn, dh).

In the Sharks and Sturgeons this fin is not symmetrical as in most
osseous fishes, but is formed chiefly by the haimal spines and their
intercalary and dermal spinous appendages ; the progressively de-
creasing bodies of the caudal vertebrte are continued along the upper
border or lobe of the fin, sending off short neural spinous pro-
cesses to increase the height of that border.

M. Agassiz calls those fishes in which, from the peculiar development
of the lower lobe of the caudal fin, the vertebral seem to be prolonged
into the upper lobe, “ heterocercal ; ” and those with the lobes of the
caudal fin equal or symmetrical, he calls “ homocercal.” The pre-
ponderance of heterocercal fishes in the seas of the ancient geological
epochs of our planet is very remarkable : the prolongation of the
superior lobe characterises every fossil fish of the strata anterior to,
and including, the Magnesian limestone. The homocercal fishes
first appear above that formation, and gradually predominate, until,
as in the present period, the heterocercal bony fishes are almost li-
mited to a single ganoid genus, e. g. Lepidosteus.

The shape, size, and number of the median azygous dorsal and

p 2

68

LECTURE III.

anal fins, depend on the development and grouping of the accessary
and intercalary spines : the true vertebral, neural, and haemal spines
give scarcely more indication of the nature or existence of those fins,
than the neural spines in the Porpoise or Fin-whales do of their not
less essentially though more histologically dermal dorsal fin ; but the
development of the dermo-skeleton, in the fish’s fin, and its inter-
calation with the spines of the endo-skeleton, and consequently its
retention in our prepared skeletons, lead me to notice it in connection
with the vertebral column, as I shall subsequently, for similar reasons,
have to describe parts of the dermo-skeleton which are intercalated
with, or appended to, the vertebras and bony arches of the head.

In the Dermopteri (Lampreys, Lancelet), the dorsal, anal and
caudal fins are simply cutaneous folds, with scarcely distinguishable soft
fibres for rays, and they are continuous, as in the embryos of higher
fish. In the Gymnotus, a very long but shallow anal is continued
into the caudal fin ; but, as the name of this fish implies*, there is
no dorsal fin. In many, both cartilaginous and osseous fishes, a single
group of dermal spines supports a single dorsal fin, as in the Sturgeon,
the Grey Shark {Heptanchus), and the Shad : in others, as the Dog-
fish ( Spinax), and the Mullet, there are two groups of dermo-neural
spines and two dorsal fins ; in the Cod and its congeners there are
three dorsals (Jig. 19. u) ; in the Polypterus there are, as its name
implies, numerous (as many as sixteen) dorsal fins ; and many ac-
cessary vertical finlets, both dorsal and anal, may be seen in the
Caranx, or Mailed Mackerel.

Cuvier called those bony fishes “ Malacopterygian,” whose verti-
cal fins were supported by soft, jointed, and branched dermal spines,
and he called those “ Acanthopterygian,” which had the fin-rays or
some of the anterior ones in the form of simple, unjointed, and un-
branched bony spines : but we have seen that these variable parts of
the dermo-skeleton form unsafe and artificial grounds for the larger
groups of the class.

Very rarely do the interneural and dermal spines coincide in
number with the neural spines : they are often more numerous, as in
Acanthurus and Pleuronectes ; more frequently less numerous, as in
the Lepidosteus or Trachinus. The Lophius has only three long de-
tached dermal rays, projecting from above the abdominal region of
the spine, and two or three above the cranial vertebrae ; the base of
these dermal spines expands, bifurcates, and the extremities curve
inwards, to be inserted into lateral depressions, or a transverse per-
foration, of the summit of the interneural spine, represented in
Lophius by a small semi-osseous disc. Those dermal spines that
sustain the caudal fin offer the lowest condition, as might be expected

* Gr. yvp.vos, naked j votos, back.

VERTEBRAX COLTOIN OF FISnES.

69

from tlieir terminal position ; they are almost always bifurcated, or
dichotomously subdivided, as the effect of the continued spontaneous
fission of their embryonic elements, or of the activity of the vege-
tative force of irrelative repetition. This part is accordingly subject
to monstrosity by excess, as is manifested by the double and tri2>le
tails of Gold-fish in confinement, where nutriment is not expended
by the due action of muscular force. The singular sucking-apparatus
upon the head of the Remora is an assemblage of peculiarly modified
and connected dermal spines. The more common modification is the
excessive development of one or more of the dermal spines, to form
peculiar weapons of defence.

The Chimeeraj, the Cestracions, and the Piked Dog-fish, show
such a stout bony spine, sometimes, as in the last-named shaidc,
sheathed with horn, at the front border of each dorsal fin, which it
also serves to strengthen. The Fire-flares ( Trygon) and Eagle Rays
(^Myliobates) have one or more strong, detached, barbed or serrated
spines, on the upper part of the tail. Agassiz has pointed out the close
resemblance of the microscopic structure of the bone of these spines
and the dentine of the teeth of the same kind of fishes : they are both
hardened by an outer layer of modified dentine, but as hard as
enamel. Many large fossil spines, called in Palaeontology “ Ich-
thyodorulites,” have been determined by their form and structure ta
have belonged to extinct cartilaginous fishes, allied to the above-cited
existing genera, of which they are sometimes the sole indications
left by the wreck of former worlds. Amongst bony fishes, the
Siluroids (Sheat-fish) and Balistes (File-fish) are most remarkable for
these dermal weapons. In our rare Balistes capriscus the anterior
dorsal is sustained by three such spines ; the first much the strongest,
and the second subservient to the use of the first as a weapon,
rather than for the support of the fin. The first spine is articulated
by a very remarkable joint to the broad interneural osseous plate :
its base is expanded and perforated, and a bony bolt passes freely
through the ring. When this spine is raised, a depression at the
back part of its base receives a corresponding projection from the
contiguous base of the second ray, which fixes it like the hammer of
the gun-lock at full-cock, and it cannot be forced down till the small
spine has been depressed, as by pulling the trigger : it is then re-
ceived into a groove on the supporting plate, and offers no impedi-
ment to the progress of the fish through the water. The name of the
genus {Balistes) and the common Italian name of the species in
question {Pesce balestra) refer to this structure : the spine of the
Balistes is also roughened with ganoid or enamel grains like a file,
whence our English name for it, ‘ File-fish.’ The margins of the ana-

p 3

70

LECTURE IV.

logous but stronger weapon of the Siluroids is usually beset with den-
ticles of the same hard substance, sometimes anchylosed to the spine,
sometimes movably articulated with it. M. Agassiz has found that the
fixed denticles have the same osseous texture, characterised by ra-
diated corpuscles in concentric layers, as the spine itself ; whilst the
movable denticles present a simpler structure, being permeated by
calcigerous tubes, radiating from a central vascular pulp cavity, like
teeth ; but the comparative anatomist who has extended his obser-
vations beyond the class of Fishes, will pause before he admits the
sweeping conclusion which the celebrated ichthyologist draws from
his interesting microscopical observations.*

The distinction between the internal or splanchnic and external
skeletons does not rest upon the microscopic character of their tissues ;
if it did, and if every calcified plate or spine that presented the cha-
racteristic radiated cells of bone, were to be classed with the pieces of
the internal skeleton, we must cease to regard the scales of the Cro-
codile, and the tesselated carapace of the Armadillo, as parts of the
external or dermal skeleton.

LECTUEE IV.

THE SKULL OE FISHES.

Passing from the trunk to the head, we find in the Lancelot {Bran-
chiostoma, xxx.), at the lowest step of the Vertebrate series, that the
cranium is not indicated by difference of size or structure of the ru-
dimental vertebral column, but consists of that gradually contracting
anterior termination of the neural canal, which retains its primitive
fibro-membranous wall, {Jig. 46. n), without any superaddition of
parts, and is suj)ported by the tapering end of the gelatinous ‘ chorda
dorsalis (ib. c/«). This part, in the Lancelot, even extends farther
forwards than the cranial end of the neural canal, indicating the non-
development 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 oblon-
gata 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 tei’minates, somewhat
obHisely, beneath what Dr. Kolliker (xxxii. p. 32.) has described as a
ciliated olfactory capsule (ib. ol). The cranium of the Lancelet,

Les genres Hypostoma et Callichthys presentent cette singuliere structure, et
prouycnt par la meine que les differences qu’on a voulu etablir, entre un squelette
paucitr ou ext^ne, et un squelette interieur ou intestinal, sont denuees de tout
toimeinent. — Poissons Fossiles, tom. iii. p. 213.

THE SKULL OF FISHES.

71

therefore, may be said to be composed of the primitive continuous
fibro-gelatinous basis of the vertebral bodies, and of the membrane
which is represented by our ‘ dura mater,’ without the superaddition
of cartilaginous or osseous coverings.

But if we were to limit our view of the skull of the Branchiostoma
by this primitive embryonic condition of the cranium proper, we
should have an incomplete idea of it. A large, jointed, cartilaginous
hasmal arch {fig. 46.4) extends on each side, from below the cranial end
of the chorda dorsalis, downwards and backwards to the orifice of the
pharynx ; this represents the labial arch of higher Myxinoids, and it
supports the jointed slender oral filaments, which may be regarded
as a continued representation, in the Vertebrate series, of the cephalic
tentacula of the Cephalopods. It is the sole chondrified part of the
skeleton in the Branchiostoma, a fact which must be borne in mind
if we would avoid the common error of supposing the neural ver-
tebral column to be the first and only rudiment of an internal
skeleton in the lower Vertebrata.

Before proceeding to the next stage at which cranial development
is arrested in the ascending series of Vertebrata, I may briefly de-
scribe the form under which the cartilaginous tissue is superinduced
upon the fibrous brain-sac in osseous fishes, according to the obser-
vation of M. Vogt on the embryo of one of the Salmonidae {Core-
gonus, XXII. tom. i. p. 3.). The chorda dorsalis advances as far as
the pituitary sac, or ‘ hypophysis cerebri,’ where it terminates in
a point ; cartilage is developed on each side of the chorda, forming a
thick occipito-sphenoidal mass*, which extends outwards, and en-
velopes the sac of the internal ear, forming the ear-ball or acoustic cap-
sule. The cartilage rises a little way upon the lateral walls of the cra-
nium, and is there insensibly lost in the primitive cranial membrane.
At the end of the chorda, the basal cartilages diverge, surround the
pituitary vesicle, and meet, in front of it, to join or be expanded in
the presphenoid plate | : these arches I term “ sphenoidal" \ {fig. 24.)

25

Base of sXulI, Ammocctc, Muller.

Side view of skull, Ammocctc, Muller.

* Plaque nuchale, Vogt ; Kmcherne basis cranii, Muller, xxi.
■f Plaque facials, y ogi. •, Gaumenplatte, '^I'uWev.
f Arises laterales, Vogt ; Fliigel-forsatze basis cranii, Miiller.

F 4

72

LECTURE IV.

The Sand-lance {^Ammoccetes) presents a condition of the skull
which corresponds with this first appearance of the cartilages in the
embryo of higher fishes (yfig. 24.). The occipital cartilages extend from
the sides of the pointed end of the chorda (ib. ch\ and expand into
the acoustic capsules {ih. 16) : the sphenoidal arches {ih. s), encompass
the pituitary or hypophysial space ( hy\ now closed by a membrano-
cartilaginous plate, and unite anteriorly to form a small vomerine plate
(ih. 13), in front of which is the single undivided nasal capsule (ib. 19).
The now expanded cerebral end of the neural canal (fig. 25. n) is
still defended by fibrous membrane only : but is divided from the
vomerine plate (ih- 13), by a backward extension of the nasal sac
(ih. 19) to the pituitary vesicle.

In the Myxine the acoustic capsules are approximated at the base
of the skull, near the end of the chorda : 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 ten-
tacles, answering to those in the Lancelot. 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
forward to the vomerine or palatine plate, which supports the nasal
capsule ; another process extends backwards to the occipital cartilage.
Other processes are also sent off from the sides, which form a complex
system of peculiarly Myxinoid cartilages.*

In the Lamprey (Petromyzon, fig. 26.) the occipital cartilage is
continued backwards, in the form of two slender processes (c), upon
the under part of the chorda dorsalis (c/i) into the cervical
region. The hypophysial space (%) in front of the oc-
cipital cartilage remains permanently open, but has been
converted into the posterior aperture of the naso-palatine
canal. f The sphenoidal arches (5) are very short, ap-
proximated towards the middle line ; and the presphenoid
and vomerine cartilage (13) is brought back closer to
the sphenoidal arches. Two cartilaginous arches (24)
circumscribe elliptical spaces outside the presphenoid
plate : these appear to represent the pterygoid arches ;
but, as in the embryo of higher fishes, are not se-
parated from the base of the skull by distinct joints. The basal
cartilages, after forming the ear-capsules (le) extend upwards upon
the sides of the cranium (fig. 11.), arch over its back part, and leave

Base of skull,
Lamprey
(Muller).

* See Muller s masterly Memoir, “ Ueber die Myxinoiden,*’ Abbandlunff. der
Berlin. Akad. 1835, p. 105. tab. iii.

t Agassiz (xxn.) describes this aperture as “un tres petit espece presque eircu-
laire (e) dans laquelle est logee I’hypophyse du cerveau,” The figure to which his
letter (e) refers is copied, like mine, from Muller.

THE SKULL OP FISHES.

73

only its upper and middle part membranous, as in tlie human embryo
when ossification of the cranium commences. Two broad cartilages
{ib. 20, 21) may represent, upon the roof of the infundibular suctorial
mouth, the palatine and maxillary bones, and anterior to these there
is a labial cartilage {ib. 22) : there are likewise cartilaginous processes
ib. r, s) for the support of the large dentigerous tongue, and the
attachment of its muscles ; besides the cartilaginous basket, before de-
scribed, which supports the modified and perforated homologue of the
large respiratory pharynx in the Branchiostoma {fig. 46.).

As regards the development of the skull, properly so called, the
ordinary course is pursued with very little deviation in the Der-
mopterous fishes ; but is arrested at more or less early embryonic
stages : yet at each of these, even the earliest, development 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 pro-
per 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.

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
very different type, apparently a simpler one, if compared with the
Myxine or Lamprey, but one which in consequence of the progress
of development in the direct vertebrate route, more nearly approxi-
mates to the type of cranial organisation in the lower forms of Eep-
tilia. The Monk-fish ( Squatina, — an intermediate 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 chorda
dorsalis and its capsule are converted into firm granular cartilage ;
and this cartilage extends from the prominent median basal ridge,
indicative of the primitive place of the chorda, on each side and for-
wards so as to constitute an oblong flattened plate forming the whole
basis cranii. The posterior margin of this ‘ occipito-sphenoidal ’
plate supports two convex condyles, as in most of the Rays, for arti-
culation with the body and parapophyses of the axis.* The lateral
margins of the basal cartilage have two notches, the intervening pro-
minence representing the primitive sphenoidal arch, here filled up
and sending off’ a rudimental pterygoid process outwai’ds. Just an-

* The body of the atlas has coalesced with the basi-occipital, as is indicated by
its slender but separate neural arch. The condyloid foramen is just above the outer
end of the condyle.

74

LECTUKE IV.

terior 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, and the cartilage then suddenly contracts, and is con-
tinued forwards to form the vomerine anterior base of the cranial
cavity. The fibro-membranous parietes of this cavity are every
where covered with, or converted into, the same firm granular carti-
lage as the base, save at the anterior and upper end, where a large
fontanelle, closed by the primitive membrane, remains : the cartila-
ginous walls are perforated by the exit of the cerebral nerves, and the
spinal chord.

The cranial cavity is not moulded upon the brain, but is of larger
size ; it communicates merely by the nervous and vascular foramina
with the acoustic labyrinth, which is buried in the thick lateral cranial
cartilage. This insulation of the ear- capsules from the brain-case is a
high grade of development common to all the typical Plagiostomes : in
the Chimserae the separation is only partial. The lai’ge pituitary de-
pression, or ‘ sella,’ marked by a ridge across the floor of the cavity,
indicates the compartment between the orbits for the mesencephalon,
and in front of this is the wide prosencephalic, or cerebral, compart-
ment, which communicates by the two large foramina with the nasal
cavities, and, in the dry skull, opens forwards by the wide persistent
fontanelle. In the vertical lateral cartilaginous walls of the cranium
we recognise the part representing the great ala of the sphenoid by
the two perforations answering to the foramina oralia and rotunda for
the exit of branches of the fifth pair of nerves. The orbital alse of
the sphenoid are indicated by the foramina optica ; the part cor-
responding to the bones in osseous fishes, called by Cuvier “ frontaux
anterieures,” by the olfactory foramina, and by their articulation with
the palatine process of the maxillary arch. Two broad and thin car-
tilaginous plates, from the upper and anterior walls of the cranium,
support anteriorly the nasal sacs, and thence extend backwards and
outwards over the sides of the anterior half of the cranium forming
the roof of the orbits. Two longitudinal and vertical ridges, which
rise from the posterior and lateral cranial parietes, extend outwards
at both extremities in the form of strong triedral conical transverse
processes. The anterior one forms the post-orbital process ; the pos-
terior answers to the mastoid ; between these is a long cavity lodging
the temporal muscle, and beneath this the parallel articular cavity
for the tympanic pedicle. The extreme point of the mastoid is per-
forated by a mucous canal extending to the upper surface of the
back part of the skull. The post-orbital processes touch, and some-

THE SKULL OF FISHES.

75

times blend with, the supra-orbital plates, and circumscribe vacuities
at the sides of the parietal region of the cranium. But the exterior
of the skull is variously and singularly modified in the different
Plagiostomous genera, development proceeding from the advanced
cartilaginous stage just described, to establish peculiar plagios-
tomous 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, articulated to
the side of the skull beneath the posterior angular (mastoid) pro-
cess, has the hyoidean, and partly the mandibular *, arches attached
to its lower end, the former by a close joint, the latter by two liga-
ments. The maxillary arch, in Squatina, is suspended by a ligament
from its ascending or palatal process, to the notch between the
vomerine and the anterior supra-cranial cartilaginous plate. From
this point the jaw is continued in one direction forwards and inwards,
completing the arch by meeting its fellow, to which it has a close
ligamentous junction ; and in the opposite direction, backwards and
outwards, as a coalesced diverging appendage to the outer side of the
tympanic pedicle, where it forms the more immediate articulation for
the lower jaw, or mandibular arch, like the hypo-tympanic continu-
ation of the upper maxillary bone in the Batrachia. Each lateral half
or ramus consists of a single cartilage, the two being united togetlier
at the symphysis by ligament.

Two slender labial cartilages are developed on each side the maxil-
lary, and one on each side the mandibular arch ; which complete the
sides of the mouth. These cartilages Cuvier regarded as rudiments,
respectively, of the intermaxillary, maxillary, and dentary bones ;
the dentigerous maxillary arch being his palatine bones, and the
mandibular ai'cli the articular piece of the lower jaw ; but both
palatines and articulars co-exist with labial caiTilages, like those of
the Squatina, in a Brazilian Torpedo {Narcine), and at the same time
with distinct pterygoid cartilages, (xxi. 1835, pi. v. Jig. 3. & 4.)

Four or five short cartilaginous rays, in Squatina, diverge from
the posterior margin of the tympanic pedicle, and support a mem-
brane answering to the opercular flap in Osseous fishes ; in their
ultimate homology these rays are the skeleton of the diverging ap-
pendage or limb of the tympano-mandibular arch.

* Throughout these Lectures 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.”

t It may be questioned whether the detached plate, called palatine by Dr. Henlc,
be not rather the ento-pterygoid.

76

LECTURE IV.

Tlie hyoid arch in the Squatina, as in most other Plagiostomes, con-
sists of two long and strong lateral pieces or cerato-hyoids {cornua
of Anthropotomy), and a median flattened symmetrical piece, the basi-
hyoid, {corpus ossis hyoidei) below. Short cartilaginous rays extend
outwards from the back part of the cornua, supporting the outer mem-
branous wall of the branchial sac : these answer to the branchiostegal
rays in osseous fishes, and support the diverging appendage or limb
of the hyoidean arch. But the fold of integument in which they
project is not liberated, and is continuous with that supported by the
opercular rays from the tympanic pedicle. Five branchial arches
succeed the hyoidean ; but are suspended, as in the Lamprey, from
the sides of the anterior vertebrae of the trunk.

The Cestracion, so interesting from its early introduction into the
seas of this planet, is not so far advanced in cranial development as is
the more modern Squatina. In the existing species of the Australian
seas {Cestracion Phillipi, v. pi. 10.), the cartilaginous basi-occipital
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 anterior end of the chorda, along
the middle of the posterior half of the basi-cranial cartilage, continues
membranous, and the pituitary 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 forwards, 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 forwards and outwards to support the
nasal sacs, and are continued backwards, interrupted by a notch filled
by membrane, to the posterior angular processes, which overhang the
joint of the maxiUo-hyoidean pedicle. The maxillary and mandibular
arches are as simple as in the 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 membranous for
a greater or less extent, except in Narcine, where it is closed by

* The basi-occipital also affords a small but distinct intermediate surface between
the two large condyles in the Zygmna.

THE SKULL OF FISHES.

77

cartilage. The anterior or vomerine part forms a long pyramidal
rostrum, to which are articulated cartilages connecting its extremities
with the radial or anterior angles of the enormously developed hand
(pectoral fin) : 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 transversely across the under part of the head.

In the ordinary Sharks the anterior 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 condyles, pro-
cesses extend backwards from each side of the occipital foramen and
clasp, as it were, the bodies of three or four anterior vertebrjE of the
trunk. The pterygoidean arches extend outwards, 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 the vomerine part of the base of
the skull, is thence extended backwards to the articulation of the
lower jaw. A simple cartilaginous pedicle forms the upper part
(pleurapophysis) of the mandibular arch, which is completed below
by the lower jaw. A few cartilaginous rays diverge outwards and
backwards from the pedicle, and support a small opercular flaj) or
fin. The hyoid arch consists of a basi-hyoid and two simple cerato-
hyoid cartilages ; the stylo-hyoid is ligamentous, as in the Squatina.
Short cartilaginous rays diverge from the cerato-hyoid 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 : from this arch, also, cartilaginous rays
immediately diverge for the support of a radiated appendage or fin ;
the third in the series counting backwards from 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 the olfactory sacs are over-arched by the nasal processes of the
epicranial cartilage.

Amongst the stranger forms in which special development radiates,
in diverging from that stage of the common vertebrate route attained
by the Plagiostomes, may be noticed the lateral transverse elongations
of the orbital processes, supporting the eye-balls at their extremity.

78

LECTURE IV.

and giving the peculiar form to the skull of certain Sharks, thence
called “ Hammer-headed ” {Zygcena). In the Eagle-ray {Myliobates)
a cartilage is attached to the anterior prolonged angle of the great
pectoral fin, and connects it with the fore-part of the cranial (inter-
nasal) cartilage ; it supports a number of branched and j ointed car-
tilaginous rays, which project forwards, 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 Muller has termed
“cranial fins;” but the parts more properly meriting that name are
the opercular and branchiostegal appendages of the tympanic and
hyoidean arches.

Having traced in the examples of cartilaginous fishes selected for
demonstration, the progressive steps by which the typical features of
the ichthyic skull are modelled, as by the hand of the sculptor, in the
yielding gristle, we have next to consider them with their leading
varieties, as they are permanently wrought out in hard bone.

We saw that the base of the skull was first formed by the anterior
prolongation of the gelatinous chorda dorsalis, and that the cranial
cavity resulted from the extension of the membrane from the fibrous
sheath of the gelatinous chorda over the anterior end of the nervous
axis. We saw next the superaddition of special capsules for the
organs of sense ; and then the cartilaginous tissue developed from
the basis cranii, according to a pattern common to the lowest forms
of the class, and to the embryos of the higher forms which the Cy-
clostomes permanently represent. We saw the cartilaginous tissue
acquiring a firmer texture, hardened 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 re-
cognised the maxillary, mandibular, and hyoidean arches, established
in a firm cartilaginous material, and on a recognisable ichthyic type.

We have next 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 in osseous fishes ; and the remark-
able transitional genus Lepidosiren, whose organisation I first made
known under the name of Protopterus (xxxm.), offers the most
natural and instructive passage in the shape and structure of its
skull, between the gristly and the bony fishes.

In the Lepidosiren ossification of the cranial end of the chorda
dorsalis extends along the under and lateral part of its sheath, back-
wards to beneath the atlas and axis 27. i), the posterior slightly

THE SKULL OF FISHES.

79

expanded end of this ossified part supporting, as in the Squatina, the
neurapophyses of the atlas {fig. 28. n\ the bases of which expand
and meet above that end of the ossified chorda and below the spinal

canal. Ossification of the fibrous sheath of the chorda, commencing
posteriorly at its under part (ib. h\ ascends upon the sides as it
advances forwards, and incloses it above, where it supports the me-
dulla oblongata, and the lateral bony plates (neurapophyses) called
28 ex-occipitals {ib. 2) ; leaving behind a wide oblique

S concavity lodging the anterior unossified end of the

n ‘chorda,’ which does not extend further upon the

^ j ‘ basis cranii.’ The ex-occipitals {fig. 27, 28. 2, 2),

Atlas and expand as they ascend and converge to meet above

occipital vertebra, , i 4

Lepidosiren. the ‘ toramen magnum which they complete. A
small mass of cartilage connects their upper ends with each other, and
with the overhanging backward projecting point of the fronto-
occipital spine {ib. 3). This cartilaginous mass answers to the base
of the supra-occipital in better ossified fishes : a similar cartilage
connects the ex-occipitals with the occipital spine in the Tetrodon.

We clearly perceive in the Lepidosiren that ossification, advancing
on the common cartilaginous mould of the plagiostomous skull, has
marked out the posterior cranial vertebra, and not only its neura-
pophyses but also its centrum ; the neural spine being left in a less com-
pletely ossified state than in the vertebrae of the trunk. The occipital
pleurapophyses (scapulae, fig. 27. 5i) are much more developed, and
appear as two strong, bony, styliform appendages, articulated by a
synovial capsule and joint, one on each side, to the persistent carti-
laginous base of the neurapophyses (ex-occipitals), and partly to the
centrum or basi-occipital. To the lower and less expanded ends of
the pleurapophyses are attached the extremities of the haemapo-
physes (coracoids, ^5'. 27. 52); and thus is completed the hasmal arch
of the occipital vertebra, here unusually developed in relation to its
office of protecting the heart and pericardium : the haemapophyses or
coracoids belong to the same category of vertebral elements as the
sternal ribs which protect the heart in higher Vertebrata. The costal
or haemal arch of the occipital vertebra of the Lepidosiren supports
an appendage {fig. 27. 57), projecting outwards and backwards like

80

LECTURE IV.

the simple diverging appendages to the abdominal pleurapophyses of
better ossified fishes, and like the costal appendages in the thorax of
birds ; but it is here cartilaginous, and consists of many segments.
It forms in fact the rudiment (a solitary ray) of the pectoral fin ; it
is the key to the homology of the anterior or upper limbs of the
higher Vertebrata, showing them to be appendages of the h^mal arch
(usually called scapular) of the occipital or posterior cranial vertebra.

In the second (parietal) and third (frontal) cranial vertebrae, ossi-
fication extends along the basal and along the spinal elements, but
not into the neural or lateral elements ; these remain cartilaginous in
continuation with the cartilage surrounding the large capsule of the
internal ear. The basal ossification, representing at its posterior end
the body of the atlas and the hasi-occipital, expands as it advances
along the base of the skull in the situation of the sphenoids, consti-
tuting the floor of the cerebral chamber, supporting 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, hounding a triangular space left between it and
the converging palatine arches, which space is filled by cattilage
representing the vomer. The occipital part of this hasi-cranial bone
may be defined by a slight transverse depression, where also termi-
nates a median longitudinal groove, traversing the under part of the
thus defined occipital portion of the hone ; and indicating, like the
corresponding membranous fissure in Cestracion, the primitive place
of the cranial end of the chorda. The expanded sides, originally
arches of the cartilaginous portion, bend down to abut against the
bases of the pterygoid plates. In this expansion of the basi-sphenoid
the Lepidosiren resembles the Plagiostomes and also the Batrachian
Eeptiles.

Two ridges rise from the upper surface of the occipito-sphenoidal
plate, near its outer margin, and supjjort the cartilaginous lateral
walls of the cranium. The cranial cavity is defended above by a
longitudinal bony roof (yfig. 27. 3, 7, li), nearly co-extensive with the
bony floor beneath ; the roof commences behind by the spine or point
which overhangs the ex-occipitals, 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 ascend-
ing process of the palato-maxillary arch, and to the base of th-^ nasal
plate. 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 supra-occipital bones,
or, in more general terms, the neural spines of the three cranial
vertebrae : but this supra-cranial bone not only covers the medulla

THE SKULL OF FISHES.

81

oblongata, cerebellum, optic lobes, pineal sac, and cerebral hemi-
spheres, but also the olfactory lobes. The lateral cartilaginous walls
of the cranium are continued forwards from the acoustic capsule
between the basal and superior osseous plates : the jiart perforated
by the fifth pair of nerves, and protecting the side of the optic lobes,
represents the great ala of the sphenoid : the next portion in advance,
protecting the sides of the cerebral hemispheres and perforated by
the optic nerve, answers to the orbital ala of the anterior sphenoid :
and the cartilage terminates by a part which is perforated by the
olfactory nerve, and which abuts laterally against the ascending or
palatine process of the maxillary arch.

The outward extension of the lateral cartilages of the cranium
downwards, in the form of a broad triangular plate, the apex of
which forms the articulation for the lower jaw, is like that which we
see in the Chimsera ; but ossification has extended along two tracts,
which converge as they descend, one 26. 28) from behind to the
outer, the other (t5. 23) from before to the inner side of the carti-
laginous maxillary joint, which these bony plates strengthen and
support like the backs of a book. The posterior of these bony arches
is obviously the homologue of the tympanic pedicle in the Squatina :
the anterior bony arch as plainly answers to the pterygoid buttress in
osseous fishes ; but it is here confluent with the coalesced palatine
and superior maxillary bones, the dentigerous part of which extends
outwards, downwards, and backwards (_^g. 29. 2i), but does not
29. reach, as in the Sharks and Rays, the mandibular
j joint. From the upper part of the palato-maxillary
portion a compressed sharp process (id. 2o) ascends
obliquely backwards, and terminates in a point : the

Cranial spines and . . , „ . . • , i i .

upperjarv of Lepi- inner Side ot this process is closely attached by liga-
ment to the fore and outer part of the frontal por-
tion of the epicranial bone (id. ii) ; the outer side of the process is ex-
cavated for the reception of the outer and anterior process of the
remarkable bone, which in my Memoir (xxxiii. p. 334.) I have
compared with the post-frontal bone. This bone (j^g. 27. 12), in con-
nection with the ascending process of the maxillary (id. 20), forms the
upper part of the orbit, and behind this connection it sends out the
post-orbital process, beyond which it extends backwards, freely over-
hanging the fronto-occipital, and gradually decreasing to a point, which
terminates just above the occipital spine, in the position of the mas-
toid, in bony fishes, and giving attachment to the anterior end of the
great dorso-lateral muscles of the trunk. This bone is flat above hke a
scale, and from its superficial position might be classed, like the similar

VOL. II.

G

82

LECTURE IV.

bones wliicb project freely backwards from the occiput of theFistularia,
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. In its
relative position and functions, it combines the characters of post-
frontal and mastoid ; and, since the basilar elements of these cranial
vertebriB are confluent, and their spinal elements also form one piece,
{fig. 29. 4, ii), we may here also have an example of a similar con-
fluence of the parapophyses of two distinct vertebr®. The mid-
frontal (i6. ll) constitutes the anterior part of the epicranial bone,
which is connected with the post-frontal and the cartilage perforated
by the olfactory nerves and representing the pre-frontals.

A more remarkable and less easily determinable bone is that tri-
angular horizontal plate (ii. is), the broad posterior base of which is
attached by ligament to the mid-frontal, to the post-frontal, and to
the pre-frontal processes of the palato-maxillary arch ; whilst the
apex forms the anterior extremity of the cranium, and supports at its
under part two vertical sharp-pointed teeth. I originally compared it
to the combined nasal and intermaxillary bones ; but I now regard
the cranial structure of the Murcenidce, in which the intermaxillaries
are absent, and the nasal bone dentigerous, as giving the true key
to the special homology of the bone in question. This nasal bone
is movable, up and down, upon its basal joint, and reminds one of
the similarly movable and attached appendage in the CallorhyncJms,
the free end or apex of which is beset at its under part with several
small teeth.

The triangular vomerine, or prefronto-vomerine, cartilage closes the
anterior and under part of the cranial cavity, and supports the origins
of the olfactory nerves, which perforate it in their passage to the
cartilaginous nasal capsules.

Each ramus of the lower jaw (fig. 27. 32) is composed of an
articular and a dentary piece, the latter anchylosed together at the
symphysis, and completing the inverted 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 forwards to near
the symphysis, where it ends in a point. The articular trochlea is
formed by a persistent cartilage, which penetrates the cavity in the
dentary, escapes from the fore-part of the groove on the outer surface
of the dentary, and joins its fellow, in a small cartilaginous mass,
which fills the hollow in front of the symphysis. The dentary piece
has the notched and trenchant dentinal plate anchylosed to it, and
sends up a strong coronoid process.

Tifk SKULL OF FISHES.

83

Behind the tympanic pedicle is the pre-opercular bone {fig. 27.
34), elongated, pointed at both ends, triedral, with the outer sur-
face concave : its lower two-thirds is attached by ligament to the
mandibular or tympanic pedicle. Behind and below this is an in-
equilateral triangular bone {ib. 37) closely attached by ligament to
the expanded cranial end of the hyoidean arch : this I originally
described as the styloid bone ; it may be the homologue of the inter-
opercular.*

Only a single ‘ cerato-hyoid’ {ih. 40) is ossified on each side : they
complete the arch by the ligamentous junction of their lower extre-
mities, having no intervening basi-hyal : their upper exjianded ends
are suspended by a short ligamentous mass to the cartilage imme-
diately behind the tympanic pedicle.

The capsules of the organs of sense are of nearly equal size ; the
eye is the smallest ; the nose the largest. The acoustic cajisules are
principally buried in the lateral cartilages of the skull ; but one of
the otolithes protrudes through a moderately wide hole into the cranial
cavity. The eye-ball occupies the space between the pre- and post-
frontals above, and the outward prolongation of the maxillary below;
its capsule, the sclerotic, is cartilaginous. The nasal capsules (ib. 19)
are also cartilaginous, with vertical slits closed by membrane ; they
are situated on each side and below the nasal plate.

You may perhaps think that I have been biased by the extrinsic
interest of personal discovery, in dwelling so long upon the cranial
structure of the Lepidosiren ; but I persuade myself that the actual
value and intrinsie importance of this remarkable type of Ichthyic
organisation, will justify the time and attention we have been be-
stowing upon it. The skeleton of the Lepidosiren affords the right
key to the complexities of those of the typical and better ossified
fishes. I believe it to manifest, upon the whole, the highest grade
which is attained in the class of Fishes, in the direct progress to
perfection, or, in what may be termed the Vertebrate high road.

The true or typical osseous fishes deviate from this road into bye-
paths of their own, and superadd endless complexities of which we
shall seek in vain for homologous parts in Reptiles, Birds, or
Mammals. Therefore it is, that, on the whole, the Lepidosiren’s
skeleton presents the closest resemblance to that of the lowest class
of Reptiles, though it differs therefrom both by a little less and a
little more development : the vertebral centres of the trunk, for ex-
ample, have not risen above the embryonic state of soft confluence ;
but secondary spines have been superadded to the neural and hasmal

* Agassiz regards the prc-opercular in fishes as the homologue of the styloid.

G 2

84

LECTURE IV.

spines ; a post-frontal extends, like a bony scale, above the roof of
the cranium, and over the strong temporal muscles, which* are at-
tached to the inner surface of that bone, as to an exo-skeleton ; and
one or two opercular bones are superadded behind the simple pe-
dicle of the jaw. But the single concave surface presented by the
basi-occipital to the vertebrae of the trunk, the lower transverse pro-
cesses [parapophyses) of the abdominal vertebrae, and the articulation
of the scapulo-coracoid arch to its proper cranial vertebra, afford
unequivocal evidence that the Lepidosiren is a true Fish.

LECTURE V.

THE SKULL OE OSSEOUS FISHES.

Having noticed the principal facts in the development of the skull in
the embryo of an Osseous Fish, and the several stages at which that
development is arrested, or diverted to acquire special modifications,
in the Cartilaginous Fishes ; and having dwelt more particularly on
the instructive semiosseous, semicartilaginous skull of the Lepi-
dosiren, I proceed, in the present Lecture, to the demonstration of
the complex skull of the Osseous Fishes, which constitute the great
bulk and the typical members of the class ; and, for that purpose, I
shall take one of our largest and most common species — the Cod-fish
{Gadus Morrhua) — in which you may easily repeat the observations
and test the conclusions about to be submitted to you. In describing
the general form and composition of this skull, according to my views
of the homologies of its constituent bones, I shall also indicate the
most instructive and remarkable modifications of the skull in other
Osseous Fishes, and notice those which, stopping short of the acqui-
sition of the most characteristic features of the fish’s skull, lead more
directly to the cranial type of higher Vertebrata.

The head is larger in proportion to the trunk in Fishes than in
any other class of animals ; it forms a cone whose base is vertical,
directed backwards and joined to the trunk without an intervening
neck, and the sides three in number, one superior and two lateral and
converging downwards : the cone is shorter or longer, more or less
compressed, more or less depressed, with a shar^ier or blunter apex, in
different species. The base of the skull is perforated by the foramen

THE SKULL OF OSSEOUS FISHES.

85

magnum ; the apex is more or less widely and deeply cleft trans-
versely by the aperture of the mouth ; the orbits are lateral, large,
and usually communicating freely with one another ; and there are
also two lateral fissures behind, called gill-apertures, with a mecha-
nism for opening and closing them. The mouth receives not only
the food, but also the streams of water for respiration, which escape
by the opercular or gill-apertures. The head contains not only the
brain and organs of sense, but likewise the heart and the whole re-
spiratory apparatus. The inferior, inverted, hjBinal protecting arches
are greatly developed accordingly, and their diverging or radiated
appendages support membranes re -acting upon the surrounding fluid,
and more or less employed in locomotion : one pair, in fact, is the homo-
logue of the pectoral extremities in higher Vertebrata, and the sus-
taining (scapular) arch frequently also supports the homologues of
the pelvic extremities. Thus 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 movements of the fish through its native element.

It may well be conceived, then, that more numerous bones enter
into the formation of the skeleton of the head of Fishes, than of any
other animals. Most of these bones present the squamous character
and mode of union, being flattened, thinned off, and overlapping one
another like scales ; and although the skull, as a whole, has less mo-
bility on the trunk than in higher animals, more of the component
bones enjoy independent movements.

The principal cavities, which are formed by this assemblage of
bones, are, the ‘ cranium,’ lodging the brain and organs of hearing ;
the ‘ orbital’ and the ‘ nasal’ fossae ; the ‘buccal’ and the ‘ branchial’
canals. Few of these cavities are well defined, and in no class of
animals is the exterior of the skull so broken by irregular depressions
and prominent spines and protuberances. The upper surface of the
cranium is commonly traversed by five longitudinal crests, inter-
cepting four channels : the principal crest is the median one, formed
by the frontal and occipital bones {Jig. 19. 3); next to this is the
pair formed by the parietals {ih. i) and par-occipitals ; and the
lateral pair of crests is formed by the post-frontals and mastoids
{ib. 12, 8) : the intervening depressions lodge the anterior origins
of the great muscles of the back and of the scapular arch : very
rarely do the temporal muscles extend their attachments (as in the
Conger, Lepidosiren and Symbranchus) to the upper surface of the
cranium. The upper border of the orbit sometimes sends off strong

G 3

86

LECTURE V.

angular processes; the lower border of the orbit, when present,
projects freely downwards; and the posterior border of the bony
operculum is often produced backwards in the form of spines.

It would seem an almost hopeless task to attempt to arrange
naturally and determine satisfactorily the numerous bones of this
most complex part of the skeleton of Fishes, so as to convey as clear
and tenable a knowledge of them as the Anthropotomist does of the
human skull : we need but glance, indeed, at the labours which Com-
parative Anatomists of the highest merit have bestowed on the cra -
niology of Fislies, in order to appreciate its difficulty, and at the same
time its importance. By these labours, however, of which the best
summary will be found in Cuvier’s great work on Recent Fishes
(xxiii. t. i.), and in Agassiz’s most valuable and original History of
Fossil Fishes* (xxii.), not only has the descriptive osteology of the
head of Fishes been rendered as complete and minute as that of the
human skull, but it may be truly averred to be more intelligible,
more philosophical, more agreeable with the natural arrangement
and true signification of the series of bones of which that complex
part of the skeleton is composed. It must be confessed that, in this
respect, Ichthyotomy, as true anatomical science, is at present in ad-
vance of Anthropotomy.

After an attentive study of the original authors in this field of
Anatomy, testing their extensive series of comparisons of the per-
manent forms of the skull in the higher Vertebrate classes, and the
transitory foetal conditions of each, with the results of my own ob-
servations, I have been led to the following view of the craniology of
Fishes.

The bones of the skull are primarily divided, in Anthropotomy,
into those of the cranium and those of the face ; but the proportions
which these divisions bear to each other in Man are reversed in
Fishes. According to this binary classification, the facial series in
Fishes includes an extensive system of bones — the hyoid — of which
part only, viz. the ‘ styloid element,’ is admitted into the skull by
the Anthropotomist, who describes it as a proeess of the ‘ temporal
bone.’ This very ‘ temporal,’ moreover, is originally and essentially
an assemblage of bones, which are always distinct in Fishes and
Reptiles; and the squamous part, which enters so largely into the

_ * The general results of the study of the skull of Fishes are briefly but clearly
given in the recent compendiums of Comparative Anatomy, by Dr. Cams (xxxiv )
Prof. Grant (xxvm.). Prof Rymer Jones (xxix.), and Dr. Kdstlin (xxxv.) The
generally accepted views of the classification and homologies of the cranial bones
are those adopted in the very useful “ Elements of the Comparative Anatomy of the
Vertebrate Animals,” by the learned Gdttingen Professor (Wagner), ably translated
by Mr. Tiilk (Longmans, 8vo. 1845). o / v

THE SKULL OF OSSEOUS FISHES.

87

formation of the cranial cavity of man and most Mammals, has no
share in its formation in the lo*Bfc^ertehrata.

The two classes of cranial andracial bones, having been originally
founded upon the exclusive study of the most peculiarly and ex-
tremely modified skull in the whole Vertebrate series — that of Man,
— their characters, as might he expected, are artificial, and applicable
to tlie same hones in only a small proportion of the Y crtebrata ; the
unity of the plan pervading the organisation of which it is the business
of the Anatomist, properly so called, to demonstrate.

The bones of the skull of Fishes are primarily divisible into
those of

A. Neuro-skeleton ;

B. Splanchno-skeleton ;

c. Dermo-skeleton.

A. The bones of the neuro- or proper endo-skeleton are arranged
here, as in the rest of the body, in a series of horizontally succeeding
segments ; each segment consisting of an upper (neural) and a lower
(hsemal) arch, with a common centre, and with diverging appendages.
As the bones, respectively entering into the formation of these seg-
ments, are the same in relative position, and nearly the same in
number, as in the typical vertebrae of the trunk — the excess arising
from subdivision of peripheral elements — the same term ought to be
extended to those cranial segments which has been usually restricted

so

Disarticulated bones of the cranial vertebrae and sense-capsules, [the haemal arches (h, h) and
appendages in diagrammatic outline,] Cod-fish, Gadus Morrhwa.

G 4

88

LECTURE V.

to their neural arches, in which the typical characters of the vertebra
are least departed from.

The vertebrse of the head are usually enumerated in a direction
contrary to those of the trunk, because, like the vertebrae of the
tail, they lose their typical character as they recede from the com-
mon centre.* The names of the cranial vertebrae are taken from
those applied in Anthropotomy to the bones composing their neural
spines, and the names of the neural arches from the significant terms
lately given (xxii. t. i. p. 145.), to the primary segments of the
brain, which they respectively protect.

Each cranial vertebra, or natural segment of the skull, is divided
into a neural arch, with which the centrum and parapophyses are
always more immediately connected, and a hcemal arch with its
appendages.

The neural arches are : —

Nos. of component bones in the Cuts.

I. Epencephalic arch (1, 2, 3, 4) ;

II. Mesencephalic arch (5 to 8) ;

III. Prosencephalic arch (9 — 12) ;

IV. Rhinencephalic arch (13 — 15).

The haemal arches are : —

i. Scapular, or scapulo-coracoid (50 to 52) ;

ii. Hyoid, or stylo-hyoid (25, 38 to 43);

iii. Mandibular, or tympano-mandibular (25 — 32) ;

iv. Maxillary, or palato-maxillary (20- — 22).

The appendages of the hamal arches are : —

1. The Pectoral (54 to 57) ;

2. The Branchiostegal (44) ;

3. The Opercular (34 — 37) ;

4. The Pterygoid (23, 24).

B. The bones of the splanchno-skeleton constitute :

The ear-capsule or petrosal, and otolite (16, 16") ;

The eye-capsule or sclerotic, and pedicle (17) ;

The nose-capsule or aethmoid, and turbinal (18, 19) ;

The branchial arches (45—49).

cohir^^in ff the leading condition of these terminal modifications of the vertebral
at both end! contained nervous axis shrinks and recedes centripetally

THE SKULL OF OSSEOUS FISHES,

89

c. The bones of the dei’mo-skeleton are : —

Supra-temporals
Supra-orbitals
Sub-orbitals
Labials -

Nos. of bones.

- 71

- 72
73, 73'

74*

SUPERIOR (neural) ARCHES OF THE CRANIAL VERTEBRA.

The first series of endo-skeletal bones constitutes the axis or back-
bone of the skull, as the rest of the vertebral neural arches do that
of the trunk ; and it includes and protects the encephalon or anterior
expanded extremity of the great nervous axis. The under and
upper parts of the annular segments are commonly formed by single
and symmetrical bones, as in the vertebral axis of the trunk ; but
sometimes, even in the present low class, the expansion of the cranial
cavity is accompanied, not only by a transverse development, but also
by a median division of the upper piece or key-bone of one or more
of the protecting arches.

Though subject to various degrees of anchylosis, the cranial ver-
tebraj always accord in number with the primary ganglions or divi-
sions of the encephalon in Fishes. For the better understanding of
this important relation, I may premise that the brain of Fishes con-
sists of four primary divisions succeeding each other in a linear
series horizontally, which, viewed from behind forwards, are : —

1. The medulla oblongata, with the superimposed cerebellum, or
the ‘ epencephalon.’

2. The third ventricle, with its upper (pineal) and lower (hypo-
physial) prolongations, and the superimposed optic lobes, or the
‘ mesencephalon.’

3. The cerebrum proper, or ‘ prosencephalon.’

4. The olfactory ganglionic or chord-like prolongation of the
cerebrum, or ‘ rhinencephalon.’

In most osseous fishes, as in this disarticulated skull of the Cod
( Gadus Morrhua), the bones encompassing, or in vertebral relation
with, the epencephalon are six in number {Jiff. 50. and 31. i.).

* In the human skull the only bones that can, with any probability, be referred
to the dermal system are the ‘ lachrymal.’ The splanchnic system is reduced to
the capsules of the organs of sense, of which only those of the ear and nose are
ossified. The endo-skeletal bones form the same number of neural and hasmal
arches as in the fish, but that of the occipital vertebra is far removed from its cen-
trum, and neither the mandibular nor hyoidean arches retain diverging appendages.

90

LECTURE V.

Disarticulated epencephalic
arch, viewed from behind :
Gadus Morrhua.

The first and lowest, called hasi-occipital (ih. i) *, is a short,
strong, sub-rhomhoidal bone, sub-cylindidcal and truncate posteriorly,
where it is excavated to form the articular
cavity, united by a jelly-filled capsule with
the corresponding hollow cone on the fore-
part of the body of the atlas ; the anterior
pointed end of the basi-occipital is wedged
into the basi-sphenoid, fitting and filling up
the deep posterior cleft of that bone. The
basi-occipital supports the ‘ oblong prolonga-
tion,’ of the spinal chord in the skull ; and
on each side offers a rough articular surface
for sutural union with two lateral bones, the
ex-occipitals (ib. 2, 2) ; behind which the
basi-occipital, also, sometimes receives the
anteriorly projecting base of the neural arch of the atlas, which,
in the Cod, is wedged into the posterior angle between the basi-
and ex-occipitals, and is firmly united to them by broad sutural
surfaces.

The articular cup for the atlas varies from the deep conical excavation
seen in the Carp, to the almost flat surface in the Holibut ; it is ex-
tremely rare to find, as in the Fistularia, the basi-occipital presenting
a convex surface for articulation with the body of the atlas. In many
fishes the under part of the basi-occipital is expanded and excavated ;
in the Carp the under surface of this part forms a broad triangular
plate, which supports the large upper pharyngeal grinding tooth ;
in the bony Gar-fish {Lepidosteus) the basi-occipital dev elopes two
plates from its upper and outer angles, which complete the foramen
magnum and support the ex-occipitals above.

The ex-occipitals (neurapophyses of the occipital vertebra, ih. 2, 2)
present, in the Cod, the form of oblong, sub-quadrate bones, thick,
and with two rough deeply indented articular surfaces below, but
expanded and produced outwards above ; they encircle the epen-
cephalon, over-arching and often meeting above it, and completing
the contour of the foramen magnum. They are perforated for
the passage of the nervi vagi, sometimes for the first spinal or
hypoglossal nerve ; the foramina being unusually large in the Carp-

* The synonymes and corresponding numbers and letters of the bones of the skull
are given in the tabular conspectus appended to this Lecture ; the numbers of the
bones in the text correspond in each of the figures.

t Dentigerous processes are developed from the under part of the cervical verte-
bral centres in the Coluber scaher of Linnaeus.

THE SKULL OF OSSEOUS FISHES.

yi

tribe ( fig, 3o. 2), where they relate also to the connection of the air-
hladcler with the organ of hearing, by means of the ossicles «, h, c, d,
and e. The ex-occipitals are immovably articulated in the Cod,
below with the basi-occipital, behind with the neurapophyses of the
atlas, above with the supra-occipital and the par-occipitals, and in
front with the petrous bones, or acoustic capsules, intercalated between
them and the alisphenoids. In a few fishes (e. g. Fistularia) the ex-
occipitals send backwards articular processes modified to allow a
slight movement upon the corresponding anterior articular processes
of the neurapophyses of the atlas. Like these elements of the ordinary
vertebi’EE of some fishes (e. g. Lepidosiren, Thynnus, Xyphias), the
bases of the ex-occipitals expand, approximate, and in most osseous
fishes, meet upon the upper surface of the basi-occipital, and imme-
diately support the medulla oblongata ; but sometimes a space is left
between them, which is filled up by the basi-occipital *, and in Lepid-
osfeus, as I have just observed, the basi-occipital protects the whole
epencephalon.

The supra-occipital (spine of the occipital vertebra, 30 & 31. 3),
of an elongated rhomboidal form in the Cod, triangular in the Carp, is
articulated by an inferior cellulo-sutural surface, with the summits of
the ex-occipitals and the mesial angles of the par-occipitals, com-
pleting the circle or forming the key-stone of the neural arch : it
usually sends upwards and backwards a strong compressed spine from
the whole extent of the middle line, and a transverse ‘ supra-occi-
pital ’ ridge outwards from each side of the base of the spine, to the
external angles of the bone. In most fishes this bone advances for-
wards and joins the frontal, pushing aside as it were the parietals :
in Balistes, the produced part of the supra-occipital is even wedged
into the hinder half of the frontal suture. In the Carp, on the contrary,
the anterior angle of the supra-occipital is truncated, forming the base
of the triangle, and is articulated by a lambdoidal suture to the parietal
bones, {fig. 35. 7), which here meet at the mid-line of the skull, and
the upper pai’t of the occipital spine is low and flattened. The
supra-occipital is also separated from the frontal by the parietals, in
the Salmonoid, Clupeoid, Mursenoid, and Salamandroid fishes {Lepid-
osteus, Polypterus''), and is itself divided, in Lepidosteus, by a median
suture ; these modifications tell strongly against extending the homo-

* M. Agassiz, who has noticed a similar interspace between the summits of the
ex-occipitals, as well as between the par-occipitals and sur-occipital above, observes,
“ On dirait alors qu’une large fente mediane entame tout I’occiput.” (Poissons
Fossiles, i. p. 118.) But this could only be affirmed correctly, if the basi-occipital
were likewise divided, and separated along the median line, of which I know not
any example.

92

LECTURE V.

logy of the supra-occipital with the supernumerary ‘ interparietal ’
bone of Mammals, beyond the anteriorly produced 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, and in the Light-horse-man fish {^Ephippus'), expands
above its origin into a thick crest of bone, giving the skull the
appearance of a helmet ; but in low fiattened skulls the spine is much
reduced, projecting merely backwards in the Pike and Salmon, and
being sometimes obsolete, as in the Remora; in a few instances the
broad posterior part of the supra-occipital articulates with the neural
arch and spine of the atlas, and sometimes on the other hand, e. g.
in the Holibut, the entire bone is pushed by the par-occipitals upon
the upper surface of the skull, where it manifests the loss of symme-
try by the absence of the expanded plate on the left side of the spine,
which immediately articulates with the left jiarietal.

The par-occipitals (par-apophyses of the occipital vertebra. Jig. 30
and 31.4, 4), are always wedged into the angles between the ex- and
supra-occipitals : they are of a sub-rhomboidal or conical form, with
the base towards the cranial cavity and the apex turned outwards and
backwards. The outer surface, in the Cod, is traversed obliquely by
a prominent ridge, ending at the lower and hinder projecting angle :
in the Carp the process is short, and comes from the middle of the
outer surface.

In broad and depressed skulls the par-occipital forms a strong
crest, and exceeds the ex-occipital in size : in narrow and deep
skulls the proportions of these bones are commonly reversed, and
the par-occipitals sometimes disappear; but in Ephippus, they are
as large as the ex-occipitals. In the Shad the par-occipitals unite
with the mastoids almost as in the Chelonia : and in the Poly-
pterus they become anchylosed to the ex-occipitals, as in Batrachian
Reptiles.

In Synodus, Callichthys, and Heterobranchus, the par-occipital is
visible only at the back part, not at the upper part of the skull.
The inner surface of the par-occipital, like that of the ex-occipital,
is excavated for the lodgment of part of the posterior and exter-
nal semicircular canal of the enormous internal organ of hearing
in Fishes. The outer projecting process supports the upper fork of
the first piece of the scapular arch, sometimes, as in Ephippus, by a
distinct articular cavity. The parts of the occipital vertebra are
those which are commonly in Fishes the most completely ossified at
the expense of their primitive cartilaginous basis, and, in the Poly-
pterus, they become anchylosed into one piece, like the occipital

THE SKULL OF OSSEOUS FISHES.

93

All the parts of the occipital vertebra
ossified in the pre-existing

cartilaginous

bone of Anthropotomy.
are developed from or
cranium.

The second ring of bones, or that which encircles the mesencepha-
lon, includes the ‘ basi-sphenoid,’ the ‘ ali -sphenoids,’ the ‘parietals,’
and the ‘mastoids’ 30. ii. & fig. 32.). The hasi-sphenoid

of mesencephalic vertebra, ib. 5), is always connate

(centrum
with the

pre-sphenoid.

