A text-book of the diseases of the ear and adjacent organs . nosus. NORMAL STATE OF THE MEMBRANA TYMPANI. 77 The lustre of the niembrana tympani is shown in the sharplydefined and usually triangular spot of light in the anterior inferiorquadrant of the membrane (Figs. 69 and 70). It commences withits apex in front of the umbo, and extends forwards and down-wards, so that it forms an obtuse angle forwards with the directionof the handle of the malleus. The shape of this light reflex varies greatly, partly on account of differ-ences in the inclination of the membrane, partly on account of variat
A text-book of the diseases of the ear and adjacent organs . nosus. NORMAL STATE OF THE MEMBRANA TYMPANI. 77 The lustre of the niembrana tympani is shown in the sharplydefined and usually triangular spot of light in the anterior inferiorquadrant of the membrane (Figs. 69 and 70). It commences withits apex in front of the umbo, and extends forwards and down-wards, so that it forms an obtuse angle forwards with the directionof the handle of the malleus. The shape of this light reflex varies greatly, partly on account of differ-ences in the inclination of the membrane, partly on account of variations iuits curvature. It is often interrupted in its continuity, so that between itsapex and its base there is a portion without reflection ; sometimes it seemsdivided into two parts in its longitudinal direction, or delicately striped. Itseldom extends to the periphery of the membrane, and often the anteriorportion of the reflection is effaced, only its apex being visible in front ofthe umbo, as a small, irregular, lustrous spot. According to Bezold, this. Fig. 69.—Normal Mem- Fig. 70.— Normal Mem-brana Tympani of brana Tympani ofthe Right Ear. the Left Ear. (Double size.) spot is blurred in 86 per cent, of cases whose hearing are normal. The know-ledge of all these variations in the normal state is of importance, becausethey might give rise to erroneous interpretations of pathological changes. As to the origin of the cone of light, the examinations (A. f. 0., vol. i.)made by me on artificial membranes and preparations of the normal auditoryapparatus have shown that its principal cause is the inclination of themembrane to the axis of the meatus, in connection with the concavity ofthe membrane produced by the handle of the malleus. In consequenceof the curvature of the membrane brought about by the traction ofthe handle of the malleus, the inclination of the various portions of themembrane is so altered that its anterior portion is placed exactly oppositethe eye of the obse
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Keywords: ., bookcentury1800, bookdecade1890, booksubjecteardiseases, bookyear
