200 



PHYSIOLOGY 



CHAP. 



The chain of ossicles consisting of the malleus, incus, and 



stapes (Fig. 77) makes the ana- 

 tomical connection between the 

 membrana tympani and the fenestra 

 ovalis, and forms a single apparatus 

 for receiving the aerial vibrations 

 and transmitting them to the fluid 

 of the labyrinth. 



The handle (manubrium) of the 

 malleus is firmly united by fibrous 

 tissue to the tympanic membrane 

 (Fig. 78). This ossicle is further 

 fixed by two ligaments, one anterior, 



FIG. 77. -The chain of auditory ossicles, the other posterior, which confine 



^ movements, and ^ only permit it 



to make slight CXCUrSlOllS from Wlth- 



- 



ma 



articulating with incus ; c., cervix ; 



pr.gr., processus gracilis or lateralis, , . . .-, 1 ., 



out inwards in an axis through its 



neck, so that when the handle faces 

 inwards its head moves in the 



partially converted in adults into liga- 

 ment; /., incus, forming an amphi- 

 arthrosis with head of malleus; co., 

 body; pr.br., processus brevis ; pr.l., 

 processus longus capped by the lenti- . _ . 



cular process ; pr.len., for articulation Opposite direction. 



with head of stapes; S., stapes with mi * 4.4. i^ j 4. 4.1^ 



cavity for articulation, a short neck, I he lUCUS IS attached to the 



fCTestra r ovalis d a base fitting int the tympanic cavity by a ligament in- 

 serted on to its short process. It 



articulates with the head of the malleus by a saddle-joint, with a 

 very thick fibrous capsule. At the 

 lower edge of its articular head 

 the malleus forms a kind of spur 

 which, when the manubrium moves 

 forward, makes with the incus a 

 single, rigid piece, called by Weber 

 the angular lever, which moves 

 round the common axis formed by 

 the ligaments of the malleus. The 

 rotation of the two ossicles round 

 this axis takes place in a plane 

 vertical to that of the membrana 

 tympani. As the long process of 

 the incus is about J shorter than 

 the handle of the malleus the ex- 

 cursions of its end must be corre- 

 spondingly smaller and more 

 powerful. 



The stapes is attached by an 

 almost rigid articulation to the 

 tip of the lenticular process of the 

 incus, so that the excursions of the latter are transmitted to the 

 fenestra ovalis, with which the stapes is connected. The excur- 



ma. 



FlG - ? 



Membrana tympani attached to 

 malleus viewed from the inner surface. 

 (Nagel.) 1, Chorda tympani passing 

 through tympanic cavity ; 2, Bustachian 

 tube ; 3, insertion of tendon of tensor 

 tympani ; s.t.p., spina tympanica posterior ; 

 pr.br., short process of malleus; l.m.a., 

 anterior ligament of malleus; ca., head ; 

 ma., manubrium adherent to membrana 

 tympani. 