{ib. 9),

Disarticulated neural arch of parietal ver-
tebra, viewed from behind : Gadus Morrhua.

forming with it a long subtriedal
bone (basi-pre-sphenoid*), usually
bifurcate posteriorly, and more or
less expanded beneath the cranial
cavity ; it is then continued for-
wards (sometimes after sending out
a pair of lateral processes, as in the
Perch, more commonly without such
processes) along the base of the in-
ter-orbital space to near the fore-part
of the roof of the mouth : its pos-
terior extremity is joined by a squa-
mous suture, as in Diodon, to the basi-occipital ; or more commonly,
as in the Cod, is firmly wedged by a kind of double gomphosis into
the basi-occipital : its expanded part supports the petrosals and ali-
sphenoids : the pre-sphenoidal prolongation (9) articulates with the or-
bito-sphenoids and the ethmoid, when this is ossified, and it terminates
forwards by a cavity receiving the pointed end of the vomer. It is
this portion of the basi-pre-sphenoid which manifests the loss of sym-
metry in the flat fishes {Pleuronectida:), 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 ali sphenoids ; rarely does
any portion enter into the direct formation of the cranial cavity, and
then, perhaps, 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 ossification of the basi-pre-sphenoid proceeds from a common centre ; but
this does not invalidate its general homology with the bodies of the second and
third cranial vertebrae, as manifested by their neurapophyses (alisphenoids and orbito-
sphenoids) and spines (parietal and frontal), any more than the ossification from a
single centre of the common supporting bifurcate bone of the neural and haemal
spines ol the caudal fin disproves the inference that that single bone represents the
coalesced bodies of the terminal vertebrae to which those spines belong. The par-
tially united radius and ulna of the frog are ossified from a common centre at their
coalesced proximal ends.

94

LECTURE V.

the cranial cavity, it usually sends upwards a little process on each
side ; or, as in Fistularia, a transverse ridge. The basi-sphenoid is
smooth below, where it is usually flattened or convex, but sometimes
is produced downwards in the form of a median ridge, and sometimes
is perforated for the lodgment of certain muscles of the eye-ball.
In the Polypterus both the ali-sphenoids and orbito-sphenoids are
anchylosed to the basi-sphenoid, and the result is a bone that answers
to the major part of the ‘os sphenoides’ in Anthropotomy. As
two large and important haemal arches of the head are suspended
from the parapophyses of the second and third cranial vertebra, this
seems to be the condition of the fixation and coalescence of the bodies
of those vertebra in all Fishes.

The ali-sphenoids (neur apophyses of the parietal vertebra,
ib. 6. 6.) are firmly articulated by broad sutural surfaces to the ex-
panded sides of the basi-sphenoid, above which their bases usually
meet and immediately support the third ventricle or mesencephalon,
or leave an interspace for its pituitary prolongation, which then rests
in a cavity or ‘sella’ of the basi-sphenoid. In some fishes, e.^. Perch
and Carp, the base of each ali-sphenoid rises some way above the
basi-sphenoid, and then sends inwards a horizontal plate, which,
meeting that of the opposite ali-sphenoid, forms the immediate support
of the mesencephalon, and at the same time the roof of a canal, ex-
cavated in the basi-sphenoid, 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, Scomberoids, and is very remarkable in
most fishes with lofty compressed skulls, as the Ephippiis ; it exists in
some Clupeoids, as the Herring, but not in the Salamandroid Fishes.
The subcranial canal resembles, but is not homologous with, being
differently formed from, the posterior prolongation of the nasal pas-
sages in the Crocodiles, and it lodges some of the muscles of the
eye- ball. The form of the ali-sphenoids 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
high plates ; in ordinary shaped skulls they present either a sub-
circular form, and are perforated as in the Carp {Jig. 35. e), or are re-
niform, the anterior border being deeply notched, as in the Cod {Jig.
30.6): they form a more definite and fixed proportion of the lateral
parietes of the skull than do the petrosals {ib. 16), which are interposed
between them and the ex-occipitals ; and theyhave their essential func-
tion in sustaining and protecting the sides of the mesencephalon, and
in affording exit to the second and third divisions of the fifth pair of

THE SKULL OF OSSEOUS FISHES.

95

nerves. The ali-splienoid articulates in the Cod with the petrosal
posteriorly, with the orhito-S2ihenoid anteriorly, and with the mastoid
and post-frontal above. Where the ali-sphenoids 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 ex-occipitals, and sometimes even join a
small part of the basi-occipital. 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 ali-sphenoids is by suture, partly
dentated, partly squamous. In the Cod the second and third di-
visions of the trigeminal nerve pass out of the cranium by the an-
terior notch ; in some other fishes they escape by foramina in the
ali-sphenoid : a part of the vestibule and the anterior semicircular
canal of the acoustic labyrinth usually encroach upon its inner con-
cavity, whence some have deemed it to be the petrous bone.*

The parietals (spine of mesencephalic arch. Jigs. 30. 32. 7), which
complete above the osseous cincture of the most expanded segment of
the brain in fishes, are most commonly two in number: in the Cyjirinoid
35. 7) and Salamandroid fishes they meet and unite by a sagittal
suture ; in the Salmonoids they soon coalesce; and in some Siluroids not
only with each other but also with the supra-occipital : in the Pike, the
Perch, the Cod, and most osseous fishes, the parietals are separated
from one another by the anterior prolongation of the supra-occipital.
They are always flat, and present much smaller proportions than in the
higher classes of Vertebrata. They are commonly articulated to the
mastoids outwardly and below, to the supra-occipital above, to the
frontal before, and to the par-occipital behind ; sometimes, but rarely
to the ali-sphenoids, and in a few fishes, as the Pike and Gurnard,
Avhere the parietals are more than usually developed, they appear upon
the hinder as well as the upper surface of the skull. In some fishes
they are perforated by the nervus lateralis which supplies the ver-
tical fins. The left parietal is broader than the right in the Holibut
and some other flat fishes {Pleuronectidce). The parietals are ossified
in and from the pei’ichoiulrium and continuous membrane closing the
great fontanelle of the primitive cartilaginous cranium.

The mastoids (parapophyses of the parietal vertebra, ih. 8) bear

* As, e. g. Meckel, Wagner and Hallman ( Vergleichendc Osteologie des
Schliifenbeines, p. 55.). Kdstlin, who approves of this view, gives, however,
the name of posterior ali-sphenoid (hintern schliifen-flugel, xxxv, p. 315.) to the
petrosal.

96

LECTURE V.

the same relation to the mesencephalic bony girdle, which the par-
occipitals do to the epencephalic one behind : and they project out-
wards and backwards further than the par-occipitals, forming the
second strong transverse process at each side of the cranium. This
process is developed from the outer margin of the mastoid ; the inner
side of the bone is expanded, and enters slightly into the forma-
tion of the walls of the cranial or rather the acoustic 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-occi-
pitals, the petrosal, the ali-sphenoid, the parietal, the frontal and post-
frontal bones. The projecting process 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 : its extremity gives attachment
to the strong tendon of the dorso -lateral muscles of the trunk. The
mastoid is ossified in and from the primitive cartilaginous wall of the
cranium.

The basal piece of the third cranial cincture, which defends the
prosencephalon, is formed by the j)r e-sphenoid (centrum of the fron-
tal vertebra, figs. 30. 33. 9) already described as connate with or

produced from the basi-sphenoid. The
sides of the prosencephalon are de-
fended by the orhito-sphenoids (neu-
rapophyses of the frontal vertebra,
ib. lo) : these are osseous plates,

usually of a square shape, sometimes
semicircular or semi-elliptic, as in the
Cod ; larger in the Malacopteri (fig.
35. 10) but very small, usually, in
Acanthopteri, and sometimes repre-
sented by a descending plate of the
frontal, as in the Garpike, or by un-
ossified cartilage, as in Mail-cheeked
fishes' They are occasionally separated
from the pre-sphenoid by the ali-sphe-
noid, to which they are articulated be-
low and behind, whilst above they are joined to the frontal and post-
frontal, completing the anterior part of the lateral walls of the cranium.

Disarticulated neural arch of frontal
vertebra, viewed from behind ; Gadus
Morrhua.

* The great cavity, ‘ otocrane,’ which the ex-occipital, par-occipital, ali-sphenoid,
mastoid, and sometimes the parietal and supra-occipital form for the lodgment of
the cartilaginous or osseous proper acoustic capsule, ‘petrosal,’ of the great labyrinth
of fishes, may be compared to the accessary cavity or orbit, which lodges the car-
tilaginous or bony capsule, ‘ sclerotic,’ of the organ of vision.

THE SKULL OF OSSEOUS FISHES'.

97

In the Carp their bases meet, like those of the ali-sphenoids, above the
sphenoid : when osseous matter is developed in the interorbital septum
the orbito-sphenoids are articulated by their under and anterior part
to that bone or bones.* The olfactory nerves pass out of the skull
by the superior interspace of the orbito-sphenoids, and the optic
nerves by their inferior interspace, or by a direct perforation ; and
the essential functions of the orbito-sphenoids relate to the pro-
tection of the sides of the cerebrum or prosencephalon, and to the
transmission of the optic nerves. The orbito-sphenoids frequently
bound or complete the foramen ovale.

The frontal or mid-frontal bone, (spine of the prosencephalic
arch, ib. il), completes the prosencephalic arch above, as the
supra-occipital does that of the epencephalon ; but it always enters
into the formation of the cranial cavity, though its major part
forms the roof of the orbits, which accessary 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 sub-triangular plates ; narrower in the lofty compressed
skulls, smaller in those with large orbits, and becoming greatly ex-
panded in the fishes with small and deep-set eyes. The frontals rest
in a small part of their extent upon the orbito-sphenoids, but are
more constantly articulated anteriorly, to the nasal and pre-frontals,
and posteriorly, with the post-frontals, the parietals, the mastoids,
and frequently also with the supra-occipitals : each frontal sends up
its own crest in the Tunny |, 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, which rests
directly upon the anterior prolongation of the sphenoid, and inter-
cepts a canal along which the olfactory nerves are continued forwards
to the prefrontals : the lateral parietes of this canal thus form not
only a complete, but a double bony partition between the orbits. J
In the Shad a corresponding descending plate takes the place of
the orbito-sphenoid. In most Acanthopteri an olfactory groove is
formed by shorter vertical descending plates from the under surface
of the frontal. The mid-frontal is single in the PleuronectidcB, but

* The specially developed interorbital septum or cranial athmoid 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.

f Reminding one of the double spine of the neural arch of the atlas in Te-
trodon. xxii., t. iv. p. 122.

VOL. II.

n

98

LECTURE V.

has undergone more modification than any of the preceding bones in
connection with the general distortion and loss of symmetry of the
head : in the Holibut the right posterior angle is truncated, and the
rest of that side scooped out, as it were, to form the large orbit of
the right side : the left side of the bone retains its normal form : a
median crest, a continuation of that upon the supra-occipital, divides
the two sides. The frontal is developed in and from the perichon-
drium and the membrane closing the upper fontanelle in the primitive

cartilaginous cranium.

The post-frontals (parapophyses* of the frontal vertebra, figs.
30.33.12,12) obviously belong to the same category of vertebral
pieces as the mastoids, whose prominent 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 tym-
panic 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 orbito-sphenoid and ali-sphenoid, above to the frontal, and by
their posterior and upper surfaces to the mastoid. The area included
by the prosencephalic cincture is widely open anteriorly, correspond-
ing with the great anterior membranous fontanelle in the Sharks, but
this relates more essentially to the fact of the true cranial or neural
canal not being terminated by the frontal vertebra.

The circle of bones f which completes the axis of the skull an-
teriorly, and protects the olfactory chords or ganglions, consists of
the ‘ vomer ’ below, the ‘ pre-frontals ’ laterally, and the ‘ nasal ’ above
{fig. 34.).

Disarticulated neural arch of nasal
vertebra: viewed from behind.
{Qadus Morrhua.)

The vomer (centrum of nasal vertebra,
figs. 30. and 34. 13) is thick and ex-
panded anteriorly, slender, and terminating
in a point posteriorly, where it is wedged
into the under part of the pre-sphenoid ; its
antero-lateral angles are articulated to the
pre-frontals ; its upper surface supports the
nasal bone, sometimes immediately, some-
times by an intervening ethmoidal cartilage.

* The position of the transverse processes fpar-occipitals, mastoids, and post-
fronta'.s] of the foregoing cranial vertebras, would seem to indicate them to be upper
ones (diapophyses) rather than lower ones (parapoph}'ses) ; but I know not any
example of diapo])hyses developed as independent, autogenous, vertebral elements ;
and we see the parapopliyses of the trunk gradually ascending in position, as they
advance towards the head, in fishes.

■f The “ vertebra olfactoria” of Bojanus, who, however, regards the spine as the
“ lamina media a;tlunoidei.”

THE SK0LL OF OSSEOUS FISHES.

99

The palatine bones abut against the expanded anterior part of tlie
vomer, the under side of which commonly supports teeth. Tlie left
ala of the anterior end of the vomer is chiefly developed in the
Holibut and other flat fishes. In the Lepidosteus, the vomer is
divided into two by a median cleft. Although its posterior end
joins obliquely to the under part of the pre-sphenoid, it is not,
therefore, less a continuation of the basi-cranial series than is the
post-sphenoid, which joins in a similar manner with the basi-occi-
pital.'* In the Lepidosiren, we have seen the basi-sphenoid confluent
with the basi-occipital ; in the Polypterus it is confluent with the
vomer.

The prefrontals (neurapophyses of the nasal vertebra, ib. 14)
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 palato-maxillary arch :
they rest below upon the pre-sphenoid and vomer, support above the
fore part of the frontal and the back part of the nasal bones, and
give attachment to the large antorbital or lachrymal scale-bone, when
this exists : they are always ossified in and from pre-existing cranial
cartilage.

Such are the essential characters of the bones which Cuvier has
called ‘ frontaux anterieures ’f in Fishes, and to which I shall 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 cra-
nial bones of Fishes, the prefrontals manifest their essential relation-
ship 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

* Straus, however, argues it to be an appendage from that mode of union
(xxxvi. t. i. p. 333.).

f “ 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 lour horde inferieure aux palatins.” (Lemons d’Anat. Comp. ii. 1837,
p. GOG.) Compare this enunciation of the essential characters of the anterior fron-
tals 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 ethmotdei of Bojanus ;
seitliche re'ichbeine, Meckel, Wagner. Without at present entering into the respec-
tive merits or demerits of these determination.s, I shall only state that the pre-
frontals, 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 the.se bones may, in every case, bo traced to the non-appreciation of
their true general homology.

II 2

100

LECTURE V.

I

from which the palatine bone is suspended.* In the MurancB, also,
the prefrontals are plainly confluent with the nasal bone, and form
the well-marked articular surfaces for the palato-maxillary bone. In
some Ashes a process of the prefrontal circumscribes the foramen by
which the olfactory nerve finally emerges from the anterior pro-
longation of the cranio-vertebral canal. In the Carp the olfactory
nerve traverses a deep notch on the inner side of the prefrontal
{Jig. 35. 14). In the Cod the palatine arch is chiefly but not wholly
suspended to the prefrontals. The right prefrontal is the smallest in
the unsymmetrical skulls of the flat-fishes.

The nasal bone (spine of the rhinen cephalic arch. Jigs. 30. and
34. 15) is usually single, and terminates forwards in a thick obtuse
extremity. In some fishes, as the SalmonidcB, the nasal is broad,
but not deep : in Istiophorus it is long and narrow : in the Dis-
coboles 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. It is articulated above and behind to the
frontal and prefrontals, and below either directly or by a vertical
cartilage, as in the Cod, to the vomer. 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 fossae than in any
other class of Vertebrates.

The backward prolongation of the usually cartilaginous, sometimes
membranous interorbital septum, in which one ( Cyprinus, Gadus) or
more {Perea') osseous plates may be present, intervenes between and
more immediately supports the olfactory nerves. In the Salamandroid
Fishes the nasal is divided by a median suture. The horn-like pro-
jection from the fore part of the skull of the JVaseus unicornis is
formed chiefly by a process of the frontal bone, to the under part of
which a small nasal is articulated with a trifid anterior end, the
lateral divisions of which articulate with the premaxillaries, as in
Citharinus. 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 basi-cranial canal.

The tui’binate bones {Jig. 30. 19), or osseous capsules of the nose,
are situated at the sides or above the nasal : the pre-maxillary and
the maxillary bones are usually attached to its extremity through the

In the Conger, Cuvier ‘ recognises the prefrontals as persistent cartilages.

Op. cit. p. 235.

THE SKULL OF OSSEOUS FISHES.

101

medium of a symmetrical cartilage*, which is articulated with the fore
part of the nasal bone, and extends forwards to the interspace of the
upper ends of the pre-maxillaries. This ‘pre-nasal’ cartilage often
forms a septum between the two ‘ ossa turbinata : ’ it is partially
ossified in the Carp.

In the MurcBnidcB the normal elements of the fourth or rhinen-
cephalic vertebra coalesce into a single bone : the pre-frontals or
neurapophysial elements are plainly manifested, as has been already
observed, by the articular surfaces which stand out in front of the
orbits for the suspension of the palato-maxillary arches : the spine
or nasal bone forms the usual obtuse expansion at its anterior extre-
mity, immediately beneath the skin of the upper part of the snout,
and it supports teeth, as in the Lepidosiren : it is intimately confluent
anteriorly with the centrum or vomer, the limits being indicated by
the interruption of the median series of vomerine and nasal teeth.

Sense-Capsules.

The sense-capsules are so intercalated with the neural arches, which
are modified to form cavities or orbits for their reception, that the
demonstration of the skull will be best facilitated by describing them
before we proceed to the haemal arches of the cranial vertebra}.

Acoustic capsule, or Petrosal^ 30. 16).

We have seen that the first developed cartilage upon the primitive
membranous walls of the skull forms a special protecting envelope
for the labyrinth, which alone constitutes the oi'gan of hearing in
Fishes {Ammocetes, fig. 24. 16). 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 basi-lateral 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 neura-
pophyses of the cranial vertebrm begin to be established in that car-
tilaginous basis, a distinct bone is likewise, in most cases, developed
for the more express defence of the labyrinth. Since, however,

* This is regarded by some homologists as the body of a fifth cranial vertebra ;
but from its relations to the nasal bone it would have better claims to be considered
the spine of such, if there were sufficient grounds for admitting vertebral segments
beyond the nasal one : and the cephalic region of the skeleton miglit well differ,
like the cervical and other regions, in the number of its vertebral segments; but I
have not found good evidence of such variation.

•j" Rocher, Cuvier; rupeal, Geoffroy ; ]>ars petrosa ossis temporis of Anthropotomy.
The nature of the ‘ os petrosiun ’ as an envelope of the acoustic bulb, and its
serial homology with the sclerotic capsule of the optic bulb, are clearly entmeiated
by Professor de Plainville, in the first part of his great “ Osteographie,” 4to. 1839,
pp. 13. C2.

H 3

102

LECTURE V.

functions are less specialised, less confined to the particular organ
ultimately destined for their performance in the lower than in the
higher classes, we find in Fishes several hones taking part with the
special acoustic capsule in the lodgment of the labyrinth ; and it is
only in the higher Vertebrata that the capsule, under the name of
the ‘ 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 ex-occipitals, ali-sphenoids, and orbito-sphenoids
have received their destined amount of ossification, the petrosal
still remains in the cartilaginous state : it is very small, yet never-
theless exists in the Carp {fig. 35. 16) and Bream, where Cuvier and
Bojanus* describe it as a dismemberment of the mastoid: in the
Perch, however, where the petrosal is a little better developed than
in the Carp, Cuvier recognises its true homology : it is somewhat
larger in the flat-fish (e. g. Holibut), and in the Cod tribe attains
an equal size with the ali-sphenoid, which it resembles in form,
except that the notched margin is posterior {Jig. 30. 16). Here it
forms the posterior lateral wall of the cranium ; articulates below with
the basi-occipital and basi-sphenoid, above with the mastoid and par-
occipital, behind with the ex-occipital, and before with the ali-
sphenoid: it supports the cochlear division of the labyrinth con-
taining the otolites. The cavities (otocranes) lodging the petrosals
and organs of hearing are completely separated from each other, and
are formed, on each side, by the ex-occipital, par-occipital, ali-
sphenoid, mastoid, and post-frontal : they are sometimes closed ex-
ternally, but open widely into the cranial cavity.

The optic capsule, or sclerotic, {fg. 30. 17) like the acoustic cap-
sule, is cartilaginous in all Chondropterygians, and also in the semi-
osseous fishes, as the Lepidosiren, the Lophius, the Tophobranchs
and Plectognathes. In most osseous fishes it is bony, and commonly

* XXXVI. p. 504. tab. 7. figs. ]. amt 5. ic.

TUE SKULL OF OSSEOUS FISHES.

103

consists of two hollow hemispheroid pieces, each with two ojiposite
einarginations ; the inner ones circumscribing 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 emarginations supporting the cornea. As this
part of the skeleton of the head retains its primitive libro-membranous
condition in Man and Mammalia, it is called the sclerotic coat of
the eye ; and the osseous plates developed in it iu 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 the
organ of hearing, and which the turbinate bones do to the organ
of smell : the persistent 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 the Cartilaginous Fishes, however, it is articulated by means of
a pedicle with the orbito-sphenoid. The osseous cavity or ‘ orbit ’
lodging the eye-ball is formed by the pre-sphenoid, orbito-sphenoid,
frontal, post-frontal, pre-frontal, and palatine bones : it opens widely
outwards, where it is, often, further circumscribed by the chain of
‘ sub-orbital ’ scale-bones below, and, but less frequently, by a
supra-orbital bone above. The bony orbits in most fishes com-
municate freely together, or rather with that narrow prolongation of
the cranial cavity lodging the olfactory nerves : but, in many
3Iulacopteri, e. g. the Shads and Erytlirinus, the CitJiarinus and
Ilydrocyon, the Synbranchus, and the genus Cyprinus {Jig- 35. 18),
an osseous septum divides the orbits. In the Lepidosteus and Poly-
pterus the orbits are divided by a double septum, forming the proper
walls of the olfactory prolongation of the cranium, as we shall find to
be the case in the Batrachia.

The bony capsules of the organ of smell pi’esent the same division
into cranial and nasal {(Ethmoidal^ Jig. 35. 18, turhinal,Jig. 30. lo) por-
tions, in Fishes as in Man, and, as in Man likewise, other bones, the
vomer and nasal, for example, contribute an accessary protective func-
tion. All the parts of the proper capsule are cartilaginous in cartila-
ginous and semi-osseous fishes ; the ethmoidal part continues cartila-
ginous in many osseous fishes, closing the fore part of the cranium,
assisting to form the interorbital septum, and contributing to support
the olfactory nerves in their exit from the skull. When ossification is
cstablislied in the ethmoidal cartilage, it is usually confined in fislies
to the cranial end, forming there a single symmetrical, slender, bifur-
cate or sub-quadrate piece, usually perforated by tlie olfactory
nerves ; but never in two distinct pieces corresiionding to the two

u 4

J04

LECTURE V.

nerves. The ethmoid forms a slender vertical compressed plate, ex-
panded and bifurcate above, in the Perch : it is a broader and larger
plate, bent upon itself, with the concavity upwards, in the Cyprinoid
{Jig. 35. 18) and Siluroid Fishes, where it articulates below to the
pre-sphenoid, behind and abo^'e to the orbito-sphenoids, and above
and before to the frontals and prefrontals, and forming the chief
part of the interorbital septum.*

The cartilaginous capsules of the terminal or pituitary expansions
of the oi'gan of smell are, proportionally, large in the Chondroptery-
gians and the Lepidosiren. They form a single tube, ivith interrupted
cartilaginous parietes, like a trachea, in several of the Cyclostomes ;
and the interposed membranous slits are present in the Lepidosiren
(Jg. 27. 19), where, as in all the higher fishes, the olfactory capsules
cease to be confluent, as the ethmoid is, but form a pair.

The turbinals {Jig. 30. 19), or bones which are developed for the
more immediate support of each olfactory capsule, in osseous fishes,
are generally tliin, more or less elongated, and turbinated scales,
situated at the sides of the nasal bone and of the ascending pro-
cesses of the jiremaxillaries ; usually free, but in the Gurnards arti-
culated with the prefrontals and nasal, and in the Cock-fish {Argy-
reiosus) suspended above the nasal bone, from the anterior prominence
of the frontal spine.

Inferior (Haemal) Arches of the Cranial VERTEiiRiE.

These, though apparently more numerous than the vertebral centres,

* Oken and Bojanus regarded the ethmoid as the body or centrum of their third
(anterior) cranial vertebra ; and M. Agassiz, combating the vertebral theory of the
skull, says — “ Ainsi que serait dans cette hypothese, le sphenoide principal, les
grandes ailes du sphenoide, et I’ethmoide, qui forment pourtant le plancher de la
cavite c^rebrale ? Des apophyses ? Mais, les apophyses ne protegent les centres
nerveux que du cote et d’en haut. Des corps des vertebres ? Mais ils se sont
formes sans le concours de la corde dorsale ; ils ne peuvent done pas etre des corps
des vertebres.” (Poissons Fossiles, t. i. p. 229.) The ethmoid, however, forms the
anterior wall, rather than the floor of the cranium ; and since it is related in all
Vertebrata to the support and )irotection of the olfactory organ, it enters into the
category of the ‘ Capsules of the organs of special sense,’ with the petrous and
sclerotic bones, and not into that of the neural arches or vertebral coverings of the
cerebro-spinal axis. The argument of M. Agassiz would be good, if change of
position involved an essential distinction of a bone, i. e. a different homology, and
a consequent change of name ; but M. Agassiz finds no difficulty in determining
the frontal and the parietal bones in all bony fi.shes, notwithstanding their variety
of proportion and position. Therefore, in determining and expressing their special
hornology, by the arbitrary names borrowed from Anthropotomy, why should not
their general homology as spines of the prosencephalic and mesencephalic vertehr®
respectively be recognised ? If M. Agassiz could show modifications of the relations
of the front, il and parietal bones, .so that they thereby ceased to be recognisable as
such, then also their more essential and gener.al characters might be so obscured as
to afford grounds for rejecting their vertebral homologies.

THE SKULL OF OSSEOUS FISHES.

105

correspond with them and the neural arches, and are essentially four
in number in the osseous fishes ; viz. the ‘ palato-maxillary,’ the
‘ tympano-mandibular,’ the ‘ hyoidean,’ and the ‘ scapular.’ Most
fishes have, likewise, appendages, which diverge or radiate from these
arches. A special (visceral) system of bony arches, called ‘ branchial,’
also persists in fishes, for the support and movements of the gills.

Palato-maxillary Arch {fig. 30. ii, iv, 20, 2i, 22).

I am induced to regard this as essentially one arch, from its con-
dition in the Lepidosiren and Plagiostomous fishes, and from the cir-
cumstance of its being completed or closed at one point only, viz. where
the premaxillaries meet or coalesce. The palatine bones are the piers
of this inverted arch, and their points of suspension are their attach-
ments to the prefrontals, the vomerine and the nasal bones. The arch
is completed by the maxillary and pi’emaxillary bones, the symphysis
of the latter forming its apex ; and it is inclined forwards, nearly or
quite parallel with the base of the skull ; which, in most fishes, ex-
tends 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 dependent, circumscribing below the nasal or respiratoiy
canal. The pterygoid bones project backwards and outwards as the
appendages of the palato-maxillary arch. Both maxillary and inter-
maxillary bones tend by their peculiar development and independent
movement in bony fishes to project freely outwards, downwards, and
backwards. 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 men-
tioned, and which I shall now proceed to point out and describe as
they recede from the parts of the vertebra to which they are sus-
pended ; taking as before the Cod-fish as the type.

The palatine (pleurapophysis of nasal vertebra*, yf <7. 30. 20) is an
inequilateral triangular bone, thick and strong at its upper part,
which sends off two processes ; one is the essential point of sus-
pension of the palato-maxillary arch, and articulates with the pre-
frontal and vomer at their point of union ; the other is convex, and
passes forwards to be articulated to a concavity in the superior
maxillary, to which, in all Fishes, it affords a more or less movable

* To Bqjanus belongs the merit of having first enunciated this general Iiomo-
logical relation, in his description of tab. xii. fig. j- 4. of his famous monograph.
“ Os palatinum, sen co.stu cor|)ori luijus vcrtchr;e (athmoidalis sen capitis cpiarta')
appensa.” (^Anatome Testudinis Euroj)o:a:, 44.)

106

LECTURE V.

joint. In the Parrot-fishes and Diodons the articulation is quite
analogous to that of the mandible below with the tympanic pedicle.
In the Salamandroid fishes it is a fixed 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 angle of the base of the palatine is
attached, in the Cod, by short and strong ligaments to the prefrontal.
The thin posterior and inner border of the bone is joined by liga-
ment to the ento-pterygoid, and its outer angle is dovetailed into 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 the Pike,
and is short and broad in the broad-headed, small-mouthed fishes.

The maxillary (hsemapophysis of nasal vertebra, fig. 30. 2l) is
usually a small edentulous bone*, concealed in a fold of the skin
between the palatine and premaxillary : it lies, in the Cod, posterior
to and p'arallel with the premaxillary, which it resembles in form,
but is longer and thinner in most osseous fishes : the expanded and
bifurcate end of the maxillary is produced inwards rather than up-
wards, and 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 liga-
ment, in which a labial gristle is developed, to the coronoid process
of the lower jaw.

In the Salmon tribe the maxillary is joined to the hinder and
lower end of the short premaxillary, forming with it a continuous arch,
and it supports teeth ; this normal and higher character of the
maxillary f prevails also in the Clupeoid fishes, and is here illustrated
in the great Sudis {fig. 36.). In the Plec-
tognathi (Globe-fish and File-fish), the
maxillaries coalesce wholly or in part with
the premaxillaries. In the Lepidosteus the
contrary condition prevails : the premax-
illary and maxillary bones constitute, in-

Disiirticuiated bones of paiato- deed, a sinffle dentiffei’ous arch or border
maxillary arch ? o o

of the upper jaw, but are subdivided

* The Os mystaceum of iclithyotomists.

j Cuvier first recognised tlie special liomology of the ‘ os mystaceum ’ by oli-
serving its modifications in the salmon.

THE SKULL OF OSSEOUS FISHES.

107

into many bony pieces, a condition which seems to have prevailed
in some of the ancient extinct Salamandroid fishes ; for example, the
genus of the Old-Red- Sandstone, which I have called Dendrodus.
In the Polypterus the maxillary is large and undivided on each side ;
it supports teeth, and sends inwards a broad 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 ihe
premaxillary, to be entirely wanting in certain Eels {^luranidce).

The premaxillary, or intermaxillary bone (hajmal spine of nasal
vertebra, fig. 30, 22), one of a symmetrical pair in the Cod and most
other osseous fishes, is moderately long and slender, slightly curved,
ex2ianded and notched at both extremities : the anterior end is bent
upwards, 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 downwards and outwards : 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. By those
who may regard the prenasal cartilage as a vestige of a fifth cranial
vertebra the premaxillaries may be viewed as its inferior arch : but such
an arch would be incomiilete, widely open ; the piers or crura diverg-
ing, instead of converging, to unite, like other inferior or hmmal
arches. In the Diodon the premaxillaries and their lamellated dental
apparatus coalesce and constitute a single symmetrical beak-shaped
bone ; Muller also found a single premaxillary in the Mormyrus.
The confluent premaxillaries constitute the sword-like anterior jiro-
longation of the snout in Xiphias, and are firmly and immovably
articulated with the pre-nasal 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, which
latter most prevails in Mammals : but there are many examples in
Fishes where their development 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 ex-
ample, in the Picarels {Menidce), the Dories {Zeus\ and in certain
Wrasses, as Coricus, and especially the Epilndus, or Spams in-
sidiatnr of Pallas {fig. 37, 22).* In tins fish the nasal branch of

* See Cuvier and Valenciennes, Hist, des Poissons, t. xiv. p. 92. The Itypo-
tynipanic or suspensory pedicle of the lower jaw is there called the ‘ malar ’ bone.

108

LECTURE V.

plays in a groove on tlie upper surface
of the skull, and reaches as far back as
the occiput when the mouth is retracted.
The descending or maxillary branch is
attached by a ligament {ib. 22"), longer
than itself, to the lower end of the max-
illary bone (ib. 21.), and consequently
draws forwards that bone, together with
the lower jaw, to which the same end of
the maxillary is attached by ligament,
when the long nasal branch of the pre-
maxillary glides forwards out of the epi-
cranial groove in which it usually lies.
The protractile action is further favoured by a peculiar modifica-
tion of the hypo-tympanic {ib. 28), which, by its great length and
movable articulation at both ends, co-operates with the long pre-
maxillary in the sudden projection of the mouth, by which this
fish seizes the small, agile, aquatic insects that constitute its prey.
In the Lophius 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 small bony piece situated above the maxillary in some Hale-
coids (Trout, Herring) and Lucioids (Pike) seems to belong to the
series of mucous or scale bones : the Flying Gurnard {Dacty-
lopterus) has two delicate cartilages in a similar position, and the •
Scice?ia. aquila a large labial cartilage in the angle of the mouth,
attached to the lower jaw.

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, Hydro-
cyon, and Lophius ; are connate with, or indistinguishable from, the
palatine in most Saltnonoids and Eels ; whilst in the Muracna 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 {Jig. 30. 23) is an oblong, thin, scale-like bone,
attached to the inner border of the co-adapted halves of the palatine
and true pterygoid, and increasing the bony roof of the mouth in

the intermaxillary {ib. 22')

Mechanism of protraction and retrac-
tion of the mouth {Epibulus insidi-
ator).

THE SKULL OF OSSEOUS FISHES.

109

the direction towards the median line. It is edentulous in the Cod
and most other fishes, but is richly beset with teeth in the Ara-
paima gigas. It principally constitutes the floor of the orbit, its
breadth depending much upon the depth of that cavity ; it sometimes
is joined by its median margin to the vomer and pre-sphenoid, as in
the Cod-tribe, Carp-tribe, and Flat-fishes ; and to the basi-sphenoid
in Lepidosteus, Erythrinus, and Polypterus, 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 ento-pterygoid
does not join the basi-sphenoid ; and in Lophius it appears to be
wanting.

The pterygoid * {jig. 30. 24) forms in the Cod an inequilateral
triangular plate, but more elongated than the palatine, with which it is
dovetailed anteriorly ; it becomes thicker towards its posterior end,
which is truncated and firmly ingrained with the anterior border of
the hypo-tympanic and pre-tympanic bones ; its lower border is smooth,
thickened and concave ; edentulous in the Cod, but more frequently
supporting teeth, as in the Perch. The pterygoid and palatine appear
to form one bone in the great Sudis {Arapaima gigas, Jig. 36. 2o, 24) :
and they are confluent in the Eel tribe. In the Conger the compound
bone is articulated anteriorly to a short lateral process of the vomer,
and posteriorly with the hypo-tympanic : it is very large in the
Gymnotus. In the Murasna the palatine processes of the vomer
do not exist, and the fore part of the long pterygoid is attached
by ligament to the sides of the vomer, behind its expanded denti-
gerous part.

The ten bones of which the palato-maxillary arch is composed in
Osseous Fishes are, in the Cod and most other species, so dispersed,
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 downwards and
outwards, except those of the last or pterygo-palatine arch, which
abut against the tympanic pedicles. The simplification or confluence
of the two first of these spurious arches is effected in the Salmonoid
Fishes, 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

Well argued by Dr. Kbstlin not to be, as Cuvier supposed, the hoinologue of
the ‘ os transversum ’ of Reptiles. — xxxv. pp. 328, 329.

110

LECTURE V.

into close articulation with the palatines in the Plectognathes, and the
consolidation of the whole series into its normal unity is effected in
the Lejndosiren. The palatines form the true bases of the inverted
arch at their points of attachment to the prefrontals ; the intermaxil-
laries constitute the true apex, at their mutual junction or symphysis ;
the approximation 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 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 30, H, in, 25 — 32).

This presents its true inverted or hsemal character ; its apex or
key-stone formed by the symphysial junction of the lower jaw hang-
ing downwards freely, below the vertebral axis of the skull. The
piers, or points of suspension of the arch, are foi-med by the epi-tym-
panics {fig. 30. 25), or upper pieces of the tympanic pedicles (pleura-
pophyses of the prosencephalic vertebra) : each epi-tympanic is
articulated to both the post-frontals and the mastoids, and is divided
artificially accordingly in fig. 30. ; its articular surface is formed in
the Cod by a single elongated condyle ; in many other fishes by a
double condyle, one for each of the above named cranial parapo-
physes. In the Diodon the upper border of the epi-tympanic is ar-
ticulated by a deeply indented suture to the frontal, the post-frontal
and mastoid bones ; its posterior margin supports, as in many other
fishes, a circular articular surface for the opercular bone. Below
the condyle, the epi-tympanic in the Cod becomes compressed laterally,
but is much expanded from before backwards. The almost constant
bifurcation of both ends of the epi-tympanic in osseous fishes, for ar-
ticulation with two cranial parapophyses above, and suspending two
inverted arches below, make it appear like a coalescence of the upper-
most pieces of both those arches. In most fishes the lower end is
bifid, and supports two inverted arches, the mandibular and the
hyoidean ; the stylo-hyoid being attached near the junction of the
epi-tympanic with the meso-tympanic. The contiguous ribs of the
Chelonia are immovably connected together to ensure fixity and

* By Bojanus they were regarded as the ribs of the second (parietal) vertebra of
the head. (^Anatome Tesiudinis Europceco, p. 44.)

THE SKULL OF OSSEOUS FISHES.

Ill

strength to the carapace : the bulky apparatus suspended from the
parietal and frontal vertebrae demanded the additional strength to
the supporting axis which is gained by the confluence of their
bodies, and apparently by the confluence of the proximal pieces of
the pleurapophyses by which the two haemal arches are suspended
from those vertebrae. The anterior division of the epi-tympanic
piece articulates with the pre-opercular (34), the meso-tympanic
(26), and pre-tympanic (27) ; the posterior division is again bifur-
cate in the Cod, supporting part of the pre-operCular and part of the
opercular bone. A strong crest projects from its outer surface in
this and many other fishes. The epi-tympanic is simple at both ends
in the Carp tribe.

The meso-tympanic {fig. 30. 26), or ‘symplectic’ of Cuvier, is
a slender, compressed, slightly curved, elongated, triangular bone,
articulated by its upper part or base to the epi-tympanic and pre-
opercular ; by its lower end to the inner side of the hypo-tympanic,
reaching almost to the mandibular trochlea; and by its anterior border
to the pre-tympanic. The upper part of its posterior border is free,
and gives attachment to the membrane that fills up the vacuity
between it, the pre-opercular and hypo-tympanic bones. The
meso-tympanic is confluent with the epi-tympanic in the Siluroid,
the Murienoid, and some other fishes ; but does not join the epi-
tympanic -in the Lepidosteus, being in that fish supported by the
pre-opercular.

The pre-tympanic {fig. 30. 27), to which part of the suspensory
pedicle of the jaw Cuvier restricts the name ‘caisse’ or ‘os tym-
panicum*,’ is an oblong bony scale, with the posterior margin thick-
ened and grooved for the reception of the fore part of the meso-
tympanic and the upper and fore part of the hypo-tympanic. It is
confluent with the hypo-tympanic in the Conger and Muraena : it
does not join either this or the meso-tympanic in the Lepidosteus.

The hypo-tympanic {fig. 30. 2s) is a triangular plate of bone, like
the epi-tympanic reversed, bearing the articular convex trochlea for
the lower jaw upon its inferior apex, and having its upper side or
base more even than the opposite base of the epi-tympanic. The

* This is pcrliaps one of the best examples of the extent to which Cuvier was
influenced by the idea or principle of homology, when a determination had origin-
ated from his own comparisons ; few of the names imposed by Geoflroy St. Hilaire,
in conformity with his peculiar views, seem more overstrained tlian the transference
of the name and signification of the little process supporting the ear-drum in man
to a small segment of a strong pedicle, wholly deprived of the proper tympanic
function, and with which the homology of the human tympanic process of the
temporal bone can only be established by taking the pedicle of the lower jaw in
Fishes as a whole.

112

LECTURE V.

posterior margin of the hypo-tympanic is grooved for the reception of
the part of the pre-opercular (34), its inner side is excavated for the
insertion of the pointed end of the meso-tympanic (26), and the
anterior angle is wedged between the pre-tympanic (27) 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 Sparus insidiator, or Sly-hream {Epihulus, Cuv.),
presents the most remarkable modification of the hypo-tympanic
\fig. 37. 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 meso-tympanic. Thus,
in the extensive protractile and retractile movements of the mouth,
the under jaw swings backwards and forwards 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 pre-oper-
culum to its angular piece 37. Z, 3o).

By the confluence of the meso-tympanic with the epi-tympanic, and
of the pre-tympanic with the hypo-tympanic, in the Eel tribe, the sus-
pensory pedicle of the lower jaw is reduced to two pieces, as it is in
the 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 MurancB, viz. the confluent
pre-tympanic and hypo-tympanic pieces. This progressive simplifi-
cation, 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 squamo-temporal bone
and tlie malar bone of higher animals, hut also the ‘symplectic’ — a
peculiar ichthyic bone — are superadded to the ‘tympanic’ or quad-
rate bone of Reptiles and Birds, in the formation of the suspensory
pedicle of the under jaw of Fishes. Ascending to the higher gene-
ralisations of homology, we see in the tympanic pedicle a serial re-
petition of the palatine bone ; and, in both, the ribs or pleurapophyses
of contiguous vertebrae specially modified for the masticatory func-
tions of the arches they support.*

The mandible, or lower jaw (haemapophysis of the frontal ver-
tebra {Jig. 30. 29, 32), is the lower portion of the arch, being arti-
culated to the hypo-tympanics above, and closed by a ligamentous
union or bony symphysis with its fellow at its lower end. The term

* The division of the pleurapophpis of the frontal vertebra into four tympanic
pieces no more destroys its individuality than does the division of the maxillary bone
in Lepidosteus the individuality of that bone.

THE SKULL OF OSSEOUS FISHES.

113

‘ 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 (ha3mapophysis
proper), articulated to the suspensory pedicle, and edentulous, ana-
logous to the maxillary ; and the other (h^mal spine) 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. That {ib. 29) which forms the sig-
moid concavity adapted to the tympanic trochlea is termed the ‘ ar-
ticular piece;’ it sends upwards a pointed coronoid process, to which
the ligament from the maxillary bone, and the masticatory muscles
are attached ; one short square plate downwards, to join with the
angular {ib. 3o) ; and a long pointed process forwards, to be sheathed
in the deep notch of the anterior piece. This (32) is characterised
by the teeth, which, when present in the lower jaw, are always
supported by it ; whence its name of the ‘ dentary piece.’ The
dentary is always deeply excavated, and receives a cylindrical car-
tilage*' from the inner side of the hypo-tympanic, and the vessels
and nerves of the teeth. The great Sudis {Jig. 38.) and the Poly-
pterus have the splint-like plate
along the inner surface of the
ramus, answering to that which
Camper and Cuvier have un-

IjOWQt {Arapauna gigas).

fortunately called ^operculaire/

in the mandible of Eeptiles, but to which I have given the name of
‘ splenial' to prevent the confusion from the synonymy with the true
opercular bones of Fishes : and in both Sudis and Lepidosteus there
is superadded a small bony piece {ib. 29 a), answering to that which
Cuvier calls the ‘ sur-angulaire ’ in Eeptiles. These modifications, co-
existing with the true opercular bones, demonstrate the fallacy of the
idea that those bones are much developed homologues of the posterior
pieces of the lower jaw of Eeptiles ; an idea wliich could never have
been entertained by its propounders, had they appreciated the ge-
neral homology of the opercular pieces, as the diverging appendage
of the haemal arch of a cranial vertebra.

The Diverging Appendage of the tympano-mandibular arch con-
sists 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 oper-
cular bones, which forms the chief medium of the attachment of the

* M. Agassiz observes that this cartilage is the “ reste de I’ancien arc embryonal,
autour duquel les pieces osseuses se sont developp^es.” (xxii. i. p. 138.)

VOL. H.

I

114

LECTURE V.

appendage to the supporting arch, is the pre-opercular {fig. 30. 34),
which is usually the longest in the vertical direction, if not the
largest of the hones : it commonly presents a crescentic or an angular
form ; it is sometimes bifurcate above, as in the Cod, and with the
lower slender angle continued downwards and forwards to beneath
the hypo-tympanic. In the Gurnards, or ‘ mailed-cheeked’ Fishes,
the pre-opercular is articulated with the enormously developed sub-
orbital scale-bones.

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 {fig. 30. 35) :
in the Cod it is principally connected with the posterior margin of
the pre-opercular, and below with the sub~opercular {ib. 36) ; but it
has usually, also, a ‘partial attachment to the outer angle of the epi-
tympanic, and is sometimes {Diodon, Lophius, Anguilla') exclusively
suspended therefrom. In the Lophius piscatorius the opercular is a
long and strong bone suspended vertically from the convex epi-
tympanic condyle, and with a long and slender fin-ray proceeding
from the back part of that joint. The sub-opercular 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
branchiostegals. The opercular itself, though shorter and retaining
more of its laminated form, also shows plainly, by its length and
curvature 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 Mursena the small
opercular bones articulate only to the under half of the tympanic
pedicle. The sub-opercular is wanting in the Shad. The lowermost
bone, called the inter-opercular {fig. 30. 37) is articulated to the pre-
opercular above, to the sub-opercular behind, and usually to the back
part of the mandible ; it is attached, also, in the Cod by ligament to
the cerato-hyoid in front. The interopercular and preopercular
are the parts of the appendage which are most elongated in the
peculiarly lengthened head of the Fistularia.

Hyoidean Arch {fig. 30. h, ii, 38 — 43).

The third inverted arch of the skull is the ‘ hyoidean,’ and is sus-
pended, in Osseous Fishes, through the medium of the epi-tympanic
bone to the mastoid ; and I regard it as the costal or haemal arch of
the parietal segment or vertebra of the skull.* The first portion of

* Bojanus, studying the vertebral homologies of the head in the fresh-water
tortoise, deemed the cornua of the hyoid to be the last costal arch of the skull, and

THK SKULL OF OSSEOUS FISHES.

115

the arch, stylo-hrjal (pleurapophysis, in part, of the mesencephalic
vertebra, fig. 30. 38) is a slender styliform bone, which is attached
at the upper end by ligament to the inner side of the epi-tympanic, n'
close to its junction with the meso-tympanic^ and at the lower end to’-^*^
the apex of a triangular plate of bone, which forms the upper portion
of the great cornu, or hgemapophysial part of the arch. I apply to
this second piece, which is pretty constant in fishes, the name of epi-
hyal (ib. 39) ; the third longer and stronger piece is the cerato-
hyal {ib. 40).

The keystone or body of the inverted hyoid arch is formed by two
small sub-cubical bones on each side, the basi-hyals {ib. 4i). These
complete the bony arch in some fishes : in most others there Is a
median styliform ossicle, extended forwards from the basi-hyal sym-
physis into the substance of the tongue, called the glosso-hyal {ib. 42),
or ‘os linguale and another symmetrical, but usually triangular,
flattened bone, which expands as it extends backwards, in the middle
line, from the basi-hyals ; this is the uro-hyal {ib. 43). It is con-
nected with the symphysis of the coracoids, which closes below the
fourth of the cranial inverted arches, and it thus forms the isthmus
which separates below the two branchial apertures. In the Conger
the hyoidean arch is simplified by the persistent ligamentous state of
the stylo-hyal, and by the confluence of the basi-hyals with the
cerato-hyals : a long glosso-hyal is articulated to the upper part of
the ligamentous symphysis, and a long compressed uro-hyal to the
under part of the same junction of the hyoid arch. The glosso-hyal
is wanting in the Murcenophis.

The Diverging Appendage of the hyoidean arch retains the form
of simple, elongated, slender, slightly curved rays, articulated to de-
pressions in the outer and posterior margins of the epi- and cerato-
hyals : they are called ‘ branchiostegals,’ or gill-cover rays, 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
fiat 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- 30. 44). They are of enormous length in the Angler,

adds a dotted outline of it to complete Ins Vertebra occipitalis, in xxxvni. tab. xii.
Jig. 32. B 1. He had not been prepared by the normal position of the true hscnial
arch of the occiput in fishes, and by the example of the extreme displacement to
which a hajmal arch and its appendages may be subject, as in the case of the pelvis
and pelvic fin in fishes, to recognise the true hsemapophyses of the occiput in the
displaced scapular arch. Bojanus considered the “ pterygoids ” as the ribs (costce)
of the parietal vertebra (ib. p. 64.).

I 2

116

LECTURE V.

and serve to support the membrane which is developed to form a
great receptacle on each side of the head of that singular fish.

Branchial Arches.

Certain bony arches, which appertain to the system of the visceral
skeleton, succeed the hyoidean arch, with the keystone of which they
are more or less closely connected. Six of these arches are pri-
marily developed, and five usually retained ; the first four of these
supporting the gills (y%. 39. 4 ', 47), the fifth {ib.Al') beset with teeth
and guarding the opening of the gullet : this latter is termed the pha-
ryngeal arch, the rest the branchial arches.

The lower extremities of these arches adhere to the sides of a me-
dian chain of ossicles, which is continued from the posterior angle of
the basi-hyal, or from above the uro-hyal, when this is ossified : the
arches curve as they ascend ; and their upper extremities, which are
usually distinct pieces, bend inwards and almost meet beneath the
base of the cranium, to which they are attached by ligamentous
and cellular tissue.

The inferior median symmetrical piece is commonly divided into
three ossicles, (the basi-hranchials, ib. 45), following each other in a
linear series along the median line : the first rests upon the uro-hyal,
when this is present ; or it is attached to the posterior interspace of
the cerato-hyals ; the second gives attachment to the first pair of
branchial arches, and the third to the second pair of arches : the third
pair of arches is attached to the extremity of the second pair and to a
ligament continued from the third basi-branchial : the fourth pair of
arches adheres to the same ligament in the angle of the third pair :
and the pharyngeal arches, forming the fifth pair, are attached to the
angle of the fourth.

Each branchial arch, independently of the basal key-bones, consists
of three or four pieces, enjoying a certain elastic, flexible movement
on each other. The first three arches consist each of a short piece
below, the hypo-branchial {Jig. 39. 46), which, in the Halibut, sends a
ridge or process downwards and inwards beneath the basi-branchials :
next, of a long bent portion, the cerato-branchial {ib. 47), grooved on
its outer convex side ; usually supporting dentigerous processes,
tubercles, or fine plates on its concave side : and, above, of a shorter,
similarly formed piece, bent inwards and forwards, the epi-branchial
{ib. 48). To the epi-branchial of the second and third arches is com-
monly attached a shorter and broader bone beset with teeth, the
pharyngo-branchial.

The fourth arch consists of the cerato-branchial, the epi-branchial,
and the pharyngo-branchial pieces. The fifth arch {ib. 47') usually

THE SKULL OF OSSEOUS FISHES.

117

consists simply of the cerato-branchial element ; but in Anahas
supports a pliaryngo-brancliial {ih. 49). It is often expanded, and
usually more or less beset with teeth : it has been termed the inferior
pharyngeal bone {ps 'pharyngieri inferieure, Cuvier), as if it were
homologically distinct from the gill-bearing arches ; and in the same
insulated sense the upper expanded dentigerous portions of these
arches are termed by Cuvier the “ os pharyngiens superieures they
are sometimes blended together into one piece, as in the Coitus.

The peculiar cribriform or labyrinthic cavities, lined by vascular
membrane, and subservient to the continuance of respiration in
certain fishes, which can live long out of water, the Climbing Percli
(Anabas) for example, and other genera of the Order called by
Cuvier “ Pharyngiens labyrinthiformes,” are due to a peculiar deve-
lopment of the epi-branchial and pharyngo-
branchial pieces of the first, second, and some-
times the third branchial arches {Jig. 39. 48).

All these gill- and tooth-bearing arches ap-
pertain to the splanchno-skeleton, or to that
category of bones to wbich the hard jaw-like
pieces supporting the teeth of the stomach of
the Lobster belong. The branchial arches are

Branchial arch, with laby- , , ^

rintiiic ph.uyngo-branchiais sometimes Cartilaginous when the true endo-

(Anabas). ^ ^ i •

skeleton is ossified : they are never ossified in
the perenni-branchiate Batrachians, and are the first to disappear in
the larvae of the caduci-branchiate species ; and both their place and
mode of attachment to the skull demonstrate that they have no essential
homological relation to its vertebral structure. All the primitive six
pairs of branchial arches are present, but cartilaginous in the Lepi-
dosiren; and the last, which answer to the inferior pharyngeal bones
in normal Osseous Fishes, supports gills, and not teeth, whilst the
second and third arches have no gills in this remarkable fish : they
otfer a striking contrast in tissue, connections, and development with
the strong, bony, persistent hyoidean arch of the true endo-skeleton.

Scapular Arch {Jig. 30. ii, i, 50, 5i, 52).

The fourth cranial inverted arch is that which is attached to
the par-occipital ; or to the par-occipital and mastoid ; or, as in the
Cod, to the par-occipital and petrosal ; or, as in the Shad, to the
par-occipital and basi-occipital : thus either wholly or in part to the
par-apophysis of the occipital vertebra, of which it is essentially the
haemal arch ; it is usually termed the ‘ scapular arch.’ In the Eel
ti’ibe, where it is very feebly developed, and sometimes devoid of any
diverging appendage, it is loosely suspended behind the skull ; and in

I 3

118

LECTURE V.

the Plagiostorae Cartilaginous Fishes it is not directly attached to its
proper vertebra, the occiput, hut is removed further hack, where we
shall usually find it displaced in the higher Myelencephala, in order to
allow of greater freedom to the movements of the head.

The superior piece of the arch {supra-scapula, fig. 30. 50) is
bifurcate in the Cod, or consists of two short columnar hones, at-
tached anteriorly, the one to the par-occipital, 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 second piece, called “scapula'^ (id. 51) is a slender, straight,
styliform bone terminating in a point below, and morticed into a
gi’oove on the upper and outer side of the lower and principal bone
of the scapular arch. The supra-scapula and scapula together repre-
sent the rih or pleurapophysis of the occipital vertebra ; they are
always confluent in the Siluroids.

The lower bone, or hseraapophysis (coracoid, ib. 52), which completes
the arch below, is commonly termed the ‘ clavicle ’ (as by Spix, Geoffroy,
Meckel and Agassiz) ; but I am induced to regard it as homologous with
that bone, the coracoid, which progressively acquires a more constant
and larger development in descending from Mammals down to Fishes,
and which is manifestly a more essential part of the arch than the
clavicle, since it contributes more or less of the surface of attachment
for the radiated appendage, which the clavicle never does. By Cuvier
the hffimapophysial portion of the occipital inverted arch in fishes
is termed the ‘ humerus ; ’ but it is unquestionably a part of the arch,
and the most important part in the present class, in no member of
whicli does it present the slightest approach to the character of a
diverging appendage, such as the humerus essentially is, whenever it
has an independent existence. By some Ichthyotomists the bone in
question has received the special name of ‘ ccenosteon.’

Whether viewed insulated, i. e. merely ichthyotomically, or by
the light of the modifications of the sustaining arch of the pectoral
member in higher Vertebrata, the essential nature of the bone in
question was little likely to be understood : its general homology can
only be appreciated by studying its relations to the general vertebrate
skeleton in the lowest class, where vegetative repetition most prevails,
and the fundamental type is least departed from. The relation to
the primary constituent segment of the skeleton being thus ascer-
tained, the special homology of the bone is to be determined by
tracing the modifications of the scapular ai’ch in the ascending di-
rection. The serial homologies of the hscmapophyses of the scapular
arch are obviously with the cerato-hyoids, the mandible, the cartilages

THE SKULL OF OSSEOUS FISHES.

119

of the ribs, or sternal ribs, &c. The modification of the coracoids,
most characteristic of fishes, is the symphysial union of their lower
extremities, like the hasmapophyses of the maxillary and mandibular
arches, either by ligament, or dentated suture ; or, as in Plagiostomes,
by cartilaginous confluence. But this mode of closing the inverted
arch seems inevitable in a class in which a true sternum ‘ hajinal
spine’ is absent; and we shall find the same symphysis of the cora-
coids in those fish-like Reptiles, the Enaliosauria, which are now
extinct.

