308 NOTES AND MEMORANDA. 



the outer increasing with much greater rapidity, so that near 

 the apex they are twice the length of the inner. 



It was generally supposed, a priori, that the«!e rods were 

 graduated so a«i to distinguish the most minute variation of 

 tone, but no one until now has been able to demonstrate 

 this. 



The rods, therefore, vary in length from about -^^-^ to -^^-^ 

 of an inch. The number of rods in each row is not the 

 same, there being about three of the inner to two of the outer, 

 and, according to calculation, there are about 5200 inner 

 rods and 3500 outer in the whole cochlea. 



Corti and most other authors considered this system of rods 

 to be the essential portion of the cochlea ; they supposed the 

 rods received the vibrations conducted to them, and being 

 set in motion, so affected the nerves as to cause the brain to 

 appreciate the various sounds. Later German writers have 

 attributed the appreciation of the various vibrations to cer- 

 tain delicate cells, Avhich are attached to the under surface of 

 the membrana reticularis. From this circumstance alone it 

 appears very evident that these investigators had not sus- 

 pected, much less discovered, the fact that the rods are most 

 exquisitely graduated, for otherwise they could sui'ely never 

 have doubted that so beautiful and suitable an apparatus 

 could have any other ostensible purpose than that of appre- 

 ciating the various sounds. I consider, indeed, that the 

 cochlea represents a musical instrument, similar in nature to 

 a harp or musical box, the strings of the one and the tooth 

 of the other represented by the rods of Corti. The spiral 

 bony lamina is simply a sounding-board; around the rods 

 are placed the various nerve-cells and nerve-fibres, and from 

 these cells the impressions are conveyed by the fibres to the 

 brain itself. 



It is possible, therefore, to trace very completely the course 

 of sounds or vibrations from a musical instrument or any 

 other source to the brain, through the medium of the ear. 

 First the vibrations are caught and collected by the auricle, 

 and transmitted through the external meatus to the drum of 

 the ear, next across the middle to the internal ear. Here 

 the sound is appreciated, merely as a sound, by the vestibule ; 

 the direction is discovered by means of tiie semicircular 

 canals ; but to distinguish the note of the sound, it must pass 

 on to the cochlea. The vibration therefore passes through 

 the fluid of the cochlea and strikes the lamina spiralis, which 

 intensifies and transmits the vibration to the system of rods. 

 There is doubtless a rod, not only for each tone or semitone, 

 but even for much more minute subdivisions of the same; so 



