340 Journal of Comparative Neurology. 



In the investigation now under way, among other things, 

 an attempt is being made to determine the number of medul- 

 lated fibers passing between the sympathetic system and the 

 region of the spinal ganglion, A preliminary statement may 

 be here inserted to the effect that, so far, the results show that 

 if all the medullated fibers so passing be included, the number 

 would not be sufficient to account for the distal excess. But 

 even if they were sufficient in number, the canon for mammals 

 at least, is that many of the medullated fibers contained in the 

 ramus are pre -ganglionic fibers, or efferent fibers from the spinal 

 cord which pass from the cord to the sympathetic ganglion by 

 way of the ventral root. 



It has been found that a few ventral root fibers divide in the 

 vicinity of the spinal ganglion. One branch may pass through 

 the ganglion and out by the dorsal branches, while the other 

 passes on in the nerve trunk. The author ('99) has observed 

 this for the frog, and a more recent publication of Cajal ('99) 

 pictures the same for the chick. However, a splitting of ven- 

 tral root fibers cannot to any great extent, contribute to the 

 distal excess. Table II, columns 3 and 7, shows that in many 

 cases the amount of the distal excess is even greater than the 

 number of fibers in the entire ventral root. 



Taking the observations altogether, the indications are at 

 present that the distal excess cannot depend on any one set of 

 fibers. The observations point to an explanation based upon the 

 architectural arrangement of the neurones within the spinal 

 ganglion. All the more recent observations on the structure 

 of the spinal ganglion tend to show that it is far more compli- 

 cated than was at one time thought. It can now be looked 

 upon as partaking the nature of a nucleus of termination as well 

 as containing cells giving origin to the Ranvier T-fibers. 



At the present stage of the investigation, it seems prob- 

 able that the distal excess is due to the following causes : 



1. It may to a small extent be due to a splitting of 

 ventral root fibers in the vicinity of the spinal ganglion. 



2. To a splitting of the peripheral prolongation of the T- 

 fiber arising from the ordinary spinal ganglion cell, 



