THE EAR 



369 



magnified) is shown in Figure 185. This is called the organ 

 of Corti, and in it are the endings of the auditory nerve fibres. 

 It is the real organ of hearing, just as the retina is the organ 

 of sight. The manner 

 in which it is affected 

 by sound is not fully 

 known, but it is prob- 

 ably something as 

 follows : 



Sound is produced 

 by vibrations or waves 

 of the air. When 

 waves reach the body 

 they pass into the 



FIG. 184. DIAGRAM 



Showing the relation of the cochlea (uncoiled) tc 

 the vestibule and other parts of the ear. 



external auditory meatus until they come against the tympanic 

 membrane or drum. As the waves fall upon this they set it to 

 moving at the rate at which they strike it. This movement of 

 the drum will evidently be transmitted to the ear bones attached 



, Hair cells 



FIG. 185. SECTION OF THE ORGAN OF CORTI 



Highly magnified. Showing the real hearing part of the ear. (Retzius) 



to it and by their motion the end of the stapes is pulled back 

 and forth in the foramen ovale. This motion will in turn 

 produce a similar set of little waves in the liquids of the in- 

 ternal ear, with the result that the whole mass of liquid will 

 vibrate just as rapidly as the air outside the head. As a re- 



