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CHAPTER V.

DISEASES OF THE MEMBRANA TYMPANI.

Anatomy of Membrana Tympani.—Its Congenital Malformations.-Injuries of: Rupture. Inflammations: Acute; Rheumatic Otitis.-Subacute: Syphilitic; Gouty.Senile Deafness.-Strumous; with Ophthalmia.-Exanthematous; Typhoid.-Chronic Thickening and Morbid Deposits in Membrane.-Cutaneous Diseases.-Collapse, with Loss of Vibration.-Operation of Perforation.-Ulceration; Apertures in Membrane; Total Destruction of.—Artificial Membrana Tympani.

THE membrana tympani, or drum-head, separates the external meatus, at the extremity of which it is placed, from the cavity of the tympanum; so that, from its position as well as the anatomical connexion of its structures, it must partake of the diseases of both cavities independent of those peculiar to itself. It is a thin, semitransparent, dry membrane, of an irregular oval shape, varying in size as much as the cornea, but generally measuring about eight-twentieths of an inch in its longest diameter, which is in a diagonal line from above forwards and downwards. It is placed obliquely from above downwards, and somewhat from before backwards and outwards, and set in a well-marked groove upon an elevated ridge, at the tympanal margin of the bony meatus, like the crystal on the besil of a watch. In foetal life this tympanic ring is a separate and distinct portion of the temporal bone, and does not become altogether incorporated with it until some time after birth. It is produced from a sepa rate and distinct point of ossification, and may, therefore, be regarded as a fourth division of the temporal bone superadded to those already enumerated at page 150. From this ring grows the osseus meatus auditorius externally, and also a portion of the floor of the cavity of the tympanum internally. This circle is never completed, as may be seen by examining a section of the temporal bone, made through the tympanum, immediately behind the groove for the attachment of the membrane. It remains deficient superiorly, where the malleus joins the membrana tympani, and

at which point the head of that bone lies in the superior sinus of the tympanum. If we examine a number of temporal bones, we will find the groove for the membrane deepest at the lower and back part, and least marked above, towards the part where the ring is generally deficient.

The manubrium, or handle of the malleus, is enclosed for about three-fourths of its length between the lamina of the membrana tympani, which are partially inserted into it. This process of the hammer-bone serves to support and also to preserve the peculiar curvature of the membrane, as well as to convey to the labyrinth the vibrations of sound which impinge upon it. At birth the tympanic ring, with its enclosed membrane, looks obliquely downwards and slightly outwards, and it is only by the formation of the floor of the tympanum that the position which it assumes in adult life is produced. The membrana tympani is also proportionally larger in the foetus than in the adult. A knowledge of these relations is important in a pathological point of view, as they show how easily disease of the meatus or the membrana tympani may be propagated to the neighbouring parts.

Viewed through the speculum, with a stream of clear, direct sunlight upon it, the membrana tympani is of a greyish hue, and semitransparent consistence; and presents externally an irregularly curved surface, as also different degrees of density, polish, and tension. It is divided by a white streak, thick above and narrow below, except at its extremity, which is slightly enlarged and indented into a navel-like depression. This white opaque line is the manubrium of the malleus, proceeding from the upper attachment of the membrane downwards, somewhat backwards and a little inwards to a point slightly below the centre of the membrane, and thus divides it into an anterior, a posterior, and an inferior portion. But the exact situation of this bone, and consequently the relative proportions of the parts which it divides, present great diversity. The anterior part of the membrane is thin,-almost transparent, or as clear as fine gold-beater's skin,-highly polished, and generally convex-a speck of bright light being reflected from its most prominent part. This may be called the anterior vibrat

ing portion. In many cases the short process of the malleus may be seen as a small round dot above the manubrium where the membrane curves off into the roof of the meatus. The bottom of the meatus, it should be remembered, is funnel-shaped, the broad end of the funnel being towards the tympanum.

