SYMPATHETIC NERVOUS SYSTEM IN MAN 207 



incorporated in the primordia of the sympathetic trunks. In 

 embryos which are somewhat further advanced in their develop- 

 ment the primordia of the sympathetic gangha appear in contact 

 with the sensory and not with the motor roots of the spinal 

 nerves, as described by Held. After this condition obtains the 

 genetic relationship of the sympathetic ganglia to the motor 

 roots of the spinal nerves is no longer apparent. 



Neal ('14) has taken exception to these findings. He admits 

 the possibility that cells of medullary origin may enter the sym- 

 pathetic primordia, but he insists that the present writer has 

 ''presented no facts which make this Inference seem more cer- 

 tain." Indeed, he does not admit that the evidence presented 

 indicates that cells of cerebrospinal origin become scattered in the 

 mesenchymal tissue along the dorsolateral aspects of the aorta. 

 He seems to regard the differentiation upon which the writer 

 based his conclusion that certain cells present in this mesenchymal 

 tissue in sections of early embryos of Acanthias are cells of cere- 

 brospinal origin which have migrated thither as the creation of a 

 too vivid imagination. The interpretation of these cells was 

 based on the size, character, and staining qualities of their nuclei. 

 These are the criteria which have commonly been employed ijri 

 the recognition of cells of nervous origin lying outside the cere- 

 brospinal nervous sj^stem in early embryos. Cells of this type 

 are present in considerable abundance in the mesenchymal tissue 

 along the dorsolateral aspects of the aorta just before the pri- 

 mordia of the ganglia of the sympathetic trunks appear as com- 

 pact cell-masses, but gradually become less abundant as these 

 cell-masses increase in size. This fact was interpreted as evi- 

 dence that these cells become incorporated in the primordia of 

 the sympathetic trunks. It might have been pointed out further 

 that it would be quite impossible to account for all the cells 

 present in the motor roots of the spinal nerves in early embryos 

 of Acanthias by the number of cells associated with the fibers 

 of these motor roots soon after the primordia of the ganglia of the 

 sympathetic trunks appear as compact cell-masses in contact with 

 the sensory roots of the spinal nerves. Neither can the rapid 

 increase in size of these ganglionic masses following their earliest 



