FUNCTIONS OF COCHLEA. 553 



musical tone-colors; the minute structure of the membra- 

 nous cochlea is such as to lead us to look for it there. An 

 old view was that the rods of Corti, which vary in length,, 

 were like so many piano-strings, each tending to vibrate at 

 a given rate and picking out and responding to pendular 

 aerial vibrations of its own period, and exciting a nerve 

 which gave rise to a particular tone sensation. When the 

 labyrinthic fluids were set in non-pendular vibrations, the 

 rods of Corti were thought to analyze these into their pendu- 

 lar components, all rods of the vibrational rate of these be- 

 ing set in sympathetic movement, but that rod most whose 

 period was that of the primary partial tone; this rod would 

 determine the pitch of the note, and the less-marked sen- 

 sation due to the others affected would give the timbre. 

 The rods, however, do not differ in size sufficiently to 

 account for the range of notes which we hear; they are 

 absent in birds, which undoubtedly distinguish different 

 musical notes; and the nerve-fibres of the cochlea are not 

 connected with them but with the hair-cells. 



On the whole it seems probable that the basilar mem- 

 brane is to be looked upon as the primary arrangement for 

 sympathetic resonance in the ear. It increases in breadth 

 twelve times from the base of the cochlea to its tip (the 

 less width of the lamina spiralis at the apex more than 

 compensating for the less size of the bony tube there) 

 and is stretched tight across, but loosely in the other direc- 

 tion. A membrane so stretched behaves as a set of separate 

 strings placed side by side, somewhat as those of a harp 

 but much closer together; and each string would vibrate at 

 its own period without influencing much those on each side 

 of it. Probably, then, each transverse band vibrates to sim- 

 ple tones of its own period, and excites the hair-cells which 

 lie on it, and through them the nerve-fibres. Perhaps the 

 rods of Corti, being stiff, and carrying the reticular mem- 

 brane, rub that against the upper ends of the hair-cells which 

 project into its apertures and so help in a subsidiary way, 

 each pair of rods being especially moved when the band of 

 basilar membrane carrying it is set in vibration. The tec- 

 torial membrane is probably a "damper;" it is soft and 



