MEMBRANA TYMPANI 



553 



which, in the macerated bone, leads into the cavity of the 

 cochlea, but, in the recent state, it is closed by a membrane 

 which is stretched across it, and receives the name of the 

 secondary membrane of the tympanum. 



The lateral wall of the tympanic cavity is formed by the 

 membrana tympani and thesquamous part of the temporal bone. 



Membrana Tympani. The membrana tympani is an 

 elliptical disc of membrane which is stretched across the 

 medial end of the meatus acusticus externus, and it forms the 

 greater part of the lateral wall of the tympanum. It is placed 

 very obliquely ; its lower and its anterior borders both inclining 

 medially. 



Posterior tympano- 

 malleolar fold 

 Lateral process 

 of malleus 

 Long crus of incus 



Membrana flaccid 

 Anterior tympano- 

 malleolar fold 



Handle of malle 



Antero-superior 

 quadrant 



Antero-inferior quadran 



Postero-superior 

 quadrant 



Postero-inferior 

 quadrant 



Cone of light 



FIG. 237. Left Tympanic Membrane as viewed from the external meatus 

 during an otoscopic examination. The dotted lines indicate the manner 

 in which the tympanic membrane is subdivided arbitrarily into four areas 

 or quadrants. (Howden.) 



Its mode of attachment deserves some attention. At the 

 medial end of the meatus a ring-like ridge of bone, very 

 distinctly grooved, forms, as it were, a frame in which the 

 membrane is set. But this ridge is deficient above, where 

 the extremities of the bony ridge are separated by a deep 

 notch (the notch of Rivinus). This notch is occupied by a 

 portion of the membrane which is not so dense in its texture 

 (seeing that the fibrous layer is absent), and not so tightly 

 stretched as the remainder ; consequently it receives the name 

 of the membrana flaccida (ShrapnelPs membrane). The edge 

 of that part of the membrane which is fixed in the circular 

 bony groove, sulcus tympanicus, is thickened, and at the notch 

 of Rivinus it is carried down, anterior and posterior to the 



