SPINAL CORD 



415 



As the nerve fibers which occupy the interstices of the neuroglia net- 

 work increase in number and acquire myelin sheaths, thus becoming larger, 

 the protoplasm of the neuroglia is compressed into stellate accumulations, 

 often surrounding a nucleus (Fig. 428, A). In Golgi preparations they 

 appear as in Fig. 427, and are described as long rayed, and short rayed 

 or mossy cells. These forms represent clumps of neuroglia fibers, some- 

 times clogged with precipitate, in the center of which there may or may 

 not be a nucleus. 



The nerve fibers of the white substance vary in diameter, the coarsest 

 being found in the ventral funiculi and lateral parts of the dorsal funiculi; 



1 h f a g 



FIG. 426. NEUROGLIA CELLS AND FIBERS FROM THE SPINAL CORD OF AN ELEPHANT. (Hardesty.) 

 c i, Successive stages in the transformation of neuroglia cells, ending with disintegrating nuclei (i) ; 1, a 

 leucocyte. Benda's stain. X 940. 



the finest are in the medial parts of the dorsal and lateral funiculi. Else- 

 where coarse and fine fibers are intermingled. Their general direction 

 is parallel with the long axis of the cord. Like other nerve fibers they 

 consist of fibrillae imbedded in neuroplasm. Most of them are medullated, 

 and in cross section the myelin often forms concentric rings. Although a 

 few observers have described nodes, it is generally considered that there 

 are no nodes in the central nervous system. During the development of 

 the myelin, fibers have been found encircled by sheath cells, Fig. 428, B, 

 as described by Hardesty (Amer. Journ. Anat., 1905, vol. 4, p. 329-354). 

 In longitudinal view, these sheath cells are seen in depressions of the 

 myelin, where they greatly resemble the neurolemma cells of peripheral 



