1 8 Journal of Comparative Neurology and Psychology. 



and along both the dorsal root and the nerve trunk towards the 

 spinal ganglion, showed a gradual increase of fibers at the average 

 rate of nearly 2 % per millimeter of length of the roots and of 

 the trunk; (3) in considering the Vlth nerves alone of a series 

 of 17 specimens ranging gradually in weight from 5 grams to 

 79 grams, it was found that in this one pair of spinal nerves 

 there was for each gram of weight gained an average gain of 

 7.4 fibers in the two nerve roots and 10.4 in the trunk and dor- 

 sal branches. As to the numerical relations of the fibers pres- 

 ent on the proximal and distal sides of the spinal ganglia, there 

 was always found (4) an appreciable excess of fibers in the 

 sum of the trunk and dorsal branches as compared with the 

 sum of the dorsal and ventral roots. This "distal excess" was 

 found to vary in the different spinal nerves, ranging from 7% 

 to as much as 61 % of the sum of the two roots. It was found 

 to be greater in those spinal nerves which have a relatively 

 greater number of fibers in the dorsal branches, but showed 

 neither a regular increase nor decrease with the increase in the 

 size of the specimens. 



BiRGE ('82) had previously counted the ventral root fibers 

 of all the spinal nerves of one side of six frogs varying in weight 

 from 1.5 to III grams and, assuming the fibers of the two sides 

 approximately equal in number, his figures show an average 

 total gain of 5 i ventral root fibers for each gram gained in body 

 weight. Hatai ('02 and '03) has since determined the number 

 of medullated fibers in the dorsal and ventral roots of three 

 given spinal nerves of each of four white rats ranging in body 

 weight from 10 to 264 grams. He finds that the number of fibers 

 in the roots of these three nerves is 2.7 times greater at maturity 

 than in the 10 gram rat, and that the increase is more rapid in the 

 younger animals. Birge, though he did not take into consid- 

 eration the dorsal branches, obtained noticeable distal excesses 

 of fibers in the several nerves, and he was the first to attach sig- 

 nificance to it. Gaule and Lewin ('96) investigating the sacral 

 nerves of the rabbit, found an excess of fibers on the distal side of 

 the spinal ganglion amounting to as much as 19%, and Buhler 



