CROCODILES. 469 



Order IX. — CROCODILIA. 



This order embraces those aquatic reptiles which have the teeth firmly implanted 

 in the jaws, the body protected by a thick, armored skin, and the four limbs and tail 

 formed for swimming as well as for crawling. While in the previous order the limbs 

 were only represented by paddles, we now come to animals which not only have these 

 appendages freely articulated, but have them ending in separate digits. The skin is 

 .thick and heavy, and bears, in its dorsal regions, strong, osseous plates. The jaws 

 proper are the only bones which bear teeth, and these are wedged into alveoli and are 

 conical in outline. The fourth tooth of the mandible often considerably exceeds its 

 fellows in size and fits into an excavation in the upper jaw. It is used as the chief or- 

 gan of prehension. The structure of the vertebral centra varies in the several sub- 

 orders, though all the existing crocodiles have them concave anteriorly. The structure 

 of the soft parts is the highest presented by living reptiles. The organs of special 

 sense are well developed. The eyes have the pupil vertical, and are protected by two 

 lids, and also by a nictitating membrane. Both nostrils and ears are provided with 

 cuticular valves. The buccal cavity has posteriorly an arrangement which prevents 

 water from passing into the pharynx, when the mouth is held open by the strug- 

 gling prey. The stomach is remarkably bird-like and passes into a zigzag intestine, 

 to which are attached no caecal appendages. The intestine decreases in size before 

 entering the cloaca, which gives attachment to the erectile copulatory organ. The 

 heart is highly developed, and, in having a distinct right and left ventricle, effectually 

 prevents the mixture of the venous with the arterial blood. The order is divided into 

 three groups, of which the procelous, existing crocodiles, and the fossil Thoracosaurus 

 will be first treated. 



The crocodiles inhabit the warmer portions of America, Asia, Africa, and Aus- 

 tralia, and naturally divide themselves into three groups : The gavials, having the 

 cutaneous plates of the top of the head and back continuous, and the canine teeth of 

 the lower jaw fitting into notches in the margin of the upper jaw ; the crocodiles 

 proper, having the plates of the head separated from those of the back, but having 

 the canine teeth fit into notches as in the previous group ; and the alligators, having 

 the plates of the back like the crocodiles, but having the teeth fit into pits rather 

 than into notches. 



The gavial, or nakoo, of India, Gavialis gangeticus, has the snout elongated, 

 linear, and swollen at the tip, and the lateral teeth oblique. This animal is one of the 

 largest of the order, and sometimes reaches a length of twenty feet. Old males have 

 the nasal sacs at the tip of the snout considerably enlarged, and are thus enabled to 

 remain below the surface for a considerably longer period than are the females. The 

 development of the snout is of peculiar interest, since the young have it broad and 

 depressed like the alligators. In some of the rivers of India, as a result of a sujjer- 

 stition among the ignorant natives, who fear to harm them lest they arouse the anger 

 of the gods, the gavials have become so abundant as to be destructive to human life. 



The genus Tomistoma has the beak conical, and the teeth erect and received into 

 pits ; it is intermediate between Gavialis and Orocodilus, and is represented by but a 

 single species, T. schlegelii, which inhabits the island of Borneo. 



Of the crocodiles proper, representatives are found in every continent. Croco- 

 dilus vulgaris, the Nile crocodile, is found throughout Africa from north to south 



