1322 



THE TYMPANUM. 



[BOOK in. 



the upper front part of the tympanum obliquely forwards, down- 

 wards and towards the median plane of the head into the pharynx. 

 The former continues the upper hind part of the tympanum 

 upwards, backwards and away from the median line of the head, 

 first as an irregular space, sometimes called the "epitympanic 

 region," and then farther backwards as a larger space, the antrum 

 mastoideum (Fig. 166 A), which in turn communicates with the 

 labyrinth of spaces or " air cells " of the mastoid bone. 



Igs 



-ch.t 



FIG. 167. DIAGRAM OF THE ODTEB WALL OF THE TYMPANUM (RIGHT EAR) AS SEEN 

 FROM THE MESIAL SIDE. Magnified twice. (After Schwalbe.) 



m.t. membrana tympani. mb. handle of M the malleus. I. the incus. E. t. 

 Eustachian tube. T. T. tensor tympani, the tendon of which is seen attached to 

 the upper part of the handle of the malleus. Iff. a. the anterior and Ig. s. the 

 superior ligament of the malleus, cli. t. the chorda tympani nerve traversing 

 the tympanic cavity. 



The ossicles are placed more or less vertically but yet obliquely 

 in the tympanic cavity in such a way that the heads and bodies of 

 the malleus and incus lie above the tympanum proper in the epi- 

 tympanic region (Fig. 167), but the handle of the malleus and 

 the shaft of the incus descend to the centre of the tympanum. 

 Opposite but rather above this centre is seen in the median wall 

 of the tympanum a funnel-shaped depression (Figs. 166, 168/ o.) 

 at the bottom of which lies the fenestra ovalis ; and to this the 

 stapes, horizontal but slightly inclined upwards, passes from the 

 end of the shaft of the incus. 



In the lower part of the median wall, some distance below the 

 fenestra ovalis, is seen an irregular depression (Fig. 166 f.r.) which 

 leads to the fenestra rotunda; and by the side and above this, 

 occupying the central portion of the median wall of the tympanum 

 proper is a projection marking the position of the first whorl 

 or base of the cochlea. The fenestra ovalis itself marks the 

 position of the junction of the utricle and saccule, and in the epi- 

 tympanic region, above a rounded ridge caused by the projection of 



