Politzer's text-book of the diseases of the ear and adjacent organs : for students and practitioners / translated at the request of Professor Politzer and edited by James Patterson Cassells.

  • Ádám Politzer
Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: Politzer's text-book of the diseases of the ear and adjacent organs : for students and practitioners / translated at the request of Professor Politzer and edited by James Patterson Cassells. Source: Wellcome Collection.

    38/824 (page 18)
    are greater than from without inwards. Although the walls forming the cavity are in some places not sharply denned, it is 3 necessary for a clear representation of the anatomical facts to describe these different parts as walls of the tympanic cavity. 0 We will therefore commence with a description of its exterior ■wall, and the first subject for our attention will be the membrana j tympani, which forms the greater part of this wall, and must be \ looked upon as an integral part of the middle ear on account of 1 its close physiological connection with the ossicular chain. The names of the walls of the tympanic cavity—exterior, inte- j rior, superior, and inferior—are not in keeping with then actual positions, as the direction of the cavity from above downwards is 1 not perpendicular, but extends in an oblique direction downwards j and inwards (towards the middle line). If we adhere to the old | names it is necessary, owing to the important practical signifi- cance of these relations, never to lose sight of the fact, that in 1 the normal position of the head the exterior wall becomes an ] exterior inferior by its inclination; the interior wall, which com- j pletely roofs the exterior wall, an mterior superior; the inferior wall an inferior interior; and the superior wall a superior exterior. a. TJie Membrana Tympani. The membrana tympani, which, in conjunction with the ossi-I cular chain, serves for the reception and conduction of the waves , of sound reaching the ear from the external air, is stretched out i as an irregularly-rounded concave membrane at the inner ex- j tremity of the osseous meatus, placed obliquely to its longitudinal j axis, so that the plane of the membrane forms an obtuse angle j with the superior wall of the meatus, and an acute angle with j the inferior. The margin of the membrane is embedded in a groove-like sulcus (sulcus tympanicus), situated at the inner end of the meatus. This sulcus belongs to the tympanic ring (Fig. 6) already mentioned, and exists on the perfect temporal _ bone (Fig. 14) only to the extent of the part taken by that ring in the formation of that bone (vide ' Development of the Osseous Mea- j tus' p. 8). In front and above, however, at the so-called Rivinian segment, the sulcus is wanting altogether, and here the mem- brana tympani is united partly with the grooveless margo tym- panicus, partly with the lining membrane of the osseous meatus. Form of the Membrana Tympani.—The form of the mem- brana tympani is dependent on the shape of the periphery ot the inner end of the meatus. This varies between the elliptic, the. irregularly oval, and the heart-shaped forms, according to tne greater or less prominence of the lateral parts of the osseous rmg. Especially at two places the membrane is bulged out towards the periphery, viz, behind and above, into a large segment of I