204 ALBERT KUNTZ 



advance along its branches and give rise to minute sympathetic 

 ganglia throughout the portion of the tongue which is innervated 

 by the glossopharj^ngeal nerve. 



SOURCES OF THE SYMPATHETIC NEURONES 



A review of the literature indicates that all the earlier investi- 

 gators who recognized the ectodermal origin of the sympathetic 

 nervous system supported the theory that the cells which give 

 rise to the sympathetic primordia are in some manner derived 

 from the cerebrospinal ganglia (or neural crest). Following the 

 introduction of the principle of the migration of these cells by 

 His, Jr. ('91), all, except the advocates of the theory of local 

 differentiation and the multicellular nature of nerve fibers, sup- 

 ported a theory according to which these cells either migrate 

 along the fibrous paths of cerebrospinal nerves and communi- 

 cating rami or in advance of these fibers either along the paths 

 later occupied by them or directly through the mesenchyme. It 

 was early observed that cells identical in appearance with those 

 which migrate from the spinal ganglia into the primordia of the 

 sympathetic trunks are present in the ventral roots of the spinal 

 nerves from the very beginning of the period of migration. It 

 was also observed that cells of nervous origin inigrate from the 

 walls of the neural tube into the motor roots of the spinal and 

 certain of the cranial nerves. Such observations made on em- 

 bryos of the lower vertebrates, especially the Elasmobranchii, 

 indicate that cells of medullary origin migrate into the motor 

 roots of the spinal nerves in considerable abundance. In em- 

 bryos of the higher vertebrates an abundant migration of such 

 cells into the motor nerve roots is less apparent. Nevertheless, 

 the recorded observations justify the conclusion that many of 

 the cells which advance peripherally along the spinal nerves are 

 derived from the ventral half of the neural tube. In spite of the 

 knowledge of the presence of these cells of medullary origin in 

 the paths along which cells advance into the primordia of the 

 sympathetic trunks, they have not generally been considered of 

 any consequence in the development of the sympathetic nervous 

 system. 



