CROCODILIA 



199 



separates the order from the dinosaurs, aside from the peculiar 

 structure of the nasal passages in the skull. On the under side of 

 the body, connected with the front end of the pubes, there are seven 

 or eight pairs of abdominal ribs, corresponding to the plastron of 

 the turtles and similar to those of the ichthyosaurs and plesiosaurs. 

 The mosasaurs have no such ribs. 



Fig. 102 Fig. 103 



Fig. 102. — Scapula (sc) and coracoid (cor) of gavial. 



Fig. 103. — Front foot of crocodile: u, ulna; r, radius; re, radiale; ue, ulnare; 

 p, pisiform. 



Furthermore, the crocodiles differ from all other living reptiles 

 in having a four-chambered heart, like that of birds and mammals, 

 that is, a heart with two auricles and two ventricles. This more 

 perfect structure of the circulatory organs does not, however, 

 insure at all times a complete separation of the pure or arterial 

 blood from the impure or venous blood, since the blood may be 

 more or less intermixed outside of the heart by a connection between 

 the venous and the arterial systems. Whether these imperfectly 



