Dunn, Nerve Fibers of the Frog. 323 



furnish an explanation for so marked a variation in diameter at 

 these adjoining levels. We must consider the possibility of the 

 disappearance from the second level of the largest fibers, and 

 the consequent measurement at that point of a set of fibers of 

 less though still large caliber. The largest fibers may have 

 passsed out by way of the thigh branches to supply the thigh 

 tissues, so their presence in those branches must be determined. 

 Reference to Table XVII shows that the average area of the 

 twenty-two largest fibers in the branches approximates that of 

 the twenty-two largest fibers at a level above the branches, 

 while the measurements of the eight largest fibers in -the 

 branches, the number proportional to the total number of fibers 

 in the branches, show an average slightly greater than that 

 recorded for the largest fibers at the level above the branches. 



With these measurements for our consideration, we can 

 arrive at but one conclusion, namely, that the largest fibers of 

 the lumbosacral plexus, formed from the Vllth, Vlllth, and 

 IXth spinal nerves, pass off in the branches to the thigh and 

 therefore run a comparatively short course to terminate in the 

 tissues which lie above the knee. 



Fixing our attention upon the results of the measurements 

 below the knee, we find that the difference between the average 

 areas above and below the shank branches is 58.6 square micra 

 or 36 ^ , a greater difference than exists in the thigh. At the 

 same time we find that the distance between the levels at 

 which the measurements were made is much greater than that 

 between the corresponding levels in the thigh, so that conical 

 diminution may here exert a more decided influence than in 

 our results for the thigh. 



Comparing for the shank the average area for the largest 

 fibers in the trunks, Table XVI, with the average for the 

 branches. Table XVII, we find that the average for the largest 

 fibers at a level above the branches is nearly equal to the 

 average for the largest fibers in the branches and is much larger 

 than the average area for the largest fibers at the level just 

 below the branches. 



* We find, then, from a study of Tables XVI and XVII, 



