4G0 



COMPARATIVE ANATOMY. 



lino, so tliat the base of the skull is more or less shut off from taking 

 any part in bounding the buccal cavity. The nasal cavities, which 

 in the Amphibia lead into the buccal cavity at the very anterior 

 edge of the skull, have their internal orifices always placed farther 

 back in the Reptilia, owing to the union of the horizontal processes 

 of the maxilhe, palatines, and pterygoids in the middle line, and in 

 front of them. In this way the nasal is more completely shut off 

 from the buccal cavity, and forms an upper cavity, the base of which 

 is the roof of the mouth — that is, is the "hard palate/' These 



Fig. 249. Side views of Skulls. A Struthio. B Orocodilus. C Python. 01 Kx- 

 occipital. Os Supra- occipital. Pi Pterygoid. Pa? Palatine. Tr Transverse. Col Colu- 

 mella,, fov Fenestra ovalis. S Foramen for the trigeminal nerve. The other letters 



as in the preceding figures. 



changes are least marked in the Saurii, Ophidii, and Aves, more 

 so in the Chelonii, and most completely so in the Crocodilini. 



The parts that form the suspensorium in Fishes (hyomandibular 

 and symplectic) have undergone just the same fate as in tlic 

 Amphibia; or, in other words, they have no longer any relation to 

 the cephalic skeleton. The "columella auris " and the parts con- 

 nected with it are developed from its rudiments, partly a bony, and 

 partly a cartilaginous skeletal bit which has entered into the service 

 of the auditory organ. 



When the quadrate is movably united with the skull (Ophidii, 



