The teeth are very numerous in reptiles; the individuals of some

species have more than two hundred. In some genera, they are implanted

on the jaws alone; in many, they occupy the palatine, vomerine, and

other bones composing the vault of the mouth, as in certain fishes. The

teeth are generally anchylosed to the bone; but in some genera they are

implanted in distinct sockets, as in the Crocodile and Plesiosaurus; in

others, as in the Ichthyosaurus, they are arranged in a deep furrow,

and retained only by the integuments; in some, they are supported upon

an elevated osseous base. In the Labyrinthodonts, and in the greater

part of the Serpent tribes, the tooth is implanted by the base in a

shallow socket, with which it is confluent.

In most of the Lacertians, or true Lizards, the attachment of the teeth

presents a peculiar modification, of which the lower jaw of the Iguana,

_Lign. 205_, p. 649, affords a good illustration. The teeth are not

placed in sockets, but are attached by the shank to an alveolar plate,

or parapet, that extends along the margin of the jaw, as shown in

_figs._ 1 and 3; the crowns of the teeth project above this plate, as

seen in _figs._ 2 and 4. From the anchylosis of the teeth to the side

of the jaw, the Lizards possessing this dental structure are termed

_Pleurodonts_.[579]

[579] The _Pleurodonts_ are those lizards in which the teeth are

anchylosed to the _side_ of the dentary bone; _Acrodonts_, those

with the teeth fixed to the upper margin or _ridge_ of the jaw-bone;

_Thecodonts_, those having the teeth implanted, either loosely, or

anchylosed to the walls of their sockets. Lacertians are also said to

be _Pleodont_ (having solid teeth), or _Cœlodont_ (hollow-toothed).

In reptiles, we have, therefore, five essential modifications in the

attachment of the teeth; namely, in distinct sockets; in a continuous

groove or furrow; attached laterally by the shank to an alveolar

parapet; anchylosed by the base to a shallow socket; and attached to an

osseous support, without sockets or an alveolar plate.[580]

[580] See the beautiful exemplification of this subject, and the

comparison between the transitory stages of the human teeth in their

progress of development, discovered by Mr. Goodsir, with the permanency

of these conditions in reptiles. Odontography, p. 182.

[Illustration: Lign. 205. The Lower Jaw of an Iguana.

(_From Barbadoes._)]

Fig. 1.--The right branch of the lower jaw of an Iguana; viewed on

its inner aspect. _Nat. size._

_a._ Dentary bone.

_b._ Opercular bone.

_c._ Complementary or coronoid bone.

_d._ Surangular bone.

_e._ Angular bone.

_f._ Articular bone.

2.--The external aspect of the same.

3.--Inner aspect of three teeth (_magnified_) attached to the alveolar

parapet; with the germ of a successional tooth at the base

of the middle tooth; and the sockets of other germs at the

bases of the outer two fully formed teeth.

4.--External view of the crowns of three teeth; slightly magnified.

The intimate structure of the teeth consists of a simple pulp-cavity,

surrounded by dentine, which is permeated by extremely minute

calcigerous tubes, radiating at right angles to the periphery, or

external surface of the tooth. One essential modification of this

structure consists in the intermingling of cylindrical processes of

the pulp-cavity, in the form of medullary or vascular canals, with

the finer tubular structure; as in the tooth of the Iguanodon, _Pl.

VI. figs. 4^b_ and _4^c_. But another modification is that to which

allusion was made when describing the teeth of the Lepidosteus (see

p. 616); in this mode, the dentine preserves its normal character, but

the external cement and surface of the tooth are deeply inflected in

longitudinal folds around the entire circumference; and this structure

is accompanied with corresponding extensions of the pulp-cavity

and dentine into the interspaces of these inflected and converging

folds.[581] This organization is shown, in its simplest form, in the

transverse section of the base of a tooth of the Ichthyosaurus, _Pl.

VI. fig. 9_; and attains its most complicated condition in that of the

Labyrinthodon, _Pl. VI. figs. 3^a, 3^b, 3^c_.

[581] There is a marked difference between the internal structure

of the teeth of true Saurians and of Sauroid Fishes. In the former,

as well as in the _Enaliosauria_, the dentine consists of tubes

radiating from a slender central pulp-cavity to the periphery of the

tooth, without any intermixture of vascular canals. In the sauroid

fish (_Dendrodus_) the central pulp-cavity is produced into numerous

irregular canals, from which vascular sinuses radiate to the

periphery, sending off branches generally at right angles throughout

their entire course; thus, there is an extensive distribution of the

vascular system through the body of the tooth, which does not exist in

any saurian reptile; the nearest analogy is in the labyrinthine teeth

of the gigantic fossil batrachians. (_Owen_: Odontography; and Art.

Teeth, Cyclop. Anat.)

With regard to the mode of development of the teeth, we must briefly

state, that the germ of the new tooth is always produced at the side

of the base of the old one; that in its progress of growth it presses

against the tooth it is destined to supplant, occasions the progressive

absorption of the fang, and ultimately displaces its predecessor;

in some instances, by splitting the crown of the tooth; in others,

by casting it off, according to the oblique or direct position the

new tooth attains in its progress, in relation to its predecessor.

Thus, in the teeth of the Crocodile, the new tooth is generally found

immediately under the conical apex of the crown, and beneath the former

a second successional tooth appears, like a series of thimbles of

various sizes placed one upon another; for in reptiles the production

of new teeth is unlimited. But in the _Pleurodont_ lizards, the new

tooth makes its way obliquely, and the crown is often shed entire.

_Lign. 205, fig. 3_, exemplifies the situation of the successional

teeth in the Iguana.

Lower Jaw of Reptiles.--It is well known that the lower jaw in

mammiferous animals is composed of a single bone on each side; and

that in many genera these pieces become united in front, and form

but one bone in the adult state. But in reptiles, the lower jaw

consists of six distinct bones on each side, as in _Lign. 205_; and

these undergo various modifications of form and arrangement in the

different genera. These bones are distinguished by names which have

reference to their office and situation, and are as follow:--_Lign.

205, a_, the _dentary_ bone, supporting the teeth; _b_, the _splenial_

or _opercular_; _c_, the _coronoid_ or _complementary_; _d_, the

_sur-angular_; _e_, the _angular_; _f_, the _articular_, which forms

the upper portion of the jaw, and includes the condyle. The form and

disposition of these bones in the Iguana, and other true lizards, are

shown in _Lign. 205_; but they differ materially in the Crocodile,

Ichthyosaurus, and other genera. We must restrict our comments to this

short notice, which, however, will suffice to enable the collector who

discovers a fragment of a lower jaw, with any traces of the structure

above described, to determine that it is reptilian; and if any portion

of the _dentary_ bone remains, indications may be obtained of the

family, and perhaps genus, to which it belonged.[582]

[582] To obtain a correct knowledge of the osteological structure of

fossil Reptiles, the student should consult Baron Cuvier’s _Ossemens

Fossiles_, tom. v. To the English reader, the translated abridgement of

Cuvier’s "Fossil Remains of the Animal Kingdom," by E. Pidgeon, 1 vol.

8vo. with plates, 1830, will be found a very instructive volume. See

also Penny Cyclopædia, Art. Saurians.

Vertebræ of Reptiles.--The bones of the vertebral column of this class

of animals present such numerous and important modifications in the

different orders and families, that reference to the works already

cited must be made for satisfactory information on this topic. From the

great number of vertebræ in many reptiles, amounting in the individuals

of some species to nearly two hundred, these bones are the most

abundant fossil relics of these animals to be found in our collections.

The vertebræ are commonly detached, and deprived of their processes;

the solid _centrum_, or body, alone remaining in most examples (as in

_Lign. 206, fig. 8_). Connected series, more or less complete, are

occasionally discovered; and the entire column, in connexion with other

parts of the skeleton, is preserved in many specimens in the British

and other museums.[583] Although, for the reasons previously stated,

minute osteological details cannot be attempted in this work, some

acquaintance with the elementary characters of the bones composing the

spinal column, and of the nomenclature employed to distinguish them,

is necessary to guide the student, and even the amateur collector, in

their researches. I have, therefore, selected a few specimens from

Tilgate Forest in illustration of the elements of Saurian vertebræ, and

of the terms by which the different processes are distinguished; the

general reader will thus be enabled to comprehend the descriptions of

these structures in other works on Palæontology.

[583] See _Petrifactions_, pp. 136-352, and pp. 362-387.

[Illustration: Lign. 206. Fossil Vertebræ or Reptiles. _Tilgate Forest._

_The figures are reduced in the proportions specified by the

fractions._

Fig. 1.--Caudal vertebra of an unknown reptile.

2.--Chevron bone of Iguanodon: seen in front.

3.--Caudal vertebra of Iguanodon, viewed laterally in an

oblique direction.

3_a_.--Front view of the same.

4.--Caudal vertebra of Iguanodon, without either transverse

process or chevron-bone. The letter _o_ marks the deep

hollow left by the removal of the transverse process, at

the suture of the annular part.

5.--Vertebra of Streptospondylus: 1/16 _nat._

6.--Lumbar vertebra of Iguanodon, with the neural spine

broken off.

7.--Vertebra of Streptospondylus: 1/16 _nat._

_c._ The pair of posterior oblique processes (_zygapophyses_).

8.--The bodies of two dorsal vertebræ of Iguanodon: viewed

laterally.

The same letters refer to the same parts in the respective

figures, with the exception of _c_ in _fig._ 7.

_a._ The body, or centrum, of the vertebra: the letter denotes

the anterior part.

_b._ The annular part, formed of the two _neurapophyses_,

which contains the spinal cord.

_c, c._ The articular or oblique processes (_zygapophyses_), which

join to the next vertebra in front.

_d._ The spinous process or neural spine of the annular part.

_e, e._ The transverse process of the annular part.

_f._ The chevron-bone, formed of the two _hæmapophyses_ and

the hæmal spine.

_g._ The double articulating head of the chevron: the passage

left by these processes (_hæmal arch_), seen in the front

view, figs. 2 and 3, is for the passage of the large

blood-vessels which supply the tail.

_h._ The spine of the chevron-bone; the inferior spinous

process, or _hæmal spine_.

_i._ Denotes the medullary cavity of the annular part.

_o, o._ Mark the sutures which connect the annular part with

the body of the vertebra.

_w, w._ Indicate the place of attachment of the chevron-bone.

]

The bones composing the spine, are not only designed to form a flexible

column of support to the trunk, but also to afford protection to the

grand nervous chords constituting the spinal marrow, and which extend

from the brain to the tail, and give off numerous lateral branches in

their course, conferring sensation and motive power to every part of

the frame. To effect this purpose, there is attached to the upper or

dorsal part of each vertebra a bony ring, called the neural-arch, which

is composed of two processes (_Lign. 206, b._), arising from each

side of the body or centrum (_Lign. 206, a._), and which unite above

into a solid piece, termed the spinal process, ox neural spine (_Lign.

206, d._). On each side of the annular paid there is a process, called

the transverse (_Lign. 206, e, e._), for the attachment of muscles;

and in the middle and the posterior dorsal regions of some reptiles,

as, for example, in the existing Crocodiles, these processes articulate

with the ribs. The vertebræ of the tail have, in addition to the above,

an inferior spinous process, termed the chevron-bone (_Lign. 206,

fig. 2_, and _fig. 3, f_.), which gives support to the inferior

layers of the caudal muscles; and, bifurcating at its attachment to the

body of the vertebra, leaves a channel for the passage of the large

blood-vessels, by which the circulation of the tail is effected.

In the generality of living reptiles (as, for example, in the

Crocodile) the bodies of the vertebræ are concave in front, and convex

behind; the bones of the spine being united by ball-and-socket joints;

but, in most fossil reptiles, both faces are either flat, or more or

less concave. In mammalian quadrupeds, the annular part is anchylosed

to the vertebral centre; but in reptiles, it is united by suture,

although, in old subjects, the connecting line is often obliterated. By

reference to _Lign. 206_, and its description, the form, arrangement,

and connexion of the different vertebral elements, in certain fossil

reptiles, may be easily understood. The bones in the vertebral column

of the same animal are considerably modified in the several regions

of the neck (_cervical_ vertebræ), back (_dorsal_ and _lumbar_), and

tail (_caudal_). The cervical are generally of the most complicated

structure; and the caudal, the most simple.

From this exposition, the reader will perceive that every vertebra

consists of the following essential parts: first, the body, or

_centrum_; and secondly, the annular part, or _neural arch_, so named,

because it protects the nervous chord; while a caudal vertebra has,

in addition, the chevron-bone, called also the _hæmal arch_, from its

affording a passage to the large blood-vessels. The bodies of the

vertebræ are in general solid, and consist of the ordinary osseous

structure; but in certain fossil vertebræ the centre of the bone is

filled with calcareous spar, indicating an irregular medullary cavity,

as in the caudal vertebræ of the Ox.[584]

[584] See _Petrifactions_, p. 166, _note_.

The _Sacrum_, which may be termed the key-stone of the pelvic arch, is

formed in existing reptiles by the union of two vertebræ; but in the

Iguanodon and the Hylæosaurus the sacrum is composed of six anchylosed

vertebræ; in the Megalosaurus probably of but five.[585]

[585] Report, Brit. Assoc. 1841, p. 105, and p. 130.

From the sides of the two anchylosed vertebræ which form the sacrum,

strong, short, rib-like processes are given off in those Saurians which

occasionally walk on dry land, and these constitute a firm support to

the hinder extremities.

In the Crocodiles, the four or five vertebræ preceding the sacrum

have no ribs attached to them, and are termed _lumbar_; in the

Lizards, there are but two lumbar vertebræ. A peculiar modification

exists in the first caudal vertebra of the adult Gavial and Crocodile;

the _centrum_ is _convex_ both in front and behind, as was first

demonstrated by me in 1836. See _Wond._ p. 419, and _Petrif._ p. 167.

