The mechanism of the ossicles of the ear and membrana tympani / by H. Helmholtz ; translated from the German, with the author's permission, by Albert H. Buck and Normand Smith.

  • Helmholtz, Hermann von, 1821-1894.
Date:
1873
Catalogue details

Licence: Public Domain Mark

Credit: The mechanism of the ossicles of the ear and membrana tympani / by H. Helmholtz ; translated from the German, with the author's permission, by Albert H. Buck and Normand Smith. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    tendon was surrounded by a perfectly free sheath, just as Toynbee describes it; in microscopic sections, however, Henle has seen the two united by pretty strong bands of connective tissue. As the hammer, however, requires exceedingly little space for its excursions, there is no need whatever that the ten- don should have much room for motion. The tensor tympani draws the handle of the hammer, and with it the membrana tympani, inward, thereby putting the latter on the stretch. This action can be readily seen on a spe- cimen where the canal of the muscle and the cavity of the tym- panum have been opened from above. By pulling upon the tendinous fibres of the nruscle within the canal, the membrana tympani becomes tense. As the point of insertion of the muscle lies but a trifle lower down than the axis-band of the hammer, the band itself will also at the same time be stretched inward, and especially the posterior portion of it, the ligamen- tum mallei posticum, which lies very nearly in the same line with the line of traction of the tensor tympani. The position of the hammer is thus made quite firm, even though the tendon be but moderately tense. We must remember here that a slight traction, when made at right angles to the length upon an inextensible cord which is already tense, can very materially increase its tension; and also that during life a muscle in a state of rest must be considered as a very yielding, though al- ways slightly tense elastic band, whose tension can be very con- siderably increased by active contraction. Aside from the fact that the tensor tympani, on account of its penniform construc- tion, is, mechanically speaking, equivalent to a muscle of much greater diameter and shorter length of fibre, we can consider its simple elastic traction, without the occurrence of any ac- tive contraction whatever, as a pretty important power. In this way it is clear that the hammer, so long as it retains Hfl natural attachments—although these be but yielding bands —and even after the division of the stapedo-incudal joint, is capable of only a limited motion in the direction of rotation about the above-mentioned axis; and that any attempts to move it in a different direction meet with very strong resis- tance. Anteriorly its axis is held securely by the ligamentum