The neural tube caudal to the fourth pair of the somites develops into the spinal cord. The wall of the neural tube consists of the neuroepithelial cells which give rise to the neurons and macroglia cells (ependymal cells, oligodendroglia, astrocytes). The neurepithelial cells differentiate into neuroblasts, which form the mantle layer (gray matter of the spinal cord). Nerve fibers emerging from these neuroblasts constitute the marginal layer (the white matter of the spinal cord). The microglia cells differentiate from the mesenchymal cells surrounding the central nervous system.
Thickening of the lateral walls of the spinal cord causes the formation of the ventral and dorsal columns separated by a longitudinal groove, the sulcus limitans.
The ventral thickenings (basal plates) or ventral horns form the motor areas, while the dorsal thickenings (alar plates) or dorsal horns form the sensory areas of the spinal cord.
A small intermediate horn contains neurons of the autonomic nervous system. The roof and floor plate serve as pathways for nerve fibers crossing from one side to the other.