248 VERTEBRATE ANIMALS. 



one another. The mixture of arterial and venous blood, how- 

 ever, which is so characteristic of Reptiles, is provided for by 

 a communication between the great vessels which spring from 

 the two ventricles in the immediate neighborhood of the heart. 

 The eyes are protected by movable eyelids, and the ear by a 

 movable earlid. The tongue is large and fleshy, and is im- 

 movably attached to the bottom of the mouth (hence the be- 

 lief of the ancients that the Crocodile had no tongue). Lastly, 

 the Crocodilia agree with the typical Lizards, and differ from 

 the Snakes in having four well-developed limbs. 



FIG. 124. Head and fore-part of the body of the common Crocodile (Crocodilus vulgaris). 



The Crocodilia abound in the fresh waters of hot climates, 

 and are the largest of all living Reptiles, not uncommonly at- 

 taining a length of sixteen feet or upward. The best known 

 of the Crocodilia is the Nilotic Crocodile, which occurs abun- 

 dantly in Egypt, and was described by both Herodotus and 

 Aristotle. 



The true Crocodiles have the feet completely webbed, the 

 hind-legs bordered by a fringe, and the fourth tooth in the 

 lower jaw received in a notch on the side of the upper jaw. 

 They belong mainly to Africa and Asia, but they are also rep- 

 resented in the West Indies and in South America. 



The Alligators have the hind-legs simply rounded, and the 

 toes not completely webbed ; while the fourth tooth in the 

 lower jaw fits into a cavity in the palate, and is concealed 

 from view when the mouth is shut. Like the Crocodiles they 

 are essentially aquatic in their habits, and lie dormant during 

 the winter in cold climates and the hot season in warm coun- 

 tries. They are extremely voracious, and live upon fish and 

 small Mammals. The best-known species are the common 

 Alligator (A. Mississippiensis) of the Southern States, the 

 Caiman (A. palpebrosus) of Surinam and Guiana, and the 

 " Jacare 1 " (A. sclerops) of South America. 



The Gavial or Gangetic Crocodile occurs in India, and is 



