158 ON THE SENSES. 



opposite to the tympanic membrane. The tendon goes obliquely through the 

 cavity, and is attached, at a right angle, to the handle of the malleus, near the 

 turning point. We must suppose it to be known what a muscle is, and shall 

 therefore only observe that every muscle has the power of contracting under 

 a certain influence of the nerves, by which means a thickening takes place in 

 the body of the muscle, and its two ends are brought nearer to one another. 

 When the muscle in question, the so-called tensor tympani, contracts at the 

 excitation of its nerve, it tends, since its interior point of origin is immovably 

 fixed, to draw its exterior point of insertion, and consequently the handle of 

 the malleus, inwards. But the malleus alone cannot freely follow this traction, 

 first, because it is itself fastened by its long projection to the wall of the cavity 

 of the tympanum ; secondly, because it is inserted between the coats of the 

 tympanic membrane ; thirdly, because it is connected by articulation with the 

 incus. It is not easy to determine with certainty in what manner this resistance 

 modifies the displacement of the malleus by the muscular traction. Were the 

 malleus and incus united in one piece, the operation of the muscle could be no 

 other than that of a condensed wave of air coming from without ; it would turn 

 the lever apparatus in such manner on the above described transverse axis, that 

 the handle of the malleus and the longer process of the incus would move in- 

 wards and upwards, and the stapes be thereby pressed deeper into the fenestra 

 ovaiis, while the membrane of the tympanum united to the handle must also 

 comply with the traction, be drawn further inwards, and consequently rendered 

 more tense. This is, in fact, the muscular effect which is genei'ally recognized, 

 and has procured for the muscle its name of "tensor tympani." There are cir- 

 cumstances, however, which justify hesitation in admitting that in this simple 

 way everything is explained. The muscle is relatively very long and its tendon 

 attached so near the turning-point of the malleus, that if, through the contrac- 

 tion, it were shortened by a very small part of its length, the result would be 

 a comparatively very large introversion of the malleus. Now, the membrane 

 of the tympanum might indeed, under strong tension, follow with the malleus 

 the traction of the muscle to a considerable extent ; but not so the incus, be- 

 cause the penetration of the stapes into i\iQ finestra ovalis would encounter in- 

 superable resistance, partly in the ligature of the foot-plate by the narrow bor- 

 der, partly in the fluid which can only yield so far as the opposed opening of 

 the labyrinth, the so-called _/e;?es<ra rotunda, permits. Hence a forcible pres- 

 sure of the stapes would render the propagation of the sound-producing move- 

 ment wholly impossible, since no condensed wave would be capable of driving 

 it more deeply inwards, no rarefied wave could move it outwards against the 

 traction of the muscle. The length of the fibres of the muscle shows, on the 

 other hand, that the magnitude of the movement for which it is intended can be 

 no such very slight one, for, throughout our body, the length of the muscular 

 fibres is found to be in direct proportion to the extent of the movement to be 

 accomplished by them. The supposition is therefore forced upon us that the. 

 muscle in question can move the malleus alone to a certain extent, without any 

 proportionable movement of the incus ; that the malleus, while, with the mem- 

 brane of the tympanum, it obeys the traction of the muscle, is pressed more 

 firmly against the incus and into the joint which connects both. This hypoth- 

 esis is the more plausible, because by this alone is explained the presence of the 

 articulation, for which there would otherwise be no apparent reason. We must 

 unfortunately renounce the design of laying before the reader proof of the cor- 

 rectness of the hypothesis drawn from the structure of the articulation, the di- 

 rection of the muscular traction, &c., for the discussion of these extremely subtle 

 relations would be impossible without the employment of preparations from 

 nature, and would perhaps even then leave the matter in doubt. We can there- 

 fore only trust to the reader's faith when we allege that the tensor muscle, in 

 contracting, draws the malleus somewhat inward, thereby occasioning greater 



