324 Journal of Comparative Neurology, 



I. Summary. 



1. The results obtained in a previous paper are corrob- 

 orated in the following particulars : 



a). The number of fibers in the ventral nerve root of the 

 frog decreases as the fibers pass from their cells of origin in 

 the spinal cord. 



b). The number of fibers in the dorsal root decreases as 

 the fibers pass from their cells of origin in the spinal ganglion. 



c). The section of the nerve trunk taken immediately dis- 

 tal to the spinal ganglion (dorsal branches excluded) contains 

 a greater number of nerve fibers than a section of the trunk 

 taken further distal. 



These relations are explained as due to growth or to the 

 processes by which a larger frog acquires the greater number of 

 fibers in its spinal nerves than a smaller one. 



d). In frogs of increasing weight, the fibers of the dorsal 

 root increase more rapidly than do those of the ventral root. 



e). The sum of the fibers in the trunk and dorsal branches 

 combined, exceeds and by a considerable amount, the sum of 

 the fibers contained in the two roots. We assume the addition 

 of fibers on the distal side of the spinal ganglion to correspond 

 to that found on the proximal side., but, owing to the mixing 

 of the dorsal and ventral root-fibers in the distal end of the 

 ganglion, nothing can be demonstrated. 



In addition to the corroborated results just enumerated, it 

 has been found : 



2. The excess of the sum of the trunk and dorsal 

 branches over the sum of the two roots can not be due to a 

 double counting of the same medullated sympathetic fibers 

 running in the trunk and then passing out in the dorsal branches, 

 because the greater the number of fibers composing the dorsal 

 branches as compared with the number contained in the corres- 

 ponding nerve trunk, the less does the sum of the trunk and 

 dorsal branches exceed the sum of the two roots. Neither can 

 it be largely due to the splitting of ventral root fibers in the 

 region of the ganglion, for the number of fibers constituting 



