A text-book of physiology, for medical students and physicians . to the external face of thecavity, the posterior ligament, andthe superior ligament, the latter at-taching the upper part of the headto the roof of the tympanic cavity. By means of these ligamentsthe bone is held steadily in position even after its connectionswith the incus are loosened. The incus is somewhat more mas-sive than the malleus, weighing about 25 milligrams. Its thickerportion articulates with the head of the malleus, and it has twoproff—cs nearly at right angles to each other. The shorter processextends posteriori;,
A text-book of physiology, for medical students and physicians . to the external face of thecavity, the posterior ligament, andthe superior ligament, the latter at-taching the upper part of the headto the roof of the tympanic cavity. By means of these ligamentsthe bone is held steadily in position even after its connectionswith the incus are loosened. The incus is somewhat more mas-sive than the malleus, weighing about 25 milligrams. Its thickerportion articulates with the head of the malleus, and it has twoproff—cs nearly at right angles to each other. The shorter processextends posteriori;, and is attached by a ligament to the posteriorwall of the tympanic cavity; the long process passes downwardparallel with the handle of the malleus, but turns in at the tipto form the rounded os orbiculare, which articulates with theof the stapes. This latter Lone is extremely light, weighingabout 3 milligrams, its oval base heing attached to the marginsof the fenestra ovalis by s Bhort, stiff membrane. The Mode of Action of the Ear Bones.—The movements of. Fig. 169.—The bones of themiddle ear in natural connections(Helmholtz): M, The malleus; Mcp,the head; Mc, the neck; Ml, the Erocessus gracilis; Mm, the rnanu-rium; Ic, body of the incus; lb,short ); //, long process; <S,the stapes. EAR AS AN ORGAN FOR SOUND SENSATIONS. 379 the tympanic membrane are communicated to the tip of the handleof the manubrium. As the handle moves in, the chain of bonesmakes a rotary movement around an axis which may be defined asthe line passing through the attachment of the short process of theincus and the anterior ligament of the malleus. The general posi-tion of this axis is represented by the line a-b in Fig. 170. This linepasses through the neck of the malleus; so that as the handle movesin the head of the malleus and the upper part of the incus move inthe opposite direction,—while the long process of the incus togetherwith the stapes, being below the axis, move in the same d
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