THE TYMPANUM. 



63a 



by skin and mnoous membrane. It is here that apertures are liable to 

 become formed in the membrane as a consequence of inflammation. 



The membrane is suiiplied -nath blood-vessels, but they are chiefly con- 

 fined to the skin and mucous membrane covering the surfaces ; a few are, 

 however, found in the proper fibrous membrane, and form a communication 

 between the two systems above named. Those of the skin are mostly sup- 

 plied by a small artery which passes from above parallel to and along the handle 

 of the malleus. Tlie nei'ves for the most part accompany the blood-vessels, 

 sui^plying them and then passing to f oiin a subepithelial plexus both in the cutis 

 and in the mucosa. Lj-mphatic vessels are, according to Kessel, tolerably 

 abundant in all three layers. 



The inner wall of the tympanum, which separates it from the internal 

 ear, is A'ery uneven, presenting several elevations and Ibramina. Near 

 its upper part is an ovoid, or nearly kidney-shaped o^tTimg— fenestra 

 ovaJis (fig. 44C, 2), which leads into the cavity of the vestibule. This 

 opening, the long diameter of which is from before backwards, with a 

 slight inclination downwards in front, is occupied in the recent state 

 by the base of the stapes, and the annular ligament connected with 

 that plate of bone. Above the fenestra ovalis, and between it and 

 the roof of the tympanum, a ridge indicates the position of the aque- 

 duct of Fallopius, as it passes backwardSj containing the portio dura 

 of the seventh nerve. Below is a larger and more rounded elevation, 

 caused by the projection outwards of the first turn of the cochlea, and 

 named the promontorji. or tuber cochlefB (fig. 446, 4) ; it is marked by 

 grooves, in which lie the nerves of the tympanic plexus. 



Fig. 446. 



Fig. 446. — Inner Wall op the Osseous TyMPANrsi as exposed by a Longitudinal 

 Sectiok of the Petkous and Mastoid Bone (from Gordon). 



1, opening of the t}inpanum into the mastoid cells ; 2, fenestra ovalis ; 3, fenestra 

 rotunda ; 4, promontory ; 5, aqueduct of Fallopius, or canal of the facial nerve ; 6, 

 junction of the canal for the chorda tympani with the aqueduct; 7, processus cochleari- 

 formis ; 8, groove above it for the tensor tjTnpani muscle ; 9, Eustachian tube j 10, 

 anterior orifice of the carotid canal. 



Below and behind the promontory, and somewhat hidden by it, is a 

 slightly oval aperture named fenestra rotunda, which lies within a 

 funnel-shaped depression (fig. 446, 3). In the macerated and dried 

 bone the fenestra rotunda opens into the scala tympani of the cochlea ; 

 but, in the recent state, it is closed by a thin membrane. 



