6o6 



BIRDS. 



there is only a diffuse sense of touch, and the sense of taste 

 is also slightly developed. 



The sense of hearing is acute. Externally the ear is 

 marked by an open tube — the external auditory meatus ; 

 the aperture of which lies behind the eye, concealed beneath 

 the feathers. Within the tube, a little beneath the surface, 

 lies the drum or tympanum ; connecting this with the 

 fenestra ovalis of the inner ear is the columella : the tym- 

 panic chamber is continued past the. ear as the Eustachian 



7J1.0. 



Fig. 266. — Brain of pigeon. 



(1) Dorsal, (2) ventral, and (3) side view, ol/., Olfactory lobes; 

 c, cerebral hemispheres; <?/., optic lobes; cb., cerebellum; 

 mo., medulla oblongata. 



tube, which unites with that of the opposite side, and opens 

 into the mouth cavity in front of the basisphenoid bone. 

 The cochlea, or curved protuberance of the sacculus, which 

 is incipient in Amphibians, and larger in Reptiles, is yet 

 more marked in Birds. 



The eye has an upper, a lower, and a third eyelid or nic- 

 titating membrane. The last is frequently twitched across 

 the eye, and helps to keep the front clean ; it is present 

 in many Reptiles and most Mammals. The front of the 



