798 HEARING, SMELL, AND TASTE. 



by the meatus. It has, moreover, this useful feature, that unlike other 

 stretched membranes, it has no marked note of its own. It is not thrown 

 into vibrations by waves of a particular length more readily than by others. 

 It answers equally well within a considerable range to vibrations, of very 

 different wave-lengths. Had it a fundamental tone of its own, we should 

 be distracted by the prominence of this note in most of the sounds we hear. 

 When sounds impinge on the solids of the head, as when a watch is held 

 between the teeth, the membrana tympaui is still functional. Vibrations are 

 conveyed from the temporal bone to it and hence pass in the usual way, in 

 addition to those transmitted directly from the bone to the perilymph. 



708. The auditory ossicles. The malleus, the handle of which de- 

 scending forward and inward, is attached to the membrana tympani, and the 

 incus, whose long process is connected by means of its os orbiculare or len- 

 ticular process and the stapes to the fenestra ovalis, form together a body 

 which rotates round an axis, passing through the short process of the incus, 

 the bodies of the incus and malleus, and the processus gracilis of the malleus. 

 [Fig. 194.] When the malleus is carried inward, the incus moves inward 



[FlG. 194. 



M.- 



The Ossicles in Position. Magnified four times. (After Hensen.) The figure represents a sec- 

 tion through tympanum in the line of the long axis of the malleus and incus ; the short process 

 of the incus, p'b', has been cut through. 



T.C, the tympanic cavity ; mbr, handle of malleus ; u, umbo ; p.b, short process of the malleus 

 shown in dotted outline as pushing outward the membrana flaccida; T.I, the attachment of the 

 tendon of the tensor tympani ; Ig, the attachment of the external ligament of the malleus ; Ig.s, 

 the superior ligament of the malleus ; t.t, the teeth of the incus ; p'l. the long process shaft of the 

 incus ; St, the stapes.] 



too, and when the malleus returns to its position, the incus returns with it, 

 the peculiar saddle-shaped joint with its catch-teeth permitting this move- 

 ment readily, but preventing the stapes being pulled back when the mem- 

 brana tympani with the malleus is for any reason pushed outward more 

 than usual ; the joint then gapes, so as to permit the malleus to be moved 

 alone. Various ligaments, the superior or suspensory, anterior, and external, 

 also serve to keep the malleus in place. The whole series of ossicles may 

 be regarded as a single-armed lever, moving on the ligamental attachment 

 of the short process of the incus to the posterior wall of the tympanum, the 

 weight being brought to bear at the end of the long process of the incus, 

 and the power at the end of the handle of the malleus. The long, malleal 



