THE SENSES 



155 



middle ear pass on the vibrations of air to the ends of the 

 fibers of the auditory nerve in the internal ear. 



The external ear consists of a large wrinkled cartilage 

 on the exterior of the head and a canal leading from it, 

 called the meatus. This passage is closed at its inner end 

 by the drum membrane or drum skin. It is often called 

 the drum, but this name is properly applied to the whole 

 middle ear. A trial will show that the drum skin cannot 



The Ha-mmer 

 (Malleus). 



The 



Shell Tube 

 (Cochlea). 



Eustachian Tube 

 FIG. 128. MIDDLE AND INTERNAL EAR (greatly enlarged). 



be seen even with the aid of a bright light, for the passage 

 is slightly curved (see Fig. 128). Hence a missile or a 

 flying insect cannot go straight against the ear drum. The 

 skin lining this passage contains wax glands, which secrete 

 a bitter sticky wax, which helps to keep the passage flex- 

 ible. This wax catches dust and usually stops insects that 

 may enter. If an insect enters the ear, it may often be 

 coaxed out by a bright light held close to the ear. The 

 ear wax in a healthy ear dries with dust and scales of epi- 

 dermis and falls out in flakes, thus cleansing the ear. It 



