60 REPTILES AND BATRACHIANS. 



By these illustrations of the skull (alluded to on p. 51) the 

 changes which occur during the growth of a frog from the tadpole 

 to maturity may be studied, as also the names of the bones. The 

 darker parts are those where the cartilage has- become hardened, 

 or is replaced by bony pieces ; one is viewed from the top of the 

 head, and the other from the interior of the mouth. 



