NOTES AND MEMORANDA. 307 



the various sounds is concerned. Tliis cochlea, it must be 

 borne in mind, consists of a spiral canal, in form and shape 

 very similar to the inside of a snail-shell. From the axis of 

 this spiral there proceeds horizontnlly a plate of bone, the 

 lamina spiralis, almost dividing this canal into two. From 

 this plate again there extend two membranes, the membrane 

 of Russner, and the Lamina spiralis membranacea, as far as 

 the wall of the canal, thus separating it into three minor 

 canals. 



Between the layers of the membranous spinal lamina are 

 situated the so-called rods of Corli. These were first dis- 

 covered and described by the Marquis de Corti ; and although 

 since then many observers have studied the subject, yet 

 scarcely two investigators are agreed as to their exact form. 



In a general view of the rods from above, they appear 

 similar to two rows of pianoforte-hammers, rather than like 

 the keys of that instrument, to which they have been likened. 

 In a lateral view, these two rows of rods are seen sloping to- 

 wards each other, like the rafters of a gabled roof. The rods 

 consist of a shaft and two enlarged extremities, but the two 

 rows differ considerably in form ; the inner rods are attached 

 by their lower extremities to the membrana basilaris at its 

 junction with the lower lip of theliinbus, and just external to 

 the spot where the nerve-filaments emerge. They are di- 

 rected outwards and upwards, with a slight undulation to 

 meet the outer rods. The lower extremity is enlarged and 

 rounded, gradually tapering to the shaft, which is cylindri- 

 cal ; 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 articulates 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 proceeding upwards, both rows increase in 

 length with great regularity, although not in the same ratio, 



VOL. XII. NEW SER. Y 