The last of the anchylosed vertebræ forming the sacrum is concave

posteriorly; hence the necessity of an anterior ball in the first joint

of the tail. (See _Lign. 217_, p. 676, illustrative of _Crocodilus

Hastingsiæ_.) The last _cervical_ vertebra in the Turtles and Tortoises

has a similar construction. This mechanism confers freedom of motion

without risk of dislocation.

Ribs.--The Ribs, which are regarded as appendages to the vertebræ,

(homologues of the pleurapophyses,) are generally slender and round in

the Lizards, and articulate with the spinal column by a single head,

supported on a short convex process or tubercle. In Crocodiles only

of all existing Reptiles, but in several extinct genera, the proximal

end of the rib forms a double articulation, by a distinct head and a

tubercle, with the vertebræ in the cervical and anterior dorsal region

of the spinal column; in the posterior dorsal region the ribs are

attached to the elongated transverse processes of the vertebræ.

As this double articulation of the ribs is invariably associated in

existing reptiles with a heart having double ventricles, while the

lacertian single-headed ribs are in like manner connected with a heart

having but one ventricle, the student will perceive the important

physiological inferences that spring from the discovery of a mere

fragment of a rib, when interpreted by the profound anatomist.[586] In

some fossil reptiles the ribs are flat and very broad; as, for example,

in the Hylæosaurus.[587]

[586] See Brit. Assoc. Report, 1841, and Memoirs, Palæont. Soc.

[587] In Crocodiles the abdominal region is strengthened by slender

ribs (_hæmapophyses_, Prof. Owen), that are affixed to a ligamentous

extension of the cartilaginous sternum, analogous to the _linea alba_

in man; and the Hylæosaurus appears to have possessed a similar

development of the costal elements, for I observed many fragments of

long, slender, sub-cylindrical rib-like bones whilst chiselling off the

stone from this species, and portions of similar bones occur in the

stone around the spinal column from Bolney. In the Maidstone Iguanodon

there are likewise some long slender bones of this character, which I

think must be prolongations of the ordinary dorsal ribs.

Extremities.--The locomotive extremities are variously constructed,

according to the adaptation of the animals to a terrestrial,

fluviatile, or marine existence. The bones of the limbs in the

extinct colossal terrestrial species much resemble those of our large

pachydermata, the Rhinoceros and Hippopotamus. The cylindrical bones

of the extremities in the Crocodilians, and other recent reptiles, are

solid. _i. e._ have no cavity filled with marrow; such also is the case

in the fossil Enaliosaurians; but the thigh-bones and leg-bones of the

Iguanodon, and of other extinct land saurians, h ave a large medullary

canal. Our limits will not admit of further osteological details; and

we are compelled to omit the description of the bones composing the

thoracic and pelvic arches.

Dermal Bones. _Ligns._ 207 and 208. In many of the reptile tribes,

particularly of the Crocodilian or loricated (_mailed_) group, there

are immediately under the external integument or skin a series of

osseous scutes, or scutcheons, variously arranged, which serve as

supports to the integumental scales and spines. In the gigantic Gavial,

that inhabits the Ganges and other rivers of India, and which is

remarkably distinguished from the common Crocodile and Alligator by an

extremely elongated slender muzzle, the nape of the neck is protected

by sixteen or eighteen transverse rows of dermal scutes; and there are

likewise six rows which extend down the back. These bones are deeply

corrugated or sculptured on their upper surface; a structure adapted

for the firm adhesion of the horny integument.

Detached bones of this character occur in the Purbeck strata; and

the first fragments I collected were supposed by me to belong to the

soft-skinned turtles (_Trionyces_); but the subsequent discovery of

perfect scutes demonstrated their analogy to the dermal bones of the

Gavial, and enabled me to determine their true character.

[Illustration: Lign. 207. Dermal Bone of the Swanage Crocodile: 1/3

_nat._

_Purbeck._

(Goniopholis crassidens.)

Fig. 1.--The external aspect.

2.--The inner surface.

_a._--The lateral connecting process.

]

In the splendid specimen of the fossil remains of a Crocodilian reptile

(_Goniopholis_), found at Swanage (_Wond._ pp. 415; and _Petrif._ p.

170), there are numerous dermal examples dispersed among the bones, as

shown in _Petrif._ _Lign._

One of these is figured _Lign. 207_; _fig._ 1 represents the external

surface, which is deeply sculptured by irregular roundish pits or

excavations; the under or inner surface, _fig._ 2, is smooth, but

marked with very fine striæ, decussating each other at right angles, as

in the dermal bones of the Hylæosaurus (_Lign. 208, fig. 1a._).

These scutes differ from those of other recent and fossil Crocodilians,

in a lateral conical projection, marked _a_, _figs. 1, 2, Lign. 207,

which fits into a depression on the under surface of the opposite angle

of the adjoining plate; resembling, in this respect, the scales of the

Lepidotus (see _Lign. 196_, p. 605). Numerous hexagonal and pentagonal

scutes, articulated together by marginal sutures, also entered into the

composition of the osseous dermal cuirass of this reptile, which must,

therefore, have possessed a flexible, yet impenetrable, coat of armour,

capable of affording protection against the attack of any assailant.

In the Oolite, the dermal bones of other slender-nosed Crocodilians

(_Teleosaurus_) are occasionally met with; the outer surfaces of

which are marked with small circular distinct pits; these scutes are

thicker and more rectangular than those above described, and slightly

overlapped each other laterally; they have no connecting process. In

another species one half of the outer surface is smooth, proving that

it was covered to that extent by the adjoining scute.[588]

[588] A description of the dermal bones of British fossil reptiles is

given in Brit. Assoc. Report for 1841, pp. 70, 79, &c.

Dermal Bones of the Hylæosaurus.--Elliptical and circular dermal

scutes, having the under surface flat and the upper convex with

a conical tubercle, were first noticed in the specimen of the

_Hylæosaurus_, figured _Wond._ pl. iv.; and I have since discovered

similar bones associated with other remains of that extraordinary

reptile; reduced figures of two specimens are represented in _Lign.

208, figs. 1, 3_.

[Illustration: Lign. 208. Dermal Bones of Reptiles. _Tilgate Forest._

Fig. 1, and 3.--Dermal bones of the Hylæosaurus: 1/3 _nat._

1_a_.--The under surface of a fragment of a dermal bone, displaying

fine spicula, decussating each other at right angles, and indicating

a similar structure to that of the Curium, in which

the bones were imbedded: nat.

1_b_.---A portion of the same, highly magnified, and viewed by

transmitted light.

2.--Horn of Iguanodon: 1/6 _nat._

4.--A Dorsal Spine of the Hylæosaurus; the original is

thirteen inches long.

]

The structure of these bodies is very remarkable; upon closely

inspecting the under side, and the surface exposed by a transverse

fracture, very minute osseous spicula, decussating each other at right

angles, are distinctly seen; as shown in _Lign. 208, fig. 1a_. In

_fig. 1b_, a thin slice of the same, highly magnified, and viewed

by transmitted light, displays medullary canals, with very fine lines

radiating from them. The peculiar character of this organization

consists in the disposition of the straight bony spicula; an appearance

which first attracted my attention when developing the original

specimen of the Hylæosaurus (see _Geol. S. E._ p. 327), and led to

the discovery of some perfect examples, which otherwise would have

been destroyed. This structure closely resembles that presented by the

ligamentous fibres of the _corium_, or skin, and seems to have resulted

from an ossified condition of the dermal integument. These bones

vary from half an inch to three or four inches in diameter, and were

disposed in one or more longitudinal series on each side the spine,

diminishing in size as they approach the end of the tail.

Dermal Spines of Hylæosaurus. _Lign. 208, fig. 4._--With the dermal

bones above described there are associated in the first discovered

specimen of the Hylæosaurus, flat, thin, angular, osseous plates, from

three to seventeen inches in length; one of which is figured _Lign_

208, fig. 4_. The manner in which they are imbedded in the rocks, in

connexion with other parts of the skeleton, is shown Wond. pl. iv.

and _Geol. S. E._ pl. v. These very remarkable processes appeared to

me to have formed part of a serrated fringe, which extended along the

back of the reptile, analogous to that observable in certain living

lizards (_Wond._ p. 436, _Lign._ 108); and were provisionally described

as such in my first memoir on the Hylæosaurus. This conjecture has

been substantiated by subsequent discoveries, and the true nature of

the large, flat, angular spines, and the conical bones resembling

the horn-cones of ruminants, which occur in the Wealden, is now

established.[589]

[589] See _Fossils, Brit. Mus._ pp. 298, 320.

Horn of Iguanodon.--In this category may be placed the nasal tubercle

or horn of a saurian, like that of the Iguana (_Lign. 208, fig.

2_; _Geol. S. E._ pl. iii.), found with the remains of the Iguanodon,

and probably belonging to that colossal reptile (_Wond._ p. 431; and

_Petrif._ p. 298). It is four inches in length and 3.2 inch by 2.1 inch

in diameter at the base, which is of an irregular elliptical form.

Several smaller specimens have recently been discovered.

Examples of dermal scutes and spines, presenting modifications of form

and structure distinct from those above described, have been brought

to me from various localities of the Wealden; but, as in no instance

a connexion with other parts of the skeleton could be traced, the

particular reptiles to which they belonged cannot be ascertained.

We proceed to notice some of the principal genera of Fossil Reptiles,

especially of those whose remains occur in the British strata; the

arrangement of Professor Owen is adopted for the convenience of

reference to the Brit. Assoc. Reports, 1839 and 1841, which should

be consulted by the student who would acquire a knowledge of this

department of Palæontology. The subject will be considered under the

following heads; namely:--

I. _Enaliosaurians_, or Marine Reptiles; Ichthyosaurus and

Plesiosaurus.

II. _Crocodilians_; Crocodile, Teleosaur, &c.

III. _Deinosaurians_; comprising the Iguanodon, Megalosaurus,

Hylæosaurus, Pelorosaurus, &c.

IV. _Lacertians_; including the Mosasaurus, Rhyncosaurus, &c.

V. _Pterosaurians_; the Pterodactyles, or flying Reptiles.

VI. _Chelonians_; or Tortoises and Turtles.

VII. _Ophidians_; or Serpents.

VIII. _Batrachians_; or the Frog tribe; comprising the Labyrinthodonts.

I. Enaliosaurians.--The extinct marine reptiles comprised in this

order constitute two genera, which are characterized by essential

modifications of osteological structure; they are named Ichthyosaurus

(_fish-lizard_), and Plesiosaurus (_akin to a lizard_). The general

appearance of these beings is so well known, from the splendid

collection of their fossil remains in the British Museum, and the

numerous specimens in provincial and private collections, and by

various works, both scientific and popular, in which their structure

and physiological relations are fully elucidated, that they must be

familiar to every reader.[590]

[590] _Bd._ vols. i. and ii. contain an admirable exposition of

their habits and organization; and Brit. Assoc. Reports, 1839, 1841,

elaborate osteological investigations of both genera. A folio volume on

these extinct Reptiles, with splendid lithographs, by Thomas Hawkins,

Esq., cannot fail to delight the reader by its graphic descriptions and

beautiful illustrations. See also the masterly paper on the Ichthyosaur

and the Plesiosaur, by the Rev. W. D. Conybeare, in the Geological

Transactions, 1st series, vol. v. p. 559, _et seq._

[Side note: ICHTHYOSAURUS. PLESIOSAURUS.]

The living Ichthyosaurus must have borne a resemblance to a Grampus or

Porpoise, with four large flippers or paddles and a long tail, having

a vertical caudal fin of moderate dimensions; the skin probably being

naked and smooth, as in the Cetaceans. The Plesiosaurus presented a

configuration still more extraordinary (_Wond._ p. 575). With a very

small head, it possessed a neck of enormous length, a body of moderate

size, with four paddles, resembling those of turtles, and a very short

tail. They were both marine, air-breathing, cold-blooded, carnivorous,

vertebrate animals; swarming in prodigious numbers during the secondary

epochs, and particularly in the seas of the Liassic period (_Ly._ p.

277, figs. 310, 311). In both genera the construction of the skeleton

presents many important variations from all known recent types; and

should be carefully investigated by the student, who will find in the

Reports of Professor Owen above referred to all the information that

can be desired.[591]

[591] The Penny Cyclopædia, Art. Plesiosaurus, contains an able

abstract of these Reports; and in the _Fossils of the British

Museum_, the student will find a full account of the discovery of

the Ichthyosaur and Plesiosaur, and of the deposits in which they

are chiefly found, as well as detailed descriptions of the most

characteristic structures of the different species.

It will suffice for our present purpose to point out a few important

and obvious characters.

[Illustration: Lign. 209. Eye of Ichthyosaurus. 1/6 _nat._

_Lias._ _Lyme Regis._

Portion of the facial part of the skull of an Ichthyosaurus, showing

the position of the nostril, and of the orbit with its circle of bony

plates, forming the sclerotic coat of the eye.

_n._ The left nasal aperture.]

In the Ichthyosaurus, the nasal apertures or openings of the nostrils

are not towards the snout, as in the Crocodile, but near the anterior

angle of the orbit (see _Lign. 209_), approaching, in this respect,

some of the recent lizards. The orbit is very large, and the sclerotic

coat or capsule of the eye has in front an annular series of bony

plates (_Bd._ pl. x. _figs._ 1, 3), which often occur in their natural

position (_Lign. 209_). This structure is not possessed by fishes,

but is analogous to that observable in the eyes of turtles, lizards,

and many birds; as for example, in the owl and eagle: it confers on

the eye additional power of adaptation and intensity of vision. The

muzzle of the Ichthyosaurus is long and pointed; the lower jaw is

formed of two branches, united anteriorly through nearly half their

length; each branch is composed of six bones, as in the Crocodile and

Lizards, but differently arranged than in those reptiles. The teeth

are very numerous, amounting to nearly two hundred in some species,

and are placed in a single row along the jaws, being implanted in

a deep continuous groove (see _Bd._ pl. xi.). These teeth are of a

pointed conical form, longitudinally striated, with an expanded base

(_Lign. 210_). The new teeth are developed at the inner side of the

base of the old, and grow up and displace them (see _Lign. 210_).

