CROCODILIA. 301 



slightly hollow behind, on which is founded the genus 

 Cetiosaurus.* The smaller opisthocoelian vertebrae described 

 by Cuvier have been referred by Von Meyer to a genus called 

 Streptosjmidylus. 



In one species from the Wealden, dorsal vertebrae measuring 

 8 inches across are only 4 inches in length, and caudal verte- 

 brae nearly 7 inches across are less than four inches in length. 

 These characterize the species called Cetiosaurus brevis. t 



Caudal vertebrae measuring 7 inches across and 5| inches 

 in length, from the lower oolite at Chipping Norton, and the 

 great oolite at Enstone, represent the species called Cetiosaurus 

 medius. 



Caudal vertebrae from the Portland stone at Garsington, 

 Oxfordshire, measuring 7 inches 9 lines across and 7 inches in 

 length, are referred to the Cetiosaurus longus. The latter must 

 have been the most gigantic and whale-like of Crocodilians. 



Dentition of Crocodiles. — The teeth of both the existing 

 and extinct crocodilian reptiles consist of a body of compact 

 dentine, forming a crown covered by a coat of enamel, and a 

 root invested by a moderately thick layer of cement. The 

 root slightly enlarges or maintains the same breadth to its 

 base (fig. 105, a), which is deeply excavated by a conical pulp- 

 cavity extending into the crown, and is commonly either per- 

 forated or notched at its concave or inner side. 



The tooth-germ c (figs. 104 and 105) is developed from 

 the membrane covering the angle between the floor and the 

 inner wall of the socket. The matrix of the young growing 

 tooth affects, by its pressure, the inner wall of the socket, 

 and forms for itself a shallow recess ; at the same time it 

 attacks the side of the base of the contained tooth ; then, gain- 

 ing a more extensive attachment by its basis and increased 



* " Keport on British Fossil Eeptiles," Trans. Brit. Assoc, for 1841, p. 96. 



f They have since been referred to the dinosaurian order under the name of 

 Pelorosaurus, but without any evidence of the true sacral characters of that 

 order ; the cavities of long bones are common to Crocodilians and Dinosaurs. 



