120 COMPARATIVE ANATOMY 



tympanic cavity, and the Eustachian canals open into the pharynx 

 by a median aperture behind the internal nostrils. 



The hyobranchial skeleton is much reduced, and consists of a 

 body with a single pair of cornua : it is not known whether these 

 belong to the hyoid or to the first branchial arch 



Birds. 



As already mentioned, the skull of Birds is formed on a similar 

 plan to that of Reptiles more particularly of Lizards, but it 

 exhibits certain special characteristics (Figs. 87 and 88). 



In correspondence with the higher type of brain, with its 

 well developed cerebral hemispheres, the brain-case is relatively 



Inter orb. septum 



Prefont (lac.) 



Prer, 



Aud. caps 



Pttryq 



Columclla Supra- Ang. ' %Pa raph. 



Aug. S d 



<l^ 



FIG. 87. SKULL OF AX EMBRYO CHICK 65 MM. IN LENGTH. From the right 

 side. (From a model by W. Tonkoff, x ). Cartilage, blue ; investing bones, 

 yellow; 



large, and correlative modifications occur, especially in the occipital 

 and auditory regions. The relatively large size of the eyes, 

 moreover, has resulted in a limitation of the cranial cavity in an 

 anterior direction and in the expansion of the brain laterally and 



