XVIII 



THE SPECIAL SENSES AND SENSATIONS 



259 



The organ of hearing is the ear. It has a very com- 

 plicated structure, but we shall try to understand the 

 different parts, and see how they work. The three 

 parts of the ear are known from their location as the 

 external, the middle, and the inner ear. 



177. The External Ear. This consists of two parts. 

 The first is an irregular shell of cartilage or gristle, cov- 

 ered with skin, that 

 projects from either 

 side of the head. It 

 serves as a funnel to 

 catch the waves of air 

 and to direct them to 

 the middle ear. The 

 second is the audi- 

 tory canal, which is 

 about one inch long 

 and arched upward 

 slightly near the mid- 

 dle. It extends to the 

 middle ear and serves 

 to conduct the sound 

 waves to the eardrum. 



The auditory canal consists of cartilage and bone 

 covered with skin. On the outer two thirds occur 

 small glands that secrete earwax or cerumen. This is 

 a yellowish sticky fluid that soon unites with some of 

 the thin scales of the epidermis, and hardens to a pasty 

 consistency. The wax has a bitter taste and serves to 

 keep insects out of the ear, to moisten the parts of the 



Concha 



FIG. 137, The external ear (Cheever). 



