414 THE NERVES AND THE SENSE ORGANS 



the pharynx, or throat (c/. 361) by the Eustachian 

 (u-stak'-e-an) tube. This tube allows the air to press on 

 the inside of the tympanic membrane, and to balance the 

 pressure of the air in the auditory canal. Otherwise a 

 sudden change in the outside air pressure might burst 

 the tympanic membrane. When cannon are being fired, 

 persons standing near are instructed to hold their 

 mouths open, so that the air shock on the inner side of 

 the membrane may be equal to that on the outer side. 



The outer ear gathers the sound waves, and the middle 

 ear passes the vibrations on to the inner ear, the real 

 organ of hearing. The inner ear is filled with liquids. 

 It is separated from the middle ear by a membrane; to 

 this membrane the last bone of the middle ear is attached. 

 As the membrane is made to vibrate, it gives its motion 

 to the liquids of the inner ear. The vestibule is the 

 first chamber of the inner ear. The cochlea (kok'-le-a) 

 is like a snail shell, and this fact gave it its name. It is 

 the part of the ear that contains the fibers of the auditory 

 nerve. 



Besides the cochlea and vestibule, the inner ear contains the semi- 

 circular canals. These are not part of the hearing apparatus, but 

 they are probably organs that tell the brain in what direction the body 

 is leaning, and so help in keeping the body balanced. 



The ears should be cared for intelligently. Sharp objects should 

 not be put into them, and they should never be pulled or " boxed," for 

 fear that the "drum head" may be burst. The earwax is intended 

 to keep insects out of the ear, and should not ordinarily be removed 

 until it comes out of the auditory canal. Clean warm water will 

 remove earwax better than anything else. An unusually large secre- 

 tion of earwax sometimes causes dull hearing and deafness, but no one 

 except a physician ought to try to remedy the trouble. 



