4 



MORPHOLOGY OF THE 



The two dorsal zones unite bv the obliteration of that 

 part of the medullary canal which separates them, and as 

 a result of this union the future posterior septum of the 

 adult spinal cord is formed. 



The portion of the medullary canal which is bounded by 

 the two ventral zones remains throughout life as the cen- 

 tral canal of the cord. 



Fig. 2. 



(Minot. 37G.) Section of the spinal cord of a human embryo of sixty-three 

 to sixty-eight days. Minot Coll., Xo. 138 (Dorsal region), a. Goll's cord. 6, 

 Burdach's cord (Keilstrang). Dr, dorsal root. Cc, central canal. Ac^ anterior 

 cornu. F. anterior fissure. 



The medullary substance of the two ventral zones in- 

 creases rapidly, and in such a manner as to leave a space 



