xv. 14 



CROCODILES 



419 



set of muscles, and the ear-drums are protected by scaly movable 

 flaps. The Eustachian tubes are very complicated, and parts of the 

 skull are pneumatized by extensions from the middle ear cavity, as in 

 birds. 



Fig. 242. Diagram of the skull of Crocodilia. 

 Lettering as Fig. 214, p. 377. (From Goodrich.) 



Fig. 243. Anterior cervical vertebrae of Crocodilus. 



c. capitulum; lip. hypocentrum; wa 1-4 , neural arches; pa. pro-atlas; pi. 1-4, pleurocentra; 

 prz. prezygapophysis; ptz. postzygapophysis; r. rib; t. tuberculum; tp. transverse process. 

 The first neural arch and the pro-atlas of the left side have been removed to show the first 

 pleuro-centrum (pi 1 ) which is the odontoid process. (From Goodrich.) 



The crocodiles use all four limbs in walking, but the front are 

 shorter than the hind, indicating bipedal ancestry. The pelvis of the 

 crocodiles shows signs of the typical triradiate structure, but there 

 are only two sacral vertebrae. Rapid swimming is produced by lateral 

 movements of the tail, but when moving slowly the partly webbed 

 feet are used to push the animal along. The ribs (Fig. 243) are two- 

 headed and there is a proatlas element between the skull and atlas. 

 The scutes of the back and, in some forms, of the belly, are rein- 

 forced by osteoderms, and there are well-developed abdominal 

 ribs. 



