740 



HEARING 



[CH. LIV. 



The ossicles are three in number; named malleus, incus, and 

 stapes. The malleus, or hammer-bone, has a long slightly-curved 

 process, called its handle, which is inserted between the layers of 

 the membrana tympani ; the line of attachment is 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 the 

 head and the handle, supports two processes: a short conical one, 

 and a slender one, processus gracilis, which extends forwards, and is 

 attached to the wall of the cavity at the Glaserian fissure. 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 

 the tooth, to the malleus. Of its two fang-like processes, one, 



Fid. 540. The hammer- 

 bone or malleus, seen 

 from the front. 1, The 

 head ; 2, neck ; 8, 

 short process ; 4, 

 handle. (Schwalbe.) 



FIG. 541. The incus, or anvil-bone. 

 1, Body; 2, ridged articulation 

 for the malleus ; 4, processus 

 brevis, with 5, rough articular 

 surface for ligament of incus ; 

 6, processus magnus, with articu- 

 lating surface for stapes; 7, nu- 

 trient foramen. (Schwalbe.) 



FIG. 642. The stapes, or 

 stirrup bone. 1, Base; 

 '2 and 8, arch; 4, head 

 of bone, which articu- 

 lates with orbicular 

 process of the incus ; 

 5, constricted part of 

 neck ; 6, one of the 

 crura. (Schwalbe.) 



directed backwards, has a free end attached by ligament to a depres- 

 sion in the mastoid bone ; the other, curved downwards, longer and 

 more pointed, articulates by means of a roundish tubercle, formerly 

 called os orliculare, with the stapes, a little bone shaped like a stirrup, 

 of which the base fits into the membrane of 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 muscles of the tympanum are two in number. The tensor 

 tympani arises from the cartilaginous end of the Eustachian tube 

 and the adjoining surface of the sphenoid, and from the sides of the 

 canal in which the muscle lies ; the tendon of the muscle bends at 

 nearly a right angle over the end of the processus cochleariformis, 

 and is inserted into the inner part of the handle of the malleus. 

 The stapedius is concealed within a canal in the bone in front of 

 the aqueductus Fallopii. The tendon issues from the aperture of 

 this canal and is inserted into the neck of the stapes posteriorly. 



