A text-book of the diseases of the ear for students and practitioners . e, are unequal. V. Troltschassumes, as the external boundary of the meatus, a sagittal plane,passing through the posterior margin of the orifice ; according tohis measurements, the length of the superior wall is 21 mm., Fig. 12.—Section of theExternal Meatus. a, Lumen of the meatus ; b, An-terior wall ; c, Mastoid cells. THE DIRECTION OF THE EXTERNAL AUDITORY CANAL n the inferior 26 mm., the anterior 27 mm., and the posterior22 mm. On an average the length of the entire meatus is24 mm., of which more than one-third is take
A text-book of the diseases of the ear for students and practitioners . e, are unequal. V. Troltschassumes, as the external boundary of the meatus, a sagittal plane,passing through the posterior margin of the orifice ; according tohis measurements, the length of the superior wall is 21 mm., Fig. 12.—Section of theExternal Meatus. a, Lumen of the meatus ; b, An-terior wall ; c, Mastoid cells. THE DIRECTION OF THE EXTERNAL AUDITORY CANAL n the inferior 26 mm., the anterior 27 mm., and the posterior22 mm. On an average the length of the entire meatus is24 mm., of which more than one-third is taken up by the carti-laginous portion. Direction.—The external meatus presents several curves fromthe external orifice to the membrane, which deserve full con-sideration in the examination of the latter, as well as in opera-tions in the canal. Although the entire meatus appears spirallytwisted about its axis, it may be assumed that the cartilaginousportion in passing inwards turns backwards and upwards, andthe osseous portion forwards and downwards. The long axes of. f e b Fig. 13.—Horizontal Section of the External Meatus. a, Concha ; b, Tragus ; c, Place of attachment of the cartilaginous portion ; d, Mas-toid process ; e, Anterior wall of the meatus ; /, Sin. meat, audit, extern. ; g,Membrana tympani; h, Tympanic cavity. (Left ear.) the two portions of the canal therefore form an open angleforwards and downwards, and as the meatus slopes inwards andoutwards from the place of union, the inferior part of theexternal auditory orifice and of the membrana tympani must lielower than the other parts of the canal. According to the investigations of Schwalbe, Zaufal and Symington in thenew-born, the lunien of the canal is absent at its internal segment, inasmuchas the larger part of the membrane lies upon the inferior wall. This isfavoured on the one hand by the sudden outward and upward direction of themeatus, and on the other hand by the strongly developed layers of epidermison
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectear, booksubjecteardi
