SYMPATHETIC NERVOUS SYSTEM IN MAN 209 



the findings of the present writer in embryos of Acanthias. In- 

 deed, the evidence seemed so clear to Ganfini that he expressed 

 surprise that, after having described this condition in embryos 

 of Acanthias, the writer should have failed to describe it in em- 

 bryos of Amia. By way of explanation it may be said here that 

 the cells of nervous origin did not react to the iron-hematoxylin 

 method in the embryos of Amia at the writer's disposal as they 

 did in the embryos of Acanthias. Therefore, he was unable to 

 recognize cells of this type scattered in the mesenchymal tissue. 

 It seems entirely probable that the primordia of the sympathetic 

 trunks arise in essentially the same manner both in embryos of 

 Acanthias and Amia. Therefore, the findings of Ganfini in em- 

 bryos of Amia are highly gratifying. 



In view of the more recent work on the development of the 

 sympathetic nervous system, especially the extensive work of 

 Ganfini, the evidence that cells of medullary origin which advance 

 peripherally along the motor nerve roots become incorporated in 

 the sympathetic primordia in embryos of all classes of verte- 

 brates seems to the writer conclusive. That cells of neural- 

 crest origin take part in the development of the sympathetic 

 nervous system has been very generally conceded. The present 

 series of observations on human embryos is in full accord with 

 this conception. Precisely what part the cells from each of these 

 two sources play in the development of the sympathetic nervous 

 system cannot be determined at present. 



That both cells of medullary and of neural crest origin enter 

 the primordia of the vagal sympathetic plexuses and certain of 

 the cranial sympathetic ganglia is not apparent. The cells which 

 may be traced from the wall of the hindbrain into the rootlets 

 of the vagi are identical in appearance with the cells which be- 

 come separated from the distal ends of the ganglia on the vagus 

 trunks and advance farther peripherally; therefore, it is quite 

 impossible to identify cells of medullary origin along the vagi 

 distal to the ganglia on their trunks. Likewise, the cells which 

 migrate from the wall of the hindbrain into the rootlets of the 

 glossopharyngeal nerve cannot be traced with certainty beyond 

 the petrosal ganglion along the lesser superficial petrosal nerve. 



