THE CENTRAL NERVOUS SYSTEM. 2 8g 



in the middle of which lies the minute central canal, the direct 



FIG. 322. 



Section of spinal cord from lower part of lumbar region of child : V, D, ventral and dorsal 

 median fissures. 



continuation of the ventricular cavities of the encephalon and the 

 remains of the large neural canal of early foetal life. That part of 



FIG. 



, 



Portion of section of spinal cord of calf, including central canal and 

 commissures : a, b, anterior and posterior median fissures ; c, central canal, 

 lined with ciliated epithelium,^/ e, surrounding substantia gelatinosa ; f, 

 gray commissure ; g, white matter ; h, white commissure ; , decussating 

 nerve-fibres ; k, nerve-fibres in section. 



the gray commissure lying in front of the central canal constitutes 



19 



