240 A MANUAL OF DENTAL ANATOMY. 



space required for the attainment of their fall size, by the 

 absorption of the older solid bone and the tooth which 

 has preceded them, in the following manner. The teeth 

 are attached to the bone by anchylosis, each tooth being 

 perched upon a little pedestal of bone which is specially 

 formed for it; and the successional teeth, the germs of 

 which originally lay at the inner sides of the old teeth, 

 commonly undermine the side of the pedestals and the 

 bases of the latter, and move bodily beneath them, so that 

 the new tooth completes its development in what was once 

 the pulp cavity of its predecessor. 



The teeth of the frog consist of a body of hard dentine, 

 coated with an exceedingly thin layer of enamel, the exist- 

 ence of which has been doubted by some writers ; but a 

 study of the tooth sac of the animal renders it probable that 

 the transparent layer which is undoubtedly there is really 

 enamel. 



The teeth of the newt and its ally the salamander are 

 remarkable for having tips of enamel, somewhat like those 

 of the eel (see Fig. 90), save that they are bifurcated, the 

 one point being larger and longer than the other. 



The tadpole has its jaws armed with tough horny plates 

 something like a turtle's bill, which are shed off, prior to 

 the development of any true teeth; at all events I have 

 myself been unsuccessful in discovering any tooth germs at 

 the period when its horny bills are still in use. 



Some extinct batrachia were of large size ; the Laby- 

 rinthodon, the structure of whose teeth has already been 

 described (page 79), was furnished with a marginal row of 

 teeth in the upper jaw, of which some few were of larger 

 size and greater length than the others. In the lower jaw, 

 the teeth, which are similar to those of the upper, are 

 disposed in some sense in an incomplete double row, the 

 series of smaller teeth not being interrupted by the occur- 

 rence of the larger tusks, but passing in unbroken series 



