SOUND 



217 



auditory canal is a thin layer of very flexible skin, the 

 tympanic membrane, which also forms the external cover- 

 ing of the middle ear. 



The middle ear is a small cavity lined with mucous 

 membrane and connected with the pharynx by the 

 Eustachian tube. It contains a chain of three .bones 

 named from their shapes the hammer (malleus) , the anvil 



""* Bone 



FIG. 192. The Human Ear Shown in Section. Co, Cochlea (location of 

 real hearing organ) ; E.b, Ear Bones ; Eu, Eustachian Tube ; Ty.m, Tympanic 

 Membrane. 



(incus), and the stirrup (stapes) (Figure 193). These bones 

 extend from the tympanic membrane to the membrane 

 which closes the opening, fenestra ovalis, into the inner ear. 

 The inner ear is located in an irregular cavity in the 

 temporal bone. Its essential part is composed of a 

 membranous sac which is filled with a liquid called 

 endolymph. In this liquid are tiny stones, otoliths. The 

 first part of the inner ear is called the vestibule. To the 

 vestibule on one side is attached the cochlea in which 



