SENSE OF HEAKING. 



889 



and the tendency would be to drag the stapes from the oval window. 

 This is, however, prevented by the loose articulation of the malleus and 

 incus, which separate to a certain extent and thus prevent dragging on 

 the stapes (Fig. 409). 



Hence, the system of ear-ossicles forms an angular lever, which 

 moves around a common axis in a plane vertical to the plane of the 

 membrana tympani, one arm of the lever on which the power of the 

 vibrations act being the hammer-handle, the other, the hammer-head with 



FIG. 409. MOVEMENTS OF THE MALLEUS AND INCUS. (Beaunis.) 



M, malleus ; E, incus ; A, short process of the incus ; R, long process of the incus ; P, handle of the 

 malleus ; A B, axis of movement of the ossicles. 



the handle, serving to set the entire fluid of the labyrinth into vibration. 

 The vibrations of the ear-ossicles are, therefore, transverse, although not 

 analogous to the transverse vibrations occurring in a stretched cord, 

 since the ear-ossicles do not vibrate on account of their elasticity, but 

 resemble a system of movable levers. As the long process of the incus 

 is only one-third the length of the handle of the malleus, of course the 

 excursions of the former, and with it the stapes, will be less than that of 

 the tip of the malleus, while, on the other hand, the force of the vibration 

 in the former will be increased ; so that the stapes is forced inward by 



