126 A MANUAL OF DENTAL ANATOMY. 



them, which is pushed out of the way as they grow larger. 

 The further progress of the tooth germ being identical with 

 that of mammalia, its description may be for the present 

 deferred. 



In ophidian reptiles (snakes) several peculiarities are met 

 with which are very characteristic of the order. A snake's 

 method of swallowing its food would seem to render the 

 renewal of its teeth frequently necessary; although I da 

 not know of any data by which the probable durability of 

 an individual tooth could be estimated, the large number 

 of teeth which are developing in reserve, all destined ta 

 succeed to the same spot upon the jaws, would indicate that 

 it is short. 



I have seen as many as seven successional teeth in a single 

 section, and their arrangement, particularly in the lower 

 jaw, which undergoes great displacement while food is being 

 swallowed, is very peculiar. The numerous successional 

 tooth sacs, instead of being spread out side by side, as in 

 the newt, are placed almost vertically, and in a direction 

 parallel with the surface of the jaw-bone ; they are, more- 

 over, contained in a sort of general investment of connective 

 tissue ; a species of bag to keep them from displacement 

 during the expansion of the mouth. 



The inward growing process of oral epithelium enters this 

 case of tooth sacs at its top j and may be caught sight of 

 here and there as its prolongations wind their way by the 

 sides of the tooth sacs to the bottom of the area t Here 

 the familiar process of the formation of an enamel organ and 

 dentine papilla may be observed, in no essential point differ- 

 ing from that which is to be seen in other animals. 



That the derivation of each enamel organ is from a part of 

 that of its predecessor is very obvious ; the dentine organs 

 are formed in relation with the enamel germs, but apparently 

 independently of one another. 



As the tooth sacs attain considerable dimensions, a curious 



