484 



THE NEKVOUS SYSTEM 



FIG. 379. TRANSECTION OF THE SPINAL CORD OF 

 A CHILD, EIGHTH THORACIC SEGMENT. 



Weigert stain, x 7. 



A transection of the spinal cord in the thoracic region is of 

 small diameter, and is very nearly circular in outline. The white 

 matter, since it contains the many nerve fibres going to and coming 

 from the lumbar enlargement, is much more voluminous than the 



grey matter. The latter is 

 reduced to a comparatively 

 insignificant central mass. 



The postero-internal col- 

 umn attains a considerable 

 size in this region, and is 

 distinctly marked off from 

 the adjacent postero-lateral 

 column by a fibrous septum 

 derived from the pia mater. 

 The posterior and the lateral 

 columns, having been much 

 augmented by the influx of 

 fibres from the large poste- 

 rior roots of the lumbar 

 nerves, form the larger part 



of the white matter. The grey matter consequently appears to be 

 pushed forward, its grey commissure lies considerably ventral to 

 the center of the spinal cord, the anterior median fissure is shorter 

 than the posterior median septum, and the tips of the dorsal grey 

 horns are far removed from the surface, being only connected 

 with the postero-lateral sulcus by the slender dorsal nerve roots. 

 In fact, the dorsal horns of grey matter in this region are reduced 

 to a minimum size ; they are short and slender and contain com- 

 paratively few nerve cells. 



At the base of each dorsal horn, on its mesial side, there is a 

 distinctly outlined cell group whose transection is of oval or cir- 

 cular outline. Indeed, this cell group, the cell column of Clarke, 

 begins in the second or third lumbar segment, and is continued 

 upward to the second or third thoracic at times even into the 

 lowermost cervical segments at which level it has dwindled to a 

 relatively insignificant group.* 



The ventral grey horns are very short and narrow, and their 

 cells can not be subdivided into groups as in the other regions of 

 the spinal cord. In the upper part of the dorsal region a distinct 



* In the lower lumbar region an ill-defined group of cells occupying a simi- 

 lar position and having the same function is known as the nucleus of Stilling. 



