8o THE COMMON FROG. [chap. 



mediately in front of the branchial arches, continues 

 to be so connected and becomes one of the two 

 " cornicula," while the rudimentary relics of the 

 branchial arches which persist become what \ve have 

 seen in the adult as the cornua of the os hyoides. 



Thus the anatomy of the tongue-bone of the frog, 

 studied in its progressive changes, reveals to us that 

 otherwise unsuspected relations exist in certain parts 

 of the tongue-bone of man. It exhibits to us the 

 cornua of his os hyoides as related to those large and 

 complex branchial arches which play so important a 

 part in the fish and form so relatively large a portion 

 of its skeleton. 



The fourth circumstance (the last here to be noticed) 

 connected with the frog's skull concerns the relative 

 position and size of certain of its enveloping bones. 



When the skull of the frog is viewed from above, a 

 large vacuity is seen to exist on each side, between 

 the brain-case and the great arch of the upper jaw. 

 In the hinder part of this space is situate the temporal 

 muscle, which by its contraction pulls up the lower 



Fic. 44.— Dorsal view of skull of Pclobates, sliowing bony lamellae behind the 

 orbits. 



jaw and closes the mouth ; and the hollow in which 

 this muscle lies is called the temporal fossa. 



