SYMPATHETIC SYSTEM IN MAMMALS 251 



roots wander out from the ventral zone and from the region in 

 which later the lateral horn of the gray matter arises. This also 

 is in full accord with the conditions in the adult nervous system. 

 The neurones in the cerebro-spinal ganglia, as far as is known, 

 are sensory in character, while the cells whose axones constitute 

 the fibers of the motor nerve-roots are located in the ventral part 

 of the neural tube. Furthermore, the investigations of Kohn- 

 stamm ('00) render the existence of efferent fibers in the dorsal 

 nerve-roots of the higher vertebrates extremely doubtful. Inas- 

 much as nervous elements which have the capacity to develop 

 into neurones migrate peripherally along both the sensory and 

 the motor nerve-roots, we are driven to the conclusion that the 

 sympathetic excitatory elements migrate from the neural tube 

 along the fibers of the motor nerve roots, while the sympathetic 

 sensory neurones, wherever such neurones exist, arise from cells 

 which wander out from the cerebro-spinal ganglia. This inter- 

 pretation makes the sympathetic neurones entirely homologous 

 with the efferent and the afferent components of the other func- 

 tional divisions of the peripheral nervous system. 



(d) A wider application of Schaper's conception. — As has been 

 shown in the preceding pages, the cells which migrate peripherally 

 from the neural tube and the cerebro-spinal ganglia have a com- 

 mon origin; they are the descendants of the "germinal" cells of 

 His; viz., the " indifferent " cells and the "neuroblasts" of Schaper. 

 Therefore, Schaper's conception of the developmental relation- 

 ships of the neurones and the supporting elements in the central 

 nervous system may be extended to the sympathetic neurones 

 and the cells of the neurilemma. 



(e) The relation of the sympathetic to the central nervous system. — 

 In the light of the present investigation, the sympathetic system 

 bears a direct genetic relationship to the central nervous system. 

 The cells giving rise to the sympathetic trunks, and the preverte- 

 bral plexuses migrate peripherally along the spinal nerves, while 

 those giving rise to the vagal sympathetic plexuses migrate 

 peripherally along the vagi. The cells giving rise to the sympa- 

 thetic neurones, however, all have the same genetic relation- 

 ships; they are the descendants of the "germinal" cells of His. 



