THE LABYRINTH. 529 



formed chiefly of a tough and tense fibrous membrane, the 

 edges of which are set in a bony groove ; its outer surface is 

 covered with a continuation of the cutaneous lining of the 

 auditory canal, its inner surface with part of the ciliated mucous 

 membrane of the tympanum. 



The small bones or ossicles of the ear are three, named 

 malleus, incus, and stapes. The malleus, or hammer-bone, is 

 attached by a long slightly-curved process, called its handle, 

 to the membrani tympani ; the line of attachment being verti- 

 cal, including the whole length of the handle, and extending 

 from the upper border to the centre of the membrane. The 

 head of the malleus is irregularly rounded ; its neck, or the 

 line of boundary between it and the handle, supports two pro- 

 cesses ; a short conical one, which receives the insertion, of the 

 tensor tympani, and a slender one, processus gracilis, which ex- 

 tends forwards, and to which the laxator tympani muscle is at- 

 tached. The incus, or anvil-bone, shaped like a bicuspid molar 

 tooth, is articulated by its broader part, corresponding with 

 the surface of the crown of a tooth, to the malleus. Of its two 

 fang-like processes, one, directed backwards, has a free end, 

 the other, curved downwards and more pointed, articulates by 

 means of a roundish tubercle, formerly called os orbiculare, 

 with the stapes, a little bone shaped exactly like a stirrup, of 

 which the base or bar fits into the fenestra ovalis. To the 

 neck of the stapes, a short process, corresponding with the loop 

 of the stirrup, is attached the stapedius muscle. 



The bones of the ear are covered with mucous membrane 

 reflected over them from the wall of the tympanum; and are 

 movable both altogether and one upon the other. The malleus 

 moves and vibrates with every movement and vibration of 

 the membrana tympani, and its movements are communicated 

 through the incus to the stapes, and through it to the mem- 

 brane closing the fenestra ovalis. The malleus, also, is mova- 

 ble in its articulation with the incus ; and the membrana 

 tympani moving with it is altered in its degree of tension by 

 the laxator and tensor tympani muscles. The stapes is mov- 

 able on the process of the incus, when the stapedius muscle 

 acting draws it backwards. 



The proper organ of hearing is formed by the distribution 

 of the auditory nerve within the internal ear, or labyrinth of 

 the ear, a set* of cavities within the petrous portion of the 

 temporal bone. The bone which forms the walls of these 

 cavities is denser than that around it, and forms the osseous 

 labyrinth ; the membrane within the cavities forms the mem- 

 branous labyrinth. The membranous labyrinth contains a 



