414 THE BODY AT WORK 



through the thin membrane which roofs the scala media, shake 

 its endolymph, and reach the lower passage through the basilar 

 membrane. It is noteworthy that, since the round window 

 at the lower end of the scala tympani is, with the exception of 

 the oval window, the only opening of the bony labyrinth, all 

 waves transmitted through the oval window must travel part 

 of the way or all the way up and down the cochlea. 



The organ of Corti is spread out on the basilar membrane. 

 It is an epithelial structure of extreme regularity and uni- 



FIG. 39. A SECTION THROUGH THE Axis OP THE COLUMN OF THE COCHLEA. 



The spiral sheet of nerve-fibres which supplies the organ of Corti is cut in eight places. If 

 the bundle to the lowest coil of the shell (on the left side of the diagram) is followed, it will 

 be seen to bear ganglion cells where it enters the bony spiral lamina. This lamina divides 

 the tube into two canals scala vestibuli above, scala tympani below. From the edge of 

 the lamina the membrane of Corti stretches to the outer wall. Above the organ of Corti 

 is the membrana tectoria, and above this a very thin membrane which cuts off the ductus 

 cochleae from the scala vestibuli. 



formity. Near to the edge by which the basilar membrane is 

 attached to the spiral lamina rests a double row of rods of 

 Corti, stiff pillars which lean one towards the other, over the 

 tunnel of Corti, the convex head of the outer rod fitting into 

 a concavity in the head of the inner one ; in some places one 

 outer rod fits against two inner rods, as the latter are rather 

 the more numerous. On the inner side of the inner rod is 

 seen, in transverse sections a single plump cell filled with cloudy 

 protoplasm, and bearing on its free surface a tuft of very short 



