61)0 HANDBOOK OF PHYSIOLOGY. 



canals is suspended free in the perilymph, and is destined more particu- 

 larly for the perception of sounds through the medium of that fluid, 

 whether the sonorous undulations be imparted to the fluid through the 

 fenestrae, or by the intervention of the cranial bones, as when sounding 

 bodies are brought into communication with the head or teeth. The 

 spiral lamina on which the nervous fibres are expanded in the cochlea, 

 is, on the contrary, continuous with the solid walls of the labyrinth, and 

 receives directly from them the impulses which they transmit. This is 

 an important advantage; for the impulses imparted by solid bodies, 

 have, cceteris paribus, a greater absolute intensity than those communi- 

 cated by water. And, even when a sound is excited in the water, the 

 sonorous undulations are more intense in the water near the surface of 

 the vessel containing it, than in other parts of the water equally distant 

 from the point of origin of the sound; thus we may conclude that, 

 cceteris paribus, the sonorous undulations of solid bodies act with greater 

 intensity than those of water. Hence, we perceive at once an important 

 use of the cochlea. 



This is not, however, the sole office of the cochlea; the spiral lamina, 

 as well as the membranous labyrinth, receives sonorous impulses through 

 the medium of the fluid of the labyrinth from the cavity of the vestibule, 

 and from the fenestra rotunda. The lamina spiralis is, indeed, much 

 better calculated to render the action of these undulations upon the 

 auditory nerve efficient, than the membranous labyrinth is; for as a solid 

 body insulated by a different medium, it is capable of resonance. 



The rods of Corti are probably arranged so that each is set to vibrate 

 in unison with a particular tone, and thus strike a particular note, the 

 sensation of which is carried to the brain by those filaments of the audi- 

 tory nerve with which the little vibrating rod is connected. The dis- 

 tinctive function, therefore, of these minute bodies is, probably, to 

 render sensible to the brain the various musical notes and tones, one of 

 them answering to one tone, and one to another; while perhaps the 

 other parts of the organ of hearing discriminate between the intensities 

 of different sounds, rather than their qualities. 



" In the cochlea we have to do with a series of apparatus adapted for 

 performing sympathetic vibrations with wonderful exactness. We have 

 here before us a musical instrument which is designed, not to create 

 musical sounds, but to render them perceptible, and which is similar in 

 construction to artificial musical instruments, but which far surpasses 

 them in the delicacy as well as the simplicity of its execution. For, 

 while in a piano every string must have a separate hammer by means of 

 which it is sounded the ear possesses a single hammer of an ingenious 

 form in its ear bones, which can make every string of the organ of Corti 

 sound separately. " (Bernstein. ) 