In the Cod-tribe the pointed upper extremity of the coracoid
{figs. 19. and 30. 52), projects behind the scapula and almost touches
the supra-scapular bone ; below this part a broad angular plate of the
coracoid projects backwards and gives attachment to the radiated
appendage of the arch : the rest of the coracoid bends inwards and
forwards, gradually decreasing to a point, which is connected by
ligament to its fellow, and to the uro-hyal bone. The inner side of
the coracoid is excavated, and its anterior margin folded imvards and
backwards ; it is continued above into the posterior angular process,
but in the rest of the coracoid it is simply bent upon the inner con-
cavity of the bone, which lodges the origin to 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 oper-
cular 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.

Like the tympano-mandibular and hyoidean arches the scapular
arch supports, in most fishes, a Diverging or radiated Appendage
on each side.

This appendage consists in Lepidosiren of a single ray : but in
Osseous Fishes it is composed usually, first, of two rarely of three
bones immediately articulated witli the coracoid ; next, of a series of
from two to six smaller bones ; which, lastly, support a series of
spines or jointed rays. These rays in the scapular appendage, or ‘ pec-
toral fin,’ are a repetition of the branchiostegal rays in the hyoidean
appendage, and of the opercular rays in the tympanic appendage.
Of the special homology of the pectoral fin-rays with the digits of
the pectoral extremity in higher animals, there has been no question.
The vegetative repetition of digits and joints, and the vegetative
sameness of form in those multiplied peripheral parts of the fins of

1 4

120

LECTURE V.

fishes, accord with the characters of all other organs on their first
introduction into the animal series. The single row of fewer ossi-
cles supporting the rays, obviously represents the double carpal series
in Mammals ; and the bones of the brachium and anti-brachium seem
in like manner to be reduced to a single series, unless the humeral
segment be confluent with the arch. In the ventral fin no segment
is developed between the arch and the digital rays: it is in this
respect like the branchiostegal fin.

The pectoral fin is directed backwards, and being applied, prone,
to the lateral surface of the trunk, the ray or digit answering to the
thumb is towards the ventral surface. The lowest of the bones sup-
porting the carpus should, therefore, be regarded as the radius
{Jigs. 19. and 30. 55), holding the position which that bone un-
questionably does in the similarly disposed pectoral fin of the
Whales and Enaliosaurs. The upper bone, which commonly affords
support to a smaller proportion of the carpal row, may be com-
pared to the ulna {ib. 54). 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 dismemberment of it. In the young Tench, however, the
humerus is a small ossicle, firmly attached to the inner surface of the
coracoid, and articulated at the other end to both the ulna and the
radius, but not reaching to the carpus. The ulna is beneath it, and
of an annular form ; the radius is much larger, and of a triangular form,
articulated by its smallest side with the humerus and ulna, by its an-
terior and outer border with the coracoid, and by its upper and hinder
border -with the carpus. 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 emarginate an-
teriorly, 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.

The radius {ib. 55) is a crescentic or sub-triangular plate with
an upper emargination completing an interosseous foramen with that
of the ulna; articulated by a small part of its upper and anterior
angle and by its produced lower and anterior angle with the coracoid,
so as to permit a slight movement, and having its upper and hinder
border equally divided between the ulna and the carpus. In the
Bull-head and Sea-scorpion ( Coitus), the radius and ulna are widely
separated, and two of tlie large square carj)al plates in their inter-
space articulate directly with the coracoid. A similar arrangement
obtains in the Gurnards and the Wolf-fish ; but the carpals in the

THE SKULL OF OSSEOUS FISHES.

121

interspace of the radius and ulna are separated from the coracoids by
a space occupied by an aponeurosis ; and in the Wolf-fish the inter-
mediate carpals are almost divided by two opposite notches. The
ulna is perforated in all these fishes. The radius is of enormous size
in the Opal (^Lampris') and in the Flying-fish ; it is anchylosed with
the coracoid in the Silurus, to give firmer support to its strong ser-
rated pectoral spine. I find both radius and ulna, which are ex-
tremely small, connate with the coracoid in a large Lopliius {fig. 40.
54, 55). This condition probably occasioned them to be overlooked
by G-eoffroy, whose figure of the bones of the pectoral extremity of
this fish* moreover represents the two long bones of the carpus,
{ib.56, 56), which he calls ‘radius’ and ‘ulna’ ujiside down.

The ossicles called carpals are usually four or five in number, as
in the Cod tribe {fig. 19. 30. 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 {MugiV). They are three in
number and elongated in the Polypterus {fig. 41. 56), but are reduced
to two in number, and more elongated in the Lopliius {fig. 40.
56) ; thus they retain in this species and in the Sharks their primi-
tive 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 Pla-
giostomes for broad and flat plates in ordinary Osseous Fishes.

The rays representing the metacarpal axvdi phalangealhon&&{fig.ZO.
40. 57) 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 movement of
the fin, like that called the ‘ feathering of an oar.’ Each soft and

Annalcs du Museum, 1807, pi. 29.

122

LECTURE V.

jointed ray splits easily into two halves as far as its base, and ap-
pears 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 “ Malacopterygians ” and “ Acan-
thopterygians in the foi’mer 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 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 enlargements of the spinal chord, and they appear
to be organs of exploration. In all the Gurnards the locomotive part
of the pectoral member is of large size ; but in one species {Dacty-
lopterus) 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 development in the true
Flying-fish {Exoco&tus).

Only in the Polypterus can any segment analogous to a metacarpus
be distinguished by modification of structure from the phalangeal
portion of the fin-rays ; there are seventeen simple cylindrical meta-
carpal bones {fig- 41. 57), the middle ones being the longest : they

are supported on two carpal bones {ib.
56), almost as remarkable for their
length as in the Lophius ; a third
shorter and broader carpal is wedged
into the interspace of the two longer

Bones of pectoral fin of Polypterus. directly joiu the

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
Salaman droid Fish in the carpal portion projecting freely from the
side of the body, as in the Lophioid Fishes. In the Lepidosiren
the diverging appendage of the scapular arch is reduced to the
condition of a single jointed ray {fig- 27. 57). From this ele-
mentary form, development may be traced in one direction, through
osseous and cartilaginous fishes, in the progressive manifestation
of irrelative repetition of parts, until the number of jointed rays
exceeds a hundred, as in the fishes thence called “Rays”; and
in another direction, through the didactyle and tridactyle Pe-
renni-branchiate Reptiles, to the perfection of the more normal
type of the anterior member in higher Vertebrata ; in each
class diverging in special dii’ections, more or less, from that

THE SKULL OF OSSEOUS FISHES.

123

common undivided embryonal bud, which is permanently typified in
the Lepidosiren. Since, howevei’, in all its modifications, the anterior
or pectoral member is essentially, in its widest homological relations,
but the diverging or radiated appendage of the hremal arch of the
occipital vertebra, we must not be surprised to find that arch retained,
as in the Synbranchi and Murmnge, where no vestige of its appendage
is developed.

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 styli-
form rib ; but in other fishes this is more frequently composed of two
pieces, as in the Perch. This single or double bone, here called
epi-coracoid {figs. 19. 40. 5s), 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 downwai’ds and backwards, and terminates freely in
the lateral mass of muscles. In its mode of attachment to the cora-
coid it resembles that of the hyoidean arch to the tympanic pedicle :
but 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 {Argy-
reiosus Vomer), the Lancet-fish {Siganus), it is joined by the lower
end to the corresponding bone of the opposite side, thus completing
an independent inverted arch, behind the scapular arch. There is
some reason, therefore, for viewing the epi-coracoids as representing
the inverted arch of the atlas, or its limmapophysial portion, and not
as parts or appendages of a cranial vertebra.

The usually free lower extremities of the epi-coracoids, together with
their taking no share in the direct support of the pectoral fin, and
their inconstant existence, oppose more strongly the view of their
special homology with the coracoids of higher Vertebrates. They
have been regarded as advanced ‘ ossa innominata’ by Carus
(xxxiv. p. 125.). To their special homology with the ‘ clavicles’ of
higher classes it has been objected that these bones are always si-
tuated in those classes in advance of the coracoids ; but this inverted
position may be a consequence of the backward displacement of the
scapulo-coracoid arch in the air-breathing Vertebrata ; and if, not-
withstanding such displacement, we are able to discern the general
homological relations of that arch as the hmmal one of tlie occipital
vertebra, we may, in like manner, discern in the clavicle a less dis-
placed haemal arch of the atlantal vertebra.

The epi-coracoids are eitlier absent or are very slender spines in
the Wolf-fish {Anarhichas), the Mullet, the Goby, the Stickleback,

124

LECTURE V.

the Remora, the Ribhand-fish {Cepola), the Uranoscopus scaber, the
Blennies, the Siluroids, and the Apodal Fishes, with the exception of
the Sand-lance, which differs from the Eels in having the epi-coracoids.

That they belong to the system of hsemal or inferior vertebrate
arches, and make a transition from the enormously developed arch of
the occipital to the ordinary costal arches of the second and sub-
sequent abdominal vertebrse, is indicated by their functions arising
out of their muscular attachments. In the Carp two ‘ musculi quad-
rat!,’ arising from the coracoid, are inserted into the epi-coracoid ; one
entirely, the other partially, and this latter is continued backwards,
to be similai’ly implanted into the rib of the second abdominal ver-
tebra; similar but more delicate muscular bands, degenerating into
aponeuroses, pass to the succeeding ribs, which are thus drawn
forward by the protraction of the epi-coracoids, or haemapophyses of
the atlas. By this action an effect analogous to the expansion of the
thorax in Mammalia is produced, the air-bladder being permitted to
dilate by the augmented capacity of the abdomen.

As the terminal segment (hand or foot) of a locomotive member is
the essential part, or the great aim, so to speak, of the development of
such radiated appendage, it is the first part to appear and the last to
disappear. It exists without intermediate segment in the ventral fins
of all fishes, and in the pectorals of some, e. g. the Rays, and
the Lepidosiren {fig- 27.) : in others there may be a carpal seg-
ment, as in the Lophius {fig. 40. 56), the antibrachial segment being
confluent with the arch : in most fishes both a carpal (56) and an anti-
brachial segment exist, as in the Cod {fig. 19. 54, 55) ; in Polypterus
a metacarpus makes its appearance : but in none is there a distinct
brachial segment or humerus, interposed between the anti-brachium
and the arch ; it is at best represented by some small, supplemental
third bone manifesting that relation very dubiously.

The special homology of the pectoral fins of fishes with the fore
limbs of quadrupeds was indicated by Aristotle, and first definitely
pointed out in later times by Artedi, in 1735, who says, — “ Ossa pec-
toris et ventris in piscibus reperiuntur ; suntque in piscibus spinosis :
1. Claviculffi ; 2. Sternum; 3. Scapulae, seu ossa quibus pinnae pec-
torales ad radicem affiguntur.” {Partes Piscium, p. 39.) Geoffroy St.
Hilaire, who has devoted special Memoirs to the determination of the
bones of the pectoral fin, had no knowledge of the primary homology
of the pectoral fin as the radiated appendage of the inferior arch of a
cranial vertebra, or of its serial homology with the branchiostegal and
opercular fins. He consequently speaks of the junction of the basis
of the fin to the cranium as something very strange : — “ Disposition

THE SKULL OF OSSEOUS FISHES.

125

veritablement tres singuliere, et que le manque absolu de cou, et une
combinaison des pieces du sternum avec celles de la tete pouvoient
seuls rendre possible.” (^Armales du Bluseum, ix. p. 361.)

Oken’s latest idea of the essential nature of 'the arms and legs is,
that they are no other than ‘liberated ribs:’ “ Freye Bewegungs-
organe konnen nichts anderes als frey gewordene Eippen seyn.”
(^Lehrbuch der Natur Philosophie, p. 330. 8vo. 1843.)

Carus (L), in his ingenious endeavours to gain a view of the primary
homologies of the locomotive members, sees in their several joints
repetitions of vertebral (^tertiar-wirbel) — vertebrae of the third

degree — a result of an ultimate analysis of a skeleton pushed to the
extent of the term ‘ vertebra ’ being made to signify little more than
what an ordinary anatomist would call a ‘ bone.’

But these transcendental analyses sublimate all differences, and de-
finite knowledge of a part escapes through the unwarrantable exten-
sion of the meaning of terms. We have seen, however, that a ver-
tebra is a natural group of bones, that it may be recognised as a pri-
mary division or segment of the endo-skeleton, and that the parts
of that group are definable and recognisable under all their teleolo-
gical modifications, their essential relations and characters appearing
through every adaptive mask.

According to the definition of which a vertebra has seemed to me
to be susceptible, we recognise the centrum, the upper (neural) arch,
the lower (luemal) arch, and the appendages, diverging or radia-
ting from the hiemal arch. The centrum, though the basis, is not less a
part of a vertebra, than are the neurapophyses, hsemapophyses, pleu-
rapophyses, &c. ; and each of these parts is a different part from the
other : to call all these parts ‘ vertebraB ’ is in effect to deny their dif-
ferential and subordinate characters, and to voluntarily abdicate the
power of appreciating and expressing them. The terms ‘secondary’
or ‘ tertiary vertebras ’ cannot, therefore, be correctly applied to the
appendages of that natural segment of the endo-skeleton to which the
term ‘ vei’tebra ’ ought to be restricted.

So likewise the term ‘ rib ’ may be given to each moiety of the
haemal arch of a vertebra ; although I would restrict it to that part
of such arch to which the term ‘ vertebral rib ’ is applied in Com-
parative Anatomy and the term ‘ pars ossea cost® ’ in Anthropotomy :
but, admitting the wider application of the term ‘ rib ’ to the whole
haemal arch, yet the bony diverging and backward projecting appen-
dage of such rib or arch is something different from the part support-
ing it. Arms and legs may be developments of costal appendages,
but cannot be ribs themselves liberated : although liberated ribs may
perform analogous functions, as in the Serpents and Dragons.

126

LKCTURE V.

A series of developments may be traced from tbe primitive form of
the appendage, as a simple plate, spine, or ray, through the many-
jointed single ray in the Lepidosiren and the bifurcate jointed ray in
the Ampiduma didactylum, up to the wing of the Bird and the arm
of the Man, without the essential nature of the part being lost sight
of ; for all these forms of the pectoral member are, in their ultimate
or general homology, ‘diverging’ or ‘radiated appendages’ of a
hcEinal arch ; but not ‘ ribs,’ nor ‘ vertebrae.’ We may further define
the fore-limb, wing, or pectoral fin to be the radiated appendage of
the arch called ‘ scapular,’ and this to be the ‘ haemal arch of the occi-
pital vertebra.’

There remain to complete the analysis of the skeleton of the Cod,
here taken as a type of Osseous Fishes, the bones of the ventral pair
of fins and the cranial parts of the dermal skeleton. The rays of
the ventral fin are supported by two bones, which represent the
lower portion of an imperfect inverted or haemal arch ; each bone is
a sub-triangular bifurcate plate in the Cod tribe, with its apex an-
terior and superior, joined by ligament to the same part of the cor-
responding bone, and suspended beneath the coracoid arch. To the
outer part of the base of each suspending bone the rays of the ventral
fin are attached without the intermedium of any series of short
ossicles ; in fact, the representatives of tarsal, tibial, and femoral
bones are wanting in all fishes, and the lower half of the pelvic arch,
{ovt\\Q pubic hones, Jig. 19. 63), and the peripheral and essential parts
of the fin, the metatarso-phalangeal rays {ib. 7o), alone repi’e-

sent the hinder or lower locomotive member in fishes. In Acan-
thopterygian Fishes one or more of the anterior rays of the ventral fin
may be hard unjointed spines, as in the other fins ; in the Malacopte-
rygians all the ventral rays are soft, multi-articulate, 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 development of the embryo fish, as a little
bud attached to the skin of the belly, and from the fact that all the

* Ichthyologists avail themselves of the number and kind of rays in the several
single and parial fins to characterise the species of fishes, and adopt an abbreviated
formula to express those characters : thus Mr. Yarrell (xxxix. i. p. 4.) uses the fol-
lowing with reference to the Perch: — n. 15, 1 + 13: p. 14: v. 1+5: a. 2 + 8;
c. 17 : which signifies that d., the dorsal fin, has in the first fin 15 rays, all spinous ;
in the second fin, 1 spinous + (plus) 13 rays that are soft, p., the pectoral fin, 14
rays, all soft, v., the ventral fin, with 1 spinous ray + 5 that are soft, a., the
anal fin, with 2 spinous rays + 8 that are soft, c., the caudal fin, 17 rays. The
formula of the fin-rays in the tiaddock is : n. 15, 21, 19 : p. 18 : v. 6 : A. 24, 18 :
c. 44. : i. e. all the rays are soft, and there are 15 rays in the first dorsal, 21 in the
second dorsal, and 19 in the third dorsal ; 18 raj's in the pectoral fin ; 6 rays in the
ventral fin ; 24 rays in the first anal, and 18 in the second anal fins ; and 44 rays
in the caudal fin.

THE SKULL OF OSSEOUS FISHES.

127

fishes in the geological formations anterior to the chalk are abdominal,
that is, have the ventral fins near the posterior end of the abdomen*,
we may conclude that the supporting bones are, essentially, the lim-
mapophyses of the last rib-bearing (or pelvic) abdominal vertebra ;
and that the rays are the diverging appendage, but are attached,
like the branchiostegal rays of the hyoidean (parietal hmmal) arch,
without the intervention of fewer short and broad bones, homo-
logous with femoral, tibial, tarsal bones, &c. The iKemapophysial
portion (pubis) of the pelvic arch is never joined to the pleu-
rapophysial portion (ilium) of the same arch in fishes ; but is
suspended more or less freely to other parts, always projecting from
the under or ventral part of the body, but subject to great diversity
of position in relation to the two extremes of the abdomen. On these
differences Linnasus based his primary classification of fishes : he
united together, for example, those fishes which have the pelvic or
ventral fins near the anus, to form the order called “ Pisces Ahdo-
minales-^ those with the ventral fins beneath the pectorals, into an
order called Pisces Thoracici;' and those with the ventrals in ad-
vance of the pectorals, into an order called “ Pisces Jugulares
lastly, those fishes in which the ventral fins are absent formed the
order called “ Pisces Apodes.” And by this name it will be ob-
served that Linmeus recognised the special homology of the radiated
appendages of the pelvic arch of fishes with the hinder or lower
extremities of the higher classes of animals.

In the Angler (Lopliius piscatorius') each pelvic bone is attached to
the under and near the fore part of the long coracoid, expands at the
opposite end, and bends inwards to meet its fellow at a kind of sym-
physis pubis ; the fin, supported by six rays with expanded imbricated
bases, diverges from the angle ; and the suspending branch above this
seems to represent an iliac bone. The pubic bones are detached from
the coracoid arch in Abdominal Fishes ; the Thoracic character de-
pends upon the peculiar length of those bones, which carries back the
ventral fins to beneath the pectorals. As the ventral fins are always the
last to be developed in the embryo abdominal, thoracic, and jugular
fishes, so the apodals may be regarded as analogous to permanent em-
bryo forms of these fishes, in which development has been arrested be-
forearriving at the abdominal stage, and growth has proceeded, in most
cases, to excess in the linear direction ; as is exemplified in the Eel
tribe, where vegetative repetition of a vast number of incomiilete
vertebrae has taken the place of the perfection of part of a fewer
number of vertebrae.

* Ag.issiz, Hist, des Poissons, t. i. p. 105.

128

LECTURE V.

There are neither pectoral nor ventral fins in the Cyclostomous
Fishes. In the Plagiostomes there are both : but the scapular arch is
detached from the occiput, the condition of its displacement being
the more posterior position of the heart in these fishes. In the Sharks
and ChimEerse it is loosely suspended by ligaments from the vertebral
column : in the Eays the point of resistance of their enormous
pectoral fins has a firmer, but somewhat anomalous attachment, by the
medium of the coalesced upper ends of the supra-scapular pieces to
the summits of the spines of the confluent anterior portion of the
thoracic abdominal vertebrje. In the Sharks the scapular arch con-
sists chiefly of the coracoid portions 42. 52), which are confluent
together beneath the pericardium which they support and defend ;
the scapular ends of the arch, connected to the coracoids by ligament,
project freely upwards, backwards, and outwards. To a posterior
prominence of the coracoid cartilage corresponding with the anchy-
losed 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 cartilages, the uppermost {ih. 56) the smallest, and
styliform ; it supports the upper or outer phalangeal ray. The
next bone {ib. 56') is the largest and triangular, attached by its
apex to the arch, and supporting by its base the majority of the
phalanges.

Cartilages of the pectoral fin and arch of the Dog-fish {Spinax aconthias)^

The third carpal {ib. 56") is a smaller but triangular cartilage, and
supports six of the lower or radial phalanges. Three joints (meta-
carpal and digital) complete each cartilaginous ray or representative
of the finger (ib. 57) ; and into the outer surface of the last are in-
serted the fine horny rays or filaments (ib. 57"), the homologues of

THE SKULL OF OSSEOUS FISHES.

129

the claws and nails of higher Vertebrata, but which on their first ap-
pearance, in the present highly organised class of fishes, manifest,
like other newly introduced organs, the principle of vegetative repe-
tition, there being three or four horny filaments to each cartilaginous
ungual phalanx.

On the fore part of the coracoid arch, near to the prominence suji-
porting the fin, there are developed a vertical series of small bony
cylindrical nuclei in the substance of the cartilage in most Sharks.
In the Hays 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 homo-
logous with the three above described in the Shark, and which imme-
diately sustain the fin-rays. The posterior cartilage answering to
the upper one in the Shark curves backwards and reaches the ventral
fin : the anterior cartilage curves forwards, and its extremity is joined
by the ant-orbital 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 ap-
proach the extremities of those cartilages. In the common Ray there
are upwards of a hundred metacarpo-phalangeal rays in each great
pectoral fin. The longest rays begin after the tenth or eleventh joint
to bifurcate ; the shorter ones bifurcate progressively nearer their
origin.

The ventral fin is better developed in the Plagiostomes than in
any other fishes. The supporting arch consists indeed of the same
simple pubic elements, united together by ligament in 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 end of each pubis ; the anterior is
the shortest in the Dog-fish, and supports three or four rays ; the pos-
terior one is much longer, and supports the remainder of tlie rays,
fifteen or sixteen in number. To the end of this cartilage likewise
is attached, in the male Plagiostomes and Chima3ra3, the peculiar ac-
cessary generative organ or clasper.

In the Torpedo the pubic arch sends forwards two processes like
marsupial bones; these processes are longer in an extinct Ray to
which its discoverer Sir P. de M. Grey Egerton has given the name
of Cyclohates oligodactylus (xL. p. 225. pi. 5.).

VOL. II. ic

130

LECTURE VI.

LECTUEE VI.

DEEMAL BONES AND TELEOLOGY OF THE SKELETON OF

FISHES.

The Sturgeon is one of the transitional steps from the Cartilaginous
to the Osseous Fishes ; but as its skeleton more especially elucidates
those bones of the Osseous Fishes which have been superadded to the
proper cranial and other bones of the endo-skeleton to form the dermal
system or exo-skeleton, I have deferred a notice of it to this place.
All the parts of the skull of the Sturgeon which belong to the endo-
skeleton are, with the exception of the appended arches, one con-
tinuous mass of cartilage, which is defended by a crust of shagreeiied,
ganoid bones of the dermal system. It seems, as Agassiz well says,
as if the space between the outer bony crust and the cerebral mem-
branes within had formed a mould into which the liquid gristle had
been thrown at a single jet, and there hardened. There is no
membranous fontanelle in this cartilaginous cranium. The base of
the skull shows the embryonic character of the prolongation of the
pointed end of the ‘ chorda dorsalis’ as far forwards as the pituitary
depression, which is persistent in the Sturgeons. The occipito-
sphenoidal cartilaginous plate is developed around the ‘ chorda,’ and
extends upon the base and sides of the skull, whence it is continued
backwards, without an intervening joint, into the cartilage of the co-
alesced anterior vertebrze of the trunk. The upper surface of the
cartilaginous skull is gently convex ; it extends outwards at its
middle part between the large orbital and branchial cavities, and
to the under part of this prominence the tympanic pedicle is articu-
lated. The cartilaginous cranial mass contracts in front of the orbits,
is deeply excavated on each side for the nasal cavities, and thence is
continued forwards into a rostral process, which gradually tapers to
a more or less obtuse point. A thin continuous crust of bone covers
the lower surface of the occipito-sphenoidal cartilage, except at the
middle line, beneath the cranial end of the chorda, where we saw the
cartilage arrested in the Cestracion ; this crust extends backwards
into the cervical region. The pituitary sella pierces the basal cartilage,
but not the subjacent osseous crust. This crust seems analogous to
the basi-sphenoid plate in the Lepidosiren ; but its extension upon the
neck, the absence of the articular concavity, and the persistence of the

DERMAL BONES OF FISHES.

131

cartilaginous basis of the skull oppose the view of its homology with
the basal elements of the cranial vertebrte. With regard to the
upper and lateral osseous plates of the head, they are, as Von Baer
has indicated (m.), the continuation of the series of dermal osseous
plates upon the upper mid-line and sides of the trunk.

Before, however, applying this instructive condition of the cranium
of the Sturgeon to the elucidation of the nature and homologies of
the bones which still remain to be noticed in the skull of the Cod, I
shall briefly describe the maxillary, mandibular, hyoid, and scapular
haemal arches of the coalesced cranial vertebrae of the Sturgeon.
The first three of these ai’ches are suspended from the tympanic
pedicle ; but this, instead of being a single piece, as in the Plagiostomos
and Lepidosiren, consists of three cartilages, articulated in Accipenser
Ruthenus, according to Muller, by a small accessory or interarticular
cartilage, with the under part of the mastoid process. The three
principal bones describe a semicircle, concave forwards, and answer
respectively to the epi-tympanic {Jig. 43. 25), the meso-tympanic {ib,
26), and hypo-tympanic {ib. 28) bones of Osseous Fishes,

The upper jaw, or maxillary arch of Plagiostomes and Lepidosiren,
is represented in the Sturgeon by a partly osseous, partly cartila-
ginous, broad arch, in which the centres of ossification have been
three in number on each side, and indicate both by their relative
position, and by the direction in, and extent to, which the bony
fibres have diverged from them, the pre-maxillary, maxillary, and
palatal bones of the Osseous Fishes. The pi-e-maxillaries {ib. 22)
form the anterior and inferior border of the arch : each bone is a
sub-triangular plate, joined by ligament to its fellow at the middle
line, trenchant anteriorly, contracted and thickened posteriorly,
whence it rises and extends in the form of an arched process, out-
wards and downwards to the outer side of the joint for the lower

K 2

132

LECTUKE VI.

jaw. This process corresponds with the outward and downward
prolongation of the transversely developed pre-maxillary in Osseous
Fishes.

The maxillary bone {ih. 21) is a small and simple oblong plate,
articulated to the under part of the base of the outer process of the
pre-maxillary, and attached by the whole of its inner and posterior
side to the palatine. Only the gradual transmutation of the similarly
insignificant ‘ os mystaceum ’ in the Osseous Fishes to its higher
form and functions in the Salmonoid and Salamandroid species, could
have made the homology of this separate bone appreciable in the
Sturgeon.

The os palati {ih. 20) articulates by its anterior angle with both
maxillary and pre-maxillary ; expands posteriorly in one direction
towards the median line, along wliich a slender pointed process is
directed forwards ; and in the opposite direction outwards and
downwards to the inner side of the cartilaginous joint of the lower
jaw ; like the pterygoid extension of the same part of the arch in the
Lepidosiren. A slender ossicle {ih. 74) extends along the outer
side of the cartilaginous joint, from the end of the premaxillary
process to the posterior ridge of the palatine bone ; homologous
with the angulo-labial cartilage in the Squatina. In the cartilagi-
nous interspace between the anterior notch of the palatines and the
premaxillary synchondrosis, I have found a small separate ossification
in a very large and old Accipenser Sturio.

The roof of the mouth is extended posteriorly by three cartilagi-
nous plates : one single {ih. 20 a) and extending backwards, from the
posterior interspace of the palatines ; this seems to be the homologue
of the two median cartilages, called ‘ palatal ’ by Dr. Henle, on the
roof of the broader mouth of the Narcine* : the two outer cartila"es

O

correspond with those called ‘ pterygoid ’ by the same author in the
same Brazilian Torpedo, f

The lower jaw {ih. 32), vrhich is joined by a concavity to the
trochlear cartilage supported by the pterygoid process of the palatine
and the premaxillary, consists principally of a single bony ramus on
each side, joined by ligament to its fellow at the symphysis, with a
posterior excavation filled by cartilage, in which there is a small
detached ossification in the old Accipenser Sturio above adverted
to. J

The whole of the above apparatus of the jaws is suspended to

* Miillev’s Myxinoiden, tab. v. fig. 3 and 4. e e. -j- lb. d d.

f The bones and gristles of the Sturgeon’s mouth are well described by J.
Miiller (xxi.); but ichthyotomlcally, i. e. without determination of homologies, and
accordingly under special names.

DERMAL BONES OF FISUES.

133

the hypo-tympanics (ib. 28), which are attached principally to the
pterygoid processes and the back part of the cartilaginous joint
of the lower jaw. The mouth of the Sturgeon opens, as in Sharks,
upon the under surface of the head, and is protruded and retracted
chiefly by the movements of the tympanic pedicle, which swings,
like a pendulum, from its point of suspension to the post-orbital
process.

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 {ib. 4o) of thrice the length, is expanded
above, and is attached by ligament extending from that part to near
the joint of the lower jaw. The basi-hyal is a short sub-cubical piece :
it gives attachment anteriorly to cerato-hyals, and posteriorly to the
anterior basi-branchial and hypo-branchial cartilages.

The three first branchial arches consist of hypo-branchials, pro-
gressively decreasing in size, of cerato-branchials, epi-branchials, and
pharyngo-branchials : the fourth arch consists of cerato-branchials
and epi-branchials : the fifth arch of cerato-branchials only.

In an old Accipenser Sturio I found the tympanic pedicle in two
pieces, and partly ossified. The epi-tympanic was cartilaginous
where it articulated with the post-frontal and mastoid, the osseous
part commencing at a definite transverse plane. This, as it de-
scended, expanded, and reverted to the cartilaginous state, forming a
broad triangular flattened plate, which supported the large opercular
dermal bone ; the hypo-tympanic was a simple strong cylindrical car-
tilage, giving attachment to the hyoid near its upper end, and to the
ligaments suspending the palatine and mandibular arches at its lower
end.

The cartilaginous representation of the par-occipital projects
boldly backwards from each angle of the occiput. A triangular
supra-scapular cartilage {ib. 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 sca-
pulo-coracoid arch {ib. 51, 52), which is completed below, as in Lepi-
dosiren, by ligamentous union, not, as in Sharks, by cartilaginous
confluence. The scapulo-coracoid cartilage expands as it descends,
sends inwards and forwards 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 below l)y sending inwards and
forwards a broad and thin plate beneath tlie pericardium, which is
joined by strong aponeurosis to tliat of the opposite coracoid. There

134

LECTURE VI.

are no separate homologues in the Sturgeon’s fin of the bones called
ulna and radius in Osseous Fishes : the carpal bones (ib. 56) imme *
diately articulate with the coracoid, and support about thirty rays
{ib. 57), two or three of which seem to have coalesced to form the
strong bony spine {ib. 57') on the outer border of the fin.

The ventral fins are small and are suspended each by a simple
cartilaginous pubis to the abdominal muscles a little in advance of
the anus.

The osseous scales on the upper surface of the skull are so ar-
ranged as, at first sight, to suggest certain analogies with the epi-
cranial bones. Thus, the scale marked a {ib. d 3) in Brandt and
Batzeburgh’s figure of the head of the Accipenser Sturio* might
be comjiared with the supra-occipital bone ; the pair in advance
{ib. d 7), marked e (loc. cit.), with the parietals ; and the pair {d 11)
marked g (loc. cit.), with the frontals ; but then these are sepa-
rated by an interfrontal osseous plate, and in Accipenser Scypha by
two or three such plates ; the supra-occipital plate is divided in the
A. brevirostris and in the A. sturio of Pallas j", and other varieties
occur which render the attempt to illustrate the homology of the
true epicranial bones in Osseous Fishes by these dermal ganoid plates
in the Sturgeons difficult and unsatisfactory. The median plates are
more obviously and essentially a continuation forwards of the dermal
spinous plates {ib. ds), from the mid-line of the back ; and we may
see their more veritable repetition amongst the Osseous Fishes in the
dermal epicranial spines, for example, of the Angler {Lophius), which
support the long fishing filaments upon the head, or in those modified
ones forming the sucking disk on the head of the Remora. Tliey are
more obviously homologous with the dermal bones forming the helmet
of the Armadillo, and bear the same relation in the Sturgeon to the
cartilaginous skull as those bones do in the Armadillo to the osseous
skull beneath.

The lateral series of dermal bony plates {ib. dp) are also con-
tinued upon the head, and seem to represent in the Sturgeons the
supra-scapular {ib. d 50) and the opercular bones {d 35) in osseous
Fishes. Other constant series of cranial scale-bones, in the Sturgeon,
circumscribe the orbits below and the temporal spaces above. But
before applying the well-contrasted states of the endo- and exo-
skeleton of the Sturgeon to the determination of the bones of the
skull in the Cod, I may advert to the reversed conditions of the endo-
and exo-skeletons in the Lepidosiren, which lends another valuable
aid in the solution of this difficult and much discussed subject. The

* Medizin Zoologie, band. ii. tab. iii.

f Fauna llosso- Asiatica, iii. p. 91.

DERMAL BONES OF PISHES.

135

supra-cranial movable plates {fig. 27. 12) are the only bones of the
head of the Lepidosiren which can be referred, with any probability,
to the dermal system. It is plain that the subjacent epicranial plate
{fig. 27. 11) in close connection with the cartilage of the cranium, is
a true part of the endo-skeleton, and is as certainly the homologue
of the mid-frontal, parietal, and supra-occipital bones. In the de-
velopment of the skull of Osseous Fishes it is found, however, tliat,
whilst the central or basilar, the neurapophysial, and the parapophy-
sial elements of the cranial vertebrie are developed out of a pre-
existing cartilaginous basis, the modified spinous elements, with the
exception of that of the occipital vertebra, are formed by the depo-
sition of the calcareous salts in the epicranial membrane ; and Dr.
Reichert, apparently not remembering that the cartilaginous, or in-
termediate histological, change between the primitive membranous
and ultimate osseous stage has been as little recognised in the de-
velopment of the epicranial bones of Man, would reject the parietal
and frontal bones from the system of the endo-skeleton.

To those who may be inclined to support this view, by reference
to the epicranial dermal plates in the species of Sturgeon where their
correspondence with the mid-frontal and parietal bones may be most
easily recognised, it may be replied, that the pre-frontals, post-
frontals, mastoids, and supra-occipitals, might also be referred to the
exo-skeleton, by a like reference to dermal plates holding the corre-
sponding positions in the Sturgeon’s head : but the skeleton of the
Lepidosiren, with the known relations of the pre-frontals, post-fron-
tals, mastoids, and supra-occipitals to the primitive cartilaginous basis
of the skull in Osseous Fishes, demonstrate the fallacy of the conclu-
sions as to the dermal origin of the frontals and parietals, based upon
the deceptive analogies of the dermo-cranial plates in the Sturgeon,
and upon the absence or brief duration of the cartilaginous stage in
the ossification of certain expanded spines of the cranial vertebrae.
That the homologues of some of the dermal plates in the Sturgeon
are retained in the skull of Osseous Fishes is, however, rendered
extremely probable by the constancy of their relative position, by
their development in a dermal basis, and by their relation to the
dermal mucous canals.

The accessary bones of the skull in Osseous Fishes, which I regard,
on the above grounds, as appertaining to the exo-skeleton, and which
are more especially connected with the mucous organs of the skin,
are the sub-orhital, the supra-orbital, and the swpra-temporal
ossicles. The first sub-orbital bone {fig. 19. 73) is always the
largest : it is triangular in the Cod, and covers the side of the muzzle,
extending from the fore part of the orbit to the anterior end of

K 4

136

LECTURE VI.

the turbinate bone, to which it is attached by ligament, and it
is articulated by its upper and posterior angle with the pre-
frontal : from its position it might be termed the pre-orbital bone.
The second sub-orbital, a much smaller and sub-quadrate bone, is
attached to the lower and posterior angle of the first ; and the rest,
four in number, of similar form, and gradually smaller in size, com-
plete the chain extending to the post-orbital angle of the os frontis.
There are no supra-orbitals in the Cod : the Carp has a single one on
each side ; the Lepidosteus has three supra-orbitals, which quite
exclude the frontal from entering into the formation of the orbit.
The supra-temporal scale bones are three in number on each side in
the Cod, extending backwards from the outer and hinder part of the
mastoid : they are very thin, transparent scales, folded on themselves
to form a prolongation of the mucous channel, which extends from
above the mastoid and frontal bones. The large pre-orbital scale-
bone is similarly folded upon itself, from above downwards, forming
a mucous channel, extending from the orbit to the nasal sac, and
analogous to the muco-lachrymal groove and canal in the lachrymal
bone of higher Vertebrata, which always presents a similar position
and connections. The smaller sub-orbitals are subservient, chiefly,
to the formation of similar mucous ducts, which are completed in
these, as in the supra-temporals, by aponeurotic processes of the
corium, and are lined by mucous membrane continued from many
small and numerous excretory pores on the outer surface of the
skin, and forming, in the Cod, ramified secreting follicles in the in-
terior of the bony canals. The bony canals themselves are ramified
in the corresponding dermal ossicles of the Herring. The turbinate
bones, from their intimate relation with the olfactory sacs, appertain
by their form and structure to the same category as the sub-orbitals,
and are, with the anterior of these mucigerous ossicles, the only hones
of the dermal system constantly retained in the higher Vertebrata,
even to Man, under the names of ‘ lachrymal’ and ‘ spongy’ bones. The
turbinate bones are very small in the Conger ; and both these and the
sub-orbital bones are wanting in the rest of the Eel tribe. The sub-
orbital bones present their maximum of development in the Mailed-
cheeked ( Trigld) and Sciajnoid Fishes ; in the Star-gazer ( Urano-
scopus) and the Lepidoleprus : in the Scicena gangetica they extend
over the tympanic pedicle almost to the pre-opercular, and have a
bold reticulate exterior, like that bone, the mastoid, and the supra-
scapular bone.

In the skull of the Cod you may observe many bones which send a
scale-like process from their outer surface, which process forms a more
or less complete canal for the ducts of mucous glands. The frontal, the

DERMAL BONES OF FISHES.

i37

parietal, the mastoid, and the pre-opercular, as well as the turbinate,
the sub- orbital, and the supra-temporal bones, offer this modification
of their outer surface. The same correspondence in the pattern of
the exterior markings usually prevails in all these bones, and is very
conspicuous in some fishes ; as in the bold net-work and deep depres-
sions of the sui’face, observable in the Pristipoma and some Sciasnoids ;
and in the entirely exposed, enamelled, and shagreened surface of
the same bones, together with the maxillary arches, in the Polypterus.
This correspondence of exterior character, though it diminishes the
contrast between the endo- and exo-skeleton bones of the skull, does
not destroy their distinction. In certain parts of fishes the endo- and
exo-skeletons are so connected together that we can scarcely find the
boundary line in nature ; yet the advantage to the Osteologist of
classifying the multiform subjects of his study according to their
typical characters must not, therefore, be abandoned.

Guided by the skull of the Lepidosiren, and by the light of tlie
general homology of the opercular bones as diverging appendages of
the tympano-mandibular arch, I consider the pre-opercular, sub-
opercular, and inter-opercular bones to be parts of the endo-skeleton.
The opercular bone is very constantly represented by the largo
dermal plate in the Sturgeon, which M. Agassiz regards as being, with
the supra-scapular dermal plate, an anterior continuation of the
lateral series of dermal scales. There is also a small dermal plate
upon the opercular flap, below the large opercular plate, and which
small plate might be regarded as the homologue of the sub-opercular
bone. All the four opercular bones forming the diverging appendage
of the tympano-mandibular arch w'ere deemed by Cuvier to be
peculiar ichthyic super-additions to the ordinary vertebrate
skeleton ; whilst by Spix, Geoffroy, and De Blainville they are
held to be modifications of parts which exist in the endo-skeleton of
other Vertebrata. The learned Professor of Comparative Anatomy in
King’s College, who regards this as “ the more philosophical mode of
considering them,” * has briefly stated the homologies proposed by
the supporters of this view, viz. that the opereular bones are gi-
gantic representatives of the ossieles of the ear (Spix, Geoffroy,
Dr. Grant j") : or that they are dismemberments of the lower jaw
(De Blainville, Bojanus), — a view refuted by the discovery of
the complicated structure of the lower jaw in certain fishes, e. y.
Sudis, {fig- 38.), which likewise possess the opercular bones : thirdly,
that they are parts of the dermal skeleton ; in short, scales modified

* Professor Rynier Jones, General Outline of the Animal Kingdom, 8vo. 18-11,
p. 509.

f Lectures, Lancet, Jan. 11. 1831, p. 573.; Outlines of Comp. Anat. p. C4.

138

LECTURE VI.

in subserviency to the breathing function ; an opinion which Professor
Jones acknowledges that he derived from my Lectures on Compara-
tive Anatomy, delivered at St. Bartholomew’s Hospital in 1835, and
which he adopts. I have subsequently seen reason to modify that
view, although it has received the sanction of the greatest Ichthyo-
logist of the present day, M. Agassiz ; and although I find that, so
early as 1826, it had presented itself under a peculiar aspect to the
philosophical mind of Von Baer. In his admirable paper on the
endo- and exo-skeleton he expresses his opinion, that the opercular
bones are (dermal) ribs or lateral portions of the external cincture of
the head. * The idea of the relationship of the opercular flaps to
locomotive organs is presented by Carus, under the fanciful view of
their homology with the wing-covers of beetles and the valves of a
bivalve shell (i. p. 122.). In 1836, M. Agassiz propounded his idea
of the relation of the opercular bones to scales in a very precise and
definite manner ; though, as I shall presently show, the chief ground
of his opinion is erroneous. He says, — “ Les pieces operculaires des
poissons ne croissent pas, comme les os des vertebres en general, par
irradiation d’un ou de plusieurs points d’ossification ; ce sont, au con-
traire, des veritables ecailles, formees, comme celles qui recouvrent le
tronc, de lames deposees successivement les unes sous les autres, et
dont les bords sont souvent meme denteles comme ceux des ecailles
du corps. Tels sont I’opercule, le sub-opercule, et I’inter-opercule. Le
supra-scapulaire meme peut-etre envisage comme la premiere ecaille
de la ligne laterale, dont le bord est egalement dentele. On pourrait

* “ In mancber Beziehiing gehbren die Kiemendeckel zu ihr, iind ich halte sie
um so mehr fiir (Haut) Rippen, d. h. fiir Seitentheile der aussern Ringe des Kopfes,
da ich sie auch in den gewohnlichen Knockenfischen fiir nichts anderes ansehen
kann. Hat bei diesen auch der oberste Knochen des Kiemendeckels wenig Aehn-
lichkeit mit Rippen, so geht dagegen der unterste so unverkennbar in die strahlen-
der Kiemenhaut iiber, das der Uebergang gar nicht zu verkennen ist. ” (^Mechel's
Archiv. 1826, 3 heft, p. 369.)

An analogous idea of the relation of the opercular bones to the inferior or costal
arches is expressed by the learned Professor of Comparative Anatomy in University
College, who, speaking of the occipital vertebrae, says — “The two external and
the two lateral occipitals form the upper arch, and the two opercular and two sub-
opercular bones constitute the lower arch.” (Lectures, Lancet, 1834, p. 523.) He
subsequently, however, adopts and illustrates (p. 573.) the homology of the oper-
cular bones with the “ ossicula auditus ” of Mammalia ; and in the “ Outlines ”
(xxvin.) cites only the Spixian and Blainvillian hypotheses (pp. 64, 65.). I have
adduced the grounds which have led me to the conclusion that the opercular bones
are neither ribs of the exo-skeleton, nor inferior arches of the endo-skeleton, but
persistent radiating appendages of an inferior (haamal) arch ; not, however, of the
occipital vertebra, but of the frontal ; just as the branchiostegal rays are the ap-
pendages of the haemal arch of the parietal, and the pectoral fins of that of the
occipital vertebrae. That parts of both endo- and exo-skeleton may combine to
constitute the opercular fin is the more probable, inasmuch as we see the same com-
bination of cartilaginous and dermal rays in the pectoral fins of the Plagiostoines,
and in the median fins of most Fishes.

DEEMAL BONES OF FISHES.

139

dire aussi que le scapulaire n’est qu’une tres grande ecallle de la
partie anterieure des flancs” (xxii. livraison 6me, 1836, tom. iv.
p. 69.). And he adds, “L’opinion que j’ai emise a leur egard prouve
que je suis loin d’admettre les rapports que Ton a cru trouver entre
les pieces operculaires et les osselets de I’oreille interne” {lb. p. 73.).

I apprehend that the idea of the development of the opercular
bones by the successive excretion or deposition of layers, one beneath
the other, according to the mode in which M. Agassiz supposes scales
to be formed, was derived merely from the appearance of the con-
centric lines on the opercular, sub-opercular, and inter-opercular
bones in many Fishes. I have examined the development of the
opercular bone in young Gold-fish and Carp, and I find that it is
effected in precisely the same manner as that of the frontal and pari-
etal bones. The cells which regulate the intus-susception and depo-
sition of the earthy particles make their appearance in the primitive
blastema in successive concentric layers, according to the same law
which presides over the concentric arrangements of the radiated
cells around the medullary canals in the bones of the higher Verte-
brata : and the term “ successive deposition,” in the sense of excretion,
is inapplicable to the formation of the opercular bones.

The inter-opercular as well as the pre-opercular bones exist in
the Lepidosiren annectens with all the characters, even to the green
colour, of the rest of the ossified parts of the endo-skeleton : the pre-
opercular as an appendage to the tympanic arch, the inter-opercular
being partly attached to the hyoid arch. Of the supra-scapular there
is no trace in the Lepidosiren ; but in the Sturgeon it plainly exists
{Jig. 43. 5o) as part of the cartilaginous endo-skeleton, under the
same bifurcate form, and double connection with the cartilaginous
skull, as we have seen it to present in most Osseous Fishes. The large
triangular bony scale {ih. d 5o) firmly adheres to its broad, triangular,
flat, outer surface. The epi- and meso-tympanic cartilages {ib. 25, 26)
in like manner expand posteriorly, and give a similar support to the
large opercular scale. Were the supporting cartilages of the oper-
cular and supra-scapular scales to become ossified in the Sturgeon,
they could doubtless become anchylosed to the dermal bony plates,
and bones, truly homologous with the opercular and supra-scapular
in ordinary Osseous Fishes, would thus be composed of parts of the
endo- and exo-skeleton blended together. I cannot, therefore, concur
with Von Baer in the opinion that the opercular bones are ribs of the
exo-skeleton, nor with Agassiz that l)oth the opercular and supra-
scapular bones arc merely modified scales. The suiu-a-scapular bone
is the ideurapophysial clement of the occipital ai’cli, i. c. the upper or
first part of the htcmal arch of that vertebra, and corresponds in

140

LECTURE VI.

serial homology with the epi-tympanic portion of the mandibular
arch, and with the palatine portion of the maxillary arch. The oper-
cular bones are the diverging appendages of the tympano-mandibular
arch, and correspond, in serial homology, with the branchiostegal
appendages of the hyoid and the pectoral appendages of the scapular
arches, and have the same title to be regarded as cephalic fins, and as
parts of the normal system of the vertebrate endo-skeleton ; but
neither opercular bones nor branchiostegal rays are retained in the
skeletons of higher Vertebrata. All diverging appendages of ver-
tebral segments make their first appearance in the vertebrate series
as ‘rays and the opercular bones are actually represented by car-
tilaginous rays, retaining their primitive form in the Plagiostomes.
In the Conger the sub-opercular still presents the form of a long and
slender fin-ray.

The opercular and sub-opercular may, in ordinary Osseous Fishes,
frequently coalesce, like the supra-scapular, with their representative
scales of the dermal system ; but they are essentially something more
than peculiarly developed representatives of those scales. M. Agassiz,
indeed, excepts the pre-opercular bone from the category of “ pieces
cutanees,” believing it to be the homologue of the styloid process of
the temporal bone in Anthropotomy, or the ‘ stylo-hyal’ of Ver-
tebrate Anatomy, as the piece, viz. which completes the hyoid
arch above. “ C’est en effet,” he says, “ cet os a la face interne
duquel I’os hyoide des poissons est suspendu, qui s’articule en haut
avec le mastoidien et tres souvent meme sur I’ecaille du temporal.”
So far as my observation has gone, it is a rare exception to find the
hyoid arch suspended to the pre-operculum ; the rule in Osseous
Fishes is' to find the upper styliform piece of the hyoid arch attached
to the epi-tympanic (mastoidien of Agassiz), close to its junction
with the meso-tympanic bone. It is equally the rule to find the pre-
opercular articulated with the epi-, meso-, and hypo-tympanics ; and
it is an exception, when it rises so high as to be connected with the
mastoid (ecaille du temporal of Agassiz). If the stylo-hyal be not
the upper piece of the hyoid arch displaced, and if the upper piece
connecting that arch with the mastoid is to be sought for in Osseous
Fishes, I should rather view it in the posterior half of the epi-
tympanic, which is usually bifurcate below and very commonly also
above, when the posterior upper fork articulates with the mastoid,
and the posterior lower foi’k with the hyoid arch.

The normal position, form, and connections of the pre-operculum
clearly bespeak it to be the first or proximal segment of the radiated
appendage of the tympano-mandibular arch : the opercular, sub-
opercular, and inter-opercular bones form the distal segment of the

DERMAL BONES OF FISHES.

141

same appendage. In some of the earliest introduced fishes on our
planet, e.g. the Cephalaspids of the Old Ked Sandstone, the oper-
cular appendages were functionally as well as homologically cephalic
fins, and the only pair of radiated appendages so developed from the
hajmal arches.

Returning to the consideration of the dermo-skeleton, we find in
the Sturgeon that, besides the cephalic plates, it is represented by
five longitudinal rows of dermal bones, one extending along the mid-
line of the back {fig. 43. ds') already noticed in the elucidation of
the skeleton of the trunk, one along each side of the body {ih. dp), and
two along the lower part of the abdomen, between the pectoral and
ventral fins. The upper lateral series of scale bones is pretty
constant in the exo-skeleton of fishes, and is usually closely related
to the mucous tube and its conduits, which form the so-called ‘ lateral
line’ in this class. The systematic Ichthyologist finds in the va-
rieties of this line characters for the distinction of genera or species.
The lateral bones, which are either perforated or grooved by its
ducts, are modified scales, and the scales of fishes are more or less
modified dermal bones : they do not belong to the horny or epidermal
system, but lie between the cuticle and cutis, their fore margin di-
rected inwards and lodged somewhat loosely in depressions of the
cutis, and their hind margin outwards, and firmly adherent to the
cuticle, when the development of the scales renders its existence
possible. The scales of the lateral line are commonly more ossified
than those of the rest of the trunk : 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.
23. 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 ; and both this fish and the Herring have been cited as
exceptional examples of fishes with a true sternum. * But the super-
ficial position of the ventral ossicles indicates their essentially dermal
character, and we may regard this as another instance of the con-
nection of the endo- and exo-skeletons in the class of fishes. Parts
analogous to a sternum are thus supplied from the exo-skeleton in
the Herring, as they are from the splanchno-skeleton in the Lamprey

Gore’s translation of Cams’ Comp. Anat. vcl. i. p. 117.

142

LECTURE VI.

{fig. 11.); but the true homologues of the sternum are first seen in
the endo-skeleton of the Batrachia. In the Trunk-fishes {Ostracion),
and Pipe-fishes {Sgngnathus) the dermal scale bones form a con-
tinuous coat of mail, like a tessellated quincuncial pavement, over the
entire body. In the Lepidosteus the scales defend the body in close-
set oblique rows, are thick, completely ossified, and with an exterior
hard, shining, enamel-like layer, having the microscopic structure of
the hard dentine of Shark’s teeth ; the subjacent osseous part exhibits
the radiated corpuscles. I described the organic structure of these so-
called ‘ ganoid’ scale bones in 1840, in both recent and extinct
fishes, showing that it militated against the theory of development
by successive deposition of layers being applied, at least, to ganoid
scales. * A like organisation prevails in the tri-radiate dermal bones
which support the strong spines of the Diodon ; and in the usually
unenamelled, less regularly formed and arranged, dermal ‘placoid’
ossicles of Sharks and Rays. The thinner subtransparent scales of
ordinary Osseous Fishes are either sub-circular and with entire
margins as in the Carp, when they are called ‘ cycloid,’ or have the
outer and hinder margin dentated or spined, as in the Perch, when
they are called ‘ ctenoid.’ We have seen that the primary classi-
fication of fishes in the system of M. Agassiz, is based on these
various modifications of the dermal skeleton.

One of the interesting generalisations which has risen out of the
vast series of researches on Fossil Fishes to which this eminent
Naturalist has devoted himself, is the discovery of the progressive
predominance of the exo-skeleton over the endo-skeleton as we
descend into the strata of the earth, or, in other words, penetrate into
past time in quest of the species that have been successively blotted
out in the revolutions of the globe. At the present day the Placoids
or Plagiostomous cartilaginous fishes form a small minority of the
class ; and amongst the existing majority of fishes called, from the
advanced development of their internal skeleton, ‘ Osseous,’ only two
genera exhibit that kind of scale called ‘ ganoid : ’ one of these, the
Lepidosteus, is peculiar to North America ; the other, the Polypterus,
to Africa : both are fresh-water fishes. As we descend to the older
tertiary deposits the number of Ganoid Fishes increases, their geo-
graphical relations expand, and their sphere of life was extended to
the salt waters of the ocean.

Thus Ichthyolites with a dense imbricated armour of polished bony
scales occur in the marine deposits of the eocene age in our own

* Odontography, part i. p. 1 5.

DERMAL BONES OF FISHES.

143

island. In the chalk formations the members of both Ganoids and
Placoids multiply rapidly, and in all the older fossiliferous strata
they exclusively represent the class of fishes. The predominance 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 endo- skeleton, like that in the Lepido-
siren of the present day ; the total absence of any trace of vertebral
centres in this fossilised skeleton of the Microdon radiatus (No. 70.
Fossil Fishes, Mus. Coll. Chirurg.), and the vacant tract, where they
should have been, between the bases of the neur- and liEcma-pophyses
which have been little disturbed ; together with the remains of the
ganoid scale-armour which has kef>t all the fossilisable parts of the
extinct fish together, show plainly enough that the primitive gela-
tinous chorda dorsalis has been persistent. In not one of the nu-
merous 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 Coccosteus they form a broad helmet upon the head,
and a back-plate and breast-plate for the fore part of the trunk, and
have been mistaken for the scutes of a Tryonyx or Mud-tortoise ;
whilst only the peripheral arches and spines of the vertebrae of this
fish were ossified, and a great proportion of the cranial vertebras was
cartilaginous. In the still better defended Pterichthys and Pam-
phractus *, which have been mistaken for extinct Crustacea, all the in-
ternal skeleton was soft and perishable, and the earthy salts were ex-
clusively developed in that peripheral skeleton, which forms the sole
calcified defence of the invertebrate classes of animals. It is a sinking
and suggestive fact this prevalence of a low and rudimental state of the
en do-skeleton, with an excessive development of the exo-skeleton, in
the fishes of the old Silurian and Devonian strata — the earliest
periods at which Geology teaches that fishes were introduced into this
planet. At the present day the Lepidosiren repeats the low con-
dition of the endo-skeleton, but without the compensating ganoid or
placoid developments of the skin •, and the Siluroids 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 Cephalaspids ;
but what is now a rare and exceptional instance of analogy to the

* See M. Agassiz’ admirable, philosophical, and splendidly illustrated mono-
graph, “ Sur les Poissons Fossilcs du Systeme Devonien,” 4to. tab. 24 — 31.

