DENTITION OF LOWER VERTEBRATES 



39 



others. In this specimen the third and ninth in the upper jaw 

 and the first, fourth and eleventh in the lower have attained 

 greater size than the rest. The young Alligator when just 

 hatched has as many teeth as the adult but the teeth are re- 

 placed from time to time by successors. Nevertheless, at what- 

 ever age the animal be, on examination it will always be found 

 to possess these particular teeth larger than their fellows. 



Fig. 7. — Jaws of Alligator (Alligator mississipiensis 81.4-1). The teeth are implanted in 

 bony sockets and certain teeth are constantly larger than others. 



A character again exemplified in the Alligators but not in 

 other Reptiles is the implantation of the tooth into a socket. 

 The tooth itself like that of the Mammal consists of dentine 

 with a cap of enamel on its projecting surface and a sheathing 

 of cement around its implanted portion. Though the teeth of 

 the Alligator resemble those of the Mammal in possessing 

 sockets in the jaws they are not strictly comparable for 

 whereas the socket in the case of the Mammal is produced by 