The microscopical structure of the teeth of the Ichthyosaurus is

beautifully illustrated by Professor Owen (_Odontography_, p. 275, pl.

lxiv.). The tooth consists of a pulp-cavity, surrounded by a body of

dentine, which is invested at the base by a thick layer of cement; and

at the crown by a coat of enamel, also covered by a pellicle of cement

3 the pulp-cavity, in fully-formed teeth, is more or less occupied by

coarse bone. The chief peculiarity of this structure consists in the

inflection of the cement into vertical folds at the base of the tooth,

by which the marginal portion of the basal dentine is divided into a

corresponding number of processes; producing, in a transverse section,

the appearance represented in _Pl. VI. fig. 9_. This organization, as

we have previously remarked, is similar to that observable in the teeth

of the _Lepidosteus_ (see p. 616), and of the extinct reptile, called

_Labyrinthodon_, hereafter to be noticed.

[Illustration: Lign. 210. Teeth of Ichthyosaurus and Plesiosaurus,

_nat._

_Lias._ _Somersetshire._

Fig. 1.--Tooth of Plesiosaurus.

1_a_. Transverse section of the lower part.

2.--Tooth of Ichthyosaurus.

2_a_. Transverse section of the middle of the tooth.

3. Vertical section of part of lower jaw of Ichthyosaurus, with a

tooth, illustrative of the mode of dentition.

_a, a, a._ Section of the lower jaw, showing the deep furrow,

_b_ in which the teeth are implanted.

_c._ The canal for the dental vessels.

_d._ Foramen for the passage of vessels to the outer integuments.

_e._ Germ of a successional tooth which has occasioned the

absorption of the inner portion of the base of the mature

tooth, _f_.

]

[Illustration: Lign. 211. Vertebra of Ichthyosaurus. 1/3 _nat._

Fig. 1.--Neural arch and spine.

2.--Body or centrum.

_a._ Socket for the reception of

the corresponding process

of the neural arch.

3.--Vertical section of the centrum.

]

[Illustration: Lign. 212. The bones composing the Pectoral Arch of

Ichthyosaurus.

1/8 _nat._

_s_, sternum.

_cl_, _cl_, clavicles.

_sc_, _sc_, scapulæ.

_c_, _c_, coracoids.

]

[Illustration: Lign. 213. The bones composing the Pectoral Arch of

Plesiosaurus.

1/8 _nat._

_s_, sternum.

_sc_, _sc_, scapulæ or omoplates.

_c_, _c_, coracoids.

_g_, _g_, the glenoid cavities or sockets

for the head of the humerus

or arm-bones.

]

The vertebræ; (_Bd._ pl. xii.; and _Lign. 211_), of which there are

upwards of one hundred and forty in the individuals of some species,

are relatively very short in their antero-posterior diameter (_i. e._

from front to back); and deeply cupped on each articulating face, as in

fishes. The annular part is not united to the body of the vertebra, as

in mammals, nor connected by suture, as in Crocodiles, but terminates

on each side in a compressed oval base, which fits into corresponding

sockets placed on the boundary line of the spinal depression on the

body (_Lign. 210, 2a_); thus completing the medullary canal (see

_Bd._ pl. xii. _fig._ D, E.). Hence the collector may easily recognise

the body of an Ichthyosaurian vertebra, by the pits or depressions on

the sides of the spinal interspace. The first and second vertebra; are

anchylosed together, and have additional subvertebral, wedge-shaped

bones, which render this part of the column a fixed point of

support.[592] (_Bd._ pl. xii. figs. 3, 6.) The form and arrangement of

the bones that enter into the composition of the pectoral and pelvic

arches, and of the paddles, are exemplified in _Bd._ pl. xii.; and

full osteological details are given in _Brit. Assoc. Rep._ 1839, p.

104. The characters of the several bones composing the pectoral arch

of the Ichthyosaur will be readily understood from the accompanying

illustration. The structure of the pectoral arch of the Plesiosaur is

also shown in an accompanying Lignograph, for the sake of comparison.

The bones of a fore-paddle of an Ichthyosaurus are represented (_Lign.

214, fig. 1_). In some species each paddle consists of nearly one

hundred bones. These locomotive extremities are very analogous in their

osteological construction to those of the Cetaceans, but they are

connected with the trunk by means of the glenoid socket formed by the

scapula and coracoid, which are firmly united to the sternum; whereas

in the Cetaceans the pectoral fin is only attached to a simple scapula,

which is merely suspended in the muscles. This structure, together

with the presence of a clavicle in the Ichthyosaurus (see _Lign.

212_), which is wanting in the Cetaceans,, indicates, in the opinion of

Professor Owen, that this marine fish-lizard was capable of some degree

of locomotion on the land; and that it might have resorted to the

shore to deposit its eggs, or, like the Crocodile, to sleep. From the

frequent occurrence of a dislocation or abrupt bend of the vertebral

series of the tail, at about one-third of its length from the end,

supposed to have been produced by the weight of a large fin, during

the progress of decomposition, and from the terminal caudal vertebræ

being laterally compressed, it is inferred that the Ichthyosaurus had a

vertical fin at the extremity of the tail, which would thus be rendered

a powerful instrument of progressive motion.[593] From the appearance

of the _Coprolites_, which occur abundantly with the skeletons of these

animals, it is obvious that the intestinal canal in the Ichthyosaurus

was furnished with spiral valves, as in the Sharks; and the comminuted

bones and scales in the coprolites prove that fishes constituted the

principal food of these marine reptiles.

[592] This structure was first demonstrated by Sir Philip Egerton. See

Geol. Trans. 2d series, vol. v. p. 187, pl. xiv.

[593] Geol. Trans. 2d ser. vol. v. p. 511, pl. xlii.

[Illustration: Lign. 214. Paddles of Ichthyosaurus and Plesiosaurus,

1/8 _nat. size_.

_Lias Shale._ _Lyme Regis._

Fig. 1.--Left fore-paddle of the Ichthyosaurus.

2.--Left fore-paddle of the Plesiosaurus.

]

The Ichthyosaurus has abdominal ribs (p. 656, note), as in the

Crocodile, and it is therefore inferred that, if oviparous, it did not

produce ova in such immense numbers as the Batrachians, &c. A specimen

found by the late Mr. Channing Pearce renders it probable that the

Ichthyosaurus may have been viviparous. A remarkably perfect adult

Ichthyosaurus, examined by this gentleman, contained the bones of a

fœtus (a few inches long) _in the cavity of the pelvis_. This specimen

is in the collection of Mr. Pearce, at Bath. Remains or traces of the

dermal integument have been discovered in some examples from the Lias

of Barrow-on-Soar, Lyme Regis, Ilminster, and the neighbourhood of

Tewkesbury.[594]

[594] See Mr. Coles’s interesting paper on the Skin of the

Ichthyosaurus, in the Quart. Journ. Geol. Soc. vol. ix. p. 79.

[Illustration: Lign. 215. Hinder Paddle of an Ichthyosaurus

(1/3 _nat._): with the impression of its integuments. _Lias._

_Barrow-on-Soar._

(_From Geol. Trans. 2d ser. vol. vi. pl. xx._)]

Integuments of the Paddle.--The importance of carefully examining the

surrounding stone before removing vegetable or animal remains from

the matrix in which they are imbedded, and which has so often been

insisted upon in the preceding pages, is strikingly exemplified in the

highly interesting example of the hinder paddle of an Ichthyosaurus

(_I. communis_) discovered by Sir Philip Egerton. _Lign. 215_ is

reduced from the exquisite representation of the specimen accompanying

the original memoir by Prof. Owen on this fossil, in the Geological

Transactions. The specimen consists of the phalangeal bones of a

posterior paddle, with the impression of the soft parts or integuments

in their natural position; _a_, marks the termination or distal

extremity of the fin, consisting entirely of the softer integuments;

these gradually widen and expand to receive the terminal rows of

the phalangeal ossicles or bones, marked _b_. The upper border of

this integumentary part of the paddle (_c_) is formed by a smooth,

well-defined line, apparently a mere duplicature of integument. But

the lower margin (_d_) exhibits the impressions of a series of rays,

by which the fold of integument was supported; these rays bifurcate

as they approach the margin of the fin, and were probably either

cartilaginous, or composed of an albuminous horny tissue, like the

marginal rays in the fins of Sharks. Dr. Buckland detected remains of

the dermal integument of an Ichthyosaurus in a specimen from the Lias

at Barrow-on-Soar (_Bd._ ii. p. 22, pl. x.); and in a fine skeleton

with the four paddles (now in the British Museum), which I obtained

from that locality, there were decided traces of the carbonized

integuments around each paddle, but which were, unfortunately,

chiselled away, in developing the bones, before I was aware of their

true nature.

In Mr. Coles’s paper, already referred to, the student has an

instructive instance of the value of a careful examination of faint or

obscure traces of organic matter accompanying these saurian remains,

and how such an examination should be made. The Plate illustrative of

the Memoir exhibits the minute, hooked, conical bodies, that form the

dense felt-like mass which the black film, frequently accompanying

these fossil bones, appears to consist of, when seen under the

microscope. To what extent this substance entered into the constitution

of the integuments, or of the exact relation of these "setiform scales"

to the surface or the interior of the skin, our present knowledge does

not enable us to judge.

[Sidenote: PLESIOSAURUS.]

Plesiosaurus. (_Bd._ pl. xvi.--xix.)--The animals of this genus present

in their osteological structure a remarkable deviation from all known

recent and fossil reptiles; uniting the characters of the head of

a lizard, with the teeth of a crocodile, to a neck of inordinate

length, with such modifications of the ribs, the pectoral and pelvic

arches, and the paddles, as to justify the graphic simile of Professor

Sedgwick, that the Plesiosaurus might be compared to a serpent threaded

through the shell of a turtle.

The character which immediately strikes the observer, is the

extraordinary length of the neck, and the relative smallness of the

head. The neck, which in most animals is formed of but five vertebræ,

and in the extremest recent example, the Swan, does not exceed

twenty-four, is in the Plesiosaurus composed of from twenty to forty;

and, in some species, is four times the length of the head, and equal

to the entire length of the body and tail; while the length of the

head (in _P. dolichodeirus_) is less than one-thirteenth of the entire

skeleton. The skull resembles that of the crocodile in its general

form, but is relatively smaller, and is more related to the lacertian

type. The parietal bone is more triquetal than in the crocodiles;

but the zygomatic bone is attached to its lower end. The breathing

apertures are situated anterior to the orbits, on the highest part of

the head. The lower jaw has the usual structure of the Saurians; but

the dentary bone is greatly expanded anteriorly, and united in front

(see _Bd._ pl. xix.). The teeth are implanted in separate sockets, as

in the crocodile, and there are from thirty to forty on each side the

jaws. They are conical, slender, long, pointed, slightly recurved,

and longitudinally grooved from the base upwards; having a long round

fang. The pulp-cavity is long and single, surrounded by a body of firm

dentine, covered on the crown with a layer of enamel, and at the base

with cement (_Odont._ pl. lxxiv.). The dentition in the Plesiosauri

differs from that of the Crocodiles, in the successional teeth emerging

through distinct apertures on the inner side of the sockets of their

predecessors, and not through the pulp-cavity. The vertebræ are

relatively longer than in the Ichthyosaurus, and their articular faces

are either flat, or slightly excavated towards the periphery, with a

gentle convexity in the centre (_Foss. Til. For._ pl. ix. fig. 4).[595]

[595] For details, see Brit. Assoc. Rep. 1839, p. 50.

The caudal vertebræ have two distinct hæmapophyses, not united into a

chevron-bone.

The cervical ribs, or hatchet-bones, are attached by two articular

facets to the bodies of the vertebræ, but with a very narrow space

between; scarcely large enough even for the passage of the sympathetic

nerve; and apparently not sufficient for the vertebral artery.

The _pectoral arch_ is remarkable for the pair of elongated and broad

coracoid bones (_Bd._ pl. xvii. and _Lign. 213_); indeed the coracoids

attain their maximum of development in the Plesiosaurus. The _ribs_,

which are very numerous, and extend throughout a great portion of

the vertebral column, are connected, anteriorly, in the abdominal

region, by several slender bones, called _costal-arcs_, consisting

of six or seven pieces to each pair of ribs; the Ichthyosaurus has a

similar structure, but the arcs are composed of but five pieces. As

these connecting bones are so constructed as to admit of a certain

degree of gliding motion upon each other, it is inferred that, by this

mechanism, considerable expansion of the pulmonary cavities in these

air-breathing marine reptiles was obtained (_Bd._ pl. xviii. fig. 3).

The paddles are composed of fewer and more slender bones than in the

Ichthyosaurus, and must have been of a more elegant form, and possessed

greater flexibility (_Lign. 214, fig. 2_). The wrist (_carpus_)

consists of a double row of round ossicles, which are succeeded

by five elongated metacarpal, and these by numerous, slender and

slightly-curved phalangeal bones.

