SENSE ORGANS. 607 



Sense Organs. 



The sense of smell does not seem to be keenly de- 

 veloped in many birds. The nostrils are longitudinal slits 

 overhung by the swollen, more or less sensitive, cere. 



The sense of hearing is acute. Externally the ear is 

 marked by an open tube the external auditory meatus ; 

 the aperture of which is surrounded by a regular circlet of 

 feathers. Within the tube beneath the surface lies the drum 

 or tympanum ; connecting this with the fenestra ovalis of 

 the inner ear is the well-developed columella ; the tympanic 



FIG. 213. Brain of Pigeon. (After BRONN.) 



i, Dorsal view; 2, ventral view; 3, side view; olf., olfactory 

 lobes ; c., cerebral hemispheres ; o.L, optic lobes ; d>., cerebellum ; 

 m.o., medulla oblongata; s.c., spinal cord. 



chamber is continued past the ear as the Eustachian tube 

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

 the mouth cavity in front of the basi-sphenoid bone. The 

 cochlea, or curved protuberance of the sacculus, which is 

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

 marked in Birds. 



As to the eye, its protection by an upper, a lower, and a 



