606 ANIMAL PHYSIOLOGY. 
The external ear in man being practically immovable, owing 
to the feeble development of its muscles, has, as compared with 
such animals as the horse or cow, but little use as a collecting 
organ for the vibrations of the air. The meatus or auditory 
canal may be regarded both as a conductor of vibrations and 
as protective to the middle ear, especially the delicate drum- 
head, since it is provided with hairs externally in particular, 
and with glands that secrete a bitter substance of an unctuous 
nature. 
The Membrana Tympani is concavo-convex in form, and, hay- 
ing attached to it the chain of bones shortly to be noticed, is 
well adapted to take up the vibrations communicated to it from 
the air; though it also enters into sympathetic vibration when 
Fig. 446.—Photographic representation of right membrana tympani, viewed from within 
(after Flint and Riidinger). 1, divided head of malleus; 2, neck ; 3, handie with attach- 
ment of tendon of tensor tympani; 4, divided tendon; 5, 6, long handle of malieus ; % 
outer radiating and inner circular fibers of tympanic membrane; 8, fibrous ring encircling 
membrana tympani; 9, 14, 15, dentated fibers of Gruber ; 10, 11, posterior pocket connect- 
ing with malleus ; 12, anterior pocket ; 13, chorda tympani nerve. 2 
the bones of the head are the medium, as when a tuning-fork 
is held between the teeth. Ordinary stretched membranes 
