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 funiculus 



Postmedian Septum 



Post, column 



Post root 



Lett, fun i cuius 

 Central canal 



Ant.colu, 



■Dura mater 



Ventral funiculus 



^Ant. 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. 



Post.medium septum 

 Post root 



Fascic. gracilis 



Fascic. cuneatus 



Substantia ge/atwosa 



Central 

 canal 



lat. 

 Column 



Ant. column 



Ant. funiculus 



Wnt.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 



