Dunn, Nerve Fibers of the Frog. 321 



and the departure of these large fibers to the thigh tissues, as 

 we shall show by our measurements upon the largest fibers at 

 the two levels and in the branches. A second factor influenc- 

 ing this decrease is the diminution in caliber in the course of 

 the individual nerve fibers. 



That the second factor is subsidiary to the first is shown 

 by the fact that the distance between the first and second levels 

 is a comparatively short one, while the decrease in average area 

 is very marked. We proceed to discuss these factors in detail. 

 3. Average areas ^/the largest fibers at the various levels. 



We have suggested that the largest fibers at a level above 

 the branches to the thigh and shank respectively are not present 

 at a level below the branches. To verify this observation and 

 to ascertain absolutely the destination of these fibers, measure- 

 ments were made of a selected number of the largest fibers at 

 these levels and also in the branches themselves. The number 

 to be measured at each level was made proportionate to the 

 total number of fibers at that level. 



Table XVI indicates for the sciatic nerve and its subdivis- 

 ions, the number of fibers measured, the level, its designation, 

 and the average area of the fibers expressed in square micra, 

 while Table XVII records the measurements for the branches. 

 The measurements recorded in Table XVI are for the levels 

 above and below the branches to the thigh and the shank, and 

 control measurements, as the third and fourth records, which 

 were made at levels lying between the level below the 

 thigh branches and that above the shank branches. In 

 Table XVII two sets of measurements are recorded; the first is 

 the average area of the number of fibers corresponding to that 

 measured in the section at a level above the branches; the 

 second shows the average of the number which correspond 

 to the proportion which the number of fibers in the branches 

 bears to the number in the trunk. The tabulated measurements 

 are for the left side of Frog II B. 



