Page:First course in biology (IA firstcourseinbio00bailrich).pdf/623

 middle ear pass on the vibrations of air to the ends of the fibers of the auditory nerve in the internal ear.

(greatly enlarged).

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