42 Journal of Comparative Neurology and Psychology. 



to correctly interpret each case, the ends of the fiber had to be 

 followed sufficiently to preclude the possibility of the T-fibers 

 of Ranvier or those of Dogiel cells being mistaken for the 

 type of bifurcation sought. As the fibers from the two roots 

 join to form the trunk and dorsal branches, they cross and in- 

 tertwine to an extent which renders teasing or following a fiber 

 in sections quite difficult. Owing to tearing and breaking and 

 the difficulty in following a fiber in question through the maze, 

 certain of the bifurcations observed had to be discarded as un- 

 certain. But including the uncertain cases would not have 

 made enough to account for the average distal excess. The 

 great majority of the fibers on the distal side of the ganglion 

 show no branching at all. 



For the same reasons I was especially unable to determine 

 the proportion of the dividing fibers belonging to each root 

 separately. Bifurcations of ventral root fibers are somewhat 

 more easily distinguished than those ot fibers arising in the spinal 

 ganglion. Of them it can only be said that they are certainly 

 not frequent enough to give percentage values similar to those 

 in column K, Table III. In most of the cases a ventral root 

 fiber was seen to bifurcate, sending one product of the division 

 to the dorsal branches while the other remained in the nerve 

 trunk. This is of interest physiologically for the muscle sup- 

 plied by the dorsal branches and by the trunk are usually consid- 

 ered independent. It is not an unheard of complication how- 

 ever. Cajal ('99) pictures such an occurrence in the chick and 

 discusses it physiologically, and Dunn ('02) finds frequent di- 

 visions of fibers in the sciatic of the frog, one product going to 

 a branch supplying one muscle or set of muscles and the other 

 going on in the trunk to be distributed to other muscles entirely 

 distinct. Most of the fibers going from the ventral root to the 

 dorsal branches do not bifurcate. Occasionally a fiber divides 

 after entering the dorsal branches, its parts going to different 

 divisions of the branches. If such a splitting occurs near 

 enough to the spinal ganglion to be included in the section 

 used in the counting, it of course would contribute to the dis- 

 tal excess. 



