300 



ALBERT KUNTZ 



(e.) Histogenesis. — In sections through the head-region of em- 

 bryos in the 96-hour stage, medullary cells may be traced from the 

 walls of the hind-brain into the rootlets of the vagus and the spinal 

 accessory nerves (fig. 10, c.m.vag.r.). That these cells migrate 

 peripherally from the walls of the hind-brain in considerable 

 numbers cannot be doubted. In many sections they may be 

 observed pushing into the nerve-rootlets in cone-shaped heaps 

 as the latter traverse the marginal veil. Occasionally medullary 

 cells are observed half in and half out of the neural tube, and 



c.m.vag.r. 



vag$ 



gj§i <£> ® <& <B®%,¥ 





j^U® <2> <5) ® ®£^ 



elm. 



-dm. 

 g.c. 



Fig. 10. Transverse section through the wall of the hind-brain of an embryo of 

 the chick (96 hours incubation), X 550. c.m.vag.r., cells migrating into roots of the 

 vagus; el.m,., external limiting membrane; g.c, germinal cells of His; i.l.m., in- 

 ternal limiting membrane; vag.r., roots of vagus nerve. 



many are present in the nerve-rootlets just outside the external 

 limiting membrane. With similar cells which wander out from 

 the vagus ganglia, these cells migrate peripherally along the 

 fibers of the vagi. As these cells migrate peripherally and the 

 vagi give rise to fibrous branches, cells wander out from the 

 vagus trunks and give rise to the vagal sympathetic plexuses. 

 That such is the origin of the cardiac plexus and the sympa- 

 thetic plexuses in the walls of the visceral organs in the chick 

 cannot be doubted. The figures of cells migrating from the 

 vagi into the anlagen of these plexuses are perfectly clear. 

 Nor can cells be traced into these plexuses from any other 



