MEMBRANA TYMPANI 515 



membrana flaccida (ShrapnelPs membrane). The circular 

 groove in the bony ridge is called the sulcus tympanicus. The 

 edge of that part of the membrane which is fixed in the sulcus 

 tympanicus is thickened, and at the incisura tympanica, the 

 thickened part, it is carried down, anterior and posterior to 

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

 respectively the anterior 2X\& posterior malleolar folds. 



The membrana tympani is composed of three layers viz., 

 a lateral cuticular layer, an intermediate fibrous lamina, and 



Tympanic antrum 

 Recessus epitympanicus 



Canalis facialis 



Tegmen tympani 



Fenestra vestibuli 



Canal for 

 Lensor tympani 



Septum tubae 

 auditivae 



Promontory 



Auditory tube 



Foramen for 

 ympanic nerve 



Fenestra cochleae 



Course of canalis facialis 



FIG. 213. Vertical section through the Left Ear : postero-medial half 

 of section viewed from the front. (Howden. ) 



a medial mucous layer. The handle of the malleus is in- 

 timately 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 lateral surface. The deepest point of that concavity 

 corresponds with the flattened extremity of the handle of 

 the malleus, and is termed the umbo. 



When the living ear is examined, with a speculum, the surface of the 

 membrane 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 malleolar 

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

 ill 33 a 