144

LECTUKE VI.

testaceous and crustaceous Invertebrates appears to liave been the
rule in the first-born fishes of our globe.

These primseval members of the vertebrate sub -kingdom manifest
other remarkable traits of embryonic life. The Cephalaspids of the
Old Eed Sandstone were shaped like the tadpoles of Batrachia ; the
breathing organs and chief part of the alimentary apparatus were
aggregated with the proper viscera of the cranial cavity, in an
enormous cephalic enlargement ; the rest of the trunk was for loco-
motion, and dwindled away to a point. The cephalic abdominal
enlargement was defended by large bony scutes ; the muscular tail-
part was, in the higher species (^Coccosteus), strengthened by an in-
completely developed vertebral axis, with intercalary and dermal
spines, supporting a dorsal and an anal fin. The position of the anal
fin proves the anus to have been situated, as in tadpoles, im-
mediately behind the cephalic abdominal expansion. In the lowest
forms, as Pterichthys, the mouth was small and inferior, as in the
young tadpole, and the post-cephalic or abdominal part of the en-
largement very short and ill-defined. In the Coccosteus it nearly
equals the cranial part of the enlargement ; the scutes are fewer,
larger, and show the progress of coalescence ; the mouth is anterior,
large, and formed by well developed dentigerous upper and lower
jaws. In this genus the cephalic or opercular appendages are in-
conspicuous or reduced to the normal proportions ; in Pamphractus
and Pterichthys they form long fin-like appendages, projecting from
the sides of the cephalic enlargement, like the external gills of the
Batrachian and Selachian larvas, and they may have supported
external fringed gills in the ancient Cephalaspids.

Genesis of Fins. — In the order of succession of Fishes the develop-
ment of locomotive organs is first restricted, as in most Cephalaspids, to
the region of the head : in Pterichthys and Pamphractus they project
like pectoral fins (whicli M. Agassiz describes them to be) from the
sides of the head j ust anterior to the division between the facial and
nuchal plates, and from the place corresponding to that occupied by the
pedicle of the lower jaw, from which the opercular fin projects in the
Sturgeon. There is no trace of true pectoral, ventral, or of vertical fins
in these Cephalaspids. In the Coccosteus these cephalic fins are reduced
to ordinary opercular proportions (they appear to be represented by
the plate h in the restored side view, given by M. Agassiz, Op. cit. tab.
xxiv.) ; but here we have the earliest manifestation of dorsal and anal
fins, without, however, any modification of the terminal vertebra to
form a caudal fin, either heterocercal or homocercal, and without the
slightest trace of true pectoral or ventral fins. In the Dipterus and
Glyptolepis there are two closely approximated dorsal and two anal

DERMAL BONES OF FISHES.

145

fins, and both are situated near the end of the tail, which runs into
the upper lobe of an unsymmetrical caudal fin. Now in the embryos
of existing Osseous Fishes these vertical fins are developed from a
single continuous fold of integument, which is extended round the
tail from the dorsal to the ventral surface ; a condition which we shall
see in the tadpoles of Batrachia, and which is persistent in the Eel
and Lepidosiren. The growth of this fold is progressive at certain
parts and checked at others ; and where development is active the
supporting dermal rays make their appearance, and the transform-
ation into dorsal, anal, and caudal fins is thus effected. At first the
caudal fin is unequally lobed and the terminal vei’tebrai extend into
the upper and longer lobe ; the dorsals and anals are also, at lU’st,
closely approximated to each other and to the caudal fin. M. Agassiz
has shown that all these embryonic characters were retained in
many of the extinct fishes of the Old Red Sandstone ; and the de-
velopment of the caudal fin did not extend in any fish beyond the
heterocercal stage until the preparation of the earth’s surface’*^ had
advanced to that stage which is called Jurassic or oolitic in geology,
(xxii. fasc. Sur le Systhne Devonien.)

Teleology of the Skeleton of Fishes. — Thus far the osteology of
Fishes has been considered chiefly from a homological point of
view, and I have aimed at relieving the dryness of descriptive de-
tail, 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
skeletons of Fishes bear to the general plan of Vertebrate organisa-
tion, and by indicating their analogies to transitory states of the
embryo skeleton in higher animals, and to those answerable conditions
of the mature skeleton which, in longer lapse of time, have successively
prevailed and passed away in the generations of species that have left
their remains in the superimposed strata of the earth’s crust.

To determine the parts of the Vertebrate skeleton which are most
constant ; to trace their general, serial, and special homologies,
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 osteological science ; as being that
which will reduce its facts to the most natural order, and their ex-
position to the simplest expressions. It is impossible, in pursuing the
requisite comparisons upwards through the higher organised classes,
not to recognise the elose and interesting analogies between the
mature states and forms of ichthyic organs, and the embryonic condi-

* “ The sea is His, and He made it, and His hands prepared the dry land.” —
Ps. xcv.

VOL. II.

L

146

LECTURE VI.

tion of the same parts, in the higher species. But these analogies
have been frequently overstated, or presented under unqualified me-
taphorical expressions, calculated to mislead the student and to ob-
struct the attainment of true conceptions of their nature. We should
lose some 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 organisation, 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 beautiful and fruit-
ful physiological principle of the relation of each adaptation to its
approiiriate function, and if we would avoid the danger of mistaking
analogy for homology or identity, and of attributing to inadequate
hypothetical secondary causes the manifestations of Design, of supreme
Wisdom and Beneficence, which the various forms of the Animal
Creation offer to our contemplation.

To revert, then, to the skeleton of Fishes, with a view to the teleo-
logical application of the facts determined by the study of this com-
plex 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 inferior to the bony
one is not so obvious. The ordinary course of age and decrepitude, or
of what may be called the 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 inorganie
state may be requisite for some special office of such calcified parts in
the individual economy ; but not, therefore, that it is an absolute ele-
vation 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 can no insight be gained into the purpose of
the all-wise Creator, in so arresting the ordinary course of osteogeny
in the highly organised fish ? Are we to entertain no other view of
it than as an unfinished, incomplete stage of an hypothetical serial
development of organic forms ?

TELEOLOGY OF THE SKELETON OF FISHES.

147

The predaceous Sharks are the most active and vigorous of fishes ;
like the 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 them-
selves near the surface of the sea, by the actions of their large and
muscular fins. The gristly skeleton is in prospective 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, lightness, toughness and elasticity are
the qualities of the skeleton most essential to the shark : to yie’d 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 vertebrce, so admirably adapt it. To have
had their entire skeleton consolidated and loaded with earthy matter
would have been an encumbrance altogether at variance with the
offices which the sharks are appointed to fulfil in the economy of the
great deep.

Yet there are some who would shut out by easily comprehended
but quite gratuitous systems of progressive transmutation and self-
creative forces, the soul-expanding appreciations of the final pur-
poses of the fecund varieties of the animal structures by which we
are drawn nearer to the great First Cause. They see nothing more in
this modification of the skeleton, which is so beautifully adapted to the
exigencies of the highest organised of fishes, than a foreshowing of
the cartilaginous condition of the reptilian embryo in an enormous
tadpole, arrested at an incomplete stage of typical development. But
they have been deceived by the common name given to the Plagio-
stomous 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
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 Yertebrata that the examples of
great and exclusive development of the exo-skeleton are most nume-
rous ; but some anatomists, in their zeal to trace the serial progression
of animal forms, seem to have lost sight of all the vertebrate instances

J48

LECTURE VI.

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” (xxvii. p. 537.), 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 mammals. 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.

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 Invertebrata, we are
in a condition to appreciate the adaptation of that external defensive
covering to such mode of life. The Sturgeons, for example, were
designed to be the scavengers of the great rivers ; they swim low,
grovel along the bottom, feeding, in shoals, on the decomposing ani-
mal and vegetable substances which are hurried down with the debris
of the continents drained by those rapid currents : thus they are ever
busied re-converting 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 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 endo-skeleton : and the weight of the armour requires that
endo-skeleton 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 level and rising with their defensive load to the
surface, by a large expansive 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 ; whereas these
Ganoids and Placoids have hitherto been viewed almost exclusively by
the light of the analogy of an embryonic “ Age of Fishes,” or explained

TELEOLOGY OF THE SKELETON OF FISHES.

149

by the hypothesis of transmuted Crustacea. Some have gone so far
as to atfirm, that in all those solid parts that cover and shield the
exterior of the body of the sturgeon and analogous fishes, “ there is
nothing in the least analogous to any part of the internal articulated
skeleton of Vertebrata,” but that “ it is entirely a remnant of the
superficial shells of Invertebrata.” (xxvii. p. 337.) You would
hardly suppose from these exaggerated expressions, that both ganoid
and placoid plates are as richly organised and permeated by nutrient
vessels as the bones within ; and that they present the same micro-
scopic structure as the ossified parts of the endo-skeleton, which they
serve to protect. I have proved this with regard to the existing
Lepidosteus, and the extinct Lepidotus. (v. p. 14.) Drs. Peters
and Muller have shown the osseous rayed corpuscles in the scales of
Polypterus and other Ganoids. Nay, many of the ganoid fishes have
these modified bony scales articulated in regular series by a kind of
gomphosis, like the pegs and sockets by which the tiles of a roof are
linked together. The dermal bones which form the carapace of the
Armadillo have the same cellulo-reticulate interior structure as the
carpal, tai’sal, or other bones of the endo-skeleton not excavated by
a medullary cavity. This is well demonstrated in the dermal bones
of the great extinct Glyptodons. *

The great proportion of the primitive cartilage which is retained
in the skull of many of the Osseous Fishes, 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 all persistent characters in Osseous Fishes, which remind the An-
thropotomist of transitional ones in the human foetus ; but the light
of teleology demonstrates the perfection of such, so termed embryonic,
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-watei’, and with the usually
more posterior position of the ventral fins.

In reference to the analogies to the form of a fish, we may be re-
minded that the head of the human embryo is disproportionately large.
True ; but the head of a fish must needs be large to meet and over-
come the resistance of the fluid, in the mode most favourable for rapid
progression : it must therefore grow with the growth of the fish.

* M. de Blainville, in the “ Generalites Osteologiques,” prefixed to his great
“ Osteographie,” admits tnat the structure of the dermal bones has a certain re-
semblance with that of true bones ; but errs in stating, “ avec cette difference
importante, qu’elle n’est jamais celluleuse et reticulee.” 4to. 1839, p. 12.

loO

LECTUKE VI.

Hence the large cranial bones always show the radiating osseous spi-
culae in their clear circumference, 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 are extending the osseous walls without ;
hut the brain undergoes no corresponding 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.
(xxiii. t. i. p. 309.) Now, this condition of the envelopes 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 facilitating its progressive motion, but it is
one which no embryo of a higher animal ever presents : it is as
peculiarly ichthyic, 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 supra-occipital, parietal, and frontal above the cranium, and of
the basi-occipital, basi-sphenoid, and pre- sphenoid below the cranium
in Lejndosiren, and the constant confluence of the posterior and
anterior basi-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 vertebrae of 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 to swing freely to and fro.
The posterior and anterior sphenoids continue distinct bones in all
Mammalia during a period of life at which they form one continuous
bone in Fishes.

The flattened form of the frontal and parietal bones in Osseous
Fishes has been associated with the small development of the brain
which they protect ; but observe how they would have impeded the
progress of the fish, had they been expanded into the dome-shaped
vault which arches over the skull of Birds and Mammals. There was
no need of that development in Fishes ; but we must not overlook the
fact that its very absence is a perfection in their structure, — an
adaptation to their sphere and mode of locomotion.

The loose connections of most of the bones of the face may likewise

TELEOLOGY OF THE SKELETON OF FISHES.

lol

remind the homologist of their condition in the imperfectly developed
skull of the embryos of higher animals ; but this condition is especi-
ally subservient to the peculiar and extensive 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 prehensile ;
the mouth may be propelled and guided by them to the food, but the
act of prehension must be performed entirely 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 development in the
opposite direction, not unfrequently, 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
(p. lOS. fig. 37.).

We must guard ourselves, 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 pieees, 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 inferioi 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 glenoid or trochlear articulation of
that pedicle, are developments beyond, and in advance of the condi-
tion of the bones supporting the lower jaw in Mammalia, 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 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 tympano-mandibular
arch, and of its diverging appendages, contributes to ensure that pro-
portion of the head to the trunk which is best adapted for the pro-
gressive motion of the fish through the water. But without the

152

LECTURE VI.

admission and appreciation of these pre-ordained adaptations to
special exigencies in the skeleton of Fishes, the superior strength and
complex development of the tympanic pedicle and its appendages
would be inexplicable and unintelligible in this lowest and first-born
class of Vertebrate animals.

In contrasting the skeletons of the Fish and Mammal, with refer-
ence to hypothetical secondary origins of organic species ; such, for
example, as that of transmutation and progressive ascent of specific
forms ; the vast disparity of the hyoidean arch, in point of size, com-
plexity, and strength, both intrinsic, and as due to its connections,
must not be overlooked. Its small size, simple structure, and loose
suspension in the flesh, have led to its being reckoned in Anthro-
potomy as a single bone ; and it is rarely preserved in the artificial
skeletons of man or beast : whilst if absolute and relative magnitude,
complexity of structure, and importance of function, are tests of the
grade of organisation of a part, the progress of development must be
held to have been reversed in respect of the hyoid arch ; which, with
its appendages, offers the highest grade in Fish and the lowest in
Man. And why this great difference — this striking exception to the
general condition of the ichthyic organisation? It is explicable only
on teleological principles. It is true the Fish tastes not with its
tongue, neither does it speak : the sole function of the human tongue-
bone, which is performed by that of the fish, is that which is in subser-
viency to deglutition. But this function is not in relation to food
alone ; all the mechanical part of breathing in the fish is a modified
act of swallowing. The hyoid arch is the chief point of suspension of
the visceral arches which support the gills ; and the branchiostegal
membranes, stretched out upon the diverging rays of the hyoid arch,
regulate the course and exit of the respiratory currents : thus the
mechanical functions of the thorax of the air-breathing classes are
transferred to the hyoid arch and its appendages in Fishes.

By the retraction of the hyoid arch the opercular doors are forced
open, and the branchial cavity is widened ; whilst all entry from be-
hind is prevented by the branchiostegal membranes, which close the
posterior branchial slits ; the water, therefore, enters by the gaping
mouth, and rushes through the sieve-like interspaces of the branchial
arches into the branchial cavity : the mouth then shuts, the opercular
doors press upon the branchial and hyoid arches, which again advance
forwards, and the branchiostegal membranes being withdrawn, the
currents rush out at the open posterior branchial orifices. These
functions are the true condition of the high development of the os
hyoides in fishes.

I have noticed the great development, the persistence, and ossifi-

TELEOLOGY OE TUE SKELETON OF FISHES.

153

cation of the branchial arches in connection with the transitory
manifestation of cartilaginous branchial arches in the larvae of the
Batrachia : this is one of those similarities that has led to the meta-
phorical expressions of “ gigantic tadpoles,” as applied to fishes.
But we see how admirably the branchial arches are adapted to the
aquatic respiration of the fish, by their advance to a grade of deve-
lopment, which they are never destined to attain in the frog.
Observe their firm ossification, their elastic joints, the sieve-like
valves developed from the side next to the mouth, pre-arranged with
the utmost complexity and nicety of adjustment to prevent the entry
of any particles of food or other irritating matters into the inter-
space of the tender, highly vascular, and sensitive gills. Observe,
also, how the last pair of these arches is reduced to the capacity of
the phai’ynx which it surrounds, how it is thickened in order to
support teeth of multiform character, according to the nature of the
food; in short, converted into an accessory pair of jaws, and the
most important of the two. In no other Vertebrate Animals is the
mouth provided with maxillary instruments at both fore and hind
apertures : in no other part of the ichthyic organisation is the special
divergence from any conceivable progressive scale of ascending
structure culminating in Man so plainly marked as in this.

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 consequent abro-
gation of the neck gives the advantage of a more fixed and resisting
connection of the head to the trunk, a greater proportion of the trunk
behind is left free for the development 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, com-
pressed form, most efficient for the lateral strokes, by the rapid alter-
nation of which the fish is propelled forwards in the diagonal, be-
tween the direction of those foi’ces. The advantage of the bi-concave
form of vertebra with intervening elastic capsules of gelatinous fiuid,
in effecting a combination of the resilient with the muscular power,
is still more obvious in the Bony Fishes than in the Shark.

You may be reminded that all the vertebral of the trunk are dis-
tinct from one another at one stage of the quadruped’s development,
as in the fish throughout life ; and you might suppose that the
absence of that development and confluence of cei’tain vertebrae
near the tail, to form a sacrum, was a mark of inferiority in fishes.

154

LECTURE VI.

But note what a hindrance such a fettering of the movements of the
caudal vertebrae would be to 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 of the body,
for the transference of more or less of the weight of the body
upon limbs organised for its support on dry land ; such a modifi-
cation would have been useless to the fish, and not only useless,
but a hindrance and a defect.

The pectoral fins, those curtailed prototypes of the fore -limbs of
other Vertebrata, with the last segment, or hand, alone projecting
freely from the trunk, and swathed in a common undivided tegu-
mentary sheath, present a condition analogous to that of the embryo
buds of the homologous members in the higher Vertebrata. 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
development, as it is termed, in relation to the prehensile limb of the
denizen of dry land, would have been an imperfection 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 forwards, 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 forwards and backwards, 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 dimi-
nished 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. For these functions, however, the hand requires as
much extra development in breadth, as reduction in length and
thickness; and mark how this is given to the so-called embryo or
rudimental fore-limb : it 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
Vertebrata. We find, moreover, as numerous and striking modi-
fications of the pectoral fins, in adjustment to the peculiar ha-
bits 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 oflence, as in many Siluroid fishes. But the modi-
fied hands have a more constant secondary office, that of touch, and
are applied to ascertain the nature of surrounding objects, and par-
ticularly the character of the bottom of the water in which the fish

TELEOLOGY OF THE SKELETON OF FISHES.

155

may live. You may witness tlie tactile action of the pectoral fins
when gold fish are transferred to a strange vessel : their eyes are so
placed as to prevent their seeing what is below them ; so they compress
their air-bladder, and allow themselves to sink near the bottom, which
they sweep as it were, by rapid and delicate vibrations of the pectoral
fins, apparently ascertaining that no sharp stone or stick projects up-
wards, 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 web, and are specially endowed
with nervous power for a finer sense of touch, as we see in the gur-
nards, where they compensate for the loss of the tactile property con-
sequent on the hard covering of the exterior of the mouth in these
mailed-cheeked fishes {Joues cuirassees, Cuv.)

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, 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, ai’e 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,
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 development of the
hands, 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 vertebrEe.

Nor is the pectoral member restricted in length where its office, in
subserviency to the special exigencies of the fish, demands a develop-
ment in that direction ; the fingers of the Exocatus or Dactylopterus,
are as long, and the web which they sustain as broad, as in the ex-
panded wing of the flying mammal. Everywhere, whatever re-
semblance 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 purpose 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 compari-

156

LECTURE VI.

son with the stages of development in a land animal — than the
pectoral fins ; and their small proportional size reminds the homo-
logist of the later appearance of the hind limbs, in the development
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 organs in
Birds, whose fore-limbs are exclusively modified, as wings, for motion
in another element. The legs are the sole organ of support and pro-
gression 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 intelligent 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 long flexible limbs would
be a grievous hindrance, a very monstrosity. So, therefore, we find
the All-wise Creator has restricted the development and connections
of the hind limbs of Fishes to the dimensions and to the 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.

In most fishes the ventral fins merely combine with the pectoral
fins in raising, and in preventing as outriggers, the rolling of the
body ; but some very interesting modifications of the ventral fins, in
relation to particular habits of certain species, may be noticed. In
the Blennies, the Forked Hake {Phycis), the Forked Beard {Rani-
ceps), and some other fishes, the ventral fins are reduced to filamentary
feelers. In the Lump-suckers ( Cyclopterus), the ventrals unite to-
gether, 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. In
the long-bodied and small-headed abdominal fishes, the ventrals are
situated near the anus, where they best subserve the office of ac-
cessory 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
forwards, to aid the pectoral fins in raising the head.

The following short account of some experiments upon fish, made
for the purpose of ascertaining the use of their fins, I give in the
words of their gifted describer, Paley, to whom Comparative Physio-
logy owes many beautiful accessions to its teleological applications.

In most fish, beside the great fin — the tail, we find two pairs of

TELEOLOGY OF THE SKELETON OF FISHES.

157

fins upon the sides, two single fins upon tlie back, and one upon the
belly, or rather between the belly and the tail. The balancing use of
these organs is proved in this manner. Of the large-headed fish, if
you cut off the pectoral fins, that is the pair which lies close behind
the gills, the head falls prone to the bottom ; if the right pectoral fin
only be cut off, the fish leans to that side ; if the ventral fin on the
same side be cut away then it loses its equilibrium entirely ; if the
dorsal and anal fins be cut off, the fish reels to the right and left :
when the fish dies, that is, when the fins cease to play, the belly turns
upwards. The use of the same parts for motion is seen in the follow-
ing observation upon them when put into action. The pectoral, and
more particularly the ventral fins, serve to raise and depress the fioh ;
when the fish desires to have a retrograde motion, a stroke forward
with the pectoral fin effectually produces it ; if the fish desire to turn
either way, a single blow with the tail the opposite way sends it
round at once ; if the tail strike both ways, the motion produced by
the double lash is progressive, and enables the fish to dart forwards
with an astonishing velocity. The result is not only in some cases
the most rapid, but in all cases the most gentle, pliant, easy, animal
motion with which we are acquainted. However, when the tail is
cut off, the fish loses all motion, and it gives itself up to where the
water impels it. The rest of the fins, therefore, so far as respects
motion, seem to be merely subsidiary to this. In their mechanical
use the anal fin may be reckoned the keel ; the ventral fins outriggers ;
the pectoral fins the oars ; and if there be any similitude between
these parts of a boat and a fish, observe that it is not the resemblance
of imitation, but the likeness which arises from applying similar
mechanical means to the same purpose.” (xli. p. 257.) *

* See also Carlisle Phil. Trans. 1806, p. 3.

SYNONYMS OF the BONES op the HEAD op FISHES, according to their SPECIAL HOMOLOGIES.

158

LECTURE YI.

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SYNONYMS OF the BONES of the HEAD op FISHES, according to their SPECIAL HOMOLOGIES : —coniirauerf.

160

LECTURE VI.

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SYNONYMS OF the BONES of the HEAD of FISHES, according to their GENERAL HOMOLOGIES.

SYNONYMS OF THE BONES OF THE HEAD OF FISHES.

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MUSCULAR STSTICIM OF FISHES.

163

LECTURE VII.

MUSCULAR SYSTEM OF FISHES.

The modification of tlie muscles, or active organs of motion, and
their deviation from the fundamental vertebrate type, proceed conco-
mitantly with the metamorphosis of the p’assive organs of motion, as
the Myelencephala rise in the scale and gain higher and more varied
endowments ; therefore, as the segments of the skeleton 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
segments, corresponding in number with the vertebrae. Each lateral
flake {Mijocomma, Jig. 44. a, h, c) is attached by its inner border to

D/

Muscular system, Perea fluviatilis.

the osseous and aponeurotic parts of tlie corresponding vertically
extended segment of the endo-skeleton, by its outer border to the
skin, and by its fore and hind surfaces to an aponeurotic septum
common to it and the contiguous myocommata. The gelatinous
tissue of these septa is dissolved by boiling, and the muscular seg-

VOL. II. *M 2

164

LECTURE VII.

nients or flakes are then easily separated, as we find in carving a cod
or salmon at table. The vegetative similarity of the myocommata of
the trunk has led to their being described, by an abuse of synthesis,
as parts of one individual ‘ great side-muscle ’ *, extending from the
occiput and scapular arch to the bases of the caudal fin-rays. The
modifications of the cranial vertebras impress corresponding changes
on their muscular segments, and the essential individuality of these
segments has, on the other hand, been lost sight of, through the
opposite excess of analytic separation : special names are, however,
conveniently applied to their constituent, and in fact often separated
and independently acting, fasciculi.

The fibres of each myocomma 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 (b), have their apices turned backwards ; whilst
a middle cone (c), formed by the contiguous parts of the preceding,
has its apex directed forwards ; this fits into the interspace between
the antecedent upper and lower cones, the apices of which recipro-
cally enter the depressions in the succeeding segment, and thus all
the segments are firmly locked together, their general direction
being from without obliquely inwards and backwards, and their peri-
pheral borders describing the zig-zag course represented in fig. 44,
in which one myocomma is represented 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 lateral ’ of Cuvier, as a group of
essentially distinct vertical masses or segments. A superficial view
of these segments, or an artificial analysis, has led to their being
regarded as forming a series of horizontal muscles extending length-
wise from the head to the tail : the upper portions (a) of the myo-
commata being grouped together, and described as a dorsal longi-
tudinal muscle with tendinous intersections directed downwards and
backwards; the lower portions (i) as a ventral longitudinal muscle, with
tendinous intersections directed downwards and forwards, whilst the
margins of the middle portions of the myocommata (c) being curved,
and usually bisected by the lateral mucous line, have been taken as
indications of two intermediate longitudinal muscles. In the Sharks,
indeed, instead of a curve the margins of the middle portions of the
myocommata form an angle with the apex turned forwards ; and in
the Rays the dorsal segments of the myocommata have actually

* “ Des grands muscles laterau.v da tronc. II n’y cn a cssentidlcmcnt rju’uii de
chaque c6t6.” (xxiii. i. p. 287.)

MUSCULAR SYSTEM OF FISHES.

165

become insulated from the middle ones, and metamorphosed into a
continuous longitudinal muscle {fig. 45. a) ; the change being essen-
tially the same as that which the bony segments themselves un-
dergo, when by anchylosis the sacral or cranial vertebrce
are blended into a continuous longitudinal piece.* In
the Mackerel Professor Muller found the middle fibres of
the caudal myocommata disposed in two entire cones :
fig. 44. a, is a transverse section of the tail to show the
two concentric series of cut segments of the sheathed
Caudal mus_ cones, on each side the spine. ']■

’rci. In ordinary osseous Fishes the myocommata of one side

are separated from those of the opposite side of the body by the
vertebra;, by the interneural and interhsemal aponeuroses, and by
the abdominal cavity and its proper walls (44, h p). The ventral
portions recede from each other to give passage to the ventral fins
(v), and the ventral and lateral tracts separate to give passage to,
the pectoral fins (p).

From this part forwards, portions of the myocommata undergo
that change, analogous to anchylosis, which justifies their being
regarded as distinct longitudinal muscles : here the separated ventral
tract (subcoracoideus, d,f) derives a firmer origin from the ossified,
though slender h^mapophysis of the atlas (epicoracoid), when it
exists ; and, in consequence of the peculiar forward curve of the
strong haemapophysis of the occiput (coracoid), it is not only ex-
panded but unusually elongated, in order to be inserted there. But
the serial homology of this fasciculus with the more normal ventral
portions of the succeeding myocommata, the ha;mapophysial attach-
ments of which have not risen above the aponeurotic state, is unmis-
takeable. The lateral portion of the anterior myocomma is attached
to the upper end of the coracoid and to the scapula ; the dorsal por-
tion to the supra-scapula, par-occipital and supra-occipital. We
recognise the dorsal portion of the posterior cranial myocomma in
the fasciculus called ‘ protractor scapulae ’ (*), which extends from
the supra-scapula forwards to the parietal and frontal cristae ; and
the middle portion in that which is exposed by the removal of the
operculum, and which extends from the scapula to the mastoid in the

* The continuators of Cuvier group the portions of the myocommata above the
lateral line into three longitudinal muscles, compared respectively to the ‘spinalis
dorsi,’ ‘longissimus dorsi,’ and ‘ sacro-lumbalis and the portions below the line
into two muscles, viz. ‘obliquus abdominis,’ and ‘rectus abdominis.’ (xiii. i.
pp. 305. 327.) : but Professor Muller has well shown that the homologues of thq
obliqui abdominis do not exist in Fishes, (xxi. p. 223.)
f See XXI. tab. ix. fig. H.

M 3

166

LECTURE VII.

Perch (j) ; and, in some fishes, also, from the aponeurotic septum
between the branchial and abdominal cavity, to the lateral and lower
parts of the cranium. The protractor scapula in the Skate and
Torpedo (45. i) is of considerable length, in consequence of the back-
ward displacement of the scapular arch (s), and of great strength, by
reason of the enormous pectoral appendage which the arch sustains.
The representatives of dorsal and middle portions of a second cranial
myocomma, in the Perch, are seen in the protractor tympani (44. k)
and in the retractor maxillse (m) : a lower parallel subquadrate por-
tion of the same segment passes from the preoperculum and tympanic
pedicle to the coronoid process of the lower jaw, and forms the ‘ levator
mandibulje ’ (n). A cephalic continuation of the ventral segments of
the myocommata is recognisable in the fasciculus which passes for-
wards in part (ff) directly from the subcoracoideus (d,f), in part
(/') from the coracoid itself, to the basi- and uro-hyals, and which,
if it does not perform, as Cuvier states, all the functions of the
sterno-hyoid, represents the muscle to which that name is given in
higher vertebrata, and proves it to be, in its general homology, the
ventral segment of a cranial myocomma.

Other dismemberments of the cranial myocommata are modified to
act specially upon the branchial arches : one of these fasciculi is the
branchi-depressor (o) : it rises from the basi-hyal, and passes obliquely
backwards to be inserted into the pharyngeal or last branchial arch :
two other fasciculi rise from the coracoid, and converge to be similarly
inserted, forming the branchi-retractores (p, q). Several small fasciculi
from the sides of the cranium are inserted into the epibranchials
and the first two pharyngo-branchials, forming the branchi-levatores
(r). There are also several transverse and oblique muscles, peculiar
to the branchial arches. The ventral portion of the most anterior
of the myocommata extends between the apex of the hyoidean and
that of the mandibular arehes : Cuvier recognises its special homo-
logy with the genio-hyoideus (k) : it protracts the hyoid arch ; it
retracts the mandibular arch ; and, when the lower jaw is left free
to move upon the tympanic pedicle, it depresses the jaw. There is
no digastricus or proper depressor of the mandible in Fishes. A
strong muscle (1) from the postfrontal is inserted into the pterygoid ;
and partly through that, and partly by direct insertion into the pre-
tympanic, it raises and protracts the tympanic pedicle. The oper-
culum, or fin of the tympanic pedicle, has a levator or extensor (A)
and a depressor muscle ; the one rises from the mastoid, the other
from the petrosal or alisphenoid.

In the Angler each of the long rays of the branchiostegal fin has

MUSCULAR SYSTEM OF FISHES.

167

its proper muscles, which rise from the sustaining hyoidean arch.
A more constant and important muscle rises from the operculum and
suboperculum, and attaches itself to the inner surface of the branchi-
ostegal rays, expanding over the whole membrane of the branchial
chamber, and the more completely as the chamber becomes more
circumscribed, and its outlet smaller. In the Lepidosiren the homo-
logous muscle rises not only from the suboperculum but from the
ramus of the jaw, and, meeting its fellow along a median raphe
beneath the head and hyoid arch, represents the ‘ mylo-hyoideus’*
The muscular investment of the branchial chamber of the Torpedo

(45. r) receives a fasciculus
from the scapula, and sends
another (zd. o) forwards to the
cranium, from which the con-
strictor of the electric battery
is continued.

In most osseous fishes there
is a decussating pair of
muscles (depressores branchi-
ostegorum) which rise from
the base of one ceratohyal,
and are inserted into the lower
branchiostegals of the oppo-
site side.

The levator and abductor
muscle (44, s) of the pectoral
fin rises from the coracoid,
and descends obliquely to its
insertion by distinct fasciculi
into the bases of the fin-rays :
the depressor and abductor {t)
of the pectoral is deeper seated, and usually rises from the radius ;
it ascends to its insertion. There are two posterior or adductor
muscles, whose fibres are oblique and decussate, but in opposite di-
rections to the abductors, and tending also, in sepai’ate action, to
raise or depress the fin. There are small special muscles in most
fishes for divaricating the fin rays. The muscles of the pectoral fin
are well developed in sharks ; enormously so in the skate and
torpedo, where the horizontal position of the fin involves further
modifications. In Jig. 45. the letter s shows the ‘ levator pectoralis,’
and t the upper radiated muscle of the digits.

* xxxm. p. 358. pi. 24. fig. 4. a.

M 4

168

XECTURE VII,

The pubic arch supporting the ventral fins, is attached in the
Perch by a pair of slender longitudinal muscles {w) to the prolonged
hsemal arch, sometimes called ‘ pelvis,’ of the first caudal, and which,
in its course to the pubic arch, surrounds the anus : the length of
these muscles is moderate in the ventral fishes, considerable in the
thoracic, and extreme in the jugular fishes, in which they simulate
the ‘recti abdominis.’ It is probable that the external ‘sphincter
ani ’ of Mammals is the reduced homologue of these muscles. In
general homology they must be viewed as the lowest ventral strip of
a single myocomma, more or less developed in accommodation to the
varying distance between the last abdominal and first caudal, its
proper, hsemal arches, which variation relates to the office required
to be performed by the ventral fins, or appendages of the last abdomi-
nal hfemal arch, in the different species of fishes. The protractors of
the pubic arch are attached, when present, to the apex of the coracoid
arch. Transverse muscles extend from one pubic bone to the other ;
and similarly disposed special muscles serve to contract the span of
the mandibular and hyoidean arches. The levators and depressors
of the ventral fin are inserted, as in the pectorals, by as many
fasciculi as there are digital rays.

The deeper seated fibres of the segments, which together constitute
the great lateral muscular masses of the trunk, alter slightly their
direction, and, in the abdomen, represent the ‘ intercostals,’ passing
from one vertebral rib to another, and from one aponeurotic repre-
sentative of the sternal rib {inscriptio tendinea, h, p.') to another.

The myocommata answering to the neural and liEBmal spines of the
suppressed centres of the terminal caudal vertebrae, change their di-
rection like those spines, slightly diverging from the axis of the trunk
to be inserted into them ; these modified terminal segments (z), by
their connection with the interlocked myocommata of the great lateral
masses, concentrate the chief force of those muscles upon the caudal
fin. Special series of small dermal muscles are inserted into the rays
of the dorsal, anal, and caudal fins : the dorsal and anal rays have each
six fasciculi, tAvo superficial (x) and four deep-seated (y), which rise
from the expanded dagger-shaped interneural and interhsemal spines.
Beneath the muscles of the tail-fin which terminate the lateral series
of myocommata, there are long and slender fasciculi which rise di-
rectly from the compressed coalesced bodies of the terminal caudal
vertebrae, and are inserted into the bases of the diverging rays. Other
small muscles pass from the bases to act upon the more distant parts
of the rays. Slender longitudinal muscles, ‘ supra carinales,’ extend
along the midline of the back from the occiput to the first dorsal, and

MUSCULAR SYSTEM OF FISUES.

169

along tlie interspaces of the dorsal fins in the Cod : similar muscles
extend from the last dorsal to the caudal fin (m) in the Perch ; and
‘ infi-a-carinales’ (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 mo-
dified 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 pectorals and
ventrals of the Lump-fish, form a sucker on the opposite 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.

The muscles of the gills, the eyeball, the air-bladder, and 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 are red, like those
of the warm-blooded classes. The want of colour relates to the com-
paratively small proportion of red blood circulated through the
muscular system* ; and to the smaller proportion 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 temperature f 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. J
The proportion of myonine is greater in fishes than in other Ver-
tebrata ; the irritability of its fibres is considerable, and is long
retained. 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.’

There are many and gi-eat modifications of the muscular system of
Fishes, especially in the aberrant orders at the two extremes of the
class : Cams has illustrated some of these in the Plagiostomes (xliu.

XLviii. pp. 4. 16.

t

{ XLIX. p. 3.

170

LECTURE VII.

tab. iv.) ; a full and accurate detail of the myology of the Myxinoids,
together with a philosophical comparison of the muscular system of
Fishes generally with that of the higher Vertebrata, will be found
in xxT. pp. 179-246. But the determination of the special, serial,
and general homologies, and the recognition of the various individual
adaptive modifications, of the muscles of Fishes, still remain a rich
and little-explored field for the labours of the myologist.

The normal character of Ichthyic myology shows itself in the vast
proportion of the vegetatively repeated myocommata, corresponding
with the vertebral arches, 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 ad-
mirably and expressly adapted to the habits and medium of existence
of the Fish. The interlocked myocommata 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 alternating 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 which 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 pro-
longs its oblique course through the air by the rapid fluttering of its
outspread pectorals. When the anterior portions 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 outstretched serrated pectoral spines ; thus
the Percoid and Cottoid Fishes strike with their opercular spines ;
and so likewise may the Saw-fish (jRrisfo's), and Sword-fish (WtpAtas),
wield their formidable 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 supra-carinales, 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 infra-carinales, in combi-

NERVOUS SYSTEM OF FISHES.

171

nation 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 ajiproximated, 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.

LECTUKE VIII.

NERVOUS SYSTEM OF FISHES.

The neural axis is a simple continuous chord in the Lancelet
{Branchiostoma, fig. 46, md.fi of opaline sub-transpai’ency, ductile

and elastic, flattened, composed entirely of nucleated cells * showing
a feeble indication of a median linear arrangement, which becomes
more general and distinct at the anterior end, where the axis becomes
cylindrical and terminates obtusely : the nerves, trigeminal {ph\ and
optic (op), in connection with this slightly modified part of the axis,
indicate it to be the brain. This is the most simple persistent con-
dition of the central organs of the nervous system known in the
vertebrate sub-kingdom : it is typified by that of the Entozoa in the
articulate sub-kingdom. In all other Fishes the fore part of the
neural axis receives the vagal, trigeminal, and special-sense nerves.

* Prof. Goodsir, Ixxxix.

172

LECTURE VIII.

and developes and supports ganglionic masses, principally disposed
in a linear series parallel with the axis : this part is called the ‘ brain’
or encephalon : the rest of the axis I term the ‘myelon’* * * § ; retaining
its columnar or chord-character, and, being lodged in the canal of
the spinal column, it is usually defined 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 Dermopteri : 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 again into a small terminal
ganglion f in most homocercal Fishes.

The Hunterian preparation of the skate {Raia Batis, No. 1347.)
shows a slight (brachial or pectoral) enlargement of the myelon
where the numerous large nerves are sent off to the great pectoral
fins J : 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. Exoccetus and Dacty-
lopterus : in the latter the small ganglionic risings upon the dorsal
columns of the cervical region of the myelon receive nerves of sen-
sation from the free soft rays of the pectorals, and the homologous
ganglions are more marked in other Gurnards ( Triglce), which have
from three to five and sometimes six pairs, e. g. in Trigla Adriatica. §
Similar myelonal cervical ganglions are present, also, in Poly-
nemus. In the heterocercal Sturgeon there is a feeble expansion of
the myelon at the beginning of the caudal region, whence it is con-
tinued, gradually diminishing to a point along the neural canal in
the upper lobe of the tail. In some bony fishes (Trout, Blenny), 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

* Gr. fiviKos, marrow. As an apology for proposing a name, capable of being
inflected adjectively, for a most important part of the body which has hitherto
received none, I may observe that, so long as the brief definitions, ‘ marrow of the
spine,’ ‘ chord of the spine,’ are substituted for a proper name, all propositions re-
specting it must continue to be periphrastic, e. g. ‘ diseases of the spinal marrow,’

‘ functions of the spinal chord,’ instead of ‘ myelonal diseases,’ ‘ myelonal functions : ’
or, if the pathologist speaks of ‘ spinal disease,’ meaning disease of the spinal marrow,
he is liable to be misunderstood as referring to disease of the spinal or vertebral
column. But, were the Anatomist to speak of the canal in the spinal marrow of
Fishes as the ‘ myelonal canal,’ he would at once distinguish it from the canal of
the spinal column. The generally accepted term ‘ chorda,’ or ‘chorda dorsalis,’ for
the embryonic gelatinous basis of the spine, adds another source of confusion likely
to arise from the use of the term ‘ spinal chord,’ applied to the myelon, or albu-
minous contents of the spinal canal.

t LIU. p 6. ; Liv. p. 26. (in the Cod),

This structure is accurately figured by Mr. Swan in uv. pi. xi.

§ Lv. pi. 2. fig. 4. p. 106. ; and mi. p. 6., j)l. 2. fig. 24, 25.

NERVOUS SYSTEM OF FISHES.

173

47 '

pair of spinal nerves. Tlie absence of this ganglion in tbe vSliark
shows that it relates 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 meta-
morphosis is extreme, as, e. g. in Orthagoriscus molu,
and where it alFects the entire condition of the niyelon,
which has shrunk into a short, conical, and, according
to Arsaki (liii. tab. iii. Jig, 10.), gangiiated appendage
to the encephalon. A like singular modification, but
without the ganglionic structure, obtains in Tetrodon
and Diodori, in a species of which latter genus I found
the niyelon {Jig. 47. m.) only four lines long in a fish
of seven inches in length, and measuring three inches
across the head. The neural canal in these Plec-
tognathic fishes is chiefly occupied by a long ‘ cauda
equina’ {ib. c. e.). But, insignificant as the niyelon
here seems, it is something more tlian merely unre-
solved nerve fibres : transverse white strias are dis-
cernible in it, with grey matter, showing it to be a
centre of nervous force, not a mere conductor. In the
Lophius a long cauda equina partly conceals a short
niyelon 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
ganglion to the end of the canal.

Brain and Mye-
lon, Diodon.
nat. size.

A shallow longitudinal fissure divides the ventral surface, and
a deeper one the dorsal surface, of the myelon, into equal moieties :
a feeble longitudinal 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 restiforni tracts. A minute cylindrical
canal extends from the fourth ventricle, beneath (ventrad of) the
bottom of the dorsal fissure, along the entii’e 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 striae. 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 Cuvier* might lead him to expect.

xxiii. i. p. 323.; xni. iii. p. 170'.

174

LECTURE Vlir.

As the myelon approaches the encephalon it expands, and the
following cdianges may be here observed, in the Cod and Shark : in
the venti-al columns a short longitudinal groove di-
vides a narrower median ‘ pre-pyramidal ’ tract
48. a), from a broader lateral ‘ olivary ’ tract {ih. b) :
in the dorsal columns a median ‘ funicular ’ tract {ib. e),
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 ‘restiform’ tract (c),
inferior part of which a distinct slender por-
tion is also sometimes defined. The post-pyramidal
tracts diverge, expand and blend anteriorly with the similarly bul-
ging restiform tracts, forming the side-walls of a triangular or
rhomboidal cavity, called the ‘ fourth ventricle ’ : the pre-pyramidal
and olivary tracts forming the floor of the ventricle, are covered below
by a thin superficial layer of transverse ‘arciform fibres’* [ib. m)
concealing their boundary fissures. At the bottom of the ventricle
the myelonal canal is exposed, and its sides swell and rise as rounded
or ‘teretial ’ tracts {ib. f) 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 Sturgeon and Selache : two
lateral prominent ‘ vagal ’ columns, also, project inwards into the
ventricle, from the conjoined restiform and post-pyramidal tz’acts ;
these vagal columns present a series of nodules, corresponding with
the fasciculi of the roots of the great vagal nerve in Selache : (Prep.
1311^).

In the Cyprinoid fishes the median inferior tract rises into the
ventricle, and is developed into a smooth hemispheric mass, the
‘nodulus’ {fig- 51. k) -. the conjoined post-pyramidal and restiform
walls swell outwards, and form large lateral ‘ vagal ’ lobes ( fig.
51. /i) : these are remarkably developed, and are nodulated in the
Carp, 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 electric! ’ ; but the vagal
lobes are scarcely less remarkable for their size in the Gymnotus,
where they have no direct connection with any of the nerves of the
electric organs. In the Cod the vagal ganglions are obsolete, and

* Homologous with the “ filamenti arciforini ” of Rolando, lviii. p. 1 70. t. i.
fig. 2.

I Three are called “ vordere pyramiden ” by Dr. Stannlus, lvi. p. 43.

Section of medulla

NERVOUS SYSTEM OF FISHES.

175

the nodulus slightly swells above, and obliterates the ‘ calamus
scriptorius.’ In the Lucioperca the vagal lobes are not very dis-
tinct, but they mark 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 Vertebrata save fishes are the
vagal lobes and the nodulus present.

The posterior pyramids, which are the encephalic 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 resti-
forme and the basis of the vagal lobes, quit those columns to
converge, ascend, and unite together above the anterior opening of
the fourth ventricle : they there form either a simple bridge or com-
missure (yfig- 54. c), or are developed upwards and backwards into a
ganglionic mass, over-arching the ventricle ; this mass is the ‘cere-
bellum ’ 47 — 53. 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 ganoid Polypterus *, and in the almost fin-
less Lepidosiren {fig. 54. c) ; it attains its highest development,
in the 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 2iredaceous fishes by numerous trans-
verse folds ( fig. 55. o'). In most osseous fishes the cerebellum is

a smooth convex body ; hemispheroid
{pi. 50. c), or transversely subelliptic
(Eel), or longitudinally subelliptic (Lepi-
dosteus, fig. 49. c), or an oblong body
(Diodon, fig. 47. c), or it is depressed and
tongue-shaped (Cod), or oval, or pyra-
midal (Perch) : it is very rarely found
extending forwards, as in Echineis and
Amblyopsis spelcEus\ {fig. 50. c), over any
part of the optic lobes ; but often back-
wards over the whole fourth ventricle, as
in the Cod, the Diodon ; or over the major
part of the ventricle, as in the Herring, tlie Eel ; but sometimes
covering only a small portion, as in the Lump-fish, the Lepidosteus,

* XXV. p. 24. pi. ii. figs 5. 7. t xxxiii. p. S39. pi. 27.

.See Dr. Wym.nn’s excellent description of this fish, in t.xxxvi.

Lepidosteus ; Amblyopsis ;

nat. size. magnified.

176

LECTURE VIII.

and the Sturgeon, The relative size of the cerehellum, accord-
ingly, varies greatly in ditferent 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 Flat-
fish {Pleuronectida), and is unsymmetrically shaped in the Sharks ;
it presents a posterior notch in the Herring, a transverse notch
dividing it into an anterior and posterior lobe in the Lophius, and
a crucial impression in the Skate. The cerebellum presents in
many fishes a small cavity or fossa at its under part, continued from
the fourth ventricle c) ; it is solid in the Tench, the Gar-

Pike, and the common Eel; some grey matter is usually found in
its interior, with feeble indications of white strias, but there is no
‘arbor vitae,’ except in the Tunny and the Sharks.

The posterior ‘crura cerebelli’
are formed, as we have seen, by
the posterior pyramids in con-
junction with part of the resti-
Section of Brain, Carp. . .^,eJ,tical fibres from

the side of the cerebellum continue to attach it to the sides of the
restiform or trigeminal lobes, and some of these are continued, as
arciform filaments, upon the under surface of the medulla oblongata :
they answer to the ‘ crura cerebelli ad pontem ’ of mammalia ; but,
as there are no lateral lobes to the cerebellum in Fishes, these crura
are rudimentary, and the ‘ pons ’ is absent. In the Shark they con-
nect the sides of the base of the cerebellum with the ‘ restiform
commissure’ (^gs. 48 and 55. L). In most Fishes two fasciculi of
medullary fibres proceed, as ‘ anterior crura,’ from the under and
fore part of the cerebellum, or converge from the lateral and fore
part forwards, to form the inner wall or septum {Jig- 52. 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 tranverse fasciculi of white
fibres, forming the ‘commissura ansulata,’ which crosses the pre-
pyramids just behind the ‘hypoaria’ {Jig. 53. n). The inferior white
surface of the cerebellum which forms the roof of the fourth ven-
tricle is called ‘ discus cerebelli,’ and from this part small tubercles
project in a few fishes (e. g. Blennius).

The restiform columns, quitting the postpyramidal 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

NERVOUS SYSTEM OF FISHES.

177

Loach and Herring {Jig. 52. i), and also in the Sturgeon and Chi-
miera, where they are closely connected with a thick vascular mass of
pia mater and arachnoid. The trigeminal lobes are large 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 cerebellum, I call the ‘ commissura restiformis ; ’
it is remarkably developed in the Carcharias, where it seems to
form a small supplemental cerebellum beneath the large normal one,
{Jig. 55. 1)* In figure 48. the medulla oblongata is cut across,
the fourth ventricle exposed from behind, and the restiform com-
missure, I, 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 in
Fishes, is called the ‘ epencephalon : ’ it is relatively larger, occupies
a greater proportion of the cranium, and is more complex and diver-
sified in this than in any of the higher classes of Vertebrata.

The next succeeding primary division of the brain, is called the
‘ mesencephalon : ’ it is usually the largest division in Osseous Fishes,
and consists of two upper spheroidal bodies, called ‘ optic lobes ’■]■ (o),
of two lower subspherical bodies, called ‘ hypoaria (?z), with inter-
vening connecting walls enclosing a cavity, called the ‘ third ventricle,’
which is prolonged downwards into the pedicle of the ‘ hypophysis ’ or
pituitary gland ( p), and upwards into that of the ‘ conarium ’ or pineal
gland {w). 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, which unites
or crosses the prepyramids before they penetrate the hypoaria, is
very obvious in the Sturgeon and Perch, where it is figured by
Gottsche (lvii. pi. iv.. Jig. 7. 1) : it may be regarded as the most
anterior of the arciform filaments, which feebly represent the pons
Varolii in fishes. The restiform columns are expended chiefly in
forming the walls of the third ventricle and the base and exterior

* The medullary lamina which Valentin describes as crossing the posterior point
of the calamus in the Chimaera, may be the homologue of the restiform commissure.
Miiller’s Archiv. 28. tab. 2. fig. 8, 9.

f ‘ Lobes creux,’ Cuvier, xxiii. i. p. 310. But the cerebellum and hypoaria are like-
wise ‘ hollow lobes,’ and the prosencephala are hollow in the Lepidosiren and Sharks.

f ‘ Lobes infcrieurs,’ ib.

VOL. II.

N

178

LECTURE VIII.

walls of the optic lobes, a small part only being continued forwards
to the cerebrum in most Osseous Fishes. The anterior cerebellar
crura are chiefly lost in the inner walls, septum, or longitudinal
commissure of the optic lobes.

These lobes are commonly of a subspherical flgure, and larger
than the cerebral lobes (as in figs. 47. 49. 51, 52. o) ; they are often
larger than the cerebellum, {ib. ib.) ; they are of equal size with the
cerebellum in the Eel; are smaller than the cerebral lobes, but
larger than the cerebellum, in the Polypterus and Lepidosiren {fig.
54. o.) ; they are smaller than either the cerebrum or cerebellum in
the Amblyopsis spelceus {fig. 50. o.), and in the Sharks {fig. 55. o).
In the latter they bear the same proportion to the optic nerves and
eyes as in other Ashes, their small relative size depending on the
advanced development of both cerebellum and cerebrum : in the
blind Amblyopsis 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 Amblyopsis 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 im-
pressions of the sense of sight, giving them form, and making them
perceptible and tenable as ideas by the animal.

The optic lobes are hollow in most Ashes. The exterior surface
shows blended grey and white matter, the white fibres converging
to the optic nerves on the outer side of the lobes, and passing trans-
versely from one lobe to the other from their inner sides across the
ventricle. * Some of these fibres unite with the anterior crura of
the cerebellum to form the ‘longitudinal commissure’ {fig- 52. r),
which consists of two or four medullary fasciculi, decreasing
in the Tench, increasing in the Cod, as they pass forwards. |
On divaricating the optic lobes from above, their cavity or ventricle
is exposed : its floor is variously configurated in different fishes.
There are one or two small white tubercles (‘tuberculi optici,’y?^. 51,
52. t) on each side of the back part of the septum : the Pike and Perch
show four of these bodies, the Carp and Herring two ; in the Carp they
are oblong, juxtaposed, and were called ‘tuberculum cordiforme’ by
Haller I ; they are not present in the Polypterus, Lepidosiren, Sturgeon,

* These transverse fibres are analogous to the ‘ corpus callosum,’ but not homo-
logous with it, as Carus (xciv.), Cuvier (xxiii.), and Gottsche (i.vii.) supposed.

f Analogous to the ‘ fornix,’ but not homologous with it, as Gottsche contends
(lviii. p. 266.)

f Lix. In the Salmo Umhla, where they are four in number, Haller called them
‘ corpora quadrigemina : ’ Cuvier, also, regards them as answering to the ‘corpora
quadrigemina ’ of Mammals (xxiii. i. p. 317.), mistaking a relation of analogy for
one of homology.

NERVOUS SYSTEM OF FISHES.

179

or Plagiostome fishes. External to these tubercles the fioor of the
ventricle usually rises into a curved eminence with its convexity
outwards; this is the ‘torus semicircularis’ of Haller * 52. zr.)

In the Carp, where the great physiologist first described and named
them, they are large, and much curved : in general the ‘tori’ describe
only a small portion of a circle ; and in some bony fish, as the Gar-
pike, Loach, and Lump-fish, they are scarcely raised above the
level of the fioor of the ventricle. They are not developed in the Po-
plyterus, the Lepidosiren or the higher Plagiostomes ; and both tori
and globuli are peculiar ichthyic developments in the ventricles of the
optic lobes. The bottom of the optic ventricle anterior and external
to the tori, is grey, and usually prominent (yfig. 52. v), with white
fibres radiating through it to rise and expand upon the walls of the
lobes. The optic lobes have almost coalesced in the Polypterus, Lepi-
dosiren, Amblyopsis, Eel, and Loach ( Cobitis). Where they appear
distinct externally, as in most osseous fishes, they are brought into
mutual communication by one or two commissures, besides the so-
called ‘corpus callosum;’ the anterior ‘ commissura transversa ’ is
shown in the Herring (Jig. 52. s) ; it crosses in front of the entry to
the third ventricle, f

protuberances {Jig. 55. n), separated below by the vascular (hypo-
physial) floor of the third ventricle. In most osseous fishes the
corresponding fibres of the prepyramidal tracts swell out suddenly,
beneath the optic lobes, into two protuberant well-defined oval

* Lix. t. iii. p. 201. It is analogous to, but not, as Gottsche supposes, liomolo-
gous with, the ‘ thalamus opticus ’ of the Mammalian brain. It is neither analogous
to nor homologous with the ‘corpus striatum.’

f Cuvier affirms (xxiii. t. i. p. ,316.) that this “necessarily answers to the an-
terior commissure of the cerebrum but it has only a remote analogy with it, in
so far as the mechanism of the whole mesencephalon of Osseous Fishes resembles
that of the cerebrum in Mammals, whilst the true homology of the mesencephalon
does not extend beyond the parts immediately surrounding the third ventricle and
the ‘ iter ’ to the fourth in the Mammalian cerebrum.

Base of brain ; Cod.

In the Myxine and Lepidosiren
the prepyramidal fibres curve sud-
denly forwards and upwards be-
fore expanding into the floor and
sides of the thii-d ventricle, and
they thus form a small protube-
rance beneath the basis of the
optic lobes {^g. 54. n). In the
Shark the same columns swell
out laterally and form two small

180

LECTURE VIII.

ganglions (‘ hypoaria,’ Jig. 53. n) * : 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 called ‘ hypoarian ventricle.’ In some Salmo-
nidcB their surface is striated ; in some Cyprinidce (Tench) they
are confluent; but commonly they are distinct, and have in their
inferior interspace a vascular medullary depressed sac (the ‘ hsema-
tosac,’ Jig. 53. d), usually oblong, as in the Cod, rarely bifid or cordi-
form, as in the Lump-fish. These prominences from the floor of
the mesencephalon, posterior to the infundibulum and hypophysis,
are peculiar to the brain of fishes, and, in their full development, 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 Polypterus, as in the still more
amphibioid Lepidosiren.

