192 CONDUCTION THROUGH TYMPANUM. [BOOK in. 



very large range. It probably has a fundamental tone of its own, 

 but this is kept in the background ; it is not prominent, and does 

 not materially influence our hearing. Were it otherwise, were the 

 tympanic membrane thrown into vibration much more readily by 

 a particular sound than by any others, that sound would be domi- 

 nant in all our hearing ; and unless, as in vision, psychical ex- 

 perience intervened to correct the mere sensation, we should be 

 misled in our judgments as to what was taking place around us. 



This general usefulness of the tympanic membrane is secured 

 partly by features proper to itself, partly by the fact that it is 

 ' damped ' by the attachment to it of the chain of ossicles. Without 

 attempting to enter into a discussion of a matter which is in many 

 ways complex, we may say that the following features contribute 

 to make the tympanic membrane sensitive to a large variety of 

 sounds. In the first place its dimensions are relatively small. In 

 the second place the material of which it is composed is peculiar, 

 so that it is in a special way unyielding and rigid ; it retains its 

 form when cut away from its bony attachments by a circular 

 incision, and the malleus, including its handle, may be removed 

 from it without distorting it. In the third place, its remarkable 

 form, that of a shallow funnel with sides gently convex towards 

 the meatus, Jias a marked effect upon its capabilities of vibration. 

 The chain of ossicles, attached at its far end, to the membrane of 

 the fenestra ovalis has a ' damping ' effect similar to that, familiar 

 to every one, of lessening or stopping the sound of a vibrating 

 empty wine-glass or tumbler by pressing the finger on it; and 

 this 'damping' while it diminishes to a certain extent all the 

 vibrations of the membrane is especially effective in the case of 

 excessive vibrations, such as those which might be produced by 

 the sound which is the fundamental note of the membrane. 



817. The vibrations thus set going in the tympanic 

 membrane are transmitted from it to the chain of ossicles. The 

 transmission might take place in two ways. In the first place the 

 vibrations, the alternate bendings inwards and outwards of the 

 membrane, might, by carrying with it the attached handle of the 

 malleus, work the chain of ossicles . as a lever, in the manner 

 described in 815, so that each inward flexion of the tympanic 

 membrane led to the membrane of the fenestra ovalis pushing the 

 perilymph of the labyrinth inwards, while the return outwards 

 again of the one led to a like return of the other. In the second 

 place the transversal vibrations of the tympanic membrane might 

 set up longitudinal vibrations in the substance of the malleus, 

 which would travel as longitudinal vibrations through the chain, 

 and so reach the perilymph. In the one case the whole chain of 

 ossicles swings to and fro, in the other case the sound is propagated 

 by molecular movement. That the ossicles do move en masse has 

 been proved by recording their movements in the usual graphic 

 method. A very light style attached to the end of the incus or to 



