THE HISTOGENESIS OF THE NERVOUS TISSUES 

 A 



303 



Fig. 307. — A, Transverse section through the spinal cord of a chick embryo of the third day show- 

 ing neuraxons (F) developing from neuroblasts of the neural tube and from the bipolar ganglion cells, d. 

 B, Neuroblasts from the spinal cord of a seventy-two-hour chick. The three to the right show neuro- 

 fibrils; C, incremental cone (Cajal). 



Dorsal root 



Spongioblasts 



Neuroblasts 



Ventral root 



Fig. 308. — Transverse section of the spinal cord from human fetus of five weeks showing pear- 

 shaped neuroblasts giving rise to ventral root fibers (His in Marshall). X 150. NC, Central canal 

 of spinal cord. 



