214 NORMAL HISTOLOGY. 



sumes differs considerably in different parts of the 

 cord, but has, in general, the form of an unsymmet- 

 rical H ; the cross-arm of the H is formed, in great 

 part, by the nerve-substance which connects the 

 lateral halves of the cord, and is called the gray 

 commissure ; the uprights of the H lie completely 

 imbedded within the white matter of the lateral 

 halves ; the anterior and broader ends being called 

 the anterior cornua, the posterior and narrow ends 

 the posterior cornua. Within the gray commissure, 

 and separating it into an anterior and a posterior 

 portion, a narrow canal, called the central canal, 

 runs the entire length of the cord ; it is lined, in 

 early life at least, with cylindrical ciliated cells, and 

 is surrounded by delicate connective tissue. From 

 the anterior and posterior cornua the spinal nerves 

 pass off, dividing the white matter into three toler- 

 ably distinct portions called the anterior, lateral, 

 and posterior columns. 



In the white substance of the cord we find nerve- 

 fibres, connective tissue, and blood- and lymph-ves- 

 sels. The fibres are for the most part medullated, 

 but have not, so far as we can determine with the 

 technical facilities at present at our disposal, any 

 neurilemma. They vary greatly in diameter, and 

 although a large majority of them run longitudi- 

 nally for the greater part of their course, we find 

 in each transverse section a considerable number 

 which run in an oblique or horizontal direction. 



