THE EAR 



389 



handle of the malleus, others being circular and placed near 

 the circumference. At the anterosuperior part of the membrane 

 is a notch in the bony ring, the notch of Rivini. That part 

 of the membrane occupying it is called the membrana flaccida. 

 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. (6) 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 



FIG. 69 



Chorda tympani 



View of inner wall of tympanum. (Gray.) 



secundaria. This is composed of three layers, and is concave 

 toward the tympanum. The middle layer is fibrous, the outer 

 and inner being continuous with the lining membrane of the 

 two cavities. The promontory indicates the first turn of the 

 cochlea, and is grooved for branches of the tympanic plexus. 

 (d) The ridge of the aquceductus Fallopii, running above the 

 fenestra ovalis and descending on the posterior wall, (e) 

 The pyramid, a hollow eminence containing the stapedius, 

 the tendon of the muscle escaping through a foramen in its 

 summit. A minute canal containing the nerve to this muscle 

 runs from the aquseductus Fallopii to the cavity of the pyramid. 



