86 4 



THE CENTRAL NERVOUS SYSTEM 



marked are (i) The tract or tracts made up by the cells of the 

 anterior horn (Fig. 342), which practically run from end to end of the 

 cord, swell out in the cervical and lumbar enlargements, where the 

 cells are very numerous and of great size (70 jj, to 140 JJL in diameter), 

 and contract to a thin thread in the thoracic region, where they are 

 relatively few, scattered, and small. In the enlargements there 

 are several groups of these cells corresponding with the segments 



of the limbs, the movements 

 of the hand, forearm, and 

 upper arm being each repre- 

 sented by a group in the 

 StillinGS Cervical cerv ^ ca ^ an< ^ those of the foot, 

 Nucleus le g> and tni g h b y groups in 



CeruLCaL *h e l um bar swelling. In the 



Enlargement 



r ll- Lateral &ft- column 

 (.column of- jfe infer- 

 txxt) 



rest of the 

 well-marked 

 are present in 

 horn, a 



cord only 

 groups of 



two 

 cells 



the anterior 

 mesial and a lateral. 



Stilling's dorsal 

 nucleus or Clark's 

 Column 



Cefls of 1tx. anterior 

 Cornu 



-Scattered cells cf 



intermedia- 



tract 



(2) Clarke's column, whose 

 cells, mostly of good size and 

 somewhat rounded in outline, 

 are situated at the inner side 

 of the root of the posterior 

 horn just where it joins on to 

 the grey cross-bar. It gradu- 

 ally increases in size from 

 above downwards, usually 

 appearing first at the level of 

 the seventh or eighth cervical 

 nerve, attaining its maximum 

 development at the eleventh 

 or twelfth dorsal and dis- 

 appearing altogether, as a 

 continuous strand, at the level 

 of the second or third lumbar 

 nerves. Scattered nerve-cells, 

 however, constituting the so- 

 called cervical and sacral nuclei of Stilling, are frequently found 

 occupying the same position towards the upper and lower ends of 

 the cord, and may be looked upon as isolated portions of Clarke's 

 column. (3) A tract of small cells calle4 the intermedia- lateral 

 tract, lateral cell column, or lateral Jiqrn* situated at the outer edge 

 of the grey matter, about midway between the anterior and pos- 

 terior horns. It is best marked in the thoracic region, up to about 

 the second thoracic segment, although jii the corresponding situa- 

 tion there are scattered cells in the lumbar swelling and the cervical 



Sacral 



Fig. 342. Diagram of Grey Tracts of Cord. 



