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es

ODONTOGRAPHY;

OR, A

TREATISE

ON THE

COMPARATIVE ANATOMY OF THE TEETH.

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- vfs M

EPIOTROEO -

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ODONTOGRAPHY:

OR, A

TREATISE

ON THE

COMPARATIVE ANATOMY OF THE TEETH;

THEIR PHYSIOLOGICAL RELATIONS, MODE OF DEVELOPMENT,

AND

MICROSCOPIC SUIRUCTURE,

IN THE

VERTEBRATE ANIMALS.

BY RICHARD OWEN, F.R:S.

CORRESPONDENT OF THE ROYAL ACADEMY OF SCIENCES OF PARIS, BERLIN, &c. &c., HUNTERIAN PROFESSOR TO THE
ROYAL COLLEGE OF SURGEONS, LONDON.

REMINGTON KELLOGG
LIBRARY OF
MARINE MAMMALOGY
SMITHSONIAN INSTITUTION

VOLUME I.

LONDON:
HIPPOLYTE BAILLIERE, PUBLISHER,

FOREIGN BOOKSELLER TO THE ROYAL COLLEGE OF SURGEONS.
219, REGENT STREET.

PARIS: J. B. BAILLIERE LIBRAIRE DE L’ACADEMIE DE MEDECINE,
LEIPZIG: T. 0. WEIGEL.

]840—1 845.

LONDON:

Printed by Schulze.& Co., 13, Poland Street.

TO

TH OM A'S) Bae By) BRS:

PROFESSOR OF ZOOLOGY IN KING'S COLLEGE, LONDON, &c.

OOO OOO OO OOOO OOOO OO OO

My DEAR BELL,

Independently of the pleasure with which I embrace this opportunity
of expressing the feelings of Friendship and Esteem which I have long
entertained towards you, there is no one to whom the present Work could
with more propriety be dedicated than the acute Observer who was the
first to point out Pathological Phenomena in the Human Teeth, consistent
only with a higher organization and mode of development than it has been
usual to attribute to them, but which it is the chief object of the following

pages to demonstrate as common to the teeth of all vertebrate animals.

I am,
Your’s, very sincerely,

RICHARD OWEN.

LONDON, JUNE 18, 1845.

oat oe

PREF A.C E.

Tue present Work includes the substance of the Lectures on
the Comparative Anatomy and Physiology of the Teeth, which
formed part of the Hunterian Courses delivered at the Royal College
of Surgeons in the years 1837, 1838, and 1839. In the first of
these courses the teeth were considered in their relation to the
Osseous System, and the intimate structure of their component
tissues was more especially treated of: in the second, they were
regarded as parts of the Digestive System, and, besides their structure,
their various configurations and proportions, in subserviency to the
habits and food of the different species, were described : in the third,
the development of the Teeth was considered in connection with
that of the epidermal appendages of the Tegumentary System, in
consequence of a close analogy in the form, structure, temporary
duration, and reproduction of the formative matrix.

The views of the structure and development of the Teeth, and
the consequent deductions as to their place in the system of
tissues, their physiological relations, and their value as zoological
characters, advanced in those Lectures and in contemporary publica-
tions,* are more fully and connectedly treated of in the following
pages.

Like the other subjects of the Hunterian Lectures, and in accord-

* ‘Report of the British Association,’ vol. vi1, 1838, p. 135. ‘Comptes Rendus de
l’Académie des Sciences,’ 4to, 1839, p. 784.

x PREFACE,

ance with the principle of arrangement of the Physiological depart-
ment of the Hunterian Museum, the Dental System is here traced
from its more simple to its more complex conditions. But this
progress is partially subordinated to the limits of zoological arrange-
ment. For, although the tooth of a Myliobates or a Labyrinthodon be,
in structure, more complex than many Mammalian teeth, yet this
complexity is associated with other characters, such as mode of
attachment, frequent shedding and renewal, &c., which indicate an
essentially inferior grade, and connect them, respectively, in closer
natural relationship with the more simple teeth of other species of
Fishes and Reptiles. A distinct Part, or division of the Work is,
therefore, appropriated to the Dental System of each of the three
great Classes of Vertebrated Animals which possess teeth.

In the Mammalian series the course of progressive complication
of the teeth is closely followed, irrespective of the general grade of
organization of the species, and the Human dentition falls, accord-
ingly, into the middle of the series. Guided by the evidence of the
teeth I have sometimes deviated from the accepted Zoological systems,
as will be seen in the last Chapter, devoted to the complex den-
tition of the great Family of Hoofed herbivorous quadrupeds,
and especially in the value there assigned to the Ruminant modifica-
tion of the Ungulate type.

In each Class, the chief characters of the teeth of the
extinct species are described in connection with those of the
allied existing forms. For so vast is now the extent, and so rapid .
the progress of Paleontology, and so important are the links in
- the chain of Being thus recovered, that no treatise on the Compa-
rative Anatomy of the enduring parts of animals can fulfil its
expected purpose, if it be restricted to the description of such parts
in existing species alone.

With regard to the Teeth, some of the most interesting and
extraordinary modifications were peculiar to species that have long
since passed away from the stage of animated existence; and,
indeed, no comprehensive view could be obtained of the dental
tissues without a knowledge of those intermediate conditions which

PREFACE. Xl

they present in fossil teeth. I need only refer to the Acrodus,* the
Spherodus,t the Saurocephalus,t the Dendrodus,§ the Labyrinthodon,|
the Iguanodon,{ and the Megatherium,** in illustration of the value
of Fossil remains, and of the microscope, as an instrument in the
determination of their nature and affinities.

This important application of the microscope has, however,
its limits, and from the difficulty of testing the described results by
repetition of the observations, and from other causes, it is liable to
be abused. !

A knowledge of the structure of the entire fossil tooth should
be obtained by longitudinal and transverse sections ; at least by a
transverse section through the entire thickness of the crown. With
this knowledge a fragment of the tooth of the same species may
afterwards be determined: and also in many cases those of other
species of the same genus, or natural family: without it, great
mistakes may be committed. If, for example, a microscopic observer
had begun his examination of an Iguanodon’s tooth by a slice of a
fragment from the outer half of the crown, and had afterwards
examined another fragment of the tooth of the same species taken from
the inner half, he would, most probably have referred such fragments
to two very distinct species of animals. The requisite knowledge of
the characteristic combination of one lateral moiety of dentine, and
another of vaso-dentine in the same tooth, pre-supposes the examina-~
tion of a section of an entire specimen. In like manner, to pro-
nounce on the generic and specific distinctions of fossil Proboscidians
from the characters of portions chipped off the exterior of their tusks,
is an abuse of the microscope, and betrays an ignorance of the mode
and limits of its application.tt

One consequence of an attempt, like the present, to determine

* Pl. i. ioe t Pl bas

§ Pl. 62 B. The teeth of this extinct Fish afford a beautiful example of the unexpected
application of microscopic characters of dental tissue in the determination of an important
geological problem.—See Appendix to Mr. Murchison’s ‘ Geology of Russia,’ p. 635.

|| Pl. 64 A. TPE. 71. ** Pl. 84;

tt Thus, out of portions of tusks of young and old individuals of the Mastodon giganteus,
the genera Missowrium, Tetracaulodon, and their different species, have been attempted to be
established.—See Geological Proceedings, June 29, 1842.

Xli PREFACE.

the true nature and mode of development of a class of organs by
tracing the modifications of such through the entire range of the
series of animals to which it is peculiar, is, that, from the length
of time required to complete and arrange the extended series of
observations, partial glimpses and illustrations of the main con-
clusions sought to be established are published by authors who
are excited to pursue some limited branch of the subject, and
have leisure for following it out. The right of priority of original
observation thus affected, is, however, a matter only of personal
interest, and of small moment in comparison with the benefit which
science derives not only from the collateral and independent evidence
thus adduced, but also from the stimulus to further research emanat-
ing from the discussion of such right. Where the concurrent
investigations are liberally pursued in the spirit of truth, they ought
to produce no other feeling than that of friendly emulation. It is
with unalloyed pleasure that I have seen the investigations com-
menced in the first Part of the present Work, extended by the
beautiful illustrations of the microscopic structure of the Teeth of
Fishes in the later Numbers of the ‘ Poissons Fossiles,’ of M. Acassiz,
in which most of my descriptions are verified,* and my indications
of the labyrinthic structure of the teeth of certain Fishes have
received direct illustration by the figures of the microscopic structure
of those of the Lepidosteus. In lke manner the Memoirs of M.M.
Erpi, Bisra, and Duvernoy,t have confirmed and extended my

* With regard to the Psammodus and allied extinct Fishes, in which the medullary canals
are affirmed by M. Agassiz to open directly upon the grinding surface of the tooth, it would
be as reasonable to suppose that the long vascular and sensitive pulp should be exposed upon
the working surface of the perpetually growing incisor of a Rodent. But apart from any
physiological objection to the opinion of the learned Ichthyologist of Neuchatel, I have made
new sections of the teeth of different species of Psammodonts, and have demonstrated their
perfect agreement with my descriptions, and with Plate 20, in the first Part of this Work,
to the satisfaction of Sir Philip Egerton, Mr. Stokes, Mr. Broderip, and other scientific
friends. All these specimens show that, as the grinding surface is worn down, the vascular
contents of the medullary canals have become calcified within a short distance from that’
surface, and thus, in the existing Fish, were the cavities of the canals defended from the
effects of friction. .

t+ I regret that the pages in Part III, descriptive of the Teeth of the Insectivora were

printed off before I received the last memoir of M. Duvernoy containing his observations and
beautiful figures of the microscopic structure of the teeth of the Shrews.

PREFACE. Xili

earlier observations on the microscopic structure of the teeth of
Mammals.

The published Parts of the great Work by Prof. De Buainvitte,
entitled ‘ Ostéographie, ou Description Iconographique Comparée du
Squelette et du Systéme Dentaire des cing Classes d’Animaux
Vertébrés,’ contain accurate and beautiful figures of the external
forms of the teeth of various genera of Mammalia. These Fasciculi, —
the immortal ‘ Ossemens Fossiles’ of Baron Cuvizr, and the express
Treatises on the Comparative Anatomy of the Teeth of Mamma-
lia by M. Fr. Cuvier, and Dr. Rovussrav, the able assistant in
the Museum of Comparative Anatomy in the Garden of Plants,
have supplied the third Part of the present Treatise with figures of
some of the instructive and valuable specimens of the dental organs
in that rich Collection; but my descriptions have been taken, in
every instance, from the specimens themselves, or from the teeth
of the same species, which, when not present in the Collections
of this country, I have examined in the Parisian Museum, or in the
Anatomical and Zoological Collections at Leyden and Frankfort.
My best acknowledgments are due to Prof. Temminck, Dr. Riippell,
and M. Laurillard, for the facilities which they kindly afforded me
in studying those valuable Foreign Collections, which impart essen-
tial aid to all who would treat systematically of the dental or
osteological characters of the Vertebrate Animals.

The present Work would, however, have been very incomplete,
if I had not been privately aided by the liberal contributions of
teeth of rare fossil and recent animals, which were not available
for the purpose of microscopic examinations when present in public
collections.

The Earl of Enniskillen and Sir Philip Egerton have supplied
me with the requisite specimens of Cochliodus, Saurichthys, the
Chimeroids, and other fossil Fishes. To Charles Darwin, Esq., I
owed the opportunity, at an early period of my investigations of
denfjal structures, of examining microscopically the fossil teeth of
the Megatherum, Mylodon, Scelidotherum, and Towodon. Through
Sir Woodbine Parish and M. Falconett, I have been able to examine
the teeth of the Glyptodon. Prof. Pflieninger, of Stuttgard, most

X1V PREFACE.

kindly transmitted to me the portions of the tooth of the great
Mastodonsaurus, or Labyrinthodon, from which the sections described
and figured in the present Work are taken. Dr. Lloyd of Leaming-
ton, liberally consented to sacrifice his specimens of the extremely
rare teeth of the English Labyrinthodonts, for the requisite com-
parison of their structure with that of the teeth of the more gigantic
species of the Wirtemberg Keuper Sandstones. To Alex. Robertson,
Esq., of Elgin, and R. I. Murchison, Esq., P.G.S., I owe the
opportunities of examining the teeth of the Dendrodus. Mr. George
Bennett of Sydney, and Dr. Hobson of Melbourne, have transmitted
to me the jaws and teeth of the rare Cestracion of the Australian
seas. Dr. Mantell has supplied me with the teeth of the Iguanodon
and Gyrodus. Dr. Buckland, Dr. Agassiz, Capt. Jones, R.N.,
Charles Stokes, Esq., Fred. Dixon, Esq., of Worthing, J. C. Bower-
bank, Esq., and other friends and colleagues in the Geological
Society, have most liberally contributed subjects described in the
present Work. Messrs. Stokes, Bowerbank, and Lister, have also
kindly granted me the use of their valuable miscroscopes when-
ever I wished so to test or verify observations made with my own.

My grateful acknowledgements are more especially due to the
PresiDENT and Councit of the Royat CoLLeGce or SurcEons: for
to them I owe the appointments which have made the pursuits
most congenial to my tastes a duty, and at the same time have
supplied the best means and opportunities of fulfilling it. In whatever
degree, therefore, I may have contributed in this or previous Works
to the advancement of Comparative Anatomy, or may have aided
in its application to collateral sciences, I can only regard myself as
instrumental, in such measure, in carrying. out the great objects
which the College of Surgeons had in view in accepting the
important trust of the Hunterian Museum, and which the College
has ever since most strenuously promoted.

CONTENTS.

INTRODUCTION

PARROT,

. —I xxiv.

DENTAL SYSTEM OF FISHES.

CHAPTER I.

GENERAL OBSERVATIONS ON THE TEETH OF
FISHES.

Page
Section 1. General characteristics eT |
», 2. Number ib.
iS. Horm : 2
, 4. Situation . ; ah have
» 9. Attachment : 3 e286
, 6. Substance. : , 8
» 7. Chemical Composition 9
» 8. Structure . . 10
» 9. Development . 14

CHAPTER II.

TEETH OF CYCLOSTOMES.

Section 10. Myxines . : ‘ 20
» 11. Lampreys ¢ ‘ 21

CHAPTER III.

TEETH OF PLAGIOSTOMES.

Section 12. General characters 23
» 18. Squaloids. 26
terse: % 40

)

Section 15.
eae LGe
eee Ye
Ss
Py cae US
EU.
pe Ps
oe RODE
by eB
AT:
Meds
le iP

TEETH OF GANOID FISHES.

| Section 27.
eeiaos
to Boe
shu cok
siole
pe ei

2? 35.

Squatina °
Raiidee

Myliobates
Cestracionts

Acrodus . °
Hybodus.

Ptychodus
Psammodus . :
Petalodus. : A
Cochliodus
Chimeeroids

Spatularize

CHAPTER IV.

Lepidoids
Pycnodonts

Sauroids .

Gymnodonts
Scleroderms .
Goniodonts

Siluroids ; :

68
70
74
77
82
85
86

xV1 CONTENTS.
CHAPTER V.
TEETH OF CLENOID FISHES. ) Section 49. Mugiloids
eee) ae pe » 50. Atherines 7
ee a rN a : we ». 51. Scomberoids .
ts OEY . he », 52. Sphyrenoids
,, 36. Sparoids 91
aii. Glaysopbegs 99 +3 a. Sphyrenodus
xi ; P 9 - b. Saurocephalus
» 938. Sargus . : 94 Sk
39. P Lethri & 98 » 58. Lucioids .
s » Se Ee ;
f ieee et », 54. Clupeoids
» 40. Scizenoids . 100 '
a y,. 0aS.. Pasoaas. =
,» 41. Teenioids is J Oe 8
are » 56. Phyllodus
5, 42. Gobioids : ~ £O2 2 ‘o
43. Ph : Fedora ;, 97. Salmonoids
. Pharyngien ‘
pe ee POOea » 58. Cyprinoids
forms . . 103 aap
E » 99. Trachinoids
,, 44. Theuties. . 104 ae
»» 60. Lophioids
» 45. Cheetodonts #05 Ds
46. Pleuronectoids 106 » :
4 é ids . : d
,» 62. Gadoids . -
CHAPTER VI. , 63. Murenoids .
TEETH OF CYCLOID FISHES. ,, 64. Lepidosiren .
Section 47. Labroids . . 108 » °65. Saurichthys .
>», 48. Scaroids . tS , 66. Dendrodus
PA RAD EE
DENTAL SYSTEM OF REPTILES.
CHAPTER I.
GENERAL CHARACTERS OF THE TEETH OF Section 76. Siren : bs
AT AESOIOEL, Fe :
REPTILES.
ee », 78. Menobranchus ,
Section 67. General characteristics . 179 4 Protenas i
» 68. Number . . 180 » 80. Amphiuma .
., 69. Situation ib. » 81. Menopoma
Sane. orm“. ib. », 82. Sieboldtia
» 71. Attachment 182 », 83. Andrias . é
,. 72. Substance 183 ,» 84. Triton .
» 73. Structure id. » 85. Salamandra .
» 74. Development . 185 » 86. Rana. .
», 87. Labyrinthodonts
CHAPTER Il. » 88. Lab. leptognathus .
TEETH OF BATRACHIANS. », 89. Lab. pachygnathus .
Section 75. General characters 187 | » 90. Cecilia . i

Page

. 188
- 189

- 196
a, UE
. 191

ib.

- 193
= ei
- 195
- 207
- 213
~ 217

CONTENTS. XVII

CHAPTER III, ) Page
| Section 104. Hyleosaurus. . . 253
TEETH OF OPHIDIANS. Cag eee < _ 945
Be » 106. Mosasaurus . - . 258
Section 91. General characters . - 219°ie ; 107. Leiodon. : : . 261
” 92. Deirodon . . a) eo = 108. Geosaurus , " . 262
” 93. Boa . . . Pei A | a 109. Varanians e i . 263
», 94. Python .. : - - 222 | » 110. Thecodonts . ° . 266
»s 95. Coluber . ° ° . 224 | » 111. Thecodontosaurus . ne
» 96. Poisonous Serpents . | 25 » 112. Palzosaurus . : . 267
» 113. Cladeiodon . . . 268
CHAPTER IV. | » 114. Protorosaurus F osaiee
»» 115. Megalosaurus d - 269
telecine 8 EL », 116. Thaumatosaurus 272
Section 97. Ophisaurians . . . 234 » 117. Ischyrodon . F ee
» 98. Scincoidians . - . 236 | » 118. Pecilopleuron ‘ <e
» 99. Chameleons . , + 238 | » 119. Pterodactylus : oe
» 100. Agamians . : . ib, | »» 120. Ichthyosaurus : es
» 101. Geckotians . ; . 240 »» 12]. Plesiosaurus . ; . 280
» 102. Iguanians 5 i - 4. », 122. Pleiosaurus . ; . 282
» 103. Iguanodon . = . 246 »» 1238. Crocodilians . - . 285
PAE T- £15,
DENTAL SYSTEM OF MAMMALS.
CHAPTER I. CHAPTER III.
GENERAL CHARACTERS OF THE TEETH OF TEETH OF BRUTA.
MAMMALS. Page
Page | Section 135. Orycteropus . : . 317
Section 124. Teeth absent or horny . 296 »» 136: Armadidlos--. ’ _ 329
» 125. Number . «ei. ot 2d. Sloth oS era
» 126. Form. . . . 297 », 138. Megatherioids . . 333
» 127. Attachment . ; - 300
» 128. Substance . 2 > stn CHAPTER IV.
ie iota cay ox 2 poe TEETH OF CETACEA.
» 130. Development . . . 304 : ;
Section 139. Balznidz : : . 345
CHAPTER II. » 140. Hyperoodon . : . 347
HORNY TEETH. » 141. Monodon ‘ - i
Section 131. Monotremes . : . 309 », 142. Delphinide . d . 350
», 132. Whales . a See 4G » 143. Physeter . : = ae
» 133. Hyperoodon . - . 316 » 144. Structure. ; » 355

» 134. Rytina . : . ae »» 145. Development . ‘ . 358

CONTENTS.

XVIlL
Page
Section 146. Zeuglodon . . 360
», 147. Halicore 364
» 148. Manatus tort
» 149. Halitherium . stole
CHAPTER V.
TEETH OF MARSUPIALIA.
Section 150. Sarcophaga . 373
», 151. Entomophaga . . 376
» 152. Carpophaga . . 381
» 1538. Poephaga . 388
» 154, Rhizophaga . . 393
, 155. Diprotodon . 394
» 156. Nototherium . . 896
,, 157. Microscopic Structure ib.
CHAPTER VI.
TEETH OF RODENTIA.
Section 158. Number and form . . 398

o>

2)

159. Structure 5 %
160. Succession . * - 410

. 404

CHAPTER VII.

TEETH OF INSECTIVORA,

Section 161. Talpidee . 412
» 162. Soricide . 416
» 163. Erinaceide . 419
» 164. Structure and Succession 420
CHAPTER VIII.
TEETH OF CHEIROPTERA.
Section 165. Number and Form. . 424

2)

166. Structure and Succession

429
CHAPTER IX.

TEETH OF QUADRUMANA,

Section 167. Galeopithecus. . 433
», 168. Cheiromys . : 435
», 169. Lemuride 5° 437
» 170. Platyrhines . r . 439
» 171. Catarhines . 441
» 172. Suecession and Structure 447

Section 173. Number and Form .

>?

Section

Isodactyle Ungulates .

Section

CHAPTER X.

TEETH OF BIMANA.

Page
. 451

174. Comparison of the deci-

duous teeth of the Orang,
Chimpanzee, and Human

Subject . 455
175. Succession ‘ . 457
176. Microscopic Structure . 458

177. Adaptation to the food and

nature of Man . 471
CHAPTER XI.
TEETH OF CARNIVORA.
178. General characters . . 473
179. Canide . - 475
180. Viverride : . 480
181. Hyena . - 482
182. Felide . . 486
183, Machairodus . . 490
184. Mustelidee . 494
185. Melide , . 498
186. Sub-Urside . : - 500
187. Urside . oul
188. Phocide. . 505
189. Composition and Micro-
scopic Structure . . 511
190. Classification of Molars of
Carnivora . f « 514

CHAPTER XII.

TEETH OF UNGULATA.

: . 523
191. Anoplotherium . Pay)
192. Ruminantia . 4 . ae
193. Microscopic Structure 537
194. Succession 540
195. Suide . A ‘ . 543
196: ue r 544
197. Phacocherus . ; . 549
198. Sucoession . 4 . 554
199. Microscopic Structure . 557

Section 200. Cheeropotamide

3)

o>

201. Hyracotherium

202. Cheropotamus

203. Hippohyus

204. Hippopotamus

205. Hexaprotodon

206. Merycopotamus .
207. Anthracotherium
208. Microscopic Structure
209. Succession

Anisodactyle Ungulates.

210. Equidze

211. Microscopic Structure
212. Succession

213. Toxodon : .
214. Elasmotherium :
215. Rhinoceros

CONTENTS.

Page
- 559
. 561
pi
- 562
- 563
- 566
oe
. 567
apni,
ov tl

. 572
. 576
. 580
. 582
- 587

ib.

Section 216.

217.
218.
219.
220.
221.
222.
223.
224.

225.
226.
227.
228.
229.

230.
231.

Microscopic Structure
Succession
Paleotherium.
Macrauchenia.
Tapirus .

Succession
Lophiodon
Coryphodon .
Dinotherium .

Proboscidians.

Mastodon. .
M. giganteus .
M. angustidens

XIX
Page
. 596
PRS bs,
Pe
. 602
. 604
. 605
. 606
. 607
. 609

. 613
. 616
- 618

Transitional Proboscidians 624

Elephas . : °
Microscopic Structure
Development .

- 625
. 640
. 648

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* ®

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INTRODUCTION.

TeeETH are firm substances attached to the parietes of the begin-
ning of the alimentary canal, adapted for seizing, lacerating, dividing
and triturating the food, and are the chief agents in the mechanical
part of the digestive function.

As secondary uses, arising out of the relations of co-existence
with other organs and endowments, or from a special development
of the teeth themselves, may be cited their subserviency to
speech(1), as ornaments, as characterizing age and sex(2), as in-
flictors of wounds either in combat(3) or defence(4), as aids to
locomotion(5), means of anchorage(6), implements of transport and
for working of building materials(7).

The dental system thus presents many and peculiar attractions
-to the anatomist and naturalist, for independently of the variety,
_ beauty and even occasional singularity of the form and structure
of the teeth themselves, they are so intimately related to the
food and habits of the animal as to become important if not essential
aids to the classification of existing species.

And, while the value of dental characters is enhanced by the
facility with which, from the position of the teeth, they may be
ascertained in living or recent animals, the durability of the teeth

renders them not less available to the Palzontologist in the determi-

(1) Man. (2) Orang, Narwhal. (3) Dog. (4) Elephant, Musk-deer. (5) Morse.
(6) Dinothere. (7) Beaver.

ll INTRODUCTION.

nation of the nature and affinities of extinct species, of whose organisa-
tion the teeth are not unfrequently the sole remains.

Teeth consist of a cellular and tubular basis of animal matter
containing earthy particles, a fluid, and a vascular pulp.

In general the earth is present in such quantity as to render the
tooth harder than bone, in which case the animal basis is gelatinous,
as in other hard parts where a great proportion of earth is combined
with animal matter. In avery few instances among the vertebrate
animals, the hardening material exists in a much smaller proportion,
and the animal basis is albuminous; the teeth here agree in both
chemical and physical qualities with horn.

True teeth consist of two or more tissues, characterized by
the proportions of their earthy and animal constituents, and by the
size, fcrm and direction of the cavities in the animal basis which
contain the earth, the fluid or the vascular pulp.

The tissue, which forms the chief part or body of the tooth,
has, hitherto, received no distinct and specific name in our
language ; a particular modification of it, which characterizes the
tusks of the elephant, is called ‘ ivory.” Some Anatomists
have extended the application of this term to the analogous sub-
stance in all teeth ; others have treated of it under the name of the
‘ bone of the tooth’(1) or ‘ tooth-bone’; by the German Anatomists
it is termed ‘ knochensubstanz’, ‘ zahnbein’ and ‘ zahnsubstanz’;
and some of the latest and most close-thinking writers on
dental anatomy have preferred the Jiteral translation of one or
other of these terms to the use of the word ‘ivory’, which

eunavoidably recalls the idea of the peculiar modification of the

(1) Hunter, Natural History of the Human Teeth. Bell’s Ed. 1835, Svo. p. 15, 16.

INTRODUCTION. ill

* tooth-substance’ in the elephant’s tusk, to which it is restricted
in common language and in the best zoological works.(1) I propose
to call the substance which forms the main part of all teeth ‘ den-
tine.’ (2)

The second tissue, which is the most exterior in situation, is the
* cement’(3).

The third tissue, which, when present, is situated between the
dentine and cement is the ‘ enamel’(4).

‘ Dentine’ consists of an organized animal basis disposed in the
form of extremely minute tubes and cells, and of earthy particles :
these particles have a two-fold arrangement, being either blended
with the animal matter of the interspaces and parietes of the tubes
and cells, or contained in a minutely and irregularly granular state
in their cavities.

The density of the dentine arises principally from the propor-
tion of earth in the first of these siates of combination ; the tubes and
cells contain, besides the granular earth, a colourless fluid, probably

transuded ‘ plasma’ or ‘ liquor sanguinis,’ and thus relate not only

(1) The accurate Illiger distinguishes the ‘ substantia ossea’ of a tooth from ‘ ebur,’ and
separately defines both these modifications of the tooth substance. Prodromus Systematis Mam-
malium, 8vo. 1811, p. 20.

(2) Dentinum.—Besides the advantage of a substantive name for an unquestionably distinct
tissue under all its modifications in the animal kingdom, the term ‘dentine’ may be inflected
adjectively, and the properties of this tissue be described without the necessity of periphrasis;
thus we may speak of the ‘ dentinal’ pulp, ‘dentinal’ tubes or cells, as distinct from the
corresponding properties of the other constituents of a tooth. The term ‘ dental’ will retain
its ordinary sense, as relating to the entire tooth or system of teeth.

(3) Camentum, Cortex osseus, Tenon. Crusta petrosa, Blake.

(4) Encaustum, Adamas, Substantia vitrea.

a2

lv INTRODUCTION.

to the mechanical conditions of the tooth, but to the nutrition of the
dentine.

Dentine, thus organized, is ‘unvascular’: the teeth of most
mammals and reptiles, and of a few fishes present this modification
of their main constituent. But the dentine in the teeth of most
fishes, of a few mammals, and of still fewer reptiles, is traversed by
canals containing blood vessels or a vascular pulp; the tooth-
substance, thus modified, I term ‘ vascular dentine.’ Both the
‘vascular’ and ‘ unvascular dentine’ may be present in the same
tooth, as in those of the sloth, the walrus, and the cachalot:
the transition from the vascular dentine to true bone is gradual
and close.

‘Cement’ always closely corresponds in texture with the
osseous tissue of the same animal, and wherever it occurs of sufficient
thickness, as upon the teeth of the horse, sloth or ruminants,
it is also traversed, like bone, by vascular canals. In reptiles and
mammals, in which the animal basis of the bones of the skeleton is
excavated by minute radiated cells, forming with their contents
the ‘corpuscles of Purkinjé’, these are likewise present, of similar
size and form, in the ‘cement’, and are its chief characteristic
as a constituent of the tooth. The hardening material of the
cement is partly segregated and combined with the parietes of the
radiated cells and canals, and is partly contained in aggregated
grains in the cells, which are thus rendered opake.

The relative density of the dentine and cement varies according
to the proportion of the earthy material, and chiefly of that part
which is combined with the animal matter in the walls of the cavities,
as compared with the size and number of the cavities themselves.

In the complex grinders of the elephant, the masqued boar and the

INTRODUCTION. Vv

capibara, the cement, which forms nearly half the mass of the
tooth, wears down sooner than the dentine.

The ‘enamel’ is the hardest constituent of a tooth, and conse-
quently the hardest of animal tissues; but it consists, like the
other dental substances, of earthy matter arranged by organic forces
in an animal matrix. Here, however, the earth is mainly contained
in the canals of the animal membrane, and, in mammals and reptiles,
completely fills those canals, which are comparatively wide, whilst
their parietes are of extreme tenuity. The hardening salts of
the enamel are not only present in far greater proportion than in the
other dental tissues, but, in some animals, are peculiarly distinguished
by the presence of fluat of lime.

The absolute and relative size, form, disposition, direction and
intercommunication of the cellular and tubular cavities characterizing
the several tissues of the teeth will be the subjects of the special
descriptions of these organs in the different classes and species of
animals ; but a brief notice of the leading steps to the present
knowledge of the structure peculiar to each tissue may be appro-

priately given in this place(1).

In a retrospect of the history of the science of the orga-
nization of animal bodies, anatomy may always be perceived
to have made a marked advance in connection with the progress
of some collateral science. With regard to the hard parts of our
frame in particular, our knowledge of the elementary constitution

of the earthy salts has been due to the refinement of chemical

(1) The review here given of the discovery of the tubular structure of the dentine is
essentially the same as that prefixed to my own observations on the subject communicated to

the British Association in August, 1838.—See Trans. of the Brit. Assoc. 1838, p. 135.

vi INTRODUCTION.

analysis: the late improvements in mechanical optics have led
to a resumption of the microscopical observations originally
commenced by Malpighi and Leeuwenhoek; and the consequent
acquisition of more exact knowledge of the mode in which the
particles of the phosphate of lime and other salts are arranged in
the animal basis or matrix of bone and tooth.

As regards the teeth, the principle of chief import to the physio-
logist arises out of the fact, which has been established by microscopic
investigations, that the earthy particles of dentine are not confusedly
blended with the animal basis, and the substance arranged in superim-
posed layers; but that these particles are built up, with the animal basis
as a cement, in the form of tubes or hollow columns, in the predeter-
mined arrangement of which there may be discerned the same relation
to the acquisition of strength and power of resistance in the due
direction, as in the disposition of the columns and beams of a work

of human architecture.
| The disposition of the calcareous particles of bone in the
parietes of the Haversian canals, Purkinjian cells and of the fine
tubes which radiate from these cavities, was ascertained before the ana-
logous conditions of the intimate structure of dentine were discovered.
Until a recent period the analogy of dentine to bone was
supposed to be confined to their chemical constitution, and the
nature of the hardening material; while the arrangement, as well
as the mode of deposition of the firm tissue, were considered to be
wholly different from that of bone, and the dentine to agree in its
general nature and mode of growth with hair and other extravas-
cular horny parts, with which most teeth closely correspond in their
vital properties.

The structure of a tooth, in fact, was regarded as simply

INTRODUCTION. Vil

laminated, and the ivory was described as being formed layer within
layer, deposited by, and moulded upon the formative superficies of
the vascular pulp. The illustrations and supposed proofs of this
structure and mode of growth were derived from the apparently
_ detached condition of the newly-formed particles of dentine on the
pulp’s surface when exposed by the removal of the calcified part
of the tooth ; from the appearances observed in the teeth of animals
fed alternately with madder and ordinary food, which undoubtedly
illustrate the true progress of dental development ; from the illusory
traces of laminated structure observed in vertical sections of teeth
when viewed by the naked eye, or with a low magnifying power ; and
lastly, and chiefly, from the successive hollow cones into which
a tooth is commonly resolved in the process of decomposition.

With regard, however, to the appearances presented by the teeth
of animals under the influence of madder, and to the separation of the
dentine into superimposed lamelle during decomposition, the same
conclusions as to intimate structure and mode of development might
be drawn respecting true bone, which also commonly resolves itself
into concentric lamelle during decomposition, and presents the
same appearance of alternate white and red layers in animals fed
alternately with madder and ordinary food during the progress of its
growth.

The lines running parallel to each other and to the contour of
the crown presented by the cut surfaces of vertical sections of teeth,
especially of the elephant’s tusk, or of the tooth of the cachalot, are
due to a totally different structure from that to which they have been
ascribed. ‘The lamellated arrangement, thus seemingly demonstrated,
is, moreover, far from being a constant appearance ; on the contrary,

the superficies of vertically cut or fractured surfaces of the human

Vill INTRODUCTION.

and most other teeth, offer a very different character, and one
which has led to many approximations and allusions to the true
structure of dentine, in the works of anatomists who have recorded
their own original observations.

Whoever attentively observes a polished section or a fractured
surface of a human tooth may learn, even with the naked eye, that
the silky and iridescent lustre reflected from it in certain directions
is due to the presence of a fine fibrous structure.

Malpighi, in whose works may be detected the germs of many
important anatomical truths that have subsequently been matured
and established, says that the teeth consist of two parts, of which
the internal bony layers (dentine) seem to be composed of fibrous,
and as it were, tendinous capillaments reticularly interwoven. (1)

Retzius cites many recent authors, as Seemmering, Schreger(2) and
Weber, (3) who mention the silky glistening lustre of the dentine ; and
Frederick Cuvier in the preliminary discourse of his admirable work
the ‘ Dents des Mammiféres,’ observes: ‘‘ Les dents de l’homme, de
singes, de carnassiers ont un ivoire d’apparence soyeuse, qui semble
formé de fibres,” p. xxvii. These intelligible hints of the true struc-
ture of the dentine, which the foregoing observers received from a
superficial but unprejudiced inspection, failed, however, to incite them
to a closer interrogation of Nature.

One of her more persevering investigators had, nevertheless, long
before obtained a true and definite answer to his more direct in-

quiries. Leeuwenhoek, having applied his microscopical observations

(1) “ Duplici excitantur parte, quarum interior ossea lamella fibrosis et quasi tendinosi

capillamentis in naturam implicetis constat.””—Anatome Plantarum, Lugd. Batav. 1687, p. 37.
(2) Isenflamm und Rosenmiillers Beitragen zur Zergliederungskunst, band i, p. 3, (1800).
(3) See his Edition of “ Hildebrand’s Handbuch der Anatomie,” band i, p. 206.

INTRODUCTION. 1X

to the structure of the teeth, discovered that the apparent fibres were
really tubes, and he communicated a brief but succinct account of his
discovery to the Royal Society of London,(1) which was published,
together with a figure of the tubes, in the 140th Number of their
Transactions. This figure of the dentinal tubes, with additional
observations, again appears in the Latin edition of Leeuwenhoek’s
works, published at Leyden in 1730. The dental substance (dentine) of
the human teeth, and of those taken from young hogs is described as
being ‘‘ formed of tubuli spreading from the cavity in the centre to
the circumference.” He computed that he saw a hundred and
twenty of the tubuli within the forty-fifth part of an inch. (2)

Leeuwenhoek also shows that he was aware of the peculiar
substance, distinct from the ivory and enamel, and now termed
the cement or crusta petrosa, which enters into the composition of
the teeth of the horse and ox(3) ; a component part of the tooth which
Hunter speaks of as a second kind of bone; and which was first
accurately and specifically described by Tenon and Blake.

But these microscopical discoveries may be said to have appeared
before their time: the contemporaries of Leeuwenhoek were not
prepared to appreciate them; besides, they could neither repeat
nor confirm them, for his means of observation were peculiarly his
own: and hence it has happened that, with the exception of the

learned Portal,(4) they have either escaped notice, or have been

(1) Microscopical Observations on the Structure of Teeth and other Bones.—Philos. Trans.
1678, p. 1002.

(2) See Hoole’s Translation of the select works of Leeuwenhoek, 4to. 1798, p. 114.

(3) Parvimolares, quos bos, dum ad huc admodum juvenis sive vitulus, habuerat, undiquaque
alio osse circumducti erant ’’ Continuatio Epistolarum, 4to. Lugd. Bat. 1689, p. 7.

(4) Histoire de ]’Anatomie et de la Chirurgie, Paris, 1770, Tom. iil, p. 460, in which

x INTRODUCTION.

,

designedly rejected by all anatomists until the time of the confir-
mation of their exactness and truth by Purkinjé in 1835.

The results of the laborious investigations of this most original
and indefatigable observer were published, as is the custom in many
German Universities, in two inaugural thesises, the one by Fraenkel
entitled ‘‘ De penitiori dentium humanorum structura observationes ;”
the other by Raschskow, entitled “‘ Meletemata circa dentium
evolutionem ;’’ both of which were defended in the University of
Breslau in the month of October, 1835.

Purkinjé states that the dentine (zahnsubstanz, substantia dentis)
consists, not of superimposed layers, but of fibres arranged in a
homogeneous intermediate tissue, parallel with one another, and
perpendicular to the surface of the tooth, running in a somewhat
wavy course from the internal to the external surface; and he
believed these fibres to be really tubular, because on bringing ink
into contact with them, it was drawn in as if by capillary attraction. (1)

Upon the publication of this discovery it was immediately put
to the test by Professor Miller, by whom the tubular structure of the

ivory was not only confirmed, but the nature and one of the offices

Leeuwenhoek’s Letter to the Royal Society is noticed as follows : ‘‘ Les dents sont composées de
trés petits tuyaux transparents et étroits, dont six ou sept cents égalent a peine un poil de la
barbe.” The merit of directing the attention of anatomists to Leeuwenhoek’s discovery of
the structure of dentine is due to Retzius.

' (1) Cruorine extravasated during intense inflammation of the pulp, or by an over-disten-
-sion of the vessels produced mechanically as in hanging or drowning, would in like manner be
carried, with the plasma, into the dentinal tubes, and occasion red spots in the tooth-substance ;
the bile-stained serum, in the case of jaundice, would equally affect the capillary tissue of the
tooth with its peculiar tinge; but it does not follow that the tubes which imbibe such coloured
fluids must necessarily be capillary blood-vessels, and these phenomena, therefore, afford no

proof of the vascularity of human dentine.

INTRODUCTION. Xl

of the tubes were determined. He observed that the white colour
of a tooth was confined to these tubes, which were imbedded in a
semi-transparent substance, and he found that the whiteness and
opacity of the tubes were removed by acids. On breaking a
thin lamella of a tooth transversely with regard to its fibres, and
examining the edge of the fracture, Miiller perceived tubes pro-
jecting here and there from the surfaces; they were white and
opaque, stiff, straight, and apparently not flexible: this appearance
is well represented in the old figure by Leeuwenhoek. If the lamellee
had been previously acted upon by acid, the projecting tubes were
flexible and transparent, and often very long. Hence, Professor
Miiller inferred that the tubes have distinct walls, consisting of an
animal tissue; and that, besides containing earthy matter in their
interior, their tissue is, in the natural state, impregnated with
calcareous salts.

Thus, the discovery by microscopical examinations that the
dentine of the teeth in man and various animals was traversed by
minute tubes disposed in a radiated arrangement in lines proceeding
every where perpendicularly from the surface of the cavity containing
the pulp, may be regarded as established, and to be due principally
to the learned and ingenious Purkinjé, who, however, was all the
while unconscious that he had been anticipated, as to the main fact,
a long time before, by Leeuwenhoek.

But the tubular structure of ivory is not the only important
fact in dental anatomy, made known in the Breslau Thesises
of 1835. Purkinjé also discovered that the distinct layer of
substance, previously known to surround the fang of the simple

teeth of man and many mammalia, contained corpuscles like those

xii INTRODUCTION.

which characterize the structure of true bone: and he observed in
one instance that this bone-like substance was continued upon the
enamel of the crown of a human incisor.

This fact I have confirmed(l) as regards the human teeth and
the simple teeth of many mammals and reptiles. The layer of
coronal cement varies in thickness ; its tenuity is extreme in the teeth
of man and the quadrumana.

Purkinjé also found that the third substance, crusta petrosa or
cement of compound teeth, as those of the horse and ox, was
in like manner characterized by the presence of numerous bone-
corpuscules or cells; and thus proved that the difference between
the so called simple and compound teeth depended, not on the pre-
sence of a third and additional substance in the latter, but on its
greater abundance and different disposition in the tooth.

At the time that these observations, were being made’ at Breslau
and Berlin, it appears that similar investigations had been set on foot
at Stockholm. Professor Retzius of the University in that city
informs us that he had been led by the iridescence of the fractured
surface of the substance of a tooth to conceive that that appearance
was due, as in the crystalline lens, to a fine fibrous structure, and
that he communicated his opinions as to the regular arrangement of
these fibres to some of his colleagues in 1854; and that the Uni-
versity having obtained, in the summer of 1835, a powerful micros-
cope, by Plessl of Vienna, he commenced a series of more exact
researches on the intimate structure of the teeth in man and the
lower animals. He operated on thin sections of teeth both before, and

after, the removal of the earthy matter by means of acid, and atten-

(1) Trans. Brit. Assoc. 1838, vol. vii, p. 136.

INTRODUCTION. xii

tively examined the fractured and polished surfaces of the ivory part :
he determined the exact arrangement, course, and size of the
tubuli in the teeth of different animals, and detected the finer rami-
fications given off by the tubuli during their divergence,(1) and the
anastomoses of their finest terminal branches with the cells in the
intertubular, or as it is sometimes termed, interfibrous tissue.

Retzius also claims to have discovered the radiated or purkin-
Jian corpuscles(2) in the dentine ; and to have thus succeeded in dis-
playing a far greater identity between tooth-bone and proper bone
than had been before anticipated.

He exhibited the preparations and drawings illustrative of these
interesting observations to Berzelius, Urede, and Professor Wahlberg
at the latter end of 1835; being then unacquainted with the disco-
veries of Purkinjé; and communicated his researches to the Royal
Academy of Sciences at Stockholm on the 13th of January, 1836.
They were published in the same year in those Transactions and in
the following year as a distinct treatise(3).

At the early part of that year, 1837, I received from Mr. Darwip

(1) Leeuwenhoek appears to have suspected the existence of such branches ; he says,“ upon
examining the tubuli round about this small cavity (the pulp-cavity) I perceived that they all
arose from thence and spread themselves all round towards the circumference. I endeavoured
to examine still farther, beyond the part where this cavity ended, in order to discover whether
from these first-formed tubuli others might not arise or branch forth; but this part of nature’s
work was inscrutable to me.” Hoole’s Leeuwenhoek, 4to. p. 113.

(2) J have not yet been able to detect the radiated cells or corpuscles in the dentine of the
horse’s tooth, in which they are described by Retzius; but they are very numerous and con-
spicuous at the peripheral portion of the dentine of the dugong’s grinder, pl. 94.

(3) Mikroskopiska Undersékningar éfver Jadernes sardeles Tandbenets struktur : Stock-
holm, 1837.

XIV INTRODUCTION.

many fragments of the teeth of the extinct Megatherium, Megalonyz,
Mylodon and Toxodon collected during hig travels in South America.
Some of these fragments were in a state of incipient decomposition :
and my attention was forcibly arrested by the fact that these frag-
ments, instead of being resolved, like the fossil tusks of the mammoth
and mastodon, into parallel superimposed conical lamelle, separated
into fine fibres, arranged at right angles to the plane of the layers
which, according to the lamellar theory of dental structure, ought
to have presented themselves to view. I exhibited the most cha-
racteristic of these specimens at my lectures on the teeth, at the
Royal College of Surgeons, in May, 1837, and stated that ‘‘ the
appearances which they presented were inexplicable on the lamellar
hypothesis: but that I should investigate the subject further, and
endeavour to elucidate the apparent anomaly before the following
session.” At the conclusion of that course, I had sections of these
fragments prepared for the microscope ; and stimulated by the amount
of clearly defined and beautiful structure which they exhibited,(1) 1
proceeded to examine similar sections of the human teeth and of
those of many of the lower animals. The excitement of the research
became heightened as the sphere of observation expanded, and I had
collected extensive materials for a Treatise expressly on the Structure
of Teeth, when the fourth number of Miiller’s Archiv fur Physiologie,
for the year 1837, containing an Analysis of Purkinjé’s and Fraenkel’s
Treatise, came into my hands, in December, 1837, and awoke me from
the dream of discovery in which I had been indulging. I received,
shortly after, the fifth number of the same volume of Miiller’s Archiv,

containing Dr. Creplin’s German Translation of the Treatise of Retzius,

(1) See Plates 79 and 84.

INTRODUCTION. XV

upon the perusal of which I abandoned my intention of publishing
those general observations on the structure of the teeth which I had
before deemed to be new, but now found to have been mainly anti-
cipated by Purkinjé and Retzius.

I was not, however, discouraged by this disappointment, but,
feeling convinced that no work on the Comparative Anatomy of the
Teeth would henceforth be regarded as complete without an account
of the leading modifications of the dentinal tissue in the different
classes of animals, I proceeded to the microscopical investigation of
that tissue in many animals in which it had not been previously so
examined. The number of characteristic differences which presented
themselves, and which are described in the body of the present work,
led to the perception of the value of the microscopic structure of
the teeth as a test of the affinities of extinct animals, and to the insti-
tution of researches into the laws of development of the dental tissues,
which, as then accepted and taught, were irreconcileable with the
general demonstration of the intimate structure of those tissues which
was yielded by the teeth of fishes, reptiles and mammals. (1)

The prelude to this generalization may be summarily recapitu-
lated as follows: the discovery of Leeuwenhoek that the dentine
was made up of very minute tubes, which proceeded from the inner
to the outer surface of the tooth, was confirmed by Purkinjé, so far
as regarded their existence ; but Purkinjé added an exact and particular
account of the direction of these tubes in the human dentine, and

showed that, in addition to them the dentine contained an interme-

(1) The chief results of these researches have been successively communicated to the
British Association at the Newcastle Meeting, August, 1838, (Transactions of the Association,
vol. vii, p. 135;) in the Proceedings of the Geological Society for 1838 and 1839, and in the

Comptes Rendus de l’Académie: des Sciences, December 12, 1839.

Xvi INTRODUCTION.

diate or inter-tubular tissue ; this he describes as homogeneous and
without structure, and as entering into the composition of the dentine
in a greater proportion than the tubes themselves.

The more extensive, varied and minute observations of Professor
Retzius led to the discovery of the celis of the intertubular
tissue, of the ramuli sent off from the main calcigerous tubes
into that tissue, and of the anastomoses of the ramuli with each other,
with the intertubular cells, and with the cells at the periphery of
the dentine. According to the researches of Dr. Schwann the
animal basis of the intertubular tissue possesses a fibrous structure.

Besides the primary and secondary branches of the calcigerous
tubes Retzius first clearly described their curvatures and undulations,
which may be defined as follows: as a general rule the dentinal
tubes are directed, as affirmed by Leeuwenhoek and Purkinjé, from the
inner to the outer surface of the tooth, and vertically to those sur-
faces; but in their course the tubes describe two, three, or more
curvatures, appreciable by a low magnifying power: these I have
termed the ‘ primary curvatures.’(1) With a higher power, the tubes
are seen to be bent throughout the whole of their flexuous course into
minute and equal oblique undulations or gyrations, two hundred of
which were counted by Retzius in one tenth part of an inch’s length
of a human calcigerous tube ; these I have termed the ‘ secondary
curvatures’ or gyrations.(2) Both the primary and secondary curva-
tures of one tube are usually parallel with those of the contiguous
calcigerous tubes, and from the radiated course of these tubes they

occasion the appearance of lines running parallel with the external

(1) Trans. Brit. Assoc. vol. vii, p. 148. See Plates 24, fig. 1; 64 A, fig. 2; 74, fig. 1; 94.
(2) Ibid, p.141. See Plates 16, fig. 3; 24, fig. 2; 64 a, fig. 3.

INTRODUCTION. Xvi

contour of the tooth; for, when the surface of a longitudinal section
of a tooth is viewed with the naked eye, the light is differently reflected
from the different parts of the oblique secondary curves of the
tube on which it falls ; but the curves being parallel to each other and
to the superficial contour of the section, they appear like the cut
edges of a series of parallel and super-imposed lamelle. In many
teeth, moreover, and especially in the tusks of the elephant, the se-
condary branches of the dentinal tubes dilate into intertubular cells
along lines, which in like manner are parallel to the coronal contour
of the tooth; hence another cause of the appearance of concentric
lamellz and of the actual decomposition of such teeth into super-im-

posed lamelliform cones.

Such appearances and modes of decomposition are peculiar to
the dense or unvascular dentine; but are by no means common to
that modification of the tissue. They are never witnessed in any of
the varieties of vascular dentine.(1) |The prolongation or persistence
of cylindrical canals of the pulp-cavity in the dentinal tissue, which
is the essential character of vascular dentine, manifests itself under a
variety of forms. In mammals and reptiles these canals, which J have
termed ‘medullary’ (2) from their close analogy with the so called canals
of bone, are straight and more or less parallel with each other ;_ they
bifurcate, though rarely ; and when they anastomose, as in the megathe-
rium, it is by a loop at, or near, the periphery of the vascular dentine.

In the teeth of fishes, in which the distinction between the dentinal

(1) This substance was first characterised as a component of tooth, ‘ distinct from ivory,
enamel, cement, and true bone, and as easily recognisable,’ in my paper communicated to the
British Association, in 1838 ; loc. cit. p. 137.

(2) Ibid.

XVill INTRODUCTION.

and osseous tissues is gradually effaced, the medullary canals of the
vascular dentine, though in some instances straight and parallel and
sparingly divided or united, yet are generally more or less bent,
frequently and successively branched, and the subdivisions blended
together in so many parts of the tooth as to form a rich reticulation.
The calcigerous tubes sent off into the interspaces of the net-work
partake of the irregular character of the canals from which they
spring, and fillthe meshes with a moss-like plexus.(1)

Closely analogous to this modification of the vascular dentine,
but differing in the presence of the radiated cells, is the tissue into
which the residue of the pulp is converted in the teeth of certain
reptiles, as the Iguanodon, Hyleosaurus and Ichthyosaurus, and of
those of a few mammalia, as the Cachalot(2). This tissue approaches,
in the combined presence of medullary canals and calcigerous cells,
as closely to that of the skeleton of the species in which it occurs,
as the reticulate modification of the vascular dentine in the teeth
of fishes does to the osseous tissue of their skeleton. It has been
uniformly described by the authors who have observed it, as Cu-
vier(3) and Conybeare,(4) as the result of ossification of the pulp.

If the first described modification of vascular dentine, which
forms the chief part of the teeth of the Sloths and Megatherium,
be regarded as a fourth dental tissue, this second modification of
vascular dentine, from its closer resemblance to bone might be reck-
oned as a fifth; in proportion, however, as it resembles bone, so
likewise it approaches to the structure of cement.

(1) See Plates 6, 7, 53, 54, 55.

(2) Plate 89, fig. 2, c.

(3) Lecons d’Anat. Comp. 1°. ed. tom. ili, p. 113; Ossem. Fossiles, 2°. ed. tom. v. 2°. partie,
p- 274.

(4) “ The teeth in these genera (the Lacertz) become completely solid, its interior cavity

being filled up by the ossification of the pulpy substance,”—Trans. Geol. Soc. vol. vi. p. 106.

INTRODUCTION. X1X

The organized structure and microscopic character of the cement
were first determined by Purkinjé and Faenkel ; and the acquisition of
these facts led to the detection of the tissue, as has been already
observed, in the simple teeth of man and carnivorous animals. The
cement is most conspicuous where it invests the fang of the tooth,
and increases in thickness as it approaches the apex of the fang.
The animal constituent of this part of the cement had been recognized
by Berzelius, as a distinct investment of the dentine, long before the
tissue of which it formed the basis was clearly recognized in simple
teeth. Berzelius describes the cemental membrane as being less
consistent than the animal basis of the dentine, but resisting longer
the solvent action of boiling water, and retaining some fine . particles
of the earthy phosphates when all such earth had been extracted from
the dentinal tissue. Cuvier, likewise, states that the cement is dis-
solved with more difficulty in acid than the other dental tissues.
Retzius, however, states that the earth is sooner extracted by acid
from the cement than from the dentine of the teeth of the horse.

In recent mammalian cement the radiated cells, like the
dentinal tubes, owe their whiteness and opacity to the earth which
they contain. According to Retzius, ‘‘ numerous tubes radiate from
the cells, which, being dilated at their point of commencement, give
the cell the appearance of an irregular star. These tubes form
numerous combinations with each other, partly direct and partly
by means of fine branches, of isumth to sao of an inch in diameter.

“‘ The cells often vary in size, and some put on the appearance
of a canal or tube; this is especially seen in recently formed
cement. The average size of the Purkinjian cells in human cement
is ;qwth of aninch. In sections made transversely to the axis of the

tooth it is clearly seen that these cells are arranged in parallel or
b2

XxX INTRODUCTION.

concentric strie, of which some are more clearly and others more
faintly visible, as if the cement were deposited in fine and coherent
layers. The layer of cement is found in the deciduous teeth, but
is relatively thinner and the Purkinjian cells are more irregular.

‘“« Tn growing teeth with fangs not fully formed, the cement is
so thin that the Purkinjian cells are not visible: it looks like a fine
membrane, and has been described as the periosteum of the fangs,
but it increases in thickness with the’age of the tooth, and is the
seat and origin of what are called exostoses of the fang which are
wholly composed of it.” These growths are subject to the formation
of abscess, and all the other morbid actions of true bone.

It is the presence of this osseous substance which renders
intelligible many well-known experiments of which human teeth
have been the subjects ; such as their transplantation and adhesion
into the combs of cocks, and the establishment of a vascular con-
nection between the tooth and the comb; the appearances which the
Hunterian specimens of these experiments present, and of the reality
of which Professor Miller satisfied himself during his visit to
London, are no longer perplexing, now that we know that the surface
of the tooth, in contact with, and adhering to the vascular comb,
is coraposed of a well organised tissue, closely resembling bone.

This correspondence of the cement, which, when it exists in
sufficient quantity, becomes almost identity, with true bone, is illus-
trated by the varieties of microscopic structure which the cement
presents in different classes of animals, and which always correspond
with the modifications of the osseous tissue of the skeleton in those
animals; thus the cement in the osseous fishes, in which the bone
is not characterized by the radiated calcigerous cells, likewise ceases

to present that character; and, in reptiles and mammals in which

INTRODUCTION. XXl

the radiated cells are present in the bone of the skeleton and in the
dental cement there is a close conformity as to their size and shape
in both tissues.

The most remarkable modification of mammalian cement is
presented by the thick layer of that substance which invests the
molars of the extinct megatherium ;(1) besides abounding in calcige-
rous cells it is here traversed by straight, parallel and occasionally
bifurcated medullary canals, arranged with regular intervals, and
directed from the exterior of the tooth somewhat obliquely to the
surface of the unvascular dentine, close to which they anastomose
by loops, corresponding with, and opposite to those formed by the
medullary canals of the vascular dentine of the same tooth(2).

Under every modification the cement is the most highly organ-
ized and most vascular of the dental tissues, and its chief use is to
form the bond of vital union between the denser and commonly un-
vascular constituents of the tooth and the bone in which the tooth is
implanted. Ina few reptiles (now extinct) and in the herbivorous
mammalia the cement not only invests the exterior of the teeth, but
penetrates their substance in vertical folds, varying in number, form,
extent, thickness and degree of complexity, and contributing to main-
tain that inequality of the grinding surface of the tooth which is
essential to its function as an instrument for the comminution of vege-

table substances.
The higher an animal is placed in the scale of organization, the
more distinct and characteristic are not only the various organs of

the body, but the different tissues which enter into their composition.

(1) Plate 84, 6. (2) Pl. 84, a.

XXli INTRODUCTION.

This law is well exemplified in the teeth, although in the comparison
of these organs we are necessarily limited to the range of a single
primary group of animals. We have seen, for example, that the
dentine is scarcely distinguishable from the tissue of the skeleton in
the majority of fishes: but that its peculiarly dense, unvascular
and resisting structure, which is the exceptional condition in fishes,
is its prevalent character in the teeth of the higher vertebrates.

So likewise with the enamel; this substance, which under all
its conditions bears a close analogy with the dentine, is hardly distin-
guishable from that tissue in the teeth of many fishes(1). The fine cal-
cigerous tubes are present in both substances, and undergo similar sub-
divisions ; the directions only of the trunks and branches being re-
versed, agreeably with the contrary course of their respective develop-
ments. The proportion of animal matter is also greater in the enamel
of the teeth of fishes than of the higher vertebrata; and the propor-
tion of the calcareous salts incorporated with the animal constituent
of the walls of the tubes is greater as compared with the sub-crystal-
line part deposited in the tubular cavities. In reptiles, the proportion
of the hardening salts and consequently the density of the enamel are
increased, but the course, size, and ramification of the calcigerous
tubes still bear considerable analogy to those of the dentine ; and the
prismatic form of the calcigerous tubes,(2) their minute striations,
and the superficial transverse wavy linear ridges, which constitute
the characteristic features of the enamel in the mammalian class, are
not present in that tissue in the cold-blooded vertebrates.

The enamel is the least constant of the dental tissues : it is more

(1) Sargus, Pl. 43, fig. 2; Phyllodus, Pl. 44, fig. 2; Scarus, Pl. 50, Pl. 52.

(2) I apply this term to the so-called prismatic fibres of human and other mammalian

enamel for reasons which will appear in the sequel.

INTRODUCTION. XXHl

frequently absent than present in the teeth of the class of fishes; it
is wanting in the entire order Ophidia among existing reptiles ; and
it forms no part of the teeth of the Edentata and many Cetacea
among mammals.

The enamel may be distinguished, independently of its micro-
scopic and structural characters, by its glistening, subtransparent
substance, which is white or bluish-white by reflected light, but of a
gray-brown colour when viewed, under the microscope, by transmitted
light.

The microscopical characters of the enamel have hitherto been
taken from the modification of that tissue in the class Mammalia,
where it presents its most distinctive and consequently highest
condition.

This condition of the enamel, however, like the corresponding
one of the mammalian dentine, in the same degree as it distinguishes
them from the true osseous tissue, and perfects them for their
mechanical applications, removes them from the influence of the
conservative and reparative powers of the living organism. The
mammalian enamel, therefore, once formed and exposed, is least able
to resist vitally the influence of the external decomposing forces ;
but this inferiority is amply compensated by its superior mechanical
endowments. Nevertheless, it undergoes more change, after becom-
ing exposed by the eruption of the tooth, than does either
the dentine or cement, especially in regard to its original mem-
branous constituent ; and no true idea of its organic structure can
be obtained except by an examination soon after its formation.

The enamel of the molar tooth of a calf, which has just begun to
appear above the gum, and which can readily be detached from the

dentine, especially near the commencement of the fangs, is resolvable

XXIV INTRODUCTION.

into apparently fine prismatic fibres; if these fibres be separately
treated with dilute muriatic acid and the residue examined, with a
moderate magnifying power, in distilled water, or, better, in dilute |
alcohol, portions of more or less perfect membranous, sheaths or tubes
will be discerned, which inclosed the earthy matter of the minute
prism, and served as the mould in which it was deposited.

Professor Retzius, who obtained a small portion of organic or
animal substance from the enamel-fibres of an incompletely-formed
tooth of a horse, conjectured that it was a deposition of that fluid
which originally surrounds the loose enamel-fibres, and that, “‘ in
proportion as these fibres are pressed tighter together, and additional
fibres are wedged between them, the organic deposition is forced
away.”

It is certain that the small proportion of animal matter which can
be obtained from the enamel of a tooth, that has been completely
formed and in use, does not yield any indication of its primitive or-
ganic form; this may, however, be ascertained, if the enamel be
examined under the conditions above described. The tubular struc-
ture of the membranous constituent of recently formed enamel has
been observed by Dr. Schwann(1) in the teeth of the hog: and he
has shown that the fine membrane of the enamel-prism is not a mere
deposition from the fluid in which the new-formed prisms are bathed,
but an organized part specially formed and arranged in the enamel
pulp in order to ensure the right disposition and direction of the cal-
careous salts of the enamel.

Retzius accurately describes the enamel-fibres of the horse as
presenting the form of angular needles, about ,i<@th of an inch in
diameter, which are traversed by minute and close-set transverse

(1) Loe. cit. p. 118.

INTRODUCTION. XXV

strie, over the whole, or a part of the fibre; and he conjectures that
if the enamel-fibre be amass of the calcareous salts, surrounded by
an organic capsule, that the striz may then belong to the capsule and
not to the enamel-fibre. The later researches of Dr. Schwann add to
the probability of this conjecture, and the absence of the minute striz
in the enamel of fossil mammalian teeth, at least in the examples
which I have submitted to microscopic investigation, may depend
upon the destruction of the original organic constituent of the
enamel.

The enamel-fibres are directed at nearly right angles to the sur-
face of the dentine, and their central or inner extremities rest in slight
but regular depressions on the periphery of the coronal dentine. Thus
in the human tooth, the fibres which constitute the masticating surface
are perpendicular or nearly so to that surface, while those at the lower
part of the crown are transverse, and consequently have a position best
adapted for resisting the pressure of the contiguous teeth, and for
meeting the direction in which external forces are most likely to im-
pinge upon the exposed crown of the tooth. The strength of the enamel
fibres is further increased by the graceful wavy curves in which they
are disposed ; these curves are in some places parallel, in others opposed ;
their concavities are commonly turned towards each other where the
shorter fibres, which do not reach the exterior of the enamel, abut by
their gradually attenuated peripheral extremities upon the longer fibres.
Other shorter enamel-fibres extend from the outer surface of the enamel
towards the dentine and are wedged into the interspaces of the longer
fibres. In the teeth of fishes, the caicigerous tubes or fibres of
the enamel, which ramify and subdivide like those of the dentine,
have their trunks turned in the opposite direction, or towards the

periphery of the tooth ; so likewise even in the human teeth the analo-

XXV1 INTRODUCTION.

gous condition may be discerned in the slightly augmented diameter of
the enamel-fibres at their peripheral, as compared with their central
extremities. When the extremities of the human enamel-fibres are
examined with a magnifying power of 300 linear dimensions, by
reflected light, they are seen to be co-adapted, like the cells of a
honey-comb, and like these to be, for the most part, hexagonal.

The external surface of the enamel is marked by fine transverse
lines or ridges, of which Retzius counted twenty-four in the vertical
extent of one tenth of an English inch of the crown of a human
incisor ; these lines are parallel and wavy, and, like the analogous
markings on the surface of shells, indicate the successive formation
of the belts of enamel-fibres that encircle the crown of the tooth.
These lines may be traced around the whole crown, but are very
faint upon its inner or posterior surface.

Retzius cites Leeuwenhoek as the discoverer of these superficial
transverse lines of the enamel: but the older observer supposed them
to be indicative of the intervals between the successive movements
in the cutting of the tooth through the gum.

The enamel by virtue of its physical qualities of density and
durability forms the chief mechanical defence of the tooth, and is
consequently limited, in most simple teeth, to the exterior surface of
the exposed portion of the dentine, forming the ‘ crown ’ of the tooth.

It sometimes forms only a partial investment of the crown,
as in the molar teeth of the iguanodon, the canine teeth
of the hog and hippopotamus, and the incisors of the Rodentia.
In these the enamel is placed only on the front of the tooth,
but is continued along a great part of the inserted base, which is
never contracted into one, or divided into more fangs; so that

the character of the crown of the tooth is maintained throughout

INTRODUCTION. XXVIl

its extent as regards both its shape and structure. The partial
application of the enamel in these ‘dentes scalprarii’ operates in
maintaining a sharp edge upon the exposed and worn end of the
tooth, precisely as the hard steel keeps up the outer cutting edge of
the chisel by being welded against an inner plate of softer iron.

In the herbivorous mammalia, with the exception of the Eden-
tata, vertical folds or processes of the enamel are continued into the
substance of the tooth, varying in number, form, extent and direction,
and producing, by their superior density and resistance the ridged
inequalities of the grinding surface on which its efficacy, in the tritura-

tion of vegetable substances, depends.

In the development of a tooth, composed of the above-mentioned
differently organised tissues, a matrix of equal complexity was first
recognised to be concerned by John Hunter ; the several parts of this
matrix, here termed respectively the ‘ dentinal pulp,’ the ‘ enamel
~ pulp,’ and the ‘capsule’ or ‘ ccemental pulp,’ being first distinctly
indicated in the ‘ Natural History of the Human Teeth.’

In this otherwise instructive and original treatise the reader will,
however, seek in vain for any definite or detailed account of the part
which each formative organ plays in the development of its corres-
ponding tissue, or of the development of the matrix itself.

The latter subject has been chiefly elucidated by the observations
of Arnold(1), Purkinjé and Raschkow(2), Valentin(3), and Goodsir(4) :

(1) Salzburg Mediz. Chirurg. Zeitung. 1831, erster band, p. 226,

(2) Meletemata circa Mammalium Dentium Evolutionem, 4to. 1835.

(3) Handbuch der Entwickelungsgeschichte des Menschen, 8vo. 1835, p. 482.

(4) On the Origin and Development of the Pulps and Sacs of the Human Teeth. Edinburgh

Medical and Surgical Journal, vol. li, p. 1.

XXVill INTRODUCTION.

the modifications in the development of the dental matrix in
different animals and their analogies with those described by the
foregoing authors in the Human Subject and other mammalia are
detailed in the body of the present work.

The dentinal pulp is always the first developed part of the
matrix, and makes its appearance in the form of a papilla, budding
-out from the free surface of a fold or groove of the mucous mem-
brane of the mouth, and generally of that which covers the inner side
of the jaws or their rudiments. In certain fishes, as the shark, the
tooth is completed without the development of the matrix proceeding
beyond this ‘ papillary’ stage.

The first papilla may be distinctly recognized in the maxillary
mucous groove of a human embryo, one inch in length; the others
quickly follow. By the growth of the contiguous mucous membrane,
the papilla appears to sink into a follicle, and, by the development of
three or four lamellar processes from opposite sides of the mouth of
the follicle, and their mutual cohesion, the papilla is inclosed by a
capsule; this ‘ capsular’ stage of development is completed in the
human foetus at the fifteenth week(1). The capsule is the part of the
matrix destined for the development of the cement. In many fishes
and in serpents, the teeth are completed without the development of
the matrix proceeding beyond this stage.

In those teeth which are defended by enamel, a pulp destined
for its production is developed from the inner surface of the capsule
opposite that to which the dentinal pulp is attached. In the human
subject the enamel-pulp makes its appearance as a soft gelatinous

substance adhering to the opercular plates closing the capsule, and

(1) Goodsir, loc. cit. p. 11.

INTRODUCTION. XX1X

the adjoining inner surface of the capsule, at the sixteenth week ;
the surface of adherence of the ‘enamel-pulp’ is progressively
extended until it is separated by a mere linear interspace from the
base of the ‘dentinal pulp.’ ‘‘ Whatever eminences or cavities
the one has, the other has the same, but reversed; so that they
are moulded exactly to each other.”’(1)

With regard to the development of the dentine, Hunter describes
it as an ‘ ossification,’ but without indicating the relation that the
pulp bears to the process. ‘‘ As the ossification advances it gradu-
ally surrounds the pulp till the whole is covered by bone, excepting
the under surface; and while the ossification advances, that part
of the pulp which is covered by bone is always more vascular than
the part which is not yet covered. The adhesion of the pulp to the
new-formed tooth or bone is very slight, for it can always be separated
from it without any apparent violence, nor are there any vessels
going from the one to the other; the place, however, where it is
most strongly attached is round the edge of the bony part, which is
the last part formed.” ‘‘ Both in the body and in the fang of a
growing tooth, the extreme edge of the ossification is so thin, trans-
parent and flexible, that it would appear rather to be horny than
bony, very much like the mouth or edge of the shell of a snail when
it is growing ; and, indeed, it would seem to grow much in the same
manner, and the ossified part of a tooth would seem to have much
the same connexion with the pulp as a snail has with its shell.’’(2)
Hunter does not explain the nature of this connexion or the mode
of formation of shell; but he has been generally regarded by Physiolo-
gists as having been the author of the theory that the pulp stood to

(1) Hunter, loc. cit. p. 42. (2) Ibid, p. 39, 40.

XXX INTRODUCTION.

the tooth-bone in the relation of a gland to its secretion ; that the
formative virtue of the pulp resided in its surface; that the dentine
was deposited upon and by the formative or secretive surface of the
pulp in successive layers ; and that the pulp, exhausted as it were,
by its secretive activity, diminished in size as the formation of the
tooth proceeded ; except in certain species, in which the pulp was per-
sistent, and maintained an equable secretion of the dentine throughout
the life-time of the animal(1).

This idea of the pulp’s function, modified only by the phraseo-
logy required to express the later-acquired knowledge of the form
and condition of the newly-developed dentine in contact with the
pulp, has predominated in the minds of most subsequent writers on the
development of teeth.

The successive steps to the establishment of the doctrine that
the cells of the ivory, under which form Dr. Schwann has described
the nascent dentine to make its first appearance, are actually part
of the pulp itself, pre-existing in that body before their calcification
and confluence, and continuing in organic connexion therewith after
their conversion into the tubular dentine, are few, well-marked, and
easily traced. The first advance was made by Purkinjé and Rasch-
kow in submitting to careful microscopical observation the structure
of the dentinal pulp prior to the formation of the dentine, and
in similarly tracing the changes which it undergoes during that

process.

(1) Cuvier, by whom this opinion of the formation of dentine is most clearly set forth,
premises the following acknowledgment: “ Quant 4 la maniére dont les dents en général
naissent et croissent, nos observations nous paroissent confirmer la théorie de Hunter, plutét
que toutes les autres, dans ce qui concerne la partie de la dent qu’on nomme substance

osseuse.”’—Ossem. Foss. 4to. 1812, p. 59.

INTRODUCTION. XXX1

These authors describe the parenchyme of the dentinal pulp as
being composed of minute uniform spherical granules, without any
of the characteristic filaments of cellular tissue, and, in this respect,
differing from the enamel-pulp. The free surface of the granular
tissue is covered by a peculiarly dense, structureless pellucid mem-
brane, which they term the ‘ preformative membrane’ because the
formation of the dentine commences therein. Blood-vessels soon
penetrate the granular pulp, form several anastomoses in their course,
through its substance, and terminate in a rich and delicate net-work
of capillaries on that part of the surface of the pulp where the
dentine has begun to be formed; the rest of the pulp’s surface is
covered by the preformative membrane and does not display any
capillary reticulation. ‘True nervous filaments cannot be distinguished
in the pulp until after its vascularity has been established. The
granules of the pulp immediately beneath the preformative membrane
have a more elongated form than the rest, and are placed either
vertically, or at an acute angle with the membrane.

The formation of the dentine is preceded by the development
of numerous minute elevations on the surface of the pulp, at and
near its apex ; these are conjectured to be subsequently transformed
into the undulating ridges in which the enamel-fibres are firmly
inserted. The preformative membrane becomes ofa stony hardness,
except at the margin of the recently formed dentine, where it is
soft and easily rent. The dentine begins to be formed at the apex
of the pulp immediately beneath the preformative membrane.

Of the exactness of the preceding observations by Purkinjé and
Raschkow I have had repeated evidence. The more obscure parts
of their description of the development of the dentine are quoted

and commented on by Dr. Schwann, whose observations on this

Xxxll INTRODUCTION.

subject are as follows: after observing that the blood-vessels of
true bone are confined to the medullary canals, and that the
presence or absence of blood-vessels in a tissue occasions no es-
sential difference in its mode of growth; he proceeds to classify teeth
with bones in an order of tissues, characterized by the parietes of their
primordial cells becoming confluent either with each other, or with the
intercellular substance(1).

Dr. Schwann identifies the pulp-granules of Purkinjé with his
nucleated cells, and asks, ‘‘ In what relation does the dentine stand
to the cells?” He then proceeds to say, ‘‘ I must confess, at the
outset, that I am unable to answer this question with certainty, and
that my observations are not mature. Purkinjé and Raschkow describe
the formation of the dentine as follows :—‘‘ Primordio substantia den-
talis e fibris multifariam curvatis convexis lateribus sese contingentibus
ibique inter se concrescentibus composita apparet.—In ipso apice iste
fibree equaliter quamcunque regionem versus se diffundunt, attamen
parietes laterales versus directio longitudinalis preevalet, dum fibree
sinuosis flexibus equalique modo se invicem contingentes ibique ubi
concave apparent lacunas inter se relinquentes, ab apice coronali
radicem versus ubicunque procedunt. Nonnisi extremi earum fines
tunc molles sunt czterze autem partes brevissimo tempore indurescunt
..Postquam....fibrarum dentalium stratum depositum est, idem
processus continuo ab externa regione internam versus progreditur,
germinis dentalis parenchymate materiam suppeditante.. .. Convex
fibrarum dentalium flexure, que juxta latitudinis dimensionem cres-

cunt, dum ab externa regione internam versus procedunt, sibi

(1) Microskopische Untersuchungen tiber die Uebereinstimmung in der Struktur und dem

Wachsthum der Thiere und Pflanzen. 8vo. 1839, p. 117.

INTRODUCTION. XXXUl

invicem apposite continuos canaliculos effingunt, qui ad substantiz
dentalis peripheriam exorsi multis parvis anfractibus ad pulpam
dentalem cavumque ipsius tendunt, ibique aperti finiuntur, novis ibi,
quamdiu substantiz dentalis formatio durat, fibris dentalibus aggre-
gandis inservientes.’’—Raschkow, |. c. p. 6.

“‘T must confess,’ Dr. Schwann proceeds to say, “‘ that there
is much obscurity in this description. If I rightly understand it, the
dentine consists of fibres, formed layer-wise out of material afforded
by the pulp, which become confluent with each other but leave inter-
spaces which are the dentinal tubes. But these tubes cannot be
mere interspaces between fibres, since Miiller has proved them to pos-
sess distinct parietes...If a young tooth be removed from its capsule
and steeped for one day in not too much diluted muriatic acid, the
animal basis of the dentine, which, at the first removal of the earth,
was of cartilaginous hardness, becomes quite soft, so that one can
only detach small pieces from it by the forceps. If this pultaceous
mass be examined, it will be seen to consist of fibres, which can be
separated from one another. These fibres are too thick to be merely
the walls of the canals ; they constitute the whole substance. Neither
can they be a mere artificial product, since the acid penetrating the
canals first dissolves the immediately contiguous substance, and then
the intertubular substance remains as a fibre; besides, they are too
regular and smooth. It appears, moreover, that the dentine is com-
posed of these reciprocally united fibres, since they are identical with
the fibres which, according to Purkinjé and Raschkow, form by their
confluence the dentinal cartilage; and this confluence of the fibres
is not so complete but that they can be again artificially separated.
The fibres in the human teeth run in the same direction as the canals.
I could not discern the canals in their interspaces. The peripheral

C

XXX1V INTRODUCTION.

layer of the dentine, immediately beneath the enamel, which was
more decomposed by the acid, could only be resolved into finer
fibres of a different nature, crossing each other in the most various
directions, and which I presume to be the remains of the dentinal tubes.

‘* The dentine thus consists of interblended fibres between which
run canals with proper parietes. Both the fibres and tubes in human
teeth are nearly perpendicular to the pulp-cavity. What relation, then,
do the fibres and the tubes bear to cells? I might incline to the old
notion that the dentine is the ossified pulp. According to Purkinjé and
Raschkow the pulp consists at first of granules nearly similar in size
and form without vessels and nerves ; then vessels and lastly nerves
penetrate it. At the superficies of the pulp the granules are more
regularly arranged and more elongated, and are directed outwards
either vertically or at a slightly acute angle. These longitudinally
drawn out globules are plainly cylindrical cells. In recent teeth they
very distinctly contain the characteristic nucleus and its nucleolar cor-
puscles and closely resemble the prisms of the enamel-membrane
(Tab. iii, fig. 4). The interior substance of the pulp consists of
round nucleated cells, between which run the vessels and nerves.
If the pulp be drawn out of the cavity of a young tooth, and the
dentine be observed either recent or after the earth has been removed
by acid, there remains on its inner surface, at least where it is yet
thin and soft, a layer of the cylindrical cells that constitute the pulp :
these are about as thick as the solid fibres of the dentine, and have
the same course, and as they cohere more firmly with the dental substance
than with the pulp and remain attached to the former, so I presume that

here a transition takes place, and that the cylindrical cells of the pulp

(1) “Ich moéchte mich zu der Alteren Ansicht hinneigen, das die Zahnsubstanz die ver-
knocherte Pulpa ist,” loc. cit. p. 124, Compare the Literary Gazette, September 21st, 1839,
p- 598, and Medical Gazette, January 3d, 1840, p p. 540, 541.

INTRODUCTION. XXXV

are only the earlier stage of the dentinal fibres, since these cells
are filled with organized substance become solid and osseous. Some-
times these cylindricules are not found on the dentine, but then we
see in their place a number of cell-nuclei ; these are very pale and
ultimately united with the dentine so that they may be easily over-
looked. When once attentively observed, they are not easily mis-
taken, and are separated by extremely minute intervals. Against
the opinion that the dentine is the ossified part of the pulp, the
facility with which the one is separated from the other has been
objected, and I allow the force of that objection. But it is at least
weakened by the fact that a part of the pulp remains attached to
the dentine, and that in half-ossified ribs, the cartilage can be easily
detached from the ossified portion, and that in teeth the separation
must be so much the easier as the difference is greater between the
dentine and the pulp.

There are at least sufficient grounds for going more closely
into the detail of this view. The pulp agrees with all the
other tissues of the foetus, and more especially with cartilage,
inasmuch as it consists of cells; it differs in consistence from mam-
malian cartilage, inasmuch as whilst the quantity of cytoblasts
(nucleated cells), on which the hardness of mammalian cartilage
depends, is very small, the cylindrical cells, at least on the surface
of the pulp, are closely aggregated together. In this respect the pulp
more nearly resembles certain cartilages in the lower animals, in which
the cytoblasts are present in smaller quantity and the consistence
of the cartilage depends upon the thickening of the walls of the cells.
Whether, in the presumed transition of the cells of the pulp
into the dentinal fibres, the obliteration of the cavity is effected
by the thickening of the walls of the cells, I know not, since

c2

XXXVI INTRODUCTION.

I have not observed this transition. If it really so happens,
then the cavities of the cells so completely disappear, as to leave
no trace of the cartilage-corpuscles. From the observations
of Retzius it might be supposed that some of the cells retained their
cavity and even were converted into radiated cells, since Retzius
observed true bone corpuscles in the dentine. If, then, the super-
ficial layer of the pulp, consisting of cylindrical cells, is converted
by ossification into the dentine, then the subjacent layer of the pulp’s
parenchyme, consisting of round cells, must first be converted into
cylinders, the vessels of this layer become obliterated, and this layer
then become ossified, &c.

‘** What then are the dentinal tubes? Retzius compares them
with the calcigerous tubes that radiate from the bone-corpuscles, and
I was at first of the same opinion, and accordingly I regarded them
as prolongations of the cells, the bodies of which lay in the pulp. [If
the pulp be drawn out of the pulp-cavity of a hog’s tooth and the
margin of the pulp be examined, it is seen that each of the superficial
cylindrical cells is prolonged, opposite the dentine, into a short fine
fibre and that these fibres correspond in diameter with the dentinal
tubes projecting from the surface of the pulp. I once believed that
they projected into the dentinal tubes, and that the intertubular tissue
was merely the intercellular substance between these elongations
of the cells. ButI have given up these ideas since I observed nothing
of the kind in human teeth, and since this explanation brings with it
a difficulty in regard to the teeth of the pike. In these teeth, accord-
ing to Retzius, there is a direct transition from dentine to bone.
If one of the large teeth of the lower jaw be sawed off, the earth
dissolved by muriatic acid, and fine longitudinal sections removed,

the dentine is seen to form a hollow cone which is filled by bone.

INTRODUCTION. XXXVli

The dentine is transparent and consists of fibres which proceed from
the point to the base of the cone. The bone is traversed by canals,
which resemble the medullary canals of ordinary bone, except in
being less regular. The dentinal tubes are connected with these
medullary canals of the proper osseous substance, and it is plain
that the tubes are continued funnel-wise from the medullary canals.
The canals ramify in the dentine and as they proceed transversely
across the thickness of the tooth-cone, so they decussate the dentinal
fibres. Accordingly here the dentinal tubes correspond with the
medullary canals of bone not with the calcigerous tubes which radiate
from the bone-corpuscles.

‘* A more certain knowledge of the whole structural relations of
dentine seems to be only possible when its development is studied in
very differently constructed teeth.” (1)

The main facts, then, which may be considered as established by
the researches of Purkinjé and Schwann, relative to the formation of
dentine and the changes which the dentinal pulp undergoes during
that process are the following: the proper tissue of the pulp consists
of minute nucleated cells, with capillary vessels and nerves, invested
by a dense structureless membrane(2) which disappears during
the formation of the dentine. The superficial pulp-cells as-
sume an elongated form; they correspond in diameter and
direction with the tubes of the contiguous cap of dentine. These or
similar cells are observed, in a state of transition into dentine, in the
interspace between the pulp and the previously formed cap of den-
tine ; they adhere to the latter when it is displaced from the pulp.

(1) Schwann, loc. cit. p. 128.

(2) The capsule of the entire dental matrix will be understood to be quite a distinct part

from the ‘ preformative membrane’ of the pulp.

XXXVIll INTRODUCTION.

The chief points that remain to be determined are the re-
lation of the dentinal pulp to the transitional cells between it
and the dentine; the nature of the transition, and the relation
of the cells to the dentinal tubes and the intertubular tissue.
From the expression used by Purkinjé and Raschkow in the
passage already quoted ;—‘‘ After a stratum of dental fibres
has been deposited between the parenchyme of the pulp and the
preformative membrane the same process is continued from the ex-
ternal to the internal region, the pulp supplying the material ;’—it
may be inferred that they considered the formation of the dentine
to be a process of deposition from the formative surface of the
pulp, like a secretion from a gland. If such were not the
idea of these authors of the relation of the formative pulp to the
dentine they nowhere clearly express the contrary opinion, and
the formation of the dentine by its deposition in successive strata
from the pulp continued to be taught in the best works on physiology
subsequently published. (1)

(1) Miiller’s Physiology, by Baly, part i, 2nd ed. p. 429.

Mr. Bell who appears to have clearly recognized, long before the publication of the
Thesis of Raschkow, the ‘ preformative’ or external membrane of the pulp, supposed that it was
persistent, and that it was the true formative organ of the dentine. (See Anatomy, Physiology and
Diseases of the Teeth, 8vo. 1829). Inhis valuable edition of Hunter’s Natural History of the
Human Teeth, in reference to Hunter’s statement that the teeth are formed from the pulp, Mr.
Bell observes: ‘“ The statement that the bone of a tooth is produced from the pulp is erroneous.
This substance constitutes only the mould upon which the ossification is formed, between which
and the pulp is placed a membrane of extreme tenuity, which I have termed the proper mem-
brane of the pulp. It is slightly attached to the surface of the pulp, which it completely covers,
and it is from the outer surface of this membrane that the bone is secreted. As the pulp recedes
on the deposit of the successive laminz of bone, the ossific membrane continues to cover it,
and ultimately forms the well-known membrane lining the internal cavity of the perfect tooth.”

—Bell’s ‘ Hunter on the Teeth,’ 8vo. 1835, p. 38.

INTRODUCTION. XXX1X

Dr. Schwann was the first to express his leaning to the ancient
doctrine that ‘ the dentine is the ossified pulp.’ But the nature of
the subjects selected by him for his observations left him in a state
of doubt and indecision on this point: and the author by whom
Dr. Schwann’s observations were communicated to the British Asso-
ciation in August, 1839, although he adopted the doctrine of the
formation of ivory by the ossific transition of cells, rejected the idea
that the dental substance was the ossified pulp, and declared ‘ the cells
of the ivory to be altogether a distinct formation.’(1)

In fact, the subjects chosen by both Dr. Schwann and his con-
tradictor, for the examination of the development of the dentine, were
inadequate to the exhibition of the relations of that substance to the
formative pulp during any part of the process of its formation.
The shape of the teeth of the mammalia selected by them for examina-
tion will not yield a view of the cap of new-formed ivory and the sub-
jacent pulp, in undisturbed connection, by transmitted light with the
requisite magnifying power ; and, if placed under the microscope as
an opake object, the light is reflected from the cap of ivory, and dis-
plays only the characters of its surface and not its relations to the
surface of the pulpin contact with it. To examine this surface micro-
scopically in either a human tooth or that of any of our domestic
quadrupeds the cap of dentine must be removed, and the exposed sur-
face of the pulp and the corresponding surface of the dentine be
examined as opake objects by reflected light. Or, if the layer of the
dentine be thin enough to allow the transmission of sufficient light, it

must be removed from the subjacent pulp before it can be so examined.

(1) Report of the Papers read at the Medical Section of the British Association at Bir-
mingham, Literary Gazette, Sept. 21, 1839, p. 598.

xl INTRODUCTION.

It is, therefore, obvious that any inference as to the structure of the
pulp’s surface, or the nature of its previous connection with the tran-
sitional cells and the superincumbent layer of dentine, which may be
founded on appearances observed under the circumstances above men-
tioned, is liable to the objection that the natural relations of the parts
observed have been destroyed. If the dentine be the ossified pulp,
as Dr. Schwann was disposed to believe, then the calcified part of
the growing tooth has been violently displaced from the uncalcified
part, and the part of the pulp which thus presents itself for examina-
tion is a lacerated and not a natural surface.

But to the observer who regarded the dentine as a secretion
from the pulp’s surface, every modification which he might detect
on that surface after the displacement of the dentine, would appear
natural, and be perhaps described as such with the view to the eluci-
dation of the secreting process. Thus the cells which might be
observed in progress of ossific transition into dentine would appear as
independent parts, and the products of a secreting property; their de-
tached condition being, all the while, a necessary result of the artificial
displacement of the new-formed cap of ivory, and the consequent
laceration of the pulp’s substance.

In the terms of the ‘ excretion theory’ the exposed surface of
the pulp over which the cells lie scattered is a ‘ formative surfaces ;
the nucleated cells are naturally ‘ detached,’ and the ivory or den-
tine resulting from their calcification and metamorphosis, is, in
respect to the pulp, ‘ altogether a distinct formation, and by no
means an ossification of the pulp.’

Such is the interpretation which an advocate of the excretion-
theory has given to the true phenomena of dental development first

observed and described by Purkinjé, Raschkow and Schwann.

INTRODUCTION. xli

Observations on the pulp, in its various stages of conversion into
dentine, whilst in undisturbed connection with the calcified portion,
in the thin, transparent, lamelliform teeth of a fetal Shark (Carcharias),
first yielded me unequivocal demonstration of the organic continuity
of the cap of dentine with the supporting vascular pulp; they also
indicated some stages of the progress of the conversion of the pulp
into dentine, and produced that clear idea of the nature and relations
of dental development, which is expressed in the ‘ Theory of dentifi-
cation by centripetal calcification of the pulp’s substance,’ submitted
to the French Academy in December, 1839.(1)

The following are the progressive steps of the calcifying pro-
cesses, according to my microscopic researches on the formation of
the different substances which compose the more complex teeth of
Reptiles and Mammals, pursued in various species of both classes,
but chiefly in the higher organized domestic animals.

Three formative organs are developed, as already described,
for the three principal or normal dental tissues. The dentinal pulp
(Pl. 122 a, figs. 5, 6, 7& 8, d), or pulp proper, for the dentine; the
‘capsule’ (ib. c) for the cement, and the ‘enamel-pulp’ (ib. e) for
the enamel. The essential fundamental structure of each formative
organ is cellular; but the cells differ in each organ, and derive
their specific characters from the properties and metamorphoses of
their nucleus, upon which the specific microscopical characters of

the resulting calcified substances depend.

(1) The general results only of this communication were given in the ‘ Comptes Rendus,’
1839, p. 784. The Commission appointed by the French Academy to report on a subsequent
Memoir on the same subject advert to some of the phenomena previously communicated by me.
‘Quant aux préparations qui montrent l’aréolité de la pulpe, non seulement nous les avons
reproduites avec succes, mais de plus nous avons constaté, 4 l'état frais, la granulation

des aréoles signalée par M. Richard Owen,” loc, cit. 1842, p. 1063.

d

xh LNTRODUCTION.

In the cells of the dentinal pulp the nucleus fills the parent
cell with a progeny of nucleoli before the work of calcification
begins: in the enamel-pulp the nucleus of the cell disappears, like
the cytoblast of the embryo plant in the formation of most vegetable
tissues: in the cells of the capsule, the nucleus neither perishes nor
propagates, but retains its individuality, and gives origin to the
most characteristic feature of the cement, viz :—the radiated cell.

The primordial material of each constituent of the tooth-matrix
is derived from the blood, and special arrangements of the blood-
vessels pre-exist to the development and growth of the constituent
substances. A pencil of capillaries is directed to a particular spot
in the primitive dentiparous groove, and terminates there by a looped
net-work, from which spot a group of nucleated cells begins to
arise in the form of a papilla. The cells of the papilla are, however,
colourless, and the plexus of capillaries is confined to its base.
In the Mammalia (embryo Calf of three inches in length) membra-
nous septa are formed, into which the vessels extend, which cross
the groove and inclose the papilla in a follicle. From the free
margin of this follicle the processes are developed, which indicate
the configuration of the future crown of the tooth, and, in the
molars of the calf, subsequently develope the re-entering folds on
which the complex structure of the crown of the molar tooth
depends.

The primary dentinal papilla and its capsule rapidly increase
by successive additions of nucleated cells, apparently derived from
material supplied by the capillary plexus at the base ; the capillaries
now begin to penetrate the substance of the pulp itself, where they
present a sub-parallel or slightly diverging penicillate arrangement,

_ but preserve their looped and reticulate termination near the apex

INTRODUCTION. xlili

of the pulp. Fine branches of nerves accompany the capillaries
and terminate also in loops.

The primary cells of the papilliform pulp, the ‘“‘ grana equalia
globosa” of Purkinje, are described by him as pre-existing to the
appearance of vessels and nerves in the pulp; they are undoubtedly
unaccompanied by the blood-vessels at ‘their first ageregation to
form the papilla; but they bear the same relation to the capillary
net-work at the base of the papilla, which the subsequently formed
cells do to the capillaries that extend into the substance of the
papilla or pulp, when it is more developed. The primary cells.
and the capillary vessels and nerves are imbedded in, and sup-
ported by a homogeneous, minutely sub-granular, mucilaginous
substance, the ‘blastema.’ The cells (Pl. 1, fig. 1, a) which are
smallest at the base of the pulp, and have large, simple, subgranular
nuclei (ib. a‘), soon fall into linear series directed towards the peri-
phery of the pulp: where the cells are in close proximity with that
periphery, they become more closely aggregated, increase in size,
and present the following changes in their interior. A_ pellucid
point appears in the centre of the nucleus which increases in size
and becomes more opake around that central point, rendering the
compressorium requisite for its demonstration. A division of the
nucleus in the course of its long axis is next observed (ib. 6). In
the larger and more elongated cells, still nearer the periphery of the
pulp, a subdivision of the nuclei has taken place, and the subdivisions
become elongated with their long axes vertical or nearly so to the
plane of the pulp, and to the field of calcification (ib. c). The
subdivided and elongated nuclei become attached by their extre-
mities to the corresponding nuclei of the cells in advance ; and the
attached extremities become confluent (ib. d). Whilst these changes

d 2

xliv INTRODUCTION.

are proceeding, the calcareous salts of the surrounding plasma begin
to be accumulated in the interior of the cells, and to be aggregated
in a semi-transparent state around the central granular part of
the elongated nuclei, which now present the character of secon-
dary cells, and the salts occupy, in a still clearer and more
compact state, the interspaces of such cells (ibe’): the elongated
granular matter of the terminally confluent secondary cells
establishes the area of the tubes, by resisting, as it would seem,
the encroachment of the calcareous salts ; the nuclear tracts (ib. f.)
receiving a smaller proportion of the salts, in the condition of
minute disgregated particles, which are usually arranged in a
linear series of nodules, and contribute to cause the white colour
of the moniliform area, of the tube when viewed by reflected
light, and its opacity when viewed by transmitted light. Thus
the primitive existence of the granular nuclei, their multiplication in
the primary or parent cell, their elongated form, their serial arrange-
ment end to end, and terminal confluence, are indicated in the calcified
pulp by the arez of the dentinal tubes (fig. 2, c) ; the interspaces of
the metamorphosed nuclei being occupied by calcareous salts in a
clearer and more compact state, with evidence, however, of a dis-
tinctness of the nucleolar membrane or secondary cell (fig. 2, 6) from
the cavity of the common containing cell, which sustains the interpreta-
tion of the proper parietes of the dentinal tube. The indications of the
primitive boundary or proper parietes of the parent-cell (fig. 2, a) are
in like manner more or less distinctly retained, through a modification
of the arrangement of the calcareous salts in the boundaries and in
the interspaces of the cells. The salts are sometimes blended with
the blastema in these interspaces in a disgregated condition which
renders them almost as opake as the aree of the tubes. When

a layer of the calcified cells is carefully detached, the exposed

INTRODUCTION. xlv

uncalcified surface of the pulp (fig. 3, b) presents the appearance
of a net-work, the meshes being formed by the exposed cells, and
the intervening very thin layer of blastema. Each mesh, however,
which gives a transparent or bright contour to the cell, when
viewed by transmitted light, instead of presenting a single stellate
nucleus, shows by well directed light under a higher power, several
points, each of which is the centre of one of the meshes of a
finer network: these points are the ends of the granular elongated
nuclei,(1) which have been torn from the cavities of the dentinal
tubes in the displaced cap of dentine. A piece of the thin trans-
parent margin of the cap of a growing tooth, which may be cut off
with a pair of fine scissors, easily affords the means of demonstrating
the corresponding structure in that calcified part of the pulp. A slight
change of focus is required to bring the ends of the tubuli in view,
from that in which the clear outline of the dentinal cell is best seen.

In proportion as the progress of calcification approximates the
cells, and as these have undergone the changes in their nucleolar
contents, preparatory to the proper arrangement of the hardening
salts within, the proportion of the basal substance in the inter-
spaces of the cells to the enlarged cells themselves decreases, and
the cells become more readily detached and seemingly independent,
when torn out in the displacement of the cap of dentine. Although
they are less adherent laterally to the basal substance of the pulp,
they are more coherent with the cells of the same linear series: the
tubes of the calcified cell accepting or effecting an union with the

peripheral ends of the elongated granular nuclei or nucleolar cavitiese

(1) The term ‘granulation des aréoles,’ used by the French Academicians in referring
to my observations in support of the theory of centripetal calcification of the pulp, expresses
the appearance produced by the nuclei, which are converted into the dentinal tubes, as- seen

in the area of their parent dentinal cell.

xlvi INTRODUCTION.

of the contiguous cell in the next central layer; the angles at
which the elongated nuclei or successive portions of the dentinal
tubuli thus unite constitute the secondary gyrations or curves of
those cells. The primary curves depend upon the arrangement of
the primary linear series of the parent-cells.

The original contour of these cells is mest discernible after
calcification in the teeth of the Mammalian class, and here with
different degrees of distinctness in different species. They are
the true dentinal cells, and must not be confounded with the so
called ‘intertubular or interfibrous cells’, the first notice of which

is due to Retzius.(1) The diameter of the dentinal or calcified

(1) The able Translator of “‘Miiller’s Physiology,” Part I, 2nd. Edit., p. 431, gives the fact

that the substance between the tubuli of the ivory is composed of distinct cells, some of which

contain smaller cells, on the authority of a “ Report of the Meeting of the British Association,”
Atheneum, No. 620, 1839. Retzius (“‘ Mikroskopiska undersékningar ofver Tandernes, sardeles
Tandbenets, struktur,” 8vo. 1837, passim) describes the intertubular cells in the dentine of several
of the animal’s teeth which he examined. In the molar of the Hog, for example, he says:
“short branches proceed from the sides of the main tubes throughout their whole extent,
some of which terminate in dilated ends, like cells ;” and a little further on: “ only a few opake
cellules” (kalk celler) ‘“‘ were visible in the interspaces of the tubes,” (pp. 33 & 34.) In the
molar of a Rhinoceros, Retzius saw many of the lateral branches of the dentinal tubes
terminating in large cells :—‘*‘ These cells,” he says, ‘‘ were thinly arranged in the intertubular
spaces,” (af hvilka manga tydligen syntes sluta sig i stora kalk celler; dessa lago glest kring
spridda i stamrorens mellanrum) p. 32. M. Serres in his Report on certain Microscopic
preparations, submitted by Mr. Nasmyth to the French Academy, in proof of his discovery of
the intertubular cells, says of four sections from the teeth of the Megalichthys, Lamna,
Cachalot, and Elk :—‘‘ Sur ces préparations et sous un grossissement de deux a quatre cents

diamétres on distingue entre les fibres dont l’ivoire se compose, des aréoles nombreuses

a parois distinctes.” He verifies this as the “fait capital du travail de M. Nasmyth,” and

gives it the character of novelty by contrasting it with an alleged opinion of Retzius, whom

M. Serres affirms to have regarded the intertubular tissue (tissue interfibreuw) as amorphous !

(‘Compte Rendu de Séance de l’Académie des Sciences,’ 5 Décembre, 1842, p- 1055.) On-

what authority M. Serres cites me (loc. cit. pp. 1056 & 1057).as contending for the

priority of the discovery of the intertubular, or interfibrous cells, I know not: he does not

|

INTRODUCTION. i xlvii

primary cells of the pulp is usually one fourth or one half larger,
than that of the blood-disc of the species manifesting them. These
cells are figured, in the present Work, in the nrolar of the Mylodon
(Pl. 79), in the incisive tusk of the Dugong (Pl. 95), in the pre-
molar (Pl. 118) and the canine (Pl. 113 a) of the Pteropus, in
the incisor of the Chimpanzee (Pl. 119 a), and of the Human
Subject (Pl. 123), and in the molar of a Rhinoceros Pl. 139. In
the calcification of the dentinal pulp the thin transparent membrane
which covers the free surface, or that in contact with the enamel-
pulp, is the first to receive or become impregnated with the
hardening salts; and hence has been called the ‘ preformative
membrane.’ But at this early stage the calcifying membrane
yields to the pressure of the ends of the prismatic cells of the
enamel pulp, which are, likewise, beginning to take from the
surrounding plasma the hardening salts and impact them in their
interior. Thus are formed the pits upon the outer surface of the
coronal dentine of enamel-covered teeth, by which the enamel gains
a firmer mechanical connection with the dentine. As the process
of calcification of the multi-nucleated cells of the dentinal pulp
extends in its centripetal course, the pulp, in most teeth, progres-
refer to any publication of mine from which he derived the idea. I describe the intertubular
cells in many of the subjects of my ‘‘ Memoir” in the ‘Transactions of the British Associa-
tion,’ 1838. In Ptychodus, for example: “‘‘The interspaces of the canals are also occupied
by the same minute anastomosing reticulate tube-work. Numerous minute calcigerous cells
are also present in the interspaces,” p. 140. But instead of putting forth this as a discovery,
and misrepresenting Retzius as describing those interspaces to be amorphous, I premise by citing
Retzius’s discovery ‘‘of the cells in the clear interspaces of the tubes,” p. 136. The true
dentinal cells, a figure of which in the tooth of the Mylodon was published in the 2nd Part
of this Work, Pl. 79, in 1840, are very different from the intertubular cells on which M. Serres
reports. In most animals they include many tubes and intertubular spaces, and it is much

more exact to say that those cells include a tubular structure, than that the intertubular

space is cellular.

xiviil INTRODUCTION.

sively decreases in size, fewer nuclei are developed in the cells, and
these do not acquire so large a size. The diminution in both
respects proceeds, however, unequally, in the cells of the same
stratum. Here and there the linear tract formed by the nuclear
wwatter in a part of a smaller calcifying cell, containing fewer
nuclei, may be observed to unite with the converging extremities
of two residuary tracts (aree of dentinal tubes) of a calcified cell
in advance (PL. I. fig. 1, g). It is thus that the bifurcation of the tubes
is produced, and a repetition of this confluence, which becomes more
frequent as the calcifying process approximates the centre and base
- of the pulp, gives rise to the dichotomous divisions of the main
tubes. In some of the cells at and near the central and basal
part of the pulp, the nucleus has undergone no division, but has
become merely elongated and sometimes angular or radiated. In
others it has disappeared; such cells occur not unfrequently close
to the field of calcification, when the process has made much
advance in its centripetal course. The altered mode of action or
change in the nuclei of the smaller central cells of the pulp is
the first and essential step in the modification of the dentinal tissue
which produces the substances which I have termed osteo-dentine
and vaso-dentine. In the former many of the cells retain their
nucleus undivided, and the hardening salts are impacted around it
in the interior of the cell, but enter only partially into the granular
substance of the nucleus, in the minutely disgregated form, which
produces the opacity and whiteness of the resulting corpuscle. In
the formation of vaso-dentine many of the cells lose their nucleus
which seems to have become dissolved. In both the latter modi-
fications of dental tissue the blood vessels remain, and establish
the wide tubular tracts in the calcified substance to which the

name of ‘ vascular canals’ is given. In true, hard, or unvascular

ee

INTRODUCTION. xlix

dentine no trace of the blood vessels remains; all has been con-
verted into a much more minute calcified tubular tissue by the
assimilative or intus-susceptive properties of cells, and by the modi-

fication of their nucleolar contents. (1)

(1) That the dentine is the ossified pulp is, as Dr. Schwann observes, an old opinion ; but
an opinion is not a theory. Almost every true theory has been indicated, with various degrees
of approximation, before its final establishment; but he has ever been held, in exact philosophy,
to be the discoverer of a theory, by whom it has been first clearly enunciated and satisfactorily
proved. Thus established, on the basis of careful and sound induction, it is sooner or later
received to the exclusion of the, till then, prevalent and generally accepted erroneous doctrine,
at which period the truth of the antecedent hints and indications of the true theory begins to
be perceived, and it is not uncommon to find their value exaggerated in quotations by the
emphasis of type. Thus the remark of Blake:—‘‘ As the bone of the tooth increases in
thickness, the pulp is proportionally diminished: and seems as it were converted into bone,”
(Essay, 8vo. 1801, p. 7) is quoted in the article “‘ Zoology,” ‘Encyclop. Metropolit.,’ vol. v11,
p- 232, with “ converted into bone” in italics. So also Mr. Conybeare’s observation that the
interior cavity of the teeth of the Ichthyosaurus was obliterated “by the ossification of the
pulpy nucleus”; and that “‘ the ossified pulp has become a spongy mass of reticulated bony
fibres,” (Geological Transactions, Second Series, vol. 1, 1824, p. 107) might be cited in italics,
as the older hypothesis of Rau (De ortu et regeneratione dentium) has been, in depreciation of
the value or necessity of researches establishing the true relation of dentification to ossification.
But the actual value and bearing of such casual expressions would have been more fairly and
truly set forth, if, when the theory of the formation of dentine by successively excreted layers,
as promulgated by Hunter and Cuvier, universally prevailed in the systems of Physiology,
that theory had been formally combatted on the strength of such facts and observations in the
development of dentine, which it could be shown that Raw, Blake, Conybeare, and others,
had advanced in support of their expressions of the seeming, or actual conversion of the pulp
into bone.

Such expressions are, however devoid of scientific value, in regard to the question
of development on which they are quoted to bear, precisely because they are unsupported by
the observations requisite to prove what they affirm, and they have, therefore, been deservedly
neglected by the best authorities in Physiology, who have treated ex professo on the develop-
ment of teeth, prior to 1839.

In the edition of the English translation of ‘‘Mifller’s Physiology” of 1837, many facts
are cited from Blake’s excellent Treatise, but not his idea of the seeming conversion of the

pulp into bone. The Translator, indeed, adds tv the text the microscopic observations ot

1 INTRODUCTION.

But the vascularity of the dentinal pulp, and, especially, the
rich network of looped capillaries that adorns the formative peri-

pheral layer at the period of its functional activity, have attracted

Purkinje on the texture of dentine, which show that, if the pulp was converted at all, it must
be into a very different tissue from bone, and consequently by a different process from
ossification.

The nature of the process not having been discovered at that period, the formation of
dentine is described to be “by the secretion of layers of dental substance,’’ and the shell of
osseous substance so formed, is said to have ‘‘no organic connection with the matrix; it is
formed by the deposition of the mineral components of the tooth mixed with some animal
matter, and may be lifted off its matrix,” (pp. 391 & 392).

So also Prof. de Blainville, in the fasciculus of his great work ‘“‘ Ostéographie d’Animaux
Vertébres,” submitted by him to the French Academy, on the same day on which I
communicated to that learned body, my “‘ Theory of the development of dentine by centripetal
calcification of the pulp,” (December 16, 1839. See the ‘Compte Rendu’ of the Séance of
that day), says: ‘ Pour bien comprendre la forme générale d’un phanéros,”’ (by this name the
Professor designates the class of organs called ‘ teeth’) il faut savoir que c’est une partie morte
et produite, exhalée a la surface d’un bulbe producteur ou phanére, en continuité organique
avec le corps animal ; et implantée plus ou moins profondément dans le derme et méme dans
les tissus sous-jacents; et que, par conséquent, la forme du bulbe producteur détermine
rigoureusement celle du produit on du phanéros. Or, par la production seule des couches
de celui-ci appliquées successivement, en dedans les unes des autres, sur le bulbe producteur
seul vivant, seul li¢é par le systéme vasculaire et par le systéme nerveux au reste de
lVorganisme, ce bulbe diminue de volume en méme temps que de puissance productrice; en
sorte qu'il arrive un moment ot les cones composants, ayant cessé de s’accroitre en diamétre
avec le bulbe lui-méme, commencent 4 diminuer avec lui.””"—Fascicule Premier, Primates, p. 15.

These formal expressions of well weighed ideas of the nature and formation of teeth, set
forth by the celebrated Professors of Berlin and Paris, afford the true indications of the state
and the needs of that branch of physiology at the close of the year 1839. By only one writer
had the casual expression by Dr. Schwann, in his general Treatise on the Correspondance
between Animals and Plants in their structure and development, of his leaning towards the
old and exploded opinion, that the dental substance is the ossified pulp, been cited prior to
that date, in reference to the question of dental development. It occurs in the full Report of
the communications by Mr. Nasmyth go the ‘ British Association’ at Birmingham, in August,
1839, in the ‘ Literary Gazette’ of September 21st, 1839; and, as these ‘ Communications’

betray a full knowledge of all that Schwann had published relative to the development of

INTRODUCTION. li

general notice, and have been described by Hunter and subsequent

authors on Dental Development. By most this phenomenon has

been regarded as evidence of the secreting function of the surface

of the pulp, and the dentine as an out-pouring from that vascular

teeth, the conclusion to which Mr. Nasmyth had then arrived as to the ‘formation of ivory
by ossification of the pulp,’ may afford some indication of the value of Schwann’s facts, and
the cogency of his observations in establishing that theory. It is true that Mr. Nasmyth has
formally denied, in his subsequent Communication to the French Academy, (Comptes Rendus,
Octobre, 1842, p. 680), that he had any knowledge of Schwann’s Treatise when he read his
Memoirs to the Meeting at Birmingham. Any one who may care to see to what extent
deliberate plagiarism from an original Author may be impudently attempted to be foisted
on the scientific public, as a record and evidence of original research, may compare the
‘ Report’ cited, with the observations, which occupy the whole of page 125 and part of the
preceding and succeeding pages of Schwann’s ‘‘ Mikroskopische Untersuchungen tber die
Uebereinstimmung in der Struktur und dem Wachsthum der Thiere und Pflanzen, 8vo. 1839.”
The unacknowledged abstract fills more than a column of the 598th page of the Literary
Gazette (Sept. 21). From the passage beginning with “‘ According to Purkinje,” and ending
with “and of the dental bone,” the report of Mr. Nasmyth’s Memoir, excepting that where

Schwann asserts ‘Mr. Nasmyth observes,” and that where Schwann believes ‘‘ Mr. Nasmyth
presumed,” is a coarsely literal translation of the German Author.

Some of the borrowed paragraphs might have excited a doubt, if rightly understood by
Mr. N., of the truth of the idea at that time maintained by him, of the formation of dentine
“‘by the calcification of detached cells on the formative surface of the pulp,” or “ of the

deposition of the ivory by thin ossific layers on the surface of the pulp.” As, for example :—

Schwann, l. c. p. 125. Literary Gazette, 1. c. p. 598.

“Diese in die Lange gezogenen kugel-
chen sind nun offenbar cylindrische

Zellen.”’

‘Da sie auf der anderer Seite doch
mit der Zahnsubstanz fester zusammen-
hangen als mit der Pulpa, und an der
ersteren hangen bleiben so vermuthe ich,

das hier ein Uebergang statt findet.”

«These longitudinally drawn out glo-
bules, Mr. Nasmyth observed, are plainly
cylindrical cells ”—<Also Medical Gazette,
Jan. 3rd, 1840, p. 540.

“As they cohere more firmly with the
dental substance than with the pulp,
and remain attached to the former, Mr.
Nasmyth presumed that here a transition
takes place.” —Literary Gazette,l.c. p. 598,
and Medical Gazette. |. c. p. 541.

lii INTRODUCTION.

surface, which was supposed to shrink or withdraw from the matter
excreted. For, it has been asked, ‘If the unvascular dentine be

the effect of conversion of the vascular pulp, by what process is

Then again, when Schwann admits the validity of an objection to the theory of the
ossification of the pulp, which I have proved to have no real weight, Mr. Nasmyth likewise,

admits its force in the words of his Author :—

Schwannn, l. c. p. 126. Literary Gazette, 1. c. p. 598.
“Gegen die ansicht, dass die Zahn- “Against the theory that the dental
substanz der verkndécherte Theil der substance is the ossified portion of the
Pulpa ist, hat man die leichte Trennbar- pulp, the facility with which the one is
keit beider von einander eingeworfen, separated from the other has been ad-
und ich erkenne das Gewicht dieses duced; and he (Mr. N.) allowed the

Einwurfs wohl an.” force of that objection.”

But the influence of the old doctrine of the discontinuity of the pulp with the calcified
layers of the ivory, was then dominant in the mind of the plagiarist of Schwann: he says in
the original part of the Report :—‘* Schwann regards the dental substance as the ossified pulp,
_ whilst Mr. N.’s observations lead him to conclude that the cells of the ivory are altogether a
distinct formation.”— Literary Gazette, p. 598. Mr. N., in fact, exaggerated at Birmingham
every statement of Schwann which led towards the doctrine of ossification of the pulp in order
that he might refute him. Thus, according to the ‘ Literary Gazette,’ he makes Schwann
“‘yegard the dental pulp as a simple cartilage ;” he drags the dubious expression of his
inclination towards the ancient doctrine of the tooth being the ossified pulp, from a remote
part of Schwann’s treatise, converts it into a positive affirmation, and places it in juxta-position
with the statement of Schwann’s ideas of the relation between the dental pulp and cartilage,
in order to formally contradict the conclusions of the original German observer, who, Mr.
Nasmyth says : “starts with a ready-made hypothesis, and founds his opinion rather on the ob-
servations of others, and on the inferences he draws from them, than on his own actual
research.”—Literary Gazette, loc. cit. p. 598.

Thus, whatever influence the observations of Dr. Schwann might have had in drawing
Physiologists back towards the old doctrine expressed by Raw and Blake, must have been
greatly deteriorated by those who might place any confidence in the labours of Mr. Nasmyth,
on which his communication to the British Association, in August 1839 was based. The
right interpretation of Schwann’s observations, required, in fact, a new series of researches, and
that interpretation only became obvious to Mr. Nasmyth, after the publication of my

“New Theory of Dental Development,” in the ‘Compte Rendw’ of December, 1839.

INTRODUCTION. hii

all trace of the vascular ramifications obliterated, since none can

be detected in such dentine?’ The same question is equally ap-

plicable to the nerves of the pulp. In the explanation of this

New Reports of the ‘Communication to the British Association,’ in August, 1839, were
then inserted in the Medical Gazette and Lancet for 1840, with various modifications, to make
the Birmingham Memoir of August, 1839, accord with the ‘ New Theory’ of December, 1839.
These interpolations may be judged of by the following paragraphs touching the ossification of

the pulp :—

** Schwann regards the den-
tal substance as the ossified
pulp, whilst Mr. N.’s observa-
tions lead him to conclude that
the cells of the ivory are alto-

gether a distinct formation.”’

“‘He concluded, therefore,
that the wory is neither more
nor less than the ossified pulp,
and that it can in nowise be con-
sidered as an unorganized body.”

—Lancet, June, 1840.

*T’ivoire n’est done pour
moi qu’une portion de la
pulpe ossifiée.””

Comptes Rendus de V Aca-
démie des Sciences, Octobre 2.

1842, p. 680 :—

—Literary Gazette, Septem-
ber, 1840, p. 598.

and by many others which I pointed out in an exposure of Mr. Nasmyth’s attempt to
appropriate to himself my discovery of the true ‘ Theory of Dental Development.’

When the inconsistencies between the reports of Mr. Nasmyth’s Papers read before the
British Association at Birmingham, in August 1839, as published in the Literary Gazette and
Atheneum of September, 1839, and the Reports of the same Papers communicated by Mr. N.
to the Lancet and Medical Gazette of June, 1840, were demonstrated : Mr. Nasmyth replied :—
“‘ My answer to this is, that I did not furnish the Report to the Literary Gazette, and that the
notice of my Papers which I sent to the Atheneum, was so abbreviated and cut to pieces that
I cannot be responsible for it.”—Medical Gazette, June 26th, 1840, p. 545. If this assertion
is to be credited, the Report in the Literary Gazette must be regarded, however marvellous the
fact, as the work of a bond fide Reporter taking down the communication of an English soi-
disant discoverer, and publishing it in the form of a literal translation of a German Work:
or, that the Reporter mistook a quotation by Mr. Nasmyth from Dr. Schwann’s work for the
terms in which Mr. N. was narrating his own observations.

But Mr. Nasmyth, in his Communication to the “ Académie des Sciences,” Oct. 3, 1842,
in reference to Schwann’s work, from which a literal translation of the observations on the
Teeth is given in the Literary Gazette of Sept. 1831, as a Report of part of Mr. N’s Paper read

in the preceding month at Birmingham, states :—‘ Son ouvrage ayant été publié 4 l’époque

liv INTRODUCTION.

process attention must first be paid to the almost straight and
sub-parallel course of the vessels in the pulp’s substance, and to

the remarkable regularity of form and size of the meshes of the

ou j’adressai mes premiéres communications au Congrés de Birmingham, je n’avais pu en avoir
connaissance.” —Comptes Rendus, Octobre, 1842, p. 680.

In the ‘Addendum to the Report of the Transactions of the Sections in 1839,’ published
in the ‘ Report of the Eleventh Meeting of the British Association,’ 1842; the Council of
the Association adduce the following testimony of the Editors of the Literary Gazette and
Atheneum :—

“Notices of Mr. Nasmyth’s papers appeared in the Atheneum and Literary Gazette of
the period: those journals usually obtain such notices either from authors themselves or from
reporters of their own: in the present case the Council have been informed by the respective
Editors, that the report in the Atheneum of the two papers read to the Medical Section was
supplied, and the proofs corrected, by Mr. Nasmyth himself, and the notice of the geological
paper by the reporter of the Athenzeum ; and that the report in the Literary Gazette was drawn
up by the reporter of that journal, from a rough manuscript furnished to him by Mr.
Nasmyth.”

Upon these ‘ Reports,’ furnished and corrected by Mr. Nasmyth, the following opinion
has been published :—

** Reference having been made to us by a Council of the British Association for our opinion
whether the report of Mr. Nasmyth’s paper, as published in the Literary Gazette and
Atheneum, or in either of those two periodicals, or the report of that paper sent by Mr.
Nasmyth to Mr. Phillips for publication in the Report of the Ninth Meeting of the Association,
held at Birmingham, is more correct with regard to the points under discussion between
Professor Owen and Mr. Nasmyth, we have carefully examined these several documents,
and it appears to us that the main point under discussion between these two gentlemen is,
whether the account of the process of dentition, contained in Mr. Nasmyth’s paper, did or did
not comprise the theory that the ivory of the teeth is formed by the ossification of the pulp.
We find, with reference to this question, that in the accounts of Mr. Nasmyth’s paper, given in
the Literary Gazette and Atheneum, his opinions on that subject are involved in considerable
ambiguity ; for, while some passages in them would imply that he considered the proper
substance of the teeth as being formed by the addition of ossific matter in the original structure
of the pulp, commencing and proceeding on its surface, these reports contain, at the same

time, other passages, in which the theory of the ossification of the pulp is distinctly and

INTRODUCTION. lv

terminal reticulation on the surface of the pulp. At the part
where calcification has commenced, I have commonly found the

extremities of the capillaries in a state of congestion and crowded

expressly disclaimed by Mr. Nasmyth; whereas in the abstract of his paper, drawn up by
himself, with a view to publication in the Report of the Association, this theory is very
explicitly and unequivocally maintained. Whether this theory was distinctly advanced in the
original paper read to the Medical Section at Birmingham, it is not in our power to determine,
because that paper is not before us, and because we have no other evidence of the nature of its

contents than the printed documents already referred to.
(Signed) JAMES MACARTNEY,

One of the Vice-Presidents of the Medical
Section at the Birmingham Meeting.

P. M. ROGET,

One of the Vice-Presidents of the Medical
Section at the Birmingham Meeting.

G, O. REES,

One of the Secretaries of the Medical Sec-

tion at the Meeting at Birmingham.
November 16th, 1840.

It will be found by comparing the Reports in the Literary Gazette and Athenzeum with
Schwann’s Treatise above cited, that the passages which imply that the proper substance of
the teeth is formed by addition of ossific matter in the original structure of the pulp, are
verbal translations, taken, without acknowledgement, from that Treatise, which is only
referred to with a view of contradicting a conclusion to which Schwann inclines, without
proving either satisfactorily to himself or to others.

Whatever testimony Mr. Nasmyth may procure as to his private views on dental
development in 1839, it is incredible that he should have discovered, in the proper sense of the
word, that ‘‘the ivory is neither more nor less than the ossified pulp,” and yet omit to state
this discovery in the Reports which, the Editors of the Atheneum and Literary Gazette affirm
that he himself furnished, and, in one Journal, corrected the proofs.

Mr. Nasmyth made another attempt to establish his date of priority ; the nature of which
will be understood by the following extract from the “ Adendum,” p. 11, ‘ Report of British

Association,’ 1842 :—

lvi INTRODUCTION.

with blood-discs, which were pressed together into polyhedrons,
and apparently stagnated and left out of the current of circu-
lation.

These aggregated blood-discs exhibited, in various and often

“The Council have since thought proper to request the Committee, to whom they have added
the President (a) and Vice Presidents (0) of the Geological Section of the Association at
Birmingham, to inquire into the authority supposed to be given to Mr. Nasmyth’s abstract by
a printed document, in the shape of a printer’s revise, purporting to be the report, by the
Editorial Secretary, Dr. Lloyd, of another paper of Mr. Nasmyth’s read to the Geological
Section, at the same meeting of the Association, which revise, he alleges, contains the following
passage, viz., ‘ the ivory is neither more nor less than the ossified pulp,’ and on which he founds an
argument that an affirmation to that effect had been distinctly made by himself in that
paper.

“ The present Committee, to whom this yuestion has been specially referred, have procured,
through the kindness of Colonel Sabine, one of the General Secretaries, a certified copy (c) of
the original manuscript report referred to by Mr. Nasmyth, and which it appears was drawn up

immediately after the paper had been received, by Dr. Lloyd, one of the Secretaries of the
Geological Section. It is as follows :”

«(It is the subjoined document marked B.)’’

“On comparing this manuscript copy with the printed revise, as quoted by Mr. Nasmyth
at p. 3 of his printed letter to the Council, it appears that several alterations have been made in
the original in its progress to that stage of revision in which Mr. Nasmyth now produces it ;
and in particular, that the expression quoted by him in italics, as especially corroborating the
fidelity of his abstract, is not contained in it.”

This needs no comment: it is here cited along with Mr. Nasmyth’s assertion to the French
Institute, that Schwann’s Treatise was unknown to him when he read his Memoir at
Birmingham, and with the statements which he hazarded in print, that he did not furnish the
Report to the Literary Gazette, and that the Report in the Atheneum had been so mutilated that
he could not be responsible for it, in order to show the value of that person’s subsequent

assertions on other points relating tothe present work.(d)

(a) Dr. Buckland. (b) Leonard Horner, Esq., Charles Lyell, Esq.
(c) “ Acopy, certified by Dr. Lloyd, of the rough copy preserved by himself of the original
manuscript.”

(d) For the refutation of these assertions see Medical Gazette, July, 1840.

INTRODUCTION. Ivii

in striking degrees, those changes of the contained matter to
which I have elsewhere suggested that their own multiplication
might be due. In the present situation and condition it is obvious
that such changes must be preparatory, either to their disappearance
and removal, or to some important share which they are destined
to take in the development of the dental tissue. The stagnant
corpuscles nearest the vascular and unchanged pulp presented the
irregularity of contour, which has given rise to the term ‘ mulberry,’
or ‘granulated’ applied to such altered blood-discs, when seen in
other circumstances. ‘These corpuscles in other respects, as colour,
size, and general form, retained their usual character. ‘The blood-
discs nearer the cap of dentine exhibited more plainly the contained
granules, to the commencing development of which the irregular
contour above-mentioned is due: this appearance was associated
with an increase of size, a change from the circular to the elliptical
form, and a gradual loss of the characteristic colour, which was
longest retained by the central granular matter. The tunics of the
capillary vessel containing the above aggregated and altered blood-
discs become gradually attenuated, and disappear, as if dissolved,
before reaching the field of conversion. I once inclined to the
belief that these modified blood-discs afforded fresh cell-material
to supply the space left by the retreat of the circulating currents.

The open mouths ‘of the central last-formed ends of the
calcified dentinal tubes are always ready to receive the plasma
transuded from the capillaries remaining in the uncalcified part
of the pulp or in those tracts of it which constitute the vascular
canals.

The enamel pulp differs from the dentinal pulp at its first
formation by the more fluid state of its blastema and by the fewer
and more minute cells which it contains. (Pl. 1, fig. 4,4.) The

e

lvili INTRODUCTION.

source of this fluid blastema (ib. g) appears to be the free inner vas-
cular surface of the capsule. As it approaches the dentinal pulp the
blastema acquires more consistence by an increased number of its
granules, and it contains more numerous and larger cells; many of
these show a nuclear spot (ib. f‘): others a nucleus and nucleolus :
the spherical nucleolar cells in the part of the blastema further
from the capsule are so numerous as to form an aggregate mass,
with a small quantity of the condensed blastema in the minute
interspaces left between the cells, which are pressed together into
hexagonal or polygonal forms, (ib. fig. 2, 2). In this state they
constitute a great part of the enamel pulp, which is of consider-
able extent in the complex molar teeth of the Ruminants. The
appearance produced by these aggregated cells, in a section of the
tooth matrix of a Calf’s molar, (Pl. 122 a, fig. 9, e) is compared
by Raschkow to the actinenchyma of certain vegetable tissues,
and the connecting condensed blastema to threads of cellular
tissue. The field of the final metamorphosis of the cells into the
moulds for the reception of the solidifying salts is confined to
close contiguity with the surface of the dentinal pulp (ib. e’, e’).
Here the cells increase in length, lose all trace of their nucleus,
and become converted into long and slender cylinders usually,
pointed at both ends, and pressed by mutual contact into a pris-
matic form (PI. I. fig. 4, k, 1). These cylinders have the property of
imbibing the calcareous salts of the enamel from the plasmatic fluid, |
and of compacting them in a clear and almost crystalline state in their
interior: the disappearance of the nucleus being evidently the
condition of the absence of any permanent cavity, cell, canal, or |
other modification of the mineral matter, at least in the enamel
fibres of the Calf. In the Human subject it is probable that the

cavity of the cylinder may be subdivided by a multiplication of

INTRODUCTION. lix

delicate nucleoli into compartments; or that the remains of such
multiplied nucleoli may cause a modification of the walls of the
cylinder, and so produce the characteristic transverse striz of the
enamel-fibre. This appearance is not present in the enamel of
the Frog’s tooth, nor in that of the teeth of the Hog, or Calf, in
which animals my observations of the development of this tissue
have been chiefly made. As the development proceeds, the cells in
immediate contiguity with the calcified prismis undergo the same
changes as their predecessors, and become united to them by their
peripheral pointed extremities, whilst the fluid plasmatic contents
of the cells are exchanged for the dense salts of which the enamel
is chiefly composed. ‘The selective surface formed by the organic
membrane of the cell would seem to be destroyed by the very
pressure resulting from its own action, and exerted by the contents
of the closely-packed contiguous prisms, when the cavities of the
cells are completely filled. The membrane ceases at least to be
distinguishable under the microscope, from the solid contents of
the cell, except at that surface of the enamel next the capsule,
and which is still in progress of growth, (as in Pl. 123, fig. 2.)
What is remarkable, here, is that not the whole of the actinen-
chymatous part of the enamel-pulp is converted into the long and
slender prismatic cellular basis of the enamel; at least, in the
valleys of the complex crown of the molar of the Ruminant and
Pachyderm, (Calf and Colt), this part of the enamel-pulp originally
occupies more space than the subsequent layer of enamel does:
and the superfluous peripheral part seems to be absorbed, and its
place to be occupied by a growth or thickening of the vascular
capsule. No capillaries pass from the capsule into the actinen-
chymatous pulp of the enamel: nor have I been able to trace a
blood vessel into that part of the capsule which was actually the
e2

Ix INTRODUCTION.

seat of the calcifying processes.(1) Here, as in the dentinal and
enamel pulps, the calcareous salts are selected and arranged by
the assimilative, selective, or intus-susceptive, properties of the cell-
walls and by the repulsive power of their nuclei.(2)

The blastema or fundamental tissue of the capsule is, at first,
semitransparent and of a pearly or opaline colour ; but is soon richly
ornamented by the plexiform distribution of the blood-vessels, (Pl. Il).
As the period of its calcification approaches, which is later than
that of the dentinal pulp, it becomes denser, and exhibits nume-
rous nucleated cells. The blastema itself (Pl. I. fig. 5, n) presents more
evidently a fine cellular or granular structure in which the calcareous
salts are impacted in a comparatively clear state constituting the frame-
work (n’) of the cemental tissue. The characteristic features of this
tissue are due to the action of the proper nucleated cells (ib. m) upon the
salts of the plasma diffused through the blastema in which those
cells are imbedded. The cells being characterised by a single large
granular nucleus (ib. p) which almost fills the clear area of the cell
itself. If, when the formation of the cement has begun in the incisor
or molar of a Colt, one of the detached specks of that substance, with
the surrounding and adhering part of the inner surface of the
capsule in which it is imbedded, be examined, these nucleated
cells are seen, closely aggregated around the calcified part, in con-
centric rows ; the cells of which are further apart as the rows
recede from the field of calcification. Those next the cement (ib. 0)
rest in cup-shaped cavities in the periphery of the calcified part just
as the first calcified cells of the thick cement which covers the

(1) This has led me to doubt whether the altered blood-discs of the capillaries of the
dentinal pulp are converted into the cells of the pulp which occupy the place of the capillaries in
the calcifying field.

(2) It might be supposed that the cell-membrane and the surface of the nucleus were in
different electrical states.

INTRODUCTION. lx

crown of a complex molar are lodged in cavities on the exterior
of the enamel. These exterior cavities of the cement are formed
by centrifugal extension of the calcifying process in the blastema
in which the cells are imbedded. The calcareous salts penetrate
in a clearer and more compact state the cavity of the cell, but
their progress is arrested apparently by the nucleus which maintains
an irregular area, partly occupied by the salts in a subgranular
opake condition, but chiefly concerned in the reception and transit
of the plasmatic fluid which enters and escapes by the minute
tubes which are subsequently developed from the nucleolar cavity
as calcification proceeds. The radiated cells or cavities (p') thus formed,
are the most common characteristic of the cement, but not the
constant one. The layer of the capsule which surrounds the crown
of the Human teeth and of the simple teeth of Quadrumana and
Carnivora, consists simply of the granular blastema, without nu-
cleated cells, and the radiated corpuscles are, consequently, not
developed in the cement which results from its calcification. In
the thicker parts of the inflected folds of the capsule of the
complex teeth of the Herbivora traces of the vascularity of that
part of the matrix are persistent, the blastema calcifying around
certain of the capillaries and forming the medullary canals. The
varieties of these canals are traversed by minute tubules continued
from or communicating with the radiated cells. These tubules, and
the more parallel ones which traverse the thickness of the cement in
many Mammalia, are the remains of linear series of the minute
granules of the blastema.

In the deep sockets of the teeth of persistent growth the
matrix is maintained by the constant additions of new blastema
and cell-material to the bases of the dentinal, enamel and cemental

pulps. I have demonstrated the partial growth of the enamel pulp

)xii INTRODUCTION.

along the side of the capsule corresponding to the convexity of the
scalpriform incisor of the under jaw of the Porcupine in the prepara-

tion, now in the Physiological Series of the Hunterian Collection,
No. 375 A.

Chemical analyses(1) of the composite substances, built up by the
organising processes in the fundamental tissues of the matrix, above

described, have yielded the following results.

INCISORS OF ADULT MAN.

Dentine. Enamel. Cement,
I It.
Organic substance. . 28.70 3.59 29.42 29.12
Inorganic substance . . 71.30 96.41 70.58 70.88
100.00 100.00 100.00 100.00

MOLARS OF ADULT MAN.

Dentine. : Enamel.
Phosphate of lime with a trace of fluate of lime . : 66.72 89.82
Carbonate of lime . 5 ° : ° 3.36 4.37
Phosphate of magnesia . ° ° 1.08 1.34
Salts 5 ° e ° ° 0.83 0.88
Chondrine (2) ; S ° 5 27.61 3.39
Fat : 3 é Ce ; ~ 0.40 0.20
100.00 100.00
BERZELIUS’ ANALYSIS GIVES:
Phosphate of lime, with a trace of fluate of lime ° : 64.0 8855
Carbonate of lime é : : A 5.3 8.0
Phosphate of magnesia . . ‘ ° 1.0 a
Soda and muriate of soda ° ° . ° 1.4 —
Cartilage and other animal matter ° : . 28.0 2.0
100.0 100.0

(1) These results are cited chiefly from Bibra’s “Chemische Untersuchungen iiber die
Knochen und Zahne,” 8vo. 1844, ;

(2) “ Knorpelsubstanz.”

INTRODUCTION.

CANINE OF A LION.

Phosphate of lime with a trace of fluate of lime .

Carbonate of lime. ° “
Phosphate of magnesia : °
Salts : ° °
Chondrine A : °
Fat . ° . ° .

Dentine.
60.03

3.00
4,21
0.77

31.57
0.42

100.00

TEETH OF A DOLPHIN. (Delphinus Delphis.)

Phosphate of lime with a trace of fluate of lime °

Carbonate of lime . . .
Phosphate of magnesia : ° °
Salts é 3 ° ° .
Chondrine : e .
Fat ° ° ° é

TUSK OF ELEPHANT.

Phosphate of Lime with a trace of fluate of lime

Carbonate of lime A A
Phosphate of Magnesia. ° °
Salts . Beat ° : :
Chondrine . . | °
Pat. -. ¢ : : F

TUSK OF WILD-BOAR,.

Phosphate of lime with a trace of fluate of lime

Carbonate of lime ; ° °
Phosphate of magnesia. ° °
Salts . ° ° - .
Chondrine - ° : -
Fate, ¥ ° ° 2

Dentine.

66.37
1.84
1.36
0.99

28.62
0.82

100.00

Ix

Enamel,

$3.33
2.94
3.70
0.64
9.39

A trace.

100.00

Cement,

69.42
1.79
1.47
0.93

25.73
0.66

100.00

Ivory.
38.48
5.63
12.01
0.70
42.94
0.24

100.00

Dentine.
60.00

2.51
6.43
0.43
30.50
0.13

100.00

lxiv INTRODUCTION.

INCISORS OF OX.

Dentine, Enamel. Cement.
Phosphate of lime with a trace of fluate of lime . 59.57 81.86 58.73
Carbonate of lime . ; ° . 7.00 9.33 7.22
Phosphate of magnesia ~ . . 0.99 1.20 0.99
Salts . ; ° . ° 0.91 0.93 0.82
Chondrine ‘ : : 30.71 6.66 31.31
Fat e e ° ° . 0.82 0.02 0.93

100.00 100.00 100.00
CROCODILE.

Dentine. Cement.
Phosphate of lime, with a trace of fluate of lime = 53.69 53.39
Carbonate of lime : ; ai : 6.30 6.29
Phosphate of magnesia . . . . 10.22 9.99
Salts e e . e ° 1.34 1.42
Chondrine . ‘ P ° 27.66 28.15
Fat . ° ° . 0.79 0.76
100.00 100.00

PIKE (Hsor Lucius).
Large teeth of lower jaw.

Phosphate of lime with a trace of fluate of lime . - 63.98
Carbonate of lime : F - ; 2.54
Phosphate of magnesia. ° : . . 0.73
Salts . . A 4 . : 0.97
Chondrine 4 : y : : : 30.60
Bat su, 5 ~ : p . 1.18
100.00

The proportion of mineral or inorganic substance would seem
to vary, within certain limits, in different individuals of the same
species: thus in the molar teeth of one man Bibra found 79.00 of
inorganic matter, and in another 71.99; whilst Berzelius found
72.0. The proportion of inorganic matter in hard dentine will
depend in some degree upon the number of dentinal tubes, from the
aree of which the salts are in part excluded: thus in the modified

dentine (ivory) of the Elephant’s tusks, in which the tubuli are

INTRODUCTION. ixv

more numerous, close-set, and extensively undulated, in a given
space, than in ordinary dentine, the organic bears a greater propor-
tion to the inorganic matter, than in the dentine of the teeth of
most other Mammals. The cement of the composite molar teeth
of the Ruminants and of the Elephant contains a little more organic
matter than the dentine does; but in the cetaceous Dolphin it

contains a rather less proportion, and is consequently harder.

The nerves of the teeth (1) are derived from the trigeminal, or
fifth pair, of which the second division supplies those of the upper
jaw, the third division those of the lower jaw. In the Human
Subject the three dental branches of the infra-orbital nerve intercom-
municate by their primary branches, from which, and from a rich
plexus formed by secondary branches upon the membrane lining the
antrum, two sets of nerves are sent off to the alveolar processes of
the upper jaw ; one set (rami dentales) supplies the teeth, the other
(rami gingivales) the osseous tissue and the gums; the latter agree
in number with the intervals of the teeth, as the proper dental
nerves do with the teeth themselves. These two sets are not,
however, so distinct but that some intercommunications are established
between the fine branches sent off in their progress to the parts
they are specially destined to supply. The rami dentales take the
more direct course through the middle part of the osseous tissue
to the teeth ; penetrate the orifices of the fangs, and form a rich
plexus with rhomboidal meshes upon the coronal surface of the
pulp; the peripheral elementary filaments returning into the plexus
by loops.

In the lower jaw the dental nerve, besides supplying the proper
nerves to the teeth, also forms a rich plexus, in which it is joined

(1) Swan, Demonstration of the Nerves of the Human Body, fol. 1830, pl. x11. Schu-
unacher, Ueber die Nerven der Kiefer und des Zahnfleisches, 4to. 1839.

Ixvi INTRODUCTION.

by some branches from the division of the nerve that afterwards
escapes by the foramen mentale, and from this plexus the cancellous
tissue of the bone and the vascular gums are supplied.

In the Dog and other Carnivora the nerve of the laniary tooth
is conspicuous from its size; that which supplies the still more
developed analogous tooth or tusk of the Boar, is still larger having
relation also to the continual reproduction of the matrix at the
base of the tusk.(1)

In the lower jaw of the Porcupine the nerve of the great incisor
is given off from the dental nerve near the middle of its course
through the osseous canal, and returns at an acute angle to penetrate
the cavity at the base of the scalpriform tooth, and supply its
persistent pulp.(2) This recurrent course indicates the progressive
change in the relative position of the pulp to the origin of its nerve.
Besides the branches for the molar teeth, many smaller filaments
penetrate the spongy texture of the bone, and form a rich plexus
from which the gum derives its filaments.

The maxillary plexus is most developed, in the Horse,
above and between the alveoli of the three premolar teeth ; it is
less complex where it supplies the molar teeth, their alveoli and the
gums. In the lower jaw of the Horse a very rich plexus begins
to be formed in the cancellous substance of the bone by branches
of the dental nerve, soon after its entry into the canal.

The intercommunications between the dental and gingival
nerves, and those supplied to the osseous tissue from the supra-
maxillary and infra-maxillary plexuses explain the sympathies
manifested in neuralgy and rheumatic pains between the teeth and

the osseous cavities in which they are implanted.

I have been represented as having arrived at the conclusion

(1) Pl. 140, fig. 2. (2) Pl. 104, fig. 1, 1*.

INTRODUCTION. Ixvil

‘that the structure of the teeth, as manifested by means of the
microscope, forms a new, distinct, and specific guide for classifying
the different members of the animal kingdom, and determining their
respective types :’’(1) the absurdity of which will be obvious to the
youngest student of Zoology, who knows that true teeth are developed
only in one of the primary divisions of the animal kingdom. What
I have stated is, that the teeth, by their microscopic structure, as
well as their more obvious characters, form important, if not
essential aids to the classification of existing, and the determination
of extinct species of Vertebrated animals: but in this compara-
tively restricted sphere the teeth have different degrees of value,
as zoological characters, in different classes; the lowest degree
being in the Class of Fishes, and the highest in that of
Mammals. Numerous rows of teeth, for example, gradually suc-
ceeding and displacing each other, characterise the higher organized
or Plagiostomous Fishes, and particular modifications of the form and

(1) “The labours of Purkinje, Muller, and Retzius on the structure of the teeth have now
been recorded, and the views entertained by these physiologists have been most ably investi-
gated and confirmed by Mr. Owen, who has submitted to microscopical examination the
teeth of several other animals, both recent and fossil. From an excellent Report of these
Researches read at the last Meeting of the British Association, I have great satisfaction
in finding that he has arrived at the same conclusion which I had previously embodied in
the first announcement of this work, viz., that the structure of the teeth, as manifested by
means of the microscope, forms a new, distinct, and specific guide for classifying the different
members of the animal kingdom, and determining their respective types. From the enduring
nature of these organs, the characteristic modifications which they present, will form, as Mr.
Owen has admirably pointed out, a most valuable accession to geological science.”—Mr.
Nasmyth, ‘Researches on the Teeth,’ 8vo. 1839, p. 123., Where this Author obtained the
idea, ‘‘which he had previously embodied” to the best of his comprehension, is of little
moment. The paragraph is cited to show that when Mr. Nasmyth penned and printed his
eulogy on my “ Report” of 1838, he seemed not to feel it as ‘‘a strange and unlooked for

opposition” as he has represented it since the exposure, in 1840, of the nature of his ‘ Papers’

read at Birmingham.

Ixvill INTRODUCTION.

size of these teeth distinguish the primary subdivisions of the same
Order. A few other groups of Fishes are well defined by dental cha-
racters, as the Pycnodonts, Gymnodonts, Goniodonts, and Cheetodonts.
But in most of the natural Orders, and in many of the subordinate
groups of the Piscine class, the dental system is subject to very great
diversity in regard to the form, number, and position of the teeth;
and in some natural families there is also a want of constancy in the
structure of the teeth. There are extremely few genera of Fishes that
can be characterized by a definite numerical dental formula, like
most of the Mammalian genera. Indeed, in the first introduction
of true teeth into the animal series, regarded in the ascending order,
they manifest, like the mouths of the Polyp, the stomachs of the
Polygastria, and the generative organs of the Tene, the principle
of vegetative or irrelative repetition; and, in many Fishes, are
too numerous to be counted. The limits within which the teeth
are applicable as means of classification in Fishes will be readily,
and I trust, accurately appreciated, by the descriptions in the first
part of this Work. Traced from species to species they are of
great importance in the determination of the fossils of this class.

With regard to microscopic structure, the second and third
of the modifications defined in Chapter I, Section 8, are peculiar
to and characteristic of the Piscine Class ; the first modification is,
with the exception of one Mammalian genus, Orycteropus,. peculiar
to Fishes; unvascular or fine-tubed dentine forms the crown of
the teeth in a few Fishes, but is more common in those of the
higher Classes.

In the Class Reptilia the teeth serve to characterize smaller and
more definite groups thanin Pisces, as, for example, the venomous and
non-venomous Ophidians ; and the acrodont, pleurodont, and thecodont

Saurians. Certain Genera, and even Species may likewise be known

INTRODUCTION. lxix

by peculiar forms of teeth; but a definite dental formula can rarely
be assigned as a generic character of a Reptile. There is no de-
cided modification of dental structure peculiar to any of the class
of Reptiles; the poison-fang is rather a modification of form.
The labyrinthic structure reaches its maximum of complexity in
the great extinct Sauroid Batrachians of the Keuper Sandstones,
but ‘‘it also exists at the base of the tooth in a few Fishes,”
(Part II, p. 201), and specific instances of it in that class (Lept-
dosteus, and a few other Sauroids) have, since Part II. was published,
received illustrations in the works of Prof. Agassiz(1) and Dr.
Wyman.(2) The only constant and general character of the teeth of
the cold-blooded classes of Vertebrata is derivable from the brief
period of their existence in the individual, so that the few teeth which
develope roots have these always simple and undivided, usually
hollow, and with the germ of a successor in or near them.

With the exception of the composite dental masses of the
Chimeeroids, and the anomalous rostral teeth in Pristis, no existing
species of Fish or Reptile could be said to have permanent teeth ;
and no extinct species of either class has yet been found with teeth
having divided roots implanted in sockets, or manifesting evidence
of perpetual growth by a persistent pulp, excepting the singular
extinct Saurians of South Africa, with two long canine tusks in the
upper jaw, which must have grown and been maintained throughout
life, of due size and strength, like the tusks of the Boar and
Walrus.(8) With the exception of these two anomalous teeth,
the jaws of the Dicynodonts were edentulous.

In the Mammalian Class the value of the dental organs, as

(1) Poissons Fossiles, Notice sur les Sauroides, Janvier, 1843.
(2) Trans. Boston Society of Natural History, August, 1843.

(3) Memoir on the Dicynodon, Geological Transactions, 2nd series, vol. vii.

Ixx INTRODUCTION.

characters of classification, is much greater than in Reptiles or
Fishes, as will be seen in Part III. Yet there is a difference in this
respect in the different Orders, and the Dental System of the
Cetacea and Bruta has a much greater range of variation, and a less
constant relation to the other characters on which the families and
genera are founded, than in the Ungulate and. higher Unguiculate
Species. But, with respect to these also, the value of the teeth
as zoological characters has been overrated. (1)

| It is true, indeed, that the most manifestly natural Mammalian
genera are those, the species of which are provided with absolutely
similar molar teeth : and, that those genera, which include species with
molars of different forms, do not present the same character of unity.
But it does not follow that, by combining species of Mammals with
similar molars, a group will be formed perfectly analogous to those
which may be considered as the most natural or perfect. Neither the
molar teeth, nor any other solitary character will serve to establish a
natural classification.

The molar teeth will least mislead in this respect where their
modification is most extreme, as when they are adapted to divide the
flesh of animals, in which case they must of necessity be associated
with the faculties and instruments for seizing and destroying prey.
But molar teeth may be similarly modified, and equally well adapted
for crushing vegetable substances, which substances may be

sought for by one species on the dry land, by a second in

(1) M. F. Cuvier says “ Cette recherche me fit reconnaitre que tous les genres manifeste-
ment naturels, et admis comme tels par tous les naturalistes, étaient formés d’espéces pourvues
de machelitres absolument semblables; que ceux qui comprenaient des espéces dont les
macheliéres différait, n’offraient point ce caractére d’unité qui était le partage des premiéres ; et,
enfin, qu’en réunissant les espéces 4 macheliéres semblables on reformait des groupes parfaite-
ment analogues 4 ceux que l’on pouvait considérer comme les plus parfaits.” Dents de Mam-

miféres, 8vo. 1825, p. ix.

INTRODUCTION. Ixxi

marshes, and by a third in the sea, or on the banks of rivers.
The grinding surface of the molar tooth, for example, may for
this purpose be elevated into a pair of transverse ridges, and
we find such molars in the Kangaroo, the Tapir, and the Manatee,
as also in the extinct Diprotodon, Nototherium, and Dhinothe-
rium. The small anterior molars of the Mastodon giganteus
likewise present this form. It would be difficult to select from
the Mammalian Class the constituents of a more heterogeneous
group than would be constituted by the character which M.
F. Cuvier has assigned as the true guide to the formation of
the most natural and uniform genera in Mammalogy.

Even in regard to teeth adapted to carnivorous habits, were
these characters to form the sole guides in classification, species
of placental Mammalia would be associated with those of the
ovoviviparous sub-class; and M. F. Cuvier, in illustrating his
generalization, observes: ‘‘ Les sarigues, les péraméles, et les
dasyures se sont réunis aux Insectivores, &c., &c., et je crois

avoir été conduit a ces modifications par des motifs légitimes.’’(1)

The class of tissues in which teeth should rank, has fre-
quently been a subject of controversy in Systems of Histology ;
the fact being overlooked that they have not the same unity of
composition as bones or epidermal appendages. One constituent
of teeth, viz., the cement, unquestionably ought to rank with the
osseous tissue; and the dentine, or ivory, which was described
for the last time in this country, in July, 1838, as being ‘‘ like the

hair, arranged in concentric layers,” (2) bears, on the contrary, a close
Oly, Lie. elt. sp. Xi,
(2) Medico-chirurgical Review, p. 43. In France the dentine continued to be described,
as late as the end of 1839, as “ composé de cones lamelleux extrémement minces, s’emboitant

les unes les autres, &c.” De Blainville, ‘ Ostéographie’ Fascicule premier, Primates, p. 14, 1839.

Ixxii INTRODUCTION.

structural resemblance to bone and is almost identical in chemical
composition: its modifications, which I have called ‘vaso-
dentine’ and ‘osteo-dentine,’(1) forming intermediate gradations
between the hard dentine and true bone. ‘True enamel is a tissue
per se; but in the teeth of Fishes there are several intermediate
stages of gradation which link enamel to dentine, as the dentine
itself, in most Fishes, passes gradually into bone.

Heusinger admits that the relation of the teeth to the corneous
tissue (Horngewebes) is not clearly elucidated in Human Anatomy,
but he affirms that it is most conclusively established in that
of the lower classes of animals. (2) No doubt in tracing the mo-
difications of the dental system through the Animal Kingdom,
we find true horny productions substituted for teeth in certain

Vertebrate Species, as the Ornithorhynchus, Whale, Tortoise, &c.

(1) These tissues are respectively defined, as follows, in the ‘Report of the British
Association, 1838.” “With respect to the component structures of atooth, Professor Owen
commenced by observing, that in addition to those usually described and admitted, there were
other substances entering into composition of teeth, and presenting microscopic characters
equally distinct both from ivory, enamel, and cement, and from true bone, and as easily recog-
nisable. One of these substances was characterized by being traversed throughout by
numerous coarse canals, filled with a highly vascular medulla or pulp, sometimes anastomosing
reticularly,—sometimes diverging, and frequently branching,—sometimes disposed nearly
parallel with one another, and presenting more or fewer dichotomous divisions. ‘The canals in
many cases are surrounded by concentric lamelle, and thus resemble very closely the Haver-
sian canals of true bone; but the calcigerous tubes which everywhere radiate from them are
relatively much larger. The highly-organized tooth-substance just described differs from true
osseous substance, and from the cementum in the absence of the Purkingian corpuscles or cells.
This structure is exemplified in the teeth of many fishes and some Edentate Mammalia.
Another component substance of tooth more closely resembles true bone and cement, inasmuch
as the Purkingian cells are abundantly scattered through it; it differs, however, in the greater
number and close parallel arrangement of the medullary canals. This structure is exhibited in
the teeth of the Megatherium, Mylodon, and other extinct Edentata,” p. 137.

. (2) System der Histologie, 4to. 1823, p. 160.

INTRODUCTION. Ixxili

So likewise the office of teeth is performed, in the Articulate Classes,
by parts (modified as to form) of the crustaceous and chitinous
integuments. But I know of no transitional or intermediate structures,
such as Heusinger alludes to, between teeth and nails, horns or hair.
The lamellar disposition traceable in the texture of the hardest
dentine, is much more closely similar to that of bone, especially
to the concentric plates surrounding the Haversian Canals, than to
the texture of nails. The structure of the tooth of the Oryc-
teropus, is essentially like that of all true teeth: the apparent
resemblance which it presents to the horn of the Rhinoceros, or
to Baleen, arises from its being compounded of many minute
parallel and elongated denticles.

And the close resemblance in intimate structure and chemical
composition between true teeth and bones being established, it
may be observed that the osseous tissue is not confined to the
endo-skeleton: it is developed largely to form the exo-skeleton
in many Fishes, in the Loricate Reptiles, and even in the Mamma-
lian Class, as, for example, in the Armadillos (Dasypus), where,
to strengthen the integument, bone is substituted for horn, which
forms the scaled armour of the allied Pangolins (Manis.) Now the re-
lation of the tooth ofthe Armadillo to that of the Ornithorhynchus is
precisely analogous to that which subsists between the osseous
plates of the Armadillo and the corneous scales of the Pangolin;
but this relation no more establishes identity of tissue or
system of tissues in the one case than in the other.

The general form of the dental matrix and its relation with its
calcified product, bear a close analogy with those of the formative organ
of hairs, bristles, and other productions of the epidermal system.
In these the papilla, or pulp, is developed from the external
skin; in the teeth from the mucous membrane, or internal skin.

F

Ixxiv INTRODUCTION.

Teeth further agree with the extravascular appendages of the
skin in being shed and reproduced sometimes once, sometimes
frequently, during the life-time of an individual: the latter may
be termed ‘interrupted’ reproduction. In some cases again, as
with certain epidermal appendages, the reproduction of the tooth
is uninterrupted, and goes on during the life-time of the indi-
vidual; new matter being added to the base as the old is worn
away from the apex, or working surface of the tooth. A tooth,
when fully formed, is subject to decay, but has no inherent power
of reparation. A tooth of limited growth can only increase in size
after its formation is completed by abnormal growth of its most
highly organised constituent, the cement. Thus, then, it appears
that, the analogy of the dental organs to those of the corneous
system holds only in their mode of development(1), in their
shedding and reproduction, and in their exposure to external
influences and to the contact of extraneous bodies: but the
antlers of Deer are similarly exposed, and are likewise shed and
reproduced annually, and also contemporaneously with the fall
of the hair; but antlers are not, therefore, classed with the
corneous tissues, any more than is the bony core of the horns of

the cavicorn Ruminants.

(1) The cells and fibres of the horny tissues are formed in and not excreted from the surface

of their formative pulps.

Page

31
103
134
136

line

7 from top,
8 from bottom,
4 from top,

15 ve
18 .
8

21

15

8 from bottom,

ERRATA.

for Goniadus read Goniodus.
Pharyngnies read Pharyngiens.
Jigure b read figure 6.

+» (f) read (fig. 5, f)
4) read 3)
Jig. 1) read fig. 5.

-. jig. 2) read fig. 6.

«. jig. 5 and 6, read figs. 1 and 2.
laminaries read laniaries

3 from bottom of note, for palates read palate

Note (1)
5 from bottom,
2 from top,

12 from bottom,

ll from top,

Pl. 91 read Pl. 90.
for fig. 3 read fig. 2
Pl. 168 read Pl. 108.

4—4 3—3
+. Mm ——: = 42. read m. ——: = 44.
4—4 3—3

+. fig. 1 & 2 read fig, 2.

9 & 7 from bottom, for osseo-dentine read osteo-dentine.

Note (1)
Note (3)
Note (1)
Note (2)

dele Pl. 122 a, fig. 1.

for Pl. 124 a, fig. 4. read Pl, 122 a, fig. 4, a.
fig. 1 & 2 read fig. 1 a
p. Ixvi read p. lviii.

remem te ets

ODONTOGRAPHY.

Pato Po,

DENTAL SYSTEM OF FISHES.

CHAPTER I.

GENERAL OBSERVATIONS ON THE TEETH OF FISHES.

Ir the ichthyologist have reason to complain of the monotony
which unavoidably pervades his descriptions of the external charac-
ters of the objects of his study,(1) the anatomist in treating of the
dental system of fishes, finds, on the contrary, his difficulty in
obtaining the command of language sufficiently varied to pourtray
the singular diversity and beauty, and the interesting physiological
relations which are manifested in that part of their organization.
The teeth of fishes, in fact, in whatever relation they are considered,
whether in regard to number, form, substance, structure, situation,
or mode of attachment, offer more various and striking modifications
than do those of any other class of animals.

2. Number.—If we commence with the lowest species, as the
glutinous hag and other myxinoid fishes, we find that, the armature
of the tongue excepted, the dental system is represented by a single
tooth developed on the median line of the palate. In the carp,
a single median tooth above the pharynx is opposed to two den-
tigerous plates below. In the Ceratodus and Ctenodus, the jaws are
armed with four teeth, two above and two below. In the chimera,
two lower maxillary teeth are opposed to four above. From these
species may be traced every gradation in the progressive multipli-
cation of the teeth up to the pike, silurus, and other fishes in
which the mouth is crowded with innumerable teeth.

3. Form.—The great variety of forms of the teeth of fishes

(1) Cuvier, Eloges, iii, p. 313.

2 FORM.

has attracted the attention of most comparative anatomists, and yet
such is the rapidity with which new species, either of the present
or a past creation, are added to the catalogues of the ichthyologist,
that this part of the subject is far from being exhausted. All the
known differences which the teeth of fishes present in this respect
may, however, be referred to modifications, either of the cone, the
plate, the prism or the cylinder.

The conical teeth may be slender, sharp-pointed, and so minute,
so numerous, and closely aggregated as to resemble the plush or pile of
velvet; these will be termed villiform teeth, they are the dents en velours
of Cuvier, and are sometimes so short as to be more easily felt than
seen: when the teeth are equally fine and numerous but longer, they will
be called ciliiform teeth : when long and slender, but a little stronger,
they are the dents en brosse (brush-teeth) of Cuvier. Conical teeth as
close-set and sharp-pointed as the villiform teeth, but of larger size, are
the dents en rape, or en cardes of the French anatomist. These modifi-
cations of the whole or a part of the dental series are common to
a great number of fishes. The perch has all its teeth en velours; the
pike presents the rasp-like teeth on the posterior part of the vomer ;
the armature of the palate hone of the silurus (Pl. 1, fig. 1,) as well
as that of other bones of the mouth of the same fish, presents all the
gradations between the dents en velours, and the dents en cardes.

The conical teeth may be so long and slender as to resemble
bristles, as in the cheetodonts (Pl. 1, fig. 2.) These setiform teeth
are sometimes bifurcate at their free extremity, as in the genus
Citharina ; or they may terminate in three diverging points, as in
the anterior maxillary teeth of the genus Plataz (Pl. 1, fig. 2*), and
here the cone merges into the long and slender cylinder.. Or the
elongated cone may be compressed into a slender trenchant plate ;
and this may be pointed, recurved, or even barbed like a fish hook, as
in the Trichiurus (Pl. 1, fig. 8,) and some other scomberoid fishes ; or
it may be bent upon itself like a tenter-hook, as in the Pimelipterus
and Gonyodontes. In other species asin the bonito, (PI. 1, fig. 3,) the
conical teeth present a progressive thickening of the base, and this
modification being combined in certain predatory fishes with an
increase of size and a slightly recurved direction, they resemble the

FORM. Pe:

Janiary or canine teeth of the carnivorous quadrupeds. Of this kind
are the Jarger teeth of the pike and Riazodus (Pl. 35), and the
anterior teeth of the Dentex, (Pl. 41). A moderately long, stout
and more or less straight cone is a form exemplified in the anterior
teeth of the wolf-fish, (Pl. 60 & 6],) and the transition by progressive
blunting, flattening and expansion of the apex is very gradual from
this form of the cone to the thick and short cylinder, such as is seen
in the posterior teeth of the wolf-fish, and similar grinding or
crushing teeth of many other existing genera. The working surface
of these short cylindrical teeth may be rounded as in the sheep’s-
head-fish (Sargus, Pl. 42, fig. 1,) or flattened as in the pharyngeal
teeth of the wrasse, (Labrus, Pl. 45, fig. 4). Sometimes the hemi-
spheric teeth are so minute and numerous as to give a granulated
surface to the part of the jaw to which they are attached (Pl. 45, fig. 1),

A progressive increase of the transverse over the vertical dia-
meter may be traced in the molar teeth of different fishes, and
sometimes in those of the same individual, until the cylindrical form
is lost in that of the depressed plate. Of this change we have a good
example in the posterior teeth of the gilt-head (Chrysophrys), when
arrived at maturity, and likewise in the fossil genus Placodus,
(PI. 30). The dental plate, instead of offering the cylindrical form,
may be ellipticai, obiong, square, triangular, semilunar, sigmoid,
and with the grinding surface variously sculptured. The broadest
and thinnest depressed lamine are seen in the component denticles
of the molar tubercle of the diodon, and in the teeth of the Phyllodus.

The incisors of the sargus, (Pl. 1, fig. 13,) flounder, and some
other fishes present the compressed laminated form, at least, in the
protruded coronal portion. Numerous wedge-shaped dental plates
are set vertically in the pharyngeal bones of the Scarus or parrot-
fish. A thin lamella, slightly concave like a finger-nail, is the sin-
gular form of the tooth of an extinct genus of cartilaginous fishes,
which I have, on that account, named Petalodus, (Pl. 22, figs. 2, 3, 4.)
Sometimes the flattened incisive crown is notched in the middle of
the cutting edge, as in the incisors of the species of bream (Sargus
unmaculatus) figured in Pl. I, fig. 9. Sometimes there is a double
notch rendering the crown of the incisor trilobate, as in the genus

B 2

4 FORM. SITUATION.

Aplodactylus, (fig. 10); in the lower maxillary teeth of the Boops,
the crown is divided into five lobes by a double notch on each side
of the middle and largest lobe, (fig. 11).

In the great barracuda-pike (Sphyrena), the crown of both the
large and small lamelliform teeth is produced into a sharp point, and
closely resembles a lancet, (Pl. 1, fig. 4, & Pl. 53). A similarly
shaped piercing and cutting tooth may be accompanied by one or
more accessory compressed .cusps at its base, as in the teeth of cer-
tain sharks, (Pl. 3 & 4,) or the margins of the crown may be variously
notched, serrate, e. g., as in the priodon, (Pl. 1, fig. 12,) and in the
teeth of the great sharks of the genus Carcharias, or crenate as in the
genus, hence called Crenidens, (fig. 7,) and in the teeth of the Acan-
thuri, (Pl. 44,) of which the species called Ctenodon is remarkable for
the deeply crenated, expanded and spatulate crowns of its teeth, (PI.
1, fig. 6). Prismatic teeth of three sides are present in the jaws
of the Myletes, where each angle of the coronal surface is produced
into a point. Thesmall teeth with which the jaws of the Scarus are
paved are four sided prisms; the strong flat teeth which form the
tesselated pavement of the jaws of the Eagle-rays (Myliobates), present
beautifully regular hexagonal or pentagonal forms (Pl. 25).

4. Situation.—Before proceeding to consider the situation of
the teeth of fishes, a few words may be premised respecting the
bones which enter into the formation of the mouth in the ordinary
osseous species. In these, the upper margin of the mouth is
bounded generally by the intermaxillary bones alone, which extend
backwards from the middle line to the angles of the mouth; in
this case, the superior maxillary bones(1) run parallel with and above
the horizontal portion of the intermaxillaries ;(2) but when, as in
the lophius and salmon-tribe, the intermaxillary bones do not
extend to the angles of the mouth, the osseous boundary is com-
pleted above by the superior maxillaries.(3) The lower border of .
the mouth is formed by the premandibular bones,(4) this name being
given to the anterior of the two pieces of which each ramus of
the lower jaw consists in fishes. The roof of the mouth is formed
anteriorly by three bones which extend backwards from the inter-
space of the intermaxillary bones; the two lateral ones are the pa-

(1) Pl. 41, &. (2) Pl. 41, a. (3) Pl. 60, fig. 1, 5. (4) Pl. 41, ¢.

SITUATION. 4)
latines, (b 6 Pl. 61), the median one is the vomer, (c Pl. 61). Two flat-
tened bones on each side, called the pterygoid and transverse bones,
complete the bony arch or buttress which extends from the inter-
maxillaries to the pedicle supporting the lower jaw. Posteriorly, the
roof of the mouth is completed by the sphenoid and sub-occipital bones.

The floor of the mouth is supported by the median longitudinal
chain of lingual bones, to the sides of which are attached the infe-
rior extremities of the branchial arches; these form the sides of the
posterior part of the mouth, which gradually contracts to the pharynx ;
this orifice is strengthened by bones above and below, varying in
number from one to six, and called the pharyngeal bones.

In the roach, dace, barbel and most other cyprinoid fishes, the
teeth are limited to the pharyngeal bones; in the carp, the upper
pharyngeal dental plate is wedged into a cavity of the occipital bone.
In the ordinary sharks and rays, on the other hand, the teeth are
confined to the maxillary cartilages bounding the anterior aperture
of the mouth. The wrasse, (Labrus), and parrot fish, (Scarus), are
instances in which the intermaxillary and premandibular, as well as
the pharyngeal bones are provided with teeth, both the anterior and
posterior apertures of the mouth being thus surrounded by instru-
ments for dividing or comminuting the food. In other fishes, we
find the teeth situated not only on the bones which bound the an-
terior and posterior orifices of the mouth, but in the intermediate
positions, as on the palatines, the vomer, the lingual bones, or the
branchial arches ; sometimes, also, but more rarely, on the transverse,
or pterygoid, the sphenoid,(1) and the superior maxillary bones, of
which latter situation the fishes of the Halecoid(2) tribe and the
extinct Lepidotus, afford examples in the present class. Among
the anomalous positions of teeth may be cited, in addition to the
occipital alveolus of the carp, the accessory rostral cartilages, which
in the Pristis are elongated, and so ossified as to be adapted to retain
in sockets the strong sharp lateral teeth, constituting its formidable
saw. In the lampreys, and in one of the osseous fishes (Helostomus)
most of the teeth are attached to the lips. Lastly, I may observe,
that it is peculiar to the class of fishes among vertebral animals, to

(1) PL 48, fig. 2. (Sudis).
(2 In this family M. Agassiz includes the Salmonoid and Clupeoid fishes of Cuvier.

6 SITUATION. ATTACHMENT.

present examples of teeth developed in the median line of the mouth,
as in the palate of the myxines, or crossing the symphysis of the
lower jaw, as in the scymnus and myliobates.

5. Attachment.—The teeth of fishes present greater diversity in their
mode, as wellas place of attachment, than is observable in those of any
other class of animals. In a few instances, they are implanted in sock-
ets, to which they are attached only by the surrounding soft parts, as
e. g., the rostral teeth of the saw-fish.(1) Some have their hollow base
supported, like the claws of the feline tribe, upon bony prominences,
which rise from the base of the socket; the incisors of the file-fish
afford this curious example of a double gomphosis, the jaw and the
tooth reciprocally receiving and being received by each other. (2)

Theteeth of the Sphyrena, Acanthurus, Dictyodus, &c., 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 parietes of the
alveolar cavity. But by far the most common mode of attachment of the
fully-formed teeth in the present class, is by a continuous ossification
between the dental pulp and the jaw; the transition being gradual
from the structure of the tooth to that of the bone: the tooth,
prior to the completion of the anchylosis, is connected by ligamentous
substance, either to a plain surface, an eminence, or a shallow depres-
sion in the jaw-bone.

Sometimes not the end, but one side of the base of the tooth is
attached by anchylosis to the alveolar border of the jaw ; it might be ©
supposed that, in this case, the crown of the teeth in both jaws
would project forwards instead of being opposed to one another,
and such, in fact, must have been their position were it not that, in
some instances, as in the Pimelipterus, the teeth have the crown
bent down at nearly a right angle with the base. In the scarus,
and likewise in the marginal teeth of the diodon, where the teeth
are straight, and attached horizontally to the margin of the jaws,
their sides instead of their crowns are actually opposed to one another.

In the cod-fish, wolf-fish, and some other species, in proportion
as the ossification of the tooth advances towards its base and
along the connecting ligamentous substance, the subjacent portior
of the jaw-bone receives a stimulus, and developes a process corres-

(1) Pl. 8, fig. 3, (2) Pl. 40, figs. 3 and 5, a

ATTACHMENT. 7

ponding in size and form with the solidified base of the tooth. In
this case, the inequalities of the opposed surfaces of the tooth and
maxillary dental process fit into each other, and for some time
they are firmly attached together by a thin layer of ligamentous
substance ; but in general, anchylosis takes place to a greater or less
extent before the tooth is shed. The small anterior maxillary teeth of
the angler (Lophius) are thus attached to the jaw, but the large posterior
ones remain always moveably connected by highly elastic, glistening
ligaments which pass from the inner side of the base of the tooth to
the jaw-bone. These ligaments do not permit the tooth to be bent
outwards beyond the vertical position, when the hollow base of
the tooth rests upon a circular ridge growing from the alveoiar
margin of the jaw ; but the ligaments yield to pressure upon the tooth
in the contrary direction, and its point may thus be directed towards
the back of the mouth ; the instant, however, that the pressure is re-
mitted, the tooth flies back, 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 osseous base of the teeth of sharks is attached by ligaments
to the ossified or semi-ossified crust of the cartilaginous jaws. The teeth
of the Salarias and of certain Mugiloids are simply attached to the gum.
The small and closely-crowded teeth of the rays are also connected by
ligaments to the subjacent maxillary membrane. The broad tesselated
teeth of the eagle-rays have their attached surface longitudinally
grooved, to afford them better holdfast ; and the sides of the contiguous
teeth are articulated together by true serrated, or finely-undulating
sutures; which mode of fixation of the dental apparatus is unique in
the animal kingdom.

If the engineer would study the model of a dome of unusual
strength, and so supported as to relieve from its pressure the floor
of a vaulted chamber beneath, let him make a vertical section of one
of the crushing pharyngeal teeth of the wrasse.(1) The base of this
tooth is slightly contracted, and is implanted ina 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 to the bone, is strengthened by an

(1) Pl. 46.

8 ATTACHMENT. SUBSTANCE.

inwardly projecting convex ridge. The masonry of this internal
buttress and of the dome itself, is composed of hollow columns, every
one of which is placed so as best to resist or transmit in the due
direction the superincumbent pressure. The advantages gained by
this beautiful example of animal mechanics will be explained when the
dental system of the labroid fishes is described.

In another case, in which long and powerful piercing and lace-
rating teeth were evidently destined, from the strength of the jaws,
to master the death-struggles of a resisting prey, we find the broad
base of the tooth divided into a number of long and slender cylindrical
processes, which are implanted, like piles, in the coarse osseous sub-
stance of the jaw; they diverge as they descend, and their extremities
bend and subdivide like the roots of a tree, and are ultimately lost
in the bony tissue. This mode of implantation of the teeth, which
I have detected in a large extinct sauroid fish (Rhizodus),(1) is, per-
haps, the most complicated which has yet been observed in the animal
kingdom. |

6. Substance.—The teeth of fishes, in respect to their sub-
stance, present various degrees of density and complexity: In most
of the chetodonts they are flexible and elastic, of a yellowish, shining,
and subtransparent tissue. The labial teeth of the helostome are
also of this kind, as are also the anterior maxillary teeth of the gonyo-
donts, and of the percoid species, hence called Trichodon. In the cyclos-
tomes, the teeth consist of an albuminous tissue, of a somewhat denser
nature. The upper pharyngeal molar of the carp, consists of a peculiar
brown and semi-transparent tissue, harder than the true horny teeth
of the lamprey.

The greater number of fishes have their teeth composed of an
osseous substance, somewhat denser than the jaws to which they
are affixed. In some instances, as in the teeth of the flying-fish
(Exocetus), and sucking-fish (Remora), the substance of the tooth is
uniform, and not covered by a layer of a denser texture. In others, as
the shark, sphyrena, &c., the tooth is coated with a dense, shining,
enamel-like substance ; but this is not true enamel, nor the product
of a distinct organ ; it differs from the body of the tooth only in the
greater proportion of the earthy particles, their more minute diffusion

(1) PL. 36.

SUBSTANCE. CHEMICAL COMPOSITION. 9

through the gelatinous basis, and the more parallel arrangement of
the calcigerous tubes ; but it is developed in and by the same matrix,
and, resulting from the calcification of its external layer, is the first
part of the tooth which is formed. In the Sargus and Balistes, the
dentine, or proper osseous substance of the tooth, is harder than that
of the fishes last cited, and is covered with a thick layer of a denser sub-
stance, developed by a distinct organ, and differing from the enamel of
the higher animals only in the more complicated and organized mode of
deposition of the earthy particles. The ossification of the capsule of the
matrix gives the enamel of the teeth of the file-fish, and some others,
a thin coating of a third substance analogous to the ‘‘ cementum,
or crusta petrosa,” of the mammalian teeth. And in the pharyngeal
teeth of the parrot-fish, a fourth substance is added to the structure
of the tooth by the coarser ossification of the pulp, after its peripheral
portion has been converted into the dense ivory. The teeth, thus
consisting of dentine, enamel, cement, and coarse bone, are the most
complicated as regards their substance that have yet been discovered.

7. Chemical composition.—With respect to the chemical compo-
sition of the teeth of fishes, little remains to be added to what has been
stated on this subject in the preliminary general observations. The
animal base of the horny teeth of the cyclostomes is albuminous, as
in true horn; that of the calcified teeth is gelatinous, and the pro-
portion of gelatin to the usual hardening salts, diminishes as their
density increases. According to the analysis of Lassaigne,(1) the teeth
of the shark yield

Puospiate of lime 52," 6
Carbonate of lime . . 13, 9
Animal matter ares ere oO

100, 0

The inferior pharyngeal teeth of the carp contain

Phosphate of ime . . 49
Carbonate Of ite... 16
Ammal matter oo"! . -'ou

100,0

(1) Berzelius, Traité de Chimie, par Esslinger 1828, tom. vii, p. 480.

10 STRUCTURE.

In the brown upper pharyngeal tooth of the carp, Stromeyer(l1)
detected a small proportion of magnesia.

8. Structure.—The tubular structure common to the dentine of
all classes of animals, though not first discovered in the teeth of
fishes, has been most frequently recognised, because most conspicuous,
in them: and, as in several fishes, the coarser features of this
structure are obvious to the naked eye, it was admitted as applicable
to a greater or less proportion of that class by some comparative
anatomists, before the researches of Purkinje and Retzius had established
its existence in the teeth of the higher vertebrate animals. Leeuwen-
hoek, indeed, in his account of the minutely tubular structure of the
teeth of man and of the ox,(2) attributes the same structure to the
tooth of the haddock, in which he states that the dental tubes are smaller
than in the ox. Mr. André(3) detected the ramified canals which
pervade the substance of the tooth of the Acanthurus. Cuvier(4) first
described the coarser tubes composing the teeth of the rays and of
the wolf-fish; and Von Born(5) ascribes to the teeth of a greater
number and variety of fishes the same structure, which was regarded
by both these anatomists as analogous to the tubular structure of the
teeth of the ornithorhynchus and orycteropus, and also compared with
that of whalebone and of the horn of the rhinoceros. Such comparisons,
however, are wanting in accuracy when applied in that loose and
general manner.

In the following pages there will be shown to he, at least,
four principal modifications of the tubular structure in the teeth
of fishes. Premising that the essential character of this structure
is a cavitas pulp, or medullary canal, from which the calcigerous
tubes radiate, the first modification which may be noticed is
where the tooth is traversed by a number of equidistant and
parallel medullary canals, each canal and its system of medul-
lary tubes representing a cylindrical or prismatic denticle, and being
separated from the contiguous denticles by a thin coat of bone or
cement. This modification is exemplified in the rostral teeth of

(1) Gilbert’s Annalen, Bd. vii, 1811.
(2) Philos. Trans., 1678, p. 1003.
(3) Ib. vol. 74, Description of the teeth of Cheetodon (Acanthurus) nigricans,

(4) Lecons d’Anat. Comparée, tome iii, p. 113 (1805).
(5) Heusinger’s Zeitschrift, Bd. i, 1827.

STRUCTURE. Il

the saw-fish, (Pristis), the tesselated teeth of the eagle-rays, (Mylio-
bates, Zygobates, &c.), and the maxillary plates of the chime-
roids. The dense dental case of the jaws of the parrot-fishes,
(Scarus), may likewise be regarded as an extreme instance of
this modification, and we shall find the same structure re-ap-
pearing in some of the inferior genera of the mammiferous class.
In the parrot-fishes, the denticles are quite distinct from one
another, but in the saw-fish, chimera, and eagle-rays, the contiguous
medullary canals occasionally anastomose together. In the chime-
roid fishes these anastomoses are more numerous, and the boundaries
of the component denticles less distinct, so that they form a
transition between the preceding, and what may be regarded as the
second variety of the tubular structure.

In this modification, the substance of the tooth is traversed by
medullary canals, somewhat less regularly equidistant and less
parallel than in the first; having the boundaries of their respective
systems of radiated calcigerous tubes indicated by the minute
calcigerous cells, with which the terminal branches of those tubes
communicate ; these boundaries being more or less obscured by
the terminal branches of the calcigerous tubes extending across
into the interspaces of the corresponding branches of an adjoining
system of tubes, and anastomosing with them immediately, or
through intervening dilatations or cells. The medullary canals
here dichotomize more frequently than in the first modification ;
their anastomoses are more numerous, and the whole tooth, which
is generally of large size, is consequently more individualized and
compacted. The teeth of the Port-Jackson shark (Cestracion Philltppi,)
afford a good example of this modification, which also prevails in
those of the extinct genera Piychodus, Psammodus, Helodus, Ctenop-
tychius, &c. In the teeth of the extinct dAcrodus, the medullary
canals, which likewise traverse in great numbers the body of the
tooth, assume a more or less wavy course; and this disposition,
combined with their numerous anastomoses, leads to the third modifi-
cation, which at the same time is the most common and characteristic
of the dental structure, in the class of fishes.

In teeth manifesting this variety of the tubular structure, the
dentine is permeated by a network of medullary canals, of which the

12 STRUCTURE.

interspaces are occupied by the calcigerous tubes and cells. The me-
dullary canals are directly continued from those of the common bone
with which the base of the tooth is anchylosed, or into which it has
been converted. As the medullary canals proceed through the tooth,
they maintain a course more or less parallel, and more or less straight,
or wavy; but they ramify abundantly, and gradually diminish in
calibre as they approach the surface of the tooth. The illustra-
tions of this modification of the dental structure in the present work,
are taken from the teeth of the extinct Lamna, Dictyodus, and Sauroce-
phalus, and from those of the recent Sphyrena and Acanthurus. In
the latter genus the dendritic arrangement of the medullary tubes
recognized by Mr. André, has subsequently been figured by V. Born.
V. Born and Retzius have described a similar structure in the teeth
of the wolf-fish (Anarrhichas), of which Mr. Nasmyth has given a
figure in his useful translation of some of the recent treatises on
dental anatomy.

The reticulate medullary tubes pervade the structure of the
teeth of the percoid, scizenoid, cottoid, and gobioid families of fishes ;
and of those of the Capros, Naseus, and other genera of the Theuties of
Cuvier, besides the teeth of the Acanthuri already cited. A similar
reticulate structure is common to the teeth of the Chetodontes and the
_ Pleuronectes: in the cycloid fishes, we find it almost universal in the
scomberoid, lucioid, salmonoid, and clupeoid families: it is ex-
changed for a higher type of structure in the maxillary teeth of the
lophioid fishes, and in the pharyngeal teeth of the cyprinoids, but
it again reappears in the teeth of the blennioid, gadoid, and mu-
renoid families; and the same coarse bone-like structure pervades
the dental plates of the supposed amphibious Lepidosiren.

The higher type of structure just alluded to is that which
characterises the teeth of most reptiles and mammalia. Here the
dentine consists of a single medullary or pulp canal, and a single
system.of calcigerous tubes radiating from the central or sub-central
canal, at right angles to the periphery of the tooth. The teeth
of the extinct sauroid fishes and pycnodonts, the maxillary teeth of
the existing file-fishes (Balistes), and angler (Lophwus), the incisors,
canines, and molars of the breams or sparoid fishes, the pharyngeal
pavement-teeth of the wrasse-tribe (Labrde), the maxillary and

STRUCTURE. 13

pharyngeal denticles of the scari, and the lamelliform denticles of
the crop-fishes, diodon and tetrodon, likewise the maxillary teeth of
some of the genera of sharks and rays, afford examples of this structure.

I have spoken of it as belonging to a higher type because it is
characteristic of the teeth of the vertebrate animals which are higher
in the scale than fishes ; but if the grade of organization of a tooth
be rated according to the proportion of vascular substance and _ vital
power which it possesses, then those teeth which most resemble bone
should be regarded as the most highly organized, and such are the
teeth most common in the class of fishes.

As the inorganic calcareous particles are deposited principally
in the parietes of the calcigerous tubes and their terminal ramuli
and cells, it follows that the density of the tooth will increase, and
its vital properties diminish as the calcigerous preponderate over the
medullary tubes, and in proportion as the calcigerous tubes in a given
space are more numerous and minute. But the change from one
modification of dental structure to another, from bone to the densest
ivory, 1s so gradual, that the physiologist, entertaining a belief in the
inorganic nature of the teeth, would be at a loss where to draw
the line, or to determine where the vital forces ceased their manifesta-
tion, and at which step in the series of tubular structures the
tooth became an inert body. The uniform result of my researches,
on the structure of the teeth in all grades of vertebrate animals,
and in their natural and diseased states, has been a conviction of
the untruthfulness of the terms inert, dead, and unorganized as
applied to the substance of any tooth whatever. Extra-vascular
undoubtedly is all that portion which consists of the calcigerous
tubes ; the capillary circulation is confined to the pulp or medul- -
lary canals; but since every secretive process and the development
of the primordial cells of every tissue are due to changes produced
in the liquor sanguinis transuded from and beyond the sphere of
the ultimate capillaries, the absence of these vessels in the dense
dental substance is as little conclusive against its vital and organized
nature, as it would be to prove the inert condition of the germinal
membrane of the ovum before the thirtieth hour of incubation.

In no teeth is the dentine rendered so dense as in those of certain

14 STRUCTURE.

fishes, especially the Scarus and Diodon, which have been cited as ex-
amples of the fourth modification of the dental structure. These teeth
strike fire with steel, yet they present an organized structure of mi-
nute complexity, and the calcigerous tubes are nowhere so numerous,
so minute, so beautifully ramified and interlaced together.

It has already been observed that the prismatic maxillary denticles
of the Scarus, being compacted together side by side and with their
single medullary canals parallel to each other, produce a compound
dental plate analogous to those which were first cited in illustration of
the present subject. In the Diodon, each denticle, which is composed
as in the Scarus of a single system of minute calcigerous tubes, assumes
the form of a thin plate: the pulp cavity instead of being contracted
into a tube, as in the elongated teeth, is here spread over the under
surface of the dental lamella; the calcigerous tubes proceed ina di-
rection more or less vertical to the upper surface (in the teeth of the
lower jaw); and the compound dental mass results from the super-
position and successive development of similar plates, separated
only by a layer of thin bone or cementum. In the pharyngeal teeth
of the Scarus, the denticles are also more or less lamelliform, but their
position is vertical, and they are joined side to side by means of the
intervening cement or the ossified capsule: compound dental masses
similarly constructed are present in the capybara, elephant, and
others of the mammalia, generally cited as affording examples of the
most complex teeth.

9. Development.—The teeth of fishes are formed according to the
general laws of dental development already discussed ;(1) but the pro-
cess, in many instances, does not extend beyond the earlier ard simpler
stages observable in the higher classes of animals. In all fishes, as
in other vertebrate animals, the first step is the production of a simple
papilla from the free surface of either the soft external integument,
as in the young Pristis,(2) or of the mucous membrane of the mouth, as

(1) Introduction, p. vi.

(2) A very close analogy exists between the dermal bony tubercles and spines of the cartilagi-
nous fishes and their teeth. The thick enamelled scales of the ganoid fishes of Agassiz exhibit
an organization similar to that of the teeth: the system of minute parallel tubes, with their
branches and anastomoses, in the thick scales of the extinct lepidotus, is as complicated as n

DEVELOPMENT. \ 15

in the rest of the class. In these primitive papillz there can be very
early distinguished a cavity containing fluid, and a dense membrane,
(membrana propria pulpi) surrounding the cavity, and itself covered by
the thin external buccal mucous membrane, which gradually becomes
more and more attenuated as the papilla increases in size. In some
fishes, as the sharks and rays, the dental papillz do not sink into the
substance of the vascular membrane from which they grow, but be-
come buried in depressions of an opposite fold of the same mem-
brane ; these depressions enlarging with the growth of the papille,
and forming the cavities or capsules in which the development of the
tooth is completed. They differ from the capsules of the matrix of
the mammifercus tooth in having no organic connexion with the
pulp, and no attachment to its base: the teeth when fully formed are
gradually withdrawn from the above described extraneous capsules, to
take their place and assume the erect position on the alveolar border
of the jaws.

Here, therefore, is represented on a large and, as it were, persis-
tent scale, the first and transitory papillary stage of the develop-
ment of the mammalian teeth ; and the simple crescentic cartilagi-
nous maxillary plate, with the mucous groove behind it containing
the germinal papille of the teeth, offers in the shark a magnified re-
presentation of the earliest condition of the jaws and teeth in the
human embryo.

In many fishes, as the lophius and pike, the dental papillz become
buried in the membrane from which they arise, and the surface to
which their basis is attached becomes the bottom of a closed sac.
But this sac is never lodged in the substance of the jaw, the develop-
ment of the tooth being completed in the tissue of the thick and soft
gum or mucous membrane from which the papille were originally
developed: hence teeth in various stages of growth are frequently
brought away with that membrane when it is reflected from the jaw-
bone. The ultimate fixation of the teeth, so formed, is effected by the
development of ligamentous fibres in the submucous tissue between
the jaw and the base of the tooth ; which fibres become the medium

many teeth, and equally militates against the theory of formation by transudation of layers
being applied, at least, to the ganoid scales.

16 DEVELOPMENT.

of connexion between those parts, either as elastic ligaments, or by
continuous ossification.