When the centre of the membrane is under examination, its anterior attachment, behind the sharp curve of the meatus, cannot at the same time be seen, nor until the tubular speculum is turned towards it, and the head of the person examined is brought into the proper angle; and the same remark holds good, except in cases of very large meatus, with respect to the posterior margin; the superior and inferior attachments are more easily observed; but, by rotating the speculum, and altering the head from side to side, we can bring in succession each portion of the membrane into view. The relative size of each portion of the membrane varies in different individuals. In making this examination the tube should not be inserted much beyond the middle of the meatus. Below and behind the malleus the membrane is also thin, clear, and glistening, but not quite so diaphanous. Beneath the point of the malleus it is flat, and behind it rather concave, but not always so. These portions do not usually present in their normal state spots of reflected light. Superiorly, from about the upper half of the malleus, the membrane becomes gradually denser until it is quite white; it also forms concave curves from the upper part of the malleus, the posterior one being deepest and whitest. Above, the membrane forms a gradually vaulted curve into the roof of the external auditory canal, with the lining of which it is imperceptibly blended; while in front, below and partly behind, there is a sharp, well-defined line of demarcation between it and the meatus, and sometimes a slight, whitish thickening, which in disease and in some old persons resembles the arcus senilis, except that in the cornea there is always a narrow clear space between the opacity and the sclerotic. In some persons there is a slight purse-like projection of the membrane. near its upper attachment and behind the tubercle of the malleus -the "membrana flaccida" of Sharpnell—rudimentary in man,

but well developed in some of the lower animals. The speck of light which is generally reflected from the most convex and prominent portion of the membrane is not always in the centre of the anterior part, but is often seen beneath it. If a horizontal section of the membrana tympani be made, it will present somewhat the form of an italic (), the middle point being the circular flattened extremity of the manubrium of the malleus.

If the patient under examination inflates the tympanum after the manner described at page 64, without moving the head, altering the position of the speculum, or in any way deranging the light, the whole of the anterior and part of the lower portion of the membrana tympani is bulged outwards, and the speck of light appears as if spread over a larger surface, or is entirely lost for the moment. Whether the membrane is then rendered more or less tense I cannot satisfactorily state. In some cases a slight elevation or outward pressure of the malleus, and even of the whole membrane, may be observed. If the inflation be continued, the upper white portion frequently becomes red, and vessels can be seen at times spreading from it along the sides of the malleus.

Great diversity of opinion exists among authors with respect to the curvature and general appearance of the healthy membrana tympani. They almost all, however, agree in pronouncing it a uniform concavity; but this I believe to be a post-mortem appearance. One of the proofs afforded by anatomists of the external concavity of membrana tympani is,-that, when the cuticular lining common to it and the meatus is removed entire, and floated in water, its extremity forms a curved pouch like the finger of a glove. This, however, is a very fallacious test; for, if we take the finger of a glove and invert its extremity, so as to present a marked convexity towards its internal surface, we can easily, either by blowing into it or drawing it through water, make it assume a concave appearance.

Well acquainted as every person familiar with the character which the membrana tympani presents upon inflation, it will appear almost incredible that Dr. Kramer should believe that even a forcible stream of air from the air-press cannot alter its concave form.

It is of great importance that we should be not only acquainted but familiar with, the external appearance of the membrana tympani in a normal condition; yet how many practitioners pass through life without ever having seen it in the living state!—all they know of it being from description or preparations shown them during their anatomical studies.*

Behind the attachment of the membrane superiorly, there is the head of the malleus, which rises above it into a large hollow in the bone, which freely communicates with the mastoid cells. Anteriorly, and somewhat below the middle line, there is the tympanic opening of the Eustachian tube, opposite the portion of membrane most easily acted upon by a stream of air, and that where it most usually gives way. Below and behind the Eustachian tube is the carotid canal, usually perforated in that part of its posterior curve nearest to the membrana tympani by a small aperture for the transit of a vessel which, being distributed to the membrana tympani from so near and large a stream, may, with its other plentiful supply, account for the pulsation which that membrane presents in certain forms of disease. Behind, and winding round its posterior and upper margin, the aqueduct of Fallopius conducts the portio dura to the stylo-mastoid foramen; and the proximity of that nerve to the cavitas tympani and its external partition, will enable us to account for the facial paralysis which frequently accompanies disease of the ear.

The structure of the membrana tympani has been carefully investigated by many eminent anatomists, and is found to consist of a proper fibrous layer, and two others borrowed from the neighbouring structures,-viz., the epidermis continuous with that reflected over the meatus externally, and the fine, delicate, mucous lining of the tympanal cavity—a portion of the great gastro-pulmonary investiture prolonged through the Eustachian tube—internally. The tegumentary or external cuticular layer is, in a healthy condition, remarkably fine, and so transparent that the fibres of the layer beneath it can be seen distinctly through it; yet, in dis

In addition to the foregoing observations, see the remarks upon the membrana tympani, at pp. 106-7. See also the author's description of this structure in the Dublin Quarterly Journal of Medical Science, vol. XXIV. p. 421. 1844.