USE OF THE PARTS IN THE EAR. 337 



every side ? The play, then, of the bones of the 

 tympanum, and of the membrane of the fenestra 

 ovahs and of the fenestra rotunda, is not only re- 

 quired to produce an undulation in the fluid within 

 the labyrinth, but that undulation must take the 

 particular course through the scala of the cochlea, 

 descending into it by the scala vestibuli and as- 

 cending by the scala tympani. (See f, vol. i., page 

 52.) In this view it becomes interesting to con- 

 sider the distribution of the nerve in the cochlea, 

 since this internal part of the organ is so obviously 

 connected with the finer exterior apparatus. We 

 have learned that the nerve passes into the medio- 

 lus and extends to the edge of the lamina spiralis, 

 so that the sonorous undulations continued through 

 these passages must affect the nerve on two sur- 

 faces ; and whether we consider the cochlea to be 

 like the bending of the spiral turns of a wind in- 

 strument, or the fibres of the lamina spiralis to be 

 like a succession of chords diminishing regularly 

 in length, we can at least imagine that at one time 

 the whole portion of the nerve may be brushed 

 and agitated, and that at another it may be par- 

 tially affected. 



In short, the concavities of the central cavity 

 of the labyrinth, the vestibule, may produce an ed- 

 dying of the fluid, so that the motion shall be con- 

 centrated to a point, on which point there is seated 

 a portion of the nerve ; or the undulation may pass 

 round the semicircular canals and affect the septun^ 

 of each ampulla ; or by being propagated through 

 30 



