THE SENSE OF HEAKING 



199 



of the auditory meatus to a special bony ring, at an angle of 55 

 from above and outwards, down and inwards (Fig. 76). It is 

 slightly stretched, and ellipsoid in form, with a maximal diameter 

 of 9 '5-10 mm. and a minimal diameter of 8 mm. Its oblique 

 position provides a more extensive surface, and allows the play 

 upon it of a larger number of vibrations. Moreover, it is not 

 stretched in one plane, but a little below its centre is drawn 

 inwards by the handle of the malleus which is attached to it, thus 

 forming a conical elevation towards the cavity of the tympanum, 



FIG. 76. Proiile view of left membrana tympani and auditory ossicles from before and somewhat 

 above. Magnified 4 times. (E. A. Schafer.) The anterior half of the membrane has been cut 

 away obliquely, m., head of malleus ; sp., spur-like projection of lower border of its articular 

 surface ; pr.br., its lateral process ; pr.gr., root of processus anterior, cut ; s.l.m., suspensory 

 ligament of malleus ; lem., its lateral ligament ; t.t., tendon of tensor tympani, cut ; i., incus, 

 its long process; st., stapes in fenestra yestibuli ; e.au.m., external auditory meatus; pR., 

 notch of Rivinns ; m.t., membrana tympani ; u., its most depressed point or urn bo ; d., declivity 

 at extremity of external meatus ; i.au.m., internal auditory meatus, a and b its upper and 

 lower divisions for corresponding parts of acoustic nerve ; n.p., canal for nerve to ampulla of 

 posterior semicircular canal; s.s.c., ampullary end of superior canal; p., ampullary opening 

 of posterior canal; c., common aperture of superior and posterior canals; e.s.c., ampullary, 

 e'.s.c., non-ampullary end of lateral canal ; s.t.c., scala tympani cochleae ; f.r, fenestra cochleae, 

 closed by its membrani ; a.F., canalis facialis (aquaeductus Fallopii). 



and presenting a convex surface outward, towards the meatus, 

 especially in the lower segment. At the upper end the conical 

 lateral process of the malleus bulges out towards the audit or-y 

 meatus. 



The membrana tympani is about O'l rnm. thick, and consists 

 of fibrous tissue with radial fibres at its periphery and annular 

 fibres within, covered externally by a very fine prolongation of 

 the skin, internally by simple pavement epithelium. Notwith- 

 standing its delicacy it is extremely resistant and practically 

 inextensible. 



