THE MIDDLE EAR. 



42-3 



aperture (iter chorda posterius) is about the centre of the 

 angle between the outer and posterior walls of the tym- 

 panum ; it leads into a canal, which terminates in the 

 aquasductus Fallopii, and serves for the entrance of the 

 chorda tympani into the tympanic cavity. 



The anterior aperture (iter chorda anterius) opens 

 above and in front of the ring of bone, for the attachment 

 of the tympanic membrane ; it leads into a fine canal 

 (Huguier), which runs parallel with the Glaserian fissure ; 

 through it the chorda tympani leaves the tympanum. 



The Glaserian fis- 

 sure, continued from 

 the glenoid fossa, opens 

 just below the anterior 

 aperture for the chorda 

 tympani ; it lodges the 

 long process of the 

 malleus, and transmits 

 the laxator tympani 

 muscle. The inner 

 wall of the tympanum 



presents the OVal Win- FlG - 185 - DIAGRAM OF THE EXTERNAL SUR- 



FACE OF THE LEFT TYMPANIC MEM- 



dow, the round win- 



j 1-1 



U.OW, tile 





a, head of the malleus : b. metis ; e, joint between mal- 

 leus and incus ; between c and d is the flaccid portion of 

 the membrane: ax. axis of rotation of ossicles. The deeply- 

 shaded central portion is called the " umbo." 



the pyramid, the open- 

 ing for the stapedius, and the ridge formed by the 

 aquaeductus Fallopii. The oval window (fenestra ovalis) 

 leads from the tympanum into the vestibule ; it is closed 

 by the lining membrane of the tympanum and vestibule, 

 and has applied to it the base of the stapes. The round 

 window (fenestra rotunda), a nearly circular opening 

 below and behind the fenestra ovalis ; it is placed at the 

 bottom of a depression, and communicates with the 

 cochlea ; it is closed by Scarpa's membrane (membrana 



