156 On the Function of the Bods of the Cochlea. 



Deiters, on the outer rods themselves, and in the corresponding little 

 cells on their bases. 



Filaments also pass directly upwards to the inner side of the first 

 row of rods, and on these filaments little modular enlargements may- 

 be seen. 



Tlie Function of the Bods. 



Corti and most of the subsequent 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, however, attributed the apprecia- 

 tion of the various vibrations to certain delicate cells (the cells of 

 Corti and Deiters) which are attached to the under-surface of the 

 membrana reticularis. From this circumstance alone, it appears 

 evident that these investigators had not suspected, much less dis- 

 covered, the fact that the rods are most exquisitely graduated, for 

 otherwise they could surely never have doubted that so beautiful and 

 suitable an apparatus could have any other ostensible purpose than 

 that of appreciating the various sounds. If the rods had been found 

 to be longer in the lower and larger portion of the canal, and shorter 

 in the upper and smaller portion, the matter might naturally enough 

 have been regarded as one of little importance ; but it must be re- 

 membered that quite the reverse is the case, for the rods actually 

 increase in length as the canal becomes narrower. This uniform 

 graduation of the rods presents to my mind so plausible and 

 reasonable a key to their use, that there can scarcely be a doubt as 

 to their real function. I consider, indeed, that the cochlea as a 

 whole represents a finely-constructed musical instrument, similar in 

 nature to a harp or musical-box, the strings of the one and the teeth 

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

 bony lamina is simply nothing more nor less than a natural sound- 

 ing board, in connection with the end of which are arranged the 

 rods, attached to a strong membrane (membrana basilaris) by their 

 feet, and supported throughout by delicate cells, the whole being 

 protected above by the thick membrana tectoria, and bathed in a 

 special fluid secreted by the epithelial cell. This fluid, it should be 

 mentioned (endolymph), is cut off from the other fluid (epilymph) in 

 the general canal by the delicate membrane of Keissner. Around 

 the rods are placed the various nerve cells and nerve fibres ; of the 

 former, I believe the cells of Corti and Deiters to be the most im- 

 portant, and these being connected through the medium of the 

 membrana reticularis to the processes (which act as levers) are, of 

 course, suitably placed to perceive the slightest vibration of the rods. 



From these cells the impressions are conveyed by the nerve fibres 



