CHAPTER VII. 



THE TEETH OF BATRACHIA AND REPTILES. 



Ix these classes the teeth are never so numerous nor so 

 widely distributed upon the bones of the mouth as in fish ; 

 a double row of teeth arranged in concentric lines in the 

 upper jaw, between which a single row of teeth upon the 

 lower jaw passes when the mouth is closed, is an arrange- 

 ment rather common amongst Batrachia. Almost all 

 Batrachians and Reptiles have an endless succession of 

 teeth ; but there are a few lizards (e.g., Hatteria), in which 

 the manner of succession, if there be any, has not been 

 definitely ascertained. The outer of the two rows of teeth 

 in the upper jaw is situated upon the premaxillary and 

 maxillary bones, and usually extends further back than 

 the vomerine or inner row. 



From this type of dentition there are many deviations ; 

 thus the toads are edentulous, and the frog has no teeth in 

 the lower jaw. 



The teeth of the frog form a single row upon the margin 

 of the upper jaw, their points projecting but little above 

 the surface of the mucous membrane, and the vomerine 

 teeth are few in number and cover only a small space. 



The edentulous lower jaw passes altogether inside the 

 row of upper teeth, and, itself having rounded surfaces 

 and no lip, fits very closely against the inner sides of the 

 teeth. Thus it leaves very little room for the young 

 developing tooth sacs, which are accommodated with the 



