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. 



