332 THE MORPHOGENESIS OF THE CENTRAL NERVOUS SYSTEM 



THE DERIVATIVES OF THE NEURAL TUBE 



The Later Differentiation of the Subdivisions of the Brain 



Myelencephalon.— We have seen that the wall of the spinal cord differen- 

 tiates dorsally and ventrally into roof plate and floor plate, laterally into the alar 



Mantle lijvcr 



Sulcus limilans 



Ependymal 

 la VI r 



Marginal 

 lay IT 



B 



Roof plate 



Alar plate 

 S. limilans 



Basal plate 



Spinal\^ i kj- 

 ganglion \;J > ^'' 



Ventral spinal root 



Fig. 334.-Transverse sections. X 44. A, Through the upper cervical region of the spinal cord in a 

 10 mm. human embryo; B, through the caudal end of the myelencephalon. 



plate and basal plate. The boundary line between the alar and basal plates is the 

 sulcus limilans (Fig. 334 A). The same subdivisions may be recognized in the 

 myelencephalon. It differs from the spinal cord, however, in that the roof plate 



