THE SKULLS OF REPTILIA AND AVES. 



225 



upon with a point, it gives way ; but this is not because it is 

 merely suturally connected with the periotic bones, as has been 

 supposed, but because the lamina of bone by which the cochlear 

 plate is fixed to the opisthotic is very thin and elastic. 



Among the many singular speculations which the historian 

 of the theory of the skull will have to record, perhaps the 

 strangest is that which identifies this cochlear loop, imagined 

 to be a distinct bone, with the entire " petrosal ' bone of the 

 Mammalia. 



In Birds, the three periotic bones anchylose with one another, 

 as well as with the adjacent supra-occipital and ex-occipital, so 

 completely, that even the Y-shaped suture becomes obliterated 

 (Fig. S8, A). 



The determination of the homologues of the periotic bones 

 in the skulls of Birds and Reptiles, and more especially of the 

 pro-otic, is not only a matter of first-rate importance in itself, 



Fig. 90. 



Ft 



B 



WL2F E ( l0 so 



Pmx 



PrOBS P n j 

 OfiO 



Fig. 90. — A, a vertical and longitudinal section of the skull of a Lizard (Cyclodus). B, a 

 similar section of the skull of a Snake {Python), f, membranous space in the roof 

 of the Lizard's skull ; * *, ossifications in the internasal cartilage ; Co, the columella 

 of the Lizard ; Cm, the bone also called " columella," which corresponds with the 

 stapes. 



Q 



