THE NERVOUS SYSTEM 237 
the dorsal root and of the sympathetic system. The first kind 
only is considered here, and they are usually called the gan- 
glionic neuroblasts s.s., because they alone remain in the spinal 
ganglia. Like the medullary neuroblasts these neuroblasts form 
outgrowths that become axis cylinder processes; but they differ 
from the latter in that each ganglionic neuroblast forms two 
axones, one from each end of the spindle-shaped cells, which are 
arranged with their long axis parallel to the long axis of the 
ganglion (Fig. 139). Thus we may distinguish a central process 
and a peripheral process from each neuroblast, the former grow- 
ing towards and the latter away from the neural tube (Fig. 139). 
In other words each ganglionic neuroblast is bipolar, as contrasted 
with the unipolar medullary neuroblasts. The central axone 
enters the dorsal zone of the neural tube, and the peripheral one 
grows out into the surrounding mesenchyme. 
Ol. 
Fig. 141. — Transverse section through the spinal 
cord of a 9-day chick, prepared by the method 
of Golgi. (After Ramon y Cajal.) 
Col., Collaterals. d.R., Dorsal root. G., Gray 
matter. Gn., Ganglion. Nbl. 4, Neuroblast of the 
ventral horn (motor). v. R., Ventral root. W., 
White matter. 
In the course of the later development the cell-body moves 
to one side so that the central and peripheral branches appear 
nearly continuous (Fig. 141). Farther shifting of the cell-body 
produces the characteristic form of the ganglionic nerve-cell with 
rounded body provided with stem from which the central and 
peripheral branches pass off in opposite directions. The central 
process enters the marginal velum near its dorsal boundary and 