Sixteen species of Plesiosaurus and ten of Ichthyosaurus have been

discovered in the British strata, and nearly forty are now known;

their geological range is from the Lias to the Chalk, inclusive.[596]

Their remains are found most abundantly in the Lias and Oolite. I have

collected many Plesiosaurian vertebræ in the Wealden, and in the Green

Sand of Farringdon. No traces of Ichthyosauri have been observed in the

Wealden; but vertebræ, and jaws with teeth, occur in the lower Chalk

and Galt of Kent and Cambridgeshire.[597] On the Continent the remains

of Enaliosaurians have also been discovered in the same formations.

[596] See _Petrifactions_, for an account of the specimens in the

British Museum.

[597] Brit. Assoc. Trans. 1845, Sect. p. 60. The Enaliosaurian bones

and teeth found in the Cretaceous deposits of England have been

fully described and illustrated by Prof. Owen, in Dixon’s _Fossils

of Sussex_, &c., and in his Monograph on the Fossil Reptiles of the

Cretaceous Formation, Palæontographical Society, 1851.

Pliosaurus.---This name designates a gigantic extinct reptile, of

which the upper and lower jaws, with teeth, considerable portions of

the vertebral column, and many bones of the extremities have been

discovered in the Kimmeridge clay of Oxfordshire, and are preserved in

Dr. Buckland’s museum. The teeth resemble those of the Plesiosaurus

in their general aspect, being of a conical form, longitudinally

grooved, and having a long fang; but they are readily distinguished by

the subtrihedral form of the crown, produced by the smooth, flat, or

slightly convex external surface; they approach in this respect the

tooth of the Mosasaurus; from the latter, however, even fragments may

be known by the presence of longitudinal ridges. The animal itself was

an enormous marine reptile, allied to the Plesiosaurians, but more

nearly related to the Crocodilians.[598]

[598] Brit. Assoc. Rep. 1841, p. 60. Odont. pl. lxviii.

II. Crocodilians.--The loricated, or mailed, Saurian reptiles, viz.

the Alligators, Crocodiles, and Gavials, are well known as the largest

living forms of cold-blooded oviparous quadrupeds.[599] No relics of

any recent species have been observed in a fossil state; except that of

the Gangetic Gavial, which has been found fossil in the Sub-Himalayas

by Capt. Cantley and Dr. Falconer; but remains of Crocodilians of

the existing generic type, having the spinal column composed of

concavo-convex vertebra; (i. e. united to each other by a ball and

socket-joint), the convexity being behind, or towards the tail, have

been found in the London Clay at Hackney and the Isle of Sheppey, and

in the eocene deposits on the coast of Western Sussex and Hants.[600]

But the Crocodiles of the Wealden, Purbeck, Oolite, and Lias differ

materially in their osteological characters from the recent species,

particularly in the structure of the vertebral column; which in one

genus is composed of concavo-convex vertebra; placed in a reversed

position to those of the existing species, the ball or convexity

being anterior, or directed forwards. In the other genera, both the

articular faces of the vertebræ are either flat, or concave.[601]

(_Geol. S. E._ p. 296.)

[599] A detailed and philosophical examination of the osteology of

the recent Crocodilia has lately been given to the scientific world

by Prof. Owen, in his Monograph on the Reptilia of the London Clay,

published by the Palæontographical Society of London, 1850. A condensed

notice, by Prof. Owen, of the dental apparatus of the Crocodilians, is

to be found in the _Cyclop. Anat._ Art. Teeth.

[600] See Brit. Assoc. Rep. 1844, Sect. p. 50; and 1847, Sect, p. 65.

[601] Cuvier, Oss. Foss. tom. v. p. 153; on the fossil Crocodiles of

Honfleur, which comprise both the types alluded to in the text.

Vertebræ of two species of Crocodilians or Alligators have been found

in the cretaceous Green Sand of the United States: these are of the

true procœlian[602] type, as in the existing species; but they present

peculiar characters in the modification of the apophyses.[603]

[602] Procœlian, concave before: amphicœlian, concave at both ends

platycœlian, flat in front and concave behind.

[603] See Quart. Geol. Journ. vol. v. p. 380, pl. x.

[Illustration: Lign. 216. Skull and Jaws of Teleosaurus. 1/8 _nat._

_Lias._ _Whitby._

Fig. 1.--Upper view of the cranium of Teleosaurus.

_c_, occipital condyle.

_t_, _t_, temporal fossæ.

_o_, _o_, orbits.

_n_, nasal apertures.

2.--Muzzle or anterior extremity of the jaws of _Steneosaurus_.

3.--The same of Teleosaurus.

4.--Lateral view of the cranium and lower jaw of Teleosaurus.

]

With this exception, the Crocodilians with broad muzzles, as the Cayman

and Alligator, have no representatives below the Tertiary formations;

the _Crocodilia_ of the Secondary deposits being all referable to the

division having elongated beaks, like the recent Gavials (_Bd._ p.

250). The fossil Crocodiles of the latter type are arranged in two

genera; namely, Teleosaurus[604] (_Lign. 216, fig. 3_), in which

the nasal apertures terminate in two orifices, (not blended into a

single opening as in the recent species,) in front of the nose; and

Steneosaurus (_Lign. 216, fig. 2_), in which the breathing canals end

in two nearly semicircular vertical openings at the extremity of the

muzzle. (See also _Bd._ pl. xxv.)

[604] The skeleton of a recent Gavial, and that of a Teleosaur, are

represented on one plate, for comparison, in Prof. Owen’s Monograph,

_loc. cit._

The British fossil species, most nearly related to the recent, occur

in the Lower and Middle Eocene of the South-East of England. Two fine

specimens of the skull of _Crocodilus toliapicus_, Cuvier and Owen

(_C. Spenceri_ of Dr. Buckland), have been found at Sheppey, as well

as a skull of _C. champsoïdes_ (Owen), and numerous vertebræ referable

to each species. The eocene deposits of Hordwell Cliff have yielded

the _Crocodilus Hastingsiæ_,[605] and the _Alligator_ _Hantoniensis_

(_Petrif._ p. 467; and _Charlesworth's Geol. Journ._ pl. i.); and the

remains of a Gavial (_Gavialis Dixoni_, Owen, in Dixon’s _Foss. Suss._)

have been found at Bracklesham.[606]

[605] This fossil Crocodile supplies a good illustration of the

biconvex body of the first caudal vertebra already described as

peculiar to these loricated reptiles, see page 656; and I have

subjoined _Lign. 217_ in illustration of this structure.

[606] Most of these valuable fossils are in the British Museum. They

are all described in detail and most elaborately illustrated in Prof.

Owen’s Monograph, already referred to.

[Illustration: Lign. 217. First Caudal Vertebra of Crocodilus

Hastingsiæ.

1/3 _nat._

_Eocene._ _Hordwell Cliff._

_s_, spinous process, or neural spine.

_z_, anterior zygapophysis or oblique process.

_z^1_, posterior zygapophysis.

_d_, left diapophysis, or transverse process.

_a, p_, body or centrum, convex at both ends.

]

In the strata of Tilgate Forest, associated with innumerable remains of

reptiles of various kinds, teeth of the Crocodilian type, belonging to

two genera, are not uncommon.[607] The first kind (_Suchosaurus_[608]

_cultridens_ of Prof. Owen) is a tooth about an inch in length, of a

slender acuminated form, compressed laterally, and gently recurved,

with a sharp edge in front and behind; resembling, in its general

figure, the tooth of a Megalosaurus, with the serrations on the edges

worn off (_Pl. VI. fig. 7_). The sides of the crown are marked with a

few longitudinal grooves. Some biconcave vertebræ found in the same

quarries, and characterized by the compressed wedge-shaped form of the

centre (_Foss. Til. For._ pl. ix. _fig._ 11), are supposed by Professor

Owen to belong to the same reptile as the teeth above described; but it

is hazardous to pronounce on the identity of these detached teeth and

bones, without more corroborative proof than has hitherto been obtained.

[607] Foss. South Downs, p. 50. _Foss. Tilg. For._ p. 64; pl. v. figs.

1-3, 7. _Cuv. Oss. Foss._ tom. v. p. 161, pl. x. See also Owen's later

examination of these remains, _Report Brit. Assoc._ 1811, p. 67; and

_Cyclop. Anat._ Art. Teeth.

[608] Brit. Assoc. Rep. 1841, p. 68. _Sucho-saurus_ is derived from

_Suchus_, or _Suchis_, the name given by Strabo to the sacred crocodile

of the Egyptians.

Swanage Crocodile. (_Goniopholis crassidens._) _Petrif._ p. 170,

_Lign. 38._--Under this name, the second species of Crocodilian teeth

will be considered; the discovery of a considerable portion of a

skeleton of a reptile with teeth of this form (_Wond._ p. 416), in

a quarry near Swanage, having disclosed some of the most important

osteological characters of the original. These teeth are distinguished

from the former by their cylindrical base, and rounded, obtuse, conical

crowns (_Petrif._ p. 171): they somewhat resemble in form those

of the Crocodile, but the crown is strongly marked with numerous,

well-defined, longitudinal grooves and ridges; and there is a sharp

ridge on the middle of each side. A small specimen, broken off at the

base, is represented _Pl. VI. fig. 5_; it shows the smooth cylindrical

base of the tooth, which is covered with cement, and the finely

striated enamelled crown; some of the teeth are more than two inches

in length, and one inch in diameter at the base (_Foss. Til For._ pl.

v. figs. 1, 2). I have found these teeth in numerous localities; they

are always well preserved, with the ridges sharp, and have a high

polish (_Geol. I. Wight_, p. 357, _Lign._ 30); a series of successional

teeth may often be detected in the pulp-cavity (see _Wond._ p. 414).

The detached teeth, and fragments of dermal bones (_Lign. 207_),

which, from their constant occurrence with this species, I had been

led to consider as belonging to the same reptile, were the only

relics that had come under my observation, until the discovery of the

Swanage specimen above mentioned.[609] On the two corresponding slabs

containing this fine fossil are imbedded many detached teeth; a portion

of the left side of the lower jaw, with two teeth in place; ribs and

numerous vertebræ, which are biconcave, and have an irregular medullary

cavity in the centre of the body; chevron bones resembling those of

the Crocodile; the bones of the pelvic arch, and some of those of the

extremities. With these are the remains of the osseous dermal cuirass,

consisting of numerous scutes (figured and described p. 657, _Lign.

207_), scattered at random among the other relics of the skeleton; some

having the inner, and others the external surface exposed; several of

these bones are perfect, and exceed six inches in length, and two and

a half in breadth. Numerous scales of a small Ganoid fish (_Lepidotus

minor_), common in the Purbeck strata, are also intermingled with these

remains. This reptile is named _Goniopholis crassidens_, by Professor

Owen.[610]

[609] Now in the British Museum: see _Petrif._ p. 170. A lithograph

of one of the slabs was given in the third edition of the Wonders of

Geology, 1839.

[610] _Gonio-pholis_:--_angle-scute_. Brit. Assoc. Rep. 1841, p. 72.

Both the slabs of the Swanage specimen are admirably arranged in the

same case in the British Museum, with bones and scutes of this reptile

from Tilgate Forest; there can be no doubt that the entire lower jaw

of the Swanage reptile might have been obtained if the quarry-men had

taken the precaution of examining the adjoining block of stone.

Pœcilopleuron.--The remains of an allied genus of Crocodile, the

_Pœcilopleuron Bucklandi_ (of Deslongchamps), occur in the Oolite,

near Caen, Normandy. This reptile, like the Goniopholis, had biconcave

vertebræ, with a large medullary cavity in the middle of the centrum.

The body of the vertebræ is contracted in the middle, the neural arch

anchylosed, with no trace of suture, and with a thin spinous process,

which is remarkable for its backward inclination. Vertebræ of this

character also occur in the Wealden strata of Tilgate Forest and the

Isle of Wight.[611]

[611] Brit. Assoc. Rep. 1841, p. 84. _Foss. Til. For._ pl. ix. fig. 8,

represents a caudal vertebra.

Teleosaurus. (_Bd._ pl. xxv.)--In the Oolite of England and the

Continent, the remains of a genus of extinct reptiles, having, like

the recent Gavial, long slender muzzles, have been discovered in

several localities. These fossils consist of the osseous scutes of

an imbricated dermal cuirass; of the cranium and jaws with teeth; of

the vertebral column; and many other bones. The characters of the

dermal scutes, and of the muzzle with its terminal nasal apertures,

have already been described (p. 659, and p. 676). There are several

species of _Teleosaurus_; a splendid specimen of _T. Chapmanni_,

fifteen feet long, from the Lias-shale on the Yorkshire coast, is

preserved in the Whitby Museum; and there are interesting examples

in the British Museum.[612] Teleosaurian remains have been found in

the Oolite at Stonesfield, and at Deddington, Oxfordshire; and Mr. C.

Moore, of Ilminster, whose museum is rich with perfect Ichthyosaurs

and Fishes from the Upper Lias of the neighbourhood, has been highly

successful in developing some charming specimens of small Teleosaurs

from out of the same deposit. In the Oolite of Caen, in Normandy, very

fine specimens of _T. Cadomensis_ have been discovered; and from these

the illustrious Cuvier first determined the character and affinities

of the original.[613] The British Oolite contains also the relics of a

reptile with biconcave vertebræ, belonging to the genus _Steneosaurus_:

the cranium with the jaws and teeth have been found in Kimmeridge clay,

at Shotover (_Bd._ pl. xxv.).[614]

[612] _Petrifactions_, p. 178.

[613] Oss. Foss. tom. v. p. 127.

[614] Report Brit. Assoc. 1841, p. 82.

From the Jura limestone at Monheim, in Franconia, the remains of a

small Crocodilian reptile (Teleosaurus priscus), with a long slender

muzzle, have been obtained. In a specimen[615] from the former

locality, the skull, jaws with teeth, the entire vertebral column, and

many parts of the skeleton are preserved: the entire length is but

three feet.

