SYMPATHETIC NERVOUS SYSTEM IN MAN 191 



occur within that portion of the mesenchyme which becomes 

 differentiated into the muscular and submucous layers of the 

 oesophageal wall. Nevertheless, some nerve cells which become 

 incorporated in the enteric plexuses penetrate into this mesen- 

 chymal tissue very early, although they do not show a definite 

 concentric arrangement until somewhat later. Such cells are 

 present in considerable abundance, especially at the lower levels 

 of the oesophagus in human embryos 7 to 9 mm. in length. 

 Doubtless, the above error in interpretation is in large measure 

 responsible for the discrepancy which Stewart ('20) has empha- 

 sized between his observations on this nervous complex in em- 

 bryos of the rat and those of the present writer in embryos of 

 the pig. 



In embryos 10 mm. in length vagus branches accompanied by 

 migrant cells are present all along the lesser curvature of the 

 stomach in the mesenchymal tissue which is becoming differ- 

 entiated to form the wall of that organ. During the succeeding 

 stages of development vagus branches spread round the stomach 

 and extend farther distally along the intestine. The cells which 

 give rise to the enteric plexuses increase in number, and as the 

 muscular and submucous layeis of the wall of the digestive tube 

 become differentiated, these minute ganghonic cell-masses be- 

 come concentrically arranged in two layers which give rise to the 

 myenteric and submucous plexuses. 



It is important to note that no paths along which cells migrate 

 from the sympathetic trunks or the prevertebral plexuses into 

 the pulmonary, the cardiac, and the enteric plexuses in the more 

 proximal portions of the digestive tube are estabhshed during the 

 early stages of development. Indeed, the latter plexuses develop 

 simultaneously with the sympathetic trunks and the prevertebral 

 plexuses. Sympathetic nerves grow into the plexuses related to 

 the vagi somewhat later, but not until the great majority of the 

 cells which enter their primordia are already present. Although 

 the possibility that some cells may be added to these plexuses 

 after fibrous connections with the sympathetic trunks are estab- 

 lished is not precluded, we must conclude that thej^ arise primarily 

 from cells of cerebrospinal origin which advance peripherally along 

 the vagi. 



