THE SPINAL CORD 



323 



wider dorsally than ventrally. Its lateral angle forms the sulcus limitans 

 (Fig 334), which marks the subdivision of the lateral walls of the neural 



Roof plate 



Dvrsal column 



Dorsal funiculus 



Neural cavity 



Marginal layer 



Ependymal layer 



Floor plate Ventral median fissure 



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



tube into the dorsal alar plate (sensory) and ventral basal plate (motor). 

 When the ependymal layer ceases to contribute new cells to the mantle 



Dorsal funiculus 



Lat. funiculus 

 Central canal 



Dura mater 



Spinal 

 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. 



layer, its walls are approximated dorsally. As a result, in 20 mm. embryos 

 the neural cavity is wider ventrally (Fig. 326). In the next stage, 34 mm., 

 these walls fuse and the dorsal portion of the neural cavity is obliterated 