Here we have the second step in the development of the mammalian
tooth represented, viz: the imbedding of the pulp in a follicle of the
mucous membrane ; but the eruptive stage of the tooth takes place
without any previous inclosure of the follicle and pulp in the sub-
stance of the jaw.

In the Balistes, Sparoids, Sphyrena, Scarus, 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
highest organized animals: the papilla sinks into a follicle, becomes
surrounded with a capsule, and is then included in a closed alveolus
of the growing jaw, where the development of the tooth takes place,
and is followed by the usual eruptive stages.

The development of the dental pulp in fishes, prior to the deposi-
tion of the calcareous particles in it, corresponds in the main with the
process described by Purkinje and Raschkow in the mammalia. The
pulp-substance, or contents of the membrana propria remain, in fishes,
for a longer period in a fluid or semi-fluid state, and the granules or
nucleated cells which are first developed, float loosely or in small
aggregated groups in the sanguineo-serous fluid: they first attach
themselves to the inner surface of the membrana propria, if these be
not originally developed from that surface, and the whole of the con-
tents of the growing pulp becomes soon after condensed by the nu-
merous additional granules which are rapidly developed in it after it
has become permeated by the capillary vessels and nerves. The ar-
rangement of these particles into linear series, or fibres, is first ob-
servable at the superficies of the pulp to which the fibres are vertical :
and, at this period, ossification has commenced in the dense and
smooth membrana propria of the pulp: it is thence continued centri-
petally in the course of the above-mentioned lines, towards the base
of the pulp, either regularly progressive, as in the incisors of the
Sargus and Balistes, or radiating, as in Sphyrena and (if we may judge
by @ posteriori observation of the structure of the fully developed teeth)
in most other fishes, from the various centres formed by the persistent
capillaries of the pulp, around which the cells or granules become

DEVELOPMENT. l?

condensed into concentric layers, which then become, as they are
successively impregnated with the calcareous salts, the walls of the
medullary canals.(1)

In the shark, and all those fishes in which the teeth are completely
formed without going beyond the papillary stage of development, there
is no distinct enamel-pulp; the dense exterior layer of the tooth is
formed by the calcification of the ‘membrana propria’ of the pulp,
which, therefore, precedes the formation of the ordinary dentine. But
in the file-fish (Balistes), the sargus, the gilt-head (Chrysophrys), and
some other fishes, a conspicuous enamel-pulp is developed from the
inner surface of the capsule which surrounds the bone-pulp: this enamel
organ terminates, as in the human subject, before the capsule is re-
flected upon the base of the pulp. It has a firmer tissue, more
closely resembling that of the ordinary pulp, than in the mammalia :
and, when examined under the microscope, presents numerous and
close-set fine fibres near that surface which is next the bone-pulp,
and to which these fibres are generally placed at right angles. The
base of the enamel organ, which is attached to the capsule, presents
a granular and fibrous tissue blended together. I have not been able
to trace any capillaries from the capsule into the substance of the

(1) In those fishes, and they include the greatest part of the class, in which the teeth are at-
tached by anchylosis to the jaws, the mode in which the calcareous particles are deposited in the
gelatinous frame-work or pulp is modified as the calcification approaches more or less gradually
towards the base of the tooth, until at length the pattern or texture of the calcified pulp cannot
be distinguished from that of the bone with which it thus becomes continuous. It is not with-
out interest to observe how Cuvier, who had clearly detected this actual ossification of the base
of the pulp in the teeth of many fishes and reptiles, should have conceived it to be a process so
distinct from that peculiar to the supposed inorganic tooth, that he felt himself called upon to
correct the error he had fallen into in stating, in his “ Legons d’Anatomie Comparée,” this
ossified base of the anchylosed tooth to be its root. Describing the teeth of lizards, in his “ Osse-
mens Fossiles,” tom. V, 2e partie, p. 274, Cuvier says:—‘‘Cette base ne se divise point
en racines; mais quand la dent a pris son accroissement, il arrive le méme phénoméne que
dans les poissons. Le noyau gélatineux s’ossifie; il s’unit intimement d’une part, a Vos
de la machoire, en contractant, de Vautre, une adhérence intime avec la dent quil a
exsudée.—J’avais déja exposé Vhistoire de cette dentition dans mes Lecons d’Anatomie
Comparée, III. iii. 113, etc.; mais j’y ai aussi commis l’erreur d’appeler racine cette partie cellu-
leuse et osseuse quis’unit 4 l’os maxillaire.” The application of the microscope to the investiga-
tion of the structure of the teeth has brought to light many instances in which the crown of
the tooth ought, for the same reasons, to have as little title to be considered a part of the tooth
as the root.

Cc

18 DEVELOPMENT.

enamel-pulp. In the incisors of the sargus, the development of the
enamel and dentine begins simultaneously upon the contiguous sur-
faces, and when we observe how close and compact is the package
of the matrix of the tooth in the alveolar cavity of the jaw, it is
hardly possible to conceive how either of these substances could be
the product of transudation from their respective pulps. It is, how-
ever, easier to separate the primary layers of the enamel and dentine
from their respective pulps than from.each other; yet if the denuded
surfaces of the uncalcified portions of the pulps be examined by re-
flected light under a compound lens of a half-inch focus, they are seen
to be ragged and punctate, and evidently different from the original
surfaces prior to the commencement of the deposition of the calcareous —
salts in them. The formation of the enamel resembles more closely
that of the dentine in the fishes cited than it does in the mammalia,
and the enamel] contains a greater proportion of persistent animal
matter.

The course of calcification of the two pulps takes opposite direc-
tions, and in the balistes, the process finishes by the ossification of
the outer layer of the capsule itself, by which both the enamelled
crown and the base of the tooth are coated with a thin layer of bone.
I have not been able to discern any radiated cells in this analogue of
the ‘‘ crusta petrosa,” or cement of the mammalian teeth. It soon
wears off from the crown of the extruded tooth.

In all fishes, the teeth are shed and renewed, and this not once
only, as in most mammalia, but frequently and during the whole
life time of the animal.(1) Fishes, indeed, can hardly be said to have
permanent teeth. The rostral teeth of the pristis constitute, perhaps,
the sole exception; and these may be regarded rather as modified
dermal spines. :

In all cases where the first teeth are developed in alveolar cavities,
the succeeding ones follow them in the vertical direction, and owe the
origin of their matrix to the continuation, from the mucous capsule of
their predecessors, of a czecal process, in which the papillary rudiment
of the dental pulp is developed according to the laws explained in the

(1) Ima few cases it is observed, that as the fish gets old, some of the deciduous teeth are not —
replaced ; in old Salmonide, the vomer thus becomes edentulous, or nearly so.

DEVELOPMENT. 19

General Introduction. But inthe great majority of fishes, the germs of
the new teeth are developed, like those of the old, from the free
mucous membrane of the mouth throughout the whole period of
succession, a condition which is peculiar to the present class. The
angler, the pike, and many of our common fishes, illustrate this mode
of dental reproduction: it is very conspicuous in the cartilaginous
fishes, in which the entire phalanx of their numerous teeth is
ever moving slowly forward in rotatory progress over the alveolar
border of both upper and lower jaws, the teeth being succes-
sively cast off as they reach the outer margin, and new teeth rising
in equal proportion from the mucous membrane behind the rear rank
of the phalanx.

This endless succession of new and sometimes, as in Balistes, and
Sargus, of highly complicated matrices,—this constant development
of a new apparatus for the production of each new tooth, even where
its final development is unaccompanied by an eruptive stage, and
where the destruction of any part of the formative apparatus is not
a necessary consequence of the completion of the tooth, could
hardly seem other than a waste of the formative energies to the
reflecting physiologist entertaining the doctrine of dental development
by transudation, and by whom the dental pulp must have been
regarded in the capacity of a gland. The destruction or waste
of other glands by no means follows the natural exercise of their
functions: the disappearance of the pulp pari-passu with the
growth of the tooth, is only an inevitable consequence when that
growth is effected by deposition of the calcareous particles in the
substance, instead of by transudation from the surface of the formative
pulp, and when fresh material is not progressively added to the base
of the pulp. In the cyclostomous fishes, where the albuminous,
horn-like teeth seem really to be transuded from the pulp, these are
persistent ; and the new teeth are formed immediately beneath the
old, and from the same surface of the reproductive pulp.

20 CYCLOSTOMES.

CHAPTER II.

TEETH OF CYCLOSTOMES.

MYXINES.

10. In the class of fishes, as in that of reptiles and mammalia, there
are species which are wholly destitute of teeth. These edentulous
fishes are most common in the cartilaginous division of the class.
The sand-prides (Ammocetes), the sturgeons (Acipenser), the paddle-
fishes (Planirostra and Aodon), are examples. The whole order of
Lophobranchu of Cuvier, which includes the pipe-fishes (Syngnathus),
and the Hippocampus, is edentulous. ;

The lowest organized fishes with worm-like bodies and parasitic
habits, as the myxinoids and lampreys, are also destitute of true
calcified teeth, but have them replaced by horny substances of a
conical, sharp-pointed, and often slightly recurved form, resembling
the teeth of the entozoa, the habits of which these suctorious fishes
simulate. The hag-fish (Myaine glutinosa), and other cognate species
now grouped together by Miiller under the genus Bdellostoma, have
a single tooth on the median line of the palate, and a double serrated
horny plate on each side of the upper surface of the tongue. The
palatal tooth(1) is moderately long, conical, and recurved, with a tumid
margin around its base, which is hollow, and supported upon a conical
pulp, firmly attached to a fibro-cartilaginous plate,(2) situated beneath
the anterior commissure of the palatal cartilage. The basal-plate
of this tooth is further attached by ligaments, the anterior of which
passes to the hinder part of the rostral cartilage, and the posterior
one to a cavity at the commissure of the marginal palatal cartilage.

The lingual dental plates(3) are four in number, two on each side,
of a curved form, hollow at the base, and implanted, like the palatal
tooth, on a reproductive pulp of a corresponding form.(4) This pulp,
and the margin of the base of the dental plates are attached to the
perichondrium of the lingual cartilage. The dentations of these —
lingual plates are conical, sub-compressed, sharp-pointed, with the —

(1) PL. 2, fig. 1, &. (2) ib. a. (3) id. fig. 2, b. (4) ib. fig. 3, d.

CYCLOSTOMES. 2)

points reflected backwards. They are usually described as distinct
teeth, and, viewed as such, form two concentric curved lines inter-
rupted at the middle of the tongue. In the Myaine glutinosa the
number of lingual teeth is $75, 2. e., there are eight teeth in both the
right and left anterior rows, while there are eight in the left posterior
row, and nine in the right posterior row. In the Bdellostoma hep-
tatrema, there are *—§ lingual teeth ; in Bdell. heterotrema, the number
is {i-12; in the Bdell. hexatrema, the lateral rows of lingual teeth are
symmetrical, being jj-j;; in Bdell. cirratum, there are jjc]i teeth ;
in Bdell. dombeyi, the number is ;—'7.. These formule appear to be
constant in the species ; this is, at least, the case in the glutinous
hag. The middle teeth are always the longest, the rest gradually
diminish towards the lateral extremities of the rows.(1)

I have already alluded to the parasitic habits of these low
organized fishes. When they first attach themselves to their prey,
the single median recurved palatal tooth is thrust into its flesh, and
serves as a holdfast, while the work of destruction is carried on by
the laterally opposed lingual saws, aided by the suctorious action
of the mouth. The usual situation in which the myxine is found,
is the interior of a cod or other large fish, into whose carcase it has
thus penetrated, and on whose soft parts it has preyed.

LAMPREYS.

11. In the lampreys (Petromyzon) (2) there are labial and inferior
maxillary, as well as palatal and lingual teeth ; all these are likewise
horny substances, of a simple, conical, sharp-pointed, form, and of a
somewhat less dense texture than in the myxinoids. They are
hollow, and supported on conical, reproductive pulps. . The pulps
of the labial teeth are firmly attached by their base to the fibrous
tissue of the lining membrane of the lip.

The labial teeth of the outer or marginal circle are the smallest ;
from these, the teeth increase in size as they approach the centre of
the cavity of the mouth. The converging series in the mesial plane
are arranged in a straight line; those of the sides in curved lines,
with the concavity towards the lower margin of the mouth. In the

(1) See Miiller, tiber den Myxinoiden, p. 20. (2) Pl. 2, figs. 4 and 5.

22 CYCLOSTOMES.

Petromyzon marinus, the innermost teeth of four of the lateral series on
each side are bicuspid, or consist each of two cones, which are
confluent at the base. There are twenty converging rows of labial
teeth in this species, and from four to eight teeth in each row.

The single tooth supported by the palatal cartilage(1) and analo-
gous to that in the myxinoids, consists here of two horny cones,
placed in the transverse direction, and joined, in the Petr. marmus,
in the median line. In the lampern (Petr. fluviatilis) the cones are
more remote. The matrix of this tooth is hollow at the base, and
is supported on a conical process of the palatal cartilage, which
Cuvier describes as the upper jaw. The broad bicuspid,palatal tooth
is opposed by the dentated semilunar horny plate, with which the
cartilage, representing the lower jaw,(2) is sheathed. This plate
consists of eight conical teeth, laterally united together ; its repro-
ductive matrix is fixed upon a prominent semilunar ridge at the
anterior part of the mandibular cartilage.

The lingual teeth consist of three dentated horny plates, the
dentations being much smaller than in the palatal or mandibular
plates, or than in the lingual plates of the myxinoids. But their
analogy with the latter can be readily traced, the third or posterior
lingual plate of the lampreys evidently corresponding with the two
posterior lingual plates of the myxinoids conjoined,

Each of the anterior lingual plates is slightly concave, with the
mesial extremity abruptly bent towards the upper surface of the
mouth ; its anterior margin is divided into eleven sharp-pointed,
recurved, minute, dental processes. The posterior and inferior dental
plate may be said to consist of two similar but smaller. semilunar
pieces, with the mesial margins approximated and conjoined; the
number of dentations on each of the lateral moieties of this lingual
armature, 1s seven.

The mode of development and reproduction of all these teeth
is the same both in the myxinoids and lampreys. The matrix is
persistent, as in most other horny productions, and the new conical
tooth is developed immediately within and beneath the base of the
old one; the same secreting surface which formed the one, produces

(RL. 2, fei, a (2) 2b. 8.

PLAGIOSTOMES. 33

the other. A vertical section of any of the teeth of the lamprey
displays one or two cones of reserve, between the tooth in use,
and the surface of the matrix ;(1) and the outermost is in general readily
displaced ; often, indeed, difficult to preserve in situ in the preparation.

Thin transverse sections of the teeth of the lamprey, viewed
by a magnifying power of a quarter of an inch focus,(2) exhibit their
structure as composed of closely-aggregated parallel tubes, placed
perpendicular to the secreting surface, and having a diameter of
mwa of an inch.

In chemical composition, the teeth of the Cyclostomes resemble
horn.

CHAPTER III.

TEETH OF PLAGIOSTOMES.

SHARKS, OR SQUALOIDS.

12. Aux the genera of true or fixed-gilled plagiostomes, save
Pristis, are characterised by numerous teeth, whichare restricted in their
situation to the upper and lower jaws. Here, they are arranged in a
greater or smaller number of rows, which succeed each other from
behind forwards, and are attached only to the mucous and fibrous
membranes covering the maxillary cartilages.

Before entering upon the consideration of the teeth, a few words
seem necessary respecting the analogies of these dentigerous car-
tilages or jaws. In the common skate, they are in the form of
simple arches, each arch consisting of a pair of cartilages joined
together by a ligamentous symphysis at one extremity, and sus-
pended by the opposite end through the medium of a common car-
tilaginous pedicle from the sides of the cranium. This pedicle is
obviously the homologue of that to which the lower jaw is suspended
in the higher oviparous vertebrates, and which includes more or fewer

(1) Pl. 2, fig. 6.
(2) The instrument employed in these observations, and referred to throughout the present
work, is the compound achromatic microscope of Ross.

24 PLAGIOSTOMES.

elements of the temporal bone. In its simplicity, in the plagios-
tomes, it participates with the character of the rest of their cartilagi-
nous cranium, in which the several distinct bony elements found
in the reptiles and osseous fishes cease to be recognisable. Of the
several bones concerned in the formation of the jaws, we have to
seek, in the simple cartilaginous arches of the skate, the pterygoid,
palatine, maxillary, intermaxillary, mandibular, and premandibular
bones; and to these may be likewise added the labial cartilages,
which are so largely developed in the cyclostomous fishes. Are all
these elements combined in the dentigerous cartilages of the skate ?
or if not all, which ? These questions have been differently answered
by different comparative anatomists. The essential character of the
pterygoid and palatine bones manifests itself, in the oviparous classes,
in the formation of buttresses extending between the vomer and the
articular pedicle of the jaw. In the Carcharias glaucus, or blue-shark,

and in the Lamna, or porbeagle, a distinct flattened process of car-
tilage extends from each side of the vomerine region of the skull,
and abuts against the proximal extremity of the pedicle, and the
contiguous part of the cranium. These processes, I regard as
analogous to the palato-pterygoidean buttresses. In the common
torpedo, there is a distinct cartilage in the corresponding situation,
and in the Brazilian torpedo,(1) Dr. Henlé has discovered a second
broader cartilage, anterior and internal to the pterygoidean pedicle,
and which he considers to be the analogue of the true palatine
bone ; this cartilage has not been found separately developed in any
other plagiostome.

With respect to the labial cartilages these are wanting, accord-
ing to Miller, in the following subgenera of the ray tribe, Raia,
Trygon, Rhinobates, Cephaloptera, and Myliobates; they are also
"absent in the Carcharias, Cestracion, and Pristis among the sharks.
They are present in the Tope (Galeus), which has one on each side
of the upper lip; in Scymnus there are corresponding cartilages, which
are elongated and extend below the angle of the mouth; in Scyllium
and Mustelus, there is one on each side of both upper and lower lips ;

(1) Torpedo braziliensis, the type of the sub-genus Narcine of Miiller and Henle.

PLAGIOSTOMES. 25

in Centrina, and Squatina, there are two on each side of the upper,
and one on each side of the lower lip; these are figured at a b and ¢,
Pl. 10, fig. 2, in the monk-fish. In the Narcine or Brazilian torpedo,
distinct labial cartilages are associated with the dentigerous maxil-
lary arches, and also with the palatine and pterygoidean cartilages ;
Professor Miller has, therefore, rejected the interpretation of Cuvier,
according to which, the anterior or superior dentigerous arch of the
plagiostomes is the homologue of the palatine bones, and the posterior
one, the homologue of the post-mandibular element of the lower jaw,
the intermaxillary, maxillary, and premandibular bones being repre-
sented by the edentulous labial cartilages. This interpretation,
besides being invalidated by the anatomy of the Narcine, also involves
the anomaly of the teeth being developed on the articular, or post-
mandibular element of the lower jaw, where they are never situated
in any other vertebrate animal. A more extended comparison than
Cuvier had the means of instituting, and especially a study of the
structure of the cranium of the Cestracion, in which the labial car-
tilages have disappeared, and the development of the dentigerous
arches have advanced nearer to the osseous type than in other
plagiostomes, clearly prove that the dentigerous cartilaginous arches
of the sharks and rays represent, the one, the combined maxillaries
and intermaxillaries, the other, the confluent articular and dentary
elements of the lower jaw.

The teeth are not immediately connected with these cartilagi-
nous arches ; no cartilaginous fish has teeth implanted in maxillary al-
veolar cavities, or confluent with the substance of the jaw even when
the external crust is ossified, but they are always attached as already
stated, to the fibrous and mucous membranes which cover the maxillary
cartilages ;(1) hence, it occurs in certain genera, as Myliobates and
Scymnus, that a single tooth in the median plane may lie directly
across the symphysis, and be supported by the two rami of the jaw.
The plagiostomes, like many other natural families of fishes, pre-

(1) Any organic fossil which exhibits a tooth implanted by two fangs in a double
socket must be mammiferous, since the only fishes’ teeth which approach such a tooth in form
are those with a bifurcate base, belonging to certain sharks, while the socketed teeth of reptiles
have only a single fang.

26 SHARKS.

sent such modifications of their common and characteristic type of
structure as fits them for very different habits of life and the acqui-
sition of different kinds of food. The active, and predatory sharks
are here associated with the sluggish omnivorous rays, and the
dental system presents every grade of modification from the laniary
to the molary type; the Lamna with its teeth exclusively adapted
for holding, piercing, and lacerating, and the Mylobates with its
maxillary mosaic pavement of flattened molars forming the two
extremes of the series.

13. The sharks, or Squaloid plagiostomes, with few exceptions,
have teeth ofa conical, sharp-pointed, more or less compressed form ;
sometimes with trenchant or serrate edges and accessary basal den-
ticles ; they are arranged along the margin and posterior surface of
the jaws in close-set vertical rows, of from three to thirteen teeth in
each row, according to the species. The teeth of the contiguous rows
in certain genera, as Selache, and Lamna, are parallel with each other,
but in Galeus, and Carchartas, they are placed alternately, so that the
base of one tooth advances laterally into the interspace of two teeth
of the contiguous row, and reciprocally ; but the laterally contiguous
teeth are never articulated with each other as in certain rays. In
the Scymnus, the median row of teeth crosses the symphysis of the jaw,
and their base overlaps the adjoining margins of the contiguous teeth;
the lateral teeth have an imbricated arrangement.

In general the anterior or external tooth only of each row is
erect, the rest being recumbent ; the contrast, in this respect, is most
marked in the lower maxillary lancet-shaped teeth of the Scymnus,
(Pl. 4, fig. 3). In Lamna, however, the second and third teeth are
commoniy seen in positions intermediate between those of the erect
anterior and the recumbent posterior teeth, (Pl. 5, fig. 1,) and in the
rays where the teeth are much more numerous in each row than in
the sharks, they exhibit every gradation between the recumbent,
reflected, erect, and porrect positions. It is scarcely necessary to
repeat, that although the teeth of the sharks possess greater individual
mobility than those of the rays, the recumbent ones cannot, as has
been supposed, be voluntarily erected; these teeth are still in
progress of development, and several of them are covered by a re-

SHARKS. 27

flection of the mucous membrane of the mouth, which would be
lacerated by such a movement ; it is by a gradual change of position
in the fibrous membrane to which their base is attached, that the
altered direction of the consolidated teeth is effected.

The teeth present the smallest relative size among the sharks,
in the sub-genus Rhinodon of Dr. Smith, where they may be com-
pared with the teeth en brosse, of certain osseous fishes ; here they
are of a simple conical, slightly recurved form; there are twelve or
thirteen teeth in each vertical row, and about two hundred and fifty
of such rows in each jaw.

In the sub-genus Selache, to which the great basking shark,
(Squalus maximus, Home), belongs, the teeth, though small, are rela-
tively larger than in Rhinodon. They are conical, recurved, and with a
somewhat obtuse apex. In a specimen about thirty-six feet in length,
the teeth, which are alike in both jaws, measure not quite half an
inch in length, and between two and three lines across their rounded
base. The sharks with teeth of larger size and more formidable
aspect present many modifications of shape, by which, with other
characters, the genera and sub-genera of squaloids are distinguishable.
The principal varieties of form are illustrated in plates 3 and 4. Varieties
of form, however, it should be remembered, are not only indicative of
generic distinctions, but sometimes of a difference of age of the same
individual. In the common spotted dog-fish, for example, the one
or two lateral denticles at the base of the principal cusp described
as characteristic of the teeth of the genus Scyllium, frequently disap-
pear in the old fishes. In the young of the blue-shark (Carcharias
glaucus) the teeth have smooth trenchant edges, but in the old ones,
the margins are dentated. In many genera, again, the teeth of the
upper differ in form from those of the lower jaw; this is most re-
markably the case in the genus Scymnus: they also frequently differ
in shape as well as in size in different parts of the same jaw. But
while a knowledge of these facts should impress the observer with
due caution in giving an opinion on the specific or generic relations
of an extinct shark from the examination of a single tooth, the pe-
culiarities of form characteristic of different genera of existing squa-
loids are sufficiently constant and well marked to render dental

28 SHARKS.

characters of great value in the determination of both recent and
extinct forms.

The teeth of the genus Lamna present an elongated triangular
sub-compressed form, with the anterior or outer surface less convex
than the posterior, especially in the median teeth and in those of the
lower jaw. ‘The margins are trenchant and converge to a sharp
point, equally or symmetrically in the median teeth, but unequally
in the lateral ones in which the point is inclined backwards. In
some species, as in the porbeagle shark (Lamna Cornubica), and in
that great extinct species of which the teeth occur in the London
clay and other members of the eocene formation in this country, and
on which Agassiz has founded his sub-genus Otodus,(1) the teeth are
complicated by a small accessory cusp on each side of the base of
the principal cone. In other species, as in the Lamna oayrhina of
Cuv. and Val., (Pl. 3, fig. 1,) the accessory cusps are wanting, at least
in large and full grown specimens: in both subgenera of Lamna, the
third vertical row of teeth counting backwards in the upper jaw is
much smaller than the contiguous rows(2) ; the rest gradually diminish
in size as they are situated nearer the angles of the mouth. In the
sub-genus Odontaspis, the teeth are narrower than in Lamna, the mid-
dle cusp is longer, straighter, and more acute, and is provided with
two similar sharp pointed cusps on each side of its base. In the
upper jaw, the fourth, fifth, sixth, and seventh vertical rows of teeth
are smaller than the contiguous ones ; in both jaws, the first tooth is
small and the posterior teeth progressively diminish asthey approach the
angles of the mouth.(3) The size and strength of the teeth thus modi-
fied for piercing and lacerating render the Odontaspis the most formi-
dable among the shark tribe; and the habits of the typical species,
(Odontaspis ferox) as indicated by its trivial name, correspond with

(1) PL. 5, fig. 5.

(2) M. Agassiz in his description of the dentition of this genus, mentions as one peculiarity
of it that, “ la troisiéme et quelquefois la quatriéme et la cinquiéme dent dela mdchoire inférieure
est sensiblement plus petite que les autres, tandis qu’a la mdchoire supérieure les dents, a l’ex-
ception de la premiére qui est plus petite que les suivantes, vont en diminuant uniformément
de grandeur jusqu’a la partie postérieure de la gueule.” Ina skull of the Lamna Cornubica now
before me, I find, as in the Lamna oxyrhina, (PI. 3, fig. 1,) that the sudden diminution of size in
the third tooth is characteristic of the upper and not of the lower jaw.

(3) Pl. 3, fig, 2.

SHARKS. 29

the destructive character of its maxillary armour. The characteristic
dentition of the shark tribe may be studied with advantage in the
spotted and spiny dog-fishes common on our coasts; the former,
which is the type of the genus Scylliwm, exhibits teeth of a triangular
form with a large middle cusp, complicated, at least, in the young
animal, with one or two small cusps on each side of its base; the
base is always more or less furrowed longitudinally. In Crossorhinus,
a sub-genus of Scyllium, the teeth are characterized by having the
osseous base divided into three lobes. In Ginglimostoma, the teeth have
a simple rhomboidal base supporting one large median cone, and from
two to four obtuse denticles on each side: the teeth of this genus of
dog-fish are remarkable for their somewhat unusual number, there
being frequently ten in each vertical row.

In the spiny or piked dog-fish (Spinaz, Cuv.), the teeth (Pl. 3,
fig. 3,) are alike in both upper and lower jaws; they are thin trian-
gular plates with the apex inclined backwards, so that the anterior
edges are opposed to each other; the enamel does not terminate
below in a horizontal line, but is continued along the middle of the
bony base. In an allied species, the teeth of the upper jaw are
smaller and of a different form from those of the lower jaw, being tri-
cuspid, as in the spotted dog-fish ; some ichthyologists restrict the
subgeneric name Spinax to the spiny dog-fishes which are cha-
racterized by this modification of the teeth.

In the genus Notidanus, the teeth are not only of different forms in
the upper and lower jaws, but also vary considerably, in this respect,
at the anterior and posterior regions of the same jaw, (Pl. 3.)
In the upper jaw, the anterior teeth are large, compressed, triangular
plates, with the pointed apex arched backwards, and the margins
slightly dentated, except in the two anterior ones. The posterior
teeth are in the form of simple obtuse furrowed tubercles. In the
lower jaw, the large anterior teeth have the apex less produced ;_ the
anterior margin is finely serrate, and the posterior divided into three
or more denticles. The posterior minute teeth resemble those in the
upper jaw. Of the larger teeth there are rarely more than four in
each vertical row.

In the subgenus Carcharias, the teeth present the form of

30 SHARKS.

triangular plates with a broad base, sharp apex, and trenchant or
finely dentated edges. The anterior surface is nearly flat, the poste-
rior slightly convex: the teeth of the lower jaw are rather narrower,
and thicker, and somewhat smaller than those of the upper jaw.
The dentition figured(1) is that of the great and formidable ‘‘ white
shark” of navigators,—the type of the subgenus Carcharodon of
Miller. In the United Service Museum there are preserved the
jaws of a Carcharodon, of which the upper one measures four feet and
the lower one three feet eight inches, following the curvature. The
length of the largest tooth is two inches, the breadth of its base one
inch nine lines: the total length of the shark was thirty-seven feet.

Fossil teeth precisely corresponding in form with those of the Car-
charodon occur abundantly in the tertiary formations of both the old and
new continents ; some of these teeth exhibit the extraordinary dimen-
sions of six inches in length, and five inches across the base. If, there-
fore, the proportions of these extinct Carcharodons corresponded with
those of the existing species, they must have equalled the great
mammiferous whales in size; and, combining with the organization of
the shark its bold and insatiable character, they must have consti-
tuted the most terrific and irresistible of the predaceous monsters of
the ancient deep.

In the blue-shark, (Carcharias glaucus, Cuv.), the teeth of the
lower jaw are longer and narrower than in the white-shark, and ap-
proach nearer to the form characteristic of the genus Lamna ; they
may be distinguished, however, by their broader base, the angles of
which are less produced downwards, and by their finely dentated edges.

In the subgenus Physodon, which is nearly allied to Carcharias, the
teeth of one or two median rows are disproportionately small.

The teeth of the hammer-headed sharks (Zygena), are triangular
flattened plates, with finely dentated margins, as in Carcharias, but
the points are bent backwards, and the posterior margin is concave. (2)

In the genus Galeus, to which the grey-shark or tope of our coast
belongs, the teeth are relatively thicker than in the Zygena, and the
posterior margin is notched, with the basal part produced backward,
and divided into three or more denticles: the anterior margin is

(1) Pl. 4, fig. 1. (2) Pl. 4, fig. 2.

SHARKS. al

finely serrated.(1) This description applies to the lateral rows of teeth
in which the points are inclined backwards and outwards; the teeth
of the mesial row in both jaws are of a symmetricai figure. The
teeth are alike in the upper and lower jaws.

There is the same correspondence, as regards the upper and
lower jaws in the singularly formed teeth, which characterize the
Squalus spnosus of Schneider,—the type of the genus Gioniadus of
Agassiz (Pl. 4, fig. 4). In these teeth, the point is so far inclined
backwards, that the anterior margin forms a nearly horizontal
trenchant edge, applied to the corresponding margin of the opposite
tooth: two denticles project horizontally forwards from the base of
the anterior margin, and one or two similar denticles from the oppo-
site side of the tooth.

In the genus Scymnus, (Pl. 4, fig. 3,) the teeth of the lower differ so
much from those of the upper jaw, that nothing save actual in-
spection of the jaws im situ could lead to the belief that they be-
longed to the same animal. The teeth of the upper jaw are small,
conical, subcompressed, with slightly recurved points ; those of the
median or anterior rows present a nearly subulate form; the poste-
rior ones are somewhat broader : their osseous base is bifurcate, as in
Lamna. The teeth of the lower jaw are about eight times larger than
those above ; they are straight, flattened, symmetrical, lancet-shaped
plates, with finely dentated margins. The base of the tooth is bifur-
cate, the divisions being parallel, and divided by a fissure which becomes
slightly dilated near the enamelled crown. The middle tooth of the series
rests upon the symphyseal line, and has one basal fork attached to
each ramus of the lower jaw; its parallel lateral edges overlap those
of the contiguous teeth; the posterior edge of each lateral tooth
overlaps in a similar manner the anterior one of the tooth behind:
this imbricated disposition is quite peculiar to the Scymnus, among
sharks. There are four recumbent teeth in each vertical row, the
apices of which are turned down in a direction diametrically opposite
to that of the erect exterior tooth. The shedding of the outer teeth
appears to be simultaneous, and the change of position of the succeed-
ing series must be very rapid, as well as extensive.

(1) Pl. 28, fig. 9.

32 SHARKS.

In the genus Mustelus, to which our “‘ smooth dog-fish ”
belongs, the teeth deviate from the form typical of the sharks and
approach those of the rays, being obtuse and rounded, with fine trans-
verse ridges, without a piercing cusp or cutting edge, but adapted for
bruising and crushing: they are numerous, small, nearly equal,
arranged like a pavement in the quincuncial order.

The maxillary teeth of the saw-fish (Pristis) resemble those of the
smooth dog-fish, but as the more formidable part of the dental system
of this genus offers some peculiar characters, it will be subsequently
described.

In the Cestracion both prehensile and crushing teeth are asso-
ciated together in the same jaws, but as we here meet with a modifi-
cation of the microscopic texture of the teeth different from that
of the teeth in the true sharks, a separate section will be devoted to
their description, and to that of the teeth of numerous cognate fossil
species of plagiostomes.

In all the genera of sharks, the body of the tooth is principally
occupied with the two kinds of canals which I have termed ‘‘ me-
dullary” and ‘“ calcigerous.”(1) The latter are, however, essentially
minute branches or continuations of the former, and although, in
the newly formed tooth distinguishable by the nature of their contents,
yet this difference is gradually obliterated by the progressive depo-
sition of calcareous matter by concentric layers in the medullary
canals.

In plate 6, a view of the structure of the tooth of an extinct species
of shark (Lamna elegans, Ag.) is given as seen in a thin longitudinal
section under a compound lens of one inch focus. With this power the
medullary canals alone are visible, the minute calcigerous tubes giving
rise to the cloudy appearance in their interspaces. The medullary
canals are continued from the short and small pulp-cavity at the base
of the tooth. The principal branches run parallel with the axis of the
tooth, but quickly give off ramuli, which are directed transversely,
and again ramify at right angles or nearly so, and anastomose, so as
to form a beautiful reticulate arrangement of tubes, very similar to a
network of capillary vessels, throughout the whole substance of the

(1) Report of the British Association, 1838, vol. vii, p. 135.

SHARKS. 33

tooth: they ultimately terminate in flattened sinuses, which anasto-
mose and form the boundary line between the central osseous and
the dense exterior enamel-like substance of the tooth. The whole of
the superficial part of the tooth is occupied by minute calcigerous
tubes,(1) which proceed in a wavy course, generally at right angles to
the external surface; they ramify at very acute angles, and their
terminal branches anastomose, and most of them end in a
series of calcigerous cells, situated beneath the outer stratum of
enamel. In this stratum, however, there are evident traces of a
series of much finer tubes, continued from the preceding layer of
cells. The medullary canals in the body of the tooth are surrounded
by concentric layers, traversed by the calcigerous tubes which are
everywhere given off at right angles from the larger canals; and
have a more irregular wavy course than the superficial calcigerous
tubes. They form, by their numerous anastomoses an inextricable
reticulation,(2) and their terminal ramuli dilate into or communicate
with calcigerous cells. :

The medullary canals of the teeth are occupied in the recent
dog-fish by a sanguineous medulla, closely resembling that which
fills the medullary cells of the coarse bone of which the base of the
tooth is composed, and with which cells the anastomosing reticulate
canals of the crown of the tooth are directly continuous. In the old
exterior teeth a great proportion of the medullary canals are con-
solidated by concentric layers of earthy deposit.

In the fully formed flat teeth of the foetal Carcharodon, which
were sufficiently transparent to render their texture perfectly discern-
ible by transmitted light, this was seen to be essentially the same as
in the Lamna; but the disposition of the medullary canals was more
regular: the median branches were continued as in Lamna to the
apex of the tooth parallel with the axis, the lateral ones gradually
inclined to the sides of the tooth, their direction being more trans-
verse as they approached the base ; and here inclining downwards to
the bilobed osseous root. The branches of the medullary canals are

(1) A highly magnified view of the calcigerous tubes continued from the peripheral medul-
lary tube 6 is given in Pl. 7.
(2) See the view of these tubes between the medullary canals a and 8, Pee
D

34 SHARKS.

given off nearly at right angles, but are relatively smaller and shorter
than in Lamna. The calcigerous tubes in the body of the tooth form
a fine but inextricable moss-like reticulation ; those at the periphery
are straighter, and run parallel to one another, and vertical to the
outer surface. A stratum of fine calcigerous cells receives the termi-
nations of these peripheral tubes, and intervenes between them and the
dense enamel-like exterior covering of the tooth.

In the great fossil teeth of the Carcharias megalodon, the calcige-
rous tubes, at the superficies of this tooth, are disposed in groups
which, with an insufficient magnifying power, appear like single
coarse tubes; but with a higher power are seen to be composed of
congeries of parallel tubes, apparently twisted together. The inter-
spaces are nearly equal to the diameter of these fasciculi: they are
occupied by more scattered tubes, and by short oblique or transverse
anastomosing branches. Atone part of a section of this tooth, which
was sufficiently transparent to be examined with the highest powers,
the peripheral coarse sinus or canal, which always runs parallel with
the superficies, gave off an infinite number of minute tubes, which
formed a plexus, (or plexiform stratum), and from the outer part of this
plexus, the tubes above described, passed, at right angles, to the sur-
face. In the longitudinal section of this tooth, the twisted appearance
above described of the peripheral calcigerous tubes was seen to be
due to the number of side branches given off at an acute angle, and
obliquely to the main tube. At the apex of the tooth, the marginal
calcigerous tubes radiate, as in the Lamna, and suddenly diverge to
proceed transversely tothe sides. In the body of the tooth, the main
canals are surrounded by concentric lamelle, traversed by radiating
and anastomosing calcigerous tubes, which form a tine net-work in
the interspaces of the medullary canals.

In the flat lancet-shaped teeth of the lower jaw of the Scymnus,
the texture of the tooth presents a closer correspondence with that in
the higher organized animals, in consequence of the principal or me-
dullary tubes being relatively smaller, more aggregated, straighter, and
more parallel in their course, than in the sub-genera of sharks just
described. These tubes advance in two fasciculi from the osseous
bifid base ; the median tubes slightly converge and proceed straight

SHARKS. 35

to the apex of the tooth, the lateral ones also run parallel to each
other, and to the axis of the tooth, at the beginning of their course,
and then bend gently outwards to the margins of the tooth. The
secondary curvatures of the medullary tubes are pretty regular, and
of an angularly undulating character; the whole of the clear outer
enamel-like covering consists of parallel and extremely minute calci-
gerous tubes with intermixed cells. The calcigerous tubes, in the
body of the tooth, are given off at an acute angle from the medullary
tubes through their whole course.

It has been already observed that the formation of the teeth of
the sharks, as of many other fishes, exemplifies, on a large scale, the
earliest or papillary stage of dental development in the higher classes
of animals. It is not succeeded here by either a follicular or an
eruptive stage; the formative papille are never inclosed, and con-
sequently never break forth. The pulp, when consolidated by the depo-
sition of the calcareous salts in the pre-existing cells and tubes, is
gradually withdrawn from the protective sheath which the thecal fold
of mucous membrane afforded it during the early stages of its forma-
tion. Ihave studied the development of the teeth of the squaloids,
in the genera Galeus, Carcharias, and Scymnus. In the uterine foetus,
one foot long, of the great white shark, (Carcharodon) the jaws seem at
first sight to be edentulous ; a fissure presents itself on the inner side
of the margin of each jaw running parallel with it, between the thin
smooth membrane covering the convex edge of the cartilage, and the
free margin of a fold of mucous membrane which lies parallel to, and
upon the inner side of the jaw. |. When this fold is drawn away from
the jaw, the minute teeth are exposed, arranged in the usual vertical
rows ; their points are all directed backwards and towards the base
of the jaw, and are seen to slip out of fosse, or sheaths in the
membranous fold, as this is gradually reflected backwards to
its line of attachment near the base of the jaw. Here the an-
terior lamina of the fold, which, from its office may be
termed ‘‘ thecal,’ is continuous with the mucous membrane at the
base of the rows of teeth; the posterior layer is reflected back-
wards to the fraenal line of attachment of the tongue. Close to the
anterior line of reflection there is a row of simple conical papillz, in

D2

36 SHARKS.

the succeeding row, the papilla are larger, the cone broader and
flatter, and its apex is covered with a small cap of dense and glis-
tening dental substance which is readily removed ; though not with-
out displacement of part of the pulp, the granules of which, adherent
to the cavity of the displaced dental cap, are always readily recog-
nizable under the microscope. The third series of papille, count-
ing from below in the lower jaw, have acquired the size and
shape of the future tooth, with the crenate edges well marked ;
half the tooth is completed, and its removal from the fleshy base
of the pulp cannot be effected without evident laceration of the
pulp ; when this is done under the microscope, the torn processes of
the pulp continued into the medullary canals of the new formed
tooth are plainly visible. The fourth tooth is completely formed,
as also the fifth and sixth, in the ascending series ; these progressively
diminish in size. The last or highest, which is first exposed on re-
flecting the thecal fold, and the first which was completed in the
order of development, consists of a simple cone, similar in form and
size to the apical third of the ordinary sized teeth below it ; yet
its growth is quite completed, and its base firmly attached to the
maxillary membrane.

In a foetus of a Carcharias, three inches long, which had not lost
its external branchie, the membranous groove between the jaw and
thecal fold was much shallower, and only two rows of papille were
present on the maxillary membrane. The minute anterior teeth in
the more advanced foetus are doubtless developed from these primi-
tive papille, which must be succeeded by others of progressively
larger size till the normal form and dimensions of the adult teeth
are attained.(1)

The unossified pulps, examined with a high power, consist of semi-
opaque polyhedral granules or cells suspended in a clear matrix, and
the whole is inclosed in a tough transparent membrane which forms
the outer surface of the pulp. Beneath this membrane at the crenate
margins, the granules or cells are arranged in lines precisely correspond-

4

(1) The feetal shark is peculiarly favourable for such comparisons, as it presents numerous

pulps and teeth in every stage of formation, easily detached and without violence from their
exposed situation, and of a flattened form well adapted for microscopical observation.

i

SHARKS. aa

ing with those of the subsequent calcigerous tubes. The formation of
the tooth commences by the deposition of earthy particles in the tough
external membrane of the pulp. I have been unable to recognize the
distinct arrangement of the hardening salts in this layer. It is trans-
parent, extremely dense, and forms the enamel-like polished coating
of the tooth; in sections of fully formed teeth, the finest terminal
branches of the parallel peripheral calcigerous tubes are lost in the
above clear enamel-like substance. When the enamel-like outer
layer of the apex of the tooth is completed, it is so easily detached
from the subjacent pulp that it might be readily supposed that there
was no organic connection between them. If, however, the so ex-
posed pulp be now examined with the microscope, and compared with
an uncalcified pulp, it is seen to be no longer covered with the
smooth dense membrane observable in the latter ; but the apical edges,
from which the enamel-like cap has been detached, appear villous
or flocular. It is obvious that the first shell of the tooth has been
neither transuded from the superficies of the external membrane of
the pulp nor has been deposited between that membrane and the
granular part of the pulp, but is due to a conversion of the external
membrane into a dense enamel-like bone. The formation of the body
of the tooth by deposition of earthy particles in pre-existing and
pre-arranged cavities is still more satisfactorily demonstrable. In
proportion as the formation of the tooth has advanced, the diffi-
culty of separating the calcified from the uncalcified portion of the
pulp is increased, and at the same time it becomes easier to detect
the continuation of the processes of the pulp into those medullary
canals which form so many separate centres of radiation of the plexi-
form calcigerous tubes.

The application of the principle of dental development by con-
version and not by transudation, as illustrated in the dentition of
the shark, to the formation of the mammiferous tooth, is by no means
forced, but natural and obvious. In the ivory part of a simple mam-
miferous tooth there is a single medullary canal, the cavitas pulpi, and
a single system of radiated calcigerous tubes ; but the plan and prin-
ciple of formation is the same as in the shark.

In proportion to the quantity of earthy matter deposited in the

38 SHARKS.

pulp, and in the ratio of the number, minuteness and aggregated
disposition of the cavities containing that earthy matter, is the fa-
cility of detaching the ossified from the unossified part of the tooth
increased. But this facility of separation is quite inadequate to prove
an absence of organic connection between the separated parts, and
a formation of the calcified layer by transudation from a free secreting
surface. The calcigerous tubes of the mammiferous tooth have
distinct parietes in both the calcified and uncalcified portions of the
pulp ; these parietes are rendered brittle by the deposition therein of
earthy particles in the calcified part of the pulp, and separate readily
from the uncalcified continuation of the tubes in the remaining pulp ;
while the minuteness of the ruptured tubes renders the irregularity
of the denuded surface of the pulp invisible to the naked eye; but
the appearance thus presented of a naturally free transuding surface is
deceptive. (1)

(1) Since these facts and the general conclusions as to the nature of dentification deduced
rom them were mentioned in my Lectures at the College of Surgeons (May 1839), and subse-
quently communicated with more detail to the French Academy, I have perused the work by
Dr. Schwann, entitled ‘“‘ Untersuchungen ueber Einstimmung der Struktur und Wachsthum
der Pflanze und Thiere,” 8vo., 1839: or, “‘ Observations on the Correspondence between Plants
and Animals in their Structure and Growth.” Not anticipating, from the title of this work, that
it contained observations bearing immediately on dental anatomy, I have to regret that some
months elapsed after its publication before I ordered it from my bookseller. Dr. Schwann
describes the results of microscopic observations, which he instituted on the development of the
dentine in mammalian teeth, and arrives at the conclusion that the process-like ossification, is one
of intus-susception. Thus the theory of dentification, which I applied analogically from observation
of the process in the shark, to the same process in the higher vertebrate animals, is established ex
visu by one of the most accurate and experienced micrographers of the present day. A full analysis
of his observations will be given in the general introduction to the present work. Cuvier, after stat-
ing that the teeth of fishes grow like those of quadrupeds, by layers, adds in the first edition of the
Lecons d’Anatomie Comparée, ili, p. 112, ‘‘ Mais les dents qui ne tiennent qu’a la gencive
seulement, comme celles des Squales, croissent 4 la maniére des épiphyses des os, c’est-a-dire
que toute leur substance est d’abord tendre et poreuse, et qu’elle se durcit uniformément, et finit
par devenir entigrement dure comme de l’ivoire.” Ihave never seen an instance of such uni-
form hardening—if by this is meant a uniform deposition of the earthy particles through the
whole substance of the pulp—in the tooth of any shark or other animal; and, were such actually
the case, it would not be like the ossification of an epiphysis. It seems that Cuvier himself had
withdrawn his confidence in the observation and conclusion above quoted, as the passage is sup-
pressed in the second edition of the Legons, by M. Duvernoy, in 1835. It is true, however, that
the teeth, not only of sharks, but of the higher animals, are developed like bones ; the harden-
ing salts in both cases are deposited in preformed cavities organized in a pre-existing mould or

eee

SHARKS. 39

As a consequence of a formation of a tooth by conversion of,
instead of transudation from a pre-existing pulp, the successive for-
mation of these pulps necessarily follows, where a succession of teeth
is required ; these reproductive pulps are developed in the shark in
the vascular mucous membrane at the angle of reflection of the
thecal fold upon the groove at the basal line of the jaws. They
gradually advance from this situation towards the margin of the jaw,
the centripetal ossification extends as they advance, and consolidation
is completed by the time they are ready to change their recumbent
for the erect position, and take the place of the tooth previously
shed.

This change of place and direction is well known to be not the
effect of muscular contraction, but of partial absorption and deposi-
tion operating upon the membrane to which the teeth are attached.
This membrane is gradually brought to the exterior of the jaw, and is
then removed together with the attached tooth, supposing the latter
not to have been already violently displaced. But the following
question now offers itself :—Does this movement of growth take place
simultaneously in the membrane and the jaw to which it is attached,
or is ita slow and gradual sliding motion of the dentigerous membrane
upon the jaw ?

To determine this question would require an experiment similar
to those by which Duhamel and Hunter traced the change of place
in the particles of growing bone; a foreign body e. g. should be in-
serted into the base of the jaw of the shark, and a tooth in the corres-
ponding place should be so marked, as at a subsequent period it might
be recognized, and its position compared with the perforated part of
the jaw. Such an experiment would not be very practicable in the
carnivorous inhabitants of the deep we are now considering, but acci-
dent has satisfactorily supplied its place. The jaws of a large
Galeus passed into the private collection of an English anatomist,
in which the barbed spine of a sting-ray (Trygon) had been driven,
during a predatory attack of the shark, into the lower jaw through

matrix of animal matter; but they differ as to the direction of the deposition, which in bone is
from the centre to the circumference, in tooth from the circumference to the centre; the pro-
gress of calcification in the one is centrifugal, in the other centripetal—See Comptes Rendus
de l’ Académie des Sciences, 1839, p. 784.

40 SHARKS.

the posterior row of teeth, and had been broken off and fixed in
that position.(1) Now, had the growth of the jaw proceeded pari
passu with the movement of the teeth, the foreign body would in
time have been brought with the posterior row of teeth, to the outer
margin of the jaw, and have been discharged. If the shark had been
captured during this change, the teeth developed behind the wounded
row, might be expected to have been of the natural size and form;
the appearances, however, presented by this interesting preparation
are as follows : a double row of imperfectly formed teeth is continued
from the perforated part of the jaw to the margin supporting the
erect teeth.(2) Hence it is obvious, that besides the original injury to
the formative pulps in existence at the time of the wound, the pre-
sence of the foreign body had continued to affect the normal deve-
lopment of the subsequently formed pulps. Thus it is proved that
the teeth and their supporting membrane advance forwards without
a corresponding movement of the particles of the cartilaginous jaw to
which they are attached. |

14. Pristis.—The maxillary teeth of the saw-fish, which is an active
and predatory shark, are notwithstanding extremely small, simple,
obtuse,(3) and wholly inadequate to destroy and secure the prey requi-
site for its subsistence; but this seemingly imperfect armature of
the mouth is compensated for by the development from the an-
terior part of the head of a very singular and formidable weapon,
provided with strong lateral teeth, and which, from its resemblance
to a saw, has given rise to the vernacular name of “ saw-fish,”
applied to the present species of shark.

In most of the plagiostomes but especially in the group of
squaloids, a conical projection or cutwater is continued from the
fore part of the head, and its frame work is composed of peculiar and
superadded cartilages, articulated to the anterior extremities of the
frontal, nasal and vomerine bones. ‘These rostral cartilages (in the
common saw-fish (Pristis antiquorum), from which the following des-
cription is taken) are blended into a horizontally flattened plate which
is produced to a length equalling one third that of the entire fish ; this
process is more completely ossified than any other part of the skeleton,

(1) Pl. 28, fig. 9, b. (2) 2. fig. 9, a.
(3) In Pristis cirratus the apex of the small maxillary teeth is produced into a sharp point.

SHARKS. 4]

and a series of deep alveoli is excavated in each of its lateral mar-
gins.

The teeth which are lodged in these sockets are elongated, com-
pressed in the same plane as that of the body of the saw, and the mar-
gins converge to a sharp point, which is situated a little behind the
axis of the tooth ; the anterior border of the tooth is convex, but grows
sharper towards the point ; the posterior margin is concave or grooved,
and the groove glides upon a corresponding ridge which projects into
the back part of the socket. The rostral tooth is solid, as shewn in
the longitudinal section of the one figured in Pl. 8, fig. 3; its base,
(fig. 5,) is slightly concave and porous, like the section of a cane, but
the pores are finer and more numerous. The walls of the socket are
formed by ossification of the rostral cartilage to the adequate extent,
(b. fig. 3) ; but as undue weight, under any circumstances, and espe-
cially at the fore end of the fish would be a cumbrous impediment to
its motions, the intervening spaces (d. fig. 3) between the sockets
are hollow and filled with a gelatinous medulla. A large vascular
canal (c. fig. 3) traversed by branches of the facial artery, and of the
second division of the fifth pair of nerves, and inclosed in a cellular
and gelatinous tissue, runs parallel with the axis of the saw along the
back part of the alveoli, and supplies the materials for the increase
of the teeth, which are not shed and renewed like, the maxillary teeth,
but grow with the growth of the body by constant addition of fresh
pulp-material progressively ossified at their base. (1)

The structure of the rostral teeth of Pristis has the nearest re-
semblance to that of the maxillary dental plates of Myliobates ; they
are traversed throughout by medullary canals which run parallel to
each other and to the axis of the tooth; but they exhibit more fre-
quent anastomoses and dichotomous sub-divisions than in Mylobates.
The diameter of the medullary canals is ;4th inch, and their inter-
spaces sth of an inch near the base of the tooth; they are sur-
rounded by concentric lamine which increase in number as _ the

(1) In the Pristis cuspidatus the rostral teeth are broad, and lancet-shaped ; in the Pristis
microdon they are very short; in the Pristis cirratus the rostral teeth vary in length, there being
from three to five smaller ones interposed between the longer teeth, which are sharp-pointed and
slightly recurved. The base of these teeth expands, and is excavated more deeply than in the

common saw-fish ; it is not socketed but anchylosed to the margin of the rostrum. The rostral
teeth in this species extend along the sides of the head beyond the angles of the mouth.

42 SHARKS.

canals approach the apex of the tooth. The calcigerous tubes
are characterized by their frequent branching and _ inosculation ;
the branches go off generally at right angles to the trunk, which
they nearly equal in size; these quickly anastomose and again
send off smaller branches which similarly anastomose with others
of corresponding size, until the terminal tubes are, for the most
part, lost in a series of minute calcigerous cells which form the
boundaries of the system of calcigerous tubes developed from
each medullary canal. Some of the terminal tubes of contiguous
systems anastomose across this boundary. Each of the systems of
calcigerous tubes represents a separate denticle, of a prismatic figure,
exhibiting in transverse section generally a more or less regular hexa-
hedron. Towards the point where two contiguous medullary canals
inosculate the terminal calcigerous tubes of each system begin to
exhibit more frequent anastomoses, and the boundary line is thus
gradually obliterated: the letters a, 6, and c, pl. 9, fig. 2, exhibit two
systems of calcigerous tubes blending together near the point where
the two contiguous medullary canals were about to inosculate.

The reticulate arrangement of the calcigerous tubes is more, and
the radiated one less, conspicuous in the rostral teeth of Pristis than
in the teeth of any other species which I have yet examined. The dia-
meter of the calcigerous tubes at their origin is ggth of an inch, their

terminal branches may be traced to the minuteness of ;j;th of an
inch.

In the embryo of a Pristis six inches long, to which the umbilical
chord was still attached, I found a series of depressions in the skin
along the margins of the rostral prolongation corresponding in num-
ber and relative position with the future teeth; and at the bottom
of each of these dermal follicles, there was a papilla which formed
the apex of a pulp, whose base had already begun to penetrate the
cartilaginous plate of the rostrum. The pulp had the usual dense
and unyielding external ‘membrana propria,’ and its apex was covered
by a continuation of the tegumentary follicle of extreme thinness,
but there was no true capsule or enamel organ. ‘The calcareous par-
ticles had not begun to be deposited in the tissue of the pulp.

The teeth of the young specimen, of which the head and saw are
figured in Pl. 8, fig. 1, were fully calcified, and except that the num-

a a

©,

RAYS. 435

ber of medullary canals were fewer, and the proportion of the calcige-
rous tubes greater, they were in every respect miniature resemblances
of the teeth of the full grown fish, such as are figured of the natural
size at Pl. 8, figs. 3 and 4.

15. Squatina.—In the monk-fish, (Squatina Angelus), which makes
the transition from the sharks to the rays, the teeth are arranged
along the jaws in well defined vertical rows; including six teeth in
the anterior and gradually decreasing to three teeth in the posterior
rows. The margins of the teeth are smooth; a small tubercle pro-
jects from the middle of the outer side of the base ; these characters
serve to distinguish them from the lower teeth of the Carcharias,
which in other respects they pretty closely resemble. It may be
further observed, that there is not that difference in the position of the
first and second teeth in each row which is so conspicuous in most
sharks; but here, as in the ray tribe, the change of direction of the
apex is very gradual and regular from the innermost to the outermost
tooth: this character, and the anterior position of the jaws are illus-
trated in Pl. 10, fig. 2.

RAIID.%.

16. The teeth of the rays are, in general, more numerous than
those of the sharks; they have less mobility, are more closely
impacted, and in some cases are laterally united together by fine
sutures, so as to form a kind of mosaic pavement on both the upper
and lower jaws. The Myliobates or eagle-rays, which present the last
mentioned condition,—unique in the vertebrate subkingdom, have
large and massive teeth; but in the rest of the present family of
cartilaginous fishes, they are remarkable for their small size, as com-
pared with those of the sharks. The teeth in some species of rays,
are adapted for crushing, but in others they have the middle or
one of the angles of the crown produced into a sharp point. In
all genera of the ray tribe, whatever the diversity of size and shape
of the teeth, they are placed in several rows and succeed each other
uninterruptedly from behind.

In the common skate, (Raia Batis), the teeth are smaller, much more
numerous and the vertical series are more closely approximated than
in the Squatina, which is the most ray-like of the sharks ; their gene-

44 RAYS.

ral form is that of a broad base or plate from which a short spine is
produced ; this is most conspicuous in the central rows of teeth where
the spine is developed from the inner angle, but it gradually dimi-
nishes as the teeth approach the sides of the jaws. The vertical series
of teeth describe nearly a complete circle at the middle part of the
jaws, and include about twenty teeth each.

The teeth of the Torpedo are somewhat stronger, their base is
more extended transversely, and the pointed cusp is more produced
than in the common rays.

In the thornback (Raia clavata), the teeth present the form of
small transversely oval, obtuse masses ; and the vertical series are so
closely arranged, that being alternate, they are less conspicuous than
the oblique rows which result from this approximation. Mr. Yarrell
describes the following sexual character in the teeth of the Thornback
ray. ‘‘ While both sexes are young, the teeth in both are alike broad
and flat; but as the male acquires age and sexual power, the teeth
that are nearest the centre begin to alter in form, and become pointed
by an elongation of the internal angle ; all the points being directed
backwards or towards the throat.’’(1)

The quincuncial arrangement of the teeth prevails in the different
species of Trygon, or fire-flare, in which the teeth are of very
small size. ‘Their crowns consist of a triangular plate, with the
internal angle or point most produced; this plate is supported on a
hollow pivot.

In the genus Rhina each tooth is supported on a short fang or
pivot, which tapers as it recedes from the crown ; there is a groove
along the posterior part of this pivot, and a perforation on each side ;
the crown is lozenge-shaped, convex above, and sculptured with a
series of transverse and slightly undulating and punctate ridges ;
presenting a pattern which somewhat resembles that of the grinding
surface of the comparatively gigantic tooth of the extinct Ptychodus.(2)
The modification of the dentigerous surface of the jaws, and the beau-
tiful quincuncial arrangement of these teeth are exhibited in Pl. 23, figs.
], and 2. The middle part of the upper jaw forms a bold prominent

(1) British Fishes, ii, p. 416.
(2) Compare the magnified view of a denticle of Rhina in Pl. 23, fig. 3, with the tooth of
Ptychodus latissimus, Pl. 17, figs. 1 and 2.

i i

RAYS. 45

convexity separated by a depression on each side from a lateral and
less produced rising. The contour of the dentigerous surface of the
lower jaw presents depressions corresponding to the eminences above,
and vice versd.

The structure of the tooth of the Rhina exhibits a modification
of the tubular structure, very different from that which characterises
the tooth of the extinct Ptychodus. A representation of this structure,
as displayed in a longitudinal vertical section of the tooth, is given in
Pl. 24, which corresponds with that of the teeth of the rays above
described.

The pivot-like base of one of the component teeth of the pave-
ment of the jaws of the Rhina consists of a bony texture, denser than
that of the ordinary bone of fishes ; it is traversed by undulating, di-
versely directed, medullary canals, with concentrically laminated walls ;
numerous wavy calcigerous tubes radiate from the medullary canals,
subdivide in their interspaces, anastomose together, and intercom-
municate with numerous minute calcigerous cells. The structure
of this part of the tooth, we shall find to be similar to that which
pervades the entire tooth in another family of plagiostomous fishes.
The crown or body of the tooth in the Riina exhibits, however, a
denser structure, and one that approaches nearer to the ordinary
structure of the dentine in the higher vertebrate classes. Some of
the medullary tubes of the base of the tooth open into the remains
of the cavitas pulpi, now closed up below by the ossification of the base
of the tooth. This cavity presents a conical form, with an oval
transverse section. A uniform system of calcigerous tubes radiates
in every direction, from the pulp-cavity towards the periphery of the
tooth, and vertical to that surface ; those which are continued from
its lower part, bend down towards the root of the tooth; the lateral
ones are continued directly outwards to the sides, and the superior
tubes proceed vertically to the upper surface; the intermediate
tubes present every gradation of oblique curvature.(1) All the tubes
have a minutely undulating course ;(2) they dichotomize as they
proceed towards the surface, and give off minute branches, generally
at an angle of 45° in every part of their course. These branches
anastomose together, and with rhomboidal calcigerous cells in the

(i) Pl. 24, fig. 1, (2) ib, fig. 2.

46 RAYS.

interspaces of the main tubes. These tubes, at their origin, present
a diameter of 5 of an inch, with interspaces equal to those of their
diameters. The smallest branches into which they are resolved, and
which are lost in the clear enamel-like external stratum of the
tooth, have a definable diameter of = of an inch. This external
layer-is thickest at the upper surface of the tooth, and the boundary
between it and the tubular substance of the tooth, is here defined
by a stratum of calcigerous cells. Some of the fine peripheral
branches of the calcigerous tubes unite and form loops, the con-
vexity of which is turned towards the cells, and from which the finer
branches proceed to communicate with the superficial calcigerous
cells.

17. Myliobates.—The modification of the plagiostomous type of
teeth, for the purpose of crushing the alimentary substances, is most
complete in this genus. A view of this armature of the mouth, as
seen from behind in the Myliobates Aquila is given Pl. 25, fig. 1. Both
jaws are covered with a pavement of broad teeth, with a flat grinding
surface, vertical and finely undulated sides, by which contiguous
teeth are joined together as by a suture, (Pl. 27, c) and a_ base
divided into a number of small parallel longitudinal ridges.

The entire phalanx of dental plates of the upper jaw describes
the segment of a circle. In the Myliobates marginata (subg. Rhi-
noptera of Kuhl), the teeth are hexagonal, the middle row being the
broadest, and the lateral ones diminishing as they recede; the
outermost are mostly pentagonal. I have seen an example of the
jaws of this subgenus of Myliobates, in which one of the rows next
the median was subdivided into two unequal series, as represented in
fig. 2, pl. 25. In Myl. Jussiewi (Zygobates, Agass.), the three middle
rows of teeth are much broader than the two marginal rows. In My-
liobates proper, the median row itself forms the principal part of the
dental covering of the jaws, which is bordered by three narrow rows of
teeth, having the same antero-posterior extent as the median plates.
Finally, in Myliobates Narinari (Aétobatis, Miller), the small marginal
teeth have entirely disappeared, and the jaws support a single row of
broad dental plates. In the upper jaw, these plates are arched, with the
convexity turned forwards; in the lower jaw, they pass straight
across, with the extremities only a little bent backwards. The jaws

RAYS. 47

which support and work these dense and heavy teeth, are pro-
portionally strong; and in Aétobatis, they nearly approach to the
density of true bone. In this subgenus, the upper jaw is shorter
and more curved than the lower one, the anterior extremity of which
projects beyond the upper jaw, and can be used, like a spade, in
digging out shell-fish, &c., from the sandy bottoms frequented by
these rays. (1)

Microscopic examination of the texture of the teeth of Mylio-
bates has yielded the following results. A longitudinal and vertical
section of a single dental plate, viewed by a compound lens of an
inch focus (Pl. 26), exhibits at its base (a) a coarse network of large
irregular canals, filled with a vascular medullary pulp. From
this network smaller medullary canals proceed, towards the flat
grinding surface, in a straight and slightly diverging course,
subdividing dichotomously with interspaces equal to their own
diameter at the base, but much wider at the working surface of the
tooth. In a transverse section of the tooth, under the same power,
the area of the medullary canals is seen to present generally an
irregular elliptical form, from which radiating calcigerous tubes are
faintly perceptible. Each canal and its series of tubes is surrounded
by a line of generally a hexagonal form, and which constitutes the
boundary between contiguous canals and tubes, the whole tooth being
thus composed of an aggregate of slender, elongated, commonly six-
sided prismatic teeth, placed vertically to the grinding surface. A
section through the roots of the tooth (0, pl. 26), shows that these
parts are occupied by a network of irregular canals, which anasto-
mose by arched branches with the network of the contiguous root,
and these with the network of coarser tubes which occupy the basis
of the tooth for an extent exceeding the length of the root itself.

With a higher power, {th inch focus, the calcigerous tubes are
seen to radiate in all directions from the medullary canals, and are
sent off throughout the whole course of the canal. These tubes are
short, wavy, richly arborescent, and form numerous anastomoses with
each other. The transverse sections of the tooth show that the area
of each medullary canal has been filled up or diminished by the depo-

CHP. Voie a.

48 RAYS.

sition of a series of concentric lamelle in proportion to its term
of use.

The ramification of the calcigerous tubes in this tooth, presents
the same general character as those of the Acrodus, but they are
shorter ; and each medullary canal, with the radiating series of tubes,
is seen in the transverse section to be separated from the contiguous
one, by the regular boundary lines above-mentioned, which lines distin-
guish the teeth of the Myliobates from those of the Acrodus, Psam-
modus, Cestracion, or any of the shark-tribe. The rostral teeth of
the saw-fish, and those of the Orycteropus, among mammalia, present
the nearest resemblance in their intimate structure to the teeth of the
Myliobates. Plate 27 gives a correct general idea of the structure of
the present tooth as displayed by a transverse horizontal section near
the root.

The teeth of the Myliobates, like those of the rest of the plagio-
stomes, are successively formed at the posterior part of the tesselated
series in proportion as they are worn away in front. A series of minute
and closely aggregated papilliform matrices rise from the mucous
membrane behind the teeth, and are covered by a fold of the same
membrane which is reflected forward so as to conceal the pulps and
the last formed teeth. The papilliform pulps are ossified by the de-
position of the calcareous salts in the peripheral cells and radiating tubes,
but the medullary or central canal of each pulp continues to retain its
organizer and vascular contents till the whole of the compound tooth
is completed; the calcified wall of the medullary canal is then thickened,
and the area diminished by the successive formation of concentric
laminz of osseous matter. In Zygobates, the subgenus in which I
have studied the development of the teeth of this family of rays, the
middle tooth of each transverse series is first developed ; the forma-
tive papille of the two broad lateral teeth begin to rise first at the
mesial and anterior parts of the tooth, and from these points succeed
each other to the posterior and outer sides: that facet which is adapted
to the posterior-lateral facet of the median tooth is first completed,
and at this period the broad lateral tooth presents a trigonal instead
of a hexagonal contour, the whole length or vertical diameter of the
mesial side of the tooth is completed before the formation of the outer

CESTRACIONTS. 49

side of the tooth is begun. These facts are strikingly opposed to the
theory of the formation of a tooth by the transudation of layers from
the superficies of a pre-existing glandular pulp.

As the teeth of the Myliobates are gradually carried forwards into
action by the direction of growth of their basis of support, the arez of
the medullary canals become progressively diminished, as in bone, by
osseous deposition in concentric layers, and are thus finally consoli-
dated in the anterior teeth.

CESTRACIONTS.

18. The dental characters of this family of cartilaginous fishes, are
chiefly manifested in a form of tooth, better adapted for crushing or
comminuting alimentary substances which offer only passive resistance,
than for piercing, cutting and lacerating a living prey ; and this less
formidable character of the maxillary armour is compensated, in gene- .
ral, by the development of two formidable spines upon the back of
the fish. In most of the species, the teeth also vary in form and
size in the same individual to a greater degree than in the sharks ;
and in all the cestracionts, their substance is traversed by medullary
canals whose systems of calcigerous tubes are not separated by well
defined boundaries, as in the Myliobates.

Of the numerous singular forms of this tribe of cartilagi-
nous fishes that once peopled the seas of the northern hemi-
sphere, and which have left their less perishable remains in the
secondary strata of the present dry land, all have now disappeared,
and the sole existing representative is the genus Cestracion,
of which the most common species is met with in the Australian
Seas: a second species has been indicated which frequents the
southern coasts of China. The ancient fossils above alluded to
would have been scarcely intelligible unless the key to their nature
had been afforded by the teeth and spines of the existing Cestracion.

In the Port Jackson shark, (Cestracion Phillippi), the jaws form
a greater proportion of the skull than in any other existing carti-
laginous and plagiostomous fish ;(1) they are also more elongated and
directed more horizontally forwards, thus approaching nearer to the

(1) Pl. 10, fig. 1.

50 CESTRACIONTS.

usual position of the jaws in the osseous fishes. In consequence also
of the greater extent of ossification in these parts, the indications of
the separation of the upper jaw into maxillary and premaxillary, and
of the lower jaw into mandibular and premandibular pieces begin to
be visible. The upper jaw, besides being suspended to the tympanic
or articular pedicle, is articulated by a distinct convex process with
a corresponding concavity on each side of the vomerine portion of
the cranium. A similar connection of the upper maxillary bone,
in the Scarus, illustrates the analogy here advanced between the upper
dentigerous arch in the Cestracion and other Plagiostomes and the
ordinary maxillary and intermaxillary bones. This arch is also
attached by ligamentous matter, as in other sharks, to the frontal and
nasal parts of the cranium, with which it is in contact. The maxil-
lary portion of the upper jaw sends outwards a strong process which
is connected with a corresponding external process of the lower jaw,
anda very strong ligament attaches the inner side of the posterior
extremity of the superior maxillary bone to the inner side of the
broad transverse condyloid extremity of the lower jaw. The inter-
space of the upper maxillary bones is occupied by a thin triangular
plate of cartilage representing the matrix in which, in osseous fishes, the
palatine bones are developed,and two lateral posterior processes of this
cartilage which abut against the tympanic pedicle, represent the trans-
verse and pterygoid bones.

The labial cartilages, regarded by Cuvier in the Squatina and
some other Plagiostomes as the rudimental and toothless represen-
tatives of the maxillary, intermaxillary, and premandibular bones,
and which in the Cestracion might have been expected, in harmony
with the general tendency of its cranial structure, to have been
present with a corresponding advance towards their hypothetical
maxillary character, have, on the contrary, totally disappeared.

The lower jaw, consisting of the articular and premandibular
elements still confluent, is suspended partly to the slender tympanic
pedicle, but principally to the expanded posterior extremity of the
superior maxillary bone. It closely resembles the upper jaw in form,
but is of greater depth, and the symphysis, which is never obliterated,
is of greater breadth, and is terminated more squarely.

The teeth are arranged, as in the Plagiostomes generally, in

CESTRACIONTS. 5]

several antero-posterior rows, along the margin and inner surface of
both jaws; but the rows are more oblique than in the sharks,
although less so than in certain rays, as Rhina; and the teeth pre-
sent greater diversity both of form and size, than in any other
existing plagiostome. The teeth of the upper jaw are delineated in
fig: 2) Pl 11.

The teeth at the anterior part of the jaws are the smallest ;
they present a transverse, sub-compressed, conical figure, with the
apex produced into a sharp point ; these points are worn away from
the used teeth at the anterior and outer parts of the jaw, but are
strongly marked in those which still lie below the margin. There are
six subvertical rows of these small cuspidate teeth on each side
of the jaw, together with a median row close to the symphyseal line ;
and from twelve to fourteen teeth inarow. Behind the cuspidate
teeth, the five consecutive rows of teeth progressively increase in all
their dimensions, but principally in their antero-posterior extent ;
the sharp-point is converted into a longitudinal ridge, traversing
a convex crushing surface; and the ridge itself disappears in the
largest teeth. As the teeth increase in size, they diminish in num-
ber, in each row; the series of the largest teeth includes from six to
seven in the upper, and from seven to eight in the lower jaw.
Behind this row, the teeth, although preserving their form as
crushing instruments, progressively diminish in size; while at the
same time, the number composing each row decreases. From
the oblique and apparently spiral disposition of the rows of
teeth, their symmetrical arrangement on the opposite sides of the
jaw, and their graduated diversity of form, they constitute the most ele-
gant tesselated covering of the jaws which is to be met with in the
whole class of fishes.

The modifications of the form of the teeth above described,
by which the anterior ones are adapted for seizing and retaining,
and the posterior for cracking and crushing alimentary substances,
we shall find to be frequently repeated with various modifica-
tions and under different conditions in the osseous fishes. They
indicate, in the present species, a diet of a lower-organized character
than in the true sharks, and a corresponding difference of habit and

E 2

ond

52 CESTRACIONTS.

disposition is associated therewith. The testaceous and crustaceous
invertebrate animals constitute, most, probably, the principal food of
the Cestracion.

The teeth are attached to the maxillary surface by a slightly
contracted and truncated basis: the part which may be termed the
crown of the tooth is covered with alayer of dense white substance,
analogous to enamel, the surface of which is impressed by nume-
rous minute pits. Below the crown, the surface of the tooth is still
more irregular, and the basis is composed of coarse fibres with inter-
vening fissures and foramina. The small anterior teeth, which
resemble those of certain sharks, may be distinguished by their rugous
base, which is also broad and flat.

When the dense outer layer is removed from the crown of the
newly formed teeth, the orifices of the medullary canals or tubes per-
forating the whole body of the tooth are brought into view.
The texture of this tooth, in fact, like that of the Mylhobates, is
precisely such as would suggest the idea of the tubular texture
assigned by Cuvier to the compound teeth of fishes. These tubes
or canals, which are visible to the naked eye, are more or less
occupied in the recent fish by a vascular and organized medulla or
pulp. They are continued directly from the irregular and reticularly
disposed cells and canals of the semi-ossified cartilaginous crust of
the jaw. In the large crushing teeth, the greater number of the
medullary canals proceed in a pretty regular and slightly wavy course
towards the grinding surface, while the outer ones incline towards the
lateral surfaces ; but they soon begin to divide, and the divisions
continue to ramify dichotomously ; the branches anastomose together,
especially near the surface, and form loops of which the convexity
is always directed but flattened, towards the unattached surface of
the tooth. The medullary canals are, in general, slightly dilated
before they dichotomize, and the branches maintain throughout nearly
the same size as the trunk.

Plate 12 shows the general appearance of the medullary canals
in a vertical section, including part of the lateral surface of the tooth,
as seen by transmitted light through a compound lens of half an inch
focus. The dark colour of the wide medullary canals is due to the

CESTRACIONTS. 53

opacity occasioned by the earthy matter deposited in them from their
peripheral extremities to within a short distance of the base of the
tooth. The fine calcigerous tubes, from the same cause, appear as
dark lines in the interspaces of the medullary canals, and as they pass
into the enamel-like superficial layer.

In Plate 13 is exhibited a portion of two of the terminal medul-
lary loops, with the calcigerous tubes continued from them as seen
under a magnifying power of 600 diameters. The interspaces of the
medullary canals are traversed throughout the substance of the tooth
by calcigerous tubes, which have a general direction vertical to the
medullary canal from which they proceed.

The calcigerous tubes present, at their origin, a diameter, gene-
rally, of s*-th of an inch. They are more ramified, and have a more
undulatory course than the medullary canals, especially those which
occupy the interspaces of these canals, where they form a moss-like
network, in the meshes of which are minute cells, with which the finest
branches of the calcigerous tubes are in communication. The cal-
cigerous tubes of the grinding surface of the tooth have a general
direction, vertical to that surface, and the enamel-like coating is
formed principally by the finest terminal branches of these tubes,
imbedded in a transparent and apparently structureless matrix.
Under a power of voth inch focus, longitudinal series of irregular and
partially confluent rhomboidal cells are discernible in many parts of
this external layer.

The jaws of the Cestracion, like those of the other sharks,
exhibit the teeth in various stages of formation. At the innermost
extremity of some of the rows, may be seen a small, flat, punctate,
milk-white, calcareous plate, ofa friable texture, resulting from the
recent deposition of the earthy particles in the microscopic cells and
tubes of the superficies of the formative matrix ; the only part which
as yet is developed from the common mucous and ligamentous basis
of the teeth. The rest of the matrix is progressively added until
the tooth acquires its full size; the deposition of the calcareous salts
proceeding from the crown to the base simultaneously along the whole
breadth of the tooth. |

The process of dentification is here most clearly seen to be one

54 CESTRACIONTS.

of conversion, not of excretion. As the teeth advance into use, the
organized pulp of each medullary canal becomes consolidated by the
formation of concentric osseous layers at its circumference, and by an
irregular calcareous deposition in its centre. The new teeth are
carried forward and outward by the same rotatory movement of the
membranes supporting them, as in the ordinary Squaloids.

19. Acrodus.—Among the extinct Plagiostomes recognizable by
teeth cr spines, the genus Acrodus, according to M. Agassiz, presents
the closest affinity with the existing Cestracion. The teeth of the
Acrodus, (Pl. 14, fig. 1,) are of an oblong form with a convex or
slightly conical crown, supported on a coarse osseous base, in the
form of a parallelogram, obliquely truncated at its inner side. The crown
swells out beyond the base, and is expanded in the middle, and con-
tracted, generally unequally, towards the extremities ; it is traversed
by fine ridges, which diverge from one which runs along the middle of
the long diameter of the tooth. Portions of the jaw of the Acrodus have
been discovered which show that these teeth were arranged, as in
Cestracion in oblique rows, with, at least, seven teeth in a row. Those
at the anterior part of the jaws were short, with the middle of the
crown raised into an obtuse cone; the posterior teeth were more
elongated and depressed.

Professor Agassiz has remarked that ancient writers on Natural
History have mistaken the teeth of the Acrodus for fossil insects or
worms: by the quarry men of this country they are commonly called
petrified leeches: by some naturalists, they have been regarded as
auditory ossicles or otolithes of fishes ; but, independently cf more
obvious evidence, a single inspection of a transparent slice of one of
these fossils in an adequate magnifying power, would suffice to de-
monstrate their real nature, (Pl. 14 and 15).

The teeth of the Acrodus nobilis are composed of two substances,
viz: a thin external almost colourless layer, which represents the
enamel, and an amber-coloured coarser dentine composing the body
of the tooth, and continuous with and passing into its coarse
cellular bony basis and support. Microscopic sections of this
tooth afford the most beautiful appearances, and, perhaps, the most
instructive illustration of the relation of dentine to bone. The body

CESTRACIONTS. 55

of the tooth consists of groups of short, branched and frequently
irregularly wavy medullary canals imbedded in a clear matrix.
These canals are surrounded by concentric layers, and closely
resemble the Haversian canals in true bone. The calcigerous
tubes, which radiate from the medullary canals, have a grace-
ful undulatory course, and are much branched; but iowards the
periphery of the tooth, the ramified tubes are all directed, as in or-
dinary dentine, at right angles to the superficies, and thus constitute a
regular layer of hollow columns disposed so as to offer the greatest
resistance to external pressure. This layer is equal in thickness to
about one-fifteenth part of the vertical diameter of the thickest part
of the tooth.

The finest or terminal branches of this peripheral layer of
tubes, I have traced in various places into what, at first sight, appears
to be the enamel. Under a magnifying power of 400 diameters, how-
ever, this outermost layer is seen to be composed of extremely minute
tubes, r*vvth of a line in diameter (Pl. 16, fig. 2,) ; they are branched
like the coarser tubes of the body of the tooth; irregularly wavy in
their course, having a general tendency to an arrangement at right
angles to the superficies, but inextricably interwoven, and connected
anastomotically together, so as to require a strong light to penetrate
even the thinnest section, and render their structure and arrangement
visible. ‘The continuation of these finer superficial tubes with the
coarser tubes of the body of the tooth, is best observed by slightly
changing the focus of the glass with which they are viewed, which
brings the transitional tubes at different depths in the section into
view. In some parts of the section, a medullary or Haversian canal
is displayed longitudinally ; and the parallel lines of the surrounding
concentric strata on each side are exhibited. The canal maintains a
general uniform diameter, but slightly dilates where it divides or
sends off a cross branch to communicate with the adjoining canals.
These canals commence from the large cells of the bony base, and
pass into the substance of the tooth towards its periphery; they
communicate by transverse canals, but all ultimately terminate in
bundles of the wavy ramified calcigerous tubes of the body of the

56 CESTRACIONTS.

tooth. The unobliterated area of the medullary canals was occupied
by a vascular pulp in the living animal, and the silicious matter with
which they are filled in the fossil, has received a dark stain, probably
from the colouring matter of the vascular pulp ; but the finer tubes,
from the want of this difference of colour, are in many parts obs-
curely visible, if at all. They are discernible in some situations
crossing the concentric lamellz at right angles to the central canal.
The chief difference between the appearance presented by the Ha-
versian canals of the tooth of Acrodus, and those in bone, is in the
absence of the radiated cells or corpuscles. At the base of the
tooth, there are cells interspersed with the medullary canals, irre-
gular in size and form, very minute, and appearing like simple
granules without radiating lines. The character of the main or
coarser canals and calcigerous tubes of the ivory of the tooth of
Acrodus, reposes on their undulating course, their rapid diminution
and branching, and the moderately acute angles at which the branches
are given off, except at the circumference of the tooth, where they run
nearly parallel to each other. The line of demarcation between the
coarser and finer ivory, is formed by a series of small cells having the
form and arrangement represented in Pl. 16, fig. 3, in which many of the
finer branches of the coarse ivory terminate, and from which the
minute tubes of the enamel-like ivory commence. The superficies
of the tooth is slightly punctated ; the depressions, however, do not
correspond with the mouths of tubes, but with the interspaces of
whole groups of the coarser tubes.

20. Hybodus.—The remains of the extinct genus of Plagiostomes to
which M. Agassiz has given the name of Hybodus occur in the
secondary formations from the upper red sandstone to the chalk in-
clusive. They consist of teeth and large osseous spines, which have
been discovered so associated together as to leave little doubt that
the recent animal was armed with a pair of spines, one to each dorsal
fin, as in the Cestracion, and that the jaws were beset with closely
packed vertical rows of teeth, containing from six to seven in each
row, (Pl. 11, fig. 1). The teeth are in the form of transversely elon-
gated depressed cones, and consist of two pretty equal parts, viz: a

CESTRACIONTS. 57

coarse, osseous, wrinkled base, and an enamelled crown. The crown
is separated from the base by a slight constriction, above which it
swells out and then quickly diminishes to an apical ridge, which
traverses its long diameter, and presents a series of pointed cusps ;
of these, the middle one is the largest and highest ; the rest quickly
diminish in size as they recede from it. The sides of the crown are
traversed by well marked but fine ridges, which converge from below
towards the middle cusp, but are variously disposed in the different
species of Hybodus.

The cusps of the exterior teeth are erect, those of the internal or
posterior ones are recumbent, but the transition from one position
to the other is gradual and progressive as in Squatina and the anterior
teeth of Cestracion. The development of these teeth corresponds
with that in the Cestracion, where the whole breadth of the pulp is
progressively ossified from above downwards, instead of from the
external surface of the whole crown inwards ; hence, the last formed
teeth are not hollow, as in the true sharks.

The teeth of some species of Acrodus, as the Acrodus minimus
of Agassiz, resemble so closely those of a Hybodus in external form,
as to be liable to be mistaken for those of that genus. The micros-
copic structure of the teeth, in these closely allied genera, is very
similar in its general plan. In Hybodus, however, the calcigerous tubes
in the body of the tooth have a less wavy disposition than in Acrodus.

21. Ptychodus.—The fossil teeth, on which M. Agassiz has established
the genus Ptychodus, have not as yet been discovered undisturbed in
their natural position in the jaws, so as to demonstrate the affinity
of the extinct fish to the recent Plagiostomes, with the same certainty
as in the case of the Hybodus and Acrodus; nevertheless, their
number, their external form, and the absence of any other parts of
the skeleton in the localities where they are most abundant, alike
bespeak that they belonged to a cartilaginous fish, which M. Agassiz
conjectures to have been nearly allied to the Cestracion. The micro-
scopic texture of these interesting fossils, which 1 described at the
meeting of the British Association in 1838, afforded the demonstra-
tion finally required of their true nature. The entire tooth (PI. 17,

58 CESTRACIONTS.

figs. 1 and 2) presents a quadrangular form, and consists of a root
and a crown ; a wide but shallow groove forms the line of demarca-
tion between these parts. The root, which presents a coarse, porous,
osseous texture, is flat below, and gradually enlarges towards the
crown. The crown suddenly expands above and beyond the root,
especially beyond its anterior part. The anterior and two lateral
surfaces of the crown are convex, the posterior surface (fig. 1) is
concave, apparently for the reception of the convexity of the succeed-
ing tooth. The broad upper surface of the crown is more or less
convex, and sculptured with minute tubercles and wrinkles at the
circumference, and with large angular transverse ridges in the centre.
These ridges are separated by wide grooves, and generally have their
extremities bent towards the anterior part of the tooth ; the surface
of the crown is smooth and polished like enamel. In fig. 2, the
sculptured grinding surface of a tooth of the Ptychodus latissimus is
represented of the natural size.

The texture of the tooth of the Ptychodus, examined ina longi-
tudinal vertical section at half an inch focus, as in Pl. 18, presents a
congeries of medullary and calcigerous tubes, having the same general
arrangement as in the Cestracion. The medullary tubes are, however,
relatively smaller ; they proceed from the coarse canals of the osseous
base in a nearly straight and parallel direction towards the surface
of the crown, diverging from each other, and branching dichoto-
mously, so as to maintain a direction vertical te the surface towards
which they proceed. Their interspaces are pretty regular, and about
five or six times the diameter of the canals themselves. They are
surrounded by concentric lamelle (fig. 2, Pl. 19), and send off through
the whole of their course numerous minute calcigerous tubes ; these
are transverse to the medullary canals near the base of the crown, and
come off at an acute angle as they approach nearer the summit, close
to the surface of which the medullary canals resolve themselves into
fasciculi of calcigerous tubes (fig. 1, Pl. 19); in a few places, two
contiguous medullary canals anastomose, and form a loop, with the
convexity directed towards the surface of the tooth ; one of these
loops is shown in fig. 1, Pl. 19. The calcigerous tubes are more

CESTRACIONTS. 59

wavy than the medullary canals ; they quickly ramify, and sub-divide
to extreme minuteness in the interspaces, and finally terminate by
anastomosing with each other, either immediately or by the inter-
position of calcigerous cells.

The intimate structure of the tooth of the Ptychodus differs from
that of the tooth of the Cestracion, in the medullary tubes being
narrower, the interspaces wider, and the terminal anastomosing loops
fewer. The calcigerous tubes, also, are relatively larger, more wavy,
and more branched. It differs from the structure of the tooth of
the Acrodus in the straighter course, and fewer divisions of the me-
dullary canals, and in the absence of the straight parallel superficial
series of calcigerous tubes.

22. Psammodus.—Under this name, M. Agassiz had formerly asso-
ciated all those teeth of fishes ‘‘ which combine a structure like that
which characterizes the teeth of the Cestracion,”—that is to say, a crown
formed of small vertical tubes,—‘‘ with a surface of the crown more or
less smooth, and presenting only that sanded or punctate character
which results from the structure of the crown.”

Here, however, I must observe that neither in the teeth of
Psammodus nor in those of Cestracion have the punctate impressions
of the enamelled surface any relation with the medullary canals or
the large visible vertical tubes to which the learned Ichthyologist just
quoted refers. These tubes always terminate at a short distance
from the surface of the tooth, either by anastomosis or by subdivision
into other tubes of such extreme minuteness that the combined
diameters of five hundred of them would barely equal the breadth
of a single superficial punctation. These impressions on the teeth of
the Psammodi, like the transverse ridges of those of the Ptychodi, are
consequences of the conformation of the original matrix, and can be
regarded only as adaptations conformable with the habits and food
of the extinct species; and as they are not due to a certain tubular
structure, so neither can they be viewed as evidence of such structure
when it has not otherwise been proved to exist.

The term Psammodus is now restricted by M. Agassiz to the
extinct fishes, the teeth of which combine a broad, flat, punctate,

60 CESTRACIONTS.

grinding surface, with a great breadth of crown. It is of one of those
teeth of the typical Psammodi which I have submitted to microscopic
examination. A transverse section of the tooth of this genus pre-
sents the appearance, under a moderate magnifying power, as if it
were composed of close-set coarse tubes, the arez of which were thus
exposed. Such a section, viewed with a power of 400 diameters,
shows that these tubes are surrounded by concentric lamelle, like the
Haversian canals; and that these lamelle, and the clear interspace,
which is generally equal to the thickness of the lamelle, are permeated
by minute irregularly disposed tubes, which anastomose in the clear
interspace, and open into extremely minute cells, scattered through
that part. A longitudinal section of the same tooth shows, in many
places, the whole course of the canals; they run nearly perpendicularly
to the convex superficies of the tooth, and, consequently, incline
outwards at the sides of the section. They lie nearly parallel with
each other, with interspaces equal to from six to eight times the
diameter of their area, and branch dichotomously once or twice in
their course. Each canal is surrounded by concentric layers of
a dark colour, encroaching upon one-third of the interspace, which
thus presents two semi-opake streaks and one intermediate clear
line ; the whole of these interspaces is perforated by the irregular
wavy, branched, anastomosing calcigerous tubes. The terminations
of the medullary canals near the periphery of the tooth are slightly di-
lated, and give off in every direction calcigerous tubes corresponding to
those in the interspaces of the canals. The calcigerous tubes, at this part
of the tooth, run obliquely along the side of the medullary canal, from
which they are continued, for a short distance before they pass off
through the concentric layers into the clear interspace; to this
structure is due the appearance, which the medullary canal presents,
of being composed towards its termination of a fasciculus of spirally
twisted tubes. I have not observed this structure in any part of the
medullary canals of the tooth of the Ptychodus, which further differs
from that of Psammodus in the more frequent bifurcation of the medul-
lary canals, and in the smaller extent of their opake concentrically-
laminated walls. The structure of the tooth of Psammodus, like that of

CESTRACIONTS. 61

Ptychodus, differs from that of Acrodus in the greater number and
more parallel course of the medullary canals, their fewer branches,
and in the absence of an external layer of fine parallel tubes.

The Psammodontoid teeth which are elongated, more or less
contracted and truncated at the two extremities, and of which the
surface of the crown is reticulated, are now regarded by M. Agassiz
as indicating a distinct subgenus, to which he gives the name of
Strophodus, (Pl. 17, fig. 4). Other fossil teeth, which resemble in
general structure those of Psammodus, but which have the centre of
the crown elevated into an obtuse transverse cone, and traversed by a
ridge, from which oblique furrows diverge, but with a more or less
transverse direction, towards the circumference and there ramify,
have been referred by the same authority to a genus called Orodus.
These fossils occur in the older secondary rocks.

Similar fossil teeth, having the crown in the form of an elevated
obtuse cone, but perfectly smooth on the surface, form the type of the
genus Helodus. Agas.

In a fourth form, the crown is compressed and elevated, and
sometimes terminates in a sharp edge like the tooth of a Carcharias ;
its base is always surrounded by a series of concentric folds. This
is the type of the genus Chomatodus. Agas.

A fifth form of Psammodontoid teeth, in which the crown is
raised, subcompressed and subdivided by deep transverse ridges into
dentations, varying as to number and degree of sharpness or obtuse-
ness, has given rise to the establishment of the genus Ctenoptychius,
Agas. . ;

23. Petalodus.—Intheteeth of many of the subgeneraof Psammodus,
the crown is produced into a median or submedian ridge ; if the body
of the tooth be supposed to be still more compressed, so that the
ridge should terminate the contour of the crown like a trenchant
edge, there will then be produced the lamelliform figure which cha-
racterizes the teeth of the subgenus in question.

In the specimen of the tooth of Petalodus Hastingsii now before me,
which I owe to the kindness of Sir Philip Egerton, the trenchant margin
is slightly convex and finely serrated, the crown of the toothis invested with
a thin layer of dense enamel, with a smooth and shining surface, the

62 CESTRACIONTS.

punctation of which is too minute for the naked eye; the enamel is
disposed in a series of concentric lines around the base of the crown ;
these lines extend lower down on the posterior than on the ante-
rior part of the tooth ; and the enamel terminates on both sides in a
line which is convex towards the base of the tooth, contrariwise to
the terminal contour of the enamel in the compressed teeth of the
sharks. The osseous basis of the tooth terminates in an expanded
obtuse convex margin. This lamelliform tooth is bent slightly upon
itself so that a vertical section exhibits a slight sigmoid flexure (see
Pl. 22, figs. 3, 4, and 5.)

In a second species of Petalodus (Pet. serratus), the trenchant mar-
gin of the tooth is more strongly serrated, and in a third species,
Pet. dentatus, it is notched or dentated.(1)

The body of the tooth of the Petalodus is everywhere traversed
by medullary canals, which are fewer, relatively larger, and more
irregularly and reticulately disposed than in the teeth of Chomatodus,
or of any other genus of Cestraciont. The interspaces of the me-
dullary canals do not quite equal the diameter of the canals them-
selves: they are traversed by calcigerous tubes, as numerous and
minute as in the Psammodus, but similar in their wavy disposition
to those of the Acrodus. The short terminal branches of the medullary
canals, which distribute the calcigerous tubes to the enamel-like outer
layer, are slightly bent downwards, or towards the base of the
tooth.

24. A very interesting modification of the teeth which resemble in
structure those of Psammodus, is presented in the extinct genus
Cochliodus of Agassiz. Here the jaws are paved with teeth arranged in
a few oblique contorted series, as in the Cestracion, but a single tooth
occupies the space covered by an entire row in the existing Australian
genus. In the specimen figured, in the collection of Capt. Jones,
R.N., there are three of these large contorted dental plates in each
ramus of the jaw, (PI. 22, fig. 1.)

The microscopic structure of these large teeth closely resembles
that of the true Psammodus; the medullary canals have the same

(1) Both these species are founded on specimens in the beautiful collection of the fossils of
the mountain limestone, in the possession of Capt. Jones, R.N. M.P.

CESTRACIONTS. 63

straight, sub-parallel course, and sparing dichotomous sub-divisions,
but they are relatively wider, and are separated by interspaces of
less breadth.

The calcigerous tubes are also wider at their origin ; they come
off not quite at right angles to the medullary canal, but are slightly
inclined to the grinding surface of the tooth ; they quickly ramify,
sending off their branches at nearly right angles, and are less flexuous
in their course than in the Petalodus ; they dilate into angular cells
at many parts of the mid-space between the medullary canals.

In the genus Ceratodus the dental system is represented by a
single large plate on each side of both upper and lower jaws, (Pl. 22,
fig. 2.) The detrition to which these plates were subject was re-~
paired by a continued development of the posterior part of the dental
plate in the manner which will be explained in the account of the
teeth of the Chimera.

The large and singularly sculptured dental plates, to which
M. Agassiz has given the name of Ctenodus, are likewise conjec-
tured not to have exceeded four in number in the mouth of the
extinct species indicated by these remains. The texture of the
tooth, like that of others of the Psammodus kind, presents a coarse
osseous structure at the base, supporting a dense osseous or enamel-
like layer; the surface of the crown is minutely punctate. The
crown is traversed by twelve nearly parallel ridges, each of which is
notched or divided into a series of obtuse cones, which gradually
increase in size towards the outer border of the tooth.

Such are the principal modifications of form and structure pre-
sented by the teeth of those extinct fishes, of which the Cestracion
of the Australian seas is the nearest living analogue.

Were this genus to become extinct, all that would remain of it
in a few years would be its teeth and dorsal spines, the only hard
and durable parts of its frame. Fortunately we still possess the
evidence of the general form and organization with which they are
associated. But had even the teeth alone of the Cestracion remained,
a microscopic investigation of their intimate structure must have
led to an insight into the close affinities subsisting between the
extinct animal and higher cartilaginous fishes. For it is peculiar to

64 CHIMZEROIDS.

the Plagiostomous order, among fishes, to include so many genera
which exhibit in the dental substance the rich organization of vas-
cular and calcigerous tubes that has already been described, and the
modifications of which become the more important and interesting,
when, as in the case of the extinct Psammodus, Acrodus, and Hybodus,
they are almost the sole features of the organization of those most
ancient vertebrate animals which remain for the contemplation of
the anatomist and physiologist.

CHIMAROIDS.

25. I next proceed to consider a well marked modification of the
same highly organized dental structure in the genus Chimera, which,
like the Cestracion, is an extreme but still more anomalous modifica-
tion of the chondropterygious type, having the branchiz unattached
externally : this genus is also the representative of several extinct forms
of fishes.

The jaws of the Chimeroid fishes are armed, says Cuvier, in the
characters assigned to this family in the Régne Animal,(1) with hard
and indivisible plates instead of teeth, four above and two below, and
in the 2nd edition of the Lecons d’Anatomie Comparée,(2) these
dental plates are described as being salient, trenchant and striated.
They have not, as yet, been more particularly described, but the
coarse medullary tubes which enter into their composition, and to
which Cuvier alludes when he compares the structure of these teeth
with those of the Orycteropus in his Histoire Naturelle des Pois-
sons,(3) are illustrated in Pl. 40, fig. 20, of the great work on Fossil
Fishes by M. Agassiz.

The teeth of the Callorhynchus or Chimera Australis, are
represented as they appear on looking into the widely opened
mouth in Plate 28, fig. 1. The upper jaw presents two anterior
dental plates, of a small size and semi-elliptic form, and two posterior

(1) Tom. ii, p. 382.

(2) Tom. iv, p. 362.

(3) Tom. i, p. 496. Cuvier’s words are, ‘‘ Leur tissu intérieur est percé de tubes fins,
comme un jonc ou comme les dents de l’oryctérope.” The tubes here mentioned are the medul-
lary or vascular canals, and are merely the centres from which the true calcigerous tubes
radiate.—See Report of British Association, 1838, p. 145.

CHIMAROIDS. 65

triangular plates, six times larger than the preceding. The anterior
angles of these plates are rounded, and conceal the posterior half of
the anterior plates: the inferior broad surface of the anterior teeth is
sinuous, and joins the lateral surface at a sharp edge; the grinding
surface of the posterior plates is convex in every direction, and there
is a raised portion in the middle of each, of the figure represented in
the plate (Pl. 28, fig. 1). The upper surface of each of these teeth is
concave from side to side, so that it encases or sheaths the alveolar
border of the upper jaw, in a manner analogous to the broad teeth of
the Cestracion.(1) Both the anterior and posterior dental plates in the
upper jaw, meet at the median line of the mouth. The two dental
plates of the lower jaw are of a subtriangular form, with the posterior
and external sides gently curved; the broad grinding surface is con-
vex on the inner and concave on the outer side; a trenchant margin
divides this from the lateral surfaces of the dental plate. When a
longitudinal vertical section is made of these teeth (as in fig. 3, pl. 28),
their coarse tubular texture is evident to the naked eye. There is a
large pulp-cavity at the posterior parts of both the upper and lower
dental plates, and, when the pulp is removed, the exposed surface of
the base of the tooth presents a reticulate character from the large arez
of the medullary tubes into which the processes of the pulp are con-
tinued. These tubes radiate towards the grinding surface of the tooth
and dichotomize as they proceed. As these tubes advance towards
the surface, their cavity becomes gradually obliterated by calcareous
salts, deposited in concentric layers and perforated every where by the
minute calcigerous tubes which radiate from the medullary canal ;
thus the substance of the tooth increases in density as it approaches
the triturating surface.

A diminished view of the appearance of a longitudinal section of the
dental plate of a Chimera, as seen under a magnifying power of 400
diameters, is given at Pl. 29, fig. 1, and ofa transverse section at fig. 2.
But before proceeding to describe this structure, a few words are requi-
site touching the modifications of form presented by the dental plates
of Chimera monstrosa, (Pl. 28, figs. 4 and 8), and of some allied ex-

(1) The genus Cochliodus appears to have been an extinct transitional form between
Cestracion and Callorhynchus.

F

66 CHIMROIDS.

tinct species which present the same intimate structure of the dental
substance.

In the Chimera monstrosa, the dental plates differ considerably in
their general form and disposition from those of the Chimera or Callo-
rhynchus australis ; they are extended in the vertical more than in the
horizontal direction, sheath the exterior of the jaws, and serve as in-
struments for cutting and dividing rather than for triturating and
crushing. The anterior teeth of the upper jaw, more especially, pre-
sent characters of which we find no trace in the teeth of the last
described recent species ; the dental substance being so arranged as to
resemble a series of oblique superimposed lamellz. The fossil dental
plates of the extinct species of Chimera, discovered and described by
Dr. Buckland, resemble the northern rather than the southern Chimera
of the present day ; some of these teeth, as those of Chimera Colei, and
Chim. Owenti, resemble in size, though they differ in form from the
dental plates of Chimera monstrosa, but the dental plate of the lower
jaw of the Chimera Townsendu, which is upwards of six inches in
length, indicates a species which, ceteris paribus, must have surpassed
eight feet in length.

In the marine eocene formation calledthe London clay, at Sheppey,
the dental plates and portions of the jaws of an extinct Chimera, three
or four times the size of the existing species, are occasionally found ;
the lamine of the anterior tooth of the upper jaw are bent obliquely,
so that the outer margin of the plate presents a series of lines, which
are horizontal on its anterior part, and bent obliquely upwards at the
side. The posterior dental plate has its outer wall composed ofa
series of vertical columnar portions, the lower ends of which, as they
are worn by attrition, cause the trenchant margin of the jaw to be
notched and irregular. The inner surface of the same plate is
convex, smooth and punctate; it encloses, as it were, a portion of the
jaw itself.

In the extinct Chimeroid subgenera Edaphodon and Puassalodon,
discovered and so called by Dr. Buckland, the teeth are long,
broad, and thick, with surfaces adapted for crushing and bruising,
like the dental plates of Callorhynchus ; but, instead of encasing the
alveolar borders of the jaws, they are themselves inclosed in the sub-

CHIMAROIDS. 67

stance of the jaw, which presents the coarse cellular structure of the
bone of osseous fishes. The teeth are not, however, loosely implanted
in these alveolar cavities, but wherever they are in contact with the
bone, they are anchylosed thereto. ‘Their structure is, nevertheless,
strikingly different from that of the jaw itself, and corresponds with
the modification of the tubular structure presented by the teeth of the
Chimera. In the Edaphodon there are three of these large teeth on
each side of both jaws: their position is nearly horizontal and their
grinding surface is pitted with small impressions.(1)

In the tooth of the Chimera, the complex structure arising, as it
were, out of an aggregation of long slender and simple cylindrical teeth
is most conspicuous. Each of the parallel medullary or vascular
canals, which from their large size are easily distinguishable by the
naked eye, is the centre of radiation to very numerous and closely
compacted calcigerous tubes, having a diameter of ;;,;th of an inch at
their origin, but ramifying and diminishing in size as they recede,
and ultimately terminating in a minute irregular cellular ossification
which occupies the interspaces of the different systems of radiated
tubes, and cements them together in a continuous mass in the recent
dental plate. The course of the calcigerous tubes is at right angles to
the medullary canal, and they have a wavy disposition ; their primary
branches are sent off at an acute angle, and the fine ramuli from these
branches dilate or terminate in minute cells considerably smaller than
the radiated cells of mammiferous bone.

In the fossil teeth of the large extinct Chimere, the coarser cel-
lular structure, which cements together the systems of calcigerous
- tubes, is generally more or less decomposed, while the denser parietes
of the medullary canals formed by the calcigerous tubes remain ; the
coarse tubular structure of the tooth thus displayed, is accurately
figured by M. Agassiz in the Chimera Townsendu. But the medullary
canals and their radiated systems of calcigerous tubes are not only
cemented together by the ossified capsules, but are still more effectually
connected together by the frequent anastomoses of the parallel medul-
lary canals themselves. The portion of the tooth figured (Pl. 29, fig. 2)
exhibits some of these anastomoses. In those parts of the section in

(1) Proceedings of the Geological Society, 1838, p. 687.
¥ 2

68 SPATULARIA.

which the parietes of the medullary canal have been divided parallel
to its course, the calcigerous tubes are cut through transversely, and
their arez, from the calcareous nature of their contents, are seen like
fine dots.

SPATULARIZE,

26. Polyodon.—Of the other free-gilled Plagiostomoustishes the Stu-
rionide or family of Sturgeons and the Planirostra are edentulous. The
Polyodon, which belongs to the same natural family as the Planirostra,
viz: the Spatularie of Miller, has small recurved teeth on the maxil-
lary and anterior branchial cartilages, at least, at the earlier periods of
life. The specimens of Polyodon, (e. g. in the Parisian Museum), which
exceed three feet in length are, like the Planirostra, edentulous; but
in a Polyodon of the same species about one foot long, there are two
rows of small and slightly recurved teeth in the upper, and a single
row of similar teeth in the lower jaw: similar teeth occur likewise on
the two anterior branchial arches, where these join the tongue; and
again on their expanded extremities which are attached to the palatal
region of the mouth :(1) here, therefore, there are both maxillary and
branchial teeth. Thus the Spatularie not only exhibit a tendency to
the structure of the ordinary osseous fishes in the condition of their
branchial apparatus, but likewise in that of their dental system; the
Polyodon being the only plagiostomous fish which has both maxillary
and branchial teeth.

CHAPTER IV.

TEETH OF THE GANOID FISHES.
LEPIDOIDS.

27. The consideration of the teeth of this family of Ganoid
fishes is not without interest, although as compared with the Pla-
giostomes, few modifications require to be noticed. All the repre-
sentatives of the family have disappeared from the present theatre of
vital phenomena ; yet although the period when they existed is the

(1) Miiller, Vergleichende Anatomie der Myxinoiden, p. 150.

LEPIDOIDS. 69

earliest of those in which paleontologists have recognized the traces
of animal life, the same peculiarities are manifested in the structure
and disposition of their dental organs, as in those of many of
the existing osseous fishes. The teeth are always present on the
palatine bones, and are arranged in several rows on the alveolar
margins of the intermaxillary and premandibular bones ; those of the
outer row are the largest, and are sometimes in the form of obtuse
cones ; the posterior ones are small, simple and close-set, like the
bristles of a brush.

In the genus Amblypterus all the teeth are of the latter kind, and
their minute slender character is the more remarkable on account of
the disproportionate magnitude of jaws. In the genera Palconiscus
and Semionotus, the maxillary teeth also resemble a fine brush ; indi-
cating, Dr. Buckland observes, ‘‘ the habit of these fishes to have been
to feed on decayed sea-weed, and soft animal substances at the bottom
of the water.”

In the large enamel-scaled fishes of the Lias formation belonging
to the genera Dapedius and Tetragonolepis, the teeth are stronger and
better developed, especially the exterior ones. In the Tetragonolepis,
the summit of the crown is simply pointed, but in the Dapedius it is
notched or bifurcate ; and this modification is not due to usage or
compression, for the teeth of all the rows and in both jaws exhibit the
same character, which is also well marked in the successional teeth
that have not come into place. In Dapedius Orbis, the teeth of both
jaws are strongly dilated and compressed from before backwards,
at their summits, and resemble a chisel with a notched cutting
edge. (1)

In the extinct genus Lepidotus, the mouth was small and
the jaws short and rounded. The intermaxillary bones form only
the anterior part of the upper margin of the mouth, the maxillaries
completing the posterior part of that border. The margins of both
these bones, according to M. Agassiz, are beset with small teeth; the
outer row presenting the form of circular obtuse cones ; and within
these are many rows of smaller sessile hemispherical teeth, more or

(1) M. Agassiz assigns pterygoid, as well as palatine and intermaxillary teeth to the genus
Dapedius, t ii, p. 187.

70 PYCNODONTS.

less constricted at their base, and supported on a short pedicle, which
is anchylosed to the osseous substance of the jaws. (Pl. 30, fig. 1).
The detached hemispherical teeth of the Lepidoid fishes are so like
those of some of the genera of the Pycnodont family, as to be scarcely
distinguishable.

The only difference which M. Agassiz recognizes between
the teeth of Lepidotus and those of Spherodus is, that in the former
they have a slight constriction at the base of the enamel. But having
ascertained this character not to be constant, I submitted the teeth of
the Lepidotus Mantellii to microscopic examination, and have compared
their intimate texture with that of the similarly shaped teeth of Sphero-
dus Bucklandi. The dense substance of the tooth of the Lepidotus (Pl.
31) is composed of fasciculate tubes continued directly from the cells
of the osseous base, radiating, with a direction vertical to the surface
of the tooth, and giving off branches, at an acute angle, from their
very commencement ; thus far the general character of the texture of
the tooth is the same as that of Spherodus, afterwards to be described ;
but the fine branches into which the fasciculate tubes resolve them-
selves in Lepidotus, diverge at a much more open angle from the main
trunk, are spread out more widely, are more curved, and pre-
sent the appearance of the stems of corn beaten down with heavy rain.
These fine terminal branches are inextricably interwoven, and present
the appearance of numerous anastomoses, but do not form so dense a
plexus of calcigerous tubes and cells as in the teeth of Spherodus in
which the corresponding tubes and cells intercept the light.

PYCNODONTS.(1)

28. In this family of fishes, of which all the representatives
are extinct, the teeth present a greater diversity of character, and
a higher degree of development than in the preceding; the preva-
lent form approaches to that of the Lepidotus ; the teeth being generally
adapted for crushing, and having a smooth convex or flattened crown.
In some genera they attain a very large size; when smaller they are
arranged in several rows. They have been observed in the intermax-
illary, premandibular, palatine and vomerine bones.

(1) zu«voc, thick, cdovc, a tooth; thick-toothed fishes.

PYCNODONTS. 71

In the genus Pycnodus the teeth are more or less elongated, with
the crown slightly expanded, and convex and smooth above. The dis-
position of these teeth on the vomerine bone is seen in figs. 1 and 2,
Pl. 34. A central row of transversely oval grinders is bounded on each
side by a double alternate row of smaller circular teeth. Similarly
shaped teeth were arranged in three or four rows on the jaws ; but the
exact number and disposition of the maxillary teeth have not yet
been ascertained.

The modifications of external form which characterize the teeth
of the different species of this genus, which have yet been discovered,
are exhibited in the great work on Fossil Fishes by M. Agassiz,
tab. 72, d, vol. ii.

Spherodus.—This genus is founded on detached teeth, which are
the sole remains of the species composing it that have as yet been
brought to light. These teeth are of a hemispherical form, with a
smooth upper surface, (Pl. 33, figs. 1 and 2), and most probably were
distributed over the same bones as in the Pycnodus. The basis of the
tooth isa bone of the coarse cellular structure usual in osseous Fishes.
(Pl. 32). The body of the toothconsists of coarse tubes, which arise in-
sensibly from the basis, where they have a diameter of s=>~ th of an inch,
and proceed directly and perpendicularly to the surface of the tooth.
The characteristics of these tubes are, first, that they are so closely ar-
ranged together that only one-fourth of their own diameter intervenes
between them at their origins. Secondly, they present the appearance
of being composed of a closely-twisted bundle of smaller tubes, —an
appearance produced by the oblique direction and acute angle at
which the calcigerous tubes are continued from them into the clear
intervening substance. Besides these smaller tubes, the main trunks
begin immediately to give off short and somewhat coarse branches at
very acute angles ; these branches increase in number, and the trunks
proportionally diminish, until they have traversed two-thirds of the
vertical diameter of the tooth ; they then resolve themselves into fas-
ciculi of extremely minute twigs, which interlace together, and in many
places dilate into, or communicate with, numerous minute calcigerous
cells, and form so dense a layer as to intercept the light, excepting

72 -PYCNODONTS.

towards the circumference of the tooth, and consequently at the two
extremities of the section, where only the structure above described is
visible. Several small twigs pass beyond this plexus into the clear
enamel-like outer layer of the tooth, in some parts of which traces were
perceptible of a plexus of still more minute tubes, or strig, which gra-
dually diminished until they escaped the highest magnifying power
employed in this examination. (Pl. 33). The enamel-like layer is
clearly a continuation of, and part of the same substance as the rest of
the tooth; its dense and clear texture indicates the extreme subdivi-
sion and abundance of the earthy salts: this stratum is of considerable
thickness in the Spherodus crassus of Agassiz.

In the genus Gyrodus the surface of the teeth is furrowed some-
times irregularly, sometimes regularly and deeply as in Gyr. rugulosus.
(Pl. 34, figs. 6 and 7). The teeth are present in the intermaxillary, pre-
mandibular, palatine and vomerine bones.

In the Gyrodus umbilicatus each premandibular bone supports four
rows of teeth (Pl. 34, figs. 4 and 5) ; those of the external and third rows
are of a transversely oval form, and are larger than those of the second
and internal rows, which have a circular contour. The intermaxillary
and premandibular teeth are fewer in number, and present an obtuse
conical form in the Gyr. circularis. The vomer in this species is
covered with five longitudinal rows of teeth; those of the middle one
being the largest as in the Pycnodus.

In the tooth of a Gyrodus cretaceus, I find that the tendency to the
structure of the dense ivory of the teeth of the higher Vertebrata, which
is obvious in the teeth of Spherodus and Lepidotus, is carried on to a
close correspondence. ‘The base of the tooth is excavated by a large
and simple pulp-cavity, presenting a quadrate figure in a vertical sec-
tion of the tooth ; this cavity is immediately continuous with the large
cells and reticulate canals of the bony base. The body of the tooth
consists of close-set minute calcigerous tubes, having a diameter of
7ooth of a line at their origin, radiating in a direct line, but with a
minute and regularly undulating course, and a gradually diminishing
diameter to the superficies: the lateral tubes pass horizontally, and
those continued from the summit of the pulp-cavity vertically, to the

PYCNODONTS. Vo

grinding surface. They give off very regular, but extremely minute
branches, which are lost in the clear and dense enamel-like superficial
laver of the tooth.

In the genus Microdon, the teeth, though presenting all the
general characters of the Pycnodontal structure, are reduced to their
smallest dimensions. They present a flattened angular form, and are
arranged in many rows on the intermaxillary, premandibular and
vomerine bones. The whole substance of the tooth is composed of
calcigerous tubes, which are straighter, more parallel, and relatively
finer than in Gyrodus, whence there results a texture of still greater
density, and one that approaches very closely to that of the molar teeth
of the Gilt-head (Chrysophrys). The arrangement of the component
tubes of the tooth of Microdon is shown in PI. 43, fig. 1.

The pavement of thick, round, convex or flattened teeth of the
genera of Pycnodonts, above described, was adapted, like the corres-
ponding teeth of existing fishes, to break and crush small testaceous
and crustaceous animals. These teeth, under the name of Bufonites,
occur most abundantly in the oolite formation.

The teeth of the extinct fishes of the genus Placodus present
reverse proportions to those of the Microdon, and here attain their
maximum of development in the Pycnodont family. Plate 40, fig. 2
exhibits the alveoli of the prehensile intermaxillary teeth, and the
molar teeth of the same bone in situ of the Placodus Andriani, Ag.
The prehensile anterior teeth were arranged in two transverse rows
of six in each row. The anterior were the largest, and presented a
singularly elongated cylindrical form, with a conical slightly recurved
obtuse crown (fig. 3). In Placodus gigas, the crown of the incisor is
more expanded and more abruptly bent. These teeth, like the diver-
gent anterior teeth of the Wolf-fish, must have served to grapple with
large Testacea or Crustacea, the crushing and comminution of which
were then completed by the posterior dental plates. These are
arranged in four rows, of which the two external ones include each
four smaller subcircular teeth ; the two internal rows consist each of
three large tetragonal dental plates with the angles rounded off, and
the upper surface flattened and smooth.

In the lower jaw it would seem that three similar dental plates in

74 SAUROIDS.

each premandibular bone were opposed to the molar teeth above.
The side view of these teeth (Pl. 30, fig. 4) shows their elevation above
the jaw. In the vomer, a median row of transversely oblong teeth is
bounded by smaller subcircular teeth, as in the other Pycnodonts.

SAUROIDS,

29. This family of voracious fishes is represented in the existing
creation by extremely few species, which are severally the types of the
genera Lepidosteus, Amia, and Polypterus ; and these genera are dis-
tributed at remote distances in the great rivers of the American and
African continents. The general character of the teeth in this family
is to have larger ones of a conical form intermixed with more nume-
rous teeth of smaller size.

The Sauroid fishes have teeth on the intermaxillary, premandi-
bular, palatine and vomerine bones. These teeth are conical and
sharp-pointed: some are large, and are separated by interspaces
occupied by similarly shaped but much smaller and more numerous
teeth. The larger teeth are grooved longitudinally at the base, and
have a large conical pulp-cavity within. ‘Their fluted base sinks into
an alveolar cavity of the jaw, but is intimately blended with its bony
walls, in amanner which will be more particularly described in the
teeth of the Rhizodus.

In the jaws of the Polypterus of the Nile, there are two rows of
equal, fine, sharp, approximated teeth ; those of the anterior row are
the largest; the posterior ones are like the teeth of a rasp.

In the Stony-gar (Lepidosteus) of the North American rivers,
the elongated jaws are also armed with similar laniary and rasp-like
teeth: the outer row consists of numerous conical sharp-pointed
teeth, which are separated by regular intervals containing the sockets
of old teeth which have been shed, and the germs of new ones.
External to these larger teeth there is a less interrupted row of
smaller conical teeth.(1) The inner border of the dentigerous margin of
the jaw is beset with a series of small rasp-like teeth; and similar
teeth are present on the vomer and the palatine bones. The larger
conical teeth are developed in alveolar cavities, but their basis becomes

(1) Pl. 35, fig. 1.

SAUROIDS. 75

anchylosed to the jaw-bone when their growth is completed ; and, as
in most other fishes, the succession of new teeth seems to be uninter-
rupted.

The extinct genera of this family were much more formidably
armed, and the great conical laniary teeth of some of the individuals
compete in size and strength with those of the largest Ichthyosaurs
and Crocodiles. Plate 35, fig. 2, is a reduced figure of the dislo-
cated and fractured premandibular bones of an extinct sauroid
species of the genus Rhizodus, a genus nearly allied to the Holop-
tychus of Agassiz, but differing in the greater number, and more
robust and obtuse shape of the smaller conical teeth. In each pre-
mandibular bone there are three elongated conical teeth, with several
smaller and more obtuse conical teeth in the interspaces.

The larger teeth have an ovate transverse section, with a trenchant
posterior margin, and terminate above in a sharp point; they are
thus alike fitted for piercing and cutting. Their base is irregularly
fluted in the longitudinal direction, and sinks deep into the substance
of the jaw, with which it is firmly anchylosed. The peculiarly
efficient mode in which these large destructive teeth are implanted
in the jaws, indicates the violence and force with which they were
wielded in the predatory contests of the living fish. Fig. 1, Pl. 36,
shows the external form of one of the larger teeth of the Rhizodus.
A longitudinal and vertical section has been removed from the
grooved base, showing its solidity, and the coarse longitudinal fibrous
structure which it presents to the naked eye. Fig. 2 exhibits the
complicated organization which a section of a portion of the basis of
the tooth presents under a magnifying power of + inch focus.

The exserted body of the tooth is hollow, as in other Sauroids,
but the pulp-cavity is relatively smaller ; the parietes of this cavity
consist of adense ivory, composed of minute calcigerous tubes. The
diameter of these tubes at their origin is x+-th of a line. They proceed
in slight curvatures from the central canal at right angles to the
periphery of the tooth, with interspaces equal to four of their diameters ;
throughout their course they are minutely undulated, and occasionally
divide dichotomously ; they give off ramuscules at very acute angles,
which are lost in the clear interspaces. The thin external enamel-

76 SAUROIDS.

like coating of the tooth receives numerous similar parallel ramuscules
from the stratum of calcigerous cells which forms the boundary
between this external layer and the ivory of the tooth. The pulp-
cavity, which has a compressed ovate section, is gradually contracted
and finally obliterated in the basis of the tooth, where it divides into
numerous minute canals which subdivide and anastomose as they
penetrate deeper into the jaw, and finally terminate in minute tor-
tuous canals, which become continuous with those of the coarse
osseous substance in which they are imbedded. All the preceding
branches of the pulp-cavity are the centres of radiation of as many
systems of calcigerous tubes, similar in size to those of the body
of the tooth. The primary curvatures of these tubes are shorter, and
the interspaces somewhat wider ; the calcigerous cells in which the
fine branches of these calcigerous tubes terminate, are also coarser.
The interspaces of the divisions of the base of the tooth are occupied
with the coarse cellular bone of which the jaw is composed.

The teeth of the Rhizodus thus include two very different types
of structure, which pass insensibly into one another; the exserted
body of the tooth is like the dense ivory of the ordinary mammiferous
or saurian tooth, the inserted basis presents the compound structure
of the teeth of the Myhobates and Orycteropus. Each division of the
tooth’s basis, however, presents in the Rhizodus greater strength and
density than the corresponding parts of the tooth of the Myliobates,
in consequence of the greater minuteness, increased number, and
more aggregated and parallel disposition of the calcigerous tubes, and
the smaller diameter of the medullary cavity in the former species.
The advantage which was obtained for the teeth of the extinct
carnivorous Sauroid by the root-like implantation above described,
in resisting displacement and fracture, is too obvious to need further
illustration. Finally, as the teeth of no species of reptile or fish are
similarly subdivided and implanted in the jaws, the teeth of the
Rhizodus, notwithstanding the organization of the crown, may be
readily and certainly distinguished from them.

The large conical laniary teeth of the extinct genera Holoptychus
and Megalichthys present a similar structure to that of the tooth
above described. The whole body of the tooth is composed in

GYMNODONTS. 77

Megalichthys of minute close-set calcigerous tubes, having a diameter
of _2,th of a line, with interspaces of twice that diameter. The
calcigerous tubes have a minutely undulated course, and pass
in nearly a straight line from the internal to the external surface of
the tooth ; the pulp-cavity extends about half-way through the body
of the tooth, and has a narrow elliptic transverse section ; it becomes
gradually smaller at the base of the tooth, and there branches out
into several ramifications, which are continued into the cylindrical pro-
cesses of the dental substance, and these are imbedded, like so many
piles, in the coarse osseous texture of the jaw.

GYMNODONTS.(1)

30. To the theory of dental development by intus-susception or the
deposition of calcareous tubes in the pulp’s substance, as opposed
to that of apposition or the transudation of layers of calcareous
matter from the pulp’s surface, may be objected the structure
and mode of formation of the compound teeth of the gymnodont
fishes, as described by Cuvier(2) and Von Born.(3) In the
Diodon, more especially, the lamellated structure of the tooth, and
its reproduction by successive transudation of layers from a_per-
sistent pulp, were supposed to be clearly demonstrated in the
broad rounded triturating tubercle which is situated behind the
alveolar border of the jaws. The exposed surface of this tooth pre-
sents, in fact, a series of transverse and parallel striz (Pl. 38, fig. 1),
which, in a vertical section (ib. fig. 2) are seen to be the margins of
thin, superimposed, horizontal, and slightly flexuous plates, which have
been partially abraded by trituration in an oblique plane. The su-
perior layers are the most worn, and are evidently, as Cuvier
observed, the oldest ; in proportion as they descend, in the lower jaw,
they increase in breadth; and finally, instead of being soldered
together, they become detached, thinner, and of a more friable tex-
ture, the lowest and incompletely developed plates lying loosely in the
cavity of the jaw beneath the superincumbent dental mass (2. fig. 2, a).
If a vertical section of the tubercle be made on one side of the median

(1) yupvo¢ naked, odove a tooth, fishes with teeth exposed.
(2) Lecons d’Anatomie Comparée, Ist and 2nd editions.
(3) Heusinger’s Zeitschrift, 1827.

78 GYMNODONTS.

plane, the laminz are seen to be developedintwo distinct lateral moieties,
which become anchylosed together by means of a thin median vertical
osseous partition at their median margins; their lateral margins are
similarly anchylosed to the outer walls of the dentigerous cavity.
It is quite clear, as Cuvier observes, that the lamin are developed
successively : and that, in proportion as the anterior ones are worn
away, the posterior ones appear in readiness to replace them, so that
the due number of ridges, on the triturating surface, is always main-
tained.

Nevertheless, these facts will be shown to be quite insufficient
to establish the theory of dental development by transudation of
layers. Any example of a continual reproduction of teeth in vertical
succession, would be as available in that point of view ; the peculiar
application of the tooth of the Diodon to illustrate the theory of
transudation, is due merely to the form of the denticles which com-
pose that compound tooth.

Cuvier, in his examination of the dentition of the gymnodonts,
had employed the microscope so far as to detect the fine reticulate
impressions on one of the surfaces of the dental lamine of the
Diodon, which he rightly attributes to the impressions of vessels ; a
low power, as that of the ordinary pocket-lens, is sufficient to demon-
strate these markings. To examine the structure of the lamelliform
denticles, it is necessary to make extremely thin sections in a direction
vertical to their plane. A portion of such a section, seen by trans-
mitted light with a focus of half an inch, presents the appearance de-
lineated in Plate 39, fig. 2. Hach plate here exhibits, instead of an
amorphous or sub-crystalline mass of excreted calcareous. matter, a
series of extremely minute calcigerous tubes, occupying its whole
extent and having a general direction vertical to its plane. The
tubes are obviously wider at the lower side ef the plate, and gradually
disappear in the clear and dense substance at the opposite surface.
When the thinnest and most transparent parts of the same section
are examined with a compound lens of $ inch focus, the horizontal
partitions, which occupy the interspaces of the lamelliform teeth, are
seen to consist of a coarse cellular osseous texture, without any radiated
(Purkinjian) corpuscles, but similar to the texture of the rest of the

=

GYMNODONTS. 79

endo-skeleton of the Diodon. The main tubes of the dental plate are
continued immediately from the cells of the osseous septum; they
proceed for a short distance vertically, or with a slight curvature,
in the substance of the dental plate, and then quickly divide and
subdivide, the branches generally coming off at an angle of 45°, being
slightly bent, crossing each other in an inextricable manner, and ter- -
minating ultimately in the clear matrix of the upper surface of
the dental plate.

Each dental lamella presents, at every part, the same organized
structure which is above described and delineated ; there is no part
which offers the crystalline characters of true or mammalian enamel.
The mucous membrane of the mouth and periosteum of the jaws, are
reflected into the cavities at the base of the compound tooth (Pl. 38,
fig. 2, a) ; the periosteum lines the parietes of the cavity, and the mu-
cous membrane forms a thick cushion, extended across its floor. From
this surface, a lamelliform pulp is developed, in which the calcifying
process takes place in a direction from above downwards: at first,
the earthy salts are deposited in the state of such minute subdivision
and in such a direction and abundance as to produce the dense and
minutely tubular structure of the dental plate ; when this has acquired
its due thickness, the rest of the pulp becomes ossified, 7.e. the cal-
careous salts are deposited in less abundance, and in the parietes
and interspaces of coarse cells, instead of those of minute tubes. The
margins of the ossified pulps, by this process, become confluent with
the parietes of the general dental cavity, and the mutual adhesion
of the flattened surfaces of the impacted lamelliform teeth is promoted
by the pressure to which their exposed surfaces is subject. By the
time that ossification has begun in one pulp, a second has been
developed beneath it, and it is the portion of the pulp solidified by
the fine tubular calcification which gives rise in the macerated and
dried jaws to the loose and thin lamellz in the dental cavity. These
lamelle become fixed by means of the coarser calcification or ossi-
fication which subsequently takes place in the remains of the pulp,
and their margins are thus anchylosed to the surrounding bone, in
a manner analogous to the fixation of the base of the ordinary
shaped teeth in other fishes.

80 GYMNODONTS.

The structure and formation of the compound tooth of the
Diodon, illustrate the nature and causes of the apparently lamellar
structure of the teeth of certain mammalia, especially of the conical
tusks, the growth of which is uninterrupted. The polished surface of
a vertical longitudinal section of one of these teeth exhibits con-
centric lines which run parallel with the outer contour of the section ;
these teeth, moreover, are commonly resolved by decomposition into
a series of superimposed laminz, or sheathed cones, and this
fact has been regarded as indubitable proof of their original
formation by successively transuded layers of dental substance.
Nevertheless, microscopic sections of such teeth have uniformly dis-
played a structure of tubes running in a direction diametrically oppo-
site to the plane of the lamella. These lamellz are, in fact, due, not to
successive transudations from the free surface of the formative pulp,
but to alternations of states of comparative activity and repose in the
organizing processes by which the stratum of the pulp, in immediate
connection with the last formed or basal surface of the tooth, is pre-
pared to receive the hardening salts, combined with alterations in the
nature itself of the organizing process. These alternate changes are
indicated by the layers of abundant calcigerous cells which are scat-
tered through the intertubular tissue of the tooth in planes corresponding
with the apparent stratification of the dental substance, and with which
cells angular inflections of the calcigerous tubes frequently correspond.
A separation of corresponding layers of parallel aggregated segments
of calcigerous tubes, in the tusks which manifest the preceding struc-
ture, is the usual result of their decomposition.

In the compound dental plate of the Diodon, similarly parallel and
aggregated series of short calcigerous tubes are separated by thin layers
of a cellular bone ; and by decomposition, such a tooth would, in like
manner, exhibit the lamellated structure; but the lamelle in this case, as
in the tusk of the elephant, or the conical molar of the cachalot, equally
present an organized structure of aggregated calcigerous tubes, di-
rected more or less at right angles to the plane of the lamella, and
indicating that higher mode of development by calcification of the
pulp, which it is the chief object of the present researches to ex-
emplify.

GYMNODONTS. 8]

The exposed margins of the upper and lower jaws of the Diodon,
which appear to be covered with a thick irregular layer of the same
dense white dental substance as that of the posterior triturating
masses above described, owe their apparently simple character to a
still more complicated structure. They consist of a series of narrow
flattened denticles lying horizontally, and at right angles to the an-
terior surface of the jaw; so that those of the exterior row of one
jaw have their sides opposed to the corresponding row in the
opposite jaw when the mouth is closed. These denticles are deve-
loped in a cavity, between the outer and inner walls of the jaws,
the floor of which is formed by a thin cribriform osseous plate, sepa-
rating the cavity containing the teeth (Pl. 38, fig. 2, 0) from the wide
vascular canal (c) which occupies the substance of the jaw. At the
bottom of the dental cavity, the denticles are seen in different stages
of formation, unattached, but closely packed, and with their lateral
margins overlapping each other. They are of an oval form, with
the under surface, or that next the floor of the cavity, slightly con-
cave and smooth: the opposite surface convex, and honeycombed:
the denticles gradually diminish in size from the middle to the
outer ends of the dentated margin. As their formation reaches its
completion, the denticles become anchylosed to each other and to
the osseous parietes of their cavity by ossification of the capsules of
the calcified pulps. The thin layer of bony matter or cement en-
closing the denticles is soon worn away when they reach the margins
of the jaws, the irregularity of which is caused by the alternately
overlapping arrangement of the exposed denticles.

The order of development and succession is the same in the mar-
ginal as in the posterior teeth, they ascend in the lower and des-
cend in the upper jaw, but are pushed on in the horizontal instead
of the vertical direction. The chief difference is, that whereas in the
posterior dental tubercle there are only two broad lamelliform teeth
in the same plane, in’the marginal series there are upwards of forty
narrower denticles.

Cuvier observes that the Tetrodons differ from the Diodons inasmuch
as they have no posterior triturating disk, but only the marginal
plates ; and have the jaws divided, each into two portions by a den-

G

82 SCLERODERMS.

tated suture. Inthe upper jaw of many species of Tetrodon, there is
a rudimental posterior dental series, consisting of three or four plates
which project downwards and backwards from the base of the inter-
maxillary bones, and intercept a space in which the apex of the
lower jaw is received when the mouth is closed. In Plate 39, fig. 1,
is given a figure of the beak-like jaws of the Tetrodon lineatus, showing
the median suture, the lines of stratification of the marginal dental
plates, and, at (a), the posterior lamelliform teeth above described. The
marginal lamelliform teeth are from ten to twelve in number in
each half of the mandible ; the innermost are the broadest, and they
become narrower as they pass outwards. The intervening portions,
or bases of their respective pulps remain longer in the unossified state
than in the Diodon. The microscopic structure of the teeth of the
Tetrodon closely agrees with that of the dental tubercle of the Diodon.

SCLERODERMS.

31. The teeth in the file-fishes (Balistes) are limited to the inter-
maxillary, premandibular and pharyngeal bones.

In the Balistes forcipatus, Pl. 40, the teeth of the upper jaw are
fourteen in number, and are arranged in two rows, seven in each inter-
maxillary bone, four in the front row and three behind. In the
lower jaw there are eight teeth corresponding with the front row above.
The anterior or external teeth of the upper resemble those of the
lower jaw ; they are strong, conical, subtrihedral, hollow at the base,
which is obliquely truncated, and rounded and obtuse at the apex.

The mesial pair is slightly curved, and is the largest; the rest de- :

crease in size to the outermost. The external facet of each tooth is |

covered with a smooth, dense, enamel-like substance, which, towards

|

the apices of the teeth, presents a yellow colour, and calls to mind the —

peculiar colour of the enamel in some of the Rodentia. These outer
maxillary teeth are arranged in close contact with one another
(Pl. 40, figs. l and 7). The form of the alveolus in which the base is
fixed, is peculiar in the dental system, resembling rather the surface
of attachment for the claw in the ungueal phalanges of the feline
quadrupeds. A conical process of the bone rises from the middle of
the alveolar depression, and is adapted to the cavity in the base of the

Se ee

SCLERODERMS. 83

tooth (Pl. 40, figs. 3and 5). The circumference of the base of the
fully formed tooth is attached by a slight anchylosis to the margin
of the alveolus, but the confluence of the tooth with the bone is much
less complete than in many other fishes.

There would seem to be a constant and pretty quick succession of
these teeth, for in all the jaws of different species which I have ex-
amined, there were the crowns of a second or new series of teeth,
generally pretty far advanced in their development. ‘The successors
of the external teeth of the right intermaxillary bone, exposed by re-
moving the outer wall of their alveoli, are represented in situ in fig. 5
' of Plate 40: (a) points to the osseous tubercle on which the tooth
about to be displaced was fixed; the absorbent process has com-
menced at its apex: at (b) the corresponding bony tubercle has been
thus entirely removed, and the obtuse apex of the new tooth has
protruded in the socket of that which it has displaced. The cavi-
ties containing these teeth communicate with the exterior of the jaw
by foramina, situated as in most other fishes, on the outer side of the
base of the teeth in place (Pl. 40, figs. 1 and 3).

The teeth of the posterior row, which are peculiar to the upper
jaw, are six in number, three in each intermaxillary bone:
they present the form of elliptical plates, compressed laterally,
rounded at the base, and slightly pointed at the apex. The
anterior tooth is the largest, measuring in Balistes forcipatus six
lines in length, and three in breadth, but scarcely half a line in
thickness ; the two other teeth progressively diminish in size (Pl. 40,
fig. 4). These posterior teeth lie in close juxtaposition with
the outer row, and like the posterior small upper incisors of the hare
and rabbit, receive part of the appulse of the inferior teeth. They
are affixed by a very oblique and slightly excavated base to a shallow
alveolus, having a convex rising of bone in its middle (PI. 40, fig. 6).
They are also.deciduous, and the presence of well deveioped reserve-
teeth in cavities of the jaw, immediately internal to those of the ex-
terior row, would indicate that the succession of the teeth of the inner
row is likewise unlimited. The foramina leading to the cavities of the
successional teeth are seen immediately above the bases of the teeth
in place. The germs of the successors of the inner row of teeth ex-

G 2

at

84 SCLERODERMS.

posed in their alveoli in the left intermaxillary bone, are figured in
Plate 40, fig. 6.

The number of the teeth is not constant in the genus Balistes, but
in no species examined by me were the posterior teeth of the upper
jaw absent. In an Australian species, I found six teeth in the outer
row and four in the inner row of teeth in the upper jaw. The apices
of the mesial pair of the posterior row projected between those of the
first and second teeth of the outer row.

In all the file-fishes, the pharyngeal teeth are small, conical, laterally
compressed, curved and sharp-pointed; regularly arranged in two
rows upon the opposed margins of each of the two upper and lower
pharyngeai bones. A view of the upper and lower left pharyngeal
bones, im situ, is given in figure 2, Plate 40. The direction of the
curvature and the relative size of the anterior and posterior teeth are
reversed in the two bones, which thus form an admirable carding
machine for ‘‘teazing” the bruised and coarsely divided sea-weeds
or other marine nutrient substances which the fish has obtained by
means of its large maxillary teeth.

Microscopical sections of these dense teeth in the Balistes forcipatus
present a structure so closely corresponding with that described by
Professor Retzius in the Balistes Vetula, that a better idea of it can-
not be conveyed than in the words of that excellent observer. He
says,(1) ‘‘ That the dentine (zahnknoche) of both the Balistes and
Sparus resembles most in internal structure that of the teeth of mam-
malia and reptiles, being white and hard, like ivory, and displaying
under the microscope beautiful, regular, minute and parallel tubes.
These, in Balistes vetula, are 4, of a Paris line(2) in diameter, and are
beautifully parallel, save in their last formed parts at the coronal end
_of the pulp-cavity. Their undulations are long and slight. Their
interspaces are equal to their own diameter. The larger branches lie
close to the trunks, while the smaller ones generally bend away in a

(1) Miiller’s Archiv. 1837, p. 523.
(2) The French inch of twelve lines is so nearly one-fifteenth more than the English inch,
that the conversion of the fraction of a French line into the fraction of an English inch by mul-

tiplying the denominator of the former by 114, is sufficiently accurate for all practical physio-

logical purposes ; thus the calcigerous tube measuring +o'roth of a Paris line, will be ++4s0th of
an English inch.

GONIODONTS. 85

direction transverse to that of the main tubes, and towards the
root. The main tubes terminate near the superficies of the tooth
in bold parallel curvatures. The greater part of the tooth of this
fish is surrounded by a thick and dense enamel, into many parts of
which the tubes of the dentine appear to be continued ; it is full of
fissures directed outwards. A kind of cement seems to surround the
base of the tooth.”

In his comparison of the structure of the enamel in the teeth of
different animals, Professor Retzius again refers to that of the Balistes,
and mentions the remarkable number and regularity of the fissures in
it, which, as he correctly states, somewhat resemble the tubes of the
dentine. ‘‘ The cementum is characterized by its large, and extremely
irregular cells, which are in many parts confluent, or communicate im-
mediately, with each other. The minute plexiform tubes have an
extremely irregular course. This coating of cement is very thin, and
seems to terminate below the margin of the enamel.’’(1)

The similarity between the enamel and dentine of the file-fish, as
of the parrot-fish (see Pl. 50), is not less close in regard to the organ-
ization of their respective pulps, and their mode of calcification,
than in their microscopic structure when completely formed. The
cementum is the result of the ossification of the capsule which
includes the pulps of the dentine and enamel; and consequently it
corresponds in its coarse cellular structure with the rest of the
“osseous system.

GONIODONTS.(2)

32. The teeth of all the species of this family are long, slender,
filiform, or setaceous, and are bent like awls or tenterhooks, whence is:
derived the name of the family. In some of the genera, the teeth of
the short and broad intermaxillaries are disposed in lines radiating
from behind towards the anterior margin, and are thus somewhat ana-
logous to the vertical rows in which the teeth of the sharks are ar-
ranged. They further resemble the squaloid teeth in being attached,
not to the bone, but to the membrane investing the maxille, and are

consequently moveable, both forwards and backwards.

(1) Loe. cit. p. 541. (2) Twyta, an angle, odes, a tooth; Pl. 48, figs. 1, 2 and 3.

86 SILUROIDS.

In the genus Acanthicus,(1) the maxillary teeth are bisinflected ;
the first, or anterior tooth of each of the radiating rows, is the
shortest, and is curved outwards, the rest, to the number of seven
or eight, being bent backwards: there are from twenty-five to thirty
of these rows on each side of both upper and lower jaws.

The setaceous teeth of the Rhimelepis(2) have a similar arrange-
ment in antero-posterior radiated rows, and a similar moveable connec-
tion with the maxillary membranes ; but the foremost tooth in each
row has its inflected summit split, and thus presents the singular form
of a bicuspid hook ; the posterior succeeding teeth, in each row, have
a simple hooked apex.

The foremost tooth of each radiated series in the Hypostoma(3)
is much shorter than the second, and is bent outwards: the second,
third and fourth teeth, counting backwards, are twice curved, with
the apex bent inwards; the succeeding teeth grow shorter, present a
simple curve, and thus gradually disappear.

In the Loricaria the bisinflected setaceous teeth are arranged in a
simple series along the alveolar border of the intermaxillary and pre-
mandibular bones: the summit of each tooth is curved inwards and
backwards.

From the constancy observed in the different sizes, shapes and
directions of the teeth composing the vertical or radiated rows in
the above genera, it is to be inferred that they do not succeed each
other, and are not on the constant move from behind forwards,
as in the Plagiostomous fishes, with which in other respects the
teeth of the Goniodonts offer some striking analogies.

SILUROIDS.

33. The dental armature of this extensive and singular family of
fresh-water fishes is never of a predatory or formidable character,
the teeth being always small and simple, or of a minutely villiform
kind. Some species are almost edentulous, but there are others
which exhibit peculiar conditions of the teeth not elsewhere ob-
servable in the vertebrate division of animals.

In the genus Cetopsis a single series of simple conical teeth

(1) Pl. 48, fig. 3. (2) Ib. fig. 2. (3) Ib. fig. 1.

eer ee ee

SILUROIDS. 87

projects from the premandibular and vomerine bones, and one or
more rows of similar teeth from the intermaxillaries. The corre-
sponding teeth in the Doras are either minutely villiform, or are
replaced by equally minute uncalcified papille, which permanently
represent the very earliest stage of dental development.

The slightly calcified papillae on the intermaxillary and pre-
mandibular bones of the Hypophthalmus are so minute as to require
the aid of a pocket lens for their detection: but the branchial arches
support more conspicuous organs, which are clearly referable to
the dental system :(1) these are slender, elongated, pointed, whitish,
rigid, and fragile lamella, attached in a close-set row to the concave
side of the arch, and with their points projecting towards the gullet.
Those of the first pair of branchial arches are most developed,
equalling the gills in length; the rest gradually diminish as they ap-
proach the pharynx.

In the Pimelodus villiform teeth are arranged in several rows upon
the intermaxillaries and premandibulars, and a few graniform teeth
upon the vomer (Pimel. Spivw). In the Pimelodus ctenodus, the first row
of jaw-teeth is composed of larger, rounded conical denticles, with an
obtuse apex. Other species of Pimelodus have teeth on the palatine
bones, but not on the vomer: and the species called by Cuvier Pi-
melodus genidens offers the singular peculiarity of a patch of moveable
calcified denticles upon the inside of each cheek, or lateral membrane
closing the mouth.

In the genus Platystoma, the intermaxillary, premandibular and
vomerine bones are beset with broad bands of strong villiform and
setiform teeth gradually increasing in length as they are placed deeper
in the mouth :(2) the pharyngeal arches are covered with similar, but
finer denticles.

In the Plotosi, the vomerine teeth are obtuse and rounded.

The premandibular teeth of the Synodontes present compressed
crowns terminated at one end by a recurved apex, and attached by
the opposite end or base to a flexible peduncle. (3)

(lt) Agassiz, Spix, Pisces Brazilienses, p. 15.

(2) Pl. 1, fig. 1, exhibits the under surface of the right intermaxillary bone of a Siluroid
fish of the subgenus Platystoma.

(3) “ La machoire inférieure porte un paquet de dents trés applaties latéralement, terminées

88 PERCOIDS.

The largest and most fully developed teeth of the Siluroids, as
those of the Platystoma, present under the microscope a modification of
the reticulo-medullary type of structure, which nearly resembles that
of the salmon and the pike: the meshes of the anastomosing me-
dullary canals being open, pretty regular, and either subcircular or
polygonal. The thin outer crust of the tooth is traversed by minute
calcigerous tubes, having the usual direction vertical to the surface.

CHAPTER V.

TEETH OF THE CTENOID FISHES.

PERCOIDS.

34. ArtHoueHs the fishes of the present tribe are of predatory and
voracious habits, like the common perch—their type, yet their
teeth are never developed to any considerable size, but in all the
species are small, numerous, and closely aggregated, resembling the
plush or pile of velvet. In the perch, (Perca fluviatilis), there is a
broad band of these teeth ‘ en velours,’ on each of the intermaxillaries
and premandibulars, a narrow band on each palatine, and across the
fore part of the vomer; a small patch of similar teeth is also present
on the anterior extremity of each external pterygoid, or transverse

bone, which is a rare locality for teeth. There is a series of small
- plates armed with similar villiform teeth along the concave surface
of each of the branchial arches; and the exposed surfaces of
the upper and lower pharyngeal bones are entirely covered with
them. The points of these minute denticles are all turned towards
the gullet; and thus, although none of the teeth are sufficiently
developed to kill by piercing or laceration, they all combine to hold,
to crush and to aid in the deglutition of a living prey.

In the genus Labraz, besides the localities above mentioned, the
tongue is covered with villous teeth.

In the Htelis, there is a row of moderately long, recurved, conical

en crochet, et suspendues chacune par un pedicule flexible, dentition dont il n’y a point d’autre
example connu.”— Cuvier, Réegne Anim, ii, p. 294,

PERCOIDS. 89

teeth on the intermaxillary and premandibular bones, besides the
villous teeth in the ordinary situations.

In the Lucio-perca, a row of longer pointed teeth are intermixed
with the villous teeth of both the maxillary and palatine bones ; they
are most developed in the lower jaw and the palatine. There are no
lingual teeth.

The Enoplose of New Holland, (Chetodon armatus, Shaw),
instead of the hair-like teeth of the genus to which it was originally
referred, has a narrow band of villous teeth on each intermaxillary,
premandibular and palatine bone, and a small transverse band upon
the vomer ; the tongue is also similarly armed at its base; the rest of
the organization of this fish is in like manner conformable to the
percoid type.

Villous teeth constitute the only armour of the mouth, accord-
ing to Cuvier, in the Percoid genera, <Apogon, Cheilodipterus,
Pomatomus, Anabassis, Aspro, Grammistes, Acerna, Polyprion, Pen-
taceros, Centropristis, Grystes, Rypticus, Chironemus, Centrarchus,
Pomotis, Priacanthus, Dules, Therapon, Datma, Pelates, Helotes and
Polynemus.

In the Uranoscopus, the mouth is cleft in the vertical direction
behind and nearly parallel with the anterior facet of its cubical head.
The teeth of the upper jaw (intermaxillaries) are villiform and arranged
in three rows, the middle ones of the posterior row being the largest.
In the lower jaw there are six large conical teeth on each side, set wide
apart in a single row, with some villiform teeth in the middle. The
vomer has a small band of villiform teeth on each of its anterior
angles; the palatines are armed with somewhat larger teeth; the
tongue and branchial arches are edentulous ; the pharyngeal bones
have rasp-like teeth.

The Mullet and Surmullet (Mullus barbatus and Surmuletus) are
but feebly provided with teeth ; the intermaxillaries and palatine bones
are edentulous ; there is a narrow band of villiform teeth on the lower
jaw; and a large oval plate covered with a pavement of small obtuse
teeth on the vomer. The Upeneus vittatus, or Mullus vittatus of
Forskael, has villous teeth like the Percoids, on the intermaxillary,
premandibular, palatine and vomerine bones ; in the Upeneus flavo-
lineatus, the teeth are wanting on the palatines.

90 COTTOIDS.

In the Serrani, or Sea-perches, the dentition begins to assume a
more carnivorous character, and long, sharp-pointed, conical teeth
are intermixed with the teeth ‘en brosse,’ which are arranged in
bands more or less broad on the intermaxillary and premandibular
bones. In the Serranus Scriba, the two or three laniary teeth
near the middle line are most developed. The palatines and pharyn-
geal bones are armed simply with villous teeth ; these are arranged
in the form of a chevron on the vomer; the tongue is edentulous.

The Plectropromes, Mesoprions and Cirrhites have the same type
of dentition as that of the Sea-perches. The larger conical teeth are
also superadded to the villiform teeth of the jaws in some species of
the genus Sillago.

In the genus Trichodon, the villiform teeth are more elongated
than usual, slightly recurved; and those of the exterior rows have
more a horny than a bony consistence, whence the name of the
species (Trachinus trichodon) which Cuvier has made the type of a
genus.

In the genus Myripristis, there are very fine villiform teeth on
the palatines, vomer, and jaw-bones ; but in front of the latter, there
are five or six of larger size, but of an obtuse conical shape. The
tongue is smooth, but the branchial arches and pharyngeal bones are
armed with villiform teeth.

The beautiful Holocentra and the large-eyed Beryx have simply
villiform teeth on the same localities as the Myripristis. ‘The weevers
(Trachinus), have also the pterygoid bones similarly armed. In the
Percis, a row of larger unciform teeth are placed in front of the villi-
form teeth of the jaws; the palatine and lingual bones are eden-
tulous.

In the Percophis, there are five long, recurved, sharp-pointed
teeth in each intermaxillary ; and a greater number of similar teeth in
the lower jaw, besides the teeth ‘ en velours.’ The palatine, as well as
the vomer, are armed with villiform teeth.

COTTOIDS.
35. In the Cottoid or mailed-cheeked fishes, (Joues cuirassées of

Cuvier), the only teeth which maintain a constant character are those
of the pharyngeal bones, which are always villiform. In the common

SPAROIDS. 9]

Gurnards (Trigle Lyra and Gurnardus), and the Bullhead, (Cottus
Gobio) the maxillary, vomerine and branchial teeth are of the same
kind ; the tongue and palatine bones are edentulous. In the Cottus
scorpius, or Father-lasher, the teeth are a little more strongly developed.
In the Cottus grunniens these larger teeth are continued from the vomer
upon the palatine arches ; while those of the jaws are villiform. In
the Stickle-backs (Gasterosteus), similar teeth are arranged in a narrow
band along the intermaxillary and premandibular bones ; but the
palatines, vomer, and tongue are edentulous. In the Flying Gurnard,
(Dactylopterus\, the teeth are likewise limited to the jaws, but they are
obtuse and form a little pavement of four or five rows, which grow
narrower towards the angles of the mouth: the pharyngeal bones
preserve their typical character ; and in the mailed Gurnards, (Periste-
dion), they are the only bones of the buccal cavity which support teeth.

SPAROIDS.

36. Inthe Bream-tribe of Fishes, the teeth are restricted to the
intermaxillary, premandibular and pharyngeal bones, but are re-
markable for their variety of form, and frequently for their large size.

Dentex.—Few fishes are armed with a more formidable apparatus,
or one better adapted for the seizure and destruction of a living prey,
than are those which belong to the genus of Sea-bream(1) called Dentex
by Cuvier. This name was, in fact, applied to a Mediterranean spe-
cies of bream by the Latins, on account of its large pointed teeth,
which project from the fore-part of the mouth. .

With the exception of a pavement of minute rounded teeth, which
defends the inner side of the alveolar wall of the jaws, all the teeth of
the Dentices are conical, sharp-pointed, and slightly recurved, corres-
ponding in shape with the laniaries or canine teeth in the mammalia.
They are limited to the intermaxillary and premandibular bones, and
form asingle row on each side of each jaw. In some species, as the
Dentex multidens, the laniary teeth are large and of nearly equal size
all round the mouth; but in most species, as in the one figured,
(Dentex argyrozona, Pl. 41), four of these teeth in the upper, and
four in the lower jaw are produced, at the anterior part of the mouth,

(1) The River-Bream (Cyprinus Brama, L.) belongs to a different family, characterized by
toothless jaws ; see Cyprinoids.

92 SPAROIDS.

into very long and strong tusks, and considerably exceed the other
teeth in size. They are supported on strong tumid processes of the
jaws, with which their bases are firmly anchylosed. In the jaws
represented at fig. 1, one of the large teeth has been shed, and the
cavity is laid open to expose its successor, of which the crown is
partly formed. Similar new teeth, preparing to take the place of the
smaller lateral laniaries, are exposed in their cavities. These reserve
teeth are situated above and a little to the outside of the base of the
tooth, which they are destined to displace ; and, in the more advanced
examples, a perforation leading to the cavity may be seen on the
outer side of the old tooth. Absorption of the anchylosed base of
the tooth commences at this part, and gradually extends inwards.

In fig. 2, an inside view of the jaws of the left side is given, to
show the pavement of minute rounded denticles along the inner side of
the bases of the laniary teeth. The jaws are of great strength in
relation to the force with which the teeth are destined to be exerted.

In the Dentex hexodon only six of the teeth in each jaw present
the laniary figure and size, the rest being small and closely aggregated
in a comb-like form. The tongue and palate are quite smooth, the
bones of these parts, as well as the vomer, being edentulous. The
pharyngeal bones, from the small size of their numerous teeth,
resemble fine combs.

The Dentices devour small fishes, cephalopods and crustacea ;
their intestinal canal is short, the pyloric ceeca few, and the stomach
simple and membranous. They frequent rocky places.

37. The gilt-heads (Chrysophrys) are distinguished by a dentition on
the same general teleological principle as in the Cestracion and Anar-
rlacas, the anterior teeth being adapted for seizing, and the posterior
ones for crushing the alimentary substances. These teeth are limited
in their position to the intermaxillary and premandibular bones.
The elongated conical anterior teeth are never fewer than four, or
more than six in each jaw. The posterior obtuse rounded grinding
teeth, are arranged in three or more rows.

In the species of Gilt-head, (Chrysophrys Australis), of which the
jaws are figured in Plate 42, fig. 3, the principal or long anterior
conical teeth are four in each jaw; those of the lower are more widely

SPAROIDS. 93

separated than those of the upper jaw, and in the interspace of the two
middle ones of the lower jaw, there are two small conical teeth. In
the upper jaw, the first tooth of the external row of molar teeth,
presents a conical crown ; the rest are rounder and more obtuse, but
present a small mammilloid apex; after the eighth, there are three
or four much smaller teeth. The molar teeth of the second row are
less than the outer ones ; some much smaller granulated teeth, less
regular in their arrangement and size, are developed at the inner side
of the base of the second series. The principal molars of the lower
jaw are also in two rows, internal to which are some smaller and
less regular teeth, which are fewer in number than those of the
upper jaw.

There is a constant and pretty quick succession of teeth in the
jaws of the gilt-heads. In the specimen figured, the outer plate,
of the intermaxillary and maxillary bones has been removed to
show the successors of the outer row of teeth, in various stages of
formation, but with the crown of the tooth nearly completed in most
of them. These germs are each lodged in a cavity close to the base
of the tooth which is to be replaced ; their course is directed towards
the outside of that base, and the cavity, which is occasioned by the
absorption consequent on the pressure, is enlarged from without
inwards, contrary-wise to the progress of the excavation which is pro-
duced in the succession of the teeth of the Reptilia.

The matrix of the teeth of the OChrysophrys, as in most other
fishes, becomes ossified when the crown of the tooth is fully com-
pleted ; and the tooth is thus fixed by anchylosis to the margins of the
jaws.

In the present and many other exotic species of Chrysophrys, the
new teeth always resemble in shape and size those which they suc-
ceed ; but in our common gilt-head (Chrysophrys aurata), some of the
posterior and internal molars, which in the young fish are hemi-
spherical, are succeeded in the mature fish by one or sometimes two
larger grinders of an oval form.

In this species there are six holders, or Biridtteda anterior teeth,
in each jaw ; they are relatively stronger, longer, and more curved
than in the Chrysophrys Australis. The obtuse grinding teeth are

94 SPAROIDS.

arranged, in the young specimens, in four rows, and all present the
hemispherical form. When the individuals have attained seven or
eight inches in length, the third row presents three teeth of con-
spicuously larger size. In a Gilt-head of eleven inches in length,
the molar teeth of the upper jaw are in five rows, and the fourth
row presents three teeth larger than the rest, of a sub-elliptic form,
with the long diameter transverse; the large elliptic molars of the
adult, of which the long diameter is in the axis of the body, is now
formed, but is still concealed in the substance of the jaw. When it
has come into place, the mature dentition may be said to be com-
plete. The base of the fully formed teeth in use is anchylosed, but
in a slighter degree than usual, to a thin osseous lamella, which forms
the floor of a shallow depression or alveolus in which the base is
lodged. The flat lamella is perforated by numerous foramina, and
the sides of the alveolar depression are grooved with numerous
radiating lines.

The texture of both the pointed and obtuse teeth is extremely
dense; it consists of a body of hard white dentine, and a coat
of organized enamel, analogous to that of the incisors of the file-
fish. The crowns of the rounded molars of the gilt-head hardly
suffer the saw to make an impression upon them. Their calcigerous
tubes are very numerous and extremely minute, and cross each other
towards the periphery of the tooth at acute angles, as in the molars
of Lepidotus. The microscopic structure of the anterior pointed
teeth resembles that of the incisors of the Sargus, which will be
described in the next section.

38. Sargus.—Fishes which present so close a correspondence in
their general conformation and zoological characters as to be included
by Linneus in the same genus, and by Cuvier in the same natural
family, may, nevertheless, differ widely in their habits and be
nourished by the most opposite kinds of food, and these peculiarities
will be associated with modifications of the digestive system, and
especially of the teeth. Of this we have a striking example in the
Bream-tribe. In the Dentex (the Sparus dentex of Linnzeus), the
dentition was of a predatory and destructive character, all the teeth
being formed to seize, and pierce, and lacerate. In the Chrysophrys

SPAROIDS. 95

(Sparus aurata, &c. Linn.), the laniary type was limited to the anterior
teeth, while those which corresponded with the lateral teeth of the
Dentex had exchanged their piercing for a crushing form, and the
small miliary denticles which are scattered over the inner side of the
alveolar border in the Dentex argyrozona, had risen, as it were, from
their rudimental condition, begun to assume a functional character,
and to be counted as a second and third row of molar teeth.

In the sub-genus, of which the dentition is now to be described,
the transition from the carnivorous to the herbivorous type is effected
by simply modifying the form of the large anterior teeth, and con-
verting them from piercing to cutting instruments.

Their crowns, instead of tapering to a point, are widened
laterally, compressed from before backwards, and truncated at the
extremity ; they are flat or slightly convex on the outer surface, and
concave on the opposite side, and in the larger species of Sargus
closely resemble, in size and shape, the incisors of the human subject.
This resemblance has caught the attention of most ichthyologists who
have had occasion to describe any of the species of the present genus.
Salviani characterises his Sargo or Sargone, among other marks, by
the ‘‘ dentibus latis, humanis similibus ;’? Klein and Cuvier extend the
same comparison to the ‘‘ Sargues ”’ in general ; and had Scheuchzer
founded his supposed discovery of the Homo diluvw testis on a fossil
incisor of the present genus, instead of the skeleton of a gigantic sala-
mander, the mistake would have been more venial, and might not so
soon have been rectified.

** Tout-a-fait semblables aux incisives de ’homme,’’(1) is, how-
- ever, a somewhat exaggerated expression of this relation, even in the
Sargus Rondeletu. The fang of the fully formed, but unattached tooth,
(such as those of which the crowns are figured(2) protruding through
the apertures exterior to the base of the incisors in place), grows
wider to its free extremity instead of contracting; while, in the
incisors in use, this fang is anchylosed to the alveolar margin of the
jaw, as in fishes generally. The antero-posterior diameter of the fang
is also greater in proportion to its lateral diameter than in the human
incisor.

(1) Cuv. and Val. Hist. Nat. des Poissons, vi, p. 16. * (2) Pl. 42, fig. 2.

96 SPAROIDS.

‘The number of these incisors is sometimes eight in the upper
and six in the lower jaw, as in the Sargus Rondeletit and Sar. Sal-
viani; sometimes it is eight in both jaws, as in the Sargus annularis,
Sargus Vetula, and in the well known Sheep’s-head fish of the coasts
of New York (Sargus Ovis). In another species (Sargus rufescens, O.)
there are six incisors in the upper and eight in the lower jaw. In the
Sargus unimaculatus,(1) in which the incisors present the same number,
their cutting margin is notched, as in the teeth of the Glyphisodons.

The incisors are arranged in close and compact order ; in some
species they are placed nearly vertically; in others, more obliquely
in the jaws ; but they always form an instrument well adapted for
cropping the sea-weed and other marine plants, which constitute the
food of the fishes of the present genus.

In the common Mediterranean species (Sargus Rondeleti) the whole
of the broad alveolar margin of the intermaxillary bones is paved with
rounded molars, similar to each other in form, but becoming larger as
they are placed further back in the mouth: they are arranged in
three rows ; those of the innermost row are the largest, those of the
middle row the smallest.

The premandibular pieces of the lower jaw are similarly paved
with two rows of hemispherical molars, those of the inner row being
the largest. In the Sargus unimaculatus there are two rows of molars
ineach jaw. In the Sargus Noct, (Ehrenb.), the molars form four rows
in the upper and three in the lower jaw. In the Sheep’s-head fish,
and in the Sargus rufescens, in which the molars are similar in number
to those of the Sargus Rondeletu, the external row present a some-
what more conical form than the others. In the Puntazzo bream
they are reduced toa single row in each jaw, and are of very small size.

There is a free and constant succession of teeth in the phytipha-
gous Sargues, as in the rest of the Sparoid tribe. At whatever age
the fish may be, foramina will be seen on the outer side of the bases
of the incisors, and external grinders, and on the inner side of the
internal grinders ; and the foramina lead to cavities which contain the
crowns of new teeth in different stages of development. The old
teeth and the alveolar surfaces to which they are anchylosed are dis-

(1) Pl. 1, fig. 9.

SPAROIDS. 97

placed by the absorbent process, and their successors become in
their turn anchylosed to the bony plate which, in the progress of
growth, has at length reached the level of the alveolar margin.

A vertical longitudinal section of the incisor of the Sargus,(1)
sufficiently thin to be examined microscopically by transmitted light,
shows that it consists of a central body of compact dentine, composed,
as in the human tooth, of fine, parallel, close-set calcigerous tubes ;
and that the crown is covered by a thick layer of a distinct substance
analogous to enamel.

The structure of the external substance is, however, very unlike
that of the true enamel of the human or mammiferous tooth: other
broadly-marked distinctions are at once seen in the continuation of
the pulp-cavity to the apex of the crown, and in the expanded fang
or base of the tooth.

The calcigerous tubes of the ivory, in the body of the tooth, make
a bend when they leave the pulp-cavity, with the convexity turned
towards the apex ; they are then slightly curved in the opposite direc-
tion, and again bend outwards, with the convexity as in the first curve,
thus describing a beautiful sigmoid undulation. At the base of the
tooth the direction of the calcigerous tubes is more transverse, and
the number of undulations is greater. Near the apex the middle bend
is gradually lost, and the tubes as they proceed outwards describe a
simple curve, with the convexity next the apex of the tooth.
The secondary curvatures of the calcigerous tubes are beautifully and
minutely undulatory (a, fig. 2). The main tubes at their commencement
near the base of the conical cavity of the pulp are more irregu-
larly flexuous, for a short distance than in the body of the tooth. They
send off minute branches throughout their whole course, at very acute
angles, except near their extremities, where the brancbes bend out-
wards and are consequently more readily discerned. The peripheral
extremities of the calcigerous tubes seem to terminate somewhat ab-
ruptly in aclear and apparently structureless space or stratum, which
intervenes between the tubuli of the ivory and those of the enamel.
External to this is an opake stratum, apparently composed of the ex-

(1) Pl. 43, fig. 2.
H

98 ‘SPAROIDS.

tremely numerous and minute extremities of the enamel-tubuli.
These, commencing as it seems from the external surface, divide
and subdivide as they pass inwards towards the dentine, not main-
taining a parallel course, but crossing each other, in an irregularly
and variously bent direction (0, fig. 2).

The pulp-cavity becomes consolidated in the old incisors by a
coarse cellular ossification of the remains of the pulp (c, fig. 2).

39. There are certain species of Sparoid fishes, which, like the
Giit-heads, have four or six strong, conical, laniary teeth at the anterior
extremity of each jaw, with hemispherical molars behind ; but these
teeth never exceed two rows, and the small graniform teeth, when
present, are limited to the space posterior tothe laniaries. This den-
tition, which characterizes the genus Pagrus of Cuvier, is represented
at fig. 15, Plate 1. The pharyngeal teeth likewise differ in form from
those of the Chrysophrys, being small and sharp pointed. In the
Braise (Pagrus vulgaris), these teeth are arranged in strong pectinated
rows. They are fewer in number, and of a conical form in the Pagrus
Orphus. In one species, the anterior conical teeth of the upper jaw are
directed forwards and project from the mouth, the two external ones
being longer than the rest ; from this structure Cuvier has designated
the species Pagrus laniarwus.

In another group of Sparoid fishes (Pagellus, Cuv.) which have
rounded molars, like the Chrysophrides and Pagri, the anterior teeth
are restricted in their development, and form one or more pectinated
or villous rows at the front of the mouth (1).

The pharyngeal teeth are unciform and stronger than in the Pagri.

There is one species of Pagellus which offers an anatomical pecu-
liarity so closely connected with the dental apparatus as to merit a
brief notice. The superior maxillary bones are expanded, and their
texture is as dense as that of the hard enamel of fishes’ teeth: but
they are edentulous as in most other fishes. The habits of the species,
hence called Pagellus lithognathus, are not sufficiently known to afford a
knowledge of the use of these petrous maxillaries : they characterize

(1) The intestinal canal is generally longer in the Pagelli, which are compelled, from the
inferior armature of the mouth, to feed on organized matter of a lower grade than do the more
formidably toothed Pagri and Dentices.

ee ee ee

a

SPAROIDS. 9G

the adult period, when the fish, for example, has acquired a length
of three feet: in a specimen measuring a foot long, the enlargement
of the maxillaries has scarcely begun to take place.

An extinct genus of Sparoid fishes, called Sparnodus by M. Agassiz,
has conical teeth on the outer margin of both jaws, but with an
apex so obtuse that they present nearly the form of the molars of Chry-
sophrys : the dentition differs from that of the Gilt-heads, inasmuch
as the molars form only a single row.

In the genus Lethrinus the intermaxillary and premandibular
bones are furnished with villiform, laniary, and molar teeth ; but the
latter are always restricted to a single row, and are sometimes of a
large size. The laniary form and development is confined to the four or
six anterior teeth, behind which are placed the minute villiform teeth ;
the single row of large molars distinguish the Lethrines from the
other Sparoid genera.

In the Lethrinus latidens, a species discovered by the French voya-
gers, MM. Quoy and Gaimard, on the coasts of New Guinea, there are
six strong laniary teeth in the upper, and four in the lower jaw; the
first molar of the upper jaw is small and round: the second is twice
as broad in the transverse as in the antero-posterior direction ; the
three following teeth are of still larger size, and are remarkable for
their great breadth : the last molar is the smallest. This dentition is
interesting on account of its analogy with that of the singular extinct
genus Placodus.

Cantharus.—The Sea-breams belonging to this genus have their
teeth of small size, and closely aggregated on the alveolar borders of
the jaws, like the teeth of a rasp; the anterior ones being a little
longer and more curved than the rest.

The Sparoids of the genus Box (Cuv.) have a single row of closely-
packed flattened teeth in each jaw; the anterior ones have simple
crowns, while those at the sides are notched in the middle of the
cutting margin.

The Scathari have a single row of flattened, pointed, but not notched
teeth, in each jaw. ,

The Oblate have a single row of flattened and notched teeth,

H 2

100 SCIZNOIDS.

like the Boges, but they have also a band of villous denticles behind
the flattened teeth.

A fish of the Red-sea, the Sparus crenidens of Forskal, has two
rows of compressed teeth in each jaw ; the external ones being larger
than those of the second row. These teeth are compressed, broad,
and their cutting edge is subdivided into five denticles, which give it
a festooned contour. Behind their crenate teeth, there are some small
granular denticles. The pharyngeal teeth in this genus form a fine
rasp. A figure of this singular dentition, after Cuvier, is given in
Pl. 1, fig. 7. It concludes the series of modifications of the dental
system which have hitherto been discovered in the fishes of the
Bream tribe.

SCIZZENOIDS.

40. In all this family of fishes, as in the Sparoids, the vomer and
palatine bones are edentulous. In the Maigres or true Sciene, there
is a single row of wide-set, moderately large, conical, pointed and
slightly recurved teeth, with several smaller ones in the interspaces,
in both jaws.

In the Corvine, the larger conical teeth are restricted to the upper
jaw ; the villiform teeth are present in both jaws ; on the pharyngeal
bones the teeth present the form of obtuse cones in the centre of the
dental group, and are villiform at the circumference. The maxillary
teeth of the Leiostomes are so minute, as to have escaped the notice
of some naturalists, and the name of the genus(l) was conceived
under this misapprehension ; extremely fine villiform teeth are, how-
ever, present, and form a narrow band on each intermaxillary and
premandibular bone ; the teeth on the posterior part of the pharyngeal
bones are obtuse and form a fine pavement.

In the genera Eques, Larimus, Lepipterus, Dascyllus and Heliasis,
the maxillary teeth are minute and villiform. But in the Boridie,
each jaw is armed with three or four rows of thick, short, blunt teeth,
of which the six or eight anterior ones are conical and larger than the
rest.(2)

(1) Aetog, smooth ; soxa, mouth. (2) Pl. 1, fig. 14.

eet ee

TENIOIDS. 101

In the Conodon there is a single row of conical teeth in each jaw ;
the six anterior ones are longer than the rest. Behind the conical
teeth there isa band of villiform teeth.

In the Otolithes there are two teeth in the upper jaw much
larger than the rest.

The Ancylodons are also characterized by the extreme length of
certain of their maxillary teeth. In the Ancylodon jaculidens these teeth
are slightly dilated in the middle, and sharp pointed, so as to present
a certain resemblance to an arrow, whence the specific name of the
fish. There are two rows of these teeth in each intermaxillary bone,
and in the anterior part of the interspace of these rows there project
two teeth much longer and more curved than the rest. The preman-
dibulars are each armed with a single row of arrow-shaped laniaries,
of which the three anterior ones and the fifth are the longest. Besides
these laniaries the jaws support a narrow band of fine villiform teeth.
The tongue is smooth and edentulous. The pharyngeal teeth are
villiform, but the middle ones above are stronger than the rest. The
Ancylodon brevipinnis has a single row of laniary teeth in each inter-
maxillary bone of which the two median or anterior ones are the
longest ; in the lower jaw the median teeth are short, and those at
the sides are most developed.

In the Amphyprions, Pomacentrums, and Glyphisodons, there is a
single row of small conical or trenchant teeth on each jaw. ‘Those of
the lower jaw in the Glyphisodon are slightly notched on the cutting
edge.

In all these genera the teeth, when fully developed, become
anchylosed to the substance of the jaws, but are subject to displace-
ment by the absorbent process, excited by the pressure of their
successors. In the Maigre (Sciena Aquila) the microscopic texture
of the teeth corresponds with the third modification, as exemplified
in the teeth of the genus Sphyrena (Pl. 53).

TZNIOIDS.

41.In the Trachypterus Falz, a species of the first genus of the
present family in the Cuvierian system, the mouth is transverse, with a
vertical aspect and nearly parabolic form. There are six or eight

102 GOBIOIDS.

conical teeth on a transverse row at the anterior margin of both the

upper and lower jaw. Three or four similar teeth are arranged longi-
tudinally along the anterior end of the vomer. The palatines are
roughened by small callous papillz, but otherwise are edentulous.
In the Trachypterus Bogmarus there are six pretty large and sharp-
pointed teeth in the upper jaw, directed backwards towards the gullet ;
the lower jaw is armed with eight similar teeth.

In the Vaegmaer or Deal-fish, (Gymnetrus arcticus) the intermax-
illaries and premandibulars are armed with small conical pointed
teeth. In the Gymnetrus gladius the maxillary teeth are so extremely
minute as hardly to be felt, and to be visible only with the aid ofa
lens.

In the Band-fish, (Cepola rubescens) there is a row of slender
pointed, slightly curved teeth on the outer margin of each jaw ; those
of the lower jaw projecting considerably. The vomer, palatine bones
and tongue are edentulous.

In the Lophotes the palatines and vomer, as well as the intermax-
illaries and premandibulars, support teeth which are small and rasp-
hike.

The teeth of the Teenioids or Ribband-shaped fishes resemble
those of the Sciznoids in their microscopic texture, fixation, and
mode of reproduction.

GOBIOIDS.

42. The Gobies (Gobius Lacépéde) are distributed by Cuvier into
four subgenera according to modifications of their dental system.
The original generic term Gobwus, is restricted by Cuvier to those
species which have only small villous or carding teeth on both jaws,
the anterior row being sometimes more developed than the rest. Of
this sub-genus our common Rock-fish (Gobius niger) is the type.

The Gobies which have a single row of pointed teeth on each jaw,
and the lower series placed horizontally, with two teeth developed in
the form of canines bebind them, form the family Apocryptide. In one
species of this group, (Amblyopus Hermannianus, Cuvier), the mouth
is cleft vertically, and the teeth are long, sharp-pointed, recurved,
and interlock when the mouth is closed; there are eight or ten of

GOBIOIDS, 103

these teeth in each jaw, and they are always exposed to view, the lips
not being sufficiently developed to cover them.

In the sub-genus Sicydium the intermaxillary bones are beset with
more than a hundred teeth, as fine and flexible as hairs ; these teeth in
the Sycidium Plumierit are of a golden colour; in the Sicydium lago-
cephalum, they are extremely delicate. In the lower jaw, behind a
series of similar, but shorter flexible denticles, there is a row of well-
developed conical sharp-pointed and slightly recurved teeth.

In the Boleophthalmus the teeth of the upper jaw resume their
functional character as piercers and lacerators; and in one species,
hence called dentatus, the six anterior ones are larger than the rest,
project from the mouth and descend in front of the lower jaw.

In the Dragonets (Callionymus) the jaws are feebly armed with
minute and villiform teeth; in the Callionymus Lyra the anterior teeth of
the lower jaw are somewhat larger than the rest. In the Comephorus or
Callionymus Baikalensis, the maxillary teeth are so minute, as to give
a scabrous character to the dentigerous surface; but the denticles are
hard, and when viewed with a lens, present a recurved sharp-pointed
form.

43. There isa small family of fishes, in which the pharyngeal
bones are so modified as to be subservient to the respiratory as well as
the digestive functions ; the surface of these bones is increased by being
produced into lamine variously convoluted, and intercepting labyrin-
thiform spaces, in which a certain quantity of water can be kept in
store. Thus provided, many of these fishes voluntarily quit their
proper element, and all of them can maintain life for a considerable
time out of water. ‘These Gobioid fishes form a separate family,
called ‘ Pharyngnies Labyrinthiforms,’ in the system of Cuvier.

The Climbing Perch (Anabas scandens), has the third pair of
superior pharyngeal bones armed with close-set conical teeth, which are
opposed to similar teeth on the inferior pharyngeals ; the posterior part
of the vomer, which lies between the dentigerous upper pharyngeals,
supports a group of villiform teeth ; and there is a transverse row of
similar teeth on the anterior part of the same bone ; this distribution
of vomerine teeth is peculiar to the Anabas. The palatines are eden-

104 GOBIOIDS.

tulous ; there is a band of villiform teeth on each intermaxillary and
premandibular bone.

The Helostomes(1) are remarkable for the small size and shape of
their mouth, which resembles the head of a nail driven into the
muzzle, whence their generic name ; their teeth are not less extraor-
dinary, being attached solely to the inside of the lips, and moving
with them ; they may be regarded, in fact, as a row of slightly calci- |
fied labial ciliiform papille. The palatines and vomer are edentulous ;
the posterior and inferior pharyngeals support small conical teeth.
In the genera Colisa, Macropodus and Trichopus, the teeth are
attached to the jaws, but are very small or villiform; the anterior
maxillary teeth in the Gourami (Osphromenus), are a little longer
than the rest. The Spirobranchus is the only genus among those with
labryrinthiform pharyngeals which has palatal teeth. These are
short, coarse and villiform; there are similar teeth on the vomer,
intermaxillary and premandibular bones; the side teeth in the latter
locality are longer than the rest. |

44. The fishes of the family called Theuties, by Cuvier, have a
small mouth, with a single row of teeth on the intermaxillary and pre-
mandibular bones ; the palate and vomer are edentulous.

The jaw-teeth of the Avinurus are extremely slender ; those of the
Naseus are simply conical and sharp-pointed.

In the genera Prionurus, Priodon, Amphacanthus and Acanthurus,
the teeth are commonly notched or serrate at the margins. Mr. André
has given an accurate magnified view of the external form of the teeth of
the Acanthurus nigricans, (Chetodon nigricans of Linnzus), in the Phi-
losophical Transactions, and had recognized the arborescent .medullary
canals in the body of the tooth, ‘“‘ through which,” he says, ‘ the
blood-vessels ramify, which are destined for its growth and nourish-
ment.” He very justly observes, that a fish having teeth of a crys-
talline hardness, and arranged in a single row, cannot be naturally
associated with the Chzetodonts, which are characterized by nume-
rous rows of flexible teeth, of a totally different form.

The medullary canals in the maxillary teeth of the <Acanthurus
nigricans are directly continued from a conical pulp-cavity at the

(1) Aog, a nail; so#a, a mouth.

CHETODONTS. 105

base of the tooth, and are occupied, not by blood-vessels only, but
by processes of the organized medulla or pulp, including the nutrient
vessels, nerves, and connecting tissue. The diameter of the medullary
canals at their origin is ;;;th of an inch, and their interspaces equal
from four to six of these diameters; their general course is parallel
to each other and to the axis of the tooth; but they begin to send
off side-branches soon after their origin, and continue to ramify
abundantly throughout their course. The ramifications anastomose
and form arches, of which the convexity is directed towards the
margin of the tooth. Both the main canals and their branches
gradually diminish in size as they approach the margins. The cal-
cigerous tubes, which are every where continued from the medullary
canals, are of extreme tenuity ; the marginal ones, which have a
direct course perpendicular to the surface of the tooth, do not
exceed ;4,th of an inch in diameter. A diminished view of four of
the teeth of the Acanthurus nigricans, as seen with a magnifying
power of sixty linear dimensions, is given in Pl. 44, fig. 1. The
imbricated disposition of the teeth is here shewn.

CHETODONTS.(1)

45. The name of this family of fishes is significative of the peculiar
form of the maxillary teeth, which resemble the hairs of a fine brush,
and are of a soft subtransparent flexible texture, in the majority of
the genera composing it. The pulp-cavity is continued to near the
apex of these slender elongated denticles.(2) The true Chetodonts
thus characterized, have no teeth on the palatine, vomerine or lingual
bones.

In the genus Chetodon proper, the setiform teeth are longer than
in the genera Heniochus or Phelmon, in the latter of which they
resemble rather the pile of velvet. In the genus Zanclus the setiform
maxillary teeth are directed forwards.

In the Holacanthus, the setiform teeth are finely pointed; but in
Platax,(3) the outer row have their extremities compressed, slightly
expanded and terminated by three pointed lobes.

(1) xatrn, a bristle; ods¢, a tooth. Pl. 1, fig. 2 (2) Pl. 44, fig.3,aandb. (3) Pl. 1, fig. 2, a.

106 PLEURONECTOIDS.

In the Toxotes and Pempherides, the jaws support only minute
villiform teeth ; but there are similar teeth on the palatines.

In the Brame, the maxillary teeth are somewhat coarser, or ‘ en
cardes’ and some of the outer and anterior ones are developed into
small canines. The palatine teeth form a narrow band ‘ en cardes,’
on each side of the roof of the mouth.

In the genus Pimelipterus(1) there is a band of villiform teeth on
each jaw ; and external to these there isa row of moderately developed
trenchant teeth, which present the singular modification of having the
part analogous to the fang, bent at right angles to the crown. This

fang is horizontal, and is anchylosed by one side to the margin of the ©

jaw. Inthe Pimelipterus Boscu it is of equal length with the vertical
crown; in Pimel. incisor it is somewhat longer; and in the Pimel.
fuscus the root is three times the length of the crown. This portion
of the tooth is generally oval, compressed, and sharp-edged. There
are between twenty and thirty of these teeth in each jaw. They are
subject to uninterrupted shedding and replacement, and their succes-
sors pierce the jaws in front of those which are displaced. In all the
Pimelipteri there are rough granular discs on the palatines, pterygoids
and vomer.

In the Dipterodons the external row of teeth are more developed
than in the Pimelipteri, and are straight; the crown is broad and
terminates in a trenchant chisel-shaped edge. There are six of these
incisors in the upper jaw, and ten in the lower jaw of the Cape Dipte-
rodon ; the middle ones are the longest. The posterior villiform teeth
are more developed than in the Pimelipterr. The vomer and palatines
are edentulous. The inferior pharyngeals are covered with. a pave-
ment of round obtuse teeth ; those above are similar but smaller.

PLEURONECTOIDS.

46. Among the Pleuronectoids or Flat-fish, the soles (Solea) mani-
fest their affinity to the preceding family in their fine ciluform teeth ;
these, in their unequal distribution, partake of the main characteristic
of the Plewronectide, which are the least symmetrical of vertebrate
animals, and are limited, in the intermaxillary and premandibular

(1) Pl. 1, fig. 5.

PLEURONECTOIDS. 107

bones, to that side which corresponds with the under or white surface
of the fish ; the pharyngeal bones are beset with similar teeth.

In the Plaice (Platessa), there is a regular curvilinear series of
about twenty teeth, which are miniature resemblances of the incisors
of the Sargus, in the left intermaxillary bone, and only three smaller
and ill-shaped teeth near the median extremity of the right intermax-
illary. A like disproportion in the number of the teeth prevails in the
premandibular bones ; there being about thirty incisors, similar to
those above in the left, and but two or three incisors in the right
premandibular bone. The dentigerous intermaxillaries and preman-
dibulars are stouter, more curved and longer than those of the opposite
side.

The food of these ground-fish being below them, and the side of
the head being applied to the bottom, instead of having the mouth
opening symmetrically upon the under surface of the head as in the
Rays, the premandibulars and intermaxillaries corresponding with the
under or white side of the fish are elongated and curved, and the
teeth, if not restricted to them, asin the sole, are more numerous and
more regularly disposed, than on the corresponding bones of the
opposite side.

The pharyngeal bones of the Plaice are paved with flattened molar
teeth, larger than the incisors, and generally presenting a cubical
form.

The pectinated processes from the concave side of the branchial
arches are sharp-pointed, but do not support teeth.

The Turbot (Rhombus) has numerous small unciform teeth in the
jaws, a small group of similar teeth on the palate, and others on the
branchial arches and pharyngeal bones.

In the Holibut (Aippoglossus), the giant of the flounder-tribe, the
arrangement of the teeth is less unsymmetrical than in the flounder
or sole, there being nearly as many teeth on the left intermaxillaries
and premandibulars as on the right. Both these and the pharyngeal
teeth are'conical, sharp-pointed, and recurved, and the same form is
presented by the minute teeth which are placed upon the branchial
arches ; the whole dental system thus presents a predatory character.

The intermaxillary teeth are arranged in two or three irregular

108 LABROIDS.

rows, the largest being external. The teeth are hollow to near the
apex. They are first attached by ligaments to prominences of the
thick alveolar margin, which ligaments become converted by the
ossific process into bony cylinders, corresponding in size with the
base of the tooth to which they are finally anchylosed. The teeth,
when shed, separate from these cylindrical bases, which are removed
by a subsequent process. The branchial teeth are arranged in small
groups on the summits of the short obtuse apophyses which project at
regular distances from the concave margin of the branchial arches.
The pharyngeal teeth resemble in form and arrangement those of the
jaws, but are smaller in size.

08 5 0.6 a On en

TEETH OF CYCLOID FISHES.

LABROIDS.

