THE SPINAL CORD 



323 



ventral portion of the layer, which is thus narrower than the dorsal portion in 

 10 to 20 mm. embryos (Figs. 325 and 326). Consequently, the ventral portion 



Roof plalc 



Dorsal funiculus 



Neural cavity 



Marginal layer 



Dorsal column 



Dorsal root 



Mantle layer 



Ventral column 



Ependymal layer 



Floor plate Ventral median fissure 



Fig. 326. — Transverse section of the spinal cord from a 20 mm. human embryo. X 44. 



of the mantle layer is differentiated first. The neural cavity is at first somewhat 

 rhomboidal in transverse section, wider dorsally than ventrally. Its lateral angle 



Dorsal fi 



Lat. funicul 

 Central ca 



sal root 



Dura mater 



Ventral 

 column 



Spinal 

 ■i^-~, ganglion 



Ventral funiculus 



Fig. 327. — ^Transverse section of the spinal cord from a 34 mm. human embryo, showing also the spinal 

 ganglion and dura mater on the left side. X 44. 



forms the sulcus limitans (Fig. 334) which marks the subdivision of the lateral 

 walls of the neural tube into the dorsal alar plate (sensory) and ventral hasal plate 



