EEPTILIA 397 



bearing them. Sternum wanting. There are no movable eyelids. The tongue is 

 protrusible, and is doubtless much used as an organ of touch, and possibly hearing. 



Snakes are, like lizards, partial to warm climates, but are also found in tem- 

 perate latitudes. Most are terrestrial, but some take to water I'eadily; and there 

 are some which never come to land. These bring forth their young alive. Many 

 snakes are beautifully and characteristically colored. In some instances the 

 coloration is deemed to be protective. 



Order III. Crocodilini {Crocodiles, Alligators, etc.). — Fresh-water reptiles 

 with elongated bodies bearing two pairs of well-developed appendages. The skin is 

 armed with dermal bony scales or scutes covered by epidermal scales. Teeth 

 occur in sockets. The quadrate is immovable and the sternum is present. The 

 adult heart is completely divided into right and left halves. The cloaca opens by 



Pig. 203. 



Fig. 203. Head of the American Alligator (.Alligator mississippiensis) . From Eckstein. 



a longitudinal slit. Here are included the gavial of the Ganges, the crocodiles 

 of the Nile and of tropical America, and the alligator of America. They are some- 

 what sluggish animals, but when hungry will attack with success the larger mam- 

 mals or man. They may attain a length of twenty feet or more. Crocodilia 

 are chiefly aquatic, though they rest and deposit their eggs on the shore. 



There are numerous orders of extinct reptiles which show close relationship 

 with the amphibians, birds and mammals of early geological times. This is 

 merely another way of saying that the early Reptilia and the other vertebrates 

 were much more generalized in their characteristics and less differentiated than 

 those of the present. Reptiles occupy a central position among the classes of land 

 vertebrates. 



426. Supplementary Topics for Investigation. 



1 . Have the venomous snakes any characteristic appearance ? 



2. Report on the habits of the rattle-snake. Whence the 

 structure giving rise to the name ?• The nature of the fang and 

 the poison gland. 



3. What is the degree of activity and strength of the reptiles 

 and cold-blooded animals, as compared with the warm-blooded ? 



