SYMPATHETIC SYSTEM IN TURTLES 



303 



e. Histogenetic relationships. The above observations on the 

 development of the myenteric and the submucous plexuses, the 

 pulmonary plexuses, and the cardiac plexus in embryos of the 

 turtle agree essentially with the writer's observations on the devel- 

 opment of these plexuses in embryos of mammals and of birds. 

 These plexuses arise from cells which have their origin in the hind- 

 brain and in the vagus ganglia and migrate peripherally along the 

 paths of the vagi. In sections passing through the vagus rootlets in 





^aU ^ 



Fig. 12 Transverse section through the anterior region of the heart in the same 

 embryo as fig. 11. X 140. B., left bronchus; C.P., anlage of cardiac plexus; 

 L.A., left atrium; L.Vag., left vagus nerve. 



embryos at about the tenth or the eleventh day of incubation 

 medullary cells may be traced from the walls of the hind-brain into 

 the rootlets of the vagi (fig. 13, Vag. R.). That such cells wander 

 into the vagus rootlets in considerable numbers cannot be 

 doubted. In many sections medullary cells are drawn out into 

 cone-shaped heaps in the vagus rootlets as they traverse the mar- 

 ginal veil. Occasionally one of these cells may be observed half 

 in and half out of the external limiting membrane, while numerous 

 cells are present in the vagus rootlets just outside the external 