The true vasculo-membranous infundibular downward prolongation
of the third ventricle exists in all osseous Fishes, and extends from
the anterior angle of the hypoaria where these exist : the infun-
dibulum 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 hypophysis lies at the fore -part
of the cranial cavity, far in advance of the cerebral lobes, f In the
Cod the hypophysis {Jig. 53. p) is a sub-spherical mass with an
irregular or slightly nodulated surface, almost half the size of the
human, so called, ‘pituitary gland,’ and well exemplifies the vast propor-
tional size of this constant appendage to the brain of Fishes. In the
Lepidosiren the infundibulum is wide, and the hypophysis a white
flattened discoid body (^g. 54. p).\ In all fishes it is richly supplied
with vessels, and is closely attached to the floor of the cranium ; but,
although its early development checks or modifies that of the cranial
vertebree, 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 development of ‘ thalami ; ’ but the parts homologous
with those recruiting ganglia are constantly indicated by the attach-
ment of the conarium, or upper prolongation of the third ventricle.

The conarium {Jigs. 50. 54, 55. w) is as constant an appendage of
the encephalon in Fishes, as the hypophysis ; but is commonly only a
vasculo-membranous pyramidal sac continued from the third ven-

* Analogous to the ‘ corpora mammillaria ’ of the human brain, but not homo-
logous with them, as Arsaki (nni,), and Desmoulins (lxxviii.) supposed. Cuvier
defines them as the ‘lobes inferieurs,’ xxiii. i. p. 318.

f LX. p. 56. t. ii. fig. 1.

t The hypophysis is marked g in xxxiii. pi. 27. fig. 4., and is called ‘mam-
millary body’ in Lepidosiren annectens, ib. p. 361.

NERVOUS SYSTEM OF FISHES.

181

tricle ; the base expanding from between the anterior interspace of
the optic lobes, and the apex directed foi’wards and attached to the
roof of the cranium. Some medullary matter mingles with the mem-
branous 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 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
consists 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 ventricle
through an interspace produced by the divarication of the main
lateral columns of the encephalon.*

The fasciculi continued forwards 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 53, r.). In Osseous
Fishes the two cerebral crura, so constituted, rarely undergo any
enlargement, homologous with the ‘ thalami,’ where they form the
anterior boundary of the third ventricle ; but after a very brief course,
as ‘ crura cerebri,’ radiate into two small subspherical ‘ prosencephalic ’
masses f of grey matter {Jig. 53. 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 smah tract of
its grey matter, converge to the anterior interspace of its lobes, and
either expand there into ‘ rhinencephala ’ {Jigs. 49, 50. e)., or are
continued forwards and outwards, as ‘ rhinencephalic crura’ {Jigs. 47.

* Is this vertical slit homologous with the encephalic ring perforated by the
oesophagus in Invertebrata ?

f Influenced by the inapplicability of the term ‘hemispheres’ to parts which
are more commonly spheres or spheroids, and to avoid misconception by those
who attach to the word ‘ cerebrum’ the idea of the whole brain minus ‘ cerebellum’
and ‘medulla oblongata,’ or who may restrict the term ‘cerebral hemispheres’ to
the super-imposed masses of the lateral ventricles in higher Vertebrata, I shall
apply the term ‘ prosencephalon ’ to the constant division of the brain in question,
and prosencephalic lobes or prosencephala to its commonly distinct moieties. It
is unfortunate for the student of anatomy that, in his introduction to the
science by the human structure, he should become acquainted with these parts of
the brain under the name of ‘ hemispheres,’ as if they were two halves of an essen-
tially spherical whole or single organ. In most Vertebrata the homologous parts
are presented to our view under a form more agreeable to their true duplex nature.

182

LECTURE VIII.

51. 55. z), to form the olfactory lobes, or ganglia {ib. k), at some
distance from the brain. Although the prosencephalic lobes are com-
monly in contact with the optic lobes, yet something analogous to the
displacement of the rhinencephala may be seen^ in the prosence-
phala of the Polypterus and Lepidosiren, in which the procense-
phalic crura advance some way before they expand into the prosen-
cephala : in the Plagiostomes, also, the prosencephalic crura {Jig. 55. x)
have a short independent course in advance of the optic lobes.

The prosencephala are distinguished from the optic lobes by their
grey pinkish exterior, and, generally, also by their fissured or nodu-
lated surface. The first of these characters must be looked for in
recent fish : the second is more permanent, and may be seen in the
preparations of the brain of theEel(^w^Mz7Za acutirostris, No. 1309,B.);
of the Lump-fish ( Cyclopterus, No. 1309, C'.) ; of the Gurnard ( Trigla
lyra. No. 1309, D') ; and especially in the specimen of the brain of
the Cod (No. 1309), which Hunter truly, though briefiy, 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 recog-
nition of the homology of the optic lobes with the anterior of the
bigeminal bodies of the human brain. With regard to the ‘ cerebrum’
of the Cod, a median tract or convolution is marked off by a longi-
tudinal fissure, which extends along the back of each prosencephalon,
defining also a posterior and inferior convolution ; the median con-
volution is vertically fissured on its inner side. In the Amblyopsis
{Jig. 50. 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 Polypterus and Le-
pidosiren {Jig. 54. p), and in the still more developed confluent mass

in the Sharks {Jig. 55. p) ; the pro-
sencephala are, also, smooth in the
Myxines, where they are relatively
smallest. The comparative ana-
Biain of Lepidosiren. tomists, who have failed to recog-

nise the true homology of the pro-
sencephalon in Osseous Fishes, appear to have been misled chiefly by
its small proportional size, which is commonly that exhibited in these
preparations of the brain of the Cod {Jig. 53, p), the Carp, and the Globe-
fish * ; in some species the prosencephalon is still smaller, as in the
Gar-fish, the Herring {Jig. 52, p), or the Lump-fish. The prosencephalon

* The preparations exhibited and here alluded to are those numbered 1309,

1 309 k, 1 309 m.

NERVOUS SYSTEM OF FISHES.

183

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, and the Skate, neither the
cerebellum nor the optic lobes are so large as the prosencephalon ; in
the large Sharks their united size scarcely equals that of the prosen-
cephalon ; and in the Salamandroid Polypterus and the Lepidosiren
the prosencephalic lobes surpass all the rest of the brain, and manifest
their true cerebral character and importance. In the Amblyopsis the
relative magnitude of the prosencephalon is due to the diminution of
the optic lobes in that blind fish ; in the Plagiostomes it is due to
absolute development ; as it is, also, in the Polypterus and Lepido-
siren, where the prosencephalon presents the closest similarity in
form and structure to that division of the brain in the Batrachian
Reptiles ; each lobe, for example, is elongated in the axis of the
skull, and is of a subcompressed oval form, and has a large ‘ lateral
ventricle ’ in its interior in the Lepidosiren 54. fo.) In the Skate
the prosencephala coalesce into a subdepressed transversely elongated
mass, their essential distinction being indicated by a mere superficial

medianfissure; in theCarcharias
{fig. 55. p.), the prosencephalon
forms an almost globular mass,
with scarcely a trace of a median
fissure. Amongst bony fishes
the prosencephalic lobes ai'e
more or less confluent in Lucio-
perca sandra, Trachinus draco,
Sargus, Mullus, Scomber tra-
cliinus, Belone, Clupea harengus, and Clupea sprattus ; they appear as
distinct symmetrical spheroids in most other fishes, their union being
reduced to a small transverse medullary band (prosencephalic com-
missure, 52. y *). The symmetrical character of the prosence-
phala, as of the optic lobes, is wanting in most Fleur onectidce.

The grey vascular neurine forms the greatest part of the prosence-
phalon in most osseous fishes ; the white fibres radiate into tliis
substance, and rarely appear on any part of the exterior surface ; the
white' neurine, however, predominates in the Plagiostomes and Lepido-
siren. As a rule, the prosencephalic lobes are solid ; but tlie preparation
of the brain of Carcharias (No. 1310, A.) shows a deep ventricular fis-
sure at the anterior and under partof the prosencephalon, with avascular

* Carus well recognises the homology of this commissure with that of the corpus
striatum, called ‘anterior commissure’ in the human brain (i. p 24.).

N 4

184

LECTURE vni.

fold of membrane or ^ choroid plexus ’ penetrating the fissure, which
is continued forward into the crus of the olfactory lobe. The lateral
ventricle is more extensive in the Lepidosiren, and is continued
directly into the olfactory lobe.

The ‘ rhinencephalon ’ {^figs. 47. 49, 50. 54, 55. k) consists of
two 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
‘ olfactory lobes,’ ‘ tubera,’ or ‘ ganglia.’ The rhinencephala 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 rhinencephalic crura
{figs. 47. 51. 55. z) vary exceedingly in length. In the Lepidosiren
{fig. 54.) they are feebly indicated by a continuous indentation
circumscribing the base of each rhinencephalon (r), and defining
it from the anterior end of each prosencephalon (p.) in Polypterus
and Lepidosteus {fig. 49.), the indentation is deeper, and the attach-
ment of the base of the now pyriform rhinencephalon sinks to the
prolonged crus or basis of the prosencephalon. It is from this sub-
stratum that the rhinencephalic crura are prolonged in all osseous
fishes ; in some they are so short that the rhinencephala are partly over-
lapped by tbe prosencephala ( Trigld), or rise into view immediately
in front of them {Amblyopsis, Anguilla, 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
capsules : this has led some excellent observers to deny the existence of
olfactory lobes in such fishes ; but the rhinencephala are truly present
in both the Tetrodon*, the Cod and Carp; they are merely removed
to j uxta-position with the olfactory capsules, with a concomitant
prolongation of their crura. These crura, so prolonged, 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, f 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 rhinen-
cephalon 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 rhinencephalic crus of the Cod, their

Dr. Desmoulins (lxxviii, t. i. p. 169.), has erroneously denied the existence
of the ‘ lobes olfactifs’ in the Diodon ; but in other fishes both he and Mr. Solly
(lxii. p. 78.), have taken a correct view of the rhinencephala or ‘ olfactory tubercles.’

t Camper, lxi. p. 95. ; Cuvier, xxiii. p. 321.

NERVOUS SYSTEM OF FISHES.

185

respective differences 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 54. l. ol.'). In the Sharks a ventricle is continued
to each rhinencephalon along its crus from the prosencephalon. The
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 rhinen-
cephalon, before it transmits the true olfactory nerves to the cap-
sule. In other words, the olfactory nerve conveys impressions 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. To say, with Cuvier, that
“ the ganglion of the olfactory nerve is sometimes at its beginning,
and sometimes at its end” (t. iii. xxm. p. 146.), or that it occurs “ in
the course of the olfactory nerve, at a greater or less distance from
the hemispheres ” (xxvii. p. 227.), is, in fact, to deny the marked ana-
tomical difference between the crus and the nerve proper ; and to
overlook the serial homology of the rhinencephalic crura with those
of the prosencephalon. The olfactory lobes or rhinencephala them-
selves are serially homologous with the optic lobes. As to the pro-
sencephalon, 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 that of the ganglions of any 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 prosencephalon in
Mammalia, 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 ‘ corpora
striata,’ with their commissures and a thin supra-ventricular cover-
ing. “ Le corps cannele,” he says, “ forme a lui seul presque tout
I’hemisphere.” {Legons d'Anat. Comp. t. ii. 1799, p. 162.) But he
failed altogether to recognise the homology of the prosencephala in
Fishes. Since Arsaki’s time their homology with the cerebral lobes
of Reptiles, Birds, and Mammals has been generally recognised.

186

LECTTIRE VIII.

Girgensohn (Lxm. p. 155.) says they may well be compared with the
‘ corpora striata ; ’ but he recognises the important difference, that,
whereas these ‘ transmission ganglia ’ (durchgangsknoten) 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 highly important to note the mode of establish-
ment 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 exca-
vations, as you perceive in these elongated prosencephala of the
Lepidosiren 54. lv\ or they are deep fissures towards the under
part, as in the coalesced hemispheres of the Shark ; whence I con-
clude that the solid prosencephalon of Osseous Fishes is not a mere
representative of a basal ganglion forming the floor of the ventricle
of the hemispheres in the higher Vertebrata, 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 Jig. 51. 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 most interesting to perceive on the
superficies of the solid prosencephalon in many fishes the fore-
shadowing of the convolutions, which are not fully established until
the Mammalian type is attained. The prosencephalon of the fish is
far, indeed, from being a miniature model, but it may be regarded as
representing the potential germ, 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. 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 precisely with the general bulk of the body.
The size of the optic lobes, e. g. has a more constant and direct re-
lation to that of the eyes, which soon acquire their full development.
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, provision for occupying the in-

NERVOUS SYSTEM OF FISHES.

187

creasing capacity of the cranium is made by a concomitant develop-
ment of the light cellular araehnoid, whieh has the further advantage
of regulating the specific gravity of the head.

As the branehial respiration is a peeuliarly aetive and important
function in Fishes, and is served by an extraordinary apparatus of bony
or gi’istly arehes with their muscles, we may associate therewith the
peculiar development and comjfiexity of the medulla oblongata, as
the centre of the vagal or respiratory nerves. The Carp and other
cyprinoid Fishes, which have not the mechanical modifications for
retaining water in contact with the gills, so characteristic of the
Apodal, the Lophioid, and Labyrinthibranch fishes, are remarkable,
nevertheless, for their tenacity of life out of water ; and the peculiaily
developed vagal lobes in them may relate to this maintenance of the
power of the respiratory organs during a suspension of their natural
aetions.

The extensive gradation of the cerebellum between the extremes
of structure presented by the Myxine and the Shark throws, as
might be expected, more direct light upon its function. With regard
to this, two views have been taken. According to 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 expe-
riments 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 ex-
periments has been objected the possibility of the convulsive mus-
cular 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 volun-
tarily through her own experiments, if we may so call the ablation
and addition of parts which comparative anatomy offers to our con-
templation.

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 car-
tilaginous Fish, and by the obsei'ved fact of the male and female
Lampreys entwining or wreathing themselves entirely about each
other, mutually aiding in tlie 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 cerebellum in the Lamprey than in
the Shark. But the reverse of this is the fact : the Lamprey has
the smallest, and the Shark the largest, cerebellum in the class of

188

LECTURE VIII.

Fishes. If, on the other hand, we compare the Cyclostome and
Plagiostome Cartilaginous Fishes, in reference to their modes and
powers of locomotion, we shall find a contrast which directly accords
with that in their cerebellar development. 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, unaided by an air-bladder, by
vigorous muscular exertion of well-developed pectoral and caudal
fins, sustains itself at the surface of the sea, soars, as it were, in the
upper regions of its atmosphere, is proverbial for the rapidity of its
course, and subsists, 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 indentation
instead of transverse laminae. 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. 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 the Polypterus the cerebellum
hardly more developed than in the Lepidosiren, whilst in the somewhat
more active and predacious Lepidosteus it is the smallest of all the
segments of the brain. In the grovelling Sturgeons the cerebellum
offers an intermediate grade of development between those that
characterise the above-cited Ganoids. 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

NERVOUS SYSTEM OE FISHES.

189

developed and enormous eyes, we might, perhaps, gain some insight
into the otSce 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 the presence of light, sufficient, perhaps, to
warn the Amblyopsis to retreat to the darker recesses of its sub-
terranean abode, that the optic lobes are not reduced in the same
proportion, but retain a form and size, which, as compared with
their homologues 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 M.
Flourens (lxiv.), 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 prosencephalon were
special seats or organs of different psychical phenomena, such phe-
nomena 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 development of the homologues of the cerebral hemi-
spheres. Some species as, for example, the Shark and Pike, are pre-
datory and ferocious : some, as the Angler and the Skate, are crafty :
some, as the Sword-fish and Stickleback, 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
can hardly differ more in shape, in relative size, or in structure, 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 devourer, broad in the prey.

190

LECTURE VIII.

The Lopliius lurks at the bottom, hidden in the sand, waiting, like
the Skate, for its prey to come within the reach of its jaws : the
difference in the shape, size, and structure of their prosencephala 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-progenitive Callichthys * has
neither the antero-lateral nor the posterior regions of the cerebrum
more developed than in bony fishes generally.

MEMBRANES OF THE NEURAL AXIS.

Both brain and myelon are immediately invested by a thin but
firm fibro-cellular and highly vascular membrane, the outer surface
of which is usually covered by a stratum of pigment-cells, belonging
properly to the central layer of the arachnoid, which has here co-
alesced with the proper vascular 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 in the ven-
tricles of the brain. There is commonly a remarkable development
of the vascular and pigmental membrane over the fourth, or epen-
cephalic ventricle. I found such a mass concealing the rudimental
cerebellum in the Lepidosiren ; it is largely developed in the Sturgeon
and Paddle-fish, where it is posterior to the cerebellum. 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
pretty compact adipose matter in the Tunny and Sturgeon. This
modified arachnoid exists, but in less quantity, in the spinal canal,
and even accompanies the cerebral nerves in their exit from the skull
in some fishes with large nerve-foramina. The quantity of the
cellular arachnoid above the cerebral lobes of Lepidosiren is a striking
example of the piscine nature of that genus.

The primitive fibrous capsule of the neural axis, the unossified or
unchondrified remains of which, or of its inner layer, form the so-
called ‘ dura mater,’ is most distinct in the low-organised Dermopteri;

* Callichthys litloralis, or Hassar-fish of Demerara. See the specimen of its
brain, No. 1309, b, and that of its nest and eggs. No. 3787, b. Phys. Series, and
an account of its habits in the Zoological Journal, vol. iv. p. 244.

f xxiii. i. p. 309.

NERVOUS SYSTEM OP FISHES.

191

in the Plagiostomi 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 continu-
ous fibrous membrane can be distinguished 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.

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 prosencephalon ; they govern the develop-
ment of the rhinencephalic arch ; and, as this advances in the elonga-
tion of the skull, and recedes from the prosencephalic arch, either the
brain is co-elongated, the rhinencephalon 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 juxtaposition with the prosencephalon, and the
olfactory nerves are prolonged through the interorbital space, per-
forate or traverse a notch in the prefrontals, and expand, as a resolved
plexus, upon the pituitary plicated sac.

The rhinenceplialon accompanies its vertebra and recedes from the
rest of the brain in Salmo, Cyprinus proper, Brama, Tinea, Gadus,
Lota, Hippoglossus, Clupea, Belone, Lucioperca, Cobitis, the Plectog-
nathi, and Plagiostomi ; it retains its primitive contiguity with the
prosencephalon in Perea, Scomber, Esox, Pleuronectes, Blennius,
Anguilla, Cyclopterus, Gasterosteus, Eperlanus, Leuciscus, Cottus,
Trigla, Amblyopsis, Echeneis, the Ganoidei and Lepidosiren. The
condition of this difference would be an interesting subject of enquiry.

As the crus of the rhinencephalon is formed not only of fibres con-
tinued from the prosencephalon, but also, and in some fishes chiefly,
of distinct white and grey tracts traceable along the base of the
mesencephalon, in part as far back as the prepyramidal bodies, so the
origin of the olfactory nerve has been described as characterised by the
same complexity and extent ; and it is true that in some instances,
where the rhinencephalon is in contact with the prosencephalon, a
small portion of the true olfactory nerve may be distinctly traced,
e. g. in the Perch, backwards as far as the mesencephalon : just as we
find in some fishes. Sturgeon, e. g., a portion of the optic nerve trace-
able as far back as the cerebellum, and in the Eel to the hypoaria,
and not exclusively terminating in the optic lobe. Most of the cha-
racteristics of origin and course attributed in works of Comparative

192

LECTURE VIII.

Anatomy to the olfactory nerves are to be understood of the crura rhin-
encephali. In the Lancelet the little ciliated olfactory sac {fig. 46. o/.)
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, it sends off the nerves by numerous very
short fasciculi : this characteristic 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, the Ide, or the Roach, shows 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 Am-
blyopsis. In the Plagiostomes, the Sturgeon, the Polypterus, and
the Lepidosiren, the optic nerves, traceable in part from the optic
lobes, closely adhere to the basis of the mesencephalon, from which
they seem to rise, anterior to the infundibulum, and are there con-
nected together by a short transverse commissure ; but they do
not cross each other. In ordinary Osseous Fishes 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 Gar-pike, and the Lump-fish, a
portion may be traced to the hypoaria : in the Cod some fibres of
the optic nerve are derived from both the hypoaria and the wall of
the third ventricle. The nerves are connected together at their
origins by a commissure ; but afterwards they cross one another
without interchange of fibres {fig. 53. 2) : sometimes the right nerve
in its passage to the left eye passes under, sometimes over, the left
nerve * : 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. 57. a). The retina
is formed by the unfolding of the nerve ; and it would be a forced and
overstrained analogy to compare it with the ganglion of the olfactory
nerve (rhinencephalon), because this happens in some fishes to be close
to the nasal capsule. The optic nerve escapes, in Osseous Fishes,
either thi'ough the anterior fibrous wall of the cranium beneath the
orbito-sphenoid, or through a notch or a foramen in that bone. In
the Flounder one optic nerve is usually shorter than the other. In

* I have seen both varieties in different individuals of Gadus morrhua. See
also Lxxv. ii. p. 203.

NERVOUS SYSTEM OP FISHES.

193

the Eel the nerves form, after decussation, a very acute angle in the
axis of the body : in the Lump-fish they form an obtuse open angle.

Since there are no muscles of the eyeball in the Lancelet, the
Myxinoids, the Amblyopsis, and the Lepidosiren, there are no motory
nerves of the orbit. In the Lamprey a small third nerve and a fourth
nerve, which are closely connected where they quit the cranium,
again separate, the one to supply the rectus superior and rectus
internus, the other the ohliquus superior ; the filaments supplying
the other muscles of the eyeball cannot be separated from the fifth pair.
In all other fishes the sixth or abducent nerve has its proper origin,
as well as the fourth and third. The third, or oculo-motorius, {Jig. 53.
55. 3.) rises from the base of the mesencephalon, behind the hypoaria, or
from the commissura ansulata ; it escapes through the orbito-sphenoid
(Carp), or the unossified membrane beneath it (Cod), and is distri-
buted 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 uniting with a branch of the fifth
nerve, and sometimes, as in the Mackerel, Gar-pike, and Lump-fish,
developing a small ciliary ganglion at the point of communication.

The fourth nerve, or trocJdearis, rises from the back of the base
of the optic lobes, between these and the cerebellum : it escapes
either through the orbito-sphenoid (Carp), or the contiguous mem-
brane (Cod), and is constantly and exclusively distributed to the
superior oblique eye-muscle.

The sixth, or abducent, nerve (fig. 53. 6) rises from the prepyra-
midal tracts of the medulla oblongata, beneath the fifth, and, in most
Osseous Fishes, by two roots, as figured by Mr. Swan (lpv. pi. viii.
fig. 2), in the Cod. 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 :
it escapes by the foramen or anterior notch of the ali sphenoid, in
advance of the fifth nerve.

This nerve, the trigeminal (fig. 53. 55. s), 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 ( Clupeidce, 52, i. Cyprinidce)
from a special ganglion or enlargement of that part of the medulla
oblongata : in a few (Conger, Lump-fish) by a smaller origin resolved
into several roots. The trigeminus shows well its spinal (myelonal)
character in Fishes, but its double root is more deeply buried in the
medulla oblongata. In Cottus, Blennius, Cobitis, and Leuciscus, the

VOL. IT. o

194

LECTURE VIII.

dorsal roots may be traced receding from the ventral ones, as they
penetrate the medullary substance. The hinder roots in the Blenny
join the facial and glosso-pharyngeal. Of the five roots of the tri-
geminal in the Sturgeon, the first, second, and fourth form a ganglion
Gasserianum. In most Osseous Fishes the first branch is sent back-
wards, to form, in conjunction with a branch of the nervus vagus, the
so-called ‘ nervus lateralis,’ 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
receives only a slender filament of the vagus : it sends off a branch
Avhich runs along the sides of the interneural spines 56. /.),

receiving branches from all the sjiinal nerves : it then curves down
along the scapular arch, gives branches to the pectoral and ventral
fins, supplies the great lateral muscular masses and the mucous canal,
and sends a nerve along the interhsemal spines, which communicates
with filaments from the corresponding spinal nerves : both interneural
and interhasmal branches terminate in the spinal 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 (r. mandibularis, seu maxillce infei'ioris), consists chiefiy of
motory filaments which supply the muscles of the hyoid and mandi-
bular arches, and send the ‘ ramus opercularis seu facialis,^ to those of
the gill-cover : the sensory filaments supply the teguments of the sides
of the head and under jaw, enter the dental canal, supply the teeth, and,
in the Cod, the symphysial tentacle. The maxillary division {r. max-
illaris') bifurcates behind the orbit, one branch passes outwards to
supply the suborbital mucous canals and integuments on the sides of
the head ; the other, after sending a branch obliquely outwards, curves
foi'wards along the floor of the orbit, gives off a palatine nerve (r.
pterygo-palatinus), and supplies the integuments, mucous tubes, and
teeth of the upper jaw : the supra-orbital division gives off the two
ciliary nerves, one of which joins the ciliary branch of the third : it
then 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 where they leave the main
trunk. The first electric nerve is given off by the non-ganglionic
part of the fifth in the Torpedo (fig. 45. 5), and many of the terminal
filaments of the tegumentary branches of the fifth swell into peculiar

* See the beautiful figure given by Mr. Swan of this nerve in liv. pi. vii.

NERVOUS SYSTEM OF FISHES.

19.3

muco-ganglionic corpuscles.* In the Sturgeon the snout and its
tentacula are supplied by branches of the infra-orbital, not from the
supra-orbital division of the fifth : the opercular or facial branch sup-
plies, in addition to the gill-cover, the integuments and lips of the
protractile mouth, and the pseudo-branchia : it communicates with
the glosso-pharyngeal.

In the Lancelet the fifth nerve {Jig. 46. oh) distributes many fila-
ments to the expanded sensitive integument which represents the
head, and forms the sides of the wide oral 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 as it were, i. e.
by fewer primary branches : it also sends filaments to the rectus ex-
ternus and r. inferior of the eyeball : the nerves to the muscular parts
of the jaws and tongue arise in the Lamprey distinct from the fifth,
and their trunk may be regarded as a facial nerve ; one of the fila-
ments 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 Vertebrata are not distinct from the rest of
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 Vertebrata, retain an
associated origin with the trigeminal. The opercular or facial di-
vision of the fifth forms the hindmost portion of its apparent origin
in the Perch f, it supplies the mandibular, opercular, and branchios-
tegal muscles ; and sends off the branch to form, with a branch of the
vagus, the dorsal division of the ‘nervus lateralis.’ In the elongated
‘medulla oblongata’ of the Sander {Lucioperca) the facial nerve has
a distinct origin between the trigeminal and acoustic.

The acoustic nerve rises so close to the fifth, in the Skate, as to
appear to be a primary branch of that great nerve ; its distribution
on the labyrinth is beautifully shown by Mr. 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. Mr. Swan calls this branch

LXXVI.

f XXIII, tom. i. p. 325. pi. vi. fig. v.

196

LECTURE VIII.

the glosso-pharyngeal ; and says, “ this nerve, on being touched
near its origin in a recently dead animal, immediately produces a
contraction of the muscular appendages of the gills.” (ib. p. 41.) In
the Cod the acoustic nerve (fig. 53. 7), which here, as in all fishes
above the Dermopteri, is of large size, rises close behind, but distinct
from the fifth pair, between it and the vagus : the acoustic nerve
receives a filament from the vagus, extends in a crescentic form upon
the labyrinth, expands upon the large sac of the otolite, and sends
filaments to the ampulliform ends of the semicircular canals. In other
Osseous Fishes (Pike, Blenny), 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.

The nervus vagus has a development proportional to the extent
and complexity of the branchial apparatus in Fishes, and is usually
larger than the trigeminal ; it rises (fig. 53. 55. s) from the restiform
tract forming the side of the medulla oblongata, and commonly from
a specially developed lobe ; and is distributed to the branchial ap-
paratus, the pharynx and pharyngeal arches, the oesophagus and
stomach ; it sends also filaments to the heart, and to the air bladder
when this exists 58. t). In the Lamprey a portion of the vagus
combines with branches of the facial and hypoglossal nerves to form
a ramus lateralis vagi, which extends to the middle third part of the
body, where it terminates. In the Cod we saw that the ‘lateral nerve’
was formed chiefly by the trigeminal ; but in many Osseous Fishes
( Cgprinus, Belone, and Cottus) the proportions are reversed, and the
lateral nerve is formed by a branch of the vagus, which receives
filaments from the trigeminal nerve : in a few genera ( Salmo, Clupea,
Acipenser) it is formed exclusively by the vagus. In all these fishes
it is continued very far back along the lateral or dorso-lateral region
of the body ; sometimes lodged deeply in the lateral mass of muscles,
ex. gr. Belone, Clupea, and Scomber (Prep. 1384 of the Mackerel):
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 ( Cottus) it has both a
deep-seated and a superficial branch. In the Carp and Herring the
vagal ‘ ramus lateralis’ sends off a strong branch to the dorsal fin : in
the Glar-pike it sends, as in the Cod, large branches to the pectoral
and ventral fins ; it distributes its smaller branches to the skin and
mucous ducts ; and those in the Cod and Lump -fish anastomose with
branches of the spinal nerves. In the Perch there are two ‘ nervi
laterales ’ on each side ; the dorsal one, which escapes through the

NERVOUS SYSTEM OF FISHES.

197

parietal bone, is formed by the union of a branch from the facial
portion of the fifth with a branch of the vagus : the proper lateral
nerve is formed exclusively by the vagus, and divides into a
superficial branch supplying the lateral line, and a deep-seated
branch, communicating with the spinal nerves, and supplying
the myocommatal aponeuroses and the skin. * Whether the vagus
forms the whole or a part of the ‘ nervus lateralis ’ it transmits
it from the fore part of its origin : the ‘ nervus accessorius ’ when
present, which is rare in fishes, forms the hindmost part of the
vagus, as in higher Vertebrata. The nervus lateralis chiefly
supplies the myocommata, vertical fins and mucous line, pecu-
liarly ichthyic parts either by their preponderating development,
or their very existence : the nervus accessorius in mammalia,
sends no branch to the ‘spinalis,’ ‘ semispinalis,’ or ‘ longissimus,
dorsi ’ — the reduced homologues of the dorso-lateral myocommata of
fishes, but exclusively supplies the ‘cleido-mastoideus’ and ‘cucullaris,’
associating them with the respiratory actions of the thorax. The
nervus lateralis may be in some respects analogous to the accessorius ;
it is not homologous with it.

The vagus sends supra-temporal branches to the head, and oper-
cular branches to the gill covers. The usually double roots of the
nervus vagus pass out, in most fishes, by a single foramen in the ex-
occipital bone. The fore part of the root is the largest, and is
ganglionic : it is the true pneumo-gastric, supplying the gills and
stomach ; in the Tunny the branchial nerves are remarkable for their
size and their radical ganglions. The hinder second origin is usually
non-ganglionic, and is the source of the supra-temporal, glosso-
pharyngeal and lateral nerves. Some filaments rising behind the
vagus have been traced to the parts surrounding the brain within
the cranial cavity. The intestinal terminal filaments of the vagus
in Osseous Fishes communicate freely with the sympathetic. Each
vagal nerve of the Sturgeon equals the spinal chord in size and rises
by numei’ous I'oots. The vagal nerve has numerous roots, and an
extensive tract of origin in the Sharks, in which a posterior fasciculus
(y?y. 55. s'), representing the ‘nervus accessorius,’ can be best de-
monstrated.

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 proportion of clear (organic) filaments
to the opaque (animal) filaments in the vagus of fishes is much greater

* XXIII. tom. i. pp. 325 — 327.
o 3

198

LECTURE VIII.

than in that nerve in higher Vertebrata, according to Bidder and
Volkmann : which illustrates the progressive character of the indivi-
dualisation (selbsstandigkeit) of the great sympathetic.

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 peculiar erectile palatal organ of the Cypri-
noids is wholly, and the peculiar electric organs of the Torpedo are, in
great part, supplied by the very remarkable and characteristic vagal
nerve of fishes.

The first spinal 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 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,
and the sterno-hyoideus (44. /,/'); it is called ‘ hypoglossal nerve ’
by some Ichthyotomists.

Each of the true spinal nerves has a dorsal or sensory, and a
ventral or motory origin ; sometimes each rises by a single root ;
sometimes, as in the Cod, by two or more roots. 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 com-
monly upon the whole sensory origin of the nerve, where it emerges
from the neural canal. In some fishes (Bream and Gar-pike) 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 emergence, and the junction of the two roots takes place
quite exterior to the neural canal.*

The connection of the nerve-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, j" The best
illustration of the peculiar combination of the dorsal and ventral

Lxxvn. ii. p. 479.

f Liv. pl.x.

NERVOUS SYSTEM OF FISHES.

199

roots of the spinal nerves in Osseous Fishes, is that given by Mr.
Swan from the Cod. * The dorsal root sends a filament { fig. 56. a)
upwards, which joins a ventral filament (h') from the preceding nerve,
and forms the ‘ ramus dorsalis ’ {d~) : the dorsal root
sends two filaments (c) downwards, Avhich unite to-
gether, and with a ventral filament (e) of the same
nerve to form the ‘ ramus ventralis ’ (u). The fila-
ment 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 dorsal and a ventral branch ; the
ramus dorsalis includes a sensory filament of its own
nerve, and a motory filament of the antecedent ner\ e :
the ramus ventralis is formed by a motory and a
sensory filament of its own nerve ; both rami ‘ ven-
ConnectioMs of spinal trales ’ and ‘ doi’sales ’ are associated together, and

and later. 1 nerves, ° ’

Cod. (Mr. Swan.) with the vagal and trigeminal nerves through the
medium of the great ‘ nervus lateralis.’

The roots of the nerves distributed to the free, exploratory,
pectoral rays of the Gurnards, rise from special ganglionic swellings
of the cervical portion of the dorsal myelonal columns.

Sympathetic. — In the Myxinoid Fishes this nerve, or system of nerves,
is represented by the intestinal branch continued from the confluence
of the two nervi vagi. The best illustrations of the symiiathetic in ordi-
nary Osseous and Plagiostomous Fishes are those given by Mr. Swan,
from the Codj" and the Skate. J Each trunk of the nerve extends
in Osseous Fishes, from the side of the basis cranii (not entering the
cranial cavity) to the tail, accompanying the aorta along the Inemal
canal. Its first or anterior communication is with a branch of the
fifth, and a filament is sent forward to the ciliary ganglion ; and, in
the Carp a filament joins the abducent nerve, to which Cuvier
thought he had also traced a filament of 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 partition of the gills : the sympathetic
trunks also receive accessions from the trunks of the vagus ; and,
converging, intercommunicate 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

* Liv. p]. viii. \ Ib. pi. vi. | Ib. pi. ix.

o 4

200

LECTURE VIII.

aorta, along the back of the abdomen, into the hcemal canal ; com-
municate, in their course, with the ventral branches of each of the
spinal nerves ; supply 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 sym-
pathetic are larger and more constant than in Osseous Fishes ; but
the intervening chords are semi-transparent.*

Special Organs oe Senses.

The essential character of the Organ of Smell in fishes is, that the
pituitary membrane lines the concave wall of 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 respira-
tory medium in its course to the respiratory organs.

The extremities of the olfactory nerves {fg. 54, 55. l) 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. 30. 19).

In the Dermopteri the olfactory organ is single : Dr. Kolliker f
regards as such a small, blind, tegumentary depression {fig. 46. ol),
beset with vibratile cilia, and connected with the anterior end of
the quasi-brain of the Branchiostoma. The more obvious and satis-
factorily determined olfactory organ of the Ammocete is in the
median line, opening above the mouth in front of the brain-sac
{fig. 25. 19), whence a narrow canal is produced backwards from the
bottom of the sac to the base of the skull. In the Myxine the pa-
rietes of the olfactory canal are similarly situated, lined by a longi-
tudinally-plicated pituitary membrane, and are strengthened by
cartilaginous rings, like a trachea. The naso-palatine tube opens
backwards upon the roof of the mouth ; and this opening is provided

* I.IV.

f x.xxii. p. 32. pi. ii. fig. 5 A ; it should be looked for over the left eye-speck.

NERVOUS SYSTEM OE FISHES.

201

with a valve. In the Lamprey the flask-sliaped nasal sac opens upon
the top of the head : a simple membranous 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 26. hy') of
the base of the skull, where the mucous membrane of the palate
passes over it entire and imperforate.*

In all Fishes, save the Dermopteri, the olfactory organs are
double : and they have no communication with the mouth. In
Osseous Fishes they are situated on the sides of the snout, and are
covered 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 ; the anterior aperture in
the biperforate sacs is often produced into a tubular process, which
acts either by muscular power, or some modification of form, as a valve.
It is provided with a moveabh; cartilage in the Conger ; and the
tubular nosti'ils of the Cyclopterus are in perpetual motion in the
living fish. 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
plicae I’adiate from its centre : when the sac is elongated, it is usually
traversed by an axial partition with a row of transverse folds on
each side. In a few Fishes these folds are further complicated by
secondary processes. The Sturgeon presents the radiated type of the
olfactory organ with secondary folds {fig. 43. 19) ; but, like the
Polypterus and Lepidosteus, each nasal sac has a double aperture.
The Lepidosiren has an elongated nasal sac, with the bi-serial
ai’rangement of pituitary folds, and with a double aperture {fig. 54.
ol) ; but neither of these communicate with the mouth : the peculiar
position of the nasal sacs on the under part of the thick upper lip,
may have deceived the German naturalists who have affirmed the
reptilian nature of this animal on the erroneous supposition that the
posterior aperture of the nasal sac communicated with the mouth : the
cartilaginous capsule of the sac is fissured, or barred, reminding one
of the more complex nasal cartilage in the Myxine.| In the Pla-
giostomes the nasal cavities are situated beneath the snout, near the
angles of the mouth, especially in the Rays : each cavity has a
single and commonly wide opening, defended by valvular processes,

* XXI. p. 4:5. ; figs. ii. and iv.

f In the first specimen of Lepidosiren annectens wliicli served for my description
of its anatomy in 1S.'39, partial decomposition of the upper lip had destroyed the
soft membrane extended over the mouth of the olfactory sac, which led me to
the belief that it had but one opening ; the second, or posterior opening, is outside
the maxillary teeth.

202

LECTURE VIII.

with special muscles ; these processes are supported by peculiar
cartilages more or less intimately connected with the proper olfactory
cartilaginous sacs, and representing the superadded cartilages of
the ‘al;e nasi’ in higher Vertebrata.* They have their proper
muscles ; whence we must conclude that these Fishes scent as well
as smell ; i. e. actively search for odoriferous impressions by rapidly
changing the current of water through the olfactory sac.

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 eye-
speck, the first mechanism for the appreciation of light, is repeated
in the Amblyopsis spelceus {fig. 50. 2). Rudimental eyeballs covered
by the skin exist in the Aptericlithys ccbcus : 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, ad-
hering to the sclerotic, forms a ‘ 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. Orthagoriscus (Prep. 1665. a), 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 Star-gazer {Uranoscopus) the eyes are ap-
proximated on the upper siu-face of a nearly cubical head, and are
directed towards the heavens : in the Hammer-headed Sharks they
ai-e supported on long outward projecting pedicles.

The optic nerve ( unfolded in fig. 57. a) usually perforates the eye-
ball 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, of course, 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 extends into the vitreous
humour, sometimes accompanied by the dark pigmental Ruyschian
layer, as is shown in the preparation of the eye of the Bonito
(No. 1651.). The fold of the vascular choroid, whether accompanied

* See the description of these ‘ nasenfUigelknorpel ’ in xxi. p. 171.

NERVOUS SYSTEM OF FISHES.

203

by the pigmental layer or not, is called the falci-
form process ’ (c) ; it carries before it a fold of
the proper tunic of the vitreous humour (‘ mem-
brana 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 con-
sists of the cellular basis, supporting the stratum
of cylindricules, standing vertically upon its con-
cave 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 cylindricules, 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 ‘bead’ runs along both the anterior
margins of the retina, and along those which form the falciform slit.

The crystalline lens (rf) is spherical, 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 cap-
sule : 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.’

The I’adiating fibres and elongated cells of the hyaloid tissue *,
with the interstitial ‘ vitreous humour,’ present a firmer consistency
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 number : the external layer
in Osseous Fishes, called ‘ membrana argentea’ (e), is composed chiefly
of microscopical acicular crystals reflecting a silvery, or sometimes 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 vasculosa,’ seu ‘ Halleri,^ {f)> ^ud, as its
name implies, is the chief seat of the ramifications of the choroid
vessels : it also supports the ciliary nerves. The innermost layer is
the ‘membrana picta,’ seu ‘ Ruyschiana' {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

Eye of Sword-fish ;
one-third natural size,

LXV.

204

LECTURE VIII.

is laid upon the central surface, not the periphery, of the choroid :
(Prep. No. 1669.)

The formation of the iris by the production of all these membranes
is well shown in this preparation of the eye of the Sword-fish {Xiphias,
No. 1661.), where its thick base or ‘ciliary ligament’ (A) overlaps the
convex border of the bony sclerotic. The pupil (^) is large and usu-
ally round : in many Plagiostomes it is elliptic : in the flat-bodied
Skates and Pleuronectidse, 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 Ashes : it is
best seen in the pupillary curtain of the Skate. The preparations
of the Sword-fish’s eye (Nos. 1661 and 1662.), and these of the eyes
of the Grey-Shark {Galeus, No. 1670), and the Basking-Shark
[Selache, No. 1670. A.), demonstrate the plicated anterior border of
the uvea, forming the so-called ‘ ciliary zone, or processes ’ {k) : they
are the most complicated in the great Shark, 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* : ” but they do not, as yet, project freely inwards and forwards
from the surface of the uvea.

The subordinate and accessory character of the sclerotic capsule (Z, I,)
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 (m), which fills the
Avide interspace between 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. 103. Jig. 30. 17) ;
but in place of these, in the Orthagoriscus, as in the Plagiostomes, the
capsule is strengthened by a single hollow, cartilaginous, perforated
sphei’oidal globe. The anterior aperture is closed by the cornea (;*),
Avhich is essentially a modified portion of the corium (o), adhering to,
as it passes over, the usually thickened borders of that aperture. In
this specimen of the eye of the Xiphias (No. 1661.) you may trace an
accession to the cornea from the outer fibrous layer of the sclerotic,
which undergoes the same change of tissue, and forms the posterior
layer of the cornea. This transparent windoAv of the eye-capsule is
quite flat: its laminated structure is well displayed in the prepa-
ration of the cornea of the Orthagoriscus (No. 1665.), and a dark-

Lxvi. iii. p. 147.

NERVOUS SYSTEM OF FISHES.

205

brown pigment here stains the soft integument or ‘ conjunctive
membrane’ (o), continued from the periphery of the cornea. In the
preparation of the eye of the same fish (No. 1649.), 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’ (o) : this is of the
class of bodies called vascular- or 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. Albers* dis-
covered the rich marginal plexuses of vessels, whose trunks (‘stiimme’)
have their origin in this body, which he believed to consist also
of a convolution 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 I found that the supposed “fibres con-
sisted, in reality, of minute, parallel, and closely disposed vessels,”
both arteries and veins. Professor Muller has detected an unex-
pected relation of co-existence between the choroid vaso-ganglion and
the pseudo- branchia, to which the Sturgeon, Lepidosiren, and the Pla-
giostomes are amongst the few exceptions having the pseudo-branchi®,
but not the vaso-ganglia. The genera Silurus, PimeJodus, Synndon,
Cobitis, and all the Eel-tribe, have neither pseudo-branchi® nor choroid
vaso-ganglia. The most remarkable exceptional peculiarity 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 perforated by two pupils.

The general form of the eyeball, or rather its capsule, in Fishes, is
a spheroid, flattened anteriorly, around which part the integuments
commonly form a circular fold, yielding to the movements of the
globe. In Orthagoriscus the circular palpebral fold is deeper, and
is pi’ovided with a sphincter : in most Scomberoid and Clupeoid Fishes
there is an anterior and a posterior vertical transparent fold or
eyelid. In the eye of the Galeus (Prep. 1762.), you may see a nictitat-
ing membrane superadded to a well-developed circular palpebral fold of

LXXVl,

j- i.xvi. vol, iii. (1836) ; p. 145. prep. 1656. : and lxvii.

206

LECTURE VIII.

the skin. A conjunctive membrane is reflected from the circular eye-
lid 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’ muscle 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 simultaneously with the raising of the third
lid.*

The proper muscles of the eyeball exist in all fishes except
the Myxinoids and Lepidosiren, and consist of the four recti
and two ohliqui : the latter rise from the nasal side of the
orbit, and are inserted most favourably 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 cartilaginous
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 f ; the origin of the
rectus externus being prolonged furthest back. But the recti muscles
are most remarkable for their length in the Hammer-headed Sharks,
since they rise from the basis cranii, and extend along the lateral
processes or peduncles, at the free extremities of which the eyeballs
are situated. In all Plagiostomes the eyeball is supported on a car-
tilaginous peduncle : this is short and broad in the Rays ; longer and
cylindrical in the Sharks ; in the Selache it is articulated by a ball and
socket synovial joint to a tubercle above and external to the entry of
the optic nerve. A fibrous ligament attaches the sclerotic to the
wall of 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 lachrymal 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

* Prof. Muller has established the family ‘ Nictitantes’ for the Sharks, including
the Galeus, Carcharias, and a few other genera, with the third eyelid.

f If, therefore, we regard this canal as part of the orbits, we must add the ali-
sphenoid, basi-sphenoid, and even the basi-occipital to the bones enumerated at
p. 1 03., as forming the chambers for the eyeballs and their appendages in Fishes ;
and this multiplicity of orbital bones interestingly repeats or parallels the charac-
teristic formation of the otocranes or ear-chambers in the present class.

NERVOUS Sl’STEM OF FISHES.

207

level with the side of the head, offers no impediment to those move-
ments. 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 convexity and refractive power of the lens are increased.
To compensate for the deviation from the spherical form of the
eyeball produced by the flattening of its fore-part, and the con-
sequent weakening of the power to resist external pressure, the
sclerotic capsule is cartilaginous or bony.

This beautiful chain of adjustments and interdependencies cannot
but raise the rightly constituted mind to the contemplation of :he
attributes of that Creative Intelligence herein so strikingly displayed.

Organ of Hearing. — 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 (^fg. 24. 16) ; they are
less conspicuous in the Lamprey {fig- 26. 16) ; they become in-
volved in the thick cartilaginous walls of the cranium in the Plagi-
ostomes ; and, in Osseous Fishes, are walled up externally either by
the surrounding cranial bones, or by a special ossification of the
exterior part of the capsule itself, forming an ‘ os petrosum,’ as, e. g.
in the Cod {fig- 30. 16). In the dry-skull the ear-chamber appears
as a lai’ge lateral compartment of the cranial cavity, and is formed as
described in p. 102.

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,’ each of which
dilates, at its origin, into an ‘ 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.

In all other Fishes the membranous labyrinth consists of a vesti-
bule and three semicircular canals ; the vestibule dilating into one
or more ‘ sacculi,’ separat’ed by a constriction, or by a narrow canal
from the ‘ alveus communis,’ and containing, besides the fluid called
‘ endolymph/ two or more masses of carbonate of lime, called ‘ oto-
lites.’ * These are compact and crystalline in Osseous Fishes.

* Figures of these bodies will be found in lxvi. iii. pi. 35. ; in lxxi. lxviii. and
in I.XXII., with microscopic figures of the crystals.

208

LECTURE VIII.

Organ of Hearing in situ, with air-bladder and ossicles, Carp (after Weber).

NERVOUS SYSTEM OF FISHES.

209

The largest ^fig. 30. le'') is an oval or round flattened body, striated
and indented at the margins ; convex, and sometimes grooved {Eph ip-
pus), 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 {Jig. 58. e,f, g)
from the ‘ alveus communis,’ (a) and communicates, by the opposite
end, either with another canal, or with the vestibule separately,
without previous dilatation : two of the canals are sub-vertical in
their course, and are anterior (e) and posterior (g) in relative posi-
tion ; the third canal {/) 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. All the parts of the labyrinth are of large
size ; yet the compartments of the otocrane which the semicircular
canals traverse “ are much too wide for them, and they are supported
in these passages by a very flne cellular membrane.” *

The ChimaerEe and Sturgeons resemble the bony fishes in the form
and position of the labyrinth. The otolites are a hard chalky sub-
stance in the Lepidosiren ; in which fish, as well as in the Elagio-
stomes, the whole labyrinth is buried in the thick basi-lateral walls of
the cranium : in both the cartilaginous capsule conforms more closely
in size and configuration to the membranous labyrinth ; its passages
and compartments are lined by a delicate perichondrium, from which
filaments are detached to support the semicircular canals. The vesti-
bule is divided in the Skate and Tope into three compartments, — the
‘ alveus communis’ {Jig. 59. a) ; the sac (ib. b) and the cysticule (ib. c),
and it has also a small caecal appendage, called the ‘ utricule ’ (ib. d) : the
otolitic contents are like soft chalk, and are disposed in two masses ; one
very large, occupying the sac and the cysticule, the other small, and
lodged in the utricule. A canal extends in Sharks from the vesti-
bular capsule to a foramen at the upper part
of the occiput, which is closed by the skin.
In the Rays, besides this ‘ fenestra capsul®’
(ib. v), a membranous canal (ib. o, p) is pro-
duced from the vestibule itself, and, as Hunter
well describes, “ from the union of the two
perpendicular canals {Jig. 59. 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,’ that
* Hunter, vii. iii. p. 101.

f Ib. p. 389. pi. xxxiii. fig. 1. Hunter’s original memoir “ On the Organ of
VOL. II. P

Organ of Hearing, Skate
(Breschet).

210

LECTURE VIII.

Scarpa may be pardoned for overlooking them, though scarcely for
the warmth with which he repudiates their existence.* The
‘ meatus vestibuli ’ (^jig. 59, p) is provided at its bent extremity
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.
Weber f discovered the latter interesting structure in the Carp,
Loach, and Sheat-fish. A canal is sent from the sac of each ves-
tibule {Jig.SS, b), to a common ‘sinus impar’ (ib. A) in the sub-
stance of the basi-occipital : this communicates on each side by
a small orifice with two subspherical ‘atria,’ on the body of the
atlas, close to the foramen magnum, which ‘atria’ are supported
externally by the ossicles I and m, and, by means of the large
ossicle 0, are brought into communication 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 ‘ canalis furcatus ’
(ib. i) is produced, the blind ends of which penetrate the alisphenoids.
In the groveling Loach (Cobitis barbatuld), the air-bladder would
seem to exist chiefiy in subserviency to the organ of hearing.
It is so small as to be wholly included within the singularly
modified parapophyses of the second and third cervical vertebrae,
which are expanded and coalesced so as to form a large ‘bulla
ossea ’ beneath their centrums.^ The three ossicles on each side,
which bring the air-bladder into communication with the ‘ atria ’ of
the labyrinth, are also concealed by the fore part of the parapophysial
bullae : it is plain, therefore, that they are not dismemberments of
those lateral or transverse apophyses of the vertebrae ; 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
‘ splanchnoskeleton.’ 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 verte-

Hearing in Fishes ” was printed in the volume of the Philosophical Transactions
for 1782, not, as Breschet states, in the year 1786. (lviii. p. 58.)

* “ Hunterum autem atque Monroum vehementer super hac re sibi hallucinates
fuisse.” (lx. pp. 1, 2.)

t LXXIII.

t Mr. Yarrell, who has given a figure of these singularly modified parapophyses
of the Loach (lxxix. i. p. 380.) compares them to ‘scapulEe ; ’ but I find the pec-
toral fins attached to the true scapular arch, and this suspended as usual to the
paroccipitals, in the Cobitis harbatula.

NERVOUS SYSTEM OF FISHES.

211

br£6 enumerated atp. 102., as entering into the formationof the cham-
ber of the acoustic organ. In the Herring a tubular prolongation of the
fore part of the air-bladder advances to the basi-occipital, and bifur-
cates ; each branch penetrates the side of the base of the skull, again
bifurcates, and terminates in two blind sacs, which are in contact with
similar caecal processes of the labyrinth. In the Holocentrum and
Sargus, caecal processes of the swim-bladder also diverge, to attach
themselves to the membrane closing the part of the otocrane con-
taining the sac of the great otolite.

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 Plagiostomous 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 compensation is
made by the prolongation of its chamber to the surface of the body
in some, and by a similar prolongation of the membranous 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 Muller con-
cludes, from his experiments, “ 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.” * 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 pro-
pagated 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 en-
cephalon harmonises with and suffices for the sensations and volitions,
and the simple series of ideas daily repeated in the monotonous ex-
istence of the scaled inhabitants of the waters. To say that the fish’s
ears and eyes were made enormous in order to strike strongly on its dull
brain — that the development of the organs of sense has been exag-
gerated to compensate for the defective size of their nervous centres
— implies a want of due appreciation of the beautiful adjustment of the

Lxxiii. p. 1245.

212

LECTURE Viri.

proportions of the labyrinth and eyeball to the conditions under
which the fish receives its impressions of the sonorous and luminous
undulations.

Electric Organs.

Extraordinary as are the modifications and appendages of the peri-
pheral extremities of the nerves of smell, sight, and hearing, other
nerves in fishes are subject to still stranger combinations, and con-
stitute organs quite unknown in any other class of Vertebrate Ani-
mals ; those, viz., which endow a fish with the wonderful property of
accumulating, concentrating, and applying in its own behoof an impon-
derable agent of a purely physical nature, which gives it the power to
communicate electric shocks, — to wield at will the artillery of the skies.

But few fishes are known to possess this faculty, and I shall limit
the demonstration of the electric organs to the two genera which
possess them in the highest state of development, and which are most
dreaded for the force of the shocks they impart ; these are the Tor-
pedo and the Gymnotus.

In the Torpedo Galvani* the organs are two in number, are
large, flattened, reniform bodies, lodged on each side the head and
gills, and encompassed by these and by the anterior borders of the
pectoral fins {fig- 45. e), and they consist of a mass of vertical, for
the most part hexagonal, prisms, the ends of which are covered by
the dorsal and ventral integuments. When you reflect these, you
find the organs immediately coated by a thin glistening aponeurosis,
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 de-
licate membranous plates inclosed by, or adherent by their margins
to a proper capsule, and separated from each other by a small quan-
tity of a limpid albuminous fluid. Each flattened cell thus formed, is
lined by an epithelium of nucleated corpuscles : the fibrous tissue of
the plates and common capsule presents the microscopic characters of
elastic tissue ; between it and the epithelium 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 columns and the larger branches of the nerves and vessels
of the organ. The transverse plates of the vertical columns are

* The electric organs in the Torp. Narce and Torp. Nobiliana do not materially
differ from those above described and illustrated by the dissections of Hunter. —
See Nos. 2167 — 2179., and lxxx.

f Some of the vertical columns do not extend through the entire thickness of
the organ. I have found them interrupted where the deep-seated nerves traverse
the substance of the battery, but have not, in any instance, succeeded in finding a
natural division of the organ into two strata of dorsal and ventral columns. — See
xci. p. 60.

ELECTRIC ORGANS OF FISHES.

213

conspicuous in Preparations 2176 and 2177. Hunter, who counted
470 columns in each organ, describes the partitions as being very
vascular : — “ The arteries,” he says, “ are branches from the vessels
of the gills, which convey the blood that has received the influence
of respiration.” But the most characteristic feature of the organi-
sation of the electric battery is, as Hunter also demonstrates, its
enormous supply of nervous matter. Each organ derives this supply
from one branch of the trigeminal (Jig. 45, 5), and from four branches
of the vagal nerves (Jbid. 8, e), and the four anterior nerves are each
as thick as the spinal chord : the last nerve is a feeble branch of the
vagus. The trigeminal 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 Professor Savi* affirms that both this and
the vagal branches consist entirely of the primitive nerve-fibres of
animal life, or “a double contour;” and that they 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
terminal elementary nerve-fibres, f

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 (see Preps. 2186, 2187).
They occupy and almost constitute the whole lower half of the trunk ;
the upper organ is much larger than the lower one, 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 verte-
bral column and its muscles, then by the air-bladder, and below this
by an aponeurotic septum. From this septum, and from that covering
the air-bladder, there extend outwards, 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 ; tliey are
of great but varying length, some being co-extensive with the whole
organ; their breadth is almost that of the semidiameter of the
plane of the body in which they are situated. 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 another.
They are intersected transversely by more delicate vertical plates,
extending from the skin to the median aponeurosis, and co-extensive
in length with the breadth of the septa between which they are

* I.XXVI. p. 318.

f Savi. “ Actes du Congres Scientifique, a Florence,” 1840.

