CROCOMLIA. 303 



and displacement are carried on uninterruptedly throughout 

 the long life of these cold-blooded carnivorous reptiles. 



From the period of exclusion from the egg, the teeth of 

 the crocodile succeed each other in the vertical direction ; none 

 are added from behind forwards like the true molars in Mam- 

 malia. It follows, therefore, that the number of the teeth of 

 the crocodile is as great when it first sees the light as when it 

 has acquired its full size ; and, owing to the rapidity of their 

 succession, the cavity at the base of the fully-formed tooth is 

 never consolidated. 



In most of the extinct species of Crocodilians the teeth are 

 characterized by more numerous and strongly developed longi- 

 tudinal ridges upon the enamelled crown, than in the recent 

 species ; and they are commonly longer, more slender, and 

 sharp-pointed. But in one of the crocodiles with sub-biconcave 

 vertebrae (Goniopholis crassidens), from the Wealden formation 

 and Purbeck limestone, the teeth have crowns which are as 

 round and as thick in proportion to their length as in the 

 recent crocodiles or alligators. 



The more ancient crocodiles, from the Oolite and Lias, 

 called Steneosauri and Teleosauri, had jaws like those of the 

 modern gavials, but sometimes longer and more attenuated, and 

 armed with more numerous, equal, and slender teeth, adapted 

 for the capture of fishes, which appear to have been the only 

 other vertebrate animals existing at those periods in numbers 

 sufficient to yield subsistence to carnivorous marine Saurians. 



In all the Teleosauri the teeth are more slender, less com- 

 pressed, and sharper pointed than in the gavial ; they are 

 slightly recurved, and the enamelled crown is traversed by 

 more numerous and better defined ridges — tw T o of which, on 

 opposite sides of the crown, are larger and more elevated than 

 the rest. The fang is smooth and cylindrical. The teeth of 

 the Steneosauri, or extinct crocodiles with long and slender 

 jaws but with subterminal nostrils, differ from those of the 



