ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 115 



the posterior border as far as the posterior limit of Clarke's column, and disappears 

 in section 186. It reappears as a small group on both sides in section 199, and again 

 on the right from section 204 to section 216. 



As regards the position of the cells, when these lie at the apex of the horn in a 

 triangular group, their long axes show no constant direction, but when they extend in 

 bands along the posterior margin, their long axes run parellel to the border (figs. 3 

 and 4). 



In the upper part of this segment a few aberrant cells of the post-postero-lateral 

 group are found among and internal to the cells of the intermedio-lateral tract 

 (fig. 3). 



A fact which is worthy of note as regards this segment is the remarkable vascularity 



£t. TL . 



Fig. 5 (D. 2, 181, R. ). — This is drawn from one of the sections which show the first appearance of 

 the reticular cells on the right side. The cells underlying the formatio reticularis are few in 

 number, hut there is a large group at the base of the lateral horn, and separated from the apical 

 cells by a slight interval. 



of the intermedio-lateral tract, vessels passing into it directly from the lateral periphery 

 of the cord. 



Third Dorsal Segment. — This segment was divided into 276 sections, in which the 

 cells of its intermedio-lateral tract number 7471 on the right side and 7297 on the 

 left. The graph of this segment presents a remarkable contrast to those of D. 2 and 

 D. 4, in both of which the groups of cells are represented as slender spires, separated 

 from each other by distinct intervals which are almost devoid of cells. In D. 3, on the 

 other hand, with one or two exceptions about the centre of the right side, the groups 

 of cells are arranged in broader masses, with less indication of a spire-like arrangement. 

 The masses are separated by less distinct intervals, in which there always remain a 

 considerable number of cells. The intervals are so indistinct that it is difficult to be 

 certain of the number of groups on the right side. Probably there are fifteen. On the 

 left side there appear to be thirteen groups, and there may have been fourteen, as some 

 sections at the lower end of the segment (owing to an accident in preparation) do not 

 show the grey matter on the left side. This great increment of the cells is due to the 