214

LECTUEE VIII.

placed. Hunter counted about 240 of these plates in a single inch
of length of the horizontal membrane. He rightly compares those
stronger membranes to the aponeurotic walls of the prisms of the
Torpedo, and the intersecting delicate plates, to the partitions of the
prisms : a pellucid liquid intervenes between the plates of the Gym-
notus ; and, if we admit the analogy of these plates, and of those of the
Torpedo, to the plates of the voltaic pile, we perceive that, in the
Gymnotus, the batteries are horizontal and the plates vertical, whilst
in the Torpedo the batteries are vertical and their plates horizontal.
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, and from behind the pectoral fins to near the end of
the tail in the other. But a more important difference exists in the
source of the nervous supply. In the Gymnotus the electric organs
are supplied by the ‘ 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 lateralis, 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, extends
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.”

The proportional size of the electric organs is 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 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 electrical apparatus. The vent even opens beneath
the head, in advance of the pectoral fins.

The electric organs of the Malapterurus electricus are described
as forming on each side the body, between the skin and the lateral
muscles, two thin strata, one consisting of minute lozenge- shaped
cells, the other of six or more fine longitudinal membranes, with a
delicate intervening cellular structure ; they thus combine the cha-

LXXX.

ELECTRIC ORGANS OP FISHES.

215

racters both of those of the Torpedo and the Gymnotus, and not only
in structure, but in some degree, likewise, in regard to the source of
their nervous energy, the outer organs being supplied by the ‘ nervus
lateralis ’ from the vagus ; the laminated inner one receiving branches
from the ‘ rami ventrales ’ of the spinal nerves. * The shock com-
municated by the Malapterurus electricus is comparatively feeble.

When the Neapolitan fishermen pull their nets to shore, their first
act usually is to wash the fishes by dashing over them bucketfuls of
sea-water ; and if a Torpedo be amongst the captured shoal, it makes
its presence instantly felt by the shock transmitted to the arm, which
is in the act of discharging the bucket. If the fish be handled, the
shock is too strong and painful to be willingly encountered a second
time, and the arm remains benumbed for some time. 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.

An animal mustbein communication with the Torpedo bytwodistinct
points, in order to receive the shock. If an insulated and prepared
frog I touches the torpedo by the end of a nerve only, no muscular
contractions ensue on the discharge of the battery ; but a second
contact by the end of another nerve, or by a portion of muscle, or any
other part of the body, immediately produces them. When the fisher-
man 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 ex-
tending from the man’s feet to the ventral surface of the prone fish.

The dorsal surface of the electric organ is always positive, the
ventral surface negative. J The Torpedo has no power of otherwise
directing the electric currents ; but Matteucci found that wounding
the electric lobes of the brain sometimes reversed the direction.
These currents, besides their effects on the living body, exercise all
the other known powers of electricity : they render the needle mag-
netic §, decompose chemical compounds, and emit the spark. || The
discharge of strong cui’rents is usually accompanied by visible con-
traction of parts of the body, usually by a retraction of the eyes of
the Torpedo, and one muscle {fig. 45. o) is arranged so as to
constrict part of the circumference of each battery ; but such con-
sentaneous muscular action, though it may add to the force of the
discharge, is not essential to its production. The benumbing effect
seems to be produced by the rapid succession of shocks delivered by

* xci. t Lxxvi. p. 148. * Lxxxiii.

§ LXXXI. II LXXVI.

216

LECTURE VIII.

the recent and vigorous fish. Matteucci ascertained that, during the
discharge, the nerves of the organ were not traversed by any electric
current.

Humboldt has given a lively narrative of the mode of capture of
the Gymnoti, employed by the Indians of South America.

They rouse the Gymnoti by driving horses and mules into the
ponds which those fish inhabit, and harpoon them when they have ex-
hausted 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 and 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 termi-
nation, 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 ap-
peared 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 with-
out receiving any shock so long as the cord was dry.*

All the circumstances narrated by the celebrated philosopher,
establish the close analogy between the Gymnotus and Torpedo in
the vital phenomena attending the exercise of their extraordinary
means of offence. The exercise is voluntary and exhaustive of the
nervous energy ; like voluntary muscular effort, it needs repose and
nourishment to produce a fresh accumulation.

I was so fortunate as to witness the experiments performed by
Professor Faraday on the large Gymnotus which was so long pre-
served alive at the ‘ Adelaide Gallery ’ in London. That the most

cv. p 55.

ELECTRIC ORGANS OF FISHES.

217

powerful shocks were received when one hand grasped the head and
the other hand the tail of the Gymnotus, I had painful experience ;
especially at the wrists, the elbows and across the back. But our
distinguished experimenter showed us that the nearer the hands
were together within certain limits, the less powerful was the shock.
He demonstrated by the galvanometer that the direction of the
electric current was always from the anterior parts of the animal to
the posterior 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 mag-
nets : iodine was obtained by polar decomposition of iodide of po-
tassium ; and, availing himself of this test. Professor 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. Referring to the admirable Me-
moir *, in which these and other experiments on the Gymnotus
are described, I shall only revert to the relation which exists between
the comparative anatomy of the organs of the Torpedo and Gym-
notus, and the diiference in the direction of their electric currents,
as determined by the physical experiments. The delicate plates sus-
taining the terminal meshes of the nerves and vessels are horizontal
in the Torpedo ; the course of the electrie current is from above
downwards. The corresponding plates in the Gymnotus are vertical ;
the direction of the electric current is from before backwards : i. c.
it is vertical to the planes of the plates of the organised voltaic piles
in both cases.

There is another analogy which the row of compressed cells con-
stituting the electric prism of the Torpedo suggests, viz. to the
striated fibre of voluntary muscle, or to the row of microscopic discoid
cells of which the elementary muscular filament appears to consist.
The looped termination of the exciting nerve is common to musculai’
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 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, Avhich 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 interrupted,

LXXXII.

218

LECTURE VIU.

and no irritant to the body has any etFect 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 irri-
tated, the discharge of electricity takes place, just as irritating the
end of the divided motor nerve in connection with muscle would
induce its contraction. If part of the electric nerves be left in con-
nection 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 apparatus, 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 appli-
cation causes simultaneously a tetanic state of the muscles of the
fish, and a rapid succession of involuntary electric discharges. *

The survey of the nervous system of fishes cannot be concluded
without a notice of two systems of mucous organs in intimate con-
nection with the nerves of sensation ; one system is common to the
Torpedo with other Plagiostomes ; the other system is peculiar to the
Torpedo, in which it was discovered by Prof. Savi.

The first or muciferous system consists of the long slender mucous
tubes {fig. 45. m), which, commencing by groups of globular vesicles
(ib. m.) situated in the Torpedo, symmetrically at the forepart of the
head and outside the electric organs, run in parallel fasciculi from which
the tubes, successively detaching themselves, perforate the skin, and
.terminate by orifices, some at the dorsal, some at the ventral surface,
between the outer border of the electric organs and that of the body
of the animal. A considerable filament of the ganglionic portion of
the trigeminal nerve expands upon the ampulliform commencement
of each of the muciferous tubes : the nerve may receive impressions
conveyed to it by the tube and its clear jelly-like contents, or it may
preside over the secretion of those contents, or combine both func-
tions.

The second or follicular system consists of linear series of minute
subcutaneous subspherical cells, situated at the anterior part of the
head of the Torpedo, chiefiy on the under surface : each cell has a
double membranous tunic, and contains a grey cerebriform matter ;

Lxxvi. p. 162.

DENTAL SYSTEM OF FISHES.

219

a branch of the anterior division of the fifth nerve enters each fol-
licle, makes a coil there, and quits it to join another filament, or to
return to its own stem.*

LECTURE IX.

DIGESTIYE SYSTEM OP PISHES.

Dentition.

The teeth of fishes, whether we study them in regard to their num-
ber, 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, the Paddle-fish (yfig. 61. a. 6.),
and the whole order of Lophobranchii, are edentulous. The Myxinoids
have a single pointed tooth on the roof of the mouth, and two serrated
dental plates on the tongue. The Carp has a single grinding tooth
on the occiput, opposed to two dentigerous pharyngeal jaws below.
In the Lepidosiren a single maxiUary dental plate is opposed to a
single mandibular one, and there are two small denticles on the nasal
bone. In the extinct Sharks with crushing teeth, called Ceratodus
and Ctenodus, the jaws were armed with four teeth, two above and
two below. In the Chimaerse two mandibular teeth are opposed to
four maxillary teeth. From this low point the number in different
fishes is progressively multiplied until, in the Pike, the Silurus, and
many other fishes, the mouth becomes crowded with innumerable
teeth.

With respect to form, I may first observe, that as organised beings
withdraw themselves more and more, in their ascent in the scale of
life, from the influence of common physical agents, so their parts pro-
gressively deviate from geometrical figures : it is only, therefore, in
the lowest vertebrated class that we find teeth in the form of perfect
cubes, and of prisms or plates with three (Myletes), four (^Scarus),

Lxxvi. p. 332. pi. iii. figs. 10. 12.

220

LECTURE IX.

five, or six sides, Myliobates, fig. 60.* The cone is the most com-*

mon 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 {dentes
villiformes, dents en velours f) ; all the
teeth of the Perch are of this kind :
when the teeth are equally fine and
Jaws and teeth ; Myliobates. numei'ous, but longer, they are called

‘ ciliiform ’ {dentes ciliiformes) : when the teeth are similar to, but
rather stronger than these, they are called ‘ setiform {dentes seti-
formes, dents en hrosse) : conical teeth, as close set and sharp
pointed as the villiform teeth, but of larger size, are called ‘ rasp-
teeth’ {dentes raduliformes, dents en rape or en cardesfi, the
Pike presents such teeth on the back part of the vomer : the teeth
of the Sheat-fish ( Silurus giants) present all the gradations
between the villiform and raduliform types. Setiform teeth are com-
mon in the fishes thence called Chastodonts | ; in the genus Citharina
they bifurcate at their free extremities ; in the genus Platax they end
there in three diverging points (V, pi. 1), and the cone here merges
into the long and slender cylinder. Sometimes the cone is compressed
into a slender trenchant blade : and this may be pointed and recurved,
as in Murcena (V, pi. 56, fig. 4.) ; or barbed, as in Trichiurus (V, pi.
\,fig 8.), and some other Scomberoids ; or it may be bent upon itself,
like a tenterhook, as in the fishes thence called Goniodonts.§ 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
increased size and recurved direction, they then resemble the laniary
or canine teeth of carnivorous quadrupeds, as we see in the large teeth
of the Pike.

The anterior diverging grappling teeth of the wolf-fish (V, pi. 60.)
form stronger cones ; and by progressive blunting, flattening, and
expansion of the apex, observable in different fishes, the cone by
degrees changes to the thick and short cylinder, such as is seen in the
back teeth of the wolf-fish (V, pi. 61.), and in similar grinding and
crushing teeth in other genera, whether phytiphagous, or feeders on
crustaceous and testaceous animals. The grinding surface of these
short cylindrical teeth may be convex, as in the Sheep’s-head Fish
(Sargus, V, pi. l.fig. 13.) ; or flattened, as in the pharyngeal teeth of

* See V. pi. 25. 49.

t The French terms are those used by Cuvier and Valenciennes in xxiir. passim.
^ Xahrj, bristle ; oSoiis, tooth. § Twvia, an angle ; 66ovs, a tooth.

DENTAL SYSTEM OF FISHES.

221

the Wrasse {Lahrus, V, pi. 4.). Sometimes the hemispheric

teeth are so numerous, and spread over so broad a surface, as to
resemble a pavement {Chrysophrys, V, pi. ^5. Jigs. 3. 6 ; and Pisodus,
pi. Al.Jig. 3.) ; or they may be so small, as well as numerous {dentes
graniformes), as to give a granulated surface to the part of the
mouth to which they are attached (premaxillaries of Labrus, V,
pi. 45. 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 (V, pi. 45.
Jig. 4) and Placodus (V, pi. 30.), until the cylindrical form is exchanged
for that of the depressed plate. Such dental plates {dentes lamelli-
formes) may be found, not only circular, but elliptical, oval, semilunar,
sigmoid, oblong, and even, as above-mentioned, square, hexagonal,
pentagonal, or triangular ; and the grinding surface presents as
various and beautiful kinds of sculpturing. The broadest and thinnest
lamelliform teeth are those that form the complex grinding tubercle of
the Diodon (V, pi. 38.y%r. 2.). The front teeth of the Flounder and
Sargus present the form of compressed plates, at least in the crown,
and are true ‘ dentes incisivL’ Numerous wedge-shaped dental plates
{dentes cuneati) are set vertically in the pharyngeal bones of the
Parrot-fish {Scarus, V, pi. 51.). A thin lamella, slightly curved like
a finger-nail, is the singular form of tooth in an extinct genus of fishes,
which I have thence called Petalodus (V, pi. 22. Jigs. 3, 4, 5.)
Sometimes the incisive form of tooth is notched in the middle of the
cutting edge, as in Sargus unimaculatus (V, pi. l.Jig. 9.). Sometimes
the edge of the crown is trilobate {Aplodactylus, ib.Jig. 10.). Some-
times it is made quinquelobate by a double notch on each side of the
large middle lobe {Boops, ib.fig. 11.). In the formidable Sea-pike
{Sphyrcena Barracuda, V, pi. 53.) 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 (V, pi. l.Jg. 12.), and the great Sharks of the
genus Carcharias, the fossil teeth of which indicate a species ( Carc/i.
Megalodon) sixty or seventy feet in length.

The lancet is changed for the stronger spear-shaped tooth in the
Sharks of the genus Lamna, and in the allied great extinct Otodus,
as in the small Porbeagle, similarly shaped, but stronger, piercing
and cutting teeth were accompanied by one or more accessory com-
pressed cusps on each side their base, like the Malay crease.

With respect to situation, the teeth, in Sharks and Rays, are limited
to the bones (maxillaiy and mandibular), which form the anterior
aperture of the mouth : in the Carp and other Cyprinoids the teeth
are confined to the bones which circumscribe the postei’ior aperture
of the mouth, viz. the pharyngeals and basi-occipital. The Wrasses

222

LECTURE IX.

{Labrus^, and the Parrot-fishes (^Scarus), have teeth on the pre-
maxillary and pre-mandibular, as well as on the upper and lower
pharyngeals ; both the anterior and posterior apertures of the mouth
being thus provided 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 pterygoids, the
entopterygoids, the basi-pre-sphenoid, and even on the nasal bone.
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. 36.), are examples of this approach to the
higher Vertebrata. Among the anomalous positions of teeth may be
cited, besides the occipital alveolus of the Carp (V. pi. 51. fig. 6.), the
marginal alveoli of the prolonged, depressed, well ossified rostrum of
the Saw -fish {Pristis, V. pi. 8.) In the Lampreys and in Helostomus
(an osseous fish), most of the teeth are attached to the lips. Lastly,
it is peculiar to the class Pisces, amongst Vertebrata, to offer ex-
amples of teeth developed in the median line of the mouth, as in the
palate of the Myxines ; or crossing the symphysis of the jaw, as in
Notidanus, Scymnus and Myliobates.

Nor is the mode less varied than the place of attachment : some
teeth, as those of Lophius, Pcecilia, Anableps, are always moveable :
in most fishes they are anchylosed to the jaws by continuous ossi-
fication from the base of the dental pulp ; the histological transition
being more or less gradual from the structure of the tooth to that of
the bone. Sometimes we find, not the base, but one side of the tooth
anchylosed to the alveolar border of the jaw : and the teeth oppose
each other by their sides instead of their summits ( Scarus, V, pi. 49.) :
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 in the normal
way. The base of anchylosed teeth is, at first, attached to the
jaw-bone by ligament ; and in the Cod-fish, Wolf-fish, and some
other species, as calcification of the tooth progresses towards its base,
the subjacent portion of the jaw-bone receives a stimulus, and
developes a process corresponding in size and form with the base of
the tooth : for some time a thin layer of ligamentous substance inter-
venes, but anchylosis usually takes place to a greater or less extent
before the tooth is shed. Most of the teeth of the Lophius retain
the primitive ligamentous connection : the ligaments 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

DENTAL SYSTEM OF FISHES.

223

tooth to be bent outwards 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 : the instant, how-
ever, 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 : the deglutition of the prey of this voracious fish
is thus facilitated, and its escape prevented. The broad and generally
bifurcate bony base of the teeth of Sharks is attached by ligament to
the semi-ossified crust of the cartilaginous jaws ; 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 tesselated
teeth of the Myliobates have their attached surface longitudinally
grooved to afibrd them better hold-fast, and the sides of the contiguous
teeth are articulated together by serrated or finely undulating sutures
27.), a structure unique in dental organisation. The teeth of
the Sphyr^na are examples of the ordinary implantation 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 are deeply implanted in sockets : 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 incisors of the Ba-
listes, e. g., afford an example of this double or reciprocal gomphosis.
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 domeshaped
tooth 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 hoUow columns, every
one of which is placed so as best to resist or transmit in the due di-
rection the external pressure. The floor of the alveolus is thus re-
lieved from the office of sustaining the tooth : it forms, in fact, the
roof of a lower vault, in which the germ of a successional tooth is in
course of development : had the crusliing tooth in use, rested, as in
the Wolf-fish, by the whole of its base upon the alveolus, the sup-

224

I/ECTUKE IX.

porting plate gradually undermined by the growth of the new tooth
must have given way and been forced upon the subjacent delicate
and highly vascular and sensitive matrix of the half-formed tooth.
But the superincumbent pressure being exclusively sustained by the
border of the alveolus, whence it is transferred to the trails dividing
the vaulted cavities containing the germs of the new teeth, the roofs
of these cavities yield to the absorbent process consequent on the
growth of the new teeth without materially weakening the attach-
ment 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 undermined, and the old worn-down tooth is shed.

With regard to the substance of the teeth of fishes, the modifica-
tions of dentine, called vaso-dentine, and osteo-dentine*, predominate
much more than in the higher Vertebrata ; and they thus more closely
resemble the bones which support them. There is, however, great di-
versity in respect of substance. The teeth of most of the Chaetodonts
are flexible, elastic, and composed of a yellowish subtransparent albu-
minous tissue ; such, likewise, are the labial teeth of the Helostome, the
premaxillary and mandibular teeth of the Goniodonts, and of that
percoid genus thence called 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 {Exocatus), and Sucking-fish {Remora), consist of osteo-
dentine. In many fishes, e.g. the Acanthurus (V, pi. 44. fig. 1.),
Sphyraena (V, pi. 53.), and certain Sharks {Lamna, V, pi. 6.), a base, or
body of osteodentine is coated by a layer of true dentine, but of un-
usual hardness, like enamel: in this hard tissue predominates.

In the Diodon the dental plates consist wholly of hard or unvascular
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, developed by a distinct organ, and differing from the ‘ enamel’
of higher animals 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 ‘ cement.’ In the pharyngeal teeth of the Scarus a fourth
substance 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, thus composed of cement, enamel, dentine, and osteodentine
(V, pi. 52.), are the most complex in regard to their substance that
have yet been discovered in the animal kingdom.

V. Introduction, p. Ixxii.

DENTAL SYSTEM OF FISHES.

225

The true teeth of all Vertebrates consist, like bone, of an animal
gelatinous basis, hardened by salts of lime, magnesia, and soda ; the
phosphates of lime predominating. Analyses of the teeth of the Pike,
Carp, and Shark, will be found in V. pp. Ixiv. and 9. ; and in Lxxxv.

The tubes which convey the capillary vessels through the substance
of the osteo- and vaso-dentine of the teeth of fishes * were early re-
cognised, on account of their comparatively large size ; as by Andre
e. g., in the teeth of Acanthuriis, and by Cuvier and Von Born in the
teeth of the Wolf-fish and other species, f Leeuwenhoek had,
also, detected the much finer tubes of the peripheral dentine of the
teeth of the Haddock. 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 (V. pi. 7.) ; the dentinal tubuli alone are found in true
dentine, and they have a straighter and more parallel course, usually
at right angles to the outer surface of the dentine (V. pi. 7. and pi. 52. h).

I give the name ‘ vaso-dentine ’ to that modification of the tissue in
which the vascular canals run nearly parallel with, and equidistant
from, each other, through the major part of the extent of such modified
dentine ; it is exemplified in the rostral teeth of the Saw-fish, the
maxillary dental plates of the ChimcErcB, Psammodonts, My lioh cites:
in the latter each medullary canal and its system of dentinal tubes
represents a slender subcylindrical denticle, being separated from the
contiguous denticles by a thin coat of bone or ‘ cement.’ The dense
covering of the jaws of the Scari consists of a stratum of quite distinct
prismatic denticles, standing vertically to the surface of the bene.

‘ Osteo-dentine’ is that tissue in which the medullary canals are
wavy, irregular, and anastomotic ; in Mammalia it contains the
Purkingian cells ; in fishes it usually is covered more or less thickly
by hard dentine. Those conical teeth which, when fully formed,
consist wholly or in great part of osteodentine or vasodentine, always
first appear with an apex of 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 fiuted character to
the base of the tooth; {Lepidosteus oxyiiriis, lxxxvi. pi. v. fig. 1.)
Sometimes such radiating vertical basal plates of dentine are wavy
in their course, and send ofi* narrow processes from their sides ; and,
as a thin layer of the outer capsule interdigitates with the outstanding

* The vaso .dentine of Pristis and Myliobates is like that of the teeth of the Cape
Anteater ( Orycteropus') ; the vaso-dentine of the Psammodonts resembles that
which forms the base of the tooth of the Sloth and Megatherium : the vaso-dentine
of Mammals differs from the osteo-dentine in the absence of the radiated ‘ Purkin-
gian’ cells.

f See V. p. 10.

VOL. II.

Q

226

LECTURE IX.

plates of the dentinal pulp, and becomes co-calcified with them, a
transverse section of such a tooth presents a series of interblended
wavy or labyrinthic tracts of thick dentine radiating from the centre,
and of thin cement converging towards the centre of the tooth. * An
analogous but more complicated structure obtains when the ra-
diating, wavy, vertical plates of dentine dichotomise, and give off
from their sides, throughout their course, numerous branch plates and
processes, which are traversed by medullary sinuses and canals with
their peripheral terminations dilated, and becoming the centres of lobes
or columns of hard dentine. The transverse section of such teeth
gives the appearance of branches of a tree, with leaf-stalks and leaves,
radiating from the central pulp-cavity to the circumference of the
tooth ; and I have called the fossil Fish in which this structure was
first detected, Dendrodus f. Thus, with reference to the main and
fundamental tissue of tooth, we find not fewer than six leading modi-
fications in Fishes: hard or true dentine (Sparoids, Lahroids, Lo-
phius, Batistes, Pycnodonts, Prionodon, Sphyrna, Megalichthys,
Rhizodus, Diodon ; Scarus) ; osteo-dentine ( Cestracion, Acrodus, Le-
pidosiren, Ctenodus, Hybodus, Percoids, Scicenoids, Cottoids, Go-
bioids, and many others) ; vaso-dentine {Psammodus, Chimceroids,
Pristis, Myliobates) ; plici-dentine {Lophius, Holoptychius, Lepidosteus
oxyurm, at the base of the teeth) ; labyrintho-dentine {Lepidosteus
platyrhinus, Boihriolepis) ; 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.

As might have been anticipated from the discovery of the 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 true law of the development of dentine “ by centri-
petal metamorphosis and calcification of the cells of the pulp,” was
first definitely enunciated and illustrated from observations made on
the development of the teeth of fishes. |

* This ren.arkable structure attains its highest complication and forms tlie
largest proportion of the tooth in the gigantic extinct Batrachia, which I have
thence called Labyrinthodonts, and from which, therefore, I have taken the illus-
trations of that complex modification of dental structure in my “ Odontography”
(pis. 63 5, 64, 64 a, 64 5). I had discovered in 1841 (lxxxvii.) the more simple
modification of this structure “ at the base of the tooth in a few Fishes,” but had
not then seen so complex an example in that class as Dr. Wyman (lxxxvi. pi. v.
fig. 4.) and M. Assassiz (xxii. ‘ Sauroides,’ 1843) subsequently described and
figured, in teeth of the genus Lepidosteus. f cxxvi. pi. b.

I In my Hunterian Lectures, delivered at the Royal College of Surgeons, May,
1839. Sec also Lxxxvm 784.; and v. Introduction, and part i. passim.

DENTAL SYSTEM OF FISDES.

227

It is interesting to observe in this class the process arrested at
each of the well-marked stages through which the development 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 papillee 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 papilliform matrix, but, as this is
converted into dental tissue, 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 (v. pi. 5.^^. 1.) Here, therefore,
is represented the first and transitory ‘papillary’ stage of dental de-
velopment in mammals ; and the simple crescentic cartilaginous
maxillary plate, with the open groove behind containing the germinal
papilliB of the teeth, offers in the Shark a magnified representation of
the earliest condition of the jaws and teeth in the human embryo.

In many Fishes, e. g., Lophius, Esox, the dental papillse become
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 Avith the
thick and soft gum, when it is stripped from the jaw-bone. The final
fixation of teeth, so formed, is effected by the develojDment of liga-
mentous fibres in the submucous tissue between the jaw and the base
of the tooth, which fibres become the medium of connection between
those parts, either as elastic ligaments, or by continuous ossification.
Here, therefore, is represented the ‘ follicular’ stage of the develop-
ment of a mammalian tooth; but the ‘eruptive’ stage takes place
without previous inclosure of the follicle and matrix in the substance
of the jaw-bone.

In Batistes, Scarus, Sphyrcena, 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 vertebrata: the papilla sinks into a follicle, becomes sur-
rounded by a capsule, and is then included within a closed alveolus of
the growing jaw, where the development 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 Balistes, Scarus,
Sargus, and Chrysoplirys.

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, and the rostral teeth of
Priotis (if these modified dermal spines may be so called) are, per-

228

LECTURE IX.

haps, the sole examples of ‘permanent teeth’ to be met with in the
whole class.

When the teeth are developed in alveolar cavities, they are suc-
ceeded by others in the vertical direction (V. pi. \8.Jig. 1.) : these owe
the origin of their matrix to the budding out from the capsule of
their predecessors of a caecal process, in which the papillary rudiment
of the dentinal pulp is developed according to the laws explained in
V (Introduction). 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 suc-
cession ; 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 (V. pi. 5, jig. L), in which the whole phalanx of their
numerous teeth is ever moving slowly forwards in rotatory pro-
gress over the alveolar border of the jaw, the teeth being successively
cast off as they reach the outer margin, and new teeth rising from the
mucous 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 Fish, illus-
trate the law of Vegetative or Irrelative Repetition, as it manifests
itself on the first introduction of new organs in the Animal King-
dom, under which light we must view the above-described organised
and calcified preparatory instruments of digestion in the lowest class
of the Vertebrate series.

Alimentary Canal.

The mouth of Fishes is the common entry and vestibule to both
the digestive {^jig. 61. dXari) and the respiratory (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 per-
formed 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 their respective localities. The branchial slits are provided
with denticles and sieve-like plates or processes to prevent the
entry of food into the interspaces of the gills, and the branchial out-
lets are guarded by valves which reciprocally prevent the regurgita-
tion of the respiratory streams back into the mouth.

The necessary co-operation of the jaws with the hyoid arch in the
rythmical 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
ot its arches to the completion of the work which the proper or

DIGESTIVE SYSTEM OF EISUES.

229

anterior jaws were compelled by their services to respiration to leave
unfinished : and thus the mouth of typical fishes is closed at both
ends by dentigerous jaws.

The first portal to the alimentary tract is usually formed by the
upper and lower jaws (y?y. 61. a, b), and their teeth; the Gym-
nodonts*, are so called on account of their conspicuous manifestation
of this character. But in some Fishes the arched and fortified barrier
is preceded by a fosse inclosed by fleshy lips : the whole genus Luhrus
owes its name to this peculiarity ; the Carp-tribe ( CyprinidcB) also
have it ; and, in some of them, the labial organs are developed to ex-
cess, as, for example, in the genus thence iQvvn&A.Labeoharhus, in which
the lips are not only unusually thick and fleshy, but the lower one is
produced downwards like a pointed beard. The labiated Fishes
have not, however, so distinct a ‘sphincter oris’ as Mammals. Many
Fishes, especially those of the Cyprinoid and Siluroid families,
have fleshy and sensitive barbs or tentacles in the vicinity of the
mouth, and subservient to its functions ; those of the Siluroids being
supported by bony or gristly stems. Tentacles depend from the
rostral prolongation of the Sturgeon, and from the mandibular sym-
physis 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. Mr. Couch I narrates an in-
stance 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.

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 Spatidaria, in which a
minutely shagreened surface on the jaws represents the whole dental
system, has had the force of development of subsidiary organs of ali-
mentation expended in the production of the still more remarkable
rostrum {fig. 61. y.), which is broad and flat, like the mandible of a
spoonbill, and is more than half the length of the entire body.

The conical lip of the suctorial Myxinoids sends off from its ante-
rior expanded border six or eight long tentacula : 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. 46. g g), and the vertically fissured aperture of its
mouth is provided on each side with a series of long slender jointed

* Gr. gumnos, uncovered ; odous, tooth.

f xcvm. p. 72,

230

LECTURE IX.

and ciliated tentacula, which mainly tend, by the per-

petual vortex they cause in the surrounding water, to bring the ani-
malcular nutriment within the grasp of the pharynx (ph). 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 glosso-
hyal, when it projects at all into the mouth, as in Jig. 61. c, is rarely
covered by integuments so organised as to suggest their being en-
dowed with the sense of taste ; they are generally callous, and either
smooth and devoid of papilla?, or, if the representatives of these be
present, they are calcified and the tongue is beset with teeth. The
integuments of the palate, however, not unfrequently present that
degree of vascularity and supply of nerves which indicate 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 * : if you prick any part of this 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 Gym-
notus there are four series of branched fieshy processes in the
mouth, one upon the dorsum of the tongue, a second depending from
the palate, and one along eaeh side of the mouth. The reddish vas-
cular body, discovered by Eetziusf between the basi-branchials and the
sterno-hyoid 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 ; ’ and its
homology with the thyroid, indicated by Mr. Simon j:, is a truer view
of its nature. The only other representatives of a salivary system in
Fishes are the mucous follicles that communicate with the mouth.
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.

In the aberrant Dermopteri and Plagiostomi, at the two ex-
tremes of the Class, in which there are numerous branchial apertures
on each side, and the respiratory streams do not necessarily enter by
the month, the last pair of branchial arches are not metamorphosed
into pharyngeal jaws, and the entry to the gullet is simply constricted

XCIX.

f CXIX.

1 cxvi. p. 300.

DIGESTIVE SYSTEM OE FISHES.

231

by a sphincter ; in the Lepidosiren it is further defended by a soft
valvular fold like an epiglottis.*

The alimentary canal is usually short, simple, but capacious in
fishes ; in a few instances, e. g. Branchiostoma ( Jig. 46. ph, as),
Myzinoids (xxi. Neurologic, tab. iii. Jig. 6.), Exocetus, Lepidosiren
(xxxiii. pl.25.), 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. It is primarily divided into a gastric and
an intestinal portion by the constriction called ‘pylorus.’ The
gastric portion is subdivided into ‘ oesophagus ’ and ‘ stomach,’ the
boundary line being more commonly indicated by a change of struc-
ture of the lining membrane than by a cardiac constriction ; the in-
testinal portion is subdivided into a ‘ small ’ and a ‘ large intestine ; ’
the latter usually answering to the ‘intestinum rectum,’ and the
boundary, when well defined, being a constriction and an internal
valvular fold ; but very rarely marked by an external ca3cum.

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 extra-abdominal part
is not contained in a thoracic division of the cavity, but extends
beyond the peritoneal region into the muscular mass of the tail ; a
portion of the intestines, for example, lies between the right myo-
commata 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 aponeurotic
septum {Jig. 61. 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 tlie alimentary canal,
(ib. d. i), the liver (/ 1), the spleen {n), the pancreas {k), or its
ca3cal rudiments, 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 {Branchios-
toma, Jig. 46. od, Lepidosiren, xxxiii. pi. 25. Jig. 1. d), or two
(Lamprey, Jig. 74. I, Eel, Salmon, Sturgeon, Planirostra, Chimasra,
and Plagiostomes, Jigs. 73. and 75. 1), orifices, situated, except in the
Lancelot, in or near the cloaca. The peritoneal orifices give exit to
the generative products (milt or roe) in the Lancelot, Myxinoids,
Lampreys, Mursenid®, and Salmonidae, but not in the Lepidosiren and
Plagiostomes. In the Myxinoids, the Ammocetes, the Sturgeon, the
Chimserae and the Plagiostomes, the peritoneum communicates also
with the pericardium. "\

* XXXIII. p. 342. fig.y rf.

f LXIX. pi. 8.

232

LECTURE IX.

We have seen that the jaws and mouth are subservient to the
respiratory as well as the digestive functions : hut in the lowest of
fishes, viz. the Lancelet, this community of offices extends through
the whole oesophageal and seemingly gastric part of the alimentary
canal, which is dilated into a capacious sac, and is richly provided
with branchial vessels and vibratile cilia arranged in transverse linear
series, like those in the respiratory pharynx of Ascidians (the
aiTow a extends from the pharynx into the intestine in fig. 46.) :
the oesophageal portion of the alimentary canal is here seen to be
longer than the whole gastric aad intestinal portions. In the Myxi-
noids lateral diverticula are derived from the oesophagus and me-
tamorphosed into special respiratory sacs, communicating by narrow
canals both with the oesophagus and with the external surface
{fig.66,fim.) : in other fishes the respiratory apparatus is more con-
centrated and brought more forwards, so as to communicate with the
pharynx, and to leave the oesophagus free for the exclusive transmis-
sion of food to the stomach.

The oesophagus {fig. 61. c?) is usually a short and wide funnel-
shaped canal with a thick muscular coat and a smooth epithelial
lining, more or less longitudinally folded to admit of increased
capacity for the deglutition of the often unmasticated or un-
divided 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 (xcix.). The cardiac half of the
oesophagus is characterised by increasing width in most Cyprinidce,
and by a more vascular or otherwise modified texture in the Pharyn-
gognathi, Lopho-branckii, the Gobioids, Blennies, Flying-fish, Gar-
fish, and some others. The inner surface of the oesophagus sends off
short processes, papilliform in Box and Ccesio, obtuse in Acipenser,
(prep. 463.), hard and almost tooth-like in Rhombus xanthurus,
Stromatceus fiatola, and Tetragonurus or the keel-tailed Mullet.
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 (prep. 664.). In the great Basking Shark {Selache) the
homologous processes, near the cardia, acquire unusual length, divid-
ing and subdividing as they extend inwards, so that the cardiac
opening is surrounded by ramified tufts directed towards the stomach.
This valvular mechanism (prep. 464. a), seems intended to prevent

DIGESTIVE SYSTEM OF FISHES.

233

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 oesophagus, 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,
Tetrodon) the great air-sac seems to be a more direct development,
as a cul de sac, of the oesophagus (prep. 2095.). These singular fishes
blow themselves up by swallowing the air, which escapes through a
large anterior oblique orifice into the sac : and this again communi-
cates with the fore-part 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 con-
striction, as in the Planirostra {fig. 61. e), and Mormyrus {fiig. 63. e) :
but an increased expansion with increased vascularity and a more
delicate epithelial lining of the mucous membrane more usually in-
dicate, 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 ‘ csecal in the first it presents the form of a bent
tube or canal, as in the specimens I from the Turbot, Flounder, Sole,
Cod, Haddock, Salmon, Carp, Tench, Ide, Lump-fish, Lepidosteus,
Sturgeon, Paddle-fish (fig. 61. e, f), and most Plagiostomes ; in the

second form the cardiac division of the stomacli terminates in a blind

* Lxvi. t. iii. p. 271. pi. 47.

f Reference was made to preparations or recent dissections on the lecture-
table.

234

LECTURE IX.

sac and the short pyloric portion is continued from its right side, as
in the Perch, the Scorpoena, the Gurnards, the BuU-heads, the Smelts,
the Angler, the Pike, the Lucio-perca, the Sword-fish, the Silurus,
the Herring, and Pilchard, the Conger, the Mursena, and the Polyp-
terus {fig. 62). A transitional form, in which the pyloric end is
bent so abruptly upon the cardiac as to make the
cffical character of the latter doubtful, is presented
by the short and capacious stomach of the Bur-
bot, the Blenny, and the Gymnotus. In the Mor-
myrus the stomach presents the rare form of a
globular sac {fig. 63. e). Where the csecal cha-

Stomach and pancreas ;
Polypterus.

Stomach and pancreas ;
Mormyrus.

racter is well marked the
length of the blind end of
the cardia varies consider-
ably ; in the Polypterus,

Conger, and Swordfish it
forms almost the whole of
the elongated stomach, the
short pyloric portion being continued from near its commencement ; in
the equally elongated stomach of the Pike, the pyloric portion is conti-
nued from the cardiac sac at a little distance from its blind end ; the
Herring, Gurnard, and Scorpoena 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
and conical ; but it dilates into a wide sac in Sargus 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 we shall find in the higher organised
Vertebrata. A proper gastric compartment of the alimentary canal
cannot be said to exist in the Lancelet ; the long caecum {fig. 46. hd,
1) 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 Cohitis and Lepidosiren, the
stomach is continued straight from the oesophagus to the intes-
tine. I have found the capacious 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 ob-
served a few 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 bruise the shells of the small fluviatile testa-
ceans that abound in the streams in which this variety of trout is

DIGESTIVE SYSTEM 01^ EISIIES.

235

peculiar.* 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
development 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
(prep. 502). In the Herring the ductus pneumaticus of the swim-
bladder is continued from the attenuated extremity of the cardie end
of the stomach. In the Basking-shark the contracted pyloric division
of the stomach {Jig. 65. f) communicates by a narrow aperture with
a second small rounded cavity {/'), which opens by a narrow pylorus
into the short and capacious duodenum {g).

These are the observed extremes of the modifications of the sto-
mach in Fishes, which it will be seen, therefore, are far from accord-
ing or parallelising those of the dental system. There is often, in-
deed, no essential dilference 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 herbivorous Carp. The
iEtobates, 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 Gymnotus
(prep. 500.) ; still more rarely papillose. The lining membrane is
thrown into wavy longitudinal rugre in the cardiac portion of the
stomach of most Sharks. The gastric follicles are conspicuous,
especially in the pyloric portion of the stomach in many Fishes, as,
e. g., the Guimards, Blennies, and Lump-suckers. The circular py-
loric valve is commonly well developed and has sometimes a fim-
briated margin. The solvent power of the gastric secretion is
conspicuously exemplified in Fishes : if a voracious species be cap-
tured after having swallowed its prey, the part lodged in the stomach
is usually found more or less dissolved, whilst that which is in the
oesophagus is entire ; and, in specimens dissected some hours after
death, one may observe, what Hunter so well describes, “ the di-
gesting part of the stomach itself reduced to the same dissolved
state as the digested part of the food.”f Tiiis surrender of the
dead membranes of the stomach to the solvent power of the pre-
viously secreted gastric juice is well exemplified in the preparation
of the Shark’s stomach, N. 507. b.

* J. Hunter, xcii. p. 126.

f XCII. p. 120.

236

LECTURE IX.

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 two-fold gyratory motion on the
contents : so that, while some portions are proceeding to the pylorus,
other portions are returning towards the cardia. More direct con-
strictive and dilative movements occur, with intervals of repose, at
both the orifices, the vital contraction being antagonised by pressure
from within. The pylorus has the power, very evidently, of con-
trolling 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 commi-
nuting operations. The fishes which afibrd the best evidence of
this ruminating action are the Cyprinoids, (Carp, Tench, Bream,)
caught after they have fed voraciously on the ground-bait previously
laid in their feeding haunts to ensure the angler good sport. A Carp
in this predicament, 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 Eel is, also, a
good subject for studying the movements of the stomach ; and,
besides at the cardiac and pyloric orifices, the direct constrictive
action of the circular fibres may be seen in this fish at the beginning
of the short pyloric division ; regulating the passage of the food from
the long cardiac sac. These observations throw light on the functions
of the pharyngeal teeth in the predatory Fishes, (the Pike, for ex-
ample,) in which one sometimes finds a recently swallowed fish in the
stomach : it may show, for example, a few marks of the large mandi-
bular canine teeth ; but it has undergone no sub-division by the
phai'yngeal rasp-teeth. It would seem, at first sight, that these took
no other part in the mechanical operations of digestion, than to aid
in the act of swallowing : the analogy, however, of the ruminant or
regurgitant function of the stomach of the Carp, suggests that the
pharyngeal teeth take a more important share in digestion, and
indicates the nature of their operations. As the gelatinous integu-
ments and intermuscular aponeuroses of the swallowed fish are dis-
solved by the gastric juice, masses of the myocommata become
detached, and these fibrous portions are most probably carried by
the regurgitating power of the stomach to the pharyngeal teeth.

DIGESTIVE SYSTEM OF FISHES.

237

are there carded and comminuted, and again swallowed, to he re-
duced to chymous pulp by the solvent power of the secretions and
by the continuous grinding pressure of the spiral movements of the
gastric parietes. It is highly probable, therefore, that the shortness
and width of the oesophagus, the masticatory mechanism at its com-
mencement, and its direct terminal continuation 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. For it will
be seen that the Fishes, as, for example, the Sturgeon, thePaddle- fish,
the Dog-fish, and the Selache, whose oesophagus is best organised
to prevent regurgitation from the stomach, are devoid of the pharynx-
geal jaws and teeth. '

Fishes disgorge the shells and other indigestible parts of their
food : and it is known to practised anglers that Fishes, when hooked
or netted, often emjity their stomach by an instinctive act of fear, or
to facilitate escape by lightening their load.*

The intestinal canal is shorter in Fishes generally than in the higher
Vertebrata : in the Dermopteri, Plagiostomes, Holocephali, Sturionidai
(see the Paddle-fish, 61. y to i), the Lepidosiren (xxxni. pi. 2^. figs.
1 and 2.), the Flying-fish, the Loach, the Gar-pike, the Wolf-fish, the
Salmon, the Herring, 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. 46. ^) ; in most fishes
it presents two or three folds ; it is sinuous in the Sword-fish ; concen-
trically and subspirally wound in the Mullet, in which the convolu-
tions are numei’ous and form a triangular mass; and it is in this
fucivorous fish, in the Clnetodonts, and the Carp-tribe, that the intes-
tinal canal attains its greatest length in the present class.

With a few exceptions, of Avhich the Dermopteri and the Lepido-
siren are examples, the intestines are divided into ‘ small’ and ‘ large.’
The beginning of the small intestine, to which is arbitrarily given
the name of ‘duodenum’ {fig. 61. i) is usually wider than the rest
of that division of the canal : it receives the ducts of the liver and
pancreas, the latter accessory organ presenting, in most Osseous
Fishes, the elementary form of simple cieca {fig. 63. K), which are
usually termed, from their communication with, or development from,
the commencement of the small intestine, ‘ appendices pyloricos.’ The
termination of the small intestine is commonly marked by a circular

* A netted Salmon is generally found with an empty stomach ; whence it has been
supposed, notwithstanding its extraordinary array of teeth, that its staple food con-
sisted of such animalcules as are alone, under those circumstances, discoverable in the
gastric mucus.

238

LECTURE IX.

valve. In the Bogue-bream {Box vulgaris) and the Flounder there
is a small csecal process at the commencement of the large intestine ;
there are two short caeca at the same part in Box Salpa* The large
intestine is usually short and straight in Fishes, answering to the
rectum of higher animals. 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 some fishes, e.g,, Gasterosteus, Centriscus, Ostracion,
Batistes, and Syngnathus, it is even narrower than the ‘ small in-
testine but most commonly it is wider, as in the Percoid family, the
Gurnards {Triglidce), the Breams (Sparidce), Scicena, Scomber,
Coitus, Labrus, Pleuronectes, Gadus, Lophius, Cyclopterus, the
Siluridce, the Plagiostomi, and the Planirostra (ib. h).

The tunics of the intestinal canal consist in Fishes, as in other Ver-
tebrates, 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
a thick inner circular stratum (see preps. 637. 639. from the
Sturgeon) ; the elementary fibres in general present the smooth
character of those of the involuntary system ; but Reichert t 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 Verte-
brates. It is commonly thick and glandular, and always highly
vascular. In the small intestines it presents, in some Fishes (Cod,
prep. 633.), a smooth and even surface ; in some it is produced into
obliquely longitudinal or wavy folds (Tui’bot, prep. 634., Salmon,
prep. 635.); in the Herring it presents feeble transverse rugae; in
many Fishes it is reticulate, as in the Wolf-fish (prep. 631.) and
Murcena (prep. 630.) ; this character is present in the peculiarly thick
and parenchymatoid mucous tunic of the small intestine of the Stur-
geon, where the larger meshes include irregular spaces, subdivided
into smaller cells (prep. 638.). In a few Fishes the mucous membrane
is coarsely villose or papillose. There is often a well-marked dif-
ference in the character of the lining membrane of the small and
large intestine : thus, in the Salmon, the rugae become fewer, larger.

XXXIII. t. vi. pp. 624. 270.

f xciii. p. 26.

DIGESTIVE SYSTEM OF FISHES.

239

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 valvuljB conniventes in the human jejunum. The straight ‘large in-
testine,’ which is relatively longer in the Amia, Polypterus, Paddle-fish
61.), Sturgeon, and ChiniaerjE, is characterised by the continuity
of such transverse folds as those in the Salmon, producing an unin-
terrupted spiral valve of the mucous membrane. In the Lepidosiren
the entire tract of the straight and short intestine is traversed by
this peculiarly piscine extension of the inner coat.* The spiral
valve characterises the large intestine 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 Myxinoid species.

The time homologue of the small intestine is extremely short in
the Plagiostomes ; it is narrow in the Rays, expanded and sometimes
sacciform i^fig. 65. g) in the Sharks, where it seems to form the com-
mencement 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 Alopecias 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. 64. The Hunterian
preparation (No. 645.) shows the longitudinal form ^g- pjti 64
of the spiral valve ; as it may be seen, also, in the
squaloid genera Carcharias, Scoliodon, Galeocerdo,

Thalassorhimis, and Zygcena. J In the second and
more common modification, the fold of mucous mem- ’

brane is disposed in close transverse coils, as shown in
.the longitudinal section of the Selache’s gut (y?y. 65. /u); and a trans-
verse section exposes only the flat surface of one of the coils. Prep.

* xxxm. p. 343. pi. 25. fig. 2.

i XLvi, t. iv. p. 314. ; t. xcvi. p. 277. pi. 2 and 3.

f Roget, c. ii. p. 205.

240

LECTURE IX.

652. A, shows a typical example of this disposition of the mucous

membrane in the Fox-shark {Alo-
pias Vulpes) ; the valve describes
thirty-four circumgyrations within
seven inches extent of the intes-
tine ; the mucous membrane is mi-
nutely honey-combed : a few scat-
tered 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 and Alopias, the
spiral valve is transverse in Galeus, Lamna, and all the Dog-fishes
(^Scylludce and Spinacidce). The trunk of the veins of the longitudi-
nally convoluted valve runs along its free thickened border, and
quits its commencement to join the vena portae*: that of the
transversely spiral valve is 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 secerning 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 accessary muscular and serous tunics by the modifications
above described. Analogous ones exist, however, in other Plagi-
ostomes, and in the Lamprey, to which the above physiological ex-
planation 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, 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 C8ecal process with a glandular inner
surface opens 75. 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, and

Spiral valve, Selache ; Clift.

Duvernoy, xcvi. p. 274. pi. 10.

DIGESTIVE SYSTEM OF FISHES.

2U

of the uterus or urinary bladder ; the Lepidosiren has the peculiarly
ichthyic arrangement of the anal, genital, and urinal outlets. *

In the Dermopteri the intestinal canal is pretty closely attached to
the back of the abdomen, though the primitively continuous mesen-
teric fold becomes reduced in the Lampreys to filamentary processes
accompanying the mesenteric vessels. Rathke has observed a similar
metamorphosis of the mesentery in the Syngnathi and Cyprinidm
into detached membranous bands. 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 along the ventral
surface of the intestines : a second mesentery is continued from this
part of the intestine to the ventral parietes of the abdomen in the
Murtena.

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, it is placed so far forwards as to remind
us of the position of the excretory outlet in the Cephalopods. It is
beneath the pectorals in the Amblyopsis spelcBus : but the more normal
posterior position of the vent obtains in most abdominal and all car-
tilaginous fishes.

Petrified fasces or ‘ coprolites ’ give some insight into the structure
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 ancient Ganoids, like their modern
representative, the Polypterus, possessed the spiral valve.

The liver makes its first appearance in the lowest vertebrated, as
in the lowest articulated species, under the form of a simple csecal
production from the common alimentary canal : commencing in the
Lancelot {Jig. 46. hd), a little beyond the orifice py, the hepatic
caecum (/) extends forwards by the side of the ciliated respiratory
sac, which appears to be the homologue of the long oesophagus with
the attached marsipo-branchial organs of the Lampreys, but which
some may view as representing the stomach of higher fishes. As
the true digestive function, however, cannot be supposed to begin
until the food has entered the canal ii, the place of communication
of the rudimental liver corresponds in the Lancelot with that in the

* XXXIII. pi. 25. fig. '1, m, V, o, 1. The Branchiostoma offers no exception to this
rule ; the opening, by which the ova and semen are expelled, is a common peritoneal
outlet.

VOL. II.

R

242

LECTURK IX.

lower organised Mollusks : other members of the Piscine class do
not show by permanent structures the gradational steps in the develop-
ment of the hepatic, as in that of the pancreatic gland. Passing to
the Myxinoids we find the liver to be, as in all higher fishes, 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, by which the bile is conveyed to the duodenum,
from which the stomach is divided by a pyloric valvular orifice.*

The texture of the liver is soft and lacerable ; its colour usually
lighter than in higher Vertebrata, being whitish in the Lophius,
in many other fishes of a yellowish-gray or yellowish-brown : it is,
however, reddish in the Bream ; of a bright red in the Holocentrum
orientate, 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 most fishes the liver is remarkable for the quantity of fine
oil in its substance, under which form almost the whole of the adi-
pose tissue is there concentrated in the Cod-ti'ibe, the Rays, and
the Sharks.f 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 tyfig. 61. I, o'), and extends backwards, 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 broad-
est, for example, in the Rays, longest in the Eels ; not, 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 and broad lobes con-
nected by a transverse lobule. The liver consists of one lobe in
most Salmonoid and Lucioid Fishes, in the Gymnodonts and Lopho-
branchs, 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

* The Bream is the only fish in which I have found the cystic duct terminating
directly in the stomach.

f I he 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 ex-
poses to them an abundant source of a pure and valuable oil.

DIGESTIVE SYSTEM OE FISHES.

243

Polypterus, the Doiy, the Coryphene, the Chietodonts, and the Cod-
tribe. In the Whiting the two chief lobes extend the whole length
of the abdomen. The liver is trilobed in the Corvina, the Clupeoid
and the Cypriuoid fishes : in many of the latter family it almost con-
ceals the convoluted intestinal canal. The broad and flat liver of the
Raiidas is trilobed. The liver is much subdivided in the Sand-lance
and in the Tunny, in which latter fish it presents remarkable modi-
fications of the vascular system. * 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 Cuvier f and Wagner. | Cuvier did not
detect a gall-bladder in Lutes niloticus, Holocentrum Sogho, Spfig-
reena Barracuda^ Trigla Lyra, Tv. Cuculus, Corvina dentex, GU-
phisodon saxatilis, Lepidopus argenteus, Labrus turdus, Ammodytes,
and Echineis remora. The gall-bladder is wanting in the Ammocete
and Lamprey, but exists in the Myxinoids ; it is absent in the Pristis,
Zygcena, and Selache, but is present in Galeus, and others of the
Shark-tribe. I have studied the rich series of observations recorded
by Cuvier § and his able Editors |[ on the gall-bladder and gall-
ducts in fishes without obtaining a clue to the law of the develop-
ment of the special receptacle of the biliary secretion in fishes. The
pouch in which the aggregated hepatic ducts terminate in the
Selache 7naxima 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. 65, /.), which passes 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 {ih. ???.) 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.
61. w^). In some Cyprinoids and Rays, and in the Sturgeon, it is
imbedded in the substance of the liver. In many Chaitodonts and
Salmonoids, in the Sword-fish, in the Eel and the Muriena, 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 pyi’iform in the Lophius, Mullet, Sea-perch {Sebastes),
Pike, Sturgeon, Planirostra, and most other Fishes : it is subspherical
in the Gray-shark {Galeus), and in the Wolf-fish: it is like a long-
necked flask in Polypterus ; is bent like a retort in Xiphias, and is

* Eschricht, ci.

§ XXIII. passim.

•f- XIII. t. iv. p. 551. I XLvii.

II XIII. t. iv. pt, ii. 'p. 559— 569.

244

LECTURK IX.

remarkably long and slender in Scimna, Upeneus, Lates nobilis, and
in the Bonito, the Tunny, and other Scomhridce. The bile is some-
times conveyed directly into the gall-bladder by hepato-cystic ducts,
and thence by a cystic duct into the duodenum (Wolf-fish, Erythrinus,
Lepidosiren) : or it is conveyed by a single hepatic duct, formed by the
union of several branches from the liver {Zygcena, 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 communis choledo-
chus ’ into the duodenum, as in Pimelodus ; or the bile is conveyed
to the duodenum 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
Turbot I found numerous hepatic ducts, some of which communicated
with different parts of the cystic duct, and four opened into the
dilated termination of the ductus communis. (Prep. 811. A.) 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, before it enters the commencement of the wide intestine,
near the beginning of the spiral valve. The gall-duct in the Sturgeon
and Planirostra {Jig. 61.) 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 orifice of the
gall-duct is often supported on a papilla, as in the Sturgeon, the Skate,
and the Lahrax lupus. In the Bream I found the short cystic duct
opening into the fore-part of the cardiac portion of the stomach.

In most Osseous Fishes the intestine buds out at its commencement
into long and slender pouches, or cieca, into which it appears
that the food never enters, and which, therefore, increase the direct
secreting surface of the alimentai-y tract, over and above the extent
of the mechanism for pounding and propelling the chyme, or of the
vascular surface which selects and absorbs the chyle. By a very
gradual series of changes of these ceecal processes, within the limits
of the class of Fishes, we are led to recognise them as homologous
with the conglomerate gland called ‘ pancreas ’ in Man. The secre-
tion of the rudimental representatives of this gland is so like the
fiuid which the ordinary mucous surface of the intestine eliminates
and sets free from its capillary system, that conditions of the ordi-
nary alimentary tract exist in some fishes which render needless the
development of the special accessory surfaces. The Dermopteri show
no trace of pancreas : their whole digestive canal is simple ; the whole

DIGESTIVE SYSTEM OF FISHES.

