Hard EST Y, Spinal Ganglion Cells. 43 



Some years ago Stannius ('49) and Freud ('78) observed 

 splitting of the peripheral process of the spinal ganglion cell, 

 the former in fishes and the latter in Petromyzon. Dogiel ('96) 

 describes the same for mammals and Buhler ('98) suggests it 

 as an explanation of the distal excess found by him in the frog. 

 It cannot be of very frequent occurrence in the trog. From 

 my own observation I am led to believe that a splitting of the 

 peripheral process of the dorsal root ^neurone is less frequent 

 than in the ventral root fibers. Of the different frog's nerves 

 examined here only three cases of the bifurcation of this pro- 

 cess was observed. In these one product went to the dorsal 

 branches and the other continued in the nerve trunk. Dogiel 

 (p. 148) pictures this arrangement occurring in mammals. Do- 

 giel ('97) also finds division of axones in the dorsal root or 

 on the central side of the spinal ganglion. 



It may be further added in explaining the distal excess 

 that if it were mostly due to the splitting of fibers representing 

 the two roots, then for it to obtain the rate of increase mani- 

 fested, these fibers would have to either divide with increasing 

 frequency as age advances or they would have to give off branches 

 (divide) after they have grown into the nerve and become me- 

 duUated. The latter at least is hardly probable, though it might 

 be urged in support of it that the bifurcation always occurs at a 

 node in the sheath. I know of no observations directly sup- 

 porting either idea. 



The greater source of the distal excess lies perhaps in the 

 presence of fibers connected with the spinal ganglion but not 

 represented in the nerve roots at all. Such fibei-s are of sym- 

 pathetic origin and have been repeatedly described (Cajal, '93. 

 HuBER, '94, Dogiel, '96a, Cajal, '99 and others) as entering 

 the spinal ganglion and breaking up into numerous twigs which 

 terminate in telodendria about the cells there, mostly the 

 Dogiel cells of Type II. Many of these sympathetic fibers 

 are described as medullated. In my preparations of the frog, 

 by comparing sections of the ramus communicans with sections 

 of the trunk and dorsal branches, there may be seen in the lat- 

 ter numerous medullated fibers similar to those considered of 



