HISTOGENESIS OF THE NERVOUS TISSUES 



303 



fl 



FIG. 307. The differentiation of neuroblasts in chick embryos of the third day. A, 

 Transverse section through the spinal cord, showing neuraxons (F) growing from neuroblasts 

 and from bipolar ganglion cells (d). B, Single neuroblasts, showing neurofibrils and incre- 

 mental cone (c). . Cajal. . 



Dorsal root 



Spongioblasts 



Neuroblasts 



Ventral root 



FIG. 308. Transverse section of the spinal cord from a human fetus of five weeks, showing 

 the origin of ventral root fibers from neuroblasts (His in Marshall) 150. X. 



