24 Journal of Comparative Neurology and Psychology. 



number of fibers in the dorsal root computed till all the nerves of a 

 specimen had been completed. 



The serial sections were always followed for some distance on either 

 side of the spinal ganglion proper in search of out-lying ganglion cells. 

 In one case these comprised the appreciable total of 31 cells. In most 

 cases the number was very small. In some cases they were more 

 abundant in the beginning of the dorsal root, in others there were 

 more in the trunk. In the Vth and Vlth nerves, the mass of the 

 ganglion shows a tendency to protrude distally along the dorsal 

 branches instead of along the trunk. This is due to the probable 

 fact that most of the fibers of the dorsal branches are cutaneous in 

 their distribution. 



///. General results of the enumeration. 



Following the procedure indicated above, the Vth, Vlth 

 and IXth spinal nerves were investigated from 7 frogs varying 

 in body weight from 7 to 63.4 grams. The number of ganglion 

 cells in the spinal ganglia of each nerve was determined and the 

 number of nerve fibers present in the dorsal root, the ventral 

 root and the number in the dorsal branches and in the trunk 

 taken close up to the peripheral border of the spinal ganglion 

 but beyond the region of outlying gangHon cells. The general 

 results of these enumerations are given in the following tabu- 

 lated form : 



Table I. Showing in their respective columns the number of fibers in the 

 dorsal roots, the number of cells in the spinal ganglia, the number of fibers in 

 the ventral roots and in the trunks and dorsal branches of the Vth, Vlth, and 

 IXth spinal nerves of 7 frogs varying in body weight as indicated in the first 

 column. The ratios of the ganglion cells to the dorsal root fibers (col. C) are 

 obtained by dividing the numbers in col. B by those in col. A. The figures in 

 col. E result from subtracting those in col. F (fibers in the ventral roots) from 

 those in col. G, and the ratios in col. D are obtained by dividing those in col. B 

 by the respective numbers in col. E. The sums of fibers in the two nerve roots 

 and the sums in the trunk and dorsal branches of each nerve are entered 

 (col's. K andG) for purposes of comparison, but especially that the correctness 

 of the amount of the excess of fibers on the distal side of the spinal ganglion 

 (col. I) may be determined. The percentage of the "distal excess" (col. J) re- 

 sults from dividing the amount of the distal excess (col. I) by the sum of fibers 

 in the dorsal and ventral roots (col. K). The ratios comparing the number of 

 fibers in the ventral roots with the number of fibers in the dorsal roots (col. L) 

 are obtained by dividing the numbers in col. A by those in col. F. 



