INNER WALL OF TYMPANUM. 83 



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 on 

 the surfaces. Those of the skin are mostly supplied by a small artery, derived from 

 the deep auricular branch of the internal maxillary, which passes from above 

 parallel to and along the handle of the malleus. The nerves for the most part 

 accompany the blood-vessels, first supplying these and then forming a plexus both 

 in the cutis and in the mucosa. They are derived, for the upper and greater part of 

 the membrane, from the auriculo-temporal ; for the lowermost part, according to 

 Sappey, from the auricular branch of the vagus. For the mucosa they come from 

 the plexus tympanicus. Lymphatic vessels are, according to Kessel, tolerably 

 abundant in all three layers. 



The inner wall of the tympanum (fig. 1);3, A & B), which separates it from the 

 internal ear, is very uneven. Near its upper part is an ovoid, or nearly kidney- 



membrana flaccida posterior ligament 



anterior ligament 



long process of incus 



end of manubrium of malleus 



Fig. 92. MEMBRANA TYMPANI, AS SEEN WITH THE OTOSCOPE. (Hensiuan.) 



shaped opening -fenestra ovalis, which leads into the cavity of the vestibule. This 

 opening, which is elongated from before backwards, with a slight inclination down- 

 wards in front, is occupied in the recent state by the base of the stapes and the 

 annular ligament connected with that plate of bone. It measures 3 mm. by 1 \ mm., 

 and lies at the bottom of a depression (fossula ovalis), which is bounded by the bony 

 prominences immediately to be mentioned. Above the fenestra ovalis, and between 

 it and the roof of the tympanum, a ridge indicates the position of the aqueduct of 

 Fallopius (aF), as it passes backwards, containing the facial nerve. Below is a 

 larger and more rounded elevation, caused by the projection outwards of the first 

 turn of the cochlea, and named the promontory, or tuber cochtece ; its surface is 

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



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

 aperture named fenestra rotunda, T5 mm. to 2 mm. in diameter, which lies within 

 a funnel-shaped depression (fossula rotunda). 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. 



The membrane closing the fenestra rotunda secondary membrane of the tympanum 

 (Scarpa) is rather concave towards the tympanic cavity and convex to the scala 

 tympani, and, like the membrana tympani, is composed of three structures, the 

 middle being fibrous, and the outer and inner derived from the membranes lining 

 the cavities between which it interposed, viz., the tympanum and the cochlea. The 



G 2 



