76 THE COMMON FROG. [chap. 



probable that this structure has independently 

 appeared through the action of peculiar conditions, 

 and hence that we have here again a remarkable 

 instance of the independent origin of similar 

 structures. 



The third peculiarity of the frog's skull consists in 

 the form and conditions of the bony supports of the 



tongue. 



It would not be easy to find a better example of 

 the need of widely extended observations in order 

 duly to understand structures apparently very simple 

 indeed. 



The bone of the tongue in man — the os Jiyoides^— 

 is a small structure, and one to all appearance of little 

 significance. It is placed at the root of the tongue 

 and above the larynx, and consists of a body with a 

 pair of processes on each side, one large (the posterior 

 or great cornu), and one small (the anterior or lesser 

 cornu, or corniculum). 



Even in man's own class (mammalia) the relative 

 development of the parts may vary greatly. Thus 

 the cornicula may be large and may each be repre- 

 sented by two or three distinct applications as in the 

 dog and horse. 



The cornua also may take- on a development very 

 much greater than that existing in man as is the case 

 in some other Mammals. These facts may prepare 

 us to expect much greater divergences in lower forms; 

 and yet throughout the two great classes of birds and 

 reptiles (as well as beasts) — though varying conditions 

 as to the proportions of the parts present themselves 



* So named from its resemblance to the Greek letter u. 



