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HUMAN PHYSIOLOGY 



CHAP. 



same shape as the bony labyrinth. Within the sac is 

 another liquid called endolymph. 



The auditory nerve, as the nerve of hearing is called, 

 has fibers going to each of the semicircular canals, to 

 the vestibule, and to all parts of the cochlea, where they 

 spread out on the surface of the membranous labyrinth. 

 The sound waves come in contact with the fibers of the 

 auditory nerve ; but only those distributed to the cochlea, 



FIG. 140. A section through the ear. (From Boas by Zuppke.) 



which is the most important part of the ear, are used in 

 hearing. Those of the semicircular canals and the 

 vestibule carry to the brain impressions that enable us 

 to judge of the position of the body in space and help 

 to keep us right side up. We become dizzy if we swing 

 about in a circle for a short time. This is because the 

 liquid in the canals, which acts like a carpenter's level, 

 is disturbed by the rotation of the body. The feeling 

 of nausea and sickness that some persons experience 

 from riding on a boat, train, street car, or carriage, and 