245

organisation for which that canal is the 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 mu-
cous coat the required concomitant complexity of the digestive canal.
The torpid Lepidosiren, which, though of a much more advanced
type of ichthyic organisation, can have but little expenditure of
nervous and muscular force to repair, seems, in like manner, to derive
from a spiral extension of its thick and glandular intestinal mucous
memhrane the equivalent of a pancreas, and no rudiment cf that
gland exists in this fish. In several Osseous Fishes either the inac-
tive nature of the species, or the extent or special modifications (as
the long intestine and glandular palate of the Carp, for example,) of
the mucous membrane in the ordinary tract of the alimentary canal,
render unnecessary the presence of a pancreas. Thus there is no
cascal production of the duodenum in the Ambassis, tlie Wolf-fish,
nor the Warty Agriope, nor in most Labroids, Cyprinoids, Lucioids,
Siluroids, nor in the Lophobranchs and Plectognats ; nor in the
genera Antennarius, 3Ialth(BUS, and Batrachus. The pancreas is re-
presented by a single pyloric caecum in the Sandlance and Polypterus
{fig. 62. k)\ by two c®ca in most Labyrinthibranchs, in many
species of Amphiprion, in the Lophius, the Turbot, and the
Mormyrus {fig. 63. k) ; by three cffica in the Perch, the percoid
Popes {Acerina), the Asprodes, and Diploprions ; of from four to
nine caeca in the genus Coitus ; of from five to nine ca3ca in the
genus Trigla ; of six cteca and upwards in Scorpcena and Holocen-
trum ; and so on, increasing to a numerous group of pendent pyloric
pouches, as we find in the Scombei’oids, Chaetodonts, Gadoids,
Halecoids, Cyclopterus, and Lepidosteus. There is a difference, how-
ever, worthy of note, in the mode and extent of attachment of these
numerous caeca : in the Salmon (prep. 773.), the Herring, and Haddock,
they rank almost in a line along the whole duodenum ; in the Gym-
notus and Lump-fish they form a circular cluster ai’ound the distal
side of the pylorus. Even in the longitudinally arranged caeca the
principle of concentration dawns : thus the fifty pancreatic 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 by a circle of six
orifices around the duodenal side of the pyloric valve. In the Tunny
a more subdivided bunch of pancreatic caeca empty themselves by
five orifices ; in the Sword-fish by two orifices ; and, finally, in the
Sturgeon and Paddle-fish {fig. 61. k) by a single opening of what
now becomes the short and wide duct of a pancreas. The interpo-
sition of cellular tissue binding together longer, more slender and

246

LECTURE X.

more ramified casca, with a concomitant increase of the vascular
supply, and a common covering or capsule, finally converts the ac-
cessory intestinal growths into a true parenchymatous conglomerate
gland ; as we see in the Holocephali and Plagiostomes, (preps. 776,
777.) : the papilliform termination of the duct of such a pancreas
is shown in the Selache at jig. 64. i.

The existence of this highly developed form of pancreas over and
above the spiral intestinal valve may relate to the high organisation
of these Cartilaginous Fishes, and to the great development of the
organs of locomotion, occasioning the necessity for rapid and com-
plete 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 mu-
cous membrane within the canal, the circumstances calling for a more
complete development of the digestive system in the predatory
Sharks and large-finned Rays not being present. Thus the Poly-
pterus, which has a spiral intestinal valve, has only one short pyloric
caecum {Jig. 62. K) ; 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 commencement
of the duodenum.

LECTURE X.

VASCULAR SYSTEM OF FISHES.

THE ABSORBENTS.

The assimilation of food in an animal body has a close analogy to a
chemical operation, the general result being the obtaining from a
combination of two substances a third distinct from both. If the
chemist operates on a solid substance, he first triturates and reduces
it to powder, then digests it in a solvent menstruum, next adds the
reagent, and if the result of the admixture be a precipitate, the su-
pernatant fluid is drawn or filtered oflf. So it is with the food : it
first undergoes the process of mastication in the mouth, next that of
solution in the stomach, then the chyme is mixed with the intestinal,
biliary, and pancreatic secretions, and lastly the chyle is filtered off
from the fascal precipitate. The instruments of this separation and
conveyance of the chyle to the circulating organs are the ‘ lacteals : ’
analogous vessels which take up the effete parts of the body are
called the ‘lymphatics;’ both together constitute the ‘absorbent

VASCULAR SYSTEM OF FISHES.

247

system.’ This system exists as a separate organic vascular apparatus
only in the Vertebrate subkingdom : it was first observed in Man and
Mammalia ; was discovered by John Hunter in Birds* * * § and Reptiles f,
and afterwards described by IVIr. 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. J

The lacteal system in Fishes commences by a reticulate or plexi-
form layer of vessels attached to the cellular side of the mucous coat
of the stomach and intestines : in the Skate § the network is so coarse
that, when inflated, dried, and cut open, it appears like a subdivided
cellular 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 receptacles, 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 corresponding diflereuces in their
lacteal systems : in the Myxinoids the lacteals are supported and con-
veyed 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 forwards, and enter the abdominal cavernous sinus be-
neath the aorta.

The lymphatic system is best demonstrated by injecting ihe large
absoi’bent trunk which runs upon the inner surface of the ventral
parietes of the abdomen, along the median line from the vent for-

* “ 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, cii. 1768, p. 220.)

f Hunter’s account of this discovery, in a manuscript copied by Mr. Clift, 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 know-
ledge, 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 de-
scriptions 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. Ilewson’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. ”

t CII. 1768, 1769.

§ In this and other Plagiostomes the gastric lacteals are confined chiefly to the
contracted pyloric canal.

B 4

248

LECTURE X.

wards to the interspace of the pectoral fins, where the size of the
vessel best favours the insertion of the injecting pipe. It receives
the lymphatics of the pectorals, and (in thoracic and jugular fishes)
of the ventral fins ; then, advancing forwards 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 when uninjected: large lymphatic trunks from the upper
(dorsal) part of this 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 ex-
tends along the lateral line, and gets a penniform character by the
regular mode in which its tributary lymphatics join it. The lym-
phatics 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 column, which combine with the lacteal plexiform trunks
continued forwards along each side of the stomach and oesophagus,
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. 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, and, converging to
enter the haemal canal, terminates there in the commencement of the
‘ vena caudalis.’ Dr. M. Hall discovered that the caudal lymphatic
sinus, in the Eel, possessed a contractile pulsating power.* Fohman
describes other and minor communications between the absorbent
and venous system of Fishes.

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 repre-
sented by the large and numerous plexuses ; and the whole absor-
bent system presents, as might be expected in Fishes, the first step
beyond the primitive condition of the common areolar or cellular
receptacle of the lymph in the Invertebrata. The chyle, as well as the

* xxxix. ii. p. 217.

f cut.

VASCULAR SYSTEM OF FISHES.

249

lymph, of Fishes is colourless and transparent : both contain cor-
puscles, or centres of assimilative force, five or six times smaller than
the blood-discs, and manifesting an inherent power of development and
change, some being granular, others with a capsule and in the con-
dition of nucleated cells.

Professor Stannius * has described ash-coloured bodies, lying near
the pylorus and spleen, which contain a whitish fluid laden with mi-
croscopic granules, much smaller than the blood-discs ; he regards
them, apparently with justice, as a residuum of the foetal vitelbcle or
yolk-bag.

THE VEINS.

As the blood moves in a circle, it signifies little at what point we
commence the description of the parts concerned in the circulation,
since there also we must end. But as, in tracing the progress of the
nutriment through the organs concerned in its chylification and san-
guification, we were led by the absorbents to the veins, we may begin
with them the account of the circulating system.

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
Invertebrata, 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 abdominal 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 veins of fishes constitute two well-defined systems ; viz. the
‘ vertebral’ and the ‘ visceral,’ answering to the division of the nerves
and muscles into those of ‘ animal’ and ‘ organic’ life : the portal
system is a subdivision of the visceral one, but also frequently in-
cludes part of the vertebral system of veins, especially in the Myx-
ines, in which the portal sinus forms a common meeting-point be-
tween portions of both systems, f

The vertebral system of veins commences by a series of capillary
roots I in the integuments and muscles, which unite to form branches

* CIV. p. 39.

f Retzius, in xxi. “ Gefasssystem,” 1841, p. 16.

The capillary system of vessels consists in Fishes, as in other Vertebrata, of
minute but similar-sized tubules, capable of carrying a single file of blood-discs,
and connecting the termination of the arteries with the commencement of the
veins.

250

LECTURE X.

corresponding with the muscular and osseous segments of the body :
these ‘ segmental’ veins consist, in the tail, of superior or neural, and
inferior or hcematal branches ; in the abdomen, of superior and of
lateral branches ; in the head, where the vertebral segments are more
modified, the veins manifest a less regular and appreciable corre-
spondence with these segments. The cephalic veins, returning the
blood from the cranial vertebrae, 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 nutritiae’ from the branchial arches,
unite together on each side to form a pair of ‘jugular’ veins, each of
which usually dilates into a large sinus, and again contracts and re-
sumes the vasiform character, as it descends to beneath the parapo-
physes of the atlas and axis, in order to join the corresponding trunk
of tlie vertebral veins of the body. * This great trunk, called ‘ vena
cardinalis’ by Rathkef, commences at the base of the tail-fin, where
it receives the lymph from the pulsating sac in the Eel-tribe. The
‘ vena cardinalis’ is double, there being one for each side of the body,
and both right and left ‘ venje cardinales’ extend forwards, in close
contact, along the heemal canal in the tail, then through the abdomen,
and in both regions immediately beneath the aorta and vertebral bodies,
to near the ‘ axis,’ where each trunk diverges and descends to join its
corresponding ‘ vena jugularis,’ forming the short ‘pre-caval’ veinj;
{Jig.19, e), which empties itself in the great auricular sinus between the
aponeurotic layers of the pericardial and abdominal septum. In the
Lamprey the ‘vena cardinalis’ is single along the tail, but it bifui*-
cates 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 symmetrical disposition of the ver-
tebral venous system is more disturbed in many osseous fishes, at the
expense of the right side ; the right cardinal vein, after some trans-
verse connecting channels with the left, finally terminating or losing
itself therein anteriorly : part of the right jugular vein, also, in this

* In the Lamprey the corresponding jugular trunks lie above the aponeurotic
representatives of the vertebral parapophyses.

t ‘ La veine cave ’ of Cuvier ; but it is not homologous with either the ‘ inferior ’
or ‘ superior venaj cavee ’ of Man.

j Ductus Cuvieri, Rathke ; quervenenstamme, Muller. 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 ‘ven* 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, or, to speak more strictly, their single homologue in the
human subject, where their normal symmetrical character becomes masked by an
extreme modification, and where their name is applicable only to so rare and ex-
ceptional a condition.

VASCULAR SYSTEM OF FISHES.

251

case enters the left or common cardinal vein.* In the Tunny the
two ‘ venm jugnlares’ unite and form a common trunk, which
enters the auricular sinus independently, f 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’
or superior twigs form with the ‘ myelonaP veins a trunk which
runs parallel with the cardinal veins, but above the vertebral
bodies in the neural canal. This trunk, which I call the ‘ vena
neuralis,’ communicates by short lateral and vertical canals with the
‘ venae cardinales, and in the region of the abdomen these short
anastomosing veins perforate the substance of the kidneys, and
receive the ‘renal veins’ before terminating in the abdominal car-
dinal 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 anas-
tomotic branches of the neural vein, in transferring its contents to
the cardinal veins, perforated the kidneys, thought 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 J in
showing that they rather receive or communicate 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 along 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 cceca and
spleen, of the generative organs and air-bladder : these, by progres-
sive union and reunion, constitute either a single trunk which forms
the portal arterial vein of tlie liver ; or, as in the Perch, a second
trunk, the true homologue of the ‘ inferior vena cava ’ which returns
the blood from the genital organs and air-bladder to the auricular
sinus, without previous ramification in the liver ; the portal trunk
being formed only by the veins of the alimentary canal and its appen-
dages. The portal trunk is single in the Ling, the Biu’bot, 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.

* XXI. ib. p. 38. t Ib. p. 37. f xxiu. p. 381.

252

LECTURE X.

In the Plagiostomes with the longitudinal spiral valve the main
root of the portal vein is concealed in the free, thickened, muscular
margin of that valve * : the trunk of the intestinal vein is 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 61. n), and
then, with the duodenal, pancreatic, and gastric veins, forms the por-
tal trunk.

Professors Eschricht and Muller f found, in the Tunny, that the veins
of the stomach, intestine, pyloric appendages, and spleen, respectively
subdivided into numerous minute venules, which interlaced with cor-
responding ‘ retia mirabilia ’ of the arterial branches sent from the
cseliac 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
veins of the rectum, and thus form part of the roots of the portal sys-
tem. But the most interesting modification of the portal system of
Fishes is that discovered by Retzius in the Glutinous Hag. In
this and also in other Myxinoids, the genital and intestinal veins
form a common trunk along the line of attachment of the me-
sentery : 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 supra-
renal 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 anterior part of
this sinus receives a vein from the right anterior parietes of the body,
which is formed by the union of all those veins 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 backwards 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 together 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

t CI.

Duvernoy, xcvi. p. 274.

VASCULAR SYSTEM OF FISHES.

253

‘ precaval ’ trunk. A corresponding precaval trunk is formed in the
same way on the left side, and the great auricular sinus is con-
stituted by these and by the wide hepatic veins, which contract before
they terminate. In many Osseous Fishes, as Salmo, Silurus, ' Belone,
Anguilla, Ammodytes, and Accipenser, the hepatic veins terminate in
the common sinus by a single trunk ; in others, as Thynnus, Gadus,
Esox, and Pleuronectes, by two trunks ; and in a few Fishes, as
Glupea, Coitus, and certain Cyprinoids, by three or more trunks.

Thus in Fishes the chyle, having already begun to manifest its
independent life by the development of distinct microscopic granular
corpuscles, as primitive centres of assimilative force, before it enters
the lacteals, undergoes in those vessels and their receptacles a fur-
ther 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 interchange 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 take 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 : a centre of superior assimilating force has already begun to
establish itself amongst them, and to grow at their expense. *

THE HEART.

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 : it is said that in some fishes
(^Myxine, Bdellostoma) a contractile receptacle accelerates its course
through the portal circulation. The venous blood has finally to be
submitted to the influence of the atmosphere, and especially to the

* Most of the stages analogous to those demonstrated by Dr. Martin Harry
(evil.), in the first periods of development of the mammiferous ovum, have been
recognised in the corpuscles of chyle, lymph, and blood. The powers of one series
of granules, the progeny of a primary centre, are concentrated in a secondary-
nucleus, which absorbs them as they liquefy ; developes itself at their expense,
generates a second series of granules, which, in their turn, give way to subserve a
third regeneration of aggregated but distinct spherular centres of force ; the final
purpose of the successive development, liquefaction, and assimilation of the inde-
pendent granular centres, being apparently to concentrate their vital energy in the
form ultimately assumed, as coloured blood-discs. The shape and relative size
of these particles are shown in Jig. 4. p. 1 3, in a plagiostomous fish at h, in a typical
osseous fish at g ; the blood-discs of the Lamprey arc circular. — See the admirable
Memoir on the Development of Blood-discs, cxxvn.

254

LECTURE X.

reaction of the oxygenous element ; and for this, the most important
and efficient cause of its conversion into arterial blood, a contractile
cavity, vrith strong muscular walls, is provided, in order to impel the
blood to the organs espeeially destined to effect its decarbonisation
and oxygenation. The propelling organ is called the ‘ heart ’ (yjig.
61. q\ the respiratory organs the ‘ gills ’ or branchiae {ib. t, u),
since 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 Lancelot, in which a venous
or branchial heart is not developed as a compact and predominant
muscular organ of circulation : a great vein answering to the ‘ vena
cardinalis ’ extends forwards along the caudal region, beneath the
chorda doi’salis, above the kidney {fig- 46. K) ; and as it extends
along the branchial oesophageal 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 rythmically, and represents rudimentally the
branchial heart of the Myxinoids : the cardinal vein {ba) divides
anteriorly, and supplies the short vascular processes {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 ten-
tacula, ( f, f), whence it returns to the pharynx by the labial vessels
which there unite together, and with the inferior trunk of the vas-
cular system, or arches, of the branchial pharynx. The free vas-
cular processes (gg) seem to me to perform most distinctly the func-
tion of gills, and they are so referred to in the characters of the
suborder Pharyngo-branchii (p. 47.) : but they may be homologous
with the supralabial tentacles of the Ammocete.

In the Myxinoids a heart consisting of an auricle and a ventricle
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
‘ column£E carnete ’ or ‘ chordae tendinem.’ The artery, single here as
in all Fishes, rises from the fore-part of the ventricle with a pair of

VASCULAR SYSTEM OE FISHES.

255

semilunar valves at the ‘ ostium arteriosum ’ behind its origin, beyond
which it slightly dilates, but has no muscular parietes constituting a
‘ bulbus arteriosus.’ In this Hunterian prepai’ation of a large Myxinoid
fish (No. 1018.) the artery divides at once into two branchial trunks,
reminding one of the separate branchial arteries of the Cephalopods.
In other species of Bdellostoma the artery extends beyond two or
three pairs of gills before it bifurcates; and Muller* saw one in-
stance in the Myxine glutinosa, where the branchial artery continued
single as far as the anterior gills.

The pericardium of the Ammocete communicates by one wide orifice
with the peritoneum: that of theLamprey is a shut sac, and is supported
by a perforated case of cartilage, formed by the last modified pair of
branchial arches {fig. 11. 47^, p. 52.). Not any of the Dermopteri pos-
sess the ‘ bulbus arteriosus this is present, and forms, as it were, a
third compartment of the heart, beyond the ventricle and auricle in all
other Fishes {fig. 61. r.fig. 70. c) : nay, if we include the great ‘ sinus
communis’ as part of the heart, then we may reckon four chambers
in that of Fishes ; but the student will observe that these succeed 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 current of
blood fi’om behind forwards, driving it exclusively into the branchial
artery and its ramifications. This is very different from the arrange-
ment and relations of the four compartments of the human heart.
Physiologically the heart of Fishes answers to the venous or pul-
monary division, viz. the right auricle and ventricle of the mammalian
heart, and its quadripartite structure in Fishes illustrates the law of
vegetative repetition, rather than that of true physiological complica-
tion.f The auricle and the ventricle are, however, alone proper to
the heart itself : the sinus is a development of the termination of the
venous system, as the muscular bulb is a superaddition to the com-
mencement of the arterial trunk.

Some of the higher organised Fishes, which present the normal
structure of the heart, have, like the Myxinoids, a perforated peri-
cardium. In the Sturgeon the communication with the peritoneum
is by a single elongated canal extending along the ventral surface of
the msophagus. In the Planirostra and Chimasroids the pericardio-
peritoneal canal is also single. In the Plagiostomes it bifurcates,
after leaving the pericardium, into two canals, which diverge and
open into the peritoneum, opposite the end of the oesophagus : no
ciliary movements have been noticed on the surface of these remark-

* XXI. ib. p. 9.

f The heart of Fishes with the muscular branchial artery will be seen to be the
true ‘homologue ’ of the left auricle, ventricle, and aorta in higher Vertebrata, as we
trace the complication of the heart synthetically; but it performs a function ‘ana-
logous’ to that of the pulmonic auricle and ventricle in them.

256

LECTURE X,

able 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 Muraena, short fibrous bands supporting vessels pass
from different parts of the pericardium 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
situated below the hind-part of the gills, and, as these are more
concentrated in the head in all Fishes above the Dermopteri, so the
position of the heart is more advanced {fig. 61. c). In the Pla-

giostomes, the Sturgeons, the Perch, the Angler {Lophius, prep. 904.),
and the Sun-fish {Orthagoriscus, prep. 905.), 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 Osseous
Fishes. The auricle, when distended, is larger in proportion to the
ventricle in Fishes than in higher Vertebrates. Its relative position
to the ventricle varies in different species, and permanently re-
presents as many similar variations displayed temporarily during the
course of the development of the heart in higher Vertebrates ; thus
in the Scorpcena scrofa, as in the Myxinoids, the auricle is posterior
to and in the same longitudinal line with the ventricle : in the Carp,
Sole, and Eel, it has advanced to the same transverse line, on the dorsal
and left side of the ventricle : in most Osseous Fishes, the Ganoids,
{fig. 70, B.),the SturionidcB {fig. 61. jo), 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 Plagiostomes. 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 are attached to the strongest
muscular bands. Only in the Lepidosiren is there any vestige of a
septum, and this is reticulate. 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 at-
tached to numerous ‘ chordae tendineae.’ 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.

VASCULAR SYSTEM OF FISHES.

257

The ventricle 61. 5') usually presents the form of a four-sided
pyramid, one side dorsad towards the auricle ; one angle ventrad, and
the base forwards. In the Lepidosteus and Polypterus, 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 Plagiostomes its
transverse diameter is the longest, as if preparatory to a division.
Its cavity is, however, simple in all fishes. The parietes of the ven-
tricle 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 locomotion 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 decomposi-
tion from the outer and more longitudinal layers. Some of the in-
ternal fasciculi send off the ‘chordae tendineae’ above mentioned in
the Sturgeon ; but in almost all other fishes those ‘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 (prep. 606.) : the Sun-fish (prep. 905.) has four such valves
there. But the Ganoids, Holocephali, and Plagiostomes have two
or more transverse rows of semilunar valves attached to the inner
surface of their long and muscular bulbus arteriosus. The prepara-
tion, No. 911., shows two rows of three valves in the Grey Shark
( Galeus) ; the same is found in the Blue Shark ( Carcharias), in
the Dog-fish {Scyllium), and in -the Chimeeroids ; the Amia has two
rows of six valves : in the genera Sphyrna, Mustelus, Acanthias,
Alopias, Lamna, Rhinobatus, Torpedo^ and Accipenser,Xh.&ve are three
rows of valves : the preparation of the Sturgeon’s heart (No. 908.)
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 tendineae’ to the parietes of the bulb. The genera Hexanthus,
Heptanchus, Centrophorus, and Trygon have four rows of valves. The
preparation of the heart of the Raia Batis (No. 909.) shows five rows,
the valves increasing in size to the last row, which is at the termina-
tion of the bulb. Scymnus, Sqiiatina, and Myliobates have also five
rows of valves. In the Cephaloptera the large bulbus arteriosus*
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 beginning, and three
at the end of the bulb. The valves are still more numerous in the

* I found its cavity more capacious than that of the contracted ventricle.

VOL. II. S

258

LECTURE X.

Ganoid fishes, and are arranged in longitudinal rather than in trans-
verse 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 longitudinal 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 sup-
plied in its long and twisted bulbus arteriosus by two longitudinal
ridges (J/g. 71. c)j'; the interesting stages, which we have been tra-
cing 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 is essentially single, but
has two ear-like appendages. J The venous sinus 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 ven-
tricle (ib. 5) is single, like the auricle ; its inner parietes are very
irregular: a Grabecula’ projects from the lower part of the cavity,
like a rudimental septum : a smaller transverse ‘ trabecula ’ arches
over and acts as a valve to the single auriculo-ventricular opening,
but there are no proper membranous semilunar valves.

The muscular pai'ietes of the ‘ bulbus arteriosus ’ are distinct in all
fishes from those of the ventricle ; they may be overlapped by these,
but an aponeurotic septum intervenes between the origin of the
bulb and the overlapping ventricular fibres (see prep. No. 910.).

BRAJ^CHIAL VESSELS AND GILLS.

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

* XXV. pi. ii. -j- XXXIII. p. 343. pi. xxvi. fig. 2. c. | Ib. p. 345.

§ A true second auricle consists essentially of a dilatation of this homologue of
the ‘vena pulmonalis.’ Hyrtl (cxxiv.) errs in stating that the fibro-cartilaginous
tubercle below the auriculo-ventricular aperture was “ weder von Bischoff noch
Owen angegeben.” It is described in my Memoir (xxiii.), p. 345. : “ It empties
its contents into the ventricle by a distinct orifice, protected hy a cartilaginous valvular
tubercle and the tubercle is figured, from the auricular side, in pi. xxvi. fig. 2.,
where a bristle is placed above it, as in fig. 71. Hyrtl gives a figure of the same
‘cartilaginous tubercle’ as “ dicken eifdrmigen harten faserknorpel ” (p. 35. ), or
“ fibro-cartilagindse Stempfel ” (p. 60.), from the ventricular side, tab. i. fig. 3. c.
It is true that this singular body escaped the notice of Dr. Bischoff, who, believing
that the Lepidosiren was a reptile, overlooked many things that were, and saw
some things that were not, in its organisation ; as, e. g. two distinct auricles, and a
nasal meatus communicating with the mouth.

A ASCTJLAR ‘system OF FISHES.

2.59

sac of a Myxine {fig. 66. 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 tivo distinct sacs, and
expose their vascular mucous surface to view. Produce these vascular
surfaces into lamellee, pectinated processes, tufts or filaments, proceed-

f

Two gill-sacs, Bdello-

stoma. Two gill-sacs, Lamprey.

ing from an intermediate arch or basis of support, and you have the
gill of an ordinary osseous or cartilaginous fish. 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. 67- conse-

quently in these Dermopteri, as in all higher fishes, a different ar-
tery 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. Before describing the branchial
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 integuments by its entire peripheral margin,
and the streams of water flow out by as many Assures in the skin
(ib. li) as those by which it enters from the pharynx (ib. y) : these are
called ‘ fixed gills,’ and the species possessing them are characterised
as ‘ pisces brancbiis fixis.’ In all Osseous, Plec-
tognathic, Lophobranchiate, Ganoid, and Holo-
cephalous fishes the outer border of the sup-
porting branchial arch is unattached to the skin,
and plays freely backwai'ds and forwards, with its
gill-surfaces, in a common gill-cavity which has a
single outlet, usually in the form of a vertical fis-
sure : the species with this structure are called
‘ pisces brancbiis liberis.’ In the INIyxine the outlets
of the six lateral branchial sacs {fig. 68. m) on each
side are produced into short tubes, which open into
a longitudinal canal {K), directed backwards, and
discharging the branchial stream by an orifice (4) near the middle

s 2

68

Branchial organs,
Myxine.

260

LECTURE X.

line of the ventral surface : between the two outlets of these lateral
longitudinal canals, but nearer the left one, is a third larger open-
ing (i), which communicates by a short duct with the end of the
long oesophagus (1) and admits the water, which passes from that
tube by the lateral orifices (/) leading into the branchial sacs.
This is the first step in development beyond that simpler condition
which prevails in the Lancelet, where the whole parietes of a
much dilated oesophagus (Jig. 46. rr) are ox’ganised 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 respir-
ation in the Myxinoids, have a highly vascular, but not a ciliated
mucous surface : this is disposed in radiated folds, and is further in-
creased by secondary plicEe. The seven branchial sacs on each side
of the oesophagus have short external ducts (Jig. 66. A), which open
by as many distinct orifices in the skin, in a species of Bdellostoma
hence called heptatrema (prep. 1018.): the internal branchial ducts
communicate by as many openings (ib./") 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 internal duct (Jig. 67. f) communicates
with a median canal, beneath and distinct from the oesophagus, ter-
minating 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. 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 Lo-
phioid fishes ; in some of the small Frog fishes (Antennarius), the
circular branchial pore is produced into a short tube above each pec-
toral fin. The power of existing long out of water depends chiefiy
on these mechanical modifications for detaining a quantity of that
element in the branchial sacs ; for fishes perish when taken out
of water, chiefiy by the cohesion and desiccation of their fine vascular
branchial processes, through which the blood is thereby prevented
from passing. * If sutficient water can be retained to keep the gill-
plates floating, the oxygen which is consumed by the capillary bran-
chial 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 Sphagebranchus ; and

* cvi. p. 124.

VASCULAR SYSTEM OF FISHES.

261

they are blended into a single orifice in Symhraoichvs, analogous to
that in the Myxine. In some Ganoids, many Plagiostomes, and all
Sturgeons, a canal leads from the fore part of each side of the bran-
chial chamber to the top of the head ; the outlets are called ‘ spiracles,’
the canals ‘ spiracular.’ The nasal sac communicates in the Lamprey
with the single homologous canal.

The main purpose of the gills of fishes is to expose the venous
blood in a state of minute subdivision to the influence of streams
of water ; for that purpose the branchial arteries rapidly divide
and subdivide until they resolve themselves into microscopic capil-
laries, which ai’e supported by a delicate membrane. Both this
membrane and the tunics of the capillaries which it covers are so
thin as to allow the chemical interchange and decomposition to take
place between the carbonated blood and the oxygenated water.
The requisite extent of the supporting membrane, or the respiratory
field of capillaries, is gained by various modes of multiplying the
surface within a limited space. In the Marsipobranchii and Pla-
giostomi, for example, by folds of the membrane on plane surfaces :
in the Lopliobranchii by filamentous processes of the membrane
grouped into tufts : in the Protopteri, by double or single fringes of
filaments : in the rest of the class by the production of the membrane
upon a double row of long, compressed, slender, pointed processes,
extending, like the teeth of a comb, from the convex side of each
branchial arch.

Each pair of processes has its flat sides turned towards contiguous
pairs, and the two processes of each pair stand edgeways towards
each other, and are commonly united for a greater or less extent
from their base : hence Cuvier describes each pair as a single bifur-
cated plate (‘ feuillet’).*

In the Swordfish (Xiphias), the processes of the same pair stand
quite free from each other ; whence Aristotle described this fish as
having double the usual number of gills.f But to comjiensate for
this independence, and to prevent the inconvenience of mutual pres-
sure, 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 a few species the processes of each pair are joined together to
near their apices : the most common extent to which they are con-
nected is about two- fifths of their whole length, as in the Salmon.
In the Ortliagoriscus the processes of each series are not opposite, but
alternate. In the Sturgeon, in which the processes of the same pair

s 3

xxiii. i. p. 379.

f XXIII. t. viii. p. 192.

262

LECTURE X.

are joined together nearly to their apices, the musculo-membranous
medium of union extends from pair to pair thi’onghout the entire
gill, forming a true ‘ septum branchiale,’ and presenting a beautiful
transition to the more complete septum which divides the respiratory
vascular surfaces in the Plagiostomes.

In some osseous fishes certain of the branchial arches support only
one series of processes; such are called ‘uniserial,’ or ‘half’ gills;
but, as a general rule, they support ‘ biserial,’ or ‘ whole ’ gills. Most
of the Labroids, the genera Coitus, Scorpcena, Sebastes, Apistes, Zeus,
Antennarius, Polypterus, Gohiesox, Lepadogaster,2ct\^ the Cyclopterus
liparis have three biserial gills and one uniserial gill ; the genera Lo-
phius, Batrachus, Diodon, Tetrodon, Monopterus, Cotylis, have three
biserial gills ; Maltlicea and Lepidosiren have two biserial gills and
one uniserial gill ; the Cuchia {Amphipnous) has only two gills.
The above enumeration refers only 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 processes which radiate- from the convexity of the branchial
arches are bony in some fishes (e. g. Salmo, Alosa), gristly in most
(Perea, Coitus, Trigla, &c.). They break up, in the Sturgeon, into
delicate branched fringes, along their outer or free margin. Small
‘ interbranchial’ muscles extend, through the uniting septum, between
the bases of the processes, for effecting slight reciprocal movements.*
The mucous membrane supported by the processes is puckered up
into minute transverse folds, crossing their flat sides and producing
an enormous extent of surface for the branchial capillaries. f

The concave borders of the branchial arches are usually beset by
defensive processes, fringes, or tubercles, and these sometimes sup-
porting small teeth which aid in deglutition ; but the chief oflice of
these appendages, which project inwards towards the mouth, is to
prevent the passage of any solid, nutrimental, or other particles taken
into the mouth from entering the interspaces of the gills, and irrita-
ting their delicate texture. In the edentulous Sturgeon and Paddle-
fish each arch supports a close-set series of such retroverted slender
tapering filaments (fig. 61. t), which ai'e 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 Mullet (prep. 1034.). Fre-
quently such a fringe is developed only from the first branchial arch
(Mackerel and Cod, fig. 69.), the I’est supporting dentated tubercles,

* CXII. CXIII.

t See Prep. 10S8. (Conger), and its description (xx. 1834, p. 83.). Dr. Hyrtl
counted 1000 transverse folds on a single process or tooth of the pectinate gill of
the Salmon, and from 1400 to 1600 in a similar process in the Sterlet.

VASCULAR SYSTEM OF FISHES.

263

and the last or pharyngeal arch beset with teeth only. In the Re-
mora 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, or Protopterus, short valvular pro-
cesses 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 Conger, all the branchial arches are devoid of defensive fringes
or tubercles.

The immediate force of the heart’s contraction is applied by a
short and rapidly divided arterial trunk upon the branchial circula-
tion. Only in a few fishes is the heart removed backwards from the
close proximity of the gills, and then the branchial artery is pro-
portionally elongated ; as in the Eel tribe, especially the Synbran-
chidcB-. the artery is long in the 61. s). The iirimary

branches are always ojiposite and symmetrical, 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 to supply the fourth and
third gills, the second going to the second, and the third to the first gill.
In the Polypterus and Skate there are only two primary branches of
each side : the first supplies the three posterior 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 {^g. 70.) give examples of four pairs of primary
branches from the branchial 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 fii'e branchial
fissures receives its artery. We saw in the Myxinoids the excep-
tional 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 jn-imaiy division ;
the upper or dorsal division sends off two branches on each side, the
posterior dividing to supply the fourth {Jig. 70, 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 {Jig. 1.), which are present in this ganoid genus, as in the
Sturgeon.* In all osseous fishes the artery of each biserial pec-
tinated gill extends along the grooved convexity of the branchial
arch, between the bases of the processes, exterior to the vein : it
gives olf two branches opposite each pair of processes, which pass

* See Prof. IMiiller’s admirable Memoir, xxv.

264

LECTURE X.

outwards to the end of the uniting substance, and there subdivide,
(in the Cod,) one twig extending along the internal margin of the
branchial process to its extremity, the other retrograding along
the same margin to its base : from these marginal twigs the minute
transverse vessels are distributed to the fine branchial laminae upon the
sides of the process. The arterialised blood is carried to an efferent

vessel, returning along the ex-
ternal margin of each branchial
process, and by these is poured
into the branchial vein {fig- 69*
b). The four veins on each side,
which are analogous to the pul-
monary veins in man, unite to
form the ‘ aortic circle’ (ib. a)
which encompasses the basi-
sphenoid (h). The current of
arterialised blood flows forward
at the fore-part of this circle
into the hyo-opercular (e') and orbito-nasal ifi) arteries ; but the main
streams are directed backwards, and converge 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 coronary
vessels of the heart, are sent off from the aortic circle. But no
systemic heart or rudiment of a propelling receptacle is developed in
any fish at the point of confluence of the branchial veins.

Small vessels are sent off from the marginal branchial venules
by short trunks, which ramify beneath the branchial membrane, and
become the ‘ arterigs nutritiae ’ of the gills : their capillaries are col-
lected 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 themselves into the pr®-
cavals, or directly into the great auricular sinus. *

Such is the outline of the general structure of the beautiful and
complex mechanism of the normal or pectinated gills of fishes.

There are many minor modifications of this form, some of which I
am tempted to notice from the explanation of their ‘ physical cause,’
which they receive from the known phenomena in the development
of the gills ; or from the light which the known habits of the
species throw upon their ‘ final purpose.’ But, first, a brief sketch

* These ‘ vense nutritiae ’ are unusually large in the Carp ; but are not, as Du
Verney supposed (cviii.), directly continued from the true ‘venae 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, xxi. 1841, p. 28.

Commencement of Systemic Circulation :
Gadus CnllariaSy Miiller.

VASCULAR SYSTEM OF FISHES.

265

of branchial development, taken chiefly from the observations of
Rathke*, must be premised.

Five branchial arches and five branchial arteries, or vascular
hoops, are developed on each side in the embryo of all fishes above
the Dermopteri, as a general rule.f At first the trunk of the bran-
chial arteries simply bifurcates, the divisions passing round the pha-
rynx and reuniting on its dorsal surface, to form the aorta. Behind
this primary circle, which corresponds with the fold developing the
hyoid and mandibular arches, four additional arterial hoops are sent
off, which traverse, without further ramifications, the convex side of
the four anterior simple bi’anchial arches, and reunite above in the
aortic trunk {^Jig. 79, n, w). If a sixth arterial arch is developed, cor-
responding with the fifth branchial arch, as its presence in the Lepido-
siren 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 sujiporting a coiTesponding loop of the branchial ar-
tery ; and, as the bifurcation and extension of the primary leaflets and
the pullulation of secondary lamime and loops proceed, the vascular
arch begins to separate itself lengthwise into two channels, traversed
by opposite currents, and thereby establishing an arterial and a
venous trunk in relation to the loops and their vascular developments
on the branchial processes. In osseous fishes the primary arterial
arch, corresponding with the anterior or hyoid arch, developes either
a simple (uniserial) gill, or a plexiform, plumose, rudiment of a gill,
or both, or neither. In the Lepidosteus the anterior vascular arch
retains its primitive connection with the extremity of the branchi-

arterial trunk, and developes on each side
a small uniserial pectinated gill ( 70. i)

from the membrane clothing the inner
surface of the cerato-hyoid and pre-oper-
cular bones : the vein or efferent vessel
(e) of this gill goes to a smaller pecti-
nated organ (ih. r), consisting likewise of
one series of vascular filaments, which
agrees with the ‘ pseudo-branchia’ 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 2iartial bifurcation of

* CIX. CX. CXI.

\ The six-gilled Shark (Hexnnchus) and the seven-gilled Shark {Heptanchus')
are among the few exceptions.

Branchiae and pseudo-branchia :
LepidosteuSy Muller.

266

LECTURE X.

the braiichi-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. 71. i), and of
one series of lamellae in the Plagiostomes : and this series is attached,
like the opercular gill of the Lepidosteus and Sturgeon, to the mem-
brane supported by the hyoid arch.

In most osseous fishes we recognise the reduced homologue of the
anterior primary vascular arch in that vessel {fig. 69. e.), which is
continued from the venous or refluent division of the second primary
vascular arch ; not, as in the foregoing fishes, from the arterial
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. 69.), but
now receives blood from it, and is called ‘ arteria hyo-opercularis
the pseudo-branchia, when pi’esent (as at e), is developed from it.

In osseous fishes the four normal biserial pectinated gills are deve-
loped 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 uniserial gill {fig. 71.6).
In the Planirostra, although the bran-
chial 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 bran-
chiostegal appendages are later de-
velopments, and the single branchial
outlet is the result of the formation of
the gill-cover. Thus the numerous
branchial apertures in the cartilaginous
fishes, like the substance of their skeleton, are retentions of embry-
onic structures. Very interesting arrests of development are also
found in bony fishes. We have seen that the primary vascular hoops
sweep over their respective arches without sending off any branches,
the (subsequently) branchial veins being in the embryo direct con-
tinuations of the branchial arteries. This primitive condition is per-
sistent in the fourth branchial arch of certain Murmnoid fishes of the

Circulating atvl respiratory Organs :
Lepidosiren.

VASCULAR SYSTEM OP FISHES.

267

Ganges {Mono'pterus, Symbranchus) * ; it is persistent in the first and
second branchial arches of the eel -like Lepidosiren { fig. 71, 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 Monopterus, goes direct to the aorta in its venous
state ; a larger quantity would pass into the roots of the aorta
(ib. o, o), and mix with the general circulation in the Lepidosiren,
were no part of the current diverted by the vessels I, V, into the lung-
like modification of its air-bladder.

The Hunterian specimens, Nos. 3255. and 3260. show the external
branchial filaments in the embryos of a Dog-fish and Shark ; three
such filaments are retained on each side, for a long period, in the
Lepidosiren annectens. Accessory respiratory organs, analogous to,
if not homologous with, the opercular gills, are developed from the
upper part of the pharynx in the Climbing Perch {Anahas scandens')
and allied fishes of amphibious habits ; they are complex folds of
highly vascular membrane supported on singular sinuous plates de-
veloped from the epibranchials of the anterior branchial arches {Jig. 39.
48) ; whence this family of fishes is called Lahyrinthihrancliii. An
accessory branchial i-amified vascular organ is similarly situated in
the genus thence called Heterohranchus. From the rich vascularity
of these organs they resemble miniature trees of red coral ; they are
hollow and muscular, serving not only for respiration, but, as Cuvier
suggests, to aid in propelling the arterialised blood into the aorta. In
the Cuchia {Amphipnous), 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 func-
tion is transferred to a receptacle on each side of the head, above the
branchial arches, covered by the upper part of the opercular 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 rudimental 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
conveyed 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

Taylor, cxvii.

268

LECTURE X.

fish, the Singio, beyond the cranium, backwards beneath the dorsal
myocommata upon the neural arches of the vertebrae 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 laminae of the 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 are analogous to the latter
in function. By this extreme modification of the opercular gill the
Singio (to which the generic name Saccobranehus is given by Cuvier)
is enabled to travel on land to a great distance from its native
rivers or marshes, and, like the Cuchia, is remarkable for surviving
the infliction of severe wounds.* In most fishes a rich development
of follicles on the walls of the gill-chamber supplies the branchial
machinery with a lubricating mucus.

ARTERIES.

The first structure most worthy of notice, in connection with
this system, is the vascular body already alluded to under the name
of ‘ pseudobranchia.’ Mormyrus, Cobitis, Silurus, Gymnotus, Murce-
nopliis, and Murana are examples of the few 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, under the form either of a small exposed roAV of
vascular filaments, like a uniserial gill (as in all Scisenoids and many
Q)\k\&x Acanihopteri, \h&Pleuronectidce, and Lepidosteus {Jig.lO.'R)-,
or, as a vaso-ganglionic body, composed of parallel vascular lobes, and
covered by the membrane of the branchial chamber (as in Esox, Cy-
prinus, Gadus, Jig. 69. r). In both cases the vein or efferent vessel
of the pseudobranchia becomes the ophthalmic artery (ib. It), and the
choroid ‘ vaso-ganglion,’ when present, is developed from it. The Stur-
geon, like the Lepidosteus and Lepidosiren, has a uniserial opercular
gill, the homologue of the first so-called ‘ half-gill ’of thePlagiostomes.
But, besides this. Von Baer discovered, on the anterior wall of the
‘ spiracular canal,’ a small vascular lamellate body, which is the
true pseudobranchia. It receives arterialised blood by a vessel sent
off from fhe vein of the first biserial gill ; which blood, after being-
subdivided amongst the innumerable pinnatifid capillaries of the
pseudobranchia, is collected again into fhe efferent vessel of that

CXVII.

VASCULAR SYSTEM OF FISHES.

269

body, which divides into the artery for the brain (encephalic), and
that for tlie eye (ophthalmic). The pseudobranchia is thus a kind of
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 ‘choroid gland’ {fig. 56. o). The pseudo-
branchia coexists with the hyoid uniserial gill in most Plagiostomes ;
and in those that have the spiracula it is developed, as in the Stur-
geon, 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 ; and it is important, also, in reference to a true and clear
idea of the function and homology of the ‘pseudobranchia’ in fishes
generally, to bear in mind that it co-exists in the Plagiostomes,
Chimasroids, Sturgeons, and some osseous fishes, with the vaso-
ganglion supplied by vessels from the anterior branchial veins,
which lies between the anterior basi-branchials and the sterno-
hyoid muscles.'!' Besides the small nasal and orbital arteries, and

* See XXI. 1841, pp. 41 — G7. 75. for a most valuable and exact specification of
the structure, relations, and varieties of the Pseudcbranchiac.

f This body has already been alluded to in connection with the salivary system
(p. 230.). Mr. Simon’s opinion, that it is the ‘thyroid gland’ of Cartilaginous
Fishes is more in accordance with its nature as a vaso-ganglion, and its relative
position. But since it co- exists in Cartilaginous Fishes with the actual homologue
of the pseudobranchiae of Osseous Fishes, these cannot be, as Mr. Simon contends,
the thyroid glands of such fishes. That the parts which the accomplished author of
the paper cxvi. describes as the thyroid glands in the Exocaetus, Pike, Anableps,
Carp, and some species of the Cod tribe, are the same bodies which Muller had
previously described as ‘ pseudobranchice ’ in those fishes, will be manifest by com-
paring the descriptions of the two anatomists. “ In the Gadida: the gland is
double ; one portion lies on each side, not as in the last case [the sublingual vaso-
ganglion of the Sturgeon is alluded to] at the anterior extremity of the first branchial
arch, but near its posterior or vertebral end.” (Simon, Philos. Trans. 1844, p. 300.
Compare with this IMiiller, xxi. 1841, p. 47. tab. iii. fig. 13.)

Prof. Miiller’s description of the ‘pseudobranchiae’ of the Carp is as follows: —
‘ Die verborgenste Lage hat das Organ bei Cyprinus Carpio und Carassius. Es ist
nicht bloss von dem beweglichen dicken Gaumenorgan bedeckt, sondern selbst von
knochen verhiillt. Man findet es nach Wegnahme des contractilen Gaumen-
organs zwischen dem hintern Ende des queren Gaumen-muskels und den obern
Sehlundknochen.” (xxi. 1841, p. 47.) Mr. Simon’s account of the thyroid gland
in the same species is as follows : —

“ In the Carp especially it is at considerable depth, being bidden by the extraor-
dinary thickness of the soft palate, and imbedded between the surface of the ptery-
goid muscle and the outer extremity of the branchial bone.” (Philos. Trans. 1844,
p. 300.)

It is obvious that all the parts described as ‘thyroid glands’ by IMr. Simon, in
Osseous Fishes, are the pseudobranchiae ; and the author recogni.ses tliat homology
in regard to the free gill-like forms of pseudobranchiae described by Broussonet
and Meckel in Acanihopterygii and Pleuronectidcc. That these ‘ pseudobranchiae ’
receive arterialised blood, and are thus e.ssentially distinct from the hyoid or oper-
cular uniserial fin in the Sturgeon, I.epidosteus, &c., had been clearly demonstrated
by Prof. Muller (1. c. 1841). There remains, then, to consider the relations of the
‘ pseudobranchiae ’ of Fishes with the thyroid glands of Mammals. These may be
either relations of analogy or of homology. The former would be determined by

270

LECTURE X.

the hyo-opercular, from which the proper ophthalmic artery is de-
rived, the carotids are usually sent olf from the ‘ circulus aorticus.’
In the Chimtera the carotids are transmitted directly from the an-
terior branchial veins ; and, in the Pike, the artery of the pectoral
tins (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 confluence, of the
branchial veins. In all higher Ashes the posterior aorta is the only
systemic trunk so formed.

This aorta extends beneath the bodies of the vertebrae along the
abdomen and through the haemal canal to the end of the tail. In
many Cyprinoid Ashes it dilates beneath each abdominal vertebra
into a sinus. It gives off intercostal arteries, and, with less regu-
larity, numerous small branches to the kidneys. The first principal
visceral branch is the ‘ caeliac,’ which sometimes, as in the Bui’bot, is

showing that the parts in question performed the same functions in the two
classes.

Mr. Simon conceives that the thyroid gland “ maintains an intimate relation to the
vascular supply of the brain." The pseudobranchise, however, are not diverticula to
the cerebral circulation in Osseous Fishes, but only to the ophthalmic circulation,
and in most cases are subsidiary, in this respect, to the choroid vaso- ganglion. The
internal carotid or encephalic artery in Osseous Fishes is a division of an artery
sent off from a part of the ‘ circulus aorticus,’ formed by the three posterior pairs
of branchial veins : the artery of the pseudobranchiae is given off from the anterior
branchial vein, or from the byo-opercular artery, or from both ; its subsequent
modification cannot therefore alFect the currents of circulation through the gills,
with whose efferent vessels it has no connection, and from which vessels the ence-
phalic arteries are derived. In the Sturgeon and Plagiostomes, indeed, the pseudo-
branchiae may, and doubtless do, act as diverticula to the cerebral circulation ;
but it is precisely in these fishes that Mr. Simon transfers the name and function of
thyroid gland to another vaso-ganglionic body, viz. Retzius’s sublingual gland.
Mr. Simon was acquainted with the existence of this body, and also of the supple-
mentary opercular gill in the Sturgeon, but he seems to have overlooked the pseudo-
branchiae, which, in this fish, hold precisely that relation to the cerebral vessels
which would have best supported Mr. Simon’s determination of the pseudobranchiae
as the thyroid gland. I consider, however. Professor Miiller’s comparison of the
pseudobranchiae in the Sturgeon with the ento-carotid plexuses of the Ruminants
to be a truer and more natural view of their analogies. As to the question of
‘ homology,’ which is to be determined by consideration of the organic connections,
relative position, and development of the parts in question, it is obvious that if,
by a consideration of these characters, we admit the sublingual body of the higher
Cartilaginous Fishes to be, of all the vascular ganglions in or near the head, that
which most nearly repeats the homological conditions of the thyroid gland of higher
Vertebrates, we cannot regard the vascular ganglions, which maintain a diametrically
opposite position in regard to the branchial arches, as being also parts answerable to
the thyroid glands.

If any thing were wanting to convince an anatomist holding that view, viz.
that the pseudobranchiae are the homologues of thyroid glands, of the fallacy of
such a view, it would be the fact of their co-existing in some fishes with a vaso-
ganglion having a much better title to be so considered, and which is actually
described by the ingenious author of the paper in the Philosophical Transactions as
the thyroid gland in those fishes ; though its relations to the heart and great ves-
sels in the Plagiostomes and Sturgeons seem to give it more claim to be regarded
as the homologue of the thymus.

VASCULAR SYSTEM OF FISHES.

271

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 caeliac. Betw'cen these, in
some fishes, the brachial arteries are sent off from the abdominal
aorta : these vessels in the large-finned Torpedos and Chimaerse have
a partial investment of muscular fibres, like secondary bulbs, to
accelerate the circulation through them.*

In the Porbeagle Shark (^Lamna cornubica) the two cailiac arteries
each split into a bundle of small arterioles, which interlace 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 ramifications of those trunks in the
ordinary way to the stomach and intestines.f 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 produc-
tion. In the Mediterranean Tunnies ( Thynnus and Auxis) the
branches of the ca3liaco-mesenteric 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 ‘spleen’ {,/ig- 61. 7i). It is not
present in the Lancelot ; and the gland-like bodies near the cardia in
the Cyclostomes, and near the pylorus in the Lepidosiren, which some
have called ‘ spleen,’ are more like the recognised remnants of the
vitellicle in osseous fishes, where a true spleen is actually present.
The vein of the spleen always contributes to form the ‘ vena portas ; ’
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 corresponding
development of the pancreas. Thus there is an accessory spleen in
the Sturgeon ; and the spleen is divided into numerous distinct
lobules in Lamna, Selache (see part of the oi’gan in Jig. 64. s), and
some other highly organised Plagiostomes. In most osseous fishes
the spleen is appended by its vessels, and a meso-splenic fold of

Duvernoy, xc.

•f XXI. 1841, p. 99. pi. 5.

27^

LECTURE XI.

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
coi’puscles.

LECTURE XL

PNEUMATIC AND RENAL ORGANS.

AIR-BLADDER.

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, and sometimes (^Gymnotus, Ophiocephalus, Coins) beneath
the caudal vertebrae to near the end of the tail. It is seldom bifur-
cated (as we see it in some species of Diodon, Tetrodon, Dacty-
lopterus, Pimelodus, Prionotus) ; still more seldom divided length-
wise into two bladders {^Arius, Gagora, Polypterus, Lepidosiren,
fig. 71.jo,jo): itisoftener divided crosswise into two compartments,
which intercommunicate by a contracted orifice {Cyprinidce, fig. 58.
p q, Characinidce) ; or are quite separate {Bagrus filamentosus,
Gymnotus equilabiatus.) In the Siluroid genus Pangasius the air-
bladder is divided into four longitudinally succeeding portions. In
the Trigla hirundo the swim-bladder is notched anteriorly by one
indent, and posteriorly by two indents, from which notches septa
project inwards ; sometimes the air-bladder is divided partially, both
lengthwise and crosswise [Cobitis fossilis, Auchenipterus furcatus,
some species of Pimelodus). Sometimes the bladder sends forwards
two blind processes from its forepart (^Sphyrcsna barracuda, Trigla
cuculus, Conodon antillanus, some species of Micropogon and Oto-
lithus) ; sometimes from its hind part ( Cantharis vulgaris, Lethrinus
atlanticus, Heliases insolatus, some species of Sillago, Mcena, and
Smaris) ; sometimes from both ends {Dales maculatus, Pimelipterus
altipennis, Lactarius delicatulus). The Bearded Umbrina has three
slender csecal processes from each side of its air-bladder j the allied

AIR-I5LADDEU OF FISHES.

273

“Maigre” and other species of ScicBna, with most of the Corvince,
have very numerous lateral pneumatic caeca, which are more or less
ramified.* In some species of Cheilonemus and Gadus blind pro-
cesses are continued from both the sides and ends of the air-bladder
(see the anterior ones in Gadus callarias. Jig. 69. A, p). In Gadus
Navavaga the lateral productions expand, and line corresponding
expansions or excavations of the abdominal parapophyses, thus fore-
shadowing the pneumatic bones of birds.

The proper walls of the air-bladder of ordinary osseous fishes
consist of a shining silvery fibrous tunic, the fibres being arranged
for the most part transversely or circularly, and in two layers
{Jig. 58, q r) : they are contractile and elastic ; but the walls of the
anterior compartment of the air-bladder of Cyprlnoids (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, f The lateral com-
partments are subdivided by transverse septa in many other Siluroids
(e. g. genus Bagrus) ; the large air-bladder of some species of Ery-
thrinus (e. g. E. salvus, E. tceniatus') is partially subdivided into
smaller cells. The cellular subdivision is such in the air-bladder of
the Amia, that Cuvier compared it to the lung of a reptile | ; and
the transition from the air- or swim-bladder to the lung is com-
pleted in the Protopterus or Lepidosiren annectens, in which the
cellular subdivision and multiplication of the vascular surface are com -
bined with a complete bilateral partition of the bladder into two
elongated sacs, with a supjily of venous blood from a true jiulmonary
artery, and with the communication of the ductus pneumaticus, as in
the Polyp ter us, 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 oeso-
phagus, 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 representative 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 suborder of Anacanthini,

* See xxxix. i. p. 94., after Cuvier et Valenciennes, xxiii. pi. 138, 139.

f cxiv. ii. p. 33. pi. 6. fig. 4. | xxiv. ii. p.377.

VOL. II.

T

274

LECTURE XI.

and not in the other family {Pleuronectidce) ; 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 explanation of the absence
or rudimental condition of the swim-bladder is not so obvious in
regard to the Acanthopterous genera Percis, Percophis, Eleginus,
Auxis, Trachypterus, and Gymnetrus. A large and often complex
air-bladder exists in most of the Siluroid fishes ; but the genera
Loricaria, Rhinelepis, and Hypostoma are exceptions in that family,
having no air-bladder. What is more inexplicable is, that while some
species of the same genus, Polynemus 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 pneumaticus) is expressed in the characters of the orders
in the Classification of Fishes, pp. 48 — 50. 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, 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 ali-
mentary tract. In the Herring the ductus pneumaticus is produced
from the posterior attenuated end of the cardiac division of the
stomach*, and opens into the fusiform air-bladder at the junction
of the middle and posterior thirds of that organ. The long, narrow,
and flexuous ductus pneumaticus is continued from the fore-part of the
posterior division of the air-bladder in the Cyprinoids, and opens into
the dorsal part of the msophagus {fig. 58. su) : the short, straight,
and wide ductus pneumaticus, in the Lepidosteus, opens also into the
dorsal part of the oesophagus, the orifice being served by a sphincter :
in the Erythrinus the air-duct communicates with the side of the
oesophagus ; in the Polypterus, with the under or ventral part of the
beginning of the oesophagus.f

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

* cxiv. ii. pi. viii. fig. 1.

f These variations show how futile is the objection drawn from the dorsal com-
munication of the swim- bladder in Lepidosteus to the determination of the Lepido-
siren to the class of fishes, and of the homology of its lungs with the swim-bladder
in that class.

AIU-BLADDETt OF FISHES.

275

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. 71. l'\ 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 pene-
trate, 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
forwards, through the sinus and auricle, to the entry into the ven-
tricle, and there terminates above the valvular cartilaginous tubercle.
Thus 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 Proto-
pterous and Ganoid fishes forms no ‘ retia mirabilia ’ or vaso-gan-
glions, but resolves itself into a generally diflfused 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 : — 1st. A resolution
of the smaller ramifications into fan-like tufts of capillaries over
almost every part of the inner surface (Carp). 2d. The formation
of similar, but larger and more localised, radiating tufts (Pike) ;
in both without any special aggregation of the capillaries to form
a ‘ vaso-ganglion.’ 3d. The conversion of the tufts by rapid subdi-
vision 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 sur-
face of the air-bladder having the ordinary simple capillary system
(Perch and Cod). In the Cod-fish, a large artery, a branch of the
CEeliac, and a still larger vein, which empties itself into the mesen-
teric, 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 fre-
quently anastomose with each other : both are inextricably inter-
woven and form the basis of the so-called ‘air-gland,’ which is
essentially a large ‘ bipolar rete mirabile ’ of Muller, or vaso-

* XXI. 1841, p. 194.

