418 REPTILES xv. 13- 



phytosaurs were derived from pseudosuchians and the two groups are 

 often placed together in an order Thecodontia. 



Compsognnthus 



Fig. 241. The skeletons of various archosaurian diapsids. 

 (Modified after various authors.) 



14. Order Crocodilia 



In the crocodiles the nostrils are at the tip of the snout and the air 

 is carried back in a long tube, the maxillae, palatines, and pterygoids 

 forming a bony secondary palate, as in mammals. There is a flap on 

 the hind end of the tongue, which, with a fold of the palate, enables 

 the mouth to be closed off from the respiratory passage and hence 

 kept open under water. The nostrils can also be closed by a special 



