THE DEVELOPMENT OF THE TEETH. 



123 



constant succession of new teeth met with amongst almost 

 all reptiles renders it easy to obtain sections showing the 

 teeth in all stages of growth : upon the inner side of the jaw 

 there will be found a region occupied by these forming teeth 

 and by nothing else, which may be called " area of tooth deve- 

 lopment ; " this is bounded on the one side by the bone and 



FIG. 60 





teeth which it carries, and on the other by a more or 

 less sharply denned wall of fibrous connective tissue. In 

 the newt, for example (Fig. 60), to the left of the tooth hi 

 use are seen four tooth sacs, in serial order, the youngest 

 being nearest to the median line of the mouth. As the sacs 

 increase in size they appear to undergo a sort of migration 

 towards the edge of the jaw, while simultaneously new ones 

 are constantly being developed beyond them. In the newt, 



(*) Section of upper jaw of Triton cristatus (newt). To the inner side 

 of the tooth attached to the bone are three younger tooth germs. 



