HIGH SCHOOL ZOOLOGY. 



115 



23. The fourth and last order of living Reptiles is that of the 

 Crocodilia, aquatic forms of large size which are found in tropi- 

 cal rivei-s over the whole world. There are three families 

 jepresented by the Gavial of the Ganges (Fig. 83), characterized 



Fig. 83. — Gavialis gang-eticxis. (After Brehm.) 



by its very long snout, the Crocodile of the 'Nile and the Alli- 

 gator of the Mississippi. Most of them are fish-eating f( rms, but 

 many of them lie in wait for the smaller Mammalia when they 

 come to drink. Their aquatic habit is associated with a power- 

 ful comj)ressed tail, and completely or incompletely webbed 

 toes, but the legs ai*e, nevertheless, strong enough to enable 

 them to leave one pond and drag themselves to another. As in 

 the other Reptiles, the horny epidermal covering is well de- 

 veloped and characteristic, but there exist also in the cutis bony 



