SYMPATHETIC SYSTEM IN MAMMALS 245 



cardiac plexus have a common origin which is distinct and sepa- 

 rate from the origin of the sympathetic trunks. They arise from 

 cells which have their origin in the vagus ganglia and the walls 

 of the hind-brain. As in the case of the sympathetic trunks, 

 however, we are not to suppose that all the cells taking part 

 in the development of the vagal sympathetic plexuses actually 

 migrate as such from their sources in the cerebro-spinal nervous 

 system. Doubtless, many arise by the mitotic division of "in- 

 different" cells along the course of migration and in the anlagen 

 of these plexuses. The vagus ganglia and the walls of the hind- 

 brain, therefore, constitute a source which is sufficient to account 



Fig. 17. Neuroblasts and indifferent cells located in the vagi and the ganglia 

 of the trunk, X 1100. 



a., Neuroblast in the vagus rootlets, b., Neuroblasts in the vagus trunks, c, 

 Neuroblasts in the ganglia of the trunk. (/., Bundles of fibers with accompanying 

 indifferent cells, from the vagus trunks. 



for all the cells which take part in the early development of the 

 vagal sympathetic plexuses. Migrant cells cannot be traced from 

 the sympathetic trunks into the anlagen of these plexuses until 

 the nerves connecting the latter with the sympathetic trunks are 

 present. At this time the vagal sympathetic plexuses are well 

 established, and the great majority of the cells taking part in 

 their development are already present. We may conclude, there- 

 fore, that the nerves entering the vagal sympathetic plexuses 



THE JOURNAL OF COMPARATIVE NEUROLOGY AND PSYCHOLOGY, VOL. 20, NO. 3. 