T 2

276

LECTURE XI.

ganglion. This organ, however, is further composed of a number of
peculiarly arranged, elongated corpuscles, which depend in two rows
from each vascular branch, and are bound together by a loose cellular
tissue : the corpuscles are beset with fine villiform processes. The
blood returns from the vaso-ganglions by small veins which rarely
accompany, more commonly cross, the arteries. 4th. 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 ‘ bipolar,’ and consist of both arterioles and venules :
their efferent trunks do not ramify in the immediate margin of the
vaso-ganglion from which they issue, as in the vaso-ganglions of the
Cod, Burbot, Acerine, and Perch, but run for some distance before
they again ramify to form the common capillary system of the lining
membrane of the air-bladder. Rathke* failed to detect the open-
ing of the air-duct with the oesophagus in the Eel ; but De la
Eoche had well desci’ibed the oblique aperture f, and accurately
cites the whole family of the Eels as fishes having both the so-
called ‘ air-gland ’ and the pneumatic duct. It had been supposed
that the vascular ‘ air-gland ’ was present only in those fishes which
could not derive the gazeous contents of their swim-bladder from
without ; and unquestionably in those fishes which have the shortest
and widest ducts (Sturgeon, Amia, Erythrinus, Lepidosteus, Lepi-
dosii’en, Polypterus), the supposed air-secreting vaso-ganglions are
not developed. Since Professor Magnus has determined the ex-
istence of free carbonic acid gas, of oxygen and of azote in the
blood, and dissolved in different proportions in the venous and
the arterial blood, it may be readily conceived, as Professor Muller
well remarks :f, 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 car-
bonic acid than when they penetrated the vaso-ganglions.

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 high pressure when the fish sinks to great depths, or
sudden expansion of the gas when they rise to the surface § : but

* cix. ‘ Ueber die Schwimtn-blase einiger Fische,’ p. 98. f cxv. p. 201.

I XXI. 1841, p. 98. See also Dr. J. Davy, in Phil. Trans. 1838.

§ 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

AIE-BLADDER OF FISHES.

277

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 fresh-water fishes,
of nitrogen, and a veiy small quantity of oxygen, with a trace of
carbonic acid gas : but in the air-bladders of sea-fishes, and espe-
cially of those which frequent great depths, oxygen pi’edominates. *

In the genera Auchenipterus, Synodon, Malapterurus, and some
other Siluroids, the axis vertebra sends out on each side a slender
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 the skull. In some species of Gadiis 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- 58. t).

Viewing the general modifications and relations of the air-bladder
throughout the class of fishes, we cannot but discern and admit, not-
withstanding 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 to rise or sink as occasion may serve. The general
law of its absence in the parasitic and suctorial Dermopteri, and
in all ground-fishes, as the Pleuronectidce and Kay -tribe, supports
the above conclusion. Borelli 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 oc-
casions from the weight of the superimposed vertebral column
and muscles when life and action are extinct. The Sharks re-
quire, by the position of their mouth and their common pursuit of
living prey, freedom in turning and great variety as well as great
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 development and force

* Humboldt found the gas in the air-bladder of the electric Gymnotus to con-
sist of 96° of nitrogen and 4° of oxygen. Biot found 87° of oxygen in some of
the deep-sea Mediterranean fishes, the rest nitrogen, with a trace of carbonic acid.
No hydrogen has ever been detected in the air-bladders of fishes.

f cxxix. cap. 23.

278

LECTURE XI.

which suffices for all the evolutions they are called upon to per-
form. With regard to the accessory offices of the air-hladder in
relation to the sense of hearing, the chief of these remarkable modifi-
cations by which it is brought into communication with the acoustic
labyrinth have been already described in a former Lecture (p. 210.).
In a few genera {Trigla, Pogonias) 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 Eeptilia, as, for
example, the salamandroid Ganoidei and Protopteri, those further
modifications are superinduced upon the air-bladder, by which it
becomes also analogous in function to the lungs of the air-breathing
Amphibia.

The species of Lepidosiren, the anatomy of which is described in
the Linnsean Transactions * and in these Lectures, inhabits a part of
the river Gambia, which in the rainy season overflows extensive
tracts, that are again left dry in the dry season. The Lepidosirens,
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 overflowing
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 Lepi-
dosiren are precisely those which adapt them to the peculiar con-
ditions 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 aU the branchial
arteries developed gills, as in normal fishes, is carried on through
the two persistent primitive vascular channels {fig. 71. 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 oesophageal orifice of which is kept
open by a laryngeal cartilage, introduces the air directly into the
bladders : the blood transmitted through the branchial arches to the
pulmonary arteries (ib. V) is distributed by their ramifications over
the cellular surface of the air-bladders, and is returned arterialised

XXXIU.

AIR-BLADDER OF FISHES.

279

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 venm cavae ; whence the ne-
cessity, apparently, for that peculiar arrangement by which the ar-
terial blood is conveyed directly to the ventricle by the pulmonary vein.
When the Lepidosiren resumes its true position as a fish, the bran-
chial circulation is vigorously resumed, a larger proportion of arterial-
ised blood enters the aorta, and both the nei’vous and muscular
systems receive the additional stimulus and support requisite for the
maintenance of their energetic actions.

Anatomists and physiologists are not yet unanimous as to the ho-
mologies and analogies of the respiratory organs of 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 : “ the gills are the lungs of animals absolutely
aquatic*;” and, with regard to the cartilaginous or osseous supports
of the gills, “ they are in our opinion, to the gills of fishes, what the
cartilaginous or osseous tracheal rings are to the lungs of the three
superior classes f we are left in doubt Avhether 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 re-
lation to the different respiratory media of the two classes. Geoffroy
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 a rela-
tion of homology. The truth of his proposition will be best tested
by first considering the homologies of the air-bladder of fishes.
Dr. Peters, 'Prof. Hyrtl, and others, who have prosecuted the
anatomy of the Lepidosiren since Dr. Bischotf advocated its rep-
tilian nature, have confirmed my previous determination of that
genus to the class of fishes : and it may be presumed that its gela-
tinous chorda dorsalis, its vertebral inferior transverse jirocesses
(parapophyses), the normal attachment of the scapulae to the occiput,
the branchiostegal covering of the permanent gills, the opercular
bones, the absence of pancreas, the presence of a spiral intestinal
valve, the relative position of the anus, the extra-oral nasal sacs, the

* “ Les branchies sont les poumons des animaux absolument aquatiques.” (xiii.
t. vii. p. 164. )

f “ Elies sont, a notre avis, aux branchies des poissons, ce que les cerceaux cavti-
lagineux ou osseux des voies aeriennes sont aux poumons des trois classes supe-
rieures.” (Ib. p. 177.)

T 4

280

LECTURE XI.

scaly integuments, the mucous tubes and pores on the head, the
‘ lateral line,’ and, in short, the totality of the organisation of the
Lepidosiren, will be deemed to fully prove its true 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 windpipe, also presenting the closest agreement with the Lepi-
dosiren in the important character of the form of the brain. The
common objection to the view of the air-bladder of fishes being
the rudimental homologue of the lungs of air-breathing Vertebrates
has been, that the artery of the air-bladder carries arterial blood,
that of the lungs venous blood. Let us compare the air-bladders
of the Polypterus and Lepidosiren in reference to this character.
The arteries of both are derived from the returning dorsal portions
of the branchial vascular arches before their union to form the aorta.
In the Polypterus, according to Muller, 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-developmeut 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 development 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 changing
the essential nature of the air-bladders themselves : 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.* 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 modifications of form or
function of such air-bladders. Between the completely divided air-
bladder of the Polypterus and the undivided air-bladder of Lepi-
dosteus there are numerous degrees of bifurcation in the series of
fishes : it is to the undivided state of the air-bladder in the Lepi-
dosteus that its more strictly dorsal position, and its communication
with that aspect of the oesophagus, are due : these modifications.

* Compare xxxiii. pi. xxvii. figs. 3 and 4. with xxv. pi. ii. figs. 5 and 6., and
fig. 54. xxxiu. p. 182. with xxv. pi. ii. fig. 7.

AIR-BLADDER OF FISHES.

281

however, do not affect its relation of homology with the divided air-
bladder of the allied ganoid genus Polypterus, any more than witli
the divided air-bladders of the Cobitis barbatula or Arius gagora, in
which the divisions are confined to the anterior part of the abdomen,
and inclosed in osseous cups developed from vertebrie answering to
the second or third cervicals.

Thus the series of transitions traceable in the organs universally
acknowledged as the air-bladders of fishes prove those of the Lepido-
siren to be the homologous organ ; whilst the development, relative
position, and connection of the lungs of the Batrachia equally prove
those lungs to be the homologues of the air-bladders of the Lepi-
dosiren. Therefore, it follows that the air-bladder of the fish is
homologous with the lungs of the Batrachian, and of all other air-
breathing Vertebrates ; although the air-bladder of the fish does not,
as a general rule, perform the functions of a lung. But the air-
bladder in most fishes is analogous to the air-chambers of the shell of
the polythalamous Cephalopods, and in some fishes it is analogous to
the tymjianum of the higher Vertebrates.*

In tracing the development of the windpipe and larynx, from the
more lung-like forms of the air-bladder in fishes, through the Peren-
nibranchiate Batrachia upwards, we obtain incontrovertible proof
that the so-called ‘ ductus pneumaticus ’ in fishes is the homologue
of the trachea. It follows, therefore, that the branchial cartilaginous
and osseous supports of the gills are not the homologues of the trachea
and bronchige, any more than the gills themselves are the homologues
of- the lungs. We shall find the branchial arches and gills developed
in the larvae of Batrachia, and disappearing as the true trachea and
lungs are formed, without being converted into them. The only
parts of air-breathing Vertebrates with which the branchiae of fishes
are homologous are the persistent or deciduous branchias of the
Batrachia. The relations of the branchial arches and gills of fishes
with the trachea and lungs of higher air-breathing Vertebrates are
those of analogy merely. The branchial apparatus, in relation to the
entire vertebrate scheme or type of organization, is to be regarded
as a temporary graft on such type, introduced to serve the purposes
of the lowest embryo-like forms, and to give way to another and
higher and more persistent form of respiratory organ : in this respect
the branchial organization is to the vertebrate series what the pla-
centa is to the mammalian individual.

* In the Loach ( Cobitis) the whole alimentary canal is analogous to a lung, in-
asmuch as this fish swallows air and voids carbonic acid.

282

LECTURE XI.

RENAL SYSTEM.

In all Vertebrates an excretory organ is very early developed in
the form of a tube, extending from each side of the cloaca forwards,
along the dorsal region of the abdomen, close to the spine, where it
communicates with a number of short slender blind tubes placed at
right angles to it ; the longitudinal trunk-tube serving as the ex-
cretory duct of the shorter transverse secerning caeca. These glands
are transitory in the air-breathing Vertebrates, and are called, from
their discoverer, ‘ corpora Wolffiana they are persistent in fishes*;
and are called ‘ kidneys : ’ in both they are renal organs and secrete
urine. A slightly opaque, slender, elongated glandular body, in the
situation marked h in Jig. 46., has appeared to me to represent the
renal organ in the Branchiostoma. The structure of this organ is
more obvious in the Myxinoids : it is double : each long duct, 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,
which communicates by a narrow opening with a blind sac. At the
bottom of this sac or caecum there is a small vaso-ganglion, free on
all sides save that by which the vessels enter and quit it f : there are
no uriniferous tubes in this ‘ placentula ; ’ the contents of the c^cum
must react through its thin parietes, and those of the capillaries with
which it is in contact, upon the blood in those capillaries, and ex-
tract therefrom the azotized uric excretion. Analogous vascular
bodies, formed chiefly by convoluted tufts of arterial capillaries, are
present in the Wolffian bodies of Mammals, and in the persistent
renal organs of all Vertebrates. They are called, after their discoverer,
‘ Malpighian corpuscles,’ and Mr. Bowman :j; has admirably shown
how the uriniferous tubes take their rise from these vascular corpus-
cles, viz. by a sacciform blind beginning applied over the vascular
placentule or tuft.

The combined secerning caeca and vaso-ganglia form in the Sand-
prides and Lampreys § a continuous narrow elongated gland, which
extends in the former {Ammocetes) throughout the abdomen, in
the latter (Petromyzoni) along the posterior two-thirds : in both con-
fined to the dorsal part of the cavity. The ureters iyjig. 74. K) open
into the short canal (ib. V), leading to the papillary production of
the peritoneal outlets close to the anus. ||

* cxxxvii. ii. p. 314. f xxi. 1841, p. 13. f cxxv.

§ In the Petromyzon marinus the diameter of the tubuli uriniferi is j^th of an
inch, that of the capillaries of the kidneys being -j^th of an inch.

II XX. iv. pi. 56. fig. 1. e.

KENAL SYSTEM OF FISHES.

283

In most osseous fishes the kidneys are long and narrow, and ex-
tend through the whole or a great part of the dorsal region of the
abdomen, firmly attached to the vertebral column ; they ai’e usually
broadest and thickest anteriorly, where they sometimes jiresent a
lobulated surface ; they contract, approximate, and frequently blend
together as tliey extend backwards (prep. 1177. Cyclojjterus) % some-
times penetrating the haemal canal in the tail. In the Gymnotus the
kidneys are distinct and thickest at their posterior ends, as they are
in the Gurnard {fig. 72. K) and in most Sharks. The kidneys have
not a well-defined capsule in osseous fishes, but their ventral sur-
face is immediately covered by an aponeurotic membrane, against
which the peritoneum, and the air-bladder Avhen present, are applied.
I’lie renal tissue is soft and spongy, firmest at the fore-part of the
gland; usually of a reddish-brown colour; sometimes soaked, as it
were, with dark pigment (as in Lepidosiren, xxxiii. p. 349.). It is sup-
plied by numerous small arteries from the abdominal aorta *, 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 sub-
stance are comparatively few ; they are in most fishes convoluted and
of equal diameter, extending through the whole renal substance,
which shows no distinction of cortical and medullary parts, and has
no mammillae : they are lined by a ciliated epithelium. Sometimes
a single common ureter quits the coalesced hinder ends of tue kidneys,
as in the Pike, and terminates in a urinary bladder. More frequently
the essentially duplex nature of the kidneys is manifested by the
emergence of two ureters from the ventral surface of their posterior
ends when these have coalesced : in some fishes these unite together
after quitting the kidneys, and terminate by a common gradually
widening canal in the urinary bladder. Sometimes 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 is, 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 Pierring a long, common ureter ter-
minates behind the anus. In the Gymnotus the common ureter is so
wide as to serve as a receptacle, and it is directed forwards to reach

* Hunter, vji. t. ii. p. 1 1 2.

284

LECTURE XI.

its termination immediately behind the advanced vent. The urinary
bladder is sometimes round 72. 6), sometimes oval or pyriform,
often bifid at its fundus or two-horned ; it is largest in those fishes,
as the Pleuronectidce, the Lophius, the Orthagoriscus, and the Cy-
clopterus, in which the air-bladder is absent. In the Callyomymus
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 long cervix
vesicm in the Salmon is surrounded by a venous plexus. In the
Sturgeon the wide ureters extend along the outer borders of the
kidneys, and receive the vasa deferentia or oviducts in their course
towards the cloaca, where they unite into a short duct which forms
the common 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 * :
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 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 {fig. 75. h) at the back of the anus, within a large
common cloaca. In the Torpedo, the ureters terminate on the
cloacal papilla by two distinct orifices.']' In the Skate and Thorn-
back each ureter terminates in the neck of a short bifid bladder :
these open by a common urethra upon the cloacal papilla. The Lepi-
dosiren has a small urinary bladder situated, as in all fishes, behind
the rectum and in front of the oviducts : the ureters do not com-
municate directly with it, but terminate separately on small papillm
in the oviducal compartment of the cloaca.]; With regard to the
circulation in the kidney in 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

* In the Ray the diameter of the terminal branches of the tubuli uriniferi are
■jJ^th of an inch, that of the capillary renal arteries being f^th of an inch.

t cxxxiv. ^ XXXIII. pi. 27.

RENAL SYSTEM OF FISHES.

28.5

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, ex-
tends from the inner and anterior part of the kidney to convey its
blood to the vena cava. The exterior vein is not, however, com-
pletely expended in the kidney, but is also continued forwards from
the anterior end to join the veins from the anterior abdominal parietes,
and sometimes those from the pectoral fins. Whether the blood
takes a retrograde course in these towards the kidney, and meets
the stream from the hinder commencement of the exterior vein, is
undetermined. In all fishes the kidneys maintain the same relations
with the cardinal veins that their transitory homologues, the ‘ Wolf-
fian bodies,’ do in the embryo of the higher Vertebrates.

SXJPRA-EENAL BODIES.

Professor Muller has described two small oval lobulated bodies,
situated in advance of the kidneys, close to the portal sinus and
near the pericardium, in the Myxinoid Fishes, as the ‘glanduloe
suprarenales. ’ * In the typical Osseous Fishes they have been re-
cognised as roundish bodies of a light grey colour ; commonly two,
rarely three in number ; situated, sometimes near the middle, oftener
at the hinder extremities of the kidneys, at or near the entry of the
htemal canal : sometimes they lie free, sometimes they are imbedded
in the renal tissue (Pike, Salmon, Eel) ; but they always possess a
proper capsule, and present what seems to be a minutely granular
texture, without distinction of cortical and medullary parts. In the
yellowish supra-renal bodies of the Sturgeon, the granules are minute
spherical cells filled by microscopic nucleated corpuscles. In the
Plagiostomes, the supra-renal glands are represented by elongated
narrow yellowish bodies, situated behind the kidneys, and sometimes
extending behind the dilated ureters.

XXI. Angeiologie, 1841, pp. 14 — 17. tab. ii. fig. 2. n.

286

LECTURE XII.

LECTURE XII.

GENERATION AND DEVELOPMENT OP PISHES.

MALE ORGANS.

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 development of a proper duct or ‘ vas de-
ferens,’ next of a vesicula seminalis and prostate, afterwards of an
intromittent organ, and finally of superadded ‘claspers,’ or mecha-
nical instruments for retention of the female in coitu. The pre-
paration of the Petromyzon marinus (No. 2373.) shows the testis
in the form of a series of thin transverse lobes, or 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 over-lapping oblique folds to the right and left of the line
of attachment indicates the duplex character of the gland. Its tissue
consists of small spherical cells filled with the minute corpuscular
spermatozoa.* 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, No. 2378.) has a single testis, com-
pacted 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,

* Sir E. Home and Mr. Bauer, misled by this close resemblance to an ovarium,
inferred the identity of the testis with that body, described the kidneys as the testis,
and the Lampreys as hermaphrodite fishes. Hunter had recognised the true
structure, (vir. t. iv. pp. 204 — 206. pi. 59. fig. 1. ^.) Mr. Bauer gives a good
microscopic view of the cellular structure of the testis in Phil. Trans. 1828, pi. xv.

GENERATIVE SYSTEM OF FISHES.

287

which is continued from the posterior end of the gland, with its
serous covering, into a short and simple ‘ vas deferens,’ which opens
usually into or receives the urethral prolongation of the urinary
Gurnard the testes 72. a) are distinct from
each other, but their ‘ vasa deferentia’ almost im-
mediately unite into a common duct, which joins
the urethra (c) behind the rectum (/<), and ter-
minates at the outlet {g). In the Salmon and
the Herring, the ‘ vasa deferentia ’ do not unite
together until near their termination in the
urethra. In the Cod and the Bull-head ( Coitus)
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 Stur-
geon : a valve prevents the regurgitation of the
urine into the spermatic duct. The urethra is
usually produced into a papilla, which pro-
jects conspicuously from the back part of the cloaca in the vi-
viparous Poecilia, Anableps, and Blenny : it is large also in the
Lump-fish. The testes are almost entirely extra-abdominal in the
Flounder and some other Pleiironectidcs, extending backwards 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 dif-
ferent Osseous Fishes, but are remarkable in all for thei” enormous
seasonal increase : when fully developed they are commonly known
as the ‘milt’ or ‘soft roe.’ In the Pipe-fishes {Syngnathi) they
present the form of two simple elongated straight tubes (prep. 2375.).
In the Lump-fishes (^Cyclopteri) they are divided by incisions into
lobes : in the Cod a vast extent of the vascular surface of the glan-
dular substance is packed into a small compass, by being disposed in
convolutions upon the edge of the ‘ mesorchium.’ The primitive
spermatic cells, which are persistent in the Cyclostomes, have coa-
lesced 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.*

In the Plagiostomes the testes {Jig- 73. a) are always distinct
from one another, and usually of a circumscribed compact form, si-
tuated far forwards in the abdominal cavity. They have a proper

bladder. In the

Renal anti Male Organs :
Trigla lyra^ Cams.

cxx. p. 105. pi. XV. fig. 7. in the Shad.

288

LECTURE Xri.

capsule or ‘ tunica albuginea,’ and a peritoneal covering : the capsule
sends many ‘septa’ into the testes ; 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 ‘ tubuli’ are plainly discernible
in the portion of the testis of the great Basking
Shark preserved in No. 2396. A. Numerous ‘ vasa
efferentia’ convey the ‘ semen’ to the beginning of
the ‘ vas deferens’* which forms a large ‘ epididymis’
(ib. d) by its manifold convolutions. These gradu-
ally decrease as the duct (e) approaches the cloaca,
when it becomes straight, and expands into an
elongated reservoir (ib. /), the mucous surface
of which is commonly increased by numerous trans-
verse plicae (Selache.) Behind the termination of
the rectum the ‘ vasa deferentia’ suddenly diminish,
approximate, communicate with the ureters, and
terminate upon the rudimental cloacal penis (ib. g, k,
and prep. 2396.).

The claspers (ib. m) are present in the Chimae-.
left sJde?sS. ^oid Fishes as well as in the Plagiostomes. They
project backwards as appendages to the bases of
the anal fins, and are sometimes bent inwards at their free ex-
tremities. Near this part may be discerned a fissure which is
the outlet of a blind sac extending forwards 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 ves-
sels, especially with veins : in the Bays a glandular body adds its
secretion to that of the surfaee of the cavity.

FEMALE ORGANS.

The gradations of structure of the female organs correspond very
closely with those of the male. In the young Lamprey the ovarium
is a simple longitudinal membranous plate, 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 deve-
loped in it, and still more so in length, being accommodated to its
locality by numerous folds 74. c). But no superadditions are
made to this primitive structure : the ova (<7) escape by rupture of their

CXXXIV.

GENERATIVE SYSTEM OE FISHES.

289

capsules into the abdomen {b), and ai’e excluded by the peritoneal aper-
tures (ib. 1). 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 de-
ferentia are developed in the male, that the
homologous ducts exist in the female : the Sal-
mon is an example in which the ova are dis-
charged 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 single in those bony fishes, as the
Perch, the Blenny, the Loach and the Ammodyte
(prep. 2675. a), in which the testis is single :
the median cleft of the ovary 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 most osseous fishes the ovaria form two elongated sacs of mu-
cous membrane, with a thin fibrous tunic and a peritoneal covei'ing :
closed anteriorly, but produced posteriorly into a short, straight, and
commonly wide oviduct, terminating behind the anus, and commonly
before the urethra. In the Pipe-fishes the oviducts continue distinct
to the cloaca. In most fishes the oviducts coalesce, sooner or later,
into a single tube before arriving at the cloaca : the common terminal
portion becomes much dilated in the Cod-fish, the Lump-fish, and
some others. The ‘ stroma,’ or cellular tissue, which is the seat of
development of the ova, is interposed between the mucous and
fibrous tunics of the ovarian sac : it sometimes, though rarely, is co-
extensive with the mucous membrane. In the Lophiiis the two
ovaria are long and large plicated tubes, flattened when empty, cylin-
drical 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 by 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. 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
VOL. II. u

Renal and Female Organs;
Petromy%on, Hunter.

290

LECTURE XII.

into numerous folds, which are transverse in the Cod and Salmon*,
oblique in the Mackerel, and longitudinal in some other fishes. 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 serve? as
a kind of uterus, and contains an abundant albuminous secretion at
the season of the internal incubation. The viviparous Blenny
( Zoarces), the Anableps, the Poecilia, and some Siluroids are ex-
amples of 0 VO- viviparous osseous fishes, and at the same time
manifest naturally, what occurs as a rare adnormality in higher Ver-
tebrates, viz. ovarian gestation. In the Plaice and other Pleuro-
nectidas 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 sub-cutaneous scrotal cavities above
the basis of the anal fin. f

In the Lamprey the short and narrow lateral infundibuliform
passages behind the rectum, into which the ureters open, and which
terminate in the peritoneal outlets {fig- 74. e, 1), 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 ‘ 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 baekwards into the common uro-genital
duct. The higher grade of the sexual organisation of the female
Plagiostome, as compared with the cartilaginous Ganoid fish, is ma-
nifested chiefly by modification of the oviducts ; they are always two
in number, and distinct from one end to the other, but are brought
into close proximity, or coalesce at both ends : they are always
distinct from the ureters, which terminate on the prominent urethral
clitoris, between the oviducal outlets. 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- 75. a) are I'elatively 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 oesophagus. The ova are much fewer in
number than in the ‘roe’ of osseous fishes, and are seen in different

* In the Salmon the free surface of the stroma is exposed.

t XLUI. V. pi. 4. fig. I.

DEVELOPMENT OF FISHES.

291

Female Organs :
Spinax, Hunter.

stages of growth, being developed more consecutively. The approxi-
mated or confluent abdominal apertures of the oviduct (ib.i) are an-
terior to the ovarium, between the liver and the peri-
cardial septum ; they form together a heart-shaped
opening, with entire margins, attached by two diverg-
ing ligaments (ib. c) to the abdominal walls. The ovi-
ducts narrow, and with thin tunics at their commence-
ment (ib. d d), 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. A glandular
body (ib. e) is developed in their coats, after the first
fifth or sixth part of their extent, and their terminal
half or third part (ib./) is dilated : the sizes of the
glandular and of the uterine parts of the oviduct are
usually in inverse proportion : in the ovipai’ons Plagi-
ostomes the gland is large, the uterus small, and the
reverse obtains in the viviparous species. The inner
surface of the Fallopian portion of the oviduct pre-
sents 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 well 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 pre-
senting minute transverse striae, beset with pores, the orifices of
secerning tubes, the aggregate of which composes the layer of
glandular substance. In the oviparous Homelyn {Raia macidata)
the lobes of the large rudimental glands are reniform. Prep. 3234.
shows well the inner free margins and interspaces of the close-set
layers of secerning tubes. In the 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 has the
lining membrane produced into longitudinal folds, with wavy
margins, each of which contains a single vessel following its sinuosi-
ties, and sending off branches to the parietes of the oviduct :
the folds gradually subside at the outlet of the oviduct. In the ovo-
viviparous 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 dis-
tributed in minute and tortuous ramifications on the folds (prep. 2683).
The preparation (No. 2684) of the Smooth Dog-fish ( Galeus levis ;
Emissole lisse, Cuvier) shows several uterine cotyledons developed

292

LECTURE XII.

from the internal surface of the dilated part ot the oviduct. Professor
Muller has well described the corresponding foetal cotyledons which
are developed from the vitellicle of the embryo.

In reviewing the various forms of the Generative Organs of Fishes,
we find that they resolve themselves into four well-marked grades of
complexity. First, reduced to the essential gland, the testis, or the
ovarium, without excretory canal. Secondly, with a simple duct,
continuous with testis or ovarium. Thirdly, a partial oviduct, as in
the Sturgeon, not continuous with the ovarium, and not separated
from the ureter. Fourth, a more compact form of testis and ovarium,
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 presenting a nidamental gland near its commencement and
dilating into an interior receptacle, with a plicated surface at its ter-
minal 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
(preps. 3226 — 3228), and the sub-abdominal marsupial pouch in the
male Hippocamps (pi-eps. Nos. 3230 and 3231).

DEVELOPMENT OF FISHES.

This, the most intricate and difficult, but the most interesting part
of the physiology of fishes, is divided, as in other animals, into seven
distinct processes: — 1. Semination, or the development of the im-
pregnating corpuscles called seminal animalcules, or ‘ spermatozoa —
2. Germination, or the development of the germ or ovum susceptible
of impregnation : — 3. Fecundation, or the act of impregnation, which
is sometimes, though rarely in the present class, accompanied by
intromission: — 4. Fcetation, or development of the embryo within
the ovum or uterus : — 5. Extrication, or escape of the embryo from
the ovum : — 6. Exclusion, or expulsion of the generative product
from the parent: — 7. Growth, or development from the period of
exclusion, or of extrication from a previously excluded ovum, to
maturity.

Exclusion of the male generative product is called ‘ emission that
of the female generative product, ‘ oviposition that of the previously
extricated embryo, ‘ birth : ’ but these are modifications of the same
essential process. The stages of development do not succeed each
other as here enumerated, in all fishes : in the Dermopteri and most
osseous fishes ‘exclusion’ precedes ‘fecundation,’ ‘fcetation,’ and
‘ extrication.’ In a few osseous fishes and a larger proportion of
the Plagiostomes, ‘ fecundation,’ ‘ fcetation,’ and ‘ extrication ’ precede

UEVELOPMENT OF FISHES.

293

‘ exclusion.’ When the membi’anes or appendages of the intra-ute-
rine embryo contract no adhesion with the parietes of the uterus, the
fish is said to be ‘ ovo-viviparous : ’ when such adhesion by inter-
lacement of vascular surfaces takes place, the species is said to be
‘ viviparous.’ The period of foetation passed within the body of the
parent is called ‘gestation:’ that which takes place in natural ca-
vities on the exterior of the body of the parent, or in nests artificially
prepared, is called ‘incubation;’ but these are accidents to foetation,
which may go on, as it does in most osseous fishes, independently
of either kind of protection.

Semination. — Tlie progress of the testis to maturity, when it
attains in all osseous fishes a larger proportional bulk than in any
other vertebrate animals, commences by the appearance in its tissue
of extremely delicate, closed cells, ‘ the sperm -sacs.’ In these the
spermatozoa are developed. * They are discharged, as we have seen,
in the lowest organised fishes, by a general rupture of the sacs into
the abdomen, and are excluded by the peritoneal canals. In the
growing milt of osseous fishes the sperm-sacs also yield to the
pressure of their contents, but partially coalesce and form tracts or
canals, frequently reticulate in their disposition, as in the Shad,
and which ultimately discharge their contents into the efferent pro-
longation of the general capsule of the gland. The spermatozoa are,
at first, mere nucleated cells ; they acquire in the Loach a pyriform
figure, with a minute knob at the apex, from which the filamentary
vibratile tail is continued (Jig. 76. a). Professor Wag-
ner estimates the length of the pyriform body at 5-o^oth
of a line, and that of the tail at 4^^!! of a line.f Pre-
vost and Dumas, and Siebold have described the vi-
bratile filamentary appendage in the spermatozoa of
other osseous fishes. In the Cyclostomes the body
of the spermatozoa is cylindrical ; in Sharks it is long
and spirally twisted ; in Rays they are developed in
f>undles 76. h), which are arranged in a radiated
mfg"nrnTd disposition in the sperm-sac before its rupture. Dr.

Davyij; observed many of the spermatozoa grouped
together in the vas deferens of the Thornback. The abundance of
these locomotive ciliated cells, and of the minuter granular matter in
the fluid in which they float, give to the secretion of the testis or soft
roe an opaque milk-white colour.

Germination. — The ova are developed in the ‘ stroma ovarii,
almost simultaneously in Dermopteri and osseous fishes, more sue-

a. Spermatozoon of
Loach

CXXXVIII.

j- cxxi. p. 68.

I cxxxiv.

294

LECTURE XII.

cessively in the Plagiostomes. They are much fewer in number in
the latter : from four to fourteen ova, for example, are developed at
each breeding season in the Torpedo marmorata.* In all fishes the
ova are formed in chambers of the ‘ stroma,’ called ‘ ovisacs.’ In
osseous fishes the ovisac f consists of a delicate membranous hollow
77. sphere — the ‘ ovarian vesicle’ {Jig. 77. a) |, surrounded

tby a thin layer of the proper tissue or ‘ stroma’ {b) of the
ovary, which, as it protrudes into the ovarian cavity,
carries before it a covering of the delicate vascular mu-
cous membrane. This tunic is not present in Cyclo-
Ovarian Ovum : stomes or Plagiostomcs. The ovum consists of the pri-
mordial or germinal vesicle, ‘ germ-cell’ (c), wdiich, in
osseous fishes, shows several nuclei or ‘germ-spots’ {d\
but in Plagiostomes only a single nucleus. Around the germ-cell
there accumulates a collection of minute yolk-granules (e) with oil-like
globules (/), the whole contained in a delicate yolk-membrane (g).
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 ap-
proach maturity. At this period the ova in osseous fishes escape into
the cavity of the ovai’ium ; and to their then outer covering, the yolk
membrane, is added a second tunic called ‘ chorion.’ The ovisac re-
mains behind and coalesces with the stroma, to form, according to
Barry§ , a “ vesicle analogous to the Graafiian vesicle of Mammals : ”
but the evacuated ovisacs collapse and speedily disappear in the
shrunken ovarium, after the discharge of the ova, in Dermopteri and
osseous fishes : they are longer recognisable in the Skate.

The periodical, but rapid and enormous increase of the hard and
soft roes in osseous fishes, admits of no rigid cinctures, no un-
yielding 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 con-
dition of their free or ‘ floating’ ribs.

Fecundation. — Certain changes and peculiar phenomena attend the
increase of size of the soft and hard roes during these primary pro-
cesses of generation. The colours of the fishes 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 claspers in the male Plagiostomes then acquire their full develop-
ment and force ; the basal glands in those of the Rays enlarge. As

* LXXXI.

I ‘ Ovisac’ of Barry, cvii. 1st series.

f XX. iv. 1838, p. 131.

§ evil. 1st series, p. 314.

DEVELOPMENT OF FISHES.

295

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 impels it as the fit place for ovi
position. 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*,
a most able observer of the development of the Salmon, states : —
“ On the 10th of January, 1836, I observed a female salmon of
about 161bs., and two males of at least 251bs., engaged in depositing
their spawn. The two males kept up an incessant conflict during
the whole 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 lash-
ing the water with their tails.” “ The female throws herself at inter-
vals 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, de-
positing, 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 clo-
acal papilla, in which the sperm-ducts terminate, doubtless serves
to ensure intromission. The superadded claspers in the male Pla-
giostomes 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.

Fcetation — The observation of the more simple mode of impregna-
tion in osseous fishes, so analogous to that of the dioecious palms in
which the fertilising pollen is wafted through the aerial ocean and
strewed over the humid papillose stigmata of the female flower,
naturally suggested the idea of artificial impregnation, of which

CXXII.

296

LECTUKE XIX.

MM. Prevost*, Rusconif, and VogtJ have availed themselves, in
the investigation of the nature of that mysterious act, and of the
changes thence ensuing in the impregnated ovum of fishes. The
first change observed when the ovum falls into the water is a separa-
tion of the outer covering, or ‘ chorion,’ from the inner tunic or
‘ membrana vitelli.’ It is probable, from observations on other
animals, but not proved in respect to the ova of fishes, that the
contents of the sperm-cell (body of the spermatozoon) enter the
ovum. After the contact of the spermatozoon with the ova, the fol-
lowing changes take place in the germ-vesicle. It loses its unim-
pregnated charactei’, becomes opaque, enlarges, and, in the ovum of
the Tench, according to Rusconi, forms with surrounding granular
matter an intumescence beneath the membrana vitelli. Rusconi
does not, indeed, interpret this appeai'ance as due to development and
metamorphosis of the germ- vesicle and its nuclei ; but Vogt has con-
firmed, by observation of the ova of the Corregonus, the important
discovery by Barry of the part which the germinal vesicle and its
nucleus or nuclei take in the first steps of embryonic development.
“ The small granules,” observes Rusconi, “ previously dispersed
through the yolk, now become collected at the base of the intu-
c h a mescence 78, a). Half an hour

after the occurrence of this first
change, two furrows intersecting each
other at right angles appeared at the
prominent part of the yolk (ib. 5, c).
A quarter of an hour later, two other
fuiTOws were observed at each side of
the first, so that the prominent part of
the yolk, which previously was divided
into four lobes, now appeared to be formed of eight lobes (ib. d).
After the lapse of another quarter of an hour, each of these eight
lobes was seen to be subdivided into four smaller lobes, by the for-
mation of six fresh furrows, intersecting each other at right angles.
At the end of another half-hour, several new furrows appeared, which
crossed those which already existed, and subdivided the lobes of the
prominent part of the yolk still further, rendering them so small and
numerous that it was now scarcely possible to count them (ib. c).
The process continued until the surface of this portion of the yolk
regained the smoothness which it had before the first furrow ap-
peared.”

If this account, abridged by Professor Muller § from the Memoir
of the celebrated Italian physiologist, be compared with the descrip-
tion of the first steps in the development of the intestinal worm

* cxxx. j- cxxxi. cxxxn. § Lxxiv. ii. j). 1510.

First steps in the development of a
Tench: Rusconi.

DEVELOPMENT OF FISHES.

297

(“ Lectures on Invertebrata,” p. 77.), the correspondence will be seen
to be extremely close. In the Entozoon the entire yolk is the seat of
the successive subdivision produced by reiterated processes of deve-
lopment, liquefaction, and assimilation of nucleated cells, until the
property of the primary impregnated germ-cell has been distributed
throughout the mass ; when the whole mass, by subsequent meta-
morphosis of the cells, is converted into the embryo. In the fish a
part only of the yolk is the seat of these processes, superficially indi-
cated by fissures of that part, and the resulting embryo is co.inected
with the remainder of the yolk ; this remainder is called the nutrient
yolk, or ‘ vitellicle;’ the other part is the ‘ germinal yolk,’ sometimes
called the ‘ germinal membrane,’ from its being thinly spread over
more or less of the nutrient yolk before the embryo arises out of it.
In the Tench and other Cyprinoids it overspreads the whole nutrient
yolk*: in the Blenny, Rathkef found the embryo considerably ad-
vanced before the nutrient yolk was so included. The surface of the
so-covered yolk is ciliated, and, with the embryonal part, performs a
slow but regular rotation within the albuminous fluid of the chorion. J
The first traces of the embryo are two parallel ridges, the ‘ laminjB
dorsales,’ which coalesce, and form the neural axis and the rudiments
of the chorda dorsalis 78. f). The germinal membrane separates
into an outer ‘vertebral’ and an inner ‘visceral’ layer: from the
former are developed the brain and myelon, the vertebras and their
appendages, the muscles and nerves, and the skin ; from the latter
are developed the digestive, excretory, and generative viscera. The
outer layer has been called the ‘serous’ and ‘animal’ layer; the
inner one the ‘ mucous’ and ‘ organic’ layer. Between these are deve-
loped the organs of circulation and respiration. The ‘laminse dor-
sales’ consist of the extension of the vertebral layer upwards (the
embryo being supposed to be prone) to inclose the neural axis : the
‘lamime ventrales’ are downward extensions of the same layer, to
inclose the viscera and the nutrient yolk ; consequently the so-
extended ‘ lamime ventrales,’ when they coalesce beloAvq form tlie
external (serous, or more properly tegumentaiy) layer of the yolk-
sac. After the trunk is developed, the head and the tail appear, and
project freely from the supporting surface, and the embryo encircles
the yolk, in the form of an apodal fish {ih. g). With regard to the
skeleton, the aponeurotic septa of the vertebral segments of the body
first appear ; then the ‘ chorda dorsalis ;’ afterwards the rudiments of
the neurapophyses along the sides of the neural axis ; and, lastly, the
luemal arches and their appendages. At this time may be discerned
the characteristic strite of the muscular fibre. The development of
the skull is described at p. 71.

* xmi. (1831).

I CXXVIII.

I CXXXII.

298

LECTURE XII.

Embr3'o Osseous Fish.

The inner (mucous) layer of the globular yolk-sac sends from its
upper part a c^cal process forwards and another backwards, almost
co-extensive at first with the trunk above. But their growth is
checked by the adhesion of their blind ends to points of the serous
layer on the under part of the cephalic and caudal extensions of the
trunk : which points of adhesion become perforated, and establish the
mouth {fig. 79. a) and vent (ib. i) : the intermediate mucous tract forms,

at first, a short and straight
I 0 \ \ alimentary canal, commu-
nicating by a gradually
constricted aperture with
the remaining yolk-sac
(ib. d). In the Cyprinoid
fishes the vitellicle is ses-
sile ; i. e., it does not
hang,as a pedunculate sac,
from the exterior of the
body : the young Salmon
quits the ovum with the vitellicle in the form of a vascular oblong
appendage from the fore part of the abdomen. In both cases the
vitellicle is included, together with the intestinal canal, within the
parietes of the abdomen (ib. c), formed by the before-mentioned deve-
lopment and coalescence of the laminae ventrales. In the Tench the
yolk is divided only by the constricted communication with the
intestine, and is said to be ‘internal in the Salmon, and, also, in
Zoarces and Coitus, the yolk is divided by a second constriction,
where it hangs from the ventral integuments ; the part within the
abdomen is called the ‘ internal yolk,’ the part without is called the
‘ external yolk.’

The vascular channels, which are excavated in the soft embryonic
tissues of both the vertebral and visceral systems, and which convey,
at first, a plasma with colourless nucleated cells, unite into a longitu-
dinal sinus in the interspace of the two systems, where the aortic
trunk {n) and the cardinal veins (m) are afterwards situated. This,
at first simple canal, receives or transmits vascular loops or arches
upwards to the lamin* dorsales, and downwards to the laminae
ventrales ; those of the latter being most conspicuous that spread
over the vitellicle : it is here, also, that the red-colour of the circula-
ting cells, or blood-discs, is first perceived. The vitelline vessels in
osseous fishes are ramifications of a mesenteric vein, analogous to that
subsequently established to form the portal system of the liver.

The heart is not developed from the longitudinal vessel in the
dorsal region of the abdomen. The larger branches, which ramify on
the vitellicle, unite into a trunk at its anterior part, which, being

DEVELOPMENT OF FISHES.

299

joined by the precaval vein (e), becomes first a pulsating tube, and
afterwards, by extension, constrictions, and intervening dilatations,
an auricle, a ventricle (A), and a bulbus arteriosus ; from which the
hyoid vascular arch (m), succeeded by the branchial vascular arches,
pass upwards to communicate with, and impart new vigour to the
flow of blood in, the primitive longitudinal dorsal vessel. The
‘ lamin® ventrales,’ continued down the sides of the head, form
vertical folds or arches, the interspaces of which are converted into
clefts communicating with the commencement of the alimentary
canal. The first of these arches is the largest, and from its blas-
tema the mandibular and hyoidean arches, with their appendages,
are developed ; the five succeeding arches are the true branchial
ones. The metamorphoses of the corresponding vascular arches, and
the development of the gills, have been already explained, (p. 265.).
The jugular (^») and cardinal (m) veins unite to form the precaval (e),
which joins the hepatic and vitelline veins in a common trunk, or
sinus, opening into the auricle.

The first three successive enlargements at the fore part of the
neural axis are connected respectively with the olfactory, optic, and
acoustic nerves ; the first (p) becomes, then, divided into prosen-
cephalon and rhinencephalon ; the second (o) rapidly gains superior
bulk in connection with the large and early-developed eyes ; and the
pineal and pituitary appendages appear. The cerebellum is the last
part which is formed, upon the epencephalon (a).

In the mean while the liver (/) has been developed from the back
part of the intestinal neck of the vitellicle ; the pancreas being a later
pullulation of caeca from the intestine itself. The kidneys (p) and
generative glands (o) are formed out of blastema beneath the primitive
vascular sinus ; but their ducts are caecal developments from the pos-
terior part of the intestine : this latter stage of development is never
attained, as regards the generative organs, in the Dermopteri. Eathke*
detected in the embryo Blenny, what Cams afterwards found in the
human foetus, germinal vesicles in the nascent ovarium prior to birth,
— two generations successively included in the parent.

The ureter {q) always makes its appearance very early before the
embryo quits the ovum; it communicates with the extremities of the
transverse parallel tubuli uriniferi formed by confluence of primitive
cells in the renal blastema. The cardinal veins traverse or groove
the kidneys, as they do the Wolffian bodies in the embryos of higlier
vertebrata ; 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.!

* CXXVIII.

f Von Baer appears to have first appreciated tills interesting homology. “ Alles

300

LECTURE XII.

The duct of tlie air-bladder (s) is developed from the dorsal aspect
of the pyloric end of the stomach ; even in those fishes where the
communication of the air-duct is afterwards found at the oesophagus ;
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. In the Herring, the primitive place of its connection with
the alimentary canal is retained. The communication is obliterated
in the fishes without the air-duct ; and the whole posterior compart-
ment disappears with the duct in the Loach. The scales are formed
late in all osseous fishes ; their integuments remain smooth and
lubricous, as in the Dermopteri, some time after the disappearance
of the vitellus.

The inferior position of the mouth is an embryonic character
common to all fishes, and is retained, together with the unossified
skeleton and the continuation of the cartilaginous vertebras into the
upper lobe of the caudal fin, in all the Plagiostomes. The singular
productions of the rostrum in many of these fishes, like the elon-
gation of the jaws in osseous species, are later phenomena of deve-
lopment. It is interesting to find the broad, depressed, obtuse embry-
onic form of head common to all the known 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.

All the Plagiostomes have the external as well as the internal di-
vision of the vitellicle {^Jig. 80.) ;
the peduncle of the external one
is longer, in some species consider-
ably so, than in osseous fishes, and
it is beset with villi in Carcharias
and Zygcena. * The tegumentary
covering of the outer yolk (ib. d),
is denser and more opaque in Pla-
giostomes : the inner yolk (ib. e)
consists, of course, only of the
proper vitelline tunic, which is
thin and transparent : it commu-
nicates with the small intestine (g)
i. e., with the short tract which
intervenes between the pylorus
and the valvular straight gut (/i) :
it receives the external yolk (rf' e') as this is progressively squeezed
into the abdomen by the contraction and interstitial absorption of its

(Uess fiihrt zu der Ueberzeugung, das der Fisch-Nieren stelien gebleibene Primor-
dial-nieren andercr Thit're sind,” (cxxxvn. 1337 p 314 'i
* cxxiii. tf. ill. > • • -j

DEVELOPMENT OF FISHES.

301

tunics : 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 from ramifications of a branch of the me-
senteric artery, and the blood is returned to the mesenteric vein. The
Hunterian preparations of the embryo Carcharias (No. 1061),
Scyllium (No. 3250), Spinax (No. 3255), and (No. 3261),

demonstrate another foetal peculiarity which later researches * have
shown to be probably 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 capillary loop f ; they disappear early, being removed by
absorption. The last remnants may be seen in the foetal Saw-fish
(Pristis, No. 3263), 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 re-act on the streams of
water admitted into the egg by the apertures (J7g. 81. 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 (No.
3255) ; so that, whilst the vitellicle administers to the nutriment of
the embryo, the external branchim may perform the respiratory func-
tion. In the speeies of Shark, the smooth Emissole, in which Prof.
Muller has shown that vascular cotyledons are developed from the
vitelline (omphalo-mesenteric) capillaries, which are firmly connected
to the uterine cotyledons, the vitellicle, like a true placenta, may per-
form both the nutrient and respiratory functions : the external branchiae
disappear some time before the exclusion of the Embryo and the
absorption of the yolk. In the Lepidosiren annectens \ three small ex-
ternal branchial filaments project from the single opercular aperture
on each side, and are long retained, if they be not permanent in that
remarkable osculant form between the osseous and cartilaginous fishes.

Some of the plagiostomous fishes are oviparous, but not as in the
majority of osseous fishes ; a remarkable transposition in the periods
of the processes of fecundation and exclusion marks the distinction.
In the oviparous osseous fishes the ova are first excluded, then im-
pregnated : in the oviparous Plagiostomes impregnation 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 common fishes, where the countless numbers
of the ova seem to compensate for the chances that may intervene to

* Rudolph!, Lxxv. Rathko, cix. ; Leuckart, cxxiii ; J. Davj’, i.xxxi.

I A. Thompson, cxi.

i Jardine, cxxxv. ; and Peters, cxxxvi.

302

LECTURE XII.

prevent the contact of the milt. The ovarian, or abdominal aperture
of the oviduct is free and distinct from the ovary itself in the Pla-
giostomes, the Lepidosiren, the Sturgeons, and Polypterus. 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.

There is reason to suppose that impregnation of the eggs of both
Sharks and Rays takes place in the ovarium or the 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 infiuence of the spermatozoa.
The form of the egg, when thus invested, is remarkable, and very dif-
ferent in different genera of Plagiostonies. In the Skate the ovum is
an oblong, four-sided, flattened ca^e, with the angles produced
forwards and backwards, like those of a butcher’s tray (prep. 3235).
The embryo skate is packed in the cavity with its broad pectorals
bent upon its back, and its tail coiled round the body : the vitellicle
is appended by a short and contracted neck. In the spotted Dog-
fish (^Scyllium, No 3249) the ova are also quadrilateral, but longer,
and the angles are extended into long filamentary tendrils, which
attach themselves to floating sea-weed, and thus keep the ovum near
the surface, where the influence of solar heat and light is greatest

The eggs of the Calorhynchus them-
selves resemble some broad-leafed fucus, and
thus, probably, deceive the fish that might other-
wise devour them : they are in the form of a long
depressed ellipse, with a broad plicated and
fringed margin (No. 3235, A and b). The large
Shark’s ovum (prep. 3245), resembles that of the
Scyllium, with the addition of a series of trans-
verse parallel ridges crossing the anterior and
posterior surfaces. An elongated pyriform shell
of a plagiostomous ovum, transmitted to me from
Australia, as that of the Cestracion, is charac-
terised by a broad ridge or plate, which is wound
edge-wise around the ovum in five spiral circumvolutions. The sub-
stance of all these egg-coverings is a light, but firm, albuminous horn-
like tissue, of a more or less deep brown colour : the orifices {Jig.
81. c) admit the sea-water to the pendant respiratory filaments of
the inclosed embryo (a). The yolk-bag is shown at b.

Hie essential difference between the oviparous and ovo-viviparous

DEVELOrJIENT OF FISHES.

303

fishes is the transposition of the periods of extrication and exclusion ;
in the Ovipara the generative product or ovum quits the parent
before the embryo extricates itself from the egg: in the Ovo-vivipara
the embryo escapes from the egg before it quits the parent : the
young Blennies tarry three months in utero, from September to
January, after extrication from the chorion. The great difference
between viviparous fishes and mammals is, that the former rupture
the chorion long before they are born, even in the Sharks where
there is a kind of pseudo-placental attachment : in the foetal mammal
birth and exclusion are commonly coincident.

Growth. — There are few fields of Natural History that have been
less cultivated, or would better reward the scientific labourer, than
that extensive and varied one relating to the generation 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 some very interesting observ-
ations ; the following are the chief results of those recorded by
Mr. John Shaw in the Transactions of the Royal Society of Edin-
burgh, for 1840.

The embryo fish, developed from the ova spawned on the 10th
January, were conspicuous by the two dark eye-specks and the
vascular vitelline sac, and presented some ajipearance of animation
in the ovum, on February 26th, that is, forty-eight days after being
deposited ; and on 8tli April, or ninety days after impregnation of
the ova, the young were excluded. The head is large in proportion
to the body, which measures -Iths of an inch in length ; the vitellicle
is fths of an inch in length, and resembles a liglit red currant ;
the tail is margined like that of the tadpole, with a continuous fin
running from the dorsal above to the anal beneath. The vitelline
sac and its contents were absorbed by the 30th May, or in about
fifty days, until which time the young fish did not leave the gravel.
This quiescent state in their place of concealment, from the period
of exclusion to the absorption of the yolk, seems to bo common
to osseous fishes ; but the time varies in different fishes, it is much
shorter in the Tench, for example, than in the Salmon. When the
young of this fish emerge, the terminal fringe-like fin begins to
divide itself into the dorsal, adijiose, caudal and anal fins ; and the
transverse bars on the side of the body make their appearance. At
this period, the young Salmon measures an inch in length, and is
very active, and continues in the shallows of its native stream till
the following spring, when it has attained the length of from three
to four inches, and is called the “ May -parr : ” they now descend into
deeper parts of the river, and are believed by Mr. Shaw to remain
there over the second winter. In April, the caudal, pectoral, and

304

LECTURE XII.

dorsal fins assume a dusky mai’gin ; the lateral bars begin to be con-
cealed by a silvery pigment ; and tbe migratory dress, characteristic
of the Salmon fry, or ‘ smolt,’ is assumed. The fish now begin to
congregate in shoals and to migrate seaward.

Incubation, — Eckstroem first published a clear account, in 1831*, of
the singular marsupial economy of the Pipe-fishes. In the Syngna-
thus 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, being fecundated in transitu,, and the valves of the pouch
immediately close over them. In the month of July the young are
hatched and quit the pouch, but they follow their father, and return
for shelter into their nursery when danger threatens.

Aristotle signalises the Phycis, since recognised as a Mediterra-
nean species of Gobius, as the only sea-fish that makes a nest and
deposits its spawn therein. Olivi confirmed the statement, and de-
scribes the nest as being composed of sea-weeds (algi and zostera),
adding that the male fish guards the female during the act of ovi-
position and the young fry during their development, f

Dr. Hancock has observed similar habits in certain fresh-water
siluroid fishes of Demerara called ‘ Hassars,’ which belong to the
genus Callichthys : the Round-headed Hassar 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 fre-
quently take them by putting their hands into the water close to the
nest; on agitating which, the male Hassar springes furiously at
them, and is thus captured.” Through the kind interest of the
Earl of Enniskillen, a trustee of the Hunterian Museum, a specimen
of the nest with the spawn and parent fish, has been transmitted
to the College and is now placed in the Hunterian series of
Nidamental structures (No. 3787. b. h). J

* See also xxxix. ii. p. 327. f xxiii. t. xh. p. 6.

:|: This specimen was exhibited at the Lecture.

END OF THE SECOND VOLUME.

London ;

Printed by A. Spottiswoode,
New- Street- Square.

305

WORKS

REFERRED TO BY ROMAN NUMERALS m THE PRECEDING LECTURES.

I. Carus. Ur-theilen des Knochen und Schalengeriistes. Fol. 1828.

II. Geoffroy St. Hilaire. Memoires du Museum. 4to. ix. 1822. p. 119.

III. Von Baer. ‘ Meckel’s Archiv fiir Physiologie.’ 1826. Heft iii.

IV. Bibra. Chemische Untersuchungen iiber die Knochen und Zalme. 8vo.

1844.

V. Owen, R. Odontography. 4to. 1840-1845.

VI. Owen, R. Fossil Mammalia, Zoology of the Voyage of the Beagle.
4to. part i. 1838.

VII. Hunter, Jno. Manuscripts printed in the ‘ Catalogue of the Physio-
logical Series in the Museum of the Royal College of Surgeons.’ 4to,
5 vols. 1832-1840.

VIII. PuRKiNJE and Deutsch. De penitiori Structura Observationes. 4to.
1834.

IX. Treviranus. Beytrage des Organischen Lebens. Breme, 1835.

X. Muller, J. Ueber die Structur, &c. der Knorpel und Knochen.
‘ Poggendorf’s Annalen der Physik. 1836.’ viii. p. 295.

XI. Hunter, Jno. ‘ Transactions of a Society for the Improvement of Medical
and Chirurgical Knowledge,’ vol ii.

XII. Owen, R. Description of the Skeleton of a gigantic extinct Sloth.
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