332 THE MORPHOGENESIS OF THE CENTRAL .NERVOUS SYSTEM 



DERIVATIVES OF THE NEURAL TUBE 



DIFFERENTIATION OF THE SUBDIVISIONS OF THE BRAIN 



The Myelencephalon. We have seen (p. 322 ff.) that the wall of 

 the spinal cord differentiates dorsally and ventrally into roof plate and 



A - B 



Roof plate 

 Roof plate 



Mantle layer \ 



Sulcus limitans 



Ependymal 

 layer 



Marginal 

 layer 



Spinal 

 ganglion 



Alar pi 

 S.limilans 



Basal plate 



'^ 



Ventral spinal root 



FIG. 334. Transverse sections from a 10 mm. human embryo. X 44 A, Through the upper 

 cervical region of the spinal cord; B, through the caudal end of the myelencephalon. 



floor plate, laterally into the alar plate and basal plate. The boundary 

 line between the alar and basal plates is the sulcus limitans (Fig. 334 A). 



