228 



ON THE STRUCTURE OF THE SKULL. 



be homologous with those of Fishes, and therefore the line of 

 argument which identified the prefrontals of the Pike with 

 the lateral masses of the ethmoid in the Man is equally 

 applicable to the same bones in Reptiles. In Birds, the post- 

 frontal s have only a doubtful and exceptional distinctness, and 

 in them the true prefrontals seem early to coalesce with the 

 ethmoid. The last-mentioned cranial element is usually ossified 

 and appears upon the upper surface of the skull, in Birds ; 

 while, in Reptilia, it almost always remains cartilaginous. In 

 the extinct Dicynodon, however, it and the presphenoidal region 

 were completely ossified. 



In Birds, in consequence of the prolongation of the snout 



Fig. 92. 



JPrf 



S.Or 



jptf PrO Fa FO S% 



Qu. 



Tr 7/ 



Fig. 92. — Lateral views of the skulls of (A) an Ostrich, (B) a Crocodile, and (C) a Python, 

 without the mandible. In the Python's skull the maxilla has also been removed. Tl, 

 turbinal bone of the Ophidian. 



