222 



11 YDEOSAURIA. 



tory animals. The flat head is 

 prolonged into a long snout; the 

 long jaws are armed with sharp 

 conical prehensile teeth, which are 

 wedged into deep alveoli ; the crowns 

 of the teeth are sometimes smooth, 

 sometimes striated or superficially 

 folded, and are gradually replaced 

 by succeeding supplementary teeth. 

 Ribs are present in great numbers, 

 not only in the very long thoracic 

 region, but also in the cervical and 

 abdominal regions. 



In the Crocodiles there is, in the 

 abdominal region, a narrow sternum 

 abdominale, which is prolonged to 

 the pelvic girdle, and bears on its 

 sides, a number of abdominal ribs* 

 the upper ends of which do not 

 reach the vertebral column (fig. 645). 

 The internal organisation probably 

 presented different grades of per- 

 fection in the various groups, of 

 which only the highest viz., that 

 found in living Crocodiles can be 

 known to us. 



Order 1. ENALIOSAURIA. 



Hydrosauria with naked leathery 

 skin, biconcave vertebrae and swim- 

 ming fins (confined to the secondary 

 period}. 



The remains of these gigantic in- 

 habitants of the sea, which lived 

 through the secondary period from 

 its beginning to its end, show that 

 they were the most powerful marine 

 animals of that time. They were 

 of extreme length, and possessed a 

 usually elongated, flat snout with 