47. The fishes included in the family Labroides of Cuvier, are
chiefly distinguished by the great size and strength of their pharyngeal
bones, of which there are two above and one below, al: armed with
teeth which vary as to their forms in different groups or genera of
the family. Besides the pharyngeal teeth, which are adapted to give
the final comminution to the food, the fishes of the genus Labrus of
Linnzus, or the ‘‘ Wrasses,” have teeth which are commonly well
developed and of aconical form on the intermaxillary and preman-
dibular bones, but none on the superior maxillaries, palatines, or
vomer.

In the sub-genus Clepticus, the pharyngeal teeth form, col-
lectively, small plates with a serrated margin. In the Clep. genzara
the superior pharyngeals support five rows of these saw-like plates,
which work upon a similar dental armature of the inferior pha-
ryngeal bone.

In the species of Chromis (Cuv.), and its subgenera Cychia,

LABROIDS. 109

Plesiops, and Malacanthus, the pharyngeal teeth are small, conical,
and arranged like the teeth of a comb. In Chromis proper and
Malacanthus, the anterior teeth of the intermaxillary and preman-
dibular bones are conical and of larger size; behind these teeth,
which form a single row, are others of smaller size which resemble
those on the pharyngeal bones. In the Cychla there is a broad band
of villous teeth in each jaw.

In the genus Labrus (Cuvier), and most of its sub-genera,
the intermaxillary and premandibular teeth are arranged in one
or two rows, the outer ones presenting a conical form, slightly
recurved, with a few at the anterior and sometimes at the
posterior part of the dental series much longer than the rest. In
the genus Anampses, however, there are only two flat and somewhat
recurved teeth in each jaw, which project from the mouth; while
in the Cossyphus there are several minute granular teeth behind the
normal conical teeth of the jaws (figs. 1 and 2, Pl. 45); and in
Ctenilabrus a band of villous teeth occurs behind the long anterior
conical maxillary teeth. In all these fishes the pharyngeal bones are
paved with hemispherical molars more or less flattened at the crown.
In the genus Lachnolaimus these teeth are confined to the posterior part
of the pharyngeals, the rest uf the bones, as the name of the genus
implies,(1) being covered with a soft villous and vascular membrane.

In the more typical Labroids (Labrus, Cossyphus, and Julis), the
whole of the unattached surface of the pharyngeals is covered with
the molar teeth.(2) They vary in size and shape in different parts of
the pharyngeal bones ; some are angular instead of round, and the
smaller ones at the external angles sometimes present a conical form.
Each tooth is attached by the circumference of a slightly contracted
base to the margin of a shallow alveolus ; this margin is traversed by
fine vertical grooves, which are morticed into corresponding grooves
in the osseous margin of the base of the tooth. The floor of the
alveolus is a thin plate, perforated by numerous foramina, and does
not become anchylosed to the base of the tooth ; nor, indeed, does it
sustain any of the superincumbent pressure. The pharyngeal tooth,
when first in place, has its base excavated by a wide but shallow

(1) Aaxvn lanugo, Aayvoc, guttur. (2) Pl. 45, figs. 3 and 4.

110 LABROIDS.

pulp-cavity. This is gradually diminished by a formation of dentine
from the margins of the base, which encroaches towards the centre,
untii it finally forms a partition between the pulp-cavity and the
alveolus.

In most of the specimens of the pharyngeal bones of the Wrasse-
tribe, some of the alveoli are empty, and the round extremity of a
new tooth is generally seen protruding for a greater or less extent
through the cribriform base. When a vertical section of one of these
paved pharyngeals is made, as in Plate 46, figure 1, a regularly formed
cavity is exposed beneath the base of each of the bisected teeth,
containing a successional tooth (6), more or less advanced in growth.
Smaller cavities for lodging processes of the formative pulp are seen
extending from the base of those containing the most advanced teeth,
and forming the rudiments of future alveoli.

When the structure of one of these pharyngeal molars is micro-
scopically examined, in a thin vertical section, numerous densely
aggregated and extremely fine calcigerous tubes are observed to
radiate in all directions from the pulp-cavity, and in a direction ver-
tical to the plane of the surface from which they are continued.
Those which descend, soon terminate in cells that communicate with
the canals in the thin plate of bone to which the tooth is affixed.
Those which pass out laterally towards the side of the tooth, follow
the curve of the side as it rises from the base, and form a band with
the convexity next the base. Those which pass to the upper surface
and upper part of the lateral surface, have a pretty direct course:
but all the tubes, when viewed with a high power, are found to be
minutely and beautifully undulated.

When they reach the clear enamel-like covering of the tooth,
the calcigerous tubes lose their undulatory disposition, and instead of
continuing parallel, they cross each other in graceful curves in all di-
rections.

In the small scale on which such a section as has been described
is figured (Pl. 46), only the general course of the calcigerous tubes
can be indicated ; but it is impossible to view the disposition of these
minute hollow columns, in connection with the mode in which the
whole tooth is fixed in its alveolus, without being forcibly struck

LABROIDS. 111

with .the beautiful illustration of the best mechanical principles by
which enormous pressure can be sustained and transferred to par-
ticular points.

To crush the hard shells of marine testacea and comminute them
for deglutition requires strong teeth and the requisite power to work
them ; and of a dentition adequate to such purposes we have frequent
examples in the class of fishes. The jaws of the wolf-fish, figured
in plate 60, are peculiarly well provided with instruments for this opera-
tion. But in the wrasse, the waste of the molar teeth consequent on
the rude attrition to which they are subject, is repaired by the develop-
ment of new teeth directly beneath those in use, whilst in the wolf-
fish the new teeth are formed by the side of the old. Here, then, a
new difficuity was to be obviated; had the crushing tooth rested by
the whole of its basis upon the alveolus, as in the wolf-fish (see the
section of the jaw of that species figured in Pl. 60, fig. 2), the sup-
porting plate, gradually undermined by the growth of the new tooth,
would have given way, and been forced upon the subjacent delicate
and highly vascular matrix with the half-formed tooth: this, there-
fore, must have either sustained the irritation and injury of the
undue pressure, or the important functions of the pharyngeal grinders
must have been temporarily suspended, until the undermined tooth had
been shed, and its successor sufficiently solidified and adequately
fixed.

To obviate this evil, the centre of the pulp of the pharyngeal
molar remains uncalcified long after the tooth has taken its place,
and the circumference only of the base of the tooth rests upon the
raised margin of the alveolus. The part of the tooth which sustains
and transmits the pressure is strengthened by the development of a
strong convex ridge projecting from its inner surface into the pulp-
cavity ; and the calcigerous tubes of this ridge, while simply following
the ordinary course of development, acquire a direction the best
adapted for diffusing the pressure equally to every point, by radiating
from the plane of resistance. The pressure received by the border of
the alveolus is transferred to the walls which divide the vaulted
cavities containing the germs of the new teeth. The roof of these
cavities, which forms at the same time the floor of the alveolus above,

12 LABROIDS.

being thus independent of the superincumbent weight, freely yields
to the absorbent process consequent on the growth of the new tooth;
and before the latter becomes subjected to any pressure from above,
its formation has been sufficiently perfected to enable it to sustain that
pressure without injury.

The lateral walls of the cavities containing the reserve teeth, to
which the pressure is transferred from the margins of the sockets of
those in use, consist of a much denser osseous tissue than the other
parts of the pharyngeal bone.

The Wrasses feed on testaceous Mollusks, Crustaceans, Echini,
&c., which they seize with their long anterior conical teeth, and
crack and bruise by means of their powerfully armed pharyngeals.
Some of the sub-genera of Labroids, Epibulus and Clepticus, have the
intermaxillary bones provided with very long ascending processes,
and an arrangement of muscles, which producing a rotatory motion
of the maxillaries and a sudden descent of the intermaxillaries,
accompanied at the same time with a protraction of the lower jaw,
produces a tubular elongation of the whole mouth, and adds to their
power of catching the smaller marine animals.

48. Scarus.(1)—There is a genus of fishes adapted to browse on the
lithophytes which clothe, with a richly tinted verdure, the bottom of
the sea, as the ruminant quadrupeds crop the herbage of the dry land.

The irritable bodies of the gelatinous polypes which constitute
the food of these fishes retract, however, when touched, into the star-
shaped cavities of their stony support, and the Scart consequently
require a dental apparatus strong enough to break away and reduce
to a pulp these calcareous recesses. Their jaws are, therefore, pro-
minent, short, and stout, and the exposed portions of the inter-
maxillaries and premandibulars are shaped like the beak of a parrot,
whence the name of “ parrot-fish,” usually given to these brightly-
tinted species of the Labroid family. But the mandibles instead of
being sheathed with horn, are encased by an extremely dense and
singularly complicated dental covering.

Each intermaxillary bone presents a triangular form, with the
superior and posterior angles produced, and separated by an oblique

(1) Pl. 49, 50, 51.

SCAROIDS. 113

excavation or concavity, in the middle of which there is a small oval
articular depression, to which a corresponding convex trochlea of
the maxillary bone is adapted. Powerful muscles are inserted into
the two produced angles of the intermaxillary bone, by means of which
it is worked upon the hinge-like joint above described. The
premandibular piece of the lower jaw differs from the intermaxillary
bone above in the absence of the posterior median process, but
in other respects it closely resembles that bone in form.

When the intermaxillary and premandibular bones are viewed
from their outer side, they appear to be edentulous, and to have
their osseous texture converted, at the anterior and outer part,
into an enamel-like substance, with a surface chequered by small
lozenge-shaped smooth or tuberculate plates arranged in a quin-
cuncial order, (Pl. 49, fig. 1). When viewed from the inside, (Pl. 49,
fig. 3), the irregular trenchant margin of these bones is seen to be
composed of short and thick sub-conical four-sided columns, placed
almost vertically to the outer surface of the jaw, along a great part
of which surface similar columns are arranged, which form by their
exposed bases the tesselated surface above mentioned. ‘These small
columns are the teeth ; the exposed base is the crown, and the oppo-
site contracted end, which is slightly excavated, corresponds with the
fang(1). Ifa vertical section of the jaw be made, as in fig. 3, these teeth
or denticles will be exposed in various stages of formation in a cavity
(b) below the dental series in the premandibulars, and in the reverse
situation in the intermaxillaries. The formative quadrilateral pulps
are contained in this cavity, with their bases attached to the vascular
membrane lining its posterior wall, and with their free extremities pro-
jecting horizontally forwards towards the anterior or outer wall.
‘Alveolar or capsular processes of vascular membrane are continued
backwards from the outer wall and inclose the pulps, like the
capsule of the matrix of ordinary teeth. At the uppermost part of
the dentigerous cavity in the upper jaw, the broad anterior extremity
of the columnar tooth is seen to be formed by calcification of the
summit of the pulp: a little lower down, the whole length of the
tooth is completed, but the base is excavated by a conical

(1) Cuvier, Lecons d’Anatomie Comparée, Nouv. Ed. Paris, 1836, tom. iv, p. 226.
i

114 SCAROIDS.

cavity containing the remains of the pulp, and the tooth is
loose, or is suspended only by its pulp and capsule: still lower
down, the capsule is observed in different stages of ossification ;
and the tooth becomes thereby anchylosed, first by its anterior, and
afterwards by its posterior extremity, to the opposite walls of the
formative cavity. The’ pulp-cavity becomes diminished in size by
the progressive calcification of its organized contents, and at length
the tooth, by the complete ossification of its external capsule,
becomes adherent laterally to the contiguous teeth, as well as to
the walls of the dental cavity by its extremities: thus the dense,
exposed anterior portions of the premaxillary and premandibular
bones are converted into an aggregated and anchylosed mass of
teeth. .

When the microscopic structure of one of the maxillary denticles
is examined in a longitudinal section, the conical pulp-cavity may
be traced to near the coronal end of the tooth. The calcigerous tubes,
which at their origin do not exceed ,,4,, of an inch in diameter, are very
closely aggregated, being separated by intervals equal to only one
and a half of their own diameters ; those at the base of the pulp-cavity
descend, and on one side of the denticle, incline inwards, tending to
close that cavity ; the greater number of the calcigerous tubes proceed —
directly outwards, at right angles to the sides of the denticle:
near the coronal surface they begin to bend towards that end, and
to pass more obliquely from the pulp-cavity, until they assume,
in the centre of the crown, a direction parallel to the axis of the
tooth. Besides the primary curvatures, which are most marked at the
two extremes of the denticle, all the calcigerous tubes present the
most regular and graceful undulations throughout their entire course :
these undulations require a compound lens of th inch focus to be
distinctly seen, and, with the fine lateral branches of the tubes, form
no mean test of the powers of the microscope employed. The pulp-
cavity becomes finally occupied by a coarse cellular bone, and a thin
coating of the same kind of tissue invests the exterior of the denticle.
The general disposition of the calcigerous tubes, and the form of the |
detached denticle and its pulp-cavity are figured in Pl. 50.

The thick external enamel-like layer of each denticle, which

SCAROIDS. 115

is indicated by its lighter colour in the plate, consists likewise of
minute fibres or tubes, which are thickest and straightest at the
periphery of the tooth, but bend and cross each other as they ap-
proach the central tubes, appearing to interlace and anastomose at
the boundary line. :

The outer wall of the common alveolar cavity in which the
denticles are developed, is much weaker than the dense and com-
pact inner wall; it becomes thinner as it approaches the margin
of the jaws, and disappears at different distances in different
species of Scari, before it reaches that margin. Where it exists
at the base of the jaws, it is sometimes, as in Scarus muricatus,
(Pl. 49, fig. 1), perforated by numerous small foramina, through
which foramina, in the recent fish, processes of the external perios-
teum are continued to the analogous membrane, lining the dentige-
rous cavity, and forming the capsule of each denticle. These
processes are analogous to the gubernacula of the second series of
teeth in the mammalia, and, like them, serve to conduct the new teeth
to the exterior of the jaw. The growing denticles become elongated
by the addition of successively calcified portions of their pulp to
their basal or posterior extremities ; the opposite end exerts a pro-
portional pressure against the circumference of the foramen, and,
causing its absorption, begins to protrude. The tuberculate crown of the
denticle is exposed about the time when its sides have become an-
chylosed to those of the previously protruded row. Thus from the
close apposition of the protruding denticles, the whole of the outer
parietes of their common alveolar cavity, subjected to the stimulus of
their pressure, is finally removed, and is replaced by the pavement of
mutually anchylosed teeth.

In certain species of parrot-fish one or more of the denticles, at
the posterior part of the intermaxillary bones, are longer than the
rest, and their coronal extremity is produced into a sharp and
sometimes recurved point ; these teeth extend beyond the pavement
formed by the other denticles and constitute a weapon of offence, as
in the Scarus aurofrenatus, Sc. vetula, Sc. quadrispinosus and the
species figured inf Pl. 49, fig 2.

In some other species, as the Scarus flavescens cf Bloch and

1:2

116 SCAROIDS.

Scarus spinidens, Quoy and Gaimard, the anterior denticles are imbri-
cated or arranged like tiles in several rows, and the lateral ones in
the upper jaw are always separated and pointed. There is, also, an
internal row of very small intermaxillary teeth. Cuvier has grouped
together the parrot-fishes with this type of dentition under the sub-
géneric term Caillyodon, which was applied by Gronovius to all the
Scart.

The parrot-fishes, like the wrasses, have no teeth on the supe-
rior maxillary, palatine or lingual bones, but are provided with
strongly developed pharyngeal bones peculiarly well furnished with
an apparatus of teeth for comminuting the coarse fragments of
blended gelatinous and calcareous matters, which the protruded jaws
are organised to break off.(1)

Certain parrot-fishes in which the tooth-paved mandibles are
more slender and spoon-shaped than in the true Scari, and hence
probably subsisting on a different diet than the madrepores on which
such species browse, have the pharyngeal bones provided, as in the
Labri, with numerous obtuse rounded denticles, but more closely
packed together ; these parrot-fishes constitute the sub-genus Odax
of Cuvier.

The typical Scari have both upper and lower pharyngeal bones
paved with strong thick lamelliform teeth, set vertically and trans-
versely in the opposed surfaces of those bones. It is the posterior

(1) The general assertion by Cuvier, that the Scari, like the terrestrial ruminants feed
exclusively on vegetables, “‘ comme les ruminans terrestres, le Scare ne se nourrissait que de
végétaux,” (Cuvier, Histoire Naturelle des Poissons, tom. xiv, p. 100)—must be received with a
certain restriction, although coming from an anatomist who so well understood, and who was
the first to describe intelligibly, the plan and principle of the powerful and complicated dental
armature of the parrot-fishes. It is true that Aristotle, in the passage quoted by Cuvier;
asserts that “the Melanurus and the Scarus subsist on sea-weed ;” but then the Greek Natu-
ralist also pushes the analogies of the Scarus to the terrestial ruminants so far as to
quote, and sanction, the belief that this fish actually ruminated. Some of the species
with weaker and sharper-edged mandibles may crop the sea-weeds as well as other sub-
stances, but both Commerson and Dussumier testify to the coral-feeding habits of the parrot-
fishes of the Isle of France and the Séchelles, etc. Mr. Darwin, who dissected several Scari
soon after they were caught, found their intestines laden with nearly pure chalk, and observed
that such, likewise, was the nature of their excrements; whence he classes these fishes among
the geological agents to which is assigned the task of converting the skeletons of the Lithophytes
into chalk.

‘

a

ee

ed Sale ate + ae

SCAROIDS. Elz

pair of the upper pharyngeals which are thus armed; the lower
pharyngeal bone is single. (1)

The superior dentigerous pharyngeals present the form of an elon-
gated, vertical, inequilateral triangular plate ; the upper and posterior
margin is sharp and concave ; the upper and anterior margin forms
a thickened articular surface, convex from side to side, and playing in
a corresponding groove or concavity upon the base of the skull; the
inferior boundary of the triangle is the longest, and also the broadest ;
it is convex in the antero-posterior direction and flat from side to
side. It is on this surface that the teeth are implanted, and in most
Species they form two rows; the outer one consisting of very small
teeth, the inner one of large teeth. These present the form of com-
pressed conical plates or wedges, with the basis excavated and the
opposite margin moderately sharp, and slightly convex to near the
inner angle which is produced into a point: these plates are set nearly
transversely across the lower surface of the pharyngeal bone, and are
in close apposition, one behind the other: their internal angles are
produced beyond the margin of the bone, and interlock with those of
the adjoining bone when the pharyngeals are in their natural position ;
the smaller denticles of the outer row are set in the external inter-
spaces of those of the inner row, (Pl. 51, fig. 2).

The single inferior pharyngeal bone consists principally of an
oblong, dentigerous plate, of the form represented in Plate 51, fig. 3 ;
its breadth somewhat exceeds that of the conjoined dentigerous
surfaces of the pharyngeals above, and it is excavated to correspond
with their convexity. ‘This dentigerous plate is principally supported
by a strong, slightly curved, transverse osseous bar, the extremities of
which expand into thick obtuse processes for the implantation of
the triturating muscles. A longitudinal crest is continued downwards
and forwards from the middle line of the inferior pharyngeal plate,
anterior to the transverse bar, to which the protractor muscles are
attached.

A longitudinal row of small oval teeth alternating with the
large lamelliform teeth, like those of the superior pharyngeals, bounds

(1) Cheselden has given a figure of this bone at the end of the first chapter of his
** Osteography.”

118 SCAROIDS.

the dentigerous plate on each side; the intermediate space is oc-
cupied exclusively by the larger lamelliform or wedge-shaped teeth,
set vertically in the bone, and arranged transversely in alternate and
pretty close-set series.

The pharyngeal denticles are developed in wide and deep cavities
in the substance of the posterior part of the lower, and of the anterior
part of the wpper pharyngeal bones. Lach denticle is inclosed in its
proper capsule which contains an enamel-forming pulp and a dentinal
pulp, in close cohesion with each other, and with the thin external
capsule. The teeth exhibit progressive stages of formation as they
approach the posterior part of the upper and the anterior part of
the lower pharyngeal bones: as their formation advances to completion
they become soldered together by ossification of their respective
capsules, and soon afterwards are anchylosed by ossification of the
base of the dentinal pulp to the pharyngeal bone itself. The line of
demarcation between the dentified and ossified portions of the pulp
is well defined, so that when the pharyngeal bone and teeth are
sawn through vertically the fully formed teeth appear as hollow cones,
set upon wedges of bone, as shown in PI. 51, fig. |.

The dentine of the pharyngeal teeth of the Scarus consists of
calcigerous tubes and a clear intermediate substance. The calci-
gerous tubes average a diameter of sith of an inch, and are
separated by interspaces equal to twice their own diameter. The
course of these tubes is shown in Pl. 52, fig. 2, 6, in which they
are exposed by a vertical section through the middle of one of the
inferior denticles. They all, on leaving the pulp-cavity, form a
curve with the convexity turned towards the base of the tooth, and
then bend slightly in the opposite direction; the sigmoid curve being
most marked in the calcigerous tubes at the base of the denticles,
whilst those towards the apex become longer and straighter. Besides
the primary curvatures exemplified in the figure, each calcigerous
tube is minutely undulated ; it dichotomizes three or four times near
its termination, sends off many fine lateral branches into the clear
uniting substance (Pl. 52, fig. 3), and finally terminates in a series
of minute cells and inosculating loops at the line of junction with
the enamel.

a

SCAROIDS. 119

This substance (Pl. 52, ¢.) is as thick as the dentine and ‘consists
of a similar combination of minute tubes and a clear connecting
substance. The tubes may be described as commencing from the
peripheral surface of the tooth, to which they stand at right angles,
and, having proceeded parallel to each other half way towards the
dentine, they then begin to divide and subdivide, the branches
crossing each other obliquely, and finally terminating in the cellular
boundary between the enamel and dentine.

The teeth, which present this complex structure, are successively
developed at one extremity of the bone, in proportion as they are
worn away at the other; not, however, as Cuvier describes, from behind
forwards, in both upper and lower pharyngeal bones,(1) but in opposite
directions in the opposite bones, the course of succession being from
before backwards in the upper, and from behind forwards in the lower
pharyngeal bones. In the progress of the attrition to which they
are subjected, the thin coat of cement resulting from the ossifi-
cation of the capsule is first removed from the apex of the tooth,
then the enamel (c) constituting that apex, next the dentine (b), and
finally the coarse cellular central bone (a), supporting the hollow-
wedge-shaped tooth, and thus is produced a triturating surface of
four different substances of different degrees of density. The enamel,
being the densest element, appears in the form of elliptical transverse
ridges, inclosing the dentine and central bone, and external to the
enamel is the cement which binds together the different denticles.

The Comparative Anatomist, conversant with the modifications
of the dental system in the mammiferous class, cannot but be struck
with the close analogy between the adherent pharyngeal denticles
of the Scarus and the complicated grinders of the elephant, both in
form, structure, and in the reproduction of the component denticles
in horizontal succession. But in the fish, the complexity of the
triturating surface is greater than in the mammal, since, from the
mode in which the wedge-shaped denticles of the Scarus are im-
planted upon, and anchylosed to, the processes of the supporting bone,
this likewise enters into the formation of the masticatory surface when
the tooth is worn down to a certain point.

(1) Histoire Naturelle des Poissons, tom. xiv, p. 116.
I

120 MUGILOIDS. ATHERINES.

MUGILOIDS.

49. The teeth in this family of fishes are so minute as to be often im-

perceptible to the naked eye. In the Mediterranean mullet, (Mugil
cephalus), they form a simple row along the margin of the upper and
lower jaws, and are attached to the gum, so as to be moveable like
the teeth of the Gonyodonts.(1) The inferior pharyngeals are covered
with flexible ciliiform teeth ; those of the superior pharyngeals are
so delicate, that the bones seem to be clothed by a soft and finely
papillose velvet. The final comminution of the food is effected, in
the present family, in the stomach itself, which presents a structure
similar to that of the gizzard of birds.

In the genus Cestreus the lower jaw is always edentulous; but
there is a row of small and slender teeth along the margin of the
intermaxillary bones; the palatines and vomer are without teeth, as
in the true Mugiles : the intermaxillary teeth are extremely fine in the
Cestreus plicatilis ; they are stronger, and disposed in several rows in
the Cestreus oxyrhynchus. In the Dajaus there are villiform teeth on
both jaws, and also on the palatines and vomer; it is interesting to
observe, that, with this modification which indicates a diet of .an
animal character, the stomach is much less muscular than in the
true mullets. In the Nestes, the jaws, vomer, and pharyngeals are
armed with teeth ‘ en cardes,’ but the palatines are edentulous. In
the Tetragonurus the maxillary teeth are more developed than in the
previous genera; there are twenty-four teeth which are simple,
conical, and slightly recurved in each intermaxillary bone; there are
fifty on each side of the lower jaw, arranged in a single row; these
are stronger, more compressed and more pointed than the upper ones.
Both series of teeth are but feebly attached to the bone, but those
of the lower jaw offer most resistance. There are longitudinal rows
of finer teeth on the vomer and palatine bones. The tongue is not
armed with teeth ; the pharyngeal bones support each an oval patch
of teeth ‘ en cardes.’

ATHERINES.

50. The sand-smelts or fishes of the family of Atherines have very
(1) Page 85.

SCOMBEROIDS. 12]

small but acute teeth ; these are sometimes present on the jaws only,
as in Atherina Brasiliensis and other species of the new world; some-
times also they are developed, but of extremely minute size, upon the
palatine bones, as in the Atherina Hepsetus; and lastly they may be
found on the jaws, palatines and vomer, asin the Atherina Boveri, and
other broad and flat-headed species of the present family. The
pharyngeal bones in the common Atherine or sand-smelt, (Atherina
Presbyter), are furnished with numerous small and close-set conical
teeth.

SCOMBEROIDS.(1)

51. In this family of cycloid fishes the dental system presents many
modifications, of which the Sword-fishes (Xiphias), and the Scabbard-
fishes (Lepidopus) offer, perhaps, the extremes.

The Sword-fish might be reckoned among the edentulous fishes,
were it not that the pharyngeal bones are covered with a villosity
of extremely fine and minute denticles ; but all the ordinary bones
of the mouth, of the tongue, and even of the branchial arches, are
without teeth. In the Opah or King-fish, (Lampris guttatus), the
ordinary bones of the mouth are likewise edentulous ; the pharyngeals
have not been examined in this species.

In the Stromateus there is a single row of denticles on each
jaw, but these are so delicate and short that they cannot be recog-
nised without the aid of a lens. The palatine, vomer, and hyoid
bones are edentulous, as in the Sword-fish.

The dentition of the Rhombus is similar to that of the Stromateus,
but the maxillary teeth are a little more developed.

The margins of the jaws are roughened by numerous close-set,
short, villiform teeth in the Tetrapturus ; the palatine and pharyngeal
bones bear similar denticles in this genus.

In the Histiophorus the broad, dentigerous margins of the jaws
are covered with minute dental granulations only, some of which are
developed, in the lower jaw, into small pointed teeth.

The dental system is not more formidable in the genus Trachurus.
In the mailed mackerels, (Caranz), the tongue is beset with villiform

(1) Pl. 53, 54, and 55.

122 SCOMBEROIDS.

teeth, and the exterior maxillary teeth are pointed. In the Carangue,
(Carane carangus), there is a row of conical teeth exterior to the
band of villiform denticles in the upper jaw ; there is also a similar,
but more close-set row in the lower jaw, the two anterior of which
are produced, like canine teeth, beyond the rest.

In the pilot-fish, (Naucrates Ductor), the maxillary teeth are
villiform, and are arranged in a narrow band on each jaw, there is
a broader, but shorter band of similar teeth in the palatines, and
along the middle of the tongue. The dentition of the genera, Kurtus,
Seriola, Gallichthys, Blepharis, Olistes, Vomer, Brachinotis and Elacates
is similar to that of the Naucrates ; but the pharyngeal teeth in the
latter genus, are more strongly developed. The pharyngeals are
paved with small obtuse teeth in the genus Hynms. In the Apolectus,
Centrolophus, and Astrodermus, the minute maxillary teeth are rather
ciliiform than villiform, and are disposed in a single row.

In the Chorinemus two rows of small conical teeth rise above
the villous band of denticles in the intermaxillary and premandibular
bones. The pterygoid, as well as the palatine, vomerine, and lingual
bones, support oval patches of villiform teeth in this genus.

The jaws of the common mackerel, the type of the Scomberoid fa-
mily, are feebly armed with a single row of small pointed and slightly
recurved teeth; the anterior part of each palatine bone is similarly
provided, and there are three or four small teeth on each anterior
angle of the vomer. The tongue is smooth, but the pharyngeal bones
are beset with teeth so long, delicate and flexible, as to resemble
hairs.

The maxillary teeth of the tunny, (Thynnus vulgaris), are rela-
tively smaller than those of the mackerel, and resemble the points of
small pins, slightly bent inwards and backwards; there are about
forty of these denticles on each side of the jaw, those of the lower
jaw being somewhat the largest. The Scomber pelamys of Linneus or
the striped-bellied bonito, (Thynnus Pelamys, Cuv.), has teeth like
those of the tunny; but the true, or striped-backed bonito (Pelamys
Sarda, Cuv.(1) has the maxillary teeth more strongly developed ; they
are conical, slightly compressed, sharp-pointed, and arched towards

(1) Plate 1, fig. 3.

SCOMBEROIDS. 128

the interior of the mouth ; the third on each side is a little longer
than the rest. There is a row of very small conical teeth, on the
outer margin of each palatine bone ; but the vomer is edentulous.

In the king-fishes, (Cybium), and the temnodonts, the maxillary
teeth are relatively larger than in the bonitos, and are lancet-shaped,
with very sharp points and edges. There are twenty-five of these
teeth on each intermaxillary bone, and twenty on each premandibular
bone. In the Cybium Commersonu the jaw-teeth present the form of
an isosceles triangle, with trenchant margins. A crescentic plate on
the anterior part of the vomer, a band on each palatine and nearly
the whole of the oral surface of the pterygoid bones are roughened
with close-set microscopic villiform teeth. The dentition of the
Scomberoids of the genus Thyrsites is distinguished from that of
the king-fishes chiefly by the increased length of a few of the anterior
intermaxillary teeth, and by the development of the palatal teeth.
into small pointed laniaries. In the genera Gempylus, Lepidopus, and
Trichiurus or hair-tail, the elongated anterior intermaxillary teeth
present a small retroverted point or barb at the posterior margin near
the apex.

In the scabbard-fish there is a row of twenty to twenty-two
compressed sharp-pointed teeth on each intermaxillary bone, and
just behind the anterior part of each row are two or three teeth
four times as large and long as the others, slightly bent inwards ;
six of these, Mr. Yarrell observes, is the correct number, but two or
three are generally observed to be broken. The under jaw has also
one entire row of teeth, with two longer ones. The vomer is eden-
tulous, but the long external edge of each palatine bone has one row .
of very minute teeth; the pharyngeal bones and branchial arches
are also furnished with teeth that are exceedingly minute. (l)

In the genus Lactarius the jaws and palatine bones are beset
with villiform teeth ; besides which there are at the fore part of each
of the intermaxillaries two or four long, curved and sharp-pointed
teeth, and in the premandibulars a row of fine, acute, recurved and
closely packed teeth. There is a small chevron-shaped group of

(1) British Fishes, i, p. 179

124 SCOMBEROIDS.

fine and pointed teeth on the vomer, and the two margins of the
tongue support minute granular teeth.

The jaws of the Nome: are provided with a single row of small,
recurved, conical teeth, without the addition of laniary or villiform
teeth.

In the dolphin, (Coryphena Hippurus), the intermaxillary and
premandibular bones support each an exterior row of small recurved
conical teeth, within which there is a broad band of teeth ‘ en cardes ;’
these latter reach further back in the lower than in the upper jaw.
There is a rhomboidal patch of similar denticles on the vomer, and a
longitudinal band on each palatine bone. The tongue supports a
broad plate of villiform teeth, which are likewise present on the
origins of the branchial arches. The pharyngeal denticles are more
strongly developed.

A narrow band of incurved teeth ‘ en cardes,’ but not very
thickly set, extends along each intermaxillary and premandibular
bone in the dory (Zeus faber), which has also a small group of
similar teeth on each side of the anterior part of the vomer, but none
on the palatines or tongue. The branchial arches are furnished with
tubercles, and these, together with the small pharyngeal bones, are
beset with the same kind of teeth as those on the vomer and jaws.
The boar-fish (Capros Aper), the type of an allied genus, has a
dentition similar to that of the dory; the maxillary and vomerine
denticles are somewhat finer and are placed deeper within the jaws,
and those of the pharyngeal bones and branchial arches are villiform.
The jaws of the Equula ensifera are provided with a narrow band
of flexible setiform teeth ; in some other species, as the Equula dentez,
two of the anterior teeth in both jaws are more developed than the
rest, and are pointed and incurved.

In the genus Alepisaurus, the mouth is as well armed as in the
hair-tail, or scabbard-fish, and the teeth present a similar inequality
of size, and the compressed, pointed, lancet-shaped figure, so common
in the Scomberoid family of fishes. ‘The margin of each long inter-
maxillary bone is serrated by a row of small compressed teeth, the
anterior being rather larger than the hinder ones, and the first
tooth projecting forwards. The anterior part of the palatine bones is

SCOMBEROIDS. 125

armed with a group of three very large, slightly recurved, lancet-
shaped teeth, placed in a triangle, of which the apex is directed
forwards ; then on each side there is a single lancet-shaped tooth,
about half the size of the preceding, and behind these, there is a row
of seven smaller and close-set teeth. The lower jaw has a pair of
long sub-conical teeth in front, one on each side, with a smaller one
between them ; and below these, on the outer side of the symphysis,
there is a single conical tooth projecting forwards. Behind the first
pair of teeth, there extends along each ramus of the jaw a row of
five much smaller teeth, followed by three rather larger, which become
eradually more compressed ; then there are two lancet-shaped teeth,
considerably larger, which lock into the interval in the upper jaw, and
after a short diastema follows a row of eleven short but broad and
compressed teeth. All these teeth, when fully formed, are firmly
anchylosed by their bases to depressions in the jaw bones.

In all the Scomberoid fishes the succession of teeth is unin-
terrupted ; the pulps of the new teeth are developed in most of
the species in the soft gum or integument covering the denti-
gerous margins of the bones, and the calcification of the pulp is
completed as it lies recumbent and buried loosely in the substance
of the gum. The point of the new tooth, which, in this state, is
directed backwards, is then exposed by a gradual rotatory move-
ment of the tooth from the horizontal to the vertical position ; the
jaw bone grows around its base, and, ossification proceeding along
the ligamentous attachment of the tooth, finally fixes it to the jaw by
continuous anchylosis.

In a large exotic Trichiurus, I find six large barbed fangs at the
anterior part of the upper jaw, three recumbent and loose, and three
erect and fixed. These are situated alternately, so that in one
specimen two of the fixed teeth may be implanted in the right, and
one opposite the interspace of the preceding, in the left palatine bone;
while in another specimen the situation of the fixed teeth is reversed,
as is also that of the recumbent and loose successional teeth. (1)

(1) The discovery of the larger teeth, lying loosely in the gum, near the base of the fixed teeth
they are destined to supplant, is apt to occasion surprise in those, who may not be acquainted
with their mode of development. Thus, the excellent Ichthyologist from whose description

126 SCOMBEROIDS.

In the Paralepis, the intermaxillary teeth are so small that they
are indistinguishable without the aid of a lens; thus magnified, they
are seen to be very numerous and close-set, like the teeth of a saw.
The premandibular and palatine teeth, on the contrary, are large,
but slender, recurved and sharp-pointed, set wide apart, with smaller
teeth in the interspaces. There are no teeth on the vomer or
tongue.

52. Sphyrena.—The most formidable dentition exhibited in the
extensive Scomberoid family of the system of Agassiz is that which cha-
racterizes the Sphyrena, and some extinct fishes allied to this predatory
genus. In the great barracuda of the southern shores of the United
States, (Sphyrena Barracuda, Cuv.) the lower jaw contains a single row
of large, compressed, conical, sharp-pointed, and sharp-edged teeth,
resembling the blades of lancets, but stronger at the base.(1) The
two anterior of these teeth are twice as long as the rest, but the
posterior and serial teeth gradually increase in size towards the
back part of the jaw; there are about twenty-four of these piercing
and cutting teeth in each premandibular bone. They are opposed to
a double row of similar teeth in the upper jaw, and fit into the
interspace of these two rows, when the mouth is closed. The outer-
most row is situated on the intermaxillary, the innermost on the
palatine bones ; there are no teeth on the vomer or superior maxil-
lary bones. The two anterior teeth in each intermaxillary bone
equal the opposite pair in the lower jaw in size; the posterior teeth
are serial, numerous and of small size ; the second of the two anterior
large intermaxillary teeth is placed on the inner side of the com-
mencement of the row of small teeth, and is a little inclined back-
wards. The retaining power of all the large anterior teeth is increased
by a slight posterior projection, similar to the barb of a fish hook,

of the “‘ Alepisaurus” most of the foregoing details of its dentakorgans are derived, observes,
with respect to the successors of the larger palatine teeth, “‘ Whether they were originally,
like the others, fixed, and are merely loose from injury or fracture, or are properly moveable and
free, I can scarcely venture to decide. At first sight and from the way in which they lie
amongst the loose gelatinous integuments of the palate, with no appearance of a regular attach-
ment by the base, their condition seems the effect of accident.”—Transactions of the Zoological
Society, vol. 1, p. 396. ;
(1) Pl. 1, fig. 4,and PI. 53, fig. 1.

SCOMBEROIDS. 127

but smaller. The palatine bones contain each nine or ten lancet
shaped teeth, somewhat larger than the posterior ones of the lower
jaw. All these teeth afford good examples of the mode of attach-
ment by implantation in sockets, which has been denied to exist in
fishes. (1)

The loss or injury to which these destructive weapons are liable
in the conflicts which the sphyrzena wages with its living and strug-
gling prey, is repaired by an uninterrupted succession of new pulps
and teeth. The existence of these is indicated by the foramina, (2)
which are situated immediately posterior to, or on the inner margin of
the sockets of the teeth in place; these foramina lead to alveoli of
reserve, in which the crowns of the new teeth in different stages of
development are loosely imbedded. It is in this position of the
germs of the teeth that the Sphyrzenoid fishes, both recent and fossil,
mainly differ as to their dental characters from the rest of the Scom-
beroid family, and proportionally approach the Sauroid type. The
base or fang of the fully-developed tooth of the Sphyrzena is an-
chylosed to the parietes of the socket in which it is inserted. The
pressure of the crown of the new tooth excites absorption of the
inner side of the base of the old, which thus finally loses the requisite
strength of attachment, and its loss is followed by the absorption of
the old socket, as in the higher animals.

It is interesting to observe that the alternate teeth are, in general,
contemporaneously shed ; so that the maxillary series is always pre-
served in an effective state. The relative position of the new teeth to
their predecessors, and their influence upon them, resemble, in the
Sphyrena, some of the phenomena which will be described in the
dentition of the Crocodilian reptiles. To the crocodiles the present
voracious fish also approximates in the alveolar lodgment of the teeth,
but it manifests its ichthyic character in the anchylosis of the fully
developed teeth to their sockets, and still more strikingly in the
intimate structure of the teeth.

Few microscopic objects are more beautiful than a longitudinal
and transparent section of the tooth of the Sphyrzna, which accurately

(1) Cuvier, Histoire Naturelle des Poissons, tom. i, p. 492.
(2) Pl. 53, fig. 1, a, a.

128 SCOMBEROIDS.

typifies that of the teeth in all the Scomberoid fishes. It consists of
a thin external coating of fine enamel-like dentine, and a body of
coarse dentine. The most successfully injected vascular membrane
could not surpass in the number and delicacy of its ramified capillaries
the arrangement of the medullary canals, which pervade the whole
body of the tooth in this fish. The smallest marginal or peripheral
divisions of the medullary canals anastomose in curved loops whose
convexity is turned towards the superficies of the tooth; the branches,
which, by their terminal division, constitute those loops, successively
anastomose, as they widen and slightly converge towards the central
part of the tooth.(1) Here the main medullary tubes run nearly
parallel to each other, with interspaces equalling from four to six
times their own diameter. In their progress towards the base of
the tooth, they give off numerous branches which subdivide and
anastomose in the interspaces of the main canals. These canals, in
the fully formed anchylosed teeth, communicate directly with the
medullary canals of the jaw-bones, which run at right angles with those
of the teeth.(2) The reticulate medullary canals every where send off
the much more minute calcigerous tubes, which quickly subdivide into
tufts or pencils; these soon begin to bend and interlace together and
fill the meshes of the medullary reticulations by their inextricable anas-
tomoses. The peripheral loops of the medullary canals, in like manner,
give off pencils of fine calcigerous tubes ; but these maintain, as do the
tubes of ordinary dentine, a more regular and parallel course ; they
penetrate, and constitute with the clear uniting substance, the exter-
nal hard and white coating of the tooth ; the first two-thirds of their
course is at right angles to the plane of the surface towards which
they are directed; their finer ramifications then begin to bend from
side to side, and terminate in reticular inosculations of extreme
minuteness, which are finally lost in the clear dense substance
of the outer layer.
Sphyrenodus.—The same general distribution of the medullary ©
(1) A diminished view of the structure, as seen in a longitudinal section of the apex of
the tooth, is given at fig. 2; ‘pl sae
(2) The solid tissue of the maxillary bones presents a close-set parallel arrangement of

undulating calcigerous tubes, and nearly resembles the texture of the dentine in the higher
mammiferous teeth. There are no Purkingian corpuscles or radiated cells in this bone.

SCOMBEROIDS. 129

and calcigerous tubes pervades the whole substance of the tooth in
many, and probably in all, of the Scomberoid Fishes, and not only in
those of the existing epoch, but the same beautiful and complicated
structure may be discovered with equal distinctness in the fossil teeth
of species and genera which are now extinct. At Plate 54 is given
a view of thé reticulate disposition of the medullary tubes, as seen
by a low power, in a transparent longitudinal section of the fossil
tooth of a large Scomberoid Fish, from the eocene formation called
the London clay, at the Isle of Sheppey. The tooth, which I for-
merly described under the name of Dictyodus,(1) in reference to the ar-
rangement of the medullary tubes, belongs to the extinct genus of
fishes called by M. Agassiz, Sphyrenodus, from its affinity te the
existing genus, Sphyrena, the largest species of which it must have
equalled in size.

The natural form of this tooth, which is from the lower jaw, is
conical and subcompressed, but relatively thicker than any tooth of the
Sphyrzna : its base is broad, but implanted asin that genus, in a deep
socket, to the bottom of which it is anchylosed. The main body of the
tooth consists of a coarse dentine, incased by a thin layer of fine and
hard enamel-like dentine. The coarse dentine is pervaded by an as-
semblage of medullary canals, directly continued from the large irre-
gular medullary sinuses and cells at the anchylosed base, and thence
proceeding in a general parallel course towards the apex, sparingly
dichotomizing, and gradually diminishing as they proceed: they are
separated by interspaces, which are generally equal to three or four —
of their own diameters, and send off, throughout their course, short
transverse branches, which anastomose and intercept in the interspaces
of the longitudinal tubes, quadrangular, sub-elliptical, pentagonal,
or hexagonal spaces, generally elongated in the axis of the tooth,
but becoming shorter as they approach the periphery, especially at
the apex, where the structure of the tooth resembles an irregular lace-
work. In this fossil I have been able to detect the fine calcigerous
tubes only in the hard peripheral layer of dentine, into which they
pass directly from the nearest medullary canals, dividing and subdi-
viding at acute angles, but with a general direction vertical to the

(1) Trans. Brit. Association, 1838, p. 142.
K

130 SCOMBEROIDS.

surface of the tooth. The relative thickness of this layer of fine-
tubed dentine is shown in the figure ; the diameter of the calcigerous
tubes at the middle of the layer does not exceed ;i,th of an inch.
The traces of the corresponding tubes in the clear interspaces of the
ramifications of the medullary canals were almost obliterated in the
fossil examined by me, but the analogy of the recent Scomberoid teeth,
and of some allied fossils, especially that about to be described, hardly
permits a doubt as to their existence.

Saurocephalus. — There are few instances in which the value
of the characters derived from the microscopic structure of teeth
has been more strikingly displayed than in regard to the Sauro-
cephalus and Saurodon, under which names two interesting fossils of
distinct species, of the same or very nearly allied genera, have been
described as extinct members of the Saurian Order of Reptiles, by
Dr. Richard Harlan(1) and Dr. Isaac Hays. (2)

These fossils consisted of portions of jaws with teeth of a simple
conical subcompressed form, arranged in a single row, fixed in dis-
tinct and deep alveoli, each with a broad and simple fang, generally
excavated by the pressure of a new tooth developed near its base.
Prof. Agassiz was led from the external characters of the jaws and
teeth in question to believe that they might belong to the Scombe-
roid family in the class of Fishes, and an inspection of Plate 55,
which gives a view of a small portion of a transparent longitudinal —
section of one of the teeth of the Saurocephalus, will demonstrate the —
accuracy of the judgment of that acute Palzontologist.

I am indebted to Dr. Richard Harlan for the opportunity of
making the requisite sections of the tooth of the genus in question.
The plan of structure closely corresponds with that already described
in Sphyrena and Sphyrenodus. The larger medullary tubes (a a,
Pl. 55), maintain a nearly parallel longitudinal course, throughout
the body of the tooth, exhibiting here and there a dichotomous sub-
division, and gradually decreasing in diameter as they approach the —
summit of the tooth. The lateral or transverse branches are, upon

(1) Journal of the Academy of Natural Sciences of Philadelphia, vol. 3, p. 331.
(2) Transactions of the American Philosophical Society, vol. 3, part 2, p. 471, In the @

Saurian system of Herm. v. Meyer these genera are placed between Phytosaurus and
Teleosaurus, see his Paleologica, 8vo. 1832, p.p. 114, 222.

LUCIOIDS. 131

the whole, relatively larger than in the Sphyrenodus, and are more
flexuous in their course ; and the spaces intercepted by their anasto-
moses are less angular. These spaces (6) exhibit every where
plexiform groups of flexuous calcigerous tubes proceeding from the
medullary canals. The clear and dense investment of the tooth
presents the same structure as the peripheral dentine in other Scom-
beroid fishes, being traversed by sub-parallel and acutely-branched
calcigerous tubes, passing from the nearest medullary tubes, at right
angles to the surface of the tooth, and diminishing to extreme tenuity
in the clear outer portion of the investing layer,c. No Saurian tooth
recent or extinct has presented the type of structure here described :
the distribution of branched and reticularly anastomosing medullary
or pulp-canals through the whole body of the tooth is a peculiarly
Ichthyic condition of the dental structure; and the modifications of
this condition presented by the tooth cf the Saurocephalus, are most
closely allied to those which characterize the teeth of the Scomberoid
Fishes.

In Plate 55 an entire tooth of the Saurocephalus lanciformis and
a portion of jaw, containing two others imbedded in their sockets,
are represented of the natural size, by the side of the magnified sec-
tion. The small foramen opposite the fang of each tooth is described
by Dr. Hay, .as being for the transmission of nerves and blood-vessels
to the teeth. I have little doubt, from the analogy of the Sphyrena,
that these foramina lead to the cavities containing the germs of the
successional teeth. They are placed as inthe Sphyrzna, on the inner
side of the alveolar process.

LUCIOIDS.

53. The fishes of the family typified by the voracious Pike, and
hence termed ‘ Lucioids,’ have a more complicated dentition than those
of the preceding family ; but the teeth are characterized by a similar
reticulo-medullary tubular structure, distinguished chiefly by the
more regular size and form of the meshes or interspaces of the anas-
tomostic net-work.

The Scomberesox is a genus which connects the Scomberoid with
the Lucioid family of fishes. The jaws of a species of this genus from

K 2

132 LUCIOIDS.

Van Diemen’s Land, now before me, which exceed six inches in length,
have the whole of their convex alveolar border beset with a band of
minute sharp conical rasp-like teeth ; along the inner border of each
band there is a row of moderately long, slender, straight and very
acute teeth, with intervals of from four to six times their own diame-
ter. Their dentition resembles very closely that of the true Sauroid
Fishes.

The Garpike, (Belone vulgaris), has a row of large sharp conical
and recurved teeth, together with many small ones upon each of its
long intermaxillary and premandibular bones ; but the palatines and
hyoid are edentulous. Thereis a small patch of villiform teeth on
the vomer. The pharyngeals are paved with small tuberculate teeth.
The Mormyri have a simple row of small compressed and notched
teeth on each jaw: and villiform teeth on the tongue and vomer.

The Esox Lucius or common Pike has an immense number of
teeth, all of which are conical, slender and sharp-pointed. They are
placed on the intermaxillary, premandibular, palatine, vomerine,
lingual, branchial and pharyngeal bones. The largest and most for-
midable of these teeth are those situated in the lower jaw, and at the
anterior part of the palatines and vomer. The intermaxillary teeth are
small and slightly recurved, placed in a single or double alternate
row: the teeth at the anterior part of the lower jaw correspond
in size and arrangement with the intermaxillary ones; but the poste-
rior teeth are much longer and stouter, especially the first ; they form
a single row, and are separated by wide intervals in which are si-
tuated the successional teeth in different stages of development in a
recumbent position, directed inwards, and concealed by the gum.

The teeth of the palatines and vomer are arranged in numerous
close-set rows, the largest being placed at the anterior part of these

bones, and along the mesial edges of the palatines; those on the
vomer are so numerous, small, and close set, as to resemble the teeth —
ofarasp. The mesial chain of hyoid. bones supports four longitu-—
dinally oblong patches of smaller rasp-like teeth. Similar teeth are
arrauged along the inner surfaces of all the branchial arches ; and the —

four superior and two inferior pharyngeal bones are beset with some-

what larger teeth of a similar conical, sharp pointed, recurved form. —

q

|
.
)
|

es

LUCIOIDS. 133

it is somewhat unusual in the present class, to find such an immense
number of teeth, so variously disposed over the parietes of the
mouth, yet presenting so uniform a shape; but all are here adapted
to pierce, seize, and retain a living prey, and are thus in perfect
conformity with the predaceous habits of the species. The fully
developed and functional teeth are attached by a confluence of their
bases with the surface of the jaw-bones, and not, as in Sphyrena,
with the parietes of an alveolar cavity. The germs of the succes-
sional teeth, also, instead of being developed in alveolar cavities,
complete their growth in the original seat of their formation, viz. the
vascular membrane or gum, which covers the dentigerous margins of
the jaws.

That the formation of a tooth is an act of conversion of the sub-
stance, and not of cells upon a formative surface of the pulp, is
clearly illustrated in the Pike. The cone-shaped cap which the half-
developed tooth forms upon the remaining matrix can only be
removed by overcoming a certain resistance, and this resistance is
seen to be due to the processes of the pulp which extend into the
medullary canals of the tooth ; the broken ends of these processes give
an irregular surface to the exposed pulp, and their continuation into
the tooth may be seen by sawing the latter across. This connection
between the substance of the tooth and of the pulp is still better
demonstrated in a finely injected specimen: the mechanical relation
between the tooth and the pulp is then seen to be of precisely the
same kind as those between an ordinary osseous nucleus and the car-
tilaginous matrix in which it is developed: it is in the course or direc-
tion of development that the chief difference exists; in the tooth
it is centripetal, in the bony epiphysis centrifugal ; but the mode of
development is the same. In both cases a soft and vascular model
and framework of the future hard part is prepared: in it the cells are
formed and the tubes are excavated according to the plan destined
for the future arrangement of the calcareous particles ; which arrange-
ment is not one of indiscriminate diffusion, but accords with the best
known mechanical principles, and is in prospective harmony with
the peculiar resistance which the calcified part is destined to over-
come. A vertical section of the matrix of a Pike’s tooth and the

134 LUCIOIDS.

supporting process of gum is represented at Piate 44, fig. 5; a is
the superficial calcified layer of the pulp c, the base of which is sunk
into a fossa, or open capsule of the gum 0; d is the nerve entering
the base of the pulp. In figure 0, Pl. 44, the course of the branches
of the fifth pair of nerves, through the permandibular bone of the
pike, to supply the pulps of the teeth, is shown; the size of the
dental nerve bears relation to the vascular and organized texture of
the tooth, and to the rapidity of its growth.

Retzius’ accurate description of the microscopic structure of the
tooth of the Pike (Esox Lucius, L.) is as follows. ‘‘ It. consists of an
internal part or nucleus with coarse tubes, and an outer thinner part,
with fine and parallel tubes, which form the covering of the nucleus.
The coarse main-tubes, which occupy the internal and imperfectly
developed parts of the ivory, present at their widest part a diameter of
about ,,,th of an inch. Their course is aimost parallel with each
other and with the axis of the tooth, and they unite by numerous
larger or smaller anastomoses. Near the basis of the anchylosed
teeth, the larger oblique anastomoses are so near together that their
interspaces are scarce equal to the diameter of the larger tubes. In
recent teeth these tubes contain a blood-red substance, which might
be regarded as a complex pulp. Beautifully minute and very short
tubules of from gq to smth of an inch in diameter, proceed mostly
in a transverse direction from the larger tubes; and subdivide, as
they proceed, into groups of finer tubes, which form innumerable reti-
cular anastomoses with each other, and thus fill up the interspaces of
the larger canals. The boundary between the central and peripheral
substances is well defined, and is formed by anastomoses of the exte-
rior longitudinal bent coarse tubes ; beyond which no coarse tube
extends, but only a series of fine and parallel tubes; these tubes
manifest the same direction as those in the thin and hollow shell of
the incompletely formed teeth of the higher organized animals: 1. e.
the fine tubes that are nearest the apex of the tooth, are almost paral-
lel with the axis of the tooth, while those which are nearest the root,
proceed transversely to the axis. They soon divide into pencils of
finer branches, which mutually and reticularly anastomose, and give
off at their peripheral extremities close-set parallel tubes, from j3%q) to

Ce

Baa! ~whP ips cis Bice 4 ~ee gee ngy s

CLUPEOIDS. 135

smth of an inch in diameter, in which I could perceive neither
branches, anastomoses nor cells. The exterior ivory-like substance
viewed in a section of a Pike’s tooth by a low magnifying power resem-
bles a layer of enamel. It is extremely thin where it commences
near the base of the tooth, and is thicker at the apex where the fine
branches of the tubes exhibit the most beautiful dendritic arrange-
ment. The central substance of the tooth is grey in recent teeth,
and yellowish in dried specimens ; the peripheral substance is of the
purest white, andis much harder and more compact than the central
substance. So hard, indeed, is it in dried teeth, that I supposed it
might be covered with an extremely thin layer of enamel, but I could
not by means of the microscope discover any such layer.”

CLUPEOIDS.

54. The Clupeoid family of Fishes, of which the Herring is the
type, is interesting in relation to the dental anatomy of the class on
account of the examples which it offers of very general and extensive
distribution of teeth over the bones which surround the oral cavity,
and of the unusual share which the superior maxillary bones, from
their relative position and development, take in supporting the
teeth of the upper jaw. The different genera, however, of the
Clupeoid, as of other natural groups of fishes, present very diver-
sified conditions of the dental system ; the almost edentulous Clupano-
don, and the rapacious Hrythrinus or the gigantic Sudis, offering the
extremes of these modifications.

In the Clupanodon an almost imperceptible coating of the finest
villiform teeth, upon the pharyngeal bones, forms the sole trace of a
dental system.

The Herring (Clupea Harengus) has very minute sharp-pointed
teeth on the jaws and tongue. |

The Pristigaster presents similar teeth on the large intermaxilla-
ries, ona small part of the superior maxillaries, and upon the hyoid,
palatine, vomerine and pterygoid bones.

The little Anchovy, the type of the genus Engraulis, is a good
example of that higher development and allocation of the superior
maxillary bones, which is so rare in the class of fishes; they here

136 CLUPEOIDS.

form the greater part of the superior margin of the mouth, and toge-
ther with the small intermaxillaries, and the slender premandibulars,
are armed with small, but very sharp-pointed teeth: the vomer and
the long palatines support similar, but smaller teeth, arranged in a
single series: the pterygoid, hyoid, branchial and pharyngeal teeth
are villiform.

The Sudis gigas, the largest not only of the Clupeoid family but
of all fresh-water fishes, is not less remarkable for the number of the
teeth, than for the number of bones over which they are distributed,
the dental system is represented in figs. 4. 5 & 6, Pl. 48. Not only do
the intermaxillary (a) the superior maxillary bones (0), the premandibu-
lars (f), the palatine (c), the vomerine (e), the lingual (fig. 6), the bran-
chial and pharyngeal bones support teeth, as in many Clupeoid and Sal-
monoid fishes, but the internal pterygoid bones (d d) and the basisphe-
noid (f) have their under surfaces beset with innumerable denticles.

The maxillary teeth are implanted in a continuous alveolar groove
of the bones which circumscribe the aperture of the mouth, and are
attached to the groove by a ligamentous union. These teeth are
conical, much compressed, with an obtuse apex, near to which the
pulp-cavity extends. The other dentigerous bones are beset with
numerous, close-set, minute, short, cylindrical teeth, with convex,
graniform summits. The surface of the tongue is formed by the hard
granulated dentigerous surface of the median ossicles of the os hyoides,
which are broad and flat; the anterior of these ossicles is much
elongated; in a Sudis gigas, seven feet in length, it measures six
inches in length and two inches in breadth.(1)

In the genus Erythrinus, the intermaxillary, maxillary and pre-
mandibular bones are formidably armed with conical sharp-pointed
teeth, alternately large and small; the palatine, pterygoid, hyoid,
and pharyngeal bones are beset with minute viiliform teeth. The
rapacity of these clupeoid fishes corresponds with the power of their
maxillary weapons. In the stomach of a specimen of the Erythrinus
macrodon, brought from Brasil in spirits, and dissected by M. Agassiz,
he found another species of the same genus, more than a third part of
the length of the fish by which it had been swallowed. (2)

(1) It is used as a rasp for culinary purposes by the Indians of the Brazils.
(2) Spix, Pisces Brasilienses, p. 41.

CLUPEOIDS. 137

In the genus Osteoglossum, the dental system of which is shown
in the large middle figure of Plate 48, the intermaxillary bones (a)
form only a small portion of the median and superior margin of the
mouth; the remainder is completed by the superior maxillaries (6 6),
which, with the premandibular bones in the lower jaw, are armed
with a single series of equal, small, conical and sharp-pointed teeth :
near the lax symphysis of the lower jaw, there is a second series of
similarly shaped retrovertedteeth. The vomer and anterior part of the
palatine bones are beset with small acute teeth ; the posterior part
of the palatines and the entire lower surface of the pterygoids are
covered with villiform denticles, but there is a row of longer sharp-
pointed teeth at the inner border of each pterygoid bone. The broad,
long, and flat lingual bone, (e), is covered with minute close-set pointed
teeth, converting the upper surface of the tongue, into a hard boney
rasp, whence the name of the genus. The branchial arches and the
inferior pharyngeals support villiform teeth.

The genus Glossodus affords additional examples of those fishes
in which the body of the os hyoides is provided with tubercular
teeth which are opposed to similar instruments for crushing the
alimentary substances, attached to the body of the sphenoid and
to the pterygoid bones. The maxillary, vomerine, palatine, branchial
and pharyngeal bones, both superior and inferior, are beset with
minute villiform teeth.

In the three preceding genera of South American tropical fresh-water
fishes the broad, long and flat dentigerous plate, into which one of the
median hyoid ossicles is developed, forms a striking characteristic of
their dental system, and I shall here describe similar dentigerous
plates, found fossil, in the eocene formation, called the ‘ London Clay,’
at the Isle of Sheppey. (1)

As these remains have hitherto been met with detached and un-
connected with the other bones of the skull, and exhibit little more
than the dentigerous covering, it cannot be unequivocally determined
whether they are the dentigerous armature of a broad lower pharyn-

(1) Specimens of these are preserved in the well known collection of Sheppey. Fossils of

J. S. Bowerbank, Esq., F.G.S., whose liberality in permitting their description on this, as on
many other occasions, I have gratefully to acknowledge.

138 PHYLLODUS.

geal bone, like that of the Scarus, or of the maxille, as in the Diodon,
or whether they belong to the hyoid system, or other median bone
of the cavity of the mouth; as, however, it is the structure of the
teeth and not of the cranium that it is proposed to describe in this
place, the ambiguity which may attach itself to the precise homology
of the supporting bone is of less consequence.

55. Pisodus.(1)—The form of the teeth scattered over the surface of
the large flat oval dentigerous bone, figured in Pl. 47, fig. 3, suggested
the name of the extinct genus of fishes, which the present remarkable
fossil unequivocally indicates. It measures four inches and a quarter
in length, two inches and a quarter in breadth, and seven lines in
depth at the thickest part, which is at the middle of the plate. The
teeth are distributed irregularly over the whole of the upper surface,
and in pretty close contact, except where they have been displaced
by attrition, as from the large flat and polished surface at the anterior
part of the bone, or where they have been broken or shed, at the in-
terspaces of the unworn teeth. These all present the same form and
nearly the same size: they have a hemispherical smooth and polished
crown, and are inserted each by a large short hollow conical tang or
base into a socket of corresponding form and dimensions. The crowns
of some of the teeth project two lines beyond the surface of the bone,
others are just protruding above that surface ; indicating that they are
shed and renewed in vertical succession: the middle of the edentulous
anterior surface is worn smooth and flat, but its circumference is
pitted with the remains of the sockets. On the under surface of the
dental plate there is a regular elliptical space occupying four-fifths of
that surface, and defined by a raised margin ; this indicates the place
of attachment of the plate to another bone of the skull, most
probably, as in the Glossodus and Sudis to a median bone of the
hyoid system.

The teeth of the Pisodus are adapted for crushing shells, crusta-
cea, or vegetable substances; their texture is extremely dense, and
corresponds with that of the teeth of the Microdon.

56. Phyllodus.(2)—The dentigerous plates, which have sug-
gested to Professor Agassiz this name for the extinct species of

(1) wioov, a pea, Ode, a tooth. (2) pddAor, a leaf, 908¢, a tooth.

PHYLLODUS. 139

fish to which they have belonged, present a contour somewhat like
that of a simple leaf: the posterior part being contracted, as if
for the attachment of a stalk, the opposite end being rounded and
thinned off. The largest specimen of this fossil, which I have
yet seen, is figured in Plate 47, fig. 1 and 2. It consists of an
anchylosed mass of superimposed more or less flattened, lamel-
liform teeth, of which those forming the middle longitudinal row are
the largest, and present a transversely elongated oblong figure: these
are surrounded by smaller oblong dental lamellz, irregularly placed,
and diminishing in size to the circumference of the mass, where they
exchange the oblong fora circular form. All the dental lamellz are con-
vex on the upper surface (fig. 1) and concave on the under surface (fig. 2.)
On a superficial inspection the middle lamellz might be supposed to be
as thick as the mass of which they form part, but this is evidently not
the case with the marginal lamelle ; these are seen to be superimposed
in nearly vertical tiers, like the lamellz of the maxillary dental mass
in the Diodon. The number of lamelliform teeth in each pile, increases
from the anterior to the posterior part of the mass, where, in the
specimen figured, nine or ten denticles might be counted in a single
tier. To ascertain whether the large middle teeth were also lamelli-
form, and similarly superimposed, I had made, by the kind permission
of Mr. Bowerbank, a vertical section through a dental mass of the
same species of Phyllodus as the one figured, and found that the same
lamellar condition and arrangement pervaded all the teeth. Between
the upper and the lower of the two longest median denticles, there
were interposed six plates similar to the two superficial ones of which
the upper surface is shown in figure 1, and the lower surface at
fig. 2. A magnified view of a thin transparent slice taken from the
surface of the vertical section, including a portion of four of the super-
imposed plates of two contiguous piles, is given at Plate 44, figure 2.
It displays a structure analogous in essential points to that of the
pharyngeal teeth of the Scarus. If, for example, the cone, of which
a section is figured at Plate 52, were flattened down and rolled out,
it would form a lamelliform tooth composed of a layer of enamel and
a layer of dentine of equal thickness, supported on a thinner layer of
coarse cellular bone. Such is the microscopic texture of a single

140 PHYLLODUS.

lamelliform tooth of the Phyllodus but these teeth being piled one
upon the other, the entire mass presents a succession of strata of
the three substances.

The osseous substance (a, fig. 2, Pl. 44), is characterized by the
large, reticularly anastomosing medullary canals, without radiated cells
in their interspaces, which are peculiar to the structure of the bones
and ossified basis of the teeth in fishes. ‘The dentine (}) consists
of numerous, close-set calcigerous tubes and the clear uniting
substance ; the tubes are characterized by their straight, and parallel
course ; at the middle part of the plate, they are directed vertically to
its plane, and at the margins which are bent down, they incline so
as to maintain the same relative position to that part of the surface
of the plate; their diameter does not exceed jth of an inch;
their subdivision into pencils of smaller tubes takes place nearer
to the enamel than usual. I could plainly discern the anastomoses
of these divisions of the calcigerous tubes in some parts of the sec-
tion. The enamel c, which, as in the denticles of the Scarus and
many other fishes, closely approximates in structure to the dentine,
exhibits, however, much less parallelism in the course of its compo-
nent tubes in the Phyllodus; but these are as numerous and
distinct, though somewhat more minute than those of the true
dentine.

It would seem that in the matrices or pulps of both the ena-
mel and dentine, the progress of calcification followed the same
law, viz: from the circumference to the centre, or from the surface
to the attached base of the pulp. In specimens of the Scarus pre-
served in spirit, and in other fishes, I find that neither surface of the
formative pulps is free, for, while that which may be termed the base
of the enamel-pulp is adherent to the capsule, and while the base of
the dentinal pulp turned in the contrary direction, coheres with the
mucous surface from which it was originally developed, the opposite
surfaces of both pulps firmly adhere to one another. It is at this
surface, however, in each case that the process of calcification com-
mences. The linear groups of cells being here irregular in their
position, form, by their confluence, tubes as. irregularly disposed ;
but as the deposition of the hardening salts proceeds, the tubes

|
|
|
|

SALMONOIDS. 14i

become more regular and parallel. This parallelism has taken place
in the Phyllodus, much sooner in the dentine than in the enamel,
as is the case in the Scarus, and hence the difference of the disposi-
tion of the fine calcigerous tubes, which mainly distinguishes the
texture of the dentine and enamel in fishes.

The fossils here described very clearly exhibit the effects of
attrition and waste at one extremity, and of renovation at the
opposite end of the dental mass; but they likewise show the
same antagonist influences operating at the upper and the lower
surfaces of the mass; the work of destruction and of reproduc-
tion has proceeded in both the longitudinal and_ vertical
directions. As the lamelliform teeth at the top of each pile were
worn away, the loss was supplied by new lamelle added to the bottom
of the pile, according to the mode of reproduction described in the
dental system of the Diodon. But as the attrition was greatest at
the anterior extremity of the dental plate, and the power of repro-
ducing the lamellae in the vertical direction limited, the loss of
entire piles of teeth was supplied by the addition of new piles to the
posterior extremity of the dentigerous plate, according to the mode
of reproduction described in the pharyngeal teeth of the Scarus. In
the Diodon we see illustrated the law of succession of the permanent
to the deciduous teeth in the Mammalia, viz: in the vertical direction,
but the process is much more frequently repeated. In the Scarus, the
course of succession of the true molars in the Mammalia, viz: in the
horizental course was followed. In the Phyllodus, both kinds
of displacement and succession are exemplified ; and the peculiarities
of the Diodon and Scarus were combined, with the same frequent and
uninterrupted repetition of the renovating processes, in a single
dentigerous bone of that extinct species.

SALMONOIDS.

57. Many fishes of the Salmon tribe, like those of the Clupeoid
family, have the superior margin of the mouth formed in a greater or
less degree by the superior maxillary as well as by the intermaxillary
bones, both of which, excepting in the edentulous species, as the
Salmo edentulus,(1) Bloch, are armed with teeth.

(1) The type of the genus Anodus of Spix.

142 SALMONOIDS.

In the Prochilodus, however, both these and the bones of the
lower jaw are feeble and are imbedded in the thick fleshy lips, to
which, and not to the bones themselves, the minute, flexible,
incurved, bristle-like teeth, characteristic of the genus, are attached :
they are arranged in a single close-set row.

The superior maxillary bones are edentulous, and are placed
backwards, transversely to the angle of the mouth in the subgenera
Schizodus, Serrasalmo, Myletes, and Xiphostoma; but in the true
Salmones and other cognate genera, they support a part, and often
nearly the whole of the teeth of the upper jaw.

In the Salmonide of the River Nile, which belong to the genus
Citharina of Cuvier, the maxillary teeth are nearly as fine and as
close-set as in the Chetodonts, but their free extremity is forked.
The pharyngeal bones are beset with velutine teeth.

In the Schizodus, the intermaxillary and premandibular teeth are
broad, and of the incisive type of form, with a crenate superior
margin. In the Serrasalmo, (Pl. 48, fig. 8,) the corresponding teeth
preserve the compressed form, but have a sharp apex, a broad base,
and trenchant and finely serrate edges; these lancetted teeth are
arranged ina single series both above and below.

The Myletes is remarkable for the prismatic three-sided figure
of its teeth, the working surfaces of which are cuspidated by the
production of the angles into sharp points, (Pl. 48, fig. 10). There
is asingle series of these teeth in each premandibular, and a double
row in each large intermaxillary bone ; behind the two median*teeth
of the lower jaw there are two simple conical pointed teeth ; similar
but much smaller pointed teeth are scattered over the pharyngeal bones.

In the genus Raphiodon(1) the teeth, as the generic name implies,
are long, slender, and extremely sharp-pointed ; they are implanted in
the short intermaxillary, the superior maxillary and the premandibular
bones ; shorter teeth of a similar shape, alternate with the longer ones ;
the pair next the symphysis of the lower jaw, exceed all the rest in
size.

The elongated jaws of the species of Xiphostoma are provided

with a single row of small, sharp-pointed, slightly-reflexed teeth ;
those on the alveolar border of the short superior maxillaries

(1) pagic, acus, 8dove, dens,

SALMONOIDS. 143

which cross obliquely the angle of the mouth, are directed forwards.
In the genus Saurus, the mouth presents the anomalous condition
among fishes of edentulous intermaxillaries, with a formidable array
of teeth in the upper jaw, supported exclusively by the superior
maxillary bones ; these meet at the middle line, and the small inter-
maxillaries, which are recognizable by their characteristic ascending
process, are placed above and parallel to the median extremities of
the maxillary bones; the teeth are slender, conical, and very acute ;
they are arranged in three or four rows, and form conical groups, with
the longest tooth in each placed innermost; these teeth have their
apices slightly expanded. Similar spear-shaped teeth are arranged on
the premandibular bones below; and likewise crowd the palate,
the tongue, the branchial arches, and the upper and lower pharyn-
geals.

The disposition and usual form of the teeth in the typical genus
Salmo are represented in a diminished view of them in the common
salmon, as seen in looking into the cavity of the open mouth, (Pl.
48, fig. 9). The teeth all present the same simple form, short,
stout, pointed, and incurved ; from four to five are implanted in each
intermaxillary bone, the remainder of the single row which arms the
upper margin of the mouth, being supported by the superior maxillary
bones. In the young salmon there are two or three teeth on each
side of the anterior part of the vomer; but, as growth proceeds, they
are reduced in number, and finally disappear in aged fish; each
palatine bone supports a single row of teeth, nearly parallel with,
but smaller than, those of the maxillary rows; there is a single row,
on each premandibular bone ; and a double row united by a crescent-
shaped series on the anterior part of the tongue. The pharyngeal
bones are armed with similar teeth.

The principal difference observable in the allocation of the teeth
in the species of Salmo obtains in the vomer; upon which, in the
salmon-trout and common trout(1) for example, the teeth are extended
backwards in a row, and deeply indent the surface of the tongue
between the two lateral rows of lingual teeth.

The teeth are anchylosed by their bases to the several dentigerous

(1) Mr. Yarrell has given a figure of the dentition of the common trout in vol. ii, p. 3, of
the British Fishes.

144 CYPRINOIDS.

bones, and are separated by intervals usually greater than their own
breadth ; in their mode of development, shedding, reproduction and
microscopic structure, they so closely resemble, in both the Clupeoid
and Salmonoid families, those of the Pike,(1) as not to require further
description in this place. The mutual affinity of the herring
and salmon-tribe, is not only manifested in that part of their
anatomy which is described in the present work, viz: the very
general distribution of the teeth, and especially their location in the
superior maxillary bones, but is also illustrated in other parts of their
organization, and is regarded by M. Agassiz as of so intimate a
nature, that he has combined the Clupeoids and Salmonoids of
Cuvier into one natural family under the name of ‘‘ Halecoids.’’(2)

CYPRINOIDS.

58. The family of Cycloid fishes, whose dental system we next
proceed to consider, is as remarkable for the paucity of teeth and the
edentulous character of the bones of the mouth, as are the Hale-
coids, for their general and formidable armature. It is only, in
fact, in one small section of the Cyprinoids that any teeth at all
are present on what may be considered the true bones of the mouth;
these being restricted in the rest of the carp-family to the bones of
the pharynx.

The exceptional genera with maxillary as well as pharyngeal
teeth are Anableps, Artedi, Pecilia, Schn., Lebias, Cuv., Fundulus,
Lacep., Molinesia, Less., and Cyprinodon, Lacep. ; all of which are
erouped together by M. Agassiz under the name of Cyprinodonts.

In the Anableps, or ‘‘ four-eyes,” the intermaxillary and pre-
mandibular bones are furnished with delicate setiform teeth, like
those of the Salmonoid genus Citharina; the pharyngeal teeth are

(1) Cuvier cites the salmon and the pike together as examples of fishes that have teeth on
all the situations of the mouth where teeth can be placed. “ Il y a des poissons qui ont des
dents dans tous les endroits de la bouche ou il peut y en avoir; tels sont le saumon, le
brochet.”—Lecons d’ Anatomie Comparée, Ed. 1835, tom. iv, p. 337. But besides the pharyn-
geal, branchial, hyoid, vomerine, palatine, premandibular, intermaxillary and maxillary teeth,
(the last are wanting in the Pike), there are examples of fishes, as the great Sudis and
Glossodus that have in addition to all these teeth, both pterygoid and sphenoid teeth.

(2) It is not to be understood that the Pisodus or Phyllodus, the dentigerous plates of

which have been described, for the sake of convenience, after those of the Glossodus, &c., belong
to the Halecold family, although this is probable as regards the Pisodus.

CYPRINOIDS. 145

small hemispherical tubercles. The jaw-teeth of the Pecilia
are also minute, but somewhat stronger than those of the Ana-
bleps. Those of Lebias are characterized by their dentated margin.
In the Fundulus, the anterior teeth in both the maxillary and_pre-
mandibular bones are conical and recurved, while the hinder ones
are villiform. In the genus Cyprinodon all the teeth are ‘ en ve-
lours.”(1)

The ordinary bones of the mouth in ail the true Cyprinoid fishes,
of which the carp and roach may be taken as types, are devoid of
teeth ; but in some species there may be perceived upon the alveolar
border of the jaws, as along the intermaxillaries in the barbel, a band
of minute, close-set and pretty firm papillae, which may be regarded
as the uncalcified analogues of a series of villiform teeth, like those
of the Cyprinodonts. The only true teeth, however, in the present
division of the family are situated on the inferior pharyngeal bones,
which work against each other, or against a very hard upper pha-
ryngeal dental plate, which is fixed in a depression on the inferior
surface of the basilar bone, and may thus be regarded as an occipital
tooth.

The dentigerous pharyngeals are a_ pair of arched bones
which may be regarded as the last of the lateral branches of the
hyoid apparatus, or as a fifth pair of branchial arches supporting
teeth instead of gills. They are smaller, stronger, and more curved
than the true branchial arches which are anterior to them; they bound
the sides and lower part of the pharynx; their anterior and inferior
extremities are connected together by ligaments, allowing a yielding
motion ; but I have found them sometimes anchylosed together in old
carp(2) ; their posterior and superior extremities are attached by
ligaments and muscles to the occipital region of the skull.

Besides the movements backwards and forwards, the pharyn-
geals admit of being approximated and divaricated, and these
movements are produced by very powerful muscles. One of these
muscles, (b, Pl. 57, fig. 1, in which the armed pharynx of
the barbel is represented as seen when looking down upon the base

(1) Cuvier, Loc. cit. p. 354.
(2) A portion of the left pharyngeal, so anchylosed to the right, is represented at
Pl. 57, fig. 7
L

146 CYPRINOIDS.

of the skull), arising from the outer margin of the anterior and
inferior moiety of the pharyngeal bone, passes inwards below the
pharynx and expands to meet its fellow at a strong median raphé.
This muscle, which is more especially developed in the barbel,
gudgeon, and those Cyprinoids which have the teeth formed for
piercing and lacerating, besides approximating the pharyngeal bones
at the median line, at the same time draws them forwards. The
antagonist muscle (c) arises from the descending spine of the basi-
occipital bone, and passing outwards and forwards, expands to be
inserted along the outer margin of the posterior half of the pharyngeal
bone ; this muscle while it draws back the pharyngeal bones, at the
same time, from the mode of attachment of the bones to the skull,
slightly divaricates them.

The teeth are attached to the inner side of the pharyngeal bones
by a confluence of their basis with the osseous substance. It might be
supposed that the food of the leather-mouthed fishes, as the Cypri-
noids without maxillary teeth are commonly termed, would be so
nearly the same, that the few teeth which were lodged in the fauces
would present much sameness of form; but this is by no means the
case, as the selection of pharyngeal teeth from the Cyprinoid genera
figured in plate 57 demonstrates. The laniary type is best shown
in the barbel (fig. 1 & 2) and the molary type in the carp (fig. 6 & 7) ;
indeed, the large lower ‘pharyngeal tooth of this species exhibits,
before it is too much worn, the most complicated triturating surface
of any single tooth in the osseous fishes, and one which most closely
resembles that of the molars of certain herbivorous mammalia.(1)

The barbel (Barbus vulgaris), which feeds on slugs, worms and
small fishes, requires teeth so shaped as to pierce and lacerate the skin
of its prey, and to tear them into fragments capable of passing the
narrow cesophagus : in this species they accordingly are elongated, coni-
cal, slightly and somewhat irregularly bent, arranged in three rows, and
increasing in number and size from the innermost to the outermost row;
the teeth in this row are generally five in number, separated by inter-
spaces, so as to interlock, when the pharyngeal bones are approximated,
as represented in plate 57, fig. 1; the probe (a) shows their relative

(1) “Inthe carp, the crowns of the teeth are observed to be so worn down as to have the
appearance of the crowns of the molar teeth of the hare.”—Yarrell, 1, c. Introduction, p. xix.

CYPRINOIDS. 147

position to the entry of the cesophagus, and it may be seen how the
teeth must sift and lacerate the alimentary substances in their passage
through the pharynx.

In the Gudgeon, (Gobio), which feeds on worms, aquatic larve
and small mollusca, the pharyngeal teeth are conical, slightly curved
at the extremity and arranged in two rows. In the Acanthopsis, the
pharyngeal teeth are sharp-pointed and placed in asingle row. In the
Loach, (Cobitis), which feeds on aquatic larvee and worms, the pharyn-
geal teeth are slender and are chissel-shaped at the extremity. The
same scalpriform type is seen in the teeth of the genus Rhodeus.

In the genus Schizothoraz lately established by the laborious Ich-
thyologist I. J. Heckel for certain Cyprinoid Fishes from Cachmir,
the pharyngeal bones have three rows of teeth, two in the first, three
in the middle, and five in the third or posterior row, which last are the
strongest, all somewhat elongated, oblique, and with the extremity
slightly curved. The outer row of pharyngeal teeth are figured in situ,
on the right pharyngeal bone of the Schzothorax esocinus, Heck. (fig.
4) where they exhibit the shape most common in the genus: in Schi-
sothorax curvifrons, Heck. the pharyngeal teeth resemble long inverted
cones, the expanded, but originally pointed summits being soon worn
down so as to appear truncated.

In the Cyprinus Nasus, L., similarly shaped teeth are arranged
in a single row, nine in number, on each pharyngeal bone ; the inferior
ones being somewhat larger, with a narrow but flat triturating surface,
supported upon a slender pedicle.

In most of the species of Leuciscus, as the ide, the chub,(1) the
dobule, the dace, the minnow, and the roach, (fig. 4) the pharyngeal
teeth are subconical, slightly curved at the apex, and more or less
truncated, in an oblique direction: their food, which includes the softer
parts of aquatic herbs with worms and insects in different stages,
corresponds with this approximation to the molar type. Some species
of Leuciscus, however, as the L. Scardinius, Bonap. have the pharyn-
geal teeth slightly dentated along theinternal margin. The Leuciscus
erythrophthalmus has two rows of seven teeth on each pharyngeal bone ;

(1) A friend informs me that the larger chub take the spinning minnow and gudgeon freely,

and mash them out of all shape.

Lie

148 CYPRINOIDS.

the five outer ones are the largest and have the triturating surface
very elegantly dentated.

The bream (Brama) has five pharyngeal teeth in a single row on
each side; they are moderately large, compressed and obliquely
bevelled to a cutting edge, which works against the occipital tooth
above. The teeth of the tench (Tinca) are similar to, but relatively
broader than those of the bream: their oblique triturating surface
is produced internally into a slightly hooked point, as represented
in Pl. 57, fig. 5; they are arranged in a single row, four or five on
each side of the pharynx, and work against a thick and dense tri-
angular superior pharyngeal plate (a) imbedded in the basi-occipital
bone. Similar pharyngeal teeth have been found to characterize two
extinct species of tench, viz. Tinca leptosoma and micropygoptera,
Agass.

Both the tench and carp combine a large proportion of vegetable
matter, derived from aquatic plants, with worms and the larve of in-
sects, for their ordinary food ; but the carp, (Cyprinus Carpio), from
the nature of its dentition ought to be the most herbivorous species
of the family. In this species, the pharyngeal teeth are arranged in
two or three rows; the innermost represented by a single tooth, the
second having sometimes two teeth of larger size ; and the outer row
including three or four, which are the largest and most complicated,
especially the middle one. The anterior and inferior tooth of this row
has a round crown, with the centre raised into a small point; the
rest are terminated by a flattened grinding surface, sculptured with
transverse undulating furrows. These are not very deep, so that
they disappear, as shown in Pl. 57, fig. 6, when the tooth is mo-

derately worn down. Fig. 7, exhibits the grinding surface on a

tooth recently anchylosed to the pharyngeal bone, and fig. 8 shows
the inferior surface of the furrowed crown of an incompletely formed
tooth as seen on looking into the wide and open pulp-cavity. The
incudeal triangular dental plate, implanted in the occipital bone, is
extremely dense, and presents a clear transparent amber-colour in the
carp as in the tench; but its contour is more equilateral in the carp,
and the surface which receives the appulse and friction of the pharyn-
geal molars is flatter.

It is sufficiently obvious from an inspection of the powerful

ee ee ee

CYPRINOIDS. 149.

muscles which work the pharyngeal bones, that the teeth, whether
adapted for piercing or lacerating aquatic animals, or for triturating
vegetable substances, must be used with such force as soon to be ren-
dered unserviceable, and to require renewal. I had formerly made
sections of the dried pharyngeal bones of our common Cyprinoid
fishes, under this cofiviction, in quest of the hidden germs of the
replacing teeth, but without success. A subsequent acquaintance
with the place of development of the successors to the maxillary teeth
in certain fishes, as already described in the pike, alepisaur, &c., led
me to renew the search in the substance of the thick and soft mucous
membrane of the pharynx surrounding the pharyngeal bones, and
I soon detected the germs of the successional teeth in this situation. (1)
The primitive papilla first developed from the surface very soon
sinks into the substance of the mucous membrane, and becomes.
inclosed by a complete capsule. I have not been able to detect in
the carp or tench an enamel-pulp developed from the surface of the
capsule covering the crown of the contained tooth: this adheres only
to the dentinal pulp, and by means of its base to a part of the circum-
ference of the capsule. The hollow cap of dentine of a half-formed.tooth
is easily displaced from the formative pulp in consequence of its dense
structure presently to be described ; but the surface so exposed when
viewed by a strong reflected light, with a 4 inch focus, is clearly seen.
to be an artificial and lacerated surface: it is minutely honey-combed,
by the rupture of the calcified from the uncalcified portions of the
nascent calcigerous tubes; and the subjacent and still unconfluent
cells, are seen torn from the substance of the pulp, and scattered irre-
gularly over its surface. When the pulp of the crown of the tooth is
completely calcified, the margin of its base begins to assume a liga-
mentous density, and attaches itself to the margin of the pharyngeal
bone, near the base of the tooth about to be displaced. I have not
observed any further stage in the singular process of transference of
the loosely imbedded tooth from its mucous capsule to the bone with
which it is destined to form a common and continuous part.

In this process of union, which is analogous to that of the sepa-
rated portions of a fractured bone, the question suggests itself, by what

(1) See Pl. 57, fig 6, in which a young tooth c is exposed by a refloction of part of its

mucous capsule, b.

150 CYPRINOIDS.

means does nature ensure in the often repeated process, that the
detached osseous parts in the fish should always be well set, and
the tooth transferred, not only to its right place in the series, but to
its right relative position upon the bone? The marvel is not diminished
when we consider that immobility is quite impracticable during the
uniting process, that the fish must eat with the teeth that remain
fixed, and that the bone to which the new tooth is in process of
becoming anchylosed must be daily rotated backwards and forwards.

The pharyngeal bones in the Cyprinoids have rarely the thick-
ness adequate to the lodgment of the matrix of a tooth beneath the
one in place; in this respect they differ materially from those of the
Labroid fishes: they are, on the contrary, in general, so thin that
they are perforated on the side opposite the anchylosed base of the
teeth in place, and the nerves and vessels of the remaining pulp
pass by these orifices directly into the cavities of the teeth.

In all the Cyprinoid fishes the pulp-cavity of the pharyngeal tooth
is extensive, and traverses almost the whole of the tooth in the
barbel and other species, where the teeth present the elongated laniary
form.- The whole of the dentine is composed of fine calcigerous
tubes, analogous to the structure of that of the simple mammalian teeth:
these tubes in the barbel radiate from the narrow and elongated pulp-
cavity, with a general course at right angles to the surface of the tooth,
and consequently to the axis of the tooth: their diameter is goth of
an inch at their origin with interspaces of thrice that diameter ; they

proceed with a slightly but regularly undulating course, branching —

dichotomously, but not frequently ; and the branches, after slightly

diverging are continued nearly parallel with each other, and in the —

direction of the trunk, until they approach the peripheral and denser —

:

portion of the tooth; here they diverge and decussate each other, —
and present a general inclination towards the base of the tooth. In —

plate 58, fig. 1 is shown the origin of a portion of the calcigerous
tubes from, and in connection with, the uncalcified portion of the
formative pulp, magnified 600 linear diameters ; the honeycombed
surface of the pulp, from which some of the calcified tubes have been
displaced is shown at the lower part of the figure. The clear calcified
walls of the tubes are scarcely, if at all, discernible in sections, which,
like the present, are taken parallel with their axis ; and the calcifying

.
?
f
|
i
i
1
‘
}

CYPRINOIDS. : L5I

cell or nascent tube appears to project from the surface of the pulp
in a pyramidal form at the base of each tube, and to pass by a con-
tracted apex into its cavity; this is, however, a deceptive appearance, for
its walls are in continuity with the transparent calcified walls of the
dental tube, and the more opake cavity of the cell alone communicates.
with the corresponding cavity of the calcified tube. The true diame-
ter of the calcigerous tube, including its transparent parietes with its
sub-opake cavity, nearly equals that of the superficial elongated cell,
at the expense of which it is about to be developed.

From the circumstance of the section, here figured, including two
or three layers of the calcigerous tubes, their interspaces are made to
appear smaller and their decussation to commence sooner and to be
more frequent than is really the case in any given layer.

In fully formed teeth calcification proceeds in the ligamentous
basis of the pulp from the circumference towards the centre ; the union
of the tooth to the pharyngeal bone takes place in the laniariform
teeth, as in those of the barbel, by numerous slender, wavy, subcylin-
drical processes, corresponding with the former fasciculi of the liga-
mentous substance ; these calcified processes are implanted, like piles,
into the subjacent bone, slightly diverging as they penetrate it, and
gradually exchanging in it their dentinal for an osseous texture. The
centripetal course of calcification proceeds more rapidly at the basis.
than in the body of the tooth, and the pulp-cavity thus becomes
closed below, (excepting at a small central aperture for the passage of
the nerve and vessels), while it remains widely open in the body of the
tooth. <A section of part of the base of a pharyngeal tooth of the
barbel, exhibiting the numerous roots or fangs by which it is anchy-
losed to the bone, and the widely open pulp-cavity at the base of the
projecting body of the tooth, is represented, as seen by a moderately
magnifying power (1 inch focus of Ross’s compound achromatic) in
plate 58, fig. 2: the figure is in the situation of the pulp-cavity :
opposite the right hand is a portion of the thin dentinal wall of the
base of the exserted part of the tooth, in which the transverse course
of the calcigerous tubes is indicated.

152 TRACHINOIDS. LOPHIOIDS.

TRACHINOIDS,

59. The dental system of the fishes of the family of Trachinoids
offers few particulars deserving attention: and I shall briefly allude
to the modifications which are exemplified in two of the genera refer-
able to this group.

In the Weevers (Trachini Draco, et Vipera) the intermaxillary,
premandibular, palatine, vomerine and pharyngeal bones are beset
with minute villiform teeth: they are arranged in two longitudinal
bands upon the palatines, and form a single transverse band in front
of the vomer. The tongue is edentulous.

In the Star-gazer, (Uranoscopus scaber), an exotic species of
Trachinoid fishes, the intermaxillaries, pharyngeals and vomer, have
their masticatory surfaces roughened like a rasp by numerous small,
but more strongly developed teeth: those on the palatines are still
larger: and the premandibulars support eleven strong canines
separated by intervals, and placed behind a small patch of villiform
teeth near the symphysis.

In microscopic structure and mode of reproduction the teeth
of the Weevers resemble those of the Pike.

LOPHIOIDS.

60. In this singular family of fishes in which the pectoral fins are
developed into terrestrial locomotive organs, the peculiarities of the
dental system will be principally illustrated by a description of the
teeth of one of the largest species, which is at the same time a native
of our own coasts.

The Angler, (Lophius piscatoriws), has teeth on the intermaxillary,
premandibular, palatine, vomerine, and pharyngeal bones. They are
of an elongated, conical, sharp-pointed, and slightly incurved form,
presenting merely differences of size, degree of curvature, and mode
of fixation, but all bespeaking the predatory and carnivorous habits of
the species.

In the upper jaw, the teeth are congregated in three or four ir-
regular rows at the median or upper third part of each intermaxillary
bone, and form a single and regular series along the lower two-thirds.

LOPHIOIDS. 153

These latter, which may be termed the serial teeth, are from fifteen
to eighteen in number, short, strong, pointed and incurved ; of nearly
equal size and placed at regular distances from each other.(1) The
two outer irregular rows of the median intermaxillary teeth are
somewhat larger and are directed forwards ; the inner rows at this
part contain the longest teeth and their points are turned back ; but
they are moveably connected with the bone by a mechanism which
_ will be described when treating of those of the lower jaw.

The premandibular teeth can hardly be said to form a regular
series, but are scattered along the alveolar margin of the lower jaw
in an irregular quincuncial disposition ; being three, four, and five
deep towards the middle and anterior part of the lower jaw, in full
grown specimens. The largest teeth in the mouth of the Lophius
are the innermost and median ones of the premandibular bones ; they
decrease in size as they are situated more laterally. The transverse
section of the body of these laniariform teeth is nearly circular, but
at their broad and expanded base it is triangular with one of the angles
directed outwards. The palatine teeth form a single row, near the
outer edge of the bones, the median ones being the largest; the
cluster of two or three teeth on each side of the expanded anterior
extremity of the vomer seem to terminate the palatine series.

The superior pharyngeal teeth are arranged in three groups upon
as many separate bones on each side; each group describes a curve
with the convexity turned forwards ; the teeth of the posterior bone
are the smallest. The inferior pharyngeal bones are two in number,
and have the teeth arranged in a double alternate row along each
margin.

The pharyngeal, palatine, and vomerine teeth are fixed by an-
chylosis to their respective bones ; this is also the case with most of
the intermaxillary teeth, and with the exterior teeth of the lower jaw ;
but the remainder, and especially the large posterior fangs of the
lower jaw, are attached by means of elastic ligaments to the margins
of slightly elevated alveolar processes. These ligaments are prin-

(1) In the Lophius Upsicephalus the corresponding serial intermaxillary teeth are described
as being short, delicate and cylindrical, by Dr. A. Smith in his excellent “‘ Zoology of South
Africa.”

154 LOPHIOIDS.

cipally inserted into the inner straight margin of the base of the
tooth, from which their glistening fasciculi radiate to be implanted into
the jaw. The rest of the base of the tooth is connected at its cireum-
ference with more lax and yielding fibrous bands, and with the
mucous membrane of the mouth, which covers the alveolar tract in the
interspaces of the teeth. To any attempt to bend these teeth out-
wards resistance is offered by the internal ligaments above described,

and by the pressure of the anterior angle of the base of the tooth

against the alveolar process or raised tubercle on which it rests ;
but the tooth readily yields to a force acting in the opposite direction,
and the largest and most prominent teeth can be bent inwards and back-
wards so as to point to the gullet when the hand is pressed over them
in the direction a body would take when drawn into the mouth to be
swallowed: the moment, however, this force ceases to act, the teeth
recoil to their erect position, as if operated on by a spring. If every
thing attached to the base of the tooth, excepting the internal pyra-
midal band of ligamentous fibres, be removed, the tooth, after being
bent down, returns with the same force to the erect position ; it is,
therefore, to this band that its resilience is due.

The teeth of the Lophius exhibit, as stated in the first chapter,
the higher type of dental structure: such as characterizes the teeth
of sauroid fishes and of most reptiles and mammals. The fully-
formed teeth are constituted by a single system of calcigerous tubes,
radiating from a single sub-central pulp-cavity: this is widely open
at the base of the tooth, but soon diminishes by the convergence of
its sides, which arch inwards and meet at the basal third of the
tooth, whence the pulp-cavity is continued as a mere line to near its
apex. The course of the calcigerous tubes is unusually uniform,
throughout the entire length of the tooth. On leaving the pulp-
cavity they ascend obliquely and then incline in a graceful curve to
the side of the tooth, to the exterior of which they are continued, in
the greater part of their course in a straight line, and nearly at a right
angle to that surface. This description applies to what I have termed the
primary curvature of the calcigerous tubes ; the secondary curvatures

that each tube exhibits throughout its whole course consist of —

undulations, which are coarser, more angular, and less regular than

=

LOPHIOIDS. 155

in ordinary mammalian dentine. The tubes divide and subdivide
dichotomously four or five times in their progress to the perhiphery ;
their diminution of diameter is not proportionate to their degree of
subdivision: their diameter at their origin is ;jth of an inch ; at their
terminations it is zo th of an inch: their interspaces equal three or
four of their diameters. The small lateral branches given off at the
angles or sharp bends of the secondary undulations into the clear
uniting substance are unusually conspicuous. A very small propor-
tion of the calcigerous tubes proceeds from the apex of the linear
pulp-cavity in the axis of that cavity. The apex of the entire and
newly-developed tooth is coated with a thin, dense, white layer of an
enamel-like substance, which is soon lost. A line of dentinal tissue,
more opake than the rest, runs parallel with the pulp-cavity through
the dentine about half way between the cavity and the external
surface; this line, analysed with a sufficiently deep power, is
seen to result from an unusual number of lateral branches sent
off from a certain extent of the calcigerous tubes along the same
parallel line, which branches anastomose together and dilate into
small opake cells in the interspaces of the tubes from which they
are given off.

Owing to the extent of the secondary inflections of the calcigerous
tubes, and the difficulty, if not impossibility of obtaining a section
which does not include three or more layers, they exhibit in every
part of the tooth the appearance of an universal plexiform inter-
weaving ; this character, in combination with their general transverse
course and the length of the linear pulp-cavity, might serve to
distinguish the tooth of the Lophius from that of a reptile or mammal
which it otherwise might most nearly resemble in general form and
texture.

The new or successional teeth are found recumbent in different
stages of development, some inclosed in their capsules, others with
their apices projecting more or less ‘from the lax gelatinous mucous
membrane covering the broad alveolar margin of the jaws. When this
membrane is stript off, the successional teeth and their matrices are
brought away with it; their basis being inserted into its substance,
just as the quills of the porcupine are attached to the skin. In the

156 BLENNIOIDS.

exterior teeth, ossification extends along the ligamentous base of
the matrix and they are thus fixed, as in the pharyngeal teeth of
the barbel and many other fishes, by continuous anchylosis to the
substance of the supporting bones; but it is peculiar to the Lophius
to have this process arrested in certain teeth, which continue to be
attached by elastic fibres instead of osseous piles, whereby the
ordinary prehensile and destructive armature of the mouth is
rendered still more effective by the additional mechanism of a
spring-trap.

An exterior view of the maxillary teeth in situis given by Mr.
Yarrell, at p. 274, vol. 1, of his excellent work on British Fishes; I
have figured a portion of the anterior part of the left premandibular
bone and teeth, of the natural size, viewed from within, at Pl. 56,
fig. 1; the second tooth of the inner row is represented as bent
backwards, and the elastic ligaments at the inner side of the base
are shortened and curved by the pressure; the dotted line shows
the ordinary position to which the tooth is returned by the resiliency
of the ligaments when the bending force is removed. Some of the
shorter, inflexible exterior teeth are shown ata a; and the larger,
moveable, inner teeth at 0 b.

The smaller species of Lophioids, forming the genera Antennarius,
Malthea and Halieutea, have the teeth reduced to the rasp-like or
villous character, and in the latter genus, which includes the Lophius
muricatus of Shaw, the palatines and vomer are smooth and eden-
tulous.

BLENNIOIDS,

61. The fishes of this family, like those of the preceding, have no
common condition of the dental system. The Blennies (Blennws,
Cuv.) present a close-set single row of long, fixed teeth, of which one

is commonly more developed than the rest, and stands up, like a canine |

tooth, at the posterior extremity of each semi-circular series: there
are no palatal or lingual teeth ; those of the pharyngeal bones are
similar to the maxillary teeth, but are moveable and disposed in
two pectinated rows. In the Blennechis ancylodon the number of

a

awe i .

BLENNIOIDS. 157

elongated maxillary teeth is greater than in the true Blennies. In
the Chasmodes, the teeth of the maxillary row, which extends along
only the anterior part of the jaws, are of equal size. The maxillary
teeth of the Salarias, with the exception of the single canine which
terminates each end of the dental series of the lower jaw, are extremely
thin and slender, and are hooked at the extremity ; but they are
chiefly remarkable in being attached, like the teeth of the Squaloids,
to the gum only, or membrane covering the intermaxillary and pre-
mandibular bones, so that they readily yield to pressure; there are
about two hundred of these teeth in each jaw. The palatine and
lingual bones are edentulous. In the genus Clinus there are always
teeth on either the vomer or palatine bones, in addition to those
supported by the jaws ; the latter are of two kinds, an outer close-set
row of longer pointed teeth, and behind these a band of villiform
teeth. The Myzodes are devoid of palatal teeth; and have only a
single row of teeth on the jaws, the largest being in the middle, and
not at the ends of the row, as in the true Blennies. The butter-fish,
(Gonellus vulgaris), has a row of conical, but rather blunt teeth on
each jaw, and behind the middle of that of the upper jaw there is a
second short row. There are some very small teeth in front of the
vomer ; the membrane covering the tongue and palatine bones is
beset with firm papille, but the calcifying process has not converted
them into teeth.

The viviparous Blenny, (Zoarces), has conical teeth arranged in
two or three rows at the middle of the upper and lower jaws, and in
a single row at their sides : the vomer, palatine, lingual and branchial
bones are edentulous.

In the Opistognathus, the teeth are villiform and arranged on a
narrow band in each jaw ;_ the exterior ones are a little stronger and
more separated than the rest. Of the other bones of the mouth,
the pharyngeals alone have teeth, which are ‘ en cardes.’

But the chief subject of interest to the anatomist in the
present family of fishes is the singular and powerfully developed
dental system of the Wolf-fish (Anarrhichas Lupus.) The general cha-
racter and physiological relations of the teeth in this species had not
escaped the attention of Hunter. In his paper on the Gillaroo trout

158 _ BLENNIOIDS.

read before the Royal Society, in 1774,(1) he observes that the teeth
of fishes which subsist chiefly on animal matter must vary according as
their food may be common soft fish or shell-fish. ‘‘ Such fish as live
on the first kind have, like the carnivorous quadrupeds and birds, no
apparatus for mastication, their teeth being intended merely for catch-
ing the food and fitting it to be swallowed. But the shells of the second
kind of food render some degree of masticatory power necessary to fit it
for its passage either into the stomach or through the intestines ; and
accordingly we find in certain fish a structure suited to the purpose.
Thus the mouth of the wolf-fish is almost paved with teeth, by means
of which it can break shells to pieces, and fit them for the cesophagus
of the fish, and so effectually disengage the food from them, that
though it lives upon such hard food, the stomach does not differ
from that of other fish.”

But in order to secure the capture of the shell-fish, the teeth of
the wolf-fish are not all crushers; some present the laniary type,
with the apices more or less recurved and blunted by use, and consist
of strong cones spread abroad, like grappling hooks, at the anterior
part of the mouth. A description of these teeth, illustrated with figures,
is given by Mr. André in a volume of the Philosophical Transac-
tions(2) subsequent to that in which they are noticed by Hunter ;
and a diminished view of the mouth of the Wolf-fish will be found in
Mr. Yarrell’s British Fishes.(3)

The oral dentigerous bones, viz: the intermaxillaries, preman-
dibulars, palatines and vomer, are figured of their natural size, in
their natural relative position and separately, in Plates 60 & 61 of
the present work. The pharyngeal bones support much smaller
conical and pointed teeth.

The intermaxillary teeth, (Pl. 60, fig. 1, and Pl. 61, fig. 2 a a)

are all conical, and arranged in two rows; there are two, three or

four in the exterior row, at the mesial half of the bone, which are

the largest ; and from six to eight much smaller teeth are irregularly

arranged behind. There are three large, strong, diverging laniaries

at the anterior end of each premandibular bone, (Pl. 61, fig. 1), and

immediately behind these an irregular number of shorter and smaller
(1) Philos. Trans. vol. lxiv, p. 310. (2) Ib. vol. Ixxiv, p. 274. (3) Vol. 1, p. 248.

BLENNIOIDS. 159

conical teeth which gradually exchange this form for that of large
obtuse tubercles ; these extend backwards, in a double alternate series,
along a great part of the alveolar border of the bone, and are termi-
nated by two or three smaller teeth in a single row, the last of
which again presents the conical form. Hach palatine bone,
(Pl. 61, fig. 2, 6 6) supports a double row of teeth; the outer ones
being conical and straight, and from four to six in number ; the inner
ones, two, three or four in number and tuberculate. I have seena
specimen where the inner row was wanting on one side. The lower
surface of the vomer, c, is covered by a double irregularly alternate
series of the same kind of large tuberculate crushing teeth as
those at the middle of the premandibulars. All the teeth are anchy-
losed to more or less developed alveolar eminences, like the anterior
teeth of the Lophius. The periphery of the expanded circular base
of the large anterior grappling teeth is divided into processes indi-
cative of the original ligamentous fasciculi at the base of the pulp
by the ossification of which their anchylosis is effected. (1)

When such anchylosed teeth and the supporting bone are
divided by a vertical section, as in Pl. 60, fig. 2, there may be gene-
rally discerned a faint transverse line indicating the original separation
between the tooth and the bone, and more clearly defining the dental
from the osseous structure than in the anchylosed teeth of other
fishes. From the enormous development of the muscles of the jaws,
and the strength of the shells of the whelks and other testacea which
are cracked and crushed by the teeth, their fracture and displacement
must obviously be no infrequent occurrence, and most specimens of
the jaws of the wolf-fish exhibit some of the teeth either separated at
this line of imperfect anchylosis, or, more rarely, broken off above
the base, or, still more rarely, detached by fracture of the supporting
osseous alveolar process.

Cuvier(2) describes the basal portion of the teeth themselves
as osseous epiphyses, attached by a kind of suture to the jaw,
and forming the medium by which the true teeth are fixed to

(1) Cuvier has given an accurate view of the plaited structure of the base of one of these teeth
in Pl. 32, fig. 7, of his Legons d’Anatomie Comparée, 1805, where it is described as the base
of the osseous tubercle which supports the true tooth.

(2) Ib. tom. iii, p. 113.

160 BLENNIOIDS.

the jaw. Retzius(1) has disproved at some length this supposed
peculiarity in the mode of attachment of the teeth to the jaw;
he observes that, ‘ at a short distance from the line of attachment
of the teeth, there is a margin resembling an alveolar edge ;’
(it is clearly shown in PI. 60, fig. 1, below the tuberculate teeth in
the right premandibular bone) : ‘ the portion of the jaw bone intervening
between this margin and the teeth consists of a peculiar porous osseous
substance,(2) and has on both sides small furrows corresponding with
the interstices of the teeth, and giving to the basilar substance the
appearance of being divided into as many processes as there are
teeth :’ this appearance is still more increased by the small openings,
one at the end of each vertical furrow nearest the quasi-alveolar edge,
which openings lead, according to Retzius, to cavities containing the
germs of the successional teeth.

The dentigerous or alveolar processes of the jaw-bone are still
more distinct at the anterior border of the premandibulars and
intermaxillary bones, but these are not more developed in the wolf-
fish than they are in the angler, the cod and other fishes with anchy-
losed teeth. The line of union of the tooth is situated at the summit
of these processes ; it is at this line that they are commonly detached;
and not by a separation of the alveolar process from the rest of the jaw,
either by interstitial absorption, analogous to that which causes
the shedding of the antler of the deer, or by any other natural
process. i

In reference to the structure of the teeth of the wolf-fish Mr.
André rightly observes ‘‘ that they are formed of a hard bony matter
not covered with enamel as in some animals,” and Retzius confirms
this statement in reference to the fully developed and fixed teeth ;
but he states that in the germs of the teeth contained in the alveoli
of reserve there is a small portion of enamel, which in the conical
teeth constituted the summit, and in the tubercular ones formed a
white elevation, one third of a line in breadth, upon the centre of the
flattened grinding surface. ‘‘ Itisno wonder,” says Retzius, ‘‘ that a
fish which uses its teeth for bruising thick shells, as those of whelks,

(1) Miiller’s Archiv. 1837, p. 529.
(2) I find it however not to differ in texture from the remaining peripheral dense part of
the jaw-bone, as shown in Pl. 60, fig. 2.

— -
a

BLENNIOIDS. GADOIDS. 161

and cockles, lobsters, sea-urchins, &c., should soon wear off these
small enamel points, which cannot therefore have much functional
importance. These transitory summits, which are composed in
reality of a fine tubular dentine, were supposed by Cuvier to be the
true teeth, and to be peculiar to the young wolf-fish: he gives a
figure of one of them in Pl. 32, fig. 6, a, of the Lecons d’Anatomie
Comparée, vol. v, 1805.

The calcification of the dentinal pulp proceeds in nearly parallel
lines from the summit to the base of the tooth ; it is this peculiarity
in the wolf-fish that occasions the solidity of the teeth, and the
general straight course of the medullary tubes; most of these run
parallel to each other and to the axis of the tooth; but the tubes
nearest the sides of the tooth slightly diverge towards that sur-
face. Tracing the medullary canals from the basis of the tooth, they
divide dichotomously into finer and parallel branches, which form
numerous reticular anastomoses together and terminate in fine
loops at the periphery of the tooth. The medullary canals are
occupied by processes of a vascular pulp; they were seen and
described by both Cuvier and Von Born, who conceived them to
be the channels of the nutrient vessels and nerves, and they were
rightly compared by the latter anatomist to the similarly conspicuous
tubes which traverse the teeth of the Orycterope ; but the structure
of both teeth is much more complicated than that of the horn of the
rhinoceros, or of the baleen of the whale. The minuter or calcigerous
tubes which traverse the firm substance occupying the interspaces of
the medullary canals were not perceived in either case, by the above-
cited anatomists ; they are extremely minute in the Anarrhichas, and
do not form by their parallel and straight course a distinct enamel-
like outer layer, as in the pike, except at the apex of the recently
formed teeth, but are confined to the fine and inextricable reticulate
anastomoses at the periphery of the tooth as well as in the inter-
spaces of the medullary canals.

GADOIDS,

62. The dental system maintains a greater uniformity in the
Cod-tribe than in most of the other natural families of the class of
M

162 ' GADOIDS.

fishes. In every subgenus teeth are present on the intermaxillary,
premandibular, vomerine, branchial and pharyngeal bones, but not
on the hyoid or palatine bones; and in all, the teeth are simple,
conical, and sharp-pointed ; varying only in regard to size and degree
of curvature.

They are distributed over a broad band upon the upper jaw,
and over a narrower band along the lower jaw in the cod (Morrhua
vulgaris), the haddock (Mor. Merlangus), the dorse (Mor. callarias),
in which the exterior row is the largest in the upper teeth
and the interior row in the lower ones. In the pout (Morrhua
lusca), the ling (Lota Molva), and the whiting (Merlangus vul-
garis), there is only a single row of long and large teeth in the
premandibulars. The exterior row of larger intermaxillary teeth

are more distinctly separated from the smaller posterior teeth of —

the same bones in the haddock, in order to receive in their
interspace the points of the single row of premandibular teeth when
the mouth is closed; but in the ling the upper teeth are numerous
and of small size. In the hake (Merlucius vulgaris), there is a single
row of slender and sharp teeth in both the upper and lower jaws.
The tadpole-fish (Raniceps trifurcata), has two rows of sharp teeth in
the premandibular bones, and numerous smaller, but not serial teeth
in the intermaxillaries. In the coal-fish (Merlangus carbonarius), the
torsk (Brosmius vulgaris), and the rock-ling (Motella 5-cirrata), the
teeth are small and ranged in a band along both jaws. The vomerine

teeth in all the cod tribe are usually arranged in a transverse crescent —

on the expanded anterior part of the bone.

All the teeth are less firmly attached to the bones in the Gadoids
than in other osseous fishes with laniariform teeth. In the cod-fish the
gelatinous conical pulp, after having formed the body of the tooth, is con-

tinued in an uncalcified state, but condensed into ligamentous firmness, —

from the base of the tooth to the alveolar margin of the jaw : ossifica-

tion then proceeds from the jaw along the ligaments towards the base ~
of the tooth, which, however, rarely become anchylosed to the ossified —

ligaments. 'Theteeth, therefore, are generally detached in the course
of macerating the head of the cod, and the broad alveolar margin of

the dentigerous bones is then covereg by the ossified dental ligaments

GADOIDS. 163

in the form of truncated cylinders of various sizes, the largest being
most external in the intermaxillary and the reverse in the preman-
dibular bones. A group of smaller but similarly shaped cylindrical
processes for supporting the teeth are arranged in the form of a chevron
across the anterior extremity of the vomer in the cod, after simi-
lar maceration. The branchial teeth are more firmly attached,
being anchylosed in small groups upon the short obtuse processes
of the branchial arches ; there is a double series of these dentigerous
tubercles along the concave margin of the second and third arches.
The upper and lower pharyngeal bones are beset with small
recurved laniary teeth, which are also more firmly fixed than those
on the vomer and jaws.

Retzius compares the dentigerous processes of these bones to
epiphyses, but I find that ossification is continued from the supporting
bone into them, and have never observed them in a detached state,
like the teeth themselves: he correctly describes their texture as
being, in the ling, intermediate between that of the bone and tooth.
In this species he describes the teeth as being “‘ semi-transparent, with
a covering of enamel upon the extreme points of such as are not too
much worn. This little covering of enamel is disposed upon the tooth
like the shoe of iron upon a spade, being continued from a trans-
verse edge forwards and backwards, but being in some produced into
a sharp point; the whiteness of the teeth is due to this substance.’’(1)

The pulp-cavity of the fully-formed tooth in the cod is continuous
with the cavity of the supporting osseous cylinder to which it is
attached ; it varies in size according to the age of the tooth, and
is, at length, reduced to a linear cavity extending along the middle
of the axis of the tooth. Processes of the pulp are conveyed by
medullary canals which diverge from all parts of the main central
cavity into the substance of the dentine; these are about <th of an
inch in diameter at their origin, but they quickly divide, and their
branches form anastomoses with those of the neighbouring tubes ; the
loops, thus formed by the smaller terminal branches, constitute a
well-defined boundary between the coarse central and the fine
external dentine. In this latter layer the calcigerous tubes, which

(1) Loe. cit, p. 268.
M 2

164 MURZENOIDS.

are about ;,,th of an inch in diameter, proceed, as usual, parallel to
each other, and parallel to the axis of the tooth at its apex, but trans-
versely to that axis at its sides.

The germs of the successive teeth are developed, as in the pike,
in the mucous membrane covering the dentigerous surface of the
jaws.

MURZNOIDS,

63. The teeth in this predatory family of apodal fishes are gene-
rally sharp at the point and cutting at the edge; in the few species
which have certain teeth approaching the molar type, these are always
placed far back in the mouth, according to the usual law of the
position of the teeth that give the final comminution to the food.

The teeth are numerous, of uniform shape and small size in the
true eels (Anguilla) : they are arranged in a narrow band along both
jaws in the sharp-nosed eei (Anguilla acutirostris): the teeth are
more numerous and form a broader band on the jaws in the broad-
nosed eel (Anguilla latiostris) Pl. 56, fig. 3; the anterior part of
the series in the upper jaw is formed by the vomerine teeth, Pl. 56,
fig. 2. In the conger (Conger vulgaris, Cuv.) the teeth are relatively
larger, especially at the anterior part of the vomer and maxil-
lary bones; the larger teeth form a regular close-set row in each
premandibular bone ; the smaller teeth are almost concealed at their
basal interspaces, except at the fore part of the bone, where they are
larger and more numerous.

The dentition of the Murene is generally of a more formidable
character than that of the Anguille. Cuvier,(1) makes mention of
their savage bite in allusion to the cruelty of Vedius Pollio, who is
said to have caused his offending slaves to be cast into his fish
ponds for the purpose of fattening the Murene. The crime which
brought this barbarity to light was the breaking of a crystal cyathus.
The slave grasped the knees of Augustus who was the guest, in
supplication. The Emperor heard his prayer that he might not be
thrown to the fishes, discovered the horrid habit of the house, bade
the slave rise up a freeman, ordered all the crystal vases to be broken,

(1) Régne Animal, vol. ii, p. 352.

MURENOIDS. 165

and commanded that the abominable fish-ponds should be filled
up.(1)

All Murznze have an external set of teeth, in one or more
rows, on each side of the upper jaw, which may be termed ‘ maxil-
lary,’ as being opposed to corresponding series on the premandibular
bones ; and, in most species there is a median series of teeth in the
upper jaw, supported by the vomer.

In the common Mediterranean species, (Murena Helena, Linn.),
Cuvier(2) describes the dentition as consisting of a single row of
acute teeth on each jaw; and a short row upon the vomer, commenc-
ing by a single large tooth.

In the Murena anguiceps, (Pl. 56, fig. 4), there is also a row
of slender sharp-pointed teeth along the middle of the vomer in addi-
tion to the single series of similarly shaped maxillary and premandi-
bular teeth. The anterior part of the external series in the upper
jaw is supported by the expanded anterior extremity of the vomer:
the first, fifth and tenth teeth of this row are much longer than the
rest, and resemble canine teeth. The first two teeth of the median
series are longer than the maxillary canines, and are situated
one behind the other on the middle of the expanded part of the
vomer: the rest of the series, which is confined to the narrow
posterior part of the vomer, includes very small teeth. The ante-
rior tooth on each premandibular bone is a long canine; the rest
are short and recurved. 3

The Murena grisea has two rows of acute teeth, on each side
of the upper jaw, besides a single row on the vomer.

The lateral teeth are round and arranged in a single row in the
Murena nebulosa ; the vomerine teeth are in two rows, and present
a conical form at the anterior part of the bone.

In the Murena Zebra the lateral teeth are also round, but in

(1) Quemadmodum, inquit, fecit Divus Augustus, quum cznaret apud Vedium Pollionem.
Fregerat unus ex servis ejus crystallimum. Rapi eum Vedius jussit, nec vulgari quidem
periturum morte, Murenis objici jubebatur, quas ingens piscina continebat....<* Evasit e
manibus puer: nihil aliud petiturus, quam ut aliter periret, nec esca fieret. Motus est novitate
crudelitatis Cesar: et illum quidem mitti, crystallina autem omnia coram se frangi jussit,
complerique piscinam.’’ Seneca, de Ira, Lib. iii, c. 40.

(2) Legons d’Anatomie Comparée, Ed. 1835, tom. iv, p. 330.

166 MURZENOIDS. LEPIDOSIREN.

two rows on each side, while the vomerine teeth are in four rows.
The teeth of the Murena Saga are small and numerous, and may be
said to be arranged ‘en carde.’

In the skull of the Murena tigrina, figured in Pl. 56, fig. 5,
ot which the jaws are upwards of four inches in length, they are
armed with a pretty close-set row of strong conical teeth, b, with the
base extended transversely and firmly anchylosed to the alveolar
margin of the jaw, and the apex narrowed off to a pointed and some-
what trenchant edge set lengthwise; on the outside of this row there
is an irregular series of small conical teeth, and in the inside a
broader stripe of small granular teeth. At the extremity of the
lower jaw two of the conical teeth are developed to a size much
exceeding the rest; they are surrounded by smaller conical teeth
which spread out like the prongs of a grappling-iron. These large
terminal teeth of the lower jaw are opposed to four similar large,
conical, sharp-pointed, divergent fangs on the expanded anterior
extremity of the vomer. A longitudinal oval plate on the vomer
supports twelve large and strong conical teeth, anchylosed by trans-
versely extended bases; these teeth are arranged in alternate pairs
in the middle of the group, but the rest form a single longitudinal
row, decreasing in size as they are placed anteriorly. The whole
dentition presents a most formidable armature for seizing and
lacerating a resisting prey. The vomerine teeth are indicated by
the letter a. In the great Oxyrhynchus the crowns of the teeth are
sub-compressed laterally and have an anterior and posterior dentated
edge.

LEPIDOSIREN.

64. At the extreme limit of the class of fishes, and con-
necting that class with the reptiles, stands the very remarkable genus
of which the name is placed at the head of the present chapter, and
the dental system is figured in Pl. 59. This consists of two small,
slender, conical, sharp-pointed and slightly recurved teeth, which
project downwards from the intermaxillary bone, and of strong
trenchant dental plates anchylosed with the alveolar border of the

LEPIDOSIREN. 167

upper and lower jaws, in each of which the plate is divided at the
middle or symphysial line so as to form two distinct lateral teeth.

The intermaxillary bone is represented by a single, horizontal,
triangular plate, the base of which is attached by ligamentous union
with the frontal and ascending process of the palatine bones,
upon which it enjoys a slight vertical movement; the rounded apex
forms the anterior extremity of the skull, and it is at the under
surface of this part that the two laniariform teeth are attached
by ligaments proceeding from their base, so as to admit of a yielding
motion in every direction for a small extent, but most resisting
inflection outwards. Their office is to pierce and retain the nutritive
substance which is afterwards divided and comminuted by the strong
maxillary dental plates.

The upper pair of these plates is supported by the anterior
part of a strong arch of bone which combines the characters of
the superior maxillary, palatine and pterygoid bones: the superior
maxillary is represented by the external process which _pro-
jects outwards and backwards and terminates in a free point on
each side of the anterior part of the arch; the palatine portion con-
stitutes the median and anterior part of the roof of the mouth ; the
pterygoid portion is indicated by its fulfilling the usual function of
an abutment extended between the palatine portion of the upper
jaw and the articular pedicle of the lower jaw: the upper dental plates
are confined to the first two parts of the arch and do not extend upon
the pterygoid portion; the lower dental plates are anchylosed to the
premandibular bone. Viewing the upper pair of plates as a single
tooth, it may be described as being indented at its outer surface by
five vertical angular notches, penetrating inwards through half the
breadth of the supporting bone, and dividing the plate into six
angular processes, which, from the direction and varying form and
breadth of the entering notches, radiate from the posterior part of
the median line or division of the tooth (Pl. 59, fig. 3). The inferior
dental plate is similarly notched on its outer side, but the propor-
tions of the angular indentations are such that they receive the
processes of the upper dental plate when the mouth is shut; thus
the median notch is wider than the two adjoining ones in the lower

168 LEPIDOSIREN.

dental plate, but is narrower in the upper one. The figures 1, 2
and 3, Pl. 59, which give respectively a side view, front view and
the working surfaces of the teeth of the Lepidosiren, will convey a truer
idea than can be given by words, of the form of the maxillary dental
plates. The two anterior lobes or divisions of both upper and lower
dental plates are the most produced in the vertical direction, and their
anterior angle is pointed and adapted for piercing. ‘The posterior
divisions are most extended in breadth and least in height, and
terminate in a sharp trenchant edge; the middle lobes present an
intermediate structure.

These teeth, in their paucity, large relative size, and mode of
adaptation to the jaws, resemble the dental plates of the Chimeroid
and some of the extinct Hybodont cartilaginous fishes, as Cochliodus
and Ceratodus Ag.; but they are unlike these in microscopic structure;
approaching in this respect, as will be presently shown, nearer to
the teeth of many osseous fishes. The maxillary armour of the Lepi-
dosiren surpasses any known dental apparatus in the class of fishes in
the modification of the working surface, by which a single tooth is
at once adapted for piercing, cutting and crushing the alimentary
substances. The strength of the jaws of the Lepidosiren and
the bulk of the muscles which work them are proportionate to
the size and nature of the maxillary dental plates.

In Pl. 59, fig. 4, is given a reduced representation of a magnified
view of a vertical section of a lobe of the lower dental plate of the Lepi-
dosiren. It consists, as in the cod and sphyrena, of a central mass of
coarse osseous substance, traversed by large and nearly parallel
medullary canals, and an external sheath of very hard enamel-like
dentine. The medullary canals are continued from a coarse reticula-
tion of similar, but wider canals, in the substance of the supporting
bone, and advance forwards, nearly parallel with each other, and
with the plane of the upper surface of the tooth; they anastomose
together by short, curved, transverse canals, which intercept spaces
increasing in length as the canals recede from the osseous basis.
The canals themselves diminish in size in the same ratio, and when
they have arrived near the dense outer layer, their divisions and
inosculations become again more frequent, the peripheral loops form-

LEPIDOSIREN. 169

ing a well marked line of demarcation between the coarse-tubed
and the fine-tubed dentine. The interspaces of the medullary canals
are occupied by a clear substance and by moss-like reticulations of
fine calcigerous tubes, which appear to be more sparing in number
than in the teeth of the sphyrzna or shark. The calcigerous tubes
of the external dentine run nearly parallel to each other, and vertically
to the external surface of the dental plate through about two thirds
of the thickness of the external hard substance ; they then bend and
cross each other in a manner very similar to those of the external
layer of dentine in the teeth of the Lepidotus, Phyllodus, &c.

In the process of attrition this external dense substance is worn
away from the upper surface of the dental processes in the lower jaw,
exposing the softer osseous, or medullary substance of the tooth; in
this state the dental plate offers an analogy to the incisors of the
rodents, a posterior softer substance being sheathed by an anterior,
denser layer ; and an external sharp edge is similarly kept up by the
unequal wearing away of the two substances. The progressive waste
at the upper surface of the dental] plate would appear to be met
by a corresponding addition of new material to its lower part.

In the structure here presented to our observation we have a
condition of the dentine which has hitherto been met with only in the
class of fishes; and the form, the extent, and the continuity
of the dental armature excepted, this part of the Lepidosiren
closely corresponds with that particular modification of the dental
structure which we have seen to be most eminently characteristic
of the class of fishes. The Sauroid character, for example, which
as in the Lepidosteus, pervades the air-breathing organs, and
which, as in the Polypterus, is traceable in the intestinal canal of
the Lepidosiren, is not at all manifested by the dental system: and
neither in the modified bone which forms the basis of the tooth, nor
in that coarser bone of which the jaw is composed, is there the
slightest trace of radiated cells or corpuscules; the other parts of the
skeleton exhibit a similar ichthyic condition.

The test of the affinities of the present paradoxical genus, afforded
by the microscopic examination of the teeth, gives additional con-
firmation to the views which | have already maintained from argu-

170 SAURICHTHYS.

ments drawn from the rest of its organization,(1) that the Lepidosiren
is in every essential point a member of the class of fishes.

SAURICHTHYS.

65. I terminate the description of the dental system of fishes with
an account of the microscopic structure of the teeth of two extinct
species of different genera, indicated as yet only by these detached
organs, and respecting which, doubts have been entertained as to
whether they be actually referable to the class of fishes or of reptiles.

To these doubts, howevery in regard to the first genus, Sau-
richthys,(2) the microscopic test satisfactorily puts an end; but with
respect to the other genus, Dendrodus, the modification of the dental
tissue approaches so closely to a new and singular condition which
will be shown to characterize the structure of the teeth of an extinct
family of Batrachian reptiles, that I hesitate in absolutely pronouncing
it to be that of a fish.

The teeth of the Saurichthys characterize the Bristol bone-bed
and the German Muschelkalk ; they are conical, rather slender, with
a subelliptical transverse section, slightly bent, with the apex not
very acute: about one fifth of the tooth next the apex is smooth and
polished, the remainder of the outer surface is traversed by fine close-
set longitudinal ridges: thus, to all outward appearance the tooth
very closely resembles the form most common among Saurians.

The specimen here described, from the Bristol bone-bed, is seven
lines in Jength, and two broad at the base. I have investigated its
structure by a transverse section through its base, and by a longitu-
dinal section through the middle of the remaining part.

This tooth is traversed by a slender, straight, longitudinal,
conical, central pulp-cavity, occupied by a coarse cellular bone, and
from which radiates a system of close-set, slightly and minute-
ly undulating calcigerous tubes, covered by a thick layer of the
enamel-like dense tissue, which coats the teeth in the Lepidotus,

(1) Linnean Transactions, vol. 18, 1839. p. 350.

(2) The term Sawrichthys (oavpoc a lizard, ty9%b¢ a fish) was applied by M. Agassiz to the
present genus, to express its transitional characters, but it is nevertheless regarded by that
distinguished Paleontologist, as being essentially a member of the class of fishes.

SAURICHTHYS. 171

Sparus, and many other fishes. The central linear pulp-cavity
extends, as also in the conical teeth of many fishes, to the extreme
apex of the dentine: the cells of the ossified pulp were occupied by
an opaque substance in the tooth examined: at its periphery and
through the whole of the base of the tooth were scattered numerous
coarse cells. The true dentine presented a mahogany brown colour:
the main calcigerous tubes of this substance radiate through it at
right angles to the periphery of the tooth, and with a slight curvature,
the concavity of which is turned towards the apex of the tooth. The
tubes give off many small lateral branches, which are curved, with
their concavity directed towards the pulp-cavity, or to the base of the
stem: they diminish in size as they approach the external enamel-
like substance, pass across the well-defined boundary which sepa-
rates this substance from the dentine, and then are immediately
resolved into fasciculi of the extremely fine and slightly diverging
fibres or minute tubes which form the only appreciable structure in
this enamel-like substance. These fine lines have a general direction
at right angles to the periphery of the tooth, like that of the calcige-
rous tubes of the dentine, from which they are continued; but many
of them are bent in different directions, so as to cross each other, in
the manner described and figured in the corresponding clear external
enamel-like substance of the tooth of the Lepidotus; they are,
however, somewhat larger and diverge in straighter lines ; they finally
terminate in fine calcigerous cells at the periphery of the tooth.

The thickness and structure of the dense external enamel-like
layer, the length and form of the pulp-cavity, and the texture of the
ossified remains of the pulp with which it was filled, are decisive
against the reptilian character of the Saurichthys. Its affinities to
that class are manifested only in the outward form of the tooth, and
the dense, minutely-tubed tissue of the dentine, a structure, however,
which is common to the teeth of all the Sauroid fishes.

DENDRODUS.

66. Dendrodus biporcatus.—The teeth indicative of the genus, for which I
have proposedthe name of Dendrodus(1), occur sparingly and detached in

(1) d&vdpoy a tree, od8¢ a tooth; in reference to its internal dendritic structure.

i772 DENDRODUS.

the central or corn-stone division of the Old Red Sandstone. The three
specimens here described are from Scat-crag, near Elgin. The largest of
these is represented of the natural size at Pl. 62 a, fig. 1. It is conical,
subcompressed, subincurved, with a round obtuse summit (a), and a
sub-circular base, the margin of which, in the specimen, was
rounded off or bent in, and the surface of the base was slightly
depressed in the centre, and rough as if it had been detached from an
anchylosed union with a shallow alveolar depression. On each side
of the tooth, a little nearer the convex than the concave surface,
there is a well marked longitudinal ridge, which gradually subsides a
little below the summit. The position of these two ridges, and the
degree of compression of the tooth at its middle part, are shown in
the outline of the transverse section of the tooth by the side of the
figure. The smooth surface of the tooth is traversed by very fine
longitudinal linear impressions extending from the base to within
one fourth of the rounded apex.

A transverse section taken one line above the base of this tooth,
exhibited a dark irregularly dotted central part, and a lighter peri-
pheral structure: it is represented at Pl. 62 8, fig. 1. A portion of
the same section corresponding with that intercepted by the two lines

in fig. 1, as viewed by transmitted light with a magnifying power of —

fifty linear dimensions, is represented on a reduced scale at fig. 2.

Thus magnified, a central pulp-cavity of relatively small size and
of an irregular lobulated form is discerned, a portion of which is
shown at a; this is immediately surrounded by the transverse sections
of large cylindrical medullary or pulp-canals of different sizes ; and,

beyond these, there are smaller and more numerous medullary canals, —

which are processes of the central pulp-cavity. In the transverse

section these processes are seen to be connected together by a net-_

work of smaller medullary canals belonging to a coarse osseous

texture into which the pulp has been converted, and this structure —

occupies the middle half of the section. All the medullary canals were

filled by the opaque matrix. From the circumference of the central —
net-work, straight medullary canals radiate at pretty regular intervals —

to the periphery of the tooth ; most of these canals divide once, rarely
twice, in their course; the division taking place sometimes at their

DENDRODUS. ve)

origin, in others at different distances from their termination, and
the branches diverge slightly as they proceed. Each of the above
medullary rays is continued from a short process of the central struc-
ture, which is connected by a concave line with the adjoining process,
so that the whole periphery of the transverse section of the central
coarse reticulo-medullary body of the tooth presents a crenate outline.
From each ray and its primary dichotomous divisions, short branches
are sent off at brief intervals, generally at right angles with the trunk,
or slightly inclined towards the periphery of the tooth. These sub-
divide into a few short ramifications like the branches of a shrub,
and terminate in irregular and somewhat angular dilatations, simu-
lating leaves, but which resolve themselves into radiating fasciculi of
calcigerous tubes. There are from fifteen to twenty-five or thirty-six
of these short and small lateral branches on each side of the medullary
rays.

In a section of the same tooth, one third from its obtuse summit
(Pl. 62 8, fig. 3), the irregular central pulp-cavity was lost, and in its
place there were a few large medullary canals connected by a fine net-
work of smaller canals. This tissue occupied rather more than one third
of the diameter of the section. From its periphery there was continued
the same system of nearly straight, sparingly dichotomizing, medullary
canals, radiating at regular distances from the central tissue to the
periphery of the tooth. The radiating canals here also give off short
lateral branches, but these do not terminate in such well marked
dilatations as those observable at the base of the tooth: the trans-
verse branches here generally spring from short alternate lateral
bendings of the main stem. There are about forty radiating medul-
lary canals in this part of the tooth, and about fifty in the section
taken from the base of the tooth.

In both sections the angular dilated terminations of the small
lateral branches of the medullary rays form, as has been said, the
centres of radiation of as many systems of the most minute calci-
gerous tubes, each system constituting a lobe of the dentine, separated
from the adjoining lobes by an extremely thin layer of cement. In
the section nearer the apex of the tvoth, the radiating systems of
calcigerous tubes, forming similar lobes of dentine are given off

174 DENDRODUS.

more frequently from the sides of the lateral branches, than from
their terminal dilatations.

The peripheral extremities, also, of the medullary rays, and of |

such of their subdivisions or branches as are nearest to and directed
towards the margin of the section, and consequently to the periphery
of the tooth, are resolved into fasciculi of calcigerous tubes, which
diverge in graceful curves from their point of origin : two of these
peripheral lobes are figured at Pl. 62 8, fig. 4. The middle tubes are
continued from the interspace of the diverging ones to the periphery
of the tooth in a line parallel with that of the main medullary canal
(a), which radiates from the central reticulation: the lateral tubes
gradually diverge more and more from this line, and those which
proceed from the sides of the extremity of the medullary canal run
at right angles to its course. The lateral tubes terminate, together
with those of the adjoining medullary canal, in a linear series of cal-
cigerous cells ; which line is continued inwards from the periphery
of the tooth, like a process of the external capsule, inclosing and
defining, as it were, each of these terminal square lobes or systems
of calcigerous tubes. There is a slight indentation of the periphery of
the transverse section at the line of the above described inflection of
the cellular structure ; and this indentation ()) is a section of one of
the fine superficial longitudinal striz already mentioned. The in-
flected line of minute cells may be traced, in most parts of both sections,

to near the central reticulate system of medullary canals, sending cff —

branches on each side, which bound in a similar manner the diffe- —

rent lobes of dentine, or systems of radiated calcigerous tubes which

are given off from the sides of the straight medullary canals. The |

external longitudinal fine grooves on the superficies of the tooth indi-
cate, as above stated, the entering lines of the fine cellular cement, or
the interspaces of the lobes of the dentine appended to the medullary
canals which radiate from the central pulp-cavity or net-work.

The medullary rays, though for the convenience of description —

they have been termed canals—as they appear to be in the transverse —
section of the tooth, yet are not cylindrical tubes. For it must be
obvious from the similarity of the structure of the two sections here

described from nearly the two opposite extremities of the tooth, that

|

DENDRODUS. 75

the radiating lines described as medullary canals are, more probably,
sections of vertical fissures, or lamelliform processes of the pulp,
radiating from the central body of the pulp to the periphery of the
tooth, and co-equal with the longitudinal extent of the tooth; but
decreasing in number as the tooth contracts towards its apex.

The species to which the tooth, exhibiting the beautiful and com-
plicated structure just described, belonged, may be indicated by the
name of Dendrodus biporcatus, in reference to the two opposite ridges
by which the tooth is characterized.

Dendrodus strigatus.—A second and smaller tooth from the same
formation and locality, differs from the preceding in its more elongated
and slender conical form, with a nearly circular transverse section ; it
also differs in the absence of the two longitudinal ridges and in the pre-
sence of broader,deeper, and closer longitudinal impressions separated
by intervening convex ridges. As those characters strongly indicate
a specific difference in the animal to which it belonged, it may be
convenient to attach to this tooth the name of Dendrodus strigatus : its
microscopic structure, as shown by a fine transverse section, proves it
to be generically allied to the Dendrodus biporcatus.

In the Dendrodus strigatus the central system of reticulate medul-
lary canals occupies a larger proportion of the mass of the tooth.
The radiated canals or processes of the pulp are shorter and more
branched: the systems of calcigerous tubes which diverge from the
numerous processes and branches are separated from each other by a
fine and clear line, and terminate in a broader band of calcigerous cells.
The appearances which the structure of the tooth thus presents in
the transverse section, somewhat resemble those of the tooth of a
Myliobates ; but the lobes or systems of calcigerous tubes are less
regular in form and size.

Dendrodus hastatus.—The third tooth presents a more com-
pressed conical figure than the two preceding, and the opposite ridges
which characterized the Dendrodus biporcatus here form, as it were,
the margins of two cutting surfaces, and the opposite ends of the
flattened elliptical transverse section of the tooth. The length of
this tooth is eight lines, the longest diameter of its base three lines ;
the shortest diameter two lines. The tooth diminishes regularly from

176 DENDRODUS.

its base to its sub-acute apex. The surface of the tooth is much
smoother than in the Dendrodus strigatus. I took a transverse section
from the base of this tooth, and finding the same essential radiated
disposition and dendritic ramifications of the medullary canals, I
made a longitudinal section of the rest of the tooth.

In this section eight principal medullary tubes were seen ; the
four largest and closest together were situated in the centre; the others
diminishing as they approached the side. The central canals run pa-
rallel to each other and to the axis of the tooth along the basal half;
the two middle canals so continuing to the apex. The small lateral
tubes bend outwards to the side of the tooth; the third on each side
sends off one or two primary branches in the same oblique direc-
tion and also finally terminates by bending towards the margin of the
tooth. The primary divisions of the large medullary tubes run parallel,
or nearly so, to the trunks, but begin slightly to diverge as they
approach the apex. The primary divisions of the small lateral tubes
are given off at different, but always acute angles. The smaller or
secondary branches are given off frequently at right angles, and those
from the primary branches sometimes retrograde to the main tubes.
The plan of branching of the whole system of medullary canals which
pervades the entire substance of the tooth is strikingly similar to that
of certain forest trees, as the elm, but with the characteristic diffe-
rence, which distinguishes in this, as in most other cases, the branching

of an animal from a vegetable structure, namely, that the terminal ;

branches anastomose, forming a coarse but elegant net-work,
occupying with considerable regularity the whole of the interspaces
of the longitudinal medullary tubes.

A transverse section of this tooth exhibits three-fourths of its —
central part occupied by a reticulo-medullary structure; and the —

peripheral portion traversed by medullary rays. In the central

structure are seen the arez of numerous, nearly equal sized and

equi-distant medullary canals, around which the dentine is disposed
in well-marked concentric layers, and from which the calcigerous
tubes radiate as in the Myliobate and Orycterope; but these tubes
are relatively fewer and less parallel in their course, and form more

decided reticulations in that course. The shape of each component |

DENDRODUS. 177

denticle, thus seen in transverse section, is more rounded and less
regular than in either of the two above-cited instances. The cellular
cement which separates each denticle is relatively thicker. The
diameter of the central medullary canal is generally equal to two
thirds the diameter of the laminated and tubular wall of the denticle,
of which it forms the axis. Inthe peripheral structure, the radiated
trunks are shorter in comparison with the central cellular part than
in the preceding species. They are relatively wider apart from each
other, are less parallel in their course, their primary divisions diverge
at a more open angle, and their lateral branches are longer.

The branches of the radiating canals, after dichotomising, are
resolved at their extremities into radiated systems of calcigerous tubes
terminating in a thin stratum of calcigerous cells. This stratum
forms the boundary of each system and thus describes an undulating
line on each side of the radiated canals, which is very similar to the
anfractuous inflected layer of the external cement in the Labyrin-
thodon. In the transverse section of the Dendrodus hastatus the
calcigerous tubes seem to form, towards their extremities, a fine
net-work with open meshes, and to be fewer and at a greater relative
distance from each other than in the first described species.

It is obvious that the plan of structure, as exhibited in the
longitudinal section of the tooth of the Dendrodus, bears considerable
analogy to that in the shark, and Scomberoid fishes, as the Sphy-
rena, Dictyodus, &c.; but one-cannot fail to recognize a greater
amount of parallelism in the medullary tubes in the Dendrodus, and
the systems of calcigerous tubes which diverge from the medullary
canals still more strikingly exhibit the difference which depends upon
their straighter and more parallel course, and which indicates the
higher type of structure in the teeth of the Dendrodus. These tubes,
in fact, instead of forming the inextricable moss-like reticulations,
which occupy the median interspaces of the medullary canals in the
Shark and Sphyrena, here run at right angles to the sides of the
tube from which they are continued, and parallel to each other, as
far as the middle of the interspace ; there they meet the extremities of
the opposite series of calcigerous tubes and are lost in minute cells.
The differences above manifested in the dental structure of the

N

178 DENDRODUS.

extinct Dendrodus, as compared with that hitherto known to cha-
racterize true fishes, is strikingly manifested both in the extent and
regularity of the radiating medullary processes, and more especially
in the straight course of the fine and close-set calcigerous tubes
which form the intervening dentine. Nevertheless I should most

—_

probably have referred these teeth without hesitation to the class

of Fishes, if so close an analogy had not been traceable between their
singular dental structure, and that still more remarkable modification
which will be shown to characterize the extinct Batrachian genus
Labyrinthodon.

If, however, as seems most probable, the Dendrodus be a
true fish, we may speculate, from the similarity alluded to, upon its
having approached in its general organization, like the Lepidosiren,
most closely to the lower confines of the reptilian class: and as this
existing annectent genus is allied to the perennibranchiate Batrachians,
so the Dendrodus may have linked some extinct group of the class of
Fishes with the equally extinct family of Sauroid Batrachians which
we have termed Labyrinthodonts. |

:
:
:
:

PAR PAM

DENTAL SYSTEM OF REPTILES.

CHAPTER I.

GENERAL CHARACTERS OF THE TEETH OF REPTILES.

67. TzxETH, properly so called, do not exist in all reptiles ; they are
absent in the whole order of Chelonia, in the Coluber scaber(1) among
the Ophidia, and in the toads among the Batrachia. In the latter eden-
tulous reptiles there is no compensating structure ; but in the Coluber
scaber, the inferior spinous processes of certain of the cervical vertebre
are unusually prolonged, and penetrate the coats of the cesophagus ;
their extremities, which are thus introduced into the alimentary canal,
are coated with a layer of hard dentine, and form substitutes for
the teeth, which, if not always entirely absent, are merely rudi-
mental in the ordinary situations in the mouth. (2)

In the tortoises and turtles the jaws are covered, as is well known,
by a sheath of horn, which in some species is of considerable thickness
and very dense ; its working surface is trenchant in the carnivorous
species, but variously sculptured and adapted for both cutting and
bruising in the vegetable feeders.

The development of the continuous horny maxillary sheath com-
mences, as in the parrot-tribe, from a series of distinct papillae, which
sink into alveolar cavities, regularly arranged (in Trionyx) along the
margins of the upper and lower jaw-bones : these alveoli are indicated
by the persistence of vascular canals long after the originally separate
tooth-like cones have become confluent and the horny sheath completed.

The teeth of the dentigerous Saurian, Ophidian and Batrachian
reptiles, are, for the most part simple and adapted for seizing and

(1) Hence called Anodon typus by Dr. Smith.

(2) Dr. Jourdan, in Cuvier, Lecons d’Anatomie Comparée, Ed. 1835, tom. 1, p 340,
tom. 4, p. 617.

nN 2

180 NUMBER. SITUATION.

holding, but not for dividing or masticating their food. The Siren
alone combines true teeth with a horny maxillary trenchant sheath
like that of the Chelonian reptiles.

68. Number.—In no reptile are the teeth reduced to so small a
number as in certain mammals and fishes, nor are they ever so
numerous as in many of the latter class. Some species of Monitor
(Varanus) with sixteen teeth in the upper and fourteen in the lower
jaw, afford examples of the smallest number in the present class, and
certain Batrachians, with teeth ‘en cardes’ at the roof of the mouth,
or which have upwards of eighty teeth in each lateral maxillary
series, present the largest number. It is rarely that the number of
teeth is fixed and determinate in any reptile so as to be characteristic
of the species.

69. Situation—The teeth may be present on the jaws only, as
in the Crocodiles and many Lizards ; or upon the jaws, and roof of
the mouth, and here either upon the pterygoid bones as in the
Iguana and Mosasaur, or upon both palatine and pterygoid bones
as in most serpents, or upon the vomer as in most Batrachia, or
upon both vomerine and pterygoid bones, as in the Axolotl, or
upon the vomerine and sphenoid bones, as in the Salamandra gluti-
nosa, Maclure. With respect to the marginal or jaw-teeth, these
may be absent in the intermaxillary bones, as in many serpents ;
or they may be present in the upper and not on the lower jaw, as in
most frogs; or in both upper and lower jaws, as in the tailed Batra-
chians ; and among these they may be supported, upon the lower jaw,
by the premandibular or dentary piece as in the Salamanders, Meno-
pome, Amphiume, Proteus ; or upon the opercular piece, as in the

Siren ; or upon both opercular and premandibular bones as in the -

Axolotl. The palatine and pterygoid teeth may, in the Batrachians,
be arranged in several rows, like the ‘ dents en cardes’ of fishes: the
sphenoid and opercular teeth are always so arranged in the few
species that possess them; the intermaxillary, maxillary and pre-

mandibular teeth are serial or in one row, with the exception of the

Cecilia and the extinct Labyrinthodon, which have a double row of
teeth at the anterior part of the lower jaw. -

70. Form.—The teeth of reptiles, with few exceptions, present a

.

FORM. | 18]

simple conical form, with the crown more or less curved, and the
apex more or less acute. The cone varies in length and thick-
ness: its transverse section is sometimes circular, but more com-
monly elliptical or oval, and this modification of the cone may be
traced through every gradation, from the thick round tooth of the
Crocodile (Pl. 62 a, fig. 9) to the sabre-shaped fang of the Varanus,
the Megalosaur (ib. fig. 6) and the Cladeiodon (ib. fig. 4). Sometimes,
as in the fully-formed teeth of the Megalosaur, one of the margins of
the compressed crown of the tooth is trenchant, sometimes both are
so ; and these may be simply sharp-edged, as in the Varanus of Timor
or finely serrated, as in the great Varanus (Pl. 68, fig. 3.), the
Megalosaur and the Cladeiodon.

The outer surface of the crown of the tooth is usually smooth ;
it may be polished, as in the Leiodon (PI. 72, fig. 1), or impressed
with fine lines, as in the Labyrinthodon (Pl. 63, 1), or raised into
many narrow ridges as in the Pleiosaur and Polyptychodon (PI. 72,
figs. 3 and 4), or broken by a few broad ridges as in the Iguanodon
(Pl. 70, fig. 1), or by a single longitudinal furrow, as in some ser-
pents.

The cone is longest and its apex sharpest in the Serpents ; from
these may be traced, chiefly in the lizard tribe, a progressive shorten-
ing, expansion of the base and blunting of the summit, of the tooth,
until the cone is reduced to a hemispherical tubercle, or plate, as in
the Thorictes (Pl. 66, fig. 6) and Cyclodus (ib. fig. 7).

In the Pleiosaur, (Pl. 68, fig. 5), the dental cone is three sided,
with one of the angles rounded off. The posterior subcompressed
teeth of the alligator present a new modification of form; here they
terminate in a mammilloid summit, supported by a slightly constricted
neck (Pl. 75, fig. 3). In the tooth of the Hyleosaur (PI. 62 a, fig. 8.) the
expanded summit is flattened, bent, and spear-shaped, with the
edges blunted. But the expansion of the crown is greatest in the
subcompressed teeth of the Iguanas (Pl. 70, figs. 6 and 7 and
Pl. 66, fig. 5), which are further complicated by having the
margins notched. The extinct Iguanodon has the crown of the tooth
expanded both in length and breadth, and combining marginal denta-
tions with longitudinal ridges, presents the most complicated external

182 ATTACHMENT.

form as yet discovered in the class of reptiles. In no reptile does
the base of the tooth ever branch into fangs.

71. Attachment.—As a general rule, the teeth of reptiles are anchy-
losed to the bone which supports them. When they continue distinct,
they may be lodged either in a continuous groove, as in the Ichthyo-
saur, or in separate sockets, as in the Plesiosaur and Crocodilians.
The base of the tooth is anchylosed to the walls of a moderately deep
socket in the extinct Megalosaur and Thecodon. In the Labyrintho-
dons and Ceciliz among the Batrachians; in most Ophidians; and
in the Geckos, Agamians, and Varanians, the base of the tooth is
imbedded in a shallow socket and confluent therewith(1). In the
Scincoidians, Safe-guards (Tejus), in most Iguanians, in the Cha-
meleons and most other Lacertian reptiles, the tooth is anchylosed
by an oblique surface extending from the base more or less upon the
outer side of the crown to an external alveolar plate of bone, as
shown in Plate 67 ; the inner alveolar plate not being developed. In the
frogs, the teeth are similarly but less firmly attached to an external
parapet of bone. The lizards which have their teeth thus attached
to the side of the jaw are termed ‘ Pleurodonts.’ In a few Iguanians,
as the Istiures, the teeth appear to be soldered to the margins of the
jaws, these have been termed ‘ Acrodonts.’ In some extinct Lacer-
tians, as the Mosasaur and Leiodon, the tooth is fixed upon a raised
conical process of bone, as shown in Plate 68, fig. ] and Plate 72,
fig. 2.

These modifications of the mode of attachment of the teeth of rep-
tiles are closely adapted to the destined application of those instruments
and to the habits of the species ; we may likewise perceive that they offer
aclose analogy to some of the transitory conditions of the human teeth.
There is a period, for example,(2) when the primitive dental pa-
pille are not defended by either an outer or an inner alveolar
process, any more than their gigantic calcified analogues in the

extinct Mosasaur. There is another stage(3) in which the groove ©

(1) Pl. 63 , fig. 8. a a, sockets of the anchylosed teeth in Varanus varius.

(2) At the sixth month, see Mr. Goodsir, On the development of the Human Teeth.—Edin-

burgh Medical and Surgical Journal, No. 138.
(3) At the seventh or eighth week.—Ibid.

—_—

SUBSTANCE. STRUCTURE. 183

containing the dental germs is defended by a single external cartila-
ginous alveolar ridge: this condition is permanently typified in most
existing lizards. Next there is developed an internal alveolar plate,
and the sacs and pulps of the teeth sink into a deep but continuous
groove, in which traces of transverse partitions soon make their
appearance: in the ancient Ichthyosaur the relation of the jaws to
the teeth never advanced beyond this stage. Finally, the dental
groove is divided by complete partitions,(1) and a separate socket is
formed for each tooth, and this stage of development is attained in
the highest organized reptiles, as in the crocodile.

72. Substance.—This may be four-fold, and a single tooth may
be composed of dentine, cement, enamel and bone; but the den-
tine and cement are present in the teeth of all reptiles.

In the Batrachian and Ophidian reptiles a thin layer of cement
invests the central body of dentine, and as usual, follows any inflec-
tions or sinuosities that may characterise the dentine. Besides the
outer coat of cement, which is thickest at the base of the teeth, a
generally thin coat of enamel defends the crown of the tooth in most
Saurians, and the last remains of the pulp are not unfrequently con-
verted into a coarse bone, both in the teeth which are anchylosed to
the jaw, and in some teeth, as those of the Ichthyosaur, which
remain free. The only modification of the dentine, which could at
all entitle it to be regarded in the light of a new or distinct substance,
is that which is peculiar, in the present class, to the teeth of the Teua-
nodon, and which will be described in the following section.

73. Structure.—The varieties of dental structure are few in the rep-
tiles as compared with either fishes or mammals, and its most compli-
cated condition arises from the interblending of the dentinal and other
substances rather than from modifications of the tissues themselves.
In the teeth of most reptiles the intimate structure of the dentine
corresponds with that which has been described as its fourth type or
modification in the teeth of fishes, and which is the prevailing structure
of mammalian dentine, viz: the radiation of a system of minute cal-
cigerous tubes from a single pulp-cavity, at right angles to the external
surface of the tooth. The most essential modification of this structure

(1) At the sixth month.—Edinburgh Medical and Surgical Journal, No. 138.

184 STRUCTURE.

is the intermingling of cylindrical processes of the pulp cavity, in the
form of medullary canals, with the finer tubular structure.(1) Another
modification is that in which the dentine maintains its normal
structure, but is folded inwardly upon itself, so as to produce a deep
longitudinal indentation on one side of the tooth: it is the expansion
of the bottom of such a longitudinal deep fold that forms the central
canal of the venom-fang of the serpent; but a glance at Pl. 65 a,
will show that, notwithstanding the singularly modified disposition
of the dentine (6), its structure remains unaltered: and although the
pulp-cavity (a) is reduced to the form of a crescentic fissure, the calci-
gerous tubes continue to radiate from it, according to the usual law.
By a similar inflection of many vertical longitudinal folds of the external
cement and external surface of the tooth, at regular intervals, around
the entire circumference of the tooth, and by a corresponding extension
of radiated processes of the pulp-cavity and dentine into the interspaces
of such inflected and converging folds, a modification of dental struc-
ture is established in certain extinct reptiles, which, by the various
sinuosities of the interblended folds of cement and processes of
dentine, with the partial dilatations of the radiated pulp-cavity,
produces the most complicated structure that has yet been met with
in the teeth of any animal, (P1.64 a). But this complication is never-
theless referable to a modification of form or arrangement rather
than of structure of the dental tissues: the calcigerous tubes in each
sinuous lobe of dentine, in the most complex tooth of the Labyrin-
thodon, exhibit the same general disposition and course as in the
fang of the Serpent and in the still more simple tooth of the Saurian.

In the Iguanodon (Pl. 71) the fine-tubed dentine is traversed
by medullary canals which run at pretty definite intervals through
the dentine, parallel with the calcigerous tubes, as in that coarser
kind of dentine which characterizes the teeth of the sloth and mega-
therium, and which, in connection with the complex form of the
teeth of the Iguanodon, peculiarly adapted that gigantic reptile for a
vegetable diet. |

The cement is simply and minutely cellular upon the crown
of the tooth, but it exhibits the radiated cells at the base of the tooth in
the anourous Batrachians, and Saurians. The enamel is subtransparent,

(1) Transactions of the British Association, 1838, p. 144.

DEVELOPMENT. 185

dense, and minutely fibrous in all the reptiles which have their teeth
defended by this substance.

74. Development.—The teeth of reptiles are never completed, as in
certain fishes, at the first or papillary stage ; but the pulp sinks into
a follicle, and becomes inclosed by a capsule: the process of develop-
ment, however, never offers the eruptive stage, in the sense in which
this is usually understood, as signifying the extrication of the young
tooth from a closed alveolus.

The completion of a tooth is soon followed by preparation for
its removal and succession : the faculty of developing new tooth-germs
seems to be unlimited in the present class, and the phenomena of
dental decadence and replacement are manifested at every period
of life: the number of teeth is generally the same in each successive
series, and the difference of size presented by the teeth of different
and distant series is considerable.

The new germ is always developed, in the first instance, at the
side of the base of the old tooth, never in the cavity of the base ; the
crocodiles form no exception to this rule. The poison-fangs of ser-
pents succeed each other from behind forwards ; in almost every other
instance, the germ of the successional tooth is developed at the inner
side of the base of its predecessor. In the frog, the dental germ
makes its appearance in the form of a papilla developed from the
bottom and towards the outer side of a small fissure in the mucous
membrane or gum that fills up the shallow groove at the inner side
of the alveolar parapet and its adherent teeth: the papilla is soon
enveloped by a capsular process of the surrounding membrane:
there is a small enamel pulp developed from the capsule opposite the
apex of the tooth; the deposition of the earthy salts in this mould is
accompanied by ossification of the capsule, which afterwards proceeds
part passu with the calcification of the dentinal papilla or pulp:
so that, with the exception of its base, the surface of the uncalcified
part of the pulp alone remains normally unadherent to the capsule.

As the tooth acquires hardness and size it presses against the
base of the contiguous attached tooth, causes a progressive absorption
of that part, and finally undermines, displaces and replaces its pre-
decessor. The number of nascent matrices of the successional teeth
is so great in the frog, and they are crowded so close together, that it

186 DEVELOPMENT.

is not unusual to find the capsules of contiguous tooth-germs becoming
adherent together as their ossification proceeds. After a brief mace-
ration the soft gum may be stripped from the shallow alveolar depres-
gion and the younger tooth-germs in different stages of growth are
brought away with it.

The mode of development of the teeth of serpents does not differ
essentially from that of the teeth of the Batrachian above described,
except in the relation of the papille of the successional poison-fangs
to the branch of the poison duct that traverses the cavity of the loose
mucous gum in which they are developed.

The situation in which the successional teeth are developed in
the Varanus is shown in Pl. 63 a, fig. 9: their relative position to,
and the mode in which they affect, the adherent teeth, by pressing
upon the inner side of their bases, is shown in the upper and lower
jaws of the Cyclodus (Plate 66, fig. 7 6): the phenomena of dental
development in these and other lizards closely correspond with those
described in the frog. In the Acrodont lizards, and those in which
the teeth are anchylosed to the summits of bony processes, the suc-
cessional teeth are in like manner developed at the inner side of
the supporting processes, gradually penetrate them as their growth
proceeds, and finally undermine and displace the tooth and become
in their turn anchylosed to new bony eminences of the alveolar
tract. The jaws of the gigantic Mosasaur exhibit on a large scale
different stages of this mode of shedding and replacement, which
is so general in the class of reptiles.

In the Ichthyosaurus, in which, by the development of an internal
as well as an external alveolar plate, the teeth are lodged in a deep

continuous groove, the successional germs were also developed in this —

extinct reptile at the inner side of their predecessors, and, from the

solidification of the implanted base of the fully formed tooth, occa- —

sioned an extensive absorption of its inner side, before it finally
yielded to the lateral pressure.

In the Crocodile, the tooth-germ is developed from the vascular —

membrane covering the base of the internal wall of the socket ; it is soon

invested by a capsule, and by its pressure causes the formation of a —

shallow recess, or secondary alveolus, in the contiguous bone (PI. 75,
fig.4). In this alveolus, however, it never becomes inclosed like the

Pn ee

BATRACHIANS. Ls7.

successional teeth in most mammalia; for, exerting equal pressure
against the fang of the contiguous tooth, which, from being incompletely
formed, has a wide pulp-cavity with very thin walls, the nascent tooth
soon penetrates that cavity, and quits the recess in the alveolar plate
in which it was originally situated. Thus the stage of develop-
ment corresponding with the ‘ eruption’ of the tooth in the mam-
malia is immediately followed by the ‘ inclusion’ of the new
tooth in the pulp-cavity of its predecessor. Further details of the
development and succession of the teeth of the Crocodiles will be
given in the chapter appropriated to the description of the dental
system in that family; but I may here observe that the rapid suc-
cession of tooth-germs, which stamps the impress of decay upon their
predecessors often before the growth of these is completed, though
common to many reptiles, is most strikingly manifested in the
Crocodiles, in which three and sometimes four generations of teeth,
sheathed one within the other, are contained in the same socket.

CHAPTER II.

TEETH OF BATRACHIANS,

75. The variations which the dental system presents in the Batra-
chian order of Reptiles are more conspicuous in the number, situa-
tion, andstructure of the teeth, than in their form or mode of attach-
ment. Certain Batrachians are edentulous, as the genus Hylaplesia,
among the tree-frogs, and the Bufonide or family of Toads, some of
the species of Bombinator excepted.

The teeth when present are generally numerous, simple, of small
and equal size, and close-set, either ina single row or aggregated
like the teeth of a rasp.

It is not without interest to observe that a characteristic condi-
tion of the dental system in fishes, viz: the absence of teeth on the
superior maxillary bone, is continued in those genera of perenni-

188 SIREN.

branchiate Batrachians which stand at the lowest step of the Reptilian
Class, and not only the superior maxillary teeth, but the bones
themselves are absent in the Siren, Menobranchus and Proteus.

76. Siren.—In the Siren (Siren lacertina, Linn.) the lower margin
of the intermaxillary bones, and the sloping anterior and upper margin
of the lower jaw are trenchant, and are each encased in a sheath of firm
albuminous, minutely fibrous tissue, harder than horn, (Pl. 62,
fig. 1). The bones thus armed slide upon each other like the blades of a
pair of curved scissors, when the mouth is closed, and are well adapted
for dividing the bodies of small fish, aquatic larve, worms, &c.
The horny substitute for teeth on the lower jaw is supported by
the bony element’ corresponding with the premandibular of the
lepidosiren and other fishes. A second osseous piece, applied to the
inner surface of the ramus of the jaw, and representing the splenial
or opercular element in the jaw of the crocodile, is beset with
numerous minute pointed teeth, arranged in short oblique rows, and
directed obliquely. backwards. The palatal surface of the mouth pre-
sents on each side two flat, thin and moderately broad bones, forming
an apparently single oblique oval plate, which converges to meet its
fellow at the anterior part of the palate, so as conjointly to constitute
a broad rasp-like surface in the form of a chevron, (Pl. 62, fig. 2).

The anterior long plate on each side, which may be regarded
as the representative of the divided vomer, supports Six or seven

oblique rows of small pointed retroverted teeth ; the smaller pos- q

terior plate, probably the homologue of the pterygoid, is beset
with four rows of similar teeth: there being thus ten or eleven
rows on each side of the palatal chevron. ‘The number of den-
ticles in the middle rows is eleven or twelve; they become fewer
in the anterior and posterior rows: they are all of similar size and
form, corresponding with those of the lower jaw to which they are
opposed.

The condition of the dental system in this, the lowest of the class

of reptiles, is not without interest independently of the absence of —

the superior maxillary teeth, and of the presence of the palatal and
inferior maxillary ‘ dents en cardes.’ If, for example, the dense sheath
of the trenchant anterior parts of the upper and lower jaws had

AXOLOTL. MENOBRANCHUS. 189

been completely calcified and converted into hard dentine, the corres-
pondence between the siren and the lepidosiren would have been
very striking in this part of their structure; but the maxillary
sheaths of the siren being composed of horn, and being, moreover,
easily detached from the subjacent bones, much more closely resem-
ble the deciduous mandibles of the tadpoles of the higher Batra-
chians. (1)

77. Axolotl.—The ichthyic character of rasp-like teeth, aggregated
in numerous series, is manifested also in the Axolotl upon the palatal
region of the mouth, and upon the splenial or opercular element of
the lower jaw ; but the superior maxiilary bones are here developed and
support teeth (Pl. 62, fig. 4). The premandibular and the inter-
maxillary bones (a), instead of presenting the larval condition of the
horny sheath, have their alveolar border armed with a single row of
small, equal, fine, and sharp pointed denticles, which are continued
above, along the maxillaries (0) ; thus establishing the commencement
of the ordinary batrachian condition of the marginal teeth of the buccal
cavity. The dentigerous bones of the palate consist of two plates on
each side, as in the siren; the anterior pair, or vomers, (c), converge
and meet at their anterior extremities ; the minute denticles which they
support are arranged quincuncially: the posterior pair of bones, (d), are
continued backwards, according to the usual disposition of the ptery-
goids, to abut against the tympanic or quadrate bones ; the denticles are
confined to the anterior part of their oral surface and resemble in their
arrangement and anchylosed attachment those of the palatal series of
which they form the posterior termination.

78. Menobranchus.—Although in this genus the superior maxillaries
and their teeth are wanting, an advance to a higher type of dentition

(1) “ Leur bord est tranchant et garni dans |’animal frais d’une gaine presque cornée, qui
se détache aisément de la gencive, et qui a son analogue dans les tétards de grenouille.”—
Cuvier, Ossem. Foss. Ed. 1837, x, p. 341. The combination of trenchant with lacerating
rasp-like dental instruments in the jaws of the Siren was recognized by Ellis, who has given
a figure of them in the 56th volume of the Philosophical Transactions, Pi. IX. c. He says,
“The mouth is small in proportion to the body; but its palate and inside of the lower jaw
are well provided with many rows of pointed teeth; with this provision of nature, added to
the sharp exterior bony edges of both the upper and under jaw, the animal seems capable of
biting and grinding the hardest kind of food.”

190 PROTEUS. AMPHIUMA.

is made by the arrangement of the teeth in a single row both upon
the roof and at the margins of the mouth. The intermaxillary bones
are produced backwards, and the single series of small pointed teeth
which they support is opposed to a similar series upon the premandi-
bular bones below ; to which elements of the lower jaw the teeth are
henceforth confined in the class of reptiles. The palatal teeth form a
single row on each of the broad bones, which correspond with those
described by Cuvier as the divided vomer in the higher Batrachians,
and extend backwards upon the pterygoids, which support a few
teeth.

79. Proteus.—The Proteus anguinus, (Pl. 62, fig. 3.) though re-
taining like the three preceding genera its external gills, offers a further
advance to the dental characters of the higher Batrachians, especially of
the amphiuma. The alveolar border of each intermaxillary bone is
armed with a row of eight or ten minute and fine sharp-pointed teeth :
each premandibular bone supports a greater number of similar but larger
teeth, likewise arranged ina single row. The palatine bones, or the
two vomers of Cuvier, support a row of denticles, similar and parallel
to the intermaxillary crescentic series: but the horns of the palatal
dental crescent are continued much further back, and terminate as in
the menobranchus, on the anterior part of the pterygoid bones: each
half of the crescentic, or chevron shaped series, contains twenty-four
teeth. The superior maxillary bones are represented in the proteus
by mere cartilaginous rudiments.

80. Amphiuma.—The Amphiume, like the proteus, presents the
batrachian disposition of the teeth in a single close-set series along
the alveolar border of both upper and lower jaws ; but the upper series
is extended along well developed maxillary, as well as intermaxillary
bones; and in the extent of the maxillary and palatal series of
teeth, especially in one species of amphiume (Amph. tridactylum),
there may be discerned the indication of a character which is of much
interest in regard to the affinities of an extinct race of gigantic Batra- .
chians with biconcave vertebra. ‘The palatal teeth in the amphiume
are arranged in a single close-set row along the lateral margins of the
vomer, meeting at an acute angle at its anterior part, from which the
series extends backwards on either side nearly longitudinally and

MENOPOMA. SIEBOLDTIA. 191

parallel with the maxillary teeth. All the teeth are conical, pointed,
slightly curved backwards and inwards; their points glisten with a
yellow metallic lustre, whence the name of Chrysodonta proposed for
this genus by Dr. Mitchell. (1)

The Amphiuma means has twenty teeth on each side of the upper
jaw, of which fifteen or sixteen are attached to the superior maxillary
and four or five to the intermaxillary bones: it has sixteen teeth on
each side of the lower jaw. There are fourteen or fifteen teeth in
each of the vomerine series.

The Amphiuma tridactylum (Pl. 62, fig. 7) has four intermaxillary
and thirty-one or two maxillary teeth on each side of the upper jaw,
and twenty-four teeth on each side of the lower jaw. It has twenty-
six to twenty-eight teeth in each vomerine series.

81. Menopoma.—The Menopome (PI. 62, fig. 5 and 6), exhibits
the same essentially batrachian condition of the teeth as the amphiume,
but in their disposition, and in the division and form of the vomer,
it makes a nearer approach to the caducibranchiate group, and allies
itself most closely with the gigantic newt of Japan, (Sieboldtia,
Bonap.) and with that equally gigantic extinct species of newt, so
noted in paleontology, as the Homo diluvw testis of Scheuchzer.(2)
In the persistence ef the branchial apertures, and the more complex
structure of os hyoides, the menopome, however, manifests its
generic distinctness from the Sieboldtia. The single close-set series
of small, equal, conical and slightly recurved teeth describes a semi-
circle on both the upper and lower jaws: the row of similar but smaller
teeth on the anterior expanded border of the divided vomer runs
parallel with, and at a short distance behind the median part of the
maxillary series, (Pl. 62, fig. 6). The premandibular teeth are received
into the narrow interspace between the two rows in the upper jaw when
the mouth is closed. The teeth of the menopome as of the amphiume
are anchylosed by their base and part of its outer side to a slightly
elevated external alveolar ridge.

82. Steboldtia.— The perennibranchiate or fish-like Batra-
chians—‘doubtful reptiles’ as they have been termed—lead by

(1) Medical Recorder, July, 1822.
(2) Philosophical Transactions, xxxiv, (1726), p. 38.

192 TRITON.

so easy a series of transitions to the caducibranchiate group, in
which all external trace of the branchial apparatus is lost, that
the artificial nature cf such a division of the order is evident,
and some Naturalists have even hesitated whether to separate,
generically, the last of the perennibranchians from the species, Sie-
boldtia gigantea, with which the description of the dental system in
the higher division of Batrachians is here commenced. As regards
the teeth, the difference between the great aquatic salamander of the
volcanic mountains of Japan and that of the Alleghanies is very
slight and merely specific ; the form, disposition and attachment of
the teeth is the same in Sieboldtia asin Menopoma ; they differ slightly
in relative size, those of the Japanese newt having the advantage in
this respect, with a somewhat deeper implantation of their anchylosed
base ; and the alveolar parapet of the intermaxillary bones is higher
and is slightly incurved. There are fourteen teeth in each intermax-
illary, seventy-two in each superior maxillary, and sixty-four teeth in
each vomer of the Szeboldtia gigantea.

83. Andrias.—The disposition, form and attachment of the teeth
in the great fossil newt or salamander, (Andrias Scheuchzeri, Tschudi),
are the same as in the menopome and Sieboldtia; but they appear to
have been relatively smaller than in the latter genus, are less com-
pressed, and present more conspicuous basal grooves. (1)

84. Triton.—All the caducibranchiate Batrachians with tails, as
the newts and land salamanders, have teeth on the inferior maxillary and
vomerine bones, as well as on the intermaxillaries and superior max-
illaries. In the common newts, as Tr. palustris, cristatus, and other
allied species of the old world, the teeth are confined to the bones above
mentioned ; they are equal, subcompressed, fine, sharp-pointed cones,

(1) Cuvier being desirous of obtaining additional evidence of the truth of his opinicn of the
real nature of the pretended Anthropolite of Scheuchzer, obtained permission, while at Harlaem,
to excavate the stone containing the celebrated fossil. ‘‘ Nous avions placé,” he says, “ devant
nous un dessin du squelette de la Salamandre, et ce ne fut pas sans une sorte de plaisir, qu’a
mesure que le ciseau enlevait un éclat de pierre, nous voyions paraitre au jour quelqu’un des os
que ce dessin avait annoncé d’avance. C’est ainsi que cette table de schiste, gravée et regravée
vingt fois depuis un siécle comme elle Vest, Pl. 253, fig. 2, fut mise dans l’état ot on la voit,
Pl. 254, fig. 2. Et d’abord nous avons trouvé autour de la rotondité, a droite et 4 gauche, une
double rangée de petites dents ; ce qui nous a fait voir que cette rotondité était produite par les
machoires et non par la crane.”—Ossemens Fossiles, Ed. 1837, tom. x, p. 372. M. Tschudi

SALAMANDRA. 193

arranged in a single close-set row along the upper and lower margins
of the mouth, and extending far back upon the roof of the mouth
ina single row along the outer margins of each vomer: these vomerine
teeth are extremely minute, (Pl. 62, fig. 9).

Most of the North American newts have a fourth locality for
teeth, which reminds us of a peculiarity of the dental system of some
of the highly organized Clupeoid fishes of the South American rivers,
viz: upon the under surface of the sphenoid bone(1) : there are four
series of these sphenoid teeth in the sub-genus Pseudotriton ; and
in the Salamandra glutinosa of Maclure, (Plethodon, Tschudi), they
are aggregated, ‘ en brosse,’ to the number of three hundred and up-
wards, upon both the basi-sphenoid and basi-occipital bones (Pl. 62,
fig. 12, e): there isa single row, set nearly transversely across the
posterior margin of each vomer c, and the marginal teeth of the mouth
of which the intermaxillary ones are shown at a and the maxillaries
at b, are arranged as usual in a single row both above and below.

85. Salamandra.—In the land salamanders, (Salamandra, Laur.)
the teeth are proportionally larger than in the newts: there are about
sixty in each lateral series of both upper and lower jaws; and forty
teeth, forming a sigmoid row on each side of the palate, in the Sala-
mandra maculata.

86. Rana.—The frogs have no teeth on the lower jaw, but in some
species the alveolar edge of this bone is finely notched or dentated, as
in the horned frogs, (Ceratophrys). The intermaxillary and max-
illary bones, support a long, close-set, single series of small,
conical, hollow teeth of which the apices only project beyond the
external alveolar ridge to which they are attached. A short trans-
verse row of similar but smaller teeth extends along the posterior
border of each vomer, except in the slender-armed frogs (Leptobra-
chium) and in some of the tree frogs, as the Euchnemis, in which the
roof of the mouth is edentulous. The teeth are relatively most deve-
loped in the Ceratophrys : they are anchylosed by their basis, and outer

has added further details respecting the dental system of this interesting Batracholite, which
prove its close alliance with the Salamandroid genera cited in the text. See his Classification
der Batrachier, 4to. 1838.

(1) M. Tschudi, |. c. p. 11.

194 RANA.

surface near the base, to a continuous alveolar groove defended by an
external wall of bone. In the common frog (Rana temporaria), there
are about forty of these teeth on each side of the upper jaw, of which
eight are supported by the intermaxillary bones. Inthe Rana esculenta,
(Pl. 62, fig. 8), there are the same number of intermaxillary, but a
greater number of maxillary teeth. In the great bull-frog, (Rana
pipiens) there are ten or twelve intermaxillary teeth, followed by
between sixty and seventy maxillary teeth (Pl. 62, fig. 10). The
largest teeth are placed in the anterior third of the series, whence
they progressively diminish in size towards the two extremities. The
vomerine bones each support a short transverse row of four or five
small teeth. The base of the teeth, besides being confluent with
the bone, are, from their close contiguity, frequently anchylosed to
one another: they are sometimes thus conjoined to near the apex.
Where the larger teeth are situated, the alternate ones are commonly
found to be displaced. The germs of the successional teeth are
developed in a groove of the mucous membrane of the mouth which ~

covers the inner side of the basis of the teeth ; as they increase in size
they press upon and cause absorption of the contiguous surface of the ©
base of the old teeth, and thus finally displace them and become in —
their turn anchylosed to the bone, then undermined and shed. As a
general rule the toads (Bufonide) are edentulous, but among the —
Bombinatores, or those species which are termed ‘< earless,’ from
having the tympanum concealed under the skin, the subgenus Hyla- —
dactylus has teeth upon the vomer and Sclerophrys has teeth on
both the intermaxillary and maxillary bones. (1) .
In microscopic structure, the teeth of the existing Batrachians —

like those of most Saurians, correspond with the simple mamma-
lian teeth.
If a longitudinal section of the tooth of a frog, including a portion
of the alveolar plate to which it is anchylosed, be examined by trans-_
mitted light under a half-inch objective, a narrow transverse line will
be seen inflected inwards from both the external and internal side of
its base, defining the limits of the tooth and bone. Below this line’
the bone is characterized by numerous large, oblong, radiated cells,
(1) M. Tschudi, 1. c. p. 3.

LABYRINTHODONTS. 195

having their long axis vertical, or in the direction of the axis of the
tooth: these cells do not extend into the substance of the tooth
itself. The dentine is composed of fine calcigerous tubes and the
intermediate clear substance, the minute cells of which are unusually
conspicuous and abundant. In acompletely formed tooth no trace of
a pulp-cavity is discernible in the prominent crown. The calcige-
rous tubes are continued into the body of the tooth at once from
the subjacent bone, in the interspace of the transverse fissure first
mentioned. The tubes nearest the external and the internal periphery of
the base of the tooth incline with a gentle curve towards those surfaces ;
but the greater number proceed vertically, and nearly parallel with
each other, to the convex line anterior to the inflected apex of the
tooth, where their extremities are slightly bent outwards, except in a
few of the tubes nearest the apex which follow its inward curvature.
The secondary undulations and branches of the calcigerous tubes are
very elegant and conspicuous: the terminal branches of these tubes
end in a rich border of calcigerous cells. The dentine is not com-
plicated with medullary canals or inflected folds of the external
cement. The convex margin of the upper half of the tooth is coated
with a layer of enamel. The concave border and the basal half of
the opposite margin exhibit a thin layer of cement. The enamel,
viewed by transmitted light, presents the same dull brownish tint as
that of the saurian and mammalian teeth ; and has a minutely undu-
lating fibrous texture.

LABYRINTHODONTS.

87. The dental system in the extinct genus Labyrinthodon is more
formidable than that of any existing Batrachian: and principally
differs, as regards its more obvious characters, in the implantation
of the teeth in distinct sockets, and in the development of certain of
the anterior teeth of both jaws into large and formidable tusks.

A close-set series of subequal teeth extends along the alveolar
border of both upper and lower jaws, and along the anterior part of
the outer margin of each broad vomerine bone: two or three canine-
shaped teeth, at least three times the size of the serial teeth, are placed

in the intermaxillary bones and at the anterior and external angle of
02

196 LABYRINTHODONTS.

each vomer, at the fore part of both the outer and inner rows of the
smaller teeth in the upper jaw; and two or three similar tusks are
implanted, somewhat irregularly, behind the anterior extremity of
the series of smaller teeth in each ramus of the lower jaw. This
allocation of teeth in a double series on the premandibular bone is
peculiar, among Reptiles, to the Cecilia and the present almost equally
aberrant form of Batrachian. It is a common dental character in
the class of fishes, and its repetition in the Labyrinthodon betrays a
tendency to the ichthyic type which is manifested by some other
of the extinct reptiles, as the Ichthyosaurus, although this genus in
its general organization is essentially related to a higher order than
that to which the Labyrinthodon belongs.

The first discovered fossils belonging to this genus were certain
detached teeth from the Keuper sandstone (Alaunschiefer) of Wirtem-
berg, of which the largest is figured at Pl. 63, fig. 1, from the ‘‘ Fossile
Reptilien in Wurtemberg,” 4to. 1828, of Prof. Jaeger, by whom the
name Mastodonsaurus was applied to these teeth under the impres-
sion that they were the remains of some gigantic Saurian reptile. (1)

Other fossil fragments of jaws and teeth, or casts of teeth, also
from the Keuper formation, (Dolomitsandstein), on which Prof.
Jaeger has founded his genus Phytosaurus, I believe to belong to the
same genus and most probably to the same species as the preceding
teeth. The most remarkable of these fossils is described as the
palatal surface of the upper jaw, measuring one foot and a half in ~
length, nine inches in breadth at the posterior part and between two —
and three inches across the narrower anterior part of the fragment.
On one side of this fragment there was a series of twenty-seven, and
probably of thirty sockets, with very narrow and not quite equal inter- —
spaces. The anterior portion containing eighteen of these serial —
sockets, and probably the fractured bases of the teeth, is copied from —
Prof. Jaeger’s work, at Pl. 63, fig. 3. At a short distance anterior to
the series of smaller teeth, there is a portion of the socket, a, or

(1) The genus Mastodonsaurus is placed in the Saurian system of M. Hermann y. Meyer, —
in the Crocodilian family, intermediate between Steneosaurus or Macrospondylus and Crocodilus : :
the species on which the genus is founded is termed, after its discoverer, Mastodonsaurus Jae-_
geri. Palzologica, 8vo. 1832, p. 107.

‘

LABYRINTHODONTS. 197

cavity for the reception of one of the great tusks. The tooth, indicated
by the letter 6, is described as exhibiting a pulp-cavity, and the adjoin-
ing tooth, c, as showing a new tooth rising into the pulp-cavity,
in progress of displacing the old tooth, after the manner of succes-
sion in the teeth of the crocodile. Pl. 63, figs. 2 and 4, repre-
sent the fossils on which Prof. Jaeger has founded respectively his
species denominated Phytosaurus cubicodon and Phytosaurus cylindri-
codon, but it is doubtful whether they are teeth or casts of the sockets of
most probably conical teeth, of which they exhibit only the shape
of the implanted base: the real teeth that have been discovered
inthe same quarry as that which yielded the preceding casts have
the form represented in fig. 5: these, like the teeth of Mastodon-
saurus Jaegeri, are conical and are marked by fine striz extending
from the base to the middle of the crown: they bear the same rela-
tive proportions to-the large tusk (PI. 63, fig. 1) as do the serial teeth
of the British species of Labyrinthodon to their anterior tusks. (1)

A third remarkable and characteristic fossil discovered in the
Keuper sandstone (alaunschiefer) and described by Prof. Jaeger, (loc.
cit. p. 38, pl. v, figs. 1 and 2), consists of the occipital portion of the
cranium with two large and separate condyles, as in the batrachian
reptiles : on this fossil the Professor founded his species called ‘‘ Sala-
mandroides giganteus.”(2) Now the teeth of the extinct Batrachians
from the New-Red Sandstone in Warwickshire correspond with
those of the so-called Mastodonsaurus, in presenting a highly cha-
racteristic and peculiar structure (Pl. 64 B, fig. 2), which has
suggested for the genus to which they belong the name of Labyrin-
thodon: and as the great teeth of the so called Mastodonsaurus
correspond in size with the cranial fragment with the batrachian
condyles above mentioned, it is highly probable that they belong
to the same species of reptile as that fragment. But it is cer-
tain that the teeth of this gigantic Keuper reptile belong

(1) The genus Phytosaurus in the Saurian system of H. von Meyer is placed between
Mosasaurus and Saurocephalus. 1 have already proved the latter to belong to the class of fishes,
and, if the Phytosawrus be identical with Mastodonsaurus, they must both be expunged from
the Saurian order.

(2) The Salamandroides giganteus of Jaeger, is placed in the system of H. von Meyer, between
the Salamandra gigantea and the Triton noachicus, in the order Batrachia: it belongs, however,

to a distinct family in that order.

198 LABYRINTHODONTS.

to the same genus as the Batrachians of the Warwick Sand-
stones, and, therefore, I shall hereafter describe the German species
under the name of Labyrinthodon Jaeger.

As the circumstances which led me to detect this generic identity
strikingly illustrate the value of the microscopic structure of teeth
as a distinctive and available test of the nature and affinities of an
extinct species, expecially in the absence of any other character, |
shall here premise the account of these investigations as communi-
cated by me tothe Geological Society of London. (1)

A question was at issue whether the light coloured sandstone of
Warwick was the equivalent of the Keuper or the Bunter division of
the New-Red Sandstone formation as developed in Germany, and its
decision had been set by one of the contending geologists upon the
issue of organic remains, more especially of the supposed Saurian
fossils of the strata in question. ‘‘ If it could be shown,” said the
able supporter of the ‘ Bunter’ theory, ‘‘ that the fossils which we
have pointed out as characterizing the upper sandstone occurred also
in the lower, and that the fragments of Saurians formed in the
sandstone of Guy’s Cliff and Warwick really belonged to the species
peculiar to the Keuper, then, indeed, we should willingly allow that
the lower sandstone also must be grouped with that formation.”

‘“* In respect to the Saurian of Guy’s Cliff, which we have had
no opportunity of examining, it is sufficient to state, that Dr. Buck-

land himself does not contend that it is either of the species of the —

Phytosaurus (Jaeger) of the German Keuper; and he hesitates even
to refer it to that genus. Now the mere existence of a Saurian in the
Warwick sandstone proves nothing; for Geologists are well aware
that various species of the family occur in all the formations, from the
lias down to the magnesian lime-stone inclusive.’ (2)

The reptilian remains figured by the authors above quoted from
the lower or Warwick sandstone were a few teeth or rather fragments

d
4

of teeth, and a portion of a vertebra: and these were the fossils to —

be compared with the reptiles peculiar to the German Keuper.

(1) Proceedings of the Geological Society, January 20th, 1841. No. 74, p. 257.

j
‘

(2) “ On the Upper Formations of the New Red Sandstone System in Gloucestershire, Wor- —
cestershire and Warwickshire, &c., by R.I. Murchison, Esq. V.P. G.S., and H. E. Strickland, —

Esq., F.G.S.”—Geological Transactions, vol. v, 2d Series, p.p. 345, 346, Pl. 28 and 29.

LABYRINTHODONTS. 199

Of such reptiles the least ambiguous and most characteristic remains
were the occipital bone of the Salamandroides giganteus of Prof.
Jaeger: and the teeth of the so called Mastodonsaurus and Phy-
tosaurus. On the other hand, the reptilian remains of the War-
wick sandstone were still more meagre: no portion of the skull
whereby their batrachian character could be tested was then known ;
the vertebra, as figured in the Memoir cited, apparently presented the
characters of those of the Saurian reptiles(1) ; and the teeth, therefore,
appeared to be the only fossils on which any comparison likely to solve
the question of the relationship between the reptiles of the German
Keuper and of the Warwick sandstone could be founded. |

Now it has been seen that the teeth of the Mastodonsaurus are of
a simple and common form; that they are far from possessing those
well-marked external characters whereby the anatomist can dis-
tinguish the teeth of the Iqguanodon, Megalosaurus or Pleiosaurus.

