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APPLIED PHYSIOLOGY 



tunnel, called the cochlea, which is like the inside of a 

 snail's shell, and also three other tunnels called the semi- 

 circular canals, from their shape. 



The labyrinth is filled with a clear liquid, and is lined 

 with epithelial cells, among which the nerves of hearing 

 end. Upon the surface of the epithelium are cilia, among 

 which are fine hard particles called the ear sand. The air 

 waves produce waves in the liquid which beat against the 



a outer air passage. 

 b membrana tympani. 

 c malleus or hammer bone. 

 d incus or anvil bone. 



Diagram of the ear. 



/ semicircular canals. 

 g vestibule of inner ear. 

 h cochlea. 

 i Eustachian tube. 



e stapes or stirrup bone. j tympanum or middle ear. 



cilia and produce the sense of sound. Waves in the fluid 

 surrounding the nerves must occur at least sixteen times a 

 second in order to produce a sound. When they occur 

 more than thirty-eight thousand times a second, they are 

 too rapid for the nerves to take account of their motion, 

 and so no sound at all will be heard. 



The semicircular canals do not seem to be essential to hearing, but 

 when they are diseased a person is unable to balance himself so as to 

 walk or even to stand. The movements of the fluid in the canal seem 

 to produce nervous impressions which, in the cerebellum, excite such 

 reflex actions as are necessary to balance the body in an upright position. 



