cisely similar, in the principles of their construction, to the teeth of the modern Iguana, as to leave no doubt of the near connexion of this most gigantic extinct reptile with the Iguanas of our own time. When we consider that the largest living Iguana rarely exceeds five feet in length, whilst the congenerous fossil animal must have been nearly twelve times as long, we cannot but be impressed by the discovery of a resemblance, amounting almost to identity, between such characteristic organs as the teeth, in one of the most enormous among the extinct reptiles of the fossil world, and those of a genus whose largest species is comparatively so diminutive. According to Cuvier, the common Iguana inhabits all the warm regions of America: it lives chiefly upon trees, eating fruits, and seeds, and leaves. The female occasionally visits the water, for the purpose of laying in the sand its eggs, which are about the size of those of a pigeon.*

As the modern Iguana is found only in the warmest regions of the present earth, we may reasonably infer that a

did not cease with the completion of the Wealden series. The individual from which this skeleton was derived had probably been drifted to sea, as those which afforded the bones found in the fresh-water deposites subjacent to this marine formation, had been drifted into an estuary. This unique skeleton is now in the museum of Mr. Mantell, and confirms nearly all his conjectures respecting the many insulated bones which he had referred to the Iguanodon.

* In the Appendix to a paper in the Geol. Trans. Lond. (N. S. Vol. III. Pt. 3) on the fossil bones of the Iguanodon, found in the Isle of Wight and Isle of Purbeck, I have mentioned the following facts, illustrative of the herbivorous habits of the living Iguana.

In the spring of 1829, “Mr. W. J. Broderip saw a living Iguana, about two feet long, in a hot-house at Mr. Miller's nursery gardens, near Bristol. It had refused to eat insects, and other kinds of animal food, until happen. ing to be near some kidney-bean plants that were in the house for forcing, it began to eat of their leaves, and was from that time forth supplied from these plants." In 1828, Captain Belcher found, in the island of Isabella, swarms of Iguanas, that appeared omnivorous; they fed voraciously on the eggs of birds, and the intestines of fowls and insects.

similar, if not a still warmer climate, prevailed at the time when so huge a Lizard as the Iguanodon inhabited what are now the temperate regions of the southern coasts of England. We know from the fragment of a femur, in the collection of Mr. Mantell, that the thigh-bone of this reptile much exceeded in bulk that of the largest Elephant: this fragment presents a circumference of twenty-two inches in its smallest part, and the entire length must have been between fourand five feet. Comparing the proportions of this monstrous bone with those of the fossil teeth with which it is associated, it appears that they bear to one another nearly the same ratio that the femur of the Iguana bears to the similarly constructed and peculiar teeth of that animal.*

It has been stated, in the preceding section, that the large medullary cavities in the femur of the Iguanodon, and the form of the bones of the feet, show that this animal, like the Megalosaurus, was constructed to move on land.

A farther analogy between the extinct fossil and the recent Iguana is offered by the presence in both of a horn of

* From a careful comparison of the bones of the Iguanodon with those of the Iguana, made by taking an average from the proportions of different bones from eight separate parts of the respective skeletons, Mr. Mantell has arrived at these dimensions as being the proportionate measures of the following parts of this extraordinary reptile:

Mr. Mantell calculates the femur of the Iguanodon to be twenty times the size of that of a modern Iguana; but as animals do not increase in length in the same ratio as in bulk, it does not follow that the Iguanodon attained the enormous length of one hundred feet, although it approached perhaps nearly to seventy feet.

As the Iguanodon, from its enormous bulk, must have been unable to mount on trees, it could not have applied its tail to the same purpose as the Iguana, to assist in climbing; and the longitudinal diameter of its caudal vertebræ is much less in proportion than in the Iguana, and shows the entire tail to have been comparatively shorter..

bone upon the nose, (Pl. 24, Fig. 14.) The concurrence of peculiarities so remarkable as the union of this nasal horn with a mode of dentition of which there is no example, except in the Iguanas, affords one of the many proofs of the universality of the laws of co-existence, which prevailed no less constantly throughout the extinct genera and species of the fossil world, than they do among the living members of the animal kingdom.

Teeth.

As the teeth are the most characteristic and important parts of the animal, I shall endeavour to extract from them evidence of design, both in their construction and mode of renewal, and also in their adaptation to the office of consuming vegetables, in a manner peculiar to themselves. They are not lodged in distinct sockets, like the teeth of Crocodiles, but fixed, as in Lizards, along the internal face of the dental bone, to which they adhere by one side of the bony substance of their root. (Pl. 24, Fig. 13.)

