CHAPTER III. 

 The Spinal Cord. 



IN transverse sections, the spinal cord shows a large mass of 

 gray matter surrounding the central canal, with white 

 matter disposed outside it. The shape of the section as 

 a whole and the shape of the mass of gray matter vary some- 

 what according to the level of the cord from which the section 

 is taken, the relative areas of gray and white matter also 

 varying (see PL V.). The gray matter, however, always 

 appears in transverse sections to have roughly the shape of 

 the letter H. The afferent nerve roots enter the cord opposite 

 the dorsal horn of the H, or dorsal column of gray matter 

 (cormc dorsalis), while the efferent fibres arise from cells in 

 the ventral horn, or ventral column of gray matter {cornu 

 ventralis), and leave the cord opposite it. The superficial 

 part of the dorsal column is distinct from the rest, having a 

 clearer appearance, and is known as the gelatinous substance 

 of Rolando {substantia gelatinosa Rolandi). This is very 

 massive in the rat, where it does not vary very greatly in 

 shape at different levels of the cord, as in man and many 

 other animals, but forms a broad, thick cap over the under- 

 lying parts. 



The section is divided into lateral halves by the deep 

 fissure which runs along the ventro-median aspect of the cord 

 {ventral or anterior median fissure) and the shallow dorso- 

 median fissure, which is continued in towards the central 

 canal by a sheet of connective tissue, the dorsal or posterior 

 median septum. In each of the lateral halves thus formed, 

 the white matter is further divided by the gray columns and 

 the nerve roots into dorsal, lateral, and ventral funiculi. The 



