CROCODILES, ALLIGATORS, AND G A RIALS. 



379 



the body. These shields, -which do not overlap, but join one another by 

 their edges, are often marked on the back by more or less distinctly developed 

 longitudinal ridges, and, at least on the back, are underlain in the deep layer 

 of the skin by solid bony plates. In the case of the ridged shields, the 

 underlying plates are similarly ridged ; and in every instance the plates are 

 marked by a peculiar honoy-comb-like sculpture. A somewhat similar 

 sculpture, although taking more the form of irregular branching ridges and 

 grooves, is likewise developed on the outer surface of the bones of the head ; 

 and in this respect the skull of every living member of the order differs from 

 that of any other existing reptile. All crocodilians — as the members of the 

 order may be collectively designated — are huge ungainly reptiles, with large 

 flat heads, depressed and lizard-like bodies, short limbs, and long, compressed, 

 and powerful tails, bearing on the upper surface a crest of horny lobes, which 

 is double in the basal half of that appendage. The toes, which are five in 

 number in the fore-limbs, but are reduced ta four in the hinder pair, are 

 more or less completely united by webs to form efficient paddles for swim- 

 ming ; and on each foot the three toes on the inner side are furnished with 

 strong and sharp claws. In the huge, ugly head, the apertures of the ears 

 can be closed by means of movable lids, so as to prevent the ingress of water ; 

 and the nostrils open at the very tip of the muzzle — whether this be short or 

 broad, as in the alligators, or long and narrow, as in the garials. The vast 

 and cavern-like mouth is armed with a formidable series of sharp, conical teeth, 

 some of which are enlarged into tusks, while all are implanted in separate 

 sockets, and form a single row on the summit of each jaw. To keep this 

 terrible armament in repair, the teeth are being consequently shed and re- 

 newed, the new ones coming up beneath the hollow bases of the old ones 

 and gradually pushing them out. Sometimes three or four teeth may be seen, 

 one beneath the other, packed together like a nest of thimbles. 



If the dried skull of one of these reptiles be examined, it will be found 

 that the whole of the palate is formed by a solid roof of bone, and also that 

 the quadrate-bone is firmly and immovably wedged in between the adjacent 

 elements of the skull. Later on, we shall see that this type of structure 

 differs very markedly from that which obtains among the lizards, and thus 

 forms a most essential feature in the definition of the order. A more de- 

 tailed examination of the skulls of all existing crocodiles will also show that 

 the posterior, or internal, nostrils open on the palate right at the hinder end 

 of the skull, close to where it joins the backbone. And it is by means of this 

 arrangement that these reptiles are enabled to hold and drown their prey in 

 their open mouths beneath the surface of the water without any danger of 

 being suffocated themselves. This is effected by means of the production of 

 the upper extremity of the windpipe well into the mouth, where it enters the 

 internal nostrils, and thus forms a closed tube from the external nostrils to 

 the lungs. 



Another peculiarity in the structure of a crocodile which has much effect 

 on its movements, is to be found in the vertebrae of the short neck. From 

 the development of long processes on the sides of this portion of the back- 

 bone, a crocodile is totally unable to turn its head. Consequently, if a man 

 be attacked on land by one of these monsters, he has but to await its rush, 

 and then leap suddenly aside, when his aggressor will continue its course 

 until able to turn its whole body. 



Members of the order are found in all the warmer regions of the globe, 

 but are happily absent from European rivers. They frequent alike rivers, 



