210 ALBERT KUNTZ 



Neither can cells of medullary orij2;in in the rootlets of the facial 

 nerve be traced beyond the geniculate ganglion along the greater 

 superficial petrosal nerve. On the other hand, the presence of 

 one or more ganglia on a nerve trunk does not preclude the possi- 

 bility that cells of medullary origin may advance along the path 

 of the latter. Consequently, cells derived from the walls of the 

 hindbrain may advance along the vagi into the primordia of the 

 vagal sympathetic plexuses or along the lesser superficial petrosal 

 and greater superficial petrosal nerves, respectively, into the otic 

 and sphenopalatine ganglia. Indeed, if we must admit a double 

 origin for parts of the sympathetic nervous system, there is no 

 good reason to assume that any part of it is derived exclusively 

 from cells which have their origin in the neural crest. 



This theory of the double origin of the sympathetic nervous 

 system does not imply that all the cells which become differen- 

 tiated into sympathetic neurones actually migrate from the cere- 

 brospinal nervous system into the sympathetic primordia. As 

 pointed out above. Carpenter ('06) interpreted the cells which 

 migrate from the midbrain along the oculomotor nerve in embryos 

 of the chick as the 'indifferent' cells of Schaper, i.e., cells which 

 have the capacity either to develop into neurones or supporting 

 elements. The writer, in an earlier paper ('10), presented evi- 

 dence which supports the conclusion that the cells which migrate 

 from the cerebrospinal nervous system toward the sympathetic 

 primordia in mammalian (pig) embryos are of the same type. 

 The present series of observations on human embryos justifies 

 the same conclusion. Schaper ('97) pointed out that the 'in- 

 different' cells which arise by the mitotic division of the 'germi- 

 nal ' cells of His do not become differentiated at once, but retain 

 the capacity for further division by which they give rise to new 

 generations of indifferent cells which in turn become differentiated 

 into neurones or supporting elements. As observed in the earlier 

 work referred to above, many of the cells of cerebrospinal origin 

 which migrate peripherally undergo mitotic division along the 

 course of migration or in the sympathetic primordia. The cells 

 which migrate toward the sympathetic primordia in human em- 

 bryos behave in the same manner. Mitotic figures are not un- 



