264 



Life and Health 



As a whole, it may be considered a peculiar form of nerve 

 ending. 



The external ear forms only a part of a most elaborate 

 apparatus whereby sound waves may be transmitted inward 

 to the real organ of hearing. The really sensitive part of 

 the ear, in which the auditory nerve ends, is buried for 

 protection so deep in the bones of the head that sounds 



cannot directly affect it. 

 Some arrangement, there- 

 fore, is required for con- 

 ducting the sounds inward 

 to this organ. 



In studying the structure 

 of the ear we may divide it, 

 for convenience, into three 

 parts : the external ear, the 

 middle ear, and the deeply 

 placed portion, the inner 

 ear. 



414. The External Ear. 

 The external ear consists of 



FIG. 139. The Pinna, or Auricle. 



an expanded portion known 

 as the pinna, or auricle, and 

 of a passage, the auditory canal, or meatus, leading inward 

 from it. The surface of the auricle is convoluted to collect 

 and transmit the vibrations of air by which sound is pro- 

 duced. Many animals move the auricle in the direction 

 of the sound. Thus the horse pricks up its ears when 

 it hears a noise, the better to judge of the direction of 

 sounds. 1 



1 The student who will take a little trouble in noticing the ears of the 

 persons whom he meets from day to day will be greatly interested and sur- 

 prised to see how much the auricle varies. 



