322 



THE MORPHOGENESIS OF THE CENTRAL NERVOUS SYSTEM 



cells of the ependymal layer. A ventro-lateral thickening first becomes promi- 

 nent in embryos of 10 to 15 mm. (Fig. 307). This is the ventral gray column, or 

 horn, which in later stages is subdivided, forming also a lateral gray column (Fig. 



Dorsal fumculus 



Post, column 



Post-median Septum 



Laf.funiculus 

 Central canal 



Ant.colu 



Post, root 



Dura, mater 



Ventral funiculus 



/Int. median fissure 



FIG. 309. Transverse section of the spinal cord from a 34 mm. embryo, showing also the spinal ganglion 

 and dura mater on the left side. X 44. 



Postmecl!um septum 

 Post root 



Post, col urn 



Fasctc. gracflls 



Lat<fun!c 



Fascic. cuneatus 



2ubstant!a gelatmosa. 



' : i V."-I-'-"'*A Centred , 

 cdna.1 



Lat. 



Column 



Ant. column 



^iiim^y \ 



Ant. funiculus ' Ant. median fissure 



FIG. 310. Transverse section of the spinal cord from a 65 mm. embryo. X 44. 



310). It is a derivative of the basal plate. In embryos of 20 mm. a dorso-lateral 

 thickening of the mantle layer is seen, the cells of which constitute the dorsal 

 gray column or horn (Figs. 208 and 209) ; about these cells end the collaterals of 