[615] Now in the British Museum: see _Petrif._ p. 178, where a detailed

description of this unique fossil is given. See also _Ossem. Foss._

tom. v. pl. vi.

Streptospondylus, _Lign. 206, figs. 5, 7._--Baron Cuvier in his

celebrated work, "_Recherches sur les Ossemens Fossiles_," has given

an elaborate description of the remains of two kinds of slender-nosed

Crocodilians, from the Kimmeridge clay of Honfleur, and the Oxford clay

of Havre.

The specimens consist of the jaws with teeth, vertebræ, and some bones

of the extremities.[616] In one species, the vertebræ are biconcave; in

the other, they are convexo-concave, and present a remarkable deviation

from the recent Crocodilian type, namely, that they are placed in a

reversed position,--the convex face of the vertebra being directed

anteriorly, or towards the cranium, and the concavity posteriorly;

the name of the genus, _Streptospondylus_ (reversed-spine), denotes

this peculiarity of structure. The bodies of three or four large

convexo-concave cervical vertebræ, were discovered in the Tilgate

strata many years since, and are described in my various works (_Geol.

S. E._ p. 300); but no suspicion was then entertained of their

belonging to this genus, although I had repeatedly compared them with

the figures of the Honfleur crocodile,[617] the imperfect state of

the processes obscuring their true characters. Professor Owen first

detected the true character of these Wealden vertebræ, in a large

cervical, six inches long (now in the British Museum), in which two

oblique processes are preserved on the concave end of the bone, their

flat, oblong, articular faces, are directed downwards and outwards,--a

character which at once proves them to be the posterior pair, for the

anterior oblique processes would be directed upwards and inwards.[618]

Vertebræ of the same species occur in the Wealden of the Isle of Wight;

and of another species in the Oolite at Chipping Norton, and in the

Lias of Whitby.

[616] Oss. Foss. tom. v. p. 143, pl. viii. ix.

[617] Reduced figures of two of these vertebræ are given in _Lign.

206_, _figs._ 5 and 7, p. 653.

[618] Brit. Assoc. Rep. 1841, p. 92. The position of the articulating

surfaces of the oblique processes (_zygapophyses_) in more perfect

specimens, subsequently discovered in various localities of the

Wealden, established the existence not only of a saurian allied to the

Streptospondylus, but also of other reptiles whose spinal column was

wholly or in part made up of vertebræ which were convex in front and

concave behind, as in the cervicals and anterior dorsals of certain

mammalia. Some of these fossil vertebræ Dr. Melville has referred,

with great probability, to the cervical region of the Iguanodon (see

_Petrif._ p. 259); others cannot at present be satisfactorily assigned

to any known genus of reptiles.

A concavo-convex caudal vertebra, with the relations of which I am

unacquainted, was found in the same quarry in Tilgate Forest; a reduced

outline of this unique fossil is given in _Lign. 206, fig. 1_. The

centrum is of a sub-cylindrical form, and the articular face in front

is concave, and that behind, convex; with a chevron-bone that is

anchylosed to the body of the vertebra, as in some of the caudals of

the Mosasaurus, and terminates in an inferior spine (_f._); the pair

of anterior oblique processes remains; the neural spinous process is

destroyed.

Cetiosaurus.--From a considerable number of vertebæ and bones of

the extremities of some gigantic aquatic reptiles, discovered in

the Oolite in various places in Oxfordshire, Northamptonshire, and

Yorkshire, the present genus was established; the name being intended

to indicate a distant general resemblance of these extinct Saurians to

the Cetaceans.[619] The vertebra; differ from those of the Iguanodon

in having their articular faces of a sub-circular form, and the body

relatively short; the anterior face is nearly flat, and the posterior

concave, in the dorsal vertebra;; but in the caudal both faces are

concave, and have a well-defined elevated margin, which gives the

body a deeply excavated character, easily recognizable. Vertebræ of

this kind were among my earliest discoveries in the strata of Tilgate

Forest. (_Geol. S. E._ p. 282.) Some specimens are eight inches in the

transverse diameter of the articular face, and but four and a half

inches in the antero-posterior length of the body.[620] The original

animals are supposed to have been of aquatic, and probably of marine

habits, on the evidence of the sub-biconcave structure of the vertebræ

and of the coarse cancellous tissue of the long bones, which are

destitute of a medullary cavity. They must have rivalled the modern

whales in bulk, for some specimens indicate a length of forty or fifty

feet; they are supposed to have had web-feet, and a broad vertical

tail.[621]

[619] Proc. Geol. Soc. vol. iii. p. 457.

[620] The osteological characters of these remains, and the

physiological relations of the original animals, are described in

_Brit. Assoc. Rep._ 1841, pp. 94-102.

[621] Brit. Assoc. Rep. 1841, p. 102.

Polyptychodon.[622]--The remains of another gigantic marine Saurian

have been discovered in the Green Sand at Hythe, in Kent; they consist

chiefly of the bones of the pelvis and hinder extremities.[623] The

femur must have been nearly four feet in length. The long bones have a

cancellated structure, without a medullary cavity 3 the outer surface

is finely striated. Probably in a recent state the cells were filled

with oil, as in the _Cetacea_. Neither the vertebræ nor the teeth of

this reptile are known; but, provisionally, these remains have been

referred to the same animal as that to which the large, conical,

longitudinally ridged teeth belonged, which have been found in the

Kentish Rag, at Maidstone, and in the Chalk of Sussex, and have been

named _Polyptychodon continuus_.[624] Teeth of _P. interruptus_ are

not unfrequent in the Cretaceous series; and a portion of the lower

jaw of this species, from the Chalk of Kent, is in Mr. Toulmin Smith’s

collection.[625]

[622] _Poly-ptych-odon_; many-wrinkle-tooth.

[623] _Geol. Proc._ vol. iii. p. 449. The bones from Hythe were

presented by their discoverer, H. B. Makeson, Esq., to the British

Museum. See _Petrifactions_, p. 200.

[624] Owen’s Monograph, Cretac. Reptilia, Pal. Soc. p. 47.

[625] Ibid. p. 55. See also Dixon’s Foss. Suss. p. 378. Teeth of the

Polyptychodon are figured in _Odontography_, pl. lxxii.

CHAPTER XVII.

FOSSIL REPTILES; COMPRISING THE DEINOSAURIANS, PTERODACTYLES, TURTLES,

SERPENTS, AND BATRACHIANS.

III. Deinosaurians.--The Order Deinosauria (_fearfully-great lizards_)

has been established for the reception of those extinct colossal

reptiles, comprising the _Megalosaurus_, _Hylæosaurus_, _Iguanodon_,

and _Pelorosaurus_, which, in their organization, present the

transition from the Crocodilians to the Lacertians, and whose essential

osteological characters Professor Owen has described as follow:--

"This group, which includes at least three well-established genera

of Saurians, is characterized by a large sacrum, composed of five

anchylosed vertebræ of unusual construction; by the height, breadth,

and outward sculpture of the neural arch of the dorsal vertebræ; by

the two-fold articulation of the ribs to the vertebra:, viz. at the

anterior part of the spine by a head and tubercle, and along the rest

of the trunk by a tubercle attached to the transverse process only;

by broad, and sometimes complicated, coracoids, and long and slender

clavicles; whereby Crocodilian characters of the vertebral column

are combined with a Lacertian type of the pectoral arch. The dental

organs also exhibit the same transitional or annectent characters,

in a greater or lesser degree. The bones of the extremities are of

large proportional size for Saurians; they are provided with large

medullary cavities, and with well developed and unusual processes, and

are terminated by metacarpal, metatarsal, and phalangeal bones, which,

with the exception of the ungual phalanges, more or less resemble

those of the heavy pachydermal Mammals, and attest, with the hollow

long-bones, the terrestrial habits of the species.

"The combinations of such characters, some, as the sacral ones,

altogether peculiar among Reptiles, others borrowed, as it were, from

groups now distinct from each other, and all manifested by creatures

far surpassing in size the largest of existing reptiles, will, it is

presumed, be deemed sufficient ground for establishing a distinct

tribe or sub-order of Saurian Reptiles, for which I would propose the

name of Dinosauria.

"Of this tribe the principal and best established genera are

the _Megalosaurus_, the _Hylæosaurus_, and the _Iguanodon_; the

gigantic Crocodile-lizards of the dry land; the peculiarities of

the osteological structure of which distinguish them as clearly

from the modern terrestrial and amphibious Sauria, as the opposite

modifications for an aquatic life characterize the extinct

_Enaliosauria_, or Marine Lizards."[626]

[626] Brit. Assoc. Rep. 1841, p. 103.

The elaborate investigation of the fossil remains of these stupendous

beings, and the luminous exposition of their organization and

physiological relations, embodied in the report to which the above

extract is introductory, are among the most important contributions

to Palæontology, and afford a striking example of the successful

application of profound anatomical knowledge to the elucidation of the

most marvellous epoch in the earth’s physical history, the _Age of

Reptiles_.

From the great size of the bones of these reptiles, their remains have

excited the curiosity even of the common observer; and although an

exaggerated idea has been generally entertained of the magnitude of the

original animals, yet, even when reduced to their natural proportions

by the rigorous formula of the anatomist, applied to the accumulated

relics which years of laborious research have exhumed from their

rocky sepulchres and deposited in our museums, their dimensions are

sufficiently stupendous to satisfy the most enthusiastic lover of the

marvellous.

Let the reader visit the British Museum,[627] and after examining the

largest thigh-bone of the Iguanodon, repair to the zoological gallery,

and inspect the recent Crocodilian reptiles, some twenty-five or

thirty feet in length; and observe that the fossil _bone_ equals, if

not surpasses, in size, the entire _thigh_ of the largest of existing

reptiles; then let him imagine this bone clothed with proportionate

muscles and integuments, and reflect upon the enormous trunk which

such limbs must have been destined to move and to sustain--and he will

obtain a just notion of the appalling magnitude of the lizards which

inhabited the country of the Iguanodon.

[627] See Fossils of the British Museum, p. 227.

The general characters of the extinct reptiles comprised in the order

_Deinosauria_[628] must be known to the intelligent reader, from the

various popular notices which have from time to time appeared; and

their names have become as familiar as household words. I shall here

restrict myself to a few general remarks on the form and structure of

the teeth, and of some of the more important bones of the best known

species of these great reptiles.[629]

[628] In the new edition of Pictet’s _Paléontologie_ (now in course of

publication), two 4to. plates (xxiii. and xxiv.) are devoted to the

illustration of the remains of these colossal reptiles.

[629] For further account of the Iguanodon, see _Petrif._ p. 224, &c.;

of the Hylæosaurus, _ibid._ p. 314, &c.; of the Pelorosaurus, _ibid._

p. 330, &c.; of the Regnosaurus, _ibid._ p. 333, &c.; and of the

Megalosaurus, _ibid._ p. 328, &c.

[Illustration: Lign. 218. Megalosaurus Bucklandi. 1/4 _nat._

_Great Oolite._ _Stonesfield, Oxfordshire._

Portion of the left ramus of the lower jaw, containing several teeth in

different stages of growth: inner aspect.

_a, a._ Crowns of successional teeth.

_b, b._ Transverse partitions of the tooth-sockets.

]

[Illustration: Lign. 219.

Tooth of the Megalosaurus Bucklandi.

(_Nat. size._)

_Wealden._ _Tilgate Forest._]

[Sidenote: MEGALOSAURUS.]

Megalosaurus (_gigantic lizard_) Bucklandi. _Lign._ 218 and 219. _Bd._

pl. xxiii. _Wond._ p 421.--The oolitic flag-stone of Stonesfield, in

Oxfordshire, has long been celebrated for the bones and teeth of a

gigantic reptile, which Dr. Buckland first described by the name of

_Megalosaurus_, in a highly interesting memoir (_Trans. Geol. Soc._

_sec. ser._ vol. i.), illustrated by figures of the teeth in a portion

of the lower jaw, the sacrum, femur, and other bones. The remains of

this reptile are also frequently discovered in the Wealden (see _Foss.

Til. For._ p. 67, pl. ix. figs. 2, 6). The most important relic of this

great carnivorous terrestrial lizard is a portion of the right ramus of

the lower jaw, containing one perfect tooth, and the germs of several

teeth (_Lign. 218_). The tooth of the Megalosaurus, (_Lign. 219_, and

_Pl. VI. fig. 7_,) has a conical, laterally compressed crown, with

the point recurved like a sabre, and the edges trenchant and finely

serrated. The implantation of the teeth is very peculiar, and exhibits

the dentition of the Crocodilians blended with that of the Lacertians.

The jaw has an outer parapet, as in the true lizards (see _Lign. 205_),

but the teeth are fixed in distinct sockets, formed by transverse

partitions, that are attached to a mesial (_inner_) parapet, composed

of a series of triangular osseous plates; the bases of the old teeth,

and the germs of the new ones, being thus enclosed and concealed.

The tooth is formed of a central body of dentine, the crown having a

coating enamel; and the whole an external investment of cement, which

forms a thicker layer around the fang; the pulp-cavity is occupied by

coarse bone, in the adult tooth. The microscopical examination shows

the dentine to consist of very fine calcigerous tubes, 1/28000th of an

inch in diameter, without any admixture of medullary canals, radiating

from the pulp-cavity at right angles with the external surface of the

tooth, and sending; off numerous secondary branches; these ultimately

dilate into, or inosculate with, a stratum of calcigerous cells

that separates the dentine from the enamel.[630] A thin slice of a

vertical section, viewed by transmitted light, is represented _Pl. VI.

fig. 7 b_; showing the calcigerous tubes radiating from the centre,

and terminating in the stratum of cells; this cellular structure is

invested with a layer of enamel, and the latter with an external coat

of cement, indicated by the dark outline.[631]

[630] Owen’s _Odontography_, p. 271, which should be consulted for more

minute details.

