[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.
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.
MEGALOSAURUS.
Lign. 219.
Tooth of the Megalosaurus Bucklandi.
(Nat. size.)
Wealden. Tilgate Forest.
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]