The teeth of most herbivorous quadrupeds, (exclusively of the defensive tusks,) are divided into two classes of distinct office, viz. incisors and molars; the former destined to collect and sever vegetable substances from the ground, or from the parent plant; the latter to grind and masticate them on their way towards the stomach. The living Iguanas, which are in great part herbivorous, afford a striking exception to this economy: as their teeth are little fitted for grinding, they transmit their food very slightly comminuted into the stomach.

Our giant Iguanodon, also, had teeth resembling those of the Iguana, and of so herbivorous a character, that at first sight they were supposed by Cuvier to be the teeth of a Rhinoceros.

The examination of these teeth will lead us to the dis

covery of remarkable contrivances, adapting them to the function of cropping tough vegetable food, such as the Clathraria, and similar plants, which are found buried with the Iguanodon, might have afforded. We know the form and power of iron pincers to gripe and tear nails from their lodgment in wood: a still more powerful kind of pincers, or nippers, is constructed for the purpose of cutting wire, which yields to them nearly as readily as thread to a pair of scisOur figures (Pl. 24, Figs. 6, 7, 8, 12) show the place of the cutting edges, and form of curviture, and points of enlargement and contraction, in the teeth of the Iguanodon, to be nearly the same as in the corresponding parts of these powerful metallic tools; and the mechanical advantages of such teeth, as instruments for tearing and cutting, must have been similar.*

sors.

The teeth exhibit also two kinds of provisions to maintain sharp edges along the cutting surface, from their first protrusion, until they were worn down to the very stump. The first of these is a sharp and serrated edge, extending on each side downwards, from the point to the broadest portion of the body of the tooth. (See Figs. 1, 2, 6, 8, 12, &c.)

The second provision is one of compensation for the gradual destruction of this serrated edge, by substituting a plate of thin enamel, to maintain a cutting power in the anterior portion of the tooth, until its entire substance was consumed in service.t

* Fig. 2. represents the front of a young tooth; and Figs. 5, 6, 7, 8 the front of four other teeth, thrown slightly into profile. In all of these we recognise a near approach to the form of the nipping pincers, with a sharp cutting edge at the upper margin of the enamel. The enamel is here expressed by wavy lines, which represent its actual structure: it is placed only in front, like the enamel in front of the incisors of Rodentia.

†This perpetual edge resulted from the enamel being placed only on the front of the tooth, like that on the incisors of Rodentia. As the softer material of the tooth itself must have worn away more readily than this enamel, and most readily at the part remotest from it, an oblique section

Whilst the crown of the tooth was thus gradually diminishing above, a simultaneous absorption of the root went on below, caused by the pressure of a new tooth rising to replace the old one, until by this continual consumption at both extremities, the middle portion of the older tooth was reduced to a hollow stump, (Figs, 10, 11,) which fell from the jaw to make room for a more efficient successor.* In this last stage the form of the tooth had entirely changed, and the crown had become flat, like the crown of worn out human incisors, and capable of performing imperfect mastication after the cutting powers had diminished. There is, I believe, no other example of teeth which possess the same mechanical advantages as instruments of cutting and tearing portions of vegetable matter from tough and rigid plants.

of the crown was thus perpetually maintained with a sharp cutting edge in front, like that of the nippers. (See Figs. 7. 8. 12.)

The younger tooth, (Fig. 1,) when first protruded, was lancet-shaped, with a serrated edge, extending on each side downwards, from the point to its broadest portion, as in the living Iguana. (Pl. 24. f. 13, and Fig. 4.) This serrature ceased at the broadest diameter of the tooth, i. e. precisely at the line, below which, had they been continued, they would have had no effect in cutting. (Pl. 24. f. 2. 6. 8. 9. 12.) As these saws were gradually worn away, the cutting power was transferred to the enamel in front, and here we find a provision of another kind to give efficacy and strength. The front was traversed longitudinally by alternate ridges and furrows, (Pl. 24, Figs. 2, 5, 6, 7, 8,) the ridges serving as ribs or buttresses to strengthen and prevent the enamel from scaling off, and forming, together with the furrows, an edge slightly wavy, and disposed in a series of minute gouges, or fluted chisels; hence the tooth became an instrument of greater power to cut tough vegetables under the action of the jaw, than if the enamel had been in a continuous straight line. By these contrivances, also it continued effective during every stage through which it passed, from the serrated lancet-point of the new tooth, (Fig. 1,) to its final consumption. (Figs. 10, 11.)

* In Pl. 24, Fig. 13, the jaw of a recent Iguana exhibits the commencement of this process, and a number of young teeth are seen forcing their way upwards, and causing absorption at the base of the older teeth. Figs. 10, 11, exhibit the effect of similar absorption upon the residuary stump of the fossil tooth of an Iguanodon.