Of the teeth which had been discovered in the Warwick sandstone,
the specimen figured in Messrs. Murchison and Strickland’s Memoir,
and which was transmitted to me for examination together with
a similar but larger tooth, most nearly resembled the teeth of the
Mastodonsaurus, in its conical figure and longitudinal striation ; but
as these were the commonest characters of Saurian teeth no weight
could be attached to them as proving a specific or generic identity,
bearing upon a geological problem of so much nicety as the one
which related to the Warwick sandstones.

There only remained, therefore, to resort to the test of the inti-
mate structure of the teeth in question, and upon application to Prof.
Jaeger of Stuttgard, I was favoured with some portions of the teeth
of the Mastodonsaurus Jaegeri from which were prepared trans-
verse and longitudinal sections for microscopical examination.

Hitherto in investigating the intimate texture of the teeth of the
Saurian reptiles, as the Crocodile, Plesiosaur, Megalosaur, Monitor,
and most recent Lacertians, I had found the dentine or body of the
tooth to consist of the finest calcigerous tubes, radiating according to
the usual law, from the pulp-cavity, at right angles to the external sur-
face of the tooth, which is covered by a simple investment of enamel ;

(1) Subsequent examination has proved this vertebra to have a concave articular surface
at both ends of the body, and to agree in other characters with the Salamandroid type.

200 LABYRINTHODONTS.

from the prevalence of this structure in the simple conical teeth of rep-
tiles, I did not build any very strong hopes of detecting such modifica-
tions of dental structure in the similarly simple teeth of the so
called Mastodonsaurus and of the tooth from the Warwick sandstone,
as would be sufficiently marked and obvious to carry conviction of
their generic, much less specific identity. But in this I was agreeably
and unexpectedly deceived.

When I refer to figure 1 in plate 64 a, and state that the first
transparenttransverse section of the tooth of the Labyrinthodon (Masto-
donsaurus) Jaegeri that was placed under the microscope and viewed by
transmitted light, with a low magnifying power, presented the singu-
larly complicated structure there exhibited, the anatomist, conversant
with the known modifications of dental structure in the animal king-
dom, may well conceive my surprize. It was not, indeed, until I
had had sections made in various directions, from the portions of the
tooth of the Lab: Jaegeri transmitted tome, and had studied them
intently at several successive examinations, comparing the appear-
ances they presented with those of numerous examples of the teeth of
Saurians, Batrachians and other animals, that I at length compre-
hended the nature and principle of the singular cerebriform convolu-
tions or sinuosities which pervaded every portion of the tooth of this
most remarkable reptile of the Keuper sandstone.

A transverse section from the base of the tooth of the Ichthy-
osaurus gave the first clue to the structure of that of the Labyrintho-
don. Before investigating the latter | had been accustomed to regard
the tooth of the Ichthysaurus as presenting, at its base, the most
complicated condition of dental structure in the class of reptiles ;
but it is simple as compared with the structure which pervades almost
the entire tooth of the Labyrinthodon Jaegeri.

To render intelligible the plan of this structure, I may first refer
to that of the base of the tooth of the Ichthyosaurus communis (Pl. 64 8B,
fig. 3). Teeth in general, as has been shown, vary in structure ac-
cording to the number of substances which enter into their composition,
and according to the disposition of those substances. In the ungulate

mammalia, as the elephant, rhinoceros, horse, etc., in which the —

crown of the tooth consists of dentine, enamel and cement, vertical
folds of the enamel and cement penetrate the body of the tooth, and

' LABYRINTHODONTS. 201

receive in their interspaces corresponding vertical processes of the
dentine: the consequence of this disposition in maintaining a
grinding surface of the tooth, by the unequal attrition of the edges of
the interblended lamine is well known.

The pattern, however, after which the folds of enamel and cement
are inflected into the substance of the tooth in these and other her-
bivorous species, although determinate in and characteristic of each
genus or species, is always more or less irregular and unsymmetrical :
there is no instance in the mammiferous class of these folds converg-
ing at regular intervals all round the circumference of the tooth towards
its centre. Such a disposition of the external substance of the tooth
may be traced at the base of the tooth ina few fishes, but is more
conspicuous in the fang of the tooth of the Ichthyosaur. Here,
the external layer of cement (for the enamel ceases at the base of
the crown) is inflected, at pretty regular distances round the circum-
ference of the tooth, towards its centre; the vertical folds being
straight or plane, and extending toa distance about equal to the breadth
of their interspaces. These interspaces are occupied by corresponding
processes of the dentine, which radiate, or diverge from the central
mass of that substance.

If we could suppose the tooth of the Ichthyosaur to be worn
down in the living animal by the masticatory uses to its complicated
basis, then an eighth part of the diameter of the tooth, around its
circumference, would present a series of ridges of the denser substance
converging in straight lines from that circumference.

The plan and principle of the structure of the Labyrinthodon’s
tooth is the same as that of the tooth of the Ichthyosaur but it is
carried out to the highest degree of complication. The converging
folds of the external cement, instead of being arrested at one fourth
of the distance from the circumference to the centre of the tooth, are
continued close to that centre; and, instead of being simple, straight,
or plane lamelle, they are bent upon themselves in a series of sinuous
folds, resembling the anfractuosities of the brain. The ordinary
laws of the complication of dental structure are here, however,
strictly adhered to, and every space intercepted by a convolution of
the converging folds of the cement, is occupied by a corresponding

202 LABYRINTHODONTS.

process of the diverging layers of the dentine, and thus is produced
the singularly complicated appearance which a transverse section of
the tooth of the Labyrinthodon or Mastodonsaurus exhibits.

The external longitudinal flutings of the base of the tooth of the
Ichthyosaur are much coarser, and more indicative of the converg-
ing vertical folds of the cement, than are the corresponding longi-
tudinal lines on the exterior of the tooth of the Labyrinthodon ;
which is owing to the layer of the inflected cement being much
thicker in the Ichthyosaur. The external strie of the Labyrintho-
don’s tooth are too little conspicuous to attract particular attention,
or to indicate that they are the lines of inflection of a series of
extensive vertical folds of the external substance. Accordingly Professor
Jaeger describes the tooth of the Mastodonsaurus as being longi-
tudinally striated on the superficies, noting where the striv termi-
nate their relative distances, and where they are most marked: the
texture of the tooth, where it was exposed by fracture, he pronounces,
as indeed it appears to the naked eye, to be uniform, homogeneous
and compact(1), and he concludes his description by stating that the
tooth resembles most closely that of the Lacerta nilotica and of some
species of Monitor.

The teeth, however, of those species of Varanus, Lacerta, Monitor,
and other Saurian genera which I have submitted to microscopic
investigation, have all presented the usual structure of simple Saurian
teeth.

The portion of the tooth of the Labyrinthodon Jaeger from
which the sections here described, were prepared, included
about the middie third part of a tusk nearly as large as the one

figured by Prof. Jaeger (2). That tooth is three inches and a_

half in length, and one inch and a half in breadth at the base,

whence it gradually contracts, with a slight bend, towards the ©

apex: this is obtuse, witha slightly depressed summit ; it is three lines
in diameter, and presents a small rising in the centre of the terminal

depression. The external longitudinal striae are regularly arranged —

with intervals of about a line at the base of the tooth ; and they main-
tain nearly the same relative position throughout the lower three

(1) Jaeger, loc. cit. p. 36. (2) Loc. cit. tab. iv. fig. 4.

LABYRINTHODONTS. 203

fourths of the tooth, by decreasing in number as the tooth diminishes
in thickness ; they finally altogether disappear about half an inch from
the summit of the tooth: and at this part, from the analogy of other
species of Labyrinthodon, itis to be presumed that the structure of the
tooth of the Lab. Jaegeri may be more simple.

The dentine or body of the tooth is invested by only a very thin
layer of cement, and it is a vertical fold or duplicature of this cement
which penetrates the substance of the tooth at each of the strie,
which, as before observed, are arranged at intervals of about one line,
around the whole circumference of the tooth. The inflected fold runs
straight for about half a line, and then becomes wavy, the folds rapidly
increasing in breadth as they recede from the periphery of the tooth ;
the first two, three, or four undulations are simple; then their con-
tour itself becomes broken by smaller or secondary undulations ;
these become stronger as the fold approaches the centre of the
tooth, when it slightly increases in thickness, and finally terminates
by a slight dilatation or loop close to the pulp-cavity, from which the
free margin of the inflected fold of cement is separated by an ex-
tremely thin layer of dentine. The number of the inflected converging
folds of dentine is about fifty at the middle of the crown of the tooth,
but it must be greater at the base. All the inflected folds of cement
at the base of the tooth have probably the same complicated disposi-
tion with increased extent; but, as they approach their termination
towards the upper part of the tooth, they also gradually diminish in
breadth, and consequently penetrate toa less distance into the sub-
stance of the tooth. Hence, in such a section as is delineated, it will be
observed that some of the convoluted folds, as those marked c c Pl. 64 a,
fig 1, extend near to the centre of the tooth ; others, as those marked
d d, reach only about half way to the centre ; and those folds, which,
to use a geological expression, are ‘ cropping out’, penetrate to a very
short distance into the dentine, and resemble in their extent and
simplicity the converging folds of cement in the fangs of the tooth of
the Ichthyosaurus.

The disposition of the dentine in the tooth of the Labyrinthodon
Jaegeri is still more complicated than that of the cement. It consists
ofa slender, central, conical column, excavated by a conical pulp-cavity

204 LABYRINTHODONTS.

for a certain distance from the base, and radiating outwards from its

circumference a series of vertical plates, which divide into two, once ~

or twice before they terminate at the periphery of the tooth. ,
Each of these diverging and dichotomizing plates gives off
throughout its course smaller processes which stand at right angles or
nearly so to the main plate ; they are generally opposite, but sometimes
alternate : many of the secondary plates or processes which are given
off near the centre of the tooth, also divide into two before they ter-

minate; and their contour is seen, in the transverse section, to .
partake of all the undulations of the folds of cement, which ~

invest and divide the dentinal plates and processes from each
other.
The dental pulp-cavity is reduced to a mere line about the upper

third of the tooth, but throughout its whole extent fissures radiate from —

it, corresponding in number with the radiating plates of dentine.
Each fissure is continued along the middle of each plate, dividing

where this divides, and extending along the middle of each bifurcation |

and process, to within a short distance of the line of cement. The
pulp-fissure commonly dilates into a canal at the origin of the lateral
processes of the radiating plates, before it divides to accompany and
penetrate those processes.

The main fissures or radiations of the pulp-cavity extend to within

a line or half a line of the periphery of the tooth, and suddenly dilate at —
their terminations into spaces, which, in transverse section are subcir- —

cular, oval or pyriform (Pl. 64, 6b) : the branches of the radiating lines,
which are continued into the lateral secondary plates or processes of
the dentinal lamellz, likewise dilate into similar and generally smaller

spaces. All these spaces or canals, in the living tooth, must have —

been occupied by corresponding processes of the vascular pulp: they

constitute as many centres of radiation of the fine calcigerous tubes,

which with their uniting clear substance constitute the dentine.
Throughout every part of this complicated tooth, the calcigerous

tubes were found, in their course, to obey the usual law, radiating or —
converging, with primary curvatures and secondary undulations, at
right angles or nearly so to the surface of the dentine which the cement —

invests. The number of these calcigerous tubes, which are themselves

a es

QO ee ee ee ee

LABYRINTHODONTS. 205

the centres of minor ramifications, defies all calculation. Their diameter
is jth line, with interspaces equal to seven diameters of their cavi-
ties. Their general disposition is shown ina section of one of the simple
Jateral processes of the radiating plates of dentine (Pl. 64 a, fig. 2).
The undulation and ramification of the extremities of two of the calci-
gerous tubes, magnified 650 diameters are figured at Pl. 64 a, fig. 3.

It has already been stated that among the few teeth, presumed to
be saurian, from the lower Warwick sandstone, the small conical exter-
nally striated one, figured in Plate 62 a, fig. 2, bears the nearest
resemblance to the teeth of the German Labyrinthodon; it is, however,
much smaller, and the cone is broader and shorter, and the base of the
tooth is more ventricose.

I subsequently received a larger tooth from Dr. Lloyd, which was
discovered in the Warwick sandstone at the Coten-end quarry. This
tooth (Pl. 64 8, fig. 1) presented a more simple and regular conical
shape, and differed from the tusk of the great Labyrinthodon Jaegeri in
being somewhat more compressed at the base, and less obtuse at the
apex. Its external surface was similarly impressed with fine longitudinal
strize continued, with a very slight degree of convergence, towards the
apex of the tooth, where the longest strize terminated. The interspaces
of the striz were more prominent and convex than in the tooth of the
Lab. Jaegeri. The apex of the tooth, though obtuse, was worn
by attrition obliquely down one side, and did not present the depression
and central eminence which Prof. Jaeger describes in the large tooth
of his species ; this difference might, however, be due to the mode
in which the tooth had been used or worn down.

The main point to be determined was whether and to what extent
the apparently simple conical tooth from the English sandstone would
‘correspond with that of the German Batrachian in the complicated struc-
ture above described. I could perceive indications, at the fractured basis
of the Warwick tooth of fissures leading from the external striz into
the substance of the tooth. Were these fissures continued to the same
extent, or in the same sinuous course which they had presented in the
tooth of the Labyrinthodon Jaeger? This could not be ascertained by
inspection of the fractured surfaces of the dense and opake tooth either
by unaided vision or the use of the microscope by reflected light.

206 LABYRINTHODONTS.

With the kind permission of Dr. Lloyd, 1 took a thin transparent
transverse section from the middle of the tooth, corresponding with
the place of the section from the German tooth above described :
at Pl. 64 8, fig. 2, is shown the structure of the tooth of the British
Labyrinthodon as seen by transmitted light in one half of the
transverse section: the complication of the interblended laminz of
dentine and cement is as remarkable, and its plan is the same as in
the tooth of the great Labyrinthodon of the German Keuper.
All the peculiarities, indeed, of this most extraordinary type of
dental structure are so closely preserved in the specimen from the
Warwick sandstone, that generic identity, at least, may be predicated
of the fossils from both localities.

The differences which require to be noticed are such as might
be expected in distinct species of the same genus. The inflected folds
of cement in the Warwick tooth are continued for a greater relative
extent before the lateral sinuosities commence, than in the German
reptile, and the inflections or anfractuosities are rather fewer in
number; some of the inflected converging folds in the Warwick
tooth, having nearly reached the central pulp-cavity, are reflected
backwards for a short distance before they terminate.

The modifications of the complex diverging plates of dentine
correspond with those of the tooth of the Labyrinthodon Jaegeri ; but
their terminal quadrilateral lobes, as seen in the transverse section,
are relatively longer.

The number of the inflected folds of cement is equal to that
in the Lab. Jaegeri and varies in the same degree at different
parts of the tooth; thus the folds which reach longitudinally to
near the apex of the tooth extend inwards to near its centre in
the section figured, and the shorter folds are inflected to a less
extent proportionate to their diminished length.

The dentine is composed of calcigerous tubes of the same
relative size and disposition as in the Labyrinthodon Jaegert. The
base of the tooth appeared to have been similarly anchylosed to the
osseous substance of the jaw.

After having adduced this evidence of the affinity of the fos-

sils of the German and British sandstones, I concluded by stating |

|

LABYRINTHODONTS. 207

that the results of the comparison might be deemed to be decisive
as to the existence of reptiles in the latter formation, which belong
to the same natural genus as does one of the most peculiar of the
extinct reptiles of the German Keuper.

So far, therefore, as the geological question, to which reference
was made at the beginning of the present section, depends upon the
determination of the generic identity of the reptilian fossils in these
formations, it must be regarded as supporting the view entertained by
Dr. Buckland of the correspondence of the Warwick and Bromsgrove
sandstones with the Keuper sandstones of Germany. And if, on the
one hand, geology has, in this instance, derived any benefit from
microscopical investigations of animal tissues, on the other hand it
must be admitted that in no instance has comparative anatomy been
more directly indebted to geology than for the fossils, and the
stimulus to their microscopic investigation, by means of which a
knowledge has been obtained of the most beautiful and complicated
modification of dental structure hitherto known, and of which no
adequate conception could have been gained from investigations,
however close and extensive, of the teeth of existing species of animals.

88. Labyrinthodon leptognathus.—When the results of this com-
parison of the microscopic structure of the tooth of the Labyrinthodon
Jaegert and of the smaller tooth of the Warwick sandstone were
communicated to Dr. Lloyd, he transmitted for my inspection all the
fossils from the same stratum which had been deposited in the local
or private museums of Warwick and Leamington, with permission to
apply the microscopic test to any of the teeth which these fossils
might contain. I shall here briefly notice such of these fossils as
throw additional light on the dental characters of the species to which
they belonged.

The most valuable and characteristic fossil in this respect is the
anterior part of one side of the upper jaw, including the nasal
bones (Pl. 63 a, figs. 1 and 3). It shows that the maxillary or facial
division of the skull was broad, much depressed and flattened,
resembling in this respect the skull of the gigantic salamander and
alligator, and having the outer surface of the bones strongly sculp-
tured by depressions and furrows as in the crocodilian family.

208 LABYRINTHODONTS.

The portion of the superior maxillary bone contains the anterior
part of the single row of small teeth, and the base of one of the great
anterior tusks, which ranges in the same line with the other teeth,
but is directed obliquely backwards; the small serial teeth pro-
ject more vertically from the alveolar margin of the jaws and
are slightly inclined outwards. In a few places the contiguous
teeth are present, but throughout the greater part of the series there
is alternately a tooth and an empty socket. The sockets are shallow,
and are so closely arranged, that, although the alveolar series in the
present fragments is but two inches, three lines in extent, it con-
tains thirty-one sockets. The large anterior fang is three times
the size of the first of the serial teeth which succeeds it; and the rest
gradually diminish as they recede backwards, so that the eighth tooth,
counting the sockets from the first, is little more than half a line in
diameter at its base; beyond this the teeth are of equal size. Hach
of the serial teeth is slender in proportion to its length, and gradually
diminishes from the middle of the crown to the apex, which is not
very acute where entire ; a linear pulp-cavity is continued along the
centre of the tooth nearly to the apex. The transverse section of
the base is elliptical, its smallest diameter being in the axis of the
jaw ; that of the apical two thirds of the tooth is circular ; the basal
third is finely fluted, the rest of the tooth is smooth. The outer wall
of the socket is very thin, and is confluent with the fluted base of
the tooth. From the flatness and thinness of the maxillary bones, the
sockets of the teeth are necessarily shallow. The length of the com-
mon sized serial teeth is about two lines, their greatest diameter one
third of a line; the diameter of the base of the large anterior tusk
is two lines and a half.

The whole of the under surface of the fossil was covered by the
sandstone matrix, but the fractured margin, opposite the alveolar
border, exhibited the edge of a thin plate of bone, uninterrupted in
the longitudinal extent, and forming the floor of a wide and shallow
nasal cavity, thus affording a strong indication that the Labyrinthodon
breathed air like the higher reptiles. That the bony palate extended
as far in the transverse as in the longitudinal extent was indicated
by the projecting base of a fractured conical tooth, twice the size

LABYRINTHODONTS. 209

of the large anterior fang of the maxillary series, and situated
internal to the anterior small serial teeth. The crocodilian affinities
of the Labyrinthodon we have just seen to have been manifested in
the character of the bones forming the upper surface of the maxillary
part of the cranium, and by the interception of a wide and shallow
nasal cavity between two horizontal plates of bone. The main test
of the value of this manifestation would be the actual condition of the
bony palate, first in regard to the bones composing it, and secondly
in relation to the dental system. In Crocodiles the floor of the nasal
cavity is chiefly formed by the maxillary bones, in Batrachians by
the divided and expanded vomer ; in all Crocodiles the bones of the
palate are edentulous, in most Batrachians they support teeth. There
was evidence in the fossil in question of a large laniary tooth project-
ing from the palatal surface of the mouth, internal to the series of max-
illary teeth ; it remained to be determined whether this was supported
upon the same bone which supported the serial teeth, viz. the superior
maxillary, or whether it was a true palatal or vomerine tooth. A
careful removal of the adherent matrix brought to light this very
instructive part of the cranial anatomy of the Labyrinthodon, (PI.
63 a, fig. 3). The palatal processes of the maxillary bones instead
of extending to the middle line, as in the Crocodiles, are very
narrow, as in the Batrachians. The osseous roof of the mouth is
principally constituted by a pair of broad and flat bones analogous
to those which Cuvier describes as a divided vomer in the Batra-
chians. These bones are, however, of greater relative extent than
in any existing Batrachians; they defend the mouth with a more
complete bony roof than is present in most Lacertian reptiles.
Physiologically the Labyrinthodon in this part of its structure
comes nearest to the crocodile, but the structure itself, morphologi-
cally, is essentially Batrachian ; that is to say, the bony palate is
formed by largely developed vomerine bones, situated, as in the
Batrachians, at a part of the skull which is occupied solely by the
maxillary bones in the crocodiles.

The divided vomer varies much in form in the Batrachians ; that
of the Menopome most resembles the vomer of the Labyrinthodon
in its broad anterior extremity, and the large tooth (fig. 3, ¢) 1s

P

210 LABYRINTHODONTS.

situated on the outer part of this expanded extremity of the vomer in
the present species of Labyrinthodon. The corresponding part of the
vomer in the Menopome and gigantic Salamander supports a trans-
verse row of small teeth; and the large tooth of the Labyrinthodon

is the outermost of a similar transverse row of teeth extending, five in ©

number, across the anterior expansion of each lateral moiety of the
vomer, the three median teeth being small and equal, the two outer-
most much larger. In the present fossil these teeth appear to have

been alternately shed; that is the first, third, and fifth, counting |
outwards from the middle line are in place; the second and fourth —

are indicated by their empty sockets. This is analogous to the |
condition of the maxillary series of teeth; it is a course or order —
of shedding and renewal which is common in many fishes, where ~

these processes succeed each other frequently and quickly, and by ~

:

which the dental series is always kept in an efficient state. The

outermost or fifth tooth is placed behind, as well as to the outer side
of the socket of the fourth displaced tooth ; and while it terminates
the transverse row of the vomerine teeth, it forms the commencement

;

of a longitudinal row of small and equal-sized teeth which is continued |
backward along the outer margin of each vomerine bone (fig. 3c); —

the whole of the vomerine series of teeth thus describes a curve, —

’
|
7
:
|

nearly concentric and parallel with the external maxillary series of
teeth ; and the large fangs occupy corresponding situations in both
the outer and the inner row of the teeth of the upper jaw.

In the Saurian reptiles, the examples of such an inner or

palatal row of teeth are comparatively few, and the series, when —

it does exist, is very short, and is situated towards the back of

the palate upon the pterygoid bones, as in the iguana, aporo-—

mera and mosasaur. In the Ophidians, the inner rows of teeth

are situated on the palatine and pterygoid bones, and are never
arranged transversely to the axis of the mouth. In the Ba-—

trachians this is the most common disposition of the palatal

teeth; they form a short transverse series at the posterior 3

part of the divided vomer in the frog, and at the anterior part |
of the vomer in the menopome and gigantic salamander ; in the
amphiume, the palatal teeth form a nearly longitudinal series, along

LABYRINTHODONTS. Ql

each outer margin of the long and narrow vomer ; the extinct Laby-
rinthodon combines both these dispositions of the vomerine teeth.
The next fossil which I proceed to describe, and which, like the
preceding one, is from the sandstone in the neighbourhood of
Warwick, also throws much light upon the dental system and
affinities of the present singular genus of extinct reptiles. It is the
anterior dentigerous part of the ramus of the lower jaw, a portion
of which is figured at Pl. 63 a, fig. 2. This ramus is slender,
straight, and with its symphysial extremity abruptly bent inwards,
the inner line of the symphysis here forming a regular and deep
curve. The breadth of the bone at the posterior fractured part
is ten lines; at the anterior part, behind the inflected symphysis,
seven lines; the breadth of the anterior fractured portion is one
inch. The structure of this long and straight ramus of the jaw
presents almost as striking a batrachian character as any of those
derived from the foregoing fossil; that is to say, the angular piece
is of great breadth, and is continued forwards to near the sym-
physis, forming the whole of the inferior part of the ramus of the
jaw extending upon the inner as far as upon the outer side of the
ramus ; the inner plate performing the function of the detached
‘“os operculare” in the lower jaw of the Saurians. The dentary
piece is supported upon a deep and wide groove, extending along the
upper surface of the angular piece and looking obliquely outwards.
The angular piece projects beyond the outer edge of the groove,
so as to form a strong convex ridge on the external side of the jaw
below the dentary piece ; this character, which in the large bull-frog
(Rana pipiens) is confined to the posterior part of the maxillary
ramus is here continued to near the anterior extremity, and forms a
conspicuous character of the jaw of the Labyrinthodon. The teeth
_in the present ramus are long and slender, and so closely correspond
in size and shape with those in the upper jaw, just described, that
they must be regarded as belonging to the same species.(1) There are
not less than fifty sockets in a single linear series, and at the anterior
inflected part of the jaw there is the base of the socket of a large
tooth, six lines in diameter: the serial teeth gradually diminish in

(1) The specific name, leptognathus, relates to the slenderness of this long lower jaw.
p 2

2T2 LABYRINTHODONTS.

size towards the anterior portion of the jaw; the posterior teeth,
which are slightly compressed at their base in the antero-posterior
direction, present at that part about a line and a half in diameter; ©
the anterior ones measure half a line across the same part ; the length of —
some of these small anterior teeth above the sockets is three lines, they —
are terminated bya sub-acute apex. The sockets do not lie between
parallel lines ; the alternate ones are placed a little more internally.
The teeth were present chiefly in the more external sockets ; but
where they remained in both, the row of teeth presented the same
slightly zig-zag disposition. ‘The sockets of the teeth are more .
shallow in the present than in the preceding fossil ; the outer alveolar
wall is rather more developed than the inner, and the anchylosed bases
of the teeth more nearly resemble in their oblique position those of the
existing Batrachians. The teeth are directed slightly inwards, and are —
probably received, like those of the Menopome, into the interval |
between the maxillary and vomerine series of the upper jaw, when the
mouth is closed. | .
The fine external striation and fluting is confined to the basal _
third of the tooth, as are also the labyrinthic inflections of the
external cement. Above this part, the dentine consists of fine |
calcigerous tubes, radiating from the linear remains of the pulp-—
cavity at right angles to the surface of the tooth; being parallel
with the axis of the tooth, where they form its apex, and gra-
dually inclining outwards until they become transverse to that
axis, which is their general disposition in the body of the tooth,
between the apex and the commencement of the inflected verti- |
cal folds of the cement. At its apical part, therefore, the tooth
of the Labyrinthodon resembles in the simplicity of its intimate
structure that of the entire tooth of the ordinary Batrachia and—
of most reptiles. The vertical inflected processes of the cement are.
at first short and straight, occurring at pretty regular distances"
around the circumference of the tooth; so that here the tooth par-
takes of the structure which has already been said to characterize }
the base of the tooth of the Ichthyosaurus. Soon, however, the
primitive inflected folds of cement sink deeper into the dentine and
commence their undulating course, and as_ the tooth expands,

a _

LABYRINTHODONTS. 913

other processes, at first simple like the preceding, begin to pene-
trate the dentine at the interspaces of the primary folds; these
likewise take on a sinuous course a little nearer the base of the
tooth ; the diverging plates of dentine send off lateral lobes or pro-
cesses corresponding with these sinuosities, and a transverse section
at this part of the tooth exhibits the modification of the labyrin-
thic structure exhibited in Pl. 63 3, fig 2.

The anchylosis of the base of the teeth to distinct and shallow
sockets is a structure in which the Labyrinthodon resembles certain
fishes, as the Sphyrena; I am disposed also to believe, from the
absence of any excavation in the base of the fixed teeth, or of any
trace of alveoli of reserve for the successional teeth, that these were
developed, as in many fishes, in the soft mucous membrane or gum
which covered the alveolar margin, and that they subsequently became
fixed to the bone by anchylosis. Thus, notwithstanding the close
resemblance to the Crocodilian type which the Labyrinthodon pre
sents in the form and superficial sculpturing of the skull, it deviate:
widely in the mode of fixation and reproduction of the teeth.
Nor is it extraordinary that the present extinct Batrachian genus
should have its relations of affinity thus radiating in different direc-
tions, since we find in the extinct reptilian forms of a later epoch
the combination of Saurian characters with Ichthyic vertebrae and
extremities.

89. Labyrinthodon pachygnathus.—A second and larger species of
Labyrinthodon is established upon certain fossils from the lower sand-
stones of Warwick, of which I shall here describe those that appertain
to the dental system. The most instructive specimen is a well pre-
served and considerable proportion of the right ramus of the lower
jaw, measuring nine inches and a half in length ; the anterior extre-
mity of this specimen is represented of the natural size at Plate 63 a,
fig.4 and 5. The bone is thick and rounded, one inch and a hal!
deep, and one inch broad at the posterior fractured part, thirteen
lines broad and eight lines deep at the anterior expanded and sub-
depressed end, which is curved inwards towards the symphysis of the
jaw, and which supports two of the great cuspidate or laniary
teeth, and the socket of a third. The structure of this lower jaw,

j
214 LABYRINTHODONTS.

which was broken across into two nearly equal portions, was the —

it appeared to be strengthened by an opercular piece in the form
of a thin plate, gradually narrowing to a point, and terminating
at the beginning of the inward curvature of the ramus (fig. 4).
Two transverse fractures of this lower jaw display the rela-
tions of the external plate of the angular piece with the thin internal
bony lamina ; the two pieces are uninterruptedly confluent, and form
a single broad and strong piece of bone, supporting the dentary piece —
upon a groove along its upper surface, and terminating anteriorly
at the bend of the expanded premandibular or dentary element, which
there receives the extremity of the angular bone in a notch; the
batrachian character is thus as clearly established by the present
as by the preceding fragment of the lower jaw. A similar portion
of the lower jaw of a Saurian would have exhibited either the dentary —
element alone, or the anterior extremity of the opercular element in !
the form of a thin plate applied and limited to the inner side of the
dentary piece. The continuation of the angular element alone, forming —
the lower half of the ramus, to near the symphysis, and supporting —
the dentary piece in a groove on its upper surface is as striking a
Batrachian character in the fossil of the British sandstone, as that
observed by Prof. Jaeger in the occipital bone of the great Labyrin-
thodon (Salamandroides giganteus) Jaegeri of the German Keuper. ©
The smaller serial teeth in the present portion of jaw are about
forty in number, and their sockets are in close contact with each
other ; they very gradually diminish in size as they approach both
ends of the series. Two of the smallest teeth (b') at the anterior part of
the jaw are recumbent, in front of the great laniaries ; they may have
been incompletely developed teeth of replacement, not yet erected and
anchylosed to the bone.
The alternate sockets are empty in a considerable portion of the
posterior part of the series, agreeably with the order of shedding
and renovation illustrated in the Labyrinthodon leptognathus, so that
the teeth thus appear to be separated by wider intervals than they
really are. The form of the teeth is conical, with the base slightly
compressed in the direction of the axis of the jaw; the largest trans-

first object of attention. On the inner side of the anterior moiety

LABYRINTHODONTS. ad

verse diameter of one of the posterior of these serial teeth, where it
emerges from the socket, is three lines; the same diameter of the
anterior serial tooth is one line and a half; its length, four lines anda
half. The great laniary teeth (a) appear to be three in number in each
symphysis, and the one nearest the symphysis is somewhat larger
than the others, but they are probably not all in place and use at the
same time. The greatest diameter of the sub-compressed base of the
largest of these fangs is five lines; its length, judging from an entire
tooth of the same species, must have been at least one inch anda
half. The lines of the inflected cement form well marked longitu-
dinal striz around the basal half of the tooth, and the interspaces
of the striz form convex ridges, as in the large tooth, the labyrinthic
structure of which was described at p. 201. These ridges are
fewest near the termination of the striz, being divided and multiplied
by new longitudinal strize, caused by new inflected folds of the
cement near the basis of the tooth; the apical half of the tooth has
a smooth and polished external surface ; the pulp-cavity is con-
tinued of small size into the centre of this part of the tooth. In the
serial teeth, which, except their less gradual diminution of size, cor-
respond with the anterior larger tusks, the central pulp-cavity is more
quickly obliterated ; the texture of the teeth is dense and brittle.

I have examined the structure of the serial teeth in a small
fragment of the upper jaw of the Labyrinthodon pachygnathus,
from the same locality as the lower jaw; this fragment was
three inches and a half in length, and included twenty-four sockets of
the serial teeth, the alternate teeth being in place though broken.
These teeth precisely corresponded in size and form with those of the
lower jaw. The labyrinthic structure is confined to the basal half of
the tooth, where it is indicated by the external striation, and becomes
more complex as it approaches the base. The blending of the exter-
nal layer of cement with the dentine, as exhibited by a transverse sec-
tion of the tooth above this part, well illustrates the principle of the
more complicated modifications of the labyrinthic structure first dis-
covered. ‘The processes of dentine which radiate from the pulp-cavity
(Pl. 63 8, fig. 1, a), are twelve in number at the line of the section
here described, but most of them divide in their course outwards ;
the corresponding pulp-fissures diverge in straight lines, bifurcate

216 LABYRINTHODONTS.

where the lobes divide, and terminate each in a dilated cavity, or
medullary canal, about half way between the centre and the circum-
ference of the tooth. In like manner the inflected folds of cement
(b, b), converging from the circumference of the section, proceed
inwards in a straight line, half way or three fourths of the way to the
central pulp-cavity; the commencement of the lateral inflection of one
of the longest of these folds is shown at b. The inflected substance con-
sists of a very thin layer of cement. The calcigerous tubes radiate
according to the usual laws, and resemble in diameter, in the
width of their interspaces, in their secondary undulations, their
dichotomous bifurcations and small lateral branches, the same
tubes in the complex labyrinthic structure of the tusk, figured in
Plate 64 a. The exterior or first formed part of the basal portion of
the tooth resembles the above described apical part in the compara-
tive simplicity of the alternate folds of cement and processes of den-
tine ; but the central mass of the basal moiety of the tooth presents
the labyrinthic disposition of these tissues: it may be said that the
simple exterior crust of the tooth incloses and is expanded by the
more complicated structure. The thickness of the exterior more
simple structure is nearly the same in the serial teeth and the large
tusks, so that the proportion of the central labyrinthic mass is greater
in the latter, and its structure is likewise more complicated. In the
serial teeth of the Lab. pachygnathus, the structure of the basal half
of the tooth resembles that of the same part in the Lab. leptognathus,
which is figured as seen in transverse section at Pl. 63 3, fig. 2.

The alveoli, in both upper and lower jaws of the Lab.
pachygnathus are large, moderately deep, but complete. _The outer
wall of the alveolar processes in the lower jaw of the Lab. pa-
chygnathus is not higher than the inner wall. In this structure,
therefore, as well as in the division of the alveolar groove into
sockets, the Labyrinthodon manifests an affinity to the Crocodilian
and Pleriosaurian reptiles ; but, on the other hand, a similarly com-
plete dental socket is present in certain Scomberoid and Sauroid
fishes ; and, as in these fishes, the base of the tooth is anchylosed to
the socket in both the Labyrinthodon pachygnathus and Lab. lepto-
gnathus. A still more striking Ichthyic character is manifested by the
Lab. pachygnathus in the continuation of the row of small teeth

CACILIA. 217

anterior and external to the three larger teeth. For a double series of
teeth, thus occasioned, does not exist in the maxillary or preman-
dibular bones of any Batrachian or Saurian reptile ; and, in the mam-
malia, the only instance of such a disposition of the teeth is the
exceptional presence of the small incisors behind the dentes scalprarii
of the hares and rabbits; but the location of large tusks in front or
behind a row of smaller teeth is a character which has hitherto been
met with only in the jaws of fishes. This, therefore, must be
regarded as another of the Ichthyic characters which are retained in
the lowest forms of reptiles, and which is thus manifested in a new
way in the primeval Batrachians, whose dental characters and pecu-
liarities we have been endeavouring to interpret.

CZECILIA,

90. In the extinct family of the Labyrinthodonts the Batrachian
type of organization was modified so as to lead directly from that order
to the highest forms of reptiles, viz: the loricate or crocodilian Sauria ;
some of the existing edentulous genera of Bufonide connect the
Batrachian with the Chelonian order ; the family founded upon the
Linnean genus Cecilia forms the transition to the Ophidian rep-
tiles. The characters which retain the Ceciliz in the Batrachian
order are generally known, and may be briefly enumerated as the
double occipital condyle, the biconcave vertebra, the smooth mucous
integument with minute and concealed scales, and the branchial aper-
tures retained by the young some time after their birth. In the fixed
tympanic pedicle and the anchylosed symphysis of the lower jaw the
Ceciliz are also far removed from the typical ophidian structures ; but
the teeth in their length, slenderness, sharp points, wide intervals and
diminished number begin to exhibit the characters of the dental system
of the serpent tribe (Pl. 65, figs. 1 & 2). They are implanted in a single
row upon the maxillary, intermaxillary and palatine bones, the upper
jaw being thus provided with two semi-elliptical and sub-concentric
series; there are also two rows of equal-sized teeth on the premandibu-
lar bones of the lower jaw, in certain species ; and the Cecilia is the last
example, in the ascending survey which we have taken of the dental

218 CECILIA.

system, of this disposition of teeth, which was so common in the —

class of fishes.
There are twenty teeth in the anterior or outer premandibular
row in the lumbricoid and white-bellied Czeciliz, and ten or twelve,

|
i

of much smaller size, in the second row. There are twenty teeth in —
the outer row of the upper jaw, of which six are supported by ©

the intermaxillaries ; and sixteen in the inner or palatine row. All
these teeth are long, slender, acute and slightly recurved.

In the rostrated Cecilia the first two teeth of the maxillary
and premandibular series are longer and stronger than the rest;
they are succeeded by small and recurved teeth ; the median margins
of the palatal bones are bristled with small teeth ; the second row
in the lower jaw is represented by two small recurved teeth on the

internal border of the premandibular bones. In the modification of ©

the dental system presented by this species may be perceived a
retention of the Batrachian type.
The annulated Cecilia (Siphonops annulatus, p. & 8.) has the maxillary

and palatine teeth strong, pointed and slightly recurved. In the
glutinous and two-banded Cecilie, (Epicrium), the teeth are slender,

acute and more inclined backwards, thus approaching nearer to the
Ophidian type; in the latter species, (Epicrium bwittatum), the palatal

series, instead of ranging concentrically with the outer row, is chevron-—

shaped with the angle turned forwards and rounded off.

The teeth of the Cecilie are sub-transparent ; their intimate
structure corresponds with that of the frog’s tooth ; but their mode of -
implantation resembles that of the teeth of the Labyrinthodonts, the

base being anchylosed to the parietes of a shallow alveolus.

CHAPTER IIL
TEETH OF OPHIDIANS.

91. THe order Ophidia, as it is characterized in the system of
Cuvier, requires to be divided into two sections according to the nature
of the food and the consequent modification of the jaws and teeth.
Certain species, which subsist on worms, insects, and other small
invertebrate animals, have the tympanic pedicle of the lower jaw
immediately and immoveably articulated to the walls of the cranium ;
the lateral branches of the lower jaw are fixed together at the sym-
physis, and are opposed by the usual vertical movement to a similarly
complete maxillary arch above ; these belong to the genera Amphis-
bena and Angus of Linneus.(1) The rest of the Ophidians(2), which
form the typical members and by far the greatest proportion of the
order, prey upon living animals of frequently much greater diameter
than their own; and the maxillary apparatus is conformably and
peculiarly modified to permit of the requisite distention of the soft
parts surrounding the mouth and the transmission of their prey to the
digestive cavity.

The two superior maxillary bones have their anterior extremities
joined, by an elastic and yielding fibrous tissue, with the small and
single intermaxillary bone: the symphysial extremities of the lower
maxillary rami are connected together by a similar tissue allowing of
a still wider lateral separation. The opposite or posterior extremity of
each ramus is articulated to a long and moveable vertical pedicle,
formed by the tympanic or quadrate bone (Pl. 65, fig. 7, e), which is
itself attached to the extremity of a horizontal pedicle formed by the
mastoid bone (fig. 7. f.), so connected as also to allow of a certain
yielding movement upon the cranium. The palatine (fig. 6 c) and
pterygoid (d) bones have similarly loose and moveable articulations,
and concur with the other dentigerous bones of the mouth in yielding
to the pressure of the large bodies with which the teeth may have
grappled.
(1) Pl. 65, figs. 3-5. (2) ib. fig. 6-15.

220 OPHIDIANS. DEIRODON.

I shall first describe the dental peculiarities of the true Serpents,
and afterwards notice those of the Amphisbene in connexion with
the teeth of the Anguis and other serpentiform genera, which lead by
a series of close transitions to the Saurian order.

All true serpents subsist on animal matter and swallow their
food whole, whether they prey on living animals, as is the case in
almost every species, or feed on the eggs of birds as in the Deirodon
scaber, O., (Coluber scaber, Linn.)

With the exception of this and some congeneric species, in which
the teeth of the ordinary bones of the mouth are so minute as to have
been deemed wanting, the maxillary and premandibular bones in all
true Ophidians are formidably armed with sharp-pointed teeth ; there
is on each side the palate a row of similar teeth supported by the
palatine and pterygoid bones ; in the great Pythons and some species
of Boa the intermaxillary bone also supports teeth.

All the teeth, whatever be their position, present a simple conical
form, the cone being long, slender and terminated by an acute apex,
and the tooth is either straight, or, more commonly, bent a little
beyond the base, or simply recurved, or with a slight sigmoid
inflection. The teeth are thus adapted for piercing, tearing, and
holding, and not for dividing or bruising. In some species certain
teeth are traversed by a longitudinal groove for conveying an acrid
saliva into the wounds which they inflict : in others two or more teeth
are longitudinally perforated for transmitting venom; such teeth are
called ‘ poison-fangs’ and are always confined to the superior maxillaries,
and are generally placed near the anterior extremity of those bones.

The serpents in which the teeth are all simple and solid, when the
pulp which occupies the basal cavity is calcified, will be first noticed.

92. Deirodon.—In the genus Deirodon(1) the teeth of the ordinary
bones of the mouth are so small as to be scarcely perceptible, and they
appear to be soon lost, so that it has been described as edentulous.
An acquaintance with the habits and food of this species has shown
how admirably this apparent defect is adapted to its well-being. Its
business is to restrain the undue increase of the smaller birds by

(1) Genus Anodon of Dr. A. Smith by whom the habits of the typical species lave been well
elucidated. The name anodon had been previously applied toa genus of Bivalves

EE

SS ee

Greer

Re pe i Oe Sa ee NOR tg

VE eS ae ol

DEIRODON. BOA. Bel

devouring theireggs. Now if the teeth had existed. of the ordinary
form and proportions in the maxillary and palatal regions, the egg
would have been broken as soon as it was seized, and much of its
nutritious contents would have escaped from the lipless mouth of the
snake in the act of deglutition ; but, owing to the almost edentulous
state of the jaws, the egg glides along the expanded opening
unbroken, and it is not until it has reached the gullet, and the
closed mouth prevents any escape of the nutritious matter, that the
shell is exposed to instruments adapted for its perforation. These
instruments consist of the inferior spinous processes of the seven or
eight posterior cervical vertebre, the extremities of which are capped
by a layer of hard cement, and penetrate the dorsal parietes of the
cesophagus ; they may be readily seen, even in very young subjects,
in the interior of that tube, in which their points are directed back-
wards. The shell being sawed open longitudinally by these vertebral
teeth, the egg is crushed by the contractions of the gullet, and is
carried to the stomach, where the shell is no doubt soon dissolved by
the acid gastric juice.

93. Boa.—The simple teeth, ‘ dentes solidi’ as they are termed
in Erpetology, are of equal length in a few species of non-venomous
serpents; in the Pythons, Boas and Lycodons they are larger
towards the fore-part of the mouth ; but in some Colubers and Tropi-
donotes the situation of the larger teeth is reversed. In Dryophis
and Psammophis there are a few very long teeth at the middle, and
again at the posterior part of the maxillary series. In Xenodon,
Coronella and many species of Homalopsis the posterior part of each
jaw is provided with alarge and simple tooth, which is long and com-
pressed in the Xenodon.

In the Boa Constrictor, the teeth are slender, conical, suddenly
bent backwards and inwards above their base of attachment, with the
crown straight or very slightly curved, as in the posterior teeth. The
intermaxillary bone supports four small teeth ; each superior maxillary
bone has eight much larger ones, which gradually decrease in size as
they are placed further back: there are eight or nine teeth of similar size
and proportions in each premandibular bone. These teeth are sepa-
rated by wide intervals, from which other teeth similar to those in

222 BOA. PYTHON.

place have been detached. The base of each of the above teeth is
extended transversely, compressed antero-posteriorly, and anchylosed
to a shallow alveolus, extending obliquely across the shaliower alveclar
groove. An affinity to the Lizard-tribes is manifested by the greater
development of the outer as compared with the inner wall of the
alveolar furrow.

The palatine teeth, of which there are three or four in each
palatal bone, are as large as the superior maxillaries, and are similarly
attached: the pterygoid teeth, five or six in number, which complete
the internal dental series on the roof of the mouth, are of smaller size
and gradually diminish as they recede backwards. In the interspaces |
of the fixed teeth in both these bones, the places of attachment of the
shed teeth are always visible, so that the dental formula, if it included
the vacated with the occupied sockets, would express a greater number
of teeth than are ever in place and use at the same time. In the
smaller species of Boa the intermaxillary bone is edentulous.

94. Python.—The dentition of the great Java Python (Python
amethystinus) is figured, after Cuvier, at Plate 65, fig. 6 and 7.
The intermaxillary bone (a) is represented as supporting four
teeth : the superior maxillary (6) as being armed with eighteen teeth,
but of these the three which are situated on the inner side of the
anterior part of the outer row are the successors of those teeth to
which they are contiguous. No serpent has a double row of fixed
and serviceable teeth implanted on the same bone.

The palatine bone, opposite to which is the letter c in fig. 6,
supports six teeth; and the remaining eight teeth of the series are
continued upon the ptervgoid bone, d. The premandibular element
of the lower jaw (fig. 7) is armed with eighteen teeth. In the tiger
Python (Python tigris) the teeth are less numerous than in the great Py-
thon. The intermaxillary bone exhibits the places of attachment of four
teeth, but I have rarely found more than two in place: these in their
size and curvature resemble the posterior teeth of the maxillary series.
There are about twelve teeth in each superior maxillary bone, which
eradually diminish in size as they recede backwards ; the number of
sockets is eighteen. There are six sockets on each palatine bone,
and generally four teeth in place; eight sockets on each pterygoid

PYTHON. 223

bone, and five teeth in place: the mode of fixation of all these teeth
corresponds with that in the Boa constrictor. Their direction prevents
the escape of the prey in which they are once fixed ; while the separate
and independent movement of each half of both upper and lower jaw,
and of the dentigerous bones of the palate, allows of the different
series of teeth being successively withdrawn and implanted in a more
advanced position in the prey, which is thus gradually drawn into the
gullet, without the retaining force being unduly relaxed during any
part of the engulphing process.

The teeth seem to be more numerous, or there is a greater
number in place at one time in the young than the old individuals of the

Python tigris: I have counted fourteen superior maxillary and fifteen
premandibulars in place on each side of the mouth, in an individual of
this species six feet in length.

The inner alveolar border is rather higher than the outer one in
the palatine bones. The pterygoid teeth are continued along the
middle of the inferior surface or towards the outer side of those bones,
whilst in the smaller Colubriform serpents they are placed on the
inner margin of the pterygoids.

The teeth of both the Python and Boa consist of a body of firm
dentine coated by a layer of cement, which is extremely thin upon
the crown, but becomes thicker towards the expanded and attached
base of the tooth. The calcigerous tubes radiate according to the
ordinary course from the central pulp-cavity to the periphery of the
tooth : the superior and central tubes proceed in the axis of the tooth ;
those nearest to them incline outwards, deviating from the axis as
they recede from the point of the tooth, until they run at right angles
to the axis, which course they maintain throughout a great proportion
of the tooth ; hence a transverse section of the tooth, as magnified in
Plate 65 3, fig. |, exhibits the whole length of the calcigerous tubes.
Their primary curvature is slight, with the concavity directed towards
the base of the tooth: their secondary undulations are faint and
regular through seven-eighths of their course, but the tubes become
bent in stronger and less regular sinuous curves in the rest of their
extent, where, alone, they divide dichotomously, the terminal
branches frequently inosculating in loops, the convexity of which is

224 ; PYTHON. COLUBER.

directed outwards, (Pl. 65 B. fig. 2). These sinuous terminations of
the calcigerous tubes give a very peculiar appearance to the dentine
of the Python, which, viewed by transmitted light in thin sections
by a low power, seems, at first sight, to be invested by a
thick layer of some distinct tissue, (fig. 1, 6). Another charac-
ter, which was detected by Retzius(1), is displayed by a longitudinal
section of the dentine of the Python, when viewed by transmitted
light with an objective of {th inch focus. It is the transmission from
the lower or concave side of the main calcigerous tubes of numerous,
minute, parallel and nearly straight branches, directed obliquely out-
wards and downwards. These minute branches are not only given
offfrom the main calcigerous tube, but also from its primary branches,
which differ from the dichotomous divisions of the calcigerous tubes
in other teeth, in being much smaller than the main tube ; they also

run parallel with each other and are given off at an acute angle from ~

the under side of the calcigerous tubes. The structure of the external
layer of cement (cc, fig. 1, Pl. 65 8B.) can only be examined in
sections taken from near the base of the tooth, as its extreme thinness
in the crown causes it to appear merely as a clear line bounding the
peripheral loops of the calcigerous tubes. It appears to be more readily
detached from the dentine where it is thickest at the base of the tooth
than in other teeth: portions of it adhering to the section figured are
shown at cc, fig. 1, Pl. 65, 8. It is a clear substance in which
the calcigerous cells are simple, very minute and inconspicuous.

95. Coluber.—The solid teeth of the smaller non-venomous serpents
correspond in structure with those of the Python and Boa. In the
Eri turcicus the largest and longest teeth are placed at the anterior
part of the series, and they diminish as they recede backwards : this
is the usual disposition. But in the common harmless snake (Naérix
torquatus) the proportions of the maxillary teeth are reversed and the
largest are at the posterior part ofthe series. In the Coluber filhforms,
the teeth are equal and of small size.

The disproportionate length of the last maxillary tooth is charac-
teristic of the colubrine genera Dryinus, Dendrophis and Heterodon ;
but the Dryinus nasutus has one tooth in the middle of the maxillary

(1) Loe. cit. p. 523, Pl. xxii, fig. 5.

COLUBER. POISONOUS SERPENTS. 225

series aS Jong as that which terminates it. The colubers, like other
true serpents, have two longitudinal rows of teeth on the roof of the
mouth, extending along the palatines and pterygoids: the genus Oli-
godon appears to form the sole exception to this rule. In the Dryinus
nasutus M. Duvernoy(1) has noticed a few small teeth on the trans-
verse bone or external pterygoid, as well as on the internal pterygoid.

In certain genera of non-venomous serpents, as Dryophis, Dipsas,
and Bucephalus, in which the superior maxillary teeth increase in size
towards the posterior part of the bone, the large terminal teeth of the
series are traversed along their anterior and convex side by a longitu-
dinal groove. In the Bucephalus capensis(2) the two or three posterior
maxillary teeth present this structure, and are much larger than the
anterior teeth or those of the palatine or premandibular series; they
add materially, therefore, to the power of retaining the prey, and may
conduct into the wounds which they inflict an acrid saliva, but they
are not in connection with the duct of an express poison-gland. The
long grooved fangs are either firmly fixed to the maxillary bones or
are slightly moveable according to their period of growth; they are
concealed by a sheath of thick and soft gum, and their points are
directed backwards. The sheath always contains loose recumbent
grooved teeth, ready to succeed those in place.

In most of the Colubri each maxillary and premandibular bone
includes from twenty to twenty-five teeth : they are less numerous in
the genera Tortriz and Homalopsis, and are reduced to a still smaller
number in the poisonous serpents, in the typical genera of which the
short maxillary bone supports only asingle perforated fang.

96. Poisonous Serpents.—The transition to these Serpents, which
was begun in the Bucephali and allied genera with grooved maxillary
teeth, is completed by the poisonous serpents of the genera Pelamis,
Hydrophis, Elaps, Bungarus and Hamadryas, which latter genus, as

(1) Annales des Sciences Nat. tom. xxvi, p. 43.

(2) Having been favoured by Dr. A. Smith with specimens of the Bucephalus Capensis the
results of my dissections are confirmatory of his own as regards the absence of a poison-appa-
ratus in that snake: the ordinary salivary gland is large, especially at its posterior part which
transmits its secretion by many pores into the sheath of the grooved fangs. The presence of a
distinct poison-gland and duct communicating with the grooved posterior teeth requires to be es-
tablished before the Serpents with these teeth can be ranked with the poisonous genera.

Q

226 POISONOUS SERPENTS.

its cervical integument can be expanded into a hood, constitutes an
immediate link between the Bungarus and Naja.(1)

The superior maxillary bone diminishes in length with the
decreasing number of teeth which it supports: the transverse or
external pterygoid bone elongates in the same ratio, so as to retain its
position as an abutment against the shortened maxillary, and the
muscles implanted into this external pterygoid style communicate,
through it, to the maxillary bone the hinge-like movements backwards
and forwards upon the ginglymoid articulations connecting that
bone with the anterior frontal and palatine bones. As the fully
developed poison-fangs are attached by the same firm basal
anchylosis to shallow maxillary sockets, which forms the characteristic
mode of attachment of the simple or solid teeth, they necessarily
follow all the movements of the superior maxillary bone; when the
external pterygoid is retracted the superior maxillary rotates back-
wards, and the poison-fang is concealed in the Jax mucous gum, with
its point turned backwards: when the muscles draw forward the
external pterygoid, the superior maxillary bone is pushed forwards
and the recumbent fang withdrawn from its concealment and
erected. | |

In this power of changing the direction of a large tooth, so that it
may not impede the passage of food through the mouth, we may perceive
an analogy between the viper and the lophius; but in the fish the move-
ment is confined to the tooth alone, and is dependent on the mere
physical property of the elastic medium of attachment: in the
Serpent the tooth has no independent motion, but rotates with
the jaw, whose movements are governed by muscular actions. In the
fish the great teeth are erect, except when pressed down by some
extraneous force: in the Serpent the habitual position of the fang is the
recumbent one, and its erection takes’place only when the envenomed
blow is to be struck.

The peculiar structure of the poison-fang was first described
by Fontana as it exists in the viper(2), and subsequently received addi-

(1) Dr. Canter, Proceedings of the Zoological Society, 1838, p. 73.
(2) Fontana’s description is as follows: “‘ The tooth of the viper has a double pipe or tubule
almost for its whole length, a circumstance hitherto entirely unknown to observers. These two

i

POISONOUS SERPENTS. 227

tional elucidation by Mr. Smith’s careful examinations of the fangs
of the Hydrus, Naja and Crotalus, and by Mr. Clift’s illustrative
drawings appended to Mr. Smith’s Paper(1). A true idea of the struc-
ture of a poison-fang will be formed by supposing the crown of a simple
tooth, as that of a Boa, to be pressed flat, and its edges to be then bent
towards each other, and soldered together so as to form a hollow cy-
linder open at both ends. The flattening of the fang and its inflection
around the poison-duct commences immediately above the base, and
the suture of the inflected margins runs along the anterior and convex
side of the recurved fang: the poison-canalis thus in front of the pulp-
cavity. The basal aperture of the poison-canal is oblique and its opposite
outlet is still more so, presenting the form of a narrow elliptical lon-
gitudinal fissure terminating at a short distance from the apex of the
fang. The relative position of the two apertures of the poison-canal
is shown in the figure of the fang of the large Cobra (Pl. 65, fig. 9),
where a fine hair is represented as passing through the poison-canal :
in figure 11, the relative position of the pulp cavity, a, to the poison-
canal, 6b, b, is shown in the plan of a longitudinal section of a poison-
fang.

The character most commonly adduced from the dental system
as distinguishing the venomous from the non-venomous serpents is
that the former have two, the latter four rows of teeth in the upper
jaw: the two outer or maxillary rows being wanting in the venomous
species and their place being supplied by the single poison-fang. (2)
canals or tubes do not communicate with each other, and are separated by a bony partition,
very brittle towards the basis, but which becomes somewhat stronger in proportion as it advances
towards the point. One of these tubes or canals, which I call the external one, because it is at
the side of the convex part of the tooth, begins, as has been seen, at the basis of the triangular
opening, and goes on enlarging by degrees to the middle of the length of the tooth, whence it
gradually narrows, and ends at the elliptical opening of the point. The inner canal on the con-
trary, which is towards the concave part of the tooth, begins with a large opening at the basis,
from whence it advances, closing by degrees, and terminates at length ina blind point above the
middle of the tooth. The partition likewise that separates the two cavities is crooked, and its
convex part is turned towards the hollow of the canal it terminates. The blind canal communi-
cates with the socket in which the tooth is fixed, and receives vessels and nerves.”—Fontana,
On Poisons, Part I. Treatise on the Venom of the Viper, &c., translated by Skinner, 8vo.

2d Ed. 1795, p. 10. (The original Treatise was published in Italian, in 1765.)

(1) Philos. Trans. 1818.
(2) Compare figure 13, Naja, with fig. 6, Python, in Plate 65: the letter 6 shows the

qa 2

228 POISONOUS SERPENTS.

The exceptions to this rule are, however, too numerous for its value as a
distinguishing character in a question of such practical moment as the
venomous or non-venomous properties of a serpent. In all the family
of marine serpents the poison-fang is only the foremost of a row of
fixed maxillary teeth: in the Hydrophs striatus (PI. 65, fig. 14) there
are four teeth, and in Hydrophis schistosa (fig. 15) five teeth, behind
the venom-fang, of rather smaller size than it ; the two-coloured sea-
snake (Pelamys bicolor) has also five maxillary teeth in addition to
the perforated one. The poison-fang, in this genus, is relatively
smaller than in the venomous serpents of the land, but presents the
same peculiar structure. The poison-gland presents a_ corres-
pondingly small development ; it is pyriform, and its structure,
according to Dr. Canter(1), is minutely cellular; it is covered
by the aponeurotic expansion of the articulo-mamillaris (Pl. 65,
fig. 15, e, f), and transmits a straight duct horizontally to the
basal opening of the venom-fang. It is a curious fact that the
smaller non-venomous teeth of the poisonous serpents all present a
trace of the structure of the functional venom-fang, being more or
less deeply grooved along the convex anterior side ;(2) and in the
Hydrus this groove commences by a depression analogous to the
oblique basal aperture of the poison-canal in the true fang.

The colubriform poisonous serpents of the land have comparatively
short venom-fangs, but they are larger than those of the pelagic serpents ;
and behind the venom-fangs there are likewise some smaller grooved
teeth in the maxillary bones: there are three such teeth in the Bunga-
rus Pama, and five in the Bungarus annulatus. In the Hamadryas or
great hooded poisonous tree-snake of India, the venom-fang is rela-
tively as large as in typical poisonous serpents, but three or four
smaller grooved teeth are implanted behind it on the maxillary
bone.

In the most deadly venom-snakes, as the viper (Berus), the puff-

maxillary, and c d. the palato-pterygoid series of teeth in both species. In the Naja the maxil-
lary series is reduced to a single fang.

(1) Zool. Transactions, vol. ii, p. 304.
(2) The presence of similar grooved teeth in Serpents.which are not armed with yenom-
angs has already been noticed: such teeth are never found in the Boas and Pythons.

POISONOUS SERPENTS. 225

adder (Vipera), the asps or hooded-snakes (Naja), the rattle-snakes
(Crotalus), the cophias and fer-de-lance (Trigonocephalus), the poison
fangs acquire their largest size, and are associated only with their
successors : these are clustered in greater or less number behind them,
presenting the same structure, but of a size proportionate to their degree
of development, and further differing in being loosely imbedded in the
thick and wide mucous gum, which likewise conceals the fixed and
functional fang in its ordinary position of retraction and repose. ‘This
fang is more strongly curved backwards than the ordinary teeth,
but its acute and slender apex is frequently bent slightly in the con-
trary direction, asin the rattle-snake, (Pl. 65, fig. 8, b).

The mechanism by which the short maxillary bone and the
poison-fang are rotated backwards and forwards upon the ginglymoid
joint that connects the maxillary with the prefrontal and palatine
bones has already been noticed, and, as some description of the
secreting apparatus to which the peculiar modification of the venom-
fang is subservient might here be expected, I have selected for its
illustration the accurate figure which Prof. Muller has given of the
salivary and poison-glands in the Trigonocephalus lanceolatus in his
great work on the Glandular System. (1)

The poison-glands (Pl. 65, fig. 12, a) occupy the sides of the posterior
half of the head ; each consists of a number of elongated narrow Icbes,
extending from the main duct whichruns along the lower border of the
gland, a, upwards and slightly backwards: each lobe gives off lobules
throughout its extent, thus presenting a pinnatified structure ; and each
lobule is subdivided into smaller secerning czca, which constitute
the ultimate structure of the gland. The whole gland is surrounded
by adouble aponeurotic capsule, b, b, of which the outermost and
strongest laver is in connection with the muscles by whose contraction
the several czeca and lobes of the gland are compressed and emptied of
their secretion. This is then conveyed by the duct, c, in the course
of the dotted line, e, to the basal aperture of the poison-canal of the
fang. We may suppose, that as the analogous lachrymal and salivary
glands in other animals are most active during particular emotions, so
the rage which stimulates the venom-snake to use its deadly weapon

(1) De Glandularum Secernentium Structura Penitiori, fol. tab. vi, fig. 1, p. 55.

230 POISONOUS SERPENTS.

must be accompanied with an increased secretion and great distension
of the poison glands ; and as the action of the compressing muscles is
contemporaneous with the blow by which the serpent inflicts its wound,
the poison is at the same moment injected with force into the wound
from the apical outlet of the perforated fang. (1)

The duct which conveys the poison, although it runs through the
centre of a great part of the tooth, is, nevertheless, as we have seen,
really on the outside of the tooth, the canal in which it is lodged and
protected being formed by a longitudinal inflection of the parietes of the
pulp-cavity or true internal canal of the tooth. This inflection com-
mences a little beyond the base of the tooth, where its nature is
readily appreciated, as the poison-duct there rests in a slight groove
or longitudinal indentation on the convex side of the fang; as it
proceeds it sinks deeper into the substance of the tooth and the sides
of the groove meet and seem to coalesce, so that the trace of the
inflected fold ceases, in some species, to be perceptible to the naked
eye ; and the fang appears, as it is commonly described, to be perfo-
rated by the duct of the poison-fang.

From the real nature of the poison canal it follows that the
transverse section of the tooth varies in form in different parts of the
tooth ; at the base it is oblong, with a large pulp-cavity of a corres-
ponding form, with an entering notch at the anterior surface ; farther
on, the transverse section presents the form of a horse-shoe, and the
pulp-cavity that of a crescent, the horns of which extend into the
sides of the deep cavity of the poison-fang, (Pl. 65, fig. 10): a little
beyond this part the section of the tooth itself is crescentic, with the
horns obtuse and in contact, so as to circumscribe the poison-canal ;
and along the whole of the middle four-sixths of the tooth the section
shows the dentine of the fang inclosing the poison cavity, and having
its own centre or pulp-canal, in the form of a crescentic fissure,

(1) The nasal salivary gland is shown at d, the labial gland at e: itis an enlargement of the
posterior part of this gland in the Serpents with large posterior grooved maxillary teeth that has
been mistaken (as in the Bucephalus) for a poison-gland. Besides the preceding glands the
lachrymal glands placed behind the eye are often largely developed, and, by a direct course of
their duct to the palatal region of the mouth, contribute likewise their secretion to the lubricating
stream which is so much wanted and for so long a time in the difficult and gradual process of
deglutition in the Serpent tribe.

POISONOUS SERPENTS. 231

situated close to the concave border of the inflected surface of the
tooth. Itis such a section of which a magnified view is given in
Pl.65 a. The pulp-cavity disappears, and the poison-canal again
assumes the form of a groove near the apex of the fang, and’ termi-
nates on the anterior surface in an elongated fissure.

If the end of each inflected fold of cement in the tooth of the
Labyrinthodon were dilated sufficiently to contain a tube, -that tooth
might convey the ducts of fifty poison-glands deeply imbedded in
its substance and yet all of them actually on the outside of the tooth
itself: it is the existence of a single fold of the same kind, but more
simple, inasmuch as it is straight instead of wavy, which forms the
complication of the viper’s fang subservient to the completion of its
peculiar offensive weapon.

The venom-fangs of the viper, rattle-snake and fer-de-lance are
coated only with a thin layer of a subtransparent and minutely cellular
cement: the disposition of the calcigerous tubes is obedient to the
general law of verticality to the external surface of the tooth;
it is represented as seen in a transverse section from the middle
of the fang in Plate 65 a. Since the inflected surface of the tooth
can be exposed to no other pressure than that of the turgescent
duct with which it isin contact, the tubes which proceed to that
surface, d, while maintaining their usual relation of the right
angle to it, are extremely short, and the layer of dentine sepa-
rating the poison-tube from the pulp-cavity is proportionally thin. The
calcigerous tubes that radiate from the opposite side of the pulp-
cavity to the exposed surface of the tooth, are disproportionately long.

The pulp-cavity following the form of the tooth itself, presents
in a transverse section of this part the form of a fissure describing
four-fifths of a circle: the fissure is widest at the middle and at the
two extremities: the exterior calcigerous tubes, in quitting the pulp-
cavity, form a graceful curve, the convexity being turned towards the
nearest horn of the crescent: at the middle of the pulp-fissure the
tubes proceed straight to the opposite surface ; and at the two extre-
mities of the crescent the central tubes are nearly straight, while the
lateral ones radiate in graceful curves which become bolder as they
diverge from the central and straighter tubes. Throughout the greater

232 POISONOUS SERPENTS.

part of the tooth the calcigerous tubes describe their various inflections
ina plane transverse to the axis of the tooth ; but towards the apex they
begin gradually to rise from that plane; and as the pulp-cavity re-
Assumes, with the tooth itself, the simple conical form beyond the
termination of the poison-canal, the calcigerous tubes extend to
equal distances from the linear remnant of the pulp-cavity, which has
again passed to the centre of the tooth, and those tubes which are
continued from its continued extremity, pass to the apex of the fang in
a line parallel with the axis of the tooth. The calcigerous tubes
present secondary curvatures of a slightly wavy character, which
become more marked and irregular near their termination. In
whatever part of the section an entire tube could be clearly traced to
its termination, it formed an anastomotic loop at the periphery of
the dentine with an adjoining tube. The calcigerous tubes present a
diameter of the ;j;th of an inch, and they are separated by interspaces
equal to four of their own diameters. Each calcigerous tube gives off
many primary branches in its course, but is rarely seen to divide dicho-
tomously until it begins to form its irregular sinuosities near the peri-
phery of the tooth. In the transverse section figured, the primary
branches were sent off from the concave side of the tube, at an
acute angle with the trunk: the secondary smaller and more nume-
rous branches proceed from the same side of the main tube or of its
primary branches, at a less acute angle, into the clear uniting sub-
stance; they are remarkably parallel with each other and straight.
In old poison-fangs the pulp-cavity or fissure is obliterated by ossifica-
tion of the remains of the pulp.

The external layer of cement is very thin where it covers the crown
of the tooth; it is best seen at the line of union of the coadapted
margins of the inflected tooth ¢. At this part the cement is more
abundant in the viper’s tooth, and its transparency permits a bristle
inserted into the poison-canal to be seen through it. The layer which
coats the inflected surface of the fang is thinner than the outer one,
which, from its transparency, has been regarded as enamel.(1)

(4) “ I should observe,” says Mr. Smith, “ that the poison-tube is not coated with enamel,
for the capsule in which the tooth is formed, and from the inner surface of which it is well known
that the enamel is deposited, does not pass between the edges of the slit into the poison tube ; as,

POISONOUS SERPENTS. 933

There is, however, no trace of true enamel upon the teeth of the
poisonous serpents any more than upon those of the innocuous species.
The cells of the cement are more minute and inconspicuous in the
poison-fang, than in the simple teeth of the Python and Boa.

The teeth of all Ophidians are developed and completed in the
original seat of the tooth-germs in all animals; viz. the mucous
membrane or gum covering the alveolar border of the dentigerous
bones. This gum presents the same lax tissue and is as abundantly
developed as in the Pike, Lophius, and many other fishes, in which it
likewise serves as the nidus and locality for the complete development
of the teeth.

The primitive dental papilla in the common harmless snake very
soon sinks into the substance of the gum and becomes inclosed by a
capsule. Assoon asthe deposition of the calcareous salts commences
in the apex of the papilla, the capsule covering that part becomes
ossified and adherent to the dentine, and the tooth begins to pierce
and emerge from the gum, before its mould, the pulp, is half com-
pleted. Fresh layers of cells are successively added to the base of
the pulp, and converted by their confluence and calcification into the
tubular dentine, until the full size of the tooth is attained, when its
situation in the gum is gradually changed and its base becomes
anchylosed to the shallow cavity of the alveolar surface of the
bone.

In the posterior part of the large mucous sheath of the poison-fang,
the successors of this tooth are always to be found in different stages
of development; the pulp is at first a simple papilla, and when it has
sunk into the gum the succeeding portion presents a depression along
its inferior surface, as it lies horizontally, with the apex directed
backwards ; the capsule adheres to this inflected surface of the
pulp. But how the cylindrical cavity of the dilated fold is occupied
in the loose growing poison-fang, and by what contrivance it is
however, it passes over that slit, it will cover it with enamel and in some cases by that means
alone the edges become soldered together.”—Philos, Trans. 1818, p. 473.

The author appears here to have been misled by the prevalent doctrines of dental develop-
ment ; no tissue of a tooth is deposited from a surface: a distinct convertible matrix or mould

is as essential to the formation of enamel, as of cement or dentine, and unless such organ be deve-
loped from the inner surface of the capsule, no enamel can be formed.

234 OPHISAURIANS. AMPHISBENIANS.

brought into the same relation with the severed duct of the poison-
gland as the displaced fang which it succeeds, is not yet clearly
understood.

CHAPTER IV.

TEETH OF SAURIANS.
OPHISAURIANS.

97. There are several genera of reptiles which, like the true snakes,
are externally devoid of locomotive extremities or have them indi-
cated only by minute rudiments, but are covered by small uniform
scales, and resemble the Saurians much more than the Ophidians in
their anatomical structure, especially in the fixed condition of the
jaws, which cannot be divaricated laterally or rotated backwards and
forwards upon a moveable tympanic pedicle: these snake-lizards have
always intermaxillary as well as maxillary teeth.

Amphisbenians.—In these snake-like reptiles there are, as in the
true Saurians, both acrodont and pleurodont species: the greater
number belong to the latter category and have their teeth applied
against the internal surface of an external alveolar wall; but in the ©
Trogonophis, the teeth are blended by their whole base with the —
alveolar ridge, and are so closely arranged, as to cohere together. —
They are unequal, conical, subcompressed and obtuse. The inter- —
maxillary teeth are in unequal number, the middle azygos tooth being |
longer than the rest.

The teeth of the Cheirotes (Lacerta lumbricoides, Shaw,) are slightly
curved, simple and nearly equal, excepting the azygos intermaxillary
tooth which is longer than the rest: these are very small at first, but
increase as they are placed backwards. |

In the true Amphisbene the teeth present the form of short and
stout cones, (Pl. 65, figs. 3 & 4): five are attached to the intermax-
illary bone, of which the middle tooth is the longest ; there are five teeth

ANGUIANS. a5

on each superior maxillary, and eight on each premandibular bone ; of
these the first is short, and the second and third teeth are the longest.

Anguians.—The typical blind-worms have only maxillary and
not palatine teeth. In the Anguis fragilis the first five of
the upper teeth on each side are small, with cutting edges, and are
situated on the intermaxillaries ; the eight following teeth are much
larger, pointed and recurved; they are separated by intervals: the
teeth of the lower jaw correspond with those above. In general
form, therefore, the teeth of the true Anguis adhere to the Ophidian
type: but in the Ophiomerus, or miliary blind-worm, and in the
Acontias they are conical, obtuse and straight: the teeth are likewise
simple and conical in the sub-genera Lerista, Ablepharus, Hysteropus,
Dibamus, Typhlinus, and the rest of the family of blind-worms.

The Pseudopus Pallasii has sixteen teeth on each side of the
upper and twelve teeth on each side of the lower jaw; the latter form
a continuous series ; but a median interval separates the two lateral
series in the upper jaw. In both jaws the anterior teeth are conical
and obtuse, the hinder ones present a hemispherical triturating crown.
The palate, in this genus, is armed with teeth which are small, conical
and simple; and are arranged in one moderately long row on each
side.

The glass-snakes (Ophisawrus) have both jaws provided with a
close-set row of small simple teeth; and very remarkably repeat a
dental character observable in certain Batrachians, especially the newts
of the same continent to which these Ophisaurs are peculiar, viz. in
having teeth at the roof of the mouth disposed in several rows, here
chiefly supported by the pterygoids, and, in asmall proportion, by
the palatine bones. The teeth composing this palatal pavement are
short and conical; the maxillary teeth are subcylindrical and simple.
There are about twenty teeth on each side of the upper, and eighteen.
teeth on each side of the lower jaw, (Pl. 65, fig. 5).

In the Pantodactylus the palatal teeth have not been detected ;
and the maxillary teeth are slightly compressed, with a tricuspid
crown. ‘The intermaxillaries are conical and simple. These teeth are
close-set and equal.

The Ecpleopus has a similar dentition to the Pantodactylus, ex-

236 ANGUIANS. SINCOIDIANS.

cept that the maxillary teeth are unequal, and terminate in a simple
obtuse summit. In the Monodactyle or Anguine Lizard (Lacerta
monodactyla, Shaw, Chamesaurus, p. & B.), these teeth are subcylin-
drical and obtusely pointed : like the two preceding genera the palatal
teeth are absent. In the heterodactyle Chalcis the maxillary teeth
are slightly compressed, straight and divided into two or three obtuse
points. Those of the annulated Chalcis are conical and terminate in
a simple obtuse summit. In both species the teeth are not implanted
in sockets, but are applied to the inner margin of the alveolar ridge.

The common Zonure (Zonurus griseus,) has about twenty equal,
conical, or subcylindrical obtuse teeth, on each side.

In Tribolonotus and Saurophis the intermaxillary teeth are coni-
cal ; the maxillaries straight, subcylindrical and with obtuse summits.
These genera are devoid of teeth on the roof of the mouth.

In the Gerrhosauri the intermaxillary and anterior maxillary teeth
are conical as inthe Tribolonoti, but the posterior teeth are compressed
and terminate in a bilobed summit ; and the Gerrhosaurs further differ
in having a row of small conical teeth on each pterygoid bone.

The Gerrhonoti have the posterior maxillary teeth simply obtuse
at the summit, and the pterygoid teeth are in smaller number.

The teeth in the genus Bipes (Scelotes, Fitzinger), are confined to
the jaw-bones, and are conical and simple. The same dentition cha-
racterizes the genus Seps: the teeth of the Seps chalcides are very
small, their obtuse apex just protrudes above the gum at the anterior
part of the mouth; but they gradually increase in size as they are
placed farther back.

SCINCOIDIANS.

98. Most of the Scincoid or smooth-scaled lizards have small
mouths and slender sharp teeth, fitted apparently for merely insect food.

In the Tropidophorus the teeth are straight, cylindrical, simple,
and slightly compressed at the summit: they are confined to the
jaws. In the true Scinks (Scincus, p. & B.) of which the officinal
Scink of ancient pharmacy is the type, the palate is also armed ; four
or five small obtuse teeth being placed on each pterygoid bone: the

CYCLODUS. 237

maxillary teeth of this genus are conical, obtuse, and sometimes
slightly incurved.

In the short-footed Scinks (Sphenops, Wagler), the palate is
unarmed ; and the maxillary teeth are conical, straight, pointed, and
smaller and more numerous than in the common Scink. The
Gallywasps (Diploglossus) have the jaws armed with equal, close-set,
simple, conical teeth, sometimes subcompressed at the crown. The
palate is edentulous. The teeth are compressed, with cuneiform
crowns in most of the species of Gongylus, p. & 8. In the sub-genus
Eumeces, they are equal, conical and only slightly compressed at the
summit. In the carinated scink, and its congeners (Euprepes) the
pterygoids are armed with teeth: these are particularly numerous in
the golden Scink (Euprepes cyprius), in which each pterygoid supports
two rows of short, straight, strong conical teeth ; the maxillary teeth
resemble those of the other Euprepes. Cuvier(1) figures the cra-
nium of a large species of Scink, allied by its short tail to the Lacerta
Scincoides of Shaw, in which the maxillary teeth have expanded
crowns with a dentated margin, (Pl. 66, fig. 5, 5”): the pterygoid
teeth are wanting.

Cyclodus.—The present genus of Australian Scincoid lizards
differs from the rest of the tribe in the subhemispherical form of
the teeth, which resemble tubercles instead of more or less pointed
cones, and the species manifest a corresponding difference in their
habits and the nature of their food.

The dentition of the Cycl. nigroluteus is figured in Plate 66, fig. 7.
The intermaxillary bone has depressions for twelve teeth, of which
only the alternate ones are usually in place: they are of very small
size, with the fang compressed laterally, and the crown antero-poste-
riorly, so as to resemble a true incisor in form, the summit sloping
to an edge from behind forwards, with the middle of the cutting
surface a little produced. Each superior maxillary bone has depres-
sions for fourteen teeth ; they quickly increase in size and exchange
their conical for a sub-hemispherical crown: the eighth to the thir-
teenth inclusive are the largest teeth, they are set obliquely, and
pretty close together. In the lower jaw there are two small incisors
at the anterior part of each premandibular bone corresponding with

(1) Ossem, Foss, 8vo. 1836, t. x, p. 56.

238 CHAMELEONS. AGAMIANS.

those of the intermaxillary ; these are succeeded by five or six coni-
cal teeth, and the rest correspond in size and form with the tubercu-
late molars of the upper jaw.

All the teeth are attached, after the pleurodont type, by their
base and outer margin to shallow depressions on the outer side of the
external alveolar parapet.

The germs of the successional teeth (0 J, fig. 7), are developed
at the inner side of the base of their predecessors, which they exca-
vate, undermine, and displace in the usual manner.

I have not seen any specimens of this genus which had the
branches of the lower jaw anchylosed at the symphysis. The ptery-
goid bones present a rugous surface at the place where they ordinarily
support teeth.

CHAMELEONS.

99. The dental system, though by no means _ formida-
ble, in the Chameieons, indicates a more substantial diet than the
poets have assigned to these singular reptiles. _

The teeth are conical, compressed, trenchant, with the summit
simple or terminating in three points, arranged in the same longitu-
dinal line: in most species the teeth gradually increase in size, and
become wider apart as they are situated farther back upon the jaws.
The teeth in place are so completely confluent with the alveolar plate
as to appear, externally, to be mere processes of that border of the
jaw ; but their true nature is evident, when viewed from the inner side
of the jaw.

The common Chameleon (Ch. vulgaris), has eighteen or nine-
teen teeth on each side of both jaws: and the five posterior ones have
a tricuspid crown.

The two-horned Chameleon (Ch. bifurcus, Pl. 66, fig. 3), has
about sixteen teeth on each side of both jaws, and they offer a
marked disparity of size at the two extremes of each series: figure 3,
gives a magnified view of one of the middle teeth, showing the mode
in which it is anchylosed to the alveolar plate, and the contour of the
transverse section of its base.

AGAMIANS.

100. The Agamoid Lizards, which are grouped together under the

:
!
i
;
.

AGAMIANS. 239

generic name of Uromastyz, (Pl. 66, fig. 1) resemble the Chameleons

in their dentition, which seems at first sight to consist of a merely

notched or dentated margin of the jaw. ‘These processes are, how- °
ever, true teeth, developed originally as independent parts, and after-

wards becoming confluent by their base and a great part of their outer

side with the alveolar parapet of bone.

In the young of the Uromastyx there are from two to four anterior
or intermaxillary teeth which subsequently become anchylosed to-
gether, so as to appear like one lobated tooth. In the lower jaw the
crown of this complex tooth is received into a wide interspace between
the two anterior teeth. The molar teeth are triangular or subcylin-
drical, with rather obtuse and subcompressed summits: they are
approximated, and increase in size as they recede backwards. PI. 66,
fig. 1, shows the form of the teeth, as seen from the inside of the jaw,
and the section below the figure demonstrates the thinning off of the
base of the tooth produced by its oblique adhesion to the alveolar bony
plate.

In the common Stellio most of the teeth, sixteen or seventeen on
each side, are triangular, with a small cusp in front and behind ; and
there are two larger, conical teeth, like canines, at the anterior part of
the upper and lower maxillary bones. The intermaxillary bones sup-
port two small conical teeth, which have no corresponding ones in the
lower jaw. The little flying Dragons (Draco), have proportionally
longer canines than the Stellios, but in other respects the dentition is
the same.

The mutable Agame (Trapelus), resemble the Stellios in having two
conical teeth longer than the rest commencing the series in the lower
jaw and superior maxillary bones; but they have four small conical
intermaxillary teeth, without corresponding teeth below ; seventeen
triangular teeth succeed the canines in the lower jaw and fifteen in
the upper jaw in the Trapelus ater. The dentition of the Agama
orbicularis resembles that of the Trapeli, except that the molar teeth
behind the canines are more conical.

The inferior maxillary dental series commences in the common
Calotes with four simple conical teeth, and in the upper jaw with six,
of which the middle smaller ones might pass for incisors, and the

240 GECKOTIANS. IGUANIANS.

external ones for canines: behind these there is a series of molar teeth
with compressed triangular and tricuspid crowns, the median cusp
being much the largest of the three: these teeth increase in size
towards the back part of the jaws.

GECKOTIANS.

101]. In this family of nocturnal insectivorous Lizards the teeth are
more pointed, more slender, more equable and more numerous than
in the preceding group. The summit of the tooth is always simple:
the base is obliquely soldered to the internal surface of an outer
alveolar parapet.

In the smooth Gecko (Thecadactylus levis, Pl. 66, fic. 4), there

are about thirty-five such teeth, forming a close-set series on each
side of both jaws ; the first five or six above being supported on the
intermaxillary bones, and being rather longer than the rest. In most
of the posterior teeth the crown is slightly expanded, with a trenchant
margin, as shown in fig. 44’; its transverse section is given below. In
the flat-headed Gecko (Ptyadactylus fimbriatus, Cuv.) there are
from seventy to seventy-four teeth on each side. In the House-
Gecko (Ptyadactylus Hasselqustu) the teeth are slightly recurved. In
the common Indian Gecko (Ptyadactylus guttatus, Cuv.) the teeth,
with the exception of a few anterior ones, are rather cylindrical than
conical, and are terminated by obtuse summits. None of the Geckos
have teeth on the roof of the mouth.

IGUANIANS.

102. The lizards of this family are characterized like the preceding
groups by a short contractile tongue, slightly notched at its extremity ;
but are distinguished for the most part by having teeth on the pterygoid
bone, and also by the complicated form of the crown of the max-
illary teeth in the typical genera, the species of which subsist
chiefly on vegetable substances.

In most of the Iguanians the teeth are lodged in a common
shallow oblique alveolar groove, and are soldered to excavations on
the inner surface of the outer wall of the groove. MM. Dumeril and
Bibron enumerate the following genera as exhibiting the pleurodont
type of dentition, and as possessing likewise pterygoid teeth: viz.

ei

IGUANIANS. 24)

Polychrus, Urostrophus, Anolis, Corythophanes, Basiliscus, Aploponotus,
Amblyrhynchus, Iguana, Metopoceros, Cyclurus, Brachylophus, Levo-
saurus, Hypsibates, Proctotretes, Ecphymotes, Stenocercus and Oplurus.

The following pleurodont genera of [guanians have no pterygoid
teeth, Hyperanodon, Tropidolepis, Phrynosoma, Callisaurus.

The Acrodont Iguanians include the genera Istiurus, Calotes,
Lophyrus, Otocryptis, and Chlamydosaurus in all of which the maxillary
teeth may be divided into anterior laniary and posterior molary teeth.

In the crested Istiwrus of Amboina the four anterior simple
conical teeth in both upper and lower jaws are very small and _ repre-
sent incisors ; the six following teeth, three on each side, are larger,
more sharply pointed and incurved; they are followed by thirteen
molars with compressed, triangular, trenchant, but undivided crowns,
which gradually increase in size as they are placed backwards ; the
posterior ones being strong teeth, separated by intervals.

In the blue Calotes may be distinguished five incisors in the
intermaxillary bone, a median and two shorter ones on each side; a
single long laniary and eighteen or nineteen tricuspid molars on each
side of the upper jaw. In the lower jaw there are two canines on
each side.

The molars are more close-set and numerous in the Lophyri,
there being sometimes twenty on each side, these are obtusely tri-
cuspid.

In the Otocrypt (Otocryptis bivittata) the intermaxillary bones
each support a single tooth, which is conical and straight; the third in
succession, in the superior maxillary bone, is a very large laniary, with
a slightly recurved point. Of the twelve molars which succeed these,
the anterior are small, simple and compressed ; they increase in size
and complexity as they recede backwards, the large posterior molars
having three lobes, but the series is terminated by teeth of small size

and simple form.

The Chlamydosaurus presents a similar dentition, but the teeth

/are relatively larger, and a greater proportion terminates in simple and
| pointed summits.

In the pleurodont Iguanians the teeth never present the true

\laniary form ; and if simply conical, as at the extremes of the maxillary
R

242 IGUANIANS.

series, the cone is more or less obtuse ; but in general it is expanded,
more or less trilobate, or dentated along the margin of the crown.

In the Polychrus, the anterior score of teeth are simple, slightly
recurved and obtuse; the remainder are straight, compressed and
tricuspid. The pterygoid teeth forma single row on each bone, and

are short and conical.
| In the Urostrophus Vautiert (p. and 8.) the upper jaw has forty-
six, or forty-eight teeth ; the lower jaw forty or forty-two teeth : the
anterior ten or twelve, are conical with obtuse apices in both jaws ; the
rest are tricuspid. The pterygoid teeth are six or eight in number
in each bone, and present the form of moderately wide cones.

The Anolians have the same anterior conical, and posterior com-
pressed tricuspid teeth as in the previous genera; but the latter are
relatively fewer in many of the species: in Anolis loysiana, for exam-
ple, out of fifty-four teeth in the upper jaw only the eight or nine
posterior ones are distinctly compressed and tricuspid: and this form
is restricted to the hinder six or seven of the forty premandibular
teeth. In the Anolis chloro-cyaneus fourteen of the sixty maxillary and
twenty of the fifty-six premandibular teeth are tricuspid ; these are as
usual at the posterior part of the series.

In the Anolis Carolinensis four or five of the posterior tricuspid
teeth are sensibly larger than the rest. In the Anolis alligator
(Lacerta bimaculata, Shaw), there are three or four short but strong
teeth on each pterygoid bone. The Anolis chameleonoides resembles
the chameleons not only in external appearance, but in its dentition,
in so far as that none of the teeth present the tricuspid form : the
thirteen anterior ones are pointed, the others simply obtuse : there are
sixty two upper and fifty lower teeth in this species.

The genus Chameleopsis (Corythophanes, Boié) has the posterior
teeth tricuspid as in the ordinary Anolises.

The dentition of the Basilisks differs little from that of the Anolis ;
the posterior teeth are rather trilobate than tricuspid : the anterior ones
are small, circular, pointed and slightly curved: there are generally
from five or six conical teeth on each pterygoid bone, but in the
Mitred Basilisk there are twelve teeth in each of these rows.

In the Aploponoti, the pterygoid teeth are arranged in two series on
each side.

IGUANIANS. 243

The Amblyrhynchus, a genus which is somewhat remarkable for
the marine habits of at least one of the species, (Amblyrhynchus ater)
whose diet is sea-weed,(1) has the tricuspid structure well developed
in the posterior teeth, and these teeth are somewhat thicker than in
the preceding Iguanians.

The typical genus of the present family of Saurians is characte-
rized by the crenate or dentated margin of the crown of the maxillary
and premandibular teeth, a few of the anterior small ones excepted ;
the pterygoid teeth are arranged in two or three irregular rows, re-
sembling somewhat the ‘ dents en cardes’ of fishes.

In the full-grown Iguana tuberculata there are from forty-seven to
forty-nine teeth in both upper and lower jaws: the number is less in
young subjects. The double row of pterygoid teeth are in close order
on each side.

In the horned Iguana (Metopoceros cornutus, p. & B., Pl. 70,
figs. 6 and 7) there are about fifty-six teeth in both the upper and
lower jaw, of which the four first are conical and slightly recurved ;
the twelve succeeding teeth are somewhat larger in size, with more
compressed and expanded crowns ; the rest are triangular, compressed,
with dentated margins. The inner surface of the crown of the tooth
is simply convex and smooth, the outer surface traversed by a median
longitudinal broad obtuse ridge.

There is a single row of small teeth implanted in each pterygoid
bone (Pl. 68, fig. 2, d). No Iguanian lizard has teeth on the palatine
bones. (2)

The teeth of the Cycluri differ from those of the Iguanas in being
trilobate or bilobate and not crenate at the margin: the pterygoid
teeth are ina single row.

In the Iguana cyclura of Cuvier there are thirty-six teeth in the

(1) This species, and probably all the known Amblyrhynchi or blunt-nosed Iguane, inha-
bit the islands of the Gallopagos group ; their habits have been well elucidated by Mr. Darwin,
(Voyage of the Beagle, vol. iii. p. 466): in specimens which he dissected he found the stomach
loaded with minced sea-weed.

(2) For the purposes of zoology the expression ‘ palatine teeth’ serves in general sufficiently
to denote their existence, whether they be vomerine as in the Batrachia or pterygoid as in the
Saurians; it is in this sense doubtless that the learned authors of the Erpétologie Générale,
describe the teeth of the Iguana and other Lacertians as being situated on the ‘ os palatines.’

R 2

244 IGUANIANS.

upper jaw and thirty on the lower jaw in full-grown individuals ; but in
a half-grown specimen M. Bibron found only twenty-six teeth both
above and below, and in a still younger individual only twenty above,
and eighteen below. The pterygoid teeth in this species are nine or
ten on each side ; small, slender, rounded, and they appear not to be
constant, at least in young specimens.

The spiny-tailed Cyclurus has more numerous teeth ; from fifty
to fifty-six in each jaw.

The banded Iguana, which is the type of the genus Brachylophus of
Cuvier, has between thirty-five and forty teeth in both the upper and
the lower jaw, most of which are compressed and tricuspid : there is
a slightly curved row of short and pointed teeth on each pterygoid
bone.

The dentition of the allied genus Enyalus differs only in the larger
proportion of simple pointed anterior teeth.
| The Iguanoid Hyperanodon, as its name implies, has no pterygoid
teeth. :

Most of the maxillary teeth of the Proctotrett are equal, com-
pressed, and trilobate, a few of the anterior ones being pointed. The
pterygoid teeth are still smaller and are pointed.

The dentition of the Tropidolepes and of the toad-like Phrynoso-
mes differs from that of the Proctotretes only in the absence of ptery-
goid teeth.

In the Callisauri all the maxillary teeth are simple, nearly equal
and conical ; here likewise there are no pterygoid teeth.

The insectivorous Ecphymotes have pterygoid teeth.

In the Doryphorus the dentition begins to exhibit a little more
variety : the palate is edentulous ; but in the upper jaw there may be
distinguished eight incisives, three laminaries, and about fourteen
molars on each side. The laniaries are a little longer than the others,
rounded and slightly curved ; both these and the incisors are separated
by intervals : the molars have compressed, tricuspid crowns with the
middle cusp longer than the rest.

The most strictly vegetable feeding reptiles are the true Iguane
and the Amblyrhynchi ; yet the size of the teeth, their mode of implan-
tation and the limited motions of the jaws permit only an imperfect

IGUANIANS. 245

comminution of the food by these instruments; and their summits
are rather chipped off than ground down by use. The appearance of
abrasion is greatest in the posterior teeth, especially in the Iguana
cornuta, in which the crowns of the teeth are thicker than in the
Iguana tuberculata, and make a nearer approach to the very remark-
able form of tooth that characterizes the gigantic Iguanodon.

Before, however, proceeding to describe the teeth of this extinct
lizard, Ishall offer a few observations on the microscopic structure of
the teeth of the existing Iguana. In both the common and horned
‘species, the teeth consist of a body of simple compact dentine, with the
crown covered externally by a thin layer of enamel, and the fang with
an investment of cement. The dentine, viewed by transmitted light in
a thin horizontal section, exhibits minute calcigerous tubes in a clear
substance, radiating from a simple conical pulp-cavity, which is
widely open at the base of the tooth and continues in a linear form
into the crown of the tooth: the calcigerous tubes at the base of the
tooth proceed in an irregular sinuous course at right angles to the
axis of the tooth: above this part they sweep outwards in a graceful
curve, with the concavity turned towards the base of the tooth: as
they approach the summit of the tooth they gradually incline towards
it, and those from the apex of the pulp-fissure proceed directly in the
axis of the tooth: throughout their course the calcigerous tubes are
disposed in minute undulations, and they send off from the concave
side of the primary flexures numerous short parallel branches at an
angle of 45°: these branches rise less regularly the nearer the main
tube is to its origin from the pulp-cavity. The diameter of the calci-
gerous tubes is sith of an inch: their interspaces are equal to be-
tween three or four of their diameters.

In general they do not divide until within a short distance from
the periphery of the tooth, near which they subdivide frequently ;
the terminal branches of the different layers decussate each other.
The tubes at the base of the tooth divide nearer their origin and more
frequently ; which, with the large oblique branches, and the stronger
undulations of the main tubes occasions the interwoven appearance
represented at Pl. 65 B., fig. 3.

The pulp-cavity in old teeth becomes occupied by a coarse bone,

246 IGUANODON.

characterized by large irregularly shaped calcigerous cells, and the
interspaces are filled with irregular moss-like reticulations of tubes,
(ib. a). Branches of the pulp-cavity are never continued in the form
of medullary canals into the substance of the dentine in the existing
Iguane.

The arrangement of the tubes, as seen inatransverse section at
the middle of the tooth is represented at Pl. 69, fig. 1; 5b is the
tubular dentine, c the enamel. The secondary curves and terminal
divisions of the calcigerous tubes are shown in fig. 3, but the small
oblique secondary branches are not accurately expressed in this
figure.

The germs of the successional teeth are developed from the
mucous membrane covering the inner side of the base of those in
place. The apex of the dentated crown is first formed ; by its pres-
sure it excites absorption of the base of the fixed tooth and soon
undermines it, and then occupies the recess in the alveolar plate in
the interspace of the two adjoining fixed teeth. After the crown is
completed, the rest of the tooth forms a contracted and elongated fang,
which at first is hollow, then becomes consolidated by ossification of
the remaining pulp, and afterwards a second time excavated by the
pressure of a new tooth.

IGUANODON.

103. The value of a knowledge of the comparative anatomy of
the teeth, and especially of their external characters in the cold-blooded
classes of animals, has never, perhaps, been placed in so striking a
point of view as in the leading steps to the discovery of the present
most extraordinary and gigantic reptile ; these, therefore, I shall re-
count in the words of Dr. Mantell, to whom is due this splendid acces-
sion to the riches of Palzontology.

After noticing the ordinary organic remains which characterize
the sandstone of the Tilgate forest, and his discovery, in the summer
of 1822, of other teeth distinguished by novel and remarkable charac-
ters, the indefatigable explorer of the Wealden proceeds to state,

‘“ As these teeth were distinct from any that had previously come
under my notice, I felt anxious to submit them to the examination of

IGUANODON. 247

persons whose knowledge and means of observation were more exten-
sive than my own. I therefore transmitted specimens to some of the
most eminent naturalists in this country and on the continent. But
although my communications were acknowledged with that candour
and liberality which constantly characterizes the intercourse of scienti-
fic men, yet no light was thrown upon the subject, except by the
illustrious Baron Cuvrer, whose opinions will best appear by the
following extract from the correspondence with which he honoured
me.

“* Ces dents me sont certainement inconnues ; elles ne sont point
d’un animal carnassier, et cependant je crois qu’elles appartiennent,
vu leur peu de complication, leur dentelure sur les bords, et le couche
mince d’émail qui les revét, a l’ordre des reptiles. A Vapparence
extérieure on pourrait aussi les prendre pour des dents de poissons,
analogues aux tétrodons, ou aux diodons: mais leur structure inté-
rieure est fort différente de celles-la._N’aurions-nous pas ici un
animal nouveau, un reptile herbivore? et de méme qu’actuellement
chez les mammiféres terrestres, c’est parmi les herbivores que l’on
trouve les espéces a plus grande taille, de méme aussi chez les rep-
tiles d’autrefois, alors qu’ils étaient les seuls animaux terrestres, les
plus grands d’entr’eux ne se seraient-ils point nourris de végétaux ?
Une partie des grands os que vous possédez appartiendrait a cet
animal unique, jusqu’a présent, dans son genre. Le temps confirmera
ou infirmera cette idée, puisqu’il est impossible qu’on ne trouve pas
un jour une partie de la squelette réunie 4 des portions de machoires
portant des dents. C’est ce dernier objet surtout qu’il s’agit de
rechercher avec le plus de persévérance.”’ _

‘*« These remarks,” Mr. Mantell proceeds to say, ‘‘ induced me
to pursue my investigations with increased assiduity, but hitherto
they have not been attended with the desired success, no connected
portion of the skeleton having been discovered. Among the speci-
mens lately collected, some however were so perfect, that I resolved
to avail myself of the obliging offer of Mr. Currr, (to whose kindness
and liberality I hold myself particularly indebted) to assist me in com-
paring the fossil teeth with those of the recent lacertz in the Museum
of the Royal College of Surgeons. The result of this examination

248 IGUANODON.

proved highly satisfactory, for in an Iguana which Mr. Stutchbury had
prepared to present to the College, we discovered teeth possessing the
form and structure of the fossil specimens.

‘* Like the teeth of the recent Iguana, the crown of the tooth is
acuminated ; the edges are strongly serrated or dentated ; the outer
surface is ridged, and the inner smooth and convex ; and, as in that
animal, the secondary teeth appear to have been formed in a hollow
in the base of the primary ones which they expelled as they increased
in size.

‘¢ From the appearance of the fangs in such fossil teeth as are
in a good state of preservation, it seems probable that they adhered to
the inner side of the maxilla, as in the Iguanz, and were not placed
in separate alveoli, as in the crocodile. The teeth appear to have
been hollow in the young animals, and to have become solid in the
adult. The curved teeth probably occupied the front of the jaw ; and
those which are nearly straight the posterior part.” (1)

A subsequent discovery by Dr. Mantell(2) of a portion of the
lower jaw of the Iguanodon confirmed the previous inference as to
the mode of attachment of the teeth, and approximates the extinct
gigantic species to the Pleurodont section of Iguanians ; whence it
may also be inferred that the teeth were all of nearly uniform size
and shape, at least not divisible into laniaries and molars asin the
Acrodont Iguanians.

The portion of jaw alluded to, which is now in the British Museum
with the rest of the Mantellian Collection, shows that the Iguanodon
differed from the Crocodile not only in the lateral adhesion of the
teeth to an alveolar wall, but in their arrangement in a close-set
series. .

Besides the opportunity of studying this unique fossil and the
extensive series of detached teeth in the British Museum, I have
availed myself of the kindness of Dr. Mantell and Mr. Dixon of
Worthing to examine the specimens in their private collections, and
I have been favoured by both these gentlemen with Iguanodon’s teeth
from which I have had sections prepared for microscopical examination.

(1) Philos. Trans. 1825, Mr. Mantell, Notice on the Iguanodon.
(2) Wonders of Geology, vol. 1, p. 393.

1GUANODON. 249

The teeth of the Iguanodon, though resembling most closely
those of the Iguana, do not present an exact magnified image of
them, but differ in the greater relative thickness of the crown, its
more complicated external surface, and, still more essentially in a
modification of the internal structure, by which the Iguanodon equally
deviates from every other known reptile.

As in the Iguana, the base of the tooth is elongated, contracted
and subcylindrical ; the crown expanded, and smoothly convex on the
inner side ; when first formed (Pl. 70, fig. 5) it is acuminated, com-
pressed, its sloping sides serrated, and its external surface traversed
by a median longitudinal ridge, and coated by a layer of enamel, but
beyond this point the description of the tooth of the Iguanodon indi-
cates characters peculiar to that genus. In most of the teeth that
have hitherto been found, three longitudinal ridges traverse the outer
surface of the crown, one on each side of the median primitive ridge ;
these are separated from each other and from the serrated margins of
the crown by four wide and smooth longitudinal grooves. The rela-
tive width of these grooves varies in different teeth; sometimes a
fourth small longitudinal ridge is developed on the outer side of the
crown as in the small anterior Iguanodon’s tooth in Plate 62 a,
Gig Disa Gh.

The marginal serrations, which, at first sight, appear to be
simple notches, as in the Iguana, present under alow magnifying
power the form of transverse ridges, themselves notched, as shown in
Pl. 62 a., fig. 5 e.(1) so as to resemble the mammillated margins of
the unworn plates of the elephant’s grinder : slight grooves lead from
the interspaces of these notches upon the sides of the marginal ridges.
These ridges or dentations do not extend beyond the expanded part of
the crown: the longitudinal ridges are continued farther down, espe-
cially the median ones which do not subside till the fang of the tooth
begins to assume its subcylindrical form.

The tooth at first increases both in breadth and thickness ; it then
diminishes in breadth, but its thickness goes on increasing (as shown

(1) This figure, and those numbered 5, 6,8, 9 and 10, Pl. 62 a., are zincographed from
drawings by Mr. Dinkel kindly communicated to me by Dr. Manteli for the present work.

250 IGUANODON.

in fig. 5, c); in the larger and fully formed teeth, the fang decreases in
every diameter, and sometimes, as in the tooth fig. 5 d, tapers
almost to a point. A fracture of this tooth shows that the pulp was
not entirely solidified, but that its cavity had continued open at the
thickest part of the tooth.

The apex of the tooth soon begins to be worn away, and it would
appear, by many specimens like that in Pl. 70, fig. 3, that the teeth
were retained until nearly the whole of the crown had yielded to the
daily abrasion. In these teeth, however, the deep excavation of the
remaining fang, represented in profile in the figure (ib. fig. 3) plainly
bespeaks the progress of the successional tooth prepared to supply the
place of the worn out grinder.

At the earlier stages of abrasion a sharp edge is maintained at the
external part of the tooth by means of the enamel which covers that
surface of the crown ; the prominent ridges upon that surface give a
sinuous contour to the middle of the cutting edge, whilst its sides are
jagged by the lateral serrations (Pl. 70, figs. 1 & 2): the adaptation
of this admirable dental instrument to the cropping and comminution
of such tough vegetable food as the Clathrarize and similar plants,
which are found buried with the Iguanodon, is pointed out by Dr.
Buckland with his usual felicity of illustration in his Bridgewater
Treatise ; Vol. i, p. 246.

When the crown is worn away beyond the enamel, it presents a
broad and nearly horizontal grinding surface, and now another
dental substance is brought into use to give an inequality to that
surface ; this is the ossified remnant of the pulp, which, being firmer
than the surrounding dentine, forms a slight transverse ridge in the
middle of the grinding surface: the tooth in this stage has exchanged
the functions of an incisor for that of a molar, and is prepared to give
the final compression, or comminution, to the coarsely divided vegeta-
ble matters(1). .

The marginal edge of the incisive condition of the tooth and the
median ridge of the molar stage are more effectually established by the

(1) A tooth, presented to me by Mr. Dixon of Worthing, exhibits this modification of its
grinding surface.

IGUANODON. 25)

introduction of a modification into the texture of the dentine, by
which it is rendered softer than in the existing Iguane and other
reptiles, and more easily worn away: this is effected by an arrest of
the calcifying process along certain cylindrical tracts of the pulp,
which is thus continued, in the form of medullary canals, analogous
to those in the soft dentine of the Megatherium’s grinder, from the
central cavity, at pretty regular intervals, parallel with the calcige-
rous tubes, nearly to the surface of the tooth. The medullary canals
radiate from the internal and lateral sides of the pulp-cavity, and are
confined to the dentine forming the corresponding walls of the tooth:
their diameter is ;3,th of an inch: they are separated by pretty regular
intervals equal to from six to eight of their own diameters; they
sometimes divide once in their course. Each medullary canal is
surrounded by a clear space: its cavity was occupied in the section
described by a substance of a deeper yellow colour than the rest of
the dentine.

The calcigerous tubes present a diameter of ;;,th of an inch,
with interspaces equal to about four of their diameters. At the first
part of their course, near the pulp-cavity, they are bent in strong
undulations, but afterwards proceed in slight and regular primary
curves, or in nearly straight lines to the periphery of the tooth.
When viewed in a longitudinal section of the tooth, the concavity of
the primary curvature is turned towards the base of the tooth: the
lowest tubes are inclined towards the root, the rest have a general
direction at right angles to the axis of the tooth; the few calcigerous
tubes, which proceed vertically to the apex, are soon worn away, and
can be seen only in a section of the apical part of the crown of an
incompletely developed tooth. The secondary undulations of each
tooth are regular and very minute. The branches both primary and
secondary of the calcigerous tubes are sent off from the concave side
of the main inflections ; the minute secondary branches are remark-
able at certain parts of the tooth for their flexuous ramifications,
anastomoses, and dilatations into minute calcigerous cells, which
take place along nearly parallel lines for a limited extent of the
course of the main tubes. The appearance of interruption in the
course of the calcigerous tubes occasioned by this modification of

252 IGUANODON.

their secondary branches is represented by the irregularly dotted
tracts in the figure (Pl. 71). This modification must contribute, with
the medullary canals, though in a minor degree, in producing that
inequality of texture and of density in the dentine, which renders the
broad and thick tooth of the Iguanodon more efficient as a triturating
instrument.

The enamel which invests the harder dentine forming the outer
side of the tooth presents the same peculiar dirty brown colour when
viewed by transmitted light as in most other teeth: very minute and
scarcely perceptible undulating fibres, running vertically to the sur-
face of the tooth, is the only structure I have been able to detect
in it.

The remains of the pulp in the contracted cavity of the com-
pletely formed tooth are converted into a dense but true osseous sub-
stance, characterized by minute elliptical radiated cells, whose long
axis is parallel with the plane of the concentric lamelle, which sur-
round the few and contracted medullary canals in this substance.

The microscopical examination of the structure of the Iguanodon’s
teeth thus contributes additional evidence of the perfection of their
adaptation to the offices for which their more obvious characters had
indicated them to have been destined.

To preserve a trenchant edge, a partial coating of enamel is
applied: and, that the thick body of the tooth might be worn away
in a more regularly oblique plane, the dentine is rendered softer as it
recedes from the enamelled edge by the simple contrivance of arresting
the calcifying process along certain tracts of the inner wall of the tooth.
When attrition has at length exhausted the enamel, and the tooth is
limited to its function as a grinder, a third substance has been pre-
pared in the ossified remnant of the pulp to add to the efficiency of
the dental instrument in its final capacity. And if the following
reflections were natural and just after a review of the external charac-
ters of the dental organs of the Iguanodon, their truth and beauty
become more manifest as our knowledge of their subject becomes
more particular and exact.

‘* In this curious piece of animal mechanism, we find a varied
adjustment of all parts and proportions of the tooth, to the exercise of

HYLEOSAURUS. 253

peculiar functions, attended by compensations adapted to shifting
conditions of the instrument, during different stages of its consump-
tion. And we must estimate the works of nature by a different
standard from that which we apply to the productions of human art,
if we can view such examples of mechanical contrivance, united with
so much economy of expenditure, and with such anticipated adapta-,
tions to varying conditions in their application, without feeling a
profound conviction that all this adjustment has resulted from design
and high intelligence.”—Buckland’s Bridgewater Treatise, vol. 1,
p- 249.

HYLEOSAURUS,

104. Dr. Mantell has discovered, in the limestone of the Tilgate
forest the remains of a second gigantic reptile generically distinct from
the Iguanodon and for which he has proposed the name of Hyleosaurus :
of this species he observes “‘ the teeth are unknown; but in the quarries
where the bones of that reptile were discovered, I have found teeth of
a very peculiar form, which appear to have belonged to a reptile, and
are entirely distinct from those of the Megalosaurus, Iguanodon,
Crocodile and Plesiosaurus, whose remains occur in the Tilgate
strata.’’(1)

One of these teeth, which may be referred with much probability
to the Hyl@osaurus,(2) is figured of the natural size in Pl. 62 a.
fig. 8. The fang of the tooth is subcylindrical; subelongate, smooth ;
the crown expanded, compressed, slightly incurved, with the narrow
sides straight and converging at a slightly acute angle to the apex.
In all these teeth which I have seen, these sloping sides show the
effects of attrition: the enamel being worn away and the dentine
exposed.

The tooth consists of a body of dentine covered by a thick coating of
clear structureless enamel, and surrounding a small central column of
true bone, consisting of the ossified remains of the pulp, which presents the

(1) Wonders of Geology, vol. 1, p. 403.

(2) They unquestionably do not belong, as has been supposed, to the Keuper genus Cylin-
dricodon of Jaeger.

254 LACERTIANS.

usual characters of the texture of the bone in the higher reptiles. The
dentine differs, like that of existing Lacertians, from the dentine of the
Iguanodon in the entire absence of the numerous medullary canals
which form so striking a characteristic of the more gigantic Wealden
reptile. The main calcigerous tubes are characterized by the slight
degree of their primary inflections ; they are continued in an unusually
direct course from the pulp-cavity to the outer surface of the dentine,
at nearly right angles with that surface, but slightly inclined towards
the expanded summit of the tooth. They are chiefly remarkable for
the large relative size of their secondary branches, which diverge from
the trunks in irregular and broken curves, the concavity being always
turned towards the pulp-cavity. In most parts of the tooth, the
number of these branches obscures even the thinnest sections.

The ossified pulp exhibits the parallel concentric layers of
the ossified matter surrounding slender medullary canals and inter-
spersed with irregular elliptical radiated cells,

LACERTIANS.

105. The genera of the typical family of the squamate Saurians
are arranged in two subfamilies by MM. Dumeril and Bibron, the
chief characteristics of which are derived from the dental system.

In the first group, the teeth are solid, or without any internal
cavity, and are very firmly anchylosed by their base to the alveolar
groove upon the inner side of the jaw; so that the extremity of the
tooth is slightly directed outwards: the species which present this
character are called ‘ pleodont’ Lacertians.(1)

In the second group, the teeth are excavated by a sort of canal,
and are less firmly fixed to the jaws, being applied vertically, like
piles or buttresses, against the outer alveolar parapet, but not adhering
by their base: this group is called ‘ Ccelodonts.’(2) The group of
Pleodonts includes the genera Crocodilurus, Thorictes, Neusticurus,
Aporomera, Monitor, Ameiva, Cnemidophora, Dicrodon, Acrantus and
Centropyz. . as

-

The Ccelodont Lacertians comprise the genera Tachydromus,

(1) mAéog, full, (2) Koudoe, hollow.

LACERTIANS. 255

Tropidosaurus, Lacerta, Ophiops, Calosaurus, Eremas, Scapteira,
Acanthodactylus and Psammodroma.

In the genus Crocodilurus, the intermaxillary bone supports eleven
small, conical, simple teeth; behind which there are, on each side,
from fifteen to seventeen maxillary teeth; these are of larger size,
compressed, the first four or five pointed and slightly recurved ; the
rest straight and with the summit tricuspid, at least in young indivi-
duals: these hinder teeth have the form of rounded tubercles in old
specimens. The teeth of the lower jaw resemble those above : there
are about twenty-two on each side.

The intermaxillary teeth of the bicarinated Lizard (Thorictes
Dracena, vp. & B.) are nine in number, conical, slightly compressed
from before backwards: there are about ten superior maxillary teeth
and twelve inferior maxillaries on each side: the first four or five in
both jaws are conical, but with obtuse summits, the posterior ones
present the form of very large tubercles, (Pl. 66, fig. 5).(1)

The intermaxillary teeth of Neusticurus are twelve in number,
of a simple conical form: there are twenty-two maxillary teeth on
each side, compressed, all obtusely tricuspid. The lower jaw supports
thirty-five teeth on each side: the first five or six being conical, and
all the others flattened laterally, and divided into three obtuse
cusps.

In the Aporomera, the intermaxillary teeth are small pointed
cones slightly recurved: the maxillary teeth and the corresponding
teeth of the lower jaw are long, strong, separated, pointed, arched

(1) “ Tlest trés-probable qu’é une époque moins avancée de leur vie les Thorictes, de méme
que les Sauvegardes, chez lesquelles l’A4ge rend les dents maxillaires postérieures tubercu-
leuses, ont ces mémes dents, plus ou moins comprimées et divisées a leur sommet, soit en deux
soit en trois points mousses, (p. 52, tom. v., Dum. and Bib. Erpetology). That the same
tooth should change a bicuspid or tricuspid for an obtuse crown through the attrition to which
they are subject during life, and thus exhibit a tubercular character in age might be conjectured
with great probability of a mammiferous animal, as, indeed, such a circumstance not unfre-
quently occurs in that class, in which the teeth are replaced in vertical succession but once,
and the second series are long retained: but that such change of form and function should
take place in the same tooth seems incompatible with the physiological laws of dental decadence
and reproduction in the cold-blooded animals. No doubt the young Dracene have their teeth
fitted for insect food; but these are probably shed, and the molar type gained by a succession
of new teeth.

256 LACERTIANS.

and compressed transversely to the axis of the jaw ; the anterior ones
are simple, the posterior have a notch on their anterior margin near
their apex. There are two rows of four or five pretty strong conical
teeth, one on each pterygoid bone bordering the posterior nasal aper-
ture.

In the Apor. ornata (Ameiva ornata, D’Orb.) there are four or five
strong teeth on each pterygoid bone.

In the genus Cnemidophorus, of which the Ameiva murina, Cuv. is
the type, the intermaxillary teeth are generally ten in number, the
maxillaries vary from eighteen to twenty-two on each side, the pre-
mandibulars from twenty-two to thirty, the posterior being tricuspid,
the others simple and compressed ; the pterygoids are dentigerous.

In an allied species of Ameiva the maxillary teeth, instead of being

compressed and tricuspid, are slightly flattened in the axis of the jaw,
and their summits are bifid: whence it has been proposed to separate
it generically under the name of Dicrodon.
_ The maxillary teeth of the Acrantus have a similar form: their
large crown is excavated by a longitudinal furrow continued from
the interspace of the cusps: but the pterygoids support teeth, which
have not been found in Dicrodon. In the green Ameiva (Acrantus
viridis, p. & B., Tejus viridis, Merrem) the pterygoid teeth are
arranged two or three in number, on each side the posterior palatal
fissure: they are small, conical and straight. The teeth, in some
species of this genus, are finely dentated in the young individuals,
whence Wagler proposed the name of Ctenodon, supposing the cha-
racter to be peculiar to and permanent in them.

The intermaxillaryteeth are ten in number in the Teguixin (Grande
Sauvegarde d’Amérique, Cuv.); the maxillary teeth are thirteen or
fifteen on each side, and gradually increase in size as they are situated
further back in the jaw: the posterior teeth are tricuspid in young in-
dividuals and present the form of simple tubercles in the old. The
inferior maxillary teeth, fifteen to eighteen on each side, correspond
in size and form to those above.

In the common or side-streaked Ameiva (Amewa vulgaris, Lich-
tenstein) there are twelve intermaxillary teeth, slightly separated ;
eighteen to twenty-four maxillary teeth on each side; and twenty to

LACERTIANS. 257

twenty-eight premandibular teeth. All the teeth save the eight or ten
anterior ones have their summit divided into three points, which in the
earlier teeth are sharper than in the later ones.

In the genus Centropyx some species, as the Centr. striatus, have
afew small pterygoid teeth on each side the palatal fissure: the
maxillary and intermaxillary teeth resemble those of the genus
Cnemidophorus.

In the ccelodont group of Lacertians the ‘ Swift Lizards’ (Tachy-
dromus) have the pterygoid bones armed with very small teeth, more
easily felt than seen: there are ten small, pointed, slightly recurved
intermaxillary teeth : twenty-six maxillaries on each side, and about
thirty premandibular teeth. The teeth in both jaws are closely
arranged, and the posterior ones are tricuspid.

The dentition of the Tropidosaurs resembles that of the Tachy-
dromes : some species, as the Algira, have small pterygoid teeth. The
true Lizards, like the other Ccelodonts, have two kinds of teeth, the
anterior small, conical and recurved, the posterior larger, subcom-
pressed and bi-or tricuspid: the pterygoid teeth are occasionally
present, but are not constant either in the species of the genus or
the individuals of the species. There are commonly eight or ten
intermaxillary teeth; from thirty to thirty-six maxillary teeth on each
side, and about forty teeth in each premandibular bone.

The viviparous Lizard (Zootoka crocea) has no pterygoid teeth :
the common Lizard (Lacerta agilis) has about twelve conical ptery-
goid teeth on each side of the palatal opening. In this species may
_ be counted from eleven to thirteen intermaxillary teeth ; forty teeth
in each superior maxillary bone, and fifty teeth in each premandibu-
lar bone.

The Lacerta ocellata and the Lacerta Galloti both have twelve
small conical obtuse pterygoid teeth on each side of the palatal
fissure.

The remaining subgenera of ccelodont Lacertians have teeth on
the jaws like those of the preceding species ; but they have no ptery-
goid teeth.

i

258 MOSASAURUS.

MOSASAURUS,

106. One gigantic extinct species of Saurian Reptile has been
found to agree with many of the species above cited in the Lacertian,
Iguanian, Anolian and Scincoid families of existing Saurians in having
the pterygoid bones armed with teeth: but the maxillary teeth com-
bine the pleodont with the acrodont characters; and the skeleton
indicates a special adaptation for swimming and a marine life.

The true affinities of the Mosasaur, the extinct reptile in ques-
tion, which was at least twenty-four feet in length, and the remains
of which characterize the chalk-formations, were first determined by
Cuvier, who places it in the Lacertine group of Saurians between the
Iguane and Monitors. Its dentition exhibits in an eminent degree
the acrodont character ; the teeth being supported on expanded coni-
cal bases anchylosed to the summit of the alveolar ridge of the jaws:
no existing Saurian exactly parallels this mode of attachment of the
teeth, either in regard to the breadth of the alveolar border, or in
the relative size of the osseous cones to the teeth which they support.
A shallow socket is left where the tooth and its supporting base are
shed. The form of the teeth is likewise different from that hitherto
observed in any existing Saurian: they are pyramidal, with the outer
side nearly plane, or slightly convex, and separated by two sharp
ridges from the remaining surface of the tooth which forms a half-
cone ; the transverse section of the tooth near its attachment to the
osseous base presenting the contour given at Pl. 72, fig. 5. All the
teeth are slightly recurved and their peripheral surfacé is smooth. The
teeth are implanted upon the intermaxillary, maxillary and preman-
dibular bones ; a series of similarly shaped but much smaller teeth
are placed upon the pterygoid bones. The superior maxillary bone
in the great cranium preserved in the Parisian Museum—the most
celebrated fossil of the present species—contained eleven -teeth :
Cuvier calculates that the intermaxillary bone may have contained
three teeth ; meaning probably three on each side: the premandibular
element of the lower jaw supported fourteen teeth : the number of the
teeth thus approximating to that which characterizes the Varanus Nilo-

MOSASAURUS. 259

ticus. They are arranged in a pretty close and regular series. There
appear to have been eight teeth on each pterygoid bone.

In the mode and place of development of the successional teeth,
the Mosasaurus resembles the Iguanze and most other Lacertians.
In the great cranium above mentioned germs of new teeth in various
stages of growth are lodged in hollows of corresponding degrees of
depth on the inner side of the bases of the adherent teeth, and have
evidently owed the commencement of their formation to the mucous
membrane which originally covered those supporting cones of the
teeth in place. ‘The attention of Camper was particularly arrested by
the observation of this fact, which appeared the more singular to him
as this mode of dental succession, which is common in reptiles and
osseous fishes, was not then known.

‘“‘ The dentition is so singular,”’ he says, ‘ in these fossil jaws
that it deserves a particular description. A small secondary tooth is
formed complete with its enamel and solid root in the osseous sub-
stance of the temporary tooth: in the progress of its growth it seems
gradually to form a cavity of corresponding size in the osseous root
of the primitive tooth ; but it is impossible for me to decide what next
befalls it, or in what manner it is shed.”

The crown of the tooth consists of a body of simple and firm
dentine, invested with a moderately thick coat of enamel; the ex-
panded base is composed of a more irregular mass of dentine which,
by its progressive subdivision into vertical columnar processes,
assumes a structure resembling that of true bone: this part is covered
with a layer of cement, which is continued as an extremely thin coat
upon the enamel.

The pulp-cavity generally remains open at the middle of the
base of the crown of the tooth; irregular processes of the cavity
extend, as medullary canals into the conical base of the tooth; but no
processes of the pulp-cavity are continued, as in the Iguanodon, into
the substance of the coronal dentine. This substance consists, as in the
Crocodile, of fine and close set calcigerous tubes, arranged according
to the usual law ; and much resembling that of the tooth of the vara-
nian Monitor figured in Pl. 67: the calcigerous tubes have a diameter _
of jsmth of an inch : with interspaces equalling about four of these dia-

s 2

260 MOSASAORUS.

meters : their secondary curvatures and branches resemble those in the
tooth of the Varanus : the commencement of the subdivision of the mass
of dentine, by the divergence of the calcigerous tubes from secondary
centres, after quitting the main pulp-cavity, is shown in the reduced
figure of a magnified view of the half of a transverse section taken
from near the base of the enamelled crown at Pl. 69, fig. 3, at the lobe
marked b, and the adjoining lobe: the curvilinear diverging extre-
mities of the calcigerous tubes terminate in fine cells. The fibrous
structure of the enamel is very conspicuous in the tooth of the Mos-
asaur, the lines to which this structure is due seem to be continued
from the peripheral cells of the dentine ; and they bifurcate repeatedly
as they traverse the enamel.

This subdivision of the pulp-cavity, and multiplication of centres
of radiation for the calcigerous tubes increase until the piles of
dentine can be scarcely distinguished from the Haversian canals of the
bone of the jaw with which the root or base of the tooth is confluent.
The gradual transition from the simple structure of the compact
crown to the multifid dentine of the anchylosed base of the tooth was
not known to Cuvier, otherwise he could not have supposed that the
crown and the base of the tooth of the Mosasaurus were formed by
vital processes of so dissimilar a nature as to forbid him considering
them as parts of one and the same body. Cuvier had originally
described the expanded base of the tooth of the Mosasaur as the root
of the tooth; but afterwards observing that the corresponding base
became anchylosed by ossification of the remains of the pulp with the
jaw, he conceived it to be incorrect to regard it as a part of a body
which he believed to be an inorganic product, and the result of excre-
tion. ‘ The tooth,” he observes, in correcting his first account of the
Mosasaurus, ‘‘ has no true root, but it adheres strongly to that
pulp which has secreted it and it is further held in connection with
it by the remains of the capsule which has furnished the enamel, and
which by becoming ossified also, and uniting itself to the maxillary
bone and the ossified pulp, implants or rivets the tooth with addi-
tional force.’’(1)

(1) La dent n’a point de vraie racine, mais elle adhére fortement ace noyau qui l’a sécré-
tée, et elle y est encore retenue par le reste de la capsule qui avait fourni l’émail, et qui, en

LEIODON. 261

The necessity under which Cuvier felt himself compelled to
regard the crown and the base of the tooth of the Mosasaur as two
distinct parts, is at once banished by the recognition of the principle,
that the processes of calcification are essentially the same at every
part of a tooth, whether it be free or anchylosed; and that they are
modified only, as I have shown in my Memoir on the formation of
the teeth of the shark,(1) according to the density of the part to be
produced.

107. Leiodon.—In the English chalk-formations a few vertebrz
have been found which are generically, if not specifically related to the
Maestricht Mosasaur; but as yet the only teeth which approach in
form to those of this genus are those from the Norfolk-chalk alluded to
by Dr. Mantell in his ‘‘ Wonders of Geology,” (vol. 1, p. 339) as
belonging to an unknown reptile or to a sauroid fish. The portion of
the jaw to which they were attached exhibits the mode of attachment
of the teeth, which so closely corresponds with that of the Mosasaur
as to leave scarcely any doubt of their near relationship: it is by no
means improbable that this fragment of jaw and teeth may belong to
the same species as the vertebrae above alluded to; for these essential
parts of the organization would retain their generic characters little
if at all altered in a species of Mosasaurus that might be distin-
guished from the Maestricht fossil and be characterized by well
marked modifications of the form of the teeth. Until, however,
this conjecture be refuted or confirmed, the reptile, to which the teeth
in question belonged, may be indicated by the name of Letodon(2), in
reference to the smooth and polished surface of the teeth. The fossil
to which the foregoing observations refer is figured, of the natural

s’ossifiant aussi et en s’unissant, et a l’os maxillaire et au noyau devenu osseux, enchasse et sertit
la dent avec une nouvelle force.” Cuvier proceeds to remark, “ On congoit trés bien que ce noyau,
identifié avec l’os maxillaire puisse, subir les mémes changemens que lui; que l’alvéole de la dent
de remplacement puisse pénétrer sa solidité ; que la compression puisse le détacher, soit en le cas-
sant, scit en oblitérant les vaisseaux quile nourrissent ; en un mot, qu’il soit exposé a des révolu-
tions analogues, comme je l’ai dit, 4 celle du bois des cerfs, mais trés différentes de celles qu’é-
prouve la dent qui est toujours un corps devenu étranger 4!’animal qui l’a sécrété, ainsi que je
Yai démontré, aprés Hunter, dans mon chapitre sur les ossemens d’éiéphans.”—Ossem, foss.
Ed. 1836, vol. x, p. 136.

(1) Comptes Rendus, Dec. 16, 1839,

(2) Asoc, smooth ; 9de¢, a tooth.

262 GEOSAURUS.

size, at Pl. 72, fig. 1 & 2. The teeth are about one half the size of
those of the Mosasaurus Hoffmann ; they differ in having their outer
side as convex as the inner side, the transverse section of the crown
being elliptic with the ends of the ellipse pointed as in fig. 1, the
points corresponding with two opposite longitudinal ridges, which
separate the outer from the inner side of the tooth: the tooth is very
slightly incurved ; the line of its anterior margin is convex, that
of the posterior one is nearly straight. The teeth are well
adapted, by their form, for piercing and cutting; their sum-
mits are sharp-pointed, and their margins trenchant: the an-
terior edge is most produced. The crown of the tooth is compressed
but gradually expands, so that its base is circular, as represented at
fig. 1, 6. This is supported, as in the Mosasaurus, upon a round
hillock of bone resting upon the broad alveolar surface of the jaw.
The close arrangement of the supporting bases of the teeth in this
acrodont reptile gives a crenate outline to the margin of the
jaw.

The teeth, in the state in which they have come under my obser-
vation, exhibit very strikingly the lamellar decomposition of the den-
tine, upon which one of the arguments for the excretion-theory
has been founded(1). Fig. 2 shows the concentric arrangement of these
lamellz at the base of the crown of a fractured tooth, the centre of
which contains a wide pulp-cavity, occupied by the chalk matrix:
this structure is also exhibited at fig. 1, 6; it probably depends upon
the immature state of the tooth’s formation.

The crown of the tooth is defended, as in the Mosasaur, by a
coat of enamel.

108. Geosaurus—The teeth of an extinct reptile, whose large
eyes, defended by broad sclerotic plates, indicate the sea to have
been its abode, but which has received the name of Geosaurus from
Cuvier, resemble those of the large Varanian lizards in their com-

(1) According to the Report in the Literary Gazette, 1839, Sept. 21, p. 598, this argument,
founded upon the appearances presented by the mammoth’s tusks when in a state of lamellar
decomposition, was brought forward by the author of the paper on the structure and develop-
ment of teeth communicated to the British Association at Birmingham, in refutation of Dr.

Schwann’s hypothesis of the formation of ivory by ossification of the pulp. The fallacy of the
argument was shown in my memoir in the ‘ Comptes Rendus’ of the December following.

VARANIANS. 263

pressed sub-recurved crown, with a trenchant anterior and posterior
edge, which likewise presents a fine and close dentation. In the best
preserved cranial fragment of this reptile, (which is now in the
British Museum), fourteen or fifteen of these teeth may be counted in
the left upper maxillary bone ; and a fragment, apparently belonging
to the same jaw, exhibits three additional teeth: the posterior of
these teeth, which, extend below the orbit, are smaller than the rest.
The fragment of the premandibular bone contains five teeth.

The crown of the teeth is covered by a coat of remarkably
smooth and polished enamel, which presents the same brown tint as
that of the glossopetrz or fossil shark’s teeth. Soemmering conjec-
tured that the Geosaurus might be a young individual of the Mosa-
saurus, but Cuvier justly observes that the teeth of the Mosasaurus
differ from these of the Geosaurus in their greater breadth, especially
from side to side; and in the non-dentated character of the ridges
which divide the internal convex from the external flattened side of
the crown.

The form of the vertebre of the Geosaurus indicates its near
affinity to the crocodihan group, and the Argenton fossil crocodile
presents the same subcompressed teeth with dentated trenchant
margins, as does the Geosaurus.

VARANIANS.

109. The Varanian family of squamate Saurians, which includes the
Monitors of the old world, and in which some of the species approach
nearest in size to the Crocodiles, manifests its affinity to that group
in the absence of pterygoid teeth, and in the number of successive
tooth-germs which may be observed at the same time behind the
fixed and functional teeth.(1) Besides these characters the Varanians
must excite our interest from exhibiting in some species a form of
tooth which most nearly resembles that which characterizes the
Megalosaurus and other very remarkable extinct terrestrial species of
gigantic squamate Saurians.

In a small species of extinct Lizard, referable to the present
family, from the gault and chalk-formations, the teeth were awl-

(1) Pl. 63 a, fig. 9, Varanus variegatus.

264 VARANIANS.

shaped, i. e. slender, round, slightly incurved, and sharp-pointed :
about three lines in length above the alveolar border, close-set, and
equal sized. Their rounded base is anchylosed to the alveolar groove,
and their outer side attached to a well developed external alveolar
wall. I have proposed for the new genus of Lizard indicated by
these remains the name of Raphiosaurus.

The following are the principal varieties which the existing Vara-
nians exhibit in the form of the teeth.

The teeth of the Heloderm are slender, almost straight, sharp-
pointed, and with a deep fissure.

In the monitor of the Nile (Varanus niloticus Pl. 68, fig. 4) there
are four teeth in each intermaxillary and eleven in each maxillary bone:
in the lower jaw there are eleven teeth in each premandibular bone.
The posterior of these are obtuse tubercles in old specimens, but all the
other Varani have trenchant teeth, often with dentated margins. The
teeth are always obliquely bevelled off at the root, which is lodged
in a common groove with the internal border slightly developed.

In the land Monitor (Varanus arenarius) the teeth are of mode-
rate size, slightly compressed and a little curved backwards.

In the Varanus Timoriensis there are about thirty teeth adhering
to the internal margin of the upper jaw and from twenty to twenty-
two in the lower jaw: they are well spaced, compressed, pointed,
slightly curved, trenchant but not dentate.

The teeth of the Draceena lizard of Shaw (Varanus bengalensis, p.
& 8.), are neither trenchant nor dentate, but moderately compressed ;
short and strong, the anterior ones especially. There are thirty of
these teeth in the upper jaw and twenty-four in the lower jaw.

The teeth of the double-banded Monitor (Varanus bivittatus) are
all much compressed, with finely dentate trenchant margins: except
the small intermaxillary teeth, which are conical, pointed and in-
curved. There are eight intermaxillary teeth, eleven maxillary teeth
on each side, and twelve teeth in each premandibular bone, where one
or two of the anterior teeth are conical, corresponding with the inter-
maxillaries above.

The variegated lizard (Varanus variegatus) presents the most
compressed form of teeth: in specimens preserved in spirits they are

Oo

VARANIANS. 265

transparent, and their fine tubular structure may be discerned
with the due microscopic power without cutting the tooth into slices.
I find nine small conical sharp-pointed teeth in the anchylosed inter-
maxillaries, the middle azygos incisor being the smallest ; and seven
large, compressed, recurved, sharp pointed and trenchant teeth in
each maxillary bone. In the lower jaw there are two small conical
incisors at the fore-part of each premandibular series, succeeded by
nine or ten long compressed teeth corresponding with the maxillaries
above. These teeth are more convex on the inner than on the outer
side ; their margins are finely crenate. They are separated by mode-
rately wide and irregular intervals, in which are contained the suc-
cessional teeth, the apices of the largest of these appearing above the
outer alveolar ridge.

These successional teeth are developed at the inner and posterior
side of the base of their predecessors : and groups of three and some-
times four teeth, placed one a little behind the other and successively
diminishing in size from the tooth in place to its third successor, are
arranged in the alveolar groove, as shown in Pl. 63 a, fig. 9. The
old teeth are not so much damaged by the growth of their successors
as in other Saurians ; and the young teeth are at no period inclosed
in a cavity in those which they succeed.

In the great crocodilian Monitor (Varanus crocodilinus, Pl. 68,
fig. 3), the large fixed compressed teeth, of which there may be about
seven in each upper maxillary bone and six in each premandibular,
are anchylosed by the whole of their base and by an oblique surface
leading upwards on the outer side of the tooth to a slight depression
on the oblique alveolar surface, as in the Var. striatus, Pl. 63 a,
fig. 8a. The base of the tooth is finely striated, the lines being pro-
duced by inflected folds of the external cement, as in the Ichthyosaur
and Labyrinthodon, but being short and straight as in those of the
former genus. The alveolar channel or groove has scarcely any
depth ; but the anchylosed base of the tooth is applied to an oblique
surface, terminating in a sharp edge, from which the outer side of
the free crown of the tooth is directly continued. The great Varanus,
like the variegated species, manifests its affinity to the Crocodilians
in the number of successive teeth which are in progress of growth to

266 THECODONTOSAURUS.

replace each other: but from the position in which the germs of the
successional teeth are developed, the more advanced teeth in this
species, as in the Var. variegatus, do not exhibit the excavation that
characterize the same parts of the teeth of the Enaliosaurs and
Crocodiles.

THECODONTS.

110. We have already seen that among the inferior or squamate
Saurians there are two leading modifications in the mode of attach-
ment of the teeth, the base of which may be either anchylosed to the
summit of an alveolar ridge, or to the bottom of an alveolar groove and
supported by its lateral wall: these modifications were indicated by
the terms ‘ acrodont ’ and ‘ pleurodont.’ <A third mode of fixation is
presented by some extinct Saurians, which, in other parts of their
organization, adhere to the squamate or Lacertine division of the
order; the teeth being implanted in sockets, either loosely, or confluent
with the bony walls of the cavity: these may be termed the ‘ theco-
dont ’(1) Lacertians: the most ancient of all Saurians belong to this
group.

111. Thecodontosaurus.—In the dolomitic conglomerate at Red-
Jand near Bristol, a formation considered to belong to the oldest or
lowest division of the new-red-sandstone series, remains of reptiles have
been discovered by Dr. Riley and Mr. Stutchbury(2) which are allied,
in the form of their teeth to the typical Varanian monitors, but dif-
fer in having the teeth imbedded in distinct sockets : to this condi-
tion, however, the Varani, among the squamate saurians, make an
approach, in the shallow cavities containing the base of the teeth
along the bottom of the alveolar groove.

In the ancient extinct genus in question the sockets are deeper,
and the inner alveolar wall is nearly as high as the outer one: the
teeth are arranged in a close-set series, slightly decreasing in size
towards, the posterior part of the jaw ; each ramus of the lower jaw is
supposed to have contained twenty-one teeth. These are conical,

(1) nxn, a sheath; ods¢ a tooth.
(2) Geol. Transactions, 1836, p. 349.

PALEOSAURUS. 267

rather slender, compressed and acutely pointed, with an anterior and
posterior finely serrated edge, the serratures being directed towards the
apex of the tooth; the outer surface is more convex than the inner
one : the apex is slightly recurved: the base of the crown contracts a
little to form the fang, which is subcylindrical. ‘The pulp-cavity
remains open in the base of the crown.

In microscopic structure, the teeth of the Palzosaurus closely
correspond with that of the teeth of the Varanus, Monitor and Mega-
losaurus. The body of the tooth consists of compact dentine, in
which the calcigerous tubes diverge from the open pulp-cavity at
nearly right angles to the surface of the tooth; they form a slight
curve at their origin, with the concavity directed towards the base of
the tooth, then proceed straight, and at the periphery bend upwards,
in the contrary direction. The diameter of the calcigerous tube
is gmth of aninch: the breadth of the interspaces is qth of an inch.
The crown of the tooth is invested with a simple coat of enamel.

This examination, which I have been enabled to make by the kind-
ness of Mr. Stutchbury, satisfactorily establishes the distinction between
the Saurian of the Bristol conglomerate and the reptiles of the later
member of the new-red-sandstone system in Warwickshire, already
described under the name of Labyrinthodon.

112. Paleosaurus.—In the same formation as contained the jaw and
teeth of the Thecodontosaurus, two other teeth were separately dis-
covered, differing from the preceding and from each other ; the crown
of one of these teeth, measuring nine lines in length and five lines in
breadth, is represented at Pl. 62 a, fig. 7. It is compressed, pointed,
with opposite trenchant and serrated margins, but its breadth, as
compared with its length, is so much greater than in the Thecodon-
tosaurus, that Dr. Riley and Mr. Stutchbury have founded upon it
the genus Palcosaurus,(1) and distinguish it by the specific name
of platyodon, from the second tooth which they refer to the same
genus under the name of Palgosaurus cylindrodon. The portion of the
tooth of the Pal. cylindrodon which has been preserved, shows that the
crown is sub-compressed and traversed by two opposite finely-serrated
ridges, its length is five lines ; its breadth at the base two lines.

(1) Loc. cit, p. 352,

268 PROTOROSAURUS.

113. Cladeiodon.(1)—In the new red sandstone (Keuper?) of War-

wick and Leamington, detached teeth occur of the size and form repre-

sented in Pl. 62 a, fig. 4,a&06; they have been found in the same

quarries as those containing the remains of the Labyrinthodon. In
their compressed form, anterior and posterior serrated edges, sharp
points, and microscopic structure, these teeth agree with those of the
Saurian reptiles of the Bristol conglomerate. In their breadth, as
compared with their length and thickness, they are intermediate
between the Thecodontosaurus and the Pal@osaurus platyodon ; they are
also larger and more recurved, and thus more nearly approach the
form characteristic of the teeth of the Megalosaurus. From these
teeth, however, they differ in their greater degree of compression,
and in a slight contraction of the base of the crown; I propose,
therefore, to indicate the genus, of which, as yet, only the teeth are
known, by the name of Cladeiodon, and for the species from the
Warwickshire sandstones the name of Cladeiodon Lloydi, in testimony
of the friendly aid of Dr. Lloyd of Leamington, to whose exertions I
owe the materials for the description of the teeth of the present genus,
and the still more remarkable ones of the British species of Laby-
rinthodon, with which the teeth of the Cladeiodon are associated.

PROTOROSAURUS.

114. In the pyritic schists of Thuringia, which, like the dolomitic
Breccia near Bristol, rank as the oldest member of the new-red-
sandstone system, the fossil remains of a small species of Saurian
reptile have long been known to occur ; and it is from the individual
specimen of this ancient extinct species, first described by Spener as a
sort of crocodile in the Miscellanea Berolinensia for the year 1710,
that the observations on the dental system are here taken.

It is well known that Cuvier, after an elaborate comparison of
the figures and descriptions of the 'Thuringian fossil Saurian by Spener,
Link, Swedenborg and Wachsmann, arrived at the conclusion that the
species was to be referred to the Monitors or Tupinambis. (2)

(1) xAadevw, to prune; dczc, a tooth ; from the resemblance of the tooth to a pruning-knife.
(2) On ne comptera donc plus les animaux de Spener et de Link parmi les crocodiles, ou

MEGALOSAURUS. 269 .

M. Hermann V. Meyer has proposed the name of Protorosaurus
Spenert for the Thuringian Monitor, but he has not added any new
fact relative to its organization.

This name I shall retain,,because the species in question actually
differs from the existing Monitors and other Lacertians by the same
character which distinguishes the Thecodontosaurus, viz: the implanta-
tion of the teeth in distinct sockets. Of these sockets, the dislocated
ramus of the lower jaw in Spener’s specimen exhibits fourteen,
which are of a square shape with the angles rounded off, close-set and
sub-equal. The teeth, of which eighteen may be counted in the
upper jaw, are relatively longer, more slender, and more cylindrical
than in the Thecodon ; they are more or less broken ; the most perfect
of them measure three lines in length, and two-thirds of a line across the
base; they are of a jet-black colour, and, being imbedded in a dark
matrix, have not enabled me to determine whether the Protorosaurus,
like the equally ancient reptiles of the Bristol conglomerate, had the
teeth armed with serrated ridges(1).

MEGALOSAURUS.

115. The compressed varanian form of tooth, with trenchant and
finely dentated margins, which characterized the ancient Paleosaur
and Cladeiodon, is continued in the comparatively more recent and
gigantic species of terrestrial lizard, of which the remains were dis-
covered by Dr. Buckland in the oolite of Stonesfield. The characters
and peculiarities of the jaws and teeth have been so accurately and
graphically described by their discoverer, that an apology would be
due rather for suppressing, than for here reproducing them.

‘* From these,” says Dr. Buckland, ‘‘ we learn that the animal
was a reptile, closely allied to some of our modern lizards, and
viewing the teeth as instruments for providing food to a carnivorous
creature of enormous magnitude, they appear to have been admirably

celui de Swedenborg parmi les guenons ou les sapajous; mais on les rangera tous parmi les
monitors ou tupinambis. Ossem. fossiles, 4to. vol. v, p. 306.

(1) Besides the thecodont type of dentition, the Protorosaurus differs from all recent Saurians,
and resembles the Pterodactyle in the great relative size of the cervical vertebre, and the ossified
tendons of the muscles of that region of the spine; it differs from all reptiles, except the extinct
Racheosaurus in the bifurcate superior spines of the caudal vertebre.

270 MEGALOSAURUS.

adapted to the destructive office for which they have been designed.
Their form and mechanism will be best explained by reference to the
figures.

“« The outer margin of the jaw (Pl. 70, fig. 8, 6) rises nearly an
inch above its inner margin, forming a contiguous lateral parapet to
support the teeth on the exterior side, where the greatest support was
necessary, whilst the inner margin throws up a series of triangular
plates of bone (c,c,) forming a zig-zag buttress along the interior of
the alveoli. From the centre of each triangular plate, a bony par-
tition crosses to the outer parapet, thus completing the successive alveoli.
The new teeth (a, a) are seen in the angle between each triangular
plate, rising in reserve to supply the loss of older teeth, as often as
progressive growth, or accidental fracture, may render such renewal
necessary, and thus affording an exuberant provision for a rapid suc-
cession and restoration of these most essential implements. They
were formed in distinct cavities, by the side of the old teeth, towards
the interior surface of the jaw, and probably expelled them by the
usual process of pressureand absorption, insinuating themselves into the
cavities thus left vacant. This contrivance for the renewal of teeth, is
strictly analogous to that which takes place in the dentition of many
species of existing lizards.

‘‘ In the structure of these teeth (Pl. 70, figs. 9 & 10), we find a
combination of mechanical contrivances analogous to those which are
adopted in the construction of the knife, the sabre, and the saw.
When first protruded above the gum, the apex of each tooth presented
a double cutting edge of serrated enamel. In this stage, its position
and line of action were nearly vertical, and its form, like that of the
two-edged point of a sabre, cutting equally on each side. As the
tooth advanced in growth, it became curved backwards, in the form
of a pruning-knife, and the edge of serrated enamel was continued
downwards to the base of the inner and cutting side of the tooth,
whilst on the outer side a similar edge descended, but to a short dis-
tance from the point (fig. 10) and the convex portion of the tooth
became blunt and thick, as the back of a knife is made thick, for the
purpose of producing strength. The strength of the tooth was
further increased by the expansion of its sides (as represented in the

= gicetioS wes

MEGALOSAURUS. o7%

transverse section, fig. 11). Had the serrature continued along the
whole of the blunt and convex portion of the tooth, it would, in this
position, have possessed no useful cutting power ; it ceased precisely
at the point beyond which it could no longer be effective. Ina tooth
thus formed for cutting along its concave edge, each movement of
the jaw combined the power of the knife and saw; whilst the apex
in making the first incision, acted like the two-edged point of a
sabre. The backward curvature of the full-grown teeth, enabled
them to retain, like barbs, the prey which they had penetrated. In
these adaptations, we see contrivances, which human ingenuity has
also adopted, in the preparation of various instruments of art.’’(1)

The teeth of the Megalosaur consist of a central body of dentine,
with an investment of enamel upon the crown, and of cement over
all, but thickest upon the fang. The marginal serrations are
formed almost entirely by the enamel, and when slightly magnified
are seen to be rounded, and separated by slight basal grooves (PI. 62, a,
fig. 6, c); the smooth and polished enamel upon the sides of the
crown presents a finely wrinkled appearance ; the remains of the pulp
are converted into a coarse bone in the completely formed tooth.

The dentine consists of extremely fine and close-set calcigerous
tubes, without admixture of medullary canals ; they radiate from the
pulp-cavity at right angles with the external surface of the tooth ;
the primary curvatures correspond with those of the calcigerous
tubes in the monitor’s tooth (Pl. 67) but are less marked, so that
the tubes appear straighter. They present a diameter of gqth of an
inch ; with interspaces varying between two and three times that
diameter ; they dichotomize sparingly, but the number of minute
secondary branches sent off into the intermediate substance is very
great. These secondary branches proceed at acute angles from the
primary tubes ; the divisions of the tubes become very frequent near
the periphery of the dentine and the terminal branches dilate into, or
inosculate with a stratum of calcigerous cells, which separates the den-
tine from the enamel. The microscopic characters of the tooth of the
Megalosaur are represented in Pl. 70 a, in part of a transverse sec-

(1) Bridgewater Treatise, vol. i, p. 237.

272 THAUMATOSAURUS.

tion of the middle of the crown, including the pulp-cavity and its
ossified contents; the natural size of the section is given at fig. 1 ;
a reduced figure of the same, magnified sixty diameters, at fig. 2,
and a more highly magnified view of the terminations of the calcige-
rous tubes, at fig. 3, a; the marginal cells being shown at b, and the
enamel with its thin coat of cement at c.

The highly organized nature of a tooth is well illustrated in this
example of one of the simplest of Saurian teeth ; in which, in addi-
tion to the tubular and cellular modifications of the dentine, there is
also enamel, cement, and an internal coarse kind of bone.

The dentition of the Megalosaurus, besides exemplifying, on a
large scale, the mechanical advantages of the varanian form of tooth,
exhibits an interesting transitional character between the squamate
and loricate types of Saurians, the distinct sockets making the ap-
proach to the crocodiles, while the raised external alveolar wall shows
the retention of the lacertine structure.

THAUMATOSAURUS.

116. Ina great extinct species of Saurian, whose remains have been

discovered in the oolitic formation at Neuffen, in Wurtemberg, and
which has received the name of Thaumatosaurus oolithicus from
M. Hermann von Meyer, the teeth were conical, slightly curved,
straighter on the inner side of the crown; implanted by a long and
strong root rather obliquely in a deep socket. The base and basal
portion of the crown presents a nearly circular transverse section ;
the wide pulp-cavity in this part of the tooth presented an elliptical
transverse contour; the tooth becomes slightly compressed towards
the apex. ;
The broadest part of the tooth is its implanted base ; the breadth
of the crown is to its height as one to three; the crown is invested
with a thin layer of enamel, the basal half of which is marked by
longitudinal striz ; these striz seem to consist of folds of the enamel,
which do not extend into the dentine.

The successional teeth penetrate into the interior of the fixed
teeth in the progress of their development.

-

PTERODACTYLUS. D73

ISCHYRODON,

117. The teeth of the Ischyrodon, a gigantic reptile from the Jura
limestone of the Canton of Aargau, somewhat resemble those of the
Thaumatosaurus, but the external longitudinal striz of the crown of
the tooth are sharper and more elevated, and between the striz
the enamel is roughened by irregular linear risings.

PECILOPLEURON.

118. The teeth of the Pecilopleuron (Deslongchamps), a gigantic
reptile whose remains occur in the oolitic beds at Caen, according to
the single tooth referred to that genus, has a more compressed
crown than the teeth of the Thaumatosaurus ; the striz are also wider
apart, and the two diametral ones are developed into ridges which
extend to the apex of the tooth.

PTERODACTYLUS.

119. The true affinities of this the most extraordinary of all the
ancient animals which Comparative Anatomy has brought to light,
were, when much conflicting evidence was apparently given by other
parts, pointed out most distinctly by the dental system. Cuvier,
after discussing the various opinions which had been promulgated
respecting the nature of the remains of the extinct volant animal in
question, says :—‘‘ The teeth, by which the examination of an animal
ought always to be commenced, here present nothing equivocal.
They are all simple, conical and nearly alike, as in the crocodiles, the
monitors and other lizards.’’(1) Their disposition in the jaws with wide
interspaces, and their separate implantation in distinct sockets are cha-
racters in which the Pterodactyle approximates to the extinct Saurian
genera, Thecodon, Megalosaurus, Plesiosaurus, and the Crocodilians.

In the Pterodactylus longirostris the teeth are of moderate and
equal size, slender, conical, sharp-pointed, recurved, with pretty

(1) “ Les dents, par ou il faut toujours commencer |’examen d’un animal, ne présentent ici
aucune équivoque. Elles sont toutes simples, coniques, et 4 peu prés semblables entre elles
comme dans les crocodiles, les monitors et d’autres lézards.” Cuvier adds, “‘ Tout le monde
sait que les dauphins seuls, parmi les mammiféres, pourraient présenter quelque chose de com-
parable.”—Ossem, foss. Ed. 1836, tom. x, p. 225.

T

274 PTERODACTYLUS.

regular interspaces, slightly increasing as the teeth are placed further
back. In the specimen described by Soemmering there are on the
preserved side of the head nineteen teeth in the lower jaw ; and eleven
in the upper jaw, which is probably only a portion of this series, but
at least gives sixty teeth in all. There is an orifice in the jaw at the
inner side of the base of each tooth, whence Cuvier supposes the
teeth of replacement to issue.(1)

In the Pterodactylus crassirostris (Pl. 63 a, fig. 6) the teeth are
relatively fewer, more unequal, but for the most part much larger than
in the previous species, and the jaws are correspondingly shorter and
stronger. The teeth are long, slender, very acute, sub-compressed and
slightly curved ; they have been described as arranged or approximated.
in pairs, but this is the case with a few only, and the hinder tooth is
always the smallest ; whence I conclude that it was a successional tooth,
which has been developed in the same relative position to its predecessor
as in the great Varanus, (compare figs. 6 & 9, Pl. 63 a). The inter-
maxillary bone, in the specimen figured, contains four teeth on one
side, of which the first three are of small size ; there are seven teeth
in the maxillary bone of the same side, of which the hinder ones,
that extend beneath the orbit, are the shortest ; the corresponding
ramus of the lower jaw contains six teeth; the supposed successional
teeth are included in the preceding enumeration.

In the Pterodactylus medius the base of the teeth have been
stated to be hollow, as in the teeth of the crocodile, and to contain
the germs of their successors ;(2) the right half of the lower jaw
contains sixteen teeth, of nearly equal size, the hinder ones becoming
smaller. They are simple, conical, slightly recurved, compressed and
smooth.

In the Pterodactylus Munsteri the teeth are slender, recurved,

(1) “ On en voit de tout semblables dans le sauvegarde, et surtout dans la dragone (Thorictes
dracena).” | have not observed in any existing reptile this mode of emergence of the successional
teeth, as in Mammalia, by an outlet distinct from the socket of the previous tooth. In the
great safe-guard (Varanus), the successional teeth rise from the alveolar groove behind those
which they succeed, as shown in Pl. 63 a, fig.9. In the Pterodactylus medius the germs of the
young teeth have been observed in the basal cavities of the old, as in the crocodile.—See Mun-
ster, Nova Acta, Nat. Cur. t.xv, 63.

(2) Munster, loc. eit.

SS ice

ENALIOSAURS. 275

pointed, laterally compressed, but not trenchant, varying in size;
their number is nine on each side of the upper jaw and seven on each
side of the lower jaw ; none of them are implanted in the intermax-
illary bone.

The teeth figured in Pl. 63 a, fig. 7, are referred by Dr. Buck-
land to the large species of Pterodactyle (Pter. macronyz), discovered
by him in the lias at Lyme Regis ; they are implanted like the teeth
of other species of the genus in separate sockets, but in the breadth
and shortness, lateral compression, and trenchant anterior and pos-
terior margins of the protruded crown, they much more closely
resemble the teeth of certain Scomberoid fishes, which are similarly
implanted in the jaws. M. H. Von Meyer observes that the jaw of a
Pterodactyle from the lias at Banz, which he refers to the species
macronyx, contains the sockets of only fourteen teeth, whilst the
fragment of jaw with the Sphyrenoid teeth from Lyme Regis above
mentioned, must have contained a much greater number.

Some portions of the skeleton of a large Pterodactyle have been
discovered by Dr. Buckland in the oolite at Stonesfield. A few teeth
from the same formation, in the collection of the Earl of Enniskillen,
bear the same proportion to these bones, as do the teeth of the Pter.
crassirostris to its skeleton ; they are long, slender, conical, slightly
curved, and sharp-pointed; their base is smooth, the enamelled
crown is marked with fine striz, converging obliquely upwards toa
longitudinal line on the convex side of the tooth. These teeth vary
from nine to fourteen lines in length, and are one line or one line and
a half across the base.

I have not had the opportunity of examining the microscopical
structure of an undoubted tooth of a Pterodactyle.

ENALIOSAURS.

120. Ichthyosaurus.—The teeth of the Ichthyosauri have a simple,
more or less acutely conical form, with a long and, usually, expanded
or ventricose base, or implanted fang. They are confined to the inter-
maxillary, maxillary and premandibular bones, in which they are
arranged ina pretty close and uninterrupted series, and are of nearly
equal size. They consist of a body of unvascular dentine, invest-

m2

276 ENALIOSAURS.

ed at the base by a thick layer of cement, and at the crown by a
layer of enamel, which is itself covered by a very thin coat of ce-
ment ; the pulp-cavity is more or less occupied in fully-formed teeth
by a coarse bone.

The external surface of the tooth is marked by longitudinal im-
pressions and ridges, but the teeth vary both as to outward sculp-
turing and general form in the different species. (1)

The teeth present the largest size in the Ichthyosauri platyodon
and communis, and they are smallest and most slender in the
Ich. tenwrostris.

Ich. communis, (Pl. 73, fig. 4). This species is characterized by
teeth which have a cylindrical, sometimes sub-ventricose base, and a
round, conical, slightly aduncate crown, tapering more rapidly and
less regularly to the apex than in the other species ; the apex is not
very acute. The crown is traversed by moderately fine and close-set
longitudinal furrows, and the base is sculptured by coarse and deep
grooves which separate longitudinal convex ridges.

There are from forty to fifty teeth on each side of the upper jaw,
eighteen of which are implanted in the superior maxillary bone ; in
the lower jaw there are on each side between twenty-five and thirty
teeth. The fine coronal grooves are abruptly divided from the coarse
basal ones at the terminal line of the enamel. The basal ridges are
sometimes transversely scored in large teeth, and bifurcate and pro-
gressively diminish in breadth as they approach the contracted
extremity of the tooth ; the base of such teeth sometimes resembles a
small contracted pentacrinite.

Ich. platyodon (P1. 73, figs. 3 & 6).—The teeth of this species —
present a ventricose base, and a conical, sub-compressed, subincurved —
crown, the outer and inner sides of which meet at two opposite sharp —
edges, which terminate above at the acute apex of the crown, which is —
thus adapted for both piercing and cutting.

2
The basal longitudinal grooves and ridges of the tooth are as

(1) Pl. 73, 73 a & 74.
(2) The principal varieties of the form of the teeth, and the species thereby indicated were
|

first observed by M. Delabeche, and are described by Mr. Conybeare in his beautiful memoir
in the Geol. Trans. vol. vi, p. 108.

ENALIOSAURS. 277

coarse as, but more regular than those of the tooth of the Ich. com-
munis ; the surface of the crown is smoother and more polished, and
the longitudinal lines are due to slightly developed angular ridges
dividing narrow flattened tracts, like those of a polyhedron.

I have not observed more than forty-five teeth on each side of
the upper, and forty teeth on each side of the lower jaw. The crowns
of the teeth are more frequently found to be snapped off in this than
in the smaller species of Ichthyosaurus, a circumstance which is indi-
cative of the greater force with which they had been used.

Ich. lonchiodon(1) (Pl. 73, fig. 2).—The teeth are more slen-
der in this gigantic species than in the two. preceding ones, and they
are straighter than in any other species. Their base is cylindrical
and regularly fluted ; a smooth boundary divides it from the crown ;
this is conical and is traversed by finer and more numerous grooves,
which are minutely and irregularly undulated, but converge with a
general longitudinal course to the apex of the tooth. The transverse
section of the crown is nearly circular; the crown tapers gradually
to its apex, which is nearer the posterior line than the central. axis
of the tooth.

Ich. tenuirostris (Pl. 73, fig. 5).—The teeth are more slender,
in proportion to their length, in this than in any other species ; and
they are also more numerous ; their base is cylindrical, and their
crown conical, gradually tapering to an acute apex, and slightly
recurved: the basal grooves are regular and longitudinal; the
coronal striz are extremely fine. I have found between sixty-five and
seventy teeth on each side of the upper jaw; of these the posterior
third part, or about twenty-five of the teeth, are implanted in the
slender maxillary bones, the rest being supported by the dispropor-
tionately long intermaxillaries. In the lower jaw there are about
sixty teeth on each side. The teeth are directed more obliquely back-
wards in this than in the preceding species.

Ich. intermedius (Pl. 73, fig. 1).—Mr. Conybeare (2) thus
characterizes this species :—‘‘ The upper part of the teeth is much
more acutely conical than in the Ich. communis, and the striz less,

(1) \oyxn, spear; °ds¢, tooth.
(2) Loc. cit. p. 108.

278 ENALIOSAURS.

prominent, yet they are less slender than in the Ich. tenwrostris.”
They are also much fewer in number; I have not found more than
forty teeth on each side of the upper jaw, or than thirty-five on each
side of the lower jaw.

In the Ich. acutirostris the teeth differ from those of the Ich.
tenuirostris in having a somewhat wider base in proportion to their
length : in the specimens which I have examined the teeth likewise
present less regularity of size, and they are fewer in number; in a
fragment of jaw, three inches in length, which included twenty-four
teeth, their exserted crowns presented a regular alternation of three
and five lines in length. In an entire head there are about fifty teeth
on each side of the upper jaw, and about forty teeth on each side of
the lower jaw.

I have investigated the microscopic structure of the teeth of the
Ichthyosaurus in the species platyodon and intermedius(1).

The dentine has the same simple compact structure as in the
teeth of existing carnivorous Saurians. The calcigerous tubes present
a diameter of smth of an inch, with interspaces of gqth of an inch.
They radiate from the pulp-cavity, and form a line continued from
its upper end to near the apex of the tooth, according to their usual
course, towards the periphery of the tooth; they describe at their
origin a graceful curve, the concavity of which is directed towards the
base of the tooth, and then proceed in straight lines at right angles tothe
periphery of the tooth(2). The secondary curvatures or undulations
of the tubes are more regular, more numerous, and more marked than
in the crocodile’s tooth ; the tubes divide dichotomously many times
during their course, and send off lateral branches obliquely into the
clear intermediate substance, and principally from their concave side ;
the terminal divisions of the calcigerous tubes (a, fig. 2) become less
regular, and appear to decussate and communicate at their extremities,
either directly with one another by inosculating loops, or through the
medium of minute cells.

The enamel (b) is a clear dense substance presenting faint traces

(1) Trans. Brit. Assoc. 1838, p. 144.
(2) The disposition of the calcigerous tubes, as seen in a longitudinal slice of the apical part
of the crown of the tooth, is figured in Plate 73, a.

Stitt in ne

Cera D tae

ENALIOSAURS. 279

of a fibrous structure, the lines being vertical to the surface of the
tooth.

The coronal cement appears only as a line of substance more
opaque than the enamel which it invests; it augments in thick-
ness at the base of the tooth, where the radiated corpuscles
or cells that characterize its structure are very conspicuous; the
cement is inflected at each of the basal grooves in the form ofa
short, straight and simple vertical fold into the substance of the
dentine. The peripheral portion of the basal dentine is thus divided,
to the extent represented in Pl. 64 B, fig. 3, into a corresponding
number of processes; fissures of the pulp-cavity radiate to their
bases, becoming there the centres of divergence of as many series of
calcigerous tubes, which obey in their course the usual law of verti-
cality to the external surface of the dentine. This structure can be seen
only in a transverse section of the base of the tooth: its correspon-
dence with that of the apex of the crown of the teeth of the Laby-
rinthodon will be obvious on comparing fig. 3, Pl. 64 8, with fig. 1,
Pl. 63, s, and, as has been already stated, it gave the key to the
nature and principle of the complicated labyrinthic interblending of
dentine and cement, which was first observed in the great tusk of
the Labyrinthodon Jaegerv.

The remains of the pulp, after the formation of the due quantity
of dentine, became converted, as in the pleodont lizards, by a pro-
cess of coarse ossification into a reticulate fibrous or spongy bone(1) ;
but it continues open at the crown after the basal part of the tooth is
thus consolidated, as shown in the longitudinal section (Pl. 73, fig. 8),
wherein a is the pulp-cavity filled with crystallized spath, 6 the
ossified pulp at the base of the tooth. The radiated cells or corpuscles
are very conspicuous in both this bone and the external cement.

The chief peculiarity of the dental system of the Ichthyosaur
is the mode of implantation of the teeth; instead of being anchylosed
to the bottom and side of a continuous shallow groove, as in most
Lacertians, or implanted in distinct sockets, as in the Thecodon,
Megalosaur or Pterodactyle, they are lodged loosely in a long and

(1) “‘ The tooth in these genera becomes completely solid, its interior cavity being filled up
by the ossification of the pulpy substance.”—Conybeare, loc. cit. p. 106.

280 ENALIOSAURS.

deep continuous furrow, and retained by slight ridges extending,
between the teeth, along the sides and bottom of the furrow (Pl. 73,
fig. 9), and by the gum and the organized membranes continued into
the-groove and upon the base of the teeth.

The germs of the new teeth are developed at the inner side of
the base of the old ones. Mr. Conybeare has given a figure of a
transverse section across the jaw-bone, (reproduced at Pl. 73, fig. 7),
in which the new tooth (c) has penetrated the osseous substance of
the base of the old tooth (b), and its point has nearly entered the
remains of the pulp-cavity which has continued open in the crown of
the tooth(a).

From the circumstance of the consolidation of the base of the
teeth in the Ichthyosaur Mr. Conybeare infers that they were
retained longer in the jaw than are the hollow teeth of the croco-
diles ; but the analogy of other Saurians, and the observation of two
new teeth at successive stages of formation at the base of an old
tooth, prove that the succession of new sets of teeth was repeated
more than once, though probably not so frequently as in the
crocodile. |

121. Plesitosaurus.—The teeth of the Plesiosaur are conical, long,
slender, curved and sharp-pointed; they appear to retain their in-
ternal cavity, as in the teeth of a crocodile; they have a very long
round fang or implanted base, which, in old teeth, contracts, as it
sinks into the jaw, and terminates almost in a point.

The chief distinction, which the dental system offers between the
present and the preceding genus of Enaliosaur, is the loose implanta-
tion of the teeth of the Plesiosaur in separate alveoli. In thus
deviating from the Ichthyosaur, the Plesiosaur proportionally approx-
imates to the crocodilian type, and this affinity is likewise manifested
in the unequal size of the teeth, and the development of some of the
anterior ones into large tusks.

The teeth are composed, as in the Ichthyosaur, of a body of
hard and simple dentine, covered at the crown by a coat of enamel,
and, at the base, by a coat of cement; but the latter is relatively
thinner than in the Ichthyosaur, and is not inflected into the substance
of the dentine, The crown is characterized by well-defined narrow

ENALIOSAURS. 281

elevated longitudinal ridges, terminating abruptly at different dis-
tances from the apex, to which, however, none of them extend.

In the lower jaw of the Ples. macrocephalus there are twenty-six
teeth on each premandibular bone: the crown of one of the large
anterior tusks, in a lower jaw, ten inches in length, measured one
inch and a half in length and one third of an inch in breadth; its
transverse section was nearly circular. The premandibular piece
of the lower jaw of the Ples. arcuatus contains fifty-four teeth, or
twenty-seven on each side, the six anterior teeth on each side being
larger and longer than the rest. In the lower jaw of the Ples.
dolichodewrus there are twenty-five teeth on each side, the four anterior
of which are the largest.

The disposition of the calcigerous tubes is shown in a longitu-
dinal section of the apical third part of a tooth of the Plesiosaurus
Hawkinsii in Pl. 74. In their general course they bear a considerable
resemblance to the same parts in the Ichthyosaurus, but the primary
cuevature presents a more graceful sigmoid line, from the inclination of
the peripheral extremities of the tubes towards the apex. The diameter
of the tubes near their origin is 3 th of an inch; their interspaces equal
five or six of their diameters ; the secondary undulations are relatively
wider than in the Ichthyosaurus, and the secondary branches are longer
and more bent; the tubes divide dichotomously several times in
their course ; the divisions, after a slight divergence proceeding in the
same parallel line with each other and with the main stem. The finer
secondary branches dilate into extremely minute cells along tracts
which run parallel with the contour of the tooth itself, and occasion
the apparent alternation of opaque and clear layers observable in the
section by transmitted light, as represented in the figure; the mode
of termination of the calcigerous tubes is shown at fig. 2, Pl. 74.
The enamel presents the same fine fibrous structure as in the
Ichthyosaurus.

The mode of succession of. the teeth of the Plesiosaur differs
from that of the Ichthyosaur in the growing tooth being developed
in a cell at the inner side of the old socket, and affecting by its
pressure the bone of the jaw, rather than the tooth about to be
displaced.

282 PLEIOSAURUS.

Notwithstanding the approximation to the crocodilian type which
the teeth of the Plesiosaur make in their persistent pulp-cavity, there
is not more than a single successional tooth in progress of develop-
ment at the base of the tooth in use at any period; and the dentition
of the Plesiosaur further differs from that of the crocodile, inasmuch
as the new tooth, instead of emerging from the pulp-cavity of the old
tooth, or even from the same socket, protrudes its apex through a
distinct foramen at the inner side of the alveolus of its predecessor.

PLEIOSAURUS.

122. Large, simple, conical teeth, with the enamelled crown tra-
versed by well-defined and abruptly terminated longitudinal or
oblique ridges, as in the Plesiosaur, have not unfrequently been dis-
covered in the Kimmeridge clay formation. These teeth differ from
those of the Plesiosaur in their greater relative thickness as compared
with their length and in the subtriedral shape of their crown ; the
outer side is slightly convex, sometimes nearly flat; it is separated
from the:two other facets by two sharp ridges; these are
more convex, and the angle dividing them is often so rounded off,
that they form a demi-cone, and the shape of the tooth thus approxi-
mates very closely to that of the Mosasaur, with which it is equal in
size. It may readily be distinguished, however, even when the crown
only is preserved, by the ridges which traverse the inner or convex
sides; the outer flattened surface alone being smooth: but an entire
tooth of the present extinct reptile presents a long fang, which at
once removes it from the acrodont group, and allies it with the
thecodont reptiles, among which it approaches nearest, in the super-
ficial markings of the crown, to the Plesiosaurus. The known parts
of the skeleton of the gigantic extinct reptile, to which the teeth in
question belong, confirm this approximation ; but the vertebrz of the
neck are so modified that the peculiarly elongated proportion of this
part of the spine, which characterizes the typical Plesiosauri, is
exchanged for one that much more nearly approaches the opposite
condition of the cervical region in the Ichthyosauri ; this abrogation
of the main characteristic of the Plestosauri, combined with the
more crocodilian proportions of the teeth in the present reptile, have

EE -_

PLEIOSAURUS. 283

induced me to found a sub-genus for its reception under the name of
Pleiosaurus.

In the collection of Prof. Buckland, at Oxford, a considerable
proportion of both upper and lower jaws of a gigantic specimen of the
Pleiosaurus brachydeirus is preserved from the Kimmeridge clay for-
mation at Market Raisin. The teeth are arranged in separate sockets,
in a close and regular series, along the alveolar borders of the inter-
maxillary, maxillary and premandibular bones. Twenty-six sockets
may be counted on the most perfect side of the upper jaw, but the
series is evidently incomplete posteriorly. An interspace not quite
equal to the breadth of a socket divides the fourth from the fifth
tooth, counting backwards, and the jaw is slightly compressed at this
interspace; the four anterior teeth, thus marked off, occupy the -
slightly expanded anterior extremity of the upper jaw, but do not
present the disproportionately large size which characterizes the
anterior teeth in the true Plesiosaurs. After the fifth tooth the
sockets progressively increase in size to the twelfth tooth, and, from
the fourteenth they begin gradually to diminish in size ; becoming, be-
yond the twentieth tooth, smaller than those at the fore part of the jaw.

The alveolar septa are narrow and are thinned off to an edge,
which is lower than either the outer or inner walls of the sockets: these
walls are equally developed. A line drawn transversely across any
of the twelve anterior sockets would be transverse to the jaws, but in
the remaining sockets it would incline obliquely from without, inwards
and backwards. The transverse diameter of the thirteenth socket is
one inch, six lines ; its antero-posterior diameter is one inch, eight
lines. The extent of the alveolar series is nearly three feet ; the
breadth of the palate at the twenty-sixth tooth is nearly one foot ;
the breadth of the upper jaw at the third tooth is four inches and
three lines ; the breadth of the socket of that tooth is one inch, three
lines.

In the lower jaw of the specimen in the Oxford Museum
the posterior extremity of the dental series is complete, but
not the anterior one; thirty-five teeth are present in each pre-
mandibular bone. The first, from its large size, I conclude to
have been received into the slight concavity at the side of the

284 PLEIOSAURUS.

upper jaw where the diastema separates the fourth and fifth teeth ;
there are probably, therefore, thirty-eight teeth on each side of the
lower jaw ; counting backwards, on this supposition, the teeth begin
to diminish in size beyond the fifteenth, and at the posterior extremity
of the series the sockets are less than half an inch in diameter ;
in their ciose arrangement and position they correspond with those of
the upper jaw.

The teeth which are preserved in this magnificent cranial frag-
ment present the characters described at the commencement of this
section ; the outer smooth surface of the crown of a tooth of the
lower jaw is represented at Pl. 68, fig. 5; the inner surface of two
of the teeth of the upper jaw is represented at 5‘ and 5”: the inserted
fang of each of these teeth is four inches and a half in length, the
entire tooth being thus seven inches in length. The ridges which
divide the outer from the inner surfaces of the tooth subside at the
base of the crown; the fang is smooth; it assumes a sub-circular
form, gradually expands for about half its length, and then contracts
to its termination, but this is always less pointed than in the fully-
formed teeth of the true Plesiosaur. In the old teeth with the elon-
gated fang, the pulp-cavity remains open, as in the Plesiosaurian
teeth ; it presents at the expanded part of the fang, a narrow elliptic
transverse section. In a tooth of the present species, six inches and
a half in length, from the Kimmeridge clay at Shotover, the diameter
of the persistent pulp-cavity was thirteen lines. In this tooth the
flattened surface is polished, but marked with minute shallow wrin-
kles ; one of the ridged surfaces, which stood at right angles to the
preceding, was traversed by eleven well-marked linear ridges, of unequal
length, separated by smooth interspaces of about three times the
breadth of the ridges ; the third surface which formed an acute angle
with the smooth outer surface was traversed by twelve ridges. These
ridges on the inner surfaces of the tooth slightly incline towards the
rounded angle dividing these surfaces ; they terminate abruptly ; some
cease half-way from the apex of the crown ; about ten are continued to
within half an inch of the apex, which is smooth; the two ridges
which divide the flat or smooth side from the ridged surfaces
of the tooth are alone continued to the sub-acute apex of the tooth.

CROCODILIANS. 285

The teeth of the Pleiosaur present varieties of form as well as of
size ; the rounding off of the angle between the ridged surfaces has
been already alluded to; the smooth outer surface is sometimes so
convex, that the transverse section of the tooth is more elliptical than
triangular. All the teeth of the Pleiosaur are slightly bent inwards
and backwards, but the smaller posterior teeth are most recurved,
and have the sharpest apex ; in the crown of these teeth, also, the
ordinary rounded or elliptical form of the cone is most nearly attained ;
but the distinction of the smooth external surface, and the ridged
internal surfaces of the crown of the tooth is retained, and would
suffice to characterize any of these teeth if found detached.

The teeth of the Pleiosaur consist, like those of the Plesiosaur
and Crocodile, of a central body of compact dentine, with a coronal
investment of enamel, and a general covering of cement, of extreme
tenuity upon the crown, but thicker upon the base of the tooth.

The dentine consists of fine calcigerous tubes, without admixture
of medullary canals ; the arrangement, division, secondary undula-
tions and branches of the calcigerous tubes correspond so closely with
those of the teeth of the Plesiosaur, as to render a particular descrip-
tion of them unnecessary.

The germs of the successional teeth are developed at the inner
side of the bases of the old teeth, but do not penetrate these teeth ;
the apices of the new teeth make their appearance through foramina
situated at the inner side, and generally at the interspace of the
sockets of the old teeth. Here, therefore, as perhaps also in the
Pterodactyle, the growing teeth may be included in closed recesses of
the osseous substance of the jaw and emerge through tracts distinct
from the sockets of their predecessors ; but this is an exceptional
condition of the reproduction of the teeth in Reptiles.

CROCODILIANS.

123. The ancient writers on Natural History appear to have been
much struck with the great number of teeth in the crocodile: and
their descriptions were exaggerated to the tone of the impressions
thus produced. According to Achilles Tatius the crocodile had as
many teeth as there were days in the year: Alkazuin assigns it two

286 CROCODILIANS.

hundred teeth; Abuhamed was more reasonable and allowed
eighty.(1)

How many teeth a crocodile may develope through the whole
course of its life in uninterrupted succession will never perhaps be
determined ; they, then, would doubtless far exceed in number the
liberal allowance of Tatius; but with regard to those teeth which
are in use in the jaws at any given time the number is now well
established, e. g. the Crocodile of the Nile has [=; = 68; that of
the West Indies (Crocodilus acutus) has 7-7 = 66; the common
Alligator (Alligator lucius) has 353 = 76. The great Gavial or
Garrhial (Gavialis gangeticus) has $= — 118. Thus the different
species and genera of Crocodiles differ from each other in the num-
ber of teeth, and also the individuals differ within small limits, as
will be presently shown.

The best and most readily recognizable characters by which the
existing Crocodilians are grouped in appropriate genera are derived
from modifications of the dental system.

In the Caimans, (Genus Alligator), the teeth vary in number
from %=8 to =: the fourth tooth of the lower jaw, or canine, is
received into a cavity of the palatal surface of the upper jaw, whére
it is concealed, when the mouth is shut ; in old individuals the upper
jaw is perforated by these large inferior canines, and the fosse are
converted into foramina.

In the Crocodiles, (Genus Crocodilus), the first tooth in the
lower jaw perforates the palatal process of the intermaxillary bone
when the mouth is closed; the fourth tooth in the lower jaw is recewed
into a notch excavated in the side of the alveolar border of the upper
jaw, and is visible externally when the mouth is closed.

In the two preceding genera the alveolar borders of the jaws
have an uneven or wavy contour and the teeth are of unequal size.

In the Gavials, (Genus Giavialis), the teeth are nearly equal in
size and similar in form in both jaws, and the first as well as the
fourth tooth in the lower jaw, passes into a groove in the margin
of the upper jaw, when the mouth is closed.

In an extinct species, the ‘ Crocodile d’Argenton ’ of Cuvier, (2)

(1) These authors are quoted by Tiedemann and Oppel in their Naturgeschichte der Am-
phibien, fol. 1817, p. 39. (2) Ossem. Fossiles, Svo. 1836, tom. ix, p. 330.

CROCODILIANS. 287

the crown of the teeth is compressed, subincurved, and terminated
by an anterior and posterior trenchant and finely serrated edge, as
in the Varanian and many of the Thecodont Saurians. In the Croco-
dilus cultridens of the Wealden strata (Pl. 62 a, fig. 10) the crown of
the teeth is thicker than in the Argenton species, and the anterior
and posterior edges are unbroken ; a few longitudinal ridges traverse
the crown of the tooth of this species, which makes the transition to
the ordinary crocodilian teeth.

In all the genera of Crocodilians the teeth of the upper and
lower jaws are so placed that their points, instead of meeting,
interlock.

In all the species of each genus, the teeth are present in the
intermaxillary, superior maxillary and premandibular bones, and are
confined to those bones, the palate being edentulous. The teeth are
relatively larger and stronger in the Alligators and Crocodiles, than
in the Gavials ; they are almost always conical, and slightly recurved ;
the crown has generally a sharp border before and behind, and it is
longitudinally striated.

The Alligator palpebrosus has nineteen teeth on each side of the
upper jaw and twenty-one teeth on each side of the lower jaw, making
eighty teeth in all. The second, third, seventh and eighth teeth are
the largest in the upper jaw; and the first and fourth are the largest
in the lower jaw. This dental character will be expressed by the
following formula, which, to save space and prevent repetition of
words, will be used to express the dental characters in all the other
species of Crocodilians.

Alligator palpebrosus, 3=3;=80. ;237- largest.

The first ten or eleven teeth in this species are more pointed
and compressed than the rest, and are slightly curved, while the
others are straight.

Alligator lucius, == 80 ¢324¢a3-— largest.

Alligator sclerops, 1372. {4"—largest.

The teeth in this species are less unequal than in the Alligator
lucius: the fourth lower canines pierce the upper jaw in old
specimens.

Alligator cynocephalus, q=s—=74 17——=largest.

a

2&8 CROCODILIANS.

The fourth or great tooth below does not pierce the upper jaw
in this species.

Alligator trigonatus,(1) 3382 72 "77s—Ilargest.

Alligator niger, {== 14 T4ireie— largest.

In almost all, if not all of these species of Alligator from eight to
ten of the posterior teeth are straight, sub-compressed, and terminated
by an obtuse mammilloid crown.

Crocodilus rhombifer, \=,—64 %7 =largest.

Crocodilus Gravesti, 3=,—66 77345;—Ilargest. This species ex-
hibits, besides the notch for the fourth lower tooth or canine, a
remarkable emargination for the elongated crowns of the ninth, tenth,
and eleventh teeth.

18—18

Crocodilus vulgaris, ==3—66 -447—Ilargest.

Crocodilus biporcatus, ais 66 or 68 jy" =largest.

Crocodilus acutus, Gaz =66 ?*—largest. In this species the
first ten teeth, counting from the anterior part of each side of both
jaws are pointed and slightly recurved: the rest are straight and
obtusely conical. |

Crocodilus intermedius. The name of this species indicates the
gradational character between the Crocodiles and the Gavials, which
it manifests in the increase of the longitudinal over the transverse
diameter of the cranium and in the comparative slenderness of its
jaws: the alveolar border is less deeply sinuous in both jaws, and
the rami of the lower jaw are united along the anterior fourth part of
their length. The teeth are relatively smaller than in the preceding
Crocodiles ; the dental formula is 7,66 j-7~= largest.

The transition, of which the first steps were made by the Croco-
dili acutus and intermedius is completed by the Gavialis Schlegeliz, in
which the head is more elongated and contracted, the teeth smaller
and more equal, and the anterior pair of the lower jaw received, like
the fourth pair, in notches at the outside of the intermaxillary bone,
between the first and second teeth of the upper jaw.

The first, second, third and ninth teeth of the upper jaw, are
larger than the rest, the ninth is the largest, and the superior max-

(1) Champsa trigonata Natterer.

a

CROCODILIANS. 289

illary bones are slightly expanded at the insertion of this pair of
teeth. The first, fourth, eleventh and fifteenth pairs are the largest
teeth in the lower jaw, but the anterior tusks do not perforate the
intermaxillary , bones.

In the foregoing gavial-like Crocodile the narrowing of the skull
to form the jaws is gradual, but in the true Gavials the cranium sud-
denly contracts into the prolonged upper, jaw. In this subgenus
the two jaws together form a long, straight, narrow, and four-sided
column, with the angles rounded off, terminating in an expansion
something like that of the beak of the spoon-bill. The terminal
expansion of the upper jaw is indented by four vertical notches,
which receive the crowns of the first and second pairs of the in-
ferior teeth when the mouth is closed. The number of teeth is
always greater in the Gavials than in the Crocodiles or Alligators.
The formula of the common Gavial(1) (Gavialis gangeticus) is F=5 =112.
The first five pairs of teeth above, are supported by the inter-
maxillary bones ; the first, third, and fourth teeth of the upper jaw,
and the first, second, and fourth of the lower jaw are the longest.
The eight or nine posterior teeth are nearly conical, the rest are
sub-compressed antero-posteriorly and present a trenchant edge |
on the right and left side, between which a few faint longitudinal
ridges traverse the basal part of the enamelled crown.(2) The
position of the opposite sharp ridges and the direction of the flat-
tening of the crown are thus reversed in the Gavial and in the
extinct Crocodile (Croc. cultridens), before-mentioned, which in other
respects most nearly resembles the Gavial in the form of the teeth.

In most of the extinct species of Crocodilians, the teeth are
characterized by more numerous and strongly developed longitudinal
ridges upon the enamelled crown than in the recent species, and
they are commonly longer, more slender and sharper-pointed. But in
one of the Crocodiles with sub-biconcave vertebrae (Gonzopholis crassi-
dens), from the Wealden formation and Purbeck limestone, the teeth

(1) Pl. 75a, fig. 3. This word ought to be written “ Gharrial” ; but the universal adoption
of the erroneous orthography in European scientific works, and its conversion into a Latin
generic name (Gavialis’, render an alteration undesirable.

(2) Plate 75, fig. 2.

290 CROCODILIANS.

have crowns which are as round and as thick in proportion to their
length as in the recent Crocodiles or Alligators. Some of the teeth
of this species are even shorter and more obtuse, as are those figured
in Pl. 62, A. fig. 9, aand 6. The crown is traversed by longitudinal
ridges, which are more numerous, more close-set, and more neatly
defined than in the Croc. cultridens (Suchosaurus) from the same
formation. Two of the ridges, larger and sharper than the rest,
traverse opposite sides of the crown ; but are placed as in the Gavial,
on the right and left sides, midway between the convex and concave
lines of the curve of the tooth. These ridges are confined to the
enamel ; the cement-covered cylindrical base of the tooth is smooth.

The more ancient Crocodiles from the Oolite and Lias, called
Steneosauwri and Teleosauri had jaws like those of the modern
Gavials, but sometimes longer and more attenuated, and armed
with more numerous, equal, and slender teeth, adapted for the
capture of fishes, which appear to have been the only other ver-
tebrate animals existing at those periods in numbers sufficient to
yield subsistence to carnivorous Saurians.(1)

In a specimen of Teleosawrus Chapmann I have counted one
hundred and seventy-eight teeth, thus arranged, 23: the Teleo-
saurus latifrons had one hundred and forty-two teeth, viz, 3-5.
The Tel. Egertont had 3-3. (Pl. 75a, fig. 4.) Cuvier calculates
the number of teeth in the Teleosaurus of the Caen Oolite, which is
a distinct species from the two above-mentioned, to be one hundred
and eighty, viz. 3-3. The enumeration will differ within small limits
in different individuals of the same species, in consequence of the
uninterrupted and irregular shedding and replacement of the teeth.
The foregoing numbers indicate those of the sockets, some of which
are almost always empty. In the Teleosaurus priscus (Crocodilus priscus,
Soemmering) the teeth appear to have been shed and renewed in a
more regular alternate order than in other species.(2)

In all the Teleosauri the teeth are more slender, less com-
pressed and sharper pointed than in the Gavial; they are slightly
recurved, and the enamelled crown is traversed by more numerous

(1) Buckland’s Bridgewater Treatise, i, p. 250.
(2) Whence the term Aelodon proposed for the species by M. H. v. Meyer.

