DIVISIONS OF REPTILIA. 273 



face are firmly united, and the two halves of the lower jaw are 

 joined by a distinct suture. The teeth form a single row in both 

 jaws, and are implanted in distinct and separate sockets. The front 

 ribs of the trunk are double-headed, and there are no collar-bones. 

 The heart consists of four distinct chambers, two auricles and two 

 ventricles, all completely sepaiated from one another. The mixture 

 of arterial and venous blood, however, 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 

 neighbourhood of the heajt. The eyes are protected by movable 

 eyelids, and the ear by a movable ear-lid. The tongue is large and 

 fleshy, and is immovably attached to the bottom of the mouth (hence 

 the belief 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. 



The Ofocodilia aboimd in the fresh waters of hot climates, and 

 are the largest of all living Reptiles, not uncommonly attaining a 

 length of sixteen feet or upwards. 



The true Crocodiles have the feet more or less 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 represented in Australia, 

 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 countries. 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. palpehrosiis) of Surinam and Guiana, and the " Jacard " 

 {A. sclerops) of South America. 



The Gavial or Gangetic Crocodile occurs in India, and is distin- 

 guished by its narrow, elongated jaws, forming a kind of beak. It 

 attains a length of more than twenty feet. Closely allied types occur 

 in the rivers of North Australia and in Borneo. 



