SYMPATHETIC SYSTEM IN MAMMALS 



223 



rami extend into the anlagen of the sympathetic trunks (fig. 2, 

 c.r.). It may be noted in passing that in some embryos 10 mm. 

 in length the number of cells accompanying the fibers of the spinal 

 nerves has materially decreased, while in other embryos of the 

 same length, the "accompanying" cells are equally as numerous 

 as in the preceding stages. We may conclude, therefore, that 



i «.*••• • • • $J % \ -V.V.7 



Fig 3. Transverse section of the dorsal part of the neural tube of an embryo 

 7 mm. in length, showing cells migrating into the dorsal nerve-root, X 275. 



there is a notable degree of individual variation in the rate of 

 development. 



(b) Cell migration. — In a recent paper 1 the writer has described 

 the migration of nervous elements from the. neural tube and the 

 spinal ganglia, along the spinal nerves and the communicating 

 rami, into the anlagen of the sympathetic trunks. The earliest 



1 A contribution to the histogenesis of the sympathetic nervous system. Ana- 

 tomical Record, vol. 3, no. 8, pp. 458-465. 