CROCODILIANS. ; 291

and better defined ridges, two of which, on opposite sides of the
crown, are larger and more elevated than the rest. The fang is
smooth, cylindrical, and always excavated at the base. The teeth of
the Steneosauri, or extinct Crocodiles with long and slender jaws
and with vertebre subconcave at both extremities, but with sub-
terminal nostrils, differ from those of the Teleosauwri in being some-
what thicker in proportion to their length, and larger in propor-
tion to the jaws.

A distinct genus of extinct Crocodile (Marmarosaurus) is indicated
by aform of tooth differing from that of the Steneosaurus in being sub-
compressed, and in having the ridges on the basal two-thirds of the
crown shorter, more frequently interrupted, irregularly alternating,
and slightly wavy ; the two opposite stronger ridges are not deve-
loped. Teeth of this kind, with crowns fifteen lines in length, and
six lines across the long diameter of the base, occur in the Forest-
marble, Pl. 75a, fig. 5.

A more remarkable and almost heart-shaped form of tooth,
is presented by the extinct Crocodilian genus denominated, from
this character, Cardiodon. The crown of the tooth suddenly ex-
pands above the neck, as in the Caiman, but is more flattened
transversely and is broader antero-posteriorly, terminating in an
edge before and behind, and contracting to a point above, which
is generally more or less abraded. The enamel is roughened by wavy
longitudinal ridges, with more minute ruge in their interspaces.
The fang of the tooth is smooth and cylindrical, Pl. 75 a, fig. 7.(1)

Structure.—The teeth of both the existing and extinct Croco-
dilian Reptiles consist of a body of compact dentine, forming a
crown covered by a coat of enamel, and a root invested by a
moderately thick layer of cement. The root slightly enlarges, or
maintains the same breadth, to its base, which is deeply exca-
vated by a conical pulp-cavity extending into the crown, (as indi-

(1) These teeth are likewise from the secondary rock, called Forest-marble, near Brad-
ford, Wilts, and I am indebted to Mr. Channing Pearce of that town, for the opportunity
of examining them. The teeth from the Wealden, supposed to belong to the Hyleosaurus, very
closely resemble those of Cardiodon in the superficial markings, and approach them in the
shape of the crown.

ure

292 CROCODILIANS.

cated by the dotted line in plate 75, fig. 1), and is commonly either
perforated or notched at its concave or inner side.

The calcigerous tubes in the crown of a fully-developed tooth
form short curvatures at their commencement at the surface of the
pulp-cavity, and then proceed nearly straight to the periphery of
the crown; they very soon bifurcate, the divisions slightly diverging ;
then continuing their course with gentle parallel undulations, they sub-
divide near the enamel, and terminate in fine and irregular branches,
which anastomose generally by the medium of cells.

The calcigerous tubes send off from both sides, throughout their
progress, minute branches into the intervening substance, and ter-
minate in the dentinal or calcigerous cells. These cells are subhex-
agonal, about g,th of an inch in diameter, and are traversed by from
ten to fourteen of the dentinal tubes: they are usually arranged in
planes parallel with the periphery of the crown, near which they
are most conspicuous and towards which their best defined outline
is directed :(1) they combine with the parallel curvatures of the
calcigerous tubes to form the striz, visible in sections of the teeth
by the naked eye or a lower power, which cause the stratified
appearance of the dentine, as if it were composed of a succession
of superimposed cones. The diameter of the calcigerous tube
before the first bifurcation is jth of an inch; both the trunks
and bifurcations of the calcigerous tubes have interspaces equal to
four of their respective diameters.

The enamel, viewed in a transverse section of the crown, pre-
sents some delicate strie parallel with its surface ; whilst the ap-
pearance of fibres, vertical to that surface, is only to be detected, and
there faintly, on the fractured edge. It is a very compact and dense
substance ; the dark brownish tint is strongly marked in the middle
of the enamel when viewed by transmitted light.

The cells with which the fine calcigerous tubes of the basal
cement communicate are oblong, about ;,th of an inch across their
long axis, which is transverse to that of the tooth; the inter-
communicating tubes, which radiate from the cells, giving them a
stellate figure.

(1) “ Report of British Association,” 1838, p. 144.

CROCODILIANS. 293

Development.—In the black Alligator of Guiana the first four-
teen teeth in the lower jaw are implanted in distinct sockets, the
remaining posterior teeth are lodged close together in a continuous
groove, in which the divisions for sockets are faintly indicated by
vertical ridges, as in the jaws of the Ichthyosaurus.(1)

A thin compact floor of bone separates this groove, and the
sockets anterior to it, from the large cavity of the ramus of the
jaw ; it is pierced by blood-vessels, for the supply of the pulps of the
growing teeth and the vascular dentiparous membrane which lines the
alveolar cavities.

The tooth-germ is developed from the membrane covering the
angle between the floor and the inner wall of the socket. It becomes
in this situation completely enveloped by its capsule, and an enamel
organ is formed at the inner surface of the capsule before the young
tooth penetrates the interior of the pulp-cavity of its predecessor.

_ The matrix of the young growing tooth affects, by its pressure,
the inner wall of the socket, as shown in fig. 4, Pl. 75, and forms for
itself a shallow recess: at the same time it attacks the side of the
base of the contained tooth, as shown in fig. 3: then, gaining a more
extensive attachment by its basis and increased size, it penetrates
the large pulp-cavity of the previously formed tooth either by a
circular or semi-circular perforation.

The size of the calcified part of the tooth-matrix which has
produced the corresponding absorption of the previously-formed
tooth on the one side, and of the alveolar process on the other, is
represented in the second exposed alveolus of fig. 4, the tooth a
having been displaced and turned round to show the effects of the
stimulus of the pressure: the size of the perforation in the tooth
and of the depression in the jaw, proves them to have been, in
great part, caused by the soft matrix, which must have produced its
effect by exciting vital action of the absorbents, and not by mere
mechanical force. The resistance of the wall of the pulp-cavity
having been thus overcome, the growing tooth and its matrix recede
from the temporary alveolar depression, and sink into the substance
of the pulp contained in the cavity of the fully-formed tooth. As

(1) Pl. 75, fig. 3i.

294 CROCODILIANS.

the new tooth grows, the pulp of the old one is removed ; the old
tooth itself is next attacked, and the crown, being undermined by the
absorption of the inner surface of its base, may be broken off by a
slight external force, when the point of the new tooth is exposed, as
in the figs. 5 and 7, Pl. 75.

The new tooth disembarrasses itself of the cylindrical base of its
predecessor with which it is sheathed, by maintaining the excitement
of the absorbent process, so long as the cement of the old fang retains
any vital connexion with the periosteum of the socket; but the frail
remains of the old cylinder, thus reduced, are sometimes lifted out of
the socket upon the crown of the new tooth, as in fig. 4, 6; when
they are speedily removed by the actions of the jaws. This is,
however, the only part of the process which is immediately produced
by violence: an attentive observation of the more important
previous stages of growth, teaches that the pressure of the growing
tooth operates upon the one to be displaced only through the medium
of the vital absorbent action which it has excited.

Most of the stages in the development and succession of the
teeth of the Crocodiles are described by Cuvier with his wonted
clearness and accuracy; but the mechanical explanation of the
expulsion of the old teeth, which Cuvier(1) adopts from M. Tenon, is
opposed by the disproportion of the hard part of the new tooth to the
vacuity in the walls of the old one, and by the fact that the matter
impressing—viz., the uncalcified part of the tooth-matrix—is less
dense than the part impressed. |

No sooner has the young tooth penetrated the interior of the old
one, than another germ begins to be developed from the angle
between the base of the young tooth and the inner alveolar process,
or in the same relative position as that in which its immediate
predecessor began to rise, and the processes of succession and
displacement are carried on uninterruptedly, throughout the long
life of these cold-blooded carnivorous reptiles.

From the period of exclusion from the egg the teeth of the
Crocodile succeed each other in the vertical direction ; none are
added from behind forwards like the true molars in Mammalia.

(1) Ossemens Fossiles, ed. 1836, Tom. ix, p- 182.

CROCODILIANS. 295

It follows, therefore, that the number of the teeth of the Crocodile
is as great when the animal first sees the light as when it has acquired
its full size; and, owing to the rapidity of their succession, the
cavity at the base of the fully-formed tooth is never consoli-
dated.

The fossil jaws of the extinct Crocodilians demonstrate that the
same law regulated the succession of the teeth at the ancient epochs
when those highly organised reptiles prevailed in greatest num-
bers, and under the most varied generic and specific modifications,
as at the present period when they are reduced to a single family,
composed of so few and slightly varied species, as to have con-
stituted in the system of Linnzus a small fraction of the genus
Lacerta.

PART III.

DENTAL SYSTEM OF MAMMALS.

CHAPTER IL.

GENERAL CHARACTERS OF THE TEETH OF MAMMALS.

124. The class Mammalia, like that of Pisces and Reptilia,
includes a few species which are entirely devoid of teeth; these are
the Ant-eaters, forming, when clothed with hair, the genus Myrme-
cophaga ; when defended by scales, the genus Manis; and when
armed with spines, the genus Echidna. A few Mammals have the
jaws provided with horny substitutes for teeth, as the Whalebone-
whales (Balena and Balenoptera), and the Ornithorhynchus ; in
the rest of the class true teeth are present. In the Feline tribe
the epithelium of the tongue is thickened at the fore-part of its
dorsum, and invests the papille there with hard sheaths, lke
prickles, which are analogous to the lingual teeth of certain Fishes
and Batrachians. The back part of the dorsum of the tongue in the
Echidna is provided with a plate of horny denticles, which bruise
its food against the hard and prickly epithelium covering the palate.
Horny processes, analogous to the palatal teeth of Fishes and Rep-
tiles, are likewise developed upon the roof of the mouth of the great
Bottle-nose Dolphin, thence termed Hyperoodon by Lacépéde.

125. Number.—In the last-named Cetacean, the true teeth are
two in number, whence its specific name, bidens: the Narwhal
likewise has but two teeth, both of which are concealed in the sub-
stance of the jaws in the female, whilst only one is ordinarily visible
in the male: but this grows to an unusual length. The Delphinus
griseus has five teeth on each side of the lower jaw; but they soon
become reduced to two on each side. Amongst the Marsupial

FORM. 297

animals, the genus Tarsipes is remarkable for the paucity as well
as minuteness of its teeth. The Elephant has never more than
one entire molar, or parts of two, in use on each side of the
upper and lower jaws, to which are added two tusks, more or less
developed in the intermaxillary bones. Some Rodents, as the
Australian Water-rats, (Hydromys), have two grinders on each side
of both jaws; which, added to the four cutting teeth in front,
make twelve in all: the common number of teeth in this order
is twenty; but the Hares and Rabbits have twenty-eight teeth.
The Sloth has eighteen teeth. The number of teeth, thirty-two,
which characterises Man, the Apes of the old world, and the true Ru-
minants is the average one of the Class Mammalia. The examples
of excessive number of teeth are presented, in the order Bruta,
by the Priodont Armadillo, which has ninety-eight teeth; and, in
the Cetaceous Order, by the Cachalot, which has upwards of sixty
teeth, though most of them are confined to the lower jaw,—by the
common Porpoise, which has between eighty and ninety teeth,—
by the Gangetic Dolphin, which has one hundred and twenty teeth,
and by the true Dolphins (Delphinus), which have from one hundred
to one hundred and ninety teeth, yielding the maximum number
in the class Mammalia.

126. Form.—Where the teeth are in excessive number, as in
the species above cited, they are small, equal, or sub-equal, and of
a simple conical form: pointed and slightly recurved in the common
Dolphin ; with a broad and flattened base in the gangetic Dolphin (Inia);
with the crown compressed, and broadest in the Porpoise ; compressed,
but truncate, and equal with the fang in the Priodon. The simple
dentition of the smaller Armadillos, of the Orycterope, and of the
three-toed Sloth presents a difference in the size, but little variety
in the shape of the teeth, which are sub-cylindrical with broad
triturating surfaces: in the two-toed Sloth, the two anterior teeth
of the upper jaw are longer and larger than the rest, and adapted
for piercing and tearing. In almost all the other Mammalia
particular teeth have special forms for special uses; thus, the
front-teeth, from being commonly adapted to effect the first coarse
division of the food, have been called cutters or incisors, and

298 FORM.

the back-teeth which complete its comminution, grinders or molars ;
large conical teeth, situated behind the incisors, and adapted by
being nearer the insertion of the biting-muscles to act with greater
force, are called holders, tearers, laniaries, or more commonly
canine teeth, from being well developed in the Dog and other Car-
nivora, although they are given, likewise, to many vegetable feeders,
for defence or combat.

The names ‘incisors,’ ‘ laniaries,’ ‘molars,’ are not, however,
always indicative of the shape of the crowns of the teeth which
occupy the relative positions above mentioned. In some Carnivora,
for example, the front teeth have broad tuberculate summits adapted
for nipping and bruising, while the principal back teeth are as
admirably shaped for cutting, and work upon each other like the
blades of shears. The front teeth in the Elephant project, from
the upper jaw, in the form and direction of long pointed horns ;
in the extinct Dinothere the lower incisors had a similar form
and development, but were bent down from the end of the
jaw. Hence, therefore, shape alone has been found insufficient to
characterize the analogous teeth in the Mammalia, and it has been
necessary to consider the position, and also the mode of succession
of the teeth, in order to their definition and classification.

Comparative Anatomists, by common consent, now apply
the term ‘incisor,’ arbitrarily, to those teeth which are implanted
in the intermaxillary bones and in the corresponding part of
the lower jaw. When the tooth which succeeds the incisors,
or the first of the upper maxillary bone, is conical, pointed,
and longer than the rest, it is called a canine, as ‘is also its
analogue in the lower jaw, which always passes in front of it
when the mouth is closed. Of the remaining teeth, those which
are shed and replaced vertically, or which have successors de-
scending into their place in the upper, and ascending in the lower
jaw, are called ‘premolars,’ or false molars, and in Human Anatomy
‘bicuspides’; the remaining teeth, which are not displaced by verti-
cal successors, but which follow each other from behind forwards,
in both jaws, are called molars, or true molars.

_ Naturalists have availed themselves of the degree of constancy

FORM. 299

with which the foregoing kinds of teeth are recognizable in the Mam-
malian genera, to indicate them by an abbreviated formula of the
initial letters, or first syllables of their respective denominations ;
thus, J or m. signifies incisor ; ¢ or can. canine ; p or prem. premolar ;
m or mol. molar: succeeding numerals, according to their relative
position to added lines, give the number of these several kinds of
teeth on the right and left sides of the upper and lower jaws. For
example, the dental formula of the genus Homo is :—

F 2—2 - 1—1 2—2 3—3
Incisors — ; canines —; premolars —; molars —: = 32.
2—2 1—1 2—2 3—3

which expresses that, on each side of both upper and lower jaws,
there are two incisors, one canine, two premolars, and three true
molars ; thirty-two in all.

The last upper premolar and the first lower true molar in the
Carnivora are termed, from their peculiar form, ‘ sectorial’ or ‘ car-
nassial’ teeth, ‘ molaires carnassiéres’ of Cuvier. Teeth of an elon-
gated conical form, projecting considerably beyond the rest, and
of uninterrupted growth are called ‘tusks ;’ such are the incisors
of the Elephant and Dugong, the canines of the Boar and Walrus:
the long and large incisors of the Rodents have been termed from
the shape and structure of their cutting edge, scalpriform or chisel-
teeth, ‘dentes scalprarii.’ The inferior incisors of the Flying Lemurs,
(Galeopithecus), have the crown deeply notched, like a comb, and
are termed ‘ dentes pectinati.’ The canines of the Baboons are deeply
grooved in front, like the poison-fangs of some serpents. The
compressed conical crowns of the molar-teeth of the small-clawed
Seals, (Stenorhynchus), are divided either like a trident, into three
sharp points, or like a saw, into four or five points, ‘ dentes
serrati.’ Molar teeth, which are adapted for mastication, have
either tuberculate, or transversely ridged, or flat summits, and
usually are either surrounded by a ridge of enamel, or are traversed
by similar ridges arranged in various patterns. Certain molars in
the Dugong, the Mylodon and the Zeuglodon, are so deeply indented
laterally by opposite longitudinal grooves, as to appear to be com-
posed of two cylindrical teeth cemented together, and the transverse
section of the crown is bilobed. The teeth of the Glyptodon were
fluted by two analogous grooves on each side. The large molars

300 ATTACHMENT.

of the Capybara and Elephant have the crown cleft into a numerous
series of compressed transverse plates, cemented together side by
side.

The ordinary teeth of the Mammalia have so much more
definite and complex a form, than those of Fishes and Reptiles,
that three parts are usually recognized in them, viz., the fang,
the neck, and the crown. The fang or root (radix) is the inserted
part, the crown (corona), the exposed part, and the constriction
which divides these is called the neck, or cervix. The term, ‘ fang,’
is properly given only to the implanted part of a tooth of restricted
growth, which gradually tapers to its extremity ; those teeth which
grow uninterruptedly have not their exposed part separated by a
neck from their implanted part, and this generally maintains to its
extremity the same shape and size as the exposed crown.

It is peculiar to the class Mammalia to have teeth implanted
in sockets by two or more fangs ; but this can only happen to teeth of
limited growth, and generally characterizes the molars and premolars.

127. Attachment.—In no mammiferous animal does anchylosis
of the tooth with the jaw constitute a normal mode of attachment.
Each tooth has its particular socket, to which it firmly adheres by
the close co-adaptation of their opposed surfaces, and by the firm
adhesion of the alveolar periosteum to the organized cement, which
invests the fang or fangs of the tooth: but in some of the Cetacea, at
the posterior part of the dental series, the sockets are wide and
shallow, and the teeth adhere more strongly to the gum than to the
periosteum : in the Cachalot I have seen all the teeth brought away
with the ligamentous gum, when it has been stript from the sockets
of the lower jaw. ;

True teeth implanted in sockets are confined, in the present
class, to the maxillary, intermaxillary, and lower maxillary bones,
and to a single row in each. They may project only from the
intermaxillary bones as in the Narwhal; be apparent only in the
lower maxillary bone, as in the Cachalot ; or be limited to the superior
and inferior maxillaries, and not present in the intermaxillaries, as
in the true Pecora, and most Bruta of Linneus ; in general, teeth are
situated in all the bones above mentioned. In Man, where the inter-
maxillaries early coalesce with the maxillary bones, where the jaws

SUBSTANCE. 301

are very short, and the crowns of the teeth are of equal length,
there is no interspace or ‘diastema’ in the dental series of either
jaw, and the teeth derive some additional fixity by their close apposi-
tion and mutual pressure. No inferior Mammal now presents this
character ; but its importance, as associated with the peculiar attri-
butes of human organization, has been somewhat diminished by
Cuvier’s discovery of a like contiguous arrangement of the teeth
in the jaws of the extinct Anoplotherium.

128. Substance.—The teeth of the Mammalia usually consist
of hard or unvascular dentine, defended at the crown with an in-
vestment of enamel, and everywhere surrounded by a coat of cement.
The coronal cement is of extreme tenuity in Man, Quadrumana and
terrestrial Carnivora; it is thicker in the Herbivora, especially in
the complex grinders of the Elephant, and is thickest in the teeth
of the Sloths, Megatherioids, Morse, and Cachalot. Vertical folds
of enamel and cement penetrate the crown of the tooth in the
Ruminants, and in most Rodents, and Pachyderms, characterizing
by their various forms the genera of the two last orders: but these
folds never converge from equidistant points of the circumference
of the crown towards its centre. The teeth of the quadrupeds of
the order Bruta, (Edentata, Cuv.), have no true enamel; this is
absent, likewise, in the molars of the Dugong, the Zeuglodon and
the Cachalot.(1) The tusks of the Narwhal, Walrus, Elephant,
Mastodon, and Dinotherium, consist of modified dentine, which, in
the large proboscidian animals, is properly called ‘ ivory,’(2) and is
covered by cement.

The central part of the fully-formed tooth in man and most other
animals contains an irregular kind of osseous substance, which is most
abundant in the Cachalot,(8) and forms around foreign bodies which
may gain admission to the pulp-cavity of tusks. A fifth substance
which, from the number and regular position of the vascular canals

(1) M. Fr. Cuvier divides the teeth of Mammalia, according to their composition, into
four classes: the first consist of ivory, (dentine), enamel and cement; the second of ivory
and enamel; the third of ivory and cement; the fourth of ivory only. ‘ Dents des Mammiferes,’
p. xxi. Ihave met with no Mammalian teeth, in which cement is absent, and believe that
the second and fourth of the above-cited classes of teeth, have no existence in Nature.

(2) “ Hoe solum est ebur,’”’ Plinius, Hist. Nat. lib. xi. c. 37.

(3) Pl. 89, fig. 2, c.

302 STRUCTURE.

in it, I have termed the ‘vascular dentine,’ forms the body or axis
of the tooth in the Sloth-tribe,(1) and is present in smaller pro-
portion in the centre of the teeth of the Armadillos. The teeth
of the Orycteropus consist of congeries of long and slender pris-
matic columnar denticles, each consisting of a body of dentine,
with a coating of cement, by which they are united together to
form a composite tooth, as in some of the Cartilaginous Fishes.

129. Structure-—-In most Mammals the body of the tooth
consists of a gelatinous animal basis and calcareous earth, com-
bined and arranged according to the plan which characterizes the
tissue called ‘‘ unvascular dentine.”(2) The compartments of the
basal substance, which I have called ‘ calcigerous’ or ‘ dentinal cells,’
and which contain the hardening salts in their densest state, are
sub-circular (Pl. 95), or sub-hexagonal (PI. 70). The calcigerous
and nutrient tubes varying from 4 to smth of an inch in diameter,
and placed with intervals equal to from two to six of their own dia-
meters, proceed, at first with strong, and then with gentle curves from
the pulp-cavity to the outer surface of the dentine, their general direc-
tion being always more or less nearly at right angles to that surface :
those tubes which proceed from the apex, and from the basal third- |
part of the pulp-cavity are the straightest. They are nearly parallel
to one another, both in their general course and curvatures; but, as
the outer surface of the tooth exceeds the inner one in extent, the
tubes slightly diverge in their course and divide, decreasing in diame-
ter to their peripheral extremities, and rapidly so near their termina-
tion where they become irregularly flexuous and often interlaced. The
dichotomizing calcigerous tubes send off from their sides much more
minute branches, which quickly divide and sub-divide in the inter-
spaces of the trunks, and penetrate the dentinal cells. In the unvas-
cular dentine of all Mammalian teeth the tubes present the ‘ primary
curvatures,” and ‘‘ secondary gyrations” described in the Introduc-
tion.(3) These curvatures are strongest and least regular in the den-
tine of the Elephant’s grinders. In that of the tusks of the Elephant
and Mastodon, the form, extent, and parallelism of the secondary
curvatures of the dentinal tubes, cause the peculiar appearance of
the decussation of curved lines, like the ornamental work called

(1) Pl. 82, fig. 1. (2) Introductior, p. iii, & iv. (3)- P. xvi.

STRUCTURE. 303

‘engine-turning,’ upon the surface of transverse or oblique sec-
tions or fractures of the tusk, which is characteristic of true
‘ivory.’

In the incisors of certain Rodents, and in the molars of the Sloths
and Megatherioids, or the large extinct phyllophagous Bruta, more
or less of the dentine is modified by the persistence of certain tracts
of the pulp-cavity, forming vascular or medullary canals; the cha-
racters of this “‘ vascular dentine”’ will be described in the sections
devoted to the dentition of the species possessing it.

The dentine of the long and slender prismatic denticles which
are aggregated to form the compound tooth of the Orycterope(1) is
unvascular, and is characterized chiefly by the frequent division and
wide angles at which the branches of the bifurcating calcigerous
tubes diverge, before resolving themselves into their minute wavy
terminations.

The cement, which, with the dentine, is present in all teeth
of mammalian animals, is characterized, except where it forms an
extremely thin layer, by the radiated calcigerous cells.(2) These
are usually arranged in lines or layers parallel with the surface of
the cemental coat and with each other; they average a diameter
of jmth of an inch in Man; they are rather smaller in the true
Carnivora ; proportionally larger in some of the Pachyderms; but
present their most minute size in some of the Ruminants, as the
Giraffe and Ox. The radiated forms of these cells arises from the
numerous minute tubes continued from or opening in them, and
which are analogous to the more parallel calcigerous tubes of the
dentine, with which they communicate.

In the thick radical cement of the Seal’s teeth, and in both the
radical and coronal cement of the teeth of most Herbivora, very con-
spicuous vascular canals are present in addition to the calcigerous
tubes and cells. These canals in the cement of the molars of the
Megatherium are numerous and constant, take a course parallel with
each other and transverse to the outer plane of the cement, and
anastomose by loops close to the dentine, towards which the con-
vexity of the loops is directed.(3)

(1)oP 1.78. (2) Corpuscula Purkingite (3) Pl. 84, 6, 6.

304 DEVELOPMENT.

The structure of the enamel presents fewer varieties than in
the lower classes of Vertebrata, and in all the Mammalian genera
in which it exists, it manifests its most distinctive and elaborate
condition. It consists of more or less curved or wavy prismatic
fibres, averaging about jgth of an inch in diameter, and having a
general direction vertical to the plane of the dentine; some of the
fibres extend through the thickness of the enamel, others are
shorter and are wedged in their interspaces ;. the fibres of the thick
enamel of the molars of the large Pachyderms are most curved
and interwoven ; they are so arranged, however, as always to have
one end directed towards the outer surface of the tooth, and the
other end to that by which the enamel is attached to the dentine :
the outer, or peripheral end of the fibre is sensibly larger than the
inner one. In Man and Quadrumana the fibres are transversely
striated: I have not detected this character in the Herbivorous
Quadrupeds. The fine horizontal lines on the exterior surface of
the enamel(l) are usually most conspicuous in the teeth of
Mammals. , |

130. Development.—tThe teeth in this, as in the foregoing classes,
are formed by superaddition of the hardening salts to pre-existing
moulds of animal pulp or membrane, organized so as to insure the
arrangement of the earthly particles according to that pattern which
characterizes each constituent texture of the tooth. The complexity
of the primordial basis, or matrix, corresponds, therefore, with that
of the fully-formed tooth, and is least remarkable in those conical
teeth which consist only of dentine and cement. The primary
pulp, which first appears as a papilla rising from the free surface
of the alveolar gum, is the part of the matrix which by its calci-
fication constitutes the dentine; it sinks into a cell and becomes
surrounded by a closed capsule, in every Mammiferous species, at
an early stage of the formation of the tooth; and, as the cement
is the result of the ossification of the capsule, every tooth must
be covered by a layer of that substance. In those teeth which
possess enamel, the mould or pulp of that constituent is developed

(1) Introduction, p. xxvi.

5

DEVELOPMENT. 30
from the capsule covering the coronal part of the dentinal pulp. In
the simple teeth the secondary or enamel-pulp covers the crown like a
cap; in the complex teeth it sends processes into depressions of the
crown, which vary in depth, breadth, direction, and number, in the nu-
merous groups of the Herbivorous and Omnivorous quadrupeds. ‘The
dentinal pulp, thus penetrated, offers corresponding complications
of form; and, as the capsule follows the enamel-pulp in all its folds
and processes, the external cavities or interspaces of the dentine
become occupied by enamel and cement ; the cement, like the capsule
which formed it, being the outermost substance, or having the
enamel interposed between it and the dentine. The dental matrix
presents the most extensive interdigitation of the dentinal and enamel
pulps in the Capybara and Elephant. The processes of formation
and calcification of the several constituents of Mammalian teeth
have been already described in the Introduction(1).

The matrix of the Mammalian tooth sinks into a furrow and
soon becomes inclosed in a cell in the substance of the jaw-bone
from which the crown of the growing tooth extricates itself by
exciting the absorbent-process, whilst the cell is deepened by the
same process and by the growth of the jaw, into an alveolus for
the root of the tooth. When the formative parts of the tooth are
reproduced indefinitely to repair by their progressive calcification
the waste to which the working surface of the crown of the tooth
has been subject, the alveolus is of unusual depth, and of the
same form and diameter throughout, except in the immature ani-
mal when it widens to its base. In teeth of limited growth, the
dentinal pulp is reproduced in progressively decreasing quantity
after the completion of the exterior wall of the crown, and forms
by its calcification one or more roots or fangs, which taper more
or less rapidly to their free extremity. The alveolus is closely
moulded upon the implanted part of the tootn; and it is worthy
of special remark that the complicated form of socket which results
from the development of two or more fangs is peculiar to animals
of the class Mammalia(2).

Cl) e Psd:
(2) On the strength of this generalization I have established the Mammalian nature of the

x

306 DEVELOPMENT.

In the formation of a single fang, the activity of the reproductive
process becomes enfeebled at the circumference, and is progressively
contracted within narrower limits in relation to a single centre,

until it ceases at the completion of the apex of the fang; which,

though for along time perforated for the admission of the vessels
and nerves to the interior of the tooth, is, in many cases, finally
closed by the ossification of the remaining part of the capsule.

When a tooth is destined to be implanted by two or more
fangs, the reproduction of the pulp is restricted to two or more parts
of the base of the coronal portion, around the centre of which
parts the sphere of its reproductive activity is progressively con-
tracted. The intervening parts of the base of the coronal pulp
adhere to the capsule, which is simultaneously calcified with them,
covering those parts of the base of the crown of the tooth with
a layer of cement. The ossification of the surrounding jaw being
governed by the changes in the soft, but highly organized dental
matrix, fills up the spaces unoccupied by the contracted and divided
pulp, and affords, by its periosteum, a surface for the adhesion of
the cement or ossified capsule covering the completed part of the
tooth(1).

huge extinct animal called Basilosaurus by Dr. Harlan, and have advocated the claims of
the diminutive Amphitherium and Phascolotherium of the oolite slate of Stonesfield, to be
admitted into the same high class, against the objections raised by Dr. de Blainville. See
Comptes Rendus de Acad. des Sciences, Oct. 22, 1838. The bifid base of the teeth of certain
Sharks not being implanted in a socket, forms no true exception to the rule enunciated in the
text. Geological Transactions, 2nd Series, vol. vi. p. 66.

(1) Cuvier ascribes the formation of the fangs of teeth partly to phenomena which are
real, but merely concomitant, partly to conditions of the pulp which have no existence.
He observes: “La production des racines est due & ce que le noyau pulpeux n’adhére pas
au fond de la capsule, par la totalité de sa base, mais seulement par certains endroits,
qui peuvent étre dés lors considérés comme des pédicules trés courts. Les lames osseuses
arrivées au bas du noyau, se glissent entre ces pédicules, et les entourent eux-mémes d’une
enceinte tubuleuse qui, s’alongeant toujours, force aussi les pédicules pulpeux 4 s’alonger,
et produit ainsi les racines.” Lecons d’Anat. Comp. ed. 1836, tom. iv. p. 215.

If the molar of an Ox be examined at the period when the outer crust of the crown
is completed, and the fangs have begun to be formed, the capsule will be found adhering —
to the base of the pulp at their interspaces as well as to their circumference. A vertical
slice of such a molar, when it is fully developed, exaimned with a magnifying power of |
300 linear dimensions, displays a layer of cement covering the concave interspaces of the
base of the fangs; this layer is as distinct in character from the dentine as that which

—

DEVELOPMENT. 307

The matrix of certain teeth does not give rise during any
period of their formation to the germ of a second tooth, destined
to succeed the first; this, therefore, when completed and worn
down, is not replaced: all the true Cetacea are limited to this
simple provision of teeth. In the Armadillos, Megatherioids, and
Sloths, the want of germinative power, as it may be called, in the
matrix is compensated by its persistence, and by the uninter-
rupted growth of the teeth. In other Mammalia the matrix of
the first developed tooth gives origin, as described in the Intro-
duction, to the germ of a second tooth, which sometimes dis-
places, sometimes takes its place by the side of its predecessor and
parent. All those teeth which are displaced by their progeny are
called temporary, deciduous, or milk teeth: the mode and direction
in which they are displaced and succeeded, viz., from above down-
wards in the upper, from below upwards in the lower jaw, in
both jaws vertically, are the same as in the Crocodile; but the
process is never repeated more than once in any Mammiferous
animal. A considerable proportion of the dental series is thus
changed; the second, or permanent teeth having a size and form
as suitable to the jaws of the adult as the displaced temporary
teeth were adapted to those of the young animal. The perma-
nent. teeth, which assume places not previously occupied by de-
ciduous ones, are always the most posterior in their position, and
generally the most complex in their form.

The successors of the deciduous incisors and canines differ
from them chiefly in size; the successors of the deciduous molars
may differ likewise in shape ; in which case they have always less

invests the rest of the fangs, and could not have existed if the dentinal pulp had been
detached from the bottom of the capsule in the interspaces of the fangs. The elongation
of the pulpy pedicles by the mechanical constriction of the surrounding bone, is an hypo-
thetical cause founded on the same imperfect conception of the vital, and especially the absor-
bent forces, as that which led Cuvier to ascribe the destruction of the conical base of the
Crocodile’s old tooth to the mechanical pressure exerted upon it by the apex of the new
tooth. The primary branches of the artery of the dentinal pulp correspond in number with
the future fangs, at least when the formation of these has begun; but this condition of the
_supplying channels may be more justly regarded as a concomitant effect of the modified
assimilative and formative processes to which the formation of the fangs is due, than as
the efficient cause of such changes in the progressive calcification of the pulp.

x 2

308 DEVELOPMENT.

complex crowns than their predecessors(1). The bicuspides, in
Human Anatomy, and the corresponding teeth, called ‘ premolars,’
in the Jower Mammals, illustrate this law.

The first true molar owes the germ of its matrix to a vege-
tation or bud, separated by the fissiparous process from the matrix of
a pre-existing tooth ; but the backward elongation of the jaw affords
space for its development by the side of its progenitor, during which
process it may in like manner give origin to a second, and this to a
third molar, succeeding each other from before backwards or horizon-
tally. In this successive germ-production we find repeated the multi-
parous property of the dental matrix of the Crocodile ; but the con-
comitant growth of the jaw allows the second, third, and sometimes
fourth generation of true molars to co-exist, and come into place side
by side. In the Unguiculate and most of the Ungulate species of the
Placental division of the Mammalian class, the fissiparous repro-
duction of horizontally succeeding teeth stops at the third gene-
ration ; in other words, they have not more than three true molars
on each side of the upper and lower jaws. In the Marsupial series
the same process extends to a fourth generation of true or hori-
zontally succeeding molars(2); and in most of the species the
four true molars are in use and place at the same time ; but in the
Kangaroos the anterior ones are shed before the posterior ones —
are developed. This successive decadence is still more characteristic
of the grinding teeth of the Elephant, which consist exclusively of
true molars. ‘:

(1) “C’est une régle générale, que les molaires de remplacement ont une couronne
moins compliquée que celles auxquelles elles succédent; mais cette couronne compliquée
se trouve reportée sur les molaires permanentes qui viennent plus en arriére.” This gene-
ralization was established by Cuvier. Legons d’Anat. Comp. ed. 1805, vol. iii. p. 135.

(2) This characteristic extension of the reproductive power of the matrices of the true
molars in the Marsupials, is an approximation to the peculiar activity and of persistence of
the same power in the vertically succeeding teeth of the cold-blooded Ovipara, and is associated
with many other instances of the same affinity in more important parts of the organization of
the implacental Mammals.

|
|

MONOTREMES, 309

CHAPTE R..h:

HORNY TEETH.

MONOTREMES,

131. In entering upon the special consideration of the teeth
in the Mammalian class, we meet, at its lowest step, as in Reptiles
and Fishes, with horny substance in the place of teeth, properly
so called. In the Myxines these dental substitutes were of a
conical form, like canine teeth; in the Siren the horny matter
sheathed the fore-part of the jaw-bones with a trenchant or incisive
plate ; inthe Ornithorhynchus it assumes the form of both incisive
and molar teeth. These bodies, in the paradoxical Mammal, have
been admitted by M. F. Cuvier amongst the ‘‘ Dents de Mam-
miféres,” with good figures and descriptions of their outward form.
Heusinger has accurately described their intimate texture, and an
affirmative reply has been given, by the common consent of all
Anatomists and Naturalists who have treated of the Ornithorhynchus,
to the remarkable anticipatory remark with which Hunter concludes
one of his philosophic generalizations on the dental organs :—
““'We may call,” he writes in 1792, ‘‘ everything teeth fitted for the
purposes before mentioned, (viz., holding or retaining, dividing,
cracking, and grinding the food), which is composed of an animal
substance and calcareous earth, called bone: how far horny sub-
stance may be so shaped as to deserve the name of teeth, I do
not yet know.” Within ten years after the decease of Hunter,
Mr. Home was enabled to describe the most conspicuous of the
horny teeth of the Ornithorhynchus as follows :—‘‘ The teeth, if
they can be so called, are all grinders ; they are four in number,
situated in the posterior part of the mouth, one on each side of
the upper and under jaw, and have broad flattened crowns. In
the smaller specimens before examined, each of these large teeth
appeared to be made up of two smaller ones, distinct from each
other. The animal, therefore, most probably sheds its teeth as
it increases in size. They differ from common teeth very materially,

310 MONOTREMES,

having neither enamel nor bone, but being composed of a horny
substance only embedded in the gum, to which they are connected
by an irregular surface, in the place of fangs. When cut through,
which is readily done by a knife, the internal structure is fibrous,
like nail; the direction of the fibres is from the crown downwards.”
Philos. Trans. 1802, p. 71. Pl. ii. fig. 2. These constituent vertical
fibres are rightly described by Heusinger as hollow tubes, forming
a texture closely similar to that of Baleen and Rhinoceros-horn(1).

In the figure which is appended to Home’s description, two
other horny teeth are accurately represented ‘‘in situ,” in the
lower jaw, and the corresponding teeth of the upper jaw have
been subsequently figured and described by F. Cuvier(2). The
horny teeth of the Ornithorhynchus are, in fact, eight in number:
the anterior tooth in the upper jaw is situated on the slender anterior
termination of the upper maxillary bone; it is much extended from
behind forwards, and pointed at each extremity, but is low, very
narrow, and four-sided: the broadest side forms the base of
attachment, and is slightly concave and unequal: the outer and
inner exposed facets converge to a serrated edge in the young
Ornithorhynchus, but this becomes worn down to a flattened
surface, which forms the fourth side of the tooth in the old animals.
The corresponding tooth in the lower jaw(3) is rather narrower,
and retains longer its trenchant edge: these teeth hold the position
of the canines and premolars in the normal Mammalia.

At a distance behind the anterior tooth equal to its own
length, is situated the horny molar, consisting of a flattened plate,
of an oblong subquadrate figure, bounded by a convex outline
externally, and a straight line internally, with the inner and an-
terior angle slightly produced: a slightly raised margin includes
two large concave surfaces a little elevated above the intervening
part of the grinding surface. The corresponding tooth of the lower
jaw(4) is narrower in proportion to its antero-posterior extent, with
a convex inner border, and has the two concave surfaces a little
more elevated. These surfaces, in both upper and lower molars,

(1) Histologie, 4to. 1822, p. 197.—Pl. 76, fig. 1, a and b. F. Cuv.
(2) Loc. cit. Pl. 83, p. 202. (3) Pl. 76, fig. 2, a. (4) Ib. fig. 2, 6.

WHALES. 311

are, prior to abrasion, the most prominent parts of the grinding
surface: they are, also, the first-formed parts of the molar, as are
the tubercles of the crown in true grinding teeth: like these tuber-
cles also, they are connected together at an early period of the
growth of the tooth, only by the vascular matrix, and in dried
Specimens are separate and distinct. The subsequent conversion
of this apparently double into a bituberculate single grinder, is
produced by the progressive extension and confluence of the bases
of the tubercles, not by a process of sheding and the formation
of a new tooth, as Home conjectured.

According to the analysis of Lassaigne, 99-5 parts of the dental
tissue of the Ornithorhynchus has the composition of horn, which is
hardened by 0-3 parts of the earthy matter of bone.

The account of the horny dental apparatus of the Ornithor-
hynchus cannot be completed without a notice of the two short
and thick conical processes which project from the fore-part of the
raised inter-molar portion of the tongue, and which, like the
before-mentioned more numerous spines on the corresponding part
of the tongue of the Echidna, represent in these low organized Mam-
mals the lingual teeth of Fishes.

WHALES.

132. Those Cetaceous Mammals which are properly called
Whales have no teeth, but horny substitutes in the form of plates
ending in a fringe of bristles, a peculiarity first pointed out by
Aristotle.(1) Of these plates, called ‘‘ Baleen” and ‘‘ Whalebone,”
the largest, which are of an inequilateral triangular form, are
arranged in a single longitudinal series on each side of the upper
jaw, situated pretty close to each other, depending vertically from
the jaw, with their flat surfaces looking backwards and forwards
and their unattached margins outwards and inwards, the direction

(1) The passage occurs in the 12th Chapter of the 3rd Book of the “ Historia Animalium,”
and has given rise to much speculation and controversy amongst the Commentators. ‘“ Mysti-
cetus etiam pilas in ore intus habet vice dentium, suillis setis similes.’” To a person looking
into the mouth of a stranded whale, the concavity of the palates would appear to be beset with
coarse hair. The species of Balenoptera which frequents the Mediterranean might have afforded
to the Father of Natural History the subject of his philosophical comparison.

312 WHALES,

of their interspaces being nearly transverse to the axis of the skull.
The smaller subsidiary plates are arranged in oblique series internal
to the marginal ones. The base of each plate is hollow, and is
fixed upon a pulp developed from a vascular gum, which is attached
to a broad and shallow depression occupying the whole of the palatal
surface of the maxillary and of the anterior part of the pala-
tine bones, the Whale being thus, like the Echidna, an example
of a Mammalian animal which may be said to have palatal teeth.
The base of each marginal plate is the smallest of the three sides
of the triangle; it is unequally imbedded in a compact sub-elastic
substance, which is so much deeper on the outer than on the
inner side, as, in the new-born Whale, to include more than one-
half of the outer margin of the baleen-plate. These margins, which
are shown at a, fig. 4, Pl. 76, are continued downwards in a
line dropped nearly vertically from the outer border of the jaw;
the inner margin of each plate(1) slopes obliquely outwards from
the base to the extremity of the preceding margin; the smaller
plates decrease in length to the middle line of the palate, so that
the form of the baleen-clad roof of the mouth is that of a trans-
verse arch or vault, against which the convex dorsum of the thick
and large tongue(2) is applied when the mouth is closed. Each
plate sends off from its inner and oblique margin the fringe of
moderately stiff but flexible hairs(3), which projects into the mouth.
In a new-born Whale (Balena australis) in which the longitudi-
nal extent of the baleen-matrix was two feet three inches, I found
the number of the large marginal plates to which it gave origin
to be one hundred and ninety. The breadth of the base of each
of the principal plates of baleen was two inches, the length of
the oblique and fringed margin three inches, that of the vertical
external margin three inches and a half, of which two inches were
embedded in the elastic substance or gum. The thickness of the
plate at the free part of this margin is one-third of a line, and
the plate becomes a little thinner at the opposite or fringed margin.
The direction of the plates is not quite transverse at every part
of the series; the inner border is turned rather forwards in the
(1) Pl. 76, fig. 4, b. (2) Pl 765g, a/c; i (3) Pl. 76, fig. 5, ¢.

WHALES. ale

anterior and obliquely backwards in the posterior plates, and the
inner margin at the basal part of the posterior plates is slightly
curved towards the back part of the mouth, to which the bristly
terminations of these parts of such plates are directed, thus pre-
senting an additional obstacle to the escape of the small marine
animals(1), for the prehension and detention of which, this singular
modification of the dental system is especially adapted.

The interspaces of the free extremities of the baleen-plates,
which, from the oblique position of their fringed internal margins,
are only visible by raising the large lip and looking on the outer
part of the series, are in general equal to five or six times the
thickness of the plates themselves; the external line of the plate
is broken by the outward projection(2) of the base of the free
portion of each plate, at least in the dry subject. In the specimen
above alluded to, the pulp-cavity at the base of each principal tooth
presented the form of a narrow, transversely-elongated fissure, from
four to five lines in depth in the larger plates. The bases of the
baleen-plates do not stand far apart from one another, but the
anterior and posterior walls of the pulp-fissure are respectively con-
fluent with the contiguous divisions of the bases of the adjoining
plates at their thin and extreme margins, which by this confluence
close the basal end of the interspace of the baleen-plates, which
interspace is occupied more than half-way down the plate, by the
cementing substance or gum. Thin layers of horn in like manner
connect the contiguous plates, and may be traced extending in
parallel curves with the basal connecting layer across the cementing
substance, as shown in the diagram, Pl. 76, fig. 6, c.

The baleen-pulp (indicated by the dotted line, at a) is situated
in a cavity at the base of the plate, like the pulp of a true tooth;
whilst the external cementing material maintains, both with respect
to this pulp and to the portion of the baleen-plate which it de-

(1) Clio borealis, Limacina, and small pelagic Crustacea. Before the naturalists of the
Arctic expeditions had determined the nature of the food of the true Balene, John Hunter had
stated “I do suppose the fish they catch are small when compared with the size of the mouth.”
On the Structure and Economy of Whales, Phil. Trans. 1787, p. 397.

(2) The letter a is placed near the line of termination of the baleen matrix in fig. 4, called
the “bead,” by Hunter, Phil. Trans, 1787, p. 397. .

314 WHALES.

velopes, the same relations as the dental capsule bears to the tooth.
According to these analogies, it must follow, that only the central
fibrous or tubular portion of the baleen-plate is formed, like the
dentine, by the basal pulp, and that the base of the plate is not
only fixed in its place by the cementing substance or capsule, but
must also receive an accession of horny material from it, as Hun-
ter first indicated; this material answers to the cement of true
teeth.

The baleen-plates are smallest at the two extremities of the |
series: in the Balena australis they rapidly increase in length to
the thirtieth, then very gradually increase in length to about the
one hundred and fortieth, from this they as gradually diminish to
the one hundred and sixtieth, and thence rapidly slope away to
the same small size as that with which the series commenced.
Besides the external and, as they may be termed, the normal plates,
which have just been described, there are developed from the inner
part of the palatal gum, in Balena australis, a series of smaller
fringed processes progressively decreasing in size as they recede
from the large external plates; the small plates clothe the middle
region of the palate with a finer kind of hair, against which the
surface of the tongue more immediately rests; they are also arranged
in longitudinal series, which, however, are not parallel with the
external one, but pass from the inner margin of that series in
oblique lines inwards and backwards. The baleen-processes in each
of these oblique series gradually but progressively diminish in size
as the series tends backwards ; the shape of the base of the smaller
median baleen-teeth is rhomboidal or sub-circular; and, from the
parallelism of the oblique series, the pulps present the same quin-
cuncial arrangement as that of the feathers of birds; we may say,
indeed, that such is the disposition of all these corneous productions
on the roof of the Whale’s mouth, but that the pattern is obscured by
the disproportionate size and lamellar form of the external series of
plates.

In the Balena mysticetus, the baleen-plates which suceeed the
large ones of the outer row, are more numerous, and are relatively
longer and larger than in the Bal. australis: Mr. Scoresby, who in

WHALES. O15

his account of the Balena mysticetus, notices only the large marginal
plates, states that they are about two hundred in number on each
side: the largest are from ten to fourteen feet, very rarely fifteen
feet in length, and about a foot in breadth at their base. These
plates are overlapped, and concealed by the under lip when the
mouth is shut.(1) In the Balenoptere, or Fin-backed Whales, the
baleen-processes internal to the marginal plates, are fewer and smaller
than in the Balene: the marginal plates are more numerous, ex-
ceeding three hundred on each side:(2) they are broader in pro-
portion to their length, and much smaller in proportion to the
entire animal: they are also more bent in the direction transverse to
their long axis.

Each plate of baleen consists of a central coarse fibrous sub-
stance, and an exterior compact fibrous layer: but this reaches to
a certain extent only, beyond which the central part projects in
the form of the fringe of bristles. John Hunter first expressed
a belief, that the part of the baleen, which was formed by the
core or pulp was the hair: and that this received the compact
layers on the outside, from the dense but vascular substance be-
tween the bases of the plates; which substance he well describes
to act as abutments to the whalebone, like the alveolar processes
of the teeth, keeping them firm in their places. And he further
observes: ‘‘ As both the whalebone and intermediate substance
are constantly growing, and as we must suppose a determined length,
necessary, a regular mode of decay must be established, not depend-
ing entirely on chance, or the use it is put to. In its growth three
parts appear to be formed; one from the rising core, which is the
centre ; a second on the outside; and a third being the intermediate
substance. ‘These appear to have three stages of duration ; for that
which forms on the core, I believe, makes the hair, and that on the
outside makes principally the plate of whalebone; this, when got
a certain length breaks off, leaving the hair projecting, becoming
at the termination very brittle; and the third or intermediate sub-
stance, by the time it rises as high as the edge of the skin of the

(1) Wernerian Trans: vol. i. p. 579.
(2) Hunter, loc. cit. p. 307, & Neill, Wernerian Trans. vol. i. p. 202.

316 HYPEROODON. RYTINA.

jaw, decays and softens away like the old cuticle of the sole of the
foot when steeped in water’’(1).

A thin transverse section of baleen, viewed with a low magni-
fying power, demonstrates that the coarse fibres, as they seem to
the naked eye, which form the central substance, are hollow tubes(2),
with concentric laminated walls. When a high magnifying power is
applied to such a section, the concentric lines are shown not to be
uniform ; but interrupted here and there by minute elliptical dila-
tations, which are commonly more opake than the surrounding
substance, and which, like the calcigerous cells of true bone, are
probably remains of the primitive cells of the formative substance :
similar long elliptical opake bodies or cells, are dispersed irregularly
through the straight parallel fibres of the dense outer lamine of the
baleen plate.

The chemical basis of baleen, according to Brande, is albumen
hardened by a small proportion of phosphate of lime.

HYPEROODON.

133. Before leaving the consideration of the horny teeth of
the Mammalia, it seems proper to notice in the present chapter the
hard horny pointed processes which are said to project from the
palate of the Bottle-nose Dolphin, thence called Hyperoodon, by
Lacepede ; which processes may be regarded as analogous to the
baleen-plates in true Whales, but I regret that no opportunity has
occurred to me of examining them.

RYTINA.

134. The singular armature of the palate and lower jaw, in
the Rytina, or Arctic Dugong, likewise falls within the present
category. According to Steller(3), this marine animal has no true
teeth, but only two large whitish dental masses, one adhering to
the palate, the other to the opposed part of the lower jaw: they
are not implanted by gomphosis, but adhere by numerous pores to
corresponding papille of the membrane covering the palate and
lower jaw; besides which, the palatal tooth is fixed at the sides of

(1) Loc. cit. p. 397. (2) Heusinger Histologie, p. 198, pl. ii, fig. 3.
(3) Nova. Comment, Petropolit. tom, il. p. 294, 1751. ;

a

ORYCTEROPUS. S17

its anterior part to furrows in the lining membrane of the thick lip.
The free surface of the dental mass is sculptured by undulating
grooves and risings, adapted to corresponding inequalities in the
opposite mass.

Dr. Brandt(1) has shown by later and more minute exami-
nation of the problematical teeth of the Rytina, deposited by Steller
in the Petersburgh Collection, that their texture is horny, consisting
of minute hollow fibres, placed vertically to the plane of the grind-
ing surface of the tooth, but of unusual density. Thus the dentition
of the Rytina closely resembles that of the Ornithorhynchus in both
the texture and implantation of the teeth, which will probably be
found to contain a similar or greater proportion of osseous matter.
M. F. Cuvier(2) has suggested, that the above described plates may
be analogous in position, as in texture, to the horny covering of the
opposed surfaces of the deflected portions of the upper and lower
jaws in the Dugong.

Lisl bis ol gl il da Ua al

TEETH OF BRUTA, (EDENTATA, Cvv.)
ORYCTEROPUS.

135.—The Orycterope, or Cape Ant-eater, differs from the
edentulous Ant-eaters of South America, in having teeth in both
jaws(3). These teeth are of a simple form, but peculiar structure;
their common number in the mature animal is 77 = 26; they all
belong to the molar series. The anterior teeth are very small, and
are not unfrequently wanting, or are concealed by the gum, especially
the first in the upper jaw: the second tooth of the upper jaw is
small, compressed and obtuse; it opposes a similar one in the
lower jaw: the third and fourth molars increase in size, have an
elliptical transverse section, and a triturating surface of two facets :
the fourth and fifth molars are the largest in the upper jaw, are
of equal size, and have a longitudinal depression in their internal

(1) Mém. de l’Acad. Imp: de Pétersb. vi. ser. t. ii. p. 103.
(2) Histoire des Cétacés, 8vo. 1836, p. 736. (3) Pl. 76, fig. 89.

318 ORYCTEROPUS..

and external sides, giving their transverse section a bilobed or
hour-glass figure: the seventh molar is smaller, and has the same
simple figure as the fourth.

The first molar in the lower jaw is similar in size and shape to
the second of the upper jaw to which it is opposed ; in one of the spe-
cimens examined by me, it was shed, and every trace of its alveolus
effaced, leaving only five molar teeth in the lower jaw. In this bone,
which measured eight inches in length, the molar series occupied
an extent of two inches, commencing about three inches and a
half from the anterior extremity of the ramus: the dentigerous
part of the bone is slightly expanded, both laterally and inferiorly.
The antepenultimate and penultimate molars of the lower jaw are
indented, like those above, by a longitudinal groove upon both their
outer and their inner sides, which grooves sink rather deeper into
the substance of the tooth, as they approach the base.

The proportions of these teeth, the depth of their sockets, and
their structure, as viewed in longitudinal section with the naked eye,
are shown in Plate 76, Fig. 10. The teeth are continued solid,
and of the same dimensions, to the bottom of the socket, and
terminate by a truncated and undivided base. M. F. Cuvier and
other Comparative Anatomists have noted the distinction which
the teeth of the Orycteropus present, as compared with those of all
other animals, in the absence at every period of their growth of a
pulp-cavity at the base. But this difference is more apparent than
real ; it could only be predicated of the teeth in question, if each
was what it seems, a single tooth, and not as it really is an aggregate
of teeth. When viewed in the latter light, it will be found that each
component denticle has its base excavated by a conical pulp-cavity, as
in other animals, and which is persistent, as in the rest of the
order Bruta. The wide inferior apertures of these pulp-cavities
constitute the pores observable on the base of the compound tooth
of the Orycterope, and give to that part a close resemblance to the
section of a cane (1): the canals to which these pores lead, are
the centres of radiation of the calcigerous tubes of the denticle,(2)

CD) Pl; 76, fig: 11.
(2) Report of the British Association, vol. vii. 1838, p. 145.

OO

ORYCTEROPUS. 319

and not the orifices of simple canals resembling, as it was supposed,
those of baleen or Rhinoceros-horn.(1) }

The compound tooth of the Orycterope consists of a congeries
of very long and slender prismatic denticles commonly six-sided, more
rarely five or four-sided, cemented together laterally, slightly de-
creasing in diameter, and occasionally bifurcating as they approach
the grinding surface of the tooth. The medullary or pulp-canal
of each denticle is widest at its base (Pl. 77, a, a,) diminishes at
first rapidly, then very gradually, and divides where the denticle
divides, to continue along the centre of each division. The walls
of the denticle consist of hard unvascular dentine, into which the
minute calcigerous tubes are sent from every part of the circum-
ference of the medullary canal (Pl. 78). The calcigerous tubes
are =,th of a line in diameter at their origin; but rapidly diminish as
they proceed, dichotomously sub-dividing, towards the interspace which
separates them from the contiguous denticles: their general course
is transverse to the axis of the denticle, and they give off numerous
branches, which form near the boundary space a moss-like reticulation
of extremely minute tubes. Nearly the whole extent of the medullary
canal is occupied by a vascular pulp, and the base of each denticle
is surrounded by a delicate vascular capsule, which becomes ossified
about a line above the base, and forms the cementing substance
of the congeries of denticles. The vascular pulp, likewise, becomes
ossified near the grinding surface of the tooth, and consequently a
transverse section taken from this part, presents the centres of the
radiation of the calcigerous tubes filled up with bone.

From the preceding account of the minute structure of the
compound tooth of the Orycterope, it will be seen to resemble the
teeth of the Myliobates and Chimeroids, among fishes, rather than
any true teeth in the Mammalian class, in which it offers a tran-
sitional step from the horny substitutes of teeth, above described
to the true teeth.

The teeth of the Orycteropus, when rightly understood, offer,
however, no anomaly or exceptional condition in their mode of

(1) Cuvier, Lecons d’Anat. Comp. ed. 1836, t. iii. p. 205. Heusinger Histologie, 1823,
p- 198.

320 ARMADILLOS.

development(1). Each denticle is developed according to the same
laws, and by as simple a matrix, as those larger teeth in other
Mammalia which consist only of dentine and cement. The dentine
is formed by the centripetal calcification of the pulp, and the
cement by ossification of the capsule: both pulp and capsule con-
tinue to be reproduced at the bottom of the alveolus, pari passu
with the attrition of the exposed crown; and the mode and time
of growth being alike in each denticle, the whole compound tooth
is maintained throughout the life of the animal. The augmentation
in the size of the whole tooth, during the growth of the jaw, is
effected by the development of new denticles, and a slight increase
of size in the old ones, at the base of the growing tooth, which
in the progress of attrition and growth, becomes its grinding surface.

ARMADILLOS,

136. It has been a subject of regret to most Naturalists that
the great Reformer of Zoology should have substituted the name
Edentata for that of Bruta, applied by Linnzus to the order of
‘Mammals which he had characterized by the absence of incisors.
The subsequent discoveries of Naturalists have much augmented
the Edentata of Cuvier, and have shown that out of the great
number of species contained in this order, two only are without
teeth, whilst almost all are destitute of incisors. The exceptions
to the Linnean character occur in the family of Armadillos, in
which the species of the existing subgenus Euphractus, and of the
extinct genera Gilyptodon and Chlamydotherium have teeth in the inter-
maxillary bones.

(1) M. Fred. Cuvier, at the close of his description of the teeth of the Orycterope
remarks: “Les macheligres de Vorycterope ont une structure qui leur est tout-a-fait par-
ticuliére ; leurs racines ne différent point de leur couronne, mais elles ne présentent point
de cavité pour la capsule dentaire, comme font toutes les espéces de dents chez les mam-
miféres; elles semblent présenter un nouveau mode de développement pour ces organes.
Comme toutes les dents dépourvues de racines proprement dites, elles paraissent croitre
constamment; mais, au lieu d’étre formées de couches successives et toujours renaissantes,
elles le sont, en apparence du moins, de fibres longitudinales, pentagones, et dont le centre
serait percé, ou rempli d’une substance de couleur plus foncée que ces fibres.” Dents de
Mammiféres, p. 200.

The present knowledge of the dental system of the Orycterope strikingly exemplifies the
manner in which anomalies disappear as we gain a deeper insight into structure.

ARMADILLOS. 32]

The teeth are more numerous in the Priodon, the largest of
existing Armadillos, than in any other land Mammal, but they
are of very small size and simple form, and are all referable to
the molar series(1). They vary in number from twenty-four to
twenty-six in each upper jaw, and from twenty-two to twenty-four
on each side of the lower jaw, amounting to from ninety-four to
one hundred in total number. They are compressed laterally, most
so where they are smallest at the anterior part of the series, in-
creasing in size, and especially in breadth, as they recede back-
wards, with oblique or horizontal flat grinding surfaces, and con-
tinued of the same size and form to their implanted extremity,
which is excavated by a large conical pulp-cavity. This absence of
roots and the undivided hollow base, indicative of the constant
growth of the tooth, are common, as has been before stated in the
general observations on Mammalian dentition, not only to the teeth
of the Armadillos, but to those of all the known species of the order
Bruta. In the Priodont the teeth, though so unusually numerous, are
separated by slight intervals ; those of the lower jaw oppose their
outer sides to the inner sides of the upper teeth when the mouth
is shut.

In the subgenus Tatusia of F. Cuvier, which includes the
7-banded, 8-banded, and 9-banded Armadillos, the upper teeth are
also confined to the maxillary bones, but are much fewer in number
and larger than in the Priodon. In the species whose dentition
is figured and described by M. F. Cuvier(2), there are eight molars
on each side of the upper jaw, and nine on each side of the lower
jaw (Pl. 85, fig. 2). It agrees, therefore, with the Dasypus octocinctus
of Linneus (Das. uroceras, Lund.), a species with a tail somewhat
shorter than the body, and a native of Central Brazil and Paraguay,
where it is called ‘‘ Tatu-verdadeiro.” In both jaws the teeth pro-
gressively increase in size from the first to the penultimate, the
last suddenly decreasing in size: those of the lower jaw alternate
in position with the upper teeth, and it results from this reciprocal
position that the grinding surface is worn down into two sloping
facets. The Dasypus novem-cinctus L., (D. longicaudus, Max.) has

(1) Pl. 85. fig. 1, a—d, ; (2) Loe. cit. Pl. Ixxx.
24

322 ' ARMADILLOS.

seven molars on each side the upper jaw, and a tail as long as
the body; it inhabits Cayenne and the northern parts of Brazil.
The Das. septem-cinctus. L., (D. hybridus, Desm.)(1) has likewise
seven molars on each side of the upper jaw, and a tail much shorter
than the body.

The Armadillos of the subgenus Euphractus, Wagler, to which
the term Dasypus is restricted by F. Cuvier, are distinguished by
having the anterior tooth, which is shaped like the succeeding
molar, implanted in the maxillary bone. The species of which the
dentition is figured by M. F. Cuvier(2), is the Dasypus sew-cinctus of
Linnzus, the Weasel-headed Armadillo of Grew. It has #5, = 38
teeth. Those of the upper jaw gradually increase in size to the
sixth, and diminish from the seventh to the ninth: they present
an elliptical, transverse section, which is narrowest in the small
anterior teeth. The two anterior teeth of the lower jaw being in
advance of the intermaxillary tooth, are, with it, arbitrarily held
to be incisors: they are compressed, but are terminated by obtuse
crowns: the rest of the series, from which the incisors are not
separated by any remarkable interval, gradually increase in size
to the penultimate molar: they have the same alternate position
and obliquely worn grinding surfaces as in the Tatusie.

Among the extinct species, that forming the type of the genus
called by M. Lund Euryodon is distinguished from all existing Arma-
dillos by having the teeth compressed from before backwards, in-
stead of laterally; but the grinding surface consists, as usual, of
two facets, which meet at a more or less acute angie in a transverse
ridge(3).

In a second extinct genus, Heterodon, Lund, the teeth exhibit
much less conformity in shape and size than in the existing Arma-
dillos. Both the anterior and posterior molars are small and
conical ; while the penultimate and ante-penultimate are much ~

larger, the former being oval, the latter heart-shaped in transverse
section.

(1) This species occurs only in the extra-tropical part of S. America.
(2) Loc. cit. Pl. lxxix.

(3) Blik paa Brasiliens Dyreverden For Sidste Jordomveltning, af Dr. Lund, Kjobenhavn,
4to. p. 7.

ARMADILLOS. 523

In the Chlamydothertum, Lund, there are eight teeth on each
side of the upper, and nine on each side of the lower jaw: of
these the two anterior ones in the upper jaw, and the three anterior
ones in the lower jaw, are incisors by position. The latter are
shaped like small cylinders, with a more or less reniform transverse
section, while the molars are very large and compressed, so that
their section resembles an elongated kidney: their sides are marked
with several canaliculate impressions, and their grinding surface
presents two projections, the effect of the action of the teeth of
the opposite jaw ; elsewhere the surface is flat, and a little hollowed
in the middle. The size of the species (Chlam. Humboldtii), of which
the dentition is here described, was six feet, or double that of the
Priodon, which is the largest of existing Armadillos; but the Chlam.
giganteum equalled in bulk the Rhinoceros.

The extinct Glyptodon(1) seems to have surpassed the Rhinoceros
in size: and its dentition(2) was more complicated, more adapted to
a vegetable diet, than that of the Chlamydothere. The total num-
ber of teeth in the Glyptodon has not yet been determined. A
fragment of the anterior part of the lower jaw shows that the teeth
extended close to the symphysis, and, therefore, indicates their
presence in the intermaxillary bones above. The single tooth, on
which the generic character of the Glyptodon was founded, is long,
rootless, as in the existing Armadillos, but compressed laterally,
and divided by two deep, angular, longitudinal, and opposite grooves
on each side, into three plates, which give the grinding surface
the form of as many rhomboidal lobes. The alveoli on the frag-
ment of jaw above mentioned, indicate the anterior teeth there to
have had the same form, and, from the allusion which Dr. Lund(3)
makes to the teeth in the Hoplophorus (Glyptodon) of the Brazilian
Caverns, it would seem that the complicated form just described,
pervaded the whole dental series.

The teeth of the Armadillo-tribe are harder than those of

(1) Sir W. Parish’s Buenos Ayres, 8vo. 1839, Geol. Trans. 2nd series, vol. vi. p. 81—85.
y p

(2) Pl. 86. fig. 1 and 2.
(3) ‘Its teeth are shaped like the molars of the Capibara, but have a different structure,

inasmuch as they are simple, and not composed of lamine.”’ Loc. cit. p. 10.
‘
ye

324 ARMADILLOS.

any other species of the order Bruta, but, as in all that order
provided with teeth, they are wholly devoid of enamel: it is not
true, however, that they have no cement, as Retzius_ believed.
They consist, in both existing and extinct Armadillos, of three
distinct substances, of which the unvascular dentine is present in
greatest proportion, and forms the main body of the tooth: but
it includes a small central axis of vascular dentine, and is sur-
rounded by an extremely thin coating of cement.

The calcigerous tubes of the dentine are continued from the
vascular or Haversian canals of the central bone: in the Dasypus
sex-cinctus(]) they present strong curvatures at their commencement,
except the few which arise from the summit of the central axis:
these ascend vertically to the grinding surface; the surrounding
tubes rapidly diverge like the outer streams of a fountain; and
throughout the rest of the body of the tooth the calcigerous
tubes bend outwards, and direct their course at right angles to
the axis of the tooth, but with a slight convexity directed towards
the grinding surface. The diameter of the calcigerous tube, where
the parallel course and moderate and regular curve begins, is
jamth of an inch; the interspace of two tubes equals four of their
diameters. The interstitial branches are not easy of detection, but
the terminal ones are sufficiently obvious: they are numerous, often
irregularly curved; many appear to anastomose, either directly or by —
intermediate cells, close to the cement(2); others are directly con-
tinued into that substance, and terminate in its cells.

The central axis of the solid part of the tooth is occupied, as
already stated, by a hard substance, closely resembling bone,(3) in ©
which the last traces of the dentinal pulp appear as the vascular
occupants of the medullary canals: these canals are few in num-
ber, have not a regular or parallel arrangement, and do not an-—
astomose by loops: some of them are continued, along with short —
processes of the osseous substance a little way into the dentine:
a rich pencil or brush of calcigerous tubes radiates in strong irregular
curves from the obtuse ends of these processes, before falling into —
the common parallel course.

(1) PL. 85, fig. 4, 2. (2) Ib. fig.4,c. (3) Ib. fig, 4, a.

ARMADILLOS. p44)

In the Gilyptodon the vascular osseous texture(1) occupies a
larger proportion of the centre of the tooth than in the small Arma-
dillos: it is harder than the dentine or cement, and rises upon the
grinding surface(2) in the form of a ridge extending along the
middle of the long axis of that surface, and in three shorter ridges
at right angles to the preceding, at the middle of each of the three
rhomboidal divisions of the tooth. The medullary canals are sur-
rounded by fine compact concentric strata, but are wider than in
true bone, and the calcigerous cells are fewer and less conspicuous :
the canals bend towards the dentine, but without any regular or
parallel arrangement. The calcigerous tubes(3) assume their parallel
and regular course sooner than in the Armadillos: they have the
same relative diameter, arrangement, and terminal ramification. The
outer coat of cement(4), though not exceeding jth of a line in thick-
ness, is relatively thicker than in the Armadillos; a large proportion
of the terminal branches of the calcigerous tubes is continued into
it, and these branches anastomose with the plexiform tubes which
surround the calcigerous cells. These cells, which generally present
an oblong form, are about ;4,th of an inch in their long diameter. ‘

Although the teeth of the largest of the extinct loricated Bruta,
present so much more complicated a form than do those of the
small existing species, their intimate texture and composition are
essentially the same, and very distinct from what has been described
in the Orycteropus and will subsequently be shown to charac-
terize the dentition of the family of the Sloths. Nevertheless,
the modification in regard to the proportions of the constituent
textures of the molars of the Glyptodon, which produce the in-
equality in the grinding surface of the crown, coincide with the
more complicated form of that surface, in adapting the tooth for
a more strictly vegetable diet than is indicated by the more simple
molars of the existing Armadillos. It is interesting to find that
the herbivorous character of the dentition of the Glyptodon was
associated with a descending process: of the malar bone(5), which,
in the Sloths, affords the masseter muscle, a more extensive and

(1) Pl. 86, fig. 3, a. (2) Th. fiend: (3) Ib. fig. 3. 5, b. (4) Ib. fig. 3,.¢.
(5) Geol. Trans. 2nd series, vol. vi. p. 86.

326 SLOTHS.

favourable attachment for producing the horizontal triturating
movements of the lower jaw.

With reference to the diet of the existing Armadillos, Dr. Lund
states, that those which he kept in his house manifested an extra-
ordinary predilection for putrid flesh, as well as a remarkable skill
in managing it; and, that he always found in the stomachs of the
wild Armadillos numerous remains of insects, particularly of beetles
and centipedes, whence he concludes, that the recent Armadillos
are insectivorous and carnivorous. The maintenance of the dental
series in both the existing species and the great extinct phytipha-
gous Armadillos is effected, as the wide conical persistent basal pulp-
cavity demonstrates, by constant renovation of the matrix, which,
by its calcification produces the different dental substances.

SLOTHS.

137.—Of the leaf-eating species of the order Bruta very few,
and these the most diminutive of the tribe, now exist. They are
called Sloths, Tardigrades, and Bradypodes, from their inability to
move otherwise than slowly and with difficulty on the ground;
but they are excellent climbers, for which their organization es-
pecially befits them.

If we restrict our survey of the dental system to existing
Mammals, that of the Sloths appears anomalous, both as respects
the number, the form and the intimate composition of the teeth.
But when the bradypodal dentition is viewed in connection with
that of the extinct phyllophagous Bruta, the repetition of all its
essential characters, under various minor modifications, in the
already known species and genera of those once numerous and
gigantic quadrupeds, gives it as important a place in the classifica-
tion of the Mammalian teeth, as that of the dentition of the pro-
boscidian Pachyderms or Ruminants.

The following are the common and constant characters of the
dentition of the phyllophagous Bruta, both recent and extinct :—
Teeth implanted in the maxillary, never in the intermaxillary
bones ; few in number, not exceeding = (1); composed of a large —
central axis of vascular dentine, with a thin investment of hard

(1) Unless the Megatherium had ten molars in the lower as in the upper jaw.

SLOTHS. and.

or unvascular dentine, and a thick outer coating of cement. To
these, of course, may be added the dental characters common to the
order Bruta: viz. uninterrupted growth of the teeth, and their
concomitant implantation by a simple, deeply excavated base, not
separated by a cervix from the exposed summit or crown.

In the mature Ai, (Bradypus tridactylus, Linn.) the teeth(1) are
small, of a simple columnar form, presenting, for the most part,
a sub-elliptical transverse section, sub-equal, and separated from
each other by short intervals. The grinding surface has a central
depression, with a raised margin, worn unequally into one or two
points. The first tooth in the upper jaw is the smallest, the second
is the largest; both approach the trihedral form. The first in the
lower jaw is more curved than the rest, and is compressed from
before backwards, the posterior surface forming a slight angle, and
bevelled down obliquely from the anterior margin, which is trenchant,
and sometimes notched: the fourth or last molar of the lower jaw
is subtetragonal, and rather larger than the rest. The teeth of
the upper and lower jaw are not opposite; but subalternate when
the mouth is closed.

The dental formula of the genus Bradypus is

Inc. 3, Canini 5, Molares =? = 18.

Dr. Brant(2) has described and figured the skull of a young
Ai, in which a very small tooth preceded the compressed one on
each side of the lower jaw, rendering the number of teeth equal
to that in the upper jaw. The remains of the alveoli of these teeth
are visible in the jaw of a young Ai in the Hunterian Museum, but
they are soon shed; and, if constant in the species, are confined
to the immature period.

In the two-toed Sloth or Unau, (Cholepus didactylus, Ilig.)
the teeth(3) offer a greater inequality of size than has yet been
observed in any other genus of Bruta; the first of each series, in
both jaws, which in the rest of the Order is the smallest, here so

(1) Pl. 81, fig. 1.

(2) Dissertatio Zoologica inauguralis de Tardigradis, 4to. figs 5 & 6. 1828. p. 31, pl. 2.
In the foetal Ai examined by Dr. Harlan, these small deciduous teeth were, perhaps, not
developed. See this Author’s Medical and Physical Researches, p. 549.

(3) Pl. 81, figs. 3, 4, 5. .

328 SLOTHS.

much exceeds the others, as with its peculiar form, to have re-
ceived the name of a canine. The Unau is the only species of
Bruta, which derives a weapon of offence and defence from
the dental system; and, instead of affording the type(1) of the
dentition of its particular family, ought rather to be regarded as
manifesting the exceptional modification.

The so-called canines of the Unau are separated by a
marked interval from the other teeth, especially in the upper
jaw; so that those above play upon the anterior part of those
below, contrary to the relative position, and mutual action of the
true canine teeth in the Quadrumana and Carnivora. They are of
a triedral form, (fig. 5. a,) with the margins of the oblique
abraded surface leading to the point, trenchant. The sockets
containing the long excavated base of each of these laniiform
molars, projects beyond the level of the outer surface of the jaw.
The second tooth (6) of the upper jaw is the smallest of the
series, it has an elliptical transverse section, and its grinding sur-
face slopes from before and behind to a sub-median transverse ridge.
The third (c), and fourth (d) molars, are a little larger, and have
two abraded surfaces, which converge to the median ridge. The
fifth molar (e), is the smallest, and has an oblique grinding surface.
In each tooth the ridge is formed by the hard dentine, and is
interrupted in the middle by an excavation of the soft dentine.
The second, third, and fourth teeth of the lower jaw correspond
with the third and fourth above ; and like the small upper molars,
are separated by short intervals: the last is the smallest and most
curved. , |

The large laniiform molars are three-sided; the upper one
has one of its sides turned outwards ; the lower, one of its angles:
the latter resembles the laniiform premolar in the lower jaw of
the slow Lemur, in working against the posterior surface of the
upper canine, which is an interesting analogy. The wedge-shaped
summits of the three lower small molars fit into the interspaces
of those of the four upper small molars, when the mouth is closed.

The teeth of the Sloths consist of a central axis of vascular

(1) Dr. Blainville, Ostéographie des Paresseux, (pp. 32, 33.)

SLOTHS. 329

dentine, occupying rather more than half the thickness of the
tooth, which is enclosed by a wall of unvascular dentine, and this,
by one of cement, of less thickness than the layer of hard dentine :
but this description applies only to the teeth of the mature animals ;
and the large anterior laniiform molars of the Unau have a very
thin coating of dark coloured cement. Before the teeth are abraded
by use, they all present a conical form, and consist chiefly of the
hard dentine, which is covered by cement, and has its cavity lined
by a layer of the unvascular dentine. Their resemblance at this
stage, to the ordinary cuspidate teeth, only wants the interposed
layer of enamel, between the coronal cement and the hard dentine
to be complete. The cement is soon abraded from the protruded
apex, and the exposed hard dentine is worn into a hollow; the
magnified section of the tooth of the young Bradypus figured in
Plate 82, shows its structure at this stage of growth. Whilst
abrasion of the summit proceeds, the base elongates by progressive
addition of the three constituent substances; and, when it has
attained the diameter of the adult tooth, these continue to be
added without variation of their respective thicknesses ; the complex
matrix alone preserving its conical form, and filling the cavity at
the base of the tooth. When the coronal hard dentine is worn
away, this constituent is afterwards added only to the vertical
surface of the central axis of vascular dentine, which henceforward
constitutes the central and deepest part of the grinding surface of
the tooth.

The intimate structure of the vascular dentine resembles that
of the entire tooth in Psammodus, Ptychodus, and some other
Cartilaginous fishes, and that of the inner half of the dentine in
the Iguanodon: it is perforated by vascular or medullary canals,
from th to ;q@th of an inch in diameter, with intervals of twice
or thrice that breadth ; which canals proceed in a slightly undu-
lating and sub-parallel course from the internal surface connected
with the pulp, to the hard dentine, at right angles, for the most
part, with the plane of the pulp-surface, and obliquely to that of
the hard dentine: those vascular canals proceeding from the summit
of the pulp are parallel, or nearly so, with the axis of the tooth,

330 SLOTHS.

whilst those from the base of the pulp are transverse to the same
axis: the intermediate canals have an intermediate course. Pro-
cesses of the vascular pulp are continued along these canals, which
consist essentially of tracts of the primitive pulp, which have
remained uncalcified. The medullary canals are cylindrical; but
not of equal diameter throughout, sometimes presenting alternate
expansions and constrictions: they everywhere give off minute
calcigerous tubes, which have a wavy course, and the finest bran-
ches of which terminate in the minute cells of the intertubular
tissue. The medullary canals occasionally bifurcate, and also,
but more rarely, anastomose together by loops, the convexity of
which is turned towards the hard dentine. Their usual termination,
in Bradypus, is by splitting into a pencil of smaller wavy branches,
close to the hard dentine, the calcigerous tubes of which, are formed
by the ultimate sub-division of those branches, as shown in Hate
82, fig. 2, on the left hand-side of the section figured.

a Phe eden cylinder, or thin layer of hard dentine, resembles
very closely that of the human tooth in structure: it consists of a clear
substance permeated by the calcigerous tubes given off from the peni-
cillate terminations of the medullary canals: the calcigerous tubes
have a diameter of jth of a line, and their interspaces are equal to
about twice that diameter. At the sides of the tooth, they proceed in
beautiful sigmoid curves parallel with each other, and almost trans-
verse to the cement, but a little inclined towards the summit of
the tooth: their first curve is convex towards the same part, their
second curve concave, and they then proceed straight to the cement,
in which they terminate, either by immediately penetrating, or by
sending into it their finer sub-divisions. In a few instances, I
have detected looped anastomoses of the peripheral ends of the
calcigerous tubes. With a magnifying power of 600 linear dimen-
sions, the minute branches sent off by the calcigerous tubes into
their clear interspaces may be discerned. The axis of vascular
dentine is not conformable with the conical pulp; but, in the
molar of the young Ai examined by me, (the third of the lower
jaw) expanded at its summit, which is bifid. The calcigerous tubes
of the hard dentine sent off from this part of the vascular dentine,

|
:

SLOTHS. DOs

do not present the curvatures observable in the lateral layer, but
pass almost in a straight line to the grinding surface of the tooth,
slightly converging and decussating each other at the middle, and
slightly diverging near the margin of the crown. The coronal portion
of the hard dentine, which is originally nearly three times the thickness
of the cylindrical or parietal portion, is worn away almost before
the Sloth reaches maturity; and, as the pulp, when once it has
taken on the incomplete process of calcification which produces
the vascular cement, is never afterwards subject to the primitive
and more complete process, the coronal hard dentine is never re-
produced. The depressed centre of the grinding surface is then
formed by the vascular dentine only; that surface having its inequality
maintained by the edge of the cylinder of hard dentine, in place of
enamel, and being thus adapted to the comminution of the softer
vegetable substances, as the leaves and tender buds of trees.(1)

The external coat of cement has an average thickness of jth of
a line; it gradually thins off to the sharp margin of the pulp-cavity,
forming the inserted base of the tooth. It is principally charac-
terized by the numerous calcigerous cells, represented by the dark
or opake dots in Plate 82, fig. 1. These present a more or .less
oblong form, with the long axis parallel with that of the tooth:
those next the hard dentine making the nearest approach to the
circular form. Their average diameter is jth of an inch in the
long-diameter, and <,th in the short diameter; but the extremely
numerous minute tortuous tubes, which open into every part of
their circumference, give the cells a greater apparent size than they
present when viewed by a sufficiently deep power for the clear
analysis of the rich and minute tubular system, with which they
are everywhere connected. The principal trunks of this system,
which, nevertheless, do not exceed the diameter of the calcigerous
tubes of the hard dentine, affect a parallel course in many parts
of the cement, at nearly right angles to its surface. They are most
conspicuous at that part of the cement, which is in contact with

(1) Cecropia peltata and Achra sapota have been particularized as affording nutriment

to the Sloths; but, probably, few of the trees forming the denser forests of tropical America
are exempt from their attacks.

BOL SLOTHS.

the dentine. They communicate freely with the dentinal tubes,
and, by their fine sub-divisions, with the calcigerous cells. I have
not observed any canal or vessel in the cement of the Sloths’
tooth, capable of carrying red blood. It is, therefore, harder than
the vascular dentine, but softer than the unvascular dentine, and
wears away, so as to form a bevelled edge at the circumference
of the grinding surface.

_ The structural appearances of the Sloth’s tooth, with unaided
vision, are, as might be expected from its unusual composition,
different from those presented by ordinary teeth. Cuvier was misled
by these appearances to describe the teeth of the Sloths as “ being
of the most simple structure imaginable. A cylinder of bone en-
veloped by enamel, and hollow at both ends; at the outer end by
attrition, at the inner end by default of ossification, and for lodging
the remains of the gelatinous pulp which has served for their
nucleus. ‘‘ Voila,’’ he concludes, ‘“‘ toute leur description.’ Cuvier,
however, adds, that ‘‘it may be further remarked that the plates
which compose their osseous substance are but imperfectly united
to each other. In sawing a tooth longitudinally, these plates are
seen to be all distinct, piled one upon another like pieces of money
or draughtmen in a tube: which tube is formed by the enamel(1).”

The parallel and nearly equi-distant vascular canals occasion
the appearance of intervals separating distinct layers of vascular
dentine. M.F. Cuvier(2) describes the substance surrounding the
central axis as being ‘‘ analogous to, but less hard than enamel.”
Dr. Richard Harlan(38) appears to have first distinguished the
cemental constituent of the Sloth’s tooth ; ‘“‘in which tooth,” he
says, ‘‘there exists first, a central cylinder of bone which is sur-
rounded by enamel, which itself is surrounded or enveloped by a
regular layer of cement.” The intimate structure of the Sloth’s
tooth was first accurately described by Retzius(4).

(1) Ossemens Fossiles, tom. v. part 1, p. 84.

(2) Dents de Mammiféres, 1825, p. 193.

(3) Medical and Physical Researches, 8vo. 1835, p. 315.

(4) Mikroskopiska undersokningar ofver Tandernes struktur, 8vo. 1827, p. 23.

MEGATHERIOIDS. aoe

MEGATHERIOIDS.

138. The larger leaf-devouring species of the order Bruta,
being too bulky to obtain their food by climbing, were compensated
by such colossal proportions and Herculean strength as enabled
them to uproot and prostrate the trees on which they fed; certain
toes on each foot were modified for support and progression of the
body by hoofs on level ground ; all the known species had complete
clavicles, closed zygomatic arches, and a powerful tail as long
as the hind-legs, ancilliary to the support of the enormous hinder
parts. Every member of this most extraordinary family of quad-
rupeds, which was peculiar to the American continents, is now
extinct ; their teeth, which governed their diet, closely resembled
those of their nearest existing congeners, the Sloths.

Megalonyr.—The teeth of the species of this genus correspond
most nearly, in form, with those of the existing Sloths, and, in
their relative size, with those of the Ai, there being no large an-
terior laniiform molar, at least, in the lower jaw. Here, on the
contrary, the first tooth is the smallest: the second and third teeth
are laterally compressed, presenting an ovate transverse section,
with the great end turned forwards: the form of the last tooth
of the lower jaw, which appears from the mutilated socket in the
jaw under consideration, to have been the largest, is not known(1).
_The tooth (Pl. 80, fig. 6), ascribed by Cuvier to the Megalonyz,
presents a somewhat irregular, elliptical, transverse section ; and,
like those in the lower jaw, has the grinding surface hollowed out
in the middle. A tooth (Pl. 80, fig. 7), found with certain bones
of a Megalonyx in a cavern in Kentucky, presents, in transverse
section, a longer and narrower ellipse than the tooth described by
Cuvier: there is, also, an irregularity of one side of the ellipse ;
the middle prominence of that side which is formed by a longitudi-
nal ridge, being stronger, and having a slight concavity or channel
on each side: it may probably be, as Dr. Harlan, who has
described these interesting remains, conjectures, an upper molar

(1) See my description of the Fossil Mammalia in the Zoology of the Voyage of the
Beagle, 4to. p. 99, Pl. xxix.

304 MEGATHERIOIDS.

of the Megalonyx: the entire tooth presents a double curvature,
its anterior and external sides being slightly convex, its posterior
and internal ones concave(1). This tooth consists, like the one
described by Cuvier, of a central body of vascular dentine, sur-
rounded by a thin layer of hard dentine, called enamel by Cuvier
and Dr. Harlan, and with an exterior coating of cement: the
central less dense axis is worn, as in the Ai’s molars, into a hollow;
but the hard boundary is uniformly obtuse, not raised into points.
Mylodon.—In this genus of extinct phyllophagous Bruta the
teeth are eighteen in number, disposed, as in the dental formula
of the Sloths, -5, or five on each side of the upper jaw, four on
each side of the lower jaw. They are, as usual, long, and of the
same thickness from the exposed to the implanted end: the latter
is excavated by a deep conical pulp-cavity, the exposed surface is
worn into a shallow depression, with a raised obtuse margin. In
the Mylodon robustus,—a species about the size of a Rhinoceros,
but in some dimensions equalling the Elephant,—the first tooth
of the upper jaw is separated by a marked interval from the rest,
and it is also more curved, the convexity being turned forwards:
its transverse section is subtriedal, with the angles rounded; it
measures not more than ten lines across its longest diameter, and
is rather more than three inches in length, with a very small
portion protruding from the socket. The second molar has an

elliptical transverse section, with the long axis parallel with that

of the skull: it is of the same size as the first. The remaining
upper molars are triedral, indented along the side which looks
inwards ; the last, of rather larger size than the others, having
its longest diameter from behind forward, the other two with theirs
transversely: the four posterior molars have short interspaces. In the
lower jaw the first molar resembles that above in its size and curvature,
but it is nearer the second tooth, and has an oval transverse section ;
it plays upon the posterior part of the upper tooth, like the inferior
canine-shaped molar in the Unau. The second tooth is bent outwards,
but less so than the first; its inner surface presents a longitudinal

(1y Harlan’s Medical and Physical Researches, Svo. 1835, pp, 323, 324, Pl. xii.
figs. 7, 8, 9.

MEGATHERIOIDS. a5

indentation ; its transverse section is triangular, and the posterior
and inner angle is produced. The third molar presents a sub-
quadrate transverse section, placed obliquely in the jaw: it is of
the same size as the second. The fourth and last molar is the
largest, and has the most complex form of any in the series: it
is slightly bent lengthwise with the convexity turned inwards,
and by the longitudinal channels which traverse its outer and
inner surfaces, the transverse section or grinding surface is made
bilobed: the inner channel is oblique and much deeper than the
outer one; the anterior surface of the anterior lobe of the tooth
is also impressed by a shallow channel. The grinding surface
of all these teeth is nearly flat; with the slight central depression
bounded by an obtuse margin: the small anterior teeth, which,
by their more advanced position and curvature, are analogous to
the large laniariform molars of the Unau, are rather obliquely worn.
The teeth of the Mylodon Harlani, very closely resemble those of
the Myl. robustus in figure: the last molar of the lower jaw presents
the most characteristic difference: it has two shallow longitudinal
channels along its outer side, the anterior one being the deepest :
and the deep and broad longitudinal channel on the inner side
of the tooth is angular, and not rounded as in the Myl. Robustus.
In the Mylodon Darwin, a third species of this extinct genus,
the posterior molar of the lower jaw is relatively smaller than in
either of the other species, and is impressed with a single longi-
tudinal channel, on both the outer and inner sides ; both penetrate
the tooth obliquely, but in opposite directions; and both are equally
deep: the anterior lobe is not impressed by any channel. The penul-
timate molar in the same species has the inner side longitudinally
indented ; but not the anterior side, as in the Mylodon Harlani :
the second molar is less deeply indented along the inner side(1).

I have investigated microscopically the structure of the teeth in
the last two species of Mylodon, and have given illustrations of that of
the Myl. robustus in the description of the skeleton of that species
published by the Royal College of Surgeons(2). Each tooth consists,
.as in the Sloth, of a central axis of vascular dentine, enclosed by a

(1) Bi 80; figs"5: (2) Memoir on the Mylodon, &c., 4to. 1842, Pl. xxiv. figs. 2 and 3.

336 MEGATHERIOIDS.

sheath of hard unvascular dentine, about one line and a half in thick-
ness, with an exterior covering of cement, about half a line in thick-
ness. The vascular dentine is permeated, as in the Sloth, by long,
nearly straight and parallel vascular canals, proceeding, for the most
part outwards, and with a slight inclination, to the grinding surface ;
this inclination is least at the base, and greatest at the summit of the
tooth, where the vascular canals are parallel with the axis of the tooth.
They have a slightly undulating course ; a diameter of jth of an
inch, which they preserve throughout with little variation; and
have intervals of about twice that diameter. They differ chiefly
from the vascular canals in the Sloths, by anastomosing together
in regular loops, turned towards, and close to the inner surface

of the hard dentine. Very fine calcigerous tubes are given off -

into the interspaces of the vascular canals, from every part of their
course; but the most abundant penicilli of these tubes proceed
from the convexity of the loops, and there diverge to enter the
hard dentine, through which they then proceed in a_ parallel
course, forming the calcigerous tubes of that substance. These
tubes are almost as minute as in the Sloth, having a diameter of th
of an inch, but have a straighter course; throughout the greater
proportion of the hard dentine, they run at right angles to the plane
of the cement. In the teeth of the Mylodon Darwini, I observed in
the hard dentine a few small vascular canals, which had an irregular
course, occasionally anastomosing together, and branching at acute or
right angles; their diameter equalled that of five or six of the calcigerous
tubes: they were more numerous near the central part of the hard
dentine, were filled with dark carbonaceous matter, and, being continued
from the larger vascular canals of the soft dentine, established a com-
munication between them and the vascular canals of the cement.
In the Sloth, no vascular canals have been detected in the hard
dentine or in the cement; in the Mylodon a few of these canals,
of larger diameter than those of the hard dentine, are present in
the cement(1). They are directed towards the plane of the dentine,
and are most conspicuous near that substance; but do not form
a series of loops, like the vascular canals of the central substance.
(1) Memoir on the Mylodon, pl. xxiv. fig. ae fe

:

""MEGATHERIOIDS. 237

and are fewer in number. The radiated calcigerous cells are as
numerous as in the cement of the Sloth’s molar, but offer more
conspicuously the elongated form; their long axis being parallel,
as in the Sloth, with that of the tooth itself. They measure ,,th
of an inch in the long diameter. The cement, in the Mylodon, is
traversed likewise by numerous and close-set calcigerous tubes,
continued from those of the dentine, with a general direction trans-
versely to the surface of the cement; but with a more wavy and
less parallel course, with more frequent bifurcations and more nu-
merous branches, the sub-divisions of which form a rich plexus
around each calcigerous cell. The dentinal cells are unusually con-
spicuous, presenting the appearance of a network in a thin section of
the hard dentine of these fossil teeth: they present a sub-hexagonal
form, and a diameter of ,j th of an inch; and are figured with the few
dispersed vascular canals of the hard dentine in Plate 79.
Scelidotherium.—The genus Scelidotherium includes three known
species, which resemble the Mylodon more nearly than the Megalonyz,
but differ from both those genera, not only in the form of the teeth
but in that of the astragalus, and in the structure of the knee-
joint. The dental formula is the same as in the Sloth and Mylodon,
viz. ¢4-(1) The sockets of the upper jaw are much closer together
than in the Mylodon, and the first is not separated by a wider
interval from the rest: they occupy an antero-posterior extent of
three inches, seven lines, in the Scelidotherium leptocephalum, and,
in the Mylodon robustus, one of five inches, four lines: yet the first
and second molars in the Scelidothere exceed those in the My-
lodon in size; but the rest are of inferior size in the Scelidothere,
and the last is the least of those in the upper jaw, contrary to its
proportions in the Mylodon. The four teeth of the lower jaw are
also in closer order than in the Mylodon ; the length of the alveolar
series is three inches, ten lines in the Scel. leptocephalum, and five
inches in the Myl. robustus, but the longest transverse diameter
of the first tooth in the Scelidothere exceeds that in the Mylodon,
whilst that of the last tooth is half an inch shorter than in the
(1) Plate 80, figs. 1 and 2. The name Scelidotherium has been left out, by mistake, at the

foot of this plate, in reference to the abuve figures.
Z

338 ; MEGATHERIODS.

Mylodon robustus; but the difference is less, as compared with
the lower molars in the Mylodon Darwimu. The two series of
upper molar teeth are separated by a narrower palate in the
Scelidothere than in the Mylodon. The first molar in the upper
jaw, (Pl. 80, fig. 1), is trihedral, and much less curved, and more
compressed than in the Mylodon. The second molar is also
three-sided, and its transverse section is triangular instead of
elliptical ; and two of its sides are slightly indented: it resembles
the antepenultimate molar in the Myl. robustus. The third and
fourth molars of the Scelidothere are more compressed, and the
long axis of their transverse section is oblique, whilst in the Mylodon
it is transverse to the line of the jaw. The fifth molar, besides
being relatively smaller, has a trihedral figure with the broadest
side turned outwards, and is slightly excavated lengthwise.

In the lower jaw, the differences in the form of the teeth are
of the same degree: a comparison of figure 2 with figure 5, in
Plate 80, will demonstrate their nature in the Scel. leptocephalum,
and Mylodon Darwinit. ‘The lower molars of the Myl. robustus and
Myl. Harlani differ still more, especially in the last species, from those
of Scelidotherium.

The composition of the teeth closely resembles that in the genus
Mylodon, but the central axis of vascular dentine is relatively smaller:
it is traversed, however, as in the Mylodon by medullary canals,
which, at the periphery of the axis anastomose by loops, from
the convexity of which the calcigerous tubes are given off, which
penetrate and constitute so large a proportion of the hard dentine.
This substance is about one line and a half in thickness, and is
invested by a coat of cement, not exceeding one third of a line
in thickness. The teeth of the Scelidothere are thus calculated to
offer more resistance than those of the Mylodon, having a larger
proportion of the hard unvascular dentine, by which they approach
nearer to the structure of the teeth in the Armadillo tribe.

Megatherium.—The teeth of this most gigantic of the extinct
quadrupeds of the Sloth-tribe are as small in proportion to the
size of the animal as in the Mylodon; they are five in number
on each side of the upper jaw, and, probably, four on each side of

MEGATHERIOIDS. 339

the lower jaw: they are more closely arranged, are longer, and more
deeply implanted than in the smaller Megatherioids ; they present
a more or less tetragonal figure, and have the grinding surface tra-
versed by two transverse angular ridges. Plate 83 exhibits a longi-
tudinal section of the five molars of the upper jaw, in situ; and
demonstrates the great extent of the persistent pulp-cavity; the
natural length of the series is ten inches.

The first or anterior molar is the second in point of size,
the last being the least, as in the Scelidothere. The first molar
is eight inches and a half in length; the pulp-cavity extends five
inches from the base: it presents two slight curvatures, one having
the convexity turned forwards, and the other inwards. The trans-
verse section gives an irregular semicircle, with the convexity turned
forward, and the flat side next the second tooth; the angles at which
this side joins the curve are rounded; the outer angle is some-
what produced, and the outer side of the curve is flattened. The
central axis of the tooth, formed by the vascular dentine, is irre-
gularly tetragonal, the cement is thick on the anterior and posterior
surfaces, thin on the sides of the tooth.

The second molar is the largest of the upper series ; it exceeds
nine inches in length, is of a tetragonal form, with two slight
curvatures, as in the first molar. The posterior and broadest side
is nearly flat, the anterior side somewhat convex, the outer and
narrowest side is concave, the inner side is sinuous, having a median
longitudinal eminence between two longitudinal concavities. The
central axis of vascular dentine is more compressed from before
backwards, than in the preceding tooth, and its posterior surface
is concave; the two transverse ridges of the grinding surface of
the tooth are nearly equal; but the sloping side formed by the
dentine, is larger than that formed by the cement.

The third tooth is of nearly the same size and form as the
second ; but is somewhat narrower, the anterior or outer angle is
less rounded off, and the external longitudinal depression is deeper.

The fourth molar is smaller than the two preceding, but of
nearly equal length, viz. eight inches and a half, and is distinguished
from all the other teeth, by being curved in only one direction,

Zz 2

340 MEGATHERIOIDS.

and that in a very slight degree, the concavity looking, as in the
other teeth, outwards: the central axis of the tooth is, in reference
to the anterior and posterior planes of the skull, quite straight :
the anterior and posterior layers of cement decrease in thickness
as they approach the base of the tooth, so as to describe a slight
curve, the convexity of which is turned, on both sides, towards
the adjoining tooth. The fourth molar is tetragonal, and with more
equal sides than the two preceding teeth ; the outer and inner sides
are concave, the anterior and posterior ones convex, the angles
rounded, and the anterior and inner one more produced than the
rest. The grinding surface presents two equal transverse ridges,
the contiguous sides of which are the longest.

The fifth molar is five inches in length, one inch two lines in trans-
verse, and ten lines and a half in antero-posterior diameter: its princi-
pal curvature presents its concavity forwards, or towards that of the
anterior tooth ; the curve in the transverse axis of the skull is scarcely
appreciable. The transverse section of this tooth is rhomboidal,
with the angles rounded, and with the longest diameter intersecting
the anterior internal, and the posterior external angles. The den-
tinal axis is transversely quadrilateral, with the posterior angles
entire, and the posterior surface concave: the layer of cement
which covers this surface is the thickest, and is convex: those
which cover the outer and inner sides of the tooth are, as in the
rest, the thinnest; the anterior layer is less than one third the
thickness of the posterior layer. I have not been able to extricate
the grinding surface of this molar tooth from the hard conglomerate,
in which it is imbedded; but from the disposition of the cement
it is obvious that the two transverse ridges must be unequal, and
the anterior one the smallest, if not almost obsolete.

No distinctly recognizable part of the lower jaw of the Mega-
therium has yet reached England, and our knowledge of the number
and kind of teeth of that jaw is derived from the descriptions and
figures of the Madrid Megatherium. These are wanting in the
requisite detail, and we have seen how little they can be trusted, even
in relation to the number and mode of implantation of the teeth of
the upper jaw. Four teeth, of similar size and shape to the large

MEGATHERIOIDS. 341

ones in the upper jaw, have been assigned to each half of the lower
jaw of the Megatherium, by Garriga,(1) Pander and D’Alton,(2) and
Cuvier.(3) One cannot suppose, that the figures in the celebrated
works of these Authors err in the general form and proportions
of the four lower molars, which in a side view are not concealed
by the ascending ramus of the jaw: but, since we have proof,
that a small molar, posterior to the corresponding teeth in the upper
jaw has been overlooked, the same oversight may have been com-
mitted in regard to a corresponding small tooth in the lower jaw. (4)

In the Collections of Megatherian remains, brought to this
country by Sir Woodbine Parish and Mr. Darwin, the following
teeth, which differ from those of the upper jaw, may with more
probability be referred to the lower jaw than to a distinct species
of Megatherium.

That which most closely corresponds with the first molar in
the upper jaw, I have referred to the same part of the lower series
of molar teeth. The anterior surface is so much less convex than
in the first upper molar, that the entire tooth presents a tetragonal
rather than a semi-cylindrical figure; the anterior facet, however,
being only two-thirds the breadth of the posterior one, by which it
differs from all the tetragonal teeth of the upper jaw. Both the inner
and outer sides which converge to the anterior surface are slightly
concave, whilst the inner side in the first upper molar is convex : it
has the same double curvature and transverse diameter as the first
upper molar.

A molar tooth of a tetragonal form, but with the anterior facet
relatively broader and flatter than in the preceding tooth, and
narrower than in any of the tetragonal teeth of the upper jaw, may
be the second molar of the lower jaw.

A third tetragonal molar resembles the third in the upper jaw,

(1) Description del Esqueleto de un Quadrupedo muy corpulento y raro, &c. fol. 1796.

(2) Das Riesen-Faulthier, Bradypus giganteus, abgebildet, beschrieben, &c. fol. 1821.

(3) Ossemens Fossiles, 4to. 1825, vol. v. pt. i.

(4) Professor Daubeny kindly undertook, at my request, to examine the jaws of the celebrated
skeleton of the Megatherium at Madrid during his recent visit to Spain, with a view to determine
the actual number of teeth: but he found the specimen so inclosed in its glazed case, as to pre-
vent any examination of the interior of the mouth, and to exhibit only those teeth that are
obvious in the published figures. This may account for the oversight of the fifth superior
molar. Permission to open the case for a nearer inspection could not be obtained,

342 MEGATHERIOIDS.

in its slight and single curvature: its anterior and posterior sides
are convex ; the outer and inner ones concave.

Another molar tooth of a Megatherium is preserved with its
own and a portion of the adjoining socket, showing it to be the last
of its series, and less than half the size of the teeth which pre-
ceded it. It is, in fact, as small as the last molar of the upper
jaw; but differs in being straighter, and in the smaller antero-
posterior diameter compared with the transverse diameter: the pos-
terior surface is flatter, and the angles dividing the four surfaces
are more marked.

The fragment of the jaw connected with this tooth is insufficient
to determine whether it be part of the upper or lower jaw: if of the
upper, the tooth clearly indicates a distinct species of Megatherium
from that of which the upper molar series is figured in Pl. 83; if
of the lower jaw, then the tooth in question may be a fifth molar, and
the two last molars in the upper jaw will be opposed by a fourth
and fifth in the lower jaw, instead of by a larger and more com-
plicated fourth molar, as in the other known Megatherioid genera.

Each molar tooth of the Megatherium is excavated by an
unusually extensive conical pulp-cavity, (Pl. 83, c) from the
apex of which a fissure is continued to the middle concavity
of the grinding surface of the tooth. The central axis of vas-
cular dentine, (Pl. 83, 6, 6) is surrounded by a thin layer of
hard or unvascular dentine, and this is coated by the cement,
(ib. a, a.) which is of great thickness on the anterior and pos-
terior surfaces ; but is thin where it covers the outer and inner
sides of the tooth. As the outer laver of the vascular dentine is
first formed by the centripetal calcification of the pulp, the thin
crust of that substance at the base of the tooth includes a space
equal to that of the vascular dentine at the crown of the tooth:
the contraction of the base of the tooth is due to the progressively
diminishing thickness of the cement, as it approaches that part ;
the intervening vacancy in the socket indicating the primitive
thickness of the capsular basis of the cement.

The vascular dentine (Pl. 84, a, d) is traversed throughout by
medullary canals, measuring j,th of an inch in diameter, which are
continued from the pulp-cavity, and proceed, at an angle of 50°,

MEGATHERIOIDS. 343

to the plane of the hard dentine, parallel to each other, with a slightly
undulating course, having regular interspaces, equal to one diameter
and a half of their own area, generally anastomosing in pairs by
a loop, (4, d,) the convexity of which is turned towards the origin
of the tubes of the hard dentine, forming a continuous reflected canal.
The loops are situated near, and for the most part close, to the
hard dentine. In a few places one of the medullary canals may
be observed to extend across the hard dentine, and to anastomose
with a corresponding canal in the cement. The interspaces of the
medullary canals of the vascular dentine are principally occupied
by calcigerous tubes, which have an irregular course, form reticulate
anastomoses, and terminate in very minute cells, at least one hun-
dred times smaller than the calcigerous radiated cells of the cement.

The more regular and parallel calcigerous tubes, which tra-
verse the thin layer of unvascular dentine, are given off from the
convexity of the terminal loops of the medullary canals. The
course of these tubes is more directly transverse to the axis of
the tooth than is that of the medullary canals from which they are
continued. They run parallel with each other, but with fine
undulations throughout their course. They have a diameter of
jwoth of an inch, and have interspaces of about twice that diameter.
As the calcigerous tubes approach the cement, they divide and
subdivide, and become more wavy and irregular: their terminal
branches take on a bent direction and form anastomoses, dilate
into small cells, and many are seen to become continuous with
the radiating tubes of the cells of the contiguous cement. The den-
tinal cells are less distinctly defined than in the Mylodon, and of a
more elliptical form: their average diameter is jth of an inch, and
they are traversed by from nine to twelve of the dentinal tubes.

The cement, which enters so largely into the composition of
the grinders of the Megatherium, is characterized in that extinct
animal by the size, number, and regularity of the vascular or
medullary canals which traverse it. ‘They present the diameter
of jth of an inch, are separated by intervals equal to from
four to six of their own diameters, commencing at the outer
surface of the cement, they traverse it in a direction slightly
inclined from the transverse axis towards the crown of the tooth

344 MEGATHERIOIDS.

running parallel with each other: they divide a few times dicho-
tomously in their course, and finally anastomose in loops, the
convexity of which is directed towards, and in most cases is in
close contiguity with the layer of hard dentine. Fine calcigerous
tubes are sent off, generally at right angles, from the medullary
canals, which quickly divide and sub-divide, form anastomosing
reticulations, and communicate freely with the similar tubes that
radiate from the calcigerous cells. These are dispersed throughout
the dentine, and present an oblong form, with the long axis transverse
to that of the tooth, measuring sth of an inch in diameter. The
cavity of the cell, which is not quite occupied by their opake
contents, is often very clearly demonstrated. The calcigerous
tubes, which radiate from the cells nearest the hard dentine, and
from the terminal loops of the vascular canals, intercommunicate
freely with the calcigerous tubes of the hard dentine.

The tooth of the Megatherium thus offers an unequivocal
example of a course of nutriment from the dentine to the cement,
and reciprocally. Professor Retzius has observed, with respect to
the human tooth, that “the fine tubes of the coementum enter
into immediate communications with the cells and tubes of the
dentine (zahnknochen), so that this part can obtain from without the
requisite humours, after the central pulp has almost ceased to exist.”
In the Megatherium, however, those anastomoses do not relate to
the performance of a vicarious office, since the pulp is maintained
in its full size and functional activity during the whole period of
the animal’s existence.

In the structure which the fossil teeth of the Megatherium
and its extinct congeners clearly demonstrate, we have striking
evidence of their rich organization, and that they were once pervaded
by vital activity. All the constituents of the blood freely cir-
culated through the vascular dentine and the cement, and the
vessels of each substance intercommunicated by a few canals
continued across the hard or unvascular dentine. With respect
to those minuter tubes, the more important as being more im-
mediately engaged in nutrition, which pervade every part of
the tooth, characterizing by their difference of length and course
the three constituent substances, and which are derived, like the

Ee

CETACEANS. 345

hypothetical “‘ vasa lymphatica” of the old physiologists, from the
ultimate blood-vessels, they form one continuous and freely inter-
communicating system of strengthening and reparative vessels, by
which the plasma of the blood was distributed throughout the entire
tooth for its nutrition and maintenance in a healthy state.

The grinding surface of the close-set molars of the Mega-
therium differs, on account of the greater thickness of the cement
on their anterior and posterior surfaces, from those of all the
smaller Megatherioids, in presenting two transverse ridges; one
of the sloping sides of each ridge being formed by the cement, the
other by the vascular dentine; whilst the unvascular dentine, as
the hardest constituent, forms the summit of the ridge, like the
plate of enamel between the dentine and cement in the Elephant’s
grinder. The great length of the teeth and concomitant depth of
the jaws, the close set series of the teeth, and the narrow palate are
also strong features of resemblance between the Megatherium and
Elephant in their dental and maxillary organization. In both these
gigantic phyllophagous quadrupeds provision has likewise been made
for the maintenance of the grinding machinery in an effective state ;
but the fertility of the Creative resources is well displayed by the
different modes in which this provision has been effected: in the
Elephant, it is by the formation of new teeth to supply the place
of the old when worn out; in the Megatherium, by the constant
repair of the teeth in use, to the base of which new matter is added,
in proportion as the old is worn away from the crown. Thus, the
extinct Megatherioids had both the same structure and mode of
growth and renovation of their teeth, as are manifested in the present
day by the diminutive Sloths.

CEPA ET Bi FV,

TEETH OF CETACEANS.

139. Balenide.—In this, as in the preceding order, the dental
system presents little fixity of character, and its variations extend
in some cases to anomalies. Surveyed in the true or carnivorous
Cetacea, it seems, on the whole, to be of a grade inferior to that

346 CETACEANS.

of the Bruta, since the teeth are all of a more or less simple, conical
form, and none of them present flat or ridged crowns like true
molars: nevertheless we here first, in the ascensive survey of
Mammalian dentition, find enamel entering into the composition
of the teeth, the sharp crowns of those of the predaceous Dolphins —
being tipped or sheathed by this hard substance.

The main anomaly of the dental system in the family Balenide has
already been treated of in the chapter on Horny teeth. But the great
Whales, before they acquire their peculiar array of baleen plates,
manifest in their foetal age a transitory condition, a true dental
system, which, though abortive and functionless, beautifully typifies
that which is normal and persistent in the majority of the order.

In an open groove, which extends along the alveolar border of
both the upper and the lower jaws, there is aseries of minute, conical,
acute, or obtuse denticles, with hollow bases inclosing the uncal-
cified remains of a vascular pulp. These were first noticed by the
philosophical anatomist, Geoffroy St. Hilaire, and have subsequently
been described and figured by Prof. Eschricht. The subject ex-
amined by the latter Author was the foetus of a Balenoptera, the
jaws of which were about four inches in length. The unclosed
alveolar groove of the upper jaw contained twenty-eight denticles(1),
that of the lower jaw forty-two. The anterior denticles in both
jaws were the smallest; but they increase in size more gradually,
and maintain a greater regularity of form in the lower jaw, where
they are also most numerous, and in which the typical dentition
of the carnivorous Cetaceans first manifests its plenary develop-
ment in the great Cachalot. In the upper jaw of the foetal Whale
some of the denticles are double, two adhering together side by
side(2), and they offer in their varying extent of confluence, no unapt
resemblance to the stages of the fissiparous multiplication of an
infusorial Monad: there can be little doubt, indeed, that these
literally ‘double-teeth’ have resulted from a spontaneous fission
of the primordial pulp-cell; the divisions of which growing to a
certain size, have again coalesced in the progress of their calcification
like the two primitively detached summits of the Ornithorhynchus’s
grinder. We cannot avoid recognising in these bicuspid denticles

(1) Pl. 90, fig. 1. ) (2) Ib. figs. 5 and 6.

CETACEANS., 347

the representatives of the molars of the gigantic extinct Cetacean,
called ‘ Zeuglodon,’ and they also call to mind the similarly shaped
ultimate molar in the Dugong.

These small teeth and their matrices entirely disappear before
birth: yet the foetal Whale comparatively long retains and palpably
exemplifies the earliest stage of dental development in the higher
Mammals, viz., the open fissure, which in these is so rapidly closed,
especially in the Human subject. But beyond this stage the true
dentition of the Balenide is not destined to proceed; and they
thus manifest, agreeably with the general laws of unity of organi-
zation, their closest relations to the typical characters of their order
at the early periods of development, divesting themselves of part
of the more general type, in order to assume their special and
distinctive characters, as they advance towards maturity.

140. Hyperoodon.—The great bottle-nose or bident Whale
offers a beautiful transitional grade between the true Whales and
the typical Delphinide: the palate is beset with small, unequal,
pointed, callous processes, which Cuvier conjectures to be rudi-
mental baleen-plates ; whilst to balance, as it might seem, this
arrest of the development of the typical garniture of the Whale’s
jaws, the foetal denticles do not all perish, but two or three
of the anterior pairs acquire a large size, as compared with their
transitory representatives in the Balenide, and one of these pairs
is long retained in the lower jaw, though functionless and hidden
by the gum.

These teeth are figured of the natural size at the extremity
of the lower jaw of an immature Hyperoodon, in Pl. 88, fig. 1.
They are conical, slightly curved, with an unusually sharp and
slender apex, tipped by enamel. Though loose in their sockets,
they project so little from them, and have such wide bases that
they are retained in situ, and do not fall out in the dried jaw:
two smaller cavities in front, and the remains of a larger socket
in the alveolar groove, behind the retained teeth, attest the former
presence of other teeth.

141. Monodon.—In the Narwhal two of the primitive dental
germs at the fore part of the upper jaw, proceed in their deve-

348 CETACEANS.

lopment to a greater extent than those in the lower jaw of the
Hyperoodon ; but every other trace of teeth is soon lost. The
two persistent matrices rapidly elongate, but in the retrograde
direction, forming a long fang rather than a crown; each tooth
sinks into a horizontal alveolus of the intermaxillary bone, or
rather at the junction of the intermaxillary with the maxillary,
and soon, by the forward growth of these bones becomes wholly
inclosed, like the germs of the teeth of the higher Mammalia at
their second stage of development. In the female Narwhal the
pulp is here exhausted, the cavity of the tooth is obliterated by
its ossification, further development ceases, and the two teeth
remain concealed, as abortive germs, in the substance of the jaws
for the rest of life; so that in the skeleton a section of the skull
must be made in order to display them, as in Plate 87, fig. 2. In
the male Narwhal, the matrix of the tooth in the left intermaxillary
bone continues to enlarge ; fresh pulp-material is progressively added,
which by its calcification elongates the base and protrudes the apex
from the socket, and the tusk continues to grow, until it acquires
the length of nine or ten feet, with a basal diameter of four inches.
This is that famous so-called horn, which figures on the forehead
of the heraldic Unicorn, and so long excited the curiosity and con-
jectures of the older Naturalists, until Olaus Wormius made an end.
of the speculative and fabulous ‘ monocerologies’ by the discovery of
the true nature of their subject ; whilst Anderson(1) in the year 1736,
took advantage of the accident of the stranding of a Narwhal
at the mouth of the Elbe, to communicate to the Zoological
world, an accurate figure of the animal which bore the supposed
single horn. The exterior of this tusk is marked by spiral ridges,
which wind from within forwards, upwards,:and to the left:
about fourteen inches of the tusk is implanted in the socket; it
tapers gradually from the base to the apex. The pulp-cavity is
continued nearly to the extreme point, but is of variable width;
at the base it forms a short and wide cone, is then continued
forwards, as a narrow canal along the centre of the implanted
part of the tooth, beyond which, the cavity again expands to a
* Cited by Cuvier, Ossem. Foss. v, pt. 1. p. 319.

CETACEANS. 349

width equalling half the diameter of the tooth; and again, but
gradually, contracts to a linear fissure near the apex; Plate 87,
fig. 4.

Thus the most solid and weighty part of the tooth is that
which is implanted in the jaw,(1) and nearest the centre of support,
whilst the long projecting part is kept as light as might be com-
patible with the uses of the tusk as a weapon of attack and defence :
the portion of pulp in which the process of the calcification has
been arrested, receives its vessels and nerves by the fissure con-
tinued from the basal expansion of the pulp-cavity.

The small abortive tusk of the right side of the male Narwhal
(Plate 87, fig. 1) has a few slight longitudinal indentations on its basal
half, and is smooth on the rest of its exterior; it is solid and closed,
generally by a bulbous accumulation of cement, at its base; the apex
is truncated with a rough prominence from its centre: the ordinary
length is between eight and nine inches. The two concealed tusks
of the female Narwhal are of a similar size and shape."

Sometimes both tusks are so developed as to project from their
sockets in this sex; Mr. Scoresby records such an example in his
Voyage to Greenland.(2) Cuvier saw at Hamburg the skull of a
Narwhal with two tusks projecting, which he ascribes to the male
sex, probably on account of their length ; and he cites two other
instances, one figured in the Ephemerides Nature Curiosorum for
1700, p. 351, the other in Albers’ Icones ad illustrand. Anat. Comp.
Pl. 2 and 3.

In the cranium of the Narwhal figured by Albers, the right tusk
projects only six inches from the socket, is proportionally slender, and
is smooth. With regard to the paper in the ‘ Ephemerides,’ or ‘ Miscel-
lanea curiosa,’ (1702, p. 350), though it is entitled “De Unicornu Ma-
rino duplici,” it gives an account, not of two projecting tusks, but of the
discovery by the author, Dr. Reisel, of the small concealed tooth in the
right maxillary bone of an ordinary male Narwhal, the tooth being eight

(t) M. F. Cuvier appears to have been misled by ordinary analogies, in describing the
Narwhal’s tusk as ‘‘ creuse dans une grande partie de sa longeur, mais surtout dans sa partie
alvéolaire,” Hist. de Cetacés, 8vo. 1836, p. 237.

(2) It would be interesting to know the condition of the ovaria in such an instance.

350 CETACEANS.

inches in length, and exposed by the laying open of the narrow socket
(‘rima’), in which it was lodged. Two very accurate views of this abor-
tive tusk are given in the figures 23 and 24 of the Plate which illustrates
the paper, and the Author conjectures that it may serve to supply the
place of the large left tusk should this be either broken away by violence,
or shed naturally in process of time. The normal tusk in the skull of the
Narwhal, ‘ Cete Narhual’ the subject of his observation, was inserted
fourteen inches deep, and projected nearly four feet from the socket,
but its extremity had been broken off. It is figured in the Plate, together
with two views of the skull from which the tusks are removed,
the fissure, or alveolus of the abortive tusk being shown in Fig. 21.
The plate bears no number, but is marked p. 35. I doubt whether
Cuvier had ever read this paper: it has the priority of Tichonius’
often cited Dissertation ‘‘ Monoceros piscis haud monoceros,” by four
years, having been printed in 1702.

The skull of a Narwhal, with two long exserted tusks, formed
part of the collection of the late Joshua Brookes; in this specimen
the alveolus of the right tusk appeared to have been artificially
enlarged, and the tusk was unquestionably cemented in its place; but
the circumstance which most militated against its authenticity was
the direction of the spiral lines which corresponded with, instead of
opposing those of the left tusk.

With regard to the conjectured ulterior use of the concealed tusk
in the male as a substitute in the event of the loss of the large tusk
—a conjecture more than once repeated since first proposed by Reisel,
—the solidity of the concealed tusk and its distorted and generally
closed base evince that the term of its growth has expired.

142. Delphinide. Inthe Delphinus griseus the dentition of the
upper jaw is transitory as in the Hyperoodon, but at least six
pairs of teeth rise above the gum, and acquire a full development
at the fore-part of the lower jaw: the crowns of these teeth soon
become obtuse ; and even their duration is limited, for the specimen
described by M. F. Cuvier(1) had but two teeth on each side of the
lower jaw. A Dolphin, perhaps an aged individual of this species,
has lately been described with the dentition reduced to two teeth

(1) Dents de Mammiféres, p. 243. It was eleven feet in length, and captured at Brest.

CETACEANS. 351

in the lower jaw(l). The permanent or mature dentition of the
Beluga (Delphinus leucas, Pall.) is more normal though scanty, nine
teeth being retained on each side of the upper jaw, and eight in each
ramus of the lower jaw; they present the form of straight, subcom-
pressed, obtuse cones. The Delphinus globiceps, which has 333 = 52
strong, conical and pointed teeth in the vigour of its age, begins
soon after to lose them, and in aged individuals none remain in
the upper jaw, and not more than eight or ten are preserved in
the lower jaw; those at the anterior part of the jaws last longest
and their summits are received in cavities in the upper jaw, or
the gum covering it, when the mouth is shut.

The most formidable dentition is that of the predaceous Grampus
(Phocena Orca) whose laniariform teeth are as large in proportion
to the length of the jaws, as in the Crocodile ; they are in
number j=, = 50, all fixed in deep and distinct sockets, separated
by interspaces which admit of the close interlocking of the upper
and lower teeth when the mouth is closed. The longest and largest
teeth are at the middle of the series, and they gradually decrease
in size aS they approach the ends, especially the posterior one;
the shortness of the anterior teeth is in great part due to the
wearing down of the sharp summits, which are best preserved
in the small posterior teeth; the position of the bruising and
piercing teeth being the reverse of what commonly obtains. An
analogy to this circumstance in the dentition of the great predatory
Dolphin, is however, manifested by the typical carnivorous qua-
drupeds in which the incisors are shaped more like grinders than
the back teeth.

In the great or Bottle-nose Dolphin (Delphinus tursio) the
teeth are fewer and larger in proportion to its size than in the
common Delphinus delphis; but proportionally less developed and
more numerous than in the Grampus, the dental formula being
>-3 — 90 with a variation of three or four more or less in each
jaw; the teeth are conical, sub-obtuse, the posterior ones smaller
and sharpest. In the common Dolphin the number of teeth amount
to 190, arranged in equal numbers above and below. They have

(1) Proceedings of the Acad. of Philadelphia, 1842, p. 127.

852 CETACEANS.

slender, sharp, conical, slightly incurved crowns, and diminish
in size to the two extremes of each dental series; the acute apices
are longer preserved than in the foregoing species. In PI. 88, fig. 2,
the teeth of the upper jaw of an immature Dolphin are exposed
in situ, and both the extent of their implanted base and that of
their pulp-cavity is displayed.

The teeth of the common Porpoise (Phocena vulgaris), are
arranged in equal number on each side of both upper and lower
jaws, and are from 80 to 92 in number; the crown -is slightly
expanded and compressed, and the fully-formed fang is recurved
and enlarged at its extremity.

The gangetic Dolphin (Platanista gangetica) differs from the
rest of the Delphinide scarcely less in the form of its teeth than
in that of the jaws; both the upper and lower maxillary bones
are much elongated and compressed; the symphysis of the lower
jaw is co-extensive with the long dental series, and the teeth rise
so close to it that those of one side touch the others by their
bases, except at the posterior part of the jaw; the lateral series
of teeth are similarly approximated in the upper jaw at the median
line of union, which line is compelled by the alternate position of
the teeth, to take a wavy course.

There are thirty teeth on each side of the upper jaw, and thirty-
two on each side of the lower jaw(1) ; in the young animal they are all
slender, compressed, straight, and sharp-pointed, the anterior being
longer than the posterior ones, and recurved. Contrary to the
rule in ordinary Dolphins, the anterior teeth retain their prehensile
structure, while the posterior ones soon have their summits worn
down to their broad bases. The most remarkable change that
occurs in the progress of growth is the antero-posterior expansion
as well as elongation of the implanted base of the tooth, which
likewise has its outer surface augmented by longitudinal folds
or indentations, analogous to, but weaker than those in the base
of the teeth of Sauroid fishes. Sometimes the posterior tooth of the
Platanista has the base divided into two short fangs,—the sole
example of such a structure which I have met with in the existing

(2) Pl. 90, fig. 7.

CETACEANS. O03

Carnivorous Cetacea. Sir E. Home in a Paper published in the
Philosophical Transactions(1) descriptive of the teeth of the Platanista,
(Delphinus gangeticus), says of their structure that ‘‘the perfect
tooth has a tolerably sharp enamelled point, and the lower portion
has no enamel.” This part which forms the implanted base, is
thickly coated by cement ; and the pulp-cavity is obliterated. The
summits of the teeth are worn or broken off rather suddenly,
beyond the tenth in the upper, and beyond the eleventh tooth
in the lower jaw; these anterior teeth are worn by mutual attri-
tion, the upper ones on the posterior and inner part of the crown, the
lower ones on the anterior and outer sides.

143. Physeter—The outward and visible dentition of the great
Sperm-whale or Cachalot (Physeter macrocephalus) is confined to
the lower jaw, the symphysis of which is co-extensive with four
fifths of the entire dental series. This series in the male Cachalot
consists in each ramus of twenty-seven subincurved conical, or
ovoid teeth, according to their state of development and usage ;
the smallest teeth are at the two extremes of the series (Pl. 89,
fig. 1). In the young Cachalot they are conical and pointed ; usage
soon renders them obtuse, whilst progressive growth expands and
elongates the base into a fang, which then contracts, and is finally
solidified and terminated obtusely.

In the lower jaw of a female Cachalot in Dr. Buckland’s
Museum, the first and the last teeth have the pulp-cavity solidified ;
in the rest it is widely open, and the lower margin of the tooth
forming the base of the conical cavity is very sharp. From the
last or hindmost, the teeth gradually increase to the tenth, then
continue of equal size to the nineteenth, and again gradually diminish
to the twenty-second, counting forwards, that being the total number
in each ramus. My friend Mr. Broderip possesses a tooth of a
male Physeter, with the base open and uncontracted, which measures
nine inches and a half in length and nine inches in circumference and
weighs three pounds. (2)

The teeth are separated by intervals as broad as themselves. In

(1) 1818, p. 417.
(2) An ingenious whale-fisher has ca rved in his leisure moments the chief incidents of his

Ie SAS

354 CETACEANS.

respect of their mode of implantation in the jaw they offer in the
Cachalot a condition intermediate between that of the teeth of the
extinct cetaceous-like Ichthyosaurus and the piscivorous Delphinus ;
they are lodged in a wide and moderately deep groove, imperfectly
divided into sockets, the septa of which reach only about half-way from
the bottom of the groove. These sockets are both too wide and too
shallow to retain the teeth independently of the soft parts, so that
it commonly happens, when the dense semi-ligamentous gum dries
upon the bone and is stripped off in that state, that it brings away
with it the whole series of the teeth, like a row of wedges half-
driven through a strip of board. A firmer implantation would
seem unnecessary for teeth which have no opponents to strike
against, but which enter depressions in the opposite gum when
the mouth is closed. That gum, however, conceals a few persistent
specimens of the primitive foeta series; these are always much
smaller and more curved than the functional teeth of the lower
jaw. One of the upper concealed teeth, which was removed by
Mr. F. W. Bennett from the gum of a large female Cachalot, is figured
of the natural size in Pl. 89, figs. 3 and 4; the latter shows a
smooth surface at the convex side of the crown-end which seems
to have been produced by contact with the end of the opposite
large lower tooth. The fang is contracted and the pulp-cavity closed
in the rudimental upper teeth. In two mature Cachalots which
Mr. Bennet examined he found eight of these teeth on each side
of the upper jaw ; they had a very slight attachment to the bone.
There is a well-marked sexual distinction in the size of the
jaws of the Physeter macrocephalus, those of the mature female being
relatively shorter by full one third than in the male. There are

exciting and dangerous occupation on one side of this very fine tooth; the other side bears
the following inscription :—

“The Tooth of a Spermatic Whale,
That was caught by the Ship Adam’s Crew,
of Albemarle Point, and made 100 bls. of Oil.
in the Year 1817.”

Below this inscription are two excellent figures of the Cachalot, one spouting, the other dead
and marked for flensing.

CETACEANS. 355

usually twenty-three teeth in each ramus of the lower jaw of a
full-sized female Cachalot.

The first-formed extremity of the tooth in the young Cachalot
may be tipped with enamel, but as yet no authentic example has
come under my notice. In all that 1 have examined, the summits
of the crown have been more or less abraded, and the tooth has
consisted of a hollow cone of dentine coated by cement, and more
or less filled by the ossified pulp. Irregular masses of this fourth
substance have been found loose in the pulp-cavity of large teeth ;
one of those which I divided had no foreign substance as a nucleus.
The external cement is thickest at the junction of the crown and
base, which are not divided by a neck. The laminated appearance
of the dentine is very conspicuous in the surface of polished sections,
such as that exhibited in Pl. 89, fig. 2; the cause of that appearance
will be described in the next section ; in this figure a is the cement,
b the dentine and c the osseo-dentine or irregularly ossified pulp.

144. Structure—The dentine of the teeth of the Carnivorous
Cetacea is chiefly remarkable, as Retzius first observed, for the
number of calcigerous cells in it, arranged generally in planes
parallel to the superficies of the tooth and giving rise, in vertical
sections, to the appearance of concentric layers of dentine; it is
also characterised by the free communication of the dentinal tubes,
either immediately or by their branches with these cells, and through
their minute prolongations, with the radiated cells of the cement.
The early closure of the pulp-cavity in the teeth of the Cetacea
may relate to this free communication of the minute canals adapted
to Circulate the liquor sanguinis through the dental tissues, and to
maintain their vital connection with the rest of the organism. The
Cetacea in which I have studied the microscopic structure of the
teeth are the Delphinus Tursio, the Platanista and the Physeter
macrocephalus. The dentinal tubes from the upper part of the
pulp-cavity, in the Delphinus, ascend and curve, even with slight
convergence, towards the apex, then begin to diverge, and lower
down the tooth they pass out at right angles to the surface: thus far
their course is nearly parallel with one another, but in the fang they
assume more considerable and irregular curves. In the Cachalot

AA 2

356 CETACEANS.

the direction of the dentinal tubes at the extremity of the crown
of the tooth is represented in Pl. 89, a, fig. 1; here they sooner
begin to diverge in graceful curves from the vertical tubes which
pass to the apex. The diameter of the main tubes in the Cachalot
is mth of an inch, in the Platanista and Dolphin it is less. The
interspaces of clear substance equal from four to five of the diameters
of the tubes. The tubes divide dichotomously several times in their
course, and send off very conspicuous lateral ramuli; they terminate
at the periphery of the dentine in numerous and very minute irre-
cularly tortuous tubes which partly anastomose together, partly
are lost in the contiguous cells; the minutely undulating course,
the bifurcations, lateral branches, and terminal anastomoses of the
dentinal tubuli, and part of the peripheral layer of cells of the
dentine in the Cachalot’s tooth is represented in Pl. 89 A,
fig. 2, a, b. As the dentine of the cetaceous tooth approximates
to cement by the size and number of the calcigerous cells, so the
cement resembles the dentine in the number and parallelism of
the fine canals, which run from its outer surface towards the dentine,
in the interspaces of the cells. The parallel tubes differ: from those
-which traverse the cement of the Megatherium’s tooth in being too
minute to convey the red particles of the blood; they scarcely
surpass the origins of the dentinal tubes in diameter; the cement
is, however, sparingly traversed in the Cachalot by vascular or
medullary canals, about som th of an inch in diameter. In this
species the radiated or calcigerous cells of the cement are very
abundant and are arranged mostly in layers parallel with the surface,
having an irregularly angular outline; a few are roundish, but
most are of an oval form, about ;,;th of an inch in the short
diameter, and ,4,th of an inch in the long diameter, which is parallel
to the plane of the Jayer, (Pl. 89 A, fig. 2, c.) The canals which
radiate from the cells, ramify and anastomose with those from
contiguous cells and with the branches of the parallel cemental
tubes. In some parts of the cement, especially near the dentine,
the ramifications of the tubuli are so numerous and dense, along
lines parallel with the contour of the dentine, as to give the
appearance of white lines to the naked eye, and almost to in-

CETACEANS. 357

tercept the light even in very thin sections, when examined in the
microscope by transmitted light.

In the Cachalot I have usually found the cement thickest
at the middle of the tooth, as represented in Pl. 89, fig. 2, a.
The cement is thickest in the Dolphins at the end of the fang
of the old teeth, where it usually blocks up the pulp-cavity; this
is similarly closed in the expanded and compressed bases of the
teeth of the Gangetic Platanista.

The formation of the ordinary dentine ceases, in the teeth of
the Platanista, at the base of the crown, the entire expanded fang
being composed of tubular cement and a narrow central plate of
irregularly ossified pulp. A few medullary canals remain in this
vertical layer for the passage of the red blood into the tooth,
whence the supply of plasma is derived for the system of minuter
tubes in the dentine and cement; there are no other remains of
the pulp-cavity and the entire fang seems one solid mass of bone to
the naked eye.

The transition from the central osseo-dentine to the ~ cement
is imperceptible ; the former is distinguishable only by the grouping
of the concentric layers of calcigerous cells around detached vascular
centres and by the presence of the vascular canals. In the cement
these appear to be extremely few ; I saw but one in the whole extent
of a transverse section from the middle of the broad base of a
large posterior tooth of the Platanista.

The calcigerous cells of the cement are elliptical, with the
extremities pointed in most, in many produced; the long axis
being in the direction of the stratum; they chiefly indicate the
concentric disposition of the layers of cement which follow the
undulations of the section or surface of the fang. The cement is
characterised, as in other Cetacea, by the number and parallelism
of the minute tubuli, which traverse it, like the tubes of the dentine,
in a direction vertical to its planes or layers of growth: these tubes
are opake and calcigerous ; are generally grouped in fasciculi with
clearer interspaces in which the ordinary irregular reticulating rays
of the elliptic cells are best seen. In each of the large or primary
bundles the tubuli are grouped together in smaller fasciculi ; and

358 CETACEANS.

every tube has a minutely wavy course. The cemental tubuli are
rather smaller and give off more numerous lateral branches than
the dentinal tubuli; these branches everywhere anastomose ex-
tensively with the radiated tubes of the calcigerous cells. The
cemental tubes are rather less and the cells larger and more elongated
in the cement of the Platanista than in that of the Cachalot.

145. Development.—The primitive seat of development of the
tooth-matrix in the vascular membrane or gum, lining an open
groove on the alveolar border of the maxillary bones, is maintained
much longer in the Cetacea than in the higher organized Mammalia ;
a greater proportion of the tooth is, also, developed before the
matrix sinks into or is surrounded by a bony alveolus, and, with the
exception of the rudimental tusks in the Narwhal, is at no period
entirely inclosed in a bony cell; in which respect the Cetacea
offer an interesting analogy to true fishes. In a preparation of the
jaw of a young Porpoise(1), which I added to the Hunterian
Series of Comparative Anatomy in 1832, the half-formed posterior
teeth are shown imbedded in the gum only, the growth of the jaw not
having yet attained their level. Hunter, whom none of the pecu-
liarities of the Cetaceous organization had escaped, was aware of
this circumstance in their dental development; but, not having
carried his researches on this subject into the earlier periods of
foetal life in man and mammalia, when the aid of a microscope
is needed, he believed the phenomena of the papillary and open
follicular stages to be peculiar to the Cetacea ; thus he says,
‘The situation of the teeth, when first formed and their progress
afterwards, as far as I have been able to observe, is very different
in common from those of the quadruped. In the quadruped the
teeth are formed in the jaw, almost surrounded by the alveoli, and
rise in the jaw as they increase in length, the covering of the
alveoli being absorbed. The alveoli afterwards rise with the teeth
covering the whole fang ; but in this” (the whale-) “ tribe the teeth
appear to form in the gum upon the edge of the jaw, and they
either sink in the jaw as they lengthen, or the alveoli rise to inclose
them ; this last is most probable, since the depth of the jaw is

(1) No. 325 A.

|

y
4
:

|

ES —— ———

CETACEANS. 359

also increased(1).”” A deeper insight into the phenomena of the
growth of teeth in the class Mammalia proves this to be no ex-
ceptional case, but one of beautiful and harmonious concordance
with the general laws of organic development. The Cetacea per-
manently represent that early embryonic stage when no cervical
constriction divides the large head from the trunk, and when the
rudimental limbs offer no outward marks of joints or digits ; they
likewise retain a preponderating proportion of brain, and manifest
for a long period, and on a magnified scale, the first stages in the
development of the teeth.

When by the increasing depth of the jaw and the reciprocal
elongation of the tooth its base or fang becomes supported by bone,
a longer time than usual elapses before the alveolus is completed
by the development of transverse partitions between the outer and
inner walls of the open groove, and in the meanwhile the teeth are
lodged like those of the Ichthyosauri in a common and continuous
bony channel. In the Delphinide the teeth are successively developed
from before backwards, and pass through all their stages of growth
in that order of position, the anterior ones having their fangs and
alveoli completed, whilst the posterior teeth are lodged in a common
groove, or may be supported at the back part of the series by the
gum only. When the formation of the entire series of teeth
approaches its completion, the Dolphin resembles the Alligator in
having the anterior teeth lodged in sockets and the posterior teeth
in an alveolar groove. In the Cachalot the large middle teeth of
the series are the last to have the fang solidified.

The calcification of the dentinal pulp in the Dolphin proceeds
so that the pulp-cavity extends to near the apex of the tooth for
a longer period than in the simple teeth of quadrupeds; for a
certain time the teeth continue widely open at their base, and of
a simple conical form, as in the Crocodiles ; but, not being subject
to displacement by successors pushing them vertically from their
sockets, the calcification of the remaining pulp proceeds to close
the basal opening, and to form a fang which, with the exception

(1) On Whales, Philos. Trans. 1787, p. 398.—The abortive tusks of the Walrus are the
sole exceptions to this rule in the true Cetacea,

360 ' CETACEANS.

of the teeth of the Platanista, contracts in every direction and gives
the tooth the form of ‘“‘a double cone,’ as described by Hunter,
one point being exserted the other having the reverse direction and
inserted. The conversion of the last remnant of the pulp produces
the irregular bone-like deposit in the centre of the tooth, and closes
up the lower aperture, one or two minute canals for the nutrient
vessels being usually left. The mass of this fourth central substance
is greatest in the Cachalot, in which the process sometimes com-
mences at an independent centre and proceeds centrifugally as in
ordinary ossification, giving rise to the detached stalactitic masses
occasionally found loose in the unclosed pulp-cavity of large teeth.

146. Zeuglodon.(1) The remains of a gigantic animal, dis-
covered in a tertiary formation in the state of Louisiana, and
originally interpreted to belong to the class of Reptiles with the
name of Basilosaurus,(2) presented in portions of both upper and
lower jaws, teeth implanted by a double fang in deep sockets.
This anatomical peculiarity of a mammiferous species, though its
occurrence in the supposed Basilosaurus has been cited in deprecia-
tion of the value of the character of the two-fanged tooth in the
determination of fossil remains,(3) has had its importance established
by the result of a closer examination of the remains of the supposed
gigantic Reptile, which has proved their mammalian and cetaceous
character. (4) '

The crowns of the teeth in the largest portion of the upper
jaw which has hitherto been obtained are more or less perfect,
and are contiguous to each other; but they are placed rather
obliquely so that the inner surface of the anterior part of the crown
of the hinder tooth is on the same line as the outer surface of
the posterior part of the tooth next in front.

The crowns are sub-compressed and conical, with an obtuse apex :

(1) ZevyAn, a yoke, odove, a tooth, expressive of the peculiarity of certain teeth of this
genus resembling two teeth linked or yoked together.

(2) Dr. Harlan, Medical and Physical Researches, 1835, pp. 337, 369.

(3) Dr. Grant, in Thomson’s British Annual, 1838, p. 265.

(4) See my Paper on the Zeuglodon, Geological Transactions, IInd Series, vol. vi. p. 69.—
An almost entire skeleton which has been since brought to light has fully confirmed the
deductions therein recorded.

CETACEANS. 361

the antero-posterior diameter of the middle one is three inches, the
transverse diameter of the same is one inch two lines; the height
above the alveolar process two inches and a half, the total length of the
tooth about four inches and a half. Later and more perfect specimens
demonstrate the upper part of the crown to have had its anterior
and posterior margins obtusely serrated. The crown is contracted
from side to side in the middle of its base, so as to give its transverse
section somewhat of the hour-glass form (Pl. 90, fig. 2,); and
the opposite wide longitudinal grooves, which produce this form,
become deeper as the crown approaches the socket, and at length
meet, and divide the root of the tooth into two separate fangs.
The anterior teeth have a single root and are somewhat smaller
than the posterior ones ; the crown is sharp-pointed, conical, slightly
recurved and laterally compressed, the transverse section of the
base forming an ellipse. The length of the anterior teeth, including
the root is five or six inches, and the longest diameter nearly two
inches. In the last discovered remains of the Zeuglodon it is stated
that ‘the enamel of the teeth is retained(1). Besides the teeth
implanted in the jaws as above described, there is a fragment of
a tooth imbedded in the matrix containing the above pieces, and
consisting of the base of the crown and beginning of the fangs.
The crown of this tooth, which is equal in size to the posterior one
in place, and was probably a tooth of the same jaw, is partly worn
down and partly broken, but is so blended with the matrix, that
its exact form could not be determined. Of this tooth I had a
transverse section made near to the base of the crown, which
presents the figure represented in Pl. 90, fig. 1, and is that form
which we may reasonably suppose would be characteristic of the
old and worn-down hinder teeth of the Zeuglodon. The crown is
here divided into two irregular rounded portions or lobes, placed
one before the other and joined by a narrow neck or isthmus.
The anterior lobe is the broadest, its grinding surface is sub-ovate,
and placed obliquely: it measures one inch three lines in the long
diameter, one inch in the short diameter; the posterior lobe is
narrower, more regularly ovate, with the long diameter (which is

(1) Silliman’s American Journal, vol, xliv, p. 411.

362 CETACEANS.

one inch, three lines), placed parallel with the axis of the jaw.
The isthmus is about three lines in breadth, and two in length;
but the breadth diminishes while the length increases as the tooth
descends in the socket, until it finally disappears, and the two por-
tions take on the character of separate fangs.

The mode of completion of the teeth in this extinct Cetacean is
different from and conforms to a higher type than that of any of the
existing carnivorous genera. It is evident that the pulp which, from
the form and structure of the crown, was originally simple, becomes
afterwards divided into two parts, and that its calcification then
proceeds towards two distinct centres, which are each separately
surrounded by concentric striz of growth. The cavitas pulpi, which
is very small in the crown of the tooth, becomes contracted as the
fangs descend, and is almost obliterated near their extremities.

Of the fragment of the lower jaw of the Zeuglodon there is
a plaster cast in the Museum of the Geological Society. It contains
four teeth of which the two posterior are nearly contiguous; the
next is separated from them by an interval of an inch and a-half,
and the most anterior is placed at a distance of two inches from
the preceding. The anterior tooth is here of smaller size, and
apparently of more simple form than those behind, and it is
described by Dr. Harlan as a canine. This interesting fragment
is preserved in the Museum of the Philadelphian Academy: it
confirms the evidence afforded by the fragments of the upper jaw,
viz :—that the teeth in the Zeuglodon were of two kinds, the
anterior being smaller, more simple in form and more remote from
each other, than those behind.

The summits of the crown of the teeth of the Zeuglodon were
most probably sheathed with enamel; their base exhibits an in-
vestment of a thin layer of cement which augments in thickness
where it surrounds the fangs.

In afine transverse section taken from below the middle of
the exposed crown, I found this cement presenting the same micro-
scopic characters as that in the Cetacea; being traversed by nume-
rous transverse parallel tubuli. The Purkinjean cells are scattered
in some places irregularly, in others arranged in parallel rows ;

CETACEANS. 363

‘they are about ;;th of a line in diameter, generally of an oval
form, but with very irregular outlines; the tubes radiating from
the cells are wider than usual at their commencement, but soon
divide and sub-divide, forming rich reticulations on the interspaces
and communicating with the branches of parallel larger tubes.
These are placed, as in the Dugong, perpendicularly to the super-
ficies of the tooth, but are less regularly arranged than the
calcigerous tubes of the dentine, with which, however, they form
numerous continuations. There is a greater proportion of the
cement at the isthmus of the bilobed base of the crown than at its
circumference.

The dentine consists of fine calcigerous tubes, radiating in the
section examined from two centres, one in each lobe, without any
intermixture of medullary tubes. The breadth of the calcigerous
tubes in the Zeuglodon is equal to one-eighth of the diameter of
an ordinary human blood-disk or globule; they present a regular
undulating course, and like the calcigerous tubes of the Cetacea
exhibit plainly the primary dichotomous bifurcations, and the
subordinate lateral branches, which are given off at acute angles.
Upon the whole the microscopic characters of the texture of
the teeth of the Zeuglodon are strictly of a mammiferous character,
and its minor modifications agree with those in the Cetacea.

If the crowns of the teeth be at no period, which is unlikely,
tipped with enamel, yet the presence of fangs, proving their restricted
time of growth, shows the Zeuglodon not to have been a member of
the order Bruta, and the microscopic structure displays no vascular
dentine which enters so largely into the composition of the teeth
of the gigantic extinct Sloths. The outer cement is much thinner
in proportion to the dentine than in the Cachalot, and there is
a much less quantity of the irregularly ossified pulp in the centre:
the teeth, moreover, were developed in both the upper and lower jaws
of the Zeuglodon. ‘The two fangs distinguish in a marked degree
the Zeuglodon from any of the true Cetacea, among which, however,
we have seen that the Platanista makes an approach to this structure
in the hindmost teeth. The obtusely serrated margins of the crowns
also form a peculiar character in the present order, but which is

364 HALICORE.

present in the dentition of some species of seal.(1) In the so-called
herbivorous Cetacea, whose dentition will next be described, the
two-fanged structure is fully established in the Manatee, whilst in
the Dugong we shall find the near resemblance to the Zeuglodon
in the composition and the intimate structure of the molar teeth.
The vertebre of the Zeuglodon prove it, however, to be a true or carni-
vorous Cetacean ; its size is estimated at near seventy feet ; it accord-
ingly affords a very interesting addition to the history of the dental
system in the Cetaceous order, and approximates the typical group
by an additional step to the Dugongs and Manatees which are more
essentially related to the Pachyderms.

147. Halicore—Two marks of inferiority in the dental system of
the carnivorous Cetacea, which they have in common with many of the
order Bruta, viz :—uniformity of shape in the whole series of teeth, and
no succession and displacement by a second or permanent set, disap-
pear when we commence the examination of the dentition of those
apodal pachyderms which have been called the herbivorous Cetacea.
In the Dugong, (Halicore Dugong) for example, we find incisores dis-
tinguished by their configuration as well as position from the molares,
and the incisive tusk is deciduous, displaced vertically and succeeded
by a permanent tusk: both these characters are shown in Pl. 92.

Of the incisors of the Dugong only the superior ones project
from the gum in the male sex, and neither upper nor lower ones
are visible in the female(2). The superior incisors are two in number
in both sexes; in the male they are moderately long, subtriedral,
slightly and equally curved, of the same diameter from the base,
which is deeply excavated to the apex, which is obliquely bevelled
off to a sharp edge, like the scalpriform teeth of the Rodentia.
The form and extent of the persistent pulp-cavity of this tooth are
shewn in the figure of its longitudinal section, two-thirds the
natural size, in Pl. 93, fig. 4. Only the extremity of this tusk
projects from the jaw, at least seven-eighths of its extent being
lodged in the socket, the parieties of which are entire and the

(1) A fossil carnivorous Cetacean with serrated teeth has been indicated by M. Grateloup,
under the hybrid name of ‘ Squalodon,’? in Leonhard and Bronn, Jahrbuch fiir Minera-
logie, 1841, p. 830.

(2) Proceedings of the Zool. Society, 1838, p. 41.

“HALICORE. 365

exterior of the great intermaxillary bones presents an unbroken
surface. In the female Dugong the growth of the permanent incisive
tusks of the upper jaw is arrested before they cut the gum, and
they remain throughout life concealed in the intermaxillary bones ;
the tusk is solid, is about an inch shorter and less bent than that of the
male; it is also irregularly cylindrical, longitudinally indented, and it
gradually diminishes to an obtuse rugged point ; the base is suddenly
expanded, bent obliquely outwards and presents a shallow excavation.

It is remarkable that the external wall of the socket is
always deficient opposite the expanded and distorted base of the
tusk of the female, and this vacuity occurs even in the young
Dugong of this sex, when the base of the growing tusk is near
the lower extremity of the deflected portion of the intermaxillary
bone; but, as the base of the tooth ascends (or rather seems to
ascend in consequence of the elongation of the bone and the tooth),
the vacuity also ascends and becomes situated in the adult at the
upper part of the exterior of the deflected portion of the intermaxil-
lary bone.

The solid tusks of the female Dugong were supposed by Sir E.
Home to be the deciduous or ‘ milk tusks’ and to be the predecessors
of those of the male, which he held to be the permanent tusks,
and he suggested that the use of these projecting scalpriform tusks
was to detach sea-weeds—the food of the Dugong—from the rocks:
one can hardly, however, assign any important function in relation
to nutrition to parts which we now know to be limited to the
male sex. This hypothesis of Sir E. Home was first called in
question by Dr. Knox(1), who, having detected the supposed
deciduous tusks in the head of a nearly full-grown Dugong,
rejected the idea that they were deciduous teeth, observing that
no evidence had been given to prove the existence of deciduous
tusks at all in the Dugong(2). I have, however, discovered

(1) Edin. Phil. Trans. vol. xi, p. 389.

(2) “‘The milk-tusks of the Dugong have never been seen by any one; that is, I have
not heard of the existence of any preparation showing the germs of the milk or permanent
teeth, together or in succession.” Dr. Knox, loc. cit. p. 398.—Sir E. Home seems, however,

to have observed the true milk-tusks, without recognising their nature, in the young female.
Dugong whose dissection he describes in the Philosophical Transactions for 1820, for he

366 HALICORE.

in the recent specimens, which I have dissected at the Zoological
Society, the true deciduous incisors of the upper jaw co-existing
with the permanent ones. They are much smaller than the perma-
nent tusks of the female, and are loosely inserted by one extremity
in conical sockets immediately anterior to those of the permanent
tusks, adhering by their opposite ends to the tegumentary gum,
which presented no outward indication of their presence. When
this gum was stripped off the bone, the deciduous tusks came away
with it; and this may account for their absence in dried crania of
immature Dugongs, in which their alveoli are sufficiently conspicuous.
The deciduous tusk (Pl. 92, a) is two inches in length, slightly
curved, sub-cylindrical, tapering to both extremities, the fang-end
being the smallest; it was perforated, in the specimen figured, by
an aperture leading to the extremely contracted cavity in which the
remnant of the exhausted matrix was lodged.

True permanent incisors are not developed in the lower jaw
of the Dugong, those which are occasionally found there are
abortive remnants of the first or deciduous series, wees are not
destined at any time to rise above the gum.

The sloping truncated surface at the anterior part of the lower
jaw presents a coarse and loose reticulate structure, and is excavated
on each side by four wide irregular sockets. The first is the shal-
lowest, the third the deepest. Sir E. Home discovered a small tooth(1)
in this socket on each side of the jaw of a young female Dugong. I
have also found in the third socket of the left side of the jaw of a
full-grown male Dugong, a similar abortive incisor, or rather the
fang of an incisor with the crown irregularly eaten away by the
absorbent process. ‘This imperfect tooth measured 10$ lines in length
23 lines in breadth, and two lines in thickness ; it was slightly bent,
with a shallow impression along the middle of the convex side,
and with the fang abruptly diminishing to a point at its extre-
mity, which was quite closed ; its surface was rougher than in ordi-
nary teeth, and presented two or three small vascular perfora-

says, “It has two incisors in the upper jaw immediately before the two milk-tusks, these are
more advanced in the gum than the tusks and, therefore, would appear before them.” p. 315.
(1) Pl. 93, fig. 3. ;

HALICORE. 367

tions. The socket containing this functionless tooth showed the in-
fluence of the stimulus of its presence by its greater depth and
smoother parietes, as compared with the other sockets, in which
the corresponding teeth had been wholly absorbed. The crown-end
of the latent incisor adheres to the thick gum in which it is buried:
this adhesion Sir E. Home describes as ‘‘ gubernacula for the incisors
not yet completely formed :”’ he says, “ these incisors enable the young
Dugong to crop the tender plants, but are no longer wanted when
the animal grows up;” and adds, “this is a curious fact, and is
so far an approach to ruminating animals, whose incisors are only
in the lower jaw,” loc. cit. p. 154. But the solidity, the exhaustion
of the formative matrix, and commencing destruction of the lower
incisors in the sockets of the lower jaw, which in Sir EK. Home’s
specimen had not cut the gum, prove that they were never destined
to come to use ; and the same thing must be inferred of those which
had disappeared. :

The truly remarkable instances already recorded in the Cetacea
of the manifestation and subsequent disappearance of the germs
of teeth, lead us to view without surprise this indication of allegiance
to a more general type, by which alone the phenomena of latent teeth
seem explicable.

A comparison of the jaws of many specimens of different
sex and age has assured me of the accuracy of Cuvier’s con-
jecture, that not more than twenty molar teeth are developed in
the Dugong; viz., five on each side of both upper and lower
jaws : but these are never simultaneously in use, the first being shed
before the last has cut the gum. In the skull of a male Dugong
measuring fourteen inches in length, having the deciduous and per-
manent upper tusks in place, the first molar of the left side, lower
jaw, was shed, and the fang of those in place had suffered from
absorption : the second, third, and fourth molars were in use, but
the last presented its primitive obtuse tuberculate summit, and had
not penetrated the gum. In a female Dugong, whose skull was
fourteen inches eight lines long, and in which the deciduous tusks
were shed and the sockets obliterated, the last molars were in place,
and the conical summit worn down to the beginning of the transverse

368 HALICORE.

constriction : the first molar was lost in both jaws, and the second
was shed on the right of the upper jaw. A male Dugong, with a
skull fourteen inches and half in length, with the sockets of the
deciduous tusks obliterated, and the permanent tusks protruded to
the usual extent and worn by use, had the molar teeth reduced
to two on each side of both jaws, the grinding surface of the last
presenting the hour-glass shape, analogous to that of the worn
posterior grinders in the Zeuglodon ; but the fang of this tooth does
not become divided in the Dugong.

The period when the molar series can be viewed in its most
complete state in the Dugong is that represented in Pl. 92. These
teeth increase very regularly in size: the fang of the first c, and
of the second d, is soon completed and solidified ; that of the third
e is more elongated and retains its basal cavity longer ; but it
becomes at length contracted to a point, solidified, partially absorbed,
and the tooth is then shed: the crown presents an irregular oval
shape in transverse section. The fourth molar tooth, when fully
formed, resembles a slightly bent cylinder with a nearly smooth
outer surface ; the crown is flat, or slightly depressed at the centre.
The opposite extremity of the tooth is excavated by a regular conical
cavity, lodging the remains of the pulp (Pl. 93, fig. 5). With age,
however, the fang contracts, takes on an irregularly fluted and tuber-
culate surface, and is at last closed at its extremity. The matrix
of the last molar tooth expands as the crown is forming and mani-
fests a tendency to divide into two fangs; but, having acquired the
size and form exhibited in fig. 6, Pl. 93, the pulp is maintained in
a wide basal pulp-cavity to supply the waste of the crown according
to that pattern.

The molar teeth of the Dugong consist of a large body of
dentine, a small central part of osseo-dentine, and a thick external
investment of cement. The disposition of the calcigerous tubes, as
displayed in a transverse section near the base of the crown of the
first molar, is shown in the reduced figure of a highly magnified view
in Pl. 94. They have a sinuous course for a certain extent from
the pulp-cavity, in which they frequently bend in opposite instead
of parallel curves, and here and there form loops, convex towards

HALICORE. 369

the periphery of the tooth. Beyond this part the tubes proceed
with the usual gentle parallel primary curvatures to the periphery
of the dentine. The cells of the dentine become more conspicuous,
their boundaries being more opake, in the outer part of the dentine:
and the analogy which this structure presents to that of the dentine
in Platanista and Delphinus is interesting in connexion with the
outward cetaceous form of the Dugong ; the dichotomous divisions and
the minute lateral branches of the dentinal tubuli are not less con-
spicuous in the Dugong than in the carnivorous Cetacea. The clear
dentinal cells present an imbricated arrangement when viewed in
vertical section, and have a diameter of ;3,th of an inch.

The calcigerous cells of the cement closely resemble in their size,
form, and disposition those in the Platanista.

The communications between the tubes of the cement and
those of the dentine are clearly discernible in several parts of the
circumference of the latter substance, and the whole system of
tubes adapted to circulate the plasma of the blood through the
solid tissues of the tooth is, perhaps, in no animal better seen than
in the molar of the Dugong. The small portion of osseo-dentine
in the centre of the tooth is permeated by a few vascular canals,
which are derived from the remains of the pulp-cavity.

The calcigerous tubes of the incisive tusks radiate from the
subcentral pulp-fissure with a well-marked double curvature, at first
convex, then concave, towards the extremity of the tusk. In a
transverse section, taken within an inch of the extremity of the
tusk, the dentinal tubes are grouped in fasciculi where they are so
crowded as to intercept the light, with narrow intervals where the
tubuli are fewer, but the unusual density of the dentine depends on
the clear and compact earthly salts combined with the animal matter
in the dentinal cells.

In the female Dugong the whole of the extremity of the tusk
is surrounded by a thin coat of true enamel, which is covered by a
thinner stratum of cement.

In the male’s tusk the enamel (PI. 95, fig. 1, e), though it may origi-
nally have capped the extremity, as in the female’s, yet, in the body of
the tusk, it is laid only upon the anterior convex and on the lateral

B B

370 HALICORE.

surfaces, but not upon the posterior concave side of the tusk ; which
is thickly coated with cement (fig. 1, c). This side accordingly is
worn away obliquely when the tusk comes into use whilst the enamel
maintains a sharp chissel edge upon the anterior part of the pro-
truded end of the tusk.

The dentinal cells are of a subcircular form, with an average
diameter of ,,;th of an inch: they seem to form an unbroken net-
work, and in sections taken parallel with the course of the calcigerous
tubes present an imbricated character, as in Plate 95, fig. 1, the free
convex border of each compartment or cell being turned towards the
periphery of the tooth, near to which the cells diminish in size and in-
crease in number. ‘The interspaces or outlines of the cells (fig. 2, b)
are dark or clear, as the change of focus causes them to intercept
or transmit the rays of light reflected from the mirror of the micros-
cope. In a section taken transversely to the course of the tubes
and parallel with the plane of the layer of cells, the reticulated takes
the place of the imbricated character: the dark extremities of from
ten to fourteen calcigerous tubes whose diameter is jy th of an inch,
may be seen included in the area of a single dentinal cell, as in
Plate 95, fig. 2.

The presence of abortive teeth concealed in the sockets of the
deflected part of the lower jaw of the Dugong, offers an interesting
analogy with the rudimental dentition of the upper jaw in the
Cachalot and of both jaws in the foetal Whales: the arrested growth
and concealment of the upper tusks in the female Dugong, and
the persistent pulp-cavity and projection of the corresponding tusks
in the male, are equally interesting repetitions of the phenomena
manifested on a larger scale in the singular dental system of the
Narwhal ; but the habitual abrasion to which the tusks of the male
Dugong are subject prevents their closer resemblance to the male
Narwhal’s tusk in regard to length.

The simple implantation of the molar teeth and their compo-
sition are paralleled in the teeth of the Cachalot: their difference
of form, and the more complex shape of the hindmost tooth are

repetitions of characters which were present in the dentition of the
extinct Zeuglodon.

MANATUS. 371

The coexistence of incisive tusks with molar teeth, and the suc-
cessive displacement of the smaller and more simple anterior ones by
the advance of larger and more complex grinders into the field of
attrition, already, as it were, sketch out characteristics which become
normally established and attain their maximum in the Proboscidian
family (Elephants and Mastodons) of the Pachydermal order.

148. Manatus.—The transition from the cetaceous to the
pachydermal type of dentition is effected by the Manatee, (Manatus,
Scopoli, Cuv.) especially by the modification of the molar series.

The deflected anterior extremities of the intermaxillary bones
each support a single deciduous tusk in the young Manatee (Pl. 96,
fig. 1, a), but this is not succeeded by a permanent one in either
sex. No germs of incisors have been detected in the corresponding
part of the lower jaw. The molars of the American Manatee,
according to Daubenton and Cuvier(1), are thirty-six in number, nine
on each side of both jaws, but they are never simultaneously in
place and use. Their crowns in the upper jaw are square, and sup-
port two transverse ridges with tri-tuberculate summits, having also
an interior and posterior basal ridge: each tooth is implanted by
three diverging roots, one on the inner and two on the outer side ;
they increase in size, very gradually, from the foremost to the last.
The crowns of the anterior molars of the lower jaw resemble those
above, but the posterior ones have a larger posterior tubercle; they
are all implanted by two fangs, which enlarge as they descend
and bifurcate at the extremity, Pl. 96, fig. 3

In the Manatee of Senegal ten isla are developed on each
side of both jaws.

The molars consist of a body of dentine, a coronal covering
of enamel and a general investment of cement, very thin upon the
crown, and a little thicker upon the fangs.

All the grinding teeth of the Manatee belong to the true

(1) ie a Fossiles, 4to. vol. v. Pl. 1, p. 250. But in the “Régne Animal,” Cuvier
assigns 3-32. The number of teeth ordinarily in use at the same time is that represented
in Pl. 96, fig. 1, where the first molar has been shed and the two last have not come into
place : in the lower jaw seven molars are usually in use in the adult : fig. 2 shows the socket

of the first which has been shed and the crown of the last, the growth of which is still
incomplete.

aon 2

ove HALITHERIUM.

molar series, none of them being displaced by vertical successors :
in this respect it manifests, like the Dugong, a cetaceous character,
and the more strongly, inasmuch as the number of molars succes-
sively developed from before backwards is greater. The anterior
teeth are, however, displaced before the posterior ones are developed,
although they have no vertical successors, which circumstance is also
characteristic of the Elephant : the shape, the structure, and the mode
of implantation of the molars of the Manatee quite accord with the
pachydermal type, and herein more especially with the Dinotherium
and Tapir.

149. Halitherium(1).—An extinct herbivorous Cetacean has been
discovered in the miocene tertiary deposits which resembles the Dugong
in many parts of its skeleton, and in having permanent tusks in the
upper jaw: but which has complex, ridged, enamelled and many-rooted
molars as in the Manatee. The grinding surface of these teeth
offers a slight modification of form; the superior molars when first
_ found detached were referred by Cuvier to the Hippopotamus dubius :
the lower molars to the Hippopotamus medius, The latter, Pl. 97,
fig. 5, have three tuberculate ridges, the posterior one the smallest ;
when worn down the crown of the tooth presents three pairs of
rounded lobes, and its margins are deeply festooned. The upper
molars (fig. 4) are more square-shaped, and the third tubercular ridge
is almost obsolete.

In a second species of the same or a nearly allied genus
(Halitherium Brochii) the crowns of the teeth are more rounded,
and beset with tuberculated mammiliform eminences. The entire
series on the left upper jaw is shown in Pl. 97, fig. 1, and a similar
series of three molars in the left ramus of the lower jaw of the
Halitherium Cuvieri (fig. 2). The ultimate discovery and restoration
of a great part of the skeleton of one of the species (Hahtherium
Cuvieri), and the determination of the small number of molar teeth
in both species, have established a very interesting intermediate genus
between Halicore and Manatus, and, at the same time, one which
pushed its infinities much nearer than either of the existing genera
towards the pachydermal aquatic genus Hippopotamus.

(1) Metaxytherium, Christo], Cheirotherium, Bruno.

MARSUPIALS. Ore

CHAPTER V.
TEETH OF MARSUPIALIA.

150. Sarcophaga(1).—There is no toothless genus in the present
Order, unless the Monotremes or implacental Edentata be regarded as
modified Marsupials. Molar and incisor teeth are present in both jaws
in every true Marsupial species, but are relatively smaller in Tarsipes
and Myrmecobius, than, perhaps, in any other mammiferous quadruped ;
the canines are but feebly represented in many, as the Phalangers
and Petaurists, are wanting in the lower jaw in the Potoroos and
Koala, and in both jaws of the Kangaroos and Wombat. The
grinders, on the other hand, present their most complicated structure
in these last cited herbivorous genera.

The Dasyures and Thylacine offer the carnivorous type of the
dental system, but differ from the corresponding group of the
Placental Mammalia in having the molars of a more uniform and
simple structure, and the incisors in greater number ; which number,
however, is different in the different predaceous genera, as is ex-
pressed in the dental formule.

That of the Thylacinus, or Dogheaded Opossum (PI. 98, fig. 1),
is as follows :

Incisors —; canines = ; premolars ae ; molars So 2 AGs

= aa 3—3 4—4

The incisors are of equal length and regularly arranged in the
segment of a circle with an interspace in the middle of the series
of both jaws. The external incisor on each side is the strongest.
The laniary or canine teeth are long, strong, curved, and pointed,
like those of the dog tribe; the points of the lower canines are
received in hollows of the intermaxillary palatal plate when the
mouth is closed, and do not project, as in the carnivorous Placentals,
beyond the margins of the maxillary bones. The spurious molars (p)

(1) By this name I first defined the present Tribe of Marsupial Animals in order to avoid

the confusion that might have arisen from the use of the word ‘ Carnivora’ usually applied to the
corresponding group in the Placental series of Mammalia.— Zoological Transactions, vol. ii, p. 315.

374 MARSUPIALS.

in this as in all other Marsupials have two roots; their crown
presents a simple compressed conical form, with a posterior tubercle
which is most developed on the hindmost. The true molars (m) in
the upper jaw are unequally triangular, the last being much smaller
than the rest; the exterior part of the crown is raised into one
large pointed middle cusp and two lateral smaller cusps obscurely
developed ; a small strong obtuse cusp projects from the inner side
of the crown. ‘The molars of the lower jaw are compressed, tri-
cuspidate, the middle cusp being the longest, especially in the two
last molars, which resemble closely the sectorial teeth (dents car-
nassieres) of the dog and cat.
The dental formula of the genus Dasyurus, is :

42.

|

: 4—4 ° l= 2—2 4—4
Incisors —; canines — ; premolars -—; molars —:

2-2 ?

The eight incisors of the upper jaw are of the same length
and simple structure, and are arranged in a regular semicircle
without any medium interval. The six incisors of the lower jaw
are similarly arranged, but have thicker crowns than the upper
ones. The canines present the same or even a greater relative
development than in the Thylacine: in an extinct species of
Dasyurus(1) they had the same form and relative proportions as in
the Leopard. Thespurious molars (p) have a pointed compressed
triangular crown with a rudimental tubercle at the anterior and pos-
terior part of its base. The grinding surface of the true molars (m)
in the upper jaw is triangular ; the first presents four sharp cusps, the
second and third each five; the fourth, which is the smallest, only
three. In the lower jaw the last molar is nearly of equal size with
the penultimate one, and is bristled with four cusps, the external one
being the longest : the second and third molars have five cusps, three
on the inner and two on the outer side; the first molar has four cusps :
these are all sharply pointed in the young animal, in which the
posterior tubercle of the posterior molar in the lower jaw is divided
into two small cusps.

The carnivorous character of the above dentition is most strongly

(1) Dasyurus laniarius: the fossil remains of this species were discovered with those of
two gigantic species of Kangaroo in the bone-caves of Wellington Valley, by Major, now Lieut.-
Col. Sir Thomas L. Mitchell.

MARSUPIALS. ! 375

marked in the Ursine Dasyure or Devil of the Tasmanian Colonists,
the largest existing species of the genus, and the dentition of which
is represented in Pl. 98, fig. 2.

In some of the smaller species of the carnivorous group, as
the Phascogales, the canines lose their great relative size, and the
molar teeth present a surface more cuspidated than sectorial: there
is also an increased number of teeth, and as a consequence of
their equable development they have fewer and shorter interspaces.
Thus the Phascogale penicillata may be said, in Hunter’s words
to have “a mouth full of teeth,” and these are adapted for the
capture and mastication of insects and other small and low organized
animals.

The genus Phascogale (Pl. 98, fig. 3) is characterized by:
Incisors —; canines — ; premolars —; molars — : = 46.

In this dental formula may be discerned a step in the transition
from the Dasyures to the Opossums, not only in the increased
number of spurious molars, but also in the shape and proportions
of the incisors. In the upper jaw the two middle incisors are
- longer than the rest, and separated from them by a brief interval ;
they are more curved and project more forward. The three lateral
incisors diminish in size to the outermost. The middle incisors
of the lower jaw also exceed the lateral ones in size, and project
beyond them but not in the same degree, nor are they separated
from them by an interval, as in the upper jaw. The canines are
relatively smaller than in the Dasyures. The spurious molars present
a similar form, but the third in the lower jaw is smaller and simpler
than the two preceding ones. The true molars resemble those of
the Dasyures.

The general character of the dentition of these small predatory
Marsupials approximates to the insectivorous type, as will be exem-
plified in the Shrew, Hedgehog, &c. among the placental Mammalia,
and corresponds with the food and habits of the species which thus
lead from the predaceous or Sarcophagous to the Entomuphagous
tribes. |

The interval is further diminished by a lost Marsupial genus

376 MARSUPIALS.

which forms one of the ancient Mammalia that have rendered the
oolitic formations at Stonesfield so celebrated. This genus, which I
have called Phascolotherium, presents the same numerical dental
formula as in Phascogale, viz. :

z ?—? - p—? ?—? ?—?
Incisors pg OF 4-43 Canines — ; premolars aes molars =e

But the incisors and canines are separated by vacant interspaces,
and occupy a large proportional space in the dental series (Pl. 99,
fig. 4). The transition from the false to the true molars is more
gradual: the latter are more compressed than in the Opossum ;
they present a large middle cusp with a smaller one in front and
behind it, and with a basal ridge, which, projecting a little beyond
both the anterior and posterior smaller cusps, gives a quinque-cuspid
character to the crown of the tooth.

151. Entomophaga.—This is the most extensive and varied of
the primary groups of the Marsupial order. In the system of Cuvier,
the species of this tribe are united with those of the preceding to
form a single family characterized by the presence of long canines
and small incisors in both jaws: but in most of the Entomo-
phagous genera of the present classification, the canines present
a marked inferiority of development, and the species are conse-
quently unable to cope with animals of their own size and grade
of organization, but prey, for the most part, upon the smaller and
weaker classes of invertebrate animals. Their intestinal canal is com-
plicated by a moderately long and large cecum; and while, in the
Sarcophaga, the feet are constructed upon the plan of those of the
ordinary placental Digitigrades, they offer in the present tribe a
variety of well-marked modifications, according to which the species
may be arranged into gressorial, saltatory, and scansorial groups.

a. GRESSORIA.
Genus Amphitherium(1).—This, which includes the oldest known

Mammalian inhabitants of our planet, is founded upon fossil remains
of jaws and teeth discovered in the Oolite slate at Stonesfield in

(1) See Geological Transactions, 2nd Series, vol. vi, and History of British Fossil Mam-
‘alia, 8vo. 1844. ;

MARSUPIALS. of

Oxfordshire, of which the most instructive specimens are represented
in Pl. 99, figs. 1, 2, and 3. The first figure illustrates the dental
formula, which is remarkable for the number of the molars :

: raat : — —? —?
Incisors 53 canines —; premolars rare molars are

The incisors (7) are small, simple, and separated by intervals as in
the existing Marsupial genus Myrmecobius: the canine (J) appears by
its socket to have had a similar size and form. The shape of the
crowns of the premolars (p) and molars (m), is shown in the speci-
mens of the larger species (Amphitherium Broderipu, fig. 3) ; their
implantation of the jaw, each by two long slender roots, is demon-
strated by one of the specimens of the smaller species (Amphitherium
Prevosti, fig. 2).

Genus Myrmecobius.—The only known existing representative
of this family is the animal described by Mr. Waterhouse, which
constitutes the type of his genus Myrmecobius, and of which the
following is the remarkable dental formula, (Pl. 98, fig. 4) :

= 4—4 < 1—1 3—3 6—6
Incisors — ; canines —; premolars —; molars —: = 54.
3-3 1—1 3—3 6—6

From this formula it will be seen that the number of true and
false molars, eighteen in both jaws, exceeds that of any other known
existing Marsupial, and nearly approaches the peculiar dental formula
of the extinct Amphitherium, as also that which characterizes some of
the existing Armadillos. The resemblance to the genus Dasypus
is further carried out in the small size of the molar teeth, their
separation from each other by slight interspaces, and their im-
plantation in sockets, which are not formed upon a well-developed
alveolar ridge or process. The molars (m), however, present a distinct
multicuspidate structure, and both the true and false ones possess
two separate fangs, as in other Marsupials. The inferior molars
are directed obliquely inwards, and the whole dental series describes
a slight sigmeid curve. The false molars (p) present the usual com-
pressed triangular form with the apex slightly recurved; and the
base more or less obscurely notched before and behind. The canines
are very little longer than the false molars ; the incisors are minute,

378 MARSUPIALS.

slightly compressed and pointed ; they are separated from each other
and the canines by wide intervals. |

The Myrmecobians are insectivorous,(1) and shelter themselves
in the hollows of trees, frequenting most, it is said, those situations
where the Port-Jackson willow abounds. In the structure and propor-
tions of its hinder feet, Myrmecobius fasciatus resembles the Dasyurine
family ; and in the slightly developed canines, the smooth external
surface of the skull, the breadth between the zygomata, and the
absence of the interparietal ridges, as well as in its general external
form and bushy tail, it offers an especial approximation to the genus
Phascogale.

Bp. SALTATORIA.
Genus Perameles, (Bandicoots).

A 5—5 + 1—1 8—3 4—4
Incisors —; canines — ; premolars —; molars —: = 48.
3—3 1—1 Seay 4—4

This dental formula characterizes a number of Marsupials com-
monly known in Australia by the name of Bandicoots ; the hind
legs are longer and stronger than the fore, and exhibit in a well
marked manner the feeble and slender conditions of the second and
third digits counting from the inside, and the sudden increase in
length and strength of the fourth and fifth, or two outer toes,
which are chiefly subservient to locomotion. In consequence of this
inequality in length in their extremities, the mode of progression
in the Bandicoots is by bounds, the hind feet being moved together,
and alternately with the fore feet, as in the hare and rabbit, and
the crupper is raised higher than the fore-quarter. The teeth which
offer the greatest range of variation in the present genus are the
external or posterior incisors and the canines: the molars, also,
which originally are quinque-cuspidate, have their points worn away,
and present a smooth and oblique grinding surface in some species
sooner than in others.

The Bandicoots which approach nearest to the Myrmecobius
in the condition of the incisive and canine teeth, are the Perameles
Obesula and P. Gunnii. There is a slight interval between the first

(1) Mr. Gould informs me that they feed exclusively on ants.

MARSUPIALS. 379

and second incisor, and the outer or fifth incisor of the upper
jaw is separated from the rest by an interspace equal to twice its
own breadth, and moreover presents the triangular pointed canine-
like crown which characterizes all the incisors of Myrmecobuus ;
but the four anterior incisors are placed close together, and have
compressed, quadrate, true incisive crowns. From these incisors
the canine is very remote, the interspace being equally divided by
the fifth pointed incisor, which the canine very slightly exceeds in
size. In Per. nasuta the incisor presents the same general con-
dition, but the canines are relatively larger. In Per. Gunnu, the
outer incisor is closer to the others, which it also more nearly
resembles in form than in the preceding species ; but in Per. lagotis
(Pl. 98, fig. 5), it is not separated from the rest by a wider interval
than that which intervenes between the first and second incisor.
In both the preceding Bandicoots the canines are long and well de-
veloped, but the true molars (m) have the grinding surface worn down
flat in the full-grown specimens which I have had the opportunity of
examining.

Genus Cheropus.—The singular animal on which Mr. Ogilby
has founded this genus differs from the true Perameles in having
but two toes on each fore-foot ; its dental formula is :

Incisors —; canines = premolars —; molars —; = 46.

All the teeth are of small size; the upper incisors are conical,
the lower ones truncated and the hindmost is notched ; the canines
are conical, compressed, the upper one simple and remote from
the incisors, the lower one near the incisors and notched anteriorly ;
the spurious molars are separated by intervals, as in Myrmecobwis ;
they are tricuspid, except the first in the upper jaw which resembles
the canine. Each true molar consists of two triangular prisms,
those of the upper jaw being broader than those below, and with
their base turned outwards contrary to those in the lower jaw.
The genus would seem by its dentition to rank between Myrmecobius
and Perameles. Its digital characters are anomalous and unique
among the Marsupialia, but are evidently a degeneration from the
Saltatorial or Bandicoot type.

380 MARSUPIALS.

Y- SCANSORIA.

Genus Didelphys, (Opossums).—These Marsupials are now exclu-
sively confined to the American Continents, although the fossil
bones and teeth of a small species attest their former existence
in Europe contemporaneously with the Peleothere, Anoplothere, and
other extinct Pachyderms, whose remains characterize the Eocene
strata of the Paris basin.

The dental formula of the Genus Didelphys (Pl. 98, fig. 6) is:

Incisors —; canines — lars —— lars =; 22 ee
pa; canines —; premolars ——; molars —: = 50.

The Opossums resemble in their dentition the Bandicoots more
than the Dasyures; but they closely resemble the latter in the
tuberculous structure of the molars. The two middle incisors of
the upper jaw are more produced than the others, from which
they are also separated by a short interspace. The canines are
well developed ; the upper being always stronger than the lower.
The false molars are simply conical, but are more compressed
than in the Carnivorous Marsupials. The posterior false molar
is the largest in the upper jaw; the middle one is the largest
in the lower jaw: the anterior is the smallest in both jaws.
The true molars are beset with sharp cusps which wear down
into tubercles as the animal advances in age. The crowns of
the upper molars present a triangular horizontal section; the
base of the triangle is turned forward in the posterior molar; and
obliquely inwards and backwards in the rest. In the lower jaw the
true molars are narrower and of more equal size than in the upper
jaw: there are five tubercles on each, four placed in two transverse
pairs, the anterior being the highest, and a fifth forming the anterior
and internal angle of the tooth: the anterior and external angle seems
as if it were vertically cut off.

The canines still exhibit a superior development in both jaws
adapted for the destruction of living prey, but the molars have a con-
formation different from that which characterizes the true flesh-feeders,
and the Opossums consequently subsist on a mixed diet, or prey upon
the lower organized animals.

MARSUPIALS. 381

The smaller species of Didelphys, which are the most numerous,
fulfil in South America the office of the insectivorous Shrews of
the old Continent. The larger Opossums resemble in their habits,
as in their dentition, the carnivorous Dasyures, and prey upon the
smaller quadrupeds and birds, but they have a more omnivorous
diet, feeding on reptiles and insects and even fruit. One large
species, (Did. cancrivora) prowls about the sea-shore and lives, as
its name implies, on crabs and other crustaceous animals. Another
species, the Yapock, frequents the fresh waters, and preys almost
exclusively on fish. It has all the habits of an Otter ; and, in
consequence of the modifications of its feet, forms the type of the
sub-genus, Chironectes, Ill. Its dentition, however, does not differ
from that of the ordinary Opossums.

152. Carpophaga.—In this tribe the teeth, especially those at
the anterior part of the mouth, present considerable deviations
from the previously described formule; the chief of which is a
predominating size of the two anterior incisors, both in the up-
per and lower jaws. Hitherto, we have seen that the dentition
in every Marsupial genus has participated more or less in a car-
nivorous character ; henceforth it will manifest a tendency to the
Rodent type.

Genus Tarsipes——The dental formula of this genus has not been
accurately determined; the molars soon begin to fall, the small
canines are also deciduous, the two long, procumbent incisors of
the lower jaw remain the longest; besides these only one small
molar was present in each ramus, in the first specimen described.
The inferior incisors are opposed to six minute incisors above,
which are succeeded by a small canine and some small molars,
but these were reduced to a single tooth on each side in M. Gervais’
specimen. This was kindly submitted by that acute observer, the
founder of the present Genus, to my examination, and the trans-
parency of the dental tissue permitted the tubular structure to be
examined by the microscope with transmitted light: it resembled
in the degree of divergence of the tubuli calcigeri the dentine of the
Mole and other small Insectivora.

The Genus Tarsipes seems, in fact, to link the Myrmecobius

382 MARSUPIALS,

and Perameles of the preceding tribe with the small insectivorous
Phalangers.

Genus Phalangista-——The Phalangers are so called from the
phalanges of the second and third digits of the hinder extremity
being inclosed in a common sheath of integument and they have
the innermost digit modified to answer the purposes of a thumb.

In the skull of a Phalangista Cooku, of which the dental formula
is given in Pl. 100, fig. 2, there are both in the upper and lower
jaws four true molars on each side, each beset with four three-
sided pyramidal sharp-pointed cusps ; thus these essential and most
constant teeth correspond in number with those of the Opossum:
but in the upper jaw they differ in the absence of the internal
cusp, which gives a triangular figure to the grinding surface of the
molars in the Opossum; and the anterior single cusp is wanting
in the true molars of the lower jaw. Anterior to the upper
grinders in this Phalanger there are two premolars of similar shape
and proportions to those in the Opossum ; then a third premolar,
too small to be of much functional importance, separated also,
like the corresponding anterior premolar in the Opossum, by a
short interval from those behind.

The canine tooth but slightly exceeds in size the contiguous pre-
molar, and here consequently occurs the first great difference between
the Phalangers and Opossums; it is, however, but a difference in
degree of development ; and in the Ursine and other Phalangers, as
well as in the Petaurists (fig. 4), the corresponding tooth presents
more of the proportions and form of a true canine.

The incisors, which we have seen to be most variable in
number in the Carnivorous section, are here three instead. of five on
each side of the upper jaw; but their size, especially that of the first,
compensates for their fewness.

In the lower jaw there is the same number of molars and
functional premolars as in the Opossums ; the three very minute
and functionless teeth, which form part of the same continuous
series, represent the two small premolars and the canine of the
upper jaw; and anterior to these there is one very large pro-
cumbent incisor on each side. From this analysis it appears that

MARSUPIALS. 383

the difference in the number of teeth between the Phalanger and
the Opossum resolves itself into the former being minus certain
incisors in the upper and lower jaws, the great development of the
lower incisor producing an atrophy of all the rest.

The interspace between the functionally developed incisors and.
molars in both jaws always in the Phalangers contains teeth of
small size, of little apparent use, and variable not only in their
proportions but their number. The canines are constant in regard
to their presence, but variable in size; they are always very small
in the lower jaw.

With respect to the functional premolars -, separated by the
dotted line from the true molars in figs. | and 2, Pl. 100, these are
always in contact with the molars, and their crowns reach to the
same grinding level; sometimes a second premolar is similarly
developed in the upper jaw, as in the Phal. Cooku, (fig. 2) and
as in the great flying Phalanger (Petaurus Taguanoides), but it
is commonly absent, or replaced by a very minute tooth, shaped
like a canine: so that in the upper jaw, between the posterior or
functional premolar and the incisors, we may find three teeth, as
in Phal. Cook and Phal. cavifrons; or there may be only two
teeth, the first representing the canine, as in Phal. ursina and Phal.
vulpina (fig 1), and the species which M. Fr. Cuvier has selected as
the type of the dentition of the Genus.

In the lower jaw similar varieties occur in these small and
unimportant teeth; thus, there may be between the procumbent
incisors and the posterior premolar either three teeth, as in Phal.
Cookw and Phal. cavifrons ; or two, as in Phal. ursina, Phal. maculata,
Phal. chrysorrhoos; or finally one, as in Phal. vulpma and Phal.
fuliginosa. The most important modification is presented by the
little Phal. gliriforms of Bell (Pl. 100, fig. 3), which has only three
true molars (m) on each side of each jaw, and has the last and penul-
timate premolars below shaped like canines.

The Phalangers, being provided with hinder hands and pre-
hensile tails, are strictly arboreal animals, and have a close external
resemblance to the Opossums, by which name they are generally
known in Australia and the Islands of the Indian Archipelago, where

384 MARSUPIALS.

alone they have hitherto been found. They differ from the Opossums
chiefly in their dentition: and in accordance with this difference
their diet is more decidedly of a vegetable kind(1). The Australian
Phalangers feed chiefly on the tender buds and the leaves of
Eucalypti : but according to Temminck(2), the Indian Phalangers
are omnivorous, and combine insects with fruits and leaves. . Mr.
Ogilby(3) states that both ‘the Phalangers and Petaurists display
so decided a preference for live birds, as to make it probable that
these constitute a main portion of their food in a state of nature.”’
I find, however, that the intestinal canal, and especially the cecum,
offers so great an additional development in length, as, with the
corresponding predominance of the incisors, and atrophy of the
canines, to indicate clearly a natural and constant tendency in the
Phalangers to a vegetable diet.

