Aids to otology / by W.R.H. Stewart.

  • Stewart, W. R. H. (William Robert Henry), 1852-1906.
Date:
[1893]
Catalogue details

Licence: Public Domain Mark

Credit: Aids to otology / by W.R.H. Stewart. Source: Wellcome Collection.

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    Nerve Supply.—Auricular branch of the pneumogastric and the auriculo-temporal. The MEMBRANA TY'SILTAm.—Situation.—The partition between the external and middle ear, is inserted obliquely at the inner end of the external meatus. Colour.—A delicate pearly grey, highly polished. Shape.—^Nearly circular, slightly concave externally and convex internally. Structure.—Three layers. An external, or dermoid^ a fine skin continuous with that of the external meatus. A middle^ or fibrous, consisting of: (1) External fibres, radiating towards and fixed to a cartilaginous structure,* attached to the posterior part of the handle of the malleus, loose at the upper part, firm below. (2) Internal circular fibres, which form a dense liga- mentous ring. This layer is attached to a ridge of bone, deficient above, and across this notch is stretched the external and internal layers only, the middle being absent; this part is called the memhrana flaccida, or SlirapnelVs membrane. The relaxing and sphincter action of these two sets of fibres preserves a balance of power when the drum-head is in a state of rest, and explains its peculiar concavo-convex shape (Helmholtz). An internal, or mucouSy continuous with the mucous lining of the tympanum. Landmarks to be noted in the Membrane. Short process of the Malleus is near the upper border. The Handle projects downwards and backwards from the short process to a point somewhat below the middle line of the membrane. Shining Spot.^A triangular reflection of light, base down- wards, extending downwards and forwards from the lower end of the handle. Due to a cone-shaped depression in this situation. Anterior and Posterior Folds of Membrane.—Kidges extending forwards and backwards from the short process of the malleus to the periphery. * A residue of the stage of development when the entire malleus was cartilaginous (Gruber).