ROOM III. 



LOWER JAW OF MEGALOSAURUS. 



329 



The specimen of the lower jaw from which the cast in Wall- 

 case A was taken, consists of a portion of the dentary bone, 

 1 1 inches long, and 3| inches vertically ; it contains one perfect 

 tooth, 3 inches high and 1 inch wide, and the germs of 

 several others. The tooth has a conical, laterally com- 

 pressed crown, resembling a sabre with the point curved back- 

 wards; the edges are trenchant and finely serrated. It is 

 composed of a central body of dentine, the 

 crown having a coating of 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, ^.Woth 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 nume- 

 rous secondary branches ; these ultimately 

 dilate into, or inosculate with, a stratum of 

 calcigerous cells that separates the dentine 

 from the enamel. 1 



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 outward parapet, as in the 

 true lizards, but the teeth are fixed in distinct sockets, formed 

 by transverse partitions, that are attached to a mesial, or 

 inner parapet, composed of a series of triangular ossaous 

 plates ; the bases of the old teeth, and the germs of the new 

 ones, being thus enclosed and concealed. 



The form of the lower jaw is but imperfectly revealed in 

 this unique specimen ; it seems to have been very much com- 

 pressed laterally, so that the original animal must have had 

 a very narrow and acute muzzle, strikingly contrasting with 

 that of its colossal herbivorous contemporary. 



The Sacrum of the Megalosaurus is composed of five (six ?) 

 anchylosed vertebra ; and of this part of the skeleton four 



LIGN. 71. 



1 "Odontography," p. 271. See also "Medals of Creation," PI. VI. 

 . 7. 



