302 



SPEAKING AND HEARING 



tions which reach it ; and yet when the sound wave meets 

 the nerves, the nerves single out each individual element, 

 and convey to the mind of the hearer, not only the tones and 

 notes of every instrument in the orchestra, but the character 

 of every accidental noise ; and almost as distinctly as if each 

 single tone or noise were heard alone." POLE. 



277. The Structure of the Ear. The external portion of 

 the ear acts as a funnel for catching sound waves and leading 

 them into the canal, where they strike upon the ear drum, 



FIG. 194. The ear. 



or tympanic membrane, and throw it into vibration. Unless 

 the ear drum is very flexible there cannot be perfect response 

 to the sound waves which fall upon it ; for this reason, the 

 glands of the canal secrete a wax which moistens the mem- 

 brane and keeps it flexible. Lying directly back of the 

 tympanic membrane is a cavity filled with air which enters 

 by the Eustachian tube ; from the throat air enters the Eusta- 

 chian tube, moves along it, and passes into the ear cavity. 

 The dull crackling noise noticed in the ear when one swallows 



