24 ALBERT KUNTZ 
cells which give rise to neurons and supporting elements in the 
central nervous system was pointed out by the writer in earlier 
papers. Furthermore, the conclusion was drawn that the sym- 
pathetic system is homologous with the other functional divi- 
sions of the nervous system. The experimental data presented 
in this paper also justify this conclusion. 
SUMMARY 
The genetic relationship of the sympathetic to the cerebro- 
spinal nervous system is experimentally demonstrated. 
The primordia of the sympathetic trunks and the preverte- 
bral sympathetic plexuses arise, in the absence of spinal ganglia 
and dorsal nerve-roots, exclusively from cells of medullary ori- 
gin which advance peripherally along the paths of the ventral 
nerve-roots. The majority of the cells which normally enter the 
primordia of the sympathetic trunks and the prevertebral plex- 
uses arise in the intermediate portions of the walls of the neural 
tube. Experimental evidence also indicates that a small quota 
of cells normally advances from the spinal ganglia into the sym- 
pathetic primordia. 
In the absence of spinal ganglia and dorsal nerve-roots, the 
efferent fibers of the spinal nerves, both in embryos of the chick 
and the frog, are accompanied by cells of medullary origin. Ob- | 
viously, cells of medullary origin become incorporated in the 
neurilemma of these fibers. 
The primordia of the vagal sympathetic plexuses arise in 
embryos in which the peripheral migration of cells of cerebro- 
spinal origin is prevented throughout the trunk region by early 
operation. They do not arise in embryos in which the vagi were 
eliminated by early operation, although the primordia of the 
sympathetic trunks and the prevertebral plexuses are present. 
These findings warrant the conclusion that the vagal sympathe- 
tic plexuses arise from cells which advance from the vagus gan- 
glia and the walls of the hindbrain along the paths of the vagi. 
However, a late contribution of cells from the primordia of the 
sympathetic trunks to the primordia of these plexuses is not 
precluded. 
