| 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. | |
| 4a.— | 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.
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.