[631] To fully comprehend the minute structure of these and the other

teeth figured in _Pl. VI._ Professor Owen’s plates should be examined;

the small scale necessarily adopted in the present work rendering it

impossible to do justice to the subject.

Four specimens of the sacrum, composed of five anchylosed vertebral

(_Foss. Til. For._ pl. xix. _fig._ 12), have been discovered; one of

these is from Tilgate Forest. The femur of the Megalosaurus has two

large rounded trochanters of nearly equal size, below the head of the

bone; its shaft is sub-cylindrical, and slightly bowed.

This colossal carnivorous Saurian, whose length is estimated at thirty

feet, appears to have been terrestrial, and an inhabitant of the same

_terra incognita_ as the Iguanodon; it probably preyed on the smaller

reptiles, and the young of the Iguanodon, Crocodilians, &c.

Hylæosaurus (_Wealden lizard_) Owenii. _Wond._ pl. iv. and p. 435;

_Geol. S. E._ pl. v.--In the summer of 1832, I obtained the interesting

specimen which first demonstrated the existence of the remains of

another extraordinary modification of Saurian organization in the

Wealden. The circumstances which led to this discovery afford an

instructive lesson to the young collector.

Upon visiting a quarry in Tilgate Forest, which had yielded many

organic remains, I perceived in some fragments of a large mass of

stone, which had recently been broken up and thrown on the road-side,

traces of numerous pieces of bone. I therefore collected all the

recognisable portions of the block, and had them conveyed to my

residence. The first step was to cement together those pieces that

would admit of juxtaposition, and these were at length united into a

block of stone five feet long, three wide, and about one foot thick.

This was firmly fixed in a stout frame, to prevent the separation of

the united portions during the process of chiselling. Guided by the

indications which the sections visible on the edge afforded, a thin

iron wedge was carefully driven in, about half an inch above the

uppermost layer of bones, and a large slab was flaked off; the three

dermal spines (_Wond._ pl. iv. 5) in the middle of the specimen were

thus exposed, and shivered to pieces; some fragments adhered to the

mass broken off, others to the block, and many were detached; every

piece, however small, was collected, and those adhering to the slab

were chiselled out; and the whole were then carefully replaced and

cemented to the bones that remained imbedded in the large block.

After an interval of some days, to allow of the firm cohesion of the

cemented parts, the task was resumed, and the stone chiselled away,

until some portion of the large bones of the pectoral arch (_Wond._

pl. iv. 7) were observed. The specimen was at length brought to the

state in which it now appears (in the British Museum[632]); but

during the progress of its development, which occupied many weeks,

it was repeatedly necessary to suspend the work, and unite displaced

fragments of bone, and resume the task after their consolidation. The

plate in the _Geol. S. E._ conveys a good idea of the original.

[632] See _Fossils, Brit. Mus._ p. 139, &c.

The specimen consists of a part of the spinal column, composed of seven

dorsal and three or four cervical vertebræ, almost in their natural

juxtaposition, with obscure indications of a part of the base of the

skull; eleven ribs; the bones of the pectoral arch (two _coracoids_

and two _scapulæ_); with numerous dermal bones and spines. A second

specimen of this reptile was found near Bolney, in Sussex; and like

the former, it was, unfortunately, almost wholly destroyed by the

labourers; but I obtained many bones, some of which are perfect, and

indicate an animal of considerable magnitude: a _scapula_, nineteen

inches long, an arm-bone or _humerus_, numerous ribs, bones of the

phalanges, &c. A fine series of twenty-six caudal vertebra, having

a total length of nearly six feet, with chevron bones and dermal

spines, was discovered in 1837, in Tilgate Forest.[633] A few detached

bones are the only other relics of this reptile that have come under

my observation.[634] The osteological characters presented by these

remains afford another example of tire blending of the Crocodilian with

the Lacertian type of structure; for we have in the pectoral arch the

scapula or omoplate of a crocodile associated with the coracoid of a

lizard. Another remarkable feature in these fossils is the presence of

the large angular bones or spines (described p. 660, figured _Lign.

208_), which, there is reason to infer, constituted a serrated crest

along the middle of the back: and the numerous small oval dermal bones,

which appear to have been arranged in longitudinal series along each

side of the dorsal fringe. (_Geol. S. E._ p. 323.)

[633] See _Fossils, Brit. Mus._ p. 323.

[634] See "Memoir on the Remains of the Iguanodon, Hylæosaurus, and

other Saurian Reptiles," by the Author, in _Philosophical Transactions_

for 1841, Part II.

The vertebræ, ribs, and other parts of the skeleton found in

these specimens also present modifications of structure of great

interest.[635] No specimens of teeth have been found associated with

the remains of the Hylæosaurus, in such manner as to afford unequivocal

proof of their belonging to that animal. But in the same quarries,

teeth, decidedly of the Lacertian structure, are occasionally found,

and may with some probability be referred to that reptile. These teeth

(see _Pl. VI. fig. 6^a_.) are about 1-1/4 inch in length, and commence

at the base with a cylindrical shank, which gradually enlarges into a

crown of an obtuse lanceolate form, convex in front, hollowed behind,

and terminating in a rounded obtusely angular apex, the margins of

which are generally more or less worn.[636] The crown is solid, but

the fang encloses a small pulp-cavity; the surface is enamelled, and

covered with very fine longitudinal striæ; the base in every specimen

appears broken transversely, as if it had been anchylosed to the jaw,

or to the base of a socket. The fang never presents an appearance of

lateral adhesion, as if belonging to a Pleurodont lizard. Sections of

these teeth expose a simple, central, medullary canal, the upper part

of which is generally filled with the ossified remains of the pulp; and

this is surrounded by a body of firm dentine, with extremely minute

calcigerous tubes radiating from the centre to the periphery of the

tooth, which is invested with a relatively thick coat of enamel, in

which no structure is apparent. _Pl. VI. fig. 6^b_ represents a small

portion of a vertical slice, highly magnified and viewed by transmitted

light. The reference of these dental organs to the Hylæosaurus must

not, however, be considered as conclusive, until confirmed by the

discovery of the teeth attached to the jaw, in connexion with other

parts of the skeleton. The locomotive organs of the Hylæosaurus are

but imperfectly known; a perfect humerus, one phalangeal bone, and

fragments of the fibula (the small bone of the leg) are the only bones

hitherto observed. The length of this reptile, which was probably

terrestrial and herbivorous, may be estimated at from twenty to thirty

feet.

[635] See Report, Brit. Assoc. 1841, pp. 111-120. Phil. Trans. 1841,

pp. 141-144, pl. x.

[636] Rep. Brit. Assoc. 1841, p. 118. Geol. S. E. England, pl. ii.

figs. 2, 4. Phil. Trans. 1841, p. 144, pl. vi. figs. 9, 10, 11.

Iguanodon. _Ligns._ 219 to 226; _Wond._ pl. ii. iii., and pp. 422,

&c.--Soon after my first discovery of the remains of vertebrated

animals in the strata of Tilgate Forest, some teeth of a very

remarkable character particularly engaged my attention, from their

dissimilarity to any that had previously come under my notice.[637]

Attention having been directed to these interesting fossils, examples

were soon discovered of teeth in various conditions, from the sharp,

unused tooth of the young reptile, to the obtuse, worn-out crown of the

adult. From the resemblance of the perfect teeth to those of the Iguana

(_Lign. 205_, p. 649), a land lizard of the West Indies, I proposed the

name of _Iguanodon_ (signifying an animal with teeth like those of the

Iguana) for the extinct reptile to which they belonged. The numerous

bones and teeth subsequently exhumed from the strata of Tilgate Forest

and other localities in the Wealden of Sussex and of the Isle of

Wight, and the considerable portion of the skeleton of an individual

discovered by Mr. Bensted in the Kentish Rag, have supplied the data

upon which our present knowledge of the characters of the original is

based.

[637] These are described in _Foss. South D._ 1822, p. 54, under the

head "_Teeth and bones of unknown animals_." This was the earliest

published notice of the fossils of the Wealden; it contains also a

description of a tooth of the Megalosaurus (p. 55, No. 42).

In Wond, pp. 422-435, a brief account will be found of the character

of the teeth, horn, femur, vertebræ, &c., and of the Maidstone

specimen[638] (_Pl. III._).

[638] In a Monograph on the Reptiles of the Cretaceous Deposits of

England, published by the Palæontographical Society, Professor Owen has

lately figured anew and described in detail this most valuable fossil

skeleton; to which description are appended the Professor’s latest

views on the structure of the teeth of this reptile.

The "Geology of the South-east of England" contains accurate figures

of the long bones of the leg (_Geol. S. E._ pl. ii), femur, clavicles

(_Geol. S. E._ pl. iv.), tympanic bone (_Geol. S. E._ pl. ii.), horn

and ungual bone (_Geol. S. E._ pl. iii.). In the "Fossils of Tilgate

Forest," there are fifteen quarto plates devoted to the illustration of

the bones and teeth of the Iguanodon and other Wealden reptiles. The

osteological structure is fully detailed in _Rep. Brit. Assoc._ 1841,

pp. 120-144. A general notice of the principal bones of the Iguanodon,

with plates, will be found in _Phil. Trans._ 1841, pp. 131-151; and in

_Petrif._ chap. iii. the author has given a detailed account of the

most important specimens, both in the British Museum and in his own

collection, together with a résumé of the palæontology and geology of

the Wealden district.

[Illustration: Lign. 220. Iguanodon Mantelli. 1/7 _nat. size_.

_Wealden._ _Tilgate Forest._

The right ramus of the Dower Jaw; [639] discovered in 1848, by Captain

Lambart Brickenden, F.G.S.]

Fig. 1.--The inner aspect, showing three teeth, and the sockets of

eighteen.

_a._ Germ of a tooth.

_b._ Perfect crown of a successional tooth.

_c._ Remains of a successional tooth, the upper part having

been broken off.

_d._ The symphysial extremity of the jaw.

_e._ The opercular furrow.

_f._ The coronoid process.

2, 3, and 4, the teeth _a_, _b_, and _c_, in _fig._ 1, represented

on a larger scale.

[639] For the outer aspect, and a restoration of the whole jaw,

_Petrif._ pp. 247 and 249.

[Illustration: Lign. 221. Lower Tooth of the Iguanodon: _nat. size_.

_Wealden._

_Tilgate Forest._

The apex slightly worn.

Fig. 1.--Inner aspect, showing the longitudinal ridges, and denticulated

margins of the crown of the tooth.

2.--View of the outer surface of the tooth.

_a._ The denticulated margin.

_b._ The apex of the crown, worn by use; b. _fig._ 2, shows the

oblique smooth surface produced by mastication.

_c._ A transverse fracture of the fang, showing a section of

the medullary cavity occupied by the ossified remains of

the pulp.

_d._ Marks the inferior limit of the denticulated margin; if a

line were carried horizontally from d, across the tooth, the

under figure would represent a tooth worn flown below the

denticulations, and deprived of its peculiar dental

characters; in this latter state the tooth somewhat resembles

an incisor of a Rhinoceros (see _Ligns. 222, 223_; and

_Petrif._ _Lign. 48_).

]

[Illustration: Lign. 222. Upper Tooth of the Iguanodon: _nat. size_.

_Wealden._ _Brook Bay, Isle of Wight._

The crown is worn down to an oblique smooth surface, and the fang is

absorbed.]

Jaw and Teeth of the Iguanodon. _Ligns. 219-223._--Although the form

and structure of the cranium are unknown, yet the half of a lower jaw,

discovered in Sussex by Capt. L. Brickenden,[640] and a fragment of an

upper jaw, found some years since,[641] enable us to form a tolerably

perfect idea of the structure and functions of the dental organs of

the Iguanodon. The unused tooth of this reptile is characterized by

the prismatic form of the crown, the presence of from two to four

longitudinal ridges on its enamelled face, the denticulated margins

(_Lign. 221, a_), and finely serrated edge of the summit, as seen in

_Lign. 220, fig. 3_. The shank or fang of the tooth (_Ligns. 221,

223, fig. 2_) is sub-cylindrical, slightly curved, and tapers to a

point. The inner surface of the crown in the lower teeth, and the outer

surface in the upper, are covered with a thick layer of enamel, but the

opposite face of the crown and the sides have but a thin coating of

this substance. The teeth of the upper jaw (_Lign. 222_) are curved in

the opposite direction to those of the lower, and have the convexity

external, and the concavity internal. Thus the upper and lower molars

were related to each other nearly as in the Ruminants; the outer aspect

below corresponding to the inner above (see _Petrif._ _Lign._ 56, p.

254). The specimens met with have almost always the apex of the crown

more or less worn down by use[642] (see _Lign. 223_), and presenting

an oblique, triangular, smooth surface, as in the fine large specimen

figured in _Lign. 221_, which was found imbedded in the trunk of a

Clathraria, as if it had snapped off while the animal was in the act of

gnawing the tough stem. The denticulated margins are well developed;

in _fig. 1_, they appear as simple serrations; but viewed laterally,

they are seen to be formed by a series of denticulated plates (_Lign.

223, fig. 6_). The crown of a tooth of a young animal, worn at the

summit, and presenting but three longitudinal ridges, is represented

_Pl. VI. fig. 4^a_. The microscropical structure consists of a simple

pulp-cavity in the centre of a body of dentine permeated by calcigerous

tubes, but with this peculiar modification, that the dentine is

traversed by vascular canals, radiating at definite intervals from

the pulp-cavity nearly to the periphery of the tooth, and running

parallel with the calcigerous tubes; thus constituting a softer and

coarser dentine than in the other reptiles, and resembling that which

characterizes the teeth of some of the herbivorous mammals.[643] The

crown of the tooth is covered with a layer of enamel, which is thickest

on the external surface: and the fang is invested with cement. The

structure here described is shown in _Pl. VI.; fig. 4^b_, a vertical,

and _fig. 4^c_, a transverse section of a tooth, seen by transmitted

light, with a high magnifying power. The calcigerous tubes are 1/25000

an inch in diameter. Sections of the teeth of the Iguanodon are

beautiful objects under the microscope, for the medullary canals are

generally of a deep yellowish brown colour.

