SYMPATHETIC SYSTEM iN MAMMALS 



231 



-'UK. 



Fig. 9 



Fiq. 10 



Fi g. 9 . Diagram illustrating the developmental relationships of the neuroblasts 

 and the embryonic supporting cells in the neural tube of mammalian embryos 

 (modified from Schaper, '97). Elongated dotted cells = ependymal cells; large 

 circular cells with crosses = germinal cells of His ; plain rounded cells = indifferent 

 cells; rounded cells with dotted crosses = indifferent cells which undergo 

 further division by mitosis; rounded cells with dots in center = neuroglia cells; 

 block cells = nerve cells. 



Fig. 10. Ganglion cells, neuroblasts, and indifferent cells, X 1100. a., Cells in 

 the spinal ganglia, b., Neuroblasts in the ventral nerve-roots, c, Neuroblasts in 

 the spinal nerve trunks, d., Bundles of fibers with accompanying indifferent 

 cells, from the spinal nerves, e., Neuroblasts in the communicating ramus. /., 

 Neuroblasts in the anlagen of the sympathetic trunks. 



of ectodermal origin undergoing mitotic division near the inter- 

 nal limiting membrane of the embryonic neural tube, giving rise 

 to cells which develop into neuroblasts. Schaper has shown that 

 the cells arising by the mitotic division of the "germinal" cells 

 of His do not all develop into neuroblasts. They are cells of an 

 indifferent character. In the lower vertebrates they are trans- 

 formed either into neuroblasts or into embryonic supporting 

 cells. In the higher vertebrates, however, many of these " in- 

 different" cells retain a capacity for further propagation by di- 



