A text-book of physiology for medical students and physicians . Fig. 168.—To show the structure of thetympanic membrane, looked at from the sideof the meatus (Hensen): ax, The axis of rota-tion of the ear bones; d, the incus; a, thehead of the malleus. 380 THE SPECIAL SENSES. of the membrane are transmitted directly to these bones. Thepeculiar form of the membrane, its funnel shape, its arched sides,and its tmsymmetrical division by the umbo are supposed to con-tribute to its value as a transmitter of the sound vibrations of theair. In the first place, the membrane shows little tendency toafte
A text-book of physiology for medical students and physicians . Fig. 168.—To show the structure of thetympanic membrane, looked at from the sideof the meatus (Hensen): ax, The axis of rota-tion of the ear bones; d, the incus; a, thehead of the malleus. 380 THE SPECIAL SENSES. of the membrane are transmitted directly to these bones. Thepeculiar form of the membrane, its funnel shape, its arched sides,and its tmsymmetrical division by the umbo are supposed to con-tribute to its value as a transmitter of the sound vibrations of theair. In the first place, the membrane shows little tendency toafter-vibrations,—that is, when set in motion by an air wave itshows little or no tendency to continue vibrating after the acting. Fig. 169.—Tympanum of right side with ossicles in place, viewed from within (afterMorris): 1, Body of incus; 2, suspensory ligament of malleus; 3, ligament of incus; 4,head of malleus; 5, epitympanic cavity; 6, chorda tympani nerve; 7, tendon of tensortympani muscle; 8, foot-piece of stirrup; 9, os orbiculare; 10, manubrium; 11, tensortympani muscle; 12, membrana tympani; 13, Eustachian tube. force has ceased. It is obvious that such a property is valuable inrendering hearing more distinct, and the peculiarity of the mem-brane in this respect is attributed partly to its special form andpartly to the damping action of the bones attached to it. In thesecond place, the arched sides of the funnel act as a lever, so thatthe movements at these parts are transmitted to the umbo with adiminution in amplitude, but an intensification in force. It is atthe umbo that the movement is communicated to the ear bones. The Ear Bones.—The three ear bones—the malleus, the incus,and the stapes—tak
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