USES OF DRUM-MEMBRANE. 551 



vibration; if they do not push the membrane at the 

 proper times, their effects will neutralize one another: hence 

 -such membranes respond well to only one note. The tym- 

 panic membrane, however, responds equally well to a large 

 number of notes; at the least for those due to aerial vibra- 

 tions of rates from 60 to 4000 per second, running over 

 eight octaves and constituting those commonly used in 

 music. This faculty depends on two things; (1) the mem- 

 brane is comparatively loosely and not uniformly stretched; 

 (2) it is loaded by the tympanic bones. 



The drumVmembrane is (p. 536) in the form of a shallow 

 iunnel with its sides convex towards its cavity; in such a 

 membrane the tension is not uniform but increases towards 

 the centre, and! it has accordingly no proper note of its own. 

 Further, whatever tendency such a membrane may have 

 to vibrate rather at one rate than another, is almost com- 

 pletely removed by "damping" it; i. e. placing in contact 

 with it something comparatively heavy and which has to 

 be moved when the membrane vibrates. This is effected 

 by the tympanic bones, fixed to the drum-membrane by the 

 Jhandle of the malleus. Another advantage is gained by the 

 damping; once a stretched membrane is set vibrating it 

 continues so doing for some time; but if loaded its move- 

 ments cease almost as soon as the moving impulses. The 

 dampers of a piano are for this purpose; and violin- 

 players have to "damp" with the fingers the strings they 

 iave used when they wish the note to cease. The tym- 

 panic bones act as dampers. 



Functions of the Auditory Ossicles. When the air in 

 the external auditory meatus is condensed it pushes in the 

 handle of the malleus. This bone then slightly rotates on 

 the axial ligament (p. 537) and, locking into the incus 

 where the two bones articulate, causes the long process (//, 

 Fig. 144) of the latter to move inwards. The incus thus 

 pushes in the stapes; the reverse occurs when air in the 

 auditory passage is rarefied. Aerial vibrations thus set the 

 chain of bones swinging, and push in and pull out the 

 base of the stapes, which sets up waves in the perilymph of 

 the labyrinth, and these are transmitted through the mem- 



