324 Journal of Comparative Neurology. 



that the area of the largest fibers at the ankle is less than one- 

 half that of the largest fibers in the sciatic nerve above the level 

 at which the first branches pass off to the thigh. While there 

 may be present a conical diminution of the nerve fibers in their 

 course, yet the actual presence of fibers in the branches equal 

 in their area to the area of the largest fibers in the trunk above 

 the branches, and the absence of fibers of equal diameter below 

 the level of the branches seems to justify the definite statement 

 that the largest fibers at each level of the sciatic nerve run the 

 shorter course, while the largest fibers which innervate tissues 

 more remote from the spinal cord are of less diameter. 



4. Possibility of conical diminution in the ■extent of the nerve 

 fiber. 



Although the foregoing explanation seems the correct one 

 for the great decrease in diameter when the largest fibers in a 

 section above the branches are compared with the largest fibers 

 in a section immediately below the branches, it is possible that 

 conical diminution of the nerve fiber in its course may be pres- 

 ent and exert some influence upon the results obtained. 



By comparison of the averages for the measurements at 

 successive levels between the first and last of which no fibers 

 are given off, we obtain certain interesting results. The levels 

 considered are those of S, , S3 , T f-P, and T and P, Table 

 XVI. Measurements are here obtained at levels of more than 

 four centimeters distance from S, which show a gradual dimi- 

 nution in the average areas of the largest fibers at successive 

 levels, with a total diminution, from the level below the branch- 

 es to the thigh, to that above the branches to the shank, of 8.2 

 square micra. 



This gradual, though slight, decrease seems to point to a 

 confirmation of the theory of the conical diminution of the 

 nerve fiber in its course. 



Stilling (1869, pp. 931 to 935) in his classical re- 

 searches upon the spinal cord, during the course of an historical 

 and critical survey of the question of the decrease in diameter 

 or the conical diminution of the nerve fiber, states that in the 



