CROCODILES. - 459 



Order IX. — CROCODILIA. 



This order embraces those Mquatic reptiles wliich have the teeth liniily iin])iante(l 

 in the jaws, tlie l)0(ly jirotected 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 

 pro]ier are the only bones which bear teeth, and these are wedged into alveoli and are 

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

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

 gan of ])rehensioii. 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 ])rotected by two 

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

 cuticular valves. The buccal cavity has posteriorly an arrangement which ])revents 

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

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

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

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

 heart is highl_v 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 T/iorcfosaurus 

 will be first treated. 



The crocodiles inh.ibit the warmer portions of America, Asia, Africa, and Aus- 

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

 cutaneous ))lates of the top of the head and back continuous, and the canine teeth of 

 the lower j.aw 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 

 tliaii into notches. 



The gavial, or nakoo, of India, Garlallx ijaiiytiimx, 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 super- 

 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 GaviaUs and ('rocodtlus, and is rcpresentc<l by but a 

 single species, T. schlegeUi, which inhabits the islaiul of Borneo. 



Of the crocodiles proper, representatives arc found in every continent. <^roco- 

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



