THE SENSE O?^ HEARING 157 



ontvvards and downwards, tli handle of th" malleus, on the other hand, and the 

 long process of the incus describe an ar- inwards and upwards, and consequently 

 till' stapes fixed at the end of this long process is pressed more deeply into the 

 oval window of the labyrinth If the membrane of the tympanum bends out- 

 wards with the receding wave, the preceduig movements are reversed, the part 

 of thi' apparatus abov.' th" axis turns inwards and upwards, the part below the 

 axis outwards and downwards, so that the base of the stapes is proportionably 

 withdrawn from the oval opening These changes of direction, alternating in 

 rapid succession, produce undulations in the fluid of the labyrinth, of which we 

 shall pi'esentl}' have occasion to speak. 



We should by no means think of the described movements of this system of 

 ossicles as being of any considei'able extent ; on the contraiy, the displacements 

 undergone by its several parts from the appulse of even the stiongest waves upon 

 the tympaiium are excessively slight ; indeed, we meet with certain arrangements 

 in the apparatus which are evidently calculated to restrict the extent of these 

 movements. This end is subserved, especially, by the ligamentous fastenings of 

 th'- axis of movement and of the base of the stapes. Were it intended that the 

 malleus and incus should follow, freely and unimpeded, the most extreme flex- 

 ions, inwards and outwards, which the membrane of the tympanum might exe- 

 cute under the influence of the air-waves, the ends of the axis must have been 

 inserted, like those of an axletree, in sockets which oppose no resistance except 

 that arising fi-om friction. But the ends of the axis in question are tightly secured 

 by tense ligatures, which are twisted by every turn of the axis, and by virtue of 

 their elasticity offer the more resistance the greater the torsion. In like manner 

 a resistance is opposed to the movements of the apparatus by the nature of the 

 ligature which unites the base of the stapes with the fenestra! opening ; the small 

 membranous border, before described, very quickly arrests by its tension the intro- 

 mission and retreat of the foot-plate. It is apparent, also, that the resistance 

 thus offered restricts the oscillations of the tympanum itself, causing them to be 

 of less extent than they would be, under an equal force of the aii-- waves, were 

 the membrane not united with the ossicles. The object of this restriction is 

 easily conjectured. Though we know not what force of the atmospberi.- undu- 

 lations can be borne by the extremities of the nerves suspended ni the fluid of 

 the labyrinth, yet we may well infer that they would be injuriously aflected by a 

 very violent shock, as the nerve of sight is dazzled by too inten:!c an undulation 

 of the luminous ether. As in the eye protective arrangements are met with which 

 in a certain degree shield the optic nerve from too strong an impression of the 

 light, an analogous intention may, with the greatest probabdity, be ascribed to 

 the adjustments which in the small bones of the tympanum act in restraint of 

 their movements. This pi-obability almost becomes certainty when we take into 

 view a further arrangement of this apparatus, for which scarcely any other object 

 can be imagined than to prevent t jo violent a percussion of the fluid of the laby- 

 rinth. This arrangement we will now examine somewhat more closely. 



Wherefoi-e do we find, in place of an inflexible lever, consisting of one piece, 

 such as is supposed in our representation of the general scheme of operations, and 

 as would have fulfilled all the conditions of those operations, an apfiaratus com- 

 posed of two separate parts, malleus and incus, connected with one another by a 

 species of hinge. What are the kind of m ovr-mt-nts for which this liinge is des- 

 tined, and what is the signification of this mobility ? Why, again, is the stapes 

 a separate bone ? To be able to answer these questions, we cannot dispense with 

 bringing to the notice of our reader the existence and mechanical reliuons of two 

 small muscles, evidently destined for the movement of these bones of the ear, 

 one of them pertaining to the malleus, the other to the stapes. The first is the 

 more important ; it springs from about the middle of the skull, passes with 

 its soft and somewhat long fasciculus of fibres, in a channel of its own, to the 

 cavity of the tympanum, into which it penetrates, with its tendinous end, 



