The American Alugator 5 



tremely rare, owing to the destruction of the large 

 specimens for their hides. Young alligators are dark 

 brown or black with bright yellow cross-bands. The 

 lighter markings become less and less distinct with 

 age, and very old specimens are a dull dark gray or 

 black. The large, regularly arranged, plate-like scales 

 on the back are underlain by plates of bone in the skin. 

 These bony plates are absent in the skin of the belly, 

 which is, therefore, more valuable for leather. 

 Caimans and the African dwarf crocodile (Osteolae' 

 mus) , have bony plates in the skin of the underparts, 

 and in the caimans these plates are closely joined on 

 the back and belly. Some fossil forms had an even 

 more complete armor. The teeth are formidable. 

 They are placed in regular sockets in the jaw-bones 

 and are regularly shed, being replaced by new teeth 

 growing into the hollow bases of the old ones. The 

 head is remarkable for the nearly complete absence of 

 flesh on its outer surface. There are no fleshy lips. 

 The skin is so closely attached to the bone that it is 

 impossible to detach it without destroying it. 



There are many adaptations to life in the water 

 in the alligator's body. The hind feet are fully 

 webbed, the front feet slightly webbed. In active 

 swimming, how;ever, the legs are held at the sides and 

 the body is propelled by sidewise strokes of the power- 

 ful tail. The tail is strongly flattened from side to 

 side and the ridge of scales along its upper edge in- 

 creases the propelling surface. The form of the head 

 is such that the alligator can float at the surface of the 

 water with only eyes and nostrils exposed. The nos- 

 trils can be closed by a valve-like flap of skin when it 

 submerges. A similar arrangement of eyes and nos- 

 trils is found in many other animals that live in the 

 water, the hippopotamus being a notable example 

 among mammals. A complicated apparatus provides 

 for the opening of the mouth at the surface of the 



[29] 



