SYMPATHETIC SYSTEM IN BIRDS 



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appear in the ventral roots of the spinal nerves (72-hour stage) 

 cells may be traced from the motor niduli, across the marginal 

 veil, into the proximal part of the ventral nerve-roots. Medullary 

 cells become aggregated in the proximal part of the ventral 



c.md.n.% 



m.nrr 



sp.n. cmvr 



Fig. 3. Transverse section of the neural tube and the spinal ganglion of an em- 

 bryo of the chick (105 hours incubation), X 190. c.m.d.n.r., cells migrating into 

 dorsal nerve-root; c.m.v.r., cells migrating into ventral nerve-root; g.c, germinal 

 cells of His; m.n.r., motor nerve-root; nc, notochord; sn.r., sensory nerve-root; 

 sp.g., spinal ganglion; sp.n., spinal nerve. 



nerve-roots and soon appear to migrate peripherally along the 

 nerve-fibers. While the spinal ganglia are becoming differentiated 

 from the neural crest, cells apparently having their origin in the 

 neural tube wander out into the spinal ganglia. Evidence of this 



