Georffc L. Streeter 



91 



rounded by protoplasm, are compactly clumped together, the whole form- 

 ing a row of pillow-like bodies whose ventral borders are lost among the 

 fibres of the ventral roots.- It was not possible to determine as to whether 

 or not the ventral borders of the ganglia are involved at this stage in 

 fibroblast formation, and contribute fibres to the nerve root, because of 



Opthal div 



Fig. 4. Reconstruction of peripheral nerves in four weeks human embryo, 6.9 mm. long. 

 His collection Embryo Br3. Enlarged 16.7 diams. 



the difiiculty of differentiating them from the mesodermal sheath cells 

 of the ventral roots. 



The fibres of the spinal nerve roots form compact bundles which 

 branch, as they extend forward, and form intersegmental anastomoses. 

 The profuse anastomosis of the nerve roots from the fourth cervical to the 

 first dorsal segment marks a primitive brachial plexus. (See Fig. 4.) 



