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, 



e.au.m 



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

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

 away obliquely, in., head of malleus ; up., spur-like project ion of lower border of its articular 

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

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

 its long process; st., stapes in fenestra vestibuli ; e.aii.m., external auditory meatus; ;./,'., 

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

 at extremity of external meatus; i.an.in., internal auditory meatus, a and l> its upper and 

 lower divisions for corresponding parts of acoustic uei \e ; ./.., eanal for nerve to ampulla "I 

 posterior semicircular canal; x.s.i:, ampullary end of superior canal; />., ampullary opening 

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

 e'.s.c., non-ampullary end of lateral canal ; s.t.c., sea la t \ mpaiii cochleae ; f.r, fenestra cochleae, 

 closed by its membrani ; a.F., canalis facialis (aquaeductua 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 auditory 

 meatus. 



The membrana tympani is about O'l mm. 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. 



