078 HANDBOOK OF PHYSIOLOGY. 



The membrana tympani i.s placed in Ji slanting direction at the bot- 

 tom of the external auditory caual, its plane being at an angle of about 

 45 with the lower wall of the canal. It is formed chiefly of a tough 

 and tense fibrous membrane, the edges of which are sot in a bony groove; 



Fig. 399. Interior view of the tympanum, with membrana tympani and bones in natural 

 position. 1, Membrana tympani ; 2,' Eustachian tube: 3, tensor tympani muscle; 4, lig. mallei 

 super. ; 6, corda-tympani nerve; a, ft, and c, sinuses about ossicula. (Schwalbe.) 



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 ossicles are three in number; named malleus, incus, and stapes. 

 The malleus, or hammer-bone, is attached by a long slightly-curved pro- 

 cess, called its handle, to the membrana tympani; the line of attachment 

 being vertical, 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 processes; a short conical one, which 

 receives the insertion of the tensor tympani, and a slender one, processus 

 yracilis, which extends forward, and to which the laxator tympani muscle 

 is aftached. 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 backward, has a free end lodged in a depression in the mastoid 

 bone ; the other, curved downward 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, correspond- 

 ing 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 move- 

 ments are communicated through the incus to the stapes, and through 



