vi FORM AND FUNCTION 133 



also a great extension, called, because it is shaped like 

 a spiral shell, the cochlea, and into this too the 

 fluid extends. A membranous bag, also filled with 

 fluid, extends throughout the ramifications of the 

 cochlea and the labyrinth. On the inside of the 

 membranous bag within the labyrinth, at certain 

 points where it is attached to the bony wall, are hairs 

 which are believed to communicate with the nerve of 

 hearing. So far, 1 have been describing the ear 

 proper. The rest of the machinery has for its object 

 the communication of the vibrations of sound to the 

 fluid in the bony labyrinth, from which they pass to 

 that in the membranous bag which lies in it, from that 

 to the hairs which connect with the nerve. The 

 apparatus for conveying sound vibrations to the laby- 

 rinth is rather complicated. There is, to begin with, 

 a membrane which stretches across the external 

 aperture of the ear. When a sound sets the air moving 

 in waves, which we speak of as vibrations, they strike 

 against the membrane. To this membrane and the 

 chamber behind is given the name of the drum of the 

 ear, and on the further side of the drum is the 

 labyrinth described above. Three bones united 

 together have their one end resting against the outer 

 membrane just mentioned, the other against another 

 membrane that at one point takes the place of bone in 

 the bony labyrinth. Thus, the vibrations of the outer 

 membrane are transmitted by the united three bones 

 to the window of membrane in the bony wall of the 

 labyrinth, from there to the fluid in the labyrinth, 

 next to the fluid within the membranous bag, and lastly 

 to the hairs within the bag that connect with the nerve. 