[640] Figured and described in the _Phil. Trans._ 1848, p. 188, pl.

xvi. xvii.

[641] Both specimens are fully described in _Petrif._ pp. 242, _et seq._

[642] Plates iv. and xvii. in the "Fossils of Tilgate Forest," contain

representations of upwards of thirty specimens of teeth in various

states of development and detrition.

[643] Tomes on the Microscopic Structure of the Tooth of the Iguanodon,

_Petrif._ pp. 239, 240. See also Owen’s _Odontography_, p. 249, and pl.

lxxi.; and _Cycl. Anat._ Art. Teeth.

[Illustration: Lign. 223. Teeth of Iguanodon. _Wealden._ _Tilgate

Forest._]

Fig. 1.--Outer aspect of an upper tooth (in a reversed position), worn

flat, and with the fang absorbed; fig. 3, inner aspect of the

same tooth.

_a, a._ Flat grinding surface, produced by mastication when all

the thickly enamelled portion of the crown is worn away.

_c._ Cavity produced by the pressure of a new tooth.

2.--Lower tooth of a young animal, slightly worn: inner aspect.

4.--Outer Surface of a lower tooth of an adult; and fig. 5, inner

surface of the same.

_a, a._ The hard cutting edge of the oblique surface worn by

mastication.

_c._ Indentation produced by the pressure of a successional

tooth.

6.--Edge view of the serration on fig. 5; magnified.

The dentine is less vascular, and therefore hardest, on that side of

the crown which has the thicker coat of enamel; hence the tooth wears

away faster on one side than on the other, and an oblique grinding

surface, with a sharp edge of enamel, is maintained until the crown

is worn away. The internal structure of the teeth of the Iguanodon is

thus in perfect accordance with their external configuration, and must

have been admirably adapted, in every stage, for the laceration and

comminution of the tough vegetable substances which, there is every

reason to conclude, constituted the food of this colossal oviparous

quadruped.

Vertebra of the Iguanodon,[644] _Lign. 206_, p. 653; _Lign. 224_.--The

remains of the vertebral column of the Iguanodon, consisting generally

of broken and water-worn dorsal and caudal vertebræ, deprived of their

processes and reduced to the state of the specimens represented _Lign.

206_, _figs._ 6 and 8, are so abundant in some of the Wealden strata,

that a short account of their characters may be useful. A reference to

_Lign. 206_, and its description, will render the following remarks

intelligible to the general reader. The vertebræ of the Iguanodon are

distinguishable from those of other reptiles which occur in the same

strata by the following peculiarities, which the figure of a perfect

specimen of a caudal vertebra (_Lign. 206, fig 3_) will serve to

illustrate. The body, or centrum, is either flat or somewhat depressed

on both articular faces; its sides are nearly flat, or somewhat convex,

vertically (as in _fig 3_), and slightly concave lengthwise, or from

front to back: in some examples, the body is more contracted towards

the inferior surface, as in _fig. 6_; and in the vertebræ, near the

middle of the tail, the sides are compressed, so as to give an angular

contour and somewhat vertical elongation to the face, as in _fig. 4_;

but in the dorsal vertebræ, the articular faces are nearly circular,

but somewhat higher than wide. In the caudal vertebræ, the inferior

angles of the body are truncated (_w, figs. 3, 4_), and present an

oblique, smooth face, to articulate with the chevron bone (_fig. 3,

f_). The annular part is united to the body by suture (_fig. 3,

o_), and anchylosed in the dorsal vertebræ; and in these bones the

neural arch is very high, and greatly expanded, and its bases extend

transversely inwards, and join each other below the spinal canal,

forming a ring, or bony channel, to contain the spinal chord.[645]

"The transverse processes are straight, and very long in the vertebræ

from the middle of the trunk, indicating a considerable expanse of the

abdominal cavity, adapted for the lodgment of the capacious viscera

of a herbivorous quadruped." (_Owen._) The spinous processes (_Lign.

206, fig. 3, d_) are large and of great height in the anterior

caudal vertebræ, _Lign. 224_; and here the chevrons, or hæmapophyses

(_Lign. 224, b_, and _Lign. 206_, _fig. 2_, and _fig. 3, f_), are

also of considerable length; the bases of the latter are always united

(_Lign. 206, fig. 2, g_), and often blended, so as to form but one

face for articulation with the truncated inferior angles of the body of

the vertebra:, leaving a vertically elongated channel for the passage

of the large blood-vessels of the tail. The external surface of the

vertebræ of the Iguanodon is more or less marked with fine longitudinal

striæ; those of the Megalosaurus have a smoother and more polished

surface.[646]

[644] A detailed account of the elements of the spinal column of the

Iguanodon, and remarks on various fossil vertebræ, the relations of

which with the Iguanodon have been considered doubtful, will be found

in _Petrif._ pp. 256-279.

[645] See also lithographs of dorsal and caudal vertebræ from the

Kentish Rag; Owen’s _Monog. Cret. Rept._ (Pal. Soc.) 1851.

[646] See Rep. Brit Assoc. 1841, pp. 125-133, where an elaborate

investigation of the vertebra: of the Iguanodon is given by Professor

Owen.

[Illustration: Lign. 224. Six Caudal Vertebra of the Iguanodon. 1/14

_nat. size_.

_Wealden._ _Tilgate Forest._

_a, a._ Spinous processes (_neurapophyses_), from 13 to 15-1/2 inches

in height.

_b, b._ Three displaced chevron bones (_hæmapophyses_), imbedded

in the stone near their original position at the junction

of the bodies of the vertebræ.

_c._ Anterior articular face of a vertebra.

]

Bones of the Extremities. _Ligns._ 225 and 226.--The thigh-bone

(_femur_), both bones of the leg (_tibia_ and _fibula_), and many of

the metatarsal and phalangeal bones have been discovered; the osteology

of the hinder extremity is, therefore, almost perfect. The thigh-bone

(_Lign. 225_; and _Petrif._ p. 292,) is of a very remarkable character,

having a closer resemblance to the femur of a huge mammalian, than to

that of a reptile.[647] Several perfect specimens have been discovered,

as well as the associated bones of the leg (_Petrif._ p. 293, _Lign._

62); but the first fragment that came under my notice, was the

middle portion of the shaft of a femur of enormous size, and of an

irregular quadrangular form; and so shapeless and unintelligible it

then appeared, that several years elapsed before its real nature was

determined. (_Foss. Tilg. For._ pl. xviii.)

[647] See Cuvier’s _Ossem. Foss._ vol. ii. p. 36.

An entire thigh-bone of an adult Iguanodon, from the Weald clay in the

west of Sussex, measured three feet eight inches in length.[648] end

thirty-five inches in circumference at the condyles; and I have a femur

of a very young animal, that is but five inches long. The form of the

thigh-bone is so peculiar, that fragments may easily be recognised. The

head of the femur (_Lign. 225, f_,) is hemispherical, and projects

inwards; there is no appearance of a _ligamentum teres_; a flattened

process or trochanter (_Lign. 225, a_,) forms the external boundary

of the neck of the bone, from which it is separated by a deep and

narrow vertical fissure; the shaft is of a sub-quadrangular shape, and

a slightly elevated ridge, produced by the union of two broad, flat,

longitudinal surfaces, extends down the middle of the anterior face,

and, diverging towards the inner condyle, gradually disappears. The

bone terminates below in two large condyles, separated in front and

behind by a deep, narrow cleft, or groove (_Lign. 225, e_). Near the

middle of the inner edge of the shaft, there is a compressed ridge,

with an angular projection, or trochanter. Thus the upper part of

the femur maybe known by the presence of the flattened, or laterally

compressed trochanter; and if that process be wanting, a fractured

surface indicating its position may be detected; the middle of the

shaft is characterized by its broad angular faces, and the inner

submedian trochanter: the condyloid or inferior extremity of the bone

may be distinguished by the deep groove between the condyles, both in

front and behind.

[648] The average length of the adult femur is estimated at about four

feet five inches.

[Illustration: Lign. 225. Left Femur of the Iguanodon. 1/10 _nat. size_.

Anterior aspect.

_Wealden._ _Brook Bay, Isle of Wight._

_a._ Outer trochanter.

_b._ Median trochanter.

_c._ Inner condyle.

_d._ Outer condyle.

_e._ Anterior infra-condyloid fissure.

_f._ Head of the femur.

]

The arm-bone (_humerus_) of the Iguanodon has been discovered in the

Wealden of the Isle of Wight by Mr. Fowlstone; it is figured and

described in _Petrif._ p. 286. The humerus is also present in the

Maidstone specimen[649] of Iguanodon, before referred to at page 692:

in pl. ii. of _Wond._ this bone is termed the _radius_. The humerus of

this reptile is much smaller than the femur; in the Maidstone specimen

the former is about 20 inches, and the latter about 33 inches in length.

[649] The two bones marked "6" in pl. ii. _Wond._ and in _Lign._ 65,

_Petrif._ (one of which is figured in outline in _Lign. 226, fig.

4_,) regarded by Prof. Owen as the _radius_ and _ulna_ (the two bones

of the fore-arm): the author’s reasons for regarding these bones as

_metacarpals_ are given in full at p. 289, _Petrif._

As separate bones of the feet of the Iguanodon, for example,

_metacarpals_, _metatarsals_, _phalangeals_, and _unguals_, often

occur in the strata of the Wealden, figures of several specimens, on

a reduced scale, are introduced in _Lign. 226_, and may enable the

student to identify those he may meet with in his researches.[650] The

ungual phalanges, or claw-bones, which were invested with the nail, are

sometimes found of an enormous size; from a quarry near Horsham, Mr.

Holmes obtained specimens more than five inches long, and three inches

wide at the articular extremity.

[650] See Rep. Brit. Assoc. 1841, pp. 137-142.

Length of the Iguanodon.--The length of the united head and trunk,

according to my estimate in _Geol. S. E._ p. 316, is seventeen feet

and a half; by Professor Owen’s estimate it is reduced to fifteen

feet;[651] a difference of no importance in such merely approximative

calculations, particularly when the form of the cranium is unknown.[652]

[651] Ibid. p. 144.

[652] The more recently discovered specimen of lower-jaw, already

referred to, page 693, indicates a length of between three and four

feet for the entire jaw, _Petrif._ p. 249.

[Illustration: Lign. 226. Bones of the Feet and Claws of the Iguanodon.

_Wealden._ _Tilgate Forest._

(See _Wond._ pl. in.)

Fig. 1.--Metatarsal: original 6 inches long: upper surface.

2.--Metacarpal bone.

3.--Under surface of fig. 1.

4.--A phalangeal bone of the fore-foot: the original 14 inches long.

4_a_.--A transverse section of the same, showing the medullary

cavity.

5.--One of the second row of phalangeal bones of the fore-foot.

6.--View from above of one of the claw-bones of the hind-foot;

1/6 _nat._

7.--Profile of claw-bone of fore-foot:[653] 1/6 _nat._

8.--Metatarsal, or bone of the hind-foot: 1/8 _nat._

_a._ Denotes the proximal articulation, or that nearest the

trunk.

_b._ The distal, or extremity most distant from the trunk.

]

[653] This bone is conjecturally referred by Prof. Owen to the

Megalosaurus.

The estimated extent of the tail has been subject to variation. My

early estimate of its length gave rise to the idea of this reptile

having attained seventy feet in length. Professor Owen, however,

considered that the abbreviated character of the anterior caudal

vertebræ indicated a far less extent of tail, which the Professor

estimated at thirteen feet; this opinion, from the evidence then before

us, seemed well founded, but from evidence since afforded by a series

of eleven caudal vertebra, belonging to the middle region of the tail,

that have been lately discovered, (_Petrif._ p. 312,) it is not at all

improbable, that, instead of all the caudal vertebræ being abbreviated,

these elements of the tail were elongated as in the corresponding part

of the skeleton of the Iguana, and that the largest Iguanodons may have

attained a length of from sixty to seventy feet.

The author’s physiological inferences as to the structure and economy

of the Iguanodon, deduced from the study of the osseous remains of this

singular creature, especially the lately discovered remains of the

jaw-bones, are given in full at pp. 307-313 _Petrif._ or _Foss. Brit.

Mus._: and at pp. 335-338, _ibid._ may be found some general remarks

on the physical geography and the nature of the fauna and flora of the

country inhabited by these stupendous reptiles, whose remains are so

characteristic of the Wealden rocks.

Jaw of the Regnosaurus. (_Petrif._ p. 333.)--A portion of the right

ramus, or side, of the lower jaw of this reptile was discovered

in a block of sandstone from Tilgate Forest. It consists of a

fragment, six inches long, of the dentary bones, with a small

portion of the opercular; and it contains the fangs of fifteen

teeth, which are closely and evenly set in a regular series, and

imbedded laterally in grooves, or sockets, in the dentary bone;

there are three or four sockets of successional teeth on the inner

side of the bases of the old teeth. (_Phil. Trans._ 1841, pl.

v. figs. 1, 2.) Unfortunately, all the crowns of the teeth are

wanting. The outer parapet of the dentary piece is entire, and its

upper margin is finely crenated. All the fangs of the teeth are

exposed, but there are traces of a thin inner wall, indicating the

probability that, as in the Megalosaurus, the teeth were supported

medially by an osseous plate, and were implanted in distinct

sockets.[654] In my memoir on this fossil jaw in the _Phil.

