2QO 



NORMAL HISTOLOGY. 



FIG. 324. 



the anterior gray commissure, while that behind the canal is the 

 posterior gray commissure. 



The histological elements entering into the composition of the 

 gray matter include the nerve-cells, the nerve-fibres, the sub- 

 stantia spongiosa, the substantia gelatinosa, and the blood- 

 vessels. 



The most conspicuous elements of the gray matter are the gan- 

 glion-cells. These are especially numerous in the apices of the 



anterior horns, where 

 they form almost con- 

 tinuous columns. The 

 motor cells are largest, 

 those found in the anterior 

 cornu being distinguished 

 by their great size (65-130 

 A), as well as by their 

 numerous branched pro- 

 cesses. The ganglion- 

 cells of the anterior 

 cornu are disposed in 

 groups, of which there 

 may be recognized usually 

 a small median group, 

 occupying the inner part 

 of the horn, but wanting 

 in the lumbar region, and 

 a conspicuous large an- 

 tero-lateral group, which 



Anterior horn of gray matter of human spinal cord : g, H^S in the OUter angle of 

 gray matter containing stellate ganglion-cells ; <u>, white fa^ hom * the posterior 

 matter penetrated by bundles (r) of root-fibres. 



outer angle, where the an- 

 terior cornu is broad and well developed, contains often additionally 

 a postero-lateral or an external group. 



The ganglion-cells of the posterior horn are much smaller 

 (15-20 pi) and irregularly distributed to the outer side of the cornu 

 and within the substantia gelatinosa. 



In certain regions of the cord, principally from the eighth cervi- 

 cal to the third lumbar nerve, much less markedly in the upper 

 cervical and in the sacral region, a distinct cluster of nerve-cells exists 

 at the juncture of the posterior root and the gray commissure, which 

 marks the position of the vesicular column of Clarke. The gan- 

 glion-cells of this tract vary in size (30-90 M), but possess an average 

 diameter of 70 //, thus standing midway between the largest motor 

 and the smallest sensory elements ; the neurits of these cells pass 



