SYMPATHETIC SYSTEM IN MAMMALS 247 



medullary cells and have variously interpreted them. Harrison 

 ('01) has shown that in the salmon the spinal ganglia arise from 

 cells which migrate out from the dorsal region of the neural tube. 

 He also observed medullary cells migrating into the ventral 

 roots of the spinal nerves, and suggested the possibility that tnese 

 cells may migrate peripherally into the ganglia of the sympathetic 

 trunks and there give rise to sympathetic excitatory neurones. 

 Bardeen ('03) observed that in mammalian embryos a certain 

 number of cells migrate from the neural tube and the spinal gan- 

 glia along the fibers of the spinal nerves. He suggested that these 

 cells take part in the development of the neurilemma. He be- 

 lieves, however, with Vignal ('83) and Gurwitsch ('00), that in 

 mammals the neurilemma is derived largely from the mesoderm. 

 Neal ('03) described medullary cells in the ventral roots of the 

 spinal nerves in Squalus acanthias, and expressed the opinion 

 that they take part in the development of the neurilemma. Car- 

 penter ('06) has shown that in embryos of the chick medullary 

 cells which he recognizes as the " indifferent" cells of Schaper, 

 migrate from the walls of the mid-brain along the fibers of the 

 abducent and the oculomotor nerves. According to Carpenter 

 most of these cells become distributed along the nerve-trunks 

 and may be recognized as the cells which give rise to the neuri- 

 lemma. In the oculomotor nerve, however, some of these " in- 

 different" cells migrate farther peripherally and give rise to 

 neurones in the ciliary ganglion. Carpenter and Main ('07) are 

 of the opinion that some of the medullary cells which they ob- 

 served migrating into the ventral roots of the spinal nerves in 

 embryos of the pig become cells of the neurilemma and there sub- 

 serve a supporting function similar to that of the neuroglia cells 

 in the central nervous system. Cajal ('08) described elements 

 which he recognizes as nerve cells in the bipolar phase, in the ven- 

 tral roots of the spinal nerves and certain of the cranial nerves in 

 the chick. 



Although the advocates of the theory of local differentiation 

 and the multicellular nature of nerve-fibers reject the theory of 

 the migration of nervous elements, the results of recent researches 

 are so convincing that we must accept the migration of medullary 



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



