554 



THE AUDITORY APPARATUS 



membrana flaccida, in the form of two bands, called respec- 

 tively the anterior and posterior tympano-malleolar folds. 



The membrana tympani is composed of three layers viz., 

 an external cuticular layer, an intermediate fibrous lamina, 

 and an internal mucous layer. The handle of the malleus is 

 intimately connected with the fibrous layer, and is covered 

 medially by the mucous layer. It draws the membrane 

 towards the tympanic cavity, and is the cause of the concavity 

 on the outer surface. The deepest point of this concavity 



Tympanic antrum 

 Recessus epitympanicus 



Canalis facialis 

 Tegmen tympani 



Fenestra vestibuli 



Canal for 

 tensor tympanP 



Processes 

 cochleariformis 



Promontory 



Auditory tube 



Foramen for 

 tympanic nerve 



Pyramid 



Fenestra cochleje 



Course of canalis facialis 



FIG. 238. Vertical section through the Left Ear : postero-medial half 

 of section viewed from the front. (Howden. ) 



corresponds with the flattened extremity of the handle of 

 the malleus, and is termed the umbo. 



In examining the living ear, with a speculum, the surface of the mem- 

 brane appears highly polished, and a cone of light extends downwards 

 and forwards from the tip of the handle of the malleus. A pair of striae 

 (Prussak's striae), which correspond to the anterior and posterior tympano- 

 malleolar folds, extend from the processus lateralis of the malleus to the 

 margins of the notch of Rivinus, and thus map out the membrana flaccida. 

 The long crus of the incus can be faintly seen through the membrana 

 tympani, parallel with and posterior to the handle of the malleus. 



Antrum Tympanicum. The tympanic antrum is a recess 

 or air-chamber, in the petrous part of the temporal bone, with a 



