SYMPATHETIC SYSTEM IN MAMMALS 253 



VI. SUMMARY 



1. The sympathetic trunks arise as a pair of cell-columns 

 lying along the sides of the dorsal surface of the aorta. In the 

 early stages, medullary cells migrate from the neural tube into 

 the dorsal and the ventral nerve-roots. The cells which migrate 

 into the ventral nerve-roots, with similar cells which wander 

 down from the spinal ganglia, migrate peripherally along the spi- 

 nal nerves. Some of these cells deviate from the course of the 

 spinal nerves and, migrating along the paths of the communicating 

 rami, give rise to the sympathetic trunks. These findings differ 

 materially from those of the earlier investigators. They agree 

 essentially with the findings of Froriep. 



2. The prevertebral plexuses arise as cell-aggregates lying 

 along the ventro-lateral aspects of the aorta in the posterior re- 

 gion of the body. They are derived directly from the sympathetic 

 trunks. 



3. The cardiac plexus and the sympathetic plexuses in the 

 walls of the visceral organs are not derived from the sympathetic 

 trunks, as has hitherto been supposed, but have their origin in 

 nervous elements which migrate from the hind-brain and the vagus 

 ganglia along the fibers of the vagi. In view of the relation of 

 these plexuses to the vagi, the author has chosen to designate 

 them as " vagal sympathetic" plexuses. These findings give the 

 vagi an importance in the development of the sympathetic sys- 

 tem which has hitherto been unrecognized. 



4. The cells migrating peripherally from the cerebro-spinal 

 system along the spinal nerves and the vagi are the descen- 

 dants of the ''germinal" cells of His; viz., the "in different" 

 cells and the "neuroblasts" of Schaper. Therefore they are 

 homologous with the cells giving rise to the neurones and the 

 supporting elements in the central nervous system. 



5. The cells migrating peripherally along the spinal nerves 

 and the vagi do not all take part in the development of the sym- 

 pathetic system. Some become distributed along the nerve- 

 fibers and give rise to the neurilemma. Therefore, the cells of 



