SYMPATHETIC SYSTEM IN BIRDS 301 



source, except possibly in the posterior region of the intes- 

 tine, until fibrous connections have been established between 

 the latter and the sympathetic trunks. By this time the great 

 majority of the cells taking part in the development of the vagal 

 sympathetic plexuses are already present. The connections of 

 these plexuses with the sympathetic trunks must, therefore, be 

 looked upon as secondary. 



The period of migration of cells from the hind-brain and from 

 the vagus ganglia along the vagi is coextensive with the period 

 of migration of cells from the neural tube and the spinal ganglia 

 along the spinal nerves. The cells which migrate peripherally 

 along the vagi are cells of the same character as those which mi- 

 grate peripherally along the spinal nerves; viz., they are the " in- 

 different" cells and the "neuroblasts" of Schaper. The cells 

 giving rise to the vagal sympathetic plexuses, therefore, have the 

 same histogenetic relationships as those giving rise to the sym- 

 pathetic trunks. Mitotic figures occur occasionally along the 

 vagi and in the anlagen of the vagal sympathetic plexuses. We 

 are not to suppose, therefore, that all the cells taking part in the 

 development of these plexuses actually migrate as such from their 

 sources in the hind-brain and the vagus ganglia. Doubtless, 

 many arise by the mitotic division of indifferent cells along the 

 course of migration. 



DISCUSSION OF RESULTS, AND CONCLUSIONS 



The observations set forth in the preceding pages have shown 

 that in birds the sympathetic nervous system has its origin in cells 

 which migrate peripherally from the neural tube and the cere- 

 brospinal ganglia. The cells giving rise to the sympathetic trunks 

 and the prevertebral plexuses, including the ganglion of Remak, 

 migrate peripherally along the spinal nerves, while the cells giving 

 rise to the vagal sympathetic plexuses migrate peripherally along 

 the vagi. These observations agree essentially with the writer's 

 observations on the histogenesis of the sympathetic nervous 

 system in mammals. My observations on the histogenesis of 

 the sympathetic system agree with the findings of Froriep ('07) 



