FAMILY CROCODILID.E ; CKOCODILES, ALLIGATORS. 549 



the skull ; so that the gape of the animals is of enormous width. 

 The lower jaw itself is composed of six pieces on each side, the 

 foremost of these constituting the greater part of the jaw, and 

 being alone furnished with teeth ; these are conical and acute, 

 and inserted into the jaws by regular sockets. The nostrils are 

 placed at the extremity of the snout, and capable of being closed 

 by a valve, to prevent the ingress of water. The tongue is fleshy 

 and fixed to the bottom of the mouth ; and the eyes, which are 

 of considerable size, have contractile pupils, which form a per- 

 pendicular line when exposed to daylight. The lungs do not 

 penetrate into the abdomen, as in other Reptiles ; and there is 

 even a trace of a diaphragm separating the thoracic and abdo- 

 minal cavities. The dermal skeleton consists of large, square, 

 bony plates imbedded in the skin, protecting the dorsal surface ; 

 and these are often of peculiar forms in different regions of the 

 body, when they furnish excellent characters for the discrimin- 

 ation of the species. These animals, as is well known, are very 

 ferocious in their disposition ; they seize their prey for the most 

 part in the water, but retire to some retreat on land to devour 

 it ; and they relish it in a state of putrescence. Their aquatic 

 habits are indicated by the vertical flattening and expansion of 

 the tail, and by the webbing of the posterior feet ; in this respect, 

 however, there is a difference between the several groups of this 

 order. They are only found in warm climates ; and inhabit the 

 rivers, lakes, and marshy places; sometimes swimming out to 

 sea, even to a considerable distance from land. 



488. In the recent species of this order, the bodies of the 

 vertebrae have the posterior surface convex, and the anterior 

 concave ; they form the single family CROCODILID^;. They 

 may be divided into two principal groups, the Crocodiles, 

 which are common to both hemispheres ; and the Alligators, 

 which are peculiar to America. The Crocodiles have the hind 

 feet webbed nearly or quite to the extremities of the toes, and 

 the long teeth, commonly called canines, which occur on each 

 side of the lower jaw near the front, are received into a notch in 

 the upper jaw ; in the Alligators, the hind feet are never com- 

 pletely webbed, and the lower canine teeth fit into a pit in the 



