1320 



THE AUDITORY OSSICLES. 



[BOOK Hi. 



processes at right angles to each other. One of these, the " short 

 process" (p 1 . b'.), takes up a horizontal position (Fig. 173 p. &'.) and 

 is attached to the wall of the tympanum by a ligament (Fig. 171 

 Ig. inc.). The other "long process" (Figs. 164, 170, 173 p'. I'.) or 



cp - 



A. 



B. 

 B'. 



C. 

 D. 



B 



FIG. 164. THE AUDITORY OSSICLES. (After Schwalbe and Helmholtz.) 



Magnified four times. 



The malleus, cp. the head (caput). *the articulating surface for the incus, t. 

 Tooth locking with tooth of incus. Ig. is placed opposite the attachment of 

 the ligaments, p.f. processus gracilis or Folianus, represented as short, p. b. 

 processus brevis. m. br. handle (manubrium.) 



The incus. * surface articulating with malleus, t. tooth locking with tooth of 

 malleus, p'. b'. processus brevis. p'. I', processus longus. 



The lower end of the processus longus seen sideway ; o, its expanded termi- 

 nation or os orbiculare. 



The stapes, c. the head. /. the foot-plate. 



The three ossicles in connection. M. malleus, I, incus, st. stapes ; the other 

 letters as above. 



' shaft,' tapering and somewhat curved, takes up a vertical position 

 parallel to the handle of the malleus, but at its end makes 

 a sudden bend mesially towards the internal ear (Fig. 162) 

 and terminates in a flattened knob, with which it is articulated to 

 the stapes (Fig. 164 D). This knob, having frequently at least an 

 independent ossification, is sometimes spoken of as the os orbiculare 

 or lenticular *e. 



The stapes or stirrup bone (Fig. 164 C and D), which is placed 

 horizontally at right angles to the shaft of the incus, consists of 

 a head (c) articulating with the extremity of the shaft of the 

 incus, and an oval foot-plate (/"), attached in a manner, which 

 we shall presently describe, to the fenestra ovalis, the two being 

 united by curved limbs after the fashion of a stirrup. 



812. The tympanum, in which these ossicles lie, may be 

 compared to a low drum placed obliquely at the end of the external 

 meatus. The outer lateral side or surface of the drum is furnished 

 by the tympanic membrane, the inner mesial side or surface by 

 the bony labyrinth ; but the two sides are not exactly parallel, 



