Hardesty, spinal Nerves of the Frog. 73 



trunk is greater than that in the roots in case of the 1st, Ilird, 

 IVth and Vth, and below that in the roots in case of the Vlth, 

 Vllth, Vlllth and IXth. Values obtained from the second 

 specimen, however, show that this cannot be considered at all 

 as a general condition. As a whole, (4) the greatest variations 

 are seen to occur in the Ilird, IVth and Vth, while the Vlth, 

 Vllth, Vlllth and IXth are more similar to one another. 



The absence of data from nerves II and X is to be de- 

 plored. The abrupt rise from the 1st to the Ilird nerves might 

 be broken by data from the llnd. The explanation of why the 

 changes in the Ilird rank so much higher than those in the 

 other nerves must be deferred till further investigation of this 

 nerve can be made. As is well known, the IlIrd is the spinal 

 nerve which, in the frog, contains the greatest percentage of 

 fibers which pass to the sympathetic system, and therefore the 

 nerve contains a greater percentage of small fibers than any 

 other nerve. But, at present, no adequate explanation based 

 upon this fact can be suggested. 



To explain the decrease in the number of fibers of the ven- 

 tral root as it passes from the spinal cord toward the point of its 

 junction with the dorsal root, we assume that those fibers, 

 which grow out from the ventral horn cells have extended un- 

 equal distances from the cord. In the dorsal root, the varia- 

 tion in the number of fibers is to be explained in the same way. 

 Here the decrease is in the opposite direction from that in the 

 ventral root, and naturally so since, as is now known, very 

 nearly all the fibers comprising the dorsal root are the central 

 prolongations of the outgrowths of the spinal ganglion cells. 



This explanation is also applied to the decrease in the num- 

 ber of fibers found in the trunk between the section next the 

 ganglion and that most distal. In the trunk the great mass of 

 the fibers, at least, being of the same origin as those compos- 

 ing the roots, the changes in the roots demand that the de- 

 crease in the trunk should occur, as it does, towards the peri- 

 phery. As is well known, no branches are given off from the 

 roots, nor, with the exception of the Ilnd nerve, are any 

 branches given off from the trunk between the spinal ganglion 



