THE SPECIAL SENSES 



255 



It is important to remember that there is a continuous 

 connection between all the passages of the inner ear, and 

 that all the winding tubes and chambers inclose and pro- 

 tect a delicate bag of membrane of exactly the same shape 

 as themselves. 



350. The Au- 

 ditory Nerve. 

 The auditory 

 nerve, or nerve of 

 hearing, passes 

 to the brain, 

 through a little 

 hole in the solid 

 bone of the skull, 

 from the inner 

 ear, where its 

 nerve fibers 



branch round FIG. 158. General View of the Organ of Hearing. 



the sense cells 

 on the inner 

 walls of the lin- 

 ing membrane. 



351. How we 

 Hear. Let us 

 learn a few of 



the simplest principles about this wonderful mechanism of 

 the ear. A bell is rung or a gun fired. The vibration is 

 communicated to the atmosphere around it, and passes away 

 in air waves from the sounding body, as the waves ripple 

 the surface of a pond after a stone has been thrown in. 



The air waves pass into the outer ear and strike upon 

 the stretched membrane of the drum, causing it to vibrate. 



A, pinna ; B, cavity of the concha, showing the openings 

 of a great number of sebaceous glands ; C, external audi- 

 tory meatus; >, tympanic membrane ; F, incus; //, mal- 

 leus ; K, handle of malleus applied to the internal surface 

 of the membrana tympani ; Z,, tensor tympani muscle ; 

 between M and K is the tympanic cavity ; N, Eusta- 

 chian tube ; O, P, semicircular canals ; R, internal audi- 

 tory canal; S, large nerve given off from the facial 

 nerve ; T, facial and auditory nerves. 