Genus Petaurus.—There are many species of Marsupialia limited
to Australia and closely resembling, or identical with, the true
Phalangers in their dental characters and the structure of the
feet. I allude to the Petaurists or Flying Opossums: these, how-
ever, present an external character so easily recognizable, and in-
fluencing so materially the locomotive faculties, as to claim for it
more consideration than the modifications of the spurious molars
which we have just been considering in the Phalangers. A fold of
the skin is extended on each side of the body between the fore
and hind legs, which, when outstretched, forms a lateral wing
or parachute ; but which, when the legs are in the position for
ordinary support or progression, is drawn close to the side of the
animal by the elasticity of the subcutaneous cellular membrane,
and there forms a mere tegumentary ridge. These delicate and
beautiful Marsupials have been separated generically from the
Phalangers under the name of Petaurus: they further differ from
the Phalangers in wanting the prehensile character of the tail,
which, in some species of Petaurus, has a general clothing of long

(1) In the stomach and intestines of specimens sent to me in spirits from Australia,
I have never found any other alimentary substances but those of a vegetable nature.

(2) Monographies de Mammalogie, p. 3.

(3) Mag. Hist. Nat. 1837, p. 458.

MARSUPIALS. 385

and soft hairs, whilst in others, the hairs are arranged in two lateral
series.

In the Petaurists, however, there is as little constancy in the
exact formula of the dentition as among the Phalangers. The largest
species of Petaurus (Pet. Taguanoides), for example, is almost identical
in this respect with the Phalangista Cookii, which M. Fr. Cuvier
has therefore classed with the Petauri. Those teeth of Pet. Ta-
guanoides which are sufficiently developed and so equal in length
as to exercise the function of grinders, are six in number on each side
of the upper jaw, and five on each side of the lower jaw. The four
posterior molars in each row are true, and bear four pyramidal
cusps, excepting the last tooth in the upper jaw, which, as in
Ph. Cookti, has only three cusps. In the upper jaw the space
between the functional false molars and the incisors is occupied
by two simple rudimentary teeth, the anterior representing the
canine, but being relatively smaller than in Ph. Cookw; the crowns
of the two anterior incisors are relatively larger. In the lower jaw
the sloping alveolar surface between the functional molars and
large procumbent incisor is occupied, according to M. Fr. Cuvier, by
two rudimentary minute teeth; but I have not found any trace of
these in the two skulls of Pet. Tagua-noides examined by me.

In Petaurus sciureus and Petaurus flaviventer (Pl. 100, fig. 4) the
dentition more nearly resembles that of Phalangista vulpina. In
the upper jaw the functional molar series consists of five teeth on each
side ; the four hinder ones being, as in Pet. Taguanoides, true tuber-
culate molars, but diminishing more rapidly in size as they are placed
further back in the jaw; the hinder tooth has three tubercles, the rest
four : the apices seem to be naturally blunter than in Pet. Taguanoides.
Between the functional premolar and the incisors there are three
teeth, of which the representative of the canine is relatively larger than
in the Pet. Taguanoides ; the second false molar is also larger and has
two parts ; the first, which is functional in Pet. Taguanoides, is here
very small. The first incisor is also relatively larger and more pro-
duced. In the lower jaw the functional series of grinders consists
of the four true tuberculate molars only, of which the last is
relatively smaller, and the first of a more triangular form than in

6 ¢

386 MARSUPIALS,

Pet. Taguanoides. The space between the tuberculate molars and the

procumbent incisor is occupied by four small teeth, of which the one

immediately anterior to the molars is large, compressed, pointed, and

has two roots; the remaining three are rudimentary and have a

single fang ; the anterior of these corresponds to the one regarded as
a canine in the upper jaw.

. Among the species exhibiting this dental formula, viz.

Incisors ——: canines —: lars — l aes (7
ae 3 premolars —; molars —:— 40.

are Pet. sciureus, Pet. flaviventer, and Pet. macrurus.

The Pigmy Petaurist differs from the preceding and larger species,
in having the spurious molars large and sharp-pointed ; and the true
molars bristled each with four acute cusps. This tendency in the
dentition to the insectivorous character, with the modification of the
tail, induced M. Desmarest to separate the Pigmy Petaurist from the
rest of the species, and constitute a new sub-genus for its reception
under the name of Acrobates(1). Mr. Waterhouse first pointed out
that the Pigmy Petaurist had but three true molars on each side
of each jaw instead of four. (Pl. 100, fig. 5). There seems, therefore,
to be better reason for accepting this sub-generic section, although
we evidently perceive a transition to this condition in the small size
of the hinder or fourth molars in the Sciurine Petaurist and its
congeners.

The description of the dentition of the Pigmy Petaurist in the —
‘Régne Animal,’ besides the omission of this remarkable particular, 7

is not quite exact in other respects. In four adult specimens, two |

of which were males, and two females with young in the pouch, I ©
find the following dental formula to be constant :

. 3—3 ' 1—1 3—3 a—3
Incisors —; canines —; premolars —; molars —: = 36.
3-3 ea 28 3-3

The three quadricuspid grinders of the upper jaw are pre- ; |
ceded by three large premolars, each of which has two fangs, and ~
a compressed triangular sharp-pointed crown,’ slightly but progres- —

(1) Axpcc, summus, Baw, gradior, as frequenting the summits of trees.

MARSUPIALS. 387

sively increasing in length as they are placed forward. An inter-
space occurs between these and the canine, which is long, slender,
sharp-pointed, and recurved. The first incisor is longer than the
two behind, but is much shorter than the canine. In the lower
jaw the true molars are preceded by two functional false ones,
similar in size and shape to the three above the anterior false
molar, and the canine are represented by minute rudimental simple
teeth ; the single incisor is long and procumbent as in the other
Petaurists.

With these differences of dentition approaching more or less
to one or other of the modifications of the dentition in the group
of Phalangers, the Petaurists may nevertheless be readily discrimi-
nated from those Phalangers which they most resemble ; for example,
the Petaurus Taguanoides may be distinguished from the Phalangista
Cookui by the greater relative length in the latter of the nasal and
maxillary portion of the skull; while in most of the other species of
Petaurus, the facial part of the skull is relatively shorter than in the
Pet. Taguanoides.

Genus Phascolarctus.—The absence of anomalous or functionless
premolars and of inferior canines appears to be constant in the only
known species of this genus. The dental formula (Pl. 100, fig. 6.) in
three examples of the Koala (Phase. fuscus, Desm.) is

° 3—3 . 1—1 1—1 4—4
Incisors —; canines —; premolars —; molars —: = 30.
i 0—0 11 4—4

The true molars are larger in proportion than in the Pha-
langers: each is beset with four three-sided pyramids, the cusps of
which wear down in age, the outer series in the upper teeth
being the first to give way; those of the lower jaw are nar-
rower than those of the upper. The spurious molars are com-
pressed and terminate in a cutting edge; in those of the upper jaw
there is a small parallel ridge along the inner side of the base.
The canines slightly exceed in size the posterior incisors; they
terminate in an oblique cutting edge rather than a point; their
fang is closed at the extremity; they are situated as in the Pha-
langers close to the intermaxillary suture. The lateral incisors of

Gow

383 MARSUPIALS.

the upper jaw are small and obtuse; the two anterior or middle
incisors are twice as long, broad, and thick as the posterior incisors ;
they are conical, slightly curved, sub-compressed, bevelled off ob-
liquely to an anterior cutting edge, but differing essentially from
the dentes scalprarii of the Rodentia in being closed at the extremity
of the fang. The two incisors of the lower jaw resemble those
of the upper, but are larger and more compressed; they are also
formed by atemporary pulp, and its absorption is accompanied by
a closure of the aperture of the pulp-cavity, as in the upper incisors.
The Koala, therefore, in regard to the number, kind, and con-
formation of its teeth, closely resembles the Phalangers, with which
it also agrees in its long coecum and the general conformation of
its digestive organs. It has also the extremities similarly organised
for prehension; each is terminated by five digits; the hind feet
are provided with a large thumb, and have the two contiguous digits
enveloped in the same tegumentary fold; the anterior digits are
divided into two groups; the thumb and index being opposed to the
other three fingers. We have already noticed a structure approaching
to this in some of the small Phalangers. The Koala, however,
differs from the Phalangers and Petaurists in the extreme shortness
of its tail, and in its more compact and heavy general form. It is
only known to feed on the buds and leaves of the trees in which it
habitually resides.

153. Poephaga.—The present tribe includes the most strictly
vegetable feeders in the Marsupial order; all the species have a com-
plex sacculated stomach, and a long simple ccecum.

Genus Hypsiprymnus. Potoroos——Guided by the modifications of
the teeth we pass from the Koala to the Potoroos and Kangaroos
—animals of widely different general form. The Potoroos, however,
present absolutely the same dentition as does the Koala, some slight
modifications in the form of certain teeth excepted. The premolars
(Pl. 100, fig. 7, p) in their longitudinal extent, compressed form, and
cutting edge, would chiefly distinguish the dentition of the Potoroo ;
but the Koala evidently offers the transitional structure between the
Phalangers and Potoroos in the condition of these teeth, of which one

C2.)

KANGAROOS. 589

only is retained on each side of each jaw in the Potoroos as in the

Koala.
The dental formula of Hypsiprymnus, the generic name of the

Potoroos, is
aes 1 Nes Sy
Incisors saat canines aoe premolars ara WiOlats, wey: y— 30:

The two anterior incisors are longer and more curved, the
lateral incisors relatively smaller than in the Koala. The pulps
of the anterior incisors are persistent. The canines are larger than
in the Koala; they always project from the line of the intermaxillary
suture; and while the fang is lodged in the maxillary bone, the
crown projects almost wholly from the intermaxillary. In the large
Hypsiprymnus ursinus the canines are relatively smaller than in the
other Potoroos, a structure which indicates the transition from the
Potoroo to the Kangaroo genus. In the skeleton of this species in
the Leyden Museum, the canines have a longitudinal groove on the
outer side.

The characteristic form of the trenchant premolar has just been
alluded to: its maximum of development is attained in the arboreal
Potoroos of New Guinea (Hypsiprymnus ursinus and Hyps. dorcoce-
phalus), in the latter of which its antero-posterior éxtent nearly
equals that of the three succeeding molar teeth. In all the Potoroos
the trenchant spurious molar is indented, especially on the outer side
and in young teeth, by many small vertical grooves. ‘The true
molars each present four three-sided pyramidal cusps; but the
internal angles of the two opposite cusps are continued into each
other across the tooth, forming two angular or concave transverse
ridges. In the old animal these cusps and ridges disappear, and the
grinding surface is worn quite flat.

Genus Macropus. Kangaroos.—In the genus Macropus (fig. 8,)
the normal condition of the permanent teeth may be expressed as
follows :—

. 3—3 . 0-0 1—1 4—4
Incisors —; canines —; premolars —; molars —: = 28.
1—I 0—0 1—1 4—4

The main difference, as compared with Hypsiprimnus, lies in

390 MARSUPIALS,

the absence of the upper canines as functional teeth; the germs,
however, of these teeth are always to be found in the young
mammary foetus of the Macropus major, and I have seen them
present, but of very small size, and concealed by the gum, in the
adults of some small species of Kangaroos, as Macropus rufiventer,
Ogilby, and Macr. psilopus, Gould. This, however, is a rare ex-
ception ; while the constant presence and conspicuous size of the
canines will always serve to distinguish the Potoroo from the Kanga-
roo. But there are also other differences in the form and pro-
portions of certain teeth. The upper incisors of the Kangaroo have
their cutting margins in the same line, the anterior ones not being
produced beyond that line, as in the Potoroos: the third or
external incisor is also broader in the Kangaroos, and is grooved
and complicated by one or two folds of the enamel, continued from
the outer side of the tooth obliquely forward and inward. In most
species the anterior fold is represented by a simple groove: the
relative size of the outer incisor, the extent and position of the
posterior fold of enamel, and consequently the proportions of the
part of the tooth in front or behind it, vary more or less in every
species of Macropus: there are two folds of enamel near the anterior
part of the tooth in Macr. major, and the posterior portion is of
the greatest extent, and the entire crown of the tooth is relatively
broadest in this species. The middle incisor is here also compli-
cated by a posterior notch and an external groove. These modifica-
tions of the external incisors of the Kangaroos were first noticed by
M. Jourdan, and subgeneric distinctions, have been subsequently
based upon them.

M. Fr. Cuvier has proposed a binary division of the genus
Macropus, as here defined, founded on the absence of permanent
spurious molars, and a supposed difference in the mode of succession
of the true molars in certain species of Kangaroo, combined with
modifications of the muzzle or upper lip, and of the tail.

The dental formula which I have assigned to the genus Macropus
is restricted in its application by that Naturalist to some small
species of Kangaroo, grouped together under the term Halmaturus,

KANGAROOS. 391

originally applied by Illger to the Kangaroos generally(1). The other
Kangaroos are characterised by M. Fr. Cuvier under the generic term
Macropus, by the following dental formula :—
Incisors -; molars —: = 24,

The truth, however, is, that both the Halmaturi and Macropi of
M. Fr. Cuvier have their teeth developed in precisely the same
number and manner: they only differ in the length of time during
which certain of these teeth .are retained(2). In the great Kangaroo,
for example, the permanent premolar which succeeds the corre-
sponding deciduous one in the vertical direction, is pushed out of
place and shed by the time the last true molar has cut the. gum:
the first true molar is soon afterwards extruded; and I have
seen a skull of an old Macropus major in the Museum at Leyden,
in which the grinders were reduced to two on each side of each
jaw by this yielding of the anterior ones to the wis a tergo of their
successors.

Remains of gigantic Kangarcos have been discovered in the
same caves in Australia which contained the teeth and jaws of the
large extinct Dasyurus laniarius, and they probably formed the prey
of that species and of its contemporary the Thylacine, which has
equally become extinct in the continent of Australia.

Portions of the lower jaw and teeth of two of these extinct species
of Kangaroos are figured of the natural size in Plate 101. They are

(1) Prodromus Systematis Mammalium et Avium, 8vo. 1811. The dental character which
this excellent naturalist gives, accurately expresses the condition of the canine or laniary
teeth, “ Laniarii aut nulli, aut superiores 2 ambigui, minuti, in medio inter primores et
molares collocati,” p. 80; but there are never more than five molars in place on each side of
each jaw in the Kangaroo.

(2) M. Fr. Cuvier was aware that a deciduous false molar existed in the great
Kangaroo and other species of his subgenus Macropus, but he believed that it was peculiar
to an early period of life, and then existed only in a rudimental state, or “‘en germe;” and
that instead of being displaced and succeeded in the vertical direction by a permanent
false molar, as in the Hulmaturi, it was displaced by the true molars, which are de-
veloped from behind forwards. I have, however, detected the crown of the permanent
false molar in the jaws of the Macropus major in a concealed alveolus, and have observed
it completely formed and in place in an individual which had nearly attained its full size.—
See M. Fr. Cuvier’s account of the Halmaturus Thetis im the “ Histoire des Mammiféres”
folio.

392 MARSUPIALS.

principally distinguished from one another by the different size and
shape of the permanent premolar tooth, or that which displaces and
succeeds the deciduous molars in the vertical direction. This tooth
is displayed in its closed alveolus in both specimens(1) in which
situation, notwithstanding their superiority of size over the largest
existing Kangaroos, I was led to seek for it, by observing the sharp,
unworn summits of the crowns of the molar teeth and other signs of
immaturity in the fossil specimens.

The total number of molar teeth successively developed in the
great extinct Kangaroos is the same as in the existing species, viz:
two deciduous molars, one premolar, and four true molars: and the
permanent series of five appears to have been longer retained than in
the large existing species.

The true molars of the upper jaw in the Macropus Titan differ
from those of the Macr. Atlas and of all the existing species in having
a well-developed ridge at the back part of the base of the crown in
addition to the two principal transverse eminences and the anterior
basal ridge. In the Macropus Atlas the posterior basal talon of the
upper molars is much smaller, the crown broader, especially its
anterior division, and the ridge connecting the two transverse emi-
nences is shorter and more simple. In the lower jaw the molars
likewise present modifications characteristic of the two species: those
of the Macropus Titan have no posterior basal ridge, but the anterior
one is longer, as is also the ridge connecting the two chief transverse
eminences ; and the antero-posterior extent of the crown is greater in
proportion to its breadth, than in the Macropus Atlas: these charac-
ters are shown in the figure of the left penultimate molar, Pl. 101,
fig. 2; the greater thickness of the transverse ridges is. shown in
fre. 1.

In the lower molars of Macropus Atlas the posterior talon exists
in the same rudimental state as in the upper jaw, and the anterior
talon is shorter than in the Macr. Titan, as is shown in the right
penultimate molar in Pl. 10], fig. 4. The upper premolar of the

(1) They are now preserved in the Museum of the Geological Society, and were originally
described by me in Sir T, Mitchell’s “ Expeditions into Australia.” 8vo. 1838, Vol. ii, p. 361,
Pl. 29. f

WOMBAT. 393

Macr. Atlas has the same remarkable size as the lower one displayed
in fig. 3, Pl. 101; the anterior end of the crown is irregularly
notched, the inner surface uniform, and its margin entire ; the outer
surface is obliquely indented, forming a notched lobe posteriorly.
The outer surface of the lower premolar is more equally divided by
an oblique vertical fissure into two lobes. The relative size of this
tooth to the true molars is not only greater than in the Macropus
Titan, but also than in the existing true Kangaroos, (Macropus),
and clearly indicates a subgeneric type connecting these with the
Potoroos, (Hypsiprymnus). The large procumbent flattened inferior
incisor displays the characteristic form of that tooth in the existing
Kangaroos, and has the same strengthening ridge along its inner
size, fig. 5.

154. Rhizophaga.—In this tribe, the stomach is simple in out-
ward form, but complicated within by a large cardiac gland ; and the
coecum, which is short and wide, is furnished with a vermiform
appendage.

Genus Phascolomys, (Pl. 100, fig. 9.)—In its heavy shapeless
figure, large trunk, and short equably developed legs, the Wombat
offers as great a contrast to the Kangaroos as does the Koala, which
it most nearly resembles in its general outward form and want of
tail. But in the more important characters afforded by the teeth
and intestinal canal, the Wombat differs more from the Koala than
the latter does from either the Phalangers or Kangaroos.

The dental system presents the extreme degree of that degrada-
tion of the teeth, intermediate between the front incisors and true
molars, which we have been tracing from the Opossum to the
Kangaroos: not only have the functionless premolars and canines
now totally disappeared, but also the posterior incisors of the upper
jaw, which we have seen in the Potoroos to exhibit a feeble degree of
development as compared with the anterior pair; these in fact are
alone retained in the dentition of the Wombat, which is thus reduced
to that of the true Rodentia.

2 ; Gerny 1-1 ro
Incisors ~; canines >; premolars —; molars——: = 24.

The incisors, moreover, are true dentes scalprarw with persistent

394 MARSUPIALS,

pulps, but are, especially in the lower jaw, shorter and less curved
than in the placental Glires; they present a subtriedral figure, and
are traversed by a shallow groove on their mesial surfaces.

The spurious molars present no trace of that compressed struc-
ture which characterizes them in the Koala and Kangaroos, but have
a wide oval transverse section; those of the upper jaw being tra-
versed on the inner side with a slight longitudinal groove. The true
molars are double the size of the premolars: the superior ones are
also traversed by an internal longitudinal groove, but this is so deep
and wide that it divides the whole tooth into two prismatic portions,
with one of the angles directed inwards. The inferior molars are in
like manner divided into two triedral portions, but the intervening
groove is here external, and one of the facets of each prism is turned
inwards. All the grinders are curved, and describe about a quarter
of a circle: in the upper jaw the concavity of the curve is directed
outwards ; in the lower jaw, inwards. The false and the true
' molars like the incisors, have persistent pulps, and are consequently
devoid of true fangs, in which respect the Wombat differs from all
other Marsupials, and resembles the extinct Toxodon, the dentigerous
Bruta, and many of the herbivorous Rodentia. The incisors and the
first molar tooth are shed when the animal is young ; the latter is
superseded by the premolar tooth and the four true molar teeth
succeed each other from before backwards.

In all the placental Rodents, which have more than three molars
in each lateral series, the additional ones are placed at the anterior
part of the row, and are subject to displacement by a permanent
successor in the vertical direction, and consequently are essentially
‘‘ premolars,” or spurious molars ; the Wombat strikingly. manifests
its marsupial character in having four true molars on each side of
both jaws.

155. Diprotodon.—The ossiferous caves and the superficial allu-
vial or pleistocene deposits of Australia have yielded evidences
of still more gigantic and extraordinary forms of the Marsupialia
than the Titanic Kangaroos. Amongst the fossils from Wellington
valley, first brought to England by Sir Thomas, then Major Mitchell,
I recognised in a large incisive tusk such marks of similarity to

DIPROTODON. 395

that of the Wombat, as to encourage me to indicate the former
existence of a Marsupial apparently as large as a Rhinoceros, and
for which I proposed the provisional generic name of Diprotodon,(1)
ranking it with the Wombat in the family ‘ Phascolomyide.’(2) I have
subsequently obtained further evidence of the marsupial nature of
the Diprotodon in the inflected angle of the lower jaw, and of its
affinities to the Phascolomys in the form and extent of the symphysis
of the jaw, and in the peculiar construction of the os calcis ;(3) but
at the same time, with proof that these characters of Phascolomys
were combined with molar teeth shaped like those in the genus
Macropus. The great incisive tusk(4) extends forwards and slightly
upwards, its socket being close to the symphysis in each ramus
of the lower jaw; it is sub-compressed, measuring in one specimen,
an inch and a half in vertical diameter, and nearly one inch in
transverse diameter ; in another specimen the same admeasurements
giving respectively one inch two lines and ten lines. This incisor
has a partial covering of enamel, which is laid upon its lower and
a considerable part of its outer surfaces ; the whole being invested
by cement which is thickest on the upper and inner surfaces of the
dentine, where there is no enamel. In three specimens of this
tusk from the different localities of Wellington Valley, Moreton
Bay, and the district of Melbourne, the protruded extremity had
been broken off; but this may be concluded to have been chisel-shaped
from the partial deposition of the dense enamel.

The molar teeth(5) are five in number in each ramus of the
lower jaw, as in the Wombat; but they are implanted each by two
fangs, and the crown is divided into two principal transverse wedge-
shaped eminences, with an anterior and posterior basal ridge or
talon. The two principal eminences are slightly curved, with the
concavity directed forwards: they are higher and more compressed
from behind forwards than in the Kangaroo, Dinothere, Tapir, or
Manatee, which present the same type of molar tooth; and there

(1) Mitchell’s Expeditions into Australia, 1838, vol. 11, p. 362, Pl. 31, figs. 1 and 2.

(2) ‘ On the Classification of the Marsupialia,’ Zoological Transactions, vol. 11, p. 332.

(3) See the Catalogue of the Fossil Mammalia in the Museum of the Royal College of
Surgeons, pp. 294, 303.

(4) Pl. 90, fig. 1, 4. (5) Pl. 90, fig 1, mm.

396 MARSUPIALS.

is but a very feeble indication of that median basal connecting ridge
which forms so characteristic a feature of the molars of the Kangaroo.
The two fangs are long, and the surfaces which are turned towards
each other are impressed by a longitudinal groove, as in the Tapir,
Dinothere, and Kangaroo. The molars progressively increase in
size from the first to the last: in a jaw, the symphysis of which
anterior to the molar series is four inches, the narrow toothless
margin between the incisor and the first molar is eight inches in
extent: the series of five molars occupies an extent of from ten
to eleven inches. The enamel of both molars and incisors is re-
markable for its reticulate and punctate exterior, as if worm-eaten ;
the holes being seen at the fractured margins of the enamel to lead
to smooth pits in that substance.

156. Nototherium.—A second genus of large Pachydermoid
Marsupial has molar teeth resembling in form, mode of implantation,
and relative size, those of the preceding genus, Diprotodon, but
apparently four in number on each side of the lower jaw, and
their crowns covered with smooth enamel ;(1). the Nototherium is
more especially distinguished by the total absence of incisors in the
lower jaw, and the much smaller size of the symphysis.

Like the Diprotodon the Notothere had no canines, and being
also devoid of defensive tusks, I have called one species Nototherium
imerme. In aramus of the lower jaw of this species, twelve inches
in length, the series of four molars, which commences within two
inches of the anterior end of the jaw is six inches in extent ;
the antero-posterior diameter of the last tooth is one inch nine
lines, and is situated internal to the base of the coronoid process.
In a rather larger species the Nototherium Mitchell, the last molar
tooth is in advance of the base of the coronoid.

157. Structure.—The dentine, enamel, and cement of the teeth
of the Marsupial animals present the usual microscopic characters
of these tissues in the Mammalia.

The dentinal tubuli of the small molars of the Phascogale,
Myrmecobius, and Petaurus have very short trunks, and are rela-
tively larger and fewer in number as compared with the size of

(1) Pl. 91, fig. 4.

MARSUPIALS., 397

the teeth than in the Thylacine, the Wombat or the Kangaroo:
the trunks resolve themselves into penicilli of minute radiating
branches, which interlace and form a rich net-work at the boundary
line between the dentine and enamel.

In the large lower incisors of the Kangaroo (Pl. 102, Fig. 1,
dd.) the dentine is very compact, and the tubuli extremely
minute : their diameter is th of an inch, and their intervals equal
three of these diameters. The tubes radiate with elegant secondary
undulations, from the central pulp-cavity to the periphery. The dicho-
tomous divisions of the tubuli are sparing until they approach their
terminations: the extremity of one of the tubes magnified 600
diameters, is represented at Pl. 102, fig. 2: the lateral branches
are unusually minute, numerous, and short, giving the tubuli.
a pilose appearance when brought into view by an adequate
magnifying power. The terminal branches of the tubuli open
into minute irregular cells, forming a thin boundary layer between
the dentine and enamel. The fibres of the enamel which in-
vest the crown of the large lower incisor, are likewise un-
usually minute ; viewed in transverse section, as in Pl. 102, e e, they
describe an abrupt curve at their commencement, and then proceed
in a nearly straight course to the outer surface; but at the trenchant
margins of the tooth their general course is curved, and they decus-
sate one another as represented in the figure; some of the enamel
lines at this part seem as fine as the dentinal tubes. An extremely
thin layer of cement may be traced over the basal half of the
enamelled crown; it is soon worn away from the remainder; the
cement increases in thickness where it invests the fang.

The dentine of the scalpriform incisor of the Wombat is charac-
terized by a few short medullary canals continued from the long
conical vascular pulp. The dentinal tubuli are rather larger than
in the procumbent incisor of the Kangaroo, but are separated by
still narrower interspaces; they dichotomize very sparingly, but
send off many fine branches from the side of the primary curve
of the tube which is directed towards the crown of the incisor.
The boundary layer of cells, in which the terminal branches of
the tubuli open, is thicker than in the Kangaroo. The layer of

398 RODENTS.

enamel is situated upon the anterior and outer part of the incisor,
forming, by the abrasion of the dentine, the cutting edge of the
tooth ; its fibres are larger than in the Kangaroo, and their transverse
striz more plainly visible, the enamel is covered by a layer of
cement continued from the thicker layer upon the back part of
the tooth.

The tubular structure of the dentine of the molars is figured
in Pl. 103, fig. 2, dd, as seen in part of a section near the base
of the crown; in this is likewise shown the lower boundary of the
investment of enamel, (e e,) and the continuation of the coronal
layer of cement, (c c,) from the fang, upon the enamel of the crown.
There are no parallel tubuli nor vascular canals in the cement ;
but the radiating tubuli from the calcigerous cells are very numerous,
and form rich plexuses in the interspaces. The outer part of the
cement is dense and devoid of radiated cells.

C Et APT Te Ta NL
TEETH OF RODENTIA. |

158.—WeE have traced in the Marsupialia a progressive diminu-
tion in the number and size of those teeth which intervene between
the anterior incisors and the true molars, until the dentition assumed
in both jaws the condition expressed by the formula of the genus
Phascolomys, p. 393. This condition of one large curved incisor
on each side, separated by a wide interval from a short series
of molars, characterizes the whole order of Rodents: the rule
being proved by the single exceptional family (Leporide) of Hares,
Rabbits, and Pikas, or tail-less Hares of Siberia, which retain a
second minute incisor behind each of the normal ‘dentes scal-
praril’ of the upper jaw.

The incisors(1) are always regularly curved, the upper ones des-

(1) Pl, 104, figs. 2& 3,7,

RODENTS. 399

cribing a larger segment of a smaller circle, the lower ones a smaller
segment of a larger circle; these are the longest incisors and usually
have their alveoli extended below or on the inner side of those of the
molars to the back part of the lower jaw.(1) Like the molars of the
Megatherium and other teeth of unlimited growth, the implanted part
of the long and large incisors retains the form and size of the exposed
part or crown, to the widely open base, which contains a long conical
persistent dentinal pulp, and is surrounded by the capsule in a
progressive state of ossification as it approaches the crown, an
enamel pulp being attached to the inner side of that part of the
capsule which covers the convex surface of the curved incisor.
The matrix is here noticed in connexion with the tooth, because
it is always found in full development and activity, to the time
of the Rodent’s death. The calcification of the dentinal pulp,
the deposition of the earthy salts in the cells of the enamel
pulp, and the ossification of the capsule, proceed contempora-
neously ; fresh materials being added to the base of the vascular
matrix as its several constituents are progressively converted into
the dental tissues in the more advanced part of the socket. The
tooth thence projecting consists of a body of compact dentine,
sometimes with a few short medullary canals continued into it
from the persistent pulp-cavity, with a plate of enamel laid upon
its anterior surface, and a general investment of cement, which is
very thin upon the enamel, but less thin, in some Rodents, upon
the posterior and lateral parts of the incisor. The substances of
the incisor diminish in hardness from the front to the back part
of the tooth; the enamel consisting of two layers, of which the
anterior and external is denser than the posterior layer, and the pos-
terior half of the dentine being by a modified number and arrange-
ment of the calcigerous tubes less dense than the anterior half.(2)
The abrasion resulting from the reciprocal action of the upper
and lower incisors produces accordingly an oblique surface, sloping
from a sharp anterior margin formed by the dense enamel, like that
which slopes from the sharp edge formed by the plate of hard
(1) Pl. 104, fig. 1, 4. (2) Pl. 106.

400 RODENTS.

steel laid upon the back of a chisel; whence the name, ‘ dentes
scalprarii,’ given to the incisors of the Rodentia.(1)

The varieties to which these incisors are subject in the different
Rodents are limited to their proportional size, and to the colour
and sculpturing of the anterior surface. Thus in the Guinea-pig,
Jerboa, and Squirrel, the breadth of the incisors is not half so
great as that of the molars, whilst in the Coypu they are as broad,
and in the Cape Mole-rats, (Bathyergus and Orycteromys), broader
than the molars.

In the Coypu, Beaver, Agouti, and some other Rodents, the
enamelled surface of the incisors is of a bright orange or reddish
brown colour. In some genera of Rodents as Orycteromys, Otomys,
Meriones, Gerbilla, Hydrocherus, Lepus and Lagomys, the anterior
surface of the upper incisors is indented by a deep longitudinal
groove. This character seems not to influence the food or habits
of the species; it is often present in one genus and absent in
another of the same natural family: in most Rodents the anterior
enamelled surface of the scalpriform teeth is smooth and uniform.

The molar teeth are always few in number, obliquely implanted
and obliquely abraded, the lateral series converging anteriorly in
both jaws; but they present a striking contrast to the incisors
in the range of their varieties, which are so numerous that they typify
almost all the modifications of form and structure which are met
with in the molar teeth of the omnivorous and herbivorous genera
of other orders of Mammalia.

In some Rodents the molar teeth are rootless, like those of the
Wombat, the 'Toxodon and Elasmothere; some have short roots
tardily developed, like the molars of the Horse and Elephant; and
some soon acquire roots of the ordinary proportional length. (2)

(1) John Hunter grouped together the quadrupeds composing this order under the name
of ‘ Scalpris-dentata ;? but the large curved, chisel-shaped incisors, though common to all the
Rodents, are not peculiar to that order: we have seen them in the Wombat amongst the
Marsupials ; they are present in the Cheiromys amongst the Lemurine group of Quadrumana,
and in the Toxodon amongst the Pachyderms ; some of the Shrews have the anterior incisors
restricted in number and developed in bulk, almost to their proportions in the Rodentia.

(2) Prof. Erdl has given a tabular arrangement of the molars of the Rodentia, according

RODENTS. 401

The Rodents which have rootless molars, comprise the families
of the Hares,(1) Chinchillas,(2) Chili-rats,(3) and Cavies(4), most of
the Voles,(5) the Houtias (Capromys), and the Cape Jerboa (Helamys).

The genera which have molars with short or incomplete roots,
developed late, are Castor (Beaver), Hystrix (Porcupine) ,(6) Calogenys
(Spotted Cavy), Dasyprocta (Agouti), Spalax (Blind-rat), Myopota-
mus (Coypu), Euryotis, Ascomys, and Aplodontia.

The families of the Squirrels, Dormice, Rats, and Jerboas have
rooted molars.

The differences in the mode of implantation of the molar teeth
relate to differences of diet. The Rodents which subsist on mixed
food and which betray a tendency to carnivorous habits, as the true
Rats, or which subsist on the softer and more nutritious vegetable
substances, as the oily kernels of nuts, suffer less rapid abrasion
of the molar teeth; a minor depth of the crown is therefore needed
to perform the office of mastication during the brief period of
existence allotted to these active little Mammals; and, as the eco-
nomy of nature is manifested in the smallest particulars as well
as in her grandest operations, no more dental substance is deve-
loped after the crown is formed, than is requisite for the firm
implantation of the tooth in the jaw. 1

Rodents that exclusively subsist on vegetable substances, espe-
cially the coarser and less nutritious kinds, as herbage, foliage, the
bark and wood of trees, wear away more rapidly the grinding surface
of the molar teeth ; the crowns are therefore larger, and their growth
continues by a reproduction of the formative matrix at their base
in proportion as its calcified constituents, forming the exposed
working part of the tooth, are worn away. So long as this repro-
ductive force is active the molar tooth is implanted, like the incisor,

to their modes of implantation, in his excellent Paper on the Teeth of that order, in the Munich
Transactions, ‘Abhandlungen der K. Bayerischen Akademie der Wissenschaften,’ Bd. 111.
1841, p. 529.

(1) Lepus, Lagomys.

(2) Lagostomus, Lagotis, Chinchilla.

(3) Abrocoma, Octodon, Schizodon, Poephagomys, Ctenomys.

(4) Hydrocherus, Dolichotis, (Pl. 104, figs. 2 & 3), Kerodon, Cavia.

(5) Lemmus, Arvicola, except A. riparia.

(6) Pl. 104, fig. 1.

402 RODENTS.

by a long undivided continuation of the crown ; when the force begins
to be exhausted the matrix is simplified by the suppression of the
enamel organ, and the dentinal pulp continues to be reproduced only at
certain points of the base of the crown, which, by their elongation,
constitute the fangs. The Beaver and other Rodents in the second
category of the order, according to the implantation of the molar teeth,
exemplify the above condition ; but in the Capybara, Dolichotis, (Pl.
104, figs. 2 & 3), and other Rodents with rootless molars, the re-
production of the molar like that of the incisor teeth, appears to
continue throughout the animal’s existence. The rootless and per-
petually growing molars are always more or less curved; they derive
from this form the same advantage as the incisors, in the relief of
the delicate tissues of the active vascular matrix from the effects
of the pressure which would otherwise have been transmitted more
directly from the grinding surface.

The complexity of the structure of the crown of the molar teeth,
and the quantity of enamel and cement interblended with the dentine,
are greatest in the rootless molars of the strictly herbivorous Rodents.
The crowns of the rooted molars of the omnivorous Rats and
Mice are almost as simple,as the tuberculate molars of the Bear
or of the Human Subject, which they appear to typify. They
are at first tuberculate, as shown in Pl. 105, fig. 9; when the
summits of the tubercles are worn off, the inequality of the grinding
surface is for a time maintained by the deeper transverse folds of
enamel, the margins of which are separated by alternate valleys
of dentine and cement, as shown in Pl. 105, fig. 10, 3. a; but
these folds sinking only to a slight depth are in time obliterated,
and the grinding surface is reduced to a smooth field of dentine
with a simple border of enamel, as shown. in the upper tooth of
figure 10, 3. A. similar change in the grinding surface, consequent.
on. age and use, is shown in the molars of the Souslik, or Ground
Squirrel, Pl. 105, fig. 3, 6, and in those of the Gerbille, fig. 8, and
is common to all that possess roots.

Examples of various forms assumed by the inflected. folds
of enamel in the molars of the Rodentia are given from the works
of the Cuviers in Pl. 105. It will be seen that these folds have

RODENTS. 403

a general tendency to a transverse direction across the crown of the
tooth. Baron Cuvier has pointed out the concomitant modification
of the shape of the joint of the lower jaw, which almost restricts
it to horizontal movements, to and fro, in the direction of the
axis of the head, during the act of mastication. When the folds
of enamel dip in vertically from the summit to a greater or less
depth into the substance of the crown of the tooth, as in those
molars which have roots, the configuration of the grinding surface
varies with the degree of abrasion, of which examples have already
been cited; but in the rootless molars where the folds of enamel
extend inwards from the entire length of the sides of the tooth, the
characteristic configuration of the grinding surface is maintained
without variation, as in the Guinea-pig, (fig. 16), the Capybara,
(fig. 17), and the Patagonian Cavy, (Pl. 104, figs. 2 & 3).

The whole exterior of the molar teeth of the Rodentia is
covered by cement, and the external interspaces of the enamel-
folds are filled with the same substance. In the Chinchillide and
the Capybara where the folds of enamel extend quite across the
body of the tooth, and insulate as many plates of dentine, these
detached portions are held together by the cement; such folds of
enamel are usually parallel, as in the large posterior lower molar
of the Capybara, which in shape and structure offers a very close
and interesting resemblance to the molars of the Asiatic Elephant.

The partial folds and islands of enamel in the molars of the
Porcupine (fig. 13), and Agouti, (fig. 14), typify the structure of
the teeth of the Rhinoceros: the opposite lateral inflections of enamel
in the molars of the Gerbille, (fig. 8), and Cape Mole-rat, (fig. 11),
represent the structure of the molars of the Hippopotamus: the
double crescentic folds in the Jerboa (fig. 7), sketch out, as it were,
the characteristic structure of the molars of the Anoplothere and
Ruminantia.

Although, as has been shown, the molar teeth in many Rodents
are rootless and of unlimited growth as in the Edentata, in none
is enamel absent or vascular dentine, as the chief constituent of
the tooth, present: these essential differences characterise the molars
‘of those Rodents which by use have their grinding surface reduced

Dvd 2

404 RODENTS.

to a simple depression bounded by a raised circular margin, as in the
great Cape-mole: that margin being formed by true enamel, but in
the Sloths by hard dentine.

159. Structure—The proportions and relative positions of the den-
tine, enamel and cement which enter into the composition of the scal-
priform incisors have already been mentioned; I have observed the
modifications of the enamel, alluded to at p. 399, in the Rat, the Water-
Vole, the Beaver, the Agouti and the Hare, and believe it to be
common to the Rodentia: the difference in the tubular structure of
the anterior and posterior halves of the dentine is more conspicuous
in the Hare, Vole and Beaver than in the Agouti.

In the Agouti a longitudinal slice from the middle of the upper
incisor shows the conical pulp-cavity extending through one half of
the tooth, and a linear tract continued from its apex to the gnawing
surface of the tooth: from this line, the end of which, in most
Rodents, is perceptible on that surface, the calcigerous tubes diverge ;
‘those passing to the anterior margin of the tooth describe a sigmoid
curve, first convex towards the cutting end, which may be called
the crown, then concave: the tubes which proceed to the opposite
margin describe a stronger and shorter curve convex towards the
crown, and then proceed straighter and more transversely to their
termination : the origin of these tubes is obscured by the cut ends
of those which were proceeding towards the sides of the tooth:
and which are chiefly formed by the posterior half of the pulp. The
tubuli are js;;th of an inch in diameter and are very closely arranged,
being separated by intervals of little more than their own diameter :
so that the dentine is unusually firm and compact. The exterior
clear and denser enamel forms about one-third the thickness of that
layer and is coated by thin and well-defined brown-coloured cement.

The fibres composing the inner and more opake part of the
enamel proceed obliquely, but almost transversely across that sub-
stance, with a gentle curve in the opposite direction to the last curve
of the contiguous dentinal tubes ; viz. with the convexity towards the
crown : the fibres of the peripheral layer of the enamel make a slight
bend towards the crown: these enamel-fibres are as thick as two
of the dentinal tubes with their interspace: their ends are lost

RODENTS. 405

in the clear peripheral substance to which the distinct apparently
structureless brown layer of cement is attached, and to which the
colour of the convex surface of the incisor is due.

In a transverse section of the incisor of the Water Vole (Arvicola
amphibia), the thin colourless and apparently structureless layer of
cement covering the concave surface of the tooth is distinctly
traceable from the dentine at the sides of the tooth upon the ante-
rior plate of enamel; and seems to be intimately blended with its
exterior surface. The layer of cement becomes thinner at the
margin of the enamel, where it is continued from the dentine upon
that part, but soon increases in thickness, acquiring the bright
brown tint, and separated by a well-defined line from the outer clear
layer of enamel.

The delicate transverse or concentric lines of this substance are
seen more distinctly in the transverse than in the longitudinal sections
of the incisor. The faint outlines of the dentinal cells, and the
traces of the concentric layers of the clear substance of the dentine
are likewise best seen in the transverse section of the incisor. No
vascular canals are continued from the pulp-cavity into the dentine of
the incisors of the Water-Vole or Agouti.

In the incisors of the Hare and Rabbit the pulp-cavity terminates
in a transversely extended fissure: the dentinal tubes proceeding to
the anterior enamelled surface after forming the curve, convex towards
the crown, proceed in a straighter transverse course to the enamelled
surface than in the Agouti. The tubes which pass to the opposite
or posterior surface of the tooth are less numerous, less parallel and
less closely packed together : they send out more and larger branches,
which decussate each other in an elegant arborescent manner. The
dentinal tubes of the Hare, figured by Retzius (loc. cit. tab. v. fig.
2 a and b) appear to have been taken from the inner and less dense
half of the dentine.

In the Beaver, as in the Hare, the tubes which are characterised
by the great number and size of their branches, are confined to the
posterior half of the incisor ;(1) the tubes of the anterior half of the
dentine(2) in the Beaver’s incisor are more numerous, more parallel

(1) Pl. 106, d’. (2) Ib. d.

406 RODENTS.

and less ramified, and thus produce a greater degree of density and
resistance, which must favour the oblique wearing and the mainte-
nance of the sharpness of the chisel-shaped extremity of the tooth.
Short medullary canals (Pl. 106, v v), are continued from the end
of the pulp-cavity into the central tract of the dentine.

The difference of structure of the anterior and posterior parts
of the enamel-plate is very clearly shown in the Beaver’s incisor.
The fibres of that half of the enamel(J) next the dentine are nearly
transverse, their diameter is equal to two dentinal tubes and their
interspace ; they describe a gentle sigmoid curve, and are distinctly,
almost coarsely, defined: the fibres of the peripheral half of the
enamel(2) are more minute, more oblique, and less distinctly defined ;
the substance being clearer and denser.

In a transverse section of the incisor the distinction hetween the
two layers of enamel is still more obvious, and the fibres of the inner
half being cut across, give the appearance of fine decussating oblique
lines ; while those of the outer half run transversely to the surface,
and are crossed by the traces of the concentric layers. The coloured
exterior layer(3) is as distinctly defined as in the incisors of the Vole :
the fine fibres of the outer layer of enamel appear to penetrate it,
but its continuation with the thin indubitable layer of cement upon
the lateral and posterior parts of the incisor lead me to conclude that
it is due to the calcification of the capsule, and that it is essentially
what Mr. F. Cuvier supposed it to be, cement, but in too small a quan-
tity to permit the development of the calcigerous cells. In a trans-
verse section of a Beaver’s incisor in my microscopical collection the
cement is distinctly continued, retaining its peculiar colour, from
the enamel, beyond the lateral boundary of that substance upon the
dentine, for a short distance. Retzius’ denial (loc. cit. p. 63) of the
presence of any cortical substance or cement upon the Beaver’s
incisor appears be founded on a non-recognition of that substance
where it is so thin as to be devoid of radiated or Purkingian cells.

In the molar teeth the enamel presents a uniform structure
throughout its thickness, which is like that of the denser outer
layer of the enamel of the incisor. It is distinctly coated by a layer
of structureless dentine as thin as the coloured layer upon the enamel

(1) Pl. 106, e. (2). Ib. e. (3) Ib. ¢

RODENTS. 407

of the incisor, and which, as it gradually augments in thickness to
enter and fill the inflected folds of enamel acquires the radiated cells
and also the medullary canals. This thin exterior layer is not repre-
sented in Prof. Erdl’s figures of the microscopic structure of the
molars of Rodentia, which, from their accuracy in other respects I
have reproduced in Plates 107—109. The size of the calcigerous
tubes is unavoidably exaggerated from the limited scale of the
drawings ; but their course is correctly given.

The structure of the rooted molar teeth with simple crowns is
correspondingly simple: the dentine consists of calcigerous tubes
radiating in the body of the tooth from a single pulp-cavity, with the
primary curves rather stronger than usual, especially in the tubules
which ascend vertically from the summit of the pulp-cavity. At the
base of the crown, where the pulp-cavity divides in order to be
continued into the fangs, the tubuli radiate from each division almost
horizontally and a section at this part displays their entire course, as
shewn in Pl. 107, fig. 1, in a molar tooth of the common Squirrel
(Sciurus vulgaris).

The section of the crown of the molar tooth of the Rat, taken
through the middle, shows the external coat of enamel, a small
portion of the cement and enamel at the bottom of the fissures and
depressions down which these substances are continued from the
summit of the crown, and the disposition of the caleigerous tubes in
relation to those depressions and to the external coat of enamel :
the third molar—the lowest and largest in Pl. 105, fig. 10, 3—shows
the crown naturally worn down almost to the degree corresponding
with the section magnified in Pl. 108, fig. 1.

The vertical section of the molar of the Flying Squirrel, the
crown of which has been worn down in a less degree, shows better
the course of the dentinal tubuli relatively to the inflected cups
of enamel upon the grinding surface. These cups or depressions,
(Pl. 108, fig. 3, e, e, e). are filled by a brown-coloured cement (¢, ¢, c).
In a transverse section of the ‘crown the inflected vertical folds of
enamel appear, as on the naturally abraded surface, in the form of
islands including the cement, whilst the lateral folds of enamel prolees
like promontories into the substance of the crown.

408 RODENTS.

The transverse section of the molar of the Water-Vole (Arvicola)
(Pl. 168, fig. 3) shows only the latter form: that of the Beaver (PI.
107, fig. 2) exhibits chiefly the islands with a single promontory
of enamel.

The transverse section of the crown of the molar of Lagostomus
displays not fewer than five islands of enamel, which hard sub-
stance is so thick that it enters more abundantly into the com-
position of the tooth than the dentine itself. The dentine of the
crown closely adheres to the surface of all the inflected folds and
cavities of enamel as well as to that of the outer investing layer; and
in the complex molars, where the folds are numerous, the layer of
dentine is in many parts thinner than that of the enamel. As the
pulp-cavity sends narrower or wider fissures into each of the processes
of dentine it assumes a very complicated form when seen in trans-
verse section, as in the molar of the Beaver, Pl. 107, fig. 2, where the
dark fissures in the substance of the tooth indicate the spaces which
contained the vascular pulp (vv). The calcigerous tubes maintain at
most parts of this complicated dentine (d d) their general course at right
angles between the pulp-cavity and the enamel with the usual graceful
flexuous sigmoid curves: but in some places, near the angles of the
folds of dentine, the curves are stronger and less regular. The
secondary minute undulations with the terminal bifurcations, anasto-
moses and loops of the dentinal tubuli are shown at Pl. 109, fig. 2.
The cavities of the enamel-folds which open upon the exterior of the
tooth are filled with cement ; and where this is accumulated in suffi-
cient quantity, as in the Beaver’s molar (Pl. 107, fig. 2, c) or in that of
the Water-Vole (Pl. 108, fig. 3, c), it presents not only the calcigerous
cells but also medullary canals. Prof. Erdl has described and figured
the concentric layers of the walls of these canals, and the minute dendri-
tic tubuli which radiate from their cavities, and establish a communica-
tion between them and the calcigerous cells ; doubtless for the con-
veyance of the nutritious colourless plasma transuded from the blood-
vessels. The calcigerous cells are larger, more numerous and more
angular in the cement of the Beaver’s tooth than in ordinary bone.

The pulp, after the formation of a certain thickness of tubular
dentine beccmes converted into osseo-dentine in both the rooted and

RODENTS. 409

rootless molars of the Rodents. This fourth substance is exhibited
at o in the magnified transverse section of the Water-Vole’s molar,
(Pl. 108, fig. 3), which shows the four different dental tissues, viz.
cement ¢, enamel e, dentine d and osseo-dentine 0, entering in more
equal proportions into the formation of the crown, than has, hitherto,
been demonstrated in any other tooth. When the crown is worn by
mastication down to the place of the section figured, the four subs-
tances appear in the same proportions on the grinding surface,
contributing to its efficiency as a triturating organ by the inequalities
consequent on their various degrees of density and resistance to the
abrading forces.

The transverse section of the molar of the Hare, (Pl. 109,
fig. 1), shows the single, but deep, lateral fold of enamel (e) extend-
ing almost across the entire breadth of the tooth, and followed
as usual by the included layer of cement (c). Inthe Capybara the fold
is carried quite across, and divides the anterior molars into two
portions of a prismatic form, with the base turned outwards, and
penetrated by a shorter fold of enamel: the posterior molar in the
lower jaw is divided into ten or more portions of which only the ante-
rior one is prismatic and indented on the outer side, the rest being
simple, compressed plates, having a microscopic structure very
similar to that in the lobes of the molar of the Hare. In this tooth
the primary curvatures of the dentinal tubes are more flexuous
than usual: the concentric layers of the clear basal substance may be
more clearly perceived than in most other Rodents: the quantity of
osseo-dentine which fills the remains of the pulp-cavity is very small.
The enamel varies in its thickness both in the outer surface and the
inflected fold in the Hare: this fold is elegantly undulated through a
greater part of its extent.

It is peculiar to some of the Rodents with rootless molars to
have the sockets of these long curved teeth open at both extremities,
so that, in the dry skull, the base of the tooth protrudes as well as
the grinding surface: the matrix in such instances adheres to the
periosteum which covered the portion of bone absorbed from the
bottom of the alveolus. The Jumping-Hare (Helamys capensis), when
full-grown, offers a good example of this curious structure.

410 f RODENTS.

160. Succession.—The molars are not numerous in any Rodent ;
the Hare and Rabbit (Lepus) have {=3, i. e. six molars on each side of
the upper jaw and five on each side of the lower jaw: the Pika
(Lagomys), has =3: the Squirrels have <j: the families of the Dor-
mice, the Porcupines, the Spring-Rats (Echimyide), the Octodonts,
Chinchillas and Cavies, have }} molars: in the great family of Rats
(Muride), the normal number of molars is =: but the Australian
Water-rat, (Hydromys), has but =; molars, making with the incisors
twelve teeth, which is the smallest number in the Rodent order :
the greatest number of teeth in the present order is twenty-eight,
which is exemplified in the Hare and Rabbit: but thirty-six teeth
are developed in these species, six molars and two incisors being
deciduous.

In all the Rodents, in which the number of molars exceeds three
in a series, the additional ones are anterior to these and are pre-
molars; i.e. they have each displaced a deciduous predecessor
in the vertical direction, and are what Cuvier calls ‘ dents de
remplacement.’ This it is which constitutes the essential distinc-
tion between the dentition of the marsupial(1) and the placental
Rodent ; the latter, like the placental Carnivora, Ruminantia and or-
dinary Pachyderma having never more than three true molars. Thus
the Rodents, which have the molar formula of <4, shed the first tooth
in each series, and this is succeeded by a permanent premolar which
comes into place later than the true molars; later, at least, than the
first and second, even when the deciduous molar is shed before birth,
as was observed by Cuvier in the Guinea-pig, Pl. 104, fig. 4. In the
Hare and Rabbit the three anterior teeth in the upper jaw and the two
anterior ones in the lower jaw succeed and displace, in like manner,
deciduous predecessors, and come into place after the first and second
true molars are in use, and contemporaneously with the last molar.

It does not appear that the scalpriform incisors are preceded by
milk-teeth, or, like the premolars of the Guinea-pig, by uterine teeth :
but the second incisor was observed by Cuvier(2) to be so preceded in
the genus Lepus, and he has figured the jaw of a young Rabbit, before

(1) See Dentition of the Wombat, p. 393.
(2) Ossemens Fossiles, tom. v, pt. i, p. 5.

RODENTS. 411

that deciduous tooth was shed, when six incisors are present in the
upper jaw.(1) This condition is interesting both as a transitory mani-
festation of the normal number of incisive teeth in the Mammalian
Series, and as it elucidates the disputed nature of the great anterior
scalpriform teeth. Geoffroy St. Hilaire contended that the scalpriform
teeth of the Rodents were canines, because those of the upper jaw ex-
tended their fang backwards into the maxillary bone, which lodged part
of their hollow base and matrix. But the scalpriform teeth are con-
fined exclusively to the intermaxillary bones at the beginning of their
formation, and the smaller incisors which are developed behind
them in our anomalous native Rodents, the Hare and Rabbit,
retain their usual relations with the intermaxillaries, and d fortiori,
prove the tooth which projects anterior to them to be also an incisor.

The law of the unlimited growth of the scalpriform incisors is
unconditional, and constant exercise and abrasion are required to
maintain the normal and serviceable form and proportions of these
teeth. When, by accident, an opposing incisor is lost, or when by
the distorted union of a broken jaw the lower incisors no longer
meet the upper ones, as sometimes happens to. a wounded hare,
the incisors continue to grow until they project like the tusks
of the Elephant, and the extremities in the poor animal’s abor-
tive attempts to acquire food also become pointed like tusks:
following the curve prescribed to their growth by the form of their
socket, their points often return against some part of the
head, are pressed through the skin, then cause absorption of the
jaw-bone and again enter the mouth ; rendering mastication imprac-
ticable and causing death by starvation. In the Museum of the
College of Surgeons there is a lower jaw of a Beaver in which the
scalpriform incisor has, by unchecked growth, described a complete
circle: the point has pierced the masseter muscle and entered
the back of the mouth, passing between the condyloid and coro-
noid processes of the lower jaw, descending to the back-part of the
molar teeth, in advance of the part of its own alveolus which
contains its hollow root. The upper jaw of a rabbit with an analo-
gous abnormal growth of the scalpriform and accessory incisors is
figured in Pl. 104. fig, 7.

(1) Pl. 104, fig. 5.

412

CHAPTER VII.

TEETH OF INSECTIVORA.

Tue dental system is here remarkable for the many varieties
and even anomalies which it presents: almost the only characteris-
tic predicable of it in the numerous small quadrupeds which consti-
tute the Insectivorous order(1) being the presence of several sharp
points or cusps upon the crowns of the true molar teeth, which are
always broader in the upper than in the lower jaw. The teeth that
intervene between these and the incisors are most variable in form
and size, but are never absent: the incisors also differ in number,
size, and shape in different species, the anterior ones approximating
in some species to the character of the scalpriform teeth of the
Rodents.

The Insectivora are divided into the families of Moles (Tulpide),
Shrews (Soricide), and Hedgehogs (Erinaceide), in which succession
their dentition will be here described.

161. Talpide.—Of all existing Insectivora the Chrysochlore,
or iridescent mole of the Cape, makes the nearest approach, by
the number of its molar teeth, to that remarkable condition which
was manifested in the most ancient period of mammalian existence
by the extinct Amphitherium described in the chapter of Marsupialia.
We must assign at least £{ true molars to the Chrysochlore(2) ac-
cording to their form, which, in the absence of the known order of
vertical displacement and succession, is the only character by which
the true and false molars can be defined. The anterior large lania-
riform tooth and the two succeeding small teeth are incisors, by
virtue of their position in the intermaxillary bones; the next small

(1) Pallas points out succinctly some of the leading differential characters which distin-
guish the Insectivora from the Carnivora or true Fere in his ‘ Zoographia Rosso-Asiatica’ where
(Vol. i. p. 119) he says “‘Continuitate etiam dentium, numero incisorum a Ferarum Ordine
semper discordante, caninis minus elongatis, plerumque uno alterove spurio stipatis, pedum
pentadactylorum structura multifaria et singulari, clavicularum perfectarum in sceleto presentia,
totoque indolis, morum, victus et habitus complexu, cuncta hec genera 4 feris omnino dis-
crepant, simul affinitate concatenata inter se successive coherent.” The Insectivora are further
distinguished from the Carnivora by the absence of cerebral convolutions and by a discoid,
instead of an annular, placenta. }

(2) Pl. 110. fig. 1.

INSECTIVORES. . 4s

tooth with a simple compressed tricuspid crown is a premolar. The
crowns of the true molars are thin plates, flattened from before
backwards, with two notches on the working edge and a longitudinal
groove along the outer and thicker margin, which divides the outer
cusp into two as shown in the figure, where the middle cusp, which
is the largest, is seen in the interspace of the bifid external cusp:
the base of the lamelliform molar divides tardily into two short roots.
The third internal simple cusp is not present in the anterior molar,
and the posterior or sixth molar has a simple tricuspid crown.
Another anomaly, more remarkable than that of the shape of the
true molars, is their separation from each other by vacant intervals,
as in many Reptiles. The crowns of the five lower true molars are
compressed antero-posteriorly but are of unusual length, and have
‘the thicker margin turned inwards, with the summit divided by a
single notch, and the inner and lower division is subdivided into two.
The anterior incisor is small and procumbent: the second has a
larger laniariform crown; the third is small and resembles the two
premolars which intervene between this and the first true molar.
The lower molars are separated by wider intervals than those above ;
the crowns of the opposing series enter reciprocally the interspaces
and interlock: in mastication the anterior margin of one tooth works
upon the posterior margin of the opposite molar.

According to M. F. Cuvier(1) each series in the upper jaw of the
Chrysochlore includes 1 incisor and 9 molars; and in the lower jaw
2 incisors and 8 molars. M. de Blainville, guided by the intermaxil-
lary sutures in the young Chrysoclore, regards the first three teeth
in each lateral series as incisors, the fourth as a canine, and the
remaining six as molars in both upper and lower jaws. My views,
as given in the foregoing description, are expressed by the following
formula: in. =3, pm. =, m. ==—40.

In the Shrew-moles of America, (Scalops), the dentition makes
an important step towards the normal mammalian condition by the
restriction of the characters of the true molars to the three pos-
terior teeth in each lateral series(2): between these and the large
scalpriform incisor, in the upper jaw, there are six teeth, the first two

(1) Dents de Mammiféres, p. 63. (2) Pl. 110, fig.2,

414 INSECTIVORES.

of which must be regarded, by the analogy of the Chrysochlore;
as incisors: the next tooth might pass for a canine; and the re-
maining three for premolars, of which the last is the largest and has
a trihedral. pointed crown: the true molars have large crowns, each
with six cusps, four on the outer and two on the inner part of the
grinding surface. In the lower jaw, the first incisor is small and
procumbent, and the second large and laniariform, as in the Chryso-
chlore ; the third is absent, and a vacant space separates the incisor
from the three premolars, the crown of each true molar consists of
two parallel three-sided prisms, each terminated by three cusps, and
having one of the angles turned outwards and one of the faces
inwards: the interspace between the angles makes the outer surface
of the long molars of the Scalops appear grooved. The dental for-
mula of this genus, according to the above description, is :
=, ce —, pm. —, mM. — rie

The dentition of the common Mole (Talpa ewropea),(1) includes
eleven teeth on each side of both upper and lower jaws. The first
three in the upper jaw are very small, with simple incisive crowns,
and are each implanted by a long and slender fang: these teeth, by
analogy with the Chrysochlore, and by the position of the incisive
foramen, must be regarded as incisors: the next tooth, by the size
and shape of the crown, represents a canine, but it is implanted by
two fangs like the three succeeding premolar teeth, and these teeth
are of small size with compressed conical crowns ; the fourth premo-
lar has a larger three-sided conical crown, supported by three fangs :
the crowns of the true molars are multicuspid, the middle one is
the largest with five points and is usually supported by four fangs,
the hindmost is the smallest, with a tricuspid crown and three fangs.
In the lower jaw, the first four teeth on each side are small, simple
and single-fanged, like the three incisors above: the fifth tooth has
a large laniariform crown, supported by two fangs, being very similar
to, but shorter than, the two-fanged canine above; but, as it passes
behind that tooth when the mouth is shut, we must regard the fourth
tooth below, notwithstanding its small size and similarity to the

(1) Pl. 110, fig. 3.

in

INSECTIVORES. 415.

incisors, as the true inferior canine: the fifth tooth is then the first
and largest of the series of four premolars, each of which has a small
posterior talon at the base of the compressed conical crown. The
three true molars are each implanted by two fangs and have quinque-
cuspid crowns, the middle molar being the largest.
The teeth of the Mole have been differently classified by different

authors : the dental formula according to M. F. Cuvier(1) is :

$ 3 I 4—4 3-3

ee a BO any lla ao bags oat = 44,
Prof. Bell, in his ‘‘ History of British Quadrupeds,”’(2) adopts. the
following :
1—1 7—7

im. —j; ¢.—; m. —:=— 44.
4—4 jf 625
Prof. de Blainville(3) prefers the formula :
° 4—4 I—1 3—3 3—3
mM. 3 C3 pm. —; Mm. aah Wi

From which it will be seen that the difference turns mainly
upon the determination of the canine teeth. M. F. Cuvier and Prof.
Bell both regard the fourth large tooth of the upper jaw as a
canine, notwithstanding it has two fangs. M. de Blainville(4)
has assured himself that it is an incisor, in which case the double
‘implantation would be still more anomalous. The position of the
incisive foramen (P1.110, 3 a), however, indicates that the double
socket of this tooth is posterior to the intermaxillary suture, and
that the number of incisors has been rightly determined by F.
Cuvier. By this justly esteemed authority the canines are held
to be wanting in the lower jaw of the Mole. Prof. Bell regards as
lower canines the large fifth tooth on each side, although posterior
to the canine above; and M. de Blainville, having assigned eight
incisors to the upper jaw, gives the same number to the lower
jaw, and calls the first premolar a canine. With regard to the
fourth tooth above, if it be not developed in the intermaxillary bone,
it claims to be regarded as a canine by the size and shape of the
crown, and to be a premolar by virtue of its two fangs; but, since
the fang of a tooth is subject to more variety than the crown, we

(1) Dents de Mammiféres, p. 61. (2) 8vo. 1837, p. 85.
(3) Ostéographie. (4) Loc. cit.

416 INSECTIVORES.

should be guided by the more fixed character, and call the tooth in
question a canine. The fourth tooth below, although so small, is
the only one which has the true relative position of a canine, in
advance of the one above, when the mouth is shut; and we shall
find in the genus Lemur a similar conformity of size and shape
between the lower canine and incisors as exists in the common
Mole.(1) There is no difficulty about the other teeth, the canines
being determined ; thus, according to my view, the dental formula
of the genus Talpa is: in. $3, c, i=, pm. (4, m. =,—44; the teeth
are here equal in number, and the same in kind in both jaws; the
true molars are reduced to the normal quantity in the Placental
series, and the entire dentition is the least anomalous of any which
is manifested in the family Talpide.

162. Soricade.—The transition from the Moles to the Shrews seems
to be made by the Water-moles, (Mygale), and the Solenodon. The
latter Insectivore combines the form of a gigantic Shrew with a
dentition resembling that of the Chrysochlore.(2) Each inter-
maxillary bone contains three incisors, the first large, canine-shaped,
grooved anteriorly with the point inclined backwards; the other
two incisors small with simple conical crowns ; these are succeeded
by seven teeth, the two anterior having three-sided conical crowns,
the other five bearing in addition an external tuberculate basal
ridge. In the lower jaw, the anterior incisor is very small, and the
second large and laniariform, as in the Scalops and Chrysochlore ; but
it is remarkable for a deep longitudinal excavation upon its inner
side,(3) (Pl. 111, 6 and c,) apparently produced by the friction of
the large upper incisors which are received into the interspace of
the lower pair; the third lower incisor is small and simple; of
the seven succeeding teeth the four last have multicuspid crowns
like true molars.

The Pyrenean Water-mole, (Mygale pyrenaica), has eleven teeth
on each side of both jaws; the first incisor above is relatively larger
than in Scalops, trihedral and sharp-pointed ; the second and third

(1) In the Talpa mooguru Temm., the inferior canine is absent, as in the genus Scalops ;
in the Condylure, or Rayed-mole, it is present with the form and proportions of a canine.

(2) See Brandt, Acta Petropol ; ii, 1835. i

(3) The name of the genus, (cody, a pipe, odovg, a tooth), relates to this structure.

INSECTIVORES. 417

incisors are very small; none of the succeeding teeth present the
form and size of a canine; the last three teeth are multicuspid, and
are true molars. In the lower jaw all the teeth anterior to the true
molars are small and simple.

The teeth in the lower jaw of a species of Water-mole, as large
as a Hedgehog, which has become extinct in England, present a
close resemblance with those of the Mygale ; the true molars have
square, quinque-cuspid crowns, but are distinguished from the teeth
of all known recent Insectivora by the presence of a minute tubercle
at the bottom of the outer vertical fissure of the crown. I have
called this extinct genus Palgospalaz.(1)

The typical Shrews always manifest their Rodent analogy
by the superior size of the anterior pair of incisors in both
upper and lower jaws; in the latter the great incisor is uniformly
succeeded by two small and three large multicuspid molars ; but
in the upper jaw the number of small premolars varies, and there
is generally a fourth true molar of small size. The sub-genera of
Shrews are chiefly based upon the form of the large incisors, and the
numeral variations of the dentition of the upper jaw. In the common
Shrew (Sorez araneus of Linneus, Pl. 111, fig. 2) there are four true
molars and three small teeth between these and the anterior incisor ;
this tooth has a pointed tubercle at the back of the base of the
crown. The long procumbent incisor of the lower jaw has the trench-
ant superior margin entire. In the Sorex (Amphisorex) tetragonurus
(Pl. 110, fig. 4) the edge of the lower incisor is notched ; the large upper
incisor appears bifurcate from the great development of the posterior
talon ; five small teeth progressively decreasing in size, intervene
between the upper large incisor and the true molars. In the Sorex
(Hydrosorex) Hermanni the trenchant edge of the lower procumbent
incisor is entire ; there are four small teeth between the large anterior
incisor and the true molars in the upper jaw, as in the great Sorex
indicus, but the three first are sub-equal and the fourth very minute ;
there is a fourth small true molar above. The enamelled tips of
the teeth of the species of Amphisorex and Hydrosorex are stained

(1) “* History of British Fossil Mammals,” p. 25.
EE

418 INSECTIVORES.

of a bright brown colour ; the teeth of Sorex proper, as the common —

Shrew (S. araneus), are not so stained.(1)

In the progress of the formation of the large notched incisors, —

the summits of the tubercles are first formed as detached points,

i
i
F

supported upon the common pulp, and do not coalesce until the ©

centripetal calcification has converted the pulp into a common

dentinal base. Some anatomists have regarded the large incisor so

formed as an aggregate of two or three teeth: but in Sore# proper
and Hydrosorex, the calcification of the lower incisor spreads from

a single point; and the interpretation of the notched incisor of the |
Amphisorer, as the representative of these incisors,(2) might, by

parity of reasoning, be applied to the human incisor teeth, the
dentated margins of which are likewise originally three or four
separate tubercles.

The determination of the small teeth between the large anterior

incisors and the multicuspid molars depends upon the extent of
the early anchylosed intermaxillaries ; the incisors being defined
by their implantation in those bones, the succeeding small and
simple-crowned molars must be regarded as premolars, not any
of them having the development or office of a canine tooth; their

analogues in the lower jaw are implanted by two roots.

The thickness of the enamel in proportion to the body of dentine
is unusually great in these small Insectivora, and the sharp points of
the teeth long retain their fitness for the office of cracking and crushing
the hard or tough teguments of insects. The capsule supporting the
enamel-pulp of the lower incisors is so large as to overlap, in the
young Shrew, the growing margin of the socket, so as to encase
with enamel and cement, not only the crown of the tooth, but also
the contiguous part of the jaw-bone.

Daubenton first drew attention to the close adhesion of the
teeth of the Shrews to the jaw-bone; and M. Duvernoy in his
excellent Memoir on these small Insectivores(3), affirms that the roots

(1) See the beautiful Monograph “Sur les Musaraignes,” by Prof. Duvernoy, in the

Mémoires de la Société d’Histoire Naturelle de Strasbourg, 4to. 1834.
(2) See Prof. de Blainville, “ Ostéographie des Insectivores, p. 55.
(3) Loc. cit., 4to. 1834.

ee ee

INSECTIVORES. 419

of the teeth become anchylosed to the jaw-bone,—a reptilian character
offered by the Soricide alone in the Mammalian Class.

163. Erinaceide.—lIn the dentition of the Tupaias (Glisorex) we
begin to trace characters intermediate between those of the dentition
of Shrews and of Hedgehogs. The dental formula of the Glisorex
tana is: in. 3, c. , pm. &, m. :—36: the upper incisors are
small, simple, and wide apart in the upper jaw(1) ; the anterior incisor
in the lower jaw is long and procumbent, but relatively smaller than
in the Shrews ; the canines are small in both jaws; the premolars
increase in size and complexity as they approach the true molars ;
the first two of these are sub-equal with six cusps in the upper and
five cusps in the lower jaw, the last true molar is smaller and is
tricuspid.

In Macroscelis (Elephant-mice of the Cape) and Gymnura each
intermaxillary bone contains three teeth, which, in the former genus
are succeeded by four premolars and three true molars, with the
same number of teeth in the lower jaw. In Gymnura(2) the first tooth
which succeeds the incisors has the form and size of a canine in both
upper and lower jaws; this is followed by four premolars, the last
of which in the upper jaw is large and quadri-cuspid like the first
and second of the true molars, which have square crowns: the last
true molar is smaller and triangular. In the lower jaw of the
Gymnura the fourth premolar has a compressed tri-cuspid crown. The
dental formula of Gymnura is: in. 33, c. jj, pm. Eiym. Ey: = 42.

The dentition of our common Hedgehog (Erinaceus euro-
peus) shows greater inequality in the upper and lower jaws, the
formula being :—im. 33, pm. $3, m. 3, = 36.8) The first in-
cisor in both upper and lower jaws is larger and longer than
the rest, and is very deeply implanted in the jaw: the tooth
which follows the incisors is small in both jaws, but especially
so in the lower, and it does not merit a distinction from the other
premolars: the last premolar is the largest in both jaws; above, it
has a quadricuspid crown with three fangs; below, a subcompressed
tricuspid crown with two fangs. The true molars decrease in size
from the first to the third in both jaws: the first and second have

(1) Pl. 111, fig. 3. (2) Pl. 111. fig. 4, 4a, 4b. (3) Pl. 110, fig. 5.
EE 2

420 INSECTIVORES.

subquadrate four-pointed crowns above: below they are narrower,
and the anterior and inner angle is produced into a fifth cusp.

The true molars of the tropical Hedgehogs, forming the subgenera
Echinops and Ericulus, are more simple, and approach the form of
those in the Chrysochlore, being compressed from before backwards,
with two outer cusps and one inner cusp in the upper jaw, and with
one outer and two inner cusps in the lower jaw. The number of
incisors is = in both subgenera, which are followed by 5= small and
simple premolars; but riculus(1) has = eniibkendaen tri-cuspid
molars, and Echinops only —(2).

The largest species of the present family, called Tenrecs(3) or
tail-less Hedgehogs of Madagascar, combine the simple molars of the
Ericulus with the most formidably developed canines which are to
be met with in the whole order Jnsectivora. The incisors are two
- in number in the upper jaw and three in the lower jaw; very small
and sub-equal in both: the canines are long and large, compressed,
trenchant, sharp-pointed, recurved, and single fanged; thus presenting
all the typical characters of those teeth in the Carnivora; they are
separated, in both jaws, by a wide space from the premolars: the
first premolar above is compressed, unicuspid, with a hinder talon, and
two-fanged ; the second has a larger prismatic tricuspid crown, and
three fangs: of the four posterior teeth, which by their antero-
posterior compression may be regarded as true molars, the first
three have tricuspid crowns as in the Echinops, and have three
fangs ; the fourth is smaller, is bicuspid, and has two fangs’: all the
lower molars have two fangs. The Tenrecs prey more upon serpents —
and lizards than on insects, and thus approximate the true Carnivora
in diet as well as dentition.

164. Structure and Succession.—The teeth of the Insectivora consist
of a basis of hard dentine with a thick coronal investment of enamel,
and an outer covering of cement. This third substance is very
recognizable in the interspaces of the coronal cusps in microscopic”
sections of the molars of the larger species, as the Tenrecs and
Macroscelles ; and is always thick where it closes the extremity of

Q) Pl. 111, fig. 6.
(2) See Mr. Martin’s Memoir in the Zoological Teac done vol, 11, p. 249.
(3) Pl. 110, fig. 6.

INSECTIVORES. 421

the fangs ; at which part it is commonly more. highly organized, tra-
versed by medullary canals which generally present concentric walls,
and thus assumes the character of true bone: in the Soricide the
cement is frequently continued into the substance of the jaw itself,
The small proportion of dentine in comparison with the thick layer
of enamel has been already alluded to in the Shrews, yet the
dentinal tubuli are, at their commencement, very little inferior in
diameter to those of the human incisors; the trunks, as Retzius has
observed, are unusually short, and are resolved into radiated peni-
cilli of undulating branches, which quickly subdivide, interlace,
and anastomose together near the boundary line between the dentine
and enamel. In most of the Insectivora, the secondary branches
of the calcigerous tubes are very conspicuous, especially in the
dentine forming the fangs. The dentinal cells are rarely well
defined ; in the large canines of the Centetes they are sub-hexagonal,
and about 4,th of an inch in diameter; but diminish in size towards
the periphery of the dentine.

The calcigerous tubes in the anterior incisor of the Hedgehog
(Erinaceus europeus) present, in a longitudinal slice of the tooth,
the usual disposition, vertical in the middle of the crown, diverging
obliquely at the sides, and gradually becoming transverse at the base,
which course they maintain throughout the long fang to its slightly
enlarged extremity, where the tubuli become irregularly and strongly
curved, crossing each other, and forming a net-work. In the incisor
here described the end of the fang was closed by cement, through
which a single vascular canal passed to the pulp-cavity: this
cavity was widely open in the rest of the fang, and extended more
than half-way up the enamelled crown.

The dentinal tubes at the middle of the crown ascend without
any primary curvature ; they dichotomize earlier and more frequently
than usual, and the secondary undulations of these sub-divisions
of the main-tubes are irregular. The oblique tubes at the sides of
the crown form a short but strong curve at their commencement,
concave towards the summit of the tooth, then proceed in a straight
and parallel course obliquely upwards, and bend gently down near
the enamel, forming at the boundary line a rich reticulation by their

422 INSECTIVORES.

numerous minute branches. As the tubes become situated lower
down the fang the number of their large curved lateral branches
becomes more remarkable ; and the reticulate or moss-like disposi-

|

tion. extends over a greater proportion of the dentine. Numerous —

minute opake cells form the boundary line between the dentine and
the cement which covers the fang. The minute transverse tubuli
of the cement are present in the thinner part, where there are no
Purkinjian cells; these cells are developed in great number, and
present the usual irregular angular figure in the mass of cement
closing the end of the fang.

The enamel fibres are disposed with a very slight curve, almost
transversely to the plane of that substance, inclining towards the
crown ; they are crossed by other lines nearly parallel with the same
plane, extending from its inner surface upwards and outwards ; these
lines are equi-distant, parallel with each other, with intervals equal
to the breadth of two enamel fibres; they indicate successive and
regular periods in the formation of the enamel; and, where they
crop out upon the outer surface of the enamel, they form the fine
transverse striz which have been often noticed on that substance
in larger teeth. I counted sixteen of these longitudinal lines
in a section of the enamel, at the middle of the side of the
crown of the incisor examined, where the enamel was th of an
inch in thickness.

Not any of the main calcigerous tubes are straight in the molars
of the Hedgehog ; those which ascend from the summit of the pulp-
cavity to the middle of the grinding surface of the crown, rise with
a wavy curve, which becomes stronger in the tubes that diverge to the
angles of the crown. At the sides of the crown the tubes curve out-

wards, with the concavity turned towards the grinding surface, and |
then bend towards the enamel in the opposite direction ; the latter cur- —

vature being lost in the transverse tubuli of the fangs, which have a

single curvature convex towards the crown; near the end of the

fang the tubuli bend down with irregular flexuosities, and here they
present very conspicuously that rich ramification which Retzius has

remarked: it is also beautifully seen in the tubuli of the dentine ©

at the base of the crown between the origins of the fangs. The ©

@

INSECTIVORES. 423

tubes in the crown retain their almost parallel course and their
character of undivided trunks, until they attain the usual proximity
to the enamel.

This substance offers no noticeable peculiarity in the molar teeth.
The fangs are invested with a layer of cement, which is suffi-
ciently thick at their extremities and at the interspace of their origins
to show the calcigerous cells; these cells present an irregular
elongated form, with angular projections continued into the radiated
tubes. The cement is likewise traversed by transverse xainute
parallel tubuli of the size of those in the dentine, which have a
diameter of j;jth of an inch.

* The deciduous teeth of the Moles and Shrews are uterine, 2.e.
are developed and disappear before birth ; they are extremely small,
and all of the most simple form. In the foetal Sorex araneus cal-
cification of the papillary exposed pulps of the teeth which are
succeeded by the first and second premolars proceeds to a very
slight extent, and these microscopic rudiments appear to be absorbed
rather than shed; the deciduous incisors are further advanced before
their displacement, and present the form of equal-sized dentinal
spicula, tipped with enamel, attached by the opposite end to the
gum, and not exceeding ,;th of an inch in length; the number of
the uterine series of teeth is =}.

In a foctal Hedgehog, two inches and a half in length, the alveolar
border of the upper jaw forms a smooth, convex ridge on each side,
and those of the lower jaw are equally entire and edentulous, but less
prominent; both are covered by a thick epithelium; the margin
of the gum easily opens longitudinally, as if the dentiparous groove
had been but recently closed, and the matrices of five deciduous teeth
on each side are brought into view; the four first, representing the
three incisors and the canine, are very minute and simple, the fifth
tooth is quadrituberculate, and 5th of an inch in breadth: calcification
has commenced in the summits of the crown of this deciduous tooth,
which is succeeded by permanent premolars of a more simple form.
M. Duvernoy alludes to M. Laurillard’s examination of the deciduous
teeth of the Hedgehog, and states that he has himself determined
their existence in the Tenrecs (Centetes), in which they are long

424 BATS.

retained. He suspects that the Shrews have but one dentition: the
minute size and rudimental state of the transitory teeth, and their
disappearance before birth having caused them to escape the obser-
vation of the accomplished continuator of Cuvier’s ‘* Lecons d’Anato-
mie Comparée.’’(1)

CHAP DPE ROV ALE

TEETH OF CHEIROPTERA.

165. Tue dental system presents more constancy in this than in

the preceding Order, and the different kinds of teeth are more easily
and unequivocally determinable.

The canines are always present in both jaws, of the normal form

and with slightly variable proportions. The molar series never

exceeds (=;, and is divisible into premolars and true molars, the latter

presenting two types of grinding surface; in one of these the crowns
are bristled with sharp points, as in the foregoing order, and this type
characterizes the great bulk of the Cheiroptera, which may be called
true Bats or volant Insectivores ; the molars of the second type have
flat crowns and characterize the large frugivorous Bats which consti-
tute the aberrant genus Pteropus, and conduct towards the Quadru-
manous Order.

The incisors are the most variable teeth in the Cheiroptera ;

(1) See the posthumous edition of the Lecons, tom. Iv, p. 242, where M. Duvernoy adds
to the text: “J’ai lieu de penser que tous les Insectivores n’ont pas cette succession de dents.
Je ai constatée, ala vérité, dans les Tenrecs qui perdent leurs dents fort tard, au contraire
de certains Rongeurs les ayant trouvées encore, en partie, chez un individu dont la taille
était a peu prés celle de l’adulte. M. Laurillard l’a vue dans les Chauve-souris et les Hérissons.
Mais dans les Musaraignes je suis porté & croire qu’il n’y a qu’une seule dentition.” M. de
Blainville goes further, and denies the existence of a deciduous series of teeth in the Mole,
Hedgehog and Tenrec, (Ostéographie des Insectivores, p. 63) ; as, indeed, he likewise did with
regard to the Bats, (Compte Rendu de Académie des Sciences, Sept. 1837, p. 420.) M.
Rousseau, in his excellent “ Mémoire sur la Chauve-souris commune,” read to the Academy
of Sciences, March 19th, 1838, described the deciduous dentition of that Cheiropter with all
the requisite detail, and its existence is admitted by M. de Blainville in the “ Ostéographie des
Chéiroptéres,” published in June 1840. Similar proofs will be found, if nature be rightly
consulted, that the other Insectivora, also, form no exception to the rule.

BATS. 425

they may be entirely wanting, or be present in the numbers of
1—1 to 2—2 in the upper, and from 1—1 to 3—3 in the lower
jaw; they are always very small, and in the upper jaw commonly
unequal and separated by a wide median vacancy. Taking the
common simple-nosed Bat(1) (Vespertilio-murinus) as a type of the
Insectivorous group, we find its dental formula to be :-—

‘ 2—2 1—1 3—3 3—3
mM. cau C. cae pm. —: = 38.

Fae We
The first upper incisor (Pl. 112. fig. 1,7.) has a slightly expanded
tri-dentate crown, separated by a basal ridge of enamel from a long,
slender, slightly curved, fusiform fang; the second upper incisor
has a sub-bifid crown. The three lower incisors (2) are tri-den-
tate, and the crown of the outermost has an additional tubercle.
The crown of both upper and lower canines (c¢ c) is sharp-
pointed, and its inner surface is indented by two grooves; a basal
ridge divides it from the long conical fang. The first premolar is
very small, both above and below, and has a sharp-pointed simple
crown with a basal ridge, and a single fang; the second premolar
is still smaller: both are soonshed. ‘The third premolar, as it may be
called from its shape, though it has no deciduous predecessor, has a
triangular pointed crown, with a basal ridge, and is implanted above by
three fangs ; in the lower jaw the crown is narrower, and is supported
by two fangs (pp). The first and second upper true molars (m), have
each a six-pointed crown supported by three fangs: the third molar
is compressed from before backwards; its crown has three points or
tubercles, and is supported by three fangs. The first and second
true molars of the lower jaw have quinque-cuspid crowns, two of
the largest points being on the outer and three small ones on the
inner side, the crown is supported by two fangs; the last molar
is the smallest, and is tri-cuspid. A well-developed ridge of enamel
surrounds the base of the crown of each molar tooth both above and
below.
(1) The insectivorous Cheiroptera are divisible into groups according to the modifications
of the tactile dermal appendages of the nose ; which may be wanting, as in the Vespertilio mur-
inus and other Leionycteride ; or be present in the form of a simple leaf, as in the Vampire-bat

and other Phyllonycteride; or be developed into more complex forms, as in the Horse-shoe
Bat and other Lophonycteride of Prof. de Blainville.

426 BATS.

All the teeth of the lower jaw touch each other; in the upper
jaw the incisors are separated by a wide interspace from the canine.

The dentition of the Long-eared Bat (Plecotus auritus) differs
from the foregoing chiefly by the absence of one of the small pre-
molars on each side of the upper jaw. In the Horse-shoe Bats
(Rhinolophus, Pl. 112, fig. 5), the Barbastelles (Barbastellus), the
Noctule (Vespertilo Noctula, Pl. 112, fig, 2), and the Pipistrelle
(Vespertiho pipistrellus), the small premolars reduced to one on
each side of both jaws, are extremely minute, and seldom visible
from without. In the Serotine (Vespertilio serotinus, Pl. 112, fig. 3)
the rudimental premolar is entirely wanting in the upper jaw, but
remains in the lower; and this condition of the molar series also
characterises the genera Rhinopoma, Noctilio, and many species
of Molossus and Nycticeus. In the genus Nycteris (Pl. 112, fig.
6 and 7) the small premolars are absent in both jaws ; and the molar
series is reduced to the large premolar and three true molars, which are
present on both sides of both jaws, in all the foregoing Bats.

The Bats with ciliated tongues, (Glossophaga, Pl. 112, fig. 4, 4"),
have three premolars and three true molars on each side of both
jaws, rather small and slender canines, and two minute incisors on
each side of both jaws.

The following are examples of the variation in the number of

incisive teeth: 5=$ in Tuphozous perforatus, Geoff. and the species of

Megaderma: ==; in Molossus and Myoptera: }=} in Nyctinoma, Rhino-

poma, Rhinolophus and Dysopus: <= in Vespertilio lasiurus and V.

paradowus: j=; in Noctilio: =; in Phyllostoma, Glossophaga and
Mormoops : ==; in Plecotus, Nycteris (Pl. 112, fig. 6''), and in most
species of the genus Vespertilio, as restricted by modern Naturalists.

The molar teeth have a more trenchant character and
fewer points in the Leaf-nosed Bats (Phyllostoma) of South
America, which are commonly called Vampyres; their canines
also, which are remarkably long and strong, sharp-pointed and
vertical in position, indicate a higher kind of animal diet than
that of the ordinary insectivorous Bats. The premolar teeth
are better developed than usual; in the Phyllostoma hastatum
the first upper premolar has a strong, thick pointed crown,

BATS. 427

with an internal and posterior talon; the second premolar is
larger than the first, with a triedral crown, and an anterior
and posterior talon at the base of the long, sharp middle cusp.
The first and second true molars have sub-compressed quin-
que-cuspid crowns ; the third molar is compressed from before
backwards, and has a tri-cuspid crown. The first and second
premolars below are simple and larger than those above, especially
the first; the first and second true molars have two large external
and three small internal cusps, and the last molar differs only by
a slight inferiority of size.

The dentition of the true blood-sucking Vampire Bats, which
form the genus Desmodus (P]. 112, fig. 9) deviates, as might be
anticipated, in a remarkable degree from that of the Insectivorous
Bats : the crushing instruments required for the food of those species
are not needed ; and the true molars, with their bristled crowns, are
entirely absent in the Desmodus. The teeth at the fore-part of the
mouth are especially developed and fashioned for the infliction of
a deep and clean triangular puncture, like that made by a leech. The
incisors (i) are two in number above, closely approximated, one
in each intermaxillary bone, with a very large, compressed, curved,
and sharp-pointed crown, implanted by a strong fang which extends
into the maxillary bone. The upper canines have similar large,
lancet-shaped crowns, and their bases touch those of the incisors.
In the lower jaw the incisors are two in number on each side, much
smaller than the upper pair, and with bilobed crowns. The lower
canines are nearly equal in size to those above. The molar series
is reduced above to two very small teeth, each with a simple com-
pressed conical crown, implanted by a single fang. The first two
molars below resemble those above; but they are followed by a
third which has a larger compressed and bilobed crown, implanted
by two fangs ; this tooth corresponds with the last premolar in the
more normal genera of Insectivorous Bats. The dental formula

of the true Vampire-bat (Desmodus) is thus reduced to :-—
. 1—1 1—I 2—2 ;
iret Bish ea Wh ih areas 20.(1)
The opposite extreme which the aberrant varieties of the

(1) The intestinal canal, like the dentition, is modified in conformity with the easily
assimilated food, viz. the blood of living animals, on which the true Vampires habitually

428 BATS.

Cheiropterous dentition attain, is manifested in the great frugivorous
Bats, which have been sometimes, but erroneously, called Vam-
pires ; but which have never been met with in South America,
the peculiar country of the true blood-sucking Bats.

The frugivorous species, sometimes called “ flying-foxes” and by
the French ‘“‘ Rousettes,”’ include the largest animals of the order Chei-

roptera, and constitute the genus Péeropus ; their dental formula is :
2—2 1-1 2—2 3—3

c. ——; m —: = B34, (Pl 112. fe, 10

mn. cae > pm. oR? Far

2-2?

The upper incisors are small, equal, contiguous, ranged in a
semi-circle, with broad, sub-incisive crowns; the inferior ones are
obtuse, the middle pair very small in some species; the number,
shape, and disposition of the incisors manifest an approximation
to the Quadrumanous type of dentition.(1) The upper canines are
long, rather slender and sharp-pointed, but are sub-tetragonal, the
four facets being separated by strong longitudinal ridges ; a transverse
ridge divides the inner side of the base of the crown from the fang ;
the lower canines are smaller, with an anterior and posterior lon-
gitudinal ridge, and an internal transverse basal ridge. A wide
space separates the upper incisors from the canines ; they almost
touch below. The first premolar above is extremely minute, and
sometimes wanting, as in Pteropus White: and the species figured (fig.
10) ; in some species it is situated in the middle of the diastema
between the canine and second premolar, in other species it is close
to the canine. In the lower jaw the first premolar is larger and more

subsist ; it extends in almost a straight line from the stomach to the vent. The dentition of the
so called ‘‘ Vampire,” minutely described by M. de Blainville in his “ Ostéographie des Chéirop-
téres,” p. 32, is that of an insectivorous species of Phyllostoma, in which the intestine is twice
the length of the body. ,

The complex stomach of a Pteropus is described as that of a Vampyre Bat in the
“Lectures of Comparative Anatomy,” by Sir Everard Home, who thereupon infers that
“the Vampyre-bat lives on the sweetest of vegetables; and all the stories related with so
much confidence of its living on blood, and coming in the night to destroy people while
asleep, are entirely fabulous,” p. 160. The blood-thirsty habits of the true Vampires have
been observed by more than one scientific traveller in South America. Dr. Spix calls one of these
bats, which he discovered in Brazil, “‘ Sanguisuga crudelissima”’ ; and Mr. Darwin has recorded
the attack of another species which fastened upon the withers of his horse, during a nocturnal
bivouac in Chile. See “ Voyages of the Adventure and Beagle,” vol. 111, p. 25.

(1) In some species of Roussette, as the Pteropus Peronti, only a single pair of incisors
has been observed in both upper and lower jaws. See M. de Blainville loc. cit. p. 38.

BATS. 429

constant, but always much less than the second premolar, and with
a simple obtuse crown. The second premolar is the largest; the
succeeding teeth diminish in size to the last true molar: the crown of
each of these teeth is impressed by a longitudinal excavation, the
outer border of which is produced into a long conical cusp, which
in the second lower premolar resembles the crown of the canine,
especially in certain African Roussettes, as Pt. Whitei, Bennett: this
pointed lobe gradually subsides in the following teeth ; it is a little
higher than the inner boundary of the triturating depressed surface
in the penultimate molars, is almost obsolete in the small posterior
molar above, and quite lost in the still smaller one below. In Pt.
Whiter and Pt. macrocephalus the last small molar would seem to be
wanting in both jaws, according to Messrs. Ogilby and Bennett.(1)

166. Structure and Succession.—In the normal or Insectivorous
‘Bats the teeth so closely resemble those of the small terrestrial
Insectivores in composition and structure, as to render a particular
description of them almost superfluous in the present work.

When the fangs of the long and slender incisors and canines
are completed, the pulp-cavity contracts as it approaches the apex
of the fang to a linear fissure, and is finally closed by the external
cement. The calcigerous tubes descend almost vertically from the
closed end to the lowest part of the dentine, in a direction diametri-
cally opposite to that of the tubes which rise from the upper end of
the pulp-cavity to the summit of the crown. Through a great extent
of the middle part of the tooth the tubuli, forming a slight bend as
they leave the pulp-cavity, pass transversely to the outer surface.
In the crown the tubuli gradually bend upwards until they acquire
a vertical direction at the middle; at the opposite termination of the
fang, the tubuli gradually bend downwards from the transverse to
the vertical direction. The primary curve of the tubuli at the base
. of the crown presents its concavity towards the fang; that of the
tubuli near the end of the fang is concave towards the crown: in
both, the concavity is towards the centre of the tooth. The short
trunks of the dentinal tubes are ;,,th of an inch thick: in the fang
they seem to be grouped in fasciculi. The dentinal cells are well defined
near the periphery of the crown; they present a diameter of qth

(1) Zool. Trans, vol. 11, p. 34. |

430 BATS.

of aninch. The fibrous structure of the enamel is very conspicuous ;
at the side of the crown the fibres make a short curve on leaving the
dentine concave towards the grinding surface, and then make a
longer bend in the opposite direction. This structure may be clearly
seen in the canines of the Rhinolophus ferrum-equinum.

The microscopic structure of the teeth of the frugivorous
Bats appears worthy of a fuller notice. I have examined it more
particularly in the canine and molar teeth of the Great Roussette
(Pteropus edulis).(1) The crown of the canine has an entire in-
vestment of enamel; the fang is covered by clear cement, thickest
at its extremity but without radiated cells. The tubuli of the
dentine are jth of an inch in diameter at their origins, and are
there about the same distance apart; they slightly diverge from
one another as they proceed from the summit of the pulp-cavity,
in the usual radiated direction ; the primary curves of the tubes which
proceed to the sides of the crown being gently concave towards the
summit in the greater part of their course, with both extremities
slightly bent in the opposite directions ; at the beginning of the fang
they pass outwards, and gradually acquire a curve convex towards
the crown; lower down they are more irregularly bent, and near the
apex of the fang, again present the curve concave towards the crown.
The tubuli in the crown rarely dichotomize, and accordingly by their
divergence leave wider interspaces of the clear basal substance, which
receive the small lateral branches that are sent off from both sides
of the tube, subalternately, throughout its course. The tubes dimi-
nish in size, like arteries after division, and near the enamel are
resolved into fine ramuli, which anastomose or dilate into minute opake
cells. ‘The secondary undulations are extremely faint in the crown ;
they become stronger as the tubes descend into the fang, crossing
each other and producing, with the side-branches, a rich arborescent,

and interlaced appearance, which becomes more complex as the tubes”

approach their termination near the cement, into which they push many
terminal ramuli : in this clear substance they dilate into minute opake
cells ; but, as has been already observed, there are no normal radiated
Purkingian cells in the cement of the canine tooth.
The tubuli of the dentine of the crown of the molar tooth differ
(1) Pl. 113, 113A. —

BATS. 431

from those in the fang in the minor degree of secondary undula-
tion; being, in fact, much straighter than the coronal tubuli of the
human tooth, which they rather exceed in size at their origin: they
diminish more rapidly in size as they approach the enamel, and give
off more numerous and conspicuous lateral branches ;(1) presenting a
stellate appearance in transverse or oblique section. The median
tubuli rise vertically to the summit of the crown, the lateral ones
diverge with a graceful curve convex towards the summit; at the
neck of the tooth they rather abruptly take the opposite curvature,
still proceeding transversely outwards ; but gradually incline down-
wards as they approach the ends of the fangs.(2) In the thick cement
at this part of the molar teeth a few of the cells assume the angular
form, and approach the size of the ordinary Purkingian cells ; in the
rest of the fang the clear cement is studded with more minute and
simple opake cells.

The boundaries of the dentinal cells,(3) which were scarcely dis-
cernable in the canine tooth, are very conspicuous in the molars,
especially near the periphery of the crown. They are of unusually
large size in proportion to the whole tooth, being absolutely larger
than the dentinal cells of the human tooth, and their interspaces
dilate here and there into semi-opake streaks. In vertical sections
of the molar teeth the part of the boundary of the cells next the
periphery of the crown was most conspicuous, forming a semi-
circular line, clear or opake, according to the focus, convex towards
the periphery, arching across from ten to twelve of the dentinal tubuli :
the whole producing the appearance of an imbricated structure. In
transverse sections the whole contour of the dentinal cells is visible : (4)
they are irregular in form and size as seen in a section exposing
them on the same plane, where they are probably cut through at
different levels, some of the largest present an irregular hexagonal
figure, and a diameter of sth of an inch.

The enamel of the teeth of the Pteropus is unusually opake,

(1) Pl. 113, fig. 2, d. (2) Ib. fig. 1.

(3) Ib. fig. 1, and Pl. 113 a, fig. 2, d', d',.
(4) Pl. 113 a, fig. 1.

432 BATS.

dark-coloured, and its fibrous structure ill defined.(1) In the canine
the fibres are ;,th inch in diameter; they are directed at the sides
of the crown, almost perpendicularly to the surface of the dentine,
with a slight convex bend towards the summit of the tooth; the
layers of growth proceed very obliquely from without, down-
wards and inwards; I counted eleven layers in a transverse section
of the enamel at the middle of the crown of the canine.

The succession of the teeth in the order of Volant Mammals
has received the most satisfactory elucidation from the careful and
minute researches of M. Rousseau on the Vespertilio murinus.(2)
The deciduous teeth make their appearance above the gum in Bats,
as in Shrews, before birth; but they attain a more completely
developed state, and are retained until a short time after birth,
when they are shed. The series consists of in. =, ¢. FH, m. 3,=22:
magnified views of the deciduous teeth mm situ of the common Bat
are given in Pl. 112, fig. 1**, and of both the deciduous and perma-
nent teeth detached on the right hand of figs. 1 and l**. The
deciduous incisors (%) have slightly expanded tridentate crowns ; the
anterior and longest does not exceed r.th of an inch in length: the
lower deciduous incisors are shorter, but of a similar form. The
canines (c’*) very slightly exceed the incisors in length, but are a
little more deeply implanted, and the middle cusp of the tridentate
crown is longer and more conical. The upper deciduous molars (p’)
resemble the incisors, but are broader in proportion to their length,
which scarcely equals one line; the lower deciduous molars are
more slender. No tooth has been observed to precede the third
tooth of the permanent molar series, (p) which, by its shape should
be regarded as a premolar: if this tooth be classed, from the
circumstance of its not displacing any predecessor, amongst the
true molars, these will then be four in number on each side of
both jaws, as in the Marsupialia.

In the foetus of a species of Pteropus so far advanced as to

(1) Pl. 113, fig. 2, e.
(2) “Mémoire zoologique et anatomique sur La Chauve-souris commun, dite ‘ Murin,’ ”

Magazin de Zoologie, 1839.

QUADRUMANES. 433

have acquired a slight covering of hair, and of which the head was
an inch and a half in length, I found the whole of the deciduous
series in place, in number as follows:
Incisors oe canines ae molars —— = 20.
2—2 Lo 2—2
The representatives of the molars were not quite one line in length,
slender, and with simple and very slightly enlarged crowns ; the
canines were larger and more curved.

CHAPTER IX.
TEETH OF QUADRUMANA.

In entering upon the study of these organs in the extensive
group of mixed-feeding placental Quadrupeds, associated together
by the common character of the opposable thumb on the hind-foot,
and to which Cuvier has applied the name Quadrumana, (though
this name be strictly applicable only to the old-world Sime
of Linnzus), we are met at the outset by two very singular and
anomalous conditions of the dental system in the genera Galeopithecus
and Cheiromys.

167.—The Colugos (Galeopithecus) resemble the Bats in the
great expanse of their parachute, formed by the fold of integument
extending on each side from the fore to the hind extremity ; but they
appertain by the essential characters of their organisation to the
Lemuride : the dental formula of the genus (Pl. 114, fig. 1, la, 10.) is:

a 2—2 * 1—1 2—2 3—3
Incisors — ; canines —; premolars —; molars —: = 34.
3—3 1-1 2—2 3—3

The two anterior incisors of the upper jaw are separated
by a wide interspace: in the Philippine Colugo they are very
small, with simple sub-bilobed crowns; but, in the common
Colugo (Lemur volans, Linn. Galeopithecus Temminckii, Wat.)
their crown is an expanded plate with three or four tubercles ; the
second upper incisor, which is unquestionably supported by the

F F

434 QUADRUMANES.

intermaxillary bone, presents the peculiarity of an insertion by two
fangs in both species of Galeopithecus; its crown is a compressed

triangular plate, with a small talon at the anterior and posterior part —

of the base in Gal. Philippinensis, and with two anterior and three
posterior dentations in Gal. Temmincku. The upper canine (c) very
closely resembles the second incisor, and is also implanted by two

fangs. The first upper premolar (p) has a trihedral crown, more —

simple and compressed in Gal. Temminckw than in Gal. Philippinensis,
in which the crown supports two triangular prisms, with one side

turned outwards and one angle inwards; the crown of the second —

premolar has, besides the two prisms, a pointed talon at the base
of the internal space between the prisms. In the true molars (m)
the internal talon is relatively larger, and when the prisms are
worn down to its level they present a broad triturating surface.

In the lower jaw the crowns of the first two incisors (%) present the
form of a comb, and are in this respect unique in the class Mammalia :
one is figured of the natural size in Pl. 115, fig. 1, and magnified at

fiz. lg. This singular form of tooth is produced by the deeper —

extension of the marginal notches on the crown, analogous to those
on the edge of the new-formed human incisor; the notches being

also more numerous as well as deeper: each of these broad pectinated

teeth is implanted by a single conical fang.(1) The third incisor,

viewed through the analogy of the Lemurs seems to be a canine, but |

in nature its crown is in advance of the last intermaxillary tooth above :

the margin of the crown is broad, horizontal, and is indented by ©

shallow notches which are four in number in the Philippine Colugo ;
in both species this tooth is supported by a single fang. The lower

canine (c’) nearly resembles the upper canine, has two fangs, but

has a rather shorter crown, which passes before that of the upper

canine when the mouth is shut: its oblique margins are dentated in

the Galeopithecus Temminckii, and entire in Gal. Philippensis. The
first premolar resembles the canine, but has a thicker and a lower

(1) The Colugos have a large ccecum, and are said to feed on the leaves of the Nanka or

Jack-fruit : they may also derive part of their diet from small birds or insects; but the mode —

Se LR INS BLES Herb 0 8 tw

in which the crowns of the molar teeth are abraded by mastication indicates the preponderance i
of vegetable food. The pectinated lower incisors may serve to trim the fine fur with which —

they are clothed. F

CHEIROMYS. 435

crown: the second premolar, like the three true molars, has a broad,
oblong quinque-cuspid crown, four cusps being in two transverse pairs,
and the fifth at the anterior and internal angle of the tooth.

In the broad pectinated incisors of the Galeopithecus the
pulp-cavity divides at the base of the crown into as many canals as
there are divisions of the crown, one being continued up the centre of
each to within a short distance of its apical extremity. The calci-
gerous tubes which radiate from these canals have a diameter at
their origin of =;;th of an inch: they quickly divide and subdivide
dichotomously with rather large and irregular secondary undula-
tions, sending off many fine branches and resolving themselves
into numerous smaller ramifications which interlace irregularly
near the enamel. The tubuli in the body of the tooth have
longer trunks, but present a very similar character: the section
figured in Pl. 115, being taken a little on one side of the central
pulp-cavity shows the diverging tubuli cut almost transversely
across in the middle of the body of the tooth, and the longi-
tudinal course of the wavy ramifying tubes at the margins of
the section. The medullary canal or branch of the pulp-cavity
is shown in some of the divisions of the crown, at m. Each
division of the crown has its proper investment of enamel, which
substance is continued for a short distance upon the common base.

The deciduous teeth appear not to cut the gum _ before
birth, as they do in the true Bats. In a fcetus of Galeopithecus
Temmincku, with a head one inch and a half in length, I found
the calcification of the first incisor just commenced in the
closed alveolus; the second incisor and the rest of the deci-
duous series being represented by the vascular uncalcified matrices.
The upper milk teeth (Pl. 114, fig. 1b) consist of two incisors,
a canine, and two molars; which latter are displaced and suc-
ceeded by the two premolars. The deciduous teeth are six in
number in the lower jaw; the incisors being pectinated, but
much smaller than their successors. The true molars are de-
veloped and in place before the deciduous teeth are shed.

168. Cheiromys.—In this genus of Lemurine animals, as in
Desmodus amongst the Bats, and Sorex amongst the Insectivores,

FF 2

436 QUADRUMANES.

the dentition is modified in analogical conformity with the
Rodent type, to which, in the present instance, it makes a very close
approximation, the canines being absent and a wide vacancy sepa-
rating the single pair of large curved scalpriform incisors in each
jaw from the short series of molars.(1)

The upper incisors are compressed, presenting a narrow oval
transverse section, with the long diameter from before backwards ;
they are curved in the segment of a circle, and deeply implanted ;
the short exserted crowns touch one another ; their simple, widely
excavated fangs diverging as they penetrate the substance of the
jaw. The short crowns project obliquely forwards and do not
extend vertically downwards as in the true Rodentia.

The lower incisors are more compressed, and of greater
breadth from before backwards, than the upper ones; they are
more curved than in the Rodentia, describing a semicircle, two
thirds of which are lodged in the socket, which extends back-
wards beyond the last molar tooth to the base of the coronoid.
The anterior edge of the oblique cutting surface does not rest
against a posterior ridge of the surface of the tooth above,
whence M. de Blainville infers that these large scalpriform
teeth were put to a different use from that to which the same
teeth of the Rodents are habitually applied. He conjectures,
that they served the -Cheiromys rather as a pair of cutting
pincers to remove the bark and perhaps the wood of trees in
search of larvze or insects, which, however, the smooth, flat
crowns of the molars would not indicate to have been the staple
food of the Cheiromys. The most important character by which
the incisors of this anomalous Lemur differ from those of the
Rodentia is the entire investment of enamel, which is, how-
ever, thicker upon the front than upon the back part of the
tooth.

The molar teeth are four on each side of the upper jaw,

(1) Pl. 114, fig. 2, M. de Blainville, who first pointed out the affinity of the Cheiromys
to the Quadrumana, has made the observation that the edentulous margin of the jaw between

the incisors and molars is sharp, as if it had lodged some spall teeth that had been shed;
whilst in the true Rodentia it is always broadly rounded off and smooth.

LEMURS. 437

and three on each side of the lower jaw, implanted vertically
and in parallel lines.(1) The molars are of simple struc-
ture, with a continuous outer coat of enamel, and a flat sub-
elliptic grinding surface: the upper ones are of unequal size,
the first being the smallest, and the second the largest: in the
lower jaw the inequality is less, and the last molar is the least.
The first and last molars above have but one root: the second
and third have each three roots. The first lower molar has two
roots, the second and third have each a single root.

169. Lemuride.—The Indris (Lichanotus, Hliger) are small tail-less
Lemurs, which, when full-grown, have but two incisors in the lower
jaw, of larger size than in other Lemurs, especially in the species
(Lich. Diadema) on which the sub-genus Propithecus has been founded.
The dental formula in the Lichanotus Indri and Lich. laniger, is :—

‘ 2—2 —2 3—3
Incisors — ; canines — ; premolars ; a molars — : = 30.

In the common Indri the upper incisors, especially the anterior
one, are proportionally larger than in the higher Lemuride, in
the woolly Indri (Pl. 114, fig. 6) they are very small. In both
species the canine has a trihedral straight compressed conical crown ;
the premolars have shorter compressed crowns: the first and second
molars have square, four-lobed crowns; the last molar is tri-
angular and of smaller size. The lower canine (c) is directed obliquely
forwards parallel with the incisor, which it closely resembles in
the Lichanotus laniger; in the common Indri it is longer and
larger. The premolar and molar teeth resemble those above, but
the last supports five tubercles.

The dentition of the Malmags or Spectre-Lemurs (Tarsius)
offers a more insectivorous eee the formula is :—

° 2—2 —3 3—3
Incisors — ; canines — marie premolars - se molars — : == 4,

The first upper incisor, as in the Shrews, is longer than the canine.
The inferior canines (c’) are characterised, as in other Lemuride,

(1) In the general characters of the teeth of the Rodentia, p. 400, the convergence of the
molar series is noticed.
(2) Pl. 114, fig. 3.

438 QUADRU MANES.

by their crowns passing in front of the upper canines; but they
here present more of the laniariform shape and proportions and have,
therefore, been recognised as canines by those Comparative Ana-
tomists, M. F. Cuvier for instance, who have regarded the analogous
teeth as incisors in the Indris and the higher Lemuride. The pre-
molars in the Tarsw are conical, and slightly increase in size as they
approach the true molars: these have the lobes of the crown, espe-
cially the outer ones, produced into sharp points.

The Galagos (Otolicnus) resemble the Malmags in the insec-
tivorous character of the crowns of the true molar teeth, but have an
additional pair of incisors and smaller canines in the lower jaw. The
dental formula in these, as in the Slow Lemurs (Stenops) is :—

2—2

F a 1—1 3-3 3—3
Incisors — ; canines —; premolars —; molars —: = 36.
2—2 1—1 3—3 343

In the Stenops tardigradus(1) the first upper incisor is larger than
the second, as in the genus Tarsius.

The true Lemurs or Makis (Lemur, Geoff.) have the same
number and kind of teeth as the Slow Lemurs. The _ inferior
canines, Pl. 114, (fig. 5, c'), first recognized as such by Geoffroy,
are compressed and procumbent like the incisors, but are a
little larger. In the upper jaw the two incisors are small and
vertical, with short, expanded crowns: the two on the right side
are separated by a wide space from the two on. the left. The
canine (c) is long, curved, compressed, sharp-edged and pointed.

The three premolars have the outer part of the crown prolonged 1

into a compressed pointed lobe, whilst the inner part forms a
tubercle, which is largest in the second and third. In the true
molars the inner division of the crown is so increased as to give
it a quadrate form: the outer division being divided into two
pointed lobes. The first of the true molars is the largest in both
jaws.

The first premolar above is implanted by two connate fangs:
in the second and third they are distinct, and a third inner fang
is developed to support the inner lobe of the crown. Each upper

molar is supported by three short and thick fangs. In the lower —

(1) Ib. fig. 4.

he

PLATYRHINES. 439

jaw both premolars and molars are severally implanted by two

fangs; the canines and incisors, in both jaws have each a single

fang, according to the normal mode of implantation of these teeth,

which is henceforth not departed from in the Mammalian Class.
The deciduous series of teeth in the genus Lemur is :—

: 2—2 : ey 3-3
Incisors ss Canines — ; molars tse 24,

170. Platyrhines.—All the Quadrumana of America are distin-
guished from the Apes and Monkeys of the old world by certain well-
marked external characters : of these, the position of the nostrils at the
sides of the broad nose, whence their collective name, is the most con-
spicuous ; but they have a more important dental distinction in the
superior number of the premolars, which are %%, instead of 35;
whereby the American Monkeys manifest their closer affinity to the
Lemurs, and their inferior position in the zoological scale.

The small and delicate platyrhine Monkeys commonly known
in this country by the name of ‘ Marmosets,’ and forming the
genera Hapale and Midas, have but two true molar teeth on each
side of both jaws, their dental formula (Pl. 114, fig. 8.) being :—

Incisors —; canines =; premolars — ; molars a sao

In the Jacchus Marmoset (Hapale Jacchus) the crowns of
the upper incisors are broad and trenchant, the first being the
largest ; but the lower incisors continue, asin the Lemurs, to be
long and pointed like the canines, to which they are but little
inferior in size. The upper canines present a character which is
peculiar among Mammalia to the Quadrumana, viz: a longitudinal
groove along the fore-part of the crown. The shape of the crowns
of the premolars is shewn in fig. 8, p: they are each implanted by
a single fang. The first true molar above has three roots, that
below has two; the second moiar has a single root in both the
upper and lower jaws. A vacant interspace separates the upper
canine from the incisors; the teeth of the lower jaw form a con-
tinuous series, as in Man.

440 QUADRUMANES.

The lemurine character of the long, narrow, inferior incisors
continues to be manifested by the Sakis (Pzthecia, Illig.), which,
like the larger species of Platyrhines called Howlers, Capuchins,
and Spider-Monkeys, have the normal number of true molar
teeth in the Quadrumanous Order, their dental formula being :—

I . 2—2 B 1—1 1 3—3 1 3—3 36
ncisors rae canines ia premolars ik molars Ba. .

The Capuchin Monkeys, (Cebus, Pl. 114, fig. 9) have the four
lower incisors (i) with broad, thick, wedge-shaped trenchant crowns ;
a form which these teeth retain with slight modifications throughout
the rest of the Quadrumanous Order. In the Howlers, (Mycetes),
the incisive margin of the lateral lower incisors is more produced ;
these are larger than the middle incisors, the proportions of the
upper incisors are reversed. The canines (c) are strong and well-
developed in both jaws; those above being marked by the deep
anterior groove; there is also a second longitudinal groove on the
inner surface of the crown near its posterior margin. The canines
are relatively stronger than in the Marmosets; especially in the
male Capuchins. ‘The upper premolars (p) have their crown divided
into two trihedral pointed cusps on the same transverse line, the
outer one the longest and largest: the transverse diameter of these
teeth exceeds their antero-posterior diameter. The first premolar
below differs in form from the rest, a short trenchant ridge being
continued forwards from the outer cusp, and opposing itself to the
inner surface of the canine tooth above: the two cusps of the
second and third premolars are less unequal than those above,
and the inner one is the most produced. The true molars (m)
decrease in size from the first to the third, which is tricuspid below,
the rest being quadri-cuspid. In the Spider-monkeys (déeles) the
second true molar below is larger than the first; and in the
Howlers (Mycetes) both the second and third lower molars ex-
ceed the first in size, and the middle one is the largest above,
(Pl. 114, fig. 10). In the attrition of the crowns by mastication,
the inner tubercles of the upper molars, and the outer ones of
the lower molars, are the first to yield; but the sub-trenchant

CATARHINES. 441

first premolar below continues longest prominent, and resembles a
small canine. (1)

The premolars are implanted by two connate fangs, those above
becoming separate, and diverging near their extremities. The first
and second true molars above have three fangs; the last has two
in Mycetes, and one in Cebus. Each of the lower true molars is
implanted, in Mycetes, by two fangs; but the last has only one
fang in Cebus.

All the platyrhine Monkeys have four more teeth in their
first dentition than the catarhine or old-world Quadrumanes
possess ; the deciduous formula being :—

. 2—2 = 1—l 3—3
Incisors 5 Canines —; molars aaa 24.

171. Catarhines.—In this division of the Order the first or
deciduous dentition consists, as in Man, of :—

2-2 11 2—2
; : . j —— © ——- © = iy
Incisors ae Canines > molars . 20.

The milk molars are displaced and succeeded vertically by the
bicuspid premolars, and are followed(2) horizontally by three true
molars on each side of both upper and lower jaws; the perma-
nent formula in all the old-world Quadrumanes being :—

: 2—2 = 1-1 2—2 3—3
Incisors —; canines — ; premolars —; molars —: = 32.
2—2 1-1 2—2 3—3

If a speculative morphological view were to be given in explana-
tion of the transition from the Platyrhine to the Catarhine type of
dentition, it might be said that the third premolar of Cebus had
been developed into a true molar, and the last true molar reduced
so low as to be confluent, as a fifth posterior tubercle, with the
second molar, now become the last true molar, in order to form
the dentition of the Baboons and Semnopitheques, at least of the
lower jaw (Pl. 116, fig. 2, m. 3) : the small size of the first true molar
in the Baboons, (ib. fig. 2, m. 1) would seem to give further counte-
nance to such an hypothesis; but this tooth, like the other true

(1) Duvernoy in Cuvier’s Legons d’Anat. Comp. t. 1v, (1836) p. 297.
(2) This word refers to position in the jaw, not to time of appearance.

442 QUADRUMANES.

molars, has no deciduous predecessor.(1) In the true Monkeys {
(Cercopitheci), the Gibbons, and the Orangs, the last molar of the —

lower jaw has a square quadri-tuberculate crown like that above.

The incisors have always a shape conformable to their name,
but are very strong and thick ; in the upper jaw the middle are larger
than the lateral ones, and both are larger than those below. In the

——

Baboons, the Monkeys, and the Semnopitheques, the lower incisors —

(Pl. 116, fig. 2, 2) are sub-equal, or the middle ones are larger
than the lateral ones in the Gibbons (ib. fig. 6), and the Orangs,
(Pl. 117, Pl. 119, fig. 1), the middle lower incisors are the smallest,
as in Man. The lateral inferior incisors of the Baboons (Pl. 116,
fig. 4°, 7) and Semnopitheques (ib. fig. 5)are further distinguished by
the oblique truncation of the outer angle of the crown. Both series
of incisors describe a deeper curve in the Baboons and Monkeys
than in the Orangs, in which they approach the rectilinear ar-
rangement which characterize these teeth in the Human subject.

The canines are conical, pointed, with trenchant posterior margins,
always longer than the adjoining teeth, and acquiring in the males
of the great Baboons and Orangs, the proportions of those teeth
in the true Carnivora. The Mandrills, (Cynocephalus maimon,) have
these dental weapons most formidable for their size and shape ;
especially the upper pair, which descend behind the crowns of the
lower incisors, and along the outside of the first lower premolars,
(Pl. 116, fig. 4°, p) the crowns of which seem as if bent back by the
action of the upper canines: the anterior longitudinal groove of these
canines (ib. fig. 4) is very deep, their posterior margin very sharp.
A long diastema divides the upper canine from the incisors, a short

one separates it from the premolars: these and the three true molars —

are arranged in a straight line. Each premolar supports a large ex-
ternal and a small internal cusp; the true molars have four pro-

minent, sharp-pointed cusps, with an anterior and posterior basal —

ridge; they progressively increase in size from the first to the
third in all the Baboons. The first ‘premolar of the lower jaw is

(1) In the private collection of the Baron Van der Capella, near Utrecht, I saw, in the ~
year 1838, a variety in the dentition of an adult Simia Satyrus, vix: six molar teeth on each —

side, but only two of these had the characters of premolars. -

oo

_CATARHINES. 443

remarkable for the anterior prolongation of the base of the crown,
which is worn to a sharp edge by the action of the upper canine;
the second premolar has a quadri-cuspid crown. The crowns of
the lower molars are narrower and longer than those above, especially
the last, in which the posterior ridge is developed into a fifth lobe
or tubercle. The premolars and molars of the upper jaw are im-
planted each by three fangs ; those of the lower jaw by two fangs.

The smaller Baboons, of the genus Macacus, repeat on a smaller
scale the dental characters of the Mandrils; but in most of them
the posterior tubercles of the second inferior premolar are reduced
to a talon or basal ridge (Pl. 116, fig. 1 & 2). In fig. 3 a view is
given of two of the fossils from an eocene tertiary formation in
Suffolk, which have revealed the former existence of a species of
Macacus, in our latitudes, at that ancient period.(1)

In the Semnopitheques (PI. 116, fig. 5) the lower incisors are
more equal in size: the canines are smaller, and the upper ones less:
deeply grooved than in the Baboons: the base of the first lower pre-
molar is less extended anteriorly : the first true molar is equal to the
second, and the last is narrower anteriorly in proportion to its
length. ‘These dental differences, however, are very slight as com-
pared with those in the structure of the stomach, by the expansion
and sacculation of which the ordinary Semnopitheques, as well as the
long-nosed species (Nasica) and the thumbless species (Colobus), differ
from the Macacques and Mandrils.(2)

In the long-tailed Monkeys with a simple stomach (Cercopithecus),
the dentition differs from that of the Semnopitheques in the last
lower molar being quadri-tuberculate, and of equal size with the rest.
In the long-armed tail-less Apes, or Gibbons, (Hylobates Pl. 116,
fig. 6) the true molars (m) are sub-equal, the lower ones being rather
narrower than those above ; the crowns have a more rounded contour
than in the inferior Quadrumana; the upper molars support four
tubercles, the lower ones five, three being placed along the outer
curve. In the skull of an old Hylobates syndactylus, 1 find these
outer tubercles of the lower molars worn into three deep depressions,

(1) See my “ History of British Fossil Mammalia,” p.1 & 16.
(2) See Trans. Zool. Society, vol. 1. pp. 70, and Proceedings of the Zool. Society, 1841,
p. 84.

444 QUADRUMANES.

which are stained black; the two inner tubercles are polished flat

by attrition, but retain their enamel: in the upper molars the outer |
tubercles are in the latter state, the inner half presents a deep 7

excavation of the dentine, which is stained black.
In the great Orang-utan (Simia Wurmbi, Pl. 117, fig. 1 & 2)
the median incisors of the upper jaw are of unusual size: and

strength ; the thickness (antero-posterior diameter) of the base of ©

the crown almost equals the breadth of the same; and they are
double the size of the lateral incisors (7 fig. 2). The abraded
surface of the front incisors in the old Orang forms a broad tract
- extending obliquely from the cutting edge to the back part of the
base of the crown ; the lateral incisors are more pointed, the outer
angle being obliquely truncated : a vacant space of their own breadth
divides them from the canines. These, in the male of the great
(Wurmb’s Pongo, c) have a long and strong slightly curved crown,
Orang extending below the alveolar border of the under jaw when the
mouth is shut, with a moderately sharp posterior margin, but
without an anterior groove: the crown is convex externally, with
a slighter convexity between two longitudinal depressions on the
inner surface. In the female Orang (fig. 3) the canines are
smaller; the crowns extend only a short distance beyond the level
of the adjoining molars. The male of the smaller and more an-
thropoid species of Bornean Orang, which I have called Sima
Mori, (fig. 4) has the canines less developed in proportion to
those of the female.(1) In both species of Orang the two cusps
of the first premolar are rather more produced than those of the
second, as is likewise the outer and anterior angle of the base of
the crown. ‘The first and second true molars are rather larger than
the third; they have each four cusps, but less developed, and
with shallower interspaces than in the Baboons and Monkeys. The

(1) Zool. Trans. vol. 11, p. 1655, Pl. 33, Oct. 1836. Mr. Brooke, the enterprising traveller
in Borneo, has transmitted skulls of both sexes of S. Morio to the Zoological Society, and fully
confirms my determination from cranial evidence of the two distinct species of that island. He
says, “The natives of the north-west coast of Borneo are all positive as to the existence of two
distinct species.” “‘ The Mias Pappan is the Simia Wurmbii of Mr. Owen, having callosities on
the side of the face. The Mias Kassar or Simia Morio, is the same colour as the Mias Pappan,
but altogether smaller and devoid of callosities either on the male or female adults.”—Pro-
ceedings of the Zoological Society, 1841, p. 55.

APES. 445

enamel covering the grinding surface is finely wrinkled before abra-
sion. In the upper jaw both premolars and molars are implanted by
three diverging fangs, twe external and one internal; the anterior ex-
ternal fang of the first premolar is the longest and strongest. In the
lower jaw the median incisors are a little larger than the lateral ones,
in which the outer angle is usually rounded off; the crowns of the
canines are less robust than those above. The outer part of the
first premolar rises to a sub-acute point, from which three ridges
descend, one to the fore part of the grinding surface, the other
to the back part, and the third to the inner part, which is developed
into a slight tubercle. In the second premolar this tubercle rises
almost to an equality with the outer one. The first and second
true molars have three cusps along the outer curve of the grinding
surface, and two upon the inner side, the anterior being the highest.
The last molar has two external cusps, and the posterior inner
one is almost obsolete. The premolar and molar teeth are each
inserted by two strong diverging fangs. The series of grinders forms
a straight line in both jaws.

The dentition of the Chimpanzee (Simia Troglodytes), though
in all its most prominent characters strictly Quadrumanous, yet,
in the minor particulars in which it differs from that of the Orang,
advances towards the human type. In the upper jaw the middle
incisors (Pl. 118, fig. 1, 2) are smaller, the lateral ones larger
than those of the Orang; they are thus more nearly equal to
each other; nevertheless the proportional superiority of the middle
pair is greater than in Man. Each incisor has a prominent posterior
basal ridge, and the outer angle of the lateral incisors is rounded
off, as inthe Orang. The diastema between the incisors and canine
is narrower than in the Orang. The crown of the canine (ib. c.),
passing outside the interspace between the lower canine and pre-
molar, extends a little below the alveolar border of the under jaw
when the mouth is shut; it is conical, pointed, more compressed
than in the Orang, and with a sharper posterior edge; convex
anteriorly, flattened at the posterior half of the outer surface, concave
on the corresponding part of the inner surface, which is traversed
by a shallow longitudinal impression: a feeble ridge divides this
from the convex anterior surface, which bears a linear longitudinal

446 QUADRU MANES.

impression. Both premolars (ib. p.) are bicuspid, the exterior
cusp of the first is the largest and most produced. The true
molars (ib. m) are quadri-cuspid, relatively larger in comparison.
with the bicuspids than in the Orang: the last is the smallest
by the feeble development of the two hind cusps. The premolars
as well as molars, are severally implanted by one internal and
two external fangs, diverging, but curving towards each other at_
their ends, as if grasping the substance of the jaw. :
In the lower jaw the lateral incisors are broader than the middle
ones, but have their outer angle rounded off; they are all much
Jarger and less vertically implanted than in Man (Pl. 119, fig. 1, 7).
The lower canines (ib. c) are two inches in length including the root ; —
the enamelled crown is three fourths of an inch in length, and two thirds
across the base ; it is conical, trihedral, the outer surface convex, the —
other two surfaces flattened or sub-concave, and converging to an ~
almost trenchant edge, directed inwards and backwards ; a ridge sepa- _
rates the outer convex from the anterior surface: both this and the ©
posterior surface, show slight traces of a longitudinal rising. The
canine almost touches the incisor, but is separated by a diastema —
one line broad, from the first premolar. This tooth (ib. p.) is larger
than the second premolar, and is twice the size of the human first —
premolar ; it has a subtrihedral crown, with the anterior and outer
angle produced forwards, still indicating the peculiar feature of —
the same tooth in the Baboons; the summit of the crown terminates
in two sharp trihedral cusps, the outer one rising highest, and it
has a well developed ridge at the inner and posterior part of its —
base. The second premolar has a sub-quadrate crown, with the
two cusps developed from its anterior half, and a third smaller one —
from the inner angle of the posterior ridge. Both the lower
premolars are implanted by two antero-posteriorly compressed,
divergent fangs, the anterior one the largest.(1) The three true
(1) M. de Blainville, in his “‘ Ostéographie des Primates” expresses himself somewhat ; :
obscurely on the mode of implantation of the molar teeth of the Chimpanzee and Orang,
and although he alludes to faint indications of the two external holes for the premolars,
leaves the impression that these superior Apes differ from the inferior ones in the struc-
ture of the alveoli of the teeth. ‘Du reste, si les quatre parties de la couronne ne sont

pas aussi nettement dessinées que dans les Singes inférieures, certainement il n’y a aucune
indice des mammelons accessoires des Gibbons.” (See, however, a demonstration of the

APES. 447

molars (ib. m.) are almost equal, the first being smaller or not
larger than the last; which is the only molar equalling in size the
corresponding tooth in the black varieties of the Human subject
(Pl. 119, fig. 2, m.), in which the true molars attain their largest
dimensions. The four principal cusps, especially the two inner
ones, of the first molar of the Chimpanzee are more pointed
and prolonged than in Man: a fifth small cusp is developed
behind the outer pair as in the Orangs and the Gibbons but
is less than that in Man. The same additional cusp is pre-
sent in the second molar, which is seldom seen in Man: the
crucial groove on the grinding surface is much less distinct
than in Man, not being continued across the ridge connect-
ing the anterior pair of cusps in the Chimpanzee. The crown
of the third molar is longer antero-posteriorly, from the greater
development of the fifth posterior cusp, which, however, is rudi-
mental in comparison with that in the Semnopitheques and Ma-
cacques. All the three true molars are supported by two distinct
and well-developed, antero-posteriorly compressed, divergent, fangs,
longitudinally excavated on the sides turned towards each other.
The molar series in both jaws forms a straight line, with a slight
tendency in the upper jaw to bend in the opposite direction to
the well-marked curve which the same series describes in the
Human subject.

172. Succession and Structure—The deciduous dentition in-
cludes in all the catarhine Quadrumana, twenty teeth, viz:

Incisors — ; canines — ; molars — : = 20.
2—2 I—l 2—2

The second deciduous molar is quadri-cuspid, and is succeeded by
a permanent premolar with a bicuspid crown; the first deciduous
molar is bicuspid, and in the lower jaw of the Baboons it has

contrary in Pl. 119, fig. 1, m.) He proceeds—“ Quant aux alvéoles des dents de ces
Singes supérieures, il est aisé de voir qu’elles doivent présenter quelques différences concor-
dantes; ainsi 4 la machoire supérieure, a peine si les deux trous externes sont indiqués
pour la premiére et surtout pour la seconde des avant molaires, aussi bien chez le Chim-
panzée que chez l’Orang-Outang. Les différences sont moins marquées pour les autres
molaires et surtout 4 la machoire inférieure,” p- 47. If there ever was an anatomical
comparison deserving a deeper and more decisive examination it is that regarding the
mode of implantation of the teeth of the Chimpanzee and Orang, which bears so imme-

448 QUADRUMANES,

a small anterior tubercle, which feebly indicates the great ex-

tension of that part of the crown of its successor. The deci- —

duous canines have short, straight, conical crowns; differing in
form and still more in size from the formidable sub-compressed

curved, piercing and trenchant teeth which succeed them: es- —

pecially in the male sex, which in this respect diverges farther
from the immature type than does the female. The permanent
incisors are also much larger than the deciduous ones, and
especially so in the Chimpanzee and Orang in which I shall
here describe the order of development and succession of the
permanent teeth; reserving the special comparison of their de-
ciduous teeth with those of the Human subject for the following
Chapter.

The deciduous teeth are shown zn situ in Pl. 120, in the young
of both these highly organised Apes, at the period when the first
permanent true molar (m 1) has cut the gum, on each side of both
jaws. The next permanent teeth that appear are the middle
incisors of the lower jaw, the corresponding deciduous teeth
being the first that are shed. Then the two large middle upper
incisors (i 1) come into place: these, in the living Orang of the
Zoological Gardens(1) occasioned the displacement not only of
the middle but the lateral milk incisors; whilst in the skull of
the young Orang, which I have described and figured in the
Zoological Transactions,(2) the middle permanent incisors and the

|

lateral deciduous ones are both in place in the upper jaw. The next

permanent tooth that cuts the gum is the second true molar of the
lower jaw, which is followed by the corresponding tooth of the upper
jaw (m2). In about eight months after the lateral inferior incisors
make their appearance above the gum, and then those of the upper
jaw (i 2). The bicuspids (p. 1 and p. 2) are the next teeth which
come into place. They are followed by the third true molar teeth.
The great canines (c) are the last of the permanent series which

diately upon the question of distinction between Man and the Ape: I have, therefore, de-
voted two plates (118 and 119) to the illustration of the striking difference which the

lowest as well as the highest races of the Human species present as compared with the '

Chimpanzee, in the insertion of the premolar teeth in both jaws.
(1) Zoological Proceedings, 1843, p. 123.
(2) Vol. ii, p. 166, pl. 30.

APES. 449

acquire their full development and functional position. In the female
the point of the canines sometimes pierces the gum before the last
molar has come into place.

The concomitant change which takes place not only in the size
but shape of the jaws is so considerable, and gives rise to such re-
markable modifications in the exterior of the cranium and the facial
angle, that the mature and immature states of the Simia Wurmbii
were for some time regarded by Naturalists as distinct species, under
the names of Orang (Simia Satyrus, Linn.) and Pongo (Papio Wurmbi,
Latr.). Nor is it surprising that the transition from the Orang to
the Hottentot should seem to be so gradual and easy, the cranial
characters of the supposed adult anthropoid Quadrumane being
those of a young animal with a full-sized brain and with deci-
duous teeth. Had the skull of the mature Chimpanzee been
transmitted from Africa at the period when Wurmb’s Pongo
was placed in the Mammalian Systems of Cuvier,(i) Fischer, (2)
and other Naturalists, as a distinct species, far below the Sima
Satyrus, it would most probably have been mistaken for that
of a lower, baboon-like Quadrumane. But its first description
was accompanied by a demonstration of the concealed germs of
the permanent teeth in the jaws of the young Chimpanzee, which
established the true nature of the adult cranium; the paternal
relation of the great Pongo of Wurmb to the young Orang being
demonstrated by the same evidence. (3)

The jaws of these highly organized Simie, during the acquisition
of the large permanent series of teeth, not only rapidly increase,
but a considerable change takes place in the extent of origin of
the temporal muscle: this leaves a well-marked impression near the
vertex in the Chimpanzee, and in the male Orang meets its fellow at
the vertex and stimulates the growth of a strong osseous crest.
The mastoid ridge also shifts its place, and retreats by progressive
absorption and deposition nearer to the plane of the occipital region

(1) Régne Animal, Ed. 1817, p. 111.

(2) Synopsis Mammalium, 1829, p. 32. Fischer thus concludes his description of the
Simia Wurmbii :—“ Sunt, qui hance speciem pro S. Satyro adulté ducant. Permulta tamen
sententiz isti repugnare videntur.” He does not cite any of the grounds of opposition.

(3) See Zoological Transactions, vol. i, p. 343.
GG

450 QUADRUMANES.

of the skull. The capacity of the cranial cavity undergoes no change,

{
; 5

but the parietes are thickened, especially at the line of the lambdoidal — |
suture, preparatory to the development of the great occipital ridge, _
which diverges from the end of the sagittal crest. The zygomatic _
arches are strengthened and expanded, the superior maxillaries I

produced, while the intermaxillaries having given passage to the —

crowns of the large permanent incisors, appear to have fallen in.
In the Orang the intermaxillary bones at this period have become
anchylosed to the maxillaries: in the Chimpanzee that confluence
is completed before the deciduous teeth are in place.

The microscopic structure of the teeth of the Quadrumana
is conformable throughout the platyrhine and catarhine groups,
and closely resembles that which Purkinje, Retzius, Miiller, and
myself have described in the Human subject. As this structure
will be more particularly elucidated in the chapter on the Human
teeth I shall here merely mention the most obvious differences
which the teeth of the Quadrumana present, and which are mani-
fested not only in the Baboons and Monkeys but in the most
anthropoid Ape, viz: the Chimpanzee(1). In the incisor and canine
the general direction of the calcigerous tubes agrees with that figured
in Fraenkel’s Thesis, fig. 1, B, and by Retzius in his ‘‘ Mikros-
kopiska undersékningar”’ Pl. z (ww), fig. 1, in the corresponding Human
teeth. The tubes(2) in the Chimpanzee describe the same primary
curvatures, but less strongly; and the secondary gyrations are
longer and more feebly marked: they are jq,th of an inch in dia-
meter, and the interspace between two tubes on the same plane

equals the width of two tubes, when viewed in transverse section

near the pulp-cavity, as in Pl. 119a, fig. 2; nearer the enamel the

interspaces are wider ; but in general they are more closely arranged
and relatively more numerous, besides being straighter than in the
Human subject. They maintain the same diameter through three-
fourths of their course ; divide sparingly, except close to the enamel

boundary and the periphery of the fang: in this part of the tooth

the minute lateral branches are most numerous. The calcigerous cells

of the dentine(3) are most conspicuous, as usual, near the periphery

of the crown, where their well-defined semi-circular contour is seen
(1) Pl.119 a, fig. 1 & 2. (2) Ib. fig. 1, ¢, t. (3) Ib. fig. 1, d:, de.

HUMAN DENTITION. 45}

with its convexity next the enamel: from ten to twelve dentinal tubes on
the same plane are included in the diameter of a peripheral calcige-
rous cell: the cells decrease in size and increase in number, and
become less definable as they become situated nearer the pulp-cavity.
The enamel fibres(1) are more wavy, even, than in the human teeth :
they are ,wth of an inch in thickness, and manifest the striated
indication of their cellular origin as distinctly as in the human
teeth. The vertical fibres ascending from the summit of the crown
of the canine of the Chimpanzee described twenty acute-angled
undulations in their course. In the section examined, the bend
in one direction transmitted more light than in the opposite, and
gave an appearance of waves upon the cut surface of the enamel.
This is the character attempted to be shown by Fraenkel in fig. 4,
of his Thesis, and which Retzius says he had not succeeded in
observing in human enamel. The lines of growth or strata of the
enamel were best displayed in transverse sections of the incisors and
canines. The cement is thickest at the apex of the fang; the Pur-
kingian cells are traceable to near the neck of the tooth, over which
the clear basis of the cement is continued upon the enamel : the tubuli
continued from the cells are most numerous on the side next the
dentine: they form likewise rich anastomotic plexuses in the in-
terspaces of the cells, besides communicating with peripheral ra-
mifications of the tubuli of the dentine: their diameter is j;,th
of an inch.

CHAPTER X.
TEETH OF BIMANA.

173. Havine reached in the Chimpanzee the highest step in
the series of the brute creation, our succeeding survey of the Human
dental system, expanded by retrospective comparisons, becomes
fraught with peculiar interest, since every difference so detected
establishes the true and essential characteristics of that part of
Man’s frame.

(1) Pl. 119 a, fig. 1 e, e.
GG 2

452 HUMAN DENTITION.

The human teeth are the same in number and in kind as
those of the Chimpanzee and Orang, nor does Man differ in
this respect from any of the inferior catarhine Quadrumanes.
The human dental formula is therefore :—

A 2—2 5 1—1 2—2 3—3
Incisors —; canines —; premolars —; molars —: = 32.
2—2 Aes 2—2 3—3

That is to say, there are on each side of the jaw, both above
and below, two incisors,(1) one canine,(2) two premolars,(3) and
three true molars.(4) They are more equal in size than in the Qua-
drumana ; no tooth surpasses another in the depth of its crown; and
the entire series, which describes in both jaws a regular parabolic
curve, is uninterrupted by any vacant space. The incisors (PI.
118, 119, fig. 2 and 3, 7) are much smaller in proportion to the
molars than in the Chimpanzee and Orang; in the upper jaw the
first exceeds the second in breadth, but in a less degree than in the
Chimpanzee. The posterior basal ridge is less prominent and
distinct in the middle incisor; it is wanting in the lateral incisor,
the outer angle of which is entire, and touches the crown of the
canine : its fang is longer in proportion to the median one than in the
Chimpanzee ; in both incisors the fang is long, slender, and sub-
compressed. The most marked distinction between the dentition of
Man and that of the highest Quadrumanes is the absence of the
interval between the upper lateral incisor and the canine, and the
comparatively small size of the latter tooth (ib. c): but its true cha-
racter is indicated by the conical form of the crown, which terminates
in an obtuse point, is convex outwards and flat or sub-concave within,
at the base of which surface there is a feeble prominence: the
conical form I find best expressed in the Melanian races, espe-
cially the Australian(5): the canine is more deeply implanted, and
by a stronger fang than the incisors; but the contrast with the
Chimpanzee is sufficiently manifest, as is shown in Pl. 118. There

(1) Dentes incisores, primores.

(2) Denies canini, cuspidati.

(3) Dentes molares anterivres, seu minores, s. spurti, s. bicuspidati.

(4) Dentes molares posteriores, seu majores, s. veri, s. muliicuspidati.

(5) Pl. 118, fig. 2,c. It is also very well marked in the dentition of the Mozambique
Negro, figured by F. Cuvier, ‘ Dents de Mammiferes,’ PI. 1.

- HUMAN DENTITION. 453

is no sexual superiority of size, either of the canine or any other
single tooth in the human subject.

Both upper and lower premolars (ib. p.) are bicuspid; they are
smaller in proportion to the true molars than in the Chimpanzee
and Orang: in the upper premolars a deep straight fissure at the
middle of the crown divides the outer and larger from the inner and
smaller cusp: in the lower premolars the boundary groove describes
a curve concave towards the outer cusp, and is sometimes oblite-
rated in the middle by the extension of a ridge from the outer
to the inner cusp, which cusp is smaller in proportion than in the
upper premolars. These teeth in both jaws are apparently im-
planted each by a single, long, sub-compressed, conical fang: but
that of the upper premolars is shown by the bifurcated pulp-
cavity to be essentially two fangs, connate, and which, in some
instances, are separate at their extremities.

The crowns of the true molars (ib, m.) are larger in propor-
tion to the jaws, are a little larger in proportion to the bicus-
pids, and still more so in proportion to the canine and incisor
teeth, than in the Chimpanzee and Orang: the contour of the
grinding surface is more rounded, and we have seen that the
higher Quadrumana already approximate to this character by the
angles of the crown being less marked than in the lower Quadru-
mana. The first and second true molars of the upper jaw sup-
port four trihedral cusps; the internal and anterior one is the
largest and is connected with the external and posterior cusp by
a low ridge extending obliquely across the grinding surface, with
a deep depression on each side of it, the anterior groove extend-
ing to the middle of the outer surface, the posterior one to the
inner surface. The enamel is first worn away by mastication from
the anterior and internal or largest tubercle: a line of enamel
extending from the outside to the middle of the crown is the last
to be removed before the grinding surface is reduced to a field of
dentine with a simple ring of enamel.(1) It is worthy of remark that
by the time when the permanent teeth have come into place the
first true molar in both jaws is much more worn, as compared
with the second and third molars, than it is in the Chimpanzee

(1) PL. 120, fig. 3, ms 1.

454 HUMAN DENTITION.

or Orang, owing to the slow attainment of maturity characteristic
of the Human species, and the longer interval which elapses be-
tween the acquisition of the first and the last true molars, than in
the highest Quadrumanes. In the last true molar, called from its late
appearance, the ‘‘dens sapientiz’’ or wisdom-tooth, the two inner
tubercles are blended together, and a fissure extends, in many in-
stances, especially in the Melanian varieties, from the middle of the
grinding surface, at right angles to that dividing the two outer
cusps, to the posterior border of the tooth.

The first upper molar is always implanted by three diverging
fangs, two external and one internal. The second molar is usually
similarly implanted, but the two outer fangs are less divergent, are
sometimes parallel (Pl. 118, fig. 2), and occasionally connate
(ib. fig. 3); this variety appears to be more common in the
Caucasian than the Melanian races. The two outer fangs of the

last molar tooth are more commonly connate or confluent, and

sometimes also the inner fang is blended with them into one
simple root, in the Caucasian race: but I have never seen these
varieties in the Melanian races; and in the Australians the
wisdom-tooth has always presented the same three-fanged implan-
tation as in the Chimpanzee and Orang.

The crowns of the inferior true molars are quinque-cuspid,
the fifth cusp being posterior and connected with the second
outer cusp: it is occasionally obsolete in the second molar. The
four normal cusps are defined by a crucial impression, the pos-
terior branch of which bifurcates to include the fifth cusp; this
bifurcation being most marked in the last molar where the fifth
cusp is most developed. In the first molar a fold of. enamel ex-
tending from the inner surface to the middle of the crown is the
last to disappear from the grinding surface in the course of abra-
sion.(1) The wisdom-tooth is the smallest of the three molars in
both jaws, but the difference, is less in the Melanian than the
Caucasian races. Each of the three lower molars is inserted by
two sub-compressed fangs, grooved along the side turned towards
each other: this double implantation appears to be constant in the
Melanian, especially the Australian race, in which the true molars

(1) PL. 120, fig. 4, m. 1.

. HUMAN DENTITION. 455

are relatively larger than in the Caucasian race. In Europeans it
is not unusual to find the fangs of the second and third inferior
molars connate along a great part or the whole of their extent, as
mo Pl: 119, fig. -3.

With respect to the reciprocal apposition of the teeth of the
upper and under jaw it is interesting to observe that the crown of
the lower canine is, as usual, in advance of that above, and fits
into the shallow notch between that and the lateral incisor. The
inferior incisors are so small that their anterior surface rests
against the posterior surface of the upper ones, when the mouth
is closed: the other teeth are opposed crown to crown, the upper
teeth extending a little more outwardly than the lower ones.

Hunter remarks that the supernumerary teeth happen oftener
in the upper than the under jaw, and he believed them to be
always incisors or canines. I have seen a skull of a male Hindoo
in which there were two well-formed canine teeth placed side by
side in the left upper jaw, the series being very regular and even.
The wisdom-tooth is sometimes not developed; but I never saw
a supernumerary premolar or molar tooth.

174. Comparison of the deciduous teeth of the Orang, Chimpanzee,
and Human Subject—The deciduous series of teeth in the Human
subject (Pl. 121) consists of in. 53, c. Sj, m. &: = 20. I shall
here describe them in immediate comparison with the same teeth in
the Chimpanzee and Orang ; because the differences, though less in
number and degree are more expressive of original specific distinc-
tion, in proportion to the immaturity of the subjects of comparison in
which they may be detected.

The upper milk incisors of the Chimpanzee (Pl. 120, fig. 1.)
are relatively larger than in Man, especially the middle pair ; but
the disproportionate size of these is still more manifest and cha-
racteristic of the Orang (ib. fig. 2.) and the outer angle of the
lateral incisors is more rounded off in this Quadrumane. The
crown of the canine is longer, and more pointed in the Chim-
panzee than in Man; still more so, and farther apart from the
incisor in the Orang. The first molar is as large in the Humap
subject as in the Chimpanzee, and its crown is divided into two
principal cusps, but the outer and larger one has a small sub-

456 HUMAN DENTITION.

division notched off posteriorly, and the inner cusp is relatively
larger than in the Chimpanzee: the first upper molar of the
Orang is simply bicuspid, but is larger than in the Chimpanzee.
The second molar of the Human child could scarcely be distin-
guished from that of the young Chimpanzee: both are quadri-
cuspid, and the same oblique ridge crosses the grinding surface from
the antero-internal to the postero-external tubercle ; but the pointed
summits of the two outer cusps are a little more produced in the
Chimpanzee. The second molar of the Orang besides its larger
size, has the four tubercles better defined, and the oblique ridge
less developed.

The lower deciduous incisors of the anthropoid Apes differ
from those of the Human subject in their superior size, greater
relative thickness, and the lateral incisor more particularly by the
rounding off of the outer angle. The lower canine of the Chim-
panzee has a larger, longer, and more pointed crown with a sharp
posterior edge: this is less marked in the canine of the Orang,
which is larger and thicker than in the Chimpanzee: the crowns
of the upper and lower canines are more obliquely opposed, the
lower one being more advanced in those Apes than in the
Human subject. The first lower deciduous molar of the Human
subject has four tubercles and a small anterior ridge, and is
larger than that of the Chimpanzee, which supports a single large
pointed cusp, and a posterior ridge: the first molar of the Orang
has a similar simple crown, but is as large as that of the child. The
second molar is of equal or superior size in the Human to that
in the Chimpanzee, but it supports three outer and two inner
cusps, while in the Chimpanzee it has but four cusps: in the
Orang the fifth external and posterior tubercle is feebly indi-
cated. The deciduous molars of the Human subject, as in the
Chimpanzee and Orang, have each three fangs in the upper and
two in the lower jaw.

The differences brought out by the foregoing comparisons, though
less striking than those exhibited by the permanent teeth, will be ap-
preciated by the philosophical Anatomist as yielding more certain evi-
dence of the essential distinction of the Bimanous species : he will
perceive that they are not due to mere adaptive developments, but are

_ HUMAN DENTITION. 457

manifested at a period when the subjects of comparison are far from
having attained the pre-ordained term of deviation from the common
primordial type, and antecedent to those changes in the dental system
itself, which more broadly characterise the species, and, in the Orang
and Chimpanzee, proceed further to mark the different sexes.

175. Succession.—The primary development of the matrices of
both the deciduous and permanent Human teeth has been described
in the ‘Introduction’. Calcification of the permanent series com-
mences first in the pulp of the first true molar, and very soon
after, if not simultaneously in that of the anterior incisor, about
five or six months after birth. The first true molar (Pl. 121, m 1)
comes into place and use between the sixth and seventh year(1):
the first permanent incisor (ib. i 1) between six years and a half,
and eight years: the calcitication of the pulps of the lateral incisor
(i 2) and canine, (c) commences about eight or nine months after
birth, and they cut the gum, the canine quickly following the in-
cisor, between the seventh and ninth years. Calcification of the
first premolar (bicuspis, p 1) begins at, or soon after, the second
year, that of the second about a year later, and both premolars
have displaced the deciduous molars, and come into use between
the eighth and tenth years. The pulp of the second molar (m 2)
begins to be calcified about the fifth or sixth year, and it cuts
the gum from about the twelfth year to the fourteenth year; but
always later than the permanent canines and premolars. The third
molar or dens sapientig, begins to be calcified about the twelfth
year, and usually comes into place at or after the twentieth
year.

Both earlier and later periods of the development of the per-
manent teeth have been observed and recorded ; but such varieties
rarely affect the general order of succession. I have described this
order as it occurs in the lower jaw, the teeth of which usually
appear earlier than the corresponding ones above. It will be seen,
therefore, that the Human subject differs from the Chimpanzee and
Orang in the order of progression of the permanent teeth. John
Hunter, after indicating the first incisor and the first molar as

(1) Hunter says it cuts the gum about the twelfth year of age; but this must be a rare
exception, if it is not a mistake. See “ Natural History of the Human Teeth,” 4to. p. 84.

458 HUMAN DENTITION.

the earliest of the adult teeth that are formed, rightly observes, ‘‘ The
teeth between these two points make a quicker progress than those
behind.”(1) In the Quadrumana the progress is slower, the second
molar preceding the bicuspids, and the last molar, the canines.
We may readily suppose that the larger grinders are sooner required
by the frugivorous Orang, than by the higher omnivorous Bimanous
species ; but the more immediate condition of the earlier deve-
lopment of the canines and premolars in Man is their smaller relative
size.

176. Microscopic Structwre.—The progressive steps in the ac-
quisition of the knowledge of the intimate structure of the Human
teeth have been pointed out in the ‘ Introduction,’ pp. v—xvi. The
body of the tooth consists of hard or unvascular dentine (Pl. 122, d) ;
the exserted part or crown is invested by enamel (ib. e) ; the whole
tooth is coated by cement, (ib. c), but this attains the thickness re-
quisite for the development of its characteristic radiated cells only
upon the fang or fangs. Every tooth has an internal cavity (PI.
122, v), which contains the remains of the vascular dentinal pulp,
and is thence termed ‘ pulp-cavity’: it is progressively diminished in
size as the dentine is completed; remains widest at the base of the
crown, and contracts as it descends along the fang or fangs, dividing
according to the number of these ; and, when they are connate and
form apparently a simple root, the pulp-cavity indicates by its division
into linear fissures, continued from the coronal dilatation, the number
of fangs which compose such undivided root. After the pulp-cavity
has been reduced by the completion of the dentine, it is further di-
minished by the conversion of part of the residuary pulp into a layer
of osseo-dentine (ib. fig. 4 a, 5 & 8 0). The cement, which is thickest
at the end of the fangs, sometimes penetrates the pulp-cavity, and
blending with the osseo-dentine closes the aperture, except where
two or more minute canals perforate it for the passage of capillary
blood-vessels, and nerve-filaments.

The pulp-cavity of the front incisor, when exposed by a lon-
gitudinal section through the breadth or transverse axis of the
tooth, (ib. fig. 9) presents the form of a long and narrow in-
verted cone; the base being concave and next the crown, the apex

(1) Op. cit. p. 82.

HUMAN DENTITION. 459

prolonged to the extremity of the fang: a linear fissure is continued
from each angle of the base towards the corresponding angle of the
crown. The same cavity, exposed by a longitudinal section through
the thickness or antero-posterior cavity of the crown (ib. fig. 2),
is fusiform,-its coronal end contracting to a linear fissure which is
continued towards the middle of the summit of the crown. The
pulp-cavity of the canine (ib. fig. 3), is relatively wider in its coronal
portion. In the upper premolars (ib. fig. 4), the coronal dilatation
sends a short and wide process to the base of each cusp, and is
continued from the opposite end in the form of two linear fissures,
one near the external, the other near the internal part of the com-
pressed apparently single fang. In the true molars (ib. fig. 7) a
short and wide process of the common coronal cavity is continued
towards the base of each tubercle of the grinding surface, and
as many linear prolongations as there are fangs, extend from the
opposite side of the cavity. In the broad fangs of the lower molars
the pulp-fissure commonly divides into two in each fang; and in
the last or wisdom-tooth, which has frequently, at least in the
Caucasian races, a single implantation, the pulp-cavity always indi-
cates by its divisions the number of connate fangs that form such
undivided base.

Every part of the surface of the pulp-cavity is pierced by
microscopic pores, about jo;th of an inch in diameter, which are
orifices of tubes radiating from the pulp-cavity to the periphery
of the dentine with a general direction vertical to that surface ;
these are the dentinal or calcigerous tubes. In the lower incisor
and canine teeth, those from the middle of the summit of the pulp-
cavity ascend vertically to the enamel-covered surface of the
dentine at the summit of the crown; the tubes on each side
of these gradually incline outwards; those which go to the
angles of the crown forming an angle of 45° with the middle
vertical tubes: at the sides of the crown the tubes incline still more
outwards until in the middle of the fang they become horizontal,
and still lower, bend downwards.(1)- The vertical tubes are nearly

(1) Pl. 122, fig. 1—3, d.

460 HUMAN DENTITION.

straight ; but, as soon as they begin to incline from the perpendicular,
they become bent into two or, more commonly, three gentle wavy
curves; at the sides of the crown and along the upper half of
the fang the tubes form a short bend concave towards the crown,
then a longer bend in the opposite, and finally a third bend in the
first direction; the general curve being concave downwards: in
the lower half of the fang the first curvature with the concavity up-
wards is the principal one. These ‘ primary curves’ are on the same
plane or nearly so. The ‘secondary curves,’(1) of which two hun-
dred may be counted in an extent of sth of an inch of the length of
a tube, are not on the same plane, but form slight gyrations through
the whole course of the tube. Both the primary and secondary curves
of adjacent tubes are parallel ; and occasionally the tubes make a
short bend along a line parallel with the outer contour of the crown,
giving rise to the appearance which may be called ‘ contour lines ;’(2)
the parallelism of the entire tubes being affected only by the
amount of their divergence in radiating from the pulp-cavity. As a
general rule the tubes are nearly perpendicular to the surface of
the dentine, and take an almost direct course from the pulp-cavity
to that surface. Thin sections of dentine taken across the tubes,
viewed by transmitted light with a five hundred times linear mag-
nifying power, show the clear area of the tube more or less occupied
by a dark subgranular opake calcareous substance,(3) and a clear
border(4) to the area, neatly defined from the intertubular sub-
stance,(5) and indicating the proper parietes of the tube. The addi-
tion of dilute muriatic acid dissolves the opake contents of the tube
and clears the whole circular area: it dissolves, at the same time,
the finer particles of lime in combination with the animal basis of
the intertubular substance and parietes of the tubes, which latter
then cease to be distinguishable. This shows that either the lime-
particles have a peculiar arrangement in the parietes of the tubes,
or are more abundant there than in the intermediate substance, since
the parietes can be distinguishable only whilst those particles are
present: the appearance can scarcely be an optical deception because

(1) Fl. 122 «, fig. 5.) Plo lode, figs te (2) Pil. 122, fig. 7, 1.
(3) Pl. 124 a, fig. 4. (4) Ib. 0. - (5) Ib. i.

-_ HUMAN DENTITION. 461

the thickness of the parietes of the dentinal tubes, in relation to their
area, varies in different animals; it is twice as great, for example,
in the incisor of the Dugong as it is in that of Man. In viewing
the dentinal tubes lengthwise, a third is usually more faintly seen
in the interspace of any two that are in focus(1); it is on a different
plane, and the tubes on different planes are commonly alternate
in position; viewed in transverse section(2) their arrangement
appears quincuncial, yet not regularly so throughout ; so viewed, the
distance between each two tubules does not exceed, and often
does not equal, the width of one, its parietes and lumen being
included. The distance between two tubes viewed longitudinally
on the same plane is generally equal to the width of two; but, if
the distance between the opake area of two parallel tubes be
estimated, irrespective of the proper tunics of the tubes, it more
than equals the width of three such opake arez. Professor Retzius
appears to have calculated the relative width of the tubes and
their interspaces in the latter mode, and his results have been
generally copied by subsequent writers on microscopic anatomy.
The method though easy, and applicable to the detection of
differential characters in the dental structure of different animals,
is inexact in reference to the actual distance between the tunics
of the dentinal tubes. The true distance is nearly the same
throughout the course of the tubes; for, as they diverge, they
divide and sub-divide dichotomously, maintaining the same diameter
to within one fourth or one fifth of their terminations. If the
tubes were described according to the order of their formation,
the peripheral extremities would be their beginnings, and the
dichotomous divisions would rather be the anastomoses of the
more numerous and smaller tubes as they gradually converged to
terminate, by fewer and wider extremities, in the pulp-cavity. The
tubes also send off into the intertubular space very minute branches
which divide, and passing into the next interspace, are lost

(1) Pl. 123. This is well shown in Retzius’ Treatise, Pl. 2, (v), fig. 1 B.
(2) In some parts of the dentine the tubes are occasionally observed to be collected
into small groups or bundles.

462 HUMAN DENTITION.

a

—

there, anastomosing, or terminating in the calcigerous or dentinal —

cells. (1)

The lateral ramuli are more numerous in the fang than in
the crown; here the finer branches are most abundant at the

peripheral extremities of the tubes, which frequently appear to
end abruptly, as if truncated; sometimes dividing and sub-dividing
quickly ; the terminal divisions diverge widely, and appear to end
in the stratum of fine cells which divides the dentine and enamel:
here and there I have seen a tube bending back to form an anas-
tomotic hoop with an adjoining tube. ‘The peripheral stratum of
minute cells receiving the terminal ramifications of the calcigerous
tubes and forming the boundary between the dentine and enamel,

is the most sensitive part of the dentine: it is not, however, so

distinct a tissue as to merit a special name.(2)

In the bicuspids(3) a larger proportion of the tubes proceeding
from the summit of the pulp-cavity are vertical than in the canines
or incisors, and a still greater proportion in the broad-crowned mo-
lars.(4) The tubes going to the apex of each cusp or tubercle are the
most vertical, and the surrounding tubes begin to incline from
the perpendicular in proportion as they terminate nearer the base
of each cusp: in the interspaces of the cusps, therefore, the tubes
incline towards each other. At the early stage of the calcification

(1) Pl. 123, fig. 1,d!. These cells, defined in my Report to the British Association in
1838, (vol. viI, p. 144) as “calcigerous cells, which form numerous layers generally ar-
ranged parallel with the contour of the cavity of the pulp, and most numerous at the circum-
ference of the ivory,” are untruly indicated by the exaggerated expression that ‘ the inter-
tubular substance is cellular’; they would be sought for in vain as cells, in the interspaces
of the tubes. The true dentinal or calcigerous cells include many tubes and intertubular spaces,
and it is much more exact to say that those cells include a tubular structure, than that the
intertubular space is cellular. The unprejudiced microscopical observer will find the tissue
in the intervals of these dentinal tubes, for the most part clear and structureless, as Pur-
kinje and Retzius have rightly described. Dr. Henle has stated that when deprived of the
hardening salts it tears into fibres, whose course is parallel to the tubes: this is not a satis-
factory indication of original structure. Sdmmering, von Baue des Mensch. Korp. 8vo. 1841,
p- 855-856.

(2) M. Duval, who has well described the vital properties of this part of the dentine,
and rightly states it to be the seat of the commencement of caries, has proposed to call it
‘ dictyodonte.’—“ Observations Anatomiques sur l’Ivoire,” Svo. 1839, p. 14.

(3) PL. 122, fig. 4. (4) Ib. fig. 6 and 7.

HUMAN DENTITION. 463

of the dentinal pulp, when the cusps are yet distinct from each
other, they constitute so many distinct radiating systems of den-
tinal tubes, and the crown of a molar seems to be formed by the
basal confluence of three, four or five simple teeth. At the circum-
ference of the crown of both premolar and molar teeth, the tubes
incline more and more towards the horizontal direction as they
approach the fangs. In the upper premolars in which the pulp-
cavity divides and is continued in the form of two linear fissures
along the connate fangs,(!) each fissure is the centre of divergence
of radiating tubes, having the same primary and secondary curva-
tures, as in the single fang of the incisor and canine. When a
molar is implanted by only two broad and compressed fangs the
pulp-cavity usually divides in each ; and when the last molar is
implanted by an undivided root, the dentinal tubes of that part radiate
also from two distinct pulp-canals. In the base of three-fanged and
four-fanged molars there are as many radiating systems of dentinal
tubes. The terminations of the tubes in the fangs are more fre-
quently resolved into fine branches than in the crown, and the
communications between these branches and the analogous minute
tubes from the radiated cells of the cement are numerous and plain.
The dentinal cells of the human tooth(2) are sub-circular, about
«oth of an inchin diameter; they seem most numerous from being
most conspicuous, near the periphery of the dentine, as origi-
nally described by me in the dentine of the Crocodile.(3) They
are best seen in sections of the crown of a permanent tooth
before it has come into place. In a longitudinal section the peri-
pheral boundary of the cell, or that next the enamel, is most
conspicuous ; it describes a slight curve: the lateral boundaries form
a very open angle: the posterior boundary is formed generally by
the convex curve of the posterior cell which appears slightly to
over-lap the one in front, and in this view of the cells their
transverse diameter exceeds the longitudinal one. In a transverse
section of the dentine the cells’ boundaries are, for the most part
hexagonal, with the angles feebly marked. From the differences

(1) Pl. 122, v°, vo. (2) Pl. 123, fig. 1, di, di.
(3) Report of British Association, 1838, p. 144.

464 HUMAN DENTITION.

observable in the two views of the cells, that surface of the cell
which is next the periphery of the tooth is shown to be more
rounded and convex, than the other surfaces. Viewed by transmitted
light, the cell-boundaries are usually opake ; but by a slight alteration
of focus the dark lines become clearer and brighter than the sur-
rounding substance: in parts of the dentine near the periphery, the
boundaries are occasionally seen to be irregularly widened ; as if
contiguous cells were separated by depositions of lime-salts in a
sub-granular state: these thickened and less regular boundaries are
always opake, and when viewed by reflected light are white. As the
dentine approaches the pulp-cavity the indications of the cells
gradually decrease in size, and their boundaries usually become
fainter and less complete ; viewed in longitudinal section the peri--
pheral margin is the last to disappear.

After noticing the cells and tubes of the dentine, the third
and least important appearance, which relates rather to the course of
formation than to the essential structure of the dentine, is that
produced by the lines, which from their parallelism with the vertical
outline of the crown I have termed ‘contour-lines.’ These are
the lines, or strize of the dentine, which, in sections of the larger
teeth of many of the inferior Mammalia, are visible by the naked
eye, through the action of a short parallel bend of the dentinal tubes,
along the course of the contour line, upon the rays of light. These
lines are not equally conspicuous in every tooth; I have usually
found them most so in the molars of the human subject, where,
without being regularly equi-distant, they have presented intervals
of about jth of an inch, commencing at thrice that distance from
the periphery of the dentine(1).

The enamel of the human teeth(2) consists of long and slender
solid, prismatic, for the most part hexagonal, fibres of phosphate,
carbonate, and fluat of lime, in the proportions mentioned in the
‘Introduction’: they are essentially the contents of extremely delicate
membranous tubes, originally sub-divided into minute depressed

(1) Pl. 122, fig. 7, 7. The dentine in fossil teeth commonly breaks up along these lines
into conical or superimposed strata.

(2) Pl. 122, fig, 1—7, e.

MICROSCOPIC STRUCTURE. 465

compartments or cells, of which membranes scarcely a trace can
be detected in fully-formed teeth. The fibres are arranged closely
together, side by side, with occasional narrow angular fissures, or
interspaces, which are most common between the ends nearest the
dentine ; their general direction is perpendicular to the surface of the
dentine, where the ends of the prisms are fixed in shallow depres-
sions; the opposite and larger ends form the exposed surface of
the enamel: the fibres proceeding to the horizontal masticating
surface are, therefore, vertical ; the greater number, which are
directed to the circumference of the crown, are horizontal or
nearly so; every fibre, as a general rule, having, like the tubes
of the dentine, that direction which is best adapted for resisting
either the external force of mastication or the effects of lateral
pressure. Besides the minute pits corresponding with the inner
ends of the enamel fibres, the outer surface of the dentine some-
times presents larger depressions, as shown at e’, fig. 1, pl. 123.
The enamel-fibres describe a flexuous course, the curves being
much stronger and shorter than the primary curves of the den-
tinal tubes(1). The parallelism of the fibres continues over a
much smaller extent of any part of the enamel than that of the
calcigerous tubes in the dentine: in some parts of the enamel
they curve in opposite directions to one another, like the vane of
a feather. Sometimes the fibres may be traced through the entire
thickness of the enamel; where they fall short, and where the
larger fibres diverge from each other, shorter complemental fibres
fill up the interspaces. Each fibre is mth of an inch in thick-
ness, and is marked throughout its entire course by faint, close-
set, transverse striz(2). When a section of enamel includes several
fibres in its thickness, certain of the overlapping curves intercept
a portion of light, and occasion the appearance of dusky, brownish
waves. Another appearance, more immediately related to the for-
mation of the enamel, is produced by lines crossing the enamel-
fibres, parallel with the outer margin of the enamel, but not always
parallel with that attached to the dentine. These lines are not of equal
clearness, but are very nearly equi-distant, being about th of an inch
(1) Pl. 122, a, fig. 1 & 2. (2) Ib. fig. 3. Pl. 123, fig. 1, e.
H H

466 ’ HUMAN DENTITION.

apart ; they are more plainly seen in transverse sections of the crown
than in longitudinal sections, and they have the same relation to the
fibres of the enamel which the contour-lines of the dentine bear to
the calcigerous tubes. Without doubt they indicate, in like manner,
strata of segments of the fibres and stages in the formation of
the substance. Where these strata, which are arranged very ob-
liquely to the vertical surface of the dentine, crop out upon that
surface they occasion those wavy transverse annular delicate
markings which Leeuwenhoek(1) noticed upon the exterior of the
enamel, and which he supposed to indicate successive stages in
the protrusion of the tooth through the gum, in taking its place
in the dental series. The various conditions of the enamel at
different periods of its formation have been mentioned in the
description of the development of the tooth.(2)

The cement in the human tooth,(3) as in other simple teeth,
is confined to the exterior surface, with the exception of a small
portion which, in old teeth, is usually reflected into the entry to
the pulp-cavity and sometimes closes it up. This third substance
is thinnest upon the crown and very gradually increases in thick-
ness as it approaches the end of the fang: it is only on the im-
planted part of the tooth that the radiated cells, which demon-
strate the close analogy between cement and bone, exist ; elsewhere
the clear basis of the cement alone is present, and this is soon
worn away from the enamel of the crown. There are no vascular
canals in human cement, except when it happens to be abnormally
thickened ; in which case, as in the naturally thickened masses of
that substance in the teeth of Herbivora, it acquires also this addi-
tional feature of resemblance to true bone. The chemical consti-
tution of both the animal basis and earthy salts of this dental
tissue and of bone is identical ; the hardening particles are chiefly
blended in the finest state of sub-division with the clear basis, a
portion being contained in a coarser state in the cells; it is this
which occasions their milk-white colour when viewed by reflected
light.(4) The cemental cells are generally oblong, sometimes cir-

(1) ‘Select Works’ by Hoole, 4to. 1800, p. 115.

(2) Introduction, p. xlvi. (3) Pl. 122, fig. 1—7, c.

(4) The calcareous matter does not occupy the whole of the cavity of the cell; space
is left as in the dentinal tubes, for the transit of fluids. Mr. Smee, (Med. Gazette,

MICROSCOPIC STRUCTURE. 467

cular, more rarely fusiform: they average about s,th of an inch
in the long diaméter: their contour is broken by the numerous
fine tubes which radiate from them, with wide angular beginnings,
but quickly contracting to the minute size of sath of an inch.
In transverse sections of the fang, the cells are generally seen to
be arranged in parallel concentric lines; their long axis being in
the direction of the lines, which vary in clearness of definition,
like the concentric strie of enamel; and, like these, indicate,
stages of formation in the cement. The radiating tubuli anasto-
mose together either directly or by their numerous fine branches ;
which latter also communicate with the terminal ramifications of
the dentinal tubes, either directly or through the medium of the
fine granular cells dispersed through the boundary line between
the dentine and cement. In the deciduous teeth the cement is
relatively thinner and the cells fewer and less regularly arranged.
The thickened cement near the end of the fang of old permanent
teeth is occasionally perforated by a vascular canal, conveying
capillary vessels to the osteo-dentine and the small remnant of
the pulp. An increase beyond the usual thickness is usually ac-
companied by the formation of vascular canals in the cement; and
it is the existence of this most highly organized of the dental
tissues which explains the possibility of engrafting teeth upon
vascular parts.(1)

In my Report to the British Association in 1838, which
contains the first announcement of some of the observations des-
cribed in detail in the present Work, I stated, with respect to the
component structures of a tooth, ‘‘that in addition to those
usually described and admitted, there were other substances en-
tering into the composition of teeth and presenting microscopic
characters equally distinct both from ivory, enamel and cement,

Nov. 20th. 1840), succeeded in injecting them with Canada balsam, and I have generally
found in fossil teeth that the mineral matter had penetrated into the cells and tubes of
the cement, as well as into the tubes of the dentine.

(1) Retzius rightly points out the cement as the seat of the abnormal growths called
‘exostosis,’ to which the fangs of teeth loosened by the scurvy or mercurial medicines are
more particularly liable. One of his figures of the thickened cement on the fang of the
tooth of an aged person is given in Pl. 122, fig. 8.

H H 2

468 HUMAN DENTITION.

and from true bone, and as easily recognizable.”(1) Of these is
the tissue, there first defined and which I have since called
‘ osteo-dentine,’ from its combining the vascular concentric-coated
canals of the osseous tissue, with a development of the fine tubes
resembling those of true dentine, but with stronger and less re-
gular curvatures. This substance is found lining the pulp-cavity
of old teeth ; and sometimes forms the middle part of the grinding
surface of much worn molars: but the conversion of the remains
of the pulp into the osteo-dentine is constant in human teeth after
the age of twenty years.(2)

To ascertain what modifications of structure the dental tissues
might present in teeth which are sometimes developed, with hair
and portions of bone, in the human ovarium, I examined micro-
scopically one of those ovarian teeth, of which a longitudinal slice,
taken through the middle, is figured in Pl. 124. The intimate
structure of the dentine d, enamel e, and cement c, was essentially
identical with those of the ordinary maxillary teeth. The dentinal
cells and tubes presented the same dimensions: the primary and

(1) “One of these substances is characterised by being traversed throughout by numerous
coarse canals, filled with a highly vascular medulla or pulp, sometimes anastomosing re-
ticularly—sometimes diverging and frequently branching,—sometimes disposed nearly parallel
with one another, and presenting more or fewer dichotomous divisions. The canals in many
cases are surrounded by concentric lamelle, and thus resemble very closely the Haversian
canals of true bone; but the calcigerous tubes which every where radiate from them are
relatively much larger. The highly organized tooth-substance just described differs from true
osseous substance, and from coementum, in the absence of the Purkingian corpuscles or cells.”
Trans. Brit. Assoc. 1838. p. 137.

(2) Lintott ‘On the structure of the Human teeth.’ 1843. John Hunter appears first
to have called attention to this process which prevents the exposure of the pulp-cavity
when the crown is worn low down; he calls the substance ‘new matter’ and says “it may
be easily known from the old, for when a tooth has been worn down almost to the neck
a spot may always be seen in the middle, which is more transparent and at the same
time of a darker colour, and generally softer than the other.” Hunter’s success in in-
jecting vessels in the cavities of the teeth in very old people is explained by the existence
of vascular canals in the osteo-dentine and their communication with similar canals per-
forating the thickened cement. I have already noticed the abundance of this substance
in the teeth of the Cetacea, and its centrifugal development from detached centres in the
substance of the pulp of the Cachalot, forming there sometimes detached masses (p. 360).
A modification of osteo-dentine forms, as we have seen, the main body of the teeth of
the Sloths and Megatheroid quadrupeds; but the transition from the normal hard dentine
to its vascular modification is more gradual in the Human teeth.

MICROSCOPIC STRUCTURE. 469

secondary curves of the tubes were equally present, but the direction
of the former somewhat different, the principal bend in the upper
and lower tubes being turned rather from, than towards, the
centre of the tooth; but the general principle of arrangement,
perpendicular to the tooth’s surface equally prevailed. The lower
end of the pulp-cavity was quite closed by dentine, the tubes of
which descended vertically ; the pulp-cavity forming a centre from
which the dentinal tubes radiated on all sides. The normal part
of the dentine was developed, as in a premolar, into two cusps,
and the pulp-cavity v was single as in a bicuspid of the lower
jaw. The enamel was unusually thick, and the cusps were divided
by a cleft extending nearly to the dentine. The enamel fibres had
the usual form, structure, and direction. ‘The cement became un-
usually thick at the closed end of the fang and there formed the
medium of adhesion between the dentine and a small portion of
true bone. Three or four vascular canals (b) were detected per-
forating the cement and dentine which closed the pulp-cavity,
and communicating with similar canals in a mass of osteo-
dentine (0) which almost blocked up the cavity of the tooth. The
thin layer of non-cellular coronal cement was conspicuous over
the whole outer surface of the enamel, and presented no increase
in thickness in the abnormal median cleft.

The presence of all the beautiful prospective arrangements of
the minutest particles of an organ, by which it is adapted to
its office, in an example of the same organ developed abnormally
under conditions unfitting it for the exercise of its proper office,
affords no argument against the contrivance, but, rightly consi-
dered, enlarges our conceptions of the liberal provision of the
contriver. The matrix of a tooth, wherever it may chance to be
formed, must so operate in the disposition of the hard building
materials of the tooth as to ensure the utmost strength and power
of resistance in all those directions in which such tooth would
have been acted on, if it had been developed in its proper po-
sition.

Of the four substances composing the human tooth that
which is most exposed to outward influences, and which is first

470 HUMAN DENTITION.

to operate upon the food in preparing it for deglutition, is the
hardest, the most solid, the least organized. We have seen that
every fibre of the enamel is so disposed, by the preliminary dis-
position of the cells in which it was moulded, as to give it
the utmost strength and power of resistance of which such a
tissue could be capable. The polished surface, the pearl-white
colour of this dense and brittle substance, adds ornament to use.
In the second and principal substance of the tooth, the dentine,
we have traced an equally beautiful arrangement of the earthy
salts in directions which best resist both vertical and lateral pres-
sure, but with the additional economy of the substitution of the
hollow column for the solid prism. The saving of material is
however, the least of the benefits gained by this tubular structure
of the dentine: the vitality of the tissue, which Hunter recognized
so forcibly, but which, being equally convinced of the non-vascu-
larity of the tissue, he was unable to explain,—willing rather to
enunciate an apparent paradox, or be taunted with dilemma, than
yield one iota of either of his convictions,(1)—is explicable by the
possible and highly probable fact of a circulation of the colourless
plasma of the blood through the dentinal tubes. That some ele-
mentary prolongations of nerve may also be continued into these
tubes, who may confidently deny? Whoever has felt the pang
produced by contact of a probe with the recently exposed surface
of the dentine, must at least allow the tubes to be most efficient
conductors of the impression to the sentient pulp. Nature has
suffered no part of the dentine to be exposed: its organization
and vital powers are adequate to its own support in health, and
to control that stimulus which, when the dentine is dead and
truly ‘an extraneous body’, operates detrimentally upon the sur-
rounding more highly organized parts: but the vitality of the
dentine is insufficient for the reproduction of its tissue, or for
the arrest or repair of decay. The third substance which is
chiefly developed around the implanted part of the tooth is more
highly organized than the dentine, more analogous to bone, and
accordingly better adapted for vital connexion with the vascular
(1) See Prof. Bell’s preface to his Edition of ‘ Hunter on the Teeth,’ p. xiii.

HUMAN DENTITION. 47]

membrane of the alveolus. It is the cement which renders a
living tooth ‘capable of uniting with any part of a living body’
as Hunter proved by his ingenious experiments.

When the tooth performs its function throughout a long
life, free from any destructive influence but that of ordinary mas-
tication, a compensating provision would seem to have been in-
tended against the decay of the alveoli in old age by the final
substitution of a more highly organized substance, the osteo-
dentine, for the ordinary dentine which has been worn away. Nor
can we help admiring the analogy which this acquisition of a
more vascular organization, with the weakening of the alveolar
implantation, presents to the condition of the teeth in many of
the lower vertebrate animals.

177. Adaptation of the teeth to the food and nature of Man.—
Whether Man was originally designed by nature to be herbivorous or
carnivorous is a question which some authors have supposed might
be absolutely determined from his dentition. If we had to judge only
by fossil remains we should be warranted in concluding from the
human teeth that the species was not intended, under all circum-
stances and in all places, to subsist upon eifher animal or vegetable
food exclusively. It would be obvious at the first glance that they
were intermediate in character between the typical carnivorous
and the typical herbivorous dentitions: the presence of canines
and the absence of the complex structure arising from the inter-
blending of vertical plates of the different dental tissues in the
molars, would prove that the food could not have been the
coarse uncooked vegetable substances for which complex molars
are adapted ; and on the other hand the feeble development of the
canines and the absence of molars of the sectorial shape and
opposed like scissor-blades, would equally show that the species
had been unfitted for obtaining habitual sustenance from the raw
quivering fibre of recently killed animals.

The Apes and Monkeys which Man most nearly resembles
in his dentition, derive their staple food from fruits, grain, the
kernels of nuts, and other forms in which the most sapid and
nutritious tissues of the vegetable kingdom are elaborated; and
the close resemblance between the Quadrumanous and Human

472 HUMAN DENTITION.

dentition shows that Man was, from the beginning, more especially
adapted ‘to eat of the fruit of the trees of the garden.’(1)

But the Quadrumana are not exclusively frugivorous. Some
are known to seek the eggs and callow-brood of birds. The African
Baboons pass whole hours in turning up great stones in quest of
insects. The young Chimpanzees and Orangs in our menageries
manifest no repugnance to cooked meat, and the avidity with
which they will pluck and devour a sparrow leads us to suspect that
their vegetable diet is occasionally varied by the capture of a
live bird.

The formidable development of the canine teeth in the Orangs
and Baboons seems, at the first glance, to relate to the predomi-
nance of animal food in their regimen; but the sexual difference in
the development of those teeth might have indicated that they
had other subserviences than to the acquisition of daily sustenance,
if observation had not shewn them to have been given to the
males for the purpose of combat and defence. The molar teeth
are those which form always the best and sometimes the sole
guides to a knowledge of the diet of a mammiferous animal :
and these clearly indicate the frugivorous and mixed regimen of
the Quadrumana and Man.(2)

We have seen that the most striking characteristic of the
human dentition is the absence of any disproportionate develop-
ment of particular teeth, and the concomitant continuity of the
series in both jaws: the more immediate comparison with the
Quadrumanous dentition, while it demonstrates the close similarity
of the molar teeth, and supports the consequent deduction of an
omnivorous diet, brings to light the very interesting difference in
the proportions and disposition of the incisive and canine teeth,
by which we may appreciate the adaptation of the human denti-
tion to Man’s peculiar and higher attributes. His reason furnishes

(1) This is the conclusion to which my friend Prof. Bell has arrived in his ‘ Physiological
Observations on the Natural Food of Man, deduced from the characters of the Teeth.’ On the
Teeth, 8vo. 1829, p. 33.

(2) John Hunter in considering the question, ‘‘ Under what class do the Human Teeth
come ?” concludes by stating, ‘“‘ He, (Man) ought, therefore, to be considered as a compound,

fitted equally to live upon flesh and upon vegetables.” Nat. Hist. of Human Teeth, 4to. 1771,
p. 120.

CARNIVORES. 473

him, in the lowest condition of savage life, with weapons more
formidable than sharp and long canine teeth, and his mastery over
fire, the prime element of cookery, enables him to dispense with
strong and prominent incisors in the reduction of the tough, raw,
and indigestible parts of vegetable or animal food.

But the moderate and equable development of the anterior
teeth, and the graceful continuous curve which they form with
the molar series, have not merely a negative relation to the sub-
stitutes which Man’s inventive faculty provides for the absence of
the large and strong incisors and canines of the Orangs. The
smooth and equable posterior surface of the incisors, their vertical
position and their close arrangement in a gentle curve with the
canines, offer the best conditions for reacting upon the tongue in
the various applications of that organ to the teeth during speech.
The appearance of the teeth in the mouth is contemporaneous
with the child’s power of forming articulate sounds; and the clear-
ness of utterance is affected both by the temporary deficiency of
the incisive series during the change of dentition, and in a still
greater degree by the final loss of the teeth and their sockets in
old age.

Lastly, the vertical symphysis of the human jaw not only
affords the most favourable position to the incisors in relation to
speech, but is accompanied in the highest races with a promi-
nence of the lower border forming the chin, which is wanting in
every inferior animal: and this remarkable feature, with the short
jaws proportioned to the small incisors and canines, harmoniously
combine with the capacious forehead in stamping the head of Man
with the impress of his intellectual superiority.

CHAP PE Ra 4

TEETH OF CARNIVORA.

178.—Havine completed in Man the survey of the dental
system of Omnivorous Mammalia, I next proceed to consider the
stronger-featured modifications of those preparatory digestive organs

474 CARNIVORES,

in the Orders which are more strictly limited to one kind of ali-
ment, and to which such modifications are more immediately and
decidedly related.

In this point of view it has seemed to me that the teeth of
the Carnivora present a higher grade of development than those
of any of the mixed or insect feeders, and, in their more essen-
tial relationship to the digestive system, their preparatory opera-
tions are much more extensive and important than in Man: the
teeth of the Carnivora being adapted not only to comminute
but obtain the food, to seize and kill the victim, to divide it
when killed, and to separate the nutritious from the inedible parts
of the prey.

Had I been guided in this ascensive survey of the dental
system by the general perfection of the species, | must have ended
with that of Man; but viewing its modifications and complexities
irrespective of the rest of his organization, it must be admitted
that, notwithstanding the admirable adaptation of the human teeth
to the nature and faculties of Man, they are far from manifest-
ing the most complex structure of those organs. This must be
sought for in the herbivorous Mammalia—the Pachyderms, the
Ruminants and especially the gigantic Proboscidian quadrupeds,
—with which, therefore, the present Treatise on the Comparative
Anatomy of the Dental System will conclude.

The predaceous Mammalia offer various kinds and degrees
of deviation from the typical carnivorous dentition, as exemplified
in the genus Felis. Throughout the Order the incisors are six
above and below; few are the exceptions in which they fall short
of that number, in none of the Carnivora do they exceed it: the
canines are always present and largely developed, with long co-
nical sharp-pointed and often trenchant crowns: the variations
from the type are played upon the molar teeth; and herein the
Carnivora offer a marked contrast with the IJnsectivora, in which
we found much constancy in the bristled molars but extreme di-
versity in the incisors and canines. In most Carnivora one molar
tooth on each side of both jaws has its crown modified, either
wholly or in part, for reacting upon the opposite tooth, like the
blades of scissors, in express relation to the division of flesh:

CANIDA. 475

whence Cuvier has applied to this tooth the name of ‘ Dent car-
nassiére,’ which I have rendered ‘dens sectorius,’ sectorial, or
scissor-tooth.(1) The compressed trenchant part of this tooth has
a sharp edge, more or less deeply cleft by one or two notches,
and with its divisions more or less pointed or produced in different
genera: this part of the crown of the sectorial tooth I call the
‘blade ;’ it is usually combined with one or more basal tubercles.
The blade of the upper sectorial always plays upon the outside,
and a little in advance of the lower sectorial. The upper per-
manent sectorial succeeds and displaces a deciduous tubercular
molar in all Carnivora, and is, therefore, essentially a premolar
tooth: the lower sectorial comes up behind the deciduous series
and has no immediate predecessor, it is, therefore, a true molar
and the first of that class. By these criteria the sectorial teeth
may always be distinguished under every transitional variety of
form which they present in the Carnivorous series, from Ma-
charodus in which the crown consists exclusively of the ‘ blade’
in both jaws, to Ursus in which it is wholly tubercular: the de-
velopment of the tubercle bearing an inverse relation to the
carnivorous propensities of the species.

