THE SENSES. 581 



"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 con- 

 trary, continuous with the solid walls of the labyrinth, and receives 

 directly from them the impulses which they transmit. This is an im- 

 portant advantage; for the impulses imparted by solid bodies have, 

 cceteris paribus, a greater absolute intensity than those communicated 

 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, cceter is pari- 

 bus, 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 audi- 

 tory 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 sen- 

 sation of which is carried to the brain by those filaments of the auditory 

 nerve with which the little vibrating rod is connected. The distinctive 

 function, therefore, of these minute bodies is, probably, to render sensi- 

 ble to the brain the various musical notes and tones, one of them answer- 

 ing 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 musi- 

 cal sounds, but to render them perceptible, and which is similar in con- 

 struction 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 sep- 

 arately. " (Bernstein. ) 



About 3000 rods of Corti are present in the human ear; this would 

 give about 400 to each of the seven octaves which are within the compass 

 of the ear. Thus about 32 would go to each semi-tone. Weber asserts 

 that accomplished musicians can appreciate differences in pitch as small 

 as ^j of a tone. Thus, on the theory above advanced, the delicacy of 

 discrimination would, in this case, appear to have reached its limits. 



