THE SENSE OF HEARING 



409 



it is attached. This process draws the membrane 

 inward, making its outer surface concave and its 

 inner convex. Externally, the membrane is covered 

 with skin, continuous with that of the meatus; inter- 

 nally, with mucous membrane continuous with that 

 of the tympanum; and between these two is a fibrous 

 layer, some of its fibers radiating from the handle 

 of the malleus, others being circular and placed near 

 the circumference. 



FIG. 143 



Chorda tympani. 



View of inner wall of tympanum. (Gray.) 



The inner wall of the tympanum is vertical and 

 uneven. It presents the following: (a) The fenestra 

 ovalis, leading into the vestibule, and occupied in the 

 recent state by the base of the stapes and its annular 

 ligament. (b) Fenestra rotunda, in a conical fossa 

 leading into the cochlea, a rounded eminence, (c) The 

 promontory, separating it from the preceding. It is 

 closed, in the recent state, by the membrana tympani 

 secundaria. This is composed of three layers, and is 

 concave toward the tympanum. 