Trans._ (1841, p. 131), I referred it to the genus Iguanodon;

but subsequent observations have led me to conclude that it is

generically distinct; and in my Memoir on the Jaw of the Iguanodon,

in _Phil. Trans._ 1848 (p. 183), I have proposed for the animal to

which it belonged the distinct generic appellation, Regnosaurus,

with the specific name _Northamptoni_.

[654] The collector will perceive the importance that attaches to

the discovery of even a fragment of the jaw of an unknown reptile,

containing teeth in their natural position.

[Sidenote: LACERTIAN REPTILES.]

IV. Lacertian Reptiles.--The recent Lacertians, or true Lizards, are

smaller and less highly organized reptiles than the Saurians of the

Crocodilian order; and their dermal covering consists of a finer and

more delicate squamous integument. They are also characterized by

important modification in their osteological structure. The spinal

column is almost always composed of concavo-convex vertebræ, with the

convexity behind; the ribs are slender and rounded, having a single

convex tubercle of attachment. The fossil species are, for the most

part, of gigantic dimensions, and deviate in a striking manner from any

that now exist. Vertebræ of the recent lacertian type are very rare in

the secondary strata; I believe a few in my cabinet, obtained from the

sandstone of Tilgate Forest, and which belonged to a very small unknown

reptile, are the most ancient examples at present known.

[Illustration: Lign. 227. Mosasaurus Hoffmanni.

(_The original is feet by 2-1/2 feet._)

Remains of the jaws of the great fossil reptile of Maestricht.]

Mosasaurus. _Bd._ pl. xx.; _Wond._ p. 311; _Petrif._ p. 193.--Of the

fossil lizard of Maestricht, named _Mosasaurus_ (lizard of the Meuse)

from the river adjacent to the quarries of St. Peter’s Mountain,

in which its remains have been discovered, I have given a detailed

account at pages 193-196 of _Petrif._ A specimen, with the jaws, and

bones of the palate armed with teeth, now in the museum at Paris, has

long been celebrated, and is still the most precious relic of this

extinct reptile hitherto discovered; a reduced representation is given

in _Lign. 227_; and _Pict. Atlas_, pl. lxx. This is the _Mosasaurus

Hoffmanni_.[655] The specimen is four and a half feet long, and two

and a half feet wide; it consists of both sides of the lower jaw, with

the right ramus of the upper jaw in its natural position, and the

left, which is displaced, lying across the articular extremity of the

left branch of the lower jaw: of the pterygoid bones, which are armed

with teeth; of the left tympanic bone (_os quadratum_), which is but

little removed from its natural situation, and connects the lower jaw

with the cranium; one of the metacarpal or metatarsal bones, and some

fragments.[656]

[655] Several fine portions of the jaws, and many vertebræ of this

animal, are in the British Museum: see _Foss. Brit. Mus._ p. 139. In a

splendid work, _Histoire Naturelle de la Montagne de St. Pierre_, by

the late Faujas St. Fond (1 vol. folio, with numerous plates), there

are admirable figures of the remains of the Mosasaurus.

[656] In the British Museum there is a cast of this specimen, in a case

near the bones of the Iguanodon.

[Illustration: Lign. 228. Mosasauroid Teeth.[657] 1/2 _nat. size_.]

Figs. 1_a_, 2_a_. Transverse sections of the

crowns of the teeth, figs. 1 and 2 respectively.

[657] Reduced from figures accompanying Dr. Gibbes’s Memoir "On

the Mosasaurus and three allied new genera," (with plates,) in the

_Smithsonian Contributions_, vol. ii. 1849. This interesting paper

comprises much information regarding the Mosasaurians of the Cretaceous

deposits of N. America; but we cannot fully coincide with the author in

his palæontological determinations.

The teeth are large, and supported on expanded conical osseous

eminences, which are anchylosed to the alveolar ridge of the jaw

(_acrodont_). The crown of the tooth is conical and recurved, with

the outer face nearly flat, and this space is bordered on each side

by a longitudinal ridge; giving the tooth somewhat of a pyramidal

figure. (See _Ligns._ 228-230.) Professor Owen states that the crown

consists of a body of simple and firm dentine, with fine and close-set

calcigerous tubes, enclosing a simple pulp-cavity; irregular processes

of the latter extend as medullary canals into the conical base of the

tooth, but not, as in the Iguanodon, into the substance of the coronal

dentine; the dentine is invested with a moderately thick coat of

enamel.[658]

[658] See Odontography, p. 258, and pl. lxxii.; the student should also

consult Cyclop. Anat. Phys. _Art._ Teeth.

The vertebræ of the Mosasaur, as is usual in the existing lizards and

crocodiles, are concave in front and convex behind, and the neural

arch is united to the centrum by suture. The entire vertebral column

of _M. Hoffmanni_ appears to have consisted of 131 vertebræ, of which

97 belonged to the tail.[659] This Mosasaur was about twenty-five feet

long.

[659] See Cuvier, _Oss. Foss._ vol. v. pp. 326-334.

[Illustration: Lign. 229. Tooth of Mosasaurus: _magn. twice._

Either a pterygoid tooth of M. Hoffmanni, or a jaw-tooth of M. gracilis.

_Chalk._ _Gravesend._

(In Mr. Wetherell’s Collection.)]

This extinct lacertian reptile forms an intermediate link between

the Saurians without pterygoid teeth (Monitors) and those with them

(Iguanas). Its crocodilian affinities are but partial.

The Mosasaurus appears to have had webbed feet, adapted or crawling on

land as well as for swimming,[660] and a long and vertically expanded

tail, serving as a powerful oar, and enabling the animal to stem the

roughest waters.

[660] See Prof. Owen’s observations on the bones that have been

regarded as referable to the extremities of this creature, and

especially on the phalangeal and other bones of the Mosasaur of the New

Jersey greensand; _Monog. Cret. Rept._ 1851, pp. 36-40.

Prof. Goldfuss has described the remains of another and smaller species

of Mosasaurus (_M. Maximiliani_), from Upper Missouri, U.S.; and Prof.

Owen, in Dixon's "Fossils of Sussex," has established a third and still

smaller species (_M. gracilis_),[661] to which he refers the four or

five mosasaurian vertebræ found in the Chalk of Sussex. Two of these

(caudal) are figured in _Geol. S. E._ p. 146, and _Petrif._ _Lign._ 44;

and these and others are lithographed in plate viii. of Prof. Owen’s

_Monog. Cret. Reptilia_, 1851.

[661] See also _Monograph on the Reptiles of the Chalk_, 1851, p. 31,

and plate ix.

The remains of Mosasaurus occur also in the cretaceous sands of New

Jersey, U. S. (See Dr. Morton’s _Synopsis of the Organic Remains of the

United States_, 1834; and the Quart. Journ. of the Geological Society,

vol. v. 1849.)

Leiodon anceps.[662]--Under this name Professor Owen has described

a splendid fossil, consisting of a portion of the lower jaw of an

acrodont reptile, with teeth, obtained by Edward Charlesworth, Esq.

from the Chalk north of the Thames. This specimen was submitted to my

inspection, many years since, by Mr. Charlesworth, and I then pointed

out the analogy of this acrodont jaw to that of the Mosasaurus.

[662] Ibid. p. 42, pl. ix. A.

Prof. Owen in 1840 (_Odontog._ p. 261), and in 1841 (_Rep. Brit.

Assoc._ p. 144), described and figured some teeth from the same

specimen, which were lent by Mr. Charlesworth. These teeth the

Hunterian Professor regarded as characteristic of a new genus of

Mosasauroid reptile, to which he gave the name _Leiodon_ (in allusion

to the smoothness of the teeth). In 1845 (_Rep. Brit. Assoc._ p. 60)

Mr. Charlesworth noticed, and in 1846 (_London Geol. Journal_, p.

23, plates iv. and vi.) figured and described, the above mentioned

portion of jaw with teeth, under the name _Mosasaurus stenodon_; and

in 1851 Prof. Owen figured and described this specimen under the name

of _Leiodon anceps_, which was originally proposed for the animal, as

known from its teeth, in 1840.

The portion of bone on which the teeth, five in number are implanted

is seven inches in length, and is, in Professor Owen s opinion, the

dentary piece of the lower jaw, and not a portion of a pterygoid bone.

Mr. Charlesworth has had a section made of four of the teeth, and finds

that the pulp-cavities are more or less occupied with solid cones of

silex, which must have permeated the osseous parietes of the teeth.

[Illustration: Lign. 230. Mosasauroid Tooth.

Resembling the back-teeth in the lower jaw of Mosasaurus Hoffmanni.

_Chalk._ _Gravesend._

(In the Collection of Mr. Wetherell.)]

The teeth of Leiodon have a simple pulp-cavity, surrounded by fine

dentine, with an external layer of smooth enamel. The apex of the crown

is sharp-pointed; the body of the crown is slightly recurved; its base

is expanded into a thick circular fang, which is anchylosed to a short

conical process of the alveolar border of the jaw: the teeth differ

from those of the Mosasaurus in having the outer side as convex as the

inner side, the transverse section being an ellipse with pointed ends,

which latter correspond with the lateral trenchant edges of the crown

of the tooth: the teeth are more closely set than in the Mosasaur and

Geosaur. (_Owen._)

Geosaurus Sœmmeringii. _Petrif._ p. 175.--In the British Museum are the

remains of a reptile from the "white Jura" (upper oolite) of Monheim,

in Franconia, which Cuvier describes as being more nearly related to

the Lizards than Crocodiles. The length of this reptile is estimated

at about ten feet. The eyes had a circle of osseous plates in the

_sclerotica_, like those of the Ichthyosaurus; the teeth resemble those

of the Mosasaurus in being sub-compressed and recurved, but they are

at once distinguished by their anterior and posterior finely serrated

sharp edges; the crown is invested with an external coat of enamel.[663]

[663] Oss. Foss. tom. v. p. 343.

Raphiosaurus subulidens.--A portion of a lower jaw, containing

twenty-two closely set, subulate teeth, anchylosed by their bases to

a shallow alveolar groove and an outer alveolar parapet of bone, as

in the Iguana, thus corresponding with the pleurodont Lizards, is

described under this name by Professor Owen, (_Geol. Trans._ 2d ser.

vol. vi. pl. xxxix.); and _Monog. Cret. Rept._ (Pal. Soc.) 1851, p.

19, pl. x. figs. 5, 6. It is from the Lower Chalk, near Cambridge, and

is in the collection of James Carter, Esq. of that place. Remains of

Raphiosaurus have been found also in the Chalk at Northfleet, Kent.

Dolichosaurus longicollis.--In the Chalk of Kent was found, some years

since, a considerable portion of the skeleton of a lacertian reptile,

consisting of the posterior half of the spinal column, with remains of

the pelvic and thigh bones; it was figured in the _Geol. Trans._ 2d

ser. vol. vi. pl. xxxix.; and is now in the collection of Sir P. G.

Egerton. From the researches of the late Mr. Dixon, it appears that a

mutilated reptilian head and anterior portion of a spinal column, with

fore-arm and scapular bones, now in the collection of Mr. Smith, of

Tunbridge Wells, belong to the same skeleton as the vertebral remains

above mentioned. Both specimens were obtained at the same time from

the well-known chalk-pit at Burham, Kent. Professor Owen has lately

described these interesting remains in detail (_Monog. Cret. Rept._

1851, pp. 22, &c.), and finds no intrinsic contradiction to exist

to the historical evidence adduced as to the probability of the two

moieties having belonged to the same individual. In the two specimens

there exist sixty-three concavo-convex (_procœlian_) vertebræ, of which

fifty-seven form the series between the skull and the pelvis, giving

the trunk a length of about eighteen inches. This unique reptile was

elongate and snake-like in its form, with the abdomen deep and narrow,

like that of the water-snakes: its limbs were short; its tail, from

the character of the few caudal vertebræ remaining, must have been

relatively long and powerful. This long and slender lacertian was

therefore probably to a considerable degree aquatic in its habits,

swimming with an undulatory eel-like movement.

The Dolichosaurus (_long-lizard_) presents somewhat of the ophidian

character in the number and size of its cervical vertebræ, in the size

and shape of its ribs, and in the slender proportions of its trunk and

head; but, with these partial exceptions, its affinities are truly

lacertian. (Owen.)

Rhynchosaurus articeps. _Lign. 231._--In a quarry of Upper New Red

Sandstone at Grinsell, near Shrewsbury, Dr. O. Ward discovered a skull

(3-1/2 inches long), vertebræ, ribs, bones of the pectoral and pelvic

arches, portions of two femora with medullary cavities, and fragments

of other bones of a very remarkable lacertian reptile (_Lign. 231_).

The lower jaw is preserved with the skull in its natural position. The

cranium in its general aspect resembles that of a turtle, rather than

of a lizard; for the intermaxillary bones are double, as in Chelonians,

and symmetrical, and are not united by a median process; they are

very long, and curve downwards, giving the fore part of the skull the

profile of a parrot. See _Lign. 231_.

[Illustration: Lign. 231. Rhynchosaurus articeps. _New Red Sandstone;

near Shrewsbury_

Fig. 1.--Lateral view of the cranium and lower jaw: 1/2 _nat size_.

Cranium.

_a, a._ Intermaxillary bones.

_b._ Nasal.

_c._ Frontal.

_d._ Maxillary.

_e._ Anterior frontal.

_f._ Lachrymal.

_g._ Malar.

_h._ Posterior frontal.

_i._ Orbital division of posterior frontal.

_k._ Temporal.

_l._ Tympanic.

Lower Jaw.

_m._ Dentary.

_n._ Coronoid.

_o._ Articular.

_p._ Angular.

_q._ Opercular or splenial.

_r._ The orbit.

Fig. 2.--The upper aspect of a dorsal vertebra: _nat. size_.]