548 COLLEGE ZOOLOGY 



follows. The vertebras are mostly procoelous; all of the cervi- 

 cal and trunk vertebrae and some of the caudal vertebrae bear 

 ribs, a number of which are attached by two heads; there is a 

 sternum, but no clavicles; the teeth are conical and are shed at 

 interval^, being replaced by others which grow up beneath j 

 them; they are set in sockets (thecodont) on the premaxillae, 

 maxillae, and dentary bones; the tongue is flat and non-pro- * 

 trusible, but can be raised and lowered, serving as a valve to 

 prevent water from entering the oesophagus when the mouth 

 is opened under water; palatal folds separate the upper air- 

 passage from the lower food passage; there are no salivary 

 glands, no intestinal caecum, and no bladder; the lungs are 

 partitioned off from the rest of the organs in the body-cavity 

 by a membrane which 'assists in respiration and is analogous 

 to the diaphragm of mammals; the ventricle of the heart is 

 completely divided into two by a septum, whereas, that of other 

 reptiles is only partially divided; the cerebellum is more highly 

 developed than in the other reptiles; the penis resembles that 

 of the turtles (see Fig. 442). 



Family Gavialid^e. — Two of the twenty-one species of 

 living Crocodilini belong to this family. Gavialis gangeticus, 

 the Indian gavial, lives in northern India, and Tomistoma schle- 

 geli, the Malayan gavial, lives in Borneo and Sumatra. The 

 Indian gavial (Fig. 451) reaches a length of twenty feet or more, 

 and has a very long, slender snout. It inhabits the Ganges 

 and Brahmaputra rivers and their territories. The food of 

 the gavial consists principally of fish ; man is seldom if ever 

 attacked. 



Family Crocodilim;. — This family contains four genera — 

 Crocodilus, Osteoloemus, Caiman, and Alligator. Crocodilus 

 americanus, the American crocodile (Fig. 451), is an inhabitant 

 of Florida, Mexico, and Central and South America. It has 

 a triangular head becoming very narrow toward the snout. It 

 attains a length of fourteen feet. In Florida the crocodile digs 

 burrows in the bank in which to hide; the openings are entirely 