The leading modifications of the Carnivorous dentition will be
described as they are presented in the families typified respectively
by the Dog, the Civet, the Hyena, the Tiger, the Stoat, the
Bear and the Seal.

179. Canide.—The normal dental formula of the genus Canis
is :—

5 ess =] 4—4 2—2
Vie sary, UGH tears) (US =e 8 ;
ape Testy) e 4 ap?

— 42. (Pl. 125. fig. 1 & 2.)

38-3
The incisors (fig. 1) form a continuous series, describing the segment
of a circle in both jaws, and progressively increase in size from
the first to the third: the trenchant margin of the crown is divided
by two notches into a large middle and two small lateral lobes:
in the large external incisor the inner lobe is obsolete, the outer

(1) ‘Fleisch-Zahn’ of the German Naturalists; the term ‘lacerator’ is more applicable

to the canine than to the trenchant molar, to which it has been applied by some English
Authors. See Gardens and Menagerie of the Zoological Society, vol. i, p, 14.

476 CARNIVORES.

one situated near the base, and the middle lobe is produced into
a strong conical laniariform crown. The canines (c) are curved, sub-
compressed ; the enamelled pointed crown forms nearly half the
length of the tooth, is smooth, without any groove; it has a slight
internal depression and a posterior, not very sharp, ridge in the
upper tooth. The premolars (p) have strong sub-compressed conical
crowns gradually enlarging from the first to the third in the upper,
and to the fourth in the lower jaw, and acquiring one or two ac-
cessory posterior tubercles as they increase in size. The fourth upper
premolar presents a sudden increase with the sectorial form : its blade
is divided into two cones by a wide notch, the anterior cone being
the strongest and most produced; the tubercle is developed from
the inner side of the base of this lobe. The first and second upper
molars (m) are tuberculate ; each supports two external cusps, and has
a broad, internal, subtuberculate basal talon; but the second is very
small, less than half the size of the first molar. The first true molar
below is modified to form the opposing blade to the sectorial tooth
above; retaining the tuberculate character at its posterior half (fig. 3, 1):
the blade is divided by a vertical linear fissure into two cones,
the posterior being the largest: behind this the base of the crown
extends into a broad, quadrate, trituberculate talon. The second
molar has two anterior cusps on the same transverse line, and
a posterior broad flat talon: the last lower molar is the smallest
of all the teeth; it is sometimes bituberculate, as in the Wolf,
Dog, and Jackall, sometimes presents an additional talon, as in
the Canis lagopus, and is sometimes entirely wanting, as in the
Canis primevus.

The incisors, canines, and first premolars (p 1) in both jaws have
each a single fang: the next two premolars above, and all the others
below have two fangs, which are usually connate in the second
of the lower jaw: the upper sectorial premolar has three fangs,
two anteriorly on the same transverse line, and a large and
strong one behind: the first true molar has four fangs, three slender
external, and one strong internal: the last molar has three fangs.
The lower sectorial and second molar teeth have each two fangs;
the last molar has but one fang.

CANIDA. 477

The normally developed deciduous molars are :—

The predecessors of the first permanent premolars in both jaws
are seldom calcified, and generally disappear after being transitorily
manifested in the papillary stage; the second, third, and fourth
' milk-molars which are developed and in use by the young animal,
are those only which are enumerated in the deciduous formula.
The incisors appear about the third week after birth, the middle
ones first cutting the gum, and the other teeth following in the
order of their position ; the last molar is in place before the end
of the sixth week. In the Dog, at three months old the succes-
sors of the deciduous teeth present the development represented
in Pl. 125, fig. 4. The deciduous incisors (2) and canines (c) differ
from their successors chiefly in their smaller size; the crowns of
the canines are more recurved. The first molar (d 1) is conical with
two widely diverging fangs, in both jaws: the second in the upper
jaw (d 2) is the sectorial tooth, and has a relatively shorter blade,
and the tubercle is continued more nearly from the middle of the
inner side, than in the permanent sectorial: the third upper molar
(d 3) resembles the first permanent tubercular molar, but has a
less tuberculate inner lobe. In the lower jaw the first deciduous
molar resembles that above, but has the anterior and posterior
basal tubercles better marked; the second is similar, but larger ;
the third is the sectorial tooth, in ‘which the biconical blade is
shorter in proportion to the posterior quadrituberculate broad lobe,
than in the permanent sectorial.

The first permanent premolar (p 1) comes into place before
any of the deciduous teeth are shed: its germinal predecessor
disappearing before birth. The second upper premolar (p 2) re-
sembles in form the first deciduous molar which it displaces. The
third upper premolar (p 3) is a more simple tooth than the sectorial
molar which it displaces : the upper permanent sectorial (p 4) displaces
the deciduous tubercular molar. The two permanent true molars
(m 1, m2) succeed each other horizontally without displacing any
teeth. In the lower jaw the second and third premolars have

478 CARNIVORES.

thicker and more obtuse as well as larger crowns than the first
and second milk-molars which they displace. The lower deciduous
sectorial is succeeded by the fourth premolar, which, as usual,
has a more simple crown than the deciduous tooth which it dis-
places. The permanent sectorial has no direct deciduous predecessor
and therefore must be held to be a true molar tooth, according to
the character assigned to those teeth in this work. The absence
of a tuberculate molar in the lower jaw of the immature Dog
brings the character of the deciduous dentition of the genus
Canis much closer to that of the typical members of the Car-
nivorous Order, and affords an interesting illustration of the law
that ‘unity of organisation is manifested directly as the proximity
of the animal to the commencement of its development.’(1) The
succession of two tubercular molar teeth behind the permanent
sectorial tooth in the adult or permanent dentition of the lower jaw
carries the genus Canis farther from the type of its Order, and
stamps it with its own proper omnivorous character: and this con-
tributes to adapt the Dog for a greater variety of climate, food,
and other circumstances, all tending in an important degree to fit
that animal for the performance of its valuable services to man.

In no other genus of Quadruped are the jaws so well or so
variously armed with dental organs: notwithstanding the extent
of the series, the vacancies are only sufficient to allow the in-
terlocking of the strong canines. These are efficient and for-
midable weapons for seizing, slaying, and lacerating a_ living
prey: the incisors are well adapted by their shape and advanced
position for biting and gnawing: the premolars, and especially
the sectorials, are made for cutting and coarsely dividing the
fibres of animal tissues, and the tuberculate molars are as admirably
adapted for cracking, crushing, and completing the comminution
of the food, whether animal or vegetable.

Amongst the aberrant species of Canide it is interesting to
find in the Proteles, which presents the most anomalously simple den-
tition in the adult state, a much greater conformity with the common

(1) This Law is defined and exemplified in my ‘ Lectures on the Invertebrate Animals,’
p. 368, 8vo. 1843.

CANIDE. 479

type in the teeth of the immature period of existence. M. de
Blainville describes the deciduous dentition as including, besides
the usual number of incisors and canines, the same number and
kind of molars, as in the other Canide ; i. e. a premolar with two
fangs, a sectorial and a complex molar each with three fangs,(1) (in
the upper jaw?). These are succeeded, in both jaws by four small,
simple, widely separated molars (PI. 125. fig. 6): the first has a sub-com-
pressed conical crown supported by a single fang; the second has
a larger crown of similar shape supported by two fangs ; the third
molar has a shorter and broader crown supported by two fangs ;
the fourth molar is the smallest, with a subtriquetral crown above,
and a simple compressed one below, where it is supported by a
single fang. In this instance of arrested development of the
molar series we may discern the retention of the more strictly
carnivorous (feline) type, though feebly manifested.

In the Megalotis or Long-eared Fox (Otocyon, Licht.) the deviation
from the typical dentition of the Canide is effected by excess of deve-
lopment ; two additional true molars being pfesent on each side of
the upper, and one on each side of the lower jaw, in the permanent
series of teeth; and an approach is made by the modified form of
the sectorial molar and of some of the other teeth to the dentition
of the genus Viverra.

The upper incisors are small, simple, the outer one separate
from the rest and pointed; the under incisors are sub-bilobed,
relatively smaller than in the Fox. The canines are shorter and
less compressed than in the Fox. The first three premolars (Pl. 125,
fig. 5, p. 1, 2, 3) have shorter and more conical crowns, especially the
last; and the sectorial tooth (p 4) is more advanced ; the trenchant
portion of the sectorial is shorter and the inner tubercle larger than
in the typical Canide, in which it retains more of the form of its
deciduous predecessor. The first, second, and third true molars have
the internal basal ridge more developed than in the tuberculate
molars of the Fox: the last molar is disproportionately small, like
that of the under jaw in the typical Camde. The lower premolars,
like the upper ones, are more conical and shorter in proportion to

(1) Ostéographie de Canis, p. 56.

480 CARNIVORES.

their height than in the Fox ; and the posterior basal ridge is more
developed: the fifth tooth or first true molar, which is the lower
sectorial, approaches still nearer to that in the Viverride —the anterior
part answering to the trenchant portion in the Fox is tri-cuspid, the
inner cusp forming the most prominent point of the crown; the
posterior bicuspid portion of the tooth is smaller than in the Fox.
The second true molar is quadri-cuspid ; the third and fourth resemble
the last two in the Fox.

180. Viverride.—This family of Carnivora which compre-
hends the Civets, Genets, Ichneumons, Musangs, Surikates, and
Mangues, is characterized, with few exceptions, by the following
formula :—

3—3 1—) 4—4 2—2

Ce ONG oe Wee ares ore 40.

in. :
4—4 2—2

3-3?
It principally differs from that of the genus Canis by the absence
of a tubercular tooth on each side of the lower jaw: but, in
thus making a nearer step to the typical Carnivorous dentition,
the Viverride, on the other hand, recede from it by the less trenchant
and more tubercular character of the sectorial tooth; as will
be seen in the figures of the teeth of the Viverra indica, in Pl. 126,
fig. 1,2 & 3.

The canines are more feeble, and their crowns are almost
smooth; the premolars, however, assume a formidable size and
shape in some aquatic species, as those of the sub-genus Cynogale,
(fig. 4) in which their crowns are large, compressed, triangular,
sharp pointed, with trenchant and serrated edges, like the teeth
of certain sharks, (whence the name Squalodon, proposed for one
of the species), and well adapted to the exigencies of Quadrupeds
subsisting principally on fish: the opposite or obtuse, thick form
of the premolars is manifested by some of the Musangs, as
Paradocurus auratus. The upper sectorial tooth is a ‘dent de
remplacement,’ and the last of the premolars; its inner tubercle is
larger than in the Dog, and is bilobate in the Bassaris astuta ;
the middle conical division of the blade is thicker and the pos-
terior one is smaller than in the genus Canis. This tooth ad-
vances to beneath the ant-orbital foramen in the Musangs (Para-

VIVERRINES. 481

doxurus), it is situated farther back in the Civets and Genets, in
which the blade of the sectorial is sharper. The first upper molar
(fig. 1 & 2, m 1) has a trihedral crown, with two small external
cusps and one low and large internal tubercle: this, in Cynogael
(fig. 5, m 1) is more developed.

In the lower jaw the sectorial tooth (fig. 3, m 1) is the first
true molar, as in the Dog, and manifests its proper character by
the presence of an additional pointed lobe on the inner side of
the two lobes forming the blade at the fore-part of the crown: the
posterior, low, and large lobe of the tooth being also tri-tuber-
culate, as in the Dog. The last molar (fig. 3, m 2) has an oval
crown with four small tubercles, resembling the penultimate lower
molar in the Dog, with which it corresponds.

The deciduous dentition consists, in the Viverrine family of :

x 3—3 . 1—1 3—3 ,
Incisors sy canines —; molars Tau ee 28.

If the first permanent premolar has any predecessor it must be
rudimental and disappear early in both jaws; the second premolar
displaces the first normally developed deciduous molar; the third
upper premolar displaces and succeeds the deciduous sectorial,
which has a sharper and more compressed blade, and a relatively
smaller internal tubercle, than the permanent sectorial. This tooth
displaces the last deciduous molar, which is a tubercular tooth,
resembling in form the first of the two upper permanent tuberculars :
these, coming into place without pushing out any predecessors,
enter into the category of true molar teeth. In the lower jaw
the third premolar displaces the deciduous sectorial, which has
three trenchant lobes, and a relatively smaller posterior talon than
the permanent sectorial. The fourth premolar displaces the third
or tubercular milk-molar. The permanent sectorial and tubercular
molars displace no. predecessors and are therefore true molars.

The first permanent premolar, which has no deciduous repre-
sentative, is not developed at any period in the Mangues (Cros-
sarchus), the Suricates (Ryg@na), or the Mangusta paludinosa: these
Viverrines, therefore, retain throughout life more of the immature
features of the family, and in the same degree approach nearer

Any

482 CARNIVORES.

in the numerical characters of their dentition, to the more typical
Carnivora.

The alternate interlocking of the crowns of the teeth of the
upper and lower jaws, which is their general relative position in
the Carnivora, is well marked in regard to the premolars of the
Viverride (fig. 4): as the lower canine is in front of the upper,
so the first lower premolar rises into the space between the
upper canine and first upper premolar; the fourth lower premolar
in like manner fills the space between the third upper premolar
and the sectorial tooth (p 4), playing upon the anterior lobe of the
blade of that tooth which indicates by its position, as by its mode
of succession that it is the fourth premolar of the upper jaw. The
first true molar below, modified as usual in the Carnivora to form
the lower sectorial, sends the three tubercles of its anterior part
to fill the space between the sectorial and the first true molar
above. In the Musangs the lower sectorial is in more direct op-
position to its true analogue, the first tubercular molar in the
upper jaw; and these Indian Viverride (Paradoxuri) are the least
carnivorous of their family, their chief food consisting of the fruit
of palm-trees, whence they have been called ‘ Palm-cats.’

181. Hyena.—The dentition of this genus presents a nearer ap-
proach to the strictly carnivorous type by the reduction of the tu-
bercular molars to a single minute tooth on each side of the upper
jaw, the inferior molars being all conical or sectorial teeth: the
molar teeth in both jaws are larger and stronger, and the canines
smaller in proportion than in the Feline species, from the formula
of which the dentition of the Hyena differs numerically only in
the retention of an additional premolar tooth on each side of
both jaws. The dental formula of the genus Hyena (Pl. 126,
fig. 6) is:—

Le 4—4 lend
C.——; pm. —; m. ——: = 04.

mM. ae on Z

3-3 7
The crowns of the incisors form almost a straight transverse line
in both jaws; the exterior ones, above, being much larger than
the four middle ones, and extending their long and thick inserted base
further back: the crown of the upper and outer incisor is strong,

HYENA. 483

conical, recurved, like that of a small canine, with an anterior
and posterior edge, and a slight ridge along the inner side of the
base. The four intermediate small incisors are divided by a
transverse cleft into a strong anterior conical lobe, and a_ posterior
ridge, which is notched vertically; giving the crown the figure
of a trefoil. The lower incisors gradually increase in size from
the first to the third; this and the second have the crown in-
dented externally, but they have not the posterior notched ridge
like the small upper incisors; the apex of their conical crown fits
into the interspace of the three lobes of the incisor above. The
canines have a smooth convex exterior surface, divided by an an-
terior and posterior edge from a less convex inner side: this surface
is almost flat and of less relative extent in the inferior canines. The
first premolar above (p 1) is very small, with a low, thick conical
crown: the second presents a sudden increase of size with an ad-
ditional posterior and internal basal ridge to the strong cone.
The third premolar exhibits the same form on a still larger scale,
and is remarkable for its powerful aspect. The posterior part of
the cone of each of these premolars is traversed by a longitudinal
ridge. The fourth premolar (p 4) is the carnassial tooth and has
its long blade divided by two notches into three lobes, the first a
small thick cone, the second a long and compressed cone, the
third a horizontal sinuous trenchant plate: a strong trihedral tu-
bercle is developed from the inner side of the base of the an-
terior part of the crown. The single true molar of the upper jaw
(fig. 7, m 1) is a tubercular tooth of small size: it is transversely
oblong in the Hyena vulgaris and H. fusca; smaller and sub-cir-
cular in the Hyena crocuta ; still smaller and implanted by a single
fang in the Hyena spelea: in all the existing species of Hyzna it
has two fangs. The first premolar of the lower jaw (fig. 6, p 2)
fits into the interspace between the first and second premolars
above, and answers, therefore, to the second lower premolar in the
Vwerride: it is accordingly much larger than the first above ; it
has a ridge in the forepart of its cone, and a broad basal talon
behind. The second (p 3) is the largest of the lower premolars,
and has an anterior and a posterior basal ridge, with a vertical ridge
ae ae

484 CARNIVORES.

ascending upon the fore as well as the back part of the strong
rounded cone: the third premolar (p 4) is proportionally less in
the Hyena crocuta than in the H. vulgaris, its posterior ridge is
developed into a small cone. The last tooth (m 1) is the sectorial
and consists almost entirely of a blade divided by a vertical fissure
into two sub-equal compressed pointed lobes: the points are less
produced than in the Felines, but the lower sectorial of the Hyena
is better distinguished by the small posterior basal talon, from which
a ridge is continued along the inner side of the base, and is slightly
thickened at the fore-part of the crown. According to the relative
position of the crowns of the premolars, the third below ought to
be the last, being analogous to the fourth in the Viverride, and
the sectorial should be the first true molar: we shall find this view
confirmed by the test of the mode of succession of the permanent
teeth. But the mode of implantation of the premolar and molar
teeth may first be noticed. The first upper premolar has but one
fang; the second and third have each two; the sectorial tooth has
three, the two anterior ones on the same transverse line, the inner.
one supporting the tubercle. The lower premolars and sectorial
have each two fangs, there being none truly answering to the first
above: the anterior root of the lower sectorial tooth is very strongly
developed in the great extinct Cave-Hyzna. |
The deciduous teeth approximate, as usual, to the typical
dentition of the Carnivora; they consist of :— |

h acs [ 1h a8
Incisors 5) Canines «—.; molars —: = 22.

The figure of the skull of the young Hyena crocuta in the posthu-
mous Edition of the ‘ Ossemens Fossiles,’ 8vo. 1836, pl. 190, fig. 3,
shows that stage when the correspondence with the formula of the
genus Felis is completed by the appearance, in the upper jaw, of
a small premolar in the interspace between the canine and first
molar of the deciduous series: but this appearance is due to the
apex of the first permanent premolar which cuts the gum before
any of the normal deciduous teeth are shed: whether it is pre-
ceded, as in the Dog, by a deciduous germ-tooth in the foetus I
know not. The first normal deciduous molar is two-fanged, and
has a more compressed and consequently more carnivorous crown

ee

HYENA. 485

than that of the second permanent premolar by which it is suc-
ceeded. The second deciduous molar is the sectorial tooth: the
inner tubercle is continued from the base of the middle lobe, and
thus resembles the permanent sectorial of the Glutton (Gulo) and
many -other Mustelide ; the deciduous tubercular molar is relatively
larger than in the adult Hyena, and offers another feature of re-
semblance to the permanent dentition of the Glutton. It is also
worthy of remark that the exterior incisor of the upper jaw is not
only absolutely, but relatively smaller in the immature than in
the adult dentition of the Hyzena, giving another feature of resem-
blance to the more common type of dentition in the Carnivora.
The first and second deciduous molars below (Pl. 126, fig. 9)
have more compressed conical crowns than their successors : the third
deciduous molar (fig. 9, 3) is the sectorial tooth, and, again, as in
Gulo, has a better developed hinder tubercle than the permanent sec-
torial; it is not displaced by this tooth, but, as in other Carni-
vora, by a premolar (p. 4) of more simple character. The per-
manent sectorial (m 1) is developed posteriorly and rises, like
other true molars, without displacing a deciduous predecessor.
The permanent dentition of the Hyena, as of other genera or
families of the Carnivora, assumes those characteristics which
adapt it for the peculiar food and habits of the adult and mark
the deviation from the common type, which always accompanies
the progress to maturity. The most characteristic modification of
this dentition is the great size and strength of the molars as
compared with the canines, and more especially the thick and
strong conical crowns of the-second and third premolars in both
jaws, the base of the cone being belted by a strong ridge which
defends the subjacent gum.(1) This form of tooth is especially
adapted for gnawing and breaking bones, and the whole cranium
has its shape modified by the enormous development of the mus-
cles which work the jaws and teeth in this operation. (2) Adapted
(1) An eminent Civil-Engineer, to whom I showed the jaw of a Hyzena, observed that

the strong conical tooth, with its basal ridge was a perfect model of a hammer for
breaking stones for roads.

(2) “The strength of the Hyzna’s jaw is such that, in attacking a Dog, he_ begins
-by biting off his leg at a single snap.” - Buckland, ‘ Reliquie Diluviane,’ p. 23.

486 CARNIVORES.

to obtain its food from the coarser parts of animals, which are
left by the nobler beasts of prey, the Hyzena chiefly seeks the
dead carcase, and bears the same relation to the Lion which the
Vulture does to the Eagle. In consequence of the quantity of
bones which enter into its food, the excrements consist of solid
balls of a yellowish white colour, and of a compact earthy frac-
ture. Such specimens of this substance, known in the old Materia
Medica by the name of ‘album grecum,’ were discovered by
Dr. Buckland in the celebrated ossiferous cavern at Kirkdale.
They were recognised at first sight by the keeper of a menagerie,
to whom they were shown, as resembling both in form and ap-
pearance the feces of the spotted Hyzna; and, being analysed
by Dr. Wollaston, were found to be composed of the ingredients
that might be expected in foecal matter derived from bones, viz. :
phosphate of lime, carbonate of lime, and a very small proportion
of the triple phosphate of ammonia and magnesia. This discovery
of the coprolites of the Hyzna formed, perhaps, the strongest of
the links in that chain of evidence by which Dr. Buckland
proved that the cave at Kirkdale in Yorkshire had been, during
a long succession of years, inhabited as a den by Hyznas, and
that they dragged into its recesses the bodies of other animals, whose
remains, splintered and bearing marks of the teeth of the Hyzna,
were found mixed indiscriminately with their own.

182. Felide.—The dentition in the well-marked and circum-
scribed genus of Cats (Felis) might be recognised as the most typical
of the order Carnivora, not only from its formidable simplicity and
peculiar adaptation to the destruction of living animals and the
mastication of their flesh; but because it is that to which the
transitory dentitions of all the other digitigrade families and genera

more or less closely approximate. The feline formula (Pl. 127,
fig. 1) is :—

Z 3—3 f i—l s=3 1
Incisors —; canines —; premolars —; molars 7: = 28.

The six incisors in both jaws are closely arranged with their crowns

in a transverse line; their fangs, for economy of space, are zig-zag,
at least in the lower jaw: the outer incisor of the upper jaw is

FELINES. 487

not so large as in the Hyena, but is conical, with a sharp ridge
on the outer side, and a small tubercle on the inner side, in which
the posterior basal ridge terminates: the smaller intermediate in-
cisors have their broad and thick crowns indented by a transverse
cleft, and the posterior ridge so defined, is sub-divided by a minute
vertical notch, which is soon worn away. The lower incisors
are smaller, especially the outer pair, which have an external basal
tubercle, and have not the posterior ridge. The canines are very
large and strong ; the fang commonly thicker and longer than the
enamelled crown: this is conical, sub-compressed, slightly recurved,
sharp-pointed ; convex anteriorly and externally ; much less convex
internally, almost flat here in the lower canines: the two surfaces are
divided by a sharp ridge behind, where they meet at an acute
angle and where feeble indications of a serrated structure may
be discerned in the larger Cats, as the Lion and Tiger: both the
outer and the inner surfaces of the crown are indented with one,
or more commonly, two parallel longitudinal grooves, which are
very characteristic of the canines of the typical Felide; they are
faintly expressed in those of the Hunting Leopard, and are not
present in the long, compressed and serrated canines of the very for-
midable extinct Feline sub-genus Machairodus.

The first upper premolar (marked p 2 in fig 1, as answering to the
second in the Hyzena and Dog) is a very small tooth with an obtuse
conical crown supported by a single fang, except in the Felis pla-
niceps in which it retains its typical structure, and has two fangs:
the opposite variety is manifested by the Short-tailed Lynxes, in
which this small premolar is commonly wanting, as in the extinct
Machairodus. The second upper premolar (p 3), of much larger
size, has a sub-compressed conical crown, with a posterior, some-
times bilobed, basal tubercle, and a small anterior prominence ; it
has two strong diverging fangs. The third upper premolar (p 4)
is the sectorial tooth ; its extensive blade is divided into three lobes
by two angular notches ; the first and second lobes are conical, the
latter the largest and with its point inclined backwards as in all
strictly flesh-eating Carnivora, an obtuse ridge is continued from its
inner side to the base of the internal tubercle ; the third lobe is

488 CARNIVORES.

flat on the inner side of the blade, and has a horizontal sinuous
edge: the internal basal tubercle (fig. 2, p 4) is developed from
the interspace between the first and second lobes of the blade: this
is relatively smaller than in the Hyzena, and almost obsolete in the
Hunting-Leopard (Felis jubata) and in a small allied extinct Feline
animal of Brazil, which Dr. Lund, adopting the sub-generic name
applied by Wagler to the Hunting-Leopard, calls Cynailurus mi-
nutus(1). In all the Felide the upper sectorial has three fangs,
the two anterior ones being on the same transverse line. The small
tubercular true molar (fig. 1 & 2, m 1) has a transversely extended
elliptical or sub-trihedral crown.

The first lower premolar (marked p 3 as being the analogue
of the third in the Dog) is implanted by two fangs which support
a middle compressed cone and an anterior and posterior basal tu-
bercle ; its crown passing behind the first upper premolar shows it
to answer to the second above. ‘The second premolar below (p 4)
is larger and has two posterior tubercles ; its crown fits into the space
between the second and the third or sectorial premolar above, oppos-
ing the anterior lobe of that tooth.; The last molar below (m 1)
is the sectorial tooth, the crown of which consists exclusively of the
blade; this is divided into two equal, compressed, pointed lobes,
with straight margins, very sharp except the anterior one of the first
lobe ; the contiguous margins of the two lobes meet at a right angle,
from which a vertical fissure extends nearly half way down the crown.
The outer surface of the crown presents an equable convexity from
before backwards; the inner side is deeply excavated between the
lobes (fig. 3). A transverse notch near the base of the posterior
margin of this tooth indicates the rudiment of the taJon or tubercle

which distinguishes the corresponding tooth of the Hyena; the in-

dication being strongest in the aberrant species of Felis, as the Lynx
and Hunting-Leopard(2). Although the lobes of the crown of the
lower sectorial tooth are equal, the anterior fang is much larger
(1) Bilk paa Brasilien Dyreverden, &c., Kjobenhavn, 4to. 1839, p. 35.
(2) M. de Blainville, by whom many interesting varieties manifested by specimens in the
Cuvierian collection have been carefully noted, figures one, from the Canada Lynx, in

which a small tubercular molar exists behind the lower sectorial tooth; thus presenting
an analogy to the Stoat and other Mustelide. ‘Ostéographie de Felis,’ pl. 14, p. 57.

ee La ree

FELINES. 489

than the posterior one. It would be difficult to recognise this meta-
morphosed molar as the corresponding tooth to the small tubercular
above, were we not assured of the fact by the constancy in the relative
position of the crowns of the molar series in the Carnivora, where the
lower ones are always in advance of the upper, and still more un-
equivocally by the relations of the permanent to the deciduous teeth.

The deciduous dentition in the genus Felis (Pl. 127, fig. 4) is :—

G 3—3 5 1—1 3—3
Incisors —; canines —; molars —: = 26.
3—3 ? 1-1 2—2

The incisors in the common Cat begin to appear above the gum when
it is between two and three weeks old ; the canines next, and then the
molars follow, the whole being in place before the end of the sixth
week. After the seventh month they begin to fall in the same
order; but the lower sectorial molar rises above the gum before
any of the deciduous molars are displaced. The longitudinal grooves
are very faintly marked in the deciduous canines. The first deciduous
molar in the upper jaw (d l) is a very small and simple, one-fanged
tooth ; it is succeeded by the corresponding tooth of the permanent
series, which answers to the second premolar of the Hyzna and Dog.
The second deciduous molar (d 2) is the sectorial tooth ; its blade
is trilobate, but both the anterior and posterior smaller lobes are
notched, and the internal tubercle, which is relatively larger than
in the permanent sectorial, is continued from the base of the middle
lobe, as in the deciduous sectorial of the Dog and Hyena; it
thus typifies the form of the upper sectorial in the permanent
dentition of several Viverrine and Musteline species. The third
or internal fang of the deciduous sectorial is continued from
the inner tubercle, and is opposite the interspace of the two outer
fangs. The Musteline type is further adhered to by the young
Feline in the large proportional size of its deciduous tubercular
tooth (d 3). In the lower jaw, the first milk-molar (d 1) is suc-
ceeded by a tooth (p 3) which is analogous to the third lower pre-
molar in the Dog and Civet(1). The deciduous sectorial (d 2), which

(1) M. de Blainville states that the first lower deciduous molar in the Felis maniculata has

an unusually thick crown supported by three roots, and hence derives an argument against
the opinion of Temminck, that this Egyptian wild Cat was the source of our domestic

490 CARNIVORES.

is succeeded by the second premolar (analogous to the fourth in the
Dog), has a smaller proportional anterior lobe and a larger posterior
talon, which is usually notched ; thereby approaching the form of the
permanent lower sectorial tooth’ in the Mustelide. We thus per-
ceive that even the fierce Feline Carnivora recede in a slight degree,
as they advance to maturity, from the more common type of the
dentition of their order, by the suppression of a few characters re-
tained in other genera ; whereby they acquire a more decidedly des-
tructive and carnivorous dentition, which more strongly marks their
own peculiar predatory characters.

A single glance at the long and strong, sub-compressed, tren-
chant and sharp-pointed canines, closely interlocking, the lower in
front of the upper, when the jaws are clenched, suffices to appreciate
their peculiar adaptation to seize, to hold, to slay and lacerate a
struggling prey. The jaws are strong, but shorter than in other
Carnivora and with a concomitant paucity of the molar teeth: thus
the canines are brought nearer to the insertion of the very powerful
temporal and masseter muscles, which work them with proportionally
greater force. The use of the small incisor teeth is obvious to any one
watching a captive Lion or Tiger at its meals: they are applied to
gnaw the soft cartilaginous ends of the bones, and to tear and scrape
off the tendinous insertions of the muscles and the periosteum. The
compressed trenchant blades of the sectorial teeth play vertically
upon each other like the blades of scissors; and the form of the
mandibular articulation almost limits the movements of the jaws to
the vertical direction. The wide and deep zygomatic arches, and the
high sagittal and occipital crests concur in completing the destruc-
tive character of the cranium of these most formidable of the Car-
nivora.

183. Machairodus(1).—This generic name was given by Dr. Kaup
to the extinct animal which was armed with canine teeth, like that
figured in pl. 127, figs. 5 & 6. Such teeth, long, compressed, fal-
ciform, sharp-pointed and with anterior and posterior finely-ser-

race, in which the first deciduous molar has the usual form and number of fangs, as in
our own Wild Cat (Felis Catus.)
(1) From payatpa a sabre, and 6¢&¢ a tooth.

FELINES. 491

rated edges, but of larger size than the specimen figured (fig. 6)
were first discovered in tertiary strata in Italy and Germany, and
were referred by Cuvier to a species of Bear under the name of
Ursus cultridens ; but similar canines were afterwards discovered in
situ with some of the molar teeth in the tertiary deposits of France,(1)
which proved the animal to belong to the Feline family; and the
same evidence is afforded by fossil specimens of both upper and
lower jaws of other species of Machairodus from the tertiary de-
posits of the Sewalik mountain range in India, transmitted by
Captain Cautley to the British Museum; as well as by remains dis-
covered in the newer tertiary deposits of Buenos Ayres, and in
the ossiferous Caves of Brasil. (2)
The dental formula of the present extinct genus of Felide is :—

. 3—3 ° 1-1 2—2 1—1
Incisors —; canines — ; premolars — ; molars —: = 28.
3—3 1—1 2—2 1-1

Here, therefore the adult dentition closely approximates the deci-
duous formula of the genus Felis. In the lower jaw of the Machai-
rodus neogeus in the British Museum the anterior premolar on each
side the lower jaw is shed, and its dentition is thus rendered numeri-
cally identical with that transitory formula. The dental characteristic
of the immature state of the existing Lion and Tiger was thus re-
tained, in combination with a most remarkable modification of the
canine teeth, in the extinct and more formidable Carnivore of the
ancient world.

The middle incisors of the upper jaw, in the depth and width
of the vertical notch bisecting the posterior ridge of the crown,
more closely resemble those of the Hyena than those of the Felines ;
they are more compressed, especially at their strong implanted base.
The external incisor is as large as, and in some species appears to
be larger in proportion to the intermediate incisors, than in the
genus Felis. In the ancient British Machairodus (M. latidens,)
the anterior convex part of the crown of the external incisor is

(1) Bravard, Monographie de deux Félis d’Auvergne, 1828.

(2) See my History of British Fossil Mammalia,’ Part 1v., 1844, p. 174. The remains
of Machairodus from the Brazilian caves were first noticed by their discoverer Dr. Lund
as indications of an extinct Hyena, for which he proposed the name of H. neogea :
subsequently he recognised its distinctive characters, and proposed for it the generic name of
Smilodon : the canine tooth figured in Dr, Lund’s second Memoir, in the Copenhagen Transac-

492 CARNIVORES.

divided from the posterior less convex surface by two finely ser-
rated ridges, at the base of each of which there is a tubercle:
the fang is longer and more compressed in Machairodus neogeus
of S. America, than in M. latidens. The canine figured in Pl. 127,
fig. 6, is one of a few specimens of similar form and size which
have been found in ossiferous caves in England, associated with
remains of a large Tiger and other extinct Mammals. The com-
pressed crown presents no trace of the longitudinal impressions
which characterise the canines of the true Felis but is provided
with a double cutting edge of serrated enamel ; the posterior con-
cave edge is continued to the base of the crown, the anterior
convex margin becomes thicker as it approaches the base, like
the back of a knife, and the strength of the crown is further
increased by the expansion of its sides. Thus in the Machairodus,
as in the Megalosaurus, whose teeth the present canines most nearly
resemble, each movement of the jaw combined the power of the
knife and saw; the points of the teeth in making the first in-
cision would act like a two-edged sabre, and their Backward cur-
vature would give them better holdfast. The first premolar of the
upper jaw (ib. fig. 5, p 3) corresponds with the second in the genus
Felis, and with the third in Canis and Viverra. The crown is elliptic,
low, with a middle compressed cone trenchant before and behind,
having a small blunt tubercle at the fore part of its base, and
two tubercles behind, the first conical and pointed, the second
obtuse. The succeeding tooth (ib. p 4) is the sectorial, and is larger
in proportion to the preceding premolar than in Felis: it is, also,
much more ‘carnassial’ to use the. Cuvierian term, having no
other indication of the internal tubercle than a slight basal thick-
ening of the blunt ridge which descends along the inner side of
the middle lobe of the blade: it is more like the deciduous than
the permanent sectorial in the true Cats. The crown of the
tooth consists of the antero-posteriorly elongated strong and
trenchant blade: it is divided into three principal lobes; but
the anterior and smallest differs from that in the permanent
sectorial of the true Cats in being sub-divided into an an-

tions, 1842, Pl. 37, fig. 5, 6, 7. agrees with that of Machairodus, to which’ genus the extinct
carnivore belongs by the namber and structure of the molar teeth.

FELINES. 493

terior obtuse tubercle and a posterior larger compressed pointed
portion: the second lobe resembles that in Felis; the third is re-
latively larger, equalling in some species, as Machairodus neogeus,
half the antero-posterior extent of the crown; its trenchant edge
being, however, as in the Cats, horizontally sinuous. The upper
sectorial differs still more from that of the typical Felde in being
supported by only two fangs. The tubercular tooth is small, with
a more rounded crown than in Felis. The canines of the lower jaw
are much shorter than those above, and form the outer teeth of the
Same transverse series with the incisors, like the lower canines of the
Ruminants, whose true nature they serve to indicate. The fore-part
of the lower jaw, which supports those teeth and the incisors is of
unusual depth, for the purpose of affording a kind of defensive but-
tress to the long sabre-shaped crowns of the upper canines, when
the mouth is closed. In this state the crown of the first lower pre-
molar (ib. p 3) is applied to the fore-part of that above, and is there-
fore strictly its analogue, answering, like the first lower premolar in
the true Felines, to the third premolar in the Dog. In Machai-
rodus neogeus it is minute and simple; in the small Machai-
rodus (M. megantereon), found fossil in France, it has a middle
compressed principal cone, with one basal tubercle in front, and two
behind. The second lower premolar (ib. p 4) is double the size, and
its true relationship to the last premolar of the upper jaw is here mani-
fested, not only by relative position, and mode of succession, but by
the form of the crown: the anterior basal tubercle is developed into a
sub-compressed cone, answering to the anterior lobe of the blade of
the upper sectorial ; the middle and largest compressed cone below
repeats the form of the middle lobe of the sectorial blade above,
whilst the sinuous edge of the posterior lobe of the upper sec-
torial is represented by the two better defined posterior basal
cones of the lower last premolar tooth. The third tooth of the
lower jaw of Machmrodus (ib. m 1) which is a true molar, retains the
peculiar sectorial modification of the crown, which characterises it
in the normal Feline animals; but its trenchant and sharp-pointed
lobes are more inclined backwards. The entire dentition of this
most extraordinary and formidable of extinct predaceous animals

494 CARNIVORES.

thus accords with the peculiarly destructive character of the

upper canine teeth, and manifests permanently that super-car-
nassial character which is temporarily typified in the dentition of
the cubs of the Lion and Tiger; and the Machairodus thus yields
another example of a lost primeval form which retained throughout
life structures that are transitory in the present races.

184. Mustelide.—Of this family the Stoats, Ferrets, and
Weasels (Putorius) are the most carnivorous, predaceous and blood-
thirsty: their canine teeth are long, slender, and very sharp-
pointed ; the incisors small, gradually increasing from the internal
one, with the crowns in zigzag series in the lower jaw, the second
incisor being posterior to the first and third. The dental formula
of the genus Putoriws is :—

. 3—3 1—1 3—8 1
Incisors — ; canines —; premolars —; molars —: = 34.
s-3 4 1 2-2

The only diastema is in the upper jaw, between the incisors and
canine. The first premolar is very small; the second is twice the
size of the first, and the third twice the size of the second:
in the sectorial tooth the blade consists chiefly of one com-
pressed pointed lobe; the tubercle is small: the true molar is
relatively larger than in Felis, and consists of an outer and
an inner tubercle; the latter being the broadest. In the lower
jaw the last premolar is twice the size of the first; the se-
' cond is intermediate in size, as it is in position: but it has no
inner tubercle to match that of the analogous tooth above; and in
general the lower molars are narrower transversely than the upper
ones. The first true molar below has a sectorial crown with a
bilobed blade and a posterior tubercle; but no internal one: the
second true molar has a small round obtuse crown. The Cape-
Stoats (Zorilla) have an inner tubercle on the same transverse
line with the posterior lobe of the blade of the lower sectorial
tooth, which thus begins to deviate from the true Carnivorous type
and to acquire the tubercular character which is proper to it as a
true molar. ;

The Grison (Galictis) and the Taira (Gal. Barbara, Pl. 128, fig. 1.)
repeat the characters of the dentition of the Zorille, with a greater

MUSTELINES. 495

relative thickness of the crowns of most of the teeth, and a larger
development of the tubercle of the upper sectorial tooth; ib. fig. 2.
p 4 (i).

The Martin-Cats (Mustela, Cuvier), have an additional premolar
at the beginning of each series, their dental formula being :—

5 3—3 c 1—1 4—4 1-1
Incisors —; canines —; premolars —; molars —: = 38.
3—3 1—1 4—4 2—2

The canines are shorter and stouter, and the upper true molar
(Pl. 128, fig. 5, m1) has a larger crown than in the Stoats. The
inner tubercle also exists in the lower sectorial (ib. fig. 6, m 1) but
is relatively smaller than in the Zorilles.

The Wolverenes and Gluttons, (Gulo, Pl. 128, fig. 7), have
the same dentition, numerically, as the Martins, but have relatively
stronger canines, and no inner tubercle on the lower sectorial tooth
(ib. fig. 9, m 1): their habits answer to this resumption of a more
carnivorous type of dentition.

The Skunks, (Mephitis and Mydaus,) with the exception of the
Mephitis Humboldiu, (Pl. 128, fig. 11) which wants the first upper
small premolar, have the same dentition, numerically, as the Stoats ;
but the internal tubercle of the upper sectorial (fig. 11, p 4,)
is so much more developed that the crown assumes a triangular
form: the true molar (fig. 11, m 1.) which follows, surpasses the
sectorial in size, and has a broad, quadrate and quadrituberculate
crown. In the lower jaw the omnivorous character is manifested
by the assumption of a tubercular crown and the almost total
loss of the sectorial form by the first true molar, which supports
six small tubercles ; three on the inner border, two on the outer
border, and one behind.

The dental formula of the Otter (Lutra) is:—

in. —; c=; pm. —: m.—; = 36. (Pl. 128, fig, 4.)
The first premolar, (p 1) very small and single-fanged, lies close upon
the inner side of the strong canine, and is not visible from with-

(1) See the excellent description, by Prof. T. Bell, of the Galictis vittata, in the Trans.
Zool. Soc. vol. 11, p. 201, Pl. 35 & 36. He assigns, however, 2-2 premolars to the upper jaw,

as M. F, Cuvier does in his dental formula of Puforius, regarding the upper sectorial as the
corresponding tooth to the lower sectorial.

496 CARNIVORES.

out : the second (p 2) almost touches the posterior surface of the canine,
has a compressed conical, sharp-pointed crown, with an anterior
and posterior talon: the third (p 3) is similar but larger: the fourth
is the sectorial tooth, (fig. 4 & 5, p 4), with its blade divided into two
lobes, each pointed and inclined backwards, and it has a small
anterior talon, and a large, flat, semi-circular inner tubercle. The
true molar (ib. m 1) has a large rhomboidal grinding surface, with
two external cusps separated by a broad concave surface from two
smaller internal tubercles. The first (fig. 4, p 2), second (p 3), and
third (p 4) premolars of the lower jaw progressively increase in size,
and have similarly shaped, compressed, pointed crowns ; the last in-
creasing in breadth posteriorly, and having the talon there more
distinct. The first true molar (fig. 6, m !) is essentially like that
of the Zorille, but is relatively broader, with a greater development
of the internal tubercle and posterior broad grinding surface: the
sectorial blade forms an accessory, rather than a principal, part of
the crown ; it is divided into two pointed compressed lobes. The
last true molar is relatively smaller than in the Civet, and has a
round sub-tuberculate crown.

The Sea-Otter (Pl. 128, fig. 12.) has one molar less on each
side of the upper jaw than the common Otter: the first small
premolar is the absent tooth, and the posterior molars are so re-
markably modified as to justify the sub-generic distinction proposed
for the marine species by the name of Enhydra maria. There
is nothing peculiar in the incisors or canines: the second pre-
molar (p 3) has a strong obtuse conical crown with a posterior basal
ridge, and is double the size of the first premolar (p 2): the third
(p 4) is more than twice the size of the second, and represents the
sectorial tooth most strangely modified ; the two lobes of the blade
are hemispherical tubercles, the first the largest; the crown of the
tooth is much extended inwards and is developed into a third similar
tubercle. The last upper tooth, which is the first true molar (m 1)
has a rather larger crown than the sectorial, and of similar transversely
extended triangular form; but the base is turned inwards, and the
apex forms a hemispheric tubercle, the rest of the broad grinding
surface being irregular. In the lower jaw the teeth are not sepa-

MUSTELIDA. 497

rated by any interspace: the first and second premolars have ob-
lique obtuse conical crowns. The third premolar is more than twice
the size of the second and supports a large anterior hemispheric
protuberance with a small internal tubercle and a posterior basal
ridge. The first true molar has an oblong quadrate crown with
an anterior small tubercle, a larger and more prominent inner one,
and the rest of the broad horizontal surface undulating. The
second true molar has a transversely elliptical crown depressed in
the centre. When the teeth are in apposition, the anterior third
of the first true molar below is applied to the inner tubercle of
the last premolar above; the rest of its crown plays upon that of its
analogue the first true molar in the upper jaw, leaving a small
part of that tooth to receive the appulse of the second true molar
below, which has no corresponding tooth in the upper jaw.

The Mustelide present great constancy in regard to the
number of their true or post-molar teeth; with one exception,
(Mellivora), the lower molar series of which is figured at Pl. 128,
fig. 10, showing the absence of the second true molar, they have
one true molar on each side of the upper jaw, and two on each
side of the lower jaw: the second of these has always a broad
tubercular crown, like the one above. The upper true molar is
supported by one inner, and sometimes by one (Putorius, Gulo),
sometimes two (Mustela, Lutra, Mephitis), outer fangs. The second
true molar below is also tubercular but has a single fang. The
crown of the first true molar below offers many gradations from
the sectorial type as manifested in Putorius and Gulo, to the
tubercular type as in the Taira, Ratel (Pl. 128, fig. 10 m 1) and
Sea-Otter (ib. fig. 12 m 1); it is usually supported by two fangs;
a small intermediate supplemental root is occasionally developed, as
in the example from the Otter figured by M. de Blainville, (Ostéog.
de Mustela, Pl. xitt.) The principal varieties occur, as usual, in
the comparatively less important premolars: in the Martins and
Gluttons (Pl. 128, fig. 7) they are as numerous as in the Dog; the
first, in both jaws, being implanted by a single fang; the rest by
two, with the exception of the last above which has three roots. In
the Otter (ib. fig. 4) we find the first premolar removed from the

K K

498 CARNIVORES.

lower jaw; and the second (now the first) shows its true analogies
by its double implantation, as well as by the position of its crown
behind the first in the upper jaw (p 1.) In the Stoats (fig. 1),
Skunks and Ratels, the premolar series is further reduced by the
loss of the anterior tooth in both jaws, and by the diminution
of the size of the second, thus become the first in both jaws,
and which is also now implanted by a single fang. In a South
American Skunk (Mepilitis Humboldtu, fig. 11), the second pre-
molar disappears in the upper jaw, leaving there only the
analogues of the third and fourth, which latter is always the
sectorial in the Mustelide, as in other terrestrial Carnivora. This
tooth, under all its modifications, retains the blade with the lobe,
corresponding to the middle one in the feline sectorial, generally
well developed and sharp pointed: the differences are principally
manifested by the proportions of the inner tubercle, and the re-
lative size of the third root supporting it. But the upper sec-
torial, being a premolar, and therefore requiring less modifica-
tion of the crown to adapt it for its special functions, manifests
a more limited extent of variety than the lower sectorial, which,
being a true molar, requires greater modification of the typical form
of its crown to fit it for playing upon the opposite blade of the
flesh-cutting pair of teeth.

185. Melide.—In this sub-family I comprise the European
Badger (Meles), the Indian Badger (Arctonyr), and the American
Badger (Taaidea) ; which, with respect to their dentition, stand at
the opposite extreme of the Mustelide to that occupied by the
predaceous Weasel, and manifest the most tuberculate and
omnivorous character of the teeth. abs formula (Pl. 128, fig. 13,
Pl, 129, fig. 1.) is :-—

. — —3 I-1
Incisors — ; canines —; premolars — ; molars—: = 30.
3—3 1-1 4—4 2—2

The canines (Pl. 129, fig. 2 and 5,) are strongly developed,
well pointed, with a posterior trenchant edge: they are more com-
pressed in Arctonye than in Meles. The first lower premolar (p 1)
is very small, single-fanged, and, generally, soon lost. The first
above, (Pl. 128, fig. 13, Pl. 129, fig. 1, p 2) corresponding with
the second in the Dog, is also small and implanted by two connate

MELIDZ. 499

fangs. The second upper premolar (ib. p 3) has a larger, but
simple, sub-compressed, conical crown, and is implanted by two
fangs: the third (ib. p 4) repeats the form of the second on a
larger scale, with a better developed posterior talon, and with the
addition of a tri-tuberculate low flat lobe, which is supported by
a third fang: the outer pointed and more produced part of this
tooth represents the blade of the sectorial and the entire crown
of the antecedent premolars. The true molar in Meles (Pl. 129,
fig. 1 & 3 m 1.) is of enormous size compared with that of any of the
preceding Carnivora: it has three external tubercles, and an exten-
sive horizontal surface traversed longitudinally by a low ridge and
bounded by an internal belt, the cingulum of Illiger: this tooth has
a similarly shaped, but relatively smaller crown in Arctonyz (Pl. 128,
fig. 13, m 1). The second premolar below (ib. p 2) is commonly the
first, through the early loss of the minute one in front: its fangs are
usually connate, as in its analogue above. ‘The third and fourth
premolars slightly increase in size, have simple compressed conical
crowns and two fangs each. The first true molar below (Pl. 128,
fiz. 13, m 1, Pl. 129, fig. 6, m 1) now retains little of its sectorial
character, the blade being represented only by the two an-
terior small, compressed pointed lobes; behind these the crown
expands into an oval grinding surface, narrower in Arctonyx than
in Meles, supporting three tubercles and a posterior tuberculate
ridge: it has generally two principal roots and a small interme-
diate accessory fang as in the Otter. The second molar (ib. m 2)
which terminates the series below, is of small size and has a rounded
flat crown, depressed in the centre and with two small external
tubercles: its two short fangs are connate. In the Labrador Badger
(Taxidea)(1) the last premolar has a larger relative size, the part

(1) Trans. Zool. Society, vol. 11, p. 343, pl. 59. The genus Meles intervenes between Lutra
and Canis in the description of the teeth of Mammalia by M. F. Cuvier. Mr. Waterhouse
(Proceedings of Zool. Soc. 1837.) and Prof. Wiegmann (Archiv fur Naturgeschichte, 1838,
p. 257.) have recognised the closer affinity of the Badgers to the Mustelide than to the Urside.
The value of the generic distinction of the European and Indian Badgers is very doubtful ;
that proposed by Mr. Waterhouse for the North American species is better supported by
the dental and cranial modifications; but unnecessary multiplication of names is much to be
deprecated.

K K 2

500 CARNIVORES.

corresponding with the blade of the sectorial is sharper and more
produced, and the internal tubercle has two lobes: the succeeding
molar tooth is reduced in size and its crown presents a trian-
gular form. The first true molar below has its sectorial lobes
better developed : these differences give the North American
Badgers a more carnivorous character than is manifested by the
Indian or European species.

186. Sub-Urside.—In other allied genera, which, like the
Badgers, have been grouped, on account of the plantigrade struc-
ture of their feet, with the Bears, a progressive approximation is
made to the type of the dentition of the Ursine species. The
first true molar below soon loses all its sectorial modification,
and acquires its true tubercular character: and the last premolar
above becomes more directly and completely opposed to its fellow
in the lower jaw. The Racoon (Procyon, Pl. 129, fig. 7) and the
Coati (Nasua, ib. fig. 8-13) present good examples of these transi-
tional modifications; they have the complete number of premolar
teeth, the dental formula being :— |

Incisors —; canines — ; premolars —; molars —: = 40.
The development of the inner part of the crown of the last upper
premolar, which constitutes the tubercle of the sectorial tooth,
now produces two tubercles on a level with the outer ones which
represent the blade; (Pl. 129, fig. 7 & 8, p 4); and the opposite
premolar below (fig. 11, p 4) which is the true analogue of the
modified sectorial above, begins to acquire a marked increase of
breadth and accessory basal tubercles. All the lower premolars, as
well as the true molars, have two fangs; the three first premolars
above have two fangs, the fourth has three, like the two true
molars above.

The dental formula of the Indian Benturong (Arctictis) and
Kinkajou (Cercoleptes) is :—

T . 3—3 ° 1—1 l 3—3 ] 2—2
ncisors ——; canines ;~; premolars -—; molars -—: = 36.

The Benturong (Pl. 129, fig. 14 & 15) differs from its South Ame-
rican analogue the Coati, not only in the absence of the anterior

URSIDE. 501
premolar in both jaws, but by the smaller size and more simple
structure of the true molar teeth, with the exception of the first
below (fig. 15, m 1), which still indicates the sectorial character by
the development of a sub-compressed pointed lobe on the outer side
of the crown. In the small size of the last true molars the Benturong
manifests its affinity with the Viverrnde. In the Kinkajou (Pl. 129,
fig. 16, 17), the true molars more nearly approach in form and
proportions those of the Coati and Raccoon: the two fangs of
the first and second premolars in both jaws are connate.

187. Urside.—The essential characteristic of the dentition of
the true Bears is the development, in the lower jaw, of the true
molar teeth to their typical number in the placental Mammalia, and
their general manifestation, in both jaws, of a tuberculate grinding
surface. The premolar teeth are so reduced both in size and
number, that for the better understanding of the nature and ana-
logies of the molar series, I shall commence by the description of
the deciduous series of teeth.

The immature or transitory dentition of the Bear, consists of :

1—l 3—3

m. —: == 22. (Pl. 130, fig. 1& 2.)

d. aaah 1? M- eet
The molars (d. 1, 2, 3) increase in size in a geometric ratio from
the first to the last, which has a middle principal subcompressed
cone and an anterior and posterior basal talon. The change of the
teeth takes place at a very early period: before any of the deciduous
teeth fall, the first small permanent premolar (p. 1) cuts the gum,
as in the Dog, without any apparent predecessor. The second pre-—
molar (p 2) pushes out the first of the deciduous series and is itself
soon shed, it has a single fang: the third premolar (p 3). is also
small, simple, and single-fanged, like its deciduous predecessor ; it
is commonly retained longer than the second premolar. The fourth
premolar (p 4) is developed for use, and is truly permanent; it dis-
places the last tricuspid deciduous molar, and though with a larger
crown, yet has a more simple one viewed exteriorly ; the anterior
talon, for example, is wanting or very feebly indicated ; the large
middle and the smaller posterior subcompressed pointed cones repeat

the proportions of those in the deciduous tooth and represent the

502 CARNIVORES.

blade of the sectorial ; the internal tubercle is developed from the
whole of the inner side of the base of the blade; in the Ursus arctos
it is of a triangular form and supports a single obtuse eminence ;
in the Ursus maritimus the internal tubercle is smaller and is de-
veloped from the posterior half of the inner base of the blade: the
outer part of the fourth upper premolar is supported by two fangs,
and a third short rudimental one is developed from the inner tu-
bercle. The first upper true molar (ib. fig. 3 & 4, m 1) makes its
appearance. above the gum, as usual, before the deciduous molars
are lost; it has a large oblong quadricuspid crown with smaller
irregularities, and is supported by three roots. The second upper
true molar (ib. m 2) has a large posterior lobe added to the
quadricuspid principal part of the crown; from which a fourth
fang is developed. In the more frugivorous bears of India and the
Indian Archipelago, the four premolars are commonly retained longer
than in the fiercer species of the Northern latitudes. M. de Blain-
ville has figured the jaws of the Ursus ornatus in which they are
all preserved in both jaws. I have seen the same condition in the
Ursus labiatus, the third small premolar above and the second and
third below having each two connate fangs: the fourth premolar
above presents three subequal obtuse tubercles in this species. In
the lower jaw as in the upper one, of all Bears, the first premolar
of the adult dentition (ib. fig. 2, p 1) cuts the gum, close to the
canine, before the deciduous teeth are shed; the second premolar
displaces the first deciduous molar; the third displaces the second,
and the fourth the third. The fourth’ premolar (ib. figs. 5 & 6, p 4)
has a functionally developed crown, supported by two distinct fangs.
It is the only one of the four lower premolars retained in the
_ dentition of the great extinct Ursus speleus: the first premolar co-
exists with it in the Ursus priscus, as also commonly in the U.
maritimus and U. Arctos: in the latter I have seen likewise the
small third premolar with the adult dentition. The second lower
premolar is soon lost in the Bears of temperate and northern
latitudes, but is longer retained in the tropical species called ‘ Sun-
bears’ (Helarctos, Horsefield). The first true molar (ib. fig. 5 & 6,
m 1) has a longer and narrower crown than the one above ; but,

URSIDA. 503

e

like it, rises above the gum before the antecedent premolar has come
into place. One may still trace in the single anterior tubercle,
and the second pointed cusp in the outer side of the crown, the
rudiment of the blade and last remnant of the sectorial character of
this tooth. This representative of the blade, moreover, still plays
upon the last premolar above, receiving upon its outer side the
inner surface of the principal pointed lobe of that tooth; but the
extensively developed tubercular posterior lobe of m 1 below is
opposed to the similarly formed crown of the first molar above.
The second true molar (m. 2, fig. 5 & 6) has a narrow oblong sub-
quadrate tubercular crown; which, like that of the first true molar,
is supported by two fangs. The crown of the third lower molar
(m. 8, figs. 5 & 6) is contracted posteriorly, and supported by two
connate fangs, it is relatively smallest in the Sun-bears and largest
in the great Ursus speleus.

Thus, guided by the important character of development and
succession for the determination of the molar teeth, the permanent
dental formula of the genus Ursus, is:

: 3-3 , 1-1 4—4 2—2
Incisors => canines — ; premolars ak molars ——: = 42. (1)

It is essentially the same both in number and kind of teeth as in the
genus Canis, but the individual or specific varieties which, in the Dog,

(1) The molar series of the Genus Ursus is lagi by M. F. oa as follows :—

3-3 ee
fausses molaires 7-7, carnassiéres is 4 tuberculeuses =— = 3: = 26.
and by M. de Blainville thus :—
in arr to 3
avant-molaires 2 =e =s principales | 1, arriére-molaires 5: = 26.

In the first formula the carnassial or sectorial teeth are rightly indicated as those marked p. 4,
fig. 3, and m 1, fig. 6, in Pl. 130; but M. F. Cuvier does not show that the sectorial character
is a subordinate modification of teeth essentially belonging to two distinct categories, and an erro-
neous idea is thereby conveyed of the number of both premolars and true molars. In M. de
Blainville’s formula the number of true molars is correctly given ; but the teeth specified as
‘ principales’ have less claim to be so distinguished than the carnassials of Cuvier; and, owing
to the absence of any natural character, different teeth are indicated as ‘ principales’, in different
animals, in the ‘ Ostéographie.’ Thus, in the genus Felis the ‘ principales’ are the teeth marked
p. 3 in fig. 1, pl. 127. (See ‘Ost: des Felis, p. 55) ; and, in the genus Simia, they are the first
of the teeth marked m in fig. 1, pl. 117, Ost. des Primates, p. 43.) The principles of the clas-
sification and notation of the teeth of the molar series in the present Work will be explained
more fully after the description of the examples selected from the Order Carnivora.

504 CARNIVORES.

affect the true molar teeth, are confined, in the Bears, to the pre-
molars. It would seem that in the genus Ursus the predominating
size of the large tubercular true molars had tended to blight the
development of the premolars.

Rarely are these teeth all manifested in the adult animal, save in
some of the small frugivorous tropical Sun-bears. The second pre-
molar is the first to fali in both jaws; the third next disappears; and
the first and fourth only are most commonly found, separated by
an interspace in which some traces of sockets are occasionally percep-
tible, as in the Grisly, the Polar, the Black and the Brown Bears. Jn
the great extinct Bear of the Caves all the three anterior small premo-
lars were early lost ; and this appears to have been the case also with
an equally large and formidable extinct species, whose remains have
been discovered by Capt. Cautley and Dr. Falconer in the tertiary
formations of the Sub-Himalayan Mountain range. In the last pre-
molar of the upper jaw of this species (Pl. 131, fig. 1 & 2, p. 4) the
anterior talon is more developed than in the typical Urside ; the in-
ternal tubercle is continued from the posterior half of the base of the
crown. ‘The first upper true molar (m. 1) has a quadri-tuberculate
crown, but the two inner lobes are smaller than the two outer ones,
and the transverse exceeds the antero-posterior diameter of the crown.
The second upper true molar (m. 2) has asquare crown, as broad as it
is long, quadri-tuberculate, and thus resembling the form of that tooth
in some of the small Sub-ursine plantigrade quadrupeds. Of the den-
tition of the lower jaw of the Sewalik Bear I know only the three
true molar teeth ; and the socket of the last premolar (p. 4, fig. 3 & 4),
which was implanted by two fangs. The first true molar, (m. 1, fig.
3 & 4) which is the representative of the lower sectorial of the more
carnivorous Ferg, has a simple compressed crown, with a middle
conical lobe and a basal talon before and behind, but no internal
tubercle. Thesecond true molar (m. 2, fig. 3 & 4) has also a remark-
ably compressed crown, divided into two principal conical lobes ; the
posterior being the broadest. The last true molar repeats the com-
pressed character, but is broader anteriorly ; it has one principal
conical obtuse lobe, with a basal talon before and behind. Each of
the lower true molars is supported, as in the true Ursi, by two fangs.

PHOCIDA. 505

The above remarkable modification of the crowns of the molar teeth
of the lower jaw indicates this great extinct Bear to have been more
‘ carnassial’ and ferocious than the Ursus speleus or any of its
existing congeners. It differs essentially from all the small Sub-
ursine Plantigrades in the full complement of true molar teeth in the
lower jaw; and is still more removed from the genus Hyena, in
which only the first true molar is present below and under its
true sectorial form: the term Hyenarctos sivalensis has, however,
been provisionally assigned by its Discoverers to the extinct species,
which, from the modification of the molars, ought to be regarded as
subgenerically distinct from the true Ursi.

188. Phocide.—We have seen a tendency to deviate from the
ferine number of the incisors in the most aquatic and piscivorous
of the Musteline quadrupeds, viz: the Sea-otter (Enhydra), in which
species the two middle incisors of the lower jaw are not developed in
the permanent dentition. In the family of true Seals, the incisive
formula is further reduced, in some species even to zero in the
lower jaw, and it never exceeds $3. All the Phocide possess power-
ful canines ; only in the aberrant Walrus are they absent in the lower
jaw, but this is compensated by the singular excess of development
which they manifest in the upper jaw. In the pinnigrade, as in the
plantigrade, family of Carnivores we find the teeth which correspond
to true molars more numerous than in the digitigrade species, and
even occasionally rising to the typical number, three on each side;
but this, in the Seals, is manifested in the upper and not, as in the
Bears, in the lower jaw. The entire molar series usually includes
five, rarely six teeth on each side of the upper jaw, and five on
each side of the lower jaw, with crowns, which vary little in size
or form in the same individual: they are supported in some genera
as the Eared Seals (Otarie), and Elephant Seals (Cystophora Pl. 132,
fig. 7), by asingle fang; in other genera (ib. fig. 1-4) by two fangs, which
are usually connate in the first or second teeth: the fang or fangs of
both incisors, canines and molars are always remarkable for their
thickness, which commonly surpasses the longest diameter of the
crown. The crowns are most commonly compressed, conical, more >
or less pointed, with the ‘ cingulum’ and the anterior and posterior

506 CARNIVORES.

basal tubercles, more or less developed; in a few of the largest spe-
cies, they are simple and obtuse, and particularly so in the Walrus,
in which the molar teeth are reduced to a smaller number than in the
true Seals(1). In these the line of demarcation between the true and
false molars is very indefinitely indicated by characters of form or
position; but, according to the instances in which a deciduous den-
tition has been observed, the first three permanent molars in both
jaws succeed and displace the same number of milk molars, and are
consequently premolars ; occasionally, in the Seals with two-rooted ~
molars, the more simple character of the premolar teeth is manifested
by their fangs being connate, and in the Stenorhynchus serridens the
more complex character of the true molars is manifested in the crown.
There is no special modification of the crown of any tooth by which it
can merit the name of a ‘ sectorial ;? but we may point with certainty
to the third molar above, and the fourth below, as answering to those
teeth which manifest the sectorial character in the terrestrial Car-
nivora.

The coadaptation of the crowns of the upper and lower teeth is
more completely alternate than in any of the terrestrial Carnivora,
the lower tooth always passing into the interspace anterior to its
fellow in the upper jaw. In the genus Phoca proper (Calocephalus,
Cuv.) typified by the common Seal (Ph. vitulina), the dental for-
mula is :

5 3-3 F 1-1 3—3 2—2
Incisors —; canines —; premolars —; molars —: = 34,
2—2 1-1 3—3 2—2

The forms and proportions of these teeth are shown in Pl. 132, fig. 1.

The first tooth above and below presents a complete confluence
of the fangs ; they are separated in the rest above; but below they
sometimes do not become free before the fourth, and sometimes
the two roots are distinct in the third and second molars. In the
Phoca anellata, Nills: the principal cusp of the molar teeth is com-
plicated with anterior and posterior smaller cusps, sometimes one
in number in the upper molars ; the anterior accessory cusp is some-
times wanting in the first, and is rudimentary in the rest ; but usually

(1) The relation of Trichechus to the Phocide is analogous to that of Machairodus to the
Felide, and also, in the simplification of the molars, to the relation of Proteles to the Canide.

SEALS. 507

there are two small cusps behind the principal one, and in the three
or four posterior molars in the lower jaw there are sometimes two
small cusps before and two behind the principal one. (1)

In the Phoca caspica the upper molars have commonly one ac-
cessory cusp before and one behind the principal lobe, the lower
molars have one accessory cusp before and two behind the lower
molars.

In the Phoca grenlandica the upper molars have no anterior basal
cusp and only one behind; the lower molars have two cusps behind
and one in front, except the first which resembles that above and,
like it, has connate fangs.

The condition of the molar teeth is nearly the same in the
Phoca barbata (Pl. 132, fig. 2); but the crowns are rather thicker and
stronger, and the three middle ones above have two posterior basal
cusps feebly indicated, the same being more strongly marked in the
four last molars below.

The following genera of Seals with double-rooted molars, (Pela-
gius & Stenorhynchus), have four incisors above as well as below,
i.e. =. An upper view of the molar teeth in the Hooded Seal of the
Mediterranean, Pelagius monachus, is given in Pl. 132, fig. 3, as when
they are worn down in anold specimen ; the crowns are thick, obtuse,
subcompressed, with a well developed cingulum, a principal lobe and
an anterior and posterior accessory basal lobule; the fangs are connate
in the first tooth both above and below.

The allied sub-genus (Ommatophoca) of Seals of the southern
Hemisphere has six molar teeth on each side of the upper, and five
on each side of the lower jaw, with the principal lobe of the crown
more incurved. The two first molars above are closely approxi-
mated ; but this may prove to be a variety.

In the Stenorhynchus the jaws are more slender and produced,
and the molar teeth are remarkable for the long and slender shape of
the principal lobe and of the accessory basal cusps. The incisors
have sharp conical recurved crowns, like the canines, and the exter-

(1) Nillson, in Wiegmann’s Archiv. 1841, p. 313. I notice these varieties of the crown, in

connection with analogous ones in the fangs of the teeth of the same species, to show the inade-
quacy of such characters as marks of subgeneric distinction,

508 CARNIVORES.

nal ones in the upper jaw are intermediate in size between the canines —
and the middle incisors.

In the Stenorhynchus leptonyx each molar tooth in both jaws is
trilobed, the anterior and posterior accessory lobes curving towards
the principal one which is bent slightly backwards; all the divisions
are sharp-pointed, and the crown of each molar thus resembles the
trident or fishing-spear; the two fangs of the first molar in both
jaws are connate. In Sten. serridens (Pl. 132, fig. 4) the three anterior
molars on each side of both jaws are four-lobed, there being one
anterior and two posterior accessory lobes; the remaining posterior
molars (true molars) are five-lobed, the principal cusp having one
small lobe in front and three developed from its posterior mar-
gin; the summits of the lobes are obtuse, and the posterior
ones are recurved like the principal lobe. Sometimes the third
molar below has three instead of two posterior accessory lobes.
Occasionally, also, the second as well as the first molar above
has its fangs connate; but the essentially duplex nature of the
seemingly single fang, which is unfailingly manifested within by
the double pulp-cavity, is always outwardly indicated by the
median longitudinal opposite indentations of the implanted base.
These slight and unessential varieties, presented by the speci-
mens of the Saw-toothed Sterrink (Stenorhynchus serridens) brought
home by the enterprising Naturalists of Sir J. Ross’s Antarctic
expedition, accord with the analogous varieties noticed by the best
observers of the Seals of our neighbouring seas, as, for example,
Nillson.(1)

The Grey Seal (Halicherus gryphus) of our own Seas begins, by
the extension of the connate condition of the two roots through a
greater proportion of the molar series, to manifest a transition to the

(1) A diligent labourer, in what our plain-speaking German fellow-zoologists call the
“Gattungsmacherei’ has seized upon the variable mode of implantation of the anterior
premolars as ground for the generic distinction of Seals; and so by the following phrase,
“ the 1st, 2d and 3d front upper, and the 1st front lower grinder single-rooted, the rest 2 rooted,”(a)
my Stenorhynchus serridens is tied as a synonym to the tail of ‘ Lobodon carcinophuga, Gray.’
Not a single additional fact does the writer find to add to those characters which I first pointed

(a) Zoology of Ross’s Antarctic Voyage, Mammalia, p. 2, 4to. 1844.

SEALS. 509

family of Seals with true single-rooted molars ; the formula of this
genus, is:

. 3—3 = 1—1 3—3 2—2
Incisors —; canines — ; premolars —_; molars — : = 34,
2—2 1—1 3—3 2—2

The four middle upper incisors are close set, with pointed recurved
crowns ; the lateral incisors are much larger and laniariform: the canines
have moderate crowns, with a sharp ridge before and behind. The
crowns of the molar teeth (Pl. 132, fig. 5) are conical, subcompressed,
longitudinally and finely grooved, with an anterior and posterior edge ;
those below have generally a slight notch at the fore and back part of
the base. The first molars, both above and below, are the smallest,
with a simple crown and a single ventricose fang; thie second and
third above, and the second, third, and fourth below, have two
connate roots ; the two roots are commonly distinct in the remaining
posterior molars: all the roots are very thick.
In the genus Ofaria (ib. fig. 6) the dental formula, is:

I e 3—3 5 1—1l 1 3—3 1] 3—3 36
neisors —; canines —~; premolars —; molars — = 36.

The two middle incisors are small, subcompressed, with the crown
transversely notched ; the simple crowns of the four incisors below fit
into these notches: the outer incisors above are much larger with a
long pointed conical crown, like a small canine. The true canine is
twice as large as the adjoining incisor, and is rather less recurved.
The molars have each a single fang; the crown is conical, sub-
compressed, pointed; in the two last recurved, with a basal ridge or
‘cingulum,’ broadest within: in the Otaria jubata, with a pointed
cusp developed from its fore-part, and in the last two molars also
from its back part. In some species, as the Otaria lobata, (Phoca

out as distinguishing the Sten. serridens from the Sten. leptonyx, except the above-cited variety
respecting the implantation of the premolars; and even this is misinterpreted, the supposed
single root being essentially two roots connate. A re-examination of the specimens of Sten.
serridens, in comparison with Sten. leptonyx, has only impressed more strongly the truth of the
observation with which I concluded my description of that new species, “‘ the modifications of
the compressed and deep-cleft molars are not of sufficient importance to justify the introduction
of a new generic name into the group of amphibious or pinnigrade Carnivora, which has already’
been overburthened in this way.’’(a)

(a) Annals of Nat. History, 1843, p. 331.

510 : CARNIVORES.

lobata, Fischer), the single molar is not developed in the upper jaw,
and the outer incisors above are not so large: in this species a thick
plicated cingulum belts the base of each molar, and developes a small
tubercle from its fore part in the molars of the lower jaw ; the crown
of the last molar above is notched.

In the great proboscidian and hooded Seals (Cystophora, fig. 7) the
incisors and canines still more predominate in size over the molars ;
but the incisors are reduced in number, the formula here, is:

fick 2-2 ‘ Lal cs 3-3 l 2—2 30
ncisors = > Canines a Pp Olars rag mo ars 7° sS= 4

All the molars are single-rooted and all the incisors are laniariform.
The two middle incisors above and the two below are nearly equal ;
the outer incisors above are larger. The canines are still more for-
midable, especially in the males; the curved root is thick and sub-
quadrate. The crowns of the molar teeth are short, subcompressed,
obtuse ; sometimes terminated by a knob and defined by a constriction
or neck from the fang; the last is the smallest.

In the Walrus (Trichechus rosmarus) the phocal incisive formula
is transitorily represented in the very young animal, which has three
teeth in each intermaxillary bone and two on each side of the fore-
part of the lower jaw; they soon disappear, except the outer pair
above, which remain close to the intermaxillary suture, on the inner
side of the sockets of the enormous canines, and seem to commence
the series of small and simple molars which they resemble in size
andform. In the adult there are usually three molars on each side,
behind the permanent incisor, and four similar teeth on each side of
the lower jaw ; the anterior one passing into the interspace between the
upper incisor and the first molar, and therefore being the analogue of
the molar. In a young Walrus’s skull, with canine tusks eight inches
long, I have seen a fourth upper molar, (fifth including the incisor),
of very small size, about a line in breadth, lodged in a shallow fossa
of the jaw, behind the three persistent molars. The crowns of these
teeth must be almost on a level with the gums in the recent head ;
they are very obtuse and worn obliquely from above down to the
inner border of their base. The molars of the lower jaw are rather
narrower from side to side, than those above, and are convex or

a a

MICROSCOPIC STRUCTURE. 511

worn upon their outer side. Each molar has a short, thick, simple
and solid root.

The canines are developed only in the upper jaw, but are of
enormous size, descending and projecting from the mouth, like
tusks, slightly inclined outwards and bent backwards; they present
an oval transverse section, with a shallow longitudinal groove along
the inner side, and one or two narrower longitudinal impressions
upon the outer side ; the base of the canine is widely open, its growth
being uninterrupted. }

The food of the Walrus consists of sea-weed and bivalves: the
molars are well adapted to break and crush shells ; and fragments of a
species of Mya have been found, with pounded sea-weed, in the
stomach. The canine tusks serve as weapons of offence and defence,
and to aid the animal in mounting and clambering over blocks
of ice.

189. Composition and microscopic structure —The teeth of the Car-
nivora, with the exception of the aberrant amphibious forms in which
we have been last considering the outward modifications of the dental
system, so closely correspond in their intimate structure, both with
each other and with those of the Quadrumana, as to require here only
a brief and general notice. They all enter into the category of
‘ simple teeth ;’ that is, the dentine or main body is not penetrated
by folds of the other component tissues, but has an even exterior,
covered at the part forming the crown with enamel, and having a
general outer investment of cement, the coronal layer ‘forming too
thin a film to manifest any of the radiated cells. The dentine is of
the kind called ‘ hard or unvascular’ : the tubuli are rather finer than
in the human teeth ; they have the same general direction from the
pulp-cavity, but present stronger primary curvatures, more frequent
dichotomous divisions, and more numerous minute lateral branches,
which latter usually curve from the trunks at right angles. The
dentinal cells are subhexagonal, about ,,th of an inch in diameter,
with the peripheral contour forming almost a regular curve. In the
Seals the dentine forms usually a smaller proportion of the tooth
than in the terrestrial Carnivora; the characteristic thickness of
the roots in this family is principally due to the thick covering of

512 CARNIVORES.

cement, and the pulp-cavity is generally closed by an unusual quantity
of the osteo-dentine. The calcigerous tubes in the dentine of the
Seal’s molar describe very strong and irregular curves on leaving
the pulp-cavity ; but, when within a third of the distance to the outer
surface, they fall into more parallel and regular undulations; they
are js,;th of an inch in diameter, and the interspace between two
tubes is about th of aninch in width. The tubes dichotomise less
frequently and less regularly than in the teeth of the Dog or Hyzna,
but send from both sides extremely numerous short branches,
which bend almost transversely across the interspaces, and the sub-
branches are continually sent off in greater abundance along lines
parallel with the outer contour of the tooth, giving the appearance of
opake striz or concentric layers to polished sections of the dentine.
The calcigerous tubes resolve themselves at their extremities into
rich tufts of curved branches which terminate in a layer of minute
cells at the crown, and in the root, communicate with the radiated
cells of the cement.

In the molar teeth of the Otaria jubata the tubes proceeding in
the long axis of the crown are pretty parallel on the peripheral half
of the dentine; towards the side of the crown they proceed in more
zigzag, almost angular curves and appear to cross each other,
conspicuous branches being continued from the angles: the inter-
spaces of the tubes were about g th of an inch in width. The den-
tinal cells are more numerous and less regular than in the teeth of
the ordinary Carnivora, and their contour is more obscured by the
deeper curves and more numerous branches of the dentinal tubes.

The enamel of the teeth of the Carnivora is extremely dense and
brittle, it consists of fibres similar to those in the Human teeth, but
relatively smaller, as for example, in the large canines of the Tiger,
and the molars of the Hyena. The transverse striz, moreover, are
_ less distinct. ;

In the molar of the Otaria the enamel fibres were very distinct,
placed at right angles to the plane of the crown, and less curved than
in Man or the Quadrumana. Instead of the transverse strie they
presented a minute granular structure.(1)

(1) Retzius failed to detect any true enamel in the teeth of the Phoca anellata.

MICROSCOPIC STRUCTURE. 513

The cap of enamel with which the teeth of the Walrus are at
first tipped is soon worn off, and, except at the abraded surface, the
rest of the teeth, both tusks and molars, are thickly coated with
cement. Retzius has left little to add to his detailed and exact
account of the microscopic structure of both the canines and molars
of the Walrus. (1)

The dentine, in this species, closely corresponds with that in
the ordinary Seals; in the molar teeth the tubes present the same
diameter, the same interspaces, and undulating curvatures ; but their
dichotomous divisions are more marked. In the canines the lateral
branches terminate in minute opake cells, dispersed throughout
almost the whole dentine, but most numerous and conspicuous near
its periphery, where the dentine is defined by a distinct layer of these
cells: only a third part of the periphery of the canine is composed of
true dentine, the central thin part of the tooth is filled up by osteo-
dentine, which, as in the teeth of the Cachalot, often projects in
irregular rounded masses, like stalactites, into the short and wide
basal pulp-cavity. The whole mass, indeed, of the osteo-dentine
consists of numerous independent calcifications of the pulp, having as
many distinct centres, usually hollow, and producing, when the sub-
stance is examined by the naked eye, the appearance which Cuvier
has compared to ‘ pudding-stone.’(2) The central cavities are for

(inne. Cli. po do; 7S.

(2) “ L’ivoire des défenses du Morse est compact, susceptible d’un poli presque aussi beau
que celui de l’hippopotame mais sans stries; la partie moyenne de la dent est formée de petits
grains ronds placés péle-méle, comme le cailloux dans la pierre appelée poudingue ; c’est ce qui
le caractérise. Les dents molaires de cet animal ont leur axe composé des mémes petits grains
que celui des défenses. Elles n’ont aucun cavité dans leur intérieur.”” Cuvier, Legons d’Anat.
Comparée, tom. iii, (1805) p.106. The cement of the Morse’s teeth is distinguished from the
osteo-dentine by its continuous uniform structure, by the absence of the detached centres and
their concentric lines; but the radiated cells are disposed in regular layers concentric and
parallel with the contour of the body of dentine. The radiating tubes from the cells forming
the layer next the dentine communicate freely with the peripheral ramifications of the dentinal
tubes and also with the proper cemental tubes which are dispersed vertically to the plane of the
cement: indeed, the evidence of an intercommunicating system of canals, too minute for the
gross fluid of the circulating system, is most striking and universal throughout the substance of
both the tusks and small teeth of the Walrus. Vascular canals are, however, present in the
cement as in the osteo-dentine, from the contents of which it may be presumed that the
colourless plasma is elaborated, which meanders through the minuter systems of cells and

tubes.
L GL

514 CARNIVORES.

the most part associated together and with the pulp-cavity by
medullary canals. The calcigerous tubes radiate from those central
cavities, in all directions, with sub-parallel, diverging curvatures ; |
dividing, subdividing and sending off numerous branches, which
anastomose with those of the adjoining masses, and, where these
are situated next the dentine, with the tubes of that tissue. In
each lobe of the osteo-dentine the concentric rings parallel with
the contour of the central medullary cavity, are well-marked.
Myriads of minute calcigerous cells are dispersed throughout the
osteo-dentine.

The pulp-cavity of the incisor and molar teeth of the Walrus
is filled up by a smaller quantity of the osteo-dentine. Minute
vascular canals convey the capillary blood vessels to this structure
from the vascular membrane attached to the solid base of the molars,
and, in the tusks, from the persistent pulp which fills the basal cavity.

190. Classification and analogies of the molar teeth of the Carnivora.
—The various forms of the teeth composing the molar series and their
concomitant diversity of function in the order Carnivora have led to
their being divided into distinct groups, to which the Anatomists,
who have more especially devoted themselves to the study of those
organs, have generally assigned special names. The most com-
monly adopted classification and nomenclature of the molar teeth,
especially, as they exist in the Carnivora, is that proposed by
Mr. F. Cuvier in his celebrated work the ‘Dents des Mammiféres;’
where, treating of the ‘macheliéres,’ cheek-teeth, or molar teeth,
he says: ‘‘ Ces derniéres se partagent en trois divisions. La {
premiere se compose de deux a quatre dents qui viennent apres
les canines, dont l’usage est assez indéterminé, et qui sont ‘ des —
fausses molaires.’ La seconde ne se compose jamais que d’une —
dent qui est la carnassiére ; c’est en elle que réside essentiellement —
la faculté de couper les fibres de la chair. La troisiéme est celle —
des dents tuberculeuses, dont le nombre ne s’éléve jamais au-dela
de deux et qui paraissent avoir pour destination principale de~
broyer les alimens susceptibles de l’étre.” p. 77. The dentition ©
of the different genera is numerically formulised, according to the —
foregoing classification: thus the genus Felis has: macheliéres > a
dont fausses molaires, +-3 carnassiéres, + 7 tuberculeuses. :

CLASSIFICATION OF MOLARS. bo 18)

In the second edition of the ‘ Lecons d’Anatomie Comparée,’
of G. Cuvier, tom. 1v, 1836, the ‘fausses-molaires’ are distinguished
from the ‘ vraies-molaires,’ by their fewer roots and narrower crown:
*‘ par moins de racines et par une couronne moins large et consé-
quemment moins propre a broyer.”’ (p. 246). And, in the Numerical
Tables, the molar series is divided into ‘ fausses molaires rudimentaires,
fausses molaires normales, vraies molaires carnassiéres,’ and ‘ vraies
molaires tuberculeuses :’ the series in Man giving :

f. Mm. ¢. —; f.m. n. —; v. m. — (p. 254.)

-2

and that in the Lion or genus Felis :-—
0—0 2-2 i—1 i—l
Pats Me nae f. M,N 3 V.m. Cc. =; v.m. t. —. (p. 262.)

Both these systems are rejected by M. de Blainville in his
‘Ostéographie d’Animaux Vertébrés.’(1) In this beautifully illus-
trated Work the molar series is divided into premolars, principal,
and true molars: ‘(avant molaires, principale et arriére-molaires,’
t. 1, p. 43); which are thus exemplified in the Human dentition:
the five teeth of the molar series are divided into two premolars,
one principal, and two true or post-molars, and, with the incisors
and canine, are indicated by the following notation :—

Ae = 2 + - c. + 2 m. dont 7 av. m. = pr. = ar. m.”’ (l..¢. p. 43)

In order to determine the analogues of these kinds of molar
teeth, and especially the ‘ principal’ molar, in other animals, the
Author gives the following definitions or characters : first, with respect
to form or shape, he divides the molars of Mammalia ‘ en avant-
molaires, en principale, et en arri€re-molaires, qu’importe qu’elles
soient simples ou complex, tranchantes, ou tuberculeuses.’ (/, c. p. 43.)

As the so called principal molar of Man is not distinguished
by the trenchant, or any other peculiar form, M. de Blainville
next points out another character taken from its position in the
jaw.- In most cases, he says, we may easily recognise the prin-
cipal molar, in the upper jaw, which is always the ‘ point de départ’

(1) “Nous avous été obligé d’abandonner cette classification des molaires des erent
et d’en établir une autre.”—Ostéogr. des Mammiferes, tom. 1. p. 43.
Lid

516 CARNIVORES.

for the signification of the teeth, by assuming that tooth to be
such which is implanted below the root of the zygomatic process
of the maxillary bone: ‘en prenant pour telle’ (la principale) ‘ celle
qui se trouve implantée sous la racine de l’arcade zygomatique, ou
mieux de l’apophyse zygomatique du maxillaire.’ p. 43. Those teeth
which are in front of the ‘ principale,’ so recognised, are premolars,
those behind it are true or post-molars. With regard to the lower
jaw it will suffice to bring the teeth in their natural apposition
with those above in order to learn their signification: that which
shall cross in front of the upper ‘principale’ will be the lower
‘principale’; whence one may readily determine the premolars
and post-molars (J. c. p. 43).

To test the value of these characters as determining the
natural species of molar teeth, and as guides to the representatives
of each through different genera of Mammalia, let us take another
example of the Author’s application of them, viz: the dentition of
the Lion. The molar formula of the genus Felis, according to
M. de Blainville, (Ost. des Carnassiers, p. 69.) is: ++ }+. ie.
there are one premolar, one principal, and two true molars in the
upper jaw; one premolar, one principal, and one true molar in the
lower jaw. This view of the nature of the Feline molars differs
from that which is given by M. Fred. and Baron Cuvier, and
equal or greater discrepancies will be found between most of the
determinations of the molar series in the work of M. de Blain-
ville, and in those of the other distinguished French Professors. —
The high reputation of these Authors, and the character and value —
of the great Work in which M. de Blainville’s views are promulgated, —
call for the present statement of the considerations which have —
compelled me to abandon them, much as I am impressed with the
advantage of uniformity in the classification and nomenclature of —
natural objects.

To return, then, to the two examples cited from the ‘ Ostéo-
graphie’ of M. de Blainville; the second of the molar series of —
the Lion (p 3, Pl. 127, fig. 1) is the representative of the third of
the molar series in Man, (first of the three marked m in PI. 118) in —
both jaws: that is to say, a tooth which displaces and succeeds

CLASSIFICATION OF MOLARS. 517

a milk tooth, and which is, therefore, a premolar according to my
definition, in the Lion, is made the analogue of a tooth which
rises above the gum without displacing any predecessor, and which
is consequently a true molar, in Man. It will, I presume, be
conceded that the teeth in the Lion, called ‘ principales’ by M. de
Blainville, in having smaller and more simple crowns than those
behind them, and in being preceded by deciduous teeth which they
replace, are more naturally analogous to the bicuspides or premolars
in the Human Subject ; and if so, it may be concluded that the
characters which have conducted M. de Blainville to the opposite
conclusion cannot be founded in nature.

These characters, moreover, seem in the instance cited, to
have been as little applicable to the detection of the tooth in the
lower jaw which is analogous to the ‘principale’ above, as to the
discovery of the ‘ principales’ in different Mammalia; and, indeed,
M. de Blainville abandons one of his own criteria, viz: that founded
on relative position, in selecting the second tooth of the Feline
molar series below, as the analogue of the second tooth in the upper
series, distinguished by him as the ‘principale’ in the preliminary
observations on the Classification of the Carnassiers (p. 69). The
same view of the analogies of the upper molar series is adopted
im the detailed descriptions given in the subsequent Monograph on
the genus Felis, but a different one is given of the lower molars: the
first tooth (p 3, fig. 1, Pl. 127) is here described as the ‘ principale,’
and the two succeeding teeth are both ‘ arriére-molaires’. (p. 55).

The relative value of the characters for the classification of the
molar teeth proposed in the present work, and of those proposed by
the Cuviers and by M. de Blainville, will be best tested by applying
them to the same instances as have been cited above. According
to my view the molar formula in Man is:—p. 5, m. =; in the
Lion it is:—p. 5, m. |: that is to say, the last tooth in the
series of both jaws of the Lion is the analogue of the first true
molar in Man, whilst the others answer to the bicuspids, of
which the Lion has one more in the upper jaw than Man possesses.
Thus the permanent teeth, indicated as the corresponding true
molars (m 1) in Felis and Homo, by their mode of succession,—neither

518 CARNIVORES.

of them being ‘ dents de remplacement,’—also agree, in the upper
jaw, in the tubercular character of the crown, and in the lower
jaw, in their superior size as compared with the antecedent teeth ;
which characters, though they be of secondary importance, tend,
when concurring, as they generally do, with the primary character,
to vindicate its value. Moreover, according to my view, the second
lower premolar in Felis, (M. de Blainville’s ‘ principale’ in the
‘Classifications des Carnassiers, p. 69), is not the fellow of the
second but of the third premolar above: and the last tooth below,
although the greater part of its crown plays upon the third above,
yet is not, as the Cuviers indicate, the fellow of that sectorial tooth,
but being somewhat posterior to it, pairs strictly with the small
tubercular tooth above. And it is important to observe that these
teeth—the tubercular above and sectorial below,—notwithstanding the
diversity in the form of their crown in the genus Felis, have the same
developmental character ; and that the first tooth (m 1) which follows
the ‘dents de remplacement’ in the upper jaw, and the first tooth
(m 1) which follows them in the lower jaw, do actually acquire,
the one by progressive increase of size, the other by gradual
acquisition of a broad tuberculate grinding surface, even in the
Carnivorous series, almost as close a correspondence in structure,
as they present in the Quadrumanous Order. It needs only to
compare the dentition of the Cat, the Grison, the Badger, and
the Bear, to appreciate the truth of this proposition and the
respective accuracy of the following dental formule :
Genus Meles according to Cuvier :—

2 B38 1-1 ep 2-2 recat It ; 11 36
in. 553 ¢. 7; fausses m. —— ; carnassiéres — ; vraies m. — = 36,
Genus Meles, as in the present work :—

—; c. —; pm. —; true m. — = 36. The last upper pre-
molar, and the first lower true molar being indicated, in the text,
as the analogues of the teeth which manifest the carnassial or
sectorial character in the typical Fere.

It will be seen that I have made no use of the term ‘ principale’,

in describing and discriminating the molar teeth of the Mammalia.

in.

ial

CLASSIFICATION OF MOLARS. 519

The character of form (‘trenchant’) in reference to this tooth,
fails, as we have seen, in its first application: the character of
relative position to the base of the maxillary zygomatic process
has as little constancy or value; and, indeed, I never found any
Comparative Anatomist, who, when asked to indicate the ‘dent
principale’ by that character in the Lion’s skull, did not point
to the third premolar or ‘ carnassial’ of Cuvier, instead of to the
second premolar or ‘principale’ of M. de Blainville. The name
‘ principale’ seems to refer to a character of size ; and in the Human
Subject, the tooth, so called by M. de Blainville, is larger than
the third molar, and not less than the second; but before we
quit the Quadrumanous series we find numerous examples in which,
in the lower jaw especially, the last molar tooth is the principal
one in point of both size and complexity of crown; and the
‘ principales’ in the Feline dentition, according to M. de Blainville,
are far from being the chief either in size or special adaptation
to the carnivorous regimen.

It may be thought, perhaps, that the principles of the classifi-
cation of the teeth, adopted by M. de Blainville, have been tested by
extreme examples in selecting the dentition of Man and the Lion;
let us take, therefore, a third instance of the Author’s application
of them from the Carnivorous order. In the Paradoxurus the upper
molar series has a different relative position to the root of the
zygomatic process from that in the Lion; and accordingly we find
the upper carnassial tooth of Cuvier, or the last of my premolars,
selected by M. de Blainville as the ‘dent principale’, leaving three
premolars in advance of it; the tooth immediately anterior to the
lower carnassial of Cuvier being selected as the corresponding
‘principale’ in the lower jaw. Ostéogr. de Viverra, p. 43. Here,
again, therefore, we find that teeth which are ‘dents de remplacement’
in one Mammiferous animal, the Paradoxure, are selected as the ana-
logues of true molar teeth rising posteriorly to the whole deciduous
series in another, the Monkey, for example. The upper ‘ principale’
in the Civet and Paradoxure not only displaces a milk-molar,
but one which had a tubercular and more complex crown; and
this is precisely what happens to the premolar which precedes the
‘principale’ in the Human and Quadrumanous dentition, but which

520 CARNIVORES.

does not happen to the ‘ principale’ in the same dentition as classified
by M. de Blainville.

Passing next to the comparison of the dentition of Quadrupeds
more closely allied, and of the same natural order, we find the upper
‘principale’ in the Lion thus described by M. de Blainville :
“‘Celle-ci, bien plus grande et de forme triangulaire et subtriquétre
& sa couronne, avec le sommet submédian et peu pointu, est pourvue
en avant et un peu en dedans d’un tubercule basilaire peu marqué,
et de deux en arriére, dont l’un, le postérieur, est une sorte de
talon.” Ostéogr. de Felis, p. 55. Then follows the description of
the first ‘ arriére-molaire’, which is rightly termed ‘ carnassiére
supérieure’. If we turn to M. de Blainville’s account of the dentition
of Viverra we find that “‘ La principale d’en haut est aussi un peu
moins carnassiére par plus d’épaisseur du talon interne antérieure
et par moins de largeur du lobe postérieur.” ‘ Ostéogr. de Viverra,
p. 42.2. The Author is comparing it with the premolar in front of
it, which is, in fact, the analogue of his ‘dent principale’ in the
Lion, the ‘dent principale’ in the Viverra being the analogue of
the ‘ dent carnassiére’ in the Lion. Thus the characters adopted
by M. de Blainville, not only fail in the determination of the
analogous teeth in different orders but also in different genera. of
the same order, and, according to his first determination of the
Feline formula, even in the upper and lower jaws of the same
species.

Neither is the author of the ‘ Ostéographie’ more consistent
with himself in a later portion of his great Work: in the Fasci-
culus on the ‘ Ostéographie de Hyena,’ (p. 25) he adopts a third
formula for the molar series of the genus Felis, apparently from
Daubenton, which differs both from that which is given in the
‘ Generalities on the Carnivora,’ (p. 69), and from that described
in detail in the ‘Ostéographie de Felis’ (p. 55): it is as
follows :— + +++; i.e. two premolars, one principal, one true
molar above; and one premolar, one principal and one true
molar below; not any remark being made on its discrepancy with
the other formule. But neither is this third view more true to
nature, than the two views previously proposed by M. de Blainville
in the same Work; for, according to the natural characters of the

CLASSIFICATION OF MOLARS. 52]

molar series, the typical Felines have not two, but three premolars
on each side of the upper jaw, and two premolars, instead of one,
en each side of the lower jaw. I have come to the conclusion,
therefore, after a long and patient series of researches upon both
the deciduous and permanent dentition of the Mammalia, that a
‘molaire principale’ does not exist in nature, that its characters
as defined by M. de Blainville are artificial, and that they utterly
fail, or mislead, in their application to a philosophic determination
of the analogous teeth in the different genera of placental and
terrestrial Mammalia. |

Having premised thus much in explanation of the grounds
which have prevented my adopting the dental formule assigned to
the genera of Mammalia, not only by M. de Blainville, but by the
Cuviers, I have only to add an explanation of the principles of
the formule substituted for them in the present work. As respects
the molar teeth, I believe my classification to be founded on a more
important, a more constant, and therefore a more natural character
than those of ‘form,’ ‘size,’ or ‘relative position.’ According to
the law of development the series of true molars begins with that
tooth which rises into place behind the last of the deciduous series
and includes all behind it; all the permanent molars in front of this
series are premolars. I have already exemplified the application of
this law to the determination of the analogous true-molar teeth in
the Lion and Man, and I may observe that it is equally applicable
to the identification of every tooth in the molar series. Accord-
ing to it, the first upper true molar tooth in the Human Subject,
(‘ principale’ of M. de Blainville), is the analogue of the last, or
tubercular molar in the upper jaw of the Lion; the first lower
true molar tooth in Man answers to the lower sectorial tooth
in the Lion; the upper sectorial in the Lion is essentially the
same tooth as the second superior bicuspid in Man; the second
upper premolar of the Lion answers to the first upper bicuspis in
Man; the first small premolar in the Lion has no analogue in the
Human dentition; the two premolars in the lower jaw of the
Lion correspond with the two inferior bicuspids in Man.

The natural character of the premolars as a distinct subdivision ot
the molar series is shown by a certain independence in their time of

522 CARNIVORES.

development: its course is the same as that of the true molars, viz.
from before backwards, and is nearly parallel in point of time, but a
little anterior; the first and generally the second true molars being in
place before the last premolar cuts the gum. I may further remark
that, when either series falls short of the typical number, which in the
placental Mammals, is four for the premolars and three for the true
molars, the absent teeth are from opposite ends of the two series,
being taken from the fore-part of the premolar, and from the back
part of the true molar series.

No character is of less importance in the determination of the
essential nature and analogies of teeth than mere shape of the crown:
peculiar modifications have obtained peculiar names ; the long, curved,
pointed incisors of the Elephant, and the similarly shaped canines
of the Walrus are called ‘tusks,’ or ‘ défenses:’ the incisors of the
Beaver and canines of the Hippopotamus are compared to the
chisel, and called ‘dentes scalprarii’, from the partial disposition of
the hard enamel, and the oblique bevelled cutting edge thence re-
sulting: we must not be surprised, therefore, to find a premolar in
one jaw and a true molar in the opposite jaw similarly modified
to cut flesh, and so placed in the alternate disposition of the teeth
of the ‘ Carcharodonta’,(1) as to play in a greater or less proportion
upon each other, like the blades of scissors. In retaining, then, the
convenient and expressive term assigned by the Cuviers to these
sectorial teeth, it must, at the same time, be borne in mind that
they are not the analogous teeth in the two jaws, but, in these, respec-
tively belong to two naturally distinct categories of the molar teeth.
So, likewise, before we quit the Carnivorous series we find both
molars and premolars taking on as complete a tubercular. structure
of the crown, and equally meriting the name of ‘ tuberculeuses’ ;(2) and
it is in restricting the terms ‘ sectorial’ and ‘ tubercular’ to secondary
indications of the differences observable in the teeth composing the
two natural primary divisions of true molars and premolars, instead
of using them as characters for the primary division of the molar
series, that I chiefly dissent from the classification adopted in the
deservedly esteemed works of the Cuvizrs.

(1) Aristotle’s name for the modern ‘ Carnivora.’
(2) See Procyon and other Sudursi.

ANOPLOTHERE. 523

CA Pol he a eee

TEETH OF UNGULATA.

THE most complex and varied systems of dentition are to be
found in the different Orders, Families and Genera of the great
natural group of hoofed Quadrupeds. From this group it will
suffice for the objects of the present Work to select certain
examples to elucidate the leading modifications of the systems of
complex teeth, and these examples will be taken from the typical
species of the Isodactyle(1), the Anisodactyle(2), and the Probosci-
dian divisions of the Ungulata.

Although the structure of the molar teeth presents very
different degrees of complication and is much modified in the
Isodactyle Ungulata, it generally produces a more symmetrical
form or pattern of the grinding surface than in the Anisodactyle
division. I shall commence with the dentition of an extinct.
genus of the Isodactyle group.

191. Anoplotherium.—The Anoplothere was one of the earliest
forms of hoofed quadrupeds introduced upon the surface of this
earth, and it is characterized by the most complete system of den-
tition: it not only possessed incisors and canines in both jaws,
but these were so equably developed that they formed one un-
broken series with the premolars and molars, which character is
now found only in the Human species.

The dental formula of the genus Anoplotherium is :—

—; ‘ —; p. = m. —: = 44, (Pl. 135. fig. 1—3.)

Those teeth which are transitorily manifested in the embryo-state

(1) Hoofed Quadrupeds with toes in even number, as two or four, and which have a more
or less complicated stomach, with a moderate sized simple cecum. Ex. Ox, Hog, Peccari,
Hippopotamus.

(2) Hoofed Quadrupeds with toes, (on the hind-foot at least,) in uneven number, as one
three, or five, the latter number being manifested by the Proboscidians. All these have a
simple stomach and an enormous cecum. zw. Horse, Tapir, Rhinoceros, Elephant: but the
last Pachyderm combines, with its proboscis, so maay other peculiarities of structure, as to have
been recognised as the type of a distinct group of Ungulata, most of the members of which group
are now extinct. ;

524 UNGULATES.

of the Ruminant, as the upper incisors and canines(l1) and the
anterior premolars, were, in the ancient Anoplothere, retained
and raised to proportional equality with the rest of the teeth.
What is suppressed in the Ruminant Order is developed in excess
in other Isodactyle Herbivora, as, for example, in the Hippopotamus
and Babyroussa; and almost every kind and degree of variety, save
that of increased number of teeth, has been superinduced in later
and existing forms of hoofed Mammals upon the primitive Ano-
plotherian formula, which may therefore be regarded as the type
or perfect standard of the dentition of the great natural group of
Ungulata.

In the Anoplotherium commune(2) the upper mid-incisor has a semi-
elliptic crown, very convex externally, with a large root expanded near
the neck: the second and third incisors have the end of the crown
slightly produced giving it a triangular form: all three have a small
cusp at the outer border. The canine differs in the greater breadth
and thickness, but not in the length of the crown; the middle part
of which forms a low cone with well-marked basal angles. In the
first upper premolar (Pl. 135, fig. 2, p 1) the anterior angle is more
developed, and the principal lobe has an internal basal ridge: the
outer surface is sinuous, convex in the middle, and the entire
tooth is enlarged. In the second premolar (ib. p 2) the depression
between the more developed inner basal ridge and the main lobe
is deepened, and forms a long enamel-island when the crown is
much worn: a second basal ridge is also developed below the former
in this and the next premolar (ib. p 3), which, with the fourth
(ib. p 4), progressively increase in size. The true molars (ib, m)
have thicker square crowns which present the following characters :
a transverse valley (6) extending, from within, two-thirds across,
divides the crown into an anterior (0) and a posterior (0°) lobe which
are continuous along the outer border of the tooth: an antero-
posterior valley (c, e) crosses the termination of the first, penetrating

(1) Goodsir, Report of British Association, 1838.

(2) This animal was the size of an Ass, and, with the other species of the extinct genus,
had a cloven-hoof, like the Ruminants, but the division extended through the metacarpus and
metatarsus. The Anoplothere was an animal of aquatic habits and had a very long and strong
tail which Cuvier conjectures to have been used like that of the Otter in swimming.

:
q
.

ANOPLOTHERE. 525

and sub-dividing each lobe with a bend convex inwards: but the
peculiar characteristic of the Anoplotherian upper molar is the large
conical tubercle (p) at the wide entry of the first valley. The outer
side of the crown is impressed by two concavities, produced into
points upon the grinding surface: these points are first worn by
attrition; a double crescentic tract of dentine (o d & 17 d) is next
exposed in each primary lobe, with a detached island upon the
summit of the internal cone; this, from the minor depth of the
valley at the fore part of its base, is finally blended with the
anterior lobe, on which the crescentic enamel-fold (e) becomes first
obliterated, as in fig. 2, m 1: thus the Ruminant pattern of the
grinding surface is reduced to that which we shall afterwards find
to characterize, with minor modifications, the upper molars of most
anisodactyle Pachyderms. The three principal stages of attrition
_of the Anoplotherian molars are well shewn in the fossil upper jaw
of the An. commune from the Montmartre gypsum, figured by Cuvier
in the ‘ Ossemens Fossiles’ 4to. 1812, tom. 111., Supplement Pl. 8,
fig. 2. The incisors and canines are severally implanted by a single
fang; the first premolar by two fangs; the rest by three, two
external and one internal ; the true molars by four fangs.

In the lower jaw the first premolar is implanted by two
connate fangs; the second to the penultimate molar inclusive by
two fangs; the last molar by three fangs, the second and third
being connate. The mid-incisor of the lower jaw is small, with a
convex or flat border: the second and third have triangular crowns
progressively increasing in size: the canine is a little larger, with
the crown rather more pointed, and the hinder basal lobe and
the two depressions on the inner side of the crown better marked.(1)
The first premolar (PI. 135, fig. 3, p 1) scarcely differs from the
canine save by a slight increase of size. The rest (p 2, p 3, p 4)
are divided into two lobes by an external vertical depression, each
lobe being convex externally, and penetrated internally by a valley
deepest at its termination, the posterior lobe having also a second

a) The difference is so slight that Cuvier described the canines of the Anoplothere as

incisors, in his original Memoir, in the ‘ Annales du Muséum,’ tom. 111. pp. 374, 376, and
before later specimens had demonstrated the extent of the intermaxillary bone.

526 UNGULATES.

notch at its posterior and inner angle: the crown is sub-trenchant and
tricuspid before it begins to be worn down. A progressive increase
of size, and especially of transverse breadth, is combined with a
similar form in the first and second true molars (m 1 & m 2);
but the outer notch is deeper, and the two divisions (0, 0) more
convex, and swollen at their base; the third molar (m 3) has an
additional small hind lobe. The unworn summits of the first and
second true molars are produced into three points in the anterior,
and into two points in the posterior lobe. The deep terminations
of the folds penetrating the inner side of these semi-cylindrical
lobes form crescentic islands of enamel at a certain stage of
attrition, and thus typify the Ruminant character of the inferior
molars; but these islands are soon obliterated and the pattern
characteristic of the same teeth in the Rhinoceros and some other
anisodactyle Pachyderms is produced. In some of the smaller
species of Anoplotherium, separated subgenerically under the name
of Dichobune, the Ruminant type of grinding surface is more closely
adhered to, and is longer retained: in the lower jaw it is produced
simply by the crescentic folds of enamel becoming more vertical
and sinking into the crown from its summit, instead of penetrating
it from the inner side.(1)

The constituent tissues of the teeth of these ancient Herbivora
are the same in number, kind, and microscopic structure as those
of existing Ruminants and ordinary Pachyderms. A dense, unvascular,
fine-tubed dentine forms the basis; the crown is defended by a
moderately thick coat of fibrous enamel; and the whole is invested
by a cement, which is thickest on the fangs, and at the bottom
of the inflected enamel folds of the teeth. The last portion of
pulp in the centre of each tooth or tooth-lobe was converted into
osteo-dentine, which forms the dark mark on the middle of the
much-worn crowns of the teeth of old individuals. The diameter
of the dentinal tubes of the canine tooth of the Anoplotherium

(1) From the close resemblance of these molars to those of the Ruminantia thus produced,
it has happened that they have been sometimes referred to that Class: the fossil lower jaw of
the species which I have called ‘ Dichobune cervinum,’ from the eocene tertiary beds in the Isle
of Wight was originally described and figured as a species of Ruminant apparently closely allied
to the Genus Moschus. . See Geol. Trans. 2nd Ser. Vol. 111, p. 451.

RUMINANTS. 527

commune iS j5,th of an inch: that of their interspaces, in the
middle of the dentine is th of an inch. The diameter of the
sub-hexagonal dentinal cells is =,th of an inch. The purkingian
cells of the cement are for the most part oblong, ath of an
inch in largest diameter.

The vast abundance of Anoplotherian remains accumulated in
the ancient lacustrine deposits which now form the gypsum-quarries
at Montmartre, afforded Cuvier evidence not only of the changes
produced in the form of the teeth by mastication, but also by
the shedding and succession of the teeth. The deciduous formula
of the Anoplotherium is :—

a 3—3 2 1—1 4—4
Incisors —_; canines —; molars —: =— 382.
Bis 4 4—4

The incisors and canines were replaced by teeth of similar form,
but of larger size: the deciduous molars by teeth of more simple
conformation ; the deciduous molars typifying, the structure of the
permanent true molars, but the last in the lewer jaw having the
third posterior lobe of larger proportional size than in the last lower
true molar. We cannot but recognize with much interest the
constancy in the number of the true molar teeth under all their
diversified forms in the existing Ungulata not proboscidian ; but
that interest is greatly heightened when we find that the
same law both as regards the number of true molars, and the —
inferior complexity of the premolars to the deciduous teeth which
they displace, has prevailed from the remote period when we first
obtain evidence of hoofed Herbivora on the surface of this planet.

192. Ruminantia.—The essential character of the dentition of
all Mammalia, which by the Ungulate modification of their loco-
motive extremities are deprived of one of the means of seizing a
living prey, is the complex structure of the molar teeth, produced
by an interblending of the dental tissues in the crown, whereby
they are made more efficient instruments for the mastication of
vegetable substances.

Different groups of Ungulata, not only Orders and Genera but
even species, are characterised by the various patterns which result
from the various forms, directions and proportions in which the

528 UNGULATES.

enamel and cement alternate with the dentine in the substance of
the crowns of the complex molars. The pattern which characterises
the Ruminantia, and which is remarkable for its degree of constancy
in that Order, is shown in the upper and lower molar teeth in
Pl. 133. The next dental characteristic in degree of constancy is
the absence of incisors and canines in the upper jaw, and the
seeming absence of canines in the lower jaw, where those teeth are
so modified in shape and position as to resemble an external or
fourth pair of incisors. Two remarkable exceptions to this
character are, however, figured in Pl. 133; one in the genus
Moschus fig. 1, the other in the Auchenia, fig. 2.
The ordinary dental formula of the Ruminantia is :—

. 0—0 4 0—0 328 3-3
Incisors — ; canines —; premolars —; molars —: = 32.
3—3 1—1 3—3 3—3

The Antelopes, the Sheep, the Ox, representatives respectively of
the families Antilopide, Ovide and Bovide, which are collectively
designated the ‘ hollow-horned’ Ruminants(1), all present this formula.
It likewise characterises many of the ‘solid-horned’ Ruminants(2)
or the Deer-tribe (Cervide), the exceptions having canine teeth in
the upper jaw in the male sex and sometimes also in the females,
though they are always smaller in these. In the male Muntjak
the upper canines protrude, like tusks, beyond the lips, descending
a little beyond the lower jaw; and they had a like development
in the extinct Dorcathere. The upper canines attain their greatest
length in the small Ruminants called Musk-deer, and especially in
the typical species (Moschus moschiferus) most famous for the
preputial scent-secretion from which it takes its name: these teeth,
indeed, in the male Musk, present proportions intermediate between
those of the upper canines of the Machairodus and of the Morse. (PI.
133, fig. 1. ce). The inverse relationship in the development of
teeth and horns exemplified by the total absence of canines in
the Ruminants with persistent and typical horns, by their first

(1) From having persistent and commonly hollow bony processes of the skull supporting
hollow cones of true horny material.

(2) From having solid bony processes undefended by horny sheaths, and which are annually _
shed and renewed. A

RUMINANTS. 329
appearance in the periodically hornless Deer, and their larger size
in the absolutely hornless Musks, is further illustrated by the
presence not only of canines, but of a pair of laniariform incisors
in the upper jaw of the Camelide. In the Camel and Dromedary
the upper canines are formidable for their size and shape, but do
not project beyond the lips like the tusks of the Musk-deer ; they
are more feeble in the Llamas and Vicugnas (Pl. 133, fig. 2, c),
and are always of smaller size in the females than the males.
The inferior canines, moreover, retain their laniary form in the
Camelide, and are more erect in position than in the ordinary

Ruminants: they are separated by a short diastema from the

incisors in the Auchenie, (ib. c). The true nature of the

corresponding teeth in the ordinary Ruminants, in which they
are procumbent and form part of the same series with the
incisors, is always indicated by the lateness of their development,
and often by some peculiarity of form: thus in the Moschus they
are smaller and more pointed than the incisors, and in the Giraffe
they have a much larger crown which is bilobed: their ordinary
proportions and position, as presented by a large Antelope, the
Gnu, is shown in Pl. 134, fig. 9, c. The laniariform tooth in
the intermaxillary bone of the Camelide, which represents the
upper and outer incisor, is smaller than the true canine which
is placed behind it in the Camel and Dromedary: but in the
Vicugna (Pl. 133, fig. 2, 7.) it is as large as, or larger than the
true canine. The lower incisors in the genus Auchenia (ib. i)
have long and narrow crowns, directed straight forward and
placed side by side: in Camelus the crowns of the lower incisors
are oblong, depressed, spatulate or leaf-shaped, with a sinuous
bend concave above; and they overlap each other, as shown in
Pl. 134, fig. 8, the outer contour of the series describing half
of an ellipse. In the Giraffe the incisors describe a semicircle. In
most of the ordinary Ruminants the lower incisors are arranged
in a transverse line at the extremity of the jaw. In these the
first is the largest, and the second and third decrease in size, and
to a greater degree in the Deer and Antelopes than in the Elk,

the Sheep and the Ox: their crowns are trenchant and procumbent,
M M

530 UNGULATES.

slightly diverging from the alveoli: they are opposed above by a
callous gum, and are thereby better adapted for cropping or tearing
the herbage and foliage on which the Ruminants subsist.

The true molars, three in number on each side of both jaws,
are constant; the premolars are subject to some variety. They
are essentially four in number in each series; but the first, in
the true Ruminants, is feebly and transitorily represented by a
rudimental matrix developed in the primitive dental groove at a
short distance in advance of the second deciduous molar, and has
no successor. The second deciduous molar, or that which is
essentially such, is developed as the first of the functional molar
series of the immature animal (Pl. 133, fig. 4, d 1), and is
displaced by the tooth, marked p 1 in figs. 1 & 4, which is the
first of the permanent molar series, and is here indicated and
described as the first premolar, although it essentially corresponds
with the second premolar of the typical dental formula of the
Ungulata. In the Camel and Dromedary the actual first premolar
is functionally developed and assumes the form of a small canine
implanted by a single fang a little way behind the true canine; it
is transitorily represented in the foetus of the true Ruminants ; and
is retained only a little longer time in the Llama and Vicugna.(1)
The second premolar soon disappears in all the Camelide; it is
long retained in the true Ruminants, where, as above stated, it
is described as the first premolar. The third premolar in the
Camelide, marked p 2 in fig. 2, Pl. 123, as being that to which
the second premolar in the true Ruminants answers, is relatively
smaller than that analogue, and is earlier lost, especially in the
lower jaw. The last premolar is persistent in the Camelide, but
is smaller and more simple, especially in the lower jaw, than it
is in the true Ruminants. The true molars in the Camel are
larger in proportion to the size of the head than they are in the

(1) Cuvier believed the laniariform premolar of the Camel to be the analogue of the first
permanent premolar in the true Ruminants, but altered in shape and position. See ‘ Ossemens
Fossiles,’ 4to. 1823, tom. 111, p. 5. The normal number, viz. four premolars and three true
molars, was functionally developed in an extinct species of the Deer-tribe, called by Dr. Kaup ~
Dorcatherium, See ‘Ossemens Fossiles de Darmstadt’, 4to. p. 91.

RUMINANTS. 53]

ordinary Ruminants, and the two lateral series in the upper jaw
converge anteriorly in a greater degree.

The characteristic complexity of the molar tooth of a Ruminant
is manifested by most of the deciduous series ; but, in the permanent
series, only by the three posterior teeth of both upper and lower
jaws, which are the true molars; the three first, or premolars,
having more simple crowns than those which they displace. The
complexity in question is the result of peculiar folds of the
formative capsule, some of which are longitudinal or project
inwards from the sides of the capsule and form peninsular folds of
enamel upon the grinding surface of the tooth, whilst others
depend vertically from the summit of the matrix into the body
of the tooth, and form islands of enamel when the crown begins
to be worn (Pl. 134). Of the longitudinal folds two, in the
upper true molars, are external, broad but shallow, and often
sinuous (fig. 1, 0, 0), and one is internal, narrow and deep (ib. ¢)
extending quite across the summit of the crown of the tooth, as
in figs. 6 & 7, and decreasing in depth towards the base of the
crown; the corresponding fold of enamel in the completed tooth
accordingly extends more or less across the crown, from within
outwards, as the tooth is less or more worn. The crown of the
tooth is thus divided into two lobes, placed one in front of the
other; the inner side (i 2, fig. 3) of each lobe being convex, the
outer side (0 0) concave but in a minor degree, and usually
sinuous or with a convex prominence in the middle (fig. 3 & 4).
The vertical folds of the capsule, two in number extend one into
each lobe, and in the upper molars are concave towards the outer
and convex towards the inner side of the lobe, which is thus
divided into two semi-cylindrical bodies or lobules (0, 2, fig. 6), with
crescentic summits, as seen in a transverse section or on the
erinding surface of the tooth; each lobule consisting of a middle
body of dentine (od, id, fig. 5) and an outer coat of enamel and
thin cement; the midspace between the lobules, answering to the
centre of the vertical fold, is filled partly by cement, and com-
monly contains portions of the vegetable food; it is inclosed by a
crescentic island of enamel (figs. 3 & 4, e e); the whole

MM 2

Bo UNGULATAS.

circumference of this complex molar is also invested by a coat of

enamel (fig. 8, e) anda thinner layer of cement (ib. c). In some Rumi-

nants(1) a small vertical column (fig. 3, p), the analogue of the
large conical one in the Anoplothere, is developed at the internal
interspace of the two lobes of one or more of the upper true
molars, varying in height, and rarely reaching the summit of the new
formed crown. Different genera of Ruminants also differ in the
depth and sinuosity of the two outer longitudinal folds, and in the
depth and complexity of the two vertical folds, which likewise are
united in some species by a longer common base than in others,
producing thereby a continuity of the enamel and complete antero-
posterior bisection of the grinding surface during a longer period
of attrition. The upper molars also differ in their breadth or
antero-posterior diameter as compared with their thickness or
transverse diameter; but, as the summit of the crown is always
relatively broader in proportion to its thickness, care must be taken
to compare teeth of the different species that have been worn to
the same extent, or to allow for the difference.

In the family of Sheep and Goats (Ovide, Pl. 134, fig. 1) the
two outer depressions (0 0) are broad and shallow with a very low
middle convexity, and are bounded by well defined, narrow promi-
nent longitudinal ridges, the posterior or third ridge being less
developed than the other two: there is no internal accessory
column: the breadth of the crown is greater in proportion to its
thickness than in the Cervide or Bovide. The vertical crescentic
folds of enamel forming the islands (e e) are narrow and simple:
the Goat and Argali offer a rudiment of a secondary fold at the
extremities of the insular crescents, which is rarely seen in the
Sheep. The little Musk-deer differs from the Sheep, principally
by the greater prominence of the middle longitudinal convexity on
the outer side of the anterior lobe, and the crescents are more
curved.

The Antilopide have the median convexity of the two outer
shallow depressions of the upper molars more marked than in the
Ovide and the crescentic enamel-folds are wider; in the Gnu

(1) Cuvier specifies the Ox, Deer, and Giraffe, loc, cit. p. 8.

RUMINANTS. 530

(fig. 2, e e) they present a secondary fold or indentation at each
end. The small internal accessory column is present in this
species, but placed deeper in the substance of the tooth than
usual, forming a circular island of enamel (p) when the crown
is worn a short way down.

In the Ox (fig. 3) the outer contour of each lobe of the
upper molars (0) is more sinuous than in the Antelope or Sheep,
the middle convexity being more prominent and the lateral
depressions deeper; the crescentic islands (e e) are not so wide
as in the larger Antelopes (fig. 2), and the secondary terminal
indentations are less marked at the fore-part of the island. The
small internal accessory column (p) forms part of the periphery
of the grinding surface at the inner interspace of the lobes, when
the crown has been worn down about half an inch, from which
part it decreases in size to the beginning of the fangs.

The upper molars of the Aurochs (Urus, fig. 4) are thicker
in proportion to their breadth(1) and have a squarer grinding
surface than in the Ox (Bos proper) ; the crescentic islands (e)
are simple, with prolonged horns: the internal accessory column
(p) is less developed, and is soon indicated by a slight bend of
the enamel at the inner interspace of the lobes.

In the Deer (Cervus) the inner crescentic sub-division (2d, fig. 5)
of each lobe is thicker transversely than in the Bovide: in the
great extinct Irish Deer (Megaceros, fig. 5) which has molar teeth
as large as those of the Aurochs, the crescentic islands are simple,
narrow, and more curved or bowed than in the Ox, and in.
consequence of the later division of the vertical fold of the
capsule, the cemental cavity of each is continued into the other
until a later period of the attrition of the crown, as shown in the
upper molar of fig. 5.

In the Elk (Subgenus Alces, fig. 6) the central crescents are
continuous for a still longer period, and the median transverse
fold retaining its full breadth for a greater extent, the crown of
the molar continues to be divided, during a longer period of
attrition, by a crucial incision; the crescentic fold—ultimately

(1) Breadth is antero-posterior diameter, thickness is transverse diameter.

534 UNGULATES.

the island of the anterior lobe (e)—presents a small accessory
fold at the inner side of its posterior horn: in the posterior
lobe the fold is represented by a small circular island of enamel (e’)
both are soon obliterated as the tooth wears down. There is an
accessory column at the internal interspace of the lobes in Alces
as in Megaceros, which is not present in the Rein-deer or Fallow-
deer, but it is rudimental and confined to the base of the fissure.
The anterior border of the outer concavity of each lobe is unusually
produced.

In the Giraffe (fig. 7) the median convexity of the outer
surface of the anterior lobe (0) is more prominent than the
anterior border of the depression from which it rises, whilst
the anterior border of the posterior lobe (0°) is more produced
than the middle prominence: this distinctive character is well
shown in the upper molars of the fossil Giraffe from the Sewalik
Hills, noticed by Captain Cautley in the ‘Journal of the Asiatic
Society of Bengal,’ Vol. vi, pp. 658-660, and figured in
his joint communication with Dr. Falconer, in the ‘ Proceedings
of the Geological Society,’ No. 98, Pl. 2, fig. 3 & 4; the last
and penultimate molars are specifically distinguished by an obtuse
lobe at the bottom of the outer interspace of the two lobes.
The crescentic enamel folds are continued into each other until
the tooth is worn low down; but their outer boundaries are earlier

completed than in the Elk: the two principal lobes are divided —

almost to the base of the crown: the internal column is reduced
to a very small basal rudiment. The enamel of the Giraffe’s
molars is unusually rugose and resembles that of the Sivatherium.
The molars of the Camel (fig. 8), present the most simple con-
dition of the ruminant type of these teeth: the transverse fold
dividing the crown being short, the dentine of the two lobes forms a
continuous tract: the common base of the crescentic vertical folds
of the capsule being likewise short, the enamel islands are soon
separated from each other: they include a shallow or narrow
crescentic cavity, with a simple but slightly sinuous contour. The
two outer shallow longitudinal depressions of the crown (0 0°) have no
middle rising; and there is no columnar process at the interspace

ey

RUMINANTS. 535

of the two inner convexities. Bojanus has well illustrated these
characteristics of the upper molars of the Camel in his Memoir on
the Merycotherium(1), a large extinct Cameloid genus of Ruminants
founded on fossil remains discovered in Siberia, and he has extended
the comparison to the Sheep, the Elk, and the Ox.

Cuvier compares the lower molars of the Ruminants to the upper
ones reversed: in the lower true molars the single median longi-
tudinal fold is external and divides the convex outer sides of the two
lobes (fig 3°, 0 0): the base of the fold extends in some species across
the molar for some depth, before it contracts towards the outer side,
and the two lobes of the crown accordingly continue to be com-
pletely divided for a longer period, as in the Elk and Giraffe
(figs. 6 & 7): the inner surface of the molar is gently sinuous,
the concavities being rarely so deep as those of the outer surface
of the upper molars: the lower molars are always thinner in
proportion to their breadth than those above, and the crescentic
islands are narrower and less bowed. The differences which the
lower molars present in different genera of Ruminants are analogous
to those in the upper molars, but are less marked: the accessory
small column when present, as in Bos, Urus, Megaceros and Alces, is
situated at the outer interspace of the convex lobes, and nearer the
base in the Cervide than in the Bovide: in the Giraffe it is present
in the first, but not in the second or third true molars; it is not
developed in the Antelopes, Sheep or Camel, and is wanting in most
of the smaller species of Deer: other differences are expressed in
Plate 134. The last true molar of the lower jaw is characterised in
all Ruminants by the addition of a third posterior lobe: this is very
small and simple in the Camel and the Gnu, is relatively larger in
the Bovide and Cervide, presents in the Megaceros and Swwatherwm(2)
a deeper central enamel island or fold, which also characterises the

(1) Nova Acta Nat. Curios. 4to. 1824, tom. xii, pt. i, p. 265, tab. xxi.

(2) The last lower molar of this most gigantic of Ruminants is figured in Pl. 133,
fig. 3. Cuvier (loc. cit. p. 5) describes the two lobes of the lower molars as being composed
of two half-cylinders forming crescentic ridges on the grinding surface, and the last lower
molar as having an additional half cylinder, and consequently a grinding surface of five
crescents : the crescentic ridges are formed by the vertical descending fold, which divides the
summit of the lobe, and the fact is that the third lobe of the last molar has also this fold; but
it is shallower and the entire lobes are smaller. In most Ruminants the crescentic enamel island
or fold is therefore soon obliterated in the third lobe; but in some species it is deeper and

536 UNGULATES.

smaller third lobe in the Giraffe. The lower molars of the genus
Auchenia are peculiarly distinguished by the vertical ridge at the fore
part of the anterior lobe (Pl. 133, fig. 2, m, 2 & 3), which does not
exist in the Camels of the Old World.

In all Ruminants the outer contour of the entire molar series is
slightly zigzag, the anterior and outer angle of one tooth projecting
beyond the posterior and outer angle of the next in advance.

The premolars are smaller and more simple than the molars
with which they form a continuous series in the true Ruminants ; in
the upper jaw they are not divided into two lobes by an internal
cleft, but resemble a single lobe of the true molars, of greater breadth
than thickness, with a single central crescentic island, and usually
with an internal basal ridge. The central crescents have a more
complex contourin Megaceros than in Bos, and the first premolar,
which is always the smallest, is relatively larger in the Deer than in
the hollow-horned Ruminants. In the small Musk-deer the crescentic
enamel island is reduced to a small internal notch or fold, and the
outer border of the crown is trenchant and pointed. In the lower
jaw the premolars decrease in size from the third to the first, which
has usually a compressed conical crown with a sinuous inner
surface: the second and third premolars have two deeper notches
on the inner side, and a small second hinder lobe slightly marked off
by a vertical depression on the outer side of the crown. All the three
lower premolars have compressed, sub-trenchant and pointed crowns
in the small Musk-deer (Tragulus): the true Musk (Moschus)
more resembles the ordinary Deer in its premolars. The aberrant
Camelide deviate most from the Ruminant type in their premolar
teeth. In Auchenia the first is soon shed; the second (Pl. 138,
fig. 2, p 2) is unusually small and simple, and the third (p 3)
does not surpass in breadth a single lobe of the true molars, in either
jaw. Inthe Dromedary and Camel the second and third premolars
bear the same proportions to the molars as in the Llama and Vicugna,
remains longer as in the last molar of the Giraffe, the great Irish Deer and the Sivatherium,
which plainly shows that the additional lobe in the last lower molar is a reduced analogue not
of half, but of a whole lobe, and that it is essentially composed of two half-cylinders, presenting
as long as its central enamel fold remains, two crescentic ridges, but of smaller size than those

in the two normal lobes which it succeeds. The essential distinction of the third lobe of the
last lower molar is that it has not a distinct root.

RUMINANTS. 537

but the first, which is placed further in advance of the molar series, is
retained in the form of a small subcompressed, recurved, trenchant and
sharp-pointed canine, implanted by a single root: the second premolar
in the Jower jaw is usually soon shed, the premolars are here indicated
by numbers according to their appearance as functional teeth.

In the ordinary Ruminants, the upper premolars are implanted
by three fangs, two outer and one inner: the upper true molars
by four fangs, two outer and two inner. In the lower jaw both
premolars and molars are implanted by two fangs, but the second
fang in the last molar is very thick and consists of two connate fangs
(Pl. 133, fig. 1). The crowns extend some way into the sockets
before dividing into fangs; but these are always formed sooner than
in the Horse, and increase in length with the age of the Ruminant.

193. Microscopic Structure—In the true vegetable-feeding hoofed
Mammalia, asin the small Rodents with a similar regimen, the crowns
of the molar teeth are complicated by the interblending of layers of
enamel and cement with the dentine or basal substance of the tooth :
the microscopic structure of the several tissues does not essentially
vary from that of the same tissues in the more simple teeth of the
Mammalia; except that in the dentine of the incisors a few vascular
canals are retained, and that the cement of the molars, being of great
thickness, also presents vascular canals in addition to the minuter
radiated cells. The calcigerous tubes of the dentine in the incisor of a
Deer, maintain their parallelism best and are least bent, in the last half
or third of their course, i. e. nearest the enamel; and fall into stronger
and less regular curves as they approach the pulp-cavity, altering
their curves somewhat abruptly, and along contour-lines indicated
by the change of curve and by the numerous minor branches there
given off, most of which communicate with or dilate into minute
cells which likewise add to the distinctness of the contour lines.
The dentinal tubes are mest curved at their commencement from,
or rather termination in the pulp-cavity, where in the incisor of the
Red Deer, they present a diameter of ;,,,th of an inch, and are
separated by interspaces of about jth of an inch in width. They
soon begin to divide dichotomously into primary branches, and then
to send off numerous fine ramuli whereby the more parallel and
straighter continuations of the main tubes which form the peri-

538 UNGULATES.

pheral third part of the dentine are reduced to less than half the
diameter of their beginnings: the primary curve of the terminal
portions of the tubes in the crown is convex towards the upper
margin; in the basal portion of the tooth it is concave towards the upper
margin and sends off, as Retzius rightly describes in the Sheep, the
most numerous ramuli from the concavity and directed towards the
upper surface of the tooth. The white colour of the dentinal
tubes, when viewed by reflected light, is well displayed in the
figures of Dr. Erdl:(1) though they give an idea of the solidity of
the tubes which is not accurate: the opacity is due to the particles
of the lime salts which the tubes contain in a disgregated state;
but the more important functions of the tubes are perforated by
that part of the area which is left unoccupied by such salts, and
through which the vital and nutritious plasmatic fluid meanders. In
the portion of dentine of a Calf’s molar, taken from the bottom
of the pulp-cavity (Pl. 109, fig. 3) the undulations of the tubes,
the stronger flexuosities of some of the terminal branches, and
the occasional anastomotic loops which they form are shown.

The clear compartments of the basal substance are relatively
smaller than in the dentine of carnivorous and mixed feeding
Mammals: those in the peripheral third part of the Deer’s incisor
are ;,th of an inch in diameter, of a subcircular figure, and with an
overlapping or imbricated arrangement when viewed in a section
taken in the axis of the tooth: they increase in size and lose their
regularity of form nearer the pulp-cavity. In an antero-posterior
longitudinal section of the incisor of the Ox, Sheep, and Deer, a linear
tract of the orifices of medullary canals is seen continued from the
summit of the pulp-cavity to the grinding surface: these canals extend
towards the lateral borders of the crown and form loops at a short
distance from the enamel.

In old teeth, especially the molars, the residue of the pulp is
converted into osteo-dentine, forming the yellow-coloured nodules
mentioned by Retzius, around which the dentinal tubes irregularly
wind. The peripheral terminations of the tubes are resolved into
rich plexuses of minute branches interspersed, close to the enamel,
with minute opake cells.

(1) Abhandlungen der Akademie der Wissenschaften, Bd, ii. tab. i.

RUMINANTS. 539

The enamel extends to the beginning of the division of the
crown of the tooth into fangs, and consequently for some distance
into the socket in young Ruminants. The enamel covering the
outer sides of the flattened crowns of the incisors is thicker than
that upon the inner sides of the sameteeth. The fibres are unusually
slender, not exceeding z,th of an inch in diameter.

Retzius has accurately and clearly described both the coronal
and radical cement in the teeth of Ruminants. He says, “ I found
only a thin layer on that part of the teeth which was covered by
enamel: the cement was more thickly deposited round the ends of
those roots which were nearly closed, and in the clefts or enamel-
folds of the crown. Both the calcigerous cells and tubes were large
and very irregularly formed. In the thin layer of cement covering
the enamel, the cells appeared more like reticular vascular glands
than actual cavities: many of these are extended into oblong or
many-pointed figures of considerable length; and, besides these,
larger (vascular) canals proceeded from within, pretty parallel but
thinly scattered. The said gland-like cells were about ,jth of an
inch in long diameter, the vascular canals about jth of an inch.
It is most worthy of remark that the cemental cells entered into
very large and numerous communications with the (minute opake)
cells in the outer part of the dentine. The cement was very porous
in the clefts of the tooth, and manifested still less regular tubes and
cells than in the situations above described. The quantity of cement
in the Ox is far greater than in the Sheep: the above-described
coarse tubes (vascular canals), were here regularly branched and
proceeded likewise in an almost horizontal direction on the sides
of the teeth. But the cells were smaller and more regular than in
the sheep: they were very closely aggregated, approaching the
circular form and about ;;th of an inch in diameter.” In Pl. 109,
fig. 4, is given Dr. Erdl’s figure of a portion of the cement from
the root of the molar of a Calf, as seen by reflected light: the
opake calcigerous radiated cells are clustered together chiefly
towards that side which was next the outer surface of the cement:
and from these cells proceed the cemental tubes, which here and
there dilate into smaller and more simple cells, as they approach the
dentine.

540 UNGULATES.

194. Succession.—The deciduous series of teeth in the Ruminants
consists of :—

The superior incisors and canines are represented in the cavicorn
Ruminants and most Cervide by minute rudiments imbedded in the
gum, and were first observed in the embryos of the Cow and Sheep by
Mr. John Goodsir.(1) I have detected similar rudiments of a molar
tooth, very near the canines, in the foetus of a Fallow-deer. These
rudiments present themselves in the form of minute papille sunk
in depressions of the primitive groove, and, as Mr. Goodsir remarks,
‘after the closure of the latter, they remain for a short time as
opake nodules imbedded in the gum, in the course of the line of
adhesion.” They do not attain to that stage of calcification which
distinguishes the rudimental hidden teeth discovered by Geoffroy
in the gums of the foetal whales. In the Camel tribe, the third or
outermost of the upper incisors together with the canine and first
premolar, are completely calcified and have permanent successors :
in the Musk-deer and the Muntjac the permanent canine attains,
as we have seen, unusual size and becomes a formidable weapon ;
but the primitive rudiments of the upper incisors and of the first
molars in both jaws, disappear without giving origin to the matrices
of any successors. The functional and fully developed milk-teeth,
commonly found in the Ruminants, are the six incisors and two
canines of the lower jaw, and the second, third and fourth molars
in both jaws, the first molar being rudimental and not calcified or
manifested above the gum except in the Camel tribe. The interest
attached to the change of dentition, as indicative of the age of the
valuable domestic cattle derived from the Ruminant order has
attracted more than usual attention to its successive phases in these.
Bojanus(2) has given the most accurate account of these phenomena
in the Sheep. The whole of the functional deciduous series, viz :
0—0 0—0 3—3

mM. pea Oo eos Lear

(1) Report of the British Association, 1839.
(2) Nova Acta Nat. Curios. tom. xii, pt. ii, p. 702.

RUMINANTS. 541

have cut the gum, in the Lamb, in the course of the first month
after birth; the first true molar (m 1, fig. 4, Pl. 133) next appears,
behind the third milk molar in both jaws at the sixth month: at
the end of the first year the second true molar comes into place and
there are five molar teeth on each side of both jaws. This
transitional period may be detected and distinguished from an older
stage, when the same number of molar teeth may have been produced
by the loss or extraction of one of the six permanent molars, by the
form of the third tooth in the lower jaw (fig. 4, d 3), which tooth in
a Sheep between one and two years old, is divided into three lobes ;
the permanent tooth (p 3) which succeeds it consists of one principal
lobe and a small posterior lobule.

In the course of the second year the first or internal deciduous
incisors fall and are replaced by the broader permanent ones. The
state of dentition in the lower jaw of a sheep of twenty months
is shown in Pl. 133, fig. 4. The first permanent incisor (7 1) and
the first and second true molars (m 1 & 2) coexist with the
second and third deciduous incisors (di 2 & 3), the deciduous
canine (d c) and the three deciduous molars (d 1, 2 & 3).
Towards the end of the second year, the third true molar (m 3)
appears above the gum, and at the same time the deciduous
molars begin to give place to their vertical successors, falling
with brief but irregular intervals, the third being sometimes pushed
out a few days or a few weeks before the first and second. The
variations in those phases of development of the molar series,
which are dependent on individual constitution, food, season and
time of birth, never prolong the process beyond the end of the
second year. The change of the incisors and canines is not
completed until a later period. The second permanent incisor
(i 2) displaces its deciduous predecessor in the course of the third
year; the third comes into place usually during the first half os
the fourth year: the outer cutting teeth of the lower jaw manifest
their essential nature as canines by the lateness of their development,
not appearing above the gum and displacing the deciduous canines
until the fifth year, the entire series of permanent teeth being in
place and use before the end of the fifth year. At the fourth

542 UNGULATES.

year the roots begin to be developed from the base of the crown
of the last molars, having previously been added to those of the
precedent teeth.

In the Calf, according to M. Rousseau,(1) the first deciduous
incisor and the first deciduous molar both cut the gum a few days
after birth: the second incisor and the second and third molars
between the fifth and tenth days: the third incisor between the
fifteenth and twentieth days, and the deciduous canine, which,
with Bojanus and, Cuvier, he terms the fourth incisor, a few
days later. The second dentition is commenced, as in the Sheep,
by the eruption of the first true molar, between the fourth and
sixth month after birth: the first or median permanent incisor
and the second true molar appear between the fifteenth and
twenty-second month: and about the latter period the first
premolar pushes out the first deciduous molar. The second
premolar and the second incisor appear between the twenty-eighth
and thirty-second months. The third premolar and the third
incisor appear between the thirty-eighth and the forty-eighth month.
The last true molar cuts the gum between the forty-fourth and
the fifty-second month. The permanent canines (fourth incisors of
M. Rousseau) are the last to appear, as in the Sheep, but at an
earlier period, according to that Author, viz., before the Ox has
attained its fifth year.

The birth and growth of a young Giraffe at the Zoological
Gardens of London have enabled me to make the following ~
observations on the course of development and succession of the
teeth in that rare Ruminant, which is the largest existing species of its
Order. The four middle deciduous incisors began to cut the gum one
week after birth, and their crowns were entirely extricated at the end
of four weeks, at which time the summits of the crowns of both the
first and second deciduous molars were visible. At two months the
third incisor had cut the gum; at three months the third deciduous
molar, and at four months a fourth molar, were in place; the latter
being the first of the permanent series of true moiars.

The progress of shedding the deciduous teeth was traced by

(1) Anatomie Comparée du Systéme Dentaire, 8vo. 1839, p. 229.

HOG-TRIBE. 543

observation of the parent Giraffe. She arrived at the Zoological
Gardens in May 1836, and was then about eighteen months old,
and had all the deciduous series with the first permanent true
molars. The two middle deciduous incisors were shed in the
month of March 1838, the second incisor on each side in the
following July, the first deciduous molars in October, and the
second deciduous molars in November and December of the same
year. At this time the second true molars come into place. The
last true molars began to appear above the gum in August 1839,
and the last deciduous molar was replaced by the third premolar
before the end of that year: the shedding of the whole deciduous
series was completed by the fall of the canines in the female
Giraffe at the period of the birth of her second fawn in May
1841, when she must have been six years and a half old: the
large bilobed crowns of the permanent canines were not completely
in place until September 1841.

The middle incisors are relatively larger in the deciduous
than in the permanent series as compared with the outer ones and
the canine, in most ordinary Ruminants; the Giraffe deviates
furthest from the typical proportions of these teeth in the superior
expanse of the bilobed crown of the permanent canine, but it is
interesting to find that the deciduous canine, though its crown is
also bilobed, is relatively smaller in proportion to the incisors, and
thus shows a less amount of deviation from the common type.
The third lobe of the last inferior deciduous molar, in the Giraffe,
as in the Sheep and Ox, is relatively larger and retains its central
enamel-crescent longer than in the last inferior true molar. This
tooth in the great extinct Sivatherium (Pl. 133, fig. 3) retained
more of the form of its deciduous analogue the last milk-molar
than is usually seen in existing species of Ruminantia.

195. Sude.—Of all the natural groups of Ungulata the Hog-
tribe offers the greatest diversity of dentition, especially in the
structure of the molar teeth: the African Wart-hogs (Phaco-
cherus) rival the Elephants in the relative size and complexity
of the last molars, whilst these teeth in the South American
Peccaris are simply tuberculate, without increase of size: so

544 UNGULATES.

likewise amongst the ancient extinct aberrant forms, the Hippohyus(1)
presents almost a ruminant pattern of the grinding surface, whilst
the Cheropotamus manifests in its whole dentition a close resemblance
to the plantigrade Carnivora.

The folds of the dental capsule upon the coronal surface of
the molar teeth of the typical Hogs are shorter than in other
hoofed Mammals, but are very numerous, and produce a multicuspid
or rather multituberculate grinding surface, especially in the last
molar, which is commonly much larger than the rest. ‘The canines
form projecting tusks, and are remarkable in most Suide for
their extraordinary size, shape, and direction, especially in the
males. The incisors are less constant, varying in number in
different genera. The progressive increase of size in the molar
teeth as they are situated further back in the mouth, may also be
noticed as a family characteristic, which, with the complication of
the crown and the development of the tusks, reaches its maximum
in the Phacocheres.

196. Sus—-The wild progenitor of our domestic breeds of Hog
(Sus scrofa, Linn.) offers as the normal formula :—

ae 1-I 4—4 ssi et eae 140, fig. 1

We es Coe ln a le

The upper incisors decrease in size from the first to the third :
the first has a short, strong, obliquely bevelled crown, which
inclines towards and touches that in the other intermaxillary by its
produced inner part; .the crown, before it is worn, presents
a depression; it is implanted by a short, thick, curved fang ;
this incisor is relatively larger in the Sus larvatus than in the
Sus scrofa. The second incisor, in the common Hog, has a
crown as broad as the first, but shorter and thinner; its edge
is trenchant and dentated, but is soon worn down: in this state
the abraded surface of both incisors shows a dark mark in the ©
centre. The third is a very small tooth, a little removed from the
second. The form and position of the short vertical crowns of
the upper incisors remind one of those of the Kangaroo; and the
resemblance is carried out by the procumbent position of the —

(1) An extinct genus so called by its Discoverers, Captain Cautley and Dr Falconer.

HOG-TRIBE. 545

incisors of the lower jaw, whose crowns oppose their upper sides
to the ends of those above, as in the herbivorous Marsupials.
But the incisors in the Hog are six in number below, as well
as above: they are long, sub-compressed, nearly straight; the
second is rather larger than the first; the third is the smallest, as
in the upper jaw. In the two larger procumbent incisors the crown
is remarkably long, and the enamel continued far into the socket,
especially upon the upper and under surfaces; the under surface is
slightly convex and even; the upper one has a peculiar character
in a strong median longitudinal rising, divided by a depression on
each side from the two margins of the crown, of which the outer
one forms a dentated ridge; these characters become obliterated
by use, but the lateral flattening or compression of the long and
straight fang may assist in the determination of one of these
incisors. The lateral incisor curves towards the second.

The upper canines, in the Wild-boar, curve forwards, out-
wards, and upwards; their sockets inclining in the same direction,
and being strengthened above by a ridge of bone which is extra-
ordinarily developed in the Masked Boar of Africa. The enamel
covering the convex inferior side of this tusk is longitudinally
ribbed, but is not limited to that part; a narrow strip of the
same hard substance is laid upon the anterior part, and another
upon the posterior concave angle forming the point of the tusk,
which is worn obliquely from before upwards and backwards to
that point. I have never seen a permanent upper tusk of either
sex of the Sus scrofa in which the enamel was limited to the
outer surface as described by M. Rousseau(]): in the lower tusks
it covers the anterior and inner as well as the outer sides. The
longitudinal ridges on the lower plate of enamel are fewer and
stronger in the Masked Boar (Sus larvatus) than in the common
Wild Boar. Jn the Sow the canines are much smaller than in
the Boar. In some domestic breeds the upper tusk has a short
descending pointed crown, with an anterior and posterior margin,
divided by indentations from a median convexity, something like

(1) ‘Anatomie Comparée du Systéme Dentaire,’ p. 206.
NN

546 UNGULATES.

the canine of a horse. Castration arrests the development of the
tusks in the male.

The teeth of the molar series progressively increase in size
from the first to the last: the first premolar (Pl. 140, fig. 1, p 1)
has a simple compressed conical crown, thickest behind, and has
two fangs: it is further removed from the second in the Sus
larvatus than in Sus scrofa. The second premolar (ib. p 2) has a
broader crown, with a hind-lobe, having a depression on its inner
surface ; and each fang begins to be subdivided. The third premolar
(ib. p 3) has a similar but broader crown implanted by four fangs.
The fourth premolar (ib. p 4) has two principal tubercles and
some irregular vertical pits on the inner half of the crown. In
the masked Boar the third upper premolar is larger, thicker, and
more pointed than in the common Boar. The first true molar, when
the permanent dentition is completed, exhibits the effects of its early
development in a more marked degree than in most other Mammalia,
and, in the Wild Boar, has its tubercles worn down, and a smooth
field of dentine exposed by the time the last molar has come into
place (Pl. 141, fig. 3, m 1): it originally bears four primary cones,
with smaller subdivisions formed by the wrinkled enamel, and
an anterior and posterior ridge. The four cones produced by the
crucial impression, of which the transverse part is the deepest,
are repeated on the second true molar (ib. m 2) with more complex
shallow subdivisions and a larger tuberculate posterior ridge. The ~
greater extent of the last molar (ib. m 3) is chiefly produced by
the development of the back ridge into a cluster of tubercles:
the four primary cones being distinguishable on the anterior main ©
body of the tooth. The hind lobe is more simple and smaller in
the masked than in the common Boar. There is generally a small
tubercle at the outer and inner interspace between the two
principal lobes of the true molars. The number of fangs increases —
‘with the increasing size of the crown. |

The crowns of the lower molars are very similar to those —
above, but are rather narrower, and the outer and inner basal
tubercles are much smaller or are wanting. The transverse

BABIROUSSA. 547

depression on the first and second true molars is deeper in the
lower than in the upper jaw; its borders of enamel are very
sinuous; in the second true molar each anterior lobe is penetrated
by a secondary fold at its posterior margin, and the posterior
division is divided into three lobes, the enamel coats of which
form three islands arranged in a triangle when the surface is
worn down to a certain extent: the last molar is divided by
two transverse depressions into three principal lobes, the last
being the longest in the common Hog, and the shortest in the
Masked Hog; the two anterior divisions are each subdivided by
the longitudinal furrow into two tubercles, and these are broken
by many secondary depressions into smaller tubercles. The inferior
canines of the Wild Boar are longer, and curve upwards, out-
wards, and backwards, in a more normal direction than those
above: they are three-sided; the broadest convex side is directed
obliquely inwards and forwards ; the outer and posterior sides are
nearly flat ; the latter surface has no enamel, and the tusk wears
obliquely from behind, upwards and forwards to a point, with two
sharp enamel edges. Both upper and lower canines have the
characters of true tusks in the projection of their crown beyond
the lips, and their insertion by a long undivided and undiminished
base, widely excavated for a persistent matrix which ensures the
uninterrupted growth of these formidable weapons. Each tusk in
a lower jaw of one foot in length, from a German Wild Boar,
measures eight inches along its curve: but tusks of twelve
inches in length have been obtained from the Wild Boars of
Assam.

The smaller species of Asiatic Hog, called Babiroussa, has
obtained from the extraordinary development and direction of its
tusks the name of ‘horned Hog’ (Pl. 140, fig. 3); and both molar
and incisor teeth offer some varieties from those of the ordinary
species of Sus. The incisors are reduced to four in number in
the upper jaw by the early loss of the two small outer ones; the
first and second, on each side, which remain, correspond in form
with those of the common Hog. The six incisors are retained in
the lower jaw. ‘The upper canines are more slender than in the

NN 2

548 UNGULATES.

Wild Boar, are compressed laterally with an elliptic transverse
section, and a smooth unenamelled exterior. Their socket seems
as if it had been pulled out or produced from the alveolar border
of the upper maxillary bone, and then bent abruptly upwards, giving
the tusk a direction upwards and backwards. The tooth pierces
the integuments of the upper lip, like a horn, and its growth,
being unchecked by any opposing tooth, sometimes forces the
tip again through the integument and into the substance of the
skull. The lower tusks have the ordinary direction, but rise rather
more vertically and much higher than in the Wild Boar; they are
subtrihedral with rounded angles, except the inner one towards the
point, and sometimes show upon their inner side slight marks of
abrasion against the outer side of the base of the upper tusks.
These tusks are well adapted by their position to defend the eyes,
and assist in the act of forcing the head through the dense en-
tangled under-wood of a tropical forest, as suggested in Home’s
Comparative Anatomy (Vol. 1, p. 221); but their use has not
been determined by actual observation: speculation, however, has
not been idle in assigning final purposes to these singularly
developed teeth, which are too absurd for repetition. The molar.
serles is speedily reduced in the Babiroussa to two premolars and
three true molars on each side of both jaws: the great activity
of the vascular matrix of the long tusks soon exhausts the
conservative force of those of the adjoining small premolars. The
upper molars much resemble those of the Hog, but are relatively
narrower ; the four principal tubercles are better marked on the
penultimate and last true molars, and the accessory tubercular
talon of the latter is relatively smaller. In the lower jaw, also,
the third lobe of the last molar is smaller, and the four principal
tubercles constitute a more conspicuous and important part of the
crown.(1)

(1) A fossil under jaw has been described and figured in Silliman’s American Journal
of Science, Vol. xliii. 1842, Pl, 3. fig. 1, under the name of Sus Americana, by Dr. Harlan,
who conceived that from “its general appearance and number of the teeth this fragment
bore a close analogy with the same part in the Sus babirussa, Buff., although the Babiroussa

was a much smaller animal.” Having compared a cast of this fossil jaw, I find that, besides
the difference of size, there is a difference in the proportions of the true molar teeth, the

WART HOGS. 549

197. Phacocherus.(1).—The rate of increase of size from the first
to the third true molar (Pl. 141, fig. 2) is carried to its maximum in
the Phacocheres or Wart Hogs of Africa, and the folds of the capsule
producing the multicuspid grinding surface here attain a depth,
number, cylindrical figure, and regularity of arrangement, which
produce so peculiar a modification of the structure of the molar
teeth, as, with other and minor differences, to justify the sub-
generic separation of those large and formidable Hogs from the
rest of the Suide.(2)

The Wart Hog of Nubia, Abyssinia and Kordofan (Phaco-
cherus Athana, Riippell)(3) has the incisors reduced to,two in the
upper jaw, corresponding with the median pair in other Hogs; a
single short, thick, and inwardly curved incisor being inserted near
the end of each intermaxillary bone: the margin of the unworn
crown of this incisor in the young animal is divided into three
equal tubercles by two notches, which are soon obliterated : they
are larger in the males than in the females, according to Riippell,
(loc. cit. p. 62). The upper tusks are longer and larger than
the lower ones and curve outwards, upwards and backwards: they

first being two-thirds the size of the last, whilst in the Babiroussa it is less than half.
The last molar in the fossil has the anterior transverse ridge proportionally larger and the
posterior lobe proportionally smaller than in the Babiroussa, resembling the Lophiodon in
the points in which it thus differs from the Sus cited. The form of the jaw differs at this’
part of the fossil from that in the Babiroussa, in which the socket of the last molar over-
hangs the inner surface of the ramus, whilst in the fossil the inner surface of the ramus
beneath the last molar describes a gentle convexity from the tooth to the Jower margin.
The outer part of the ramus of the jaw of the Babiroussa begins to expand below the
fourth and fifth molars, counting forwards from the last,'to form the socket of the large
tusk, but the fossil jaw does not offer the least indication of an enlargement for that
purpose, and the fractured anterior end, as displayed in the cast, is very different in
shape from the corresponding part of the jaw in the Babiroussa, and shows merely the
dental canal and no socket for the tusk which would be here situated in the Babiroussa
or Wild Boar. The nearest approximation which the fossil in question allows to be made
to any known existing or extinct animal is to the great tapiroid Pachyderms.

(1) gaxdc a Wart, xoipos a Hog.

(2) M. F. Cuvier says, “ Nous voici arrivés 4 un systéme de dentition tout-d-fait
différent de celui des sangliers.” Dents de Mammiferes, p. 213; but this is rather too
strong an expression.

(3) ‘Atlas zu der Reise im Nordlichen Afrika,’ fol. 1826, Erste Abth. p. 61, fig. 25
& 26. The ‘Sanglier du Cap Verd.’ of ‘Buffon,’ (t. xiv., p. 409), is of this species.

550 UNGULATES.

are four-sided, with rounded angles, gradually diminishing to a
point, and showing the action of the lower tusk upon the fore
part of their basal half: both upper and under surfaces are
traversed longitudinally by a broad and shallow groove; and the
tip of the first formed end of the tusk is similarly impressed
on its fore-part, but this is subsequently worn away; the enamel,
also, with which the end of the tusk is at first covered, is soon
rubbed off. The number of molar teeth present at one time on
either side of the upper jaw appears not to exceed five, and is
soon reduced to four, and finally to two or one.(1)

I have not been able to obtain evidence of more than two
premolars in the upper jaw, which correspond with the third and
fourth in the common Hog. The anterior premolar (Pl. 141,
fig. 2, p 3) is implanted by one anterior and two posterior short and
thick fangs, and has an oval crown, four lines by three lines across,
and presenting, in a much worn specimen, a notch or enamel-fold
on the inner side: the last premolar, (ib. and Pl. 140, fig. 4, p 4)
with a grinding surface nearly circular, and five lines in diameter,
presents four peripheral enamelled lobes or islands, surrounding a
central lobe: when much worn these are reduced to an external
and an internal lobe, with a central enamel fold or island. The
first true molar, which cuts the gum and is in use long before
the preceding teeth are developed, or their deciduous predecessors
are shed, presents itself, in the mature Nubian Phacohere (Pl. 141,
fig. 2, m 1), as a smooth almost worn-out stump; squeezed, as it
were, between the last premolar and the second true molar: more
commonly its place only is indicated by a short diastema separating
these teeth, and showing a remnant of the socket of the displaced
tooth; and this vestige soon disappears, the second true molar
being pushed forward in contact with the last premolar, as shown

(1) This is the state of dentition in the old Phacocherus Atliani, figured in Home’s
‘Lectures on Comparative Anatomy, Vol. 11, pl. 38, which M. F. Cuvier cites, in the Mé-
moires du Muséum, t. viii, p. 453, as “une jeune téte de phacocherus tout-a-fait dépourvue
dincisives.” The single incisor of the upper jaw and the sockets of two incisors in the lower
jaw are, however, plainly shown in the engraving: the original specimen demonstrates six
incisive sockets below, and the incisor in each intermaxillary above, with other characters
of the Nubian species of Wart Hog, as the cartilaginous ‘septum narium,’

WART HOGS. at)

in Pl. 140, fig. 4, and in the figures given by Dr. Riippell. In
the young individual, the crown of the first true molar (Pl. 141, fig. 1, »
m 1) is divided into two principal lobes, each lobe resembling the
entire crown of the last premolar, and having a central enamel-
island surrounded by four or five similar peripheral ones: it is
implanted by four long and strong fangs; the antero-posterior
diameter of the grinding surface measures nine lines. The second
true molar (Pl. 140, fig. 4, & Pl. 141, fig. 1 & 2, m 2), which does
not cut the gum until the first is more than half worn down,
presents a broader subquadrate crown, nine lines by seven lines
across the grinding surface, which presents a central enamel island,
surrounded by four principal and some smaller islands or lobes.
The third and last true molar (ib. m 3) is the most characteristic
tooth of the Phacocheres, and perhaps the most peculiar and
complex tooth in the whole class of Mammalia: the surface of
the crown in the specimen before me, measures two inches in
antero-posterior extent and eight lines in transverse breadth, and
presents three series of enamel-islands, in the direction of the
long axis of the grinding surface: the middle row of eight islands
are elliptic and simple; those of the other rows are in equal
number, but are sometimes subdivided into smaller islands :
these islands or lobes are the abraded ends of long and
slender columns of dentine, encased by thick enamel, and
the whole blended into a coherent crown by abundant cement,
which fills up all the interspaces and forms a thick exterior
investment of the entire complex tooth. In the closed alveolus
of the third molar of a young Phacochere, I found a number of
the hollow prisms of enamelled dentine detached (Pl. 141, fig. 1,
m 8): the formative matrix continues for a long period to be
reproduced, maintaining by its successive calcification the crown of
the tooth entire to the bottom of the socket, where the orifices of
the constituent cylinders and the vacant interspaces, which lodged
the complex vascular matrix are seen in the dried tooth.

In the lower jaw of the Nubian Phacochere the four middle
incisors are strong, subtetragonal, porrect, subequal, with the ridge
and grooves upon the upper side of the crown as in the ordinary

552 UNGULATES,

Wild Boar, but less obliquely abraded. The two small lateral
incisors are more incurved towards the intermediate ones. The
incisors are disposed more nearly in a transverse line on the
broad expanded symphysis of the Phacochere than in the narrower
jaw of the Hog. The lower canines are more slender, more
divergent, and sharper than in the Wild Boar; but otherwise
resemble them in their trihedral shape and in the partial dis-
position of the enamel, and its continuation into the alveolus. I
have seen but one premolar tooth on each side of this jaw, with
a crown reduced by attrition to one anterior and two posterior
lobes, five lines in long diameter. In one specimen the stump of
the first true molar remained, wedged in between the last premolar
and the second true molar; in another a short vacancy showed
the place whence the first true molar had been expelled: the
second and third molars resemble those above, but are rather
narrower transversely. The crown of the first true molar,
examined at a_ period before its characteristic structure is
obliterated, as in the young Phacochere before the second true
molar has cut the gum, has the same complex pattern as that
above ; and measures nine lines by three lines, on the grinding
surface: it is supported by four fangs, the hind pair being very
long and strong.(1) The last molar in this jaw has the same

(1) The first true molar tooth, in both jaws of the Phacocherus Alliant appears to
have escaped the attention of MM. F. Cuvier and Riippell. M. F. Cuvier in his
Monograph on the two species of Phacochere in the ‘Mémoires du Muséum’ tom. vim.
1822, p. 450, represents a skull of the Nubian species with the last upper molar only in
place: and in the ‘Dents de Mammiféres, p. 213, he assigns but three molars to each
side of the upper jaw in both species, which teeth appear from his description to be the
two premolars and the last true molar. ‘The figure of the teeth of the upper jaw, in
Pl. 87 of the ‘Dents de Mammiféres, is taken from the South African Wart Hog (Pha-
cocherus Pallasii, v. der Hoeven.) Dr. Riippell’s elaborate Monograph relates exclusively to
the Nubian or North African Phacochere. He says, ‘In all our specimens of both young
and adults, and of both sexes, the upper jaw has four, the under jaw three molars: the
first and second are small, narrow, roundish, with simple crowns, and each implanted by
two roots in two separate sockets: the third (in the upper jaw; second in the lower) is
strong (stark) ‘and as broad as the fourth; its grinding surface has five simple crowns’
(‘kronen-kerne’, our enamel-islands) ‘four at the angles and one in the middle: it has
four roots wedged into fonr separate sockets.’” Then follows the description of the complex

last molar tooth, the fourth in the upper, the third in the lower jaw. The smaller rooted
teeth above described are the two premolars, and the second true molar in the upper jaw;

WART HOGS. 553

rootless condition as the one above, upon which its longer
duration than the preceding rooted molars depends, as Dr. Riippell
well remarks. (loc. cit. p. 63.)

In the Wart Hog of South Africa, (Phacocherus Pallasii, v.
der Hoeven)(1) there are no incisive teeth in the upper jaw of the
mature animal, and the traces of four small incisors are almost
obliterated in the lower jaw of the skull before me.(2) The large
upper tusks differ from those of the Ph. Aliant in the deeper
and narrower groove along their front and back part, and they
are inclined more forwards. One simple, single fanged premolar,
remains in the place near the base of the tusk corresponding with
that of the first of the three deciduous molars in the young
animal. The analogues of the two premolars in the specimen of
Ph. Pallasii described, are shed, together with the first and
second true molars, and the work of mastication has been carried
on by the last large complex molar exclusively. The three series
of columns of which this tooth consists appear to be more regular
in form than in the Ph. Ahan; but this may depend on the
tooth having been worn lower in the specimen of Ph. Pallasiz here
described, in which the long diameter of the grinding surface is
two inches one line, the short or transverse diameter half an inch.
In the lower jaw the stumps of four small incisors may be seen
razed to the level of the edge of the symphysis. The canines,

and the figures (loc. cit. tab. 26, figs, c, d,) well exemplify this stage of dentition,
which is the most common in the adult Phacocherus Atliani. How the first true molar,
or the vestiges of its socket and the vacancy between the last premolar and second true
molar should have escaped the observation of the accomplished Abyssinian traveller, in
the younger specimens to which he alludes, I cannot explain: they are obvious in three
out of five examples of this species in the Hunterian Museum. In the immature Nubian
Phacochere five molars are present when the second true molar has risen into place ;
and it will be seen from the description of the deciduous dentition of the Phacocherus
A‘liani in the text that it had escaped the notice of Dr. Riippell. The skull of the
Phacocherus Aéliani figured in Home’s Comparative Anatomy, tom. 11, Pl. xxxix, shows
the two premolars and the second and third true molars.

(1) Sus Aihiopicus, Pallas, Miscell. Zool., 16, tab. x1.

(2) M. F. Cuvier first pointed out the absence of incisors as a specific distinction of the
South African species: but he had also observed on the margin of the symphysis of the lower
jaw ‘quatre dépressions a égale distance lune de l’autre.’ ‘ Mém. du Mus.’ viii, p. 453. Similar
depressions contain stumps of incisors in the specimen here described.

554 UNGULATES.

like those above, are larger than in the A¢lian Wart Hog. The
stump of a premolar is retained on one side, separated by an
interval of an inch from the last molar, the rest having been
shed, as in the upper jaw: the grinding surface of the molar is
of the same length as that above, and is five lines in breadth:
it presents a middle row of eight columns and two lateral rows of
seven each, twenty-two in all.

198. Succession.—Before proceeding to the Peccari, which deviates
still further in its dentition from the characteristics of the Suide and
represents that of the extinct forms of the family, which lead on
the one hand to the Plantigrades and onthe other, by closer steps
of affinity, to the Hippopotamus, I shall notice the succession and
structure of the teeth in the more typical Hogs.

The first or deciduous dentition of the Hog consists of :—

¢ 3—3 ° 1—1l 3—3
Incisors —-; canines —; molars —: = 28.
3-3 1 a~8

The first milk incisor, above, is large, oblique, trenchant, and
with a depression on the inner surface of the crown: the second
and third are small and pointed. The first and second incisors,
below, are trenchant and oblique; and have the indentations and
ridge slightly marked on the upper or inner side of the long and
narrow crown; the third is pointed. The canines are feeble and
have their normal direction in both jaws, the upper ones des-
cending according to the general type, which is not departed
from until at a later period of life. The first and second
deciduous molars (Pl. 140, fig. 2, d 1, d 2) have simple com-
pressed conical crowns crenate at the edge, and with an anterior
and posterior basal tubercle; the second is a little larger than
the first: the third manifests the characteristic increase of size
and complexity, yet is kept within the bounds of the more
common type: in the upper jaw it has four principal tubercles,
and thicker ridges at the fore and back part of the base of the
crown: when the enamel is worn from the middle of the sub-
dividing valley, and the dentine of the two tubercles is united,
the pattern closely resembles the characteristic trefoil of the
grinders of the Hippopotamus. In the lower jaw, the last

HOG-TRIBE. 566

deciduous molar (ib. d 3) has the crown divided into three lobes
and a posterior tubercle ; each lobe being subdivided into an outer
and an inner cusp with irregular, subtuberculate surfaces: the
lobes increase in thickness from the first to the third, the entire
tooth bearing a strong resemblance in miniature to the corres-
ponding deciduous molar of the Hippopotamus.

The second and third deciduous molars appear before the
first, and the first and third incisors, with the canine, rise into
place before the second incisor: the development of this tooth
and of the first molar completes the caducous dentition. ‘The first
permanent true molar (ib. m 1) next comes into place behind the
deciduous series, and the first premolar (ib. p 1) appears in front
of that series, not displacing any predecessor: the second permanent
true molar (ib. m 2) also cuts the gum before any of the deciduous
teeth are shed.(1) The fall of the milk-teeth follows the order of
their appearance: the iter dentis of each of the three replacing
premolars (‘dents de remplacement’ of Cuvier) opens upon the
inner side of the alveoli of the teeth which they displace. With
respect to the anterior and smaller premolar (p 1) I am doubtful
whether to regard it as belonging to the first or the second dentition :
it maintains its place sometimes longer than the adjoining posterior
premolars (p 2, p 3), and would, therefore, appear, like its analogue
in the Bear and Dog, to be the first of the permanent series:
but I have seen an instance in an Indian Wild Boar, in which,
on the right side of the upper jaw, a premolar with a larger
crown (Pl. 141, fig. 3, p. 1:) had been developed between the
small anterior premolar and the second normal premolar, and a
little to the inner side of the anterior tooth, which it seemed,
therefore, to have been destined to succeed, but had not displaced;
there being five premolars and three true molars, or eight teeth
on that side of the upper jaw.(2) The third large true molar

(1) The figure which Cuvier gives (Ossemens Fossiles, 4to. 1822, tom. 11, Cochons, pl. 1,
fig. 4 & 6), as the dentition “d’un jeune animal qui n’a encore que des molaires de lait :”
exhibits the first and second true molars which are certainly not milk-teeth, together with the
small anterior premolar which, likewise, is not displaced by a successor as a true milk-tooth
always is.

(2) Cuvier regards 'the anterior small molar (p 1) as the first of the deciduous series, and
describes its displacement and succession by a ‘dent de remplacement,’ as constant, though

556 UNGULATES.

(Pl. 140, fig. 2, m 3) does not come into place until all the
deciduous teeth have been shed; it is the last molar: the cavity
in the lower jaw figured by Home, ‘Lectures on Comparative
Anatomy,’ Vol. 1, Pl. 27, fig. 3, as ‘‘ a new cell formed for a
succeeding tooth,” is a medullary cell of the osseous tissue, not
a closed alveolus with a tooth-germ.

In the Phacochere the first small and simple equivocal
premolar is not developed in either jaw. The three deciduous
molars are present in the upper jaw, but only two, the second
and third, in the lower jaw, of a young Phacocherus Aliant
with the deciduous incisors still retained, and the second
true molar not yet protruded: nor is there any trace of an
alveolus of the first. deciduous molar of the lower jaw, which
may, therefore, be transitorily manifested, ‘en germe’ and never
functionally developed. With this reduction in number, the
deciduous dentition of the Phacochere, nevertheless, departs much
less from the typical characters of the Suide than does the
dentition of the adult. The three milk molars of the upper jaw
present the same degree of increase of size, as do the three true
molars of the Wild Boar. But the first is much more simple, has
a compressed crown three lines long, supported by two fangs: the
second milk-molar has a triangular crown broadest behind, and is
supported by one anterior and two posterior fangs; the third is
subtetragonal, with a grinding surface of six lines by four lines,
with a central enamel island, surrounded by six somewhat larger
islands ; it is implanted by four fangs. The same cause, viz. the
large matrix of the tusk, would seem to have drawn off the
supply from the first and second premolars, and to have prevented
their development; the third and fourth premolars, which have
been above described in the A‘lian Phacochere are more simple,
especially the fourth, than the teeth which they displace. The
last deciduous molar in the lower jaw (Pl. 141, fig. 1, d 3) very
closely resembles in size and shape the corresponding tooth in the
late, in the upper jaw; but with regard to the lower jaw, he says ‘ peut-étre méme n’est-elle
jamais remplacée en bas.’ (Ossemens Fossiles, 4to. 1822, tom. 11, pl. 1.) I have not, hitherto,
found a successor to the small tooth in question, unless the above-cited Indian Wild Boar be

regarded as an instance, but as this tooth p 1! has not displaced p 1, it seems rather to be an
a noma lous or supernumerary premolar,

HOG-TRIBE. 557

young Sus scrofa. I could find no germ of a successor to the
small anterior deciduous molar (ib. cl. 2); and we have seen that
the lower jaw of the nearly full-grown Phacochere presented only
one premolar (Pl. 140, fig. 4, p 4). The germ of this tooth is shown
in Pl. 141, fig. 1, p4: the first true molar (ib. m 1 has already
lost half its crown by the wear of mastication, and its early loss,
with the obliteration of its alveolus, as in Pl. 140, fig. 4, accounts
for its having hitherto escaped the notice of the Naturalists who have
paid most attention to the remarkable dentition of the Phacocheres.

The single permanent incisor in each intermaxillary of the
Phacocherus Ailiani is preceded by a deciduous and more simple
incisor.

199. Microscopic structure-—The dentine of the teeth of the
common Hog is dense, unvascular, susceptible of abright polish. In
a vertical section of the second premolar the calcigerous tubes radiate
from the pulp-cavity, passing from its summit into the crown in
almost straight lines, and with a flexuous course from its sides: the
strongest curve is at their commencement, but it is short, and they
then proceed straight towards the enamel, with a few dichotomous
acute-angled divisions, the terminal third part of the thus divided
tubes bending gently from the grinding surface in curves which di-
verge slightly from the centre of each tubercle ; the ultimate divisions
at the outer surface of the dentine are extremely numerous, fine,
and plexiform. The diameter of the tubes at the middle straight
part of their course is gmth of an inch, and here they are separated
by interspaces equal in diameter to the breadth of nearly two tubes:
they gradually diminish as they approach the enamel. Fine ramuli
are sent off from the sides of the main-tubes, which curve across
the interspaces, and are mostly lost in the compartments of the
basal substance.

The dusky yellow-coloured osteo-dentine, into which sub-
stance the pulp is finally converted, presents a much more flexuous
arrangement of dentinal tubes, the ramuli of which not unfrequently
dilate into angular calcigerous cells ; these in the osteo-dentine of the
base of the teeth are numerous, and present in some parts a con-
centric arrangement.

558 UNGULATES.

The enamel-fibres are smaller than those of the teeth of the
Carnivora: and the cement is much thicker upon the roots of the
teeth of the Hog, and can be more readily traced over the enamelled
crown, especially in hollows of the irregular grinding surface, and
upon those parts of the dentine of the tusks which are not covered
by enamel. Here, and upon the roots of the teeth, the Purkingian
cells were developed, and of a full oval figure, about =th of an
inch in long diameter: the cemental tubuli, communicating with
these cells on the one hand, and with the terminal plexuses of the
dentinal tubuli on the other, traverse the thicker layers of cement
in horizontal and parallel directions, resembling in this respect the
dentinal tubes.

The complex molar of the Phacochere yields a beautiful demon-
stration of the microscopic characters of the several tissues of a
tooth.

The dentine, as we have seen, is broken up into detached, long,
and slender prisms. In a longitudinal section of one of these
denticles, the calcigerous tubes ascend vertically through the central
third part of the prism, and in the lateral parts gently diverge
or bend away towards the periphery; and when they are close to
the enamel increase their outward curve and the width of their
clear interspaces, bifurcating there once or twice : several of the
terminal branches dilate into opake cells close to the enamel; the
secondary undulations of the tubes are minute but well marked,
especially in the ends of the tubes. One or two medullary canals,
with a thin coat of osteo-dentine, extend along the centre of the
prism. In transverse sections the ends of the tubes, cut across,
occupy all but the marginal part: they rarely shew interspaces
wider than the breadth of a tube, and are in some places even closer
together. The peripheral terminations of the tubes, appear to
be more strongly bent than when seen in longitudinal sections.
The tubes are smaller, more numerous, and send off much fewer
lateral ramuli than in the dentition of the Horse.

In the middle part of the transverse section the dentinal oil
are sub-elliptic, with a clear outline, and include about twenty
of the dentinal tubes ; towards the periphery they are indicated by

HOG-TRIBE. 559

slightly curved lines, with the feeble convexity turned towards the
periphery.

In the middle of the transverse section of the dentinal prism,
a narrow tract of osteo-dentine is seen surrounding the area of
the central vascular canal: it is characterized by its more trans-
parent texture ; its fewer and more contorted tubuli, and the minute
opake cellules dispersed through it. The clear substance is arranged
in concentric layers around the canal, and the outer boundary
of this small sub-circular patch of osteo-dentine is very well defined
from the true dentine: the central ends of the tubes of this
tissue are closely crowded round the clear boundary of the osteo-
dentine, but a very few are traceable into that substance.

The enamel-fibres, as exposed by a vertical section of the
complex tooth, extend obliquely upwards and outwards in a straight
line, for the first half of their course, then bend outwards to the
periphery of the enamel, which is very irregular. The transverse
section of the cylinder of enamel displays a strong wavy, or crenate
outline: the rounded lobes which project into the cement being
of nearly equal breadth with the intervening notches. The contour-
lines of the enamel are well shown in this section, and alter their
course from the parallel of the even margin of the dentine to
that of the crenate outer margin of the enamel.

A very small outer part of the exterior cement of the molar
is nearly clear, with the fine cemental tubes penetrating the substance
at right angles to the surface. A thick and densely aggregated
stratum of Purkingian cells, mostly of a full oval figure, are next
seen, these cells being rather less thickly arranged in the middle
of the cement. The vascuar canals of the cement are chiefly
present near the enamel; some were seen forming loops turned
towards the outer surface of the cement.

200. Cheropotamide.—The dental formula of the Peccari
(Dicotyles,) is :—

ici RED ; il 1 3—3 ] ans 38
ncisors Ra canines ely premolars reat molars 2s thee e

The two middle upper incisors are the largest, and are thick,
short, curved and convergent, as in the Hog. The external surface

560 UNGULATES.

of the crown has two lateral ridges; the internal surface presents a
strong basal ridge. The margins of the crowns of the lateral incisors
are notched. In the lower jaw the incisors are long, narrow, and
procumbent; similar in form, as well as position, to those in
the Hog.

The upper canines have moderately long, narrow, compressed,
two-edged, straight, descending crowns, with an entire covering
of enamel; the fang has a longitudinal groove on both the outer
and inner surface ; the socket is strengthened by an anterior semi-
lunar ridge. The canine is separated from both incisors and molars
by an interspace of nearly an inch, both before and behind it.
The three premolars are contiguous, and gradually increase in size ;
their crowns are more or less triangular: each has two outer cusps
and one inner cusp, with an accessory tubercle behind the inner
one, which progressively increases in the second and third premolar.
The true molars are quadricuspid, with an accessory tubercle at
the fore part of the interspace of each transverse pair of cusps,
and with an anterior and posterior crenate ridge. There is a slight
increase in the size, and in the development of the accessory ridges
of the grinding surface in the second and the last molars.

The lower canines have a long, slightly curved, and trihedral crown;
the narrow posterior side having no enamel, and playing upon the
anterior margin of the upper canine, which thus becomes blunted
and deprived of enamel. The first premolar has one blunt tubercle,
the second has two: both have also anterior and posterior ridges,
the latter being developed in the third premolar into a second pair
of tubercles. The true molars of the lower jaw are quadri-cuspid,
with an accessory tubercle at the posterior interspace of each
transverse pair of cusps, the second of which is developed into a
small third lobe in the last molar tooth. . Each true molar has also
an anterior basal ridge.

This type of dentition was closely adhered to, or rather fore-
showed, by some very interesting forms of ancient extinct Pachy-
derms, amongst which, remains of the following genera have been
found in the oldest tertiary deposits in England and on the
Continent.

HOG-TRIBE. 561

201. Hyracotherium.(1)—In the Hyracotherium leporinum, an animal
about half the size of the Peccari, the upper canines were compressed
and directed downwards: the typical number of premolars, (which
probably are transitorily represented in the Peccari) was here constant,
the first of the four being situated near the middle of the diastema
between the canine and the second premolar; like the latter it
had a simple subcompressed short conical crown with an anterior
and posterior basal talon and two fangs. The third and fourth
premolars suddenly assume an increased size and complication
of crown, resembling the two last premolars in the Peccari: they
present one internal and two external cusps, with two inter-
mediate smaller tubercles, and a cingulum or basal ridge almost
surrounding the entire crown. Each true molar (Pl. 140, fig. 6)
has the four principal and the two accessory cusps, as in
the Peccari, but the anterior and posterior basal ridges are
united by internal and external ones so as to form a cingulum, and
the last molar is not longer, and is narrower posteriorly, than the
penultimate one: no vestige now remaining of the characteristic
predominance of size of the last molar in the typical Suide. Each
principal cusp of the molars in the specimen described by me had
its summit worn into a little pit. The dentition of the lower jaw
and the incisive formula of the Hyracotherium are as yet unknown.

202. Cheropotamus.—The Cheropotamus Cuvieri(2) was about one
third larger than the Peccari, and deviated further than the Hyraco-
there in a direction towards the Hippopotamus. All the premolars
were more simple in comparison with the true molars; the last
premolars had each an external large and an internal low and small
tubercle, both inclosed by the cingulum. The true molars are each
like two premolars combined, and with the inner tubercles developed
to equality with the outer ones; they have also the two small
intermediate tubercles and a well-developed cingulum (Pl. 140,
fig. 5): the last upper molar resembles that of the Hyracothere in
form and proportions. In the lower jaw the canine had much of the
form and proportions of that of a Carnivore. There are three

(1) Geological Transactions, 2d Series, Vol. v1, p. 203, Pl. 21.
(2) Geological Transactions, 2d Series, Vol. vi. p. 41, Pl. 4.

rs
562 UNGULATES.

premolars in this jaw, the first with a compressed pointed crown
and a small posterior talon, like that above; the second and third
increasing in breadth, but narrower and more simple than those
above. The true molars below are also narrower than the upper
ones, but are quadricuspid with accessory tubercles, and a largely
developed hinder talon in the last molar. Nothing as yet is known
of the incisors of the Cheropotamus ; the rest of the dentition
closely resembles that of the Peccari, but the premolars are more
simple and the canines by their size, shape, and direction, and
the lower jaw by the backward prolongation of its angle, alike
manifest a marked approximation to the Ferine type. The occasional
carnivorous propensities of the common Hog are well known, and
they correspond with the minor degree of resemblance, which this
existing Pachyderm presents to the same type. The extinct
Cheropotamus, still better adapted by its dentition for predacious
habits, presents an interesting example of one of those links,
completing the chain of affinities, which the revolutions of the
earth’s surface have interrupted, as it were, and for a time
concealed from our view. .

203. Hippohyus.—In this extinct genus of quadrupeds from the
Himalayan tertiary deposits, the dental formula shows incisors
3 and corresponds with that of the Cheropotamus in the number
of canines, premolars, and molars ; but the true molars have a more
complex crown, approaching nearer to those of the typical Suide¢ in
the depth and number of the secondary enamel-folds. Each upper true
molar (Pl. 140, fig. 7) has its crown cleft by the common or primary
crucial valleys, the transverse one passing somewhat obliquely from
within forwards and outwards. Each of the four principal lobes is
subdivided, not by a vertical central depression, but by a fold
penetrating its anterior and posterior margins: the enamel at first
shows additional minor plications ; but is worn down progressively to
the simpler pattern above described; the outer lobes are convex
externally. The first premolar is very small and simple, separated
by an interval of its own breadth from the second: both this and
the third have transversely compressed crowns, the fourth has a
sub-trihedral crown. The Hippohyus equalled in size the Cheropo-

ied

HIPPOPOTAMUS. 563

tamus ; but exhibits as strong a tendency towards the Hippopotamoid
family as that does towards the plantigrade Carnwora.

HIPPOPOTAMID.

204. Hippopotamus.—The tendency to excessive and, as it may be
termed, monstrous development, which characterises the canine teeth
in the typical Suide affects both these and the incisors in the present
remarkable family, of which the Hippopotamus of the great rivers of
Africa is now the sole existing representative. Figure 4 in Pl. 141
gives an oblique view of the formidable apparatus of variously
directed prominent incisive and canine tusks in this animal. The
upper incisors, two in each intermaxillary bone, curve downwards
and oppose their extremities to the sides or upper surface of
the straight and porrect incisors, also four in number, in the lower
jaw ; and they thus repeat in their relative position the characters
of the upper and lower incisors of the Suide. The mid-incisor above
_ @1)is subcylindrical, slightly curved, with the apex obliquely abraded
along the inner side: the outer incisors (i 2) are placed behind and
to the outer side of the median pair, are more curved, and oppose
themselves more directly to the outer pair below.

The two median inferior incisive tusks are cylindrical, of great
size and length, obliquely abraded at the upper and outer part of their
extremity: the basal portion which is lodged in the deep alveolus is
longitudinally grooved : the two outer incisors are likewise cylindrical
and straight, are much smaller and are worn towards the inner side of
their point. The upper canines (c) curve downwards and outwards,
their exposed part is very short and is worn obliquely at the fore
part, from above downwards and backwards; they are three-sided,
with a wide and deep longitudinal groove behind. The lower
canines (c) are extremely massive and large, curved in the arc of a
circle, subtrihedral, the angle rounded off between the two anterior
sides, which are convex and thickly enamelled, the posterior side
of the crown being almost wholly occupied by the oblique abraded
surface opposed to that on the upper canine.

The implanted base of each of these incisive and canine teeth
is simple and excavated for a large persistent matrix contributing to

002

564 UNGULATES.

their perennial growth by constantly reproducing the matter to replace
the abraded extremities. The direction of the abraded surfaces is
in part provided for by the partial disposition of the enamel: in the
upper median incisor this is laid upon the fore and outer part of
the tooth: in the lateral incisor there is a narrow strip of enamel
along the convex side of the tooth. The enamel is soon entirely
worn away from the crowns of the lower incisors ; but it is per-
sistent in the canines, where it extends to the end of the implanted
base; in the upper canine being laid upon the posterior and outer,
and not on the fore part, whilst its position is reversed upon the
inferior canine. The grooves and ridges upon the enamel of this
tusk are strongly developed: most of them are longitudinal, but the
prominent anterior part of the outer surface is traversed by a series
of oblique ridges; and strongly marked transverse grooves and
ridges cross the tusk at irregular distances, apparently indicating
epochs of the eruption of the tusk.

The molar series consists of p. (4, m. $3, = 28.(1) The first
premolar has a simple subcompressed conical crown and a single
root: it rises early, and at some distance in advance of the second
premolar, and is soon shed, the other premolars form a continuous
series with the true molars in the existing species ; but in the extinct
Hippopotamus "major, whose remains are found in the superficial
deposits of this island and on the continent, the second premolar is
in advance of the third by an interval equal to its own breadth. This
and the fourth premolar retain the simple conical form but with
increased size, and are impressed by one or two longitudinal grooves
on the outer surface, which when the crown is. much worn give a
lobate character to the grinding surface: there is a strong tuberculate
ridge on the inner and hinder part of the base of the crown, and in
the anterior premolars the ridge on the fore and back part of the
cone, extending to the summit of the crown is notched or
tuberculate near its base. In the premolars of apparently the
Hippopotamus minor figured in the work of Scilla ‘De Corporibus

(1) M. Fr. Cuvier assigns ‘ fausses- molaires 3, molaires $, to the genus Hippopotamus
in the ‘Dents des Mammiféres’ p. 206; but the first molar was shed and the last deciduous
molar was not shed in the lower jaw of the specimen which he figures and describes, whence
the mistake.

[IILPPOPOTAMUS. 565

marinis,’ tab. xii, fig. 1, (1747) the notches extend to the summits of
these ridges. I have given an original figure (Pl. 142, fig. 3) of one
of these problematical teeth, from the specimen which now forms
part of the Woodwardian Collection at Cambridge, by the kind
permission of the eloquent Professor of Geology in that University ;
the anterior border is not so regularly notched as in Scilla’s figure ;
and the two fangs shew the moderate proportions of those of the
premolars of the Hippopotamus, and by no means the ventricose
character of the roots of the teeth of a seal, to which family of
Carnivora this ancient fossil has been referred (2).

