154 On the Structure and Function' of the Bods 



base of the cochlea, the outer rods are as nearly as possible equal 

 in length to the inner, but as we proceed upwards, both rods increase 

 in leDgth with great regularity, although not in the same ratio. 

 The outer increases with much greater rapidity, so that near the 

 apex they are twice the length of the inner. This fact is clearly 

 demonstrated by referring to one of my preparations, in which the 

 various measurements were found to be as follows ; beginning at 

 the lowest section of the lamina and proceeding upwards in regular 

 succession : — 



1st Section / Inner rod measures rrnroo of an inch - 



\Outer rod „ as nearly as possible the same. 



Inner rod measures -n 2 ?^ of an inch. 

 Outer rod 



2nd Section { £ 



1 I ) u 1 ) c I 



q a e f / Unfortunately this is not sufficiently perfect to admit of 

 rfra bection j measurement. 



.,, o, , . ( Inner rod measures .- A S rtri of an inch. 

 4th Section < ^ i4 . , 10 A 



Outer rod 



1 u u 



The 5th and 6th are not sufficiently perfect to allow of measure- 

 ment, although in the latter the rods may be seen to have increased 

 in about the same ratio. Further confirmation of this statement 

 may be obtained by comparing the rods shown in any vertical 

 sections of the lamina. 



Fig. III. represents three pairs of rods carefully drawn from 

 three sections of the cochleae of the same animal (cat). The upper- 

 most taken from near the apex of the cochlea, the next from about 

 the middle, and the lowest from near the base. 



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 r ^ T to 5 ^ of an 

 inch. Their other measurements are as follow : — 



Inch. 



Diameter of base of inner rod, about ' 0006 



„ „ outer rod „ -00075. 



„ shaft inner,, -00015. 



„ outer „ .. -00015. 



Anterioposterior measurement of upper extremity of 



inner rod, about ' 0005. 



Anterio-posterior measurement of upper extremity of 



outer rod, about " 000G. 



Lateral posterior measurement of upper extremity of 



inner rod, about ' 0002. 



Lateral posterior measurement of upper extremity of 



outer rod, about -0003. 



Length of process of upper extremity of inner rod, about ■ OOOG. 



„ „ „ outer „ -00075. 



The number of rods in each row is not the same, there being 

 three of inner for every two of the outer, and, according to a rough 

 calculation that I have made, there are about 5200 inner rods, and 

 3500 outer in the whole cochlea. 



