Diseases of the ear : a text-book for practitioners and students of medicine / by Edward Bradford Dench.

  • Dench, Edward Bradford, 1864-1936.
Date:
1900
Catalogue details

Licence: Public Domain Mark

Credit: Diseases of the ear : a text-book for practitioners and students of medicine / by Edward Bradford Dench. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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    section, with the anterior and posterior walls in contact except at the upper part. The membranous tube is attached to the inner extremity of the bony canal, the posterior cartilaginous plate uniting with a prolongation of the corresponding bony wall. Beyond the isthmus the tube is suspended from the base of the cranium by fibrous bands passing to its superior wall, until it terminates in the lateral aspect of the pharyngeal vault. As described in the foregoing pages, the conducting mechanism consists of a canal, the walls of the central por- tions being osseous, while at either extremity they are fibro- cartilaginous, communicating upon one side with the outer surface of the body directly, while upon the other this com- munication is effected indirectly through the oral and nasal passages. This tube is brought into intimate relation with the receptive mechanism through the agency of the ossicular chain, and at this point the osseous conduit is dilated, forming the tympanum. This chamber, situated midway in the pas- sage, is occupied by a special device for bringing the two portions of the auditory apparatus into relation with each other. For the protection of the intratympanic parts chiefly, and, to a certain extent, to aid in the transmission of sonorous impulses, a fibrous partition divides the external auditory meatus from the tympanum and Eustachian tube. This parti- tion constitutes the membrana tympani. The Membrana Tympani.—The membrana tympani con- sists of a transverse fibrous septum, lying in the middle of the conducting tube, and bounded by the tympanic ring, which, it will be remembered, is incomplete at its upper part. This connective-tissue lamella, called the substantia propria of the drum membrane, is inserted into the sulcus tympanicus. At the point of insertion the fibrous tissue is somewhat thick- ened, forming the annulus tendinosus, sometimes called the cartilaginous ring. From the cartilaginous ring certain connective-tissue fibres extend outward to the periosteum of the meatus, while others, passing in the opposite direction, merge into the periosteal lining of the tympanum. The sub- stantia propria is made up of two layers. In the outer layer the fibres radiate from the tip of the malleus toward the peripheral wall, while in the internal layer they are disposed in concentric circles about this point as a centre. The manu- brium of the malleus joins the substantia propria through the