A text-book of physiology for medical students and physicians . ; 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
A text-book of physiology for medical students and physicians . ; 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—taken together form a chain connecting the tym-panic membrane with the membrane of the fenestra ovalis. Bythis means the vibrations of the tympanic membrane are com-municated to the membrane of the fenestra ovalis and thus to the EAR AS AN ORGAN FOR SOUND SENSATIONS. 381. perilymph filling the cavity of the internal ear. The bones consistof spongy material with a compact surface layer. Their generalshape and connections are illustrated in Figs. 169 and 170. Tounderstand the manner in which the chain of bones acts in con-veying the vibrations from one membrane to the other some pointsin their structure and connections may be recalled. The malleusis about 18 to 19 mms. long, and has an average weight of 23 milli-grams. Its long handle is imbedded in the tympanic membrane,the tip reaching to the umbo. The large, rounded head projectsabove the upper edge of the tympanic membrane and forms a truejoint of a peculiar nature with theincus. It has two processes in ad-dition to the manubrium: a shortone, processus brevis, that pressesagainst the upper edge of the tym-panic membrane, and a longer one,the processus gracilis or processusFolianus, which projects forwardand is continued by a ligament, th
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Keywords: ., bookautho, bookcentury1900, bookdecade1910, booksubjectphysiology
