1872.] 



Function of the Rods of the Cochlea. 



371 



lower extremities to the membrana basilaris at its junction with the lower 

 lip of the limbus, and just external to the spot where the nerve-filaments 

 emerge ; they are directed outwards and upwards, with a slight undula- 

 tion to meet the outer rods. The lower extremity is enlarged and rounded, 

 gradually tapering to the shaft, which is cylindrical ; the upper extremity 

 is somewhat cuboid in form, but the outer surface is deeply concave, and 

 the upper lip of the concavity is prolonged into a process. 



The outer rods are attached to the membrana basilaris by a broad base, 

 which also gradually tapers to a cylindrical shaft. Their upper extremity 

 is less cuboid in form, and presents a convex internal surface, which arti- 

 culates with the corresponding concavity in the inner rods just mentioned ; 

 from the outer and upper part there extends outwards a slender process. 



One of the most important features with regard to these rods is their 

 relative length. Most authors state that there is very little difference in 

 the length of the two rods ; in this, however, they are much mistaken ; for 

 not only do the two sets of rods differ in this respect, but the length of 

 each varies according to its position on the cochlea. Thus, at the base, the 

 outer rods are as nearly as possible equal in length to the inner ; but pro- 

 ceeding upwards, both row*s increase in length with great regularity, 

 although not in the same ratio, 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 these rods were graduated so 

 as 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 -^-i-^ to -^yo °^ an i ncn « 

 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. 



Most authors, with the exception of Deiters, describe nuclei situated in 

 various parts of these rods, principally in the lower extremities ; but al- 

 though seen from above this appears to be the case, on closer observation 

 these so-called nuclei of the rods are found to be nothing more than the 

 nuclei of cells surrounding them. 



The arrangement of the nerves. — The cochlear nerve-fibres from the 

 portio mollis pass up the modiolus, and turn off at the lamina spiralis. 

 Just at this junction we find in the bone itself a ganglion, from which the 

 fibres proceed outward. Immediately before the end of the lower lip of 

 the limbus, the nerve-filaments pierce its upper surface, and appear close 

 to the base of the inner row of rods ; concerning the termination of these 

 nerve-filaments little is really known. 



Corti and most other authors considered this system of rods to be the 

 essential portion of the cochlea ; they supposed that 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 



