THE STRUCTURE AND ACTIVITIES OF MAMMALS 409 



transmits the image to the brain by way of the optic nerve. 

 The eyelids and eyelashes protect the eyes from injury. 



THE EAR. The ear (Fig. 279) is the organ of hearing. In 

 most mammals external, funnel-shaped projections catch the 

 sound waves. These waves enter the ear passage and induce 



the hammer 



meatus 

 the drum 

 of the ear 



(Tympanic 

 Membrane) 



the loops 



(Semicircular 

 Canals) 



the 



shell tube 

 (Cochlea) 



the anvil the stirrup 



Eustachian tube 

 FIG. 279. Middle and inner human ear. (From Peabody and Hunt.) 



vibrations in the tympanic membrane, which are transmitted 

 to the small bones of the ear lying in the cavity of the tympanum. 

 The end of the innermost of the small ear bones (stapes) is 

 applied to a fine membrane of the inner ear, or labyrinth, which 

 lies in a corresponding bony cavity. This membrane in its turn 

 receives the vibrations and transmits them to a fluid contained 

 in the labyrinth. Thence the vibrations reach the terminations 

 of the auditory nerve, and are conveyed to the brain, where they 

 enter into the consciousness in the form of tones or noises. 



TOUCH. Sensations of touch are conveyed by the whole 

 skin; as special organs of touch we may enumerate the tips of 

 the fingers, the lips with the special bristles, the wing mem- 

 brane in bats, as well as the tongue 