The true molars are primarily divided into two lobes or cones
by a wide transverse valley, and each lobe is subdivided by a narrow
antero-posterior cleft into two half cones, with their flat sides next
each other ; the convex side of each half cone is indented by two
angular vertical notches, bounding a strong intermediate prominence,
the analogue of that which rises out of the outer depression of the
Ruminant’s molar (Pl. 134, fig. 3, 0 0): a strong ridge bounds the
fore and the back part of the base of the crown and extends
completely round the last upper molar. A view of the unworn
summits of the crown of a true molar of the Hippopotamus is given
in Pl. 143, fig. 3. When these summits begin to be abraded each
lobe or pair of demi-cones presents a double trefoil of enamel on the
grinding surface: when attrition has proceeded to the base of the
half cones, then the grinding surface of each lobe presents a
quadrilobate figure, as shown in Pl. 143, fig. 4. The crown of the
last molar tooth of the lower jaw is lengthened out by a fifth cone,
developed behind the two normal pairs of half cones, and smaller
in all its dimensions. The enamel on all the molars of the
Hippopotamus is thick and has a wrinkled and punctate exterior.
The three last persistent premolars have each two fangs in both jaws.
The true molars have four fangs, except the last below, which has five.

Extinct Hippopotamide.—The fossil Hippopotamus major adheres
closely to the type of the dentition of the existing species, the most
marked distinction being the diastema between the second (first per-

(2) It is the Phoca dubia melitensis of M. de Blainyille, ‘ Ostéographie de Phoca, 4to. p. 46;
apparently on the authority of M. Agassiz, p. 44.

566 UNGULATES.

sistent) and third premolars. The smaller extinct species (Hippopotamus
minor) has the same close resemblance in its dentition, and though
much reduced in size, yet in both the number (four) and the
cylindrical form of the procumbent lower incisors, it adheres to the
typical dentition of the Hippopotamus.

205. Hexaprotodon.—The fossil Hippopotamus of the Sewalik
tertiary beds, had the same number of incisors as the Hog, viz:
six in both jaws, or =3: those below are more equal in size than
they are in the Hippopotamus, the median being rather less than
the two outer incisors ; they are all more oblique in position and
the abraded surface is more confined to the extremity. The lower
tusks are relatively shorter (Pl. 143, fig. 1,c¢). The first premolar
(p. 1) is retained longer than in the Hippopotamus: the second
(p 2) is removed from the third as in the European fossil Hippo-
potamus, but is relatively thicker ; the second and third deciduous
molars are retained in the specimen figured. The form of the true
molars, and the pattern of their grinding surface resemble those in
the true Hippopotamus.

206. Merycopotamus(1).—In the true molars of the Merycopotamus
(Pl. 140, fig. 8) the inner demi-cones, i 7, are simply convex, and the
two grooves on the outer ones form a deep external depression, at the
bottom of which is the convex ridge, 0 0: the antero-posterior cleft
dividing the primary lobes, instead of being straight as in the Hippo-
potamus, forms two bends convex inwards, and thus the symmetrical
pattern of the Hippopotamic molar is converted into the double-cres-
centic one of the Ruminant molar. The cement at the bottom of the
valleys is thinner than in the Ruminants, the enamel is as rugose
as in the Giraffe or Sivathere; but the strong rugged ridge along
the inner half of the base of the crown forms the chief distinction
between the molars of the Merycopotamus and those of the Ruminant.
The teeth in the lower jaw make a similar approximation to the
Ruminant type, but the anterior and posterior primary divisicns
are separated by a wider cleft; the last molar has a third hinder
lobe, the lower molars are implanted by two roots. The forms,

(1) This genus, together with Hexaprotodon, was discovered in the sub-himalayan tertiary
deposits and determined by Capt. Cautley and Dr. Falconer.

HIPPOPOTAMUS. 567

proportions, and relative position of the canines and incisors of the
Merycopotamus closely accord with the Hippopotamic type of these teeth.

207. Anthracotherium.—In this genus although the molars, espe-
cially those of the lower jaw, depart from the Hippopotamic type less
than the molars of the Merycopotamus, yet the canines and incisors
retain more of the ordinary forms and proportions of those teeth in
other Pachyderms: the canines, for example, though large are simply
conical, the premolars have strong conical crowns with a basal
ridge ; the upper true molars have four principal cones, and a basal
cingulum, the two outer cones encroach upon the two inner ones,
and manifest, like those of Merycopotamus, an approximation to the
Ruminant type.(1) In the lower jaw, the cones are more equal
and symmetrical: the last molar, of which a reduced view is given
in Pl. 135, fig. 10, has four distinct cones, and a large and slightly
bifid posterior lobe: the surfaces of the four chief cones which are
turned towards each other are somewhat angular and _ support
projecting ridges, the opposite surfaces are simply convex. The
entire dentition of the Anthracotherium is not yet known, but
sufficiently so to prove that this extinct genus formed, with the
closely allied Merycopotamus, links connecting the Hippopotamide
with the Ruminantia,

208. Microscopic Structure —The dentine is hard and unvascular in
all the teeth of the Hippopotamus, and the sections of this compact
substance take a fine polish: the dentinal cells are very conspicuous
in the deciduous teeth, in an incisor of the first dentition they are
subhexagonal, about jj th inch in diameter, arranged in layers
parallel with the outer surface of the dentine and are pierced by the
dentinal tubes which proceed at right angles to that surface; about
twelve tubes are included in the area of a single cell. There is no
peculiarity in the size, course, division, branching or termination of
the dentinal tubes of the molars of the Hippopotamus. ‘The
calcigerous tubes of the dentine of the tusks are smaller, their
diameter does not exceed ,3,,th of an inch, and their intervals not
more than g,th of an inch. They radiate from the pulp-cavity to
the periphery of the tusk, inclined obliquely towards its extremity,
_ and describe numerous subspiral curves, or waves succeeding each

(1) See Cuvier, Ossemens Fossiles, tom. iii, pl. Ixxx. fig. 1.

558 UNGULATES.

other at equal distances of about ;,th of an inch, throughout their
whole course, the waves of adjoining tubes being parallel along
planes which are parallel with the outer conical surface of the
exposed end of the tusk before it is worn. LEach bend of the tube
appears to equal the thickness of the layers into which the dentine
of the tusk is resolved in decomposition, and which form the fine
concentric lines upon the cut or broken transverse sections of the
ivory. The tubes gradually diminish in size as they approach the
periphery of the dentine; they give off minute branches; and in
some places these dilate into very minute corpuscles, along the lines
of the concentric rings of the transverse sections, and the contour
lines of the longitudinal sections of the tusk.

The dentinal tubes at their commencement from the pulp-cavity
of the molar teeth give a diameter of ,sth of an inch; and their
dichotomous bifurcations are more conspicuous than in the tusks.

The fibres of the enamel of the tusk have the usual disposition
vertical to the plane of the dentine, but are little curved, and have
no transverse striz ; most of these fibres are hexagonal and extend
through the entire thickness of the enamel: near the base of the
tusk they may be detached singly or separately from the part where
they had been last laid on. In the thicker enamel of the molars
the fibres are more wavy in their course, and I could perceive none
that extended through the entire thickness of the section; but new
ones every where arise by small ends wedged into the intervals of
those next the dentine, the larger ends of the fibres being always
towards the periphery. The cement which covers thickly those
parts of the incisive and canine tusks which are bare of enamel,
also extends in a very thin layer upon that substance, from which
it is soon worn in the teeth in use. The coronal cement of the
molar teeth forms a thicker layer, especially in the angles of the
folds, but it is by no means so abundant as in the teeth of the corres-
ponding folds of the molar teeth of the Ruminants.

In the parts of the crown where the cement is thickest, and
upon the fangs, a few vascular canals are present: the radiated
cells are most numerous at the periphery of the cement, generally
affecting an oval form, arranged in concentric layers, with the
long axis in the direction of the layer, these layers being crossed

HIPPOPOTAMUS. 569

00
the branches of which anastomose freely with the tubes radiating
from the cells.

The osteo-dentine forms a pretty thick layer in the centre of
the lobes of the crown, and of the fangs of old molars. The tortuosity
of the fine tubes inthis substance is extreme and they are very
irregular.

In the ordinary-sized tusks the fine-tubed dentine, which forms
the concentric-lined ivory, continues with little or no alteration of
texture from the periphery to the pulp-cavity: but in very large
and old tusks the apex of that cavity contains osteo-dentine, and
this tissue is abundantly developed when the normal function of the
dentinal pulp is disturbed by injury or disease. I have been favoured
by Dr. Malcolmson, with a very remarkable example, in the inferior
canine tusk of the Hippopotamus (Pl. 142, figs. 1 & 2), of the
subserviency of the osteo-dentine in the reparation of a complete
fracture. The injury was indicated externally by a sudden trans-
verse constriction of the tusk at xx, with an interruption in the
enamel at that part, and irregular deposits of dentine both there
and at the adjoining concavity of the tusk. A longitudinal section
of the tusk showed the pulp-cavity obliterated at the fractured
part and for some distance below it, towards the base of the tusk,
by a mass of osteo-dentine, deposited principally in the form of
nodules closely impacted together, their convex sides projecting
into the re-established pulp-cavity next the base: the general dispo-
sition of the osteo-dentine being very like that in the centre of the
tooth of the Cachalot. The remains of the pulp-cavity in the pro-
truded part or crown of the tusk were unusually conspicuous in the
form of a narrow canal near the concave side of the tusk, and
opening, like a fistula, upon that surface just beyond the fracture,
another irregular slender canal extended transversely through part
of the uniting substance and opened upon the concave side of the
tusk, just below the preceding. From these appearances it may be
concluded that the tusk, either by the action of a shot, or other
- violence, had been snapped across its implanted and hollow base
with probably also fracture and injury to the prominent socket ;
but that the broken portions being held together by their adhesion

by sub-parallel cemental tubuli, about 3,th of an inch in diameter,

570 UNGULATES.

to the surrounding parts, inflammation of the pulp and capsule
had ensued, ending in an altered mode of action in the calcifying
processes, which produced the substance, called from its nearer
resemblance to bone ‘ osteo-dentine.’ In this substance is seen the
transition of the normal dentinal tubes into the radiating tubes of
the calcigerous cell ; and a well-marked stage in the transformation
of dentine into bone. In ordinary teeth the change in the mode
of conversion of the last part of the pulp is sometimes so gradual as
to render the confluence of the dentine with the osteo-dentine com-
plete ; and the present instance demonstrates the same confluence of
the osteo-dentine with the ivory of the upper part of the tusk
formed before the fracture, and with that at the base formed after
the fracture, when the ordinary processes in the development of
the tusk had been resumed. In the complete resumption of these
processes, after the entire conversion of the matrix at the fractured
part of the tusk into the mass of osteo-dentine which constitutes
the uniting medium, we have a striking example of the truth of
the conversion-theory of dental development. It will scarcely be
contended that the calcified substance which manifests, besides the
complex tortuous tubuli, numerous concentric series of radiated
purkingian cells, and the larger vascular or medullary canals, called
‘ Haversian,’ in osteology, is the product of a disordered secretion
of a pulp inflamed by injury; we see, on the contrary, evidence of
the conversion of such altered pulp by a series of centripetal
processes of calcification, resulting in the aggregate of subspherical
nodules of the osteo-dentine. Now, if the pulp of a continually
growing tusk were a persistent secreting organ, an accident
occasioning such destruction of it as is manifested by the microscopic
structure of the mass uniting the fractured parts of the Hippopo-
tamus’s tooth under consideration, must have put an end to the
secreting actions of such matrix, and to the future formation of the
tusk. But here, on the contrary, it is shown that the inflammatory
effects of the injury terminated in the abnormal conversion of the
affected pulp into a bone-like substance, and yet that the subsequent
development of the tusk was effected by the reproduction of a
vascular basis or pulp, undergoing the ordinary processes of calcifica-
tion to which the formation of the dentine, enamel and cement is due.

HIPPOPOTAMUS. 571

209. Succession.—The true natural affinities of the Hippopotamus
are clearly manifested by the character of its deciduous dentition ;
and, if this be compared with the same dentition in other Ungulata,
it will be seen, by its close correspondence with that of the Hog-
tribe, and more especially with the Phacochere, that the Hippo-
potamus is essentially a gigantic Hog. The formula of the teeth

which are shed and replaced is :

2-2 1—l 3-3
——; ¢.—; m—: = 24.
2—2 1-1 3-3

If the simple premolar which is developed anterior to the deciduous
molars, and which has no successor, be regarded from its early
loss in the existing Hippopotamus, as the first of the deciduous
series, we must then reckon, with Cuvier, four milk molars on each
side of both jaws. The incisors in both jaws are simply conical
and subequal, with an entire cap of enamel on the crown. The
deciduous canines scarcely surpass them in size in the upper jaw,
and not at all in the lower; projecting forwards here, from the angles
of the broad and straight symphysis, they appear like an additional
pair of incisors; and we have seen that the character of equality
of development was retained, with the more typical number of in-
cisors, by the ancient form of Hippopotamus which formerly inhabited
India. The first true deciduous molar (d 1) has a conical crown
and two fangs in both jaws: that above has also a conical crown
with one strong posterior and two anterior ridges. The second
deciduous molar has a large trilobate crown, the first lobe small
with an anterior basal ridge; the second large, conical, with three
longitudinal indentations ; the third lobe still longer and cleft into
two half cones by an antero-posterior fissure assuming the normal
pattern of the true molars; the third deciduous molar above more
closely resembles the ordinary upper true molar, but its second pair
of demi-cones is relatively larger. In the lower jaw the last deci-
duous molar has a more complex crown than that of any other tooth,
whether of the permanent or deciduous dentition(]) ; it has three pairs
of demi-cones, progressively increasing in size, from before back-
wards, with an anterior and posterior basal ridge and tubercles:

t.

(1) This tooth is described as the first.of the four true molars by M. F. Cuvier, loc. cit.
p- 207; but its true nature was recognised by Baron Cuvier, see ‘Ossemens Fossiles,’ 4to., i.
p- 289

572 UNGULATES.

like the last trilobate deciduous lower molar of the Hog it increases
in thickness posteriorly, instead of diminishing here like the last
true molar of the lower Jaw of the adult Hippopotamus.

ANISODACTYLE PACHYDERMS.

210. Equide.—The Horse will yield us the first example of the
dentition of the hoofed quadrupeds with toes in uneven number,
because it offers in this part of its organisation some transitional
features between the dental characters of the typical members of
the Isodactyle and of those of the Anisodactyle Ungulata.

All the kinds of teeth are retained and in almost normal
numbers in both jaws, with as little unequal or excessive develop-
ment as in the Anoplothere; but the prolongation of the slender
jaws carries the canines and incisors to some distance from the
molars, and creates a long diastema, as in the Ruminants and Tapirs.
The first deciduous molar is very minute, and is not succeeded, as
in the Anoplothere, by a permanent premolar; yet remaining longer
in place than the larger deciduous molars behind, it represents
the first premolar and completes the typical number of that division
of the grinding series. If the dental formula of the genus Equus
be restricted to the functionally developed permanent teeth, it
will be : :

- 3—3 ° 1-1 3—3 =
Incisors —; canines —; premolars —; molars —: = 40.
3-3 1—1 3—3 3—3

The incisors are arranged close together in the arc of a circle
at the extremity of both jaws; they are slightly curved, with long
simple subtrihedral fangs, tapering to their extremity. The crowns
are broad, thick and short, the contour of the biting surface, before it
is much worn, approaches an ellipse. These teeth, if found detached,
recent or fossil, are distinguishable from those of the Ruminants by
their greater curvature, and from those of all other animals by the fold
of enamel, (Pl. 136, fig. 11, a) which penetrates the body of the crown
from its broad flat summit, like the inverted finger of a glove. When
the tooth begins to be worn, the fold forms an island of enamel,
inclosing a cavity (a, figs. 8 & 9) partly filled by cement, and partly
by the discoloured substances of the food, and is called the ‘ mark.’
In aged Horses the incisors are worn down below the extent of the
fold, (fig. 11, @) and the ‘mark’ disappears. The cavity is usually

HORSE. 573

obliterated in the first or mid-incisors at the sixth year, in the second
incisors at the seventh year, and in the third or outer incisors at the
eighth year, in the lower jaw. It remains longer in those of the upper
jaw, and in both the place of the mark continues for some years to be
indicated by the dark coloured cement, as in the incisors (fig. 10) of
a Horse about sixteen years old. At this period the worn summits
of the incisors present a subtriangular form.

The canines (figs. 9 & 10 c) are small in the Horse and rudi-
mental in the Mare ; the unworn crown is remarkable for the folding in
of the anterior and posterior margins of enamel, which here includes an
extremely thin layer of dentine. The upper canine is situated in
the middle of the long interspace between the incisors and molars ;
the lower canine is close to the outer incisor as in the Ruminants,
but is better distinguished by its cuspidate form. The representative
of the first premolar (figs. 1 & 6, p, 1) is a very small and simple
rudiment, and is soon shed. The three normal premolars (p 2,3 & 4)
are as large and complex as the true molars; the anterior one,
(p 2) is usually the largest of the series in the upper jaw, the anterior
lobe extending forwards into an obtuse angle.

The upper molar teeth of the Horse present a modification
of the complex structure intermediate between the Anoplotherian
and Ruminant patterns. The crown is cubical, impressed on the
outer surface by two wide and deep longitudinal channels, penetrated
from within by a valley 6 entering obliquely from behind forwards
and dividing into, or crossed by the two crescentic valleys c & e,
which soon became insulated as in the Camel; but a large internal
lobe (p), at the end of the valley 6, presents more of the Anoplo-
therian proportions than is shown by any Ruminant; it is also at
first distinct, as in p 4, and though it soon becomes confluent with
the anterior lobe in the existing species of Horse, it continued
distinct much longer, and with more of the conical or columnar
form in the primigenial Horse (Hippotherium, fig. 3, p) of the
miocene tertiary period.

The molar teeth of the Horse have also, Cuvier remarks, a
closer analogy with those of the Rhinoceros than might at first be
supposed. The anterior crescentic enamel island (e) represents the
termination of the principal valley (6), which is cut off by a bridge

574 UNGULATES.

of dentine analogous to that in the leptorhine Rhinoceros (PI. 138,
fig. 7). The posterior crescentic enamel island (c) is a further
development of the fold (c) in the Rhinoceros’ molar, but is much
earlier insulated in the Horse. :

In the lower jaw the same analogies may be traced: the teeth
here, as is usual in other quadrupeds, are narrower transversely
than in the upper jaw; they are divided externally into two convex
lobes (Pl. 136, fig. 2,m 1, 0 0) by a median longitudinal fissure,
and on the inner side they present three principal unequal convex
ridges, and an anterior and posterior narrower ridge; but the
crown of the molar is penetrated from the inner side by deeper and
more complex folds than in the Anoplothere and still more so than
in the Rhinoceros or Palzothere. The anterior valley between the
narrow ridge and first principal internal column expands into a
sub-crescentic fold: the second is a short simple fold and terminates
opposite that which penetrates the tooth from the outer side: the
third inner fold expands in the posterior lobe of the tooth like the
first ; two short folds partially detach a small accessory lobe at the
posterior part of the crown. All the valleys, fissures or folds in both
upper and lower molar teeth, are lined by enamel, which also coats
the whole exterior surface of the crown.

The character by which the Horse’s molars may best be dis-
tinguished from the teeth of other Herbivora corresponding with
them in size, is the great length of the tooth before it divides
into fangs. This division, indeed, does not begin to take place
until much of the crown has been worn away; and thus, except
in old Horses, a considerable proportion of the whole of the molar
is implanted in the socket by an undivided base. This is slightly
curved in the upper molars, the outer side of the bases of which is
shown in Pl. 136, fig. 5, the inner side in fig. 6. The deciduous
molars have shorter bodies and sooner begin to develope roots, as
in fig. 5, d2, 3 & 4; but in these, or in an old permanent molar
with roots, the pattern of the grinding surface, as it is shewn in
figs. 1 & 2, though it be a little changed by partial obliteration of
the enamel folds, yet generally retains as much of its character as
to serve, with the form of the tooth, to distinguish such tooth
from the rooted molar of a Ruminant.

HORSE. 575

Cuvier(1) was unable from the materials at his command to
detect any characters in the bones or teeth of the different existing
species of Hquus or in the fossil remains of the same genus, by
which he could distinguish them, save by their difference of size.
Amongst the numerous teeth of a species of Equus, as large asa
horse fourteen hands and a half high, collected from the Oreston
cavernous fissures, I have found specimens clearly indicating two
distinct species, so far as specific differences may be founded on
well-marked modifications of the teeth.

One of these, like the ordinary Equus fossilis of the drift and
pleistocene formations, differs from the existing Equus caballus by
the minor transverse diameter of the molar teeth ; the other, in the
more complex and elegant plication of the enamel, and in the
bilobed posterior termination of the grinding surface of the last upper
molar more closely approximates to the extinct Horse of the miocene
period, which H. v. Meyer has characterised under the name of
the Equus caballus primigenius. The Oreston fossil teeth differ,
however, from this in the form of the fifth or internal prism of
dentine in the upper molars, and in its continuation with the anterior
lobe of the tooth ; the fifth prism p being oval and insulated in the
Equus primigenius of v. Meyer, (Hippothertum, Kaup. Pl. 136, fig. 3).

The Oreston fossil molar teeth, which in their principal
characters manifest so close a relationship with the miocene Equus
prumgenius, differ, like the later drift species (Hq. fossilis), from the
recent Horse in a greater proportional antero-posterior diameter of
the crown and also in a less produced anterior angle of the first
molar. J have named this ancient British fossil Horse Equus
plicidens(2). The fossil Horse (Equus curvidens) of South America
which coexisted with the Megatherium and, like it, became extinct
apparently before the introduction of the Human Race, differs from
the existing Horse by the greater degree of curvature of the upper
molars.(3).

(1) ‘Ossemens Fossiles,’ 4to. 1822, tom. 11. pt. i, p. 111.

(2) * History of Brit. Fossil Mammalia, 8vo. p. 392.

(3) See ‘Catalogue of Fossil Mammalia in the Museum of the Royal College of Surgeons,’
4to. p. 235. .

576 UNGULATES.

211. Microscopic Structure.—The body of the long molar teeth of
the Horse consists of columns of fine-tubed unvascular dentine
(Pl. 137, a), coated by enamel (6) which descends in deep folds into
the substance of these teeth ; the enamel is covered by cement (c),
thickest in the interspaces of the inflected enamel-folds and upon the
crowns of the moiars, where it is permeated by vascular canals,
thinnest on the crowns of the canines and incisors. At the roots of
these teeth, and on those developed from the worn down molars,
the dentine is immediately invested by cement.

In a vertical section of the incisor, as in Pl. 136, fig. 11, the pulp-
cavity, contracting as it approaches the vertical enamel-fold, divides
near the end of that fold, and extends a little way between it and
the periphery of the incisor, or leaves a few medullary canals and
a modified thin tract of irregularly formed dentine, between the
reflected and the outer coat of enamel but rather nearer the former.
Above this tract, near the summit of the crown, the dentinal tubes
proceed in a nearly vertical direction, with a gentle sigmoid primary
flexure, where they diverge from the perpendicular; lower down
the dentinal tubes diverge in opposite directions, curving from the
remains of the pulp-fissure towards the outer and the inner enamel ;
and are described by Retzius as being bent in the form of the Greek
e(1); but the course of two distinct series of dentinal tubes, and
not that of a single tube is illustrated by this comparison; when the
pulp-cavity becomes single and central, as at the lower half of the
tooth, the tubes diverge to the periphery, with one principal primary
curve, convex towards the crown. Each tube is bent in minute
secondary gyrations to within a short distance of its peripheral
termination, where it is much diminished in size, and is dichoto-
mously branched. The tubes at their commencement from the
upper calcified tracts of the pulp-cavity, which usually retain some
remnants of that vascular receptacle in the form of medullary canals,
are strongly and irregularly flexuous, before they fall into the
ordinary primary curves. Those tubes proceeding towards the inner
reflected fold of enamel, are more vertical than the tubes going
to the periphery.

(1) Loc. cit. p. 27.

HORSE. Bd.

A transverse section of the incisor of a young Horse or Ass
taken across the part marked a in fig. 11, shows a long oval island
of vascular cement in the centre, bounded by a border of enamel,
with an irregular crenate edge next the cement, and an even edge
next the dentine; which is here clearly seen to be divided into an
inner and an outer tract by an irregular series of the vascular canals
continued from the summit of the pulp-cavity, and by the irregularly
tortuous dentinal tubes which, with the canals, indicate the last
converted remnant of the pulp in this part of the crown. The inner
tract of dentine next the island of enamel is well defined, and a
little broader than the section of the enamel itself, and shows the
extremities of the tubes cut transversely across, which tubes, as
before observed, were at this part directed chiefly in the axis of
the incisor towards the working surface of the crown. The tubes
in the outer tract of dentine, inclining more towards the sides of the
tooth, are more obliquely divided and at the ends of the section they
are seen lengthwise elegantly diverging towards the sides of the
section. This tract of dentine is bounded externally by a layer
of enamel, one sixth part thicker than that forming the central
island; and the enamel is coated by an outer layer of cement, of its
own thickness at the sides, but thinning off at the two ends of the
section. The dentinal tubes proceeding from the residuary pulp-
tract make strong and irregular curvatures, diverging to include
the divided arez of the vascular canals, and in the outer layer
at one side of the section, they describe strong zig-zag curves at
the middle of the outer division of the dentine. |

The diameter of the dentinal tubes at their central and larger
ends is pretty regularly, about jth of an inch; at the middle
of their course ~th of an inch ; thence decreasing, and very rapidly
after the terminal bifurcations commence.

The dentinal tubes are separated from one another by intervals
varying between once and twice the thickness of the tubes; in some
parts of the dentine of the incisor they are more closely crowded
together, especially near their origin from the pulp-cavity. The
secondary gyrations of the dentinal tubes describe a curve about 7th
of an inch in length; these subside in the slender terminations

PP

578 UNGULATES.

of the tubes, which bifurcate dichotomously once or twice, and
send off small lateral branches near the enamel. The small lateral
branches are chiefly visible in the peripheral third part of the
tubes, and are sent off at very acute angles, except in the strongly
and irregularly bent origins from the pulp-tract. J have never seen
these small branches of the dentinal tubes terminating in radiated
cells like those of cement and bone, as Retzius describes, (loc. cit.
p. 27), and figures (Tab. V, fig. 3); but the peripheral smallest
branches near the enamel occasionally dilate into corpuscles much
more minute than the radiated cells, as they do in the teeth of
most quadrupeds. The dentine, as seen in a longitudinal section
of the crown of a molar, by a magnifying power of three hundred
linear dimensions is figured at a, Pl. 137. The tubes are here
separated by rather wider interspaces than those of the incisor,
and do not decrease in size so rapidly: the convexity of the terminal
bend of the tubes is turned towards the summit of the crown.

The clear dentinal cells are very. small near the peripheral
part of the dentine in the incisor, but increase in size as they
approach the pulp-cavity: they are of a sub-circular figure, with
bright transparent outlines.

The central cement in the crown of the incisor is permeated
by vascular canals, separated by intervals of from two to three
times their own diameter, directed in the middle of the substance
in the axis of the tooth, but diverging like rays obliquely towards
its periphery: the clear substance forming the walls of the canals
is arranged in concentric layers; the thickness of the wall being
about equal or rather less than the area of the canal. The radiated
cells, generally of a full oval, sometimes of an angular form, are
chiefly dispersed in the interspaces of the vascular canals, and with
their long axis parallel with the plane of the layers of the coats.
The finer system of tubes radiating from the cells, and corresponding
by minute branches from the vascular canals, freely intercom-

municate. In the peripheral cement of the incisors examined by —

me, I found no vascular canals, but only the radiated cells, and
the fine tubuli which I have called ‘ cemental’, and which traverse

the cement at right angles to its plane, and communicate with the ~

HORSE. 579

tubes radiating from the cells. These are more usually elliptical
than in the thicker central cement, their long axis being parallel
with the borders of the cement; they are most abundant next the
enamel and rarely encroach upon the clear peripheral border
of the cement. The exterior coronal cement of the molars (Pl. 137,
c,) is as richly permeated by vascular canals (v) as is the central
cement of the incisor.

The enamel-fibres of the Horse’s incisor are very slender, not
exceeding twice the diameter of the dentinal tubes: they extend
with a gentle sigmoid curve through the entire thickness of the
layer; contiguous fibres curving in opposite directions. The
peripheral border, or that next the cement, is everywhere indented
with hemispherical pits from ;,th to s;th of an inch in diameter,
four to six of the radiated cells of the cement being often clustered
together in the larger depressions. The inner or dentinal border
of enamel is nearly even and straight; here are seen the short
cracks or fissures extending into the enamel. The fibres are rather
more wavy in the thicker enamel of the molar teeth (Pl. 137, 5)

If the enamel is viewed in sufficiently thin sections, it is free
from those wavy dusky markings which are produced by the more
tortuous fibres of the human enamel; and I have been unable to
distinguish any transverse striz in the fine fibres of that tissue in
the Horse: the appearance of such is given by thicker sections of
the enamel-fibres taken obliquely across them, and is produced by
the cut ends of the fibres.

I may here briefly describe a very rare diseased state, which I
have met with in a fossil molar tooth of a large-sized Horse,
from the tertiary formations near Cromer. The tooth, which was
from the lower jaw, with a grinding surface measuring one inch
five lines in long (antero posterior) diameter, and eight lines in
short. (transverse) diameter, presented a swelling of one lobe, near
the base of the implanted part of the tooth. To ascertain the nature
and cause of this enlargement, I divided it transversely, and exposed
a nearly spherical cavity, large enough to contain a pistol-ball, with
a smooth inner surface. The parieties of this cavity, composed
-of dentine and enamel of the natural structure, were from one to
PP 2

580 UNGULATES.

two lines and a half thick and were entire and imperforate. The
water percolating the stratum in which this tooth had lain, had
found access to the cavity through the porous texture of its walls,
and had deposited on its interior a thin ferruginous crust, but the
cavity had evidently been the result of some inflammatory and
ulcerative process in the original formative pulp of the tooth, very
analogous to the disease called ‘spina ventosa’ in bone. I have
given two figures of this singular case of primeval disease in my
‘ History of British Fossil Mammalia.” :

212. Succession.—The practical inducements to pay attention
to the times of cutting and shedding the teeth have operated more
strongly in the case of the Horse than in that of the domestic
Ruminants, and have led to more numerous and persevering re-
searches on the development and succession of the teeth. The

deciduous formula of the genus Equus is :—
3—3 ’ 1—1 4-4

—: 32.

n Rin mm. a8

The second molar (‘first grinder’ of Veterinary Authors, dm,
fig. 4, Pl. 136) is the first to pierce the gum: the white summits of
the ridges of the crown are usually apparent at birth, but sometimes
the gums do not yield until from the second to the fifth day ; the third
molar (‘second grinder’, fig. 5, d 3) rises a day or two later, often
simultaneously with the proceeding: their appearance is speedily
followed by that of the first incisor (‘ centre nipper’, fig. 4, di 1),
which usually cuts the gum between the third and sixth days. The
second incisor (di 2) appears between the twentieth and fortieth
days, and about this time the first small deciduous premolar
(fig. 4, p. 1) takes its place, and the fourth deciduous molar
(‘third grinder’, fig. 5, d 4) also. begins to cut the gum. About
the sixth month the inferior lateral or third incisors, (fig. 4, da 3)
make their appearance together with the small deciduous canine
(fig. 4, dc.) This minute tooth is shed, in the lower jaw at least,
almost as soon as the crown of the contiguous incisor is in full
place, being carried out by the same movement; whence the small
canine had almost escaped notice until Bojanus drew the attention
of veterinary authors to it by his memoir, ‘De dentibus caninis

Se ee ee ee ee ee ee

HORSE. 581

caducis,’ &c.(1) Bojanus never found the lower deciduous canine
retained beyond the first year. The deciduous canine of the upper
jaw, being developed at a short distance behind the incisors, in
the maxillary bone, is less disturbed by the eruption of the outer
incisor, but is neverthess shed in the course of the second year.
The deciduous canines appear from Camper’s observations, to retain
their place longer in the Zebra than in the Horse. (2)

M. Rousseau, who describes the first dentition as being terminated
by the appearance of the lateral incisors, assigns from the seventh to the
tenth month as the period of its completion.(3) The deciduous in-
cisors have thinner and more trenchant, normally-shaped crowns than
those of their permanent successors. The first true permanent molar
(fig. 5, m 1) appears between the eleventh and thirteenth months.
The second true molar (ib. m 2) follows between the fourteenth
and twentieth month. The crowns of the premolars and the last
true molar are now advancing in the closed sockets of reserve,
as shown in Pl. 136, fig. 5. The first premolar (p 2) (essentially
answering, as in the Ruminants, to the second of the Anoplothere),
displaces the second (d 2) and, usually at the same time, the first very
small deciduous molar, at from two years to two years and a half
old. ‘The first permanent incisor (fig. 6, 71) rises above the gum
between two years and a half and three years. At the same period
the second premolar (ib. & fig. 5, p. 3) pushes out the third deci-
duous molar (d 3). The last premolar (ib. p. 4) displaces the last
deciduous molar (ib. d 4) about the completion of the fourth year,
and the appearance above the gum of the last true molar (ib. m 3)
is usually anterior to this. Figure 6 shows the state of the den-
tition about this period, and should the last deciduous molar (d 4)
have been prematurely drawn, the position of the crown of its

(1) Nova Acta Nat. Cur., tom. x11, pt. ii, 1825. p. 697. The tooth which M. Rousseau
figures in his ‘Anatomie Comparée du Systéme Dentaire,’ Pl. xxv, fig. 2, as the “crochet
caduc de lait,” in a Horse about three years old, appears rather to be the small canine of a
Mare. Compare with fig. 8, Pl. 26, of the same work, where no trace of the ‘ crochets caducs,’
appears in a Horse of two years old.

(2) CHuvres de Pierre Camper, Paris, 1805.

(3) The appearance of the third deciduous incisors, or ‘ corner nippers’, completes the
stage of dentition called the ‘colt’s mouth’ by Veterinary Authors.

5&2 UNGULATES.

successor below the level of the second and fourth of the large
grinders, and especially the non-development of the last grinder
will betray the fact that the young Horse has not passed his
third year. The incisors give evidence with which it is still more
difficult to tamper without detection. The first permanent incisor
as above stated, takes its place before the end of the third year;
and should its growth have been accelerated by extraction of its
predecessor the strong ‘mark’ on the third deciduous incisor will
indicate the deception. The second incisor (fig. 6, 2 2) pushes out
its predecessor between three and a half and four years. The
small persistent canine, or ‘tusk’ contrary to the usual rule, next
follows, its development having received no check by the retention
of its rudimental predecessor: its appearance indicates the age of
four years; but it sometimes makes its appearance earlier, rarely
later. The third incisor pushes out the deciduous one about the
fifth year, but is seldom completely in place before the Horse is
five years and a half old.(1) The third premolar is then usually
on a level with the other grinders.

213. Toxodon.—This extinct genus of large pachydermal Quadru-
peds is represented by two species, both equalling the Hippopotamus
in size, whose remains have been discovered by Mr. Darwin and
M. de Angelis in the recent tertiary deposits of South America.
In both, the teeth consist of molars and incisors, separated by a long
diastema, or toothless space. In the upper jaw the molars are
fourteen in number, there being seven on each side; the incisors four,
which differ in their proportions in the two species. In the Toxodon
platensis the outer or second incisor is very large, and the inner one
small, in each intermaxillary bone. In the lower jaw there are six
incisors and twelve molars. .

The general form and nature of the teeth are indicated by the
sockets, and the structure of the grinders is exhibited in a broken
molar, the last in the series on the left side of the skull of the.

Toxodon platensis, discovered by Mr. Darwin; and by another perfect

(1) Upon the rising of the third permanent incisors or ‘ corner nippers’ the ‘ colt’ becomes
a ‘horse’, and the ‘ filly’ a ‘ mare’, in the language of the dealers. For the subsequent changes
in the character of the teeth, see the descriptions of the Plate 136.

TOXODON. 583

molar, the last but one on the right side of the upper jaw. This
tooth is curved, with the convexity turned outwards when lodged in the
socket, contrary to the position*of the superior curved molars in the
Guinea-pig and Wombat. The outer surface of the tooth is traversed
by two slight convex longitudinal risings: the inner side presents,
anteriorly, a slightly concave surface, and posteriorly two prominent
longitudinal convex ridges separated by a deep channel, which is flat
at the bottom: a fold of enamel is continued from the anterior angle
of this channel obliquely forwards half-way across the body of the
tooth. The outer coat of enamel is interrupted at the anterior and
posterior margins of the grinder. The form of the grinding surface of
this molar is shewn in Pl. 86, fig. 4.

All the molar teeth are long and curved, and without fangs, as in
the Wombat and most of the herbivorous species of the Rodent order:
in those, however, with curved grinders, as the Aperea, or Guinea-pig,
the concavity of the upper grinders is directed outward, the fangs of the
teeth of the opposite sides diverging as they ascend in the sockets; but
in the Toxodon the convexity of the upper grinders is outward, as in
the Horse, but with so much greater curvature that the fangs converge
and almost meet at the middle line of the palate, forming a series of
arches, capable of resisting great pressure. It is this structure which
suggested to me the generic term proposed for this most remarkable
extinct Mammal.(1)

Of the upper incisors, the two small ones are situated in the
middle of the front of the intermaxillaries, and the two large ones in
close contiguity with the small incisors, which they greatly exceed in
size. The sockets of the two large incisors extend backwards, in an
arched form, preserving a uniform diameter, as far as the commence-
ment of the alveoli of the molar teeth ; the curve which they describe
is the* segment of a circle; the position, form, and extent of the
sockets are such as are only found in those of the corresponding teeth
of the Rodentia among existing Mammalia. The matrix, or forma-
tive pulp of the large incisors was lodged, as in the Rodentia, in close
contiguity with the sockets of the anterior molars ; and we are enabled
to infer, from the form of the socket, notwithstanding the absence of

(1) Toor, arcus ; ddovs, dens. ‘ Zoology of the Beagle, Fossil Mammalia,’ 4to. 1839, p. 16.

584 UNGULATES. —

the teeth themselves, that the pulp was persistent, and that the grewth
of these incisors, like those of the Rodentia, continued throughout
life. This condition, joined with the curvature of the socket, neces-
sarily implies a constant wearing away of the crown of the tooth, by
attrition against opposing incisors of a corresponding structure in the
lower jaw: and as a corollary, we infer that the teeth in question had
a partial coating of enamel, to produce a cutting edge, and were in
fact, true dentes scalpraru. The number of incisors in the upper jaw
of Toxodon,—four, instead of two—is not without its parallel in the
Rodent order, the genus Lepus being characterized by a similar num-
ber of incisors, and of a similar relative size, but with a different
relative position, the small incisors in the Hare and Rabbit being so
placed immediately behind the large pair, as to receive the appulse of
the single pair of incisors in the lower jaw. Since the sockets of the
small mesial incisors of Toxodon gradually diminish in size as they
penetrate the intermaxillary bones, we may infer that, like ordinary
incisors, their growth was of limited duration, and their lodg-
ment in the jaw effected by a single conical fang. The lower
jaw of the Tozxodon platensis, which was discovered at Bahia
Blanca, in latitude 39°, on the east coast of South America, was
remarkably compressed or narrow from side to side; while the
rami were of considerable depth, in order to give lodgment to the
matrices and bases of grinders enjoying uninterrupted growth. The
pulps of the six incisors of the lower jaw are arranged in a pretty
regular semicircle, whose convexity is downwards; the teeth them-
selves are directed forwards and curved upwards like the inferior
incisors of the Rodentia. These incisors are nearly equal in size:
they are all hollow at their base, and the indurated mineral substance
impacted in their basal cavities well exhibits the form of the vascular
pulps which originally occupied them: they have, likewise, a’ partial
investment of enamel; but though, in this respect, as well as in
the curvature and perpetual growth, they resemble the ‘ dentes
scalpraril,’ of the Rodentia, they differ in having a prismatic figure,
like the inferior incisors of the Sumatran Rhinoceros or the tusks
of the Boar. Two of the sides, viz., those forming the anterior
convex and mesial surfaces of the incisor, have a coating of

TOXODON. 585

enamel about half a line in thickness, which terminates at
the angles between these and the posterior or concave surface.
From the relative position of the bases or roots, we may infer
that they diverged from each other, like the incisors of the Horse, as
they advanced forwards in order to bring their broadest cutting
surface into line. That they were opposed to teeth of a corresponding
structure in the upper jaw, is proved by their oblique chisel-like
cutting edge.

The molar teeth in this mutilated lower jaw, like those in the
upper jaw of the Toxodon platensis, had persistent pulps, as is proved
by the conical cavity at their base: they consequently required a
deep socket and a corresponding extent of jaw to form the sockets
and protect the pulps. In order to economize space and to increase
the power of resistance in the tooth, and perhaps also to diminish
the effects of direct pressure on the highly vascular and sensible
matrix, the molars and their sockets are curved, but in a less degree
than those of the upper jaw. They correspond with the superior
molars in the long antero-posterior diameter, in being small and
simple at the anterior part of the jaw, and by increasing in mag-
nitude and complexity as they are situated more posteriorly. They
are, however, narrower from side to side, the Toxodon agreeing in
this respect with most other large herbivorous Mammalia, the fixed
surface for attrition in the upper jaw being from obvious principles
more extensive than the opposed moveable surface in the lower jaw.
In the first three teeth, which are premolars, the enamel is confined
to the outer surface: in the last three or true molars a plate of enamel
is also laid upon the middle of the inner surface, and sends one or
two simple folds obliquely forwards into the substance of the tooth.
(Pl. 145, fig. 3).

The first grinder in the lower jaw is of small size and simple
structure. It is more curved than any of the other molars, and appears
to have differed from the external incisor only in its more compressed
form and vertical direction of growth: it is interesting, indeed, to
find so gradual a transition, in structure, from molar to incisive teeth
as this jaw presents ; for the robust incisors may here be regarded as
representing molars simplified by the greater deficiency of enamel,

586 UNGULATES.

and with a change in their direction. The second molar presents an
increase in antero-posterior diameter and in length, and the enamel
of the middle of the outer side makes a fold which penetrates a little
way into the tooth; the cement covering the inner side is slightly
concave and unbroken. The third molar presents an increase of
dimensions in the same directions as the second; the enamel on the
outer side of the tooth presents a similar fold. In the fourth, or first
molar, besides a further increase of size and a corresponding but
deeper fold of enamel on the external side and nearer the anterior
part of the tooth, the grinding surface is rendered more compli-
cated by the two folds of enamel entering the substance of the tooth
from the distinct plate on the middle of the inner side: these folds
divide the antero-posterior extent of the tooth into three nearly equal
parts; they are both directed obliquely forwards, the hinder one
goes half-way across the substance of the dentine. The fifth molar
presents the same structure as the fourth, which it exceeds only
slightly in size. The sixth molar has a much longer antero-posterior
diameter, which measures two inches; but the lateral diameter is
but slightly augmented ; its structure resembles that of the fifth. The
outer coat of enamel extends over half the anterior and posterior
ends of the tooth.

The partial disposition of the enamel upon the molars of the
Toxodon is peculiar to that genus; but the enamel is continued, as
in other rootless teeth, to the open end of the implanted base; it is
thinner than in the Rhinoceros. The unenamelled parts of the tooth
are coated by a thin layer of cement. The entire body of the tooth is
composed of compact dentine, the pulp-fissure which penetrates the
middle of the lobes defined by the inflected folds of the enamel, extends
from the apex of the open basal pulp-cavity to the grinding surface.
‘The dentinal tubes are ith of a line at their origin, and radiate
in directions vertical to the superficies of the tooth, and of the
inflected enamel-folds, and are but little inclined upwards from the
horizontal plane. They maintain their original diameter, and their
relative distance from each other, viz. th of a line, to near their
peripheral ends. The dentinal cells are sub-hexagonal, and about
,J,th of an inch in diameter in the peripheral part of the substance.

-—

RHINOCEROS. 587

In the discontinuity of the enamel covering the molars, the Toxodon
differs from all known Pachyderms, and manifests a slight approach
to the Bruta.

214. Elasmotherium(1).—This name has been given to an extinct
Pachyderm with rootless molars, surpassing the Toxodon in size, and
of which only the lower jaw and its dentition are as yet known ; but
the characters of the teeth are sufficiently remarkable to call for
notice here. The molar teeth of the Elasmotherium are. five in
number in each ramus of the jaw, the anterior one being very
small; the penultimate one is the largest, measuring three inches
in the antero-posterior diameter, and two inches in the transverse
diameter of the crown. The enamel is remarkable for its beautiful
undulating folds; but its general disposition most resembles that
in the inferior molars of the Rhinoceros(2). The teeth of the
Elasmotherium differ from those of the Rhinoceros, and resemble
those of the Horse in the great depth to which they are implanted in
the jaw, before being divided into roots: the socket of the penul-
timate grinder extends, in fact, to the lower margin of the jaw
without any indication of partitions for the lodgment of fangs:
there is no trace of incisive teeth in the portion of symphysis which
is preserved, and which extends a little more than three inches in
advance of the first small molar. The above account is taken from a
cast and the description by Cuvier, in the ‘ Ossemens Fossiles’, 4to.
tom. 11. pt. i, p. 96. The original is preserved in the Museum of
Moscow, and is unique; it was discovered in the frozen drift or
diluvium of Siberia.

215. Rhinocerotide.—The present family of anisodactyle Pachy-
derms includes the typical Rhinoceros, the extinct Aceratherium which
had no horn, and the equally hornless small existing genus Hyraz.
The essential characteristics of the dentition of the genus Rhinoceros
are to be found in the form and structure of the molar teeth. In the
first place, they differ essentially from those of the Horse or Elasmothere
by being implanted by distinct roots. In the upper jaw the crown is

(1) EXacpa a plate, Onpioy beast: in allusion to the plicated plates of enamel in the
substance of the molar teeth.
(2) Compare figure 12 in Plate 136, with p. 3, fig. 11 in Plate 138.

588 UNGULATES.

subcubical, and the grinding surface, when moderately worn, sub-
quadrate, and penetrated by two folds or valleys of enamel: the
principal valley (Pl. 138, fig. 5, 6) commences at the middle of the
inner side, and extends obliquely outwards and forwards towards
the antero-external angle of the crown about two-thirds across,
where it terminates, according to the species, in a more or
less expanded, sometimes bilobed, cul de sac, (e): the second
and shorter valley (ib. c) is usually of a triangular form, and
indents more or less deeply the posterior border of the crown:
in most Rhinoceroses this is wanting in the last molar, which has
a trihedral conical crown: both valleys are usually deepest at their
blind terminations: the outer surface of the crown is gently un-
dulated by one of the convexities (ib. 0°) being sometimes produced
into a longitudinal ridge. In the lower jaw the molars (ib. fig. 9)
have an oblong, laterally compressed crown, divided into two cres-
centic lobes, placed obliquely, with their convexities (0 0) outwards
and a little backwards; the anterior horn of the hinder crescent,
before it is worn down, abuts against the middle of the convexity
and below the upper margin of the crescent in front.

The normal formula of the molar series is:—p. <3, m. =: — 28.
There are no canines. As to the incisors, the species vary not only
in regard to their form and proportions but also their existence; and
in the varieties of these teeth we may discern the same inverse
relation to the development of the horns which is manifested by the
canines of the Ruminants. Thus, the two-horned Rhinoceroses of
Africa, which are remarkable for the great length of one(1) or both(2)
of the nasal weapons, have no incisors in their adult dentition (Pl. 138,
fig.2); neither had that great extinct two-horned species (Rh. tichorhinus),
the prodigious development of whose horns is indicated by the sin-
gular modifications of the vomerine, nasal, and intermaxillary bones
in relation to the firm support of those weapons. (3)

The Sumatran bicorn Rhinoceros, combines with comparatively

(1) Rhinoceros bicornis, Rh. simus. .

(2) Rb. Keitloa, Smith.

(3) These bones in the fossil skull of the species cited are confluent with each other,
forming a solid obtuse termination to the upper jaw, and are anchylosed to a strong bony
partition wall extending from the vomer to the anterior outlet of the nasal passages, and thus

RHINOCEROS. 589
small horns, moderately developed incisors in both jaws; and the
same teeth are present in the nearly allied extinct two-horned Rhzno-
ceros called after its discoverer Schleiermacher. The incisors are
well developed in both the existing unicorn Rhinoceroses, Rh. indicus
and Rh. sondaicus ; but they attain their largest dimensions in the
singular extinct hornless species, the Rhinoceros incisivus of Cuvier,
which makes the transition to the extinct genus Palgotherium, and
forms the type of the aberrant subgenus Acerotherium of Dr. Kaup :
(Pl. 138, fig. 1). The normal incisive formula is:—=3 — 8: the
median pair being the largest above and the smallest below: in the
existing species the smaller incisors are disproportionally minute, and
usually have no permanent successors, or are soon shed: the larger
incisors are preceded by deciduous teeth which they succeed and
replace. In the under jaw of a Sumatran Rhinoceros, now before me,
the extremity of which is figured in Plate 138, fig. 15, the tips of
the large permanent outer pair of incisors (¢ 2) are visible, but have
not pushed out their deciduous predecessors (d 2); and the sockets
(d 1) of those of the two small median incisors (2 1) are also retained.
In one of the extinct species of Rhinoceros from the Himalayan
tertiary beds Dr. Falconer informs me that there are six incisors in
both jaws: the typical number was, therefore, retained in this
ancient species, as in the contemporary Hippopotamus of the same
formations. Cuvier believed that the ex-incisive character of the
two-horned Rhinoceros of Africa was absolute. ‘‘ Not only,” he
observes, ‘‘is its hide without folds, not only has it constantly two
horns, but it has never more than twenty-eight teeth, all molars ;
and never possesses incisors, nor even a place for them at the
anterior extremity of its jaws.”’(1)

affording extra support to the horn-bearing bones of the face whence the name tichorhinus
given by Cuvier to this most common of the extinct Rhinoceroses of our Northern Hemis-
phere.

(1) “‘Non-seulement sa peau n’a point de plis; non-seulement il a constamment deux
cornes, mais il n’a jamais que vingt-huit dents, toutes molaires ; il manque toujours d’incisives,
et n’a méme point de place pour elles 4 l’extremité antérieure de ses machoires.” ‘ Ossemens
Fossiles,’ 4to. 1822, tom. ii. pt. 1, p. 27. The otherwise excellent zoological descriptions of the
two-horned Rhinoceroses in Dr. Smith’s ‘ Illustrations of the Zoology of South Africa, do not

590 UNGULATES.

I have shown in many parts of this Treatise how strikingly the
duly defined law of Unity of Organization is exemplified by the dental
system; and, anticipating that this system would adhere to the typical ©
formula by transitory representatives of the defective teeth in the adult, —
I made search for the germs of incisors in the dried jaws of a fcetal
Rhinoceros bicornis of South Africa. The alveolar border of the
short symphysis of the lower jaw was apparently edentulous, and
thickly coated with the dried gum ; after soaking this for some hours —
in warm water, and cutting down into its substance, I detected the _
germs of the four lower incisors, which are figured, of half the natural —
size, in Pl. 138, fig. 14, 71,72. Although these teeth are destined
to be absorbed and never to make their appearance above the gum
in the living animal, they manifest the typical relative proportions
to one another, the outer pair (i 2) being more than double the size —
of the inner pair (@ 1). The outer incisor is six lines in length,
and in great part lodged in the socket; the crown is one line and a half
in breadth, convex anteriorly, flattened behind ; it protrudes from the
jaw about five lines in advance of the alveolus of the first molar,
and close to the anterior border of the jaw. At the same border,
about one line nearer the symphysis, the first or inner incisor is ©
situated ; it is about two lines in length, and half a line across the
crown, which just peeps above the bone. There were no sockets
of reserve beneath or behind these deciduous germs of incisors.
The anterior end of the thin and small intermaxillary lamella of —
the same skull is expanded, and was covered by a thick, dried
gum, but I could find no calcified rudiments of upper incisors; it
is highly probable, however, that germs of these teeth or their —
matrices, may be manifested at an earlier period. ‘-

The permanent median incisors of the upper jaw have a peculiar —
and easily recognizable generic form in all the species possessing
them; they are short, broad, much compressed, rhomboidal, or
sub-triangular, the crown forming the base of the triangle and the ~
contain any reference to the teeth: Mr. Macleay, in the Entomological number of the same

work, exaggerates in affirming of the genus Rhinoceros, “that the dentition varies extensively
in almost every species.” No. 111, p. 6. .

RHINOCEROS. 591

end of the fang the truncated apex: the crown, which is very
short and thin in proportion to its breadth, usually commences
by a sudden expansion, and terminates before it has suffered much
abrasion, by aa oblique trenchant edge, directed vertically down-
wards; they are less parallel in position, and are thicker in the
Indian than in the Javanese one-horned Rhinoceros; they are a
little smaller in the Sumatran two-horned species (Pl. 138, fig. 12,
71). The external incisors are very small in all the above-cited
species; and are lost before the animals attain maturity. They
are each seven lines in length and two in breadth in the skull
of a nearly full-grown Sumatran Rhinoceros (ib. 7 2), and are situated
close to the suture with the maxillary bone. In the nearly allied
extinct Rhinoceros Schleiermachert Dr. Kaup found them with an
enamelled crown of four lines extent, which is longer than in the
Rh. Sumatranus: the large mid-incisors of the Rh. Schlevermachert
are about two inches long, with a crown one inch and a quarter
broad. In the Rh. incisivus (Pl. 138, fig. 1) these incisors have been
found of nearly four inches in length, and with a short, oblique
crown measuring upwards of two inches in breadth, but are relatively
thinner.

The large external inferior incisors are procumbent, or project
almost horizontally from the angles of the symphysial end of the
lower jaw; inthe Sumatran Rhinoceros the crown is an inch and
a half in length, almost flat above and on the outer side, and convex
below. The enamel is only laid upon the under and outer sides,
terminating by a sharp edge along the inner part of the crown,
and at its rounded termination. In the Javanese Rhinoceros they
have a more definite trihedral form, and terminate anteriorly in a
sharp-point: they are relatively thicker than in the Indian species
in which Cuvier(l1) has figured them as worn down to a thick
truncated base. The small mid-incisors of the lower jaw are
relatively larger and longer retained in the Rhinoceros Schleier-
macheri(2), the outer incisors resemble those of the Rh. Sumatranus.
In the RA. inciswus (Pl. 138, fig. 1) these teeth acquire their greatest

(1) Loc. cit. Pl. 11, fig. 4.
(2) Kaup, loc cit., tab. x1.

592 UNGULATES.

size, are more divergent, and directed more upwards; they have
been found of the length of from eight to ten inches, of which the
implanted base measured three-fifths of the entire length of the
tooth, and the crown was one inch and a quarter in breadth ; this is
worn obliquely inwards at its upper enamelled part.

Not a trace of a canine tooth or its alveolus has been observed
in the skull of a mature individual of any existing or extinct species
of Rhinoceros, but such we must consider the small and simple tooth
(Pl. 138, fig. 13, c) developed at the fore part of the superior
maxillary bone in the foetal Rhinoceros indicus, two lines in advance
of the alveolus of the first small deciduous molar (p 1) and one
line behind the suture which unites the maxillary with the inter-
maxillary bone. The specimen in which I detected this tooth, the
crown of which had pushed through the jaw, but not through the
gum, appeared to be at the full-time, or newly born. The tooth
and its socket must soon disappear, for in the specimen of the
upper jaw of a young Indian Rhinoceros figured by Cuvier in the
‘Ossemens Fossiles,’ tom. cit. Pl. v, fig. 3, there is no trace of
the alveolus of the rudimental canine in the tract of bone between
the first deciduous molar and the intermaxillary suture; anterior
to this the intermaxillary bone shows the sockets of the two com-
paratively large incisive teeth. This discovery of vestiges of
canines in the genus Rhinoceros shows an additional character,
although a transitory one, linking that genus with the nearly allied
extinct Palzotherium.

The first of the permanent series of seven molar teeth is very
small in both jaws, and is soon shed. The first upper premolar
is notched on the inner side in the one-horned Rhinoceros
(Pl. 138, fig. 3, p 1); the notch sinks deeper and expands
in the African two-horned species; and in the Sumatran bicorn
Rhinoceros it presents a detached lobe on the inner side: the second
upper premolar is more suddenly enlarged in the one-horned than
in the two-horned Rhinoceros. Before the crowns of these large
and complex premolars and molars begin to be abraded, the
eminences bounding the valleys terminate in sharp enamelled ridges,
the principal extending along the outer border of the grinding

RHINOCEROS. 593

surface, and two others continued from this obliquely backwards
to the inner border, one from the antero-external angle, the other
from near the middle of the outer wall; the inner terminations of these
two parallel oblique ridges form the summits of the two cones which
constitute the inner half of the crown.(1) Small or secondary ridges pro-
ject from the sides of the principal ridges into the intervening valleys,
in extent and number varying according to the species, the most
constant being the one, marked f in fig. 5, from the posterior oblique
ridge. The first effect of mastication is to wear away the enamel from
the summits of the ridges, and to expose a tract of dentine which widens
as attrition proceeds, varying the pattern of the grinding surface as
the valleys are thus progressively obliterated. These changes are
illustrated by the figure of the molar series of the upper jaw of the
Rhinoceros indicus (Pl. 138, fig. 3). The chief valley, marked D in fig. 5,
is expanded and bilobed at its termination, and is deepest at each
terminal division, and at the middle of its course; in the second
true molar (m 2) its entire extent is shown; in the last molar (m 3)
the posterior terminal division is insulated by the wearing away of
the enamel from the shallower part of the valley between the two
divisions : the same insulation has taken place in m 1, and the shallow
entry of the valley is almost worn away; in p 4 it is obliterated,
and the peninsular fold of enamel is converted into an island.
The same change is effected in the short posterior fold c, it deepens
as it penetrates the crown, and in m 4 its beginning has been worn
down to the dentine, and its end converted into an island of enamel.
The same three islands are shown in p 3 and p 2, with the addition
of linear tracts formed by the wearing down of the crown to the
basal ridge at the antero-internal lobe. The grinding surface is
sometimes reduced to a plain tract of dentine before the molar is
shed. There is no posterior fold c in the last molar.(2)

The modifications in the form of the valleys and secondary

(1) See the germ of the upper molar, Pl. 138, fig. 8.
(2) These, and similar details in other chapters of this work, may be deemed tediously,
perhaps unnecessarily, minute: they are, however, indispensable to whoever would make suc-

cessfully the noble application of anatomy to the restitution of lost species and the past history
of the globe.

QQ

594 UNGULATES.

ridges of the upper molars are constant and characteristic of the
species, and materially aid in the determination of fossil remains.

Even in existing species so nearly allied as the unicorn Rhino-
ceroses of India and Java, each might be determined by a single
detached molar tooth. The principal valley is bent back at its
termination in the Java species, but being shallower than the rest
of the valley, it is obliterated and the valley simplified in form
as in fig. 4. The posterior fold (e) is soon converted into an island ;
the chief fold is next insulated by the wearing down of the dentine
to its beginning, and is the last to disappear.

The African Rhinoceros bicorms has a relatively larger molar,
especially in its antero-posterior extent; the beginnings of the two
folds (ib. fig. 5, b & c), being deeper than their terminations, no
islands are formed in the progress of abrasion. In the Sumatran
Rhinoceros the valley (0) is relatively wider at its commencement,
and contracts to its termination, which is pointed, in little-worn
molars ; a simple secondary process projects from the posterior ridge
into the valley, and partially detaches the narrow and at first
triangular termination; when attrition has reached the shallow
part of the valley at the end of the process, answering to f in fig. 5,
the entire termination of the valley is insulated: a second and
posterior island is formed when abrasion has removed the enamel
from the wide and shallow beginning of the posterior valley c.
Thus with regard to the first formed island c, which characterises
the abraded molars of the Indian one-horned and Sumatran two-
horned Rhinoceros, this results from the insulation of part of the
blind termination of the principal valley in the one-horned species,
and from the cutting off of the whole termination of the valley
in the two-horned species. Cuvier, not having attended to this diffe-
rence, failed to perceive that the fossil molar teeth which he
figures, loc. cit. Pl. VI, fig. 5, and Pl. XIII, fig. 4, and which
are copied in Pl. 188, figs. 6 & 7, belonged to two distinct species
of Rhinoceros.(1) Figure 6 is the second true upper molar tooth

(1) He describes the tooth (Pl. 138, fig. 6) figured in his ‘ Ossem, Foss. Rhinoceros,’ PI. v1,
fig. 5, as follows :—“ Fig. 5, est la cinquiéme du cété gauche peu usée. On y voit aussi trés-bien
la fossette, résultant de l’union du crochet postérieur avec Ja colline antérieure et l’échancrure

scant aml

RHINOCEROS. 5Y5

of the Rhinoceros tichorhinus. It most nearly resembles the one-
horned Indiau Rhinoceros in the pattern of the grinding surface of
the molars, the valley @ has at first the same contracted beginning
and expanded bilobed terminax.,, and the island (e) is formed by

the cutting off of the hinder lobe. my 7 3, , corresponding molar :
of the Rhinoceros leptorhinus, which in the ~ J oture of its upper
molars, most nearly resembled the Sumatran Fira_.,, Broa tt itie
valley (6) has the same wide beginning and contracted ena, ,,; a
is wholly insulated at ¢ by the obliteration of the enamel covering
the shallow part of the valley between the end of the secondary
process f, and the anterior lobe or ridge of the grinding surface :
the upper molars of the RA. leptorhinus are further distinguished
from those of the Rh. tichorhinus by the longer ridge (n) along the
base of the anterior side, and by the narrow prominent longitudinal
ridge o’ on the outer side of the crown. Both the above-named
extinct species of Rhinoceros have left their remains in England as
well as on the continent. The RA. incisivus, which has not hitherto
been found in British strata, is readily distinguished by the more
simple form and almost uniform width of the valley 6; and still better
by the basal ridge which is continued from the anterior side along
the whole of the inner to the posterior side of the crown of the
molar, at some distance above the basal termination of the enamel ;
in these modifications it offers the nearest approach to the con-
figuration of the upper molars in the Palgotherium. This basal
ridge is also well developed in the molars of the Hyraz.

There are corresponding, but less marked differences in the
molar teeth of the lower jaw of the different species of Rhinoceros ;
on which, however, I shall not here dwell. The first premolar is
the smallest and simplest; the bilobed structure is at best feebly
indicated by the undulations of the outer surface: and on the inner
surface, by a simple depression or a notch: in the Sumatran Rhino-
ceros the notch is near the front margin of the tooth; it aifords
postérieure commence a étre cernée,” p. 57. And the tooth (Pl. 138, fig. 7) figured in his
Pl. x11, fig. 4, as follows: “Fig. 4, Pl. x11, est un sixiéme du cété gauche, peu usée, des
Crozes, Département du Gard. Le trou antérieur y est déja distinct par l’union du crochet
de la colline postérieure avec la colline antérieure, mais l’échancrure postérieure n’y est point

239
encore cernee.

@ 0, 2

596 UNGULATES.

a more marked difference by its. position in relation to the sv=phisial
termination of the jaw; in the Rhinoceroses with r-+>!Stent incisive
teeth the symphysis is prolonged beyon? “7 first premolar ; but

in the African species this tooth ~ situated close to the anterior
end of the jaw. In the _aunct tichorhine Rhinoceros in which

the germs of the le-~* incisors endured longer and attained a greater
Sehr. giao they do in the living Rh. bicornis, the depressed
gno tate symphysis is prolonged, as in the Indian and Sumatran
Rhinoceroses, beyond the molar series, which begins opposite the
posterior border of the symphysis, as shown in Pl. 138, fig. 10.
In the leptorhine Rhinoceros (ib. fig. 11) the molar series extends
closer to the anterior end of the symphysis, which both in form
and relation to the molar teeth, more resembles that of the two-
horned African Rhinoceroses. The first premolar (p 1) is soon
shed, and all traces of its socket soon obliterated ; this has led to
the supposition that some of the fossil Rhinoceroses had only six
molars on each side of the lower jaw; but specimens of young
individuals have demonstrated the normal number in species where
it has been most formally denied.(1) The second lower molar (p 2)
has its lobes distinctly defined by the vertical furrow on the outer
surface, but the variations of the form of its inner surface in different
species are such as to make it, perhaps, the most characteristic tooth
of the lower jaw; the anterior lobe is always the smallest and |
thinnest ; and its internal indentation is shallow. The two lobes
assume a more equal size and crescentic figure in the third (p 3)
and fourth (p 4) premolars, which progressively increase in size:
the three true molars resemble the fourth premolar, the last tooth
not being distinguised by an accessory lobe.

216. Microscopic Structure. Rotate (2) describes si dentinal
tubes as he saw them in longitudinal sections of the root of a molar
tooth of a Rhinoceros, to proceed transversely from the pulp-cavity

(1) The specimen in Dr. Buckland’s Museum, from Lawford near Rugby, Pl. 138, fig. 10,
shows the first of the four premolars in situ, in the lower jaw of the Rhinoceros tichorhinus.
M. Christol, who has figured a very perfect lower jaw of an older individual of the same
species, in which the first premolar has been shed, describes it as ‘munie de toutes ses
molaires.’ Annales des Sciences, 1835, p. 46, Pl. 2, fig. 1.

(2) Loc. cit., p. 32 5

RHINOCEROS. 597

with an irregular and, in some parts, slightly curved course, but
he could not consider them as being undulated: they were sath
of an inch in diameter at their beginning, soon bifurcated, and
gave off very numerous branches; the interspaces between the
origins of the tubes, equalled the breadth of two tubes. The
peripheral part of the dentine, close to the investing layer of cement
contained a dense stratum of opake cells, in which many of the
branches of the calcigerous tubes terminated; the extremities of the
tubes meander through the interspaces of the cells, some terminating
in the cells, other anastomosing with adjoining tubes in beautiful
curves.

I have examined the microscopic structure of the molar of the
Indian Rhinoceros, in vertical and horizontal sections of the crown.
The pulp-cavity is continued in the form of fissures, into the middle
of the eminences bounding the valleys of the uneven-grinding
surface, and a few short vascular canals are continued into the
dentine from the summits of the pulp-fissures, especially at their
terminal angles. In horizontal sections dividing the vascular canals,
their arez appear like large opake cells, with a clear border, and
the adjoining dentinal tubes diverge, as it were, to give place for
them: the ends of a few tubes, which were given off from those canals
being seen in the clear border. Retzius makes mention of larger
groups of opake cells in the middle of the dentine of the root of
the molar, which seemed to have forced aside the main-tubes, which
bent round these groups of cells, and sent off some branches which
there terminated.

The major part of the coronal dentine of the Rhinoceros’s
molar, is fine-tubed and unvascular: I found the dentinal tubes,
at their origin from the pulp-fissure, to have a diameter of <.th
of an inch, with interspaces averaging ;,th of an inch. They
ascend (in the lower molar), inclining at first very slightly from the
pulp-fissure, and gradually bending more outwards with the con-
vexity of the curve upwards, until near their termination, when
they gently curve in the opposite direction. Throughout their
course they are undulated, the secondary waves being pretty regular
and stronger than in the Human dentinal tubes. Transparent tracts,

598 UNGULATES.

wider than the interspaces of the tubes, extend here and there
from the pulp-cavity, in the directions ‘of the tubes and of the
short vascular canals; the tubes next these tracts make a sudden
bend obliquely across them with wider clear intervals. The tubes
divide sparingly in the first half of their course; and, not decreasing
much in diameter, appear closer packed as they approach the
enamel. In the outer third of their course they make here and
there abrupt secondary bends, and send off the minute lateral
branches from both sides. Here and there the tubes present slight
partial enlargements ; they very gradually decrease in size, until
close to the peripheral stratum of minute opake cellules, (Pl. 139,
d" d") where they chiefly end by a bifurcation, the forks diverging
at an angle of 45°, and bending in opposite directions, sometimes
anastomosing, sometimes irregularly dilating into, or communicating
with, the opake cellules. The traces of the compartments of the
basal substance, or dentinal cells, are very faint; they are best
seen in transverse sections, as in Pl. 139, d'd'; especially that
part of their: contour next the enamel which curves across from
four to five of the dentinal tubes ; the compartments or cells increase
in size as they approach the pulp-cavity, but soon become fainter
and disappear from view.

The contour lines (ib. J 7) are unusually conspicuous and nume-
rous, with interspaces of jth of an inch; they are not due to abrupt
parallel bends of the tubes, nor to branches or opake cells, but to
a slight increase of opacity of the basal substance which seemed
to be due to oblique cracks along the lines in question. The enamel
fibres (ib. e e), in a transverse or horizontal section of the crown,
proceeded from the surface of the dentine across the thickness of
the layer, with a gentle degree of flexuosity ; their diameter is ;;th
of an inch. I could discern only a faint granular appearance in
the fibre, certainly no transverse segmentation. The whole thickness
of the layer of enamel is traversed by contour lines at varying
intervals, running parallel to the border of the dentine. Here
and there the fissures occur at the dentinal surface of the enamel,
with irregular or stronger bends of the adjoining fibres. In a vertical
section of the enamel the fibres were seen to run more obliquely

aad

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_

a cg ee gc alge

i
:
:
:
:
j

RHINOCEROS. 599

across the section, and those of one layer in an opposite direction
to that of the subjacent layer of fibres.

Retzius notices the existence of radiate cells in both the
radical and the coronal cement of the Rhinoceros’s grinder: they
were of various shapes, some round and .,th of an inch in diameter,
some angular, and others prolonged in the form of tubes; all receive
numerous fine tubuli which are clustered around them.

217. Succession.—The deciduous dentition of the genus Rhino-
ceros, is :—

. . 2—2 4—4
incisors — ; molars Fe a 24.

In the Sumatran Rhinoceros the small mid-incisors of the
lower jaw (Pl. 138, fig. 15, d 1) are first shed and replaced by
a larger pair (¢ 1), which protrude beneath them; these are small
in comparison with the lateral pair, and are also shed before the
last true molar cuts the gum. The first true molar appears before
any of the deciduous set are shed, but the first milk-molar soon
yields place to the first premolar; the second milk-molar gives
way to the second premolar, and about the same time the second
true molar advances into place. Next the deciduous outer incisors
(ib. d 2) their fang deeply excavated by the absorbent process
excited by the pressure of their large successors (2 2), are pushed
or broken out; the last deciduous molar is displaced, and the last
premolar rises above the gum about the same time that the last
true molar comes into place. Thus, notwithstanding the close
similarity of form and structure between the premolars and molars,
each division of the permanent masticatory series has its own
order and progression of development, and thereby manifests its
essential distinction. The last milk-molar is not more complex
than the last premolar which takes its place.

218. Paleotherum—The vast hiatus, which, in the series of
existing Mammals, divides the Rhinoceros from the Tapir and this
from the Elephant, was once filled up by interesting transitional
species of anisodactyle Pachyderms which have long become extinct.
I shall briefly notice the leading features of the dentition of some
of those ancient forms of Mammalia, as indeed, this enduring part

600 UNGULATES.

of their frame best exemplifies the progress of the affinities which
the lapse of ages has interrupted.

The species of Palzeotherium which appear to have accompanied
the Anoplotheres in the first introduction of hoofed Quadrupeds
upon this planet, were characterised by the same complete dental
formula, viz :—

: 3—3 * 1—] id 3—3
Incisors — ; canines —; premolars —; molars —: = 44.
3—3 1—1 4—4 3—3

(Pl. 135, fig. 4.) But the canines are developed to the proportions
which these teeth usually bear as weapons of offence and defence,
proportions such as are still manifested by the canines of the Tapir:
there is consequently, in the Palzothere, a vacancy in the series of
teeth between the incisors and canine in the upper jaw to receive
the crown of the lower canine when the mouth was closed ; and there
is a longer vacancy between the canines and the premolars in both
jaws.

The crown of the upper molars is bounded by four unequal
sides, the outer side (0 o fig. 5) being the longest; in the new-
formed and unworn crown this side inclines inwards as it descends ;
it is divided by three longitudinal ridges into two concavities, rounded
towards the root and terminating in a point at the grinding surface of
the tooth : the angles of the base of each projecting triangle rest on
the extremities of the salient longitudinal ridges. In the growing
molar two vertical sinuous folds of the capsule penetrated the sub-
stance of the crown, one (0) entering from within outwards, the other
(c, e) crossing it from before backwards. The antero-posterior fold
described two curves, parallel with the exterior concavities ; and,
entering at the posterior margin, where the valley is widest and
deepest, it terminated in a cul-de-sac close to the anterior and outer
angle of the tooth, or at a little distance from the anterior
margin: the transverse fold commencing at the inner side of —
the tooth terminated close to the middle longitudinal ridge on the —
opposite side, expanding and deepening where it crossed the pre- —
ceding ridge. Of the salient ridges of enamel left by these folds, and
defined by the corresponding valleys, the principal is the zig-zag one
which forms the outer boundary of the grinding surface ; from the

PALAOTHERE, 601

posterior angle of this a second is continued, first downwards, and
then along the posterior border of the tooth to the posterior and
internal angle where it forms a small eminence or lobe; a third
ridge is continued along the anterior border of the crown to the
internal and anterior angle, where it is continued into the summit of a
trihedral crucial eminence, forming the anterior half of the inner side
of the tooth. A strong conical eminence is developed between the
anterior and posterior angles of the inner border of the tooth, and
the whole base of the crown is belted by a ridge. As soon as the
surface of the crown becomes worn by mastication, and part of the
dentine is exposed, it is bounded by two parallel salient lines of
enamel, and those upon the outer zigzag ridge form a double
crescent, asin m3: if the two inner lobes were equally developed
and the intermediate one reduced in size, they would also present
their double crescents of enamel, separated by the antero posterior
depression from the anterior crescents, and the Ruminant type of
molar would be manifested. By the rudimental state of the posterior
angular lobes and the varying depth of the crucial fissures, the
progress of attrition blends together different eminences and produces
a pattern which is very like that of the molars of the Rhinoceros
(Pl. 135, fig. 5, m1). The antero-posterior depression, which is the
shallowest, is first obliterated, and, with it, the chief resemblance
to the Ruminant molar. The transverse fissure is arrested at the
point (c) in the hind lobe: a portion of this fissure is sometimes
insulated as at e, p4. As attrition proceeds, both folds are converted
into islands of enamel, and, first, the antero-posterior fold c: the
islands are finally obliterated before the crown is quite exhausted.

The first premolar (fig. 5, p 1) is the smallest of the series and
has a simple compressed pointed crown, with a strong basal ridge,
broadest on the inner side, and a small posterior cusp. The other
premolars increase in size until they equal the true molars, from
which they searcely differ in structure. The last true molar has its
crown more extended from before backwards, but is contracted
posteriorly, that side being the shortest. The first premolar is
implanted by three roots: all the others have four roots.

The crowns of the lower molars are narrower and simpler than
those above. The first of the series of seven molars in the lower

602 UNGULATES.

jaw (fig. 6, p 1) is the smallest and has a more simple crown than that
above; the crowns of the succeeding teeth to the sixth inclusive are
formed externally by two upright half cylinders (m 1, 0 0), and differ
from the same teeth in the Rhinoceros chiefly by the equal height of the
demi-cylinders. The seventh tooth, or third true molar (m 3), has a
third similar but smaller lobe. On the inner side of the crown a
longitudinal impression sinks, as it were, into each of the external
convexities, and a corresponding internal convexity receives the
entering angle between the two half-cylinders: the anterior of the
inner depressions is the shallowest, especially in the second premolar,
and both internal depressions contract as they descend. The base of
the crown is usually surrounded by a ridge, which is continued at
each end obliquely upwards to the angle formed by the backward
folding of the half-cylinders. When the summits of those teeth
begin to be abraded, two, and in the last molar, three, crescentic
tracts of dentine, bordered by enamel, are exposed.

All the species of Palzotherium became extinct before the close
of the middle (miocene) tertiary period. The largest surpassed the
Tapir in size, and must have resembled it in external appearance.

219. Macrauchenia.—An extinct Pachyderm equalling the largest
Camel in size, with very long and slender cervical vertebrz, as in the
Auchenia, and having imperforate transverse processes, as in all the
Camel-tribe, but with three toes on each foot, and an astragalus
closely resembling that of the Paleothere, has been in great part
restored(1) from fossil remains discovered in the tertiary deposits of
South America, of much more recent date than any of those which
in Europe have furnished evidences of tridactyle Ungulates. The
parts most required to establish the affinity of the Macrauchenia to
Paleotherium were undiscovered when the first account of it was
published. A single tooth obtained by Mr. Darwin from a locality
near Patagonia (Bahia Blanca) remote from that, (Port St. Julien’)
where the bones were discovered, bore sufficiently close resemblance
to the inferior molars of the Palzothere to lead me to suspect that it
might belong to the three-toed Pachyderm of Patagonia.(2) Subse-

(1) Fossil Mammalia of the Voyage of the Beagle, 4to. 1839, p. 35.
(2) See the ‘Catalogue of Fossil Mammalia in the Royal College of Surgeons,’ 4to. p. 229,
No. 952.

MACRAUCHENIA. 603

quently, the left ramus of a lower jaw, found in tertiary deposits of
Buenos Ayres, has been received at the British Museum, containing
six molar teeth, three true and three false, most of which manifest the
same pattern as the single fossil tooth above adverted to, and more
decidedly and fully determining the resemblance to the lower molar
series of the Paleothere, as will be obvious by comparing the
figure of the grinding surface of the Buenos Ayrian fossil teeth
(Pl. 135, fig. 7,) with those of the Paleothere (ib. fig. 6). The
chief generic distinction is the absence of the third lobe in the last
molar of the South American Pachyderm, by which it more closely
resembles the Rhinoceros; but it differs, like the Paleothere, from
the Rhinoceros in the greater exterior convexity and the equal height
of the two demi-cylindrical lobes of which the last premolar and the
three true molars are composed : and it differs from both Palzothere
and Rhinoceros in the more simple form of the second and third
premolars: the first small premolar of the South American Pachy-
derm may have existed in the part of the fossil jaw which is
mutilated, anterior to the second premolar in the British Museum
specimen: it is hypothetically added to the series, in Pl. 135, fig. 7,
at p. 1. If, however, it was not functionally developed in the
Macrauchenia, this genus would again differ from the Palzothere
and resemble the Lophiodon and Tapir, in the number of the
grinding teeth of the lower jaw. In the figure above cited, the
teeth are given of half their natural size: the enamel is smooth,
the dentine compact, and the coronal cement forms a very thin
layer, as in both Rhinoceros and Palzothere. In the more simple
form of the second and third molars we may trace a slight approxi-
mation to the Anoplotherian and Ruminant types; and, since no
other Pachyderm of the size required to correspond with that
indicated by the jaw and teeth here described, and, at the same
time, with close affinities to the Paleothere and the Cameloid
Ruminants, has, hitherto, been discovered in South America,
excepting the Macrauchenia, I deem it to be highly probable that
the teeth in question belong to that interesting annectant genus of
Anisodactyle Pachyderms.

604 UNGULATES.

220. Tapirus.—The dental formula of the Tapir is :—
3c; p. a3 m. —; = 42. (PL 96. figs. 4 & 5.)
The median incisors above have a broad trenchant crown, separated
by a transverse channel from a large basal ridge; the wedge-shaped
crowns of the opposite pair below fit into the channel, and have no basal
ridge: the outer incisors above are very large and like canines ; those
below are unusually small. The canines have crowns much shorter
than their roots, and not projecting, like tusks, beyond the lips: they
are pointed, with an outer convex, separated by sharp edges from
an inner, less convex, surface: the lower canines form part of
the same semi-circular series with the incisors: the upper ones
project close to the intermaxillary suture, separated from the
incisors by a short space for the reception of the crown of the
lower canine: this first shows the effects of abrasion at the fore-
part of the crown occasioned by the action of the upper laniariform
incisors. A long edentulous ridge of the jaw-bone separates the
canines from the molar series. |

The first three premolars above have the outer part of the
crown composed of two half-cones, the posterior one having a
basal ridge: the rest of the crown is impressed by two grooves
at right angles in the shape of a T, one dividing it from the two
outer demi-cones, the other and deeper groove dividing the rest
of the crown into two transverse wedge-shaped eminences; there
are, also, anterior and posterior basal ridges: the anterior eminence
is almost obsolete in the first premolar, which is the smallest and
triangular: they are nearly equal in the rest, and their summits
extend obliquely to the anterior part of the opposite demi-cones,
which have a small tubercle at the inner angle of their interspace ;
when much worn these teeth present two peninsular folds of enamel
one extending from the inner to near the outer part of the crown ; the
other, shorter and wider, continued a little way from the posterior
margin of the crown. The type of the molars of the Palzothere
and Rhinoceros is, here, feebly repeated. The anterior basal ridge
rises into a small cusp in the second premolar, which increases
in size in the third and fourth: in this tooth the transverse

/

Me SE A a A nn

/
.

TAPIR. 605

depression divides at the base of the anterior and outer demi-
cone and the posterior division is continued into the interspace
of the two demi-cones; these, therefore, now become the outer
ends of the two transverse wedge-shaped eminences, giving their
summits a curve whose concavity is turned backwards : the last molar
may be known by the shorter and more curved posterior eminence.

In the lower jaw the double transverse-ridged type of tooth,
which has been before described in the Kangaroo, Diprotodon and
Manatee, prevails throughout the molar series (Pl. 96, fig. 5): the
teeth are narrower in proportion to their antero-posterior extent
than in the upper jaw, especially the first premolar, in which the
anterior basal talon is developed in a conical lobe, connected by a
longitudinal ridge with the outer part of the first transverse eminence.
This ridge is narrower than the posterior one, which has both its
angles bent forwards, and the outer one produced as far as the
anterior eminence. The two transverse eminences become more
equal in the succeeding teeth; the angles of each are, as it were,
slightly folded forwards and inwards, making the fore-part of each
eminence concave: the anterior basal ridge decreases in breadth,
and the posterior one, which is obsolete in the first and second
premolars, gradually increases in the others, but is not developed
into a third lobe or eminence in the last molar, nor is relatively
so large in any of the molars as in the corresponding teeth of the
Manatee. There is a small eminence at the outer part of the
valley between the two transverse ridges, but no connecting ridge
crossing the middle of the valley as in the Kangaroos ; the transverse
eminences are thicker and less elevated than in the Diprotodon and
Notothere, but are higher than in the Manatee. From the relative
position of the teeth in fig. 4, it will be seen that the corresponding
tooth of the first premolar above is wanting in the lower jaw, and
that the first there answers to the second lower premolar in the
' Paleothere. The upper molar teeth, with the exception of the first,
are implanted by four fangs; the lower molars by two, which are
more divergent than in the Manatee.

221. Succession.—The number of deciduous molars is =: the
first above is relatively broader anteriorly than the premolar which
succeeds it: the rest resemble the true molars of the permanent

606 UNGULATES.

series, their crowns being quite crossed by the transverse valley,
which divides the grinding surface into two principal ridges. Cuvier
well observes that, as the last true molar is not more complex than
the others, so neither is the last of the deciduous series more complex
than the premolar which displaces it. In the lower jaw two of the
deciduous molars present the narrow elongated subtriangular crown,
which is repeated by the first only of the permanent series; the
third deciduous molar had the typical square double ridged crown.

222. Lophiodon.—Although the analogous instances(1) are so
numerous as almost to establish a law, yet it was with unabated
interest that I found in the Lophiodon another example of the
retention throughout life, by an ancient extinct species, of a charac-
ter which is transient and limited to the immature period of existence
in its modern representative. The Lophiodons which rank amongst
the most ancient of Pachyderms(2), had the same numerical dental
formula as the Tapirs; but the compressed and more simple form
of the crown was retained in the three premolars of the lower jaw,
the square-shape and double transverse-ridged structure being
established only in the three true molars.

In the upper jaw both the first and second premolars resemble
the first premolar of the Tapir, having the outer wall of the crown
divided into two demi-cones, and therinner part traversed by an
oblique ridge continued from the cone which rises from the inner
angle of the crown, and the anterior angle of the outer wall: this
ridge is higher and more simple than in the Tapir; the valley on
each side is bounded by a basal ridge. In the remaining molars
the outer wall of the crown presents three demi-cones, in con-
sequence of the great size of the angle of the anterior ridge:
the inner side developes two cones which are continued by parallel
oblique ridges, one to the anterior outer cone, the other to the
interspace between the middle and posterior cone. The intervening
valley stops at the base of the middle outer cone which is the highest,
and does not cut quite across the crown in any of the true molars:

(1) Dorcatherium, p. 530, Anoplotherium, p. 523, Machairodus, p. 494, &c.

(2) The Tapirus priscus of the older pliocene or the miocene formations of Germany and
France, had the same essential dental characters as the existing Tapirs ; but the extinct species
first appears at a more recent period than the Lophiodonts of the eocene marls and clays.

——
—

nee

a eli A ge i lI TED A ALY

CORYPHODON. 607

they, therefore, retain the structure of the second and third premolars
in the Tapir, with slight modifications which make a_ nearer
approach to the structure of the molars of the Rhinoceros. The
first and second are implanted by three roots; the rest by four, the
two inner ones being connate for some extent.

In the lower jaw the first premolar is relatively smaller and
simpler than in the Tapir: the crown supports a subcompressed
conical obtuse cusp, with a small anterior and larger posterior talon,
and is girt by a basal ridge: in the second the anterior and especially
the posterior basal lobes increase in size: in the third the posterior
lobe almost equals the principal eminence, and is connected to it by
a longitudinal ridge crossing the intervening valley: there is a basal
ridge on each side the posterior lobe: in the three true molars of the
lower jaw the crown is broader, quadrate, and supports two transverse
anteriorly-curved eminences, with an anterior and posterior basal
ridge, and they very closely resemble those of the Tapir: but the last
molar differs by the development of the posterior talon into a wedge-
shaped eminence half the height of the two that precede it. (Pl. 135,
fig. 8.)

223. Coryphodon.(1)—This extinct Pachyderm, which was as
large as a Horse, and of equal antiquity with the true Lophiodons,
differed from them in having the second and third eminences of the
last lower molar (Pl. 135, fig. 9) blended together into an obtuse-
angled ridge, with each angle developed into a point; the anterior
eminence is straight and is higher than the posterior one ; it has each
extremity prolonged into a point.

From the outer extremity of each of the two principal transverse
eminences a ridge is continued obliquely forwards, inwards and
downwards: the anterior one extends to the inner and anterior
angle of the base of the crown: the posterior one terminates at
the middle of the interspace between the two ridges. From the
back part of the posterior transverse eminence a ridge, or talon,
extends downwards and outwards.

Thus the crown of the last molar of the present species has
the two transverse eminences of a Lophiodon’s molar so modified

(1) History of British Fossil Mammalia, 8vo. p. 299.

608 UNGULATES.

that it supports two pairs of points and one single point, like
the last lower molar tooth of the fossil jaw from Lot-et-Garonne,
described by Cuvier in the ‘Ossemens Fossiles,’ 1822, tom «11.
p- 404; and like that from the Puy en Velay, described in the
posthumous 8vo. edition of the same work, vol. v. p. 480, both
of which are referred by Cuvier to the genus. Anthracotherium.
The last molar in the present fossil differs, however, from the
teeth above cited, in the height of the connecting ridge of the
anterior pair of points, and in the development of the fifth or
posterior point from the apex of the angular ridge connecting the
posterior pair of points.

From the closer resemblance which the fossil presents to the
true Lophiodons, it must be regarded as a member of the same
family of Tapiroid Pachyderms; indicating therein a distinct sub-
genus, characterised by the want of parallelism of the two prin-
cipal transverse ridges, and the rudimental state of the posterior
talon in the last molar tooth of the lower jaw. The name
Coryphodon, which I have proposed for this subgenus, is derived
from xopven a point and dds a tooth, and is significative of the
development of the angles of the ridges into points.

A right canine tooth, obtained from the same eocene formation
as the foregoing molar, but from a different locality in England, either
belongs to the same extinct genus of Pachyderm or indicates
another. The general proportions of this tooth, its degree of
curvature, and the relative length of the crown and the fang,
accord pretty closely with those of the canines of different species
of Lophiodon figured by Cuvier in the ‘Ossemens Fossiles,’ 1822,
tom. u. pt. 1. pl. 10, figs. 312. & pl. 9, fig. 11. The crown
must have projected but a small distance beyond that of the
adjoining teeth, and have been quite concealed by the lips, as in
the Tapir, not forming a projecting tusk, and being shorter and
thicker than the canine of a carnivorous quadruped. Cuvier does
not give a figure of the transverse section of the crown of the

canine in any of his Lophiodons: that of the present tooth —

is very characteristic, and resembles the transverse section of
the crown of the teeth of the great extinct reptile called

-

DINOTHERIUM. 609

Pliosaurus ; the outer surface being nearly flat, and the rest of
the crown so convex as to describe a semi-circle: a ridge of
enamel along each border of the flattened side separates it from
the convex side of the crown. This fossil tooth presents a pecu-
liarity which I have not before observed, or found described, in
having the crown defended by two layers of enamel: the outer
and thicker layer has a minutely wrinkled surface and terminates
near the base of the crown by a finely plicated border, extending
lower upon the posterior and outer than upon the anterior and inner
sides of the crown: the thin and smooth layer of the enamel
extends to and defines the base of the crown, the outer layer
being co-extensive with the inner one only at the two boundary
ridges, and the inner layer being extended further upon the tooth
at its anterior and inner sides. The length of this tooth must
have been three inches when entire; the circumference of the base
of the crown is two inches, nine lines.(1!)

224. Dinotherium.—The most extraordinary of extinct Pachy-
derms is that which Cuvier regarded as a gigantic Tapir, on
account of the character of the molar teeth, and which subsequent
discovery of the cranium and the enormous tusks of the lower jaw
(Pl. 99, fig. 6) has proved to be a genus connecting the Tapiroid
with the proboscidian families of Pachyderms.

The permanent dentition of the genus Dinotherium is :—

0—0 “5 0—0 2—2 3-3 ?
Incisors —; canines —; premolars —; molars —: = 22.
1—1 0—0 pam 3-3
the deciduous dentition was most probably :—
° 1—1 A 0—0 3—3
Incisors <3 canines —; molars Sree ae 16.

The first deciduous molar of the upper jaw has not yet been
detected ; it is highly probable that such a tooth existed, and I
concur with Professor Kaup in regarding the two deciduous
molars in situ, on each side of the fragment of the upper jaw of
the young Dinotherium which he has figured in Tab. 1, of his
‘Ossemens Fossiles de Darmstadt’, as the second and third.

The crown of the second milk-molar supports two transverse

(1) History of British Fossil Mammalia, Pl. 306, fig. 105.
RR

610 UNGULATES.

ridges with an anterior and posterior basal ridge; its contour is
almost square. The third milk molar has a greater antero-
posterior extent, and supports three transverse eminences with —
an anterior and posterior basal ridge, the anterior ridge being
developed into a pointed tubercle at its outer end. The crowns
of the first two permanent molars, or the premolars, were dis-
covered by Dr. Kaup in their closed alveoli above the second
and third deciduous molars, in a portion of the upper jaw.(l)
These two premolars were in place, fully developed, with the crowns
a little abraded, in the entire cranium subsequently discovered. (2)
They conform to the general rule in being more simple than the
teeth which they displace and succeed. The first upper premolar
supports a longitudinal ridge on the outer side of the crown, and
two mamilloid tubercles with confluent bases along the inner side
of the crown, which is surrounded, except at its outer part, by a
basal ridge. The unworn summits of both the ridge and tubercles
are divided into smaller tubercles by a series of notches. The
crown of the second premolar supports four tubercles, the outer
ridge being deeply cleft, and the two anterior tubercles are united
by a continuous ridge, which converts them into a transverse
eminence, like those which characterise the true molar teeth.
The transverse diameter of the second premolar exceeds the
antero-posterior one, the proportions being the reverse of those of
the deciduous molar which it displaces. The first true molar
repeats the structure of the hindmost deciduous molar, its crown
having a disproportionate antero-posterior extent and supporting ©
three transverse eminences, with an anterior, posterior, and internal —
basal ridge. The Dinothere resumes the Tapiroid character and
differs essentially from the Mastodon inasmuch as the posterior
molars, instead of having an increased antero-posterior extent and —
more complex crowns, increase only in thickness and support two
instead of three transverse eminences: they have also an anterior —
and a posterior basal ridge.

In the lower as in the upper jaw it is uncertain whether the

(1) Akten der Urwelt, Svo. 1841, tab. viit, fig. 1.
(2) Ibid. tab. vir.

DINOTHERIUM. 61]

two permanent premolars succeed two or three deciduous ones,
nor has any specimen with the deciduous molars im situ, ana-
logous to the fragment of the upper jaw above cited, been yet found.
The last deciduous inferior molar has been found separate ; it sup-
ports, like that above, three transverse eminences, but the first is
narrower and the third is broader than in its analogue of the upper
jaw. The first lower premolar is implanted like that above by two
fangs ; but it has a smaller and simpler crown, which is narrower
in proportion to its antero-posterior extent, and is almost entirely
occupied by the antero-posterior ridge: only the posterior of the
two inner tubercles being developed: thus the crown presents more
of a trenchant than a grinding character. The second premolar
supports two transverse ridges. The third of the permanent
series, which is the first true molar, has three transverse ridges
like the one above, but is relatively narrower. The second and
third true molars, the penultimate and last of the series, have
each large square crowns, with two transverse ridges and an
anterior and posterior talon, the latter being more developed than
in the corresponding molars of the upper jaw (Pl. 96, fig. 7).

As the three-ridged or first true molar tooth is the first of
the permanent series which comes into place, its crown, conform-
ably with the general law, exhibits most abrasion; this character
is well shown in Cuvier’s Plate 5, ‘Animaux voisins de Tapirs,
Ossemens Fossiles,’ tom. 1., in the portion of jaw discovered
in 1783 at Comminge, near the River Louze. The beautifully
entire crown of Cuvier’s gigantic Tapir, figured at Pl. 4, fig. 3,
of the same volume is the penultimate molar of the lower jaw of
the Dinotherium giganteum. Dr. Kaup was led, by the inspection
of a drawing of a fossil tooth made in 1785, of which he has
given a lithograph in his excellent Work ‘Ossemens Fossiles de
Darmstadt’, Pl. 5, fig. 2, to conceive that the Dinotherium had three
premolars, and that the tooth above cited was the first: there is
no trace, however, of the alveolus of such a molar in the mag-
nificent cranium discovered at Epplesheim in 1836, which from
the unworn state of the last two molars cannot have belonged
to an old animal. The same cranium also negatives the suppo-~

RR 2

612 UNGULATES.

sition that the Dinotherium had a seventh molar or fourth true
molar, to which Kaup originally referred the comparatively small
and simple tooth which he has figured in his ‘Ossemens Fossiles
de Darmstadt’, Pl. 1, figs. 7, a, b & c, and which I regard as
being more probably the first deciduous molar of the lower jaw.

As the Tapir recedes from the Palzothere by the non-de-
velopment of the tooth answering to the first lower premolar, so
the Dinothere recedes from the Tapir in the non-development of
the teeth answering to the first and second premolars in both
jaws. And as the Lophiodon manifested a more simple form of
the posterior premolars than in the existing Tapir, so also, the
Dinothere manifested a still more simple form of the tooth cor-
responding to the second lower premolar in Lophiodon, and to
the third in the Paleothere. By the third ridge of the last
deciduous molar, the Dinothere manifested in this transitional
dentition a character which is retained in the permanent dentition
of the Lophiodon.

The generic peculiarity of the Dinotherium is most strongly
manifested in its tusks. These tusks (Pl. 96, fig. 6) are two in
number, implanted in the prolonged and deflected symphysis of
the lower jaw, in close contiguity with each other, and having
their exserted crown directed downwards and bent backwards,
gradually decreasing to the pointed extremity: each tusk has a
slight longitudinal depression on its outer side: the long implanted
base is excavated by a wide and deep conical pulp-cavity, like the
tusks of the Mastodon and Elephant. In jaws with molar teeth of
equal size the symphysis and its tusks offer two sizes: the larger
ones, which have been found four feet in length with tusks of two
feet, may be attributed to the male Dinotheres, the smaller specimens
with tusks of half the size, to the females. The ivory of these tusks
presents the fine concentric structure of those of the Hippopo-
tamus, not the decussating curvilinear character which characterises
the ivory of the Elephant and Mastodon. No corresponding tusks,
nor the germs of such, have yet been discovered in the upper
jaw of the Dinotherium.

It is highly probable from the shape of the skull of the

ee ee ee

Sage i ae

MASTODON. 613

Dinotherium that this gigantic extinct Pachyderm was of aquatic
habits like the Hippopotamus, and that the inferior tusks served
to detach and tear up by the roots the aquatic plants on which
it fed. From the apparently superior size of those remarkable
teeth in the male, it may be concluded that they also served as
weapons of defence and sexual combat.(1)

PROBOSCIDIANS.

225. Mastodon.—No family of Mammalian Quadrupeds has
suffered more from the destructive operations of time than that
which is characterised by the gigantic size of the individuals com-
posing it and their peculiar endowment of a long and prehensile
proboscis. Two species alone, the Indian and the African Elephants,
continue to represent the Proboscidian type in the Mammalian series
of the present day; whilst those that manifested the modifica-
tions of the dental system, which gradually reduce the complexity
of the Elephantine dentition to the comparative simplicity of that of
the Dinothere and Tapir, have long since been blotted out of the
series of living beings. The name Mastodon was applied by Cuvier
to certain species which, being at the Tapiroid or Dinotherian ex-
tremity of the Proboscidian series, manifested modifications of the
teeth most meriting to be held generically distinct from those of
the existing Elephants: the grinding surface of the molars, instead
of being cleft into numerous thin plates, was divided into wedge-
shaped transverse ridges, and the summits of these were subdivided
into smaller cones more or less resembling the teats of a cow,
whence the generic name.(2) A more important modification ap-
peared to distinguish the extinct genus, in respect of the structure of
the molar teeth: the dentine, or principal substance of the crown
of the tooth, is covered by a very thick coat of dense and brittle
enamel; a thin coat of cement is continued from the fangs upon
the crown of the tooth, but this third substance does not fill up
the interspaces of the divisions of the crown, as in the Elephants.
Such, at least, is the character of the molar teeth of the typical,

(1) For other conjectural uses of the tusks of the Dinothere see the interesting Chapter xiv.
in Dr. Buckland’s ‘ Bridgewater Treatise.’
(2) faorog a nipple, odovs a tooth.

614 UNGULATES.

and first discovered species of Mastodon, which Cuvier has termed
Mastodon giganteus and Mastodon angustidens. Fossil remains of
Proboscidians have subsequently been found, principally in the
tertiary deposits of tropical Asia, in which the number and depth
of the clefts of the crown of the molar teeth, and the thickness
of the intervening cement, are so much increased as to establish
transitional characters between the lamello-tuberculate teeth of the
Elephants, and the mammillated molars of the typical Masto-
dons ;(1) showing that the characters deducible from the molar
teeth are rather the distinguishing marks of species than of
genera, in the gigantic proboscidian family of Mammalian qua-
drupeds.

All Mastodons differ from the Dinotheres and resemble the
Elephants in the presence of two large tusks in the intermaxillary
bones. But those Mastodons with the more simple and typical
molar teeth likewise manifest the Dinotherian character in having
tusks in the lower jaw in the male: these are largest in the Kuropean
species (M. angustidens, Pl. 90, fig. 6, 2: they appear to have
been present in the young of both sexes, and are shown in the
immature jaw of the North American species (Mastodon giganteus)
in Pl. 144, fig. 13, d7;(2) but it would appear from the examples

(1) Mr. Clift had foreseen the possibility of the discovery of such a link, since supplied by

the praiseworthy exertions of Captain Cautley and Dr. Falconer, in his description of the
Fossil Remains from Ava, in the Geological Transactions, second series, vol. 11. “ It is not
impossible,” he says, “ that there may yet be a link wanting, which might be supplied by an
animal having a tooth composed of a greater number of denticles, increasing in depth, and
having the rudiments of crusta petrosa, that necessary ingredient in the tooth of the Elephant :
the entire absence of which distinguishes the tooth of the Mastodon.” Cuvier had previously
enunciated the same supposed distinctive character between the structure of the teeth of the
Elephant and Mastodon. ‘‘ Dans l’éléphant ces vallons sont entiérement comblés.par de cortical,
tandis que dans le Mastodonte ils ne sont remplis de rien.” Ossemens Fossiles, tom. 1., 4to.
1821, p. 225. The truth is, that the exterior of the fangs in all Mastodons is covered by a
moderately thick coat of cement (cortical of Cuvier, crusta petrosa of Clift) ; and that this sub-
stance extends upon the enamel of the crown, in a very thin layer, requiring microscopical
sections and examination in the typical Mastodons; but augmenting in thickness in the Ele-
phantoid and other species, with thinner and more numerous transverse divisions of the
crown of the grinders.

(2) First described and figured by Dr. Godman, as indicative of a new genus, under the
name of Tetracaulodon, in the “Transactions of the American Philosophical Society,” New
Series, Vol. 111, 1830, pp. 478—485, Pls. 17 and 18,

MASTODON. 615

in the British Museum, that only one of the lower tusks, usually
the right, was retained or succeeded by a permanent tusk in
the adult male (ib. fig. 14, 7).(1) I first pointed out the inferior
tusks, whether transitory or persistent, as a well-marked generic
character of Mastodon, as contradistinguished from Elephas, in my
‘** History of British Fossil Mammalia” (p. 275); and also defined
a second character, in the displacement of the first and second
molars, in the vertical direction, by a tooth of simpler form than
the second, a true ‘dent de remplacement’, developed above the
deciduous teeth in the upper, and below them in the under jaw.
Both these dental characters, which are of greater importance
than many accepted by modern Zoologists as sufficient demarca-
tions of existing generic groups of Mammalia, have been recog-
nised in the Mastodon giganteus, of North America, and in the
Mastodon angustidens which is the prevailing species of Europe.

The molar formula of the genus Mastodon, according to the
total number of grinders developed, is:—5j = 28.(2) But in this
number are combined both the deciduous and permanent teeth,
contrary to the dental formule of most other Mammalia. The
two series may, however, be distinguished in the Mastodon, not-
withstanding the successive fall of the true theoretically permanent
molar teeth. The first two molars in the upper jaw, for example,
are unequivocally proved to be the analogues of the deciduous teeth
in ordinary Pachyderms by their relation to a vertical successor,
premolar, or ‘dent de remplacement.’ There are good grounds
also, for regarding the third molar in the order of development,
as the last of the theoretically deciduous series, although it has no
vertical successor. According to these views of the teeth analogous
to the permanent series in ordinary Pachyderms, the formula of
Mastodon is :—

1—1 0—0 1—l 3—3

in. a or — (mas), — (fem.:) . op? De 3 ™ St = 20.

(1) See my Memoir on the so-called Missourium and Tetracaulodon, Proceedings of the
Geological Society, 1842, No. 87, p. 689.

(2) The presence of the small premolar in the lower jaw has not yet been determined ;
neither has its absence. An excavation in the jaw of the young Mastodon described by
Dr. Godman, at the place where the germ of the premolar is hypothetically sketched in
Pl. 144, fig. 7, p 1, would determine this point in regard to the JZ, giganteus.

616 UNGULATES.

The deciduous formula, is :—
° - 1—1 3-—-3
incisors — ; molars == 16.

226. Mastodon giganteus.—I shall first describe the molar teeth in

the Mastodon giganteus, as these best exhibit the tapiroid character of the
grinding surface. This character is most strongly manifested, agreeably
with the law which has been so frequently illustrated in the present
work, by the molars which are first developed in the young animal, at
the period of dentition when it has receded least from the common
type. The crown of the first deciduous molar in the lower jaw
(Pl. 144, fig. 1, d 1) is subquadrate, one inch four and a half lines
in antero-posterior diameter, one inch three lines across its broadest
part ; it supports two transverse ridges, the anterior one most deeply
cleft into two mastoid eminences, the posterior and broader ridge
having one angle produced forwards: the front, back and outer
part of the bases are girt by a tuberculate ridge ; the whole is sup-
ported by two long subcompressed divergent fangs.(1)
The second deciduous molar (Pl. 144, fig. 2, d 2) has a crown,
like the first in shape, but measuring one inch eleven lines, by
one inch eight lines, and having both transverse ridges subdivided
into two mastoid eminences, and a larger posterior basal ridge;
it is supported by two fangs.(2) It is displaced and succeeded ver-
tically by a tooth (ib. fig. 3, p 1) of a more simple form, having
a crown broader in proportion to its length, supporting two bifid
transverse ridges, and girt by a basal cingulum ; it measures one
inch five lines by one inch four lines. This tooth may be regarded
as the first of the theoretically permanent or adult series of teeth:
it answers to the penultimate premolar in the Dinothere and Tapir,
but is very soon shed.

The tooth (ib. figs. 4 & 5, d 3) which answers to the last
milk molar in the above cited Pachyderms, rises into place and
use, as in these and other Quadrupeds, before the premolar is
developed: its crown supports three bifid transverse eminences,

(1) On this tooth is founded the nominal species Mastodon tapiroides of Koch and
Grant. Geol. Proceedings, vol. 111, p. 771. It is figured on the left side of the lower jaw
of the young Mastodon referred by Godman to the Tetracaulodon, loc. cit. Pl. 18.

(2) This tooth is also figured in the Plate above cited of Dr. Godman’s Memoir.

MASTODON. 617

and a tuberculate ridge along the front, back and outer part of
its base: specimens vary in antero-posterior diameter from two
inches ten lines, to three inches three lines in length; the tooth
here figured was two inches four lines across the broadest pos-
terior lobe. The crown is supported by two small anterior fangs
and one large posterior root. This tooth ought, theoretically, to
be succeeded and displaced vertically by a premolar, answering to
the last in the Tapir; but the rapidity of the horizontal progress of
the true molars, and their progressive increase of size and com-
plexity, appear to be the conditions of the interrupted development
of the premolar series, and which operate to their entire suppression
in the genus Elephas.

The antepenultimate or first true molar, the fifth of the series
developed in succession, (Pl. 144, fig. 6 & 7, m 1) resembles the
preceding in conformation, but is larger, and the basal ridge is
commonly less distinct on the outer side: its antero-posterior
diameter is four inches one or two lines, its breadth whieh is
more equable than in d 3, is three inches.(2) In the young
tooth figured, the marks of the subdivision of the eminences of
‘the primary mastoid lobes are not obliterated.

The penultimate, or second true molar, the sixth of the series
in succession, (ib. fig. 8 & 9, m 2) has also the crown divided into
three transverse eminences, each cleft down the middle, but the pos-
terior basal ridge is usually more developed. The antero-posterior
diameter of the crown is from five inches to five and two thirds;
its transverse diameter three inches and a half to three and two-
thirds. The first transverse eminence is supported by a single
fang, the remainder of the tooth by a broad thick base, sub-
divided into three or more roots.(3)

(1) The lower jaw of the Mastodon giyanteus figured by Dr. Hays, Transactions of the
American Philosophical Society, Vol. tv, 1831, Pl. 20, shows the stage of dentition when the
two true deciduous molars have been shed, the first true molar (c) in place, and before the first
premolar (if this tooth be developed in the lower as in the upper jaw) had risen. The fractured
state of the symphysis prevented the recognition of the remains of the alveoli of the deci-
duous tusks ; the specimen being most probably of a young female Mastodon.

(2) A portion of this tooth is figured by Dr. Hays, loc. cit. Pl. 20, fig. 1, d.

(3) This tooth is figured by Dr. Hays, loc. cit. Pl. 21, e., and by Cuvier, ‘Ossemens
Fossiles’ tom. 1. Grand Mastodonte, Pl. 1, fig. 5.

618 UNGULATES.

The last, or third true molar, (ib. fig. 10 & 11, m 3) is subject
to some variety of configuration, as well as size; it supports four
bifid transverse eminences and a posterior talon ;(1) but this is
often developed into a fifth bifid transverse eminence, smaller than
the others, and is sometimes followed by a sixth tuberculate lobe
or talon. The antero-posterior diameter of the crown ranges from
seven and a half inches to eight and a half inches, its transverse
diameter at its thickest (anterior) part, from four inches to four
and a half inches. The remains of the lateral basal ridges are
usually present in this and the two preceding molars as tubercles
at the outer and inner ends of the transverse valleys. The first
and second transverse ridges are usually supported by a single
root, the rest of the molar by a large conical mass subdivided
into four or more roots.

The successive molars have here been described as they appear
in the lower jaw; those above scarcely differ save in a slight increase
of transverse diameter and more subdivided roots.

The superior tusks of Mastodon giganteus project more forwards
than in the Elephant, and are slightly curved upwards and outwards.
The length of the exserted part of those in the skeleton of the
adult male Mastodon in the British Museum surpasses seven feet,
along the curve. Some smaller and straighter specimens, which,
from the contraction of their open basal end, would seem to have
belonged to aged individuals, indicate a sexual inferiority in the
length of the upper tusks in the female of this species.

The inferior persistent tusk in the lower jaw is commonly
about three inches in diameter and one foot in length; it is nearly
straight. Cuvier has apparently figured the end of one of these
tusks in the first Edition of the ‘Ossemens Fossiles, Grand Mas-
todonte’ Pl. 3, fig. 4 & 5. In the same plate he has well repre-
sented a lower jaw of an old male Mastodon showing the persistent

alveolus of the single tusk, in fig. 2. The original of this figure

(1) This variety is figured by Dr. Hays in the lower jaw of an old female Mastodon, loc.
cit. Pl. 23, & Pl. 24, and in that of an old male Mastodon, with one tusk, in PJ. 29. Also by
Cuvier, loc. cit. ‘Grand Mastodonte,’ Pl. 1, figs. 3 & 4.

(2) This variety is figured by Dr. Hays, loc. cit. Pl. 21, £, and by Cuvier, loc. cit, fig. 2.

MASTODON. 619

is now in the Cabinet of the American Philosophical Society at
Philadelphia. Dr. Hays has refigured the specimen, as a lower jaw
of the Tetracaulodon, in his Memoir in the Transactions of the
Society for 1831. Why Cuvier should have suppressed the in-
structive plate of this lower jaw in his 2nd Kdition of the
‘Ossemens Fossiles’ I know not. The Plate 26 in Dr. Hay’s
Memoir would indicate that both lower tusks were occasionally
retained in the male Mastodon giganteus as they commonly are in
the male Mastodon angustidens.

227. M. angustidens—The molar teeth of this extinct European
Mastodon are narrower in proportion to their antero-posterior extent,
and their grinding surface is more mammillated and less transversely
ridged than in the Mastodon giganteus. As in this species the molar
series, on each side of the upper jaw and probably also of the lower,
includes two deciduous teeth which are succeeded by one tooth ina
vertical direction, and this by four other molars progressively in-
creasing in size, and pushing out their predecessors as they advance:
the total number of molars developed on each side of the upper jaw
being seven; the greatest observed number in use, or exposed at
the same time is three on each side; which is reduced in the old
animals to one on each side. ;

The first milk-molar Pl. 144, fig. 12, d 1,(1) has an oblong
subquadrilateral transverse section, rounded anteriorly: it is ob-
scurely quadricuspid; the two anterior cusps are first blended
together by attrition, then the posterior external cusp is worn
down into the same surface; the posterior internal cusp remaining
longest distinct. It has two fangs.

The second milk-molar (ib. d 2)(2) is at least three times
as large as the first and supports three pair of cusps, the posterior
ones being the largest: and the outer one of the middle pair
indicates by its lateral projection the outer side of the tooth: a
narrower tuberculate ridge is developed at the anterior and pos-
terior margins of the crown. Lach pair of cusps is reduced by
progressive attrition to a transverse oval depression, the two ex-
terior and posterior cusps being the last to yield. It has two

(1) Kaup, ‘ Ossemens Fossiles de Darmstadt,” Pl. 16, fig. 1, & 1a, Pl. 20, fig. 2.
(2) Ibid. Pl. 16, fig. 1, & 1a, Pl. 17, fig. 12, Pl. 21, fig. 1.

620 UNGULATES.

fangs, the anterior and smaller one supporting the anterior pair
of cusps, the posterior the remainder of the crown.

The vertically succeeding tooth of the second molar (ib. p 1)
follows the usual law in having a less complicated crown than the
tooth which it replaces: it has only two pairs of principal cusps,
and is a sort of magnified representative of the first small deci-
duous molar, which has no successional tooth.(1) The external
and anterior cusp is the longest, the base of the crown is partially
surrounded by a tuberculate ridge. This tooth, when fully deve-

loped, has three roots, of which the outer and anterior one

supports the corresponding cusp; the other two supporting the
rest of the crown. Specimens have been found in which all the
four cusps have been worn down to their base; but the insular
patches of dentine have been distinct and severally surrounded by
their thick enamel. |

The fourth molar,(2) in the order of size, is anterior to the
preceding in the order of development, and is the third in the order
of position (ib. fig. 12, d 3) before the fall of the two deciduous teeth,
_and the second after the acquisition of the vertically succeeding molar.
I regard it as being essentially the last of the true deciduous
series, but which has no vertical successor. The grinding surface
presents four pairs of cusps and a small posterior ridge or talon :(3)

the first pair of cusps is the smallest and is most complicated with

accessory tubercles: the bases of the cusps encroach reciprocally
upon each other’s interspaces across the middle longitudinal valley,

(1) If the premolar (p 1) succeeded the first small molar, as described by Dr. Kaup, (Sur le
Mastodon longirostris, 4to. 1835, p. 70.) it would form an exception to the rule; but the spe-
cimen of the upper jaw of Mastodon angustidens from Dax figured by Cuvier, Ossem. Fossiles,
Divers Mastodontes, Pl. 111, fig. 2, shows the unworn cusps of the quadri-cuspid successional
molar projecting into the socket, whence the sex-cuspid deciduous tooth has been extruded.
Cuvier figures one of these teeth, from Dax, loc. cit., Pl. 1, fig. 2, in which the two anterior
cusps are blended into a single irregular surface; behind which are the worn tips of the
posterior pair of cusps.

2) Kaup, ib. Pl. xvi, fig. 1 & 1a; Pl. xx, fig. 2; Pl. xvi, fig. 13 & 14.

(3) This tooth is described in my ‘ History of British Fossil Mammalia,’ p. 286, as having
three pairs of mastoid tubercles and ‘a large posterior tuberculate talon’, two of the tubercles in
that talon (fig. 100, p. 284) corresponding with the fourth pair, here described. The two
extremes in the varieties of the talon in this tooth may be seen in Cuvier’s ‘ Divers Mastodons’
Pl. iii, fig. 2, and Kaup’s PI. xvi, fig. 1 & 1a, and I have, as yet, no evidence that they charac-
terize distinct species. The English fossil (fig. 100, ‘ Br. Foss. Mam.’) is an intermediate variety,

a

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e- ' -
Oe a ee

MASTODON. 621

and thus appear to alternate, when worn down. The anterior
talon is continued from the internal cusp; the posterior talon
consists of three tubercles.

The antepenultimate tooth would seem to be the analogue of the
first of the three true molars in the Tapir and ordinary Pachy-
derms, since it presents, as in the M. giganteus, a marked increase of
size, and consists of four pair of cusps and two talons, one anterior
the other posterior ; but these accessory elevations are relatively
larger and more complicated. Dr. Kaup figures one molar in
which the hinder talon is divided into nine tubercles; in another
it was divided into three unequal tubercles. The large pairs of
cusps are accompanied by small accessory tubercles which are
worn away in the course of mastication.

The penultimate molar (Pl. 90, fig. 6, m 6)(1) differs in
little else than size, from the preceding; the number of accessory
tubercles to the normal cusps, which is always irregular, appears
to be greater; and the terminal talons to be more sub-divided.

The last molar of the upper jaw, the seventh in the order of develop-
ment, (ib. m 7)(2) has five pairs of cusps, the anterior talon of the ante-
cedent teeth being here developed into a normal pair, which is also
the largest: the posterior talon sometimes consists of a group of
tubercles, the posterior of which represents an accessory talon : some-
times the anterior tubercles of the talon are so developed as to resem-
ble a sixth pair of cusps; at other times the talon presents only two
or three tubercles in the same transverse row ; and is thus subject to
great variety, as is also the entire tooth in respect of size. The tooth
is supported by two principal roots, of which the anterior and
smaller supports the two anterior pairs of cusps ; the posterior mass
the rest of the tooth: this broad fang becomes sub-divided into
two or more, in the progress of age. Not any of the preceding
molars have remained long enough in their sockets to exhibit the
effects of such extensive abrasion as has been observed in specimens
of the last molar: this, therefore, becomes itself a character of the
tooth which is longest retained, when the distinguishing tubercles
have thereby been destroyed.

(1) Kaup, Pieces, fsa (2) Ib. Pl. xvmi1.

622 UNGULATES.

Cuvier has given a very interesting figure of a last molar in
this stage, (loc. cit. Pl. 111, fig. 5) which has its grinding surface
reduced to an uniform disc of smooth dentine.

The first molar(l) of the lower jaw of the Mast. angustidens,
was as small and apparently more simple in the crown, than that
_ above. M. M. Croizet and Jobert consider that it had but one pair
of cusps ; Dr. Kaup states that it is succeeded by a ‘ dent de remplace-
ment,’ a figure of which he cites from Meyer’s ‘ Fossiles de Georgens-
mund,’ Pl. 1, fig. 2.

The second molar of Kaup, which, if the first be so succeeded
vertically, should be the third, has three pairs of cusps, and an
anterior talon. The first pair of cusps or ‘tubercles, are so much
smaller than the second, as to appear like a large bi-tuberculate
talon: the second pair is the largest, and forms the broadest part
of the grinding surface ; in the middle of the valley between this and
the third pair, there is ordinarily a small tubercle, which Dr. Kaup
found to be, in one instance, eaten away by caries. The posterior
talon is sometimes tuberculate, sometimes flat. Dr. Kaup indicates
the resemblance between these teeth, and that of the Mastodon
augustidens, from Simorre, figured by Cuvier, loc. cit. Pl. 1, fig. 4.

The lower molar, corresponding to the last of the deciduous series
(d 3) in the upper jaw, has three pairs of cusps and a posterior,
often large, talon ; the anterior pair is rather larger than the second ;
the posterior has a slight increase of breadth. Dr. Kaup figures one

of these teeth in which each pair of cusps has been worn down,

toa single transversely oval cavity surrounded by enamel.

The ante-penultimate lower molar has four pairs of cusps and.
a posterior talon which consists of a small and single tubercle. The

anterior pair of cusps is complicated, with some small tubercles,
which are soon worn down. Ina fully developed tooth, figured by
Dr. Kaup, Pl. xrx, fig. 5, the two anterior pairs of cusps are abraded
to a single quadrilobate surface, and this is followed by five sub-

circular depressions, formed by the abraded summits of the two

posterior pairs of cusps, and the talon. The anterior pair of cusps
and part of the second pair are supported by a vertical and slender

(1) Meyer, ‘ Fossiles de Georgensmund,’ Pl. 1, fig. 3.

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Ne ne eee ay

MASTODON. 623

fang ; the rest of the crown by a thicker fang, which inclines obliquely
backwards: these roots have sometimes a longitudinal channel on
each side.

The penultimate molar (Pl. 90, fig. 6, m 6)(1) has four pairs
of cusps, and a posterior bituberculate talon, which represents a
fifth smaller pair of cusps: in the corresponding upper molar the
posterior talon is divided into a greater number of tubercles, and
the whole tooth is broader. Cuvier has likewise figured (loc. cit.
Pl. 111, fig. 14) a quadricuspid tooth of the Mastodon angustidens,
from the collection of M. Hammer, which he compares with that of
the upper jaw from Dax.

The last molar (PI. 90, fig. 6, m 7) varies in size in different
individuals, even more than the last molar of the upper jaw: it has
usually five pairs of cusps, and a posterior talon. The cusps are
slightly inclined outwards, and it is further distinguished from the
last molar of the upper jaw by its narrower figure and the more coni-
cal shape of the talon. Its two roots are simple, but of very unequal
size, and inclined backwards : the first, which is very long and slender
in old teeth, supports only the anterior pair of cusps ; the rest of
the molar being supported by the large conical compressed posterior
fang; a third small and short fang is sometimes sas from
the interspace of the two longer ones.

I have been induced to characterise the different molars of the
Mastodon angustidens, because the most common remains of the
Mastodon in this country are detached grinding teeth of this species,
which may thus be determined. Portions of the large upper tusks
are occasionally found in the older pliocene crag of Norfolk and
Suffolk, and I have recently received a large portion of the straight
tusk of the lower jaw. It was about sixteen inches long, and part of
the tusk which protruded from the jaw, the base of the fragment being
as solid as the apex, and the whole being traversed by a sub-central
canal, of nearly the same diameter, about two lines from one end
of the fragment to the other. The outer layers of the ivory had
been detached, excepting a very small portion near the apex, which
retained its thin coating of cement. The transverse section of this
tusk gave an irregular oval disk, one side being less convex than

(1) Kaup, Joc. cit, Pl. xrx, figs, 1 & 2.

624 UNGULATES.

the other; and on the lower half of the more convex (outer) side
of the tusk, faint traces were distinguished of longitudinal grooves,
about a line in breadth. In all these characters, the fragment in
question agreed with a similar fragment of a tusk, ten inches in
length, obtained from the miocene, or older pliocene tertiary deposits
at Eppelsheim, in Germany, which specimen Dr. Kaup had ascer-
tained to belong to the lower jaw of the same species of Mastodon.

The division of the transverse eminences of the surface of the
molar teeth into large rounded mammillz, often placed sub-alter-
nately, is common, with slight modifications, to the European
Mastodon angustidens, with allied species in South America, Australia,
and Southern Asia.

228. Transitional Mastodons.—Mr. Clift(1) has described and
beautifully illustrated the dentition of one of the Asiatic Mastodons
with molar teeth, which differ chiefly from those of the Mast. angus-
tidens in their greater relative breadth: he has, therefore, termed the
species Mast. latidens.(2) The last lower molar tooth is figured in Pl. 38,
fig. 1, of the volume cited: it presents a grinding surface nine inches
in length, and nearly four inches in breadth; divided into six trans-
verse eminences and a posterior talon; each eminence is divided into
two principal mammillz, and these are again sub-divided into two
smaller rounded mammille, except in the fifth eminence, which
consists only of the two principal mammille, whilst the sixth
division or talon, is formed by a single large obtuse eminence. (3)

In the same plate Mr. Clift figures part of the lower jaw with
the last molar tooth of another more remarkable species of Probosci-
dian, which he has termed Mastodon elephantoides.(4) This tooth
(Pl. 145, fig. 2) is twelve inches in antero-posterior extent, and three
inches in breadth: its grinding surface is divided into ten nearly
equal low transverse ridges, the summits of which are sub-divided

into five or six small and equal obtuse mammille. The interspaces —
of the ridges are not filled with cement, as in the true Elephants; —

(1) Geological Transactions, Second Series, vol. 11, 1829, p. 369.

(2) This appropriate name was suggested to Mr. Clift by Mr. Broderip, the learned

Secretary of the Geological Society.

(3) Pl. 145, fig. 1. This and other characteristic remains of the M. latidens were dis-
covered in newer tertiary deposits on the banks of the Trawadi, in Ava.

(4) This name was likewise suggested by Mr. Broderip, the species was found in Ava.

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4

:

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ELEPHANT. 625

only a thin layer of that substance is continued upon the unworn
enamel, as in the true Mastodons.

With reference to the molar teeth of the M. latidens, Mr. Clift
remarks that, in comparison with those of the M. giganteus, the
ridges are more numerous, less distant, and the interstices less
deep: they are also more sub-divided, and the teeth begin to assume
the appearance of those of the Elephant :—‘‘ On advancing to
Mastodon elephantoides, we shall find all these features of similarity
more strongly developed :—the points and ridges are still more
numerous, and the structure, were it not for the absence of ‘ crusta
petrosa’, becomes almost that of the tooth of the Elephant.”

The difference, in regard to the coronal cement, or ‘crusta
petrosa,’ between Mastodon and Elephas, is not absolute, but pro-
portional; although the quantity in the more deeply cleft crowns
of the Elephants’ molars is considerably greater, the cement there
fulfilling its office of binding together the plates of the crown, whose
interspaces it completely fills.

Whether the more essential characters of the genus Mastodon,
viz: the premolars, are present in the M. elephantordes of Clift,
has not yet been determined. Dr. Falconer informs me that he has
satisfied himself of the absence of the tusks in the lower jaw of very
young individuals, which forms another striking feature of the transi-
tional character of this extinct species. The same distinguished
Palzontologist, in conjunction with his accomplished and scientific
coadjutor, Captain Cautley, has brought to light the remains of
extinct species of Proboscidians with more deeply cleft molars,
occupied by the abundant cement which characterises the structure
of the grinding teeth of the Elephantine genus. The difference in
the thickness and height of the divisions of the crown of these
teeth in the Elephas planifrons and Elephas Hysudricus, F, & C.,
establishes two intermediate links between the Elephantoid Mas-
-todon and the Indian Elephant, in which latter species, amongst
existing animals, the teeth present the greatest complexity of structure.

229. Elephas.—The dentition of the sole surviving genus of
the great Proboscidian Family includes two long tusks (Pl. 146,

fig. 1, 7) one in each of the intermaxillary bones, and large and
Ss

626 UNGULATES.

complex molars (ib. m 3, 4 & 5) in both jaws: of the latter
there is never more than one wholly, or two partially, in place
and use, on each side at any given time; for, like the molars of
the Mastodons, the series is continually in progress of formation
and destruction, of shedding and replacement; and in the Elephants
all the grinders succeed one another, like true molars, horizon-
tally, from behind forwards; none being displaced and replaced
by vertical successors or premolars.

The total number of teeth developed in the Elephant appears

to be:—in. 2: m. &§ = 28. The two large permanent tusks

being preceded by two small deciduous ones, and the number of
molar teeth which follow one another on each side of both jaws
being at least six.

The deciduous tusk (ib. fig. 3, di) makes its appearance beyond
the gum between the fifth and seventh month: it rarely exceeds
two inches in length, and is about a third of an inch in diameter
at its thickest part, where it protrudes from the socket; the fang
is solidified, and contracts to its termination, which is commonly a
little bent, and is considerably absorbed by the time the tooth is
shed, which takes place between the first and second year.(1)

The socket of the permanent tusk, (ib. fig. 3, 2) in a new-born
Elephant, is a round cell about three lines in diameter, situated

on the inner and posterior side of the aperture of the temporary }
‘socket. The permanent tusks cut the gum, when about an inch :
in length, a month or two usually after the milk-tusks are shed.
At this period, according to Mr. Corse,(2) the permanent tusks are ~
‘black and ragged at the ends. When they become longer, and
project beyond the lip, they soon are worn smooth by the motion ~
and friction of the trunk.” The widely open base of the tusk ;
is fixed upon a conical pulp, which, with the capsule surround- q
ing the base, progressively increases in size, stimulates a .con-—
comitant increase in the capacity and depth of the socket, which
cavity soon obliterates that of the deciduous tusk, and finally extends ]

(1) ‘Memoir on the Teeth of the Elephant,’ in the Philosophical Transactions, 1799, |

p. 211: in which a good figure of the deciduous tusk is given in Plate 5.
(2) Loe. cit., p. 212.

ELEPHANT. 627

its base close to the nasal aperture (PI. 146, fig. 1). The tusk,
conical at its first-formed part, afterwards sub-cylindrical, being
subject to no habitual attrition from an opposed tooth, and worn
only by the occasional uses to which it is applied, arrives at an
extraordinary length, following the curve originally impressed upon
it by the form of the socket, and gradually widening from the
projecting apex, to that part which was formed when the matrix
and the socket had attained their full size.

These incisive teeth of the Elephant not only surpass other
teeth in size, as belonging to a quadruped so enormous, but they
are the largest of all teeth in proportion to the size of the body ;
representing in a natural state those monstrous incisors of the
Rodents which are the result of accidental suppression of the
wearing force of the opposite teeth.

The tusks of the Elephant, like those of the Mastodon, consist
chiefly of that modification of dentine which is called ‘ivory,’ and
which shows, on transverse fractures or sections, striz proceeding
in the arc of a circle from the centre to the circumference, in
opposite directions, and forming by their decussations curvilinear
lozenges (Pl. 146, fig. 8,7) This character is peculiar to the tusks
of the Proboscidian Pachyderms.

In the Indian Elephant the tusks are always hat and straight
in the female, and less deeply implanted than in the male: she thus
retaining, as usual, more of the characters of the immature state.
In the male they have been known to acquire a length of nine feet,
with a basal diameter of eight inches, and to weigh one hundred and
fifty pounds ; but these dimensions are rare in the Asiatic species.

Mr. Corse, speaking of the variety of Indian Elephant, called
‘ Dauntelah’ from its large tusks, which project almost horizontally
with a slight curve upwards and outwards, says, ‘‘ The largest I have
known in Bengal, did not exceed seventy two pounds avoirdupois ;
at Tiperah they seldom exceed fifty pounds.”(1) There are varieties
of the Dauntelah in which the large tusks of the male are nearly

(1) Loe,‘ cit,, :p. 272:
ss 2

628 UNGULATES.

or quite straight; and in a more marked breed called ‘Mooknah’
the tusks are much smaller, are straight, and point directly down-
wards. These ascertained varieties in an existing species ought ~
to weigh with the observers of analogous varieties in the teeth of
fossil Proboscidians, before they pronounce definitely on their value
as characters. of distinct species. More anomalous varieties occa-
sionally present themselves in the Indian Elephant, as when one
tusk is horizontal, the other vertical; or when, from some distortion —
of the alveolus, a spiral direction is impressed upon the growth of
the tusk, as in that specimen figured by Grew in the ‘ Rarities of
Gresham College,’ Tab. 4, and which is now in the Museum of
the English College of Surgeons. The tusk of the Elephant is
slightly moveable in its socket, and readily receives a new direction
of growth from habitual pressure: this often causes distorted tusks
in captive Elephants, and Cuvier(1) relates the mode in which
advantage was taken of the same impressibility, in order to rectify —
the growth of such tusks in an Elephant kept at the Garden of —
Plants. , )

The tusks of the extinct Elephas primigenius, or Mammoth, —
have a bolder and more extensive curvature than those of the
Elephas indicus: some have been found which describe a circle but, —
the curve being oblique, they thus clear the head, and point outwards, —
downwards, and backwards. The numerous fossil tusks of the —
Mammoth which have been discovered and recorded, may be ranged
under two averages of size :—the larger ones at nine feet and a half, —
the smaller at five feet and a half in length. I have elsewhere(2)
assigned reasons for the probability of the latter belonging to the»
female Mammoth, which must accordingly have differed from the
existing Elephant of India, and more resembled that of Africa in
the development of her tusks; yet manifesting an intermediate
character by their smaller size. Of the tusks which are referable
to the male Mammoth, one from the newer tertiary deposits in
Essex, measured nine feet ten inches along the outer curve, and

(1) ‘ Ossemens Fossiles,’ 4to. 1821, tom. i, p. 47.
(2) ‘ History of British Fossil Mammalia,’ 8vo. 1844, p. 244.

ELEPHANT. 629

two feet five inches in circumference at its thickest part: another
from Eschscholtz Bay, was nine feet two inches in length, and
two feet one and a half inches in circumference, and weighed one
hundred and sixty pounds. A Mammoth’s tusk has been dredged
up off Dungeness which measured eleven feet in length. In several
of the instances of Mammoth’s tusks from British strata, the ivory
has been so little altered as to be fit for the purposes of manufacture ;
and the tusks of the Mammoth, which are still better preserved
in the frozen drift of Siberia, have long been collected in great
numbers as articles of commerce.(1)

Cuvier(2) states that the Elephant of Africa, at least in certain
localities, has large tusks in both sexes, and that the female of this
species, which lived seventeen years in the Menagerie of Louis XIV,
had larger tusks than those in any Indian Elephant, male or female,
of the same size which he had seen. The ivory of the tusks of
the African Elephant is most esteemed by the manufacturer for
its density and whiteness.

The molar teeth of the Elephant are remarkable for their great
size, even in relation to the bulk of the animal, and for the extreme
complexity of their structure. ‘The crown, of which a great propor-
tion is buried in the socket, and very little more than the grinding
surface appears above the gum, is deeply divided into a number
of transverse perpendicular plates, consisting each of a body of
dentine, (Pl. 146, figs. 6 & 7, d) coated by a layer of enamel (e),
and this by the less dense bone-like substance (c) which fills
the interspaces of the enamelled plates, and here more especially
merits the name of ‘cement,’ since it binds together the several
divisions of the crown, before they are fully formed and united by
the confluence of their bases into a common body of dentine. As
the growth of each plate begins at the summit, they remain detached

(1) In the account of the Mammoth’s bones and teeth of Siberia, published in the ‘ Philo-
sophical Transactions’ for 1737, (No. 446), tusks are cited which weighed two hundred pounds
each, and “are used as ivory, to make combs, boxes, and such other things ; being but little
more brittle, and easily turning yellow by weather and heat.” From that time to the present
there has been no intermission in the supply of ivory, furnished by the tusks of the extinct

Elephants of a former world.
(2) Loc. cit., p. 55.

630 UNGULATES.

and like so many separate teeth or denticles, until their base is
completed, when it becomes blended with the bases of contiguous
plates to form the common body of the crown of the complex
tooth, from which the roots (ib. 7 r) are next developed.

But the growth of each constituent plate is analogous to, and
almost as complex as that of the entire tooth ; for each plate consists
at the beginning of a series of separate slender conical columns
or digital processes (Pl. 146, fig. 4), arranged transversely across
the tooth. The formation of these columns likewise begins at their
summit, and descends, their bases gradually expanding until they
are blended together to form a continuous transverse plate (ib.
fic. 5.)(1); just as the plates are subsequently blended together to
form a continuous longitudinal crown of the grinder. After the
digital processes have coalesced to form the transverse plate, the
sides of this plate, which in the Asiatic Elephant are parallel, become
wrinkled or undulated: giving a similar character to the line of
enamel, when the surface of the tooth has been worn down to this
point. The lateral margins of the plates are rounded and, though
covered by a thick cement, still project so as to give a vertically
ribbed surface to the sides of the complex molar (PI. 148, fig. 5); _
when the cement is detached the margin of the plate is seen to
be undulated by a number of small transverse risings: this structure —
is beautifully shown in some of the molars of the Mammoth, a
portion of one of these is figured in Pl. 148, fig. 7.(2)

The plates of the molar of the Elephas primigenis are thinner
in proportion to their breadth, and: are generally a little expanded
at the middle: the enamelled border is often undulated, as in
the Elephas asiaticus, and sometimes with a greater degree of
regularity. The coronal plates are in general more numerous in
proportion to the size of the crown in the Mammoth, than in the
El. asiaticus. (Compare fig. 6, molar of Mammoth, with fig. 3, —
molar of Indian Elephant in Plate 148). In the El. africanus

(1) Such detached plates of the large molars of the Mammoth offer a rude resemblance to
a hand, and may be found figured in the works of the older collectors of petrifactions, under
the name of ‘ Cheirolites,’ as the fossilized hand of a monkey or a child.

(2) See ‘ History of British Fossil Mammalia,’ 8vo. p. 337, fig. 91.

ELEPHANT. 631

fig. 4), on the other hand, the lamellar divisions of the crown
are fewer and thicker, and they expand more uniformly from
the margins to the centre, yielding a lozenge-form when cut or worn
transversely.

The horizontal as well as vertical course of development of the
Elephant’s grinder is well illustrated by the Mammoth’s molar,
the last of the lower jaw, in Pl. 148, fig. 5. The separate digital
processes (ff) of the posterior plates are still distinct, and adhere
only by the remaining cement; a little in advance we see them
united to form the transverse plate; and, at the opposite extremity
of the tooth, the common base of dentine (d') is exposed by which
the plates are finally blended into one individual complex grinder(1) :
this never takes place simultaneously along the whole course of the
tooth in the larger molars of the existing Indian Elephant, or its
extinct congener, the Mammoth. The African Elephant, and some
of the extinct Indian species, as the El. planifrons, (Pl. 147, fig. 1),
manifest their affinity to the Mastodon by the basal confluence
of the hindmost plates before the foremost ones are worn out. The
grinders of the El. planifrons are also distinguished from the existing
species by the number of roots (ib. d d), and the extent of the
base (a a) from which they are simultaneously developed.

The formation of each grinder begins with the summits of the
anterior plate, and the rest are completed in succession ; the tooth is
gradually advanced in position as its growth proceeds, and, in the
existing Indian Elephant, the anterior plates are brought into use
before the posterior ones are formed. When the complex molar cuts
the gum the cement is first rubbed off the digital summits: then
their enamel cap is worn away, and the central dentine comes into
play with a prominent enamel ring: the digital processes are next
ground down to their common uniting base, and a transverse tract

(1) Some anatomists describe the divisions of the crown of the Elephant’s grinder as
entire teeth; and Mr. Corse, (loc. cit. p. 213) who first propounded this view, calls
each complex grinder ‘a case of teeth,’ and states “‘that these teeth are merely joined to each
other by an intermediate softer substance, acting like a cement.” But this description applies
only to the incompletely formed tooth ; and the detached eminences of the crown of any complex
tooth, at that stage of growth when they are held together only by the still uncalcified sunper
ing matrix, might with equal justice be regarded as so many distinct teeth.

632 UNGULATES.

of dentine with its wavy border of enamel is exposed; finally the
transverse plates themselves are abraded to their common base of
dentine, and a smooth and polished tract of that substance is
produced.(1) From this basis the roots of the molar are developed,
and increase in length, to keep the worn crown on the grinding
level, until the reproductive force is exhausted. When the whole
extent of a grinder has thus successively come into play, its last
part is reduced to a long fang supporting a smooth and polished
field of dentine, with sometimes a few remnants of the bottom of the
enamel folds at its hinder part, as shown in Pl. 148, fig. 8. When the
complex molar has been reduced to an uniform surface it becomes use-
less as an instrument for grinding the coarse vegetable substances on
which the Elephant subsists : it is then attacked by the absorbent ac-
tion, by which and the pressure of the succeeding tooth it is finally shed.

The grinding teeth of the Elephant progressively increase in
size, and in the number of lamellar divisions, from the first to the
last ; and, as the rate of increase in both respects is nearly identical
in both jaws, I shall describe them chiefly as they appear in the
lower one.

The first molar which cuts the gum in the course of the second
week after birth, has a sub-compressed crown, nine lines in antero-
posterior diameter, divided by three transverse clefts into four plates,
the third being the broadest and the tooth here measuring six lines —
across(2) : the first and second plates have two mammilloid summits ;
the third and fourth have three or four such; there is a single, and ~
sometimes a double mammilloid summit, at the fore and back part ’ :
of the crown: the base slightly contracts, and forms a neck as long ©

as the enamelled crown, but of less breadth, and this divides into |

an anterior and posterior, long, sub-cylindrical, diverging, but —
mutually incurved fangs: the total length of this tooth is one inch |
and a half. The corresponding upper molar (Pl. 148, fig. 1 & 2), ©

(1) In the fossil specimen, figured in Pl. 147, the left molar fig. 2, J, exhibits all the above : ;

described gradations of use; but the right molar 7, through some accident to the opposing q }
tooth in the lower jaw, has not been so worn, but projects beyond the level of the left molar,

with the mammillated margins of the plates entire. |
(2) These are also the dimensions of the first lower molar figured by Mr. Corse, loc. cit., 7
Pl. vi, fig. 1, D, and fig. 3; but I have seen the first lower molar of smaller dimensions.

ELEPHANT. 633

which Mr. Corse describes as cutting the gum a little earlier than
the lower one, has the anterior single digital process or mammilla,
and the posterior talon developed into a fifth plate smaller than the
fourth with which its middle part is confluent: the neck of this

tooth is shorter, and the two fangs are shorter, larger, and more
- compressed than those of the lower first molar.(1) This tooth is
the analogue of the first deciduous molar in other Ungulates: it
is not a mere miniature of the great molars of the mature animal,
but retains, agreeably with the period of life at which it is developed,
a character much more nearly approaching that of the ordinary
Pachydermal molar, manifesting the adherence to the more general
type by the minor complexity of the crown, and by the form and
relative size of the fangs. In the transverse divisions of the crown
is indicated the affinity to the Tapiroid type, the different links con-
necting which with the typical Elephants are supplied by the extinct
Lophiodons, Dinotheriums, and Mastodons. The sub-division of the
summits of the primary plates recalls the character of the molars,
especially the smaller ones, of the Phacochere in the Hog-tribe. As
the Elephant advances in age the molars rapidly acquire their more
special and complex character.

The first molar is completely in place and in full use at
three months, and is shed when the Elephant is about two
years old.

The sudden increase and rapid development of the second molar,
(Pl. 146, fig. 3, m 2), may account for the non-existence of any
vertical successor or ‘premolar’, in the Elephant. The eight or nine
plates of the crown are formed in the closed alveolus, behind the
first molar by the time this cuts the gum, and they are united with
the body of the tooth, and most of them in use, when the first molar is
shed. The average length of the second molar is two inches and a
half; ranging from two inches to two inches and nine lines. The
ereatest breadth, which is behind the middle of the tooth, is from

(1) This molar is represented, one third the natural size, by M. de Blainville in his
‘ Ostéographie des Eléphans,’ Pl. vit, as being divided into four plates, with anterior or poste-
rior tubercles.

634 | UNGULATES.

one inch to one inch three lines. There are two roots, the cavity
of the small anterior one expands in the crown, and is continued
into that of the three anterior plates. The thicker root supports
the rest of the tooth. The second molar is worn out and shed,
before the beginning of the sixth year.

The third molar has the crown divided into from eleven to
thirteen plates; it averages four inches in length, and two inches
in breadth, and has a small anterior, and a very large posterior
root ; it begins to appear above the gum about the end of the second
year, is in its most complete state and extensive use during the
fifth year, and is worn out and shed in the ninth year. The last
remnant of the third molar is shown at m3, fig. 1. It is probable
that the three preceding teeth are analogous to the true deciduous
molars of ordinary Pachyderms. )

The fourth molar presents, as M. de Blainville well observes,
a marked superiority of size over the third, and a somewhat
different form: the anterior angle is more obliquely abraded, giving
a pentagonal figure to the tooth in the upper jaw (ib. fig. 1 m 4).
The number of plates in the crown of this tooth is fifteen or
sixteen: its length between seven and eight inches; its breadth
three inches. It has an anterior simple and slender root sup-
porting the first three plates; a second of larger size and _ bifid,
supporting the next four plates; and a large contracting base for
the remainder. The fore part of the grinding surface of this tooth
begins to protrude through the gum at the sixth year: the tooth
is worn away and its last remnant shed about the twentieth or
twenty-fifth year. It may be regarded as the analogue of the first
_ true molar of ordinary Pachyderms.

The fifth molar with a crown of from seventeen to twenty
plates, measures between nine and ten inches in length and
about three inches and a half in breadth. The second root is
more distinctly separated from the first simple root than from
the large mass behind. It begins to appear above the gum
about the twentieth year: its duration has not been ascertained
by observation ; but it probably is not shed before the sixtieth year.

ELEPHANT. 635

The siath molar, which from the analogy of the Mammoth(1),
I regard, with M. de Blainville, as the last, has from twenty-two
to twenty-seven plates; its length or antero-posterior extent, fol-
lowing the curvature, is from twelve to fifteen inches: the breadth
of the grinding surface rarely exceeds three inches and a half.

The reproductive power of the matrix in some cases surpasses
that of the formative development of the cavity for lodging the
tooth and the last lamella are obliged to be folded from behind
forwards upon the side of the tooth. I have described and figured
this condition in the last lower molar of the Mammoth in my
‘History of British Fossil Mammalia.’(2) M. de Blainville has
represented the same structure of the last molar tooth of both
the upper and lower jaw of the Hlephas wdicus, in the Fasci-
culus of the ‘ Ostéographie des Eléphans.’

One may reasonably conjecture that the sixth molar, if it make
its appearance about the fiftieth year, would, from its superior depth
and length, continue to do the work of mastication until the pon-
derous Pachyderm had past the century of its existence.

Mr. Corse has figured the sixth molar (which he calls the
seventh or eighth) with twenty-three plates, in tab. x of his
Memoir, and a small cavity c is marked as an incipient alveolus
for a succeeding grinder. Had it actually been such it might
have been expected to contain some calcified portions of the
anterior plates of such succeeding grinder. If, however, better
evidence should subsequently establish the existence of a seventh
grinder, it will at the same time add to the probability of the
longevity ascribed by the ancients to the Elephant.

(1) I was not able to trace the series of molars of the upper jaw of this extinct Elephant,
out of several hundreds which I have compared, beyond the sixth, ‘ with twenty-two coronal
plates, and an antero-posterior extent of fifteen inches.’ See ‘ British Fossil Mammalia, Part V,
2nd September, 1844, p. 225. The number of molars successively developed in the Indian
Elephant is stated at seven or eight, on the authority of Mr. Corse; but I fully participate in
M. de Blainville’s doubts as to the adequacy of the grounds for such a conclusion.—See the
‘Ostéographie des Eléphans,’ 4to. My earliest knowledge of this valuable Part of M. de
Blainville’s great Work was from a copy transmitted by the Author, which I received from the
hands of Professor Matteucci at the Meeting of the British Association at York, Septem-

ber 30th, 1844: it bears no date of issue.
(2) Part v, fig. 90, p. 233

636 UNGULATES.

The phenomena of the course and changes of the dentition
of the extinct Hlephas primigenius are closely analogous to those
of the existing species of India. The first small molar having
the same comparatively simple, four-plated, crown, with two long
fangs,(1) was interpreted as evidence of a new genus of Pachy-
derms, when first discovered in a mutilated state.(2) The second
molar, eight-plated, is three inches in length and one inch and
a half in breadth :(3) and already indicates the specific difference
of the Elephas primigenius, in the superior breadth of the molars. The
third upper molar has from twelve to fourteen plates, measures three
inches and a half in length, and one inch two-thirds in breadth.
The fourth molar is subject to more variety, and presents, as in
the existing Elephant, a sudden increase of size, but seems to
have been subject to a greater range of variation in regard to
the number and proportions of its coronal lamellz: these I have
estimated at from twelve to sixteen; the greater number being
usually in the lower molar; its length at from six and a half to
nine inches, and its breadth at three and a half inches in the
upper and three inches in the lower jaw. The fifth molar, with
an antero-posterior diameter of from eight to eleven inches, has
from sixteen to twenty-four plates.(4)

The largest upper molar of the Mammoth which I have yet
seen, measured fifteen inches in length and had _ twenty-two
coronal plates: it was discovered in the drift at Wellsborne in
Warwickshire. Mammoths’ molars of less dimensions have had
the crown divided into twenty-five and twenty-six transverse
plates.

The largest lower molar of a Mammoth that has come under
my observation, is the one figured in Pl. 148, fig. 5, its length,

(1) Hist. of British Fossil Mammalia, Part. V, p. 223.

(2) Kaup, Akten der Urwelt, 8vo. 1841, p. 11, tab. iv, Cymatotherium antiquum. M. de
Blainville hints a suspicion of its true nature, loc. cit. p. 190. The Mammoth’s molar from the
drift at Fouvent, figured by Cuvier in the ‘Ossemens Fossiles,’ vol. i. pl. vi. fig. 2, as “ une
vraie molaire de lait,” is a much worn and naturally shed second molar: the figure is half the
natural size.

(3) Hist. Brit. Foss. Mam. p. 224. fig. 87.

. (A) See the fifth upper molar of a Mammoth, with egies plates in ‘ Hist. Brit. Foss.
Mamm,’ p. 336. figs. 91 & 92.

,
ELEPHANT. 637

or antero-posterior diameter, following the curve on the convex
side is one foot seven inches: the number of the lamelliform
divisions of the crown is twenty-eight: this remarkably fine molar
exhibits the most complete state in which the actions of masti-
cation permit so large a grinder to be seen: the anterior portion
of the crown having been worn down to the common base of
dentine, from which the fang is continued, and the digital divi-
sions, which form, by their basal confluence, the last or hindmost
plates, are calcified. These terminal portions of the last molar,
always in the Proboscidians the most subject to variation, manifest
the same anomalous position which has been noticed in the cor-
responding tooth of the Asiatic Elephant, and are folded upwards
and laterally upon the concave part of the tooth; the sides of
the digitated plates being parallel with the grinding surface of the
tooth.

The above generalisations have been derived from a com-
parison of some hundreds of the molar teeth of the Hlephas
primgenius, which have been disinterred from the superficial
deposits of this Island, and are published with further details and
observations on the varieties of race, age, and sex, in my ‘His-
tory of British Fossil Mammalia.’ They prove that the deve-
lopment, progressive complication, and succession of the molar
teeth, obeyed the same laws in the ancient Mammoth, as in the
existing Elephant; it may, indeed, be affirmed that these most
remarkable phenomena in the comparative anatomy and physiology
of teeth, are more fully and perfectly illustrated by the fossils
which the primigenial Elephants have left in the superficial deposits
of England, than by any collection of the molars of the Indian
or African Elephants now existing in our metropolitan museums.
John Hunter owed most of his illustrations of the succession
and shedding of the teeth in the Elephant, to the fossil molars
of the Mammoth, which, with similar remains, he had been
silently collecting at a time when they attracted little, if any
attention.

Cuvier first pointed out that the molars of the fossil Elephant
were broader than those of the existing species, and that the

638 UNGULATES.

transverse plates were thinner and more numerous; they are also
deeper, and more subdivided into digitated summits: and we may
infer from the resulting increase of the dense enamel which enters
into the formation of the broad grinding surface, that the extinct
species had to subsist on a coarser and more ligneous vegetable
diet, in conformity with the colder regions of the ancient world
in which its peculiar warm clothing of wool and hair adapted it
to exist.

The phenomena of the course and changes of the dentition
of the Elephas Africanus have a close analogy with those of the
preceding species with more complex teeth. The first molar has
a four-ridged crown, with two long diverging fangs; the specific
characters are least manifested in this early-developed tooth: they
become more marked in the subsequent molars. The second has
seven plates, five of normal size and already manifesting the cha-
racteristic median expansion; the first and last plates are much
smaller: the length of this tooth is two inches and a quarter.
The third molar manifests an increase in the size and thick-
ness of the coronal plates, and of the width of their cement-filled
interspaces, but not any in the number of the divisions; the first,
however, presents more of the normal proportions. The fourth molar
manifests a marked increase of size and especially of breadth, but its
crown is not divided into more than seven plates. The fifth molar,
(Pl. 148, fig. 4) which is about seven inches in length, has eight
or nine coronal plates. The sixth molar, eight or nine inches in
length has from ten to twelve plates in the lower jaw.

The molar teeth in all the species of Elephant succeed each
other from behind forwards, moving, not ina right line, but in the arc
of acircle (Pl. 146, fig. 1): the position of the growing tooth in the
closed alveolus (m 5) is almost at right angles with that of the molar in
use, the grinding surface being at first directed backwards in the upper
jaw, and forwards in the lower jaw, and brought by the revolving
course into a horizontal line in both jaws, so that they oppose each
other, when developed for use. The imaginary pivot on which
the grinders turn is next their root in the upper jaw, and is
next the grinding surface in the lower jaw; in both towards the

ELEPHANT. 639

frontal region of the skull: viewing the upper and lower molars
as one complex whole, subject to the same revolving movement,
the section dividing such whole into upper and lower portions
runs parallel to the curve described by that movement, the upper
being the central portion or that nearest the pivot, the lower the
peripheral portion: the grinding surface of the upper molars is
consequently convex from behind forwards, and that of the lower
molars concave: the upper molars are always broader than the
lower ones. The bony plate (ib. fig. 2, a) forming the sockets o1
the growing teeth is more than usually distinct from the body ot
the maxillary, and participates in this revolving course, advancing
forwards with the teeth. The partition between the tooth in use
and its successor is perforated near the middle; and in its pro-
gress forwards that part next the grinding surface is first absorbed ;
the rest disappearing with the absorption of the roots of the pre-
ceding grinder.

There are few examples of organs that manifest more strik-
ingly the adaptation of a highly complex and beautiful structure to
the exigencies of the animal endowed with it, than the grinding
teeth of the Elephant. We perceive, for example, that the jaw is
not encumbered with the whole weight of the massive tooth at
once, but that it is formed by degrees as it is required; the sub-
division of the crown into a number of successive plates, and of
these into subcylindrical processes, presenting the conditions most
favourable to progressive formation. But a more important advan-
tage is gained by this subdivision of the tooth: each part is formed
like a perfect simple tooth, having a body of dentine, a coat of enamel,
and an outer investment of cement: a single digital process may
be compared to the simple canine of a Carnivore; a transverse
row of these, therefore, when the work of mastication has com-
menced, presents, by virtue of the different densities of their
constituent substances, a series of cylindrical ridges of enamel,
with as many depressions of dentine, and deeper external valleys
of cement: the more advanced and more abraded part of the
crown is traversed by the transverse ridges of the enamel inclos-
ing the depressed tracts of the dentine, and separated by the

640 UNGULATES.

deeper channels of the cement: the fore-part of the tooth exhibits
its least efficient condition for mastication; the inequalities of the
grinding surface being reduced in proportion as the enamel and
cement which invested the dentinal plates have been worn away.
This part of the tooth is, however, still fitted for the first coarse
crushing of the branches of a tree: the transverse enamel ridges
of the succeeding part of the tooth divide the vegetable food
into smaller fragments, and the posterior islands and tubercles of
enamel pound it to the pulp fit for deglutition. The structure and —
progressive development of the tooth not only give to the Ele-
phant’s grinder the advantage of the uneven surface which adapts
the millstone for its office, but, at the same time, secure the
constant presence of the most efficient arrangement for the finer
comminution of the food, at the part of the mouth which is nearest
the fauces.

230. Microscopic Structure.—The peculiar condition of the dentinal
tubes in the tusks of the Elephant, upon which the texture of
ivory depends, has been well described by Retzius; it consists in
the minute size of the tubes, which at their origin from the pulp-
cavity do not exceed ;4,th of an inch in diameter, in their close
arrangement at intervals scarcely exceeding the breadth of a single
tube, and above all on their strong and almost angular gyrations,
which are so considerable that Retzius does not recognize them as
analogous to the secondary curvatures in the dentinal tubes of ordi-
nary teeth. (Pl. 149).

The dentinal tubes of ivory, as they radiate from the pulp-
cavity, incline obliquely towards the pcinted end of the tusk, and
describe two slight primary curves, the first convex towards that
end, the second and shorter one concave: these curves in narrow
sections from near the open base of the tusk are almost obscured
by the strong angular parallel secondary gyrations. The tubes
divide dichotomously, at acute angles, and gradually decrease in
size as they approach the periphery of the ivory, where they
sub-divide, send off many minute branches, and terminate in a
thin layer of the basal substance of a yellowish colour by transmitted
light, which divides the ivory from the cement. In sections from

ELEPHANT. 641

the extremity of the tusk, the ivory itself presents a modification of
the exterior layer which is analogous to cement.

The characteristic appearance of decussating curved striz, with
oblique rhomboidal spaces, so conspicuous on transverse sections
or fractures of ivory, is due to the refraction of light caused by the
parallel secondary gyrations of the tubes above described. The
strong contour lines observed in longitudinal sections of ivory,
parallel with the cone of the pulp-cavity, and which are circular
and concentric when viewed in transverse slices of the tusk, are
commonly caused by strata of extremely minute opake cellules, which
are unusually numerous in the interspaces of the tubes throughout
the substance of the ivory, and, by their very great abundance and
larger size in the peripheral layers of the ivory at the extremity
of large tusks give them the character of cement. The close-set
lateral branches of the calcigerous tubes unite with the tubuli of
these minute cells. The decomposition of the fossil tusks into super-
imposed conical layers takes place along the strata of the opake
cellules, and directly across the course of the calcigerous gyrating
tubes.

The radiated cells of the true cement are larger and more
uniform in size and shape; many of them approach nearer the
circular figure, than in ordinary teeth; the long axis of the more
elliptical ones is parallel with the plane of the stratum of cement:
their average diameter is z,th of an inch, and their interspaces
sometimes do not exceed that dimension. The cemental tubuli
appear from their course, and sometimes from the overlapping of
the substances in the sections examined, to be directly continued
from the tubuli of the ivory; but Retzius expressly denies the con-
tinuation, and states that the cemental tubes at both the outer
and the inner surface of the cement have terminations of less
diameter than their middle part. This is exact with respect to
the major part of the cement. In that near the base of the tusk
I have seen a few vascular canals. The contour lines of the cement
are usually wavy, and not parallel with the line of the outer surface
of the ivory.

In the tusks of the Mastodon giganteus the outer layer of

Te

642 UNGULATES.

cement is relatively thicker than in the tusks of the Mammoth
or Indian Elephant, and in the section from the worn end of a
Mastodon’s tusk, of which a magnified view is given in Plate 103,
figure 1, the minute terminations of the calcigerous tubes of the
ivory are seen to be directly continued into the system of fine
parallel tubes of the cement. The minuteness of the tubes of the
ivory is illustrated by contrast with those of the tooth of the small
Marsupial quadruped figured in the same plate. Some of the forms
of the radiated cells which are so thickly distributed through the
cement of the Mastodon’s tusk are shown at c. The irregular
disposition of the calcareous salts of these cells give them the
appearance of being subdivided, like the granular cell-nuclei of
which they are the remains: but their cavity, though irregular, is
single, and has generally been filled by the crystalline matter of
the fluids percolating the stratum in which such tusks have be-
come fossilized. The general character of the microscopic structure
of the ivory of the Mastodon’s tusk is the same as that of the
Elephant. The peripheral extremities of the dentinal tubes are,
in some parts of the tusk, straighter than in the rest of their
course; the straighter extremities were those which were first
formed in the calcification of the peripheral part of the pulp, and
this first-formed ivory is accordingly, in such parts, more like the —
ordinary dentine, and is analogous to the thin peripheral cap of —
such substance in the teeth of the Sloth and of some Fishes, — :
The pulp soon, however, becomes subject to that modification —
of the calcifying processes by which the more tortuous disposition
of the tubuli and the more frequent interposition of opake cellules
are produced; modifications which, in establishing the characters —
of ivory, present a step in the transition from true dentine to
osteo-dentine. :

By the minuteness and close arrangement of the tubes, and —
especially by their strongly undulating secondary curves, a tougher
and more elastic tissue is produced than results from their dis-_
position in ordinary dentine ; and the modification which distinguishes —
‘ivory’ is doubtless essential to the due degree of coherence of so-
large a mass as the Elephant’s tusk, projecting so far from the ©

ELEPHANT. 643

supporting socket, and destined to be frequently applied in dealing
blows and thrusts.

The central part of the tusk, especially near the base of such
as have reached their full size, is occupied by a slender cylin-
drical tract of modified ivory, perforated by a few vascular canals,
which is continued to the apex of the tusk. It is not uncom-
mon to find processes of osteo-dentine, or imperfect bone-like ivory,
projecting in a stalactitic form(l) into the interior of the pulp-
cavity, apparently the consequence of partial inflammation or mal-
formation of the vascular pulp. The musket-balls and other foreign
bodies which are occasionally found in ivory, are immediately sur-
rounded by osteo-dentine in greater or less quantity. It has long
ceased to be a matter of wonder how such bodies should become
completely imbedded in the substance of the tusk, sometimes without
any visible aperture, or how a leaden bullet may have become lodged
in the solid centre of a very large tusk without having been flattened.
Such a ball, aimed at the head of an Elephant, may penetrate
the thin bony socket and the thinner ivory parieties of the wide
conical pulp-cavity occupying the inserted base of the tusk; if the
projectile force be then spent the ball gravitates to the opposite
and lower side of the pulp-cavity, as is indicated in Pl. 146,
fig. 1.(2) The presence of the foreign body exciting inflammation
of the pulp, an irregular course of calcification ensues, which
results in the deposition around the ball of a certain thickness
of osteo-dentine. The pulp then resuming its healthy state and
functions, coats the surface of the inclosing mass of osteo-den-
tine, together with the rest of the conical cavity into which
that mass projects, with’ layers of normal ivory.(3) The ivory,

(1) Haller seems to have been the first to notice these irregular internal deposits
in the pulp-cavity of the Elephant’s tusk. ‘Elementa Physiologie, tom. viii, p. 519.

(2) Camper, ‘ Description Anatomique d’un Eléphant Male’ fol. p. 54. Cuvier, ‘ Annales
du Muséum, tom. viii, 1806, p. 115.

(3) Cuvier, ‘Annales du Muséum,’ tom. vii. p. 115, 1806. ‘Sur les défenses des
Eléphans, la structure, l’accroissement les caractéres distinctifs de l’ivoire et sur les maladies,”
first clearly stated that the ball or foreign body in the tusk of the Elephant was immediately
surrounded by a substance different from the regular ivory. The great Anatomist observes,

“Toute la portion d'ivoire en dehors de la balle est semblable au reste; il n’y a que ce qui
Pentoure immédiatement qui soit irrégulier.” Mr. Goodsir has confirmed this statement by

tT 2

644 UNGULATES.

as it approaches the osteo-dentine, becomes modified by the presence
of vascular canals, and assumes the character of vaso-dentine ; and
the canals frequently form loops directed towards the osteo-dentine.
In this substance the medullary canals diverge, leaving clear inter-
spaces into which numerous irregular branches proceed from the
canals, partially uniting to form a net-work, and finally breaking
up into distinct cells, of larger size than the purkingian cells of the
external cement. In the small detached fusiform nodules of osteo-
dentine, one or more vascular canals are present with concentric
coats of the clear basal substance, studded by purkingian cells of
the size of those in the cement, but with richer radiating systems
of tortuous calcigerous tubes. Some of the larger-sized cells are
likewise frequently here present. From both the medullary canals,
their sub-divisions and the cells, minute calcigerous tubes diverge,

numerous interesting examples given in his Memoir in the ‘ Edinburgh Philosophical Transac-
tions for 1841, where he states ‘“‘ One circumstance was at once detected in all these specimens,
and its importance was evident, as affording a clue to the explanation of the mode of inclosure.
The circumstance to which I allude is, that in none of the specimens are the bullets of foreign
bodies surrounded by regular ivory. They are in every instance inclosed in masses, more or
less bulky, of a substance which, although abnormal in the tusk of the Elephant is nevertheless
well known to the Comparative Anatomist, as occupying the interior of the teeth of some of the
other Mammals, and usually considered to be the ossified pulp.” p. 93. Mr. Goodsir cites
(p. 97) a paper read by his countryman Dr. Knox to the Royal Society of Edinburgh, five years
before the date of his own Memoir (January 1841) in which the osteo-dentine (tissue like pud-
dingstone of Cuvier) which fills the pulp-cavities of the tusks of the Walrus and the teeth of the
Cetacea, was. “‘first announced as a distinct species of dental tissue.” I have not found any
distinctive characters, microscopic or otherwise, of such tissue, pointed out in the publications
of the Society referred to by Mr. Goodsir. The first clear definition of substances entering into
the composition of teeth and presenting microscopic characters equally distinct from ivory,
enamel and cement, and from true bone, is that which I communicated to the British Associa-
tion in 1838. (See the Volume of Reports, 1838, p. 137). Of the two kinds there defined,
“<The first, or ‘ vaso-dentine’, characterized by being traversed throughout by numerous coarse _
canals, filled with a highly vascular medulla or pulp,” but ‘ differing from true osseous sub-
stance, and from the ccementum in the absence of the purkingian corpuscles,’ (loc. cit. p. 137),
is not abnormal in the Elephant’s tusk, but is a constant constituent of its central part; this
fact I demonstrated by microscopic sections exhibited in my Hunterian Lectures on the
Comparative Anatomy of the Digestive System, in the Theatre of the College of Surgeons in
1838, and at the same time showed the identity of the irregular ivory of Cuvier which surrounds
the foreign bodies, with “the second distinct component substance of tooth, which more
closely resembles true bone and cement, inasmuch as the purkingian cells are abundantly
scattered through it,” loc. cit. ;

| ELEPHANT, 645

with wider intervals and a more wavy and irregular course than the
normal tubes of the ivory.

The portion of the cement-forming capsule surrounding the base
of the tusk, and the part of the pulp, which were perforated by the
ball in its passage, are soon replaced by the active reparative
power of these highly vascular bodies. The hole formed by the
ball in the base of the tusk is then more or less completely filled
up by a thick coat of cement from without and of osteo-dentine
from within. Traces of such a cicatrix closing the entrance have
been more than once noticed: and Blumenbach deduced, there-
from, a property in the Elephant’s tusk to pour out bony matter
in order to heal such wounds. The reparation is, however, effected
by the calcification of the reproduced parts of the capsule and
pulp.

By the continued progress of growth, the ball so inclosed is
carried forwards, in the course indicated by the arrow in PI. 146, fig. 1,
to the middle of the solidified exserted part of the tusk, as in the
example in Blumenbach’s collection which he considered so curious.
Should the ball have penetrated the base of the tusk of a young
Elephant it may be carried forwards by the uninterrupted growth
of the tusk until that base has become the apex, and be finally
exposed and discharged by the continual abrasion to which the
apex of the tusk is subjected. Yet none of these phenomena
prove the absolute non-vascularity of the tusk, but only the low
degree of its vascularity. Blood circulates, slowly no doubt, through
the minute vascular canals which are continued through the centre
of the ivory to the very apex of the tusk: and it is from this
source that the fine tubular structure of the ivory obtains the es-
sential plasmatic colourless fluid by which its low vitality is
maintained.

In order to obtain a complete and connected view of the micro-
scopic structure of the molar teeth of the Elephant, I made vertical
and transverse sections of the first molar, which, from its small size
permits the entire course of the dentinal tubes to be traced.

The tooth examined was from the lower jaw, and was com-
pletely formed ; the two fangs being of their full length. The pulp-

646 UNGULATES.

cavity was divided at its upper part into two conical prolongations, one
for each of the principal lobes of the crown. A few vascular canals
were continued from the apex of each cone into the two sub-divisions
or plates of each lobe.

The dentinal tubes which radiate from the pulp-cavity and its
prolongations, are as remarkable as those of the tusk for their minute-
ness and closeness of arrangement ; but, in the tooth examined, they
presented at only a few points secondary undulations approaching
in extent to those which characterise the tubes of ivory. A few
tubes from the end of the vascular canal in the centre of the cone
of dentine go straight to the summit of that cone; the rest diverge
from the vascular canals and apex of the pulp-cavity to the sides
of the cone of dentine, with one general primary curve, whose
convexity is turned towards the centre and summit of the cone, the
terminations of the tubes being slightly bent in the opposite direc-
tion: in the roots the dentinal tubes pass, as usual, almost trans-
versely. ; :

_ The places where the tubuli exhibited the strong secondary
undulations were along a contour line at the middle of the dentine.
At their commencement the tubuli are straight, they then fall into
slight waves, and after forming three or four stronger ones at the
middle of their course, again resume the more feeble and irregular
undulations: their close arrangement renders it difficult to distin-
euish bifurcation from decussation; yet in some parts I had clear
evidence of division of the main tubes, which left little doubt that
the usual dichotomy prevailed, to produce the same dense arrange-
ment of tubuli at the broad peripheral as at the narrower central
part from which the tubes diverge.

The number of minute lateral branches is extreme; especially

in the peripheral third part of the tube. Those from near the usually ~

bifurcated terminations of the tubes are lost in the stratum of minute |

opake cellules near the outer surface of the dentine. Many of the ©
terminal bifurcations of the tubuli here bend back, and form loops —

by anastomosing with adjoining branches. |
The fibres of the enamel present a minutely jagged, or cre-—

nate outline, but are not crossed, by transverse lines. Their

ELEPHANT. 647

diameter is jth of an inch: they are much less wavy than in the
human teeth. The enamel fibres cross the plane of the layer
on a less transverse direction than that of the ends of the tubes
of the dentine directed towards the enamel: the outer surface to
which the cement is attached, shows more pits and irregularities
than that attached to the dentine.

A well-defined layer of cement covers the bottom of the crown
at the interspaces of the two fangs, and extends over these to their
extremity. The sub-circular or full-elliptic radiated cells are closely
arranged, with their long axes parallel with the surface of the
cement ; numerous minute cemental tubuli run parallel to that sur-
face, and communicate with the radiated tubes of the cells and
with the terminal ramifications of the dentinal tubuli. The larger.
vascular canals are present only in the thicker deposit of cement
at the bottom of the interspaces of the coronal plates.

Dr. Falconer having kindly permitted me to take a longitudinal
‘section from a rare specimen of the first upper molar of the Elephas
planifrons, one of the extinct species whose remains he has discovered
in the Himalayan tertiary beds, I am able to give the following
comparison of the microscopic structure of this tooth, and that of
the nearly allied existing Indian Elephant.

The dentinal tubuli are as minute and as closely aggregated ; they
have the same general direction and primary curve ; in parts of the
dentine, as at the summits of the conical sections of the lamellar
divisions of the crown, their secondary undulations are as minute
and irregular; but the number of the strong undulations along the
contour lines at the middle of the dentinal cone is greater. The
strongest contour lines are accompanied by the strong undulations,
but there are many other lines which appear to be formed by a
slight opacity of the basal substance as in the Rhinoceros.

The stratum of opake cellules near the peripheral ends of the
tubes is thicker ; the terminal bifurcations and occasional anastomotic
loops are the same as in the Indian Elephant. ‘The enamel is thicker,
and the component fibres are more flexuous in the El. planifrons,
but in their size and other characters they agree with those of the
recent species. The cells of the cement which covers the crown and

648 UNGULATES.

fills part of the interspaces of the coronal plates are sub-circular,
with often a slightly angular outline ; they are densely aggregated.
There are no vascular canals in the thinner layer of cement which
covers the fang, but these are always present in the thicker cement of
the crown.

In portions of larger molars of the Indian Elephant which I have
examined, the dentinal tubes have the same minuteness and close
arrangement, and the same general primary curve, as in the small
first molar; but the extent to which they manifest the strong undu-
lations characteristic of ivory is greater(1). In old molars the pulp-
cavity becomes in part obliterated by the modified ivory called osteo-
dentine, and the tubes in the dentine of the roots describe nume-
rous considerable undulations. The enamel does not extend upon
the roots but terminates, as in other teeth, at the base of the crown ;
the cement is continued in a thin layer to the end of the roots
(Pl. 150, fig. 2, cc), and there becomes continuous with the osteo-
dentine which fills the central part of the pulp-cavity. The disposi-
tion of the calcigerous tubes in a longitudinal section of one of the
fangs, with the central osteo-dentine, and the peripheral cement is
shown in Pl. 150. The dentinal tubes come off from the clear part
of the csteo-dentine by fasciculi, in certain parts of the pulp-tract ;
they are minutely and irregularly undulated throughout the course of
the stronger undulations which here assume the character of primary
curvatures. The terminations of the tubes at the semi-opake peri-
pheral tract, along which the minute opake cellules are dispersed,
seem to dilate slightly, and to be less sharply defined (ib. fig. 1, d'’.)
Many of the terminal branches of these tubes pass into the
cement, and anastomose with the fine tubes of that tissue; the
cemental tubes are largest at its peripheral part (ib. c"’). |

231. Development.—The matrix of the tusk consists of a large —
conical pulp, which is renewed quicker than it is calcified, and thus |
is not only preserved, but grows, up to a certain period of the ©
animal’s life: it is lodged in the cavity at the base of the tusk; :
this base is surrounded by the remains of the capsule, a soft —

(1) These undulations produce on the fractured surfaces of the dentine of the molars in
which they occur, the engine-turned character of true ivory.

ELEPHANT. 649

vascular membrane of moderate thickness, which is confluent with
the border of the base of the pulp, where it receives its principal
vessels.

The account which Cuvier(1) has given of the formation of the
complex molars of the Elephant is remarkably clear and comprehen-
sive, but is vitiated by the terms of the ‘ excretion-theory’ in which
the different processes are explained: it is otherwise so minute and
accurate that it needs little more than the substitution of the language
of the ‘conversion-theory’ to convey all the requisite knowledge of
the process.

Each molar of the Elephant is formed in the interior of a mem-
branous sac—the capsule, the form of which partakes of that of the
future tooth, being cubical in the first molar, oblong in the last, and
rhomboidal in most of the intermediate teeth ; but always decreasing
in vertical extent towards its posterior end, and closed at all points,
save where it is penetrated by vessels and nerves. It is lodged in
an osseous chamber of the same form as itself, and usually in part
suspended freely (as at a, fig. 2, Pl. 146) in a large cavity excavated
in the maxillary bone; the bony case being destined to form part
of the socket of the tooth. The exterior of the membranous capsule
is simple and vascular, as shown at m 5, fig. 1, Pl. 146; its internal
surface gives attachment to numerous folds or processes, as in most
other Ungulate animals.

The dentinal pulp rises from the bottom of the capsule, or that
part which lines the deepest part of the alveolus, in the form of
transverse parallel plates extending towards that part of the capsule
ready to escape from the socket. These plates adhere only to the
bottom of the capsule; their opposite extremity or summit is free
from all adhesion. This summit is thinner than the base; it might
be termed the edge of the plate, but it is notched, or divided into
many digital processes. The tissue of these digitated plates is iden-
tical with that of the dentinal pulp of simple Mammalian teeth ; it
becomes also highly vascular at the parts where the formation of
the dentine is in active progress.

(1) ‘Annales du Muséum,’ tom. vi1t, (1806) p. 94. The account is repeated verbatim in
the posthumous edition of the ‘ Ossemens Fossiles,’ 1834.

650 UNGULATES.

Processes of the capsule descend from its summit into the
interspaces of the dentinal pulp-plates, and consequently resemble
them in form; but they adhere not only by their base to the surface
of the capsule next the mouth, but also by their lateral margins to
the sides of the capsule, and thus resemble partition-walls, confining
each plate of the dentinal pulp to its proper chamber; the margin
of the partition opposite its attached base is free in the interspace
of the origins of the dentinal pulp-plates. The enamel-pulp, which
Cuvier appears to have recognized under the name of the internal
layer of the capsule, is distinguishable by its light blue sub-trans-
parent colour and usual miscroscopic texture, adhering to the free
surface of the partitions formed by the true inner layer of the capsule.
Although the enamel-pulp be in close contact with the dentinal pulp
prior to the commencement of the formation of the tooth, one may
readily conceive a vacuity between them, which is continued unin-
terruptedly, in many foldings, between all the gelatinous plates
of the dentinal pulp, and the partitions formed by the combined
enamel-pulp and the folds of the capsule. According to the excre-
tion-hypothesis this delicate apparatus must have been subjected
to compression in the unyielding bony box by the deposition of
the dense matters of the tooth in the hypothetical vacuity be-
tween the enamel and dentinal pulps; a process of absorption
must have been conceived to be set on foot immediately upon
such altered condition of the gelatinous secreting organs; and the
secreting function must be supposed to have proceeded, without
any irregularity or interruption, while the process of absorption was
superinduced in the same part to relieve it from the effects of
pressure produced by its own secretion.

The formation of the dentine commences srasteedleid beneath
the membrana propria of the pulp: a part which Cuvier distinctly ’
recognised, and which he accurately traced as preserving its relative —
situation between the dentine and enamel, throughout the whole ~
formation of the dentine, and discernible in the completed tooth ‘as _
avery fine greyish line, which separates the enamel from the internal
substance’ or deutine.

The calcification and conversion of the cells of the dentinal pulp q

ELEPHANT. 651

commence as usual at the peripheral parts of the lamelliform pro-
cesses furthest from the attached base. It may readily be conceived,
therefore, that, at the commencement, there is formed a little cap
upon each of the processes into which the edges of the pulp-plates
are divided. As the centripetal calcification proceeds the caps are
converted into horn-shaped cones (Pl. 146, fig. 4); when it has
reached the bottom of the notches of the edge of the pulp-plate all
the cones become united together into a single transverse plate (ib. 5) ;
and, the process of conversion having reached the base of the pulp-
plate, these plates coalesce to form a common base to the crown of
the tooth, which would then present the same eminences and notches
that characterized the gelatinous pulp, if, during the period of con-
version, other substances had not been formed upon the surface and
in the interspaces of the pulp-plates.

Coincident, however, with the formation of the dentine, is the
deposition of the hardening salts of the enamel in the extremely
slender prismatic cells, which are for the most part vertical to the
plane of the inner surface of the folds of the capsule to which they
are attached; these cells or moulds give a sub-transparent bluish
tint to the enamel-pulp, which Cuvier distinguishes as the internal
layer of the capsule. The true inner part of the capsule forms those
thick transverse folds or partitions which support the enamel-organ,
and with it fill the interspaces of the dentinal pulps. With regard
to the formation of the cement, Cuvier, after citing the opinion of
Tenon—that it was the result of ossification of the internal layer of
the capsule, and that of Blake—that it was a deposition from the
opposite surface of the capsule to that which had deposited the
enamel, states his own conviction to be—that the cement is produced
by the same layer and by the same surface as that which has pro-
duced the enamel. The proof alleged is, that so long as any space
remains between the cement and the external capsule, that space
is found to contain a soft internal layer of the capsule with a free
surface next the cement. The phenomena could not, in fact, be
otherwise explained according to the excretion-theory of dental
development. To the obvious objection that the same part is made,
by this explanation, to secrete two different products, Cuvier replies,

652 UNGULATES.

that it undergoes a change of tissue: ‘‘ Whilst it yielded enamel
only it was thin and transparent, to give cement it becomes thick,
spongy, and of a reddish colour.”(1) The obvious characters of the
enamel organ and cement-forming capsule, are here correctly defined ;
but the one instead of being converted into the other, is, in fact,
changed into its supposed transudation: the enamel fibres being
formed, and properly disposed in the direction in which their chief
strength is to lie, by the assimilative properties of the pre-arranged
elongated prismatic non-nucleated cells of the enamel pulp, which
take from the surrounding plasma the required salts and compact
them in their interior.

Whilst this process is on foot, and before the enamel-fibres
are firm in their position, the capsule begins to undergo that
change which results in the formation of the thick cement: the
calcifying process commences from several points, and proceeds
centrifugally, radiating therefrom, and differing from the ossifica-
tion of bone chiefly in the number of these centres, which,
though close to the new-formed enamel, are actually in the substance
of the inner vascular surface of the capsular folds. The cells arrange
themselves in concentric layers around the vessels, and act like
those of the enamel pulp in receiving into their interior the bone-salts
in a clear and compact state; during this process they become
confluent with each other, their primitive distinctness being indicated
only by their persistent granular nuclei, which now form the radiated
Purkingian corpuscles. The interspaces of the concentric series of
confluent cells become filled with the calcareous salts in a rather
more opake state, and the conversion of the capsule into cement
proceeds according to the processes more particularly described
in the Introduction, until a continuous stratum is formed in close
connection with the layer of enamel.

The uncalcified part of the capsule, always much softer than
cartilage, is very readily detached from the calcified part, and to

(1) “Seulement elle change de tissu: tant qu’elle ne donnait que de 1’émail, elle était

mince et transparente; pour donner du cortical elle devient ¢paisse, spongieuse, opague et —

rougeatre.’—Annales du Muséum, tom. vir, p. 99. ‘ Ossemens Fossiles,’ Ed. 1834, 8vo.
tom. I, p, 514 -

ELEPHANT. 653

the naked eye the separated surface seems entire, and might readily
pass, as with Cuvier, for a secreting surface. The fine vascular
processes which have been torn from the medullary canals of the
calcified part are, however, conspicuous, and resemble villi, when the
detached surface is examined, even with a moderate magnifying
power, under water.

Calcification extending from the numerous centres, the
different portions coalesce and progressively add to the thickness
of the cement until all the interspaces of the coronal plates and
the whole exterior of the crown is covered with the bone-like
substance. The enamel-pulp ceases to be developed at the base
of the crown; but the capsule continues to be formed, part passu
with the growth of the pulp, as this continues, progressively
contracting, from the base of the crown, to form by its calci-
fication the roots. The calcification of the capsule going on
at the same time, a layer of cement is formed in immediate con-
nection with the dentine. The circumscribed spaces at the bottom
of the socket to which the capsule and dentinal pulp adhere, where
they receive their vessels and nerves, and which are the seat of
the progressive formation of these respective moulds of the two
dental tissues, become gradually contracted, and subdivided by
the further localization of the reproductive forces to particular
spots, whence the subdivision of the base into roots. The sur-
rounding bone undergoes corresponding modifications, growing and
filling up the interspaces left by the dividing and contracting points
of attachment of the residuary matrix. All is subordinated to one
harmonious law of growth by vascular and cell-formations, and of
modified form by absorption: mechanical squeezing and drawing out
have no share in these changes of the pulp or capsule: pressure
at most exercises only a healthy stimulus to the vital processes.

Cuvier believed that there were places where the dentinal pulp
and the capsule were separate from each other: I have never
found such except where the enamel-pulp was interposed between
them in the crown of the tooth, or where both pulp and capsule
adhered to the periosteum of the socket, below the crown. Cuvier
affirms that the number of fangs of an Elephant’s molar depends

654 UNGULATES.

upon the number of points at which the base of the gelatinous
(dentinal) pulp is attached to the bottom of the capsule; and that
the interspaces of these attachments constitute the under part of
the crown or body of the tooth, the attachments themselves
forming the first beginnings of the fangs. True to his hypothesis
of the formation of the dental. tissues by excretion he says(1)
that the elongation of the fangs is produced by two circumstances :
first, the progressive elongation of the layers of osseous substance
(dentine) which force the tooth to rise and emerge from its socket :
secondly, the thickening of the body of the tooth by the addition
of successive layers to its inner surface, which, filling up the

interior cavity, leaves scarcely room for the gelatinous pulp and

forces it down into the interior of the roots.

This pulling up of the fang on the one hand and squeezing
down of the pulp on the other, are forces too gross and mecha-
nical to be admitted for a moment in a physiological explanation
of the growth of the root of a tooth or of any other brganized
product; such modes of explanation were nevertheless inevitable
consequences of the adoption of the excretion-theory of dental
development ; and their proposition by the great Anatomist recalls
the analogous attempts of the great Master of Physical Science
to explain some of the phenomena of polarized light in the terms
of the ‘ emission-theory.’

But Newton, whatever difficulties of explanation his theory
entailed upon him, is accurate as to the facts or phenomena:
Cuvier, however, is compelled by his hypothesis to deny a matter
of fact.(2) The cement (cortical), being, according to him, an
excretion from the internal layer of the capsule, could: only be

(1) “Ces racines et les pédicules qui leur servent de noyaux s’alongent ensuite par deux :

raisons: d’abord les progrés des lamés de substance osseuse qui, s’alongeant toujours, forcent la
dent s’élever et 4 sortir de l’alvéole ; ensuite l’épaississement du corps de la dent par la forma-

tion des couches successives qui, en remplissant le vide intérieur, n'y laissent presque plus de
place pour le noyau gelatineux, et le refoulent vers ]’intérieur des tubes des racines.” Annales —

du Muséum, viii, 1807, p. 108, Ossem. Fossiles, 1834, p. 527.

(2) “Il ne se produit point d’émail ni de cortical sur les racines, parce que la lame interne —
de la capsule, qui a seule le pouvoir de sécréter ces deux substances, ne s’étend pas jusque la.”

loc. cit. (1807) p. 109; 1834, p. 527.

OL eee ee ee

ELEPHANT. 655

present on that part of the tooth over which such layer extended :
but the enamel-pulp, which passed with Cuvier for the internal
layer, unquestionably ceased to exist at the base of the crown or
body of the tooth; therefore Cuvier denies that the fang has any
covering of cement. That substance, nevertheless, does cover
the whole exterior of the fang, though it forms a much thinner
layer than upon the crown: its characteristic tissue is shown in
Pl. 150, fig. 2, c, in a magnified section of the end of a root of
an Elephant’s molar, and it is often thickest at this part, where, in
the Cuvierian hypothesis, it would be furthest from its formative
organ, the inner layer of the capsule.

The conversion-theory of dental development as propounded
and established in the present Work leads to no such difficul-
ties: its truth is manifested in the same way as that of the un-
dulation-theory of light and of every other right theory: viz. by
its concordance with facts which are denied or misinterpreted on
the wrong theory, and by its more rational explanation of all the
phenomena.

THE END.

LONDON:

Printed by Schulze and Co., 18, Poland Street.

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