THE OSSICLES OF THE EAR. 395 



concave surface, Figs. 75, 76, on the thick part of the incus. The 

 incus, or anvil-like bone, b, consists of a massive part or body, and of 

 two processes, or legs, being shaped somewhat like a double tooth. 

 Besides being articulated with the malleus, the incus is attached, by 

 its shorter leg, to the hinder wall of the tympanum ; by its long leg, 

 it is articulated with the third ossicle or stapes, which is the innermost 

 of the three bones, by a little tubercle named the orbicular bone, 0, 

 which is sometimes regarded as a separate bone. The stapes, Figs. 

 75, 76, c, so named from its remarkable resemblance to a stirrup, is 

 placed horizontally, and is attached, by its foot-piece or base, to the 

 inner wall of the tympanum, where it is fixed, by fibrous membrane, 



Fig 76. The membrana tympani, seen from the inner side, with the ossicles of the ear attached, d, the 

 membrana tympani, set in the tympanic ring, r, of the temporal bone, a, the malleus, its lone process or 

 handle attached to the inner side of the membrana tympani, its slender process fixed in a recess in the 

 wall of the tympanum, its head connected with the next ossicle. 6, the second ossicle, or incus, its body 

 joined with the malleus, its short leg standing out towards the side of the tympanum, and its long leg 

 reaching to the third ossicle, to which it is fixed by a little tubercle, o, sometimes named the orbicular 

 bone. c. the third ossicle or stapee, placed horizontally, with its base, in the natural condition, turned in 

 the direction of the inner wall of the tympanum. 



to the margin of an oval aperture in the bone, called the fenestra 

 ovalis, leading into the labyrinth ; it is so attached, as to be able to 

 undergo certain movements. The foot-hole in this diminutive stirrup, 

 is closed by a membrane, in its perfect state. These little bones, 

 which weigh only a few grains, are covered with periosteum, supplied 

 with bloodvessels, articulated together by perfectly movable joints, 

 and provided with minute muscles, which, acting on the small levers 

 formed by this jointed rod, influence the condition of the membrana 

 tympani on the one hand, and of the fibrous membrane uniting the 

 base of the stapes to the margin of the fenestra ovalis, on the other. 

 The conjoined bones rotate upon a horizontal axis, passing through the 

 slender process of the malleus, the head of that bone, and the body 

 and short process of the incus. 



The muscles of the tympanum are, like the bones, three in num- 

 ber. Two of these, the tensor tympani, and the so-called laxator 

 tympani, arise from definite points of the surrounding petrous bone, 

 and are inserted into the malleus; the first named is undoubtedly 

 muscular, and draws the membrana tympani inwards, and tightens it ; 

 the latter was formerly described as a muscle having the opposite ac- 

 tion, but it is either seldom present, or, as maintained by some au- 

 thorities, is merely a reddish ligamentous structure. The tensor tym- 



