260 HUMAN PHYSIOLOGY CHAP. 



canal, and to remove the little flakes of epidermis as 

 they scale off. In a healthy ear there is very little 

 wax and one never needs to remove it. Sometimes, 

 however, it may collect in the ear and interfere with the 

 free movement of the eardrum. It must then be care- 

 fully removed by a skillful aurist. 



178. The Middle Ear. This consists of a thin mem- 

 brane, the drumhead, stretched across the auditory 



canal as its outer boundary. 

 It is this membrane that vi- 

 brates in order to enable us to 

 hear. If the earwax should 

 accumulate on the outer sur- 

 face of the drumhead, or if the 

 drumhead should be punc- 

 tured, we could not hear so 



FIG. 138.- The chain of bones well J ust beyond the drum- 



of the middle ear. (Drawn head is a chain of three small 



by Johnstone.) . i i v j 



bones which bridges the cavity 



of the middle ear. The malleus is attached to the center 

 of the drum by means of its long handle, the anvil 

 joins the round head of the malleus with the small end 

 of the stapes, and the large end of the stapes fits into 

 an opening of the inner ear, called the oval window. 

 These three bones are so shaped and fastened together 

 that they transmit the sound waves to the internal ear 

 precisely as they receive them, except that the waves 

 are focused on a smaller area and much intensified. 

 The Eustachian tube extends from the cavity of the 

 middle ear down to the pharynx, and keeps the air 



