242 Journal of Comparative Neurology 



same level contains 2868 nerve fibers in an area of .362 of a 

 square millimeter, and gives an average of 126 square mi era for 

 each nerve fiber. 



Hence the average area for each fiber innervating the 

 shank and foot in frog B, is 125 square niicra for the left side, 

 126 square micra for the right side. 



4. Comparison of the average area for the fibers to' the thigh 

 with that for the fibers to the shank and foot. 



The average area for each nerve fiber to the thigh has al- 

 ready been considered. The averages, as given in Table XI, 

 are 170 square micra for each fiber of the left thigh, 166 square 

 micra for each fiber of the right thigh. In contrast to this aver- 

 age, we find, from Table XII, that the average area for each fiber 

 to the shank and foot is 125 square micra for the left leg, 126 

 square micra for the right leg. The shank and foot fibers are 

 thus shown to be of a less caliber than those to the thigh. 

 The significance of this superiority in size of the thigh fibers is 

 very great when we consider that in accordance with the gen- 

 erally accepted law of Schwalbe,^ the greater caliber should 

 belong to the fibers of the nerve which has the greater extent, 

 and so to the fibers which innervate the shank and foot. In 

 order to complete the proof that the largest sciatic fibers in- 

 nervate the tissues of the thigh, measurements for the areas 

 were made upon the ten largest fibers in the section of the sci- 

 atic nerve above the branches. The average area for these ten 

 fibers was 287 square micra. Similar measurements on the 

 sciatic nerve section below the branches yielded an average area 

 of 186 square micra, thus showing that the very largest fibers 

 were absent at the lower level. Measurements of the largest 

 fibers in the branches to the thigh yielded fiber areas equal to 

 those in the section above the branches. From this observation 

 we may justly conclude that the largest sciatic fibers do not run 

 the longest course. The discussion of this superiority in size 

 of the thigh fibers will be postponed until a study of the sciatic 

 fibers to the shank has been completed. 



' Ueber die K aliberverhaltnisse der Nervenfasern. von G. Schwalbe, 

 Leipzig, 18S2. 



