388 



PHYSIOLOGY AND HEALTH. 



910. TJie human ear, in its natural condition, stands out 

 from the head at a considerable angle. This position gives 

 it the greatest advantage for catching sounds. Uut the cus- 

 tom of wearing caps and other head dresses, and the manner 

 of dressing the hair, press the ear near, and in some persons 

 close to, the head, and thus diminish their acuteness of 

 hearing. 



911. The entire external ear stands open for the reception 

 of sounds ; but when any of its parts, or the whole, is covered 

 with the hair or any dresses, the access of sound is obstructed, 

 and the hearing somewhat impaired. 



Fm. LXIX. Ear. 



a, a, External Ear. 



5, Opening to the internal ear. 



c, Canal leading to the drum. 



d, Membrane of the tympanum. 



e, Semicircular canals. 

 /, Snail-shell, or cochlea. 



912. The external canal or meatus, (Fig. LXIX. c,) opens 

 from the external to the internal ear. It is about an inch 

 long. Its course is not straight nor direct, but somewhat for- 

 ward and curved. There are many little cells in its lining, 

 in which the ear-wax is prepared. There are, also, hairs 

 about this canal. The wax and the hairs protect this canal 

 from the entrance of insects. 



The ear-wax is sometimes secreted in so great quantity as 

 to fill the canal, and prevent the access of sound. 



913. The membrane of the tympanum, or covering of the 

 drum of the car, is spread across the bottom of the canal and 



