5M 



THE AUDITORY APPARATUS 



and at the bottom of the fossa there is an aperture called 

 the fenestra cochlea', in the macerated bone the aperture 

 leads into the cavity of the cochlea, but, in the recent state, 

 it is closed by a membrane called the secondary membrane of 

 the tympanum. 



The lateral wall of the tympanic cavity is formed, for the 

 most part, by the membrana tympani, but, above the tympanip 

 membrane, the lateral wall of the recessus epitympanicus is 

 formed by a portion of the squamous part of the temporal 

 bone (Figs. 209, 210). 



Membrana Tympani. The membrana tympani is an 

 elliptical disc of membrane which is stretched across the 



Membrana flaccida 



Anterior 



malleolar fold 



Handle of malleus 



Antero-superior 

 quadrant 



Antero-inferior quadrant 



Posterior 

 malleolar fold 

 Lateral process 

 of malleus 

 Long crus of incus 



Postero-superior 

 quadrant 



Postero-inferior 

 quadrant 



i - Cone of light 



FIG. 212. 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.) 



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. 



The mode of attachment of the membrane deserves some 

 attention. At the medial end of the meatus a ring-like ridge 

 of bone, very distinctly grooved, forms a frame in which the 

 membrane is set (Fig. 210). But the ridge is deficient above, 

 where its extremities are separated by a deep notch called the 

 incisura tympanica. The 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 



