THE EAR. 



one of the small bones of the tympanum, descends in contact with the inner 

 surface of the membrane, covered by mucous membrane, to a little below the 

 centre, where it is firmly fixed ; and, as this process of the bone is directed inwards, 

 the outer surface of the membrane is thereby depressed in a conical form (fig. 102). 

 The membrana tympanitis about O'l mm. thick, but at its insertion into 

 the sulcus tympanicus it becomes thickened and firmly attached to the bone by a 

 considerable accumulation of fibres (annulus fibrosus), and this thickened margin is 

 prolonged from the spines of the tympanic ring as two ligamentous bands which 

 pass to the short process of the malleus, constituting the so-called anterior and 

 posterior tympano-malleolar folds or ligaments ("fig. 92), and forming the lower boundary 

 of the membrana tiaccida (see below). Covering it externally is a prolongation of the 

 skin of the external meatus ; internally is a prolongation of the mucous membrane 

 lining the cavity of the tympanum ; and between the two is the proper substance 

 of the membrane, composed of fibrous tissue. The greater number of the fibres 

 radiate from the attachment of the handle of the malleus (fig. 91), but there are 

 also circular fibres (fig. 90) which are situated within or mesially to the radial, and 

 near the circumference of the membrane, form a dense, almost ligamentous 

 thickening. Besides these two sets of fibres there are others met with, especially 



Fig. 91. VIEW OF THE OUTER SURFACE OF THE LEFT MEM- 

 BRANA TYMPANI, AFTER REMOVAL OF THE CUTANEOUS 

 LATER (E. A. S. ) * 



The handle of the malleus is distinctly seen, and the long 

 process of the incus appears as a faint light band parallel with 

 and a little behind the handle of the malleus. The other 

 light band nearly at right angles to the malleus is caused by 

 the chorda tympani nerve. The notch of Bivinus is seen above 

 the handle of the malleus. 



in the posterior half of the membrane, which are 

 irregularly disposed and form at places prominent 

 fibrous bands in and upon the mesial surface of the 

 membrane (covered of course by the mucous mem- 

 brane), and even extend here and there across part 

 of the cavity of the tympanum. At the inser- 

 tion of the malleus the membrane, especially its 



integumental layer, is thickened. The fibrous tunica propria here becomes con- 

 tinuous with the periosteum of the malleus, but along the line of contact of the 

 bone with the membrane there is generally a streak of cartilage forming the actual 

 uniting tissue : a similar thin layer of cartilage may also be found along the opposite 

 (free) border of the manubrium mallei, and also forming a complete cap to the end 

 of the manubrium. In the thickening of the integumental layer above mentioned 

 vessels and nerves to the membrane are seen in section. The epidermal layer is 

 stratified, as elsewhere in the external auditory meatus : it is also somewhat thickened 

 along the malleolar line, and here small papillse of the cutis project into it. The 

 radial fibres are not straight, but are slightly bowed outwards, so that between the 

 most depressed point or umbo, and the attached border, the membrane is slightly 

 convex outwardly. This shape is maintained by the annular fibres. 



At the upper and anterior part, the annular fibres stretch, as just related, across 

 the mouth of a small notch in the bony ring to which the membrane is attached 

 (notch of Bivinus). The notch is occupied by a lax membrane (membrana flaccida, 

 Shrapnell) (fig. 92), consisting of loose connective tissue, with vessels and nerves, and 

 covered by skin and mucous membrane. It occasionally happens that a fissure or 

 perforation is to be detected at this place. 



The membrane is supplied with blood-vessels, but they are chiefly confined to the 



