xvii THE CROCODILE 217 



fairly constant in a given species. Sixty-eight or 

 seventy teeth is not an uncommon number for a croco- 

 dile of the Nile. In some species of these reptiles the 

 teeth interlock as thoroughly as the teeth of a rat-trap ; 

 in others the interlocking is not so complete, but they 

 are very efficient, for the strength of the teeth and jaws 

 of crocodiles is such that they rarely let go any animal 

 that is fairly seized. 



The teeth are conical somewhat compressed from 

 side to side which gives them sharp edges : they vary 

 much in size, and the fourth in the lower (mandibular) 

 set is so constantly larger than the teeth immediately 

 adjacent that it is sometimes termed the canine tooth. 

 This long tooth fits into a notch in the side of the upper 

 jaw. The teeth consist of dentine, capped by enamel, 

 and the roots have a coating of cementum. 



Crocodiles shed their teeth throughout life, but they 

 are quickly replaced. The method of replacement is 

 after this fashion : The young tooth grows on the 

 median side of the functional tooth ; as the new tooth 

 increases in size the adjacent wall of the root of its pre- 

 decessor is absorbed. Eventually the new tooth is found 

 within the pulp cavity of the one it is destined to replace. 

 In due course the persistent growth of the young tooth 

 pushes the old one out, and takes its place : when this 

 happens a new tooth has started to supplant it in 

 turn. 



A newly-cut tooth has a sharp point : by use the 

 point is worn down, but the edges are retained ; coinci- 

 dent with the wear of the crown, erosion takes place at 

 the margin of the enamel-cap and a definite groove forms 

 around the tooth, dividing it into a crown, neck, and root. 

 This is only seen in old teeth. Sometimes the crown of 

 an old tooth has facets due to wear. 



The digestive organs of crocodiles are very powerful. 

 Birds, small mammals and portions of large animals are 

 retained in a wide and capacious gullet until the stomach 

 is ready to receive them. 



