LACERTILIA AND CROCODILIA. 



469 



special notice are that the eyes are protected by movable eye- 

 lids; the ear is covered by a movable ear-lid; the nasal cavities 

 open in front by a single nostril, and are shut off from the 

 cavity of the mouth, but open far back into the cavity of the 

 pharynx ; and lastly, the tongue is large and fleshy, and is im- 

 movably attached to the bottom of the mouth. (Hence the 

 belief of the ancients that the Crocodile had no tongue.) The 

 tail is long and compressed, with two rows of keeled plates, 

 which unite about its middle to form a single crest, which is 

 continued to its extremity. The feet are palmate or semi- 

 palmate, and only the three inner toes on each foot possess 

 claws. The eyes possess three distinct lids, and there are two 

 glands under the throat secreting a musky substance. 



The Crocodilia abound in the fresh waters of hot countries, 

 and are the largest of all living Reptiles, not uncommonly 

 attaining a length of twenty feet or upwards. They are divided 

 by Owen into three sub-orders, according to the shape of the 



Fig. 203. Crocodilia. Head and fore-part of the body of the Common Crocodile 

 (Crocodilus vulgaris). 



dorsal vertebrae, termed the Proccelia^ Amphic&lia, and Opis- 

 thoccelia. 



Sub-order i. Procoslia. In this sub-order are all the living 

 members of the Crocodilia distinguished by having the bodies 

 of the dorsal vertebrae concave in front (proccelous). Three 

 distinct types may be distinguished amongst the living Croco- 

 dilia. The Gavial is distinguished by its elongated snout, at 

 the extremity of which the nostril is placed, and by the fact 

 that the teeth are pretty nearly equal in size and similar in 

 form in the two jaws. In the true Crocodiles (fig. 204) the 

 fourth tooth in the lower jaw is larger than the others, and 

 forms a canine tooth, which is received into a notch excavated 

 in the side of the alveolar border of the upper jaw, so that it is 

 visible externally when the mouth is closed. In the Caimans 

 or Alligators the same tooth in the lower jaw forms a canine, 

 but it is received into a pit in the palatal surface of the upper 

 jaw, where it is entirely concealed when the mouth is shut. 



