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nervous system than is commonly assumed. It is also hoped that these 

 facts concerning their developmental relations may throw some new 

 light on the functional relations of the vagi and the sympathetic system. 

 The writer is well aware that in this brief consideration many 

 points of importance have been inadequately treated or entirely omitted. 

 Some of these points he intends to consider in a later paper on the 

 development of the sympathetic nervous system. 



Summary. 



1) The anlagen of the myenteric and submucous plexuses, the 

 pulmonary plexus, and the cardiac plexus have their origin in nervous 

 elements which migrate from the vagus ganglia and the walls of the 

 hind-brain along the fibers of the vagus nerves. 



2) Cells migrate from the vagus trunks, either directly through 

 the tissues or along the fibers of growing branches, and gradually 

 become aggregated into cell-groups which are arranged in two broken 

 rings around the oesophagus. These cell-aggregates constitute the 

 anlagen of the myenteric and submucous plexuses. From the anlagen 

 of these plexuses in the anterior regions of the digestive tube cells 

 migrate posteriorly and give rise to the plexuses in the walls of the 

 intestine. 



3) The pulmonary plexuses have their origin in cells which, in 

 their migration from the vagus trunks, are carried out along the dorsal 

 and anterior surfaces of the bronchi. 



4) The anlagen of the cardiac plexus first appear as cell-groups 

 ventral to the trachea in the angle between the aorta and the pul- 

 monary artery. These groups are composed of cells which have 

 migrated thither from the vagus trunks. The earliest fibrous con- 

 nections are established with the vagus nerves. Sympathetic nerves 

 enter the cardiac plexus later, but continue to show migrating cells 

 after such cells no longer appear in the vagus branches. It is prob- 

 able, therefore, that cells from the ganglia of the sympathetic trunks 

 take part in the later development of the cardiac plexus. 



5) Medullary cells migrate from the walls of the hind-brain into 

 the rootlets of the vagus and spinal accessory nerves. The vagus 

 nerves contain numerous cells which are apparently migrating peri- 

 pherally. Most of these cells are to be regarded as the "indifferent 

 cells" of ScHAPER, while a few among them are to be regarded as the 

 "neuroblasts" of Schaper. Mitoses occur frequently in the ganglion 

 of the trunk and occasionally all along the vagus nerve. 



