114 



L)R ALEXANDER BRUCE 



Second Dorsal Segment. — This segment contained 228 sections. The cells of its 

 intermedio-lateral tract number 3635 on the right and 3931 on the left side. The 

 groups of cells, as represented in the graph, retain their spire-like appearance, the rise 

 and fall of the cells in each group being still rapid. The spires are more slender on the 

 right side. The intervals separating them are shorter than in D. 1, and not always 

 complete. The groups are wider here than in D. 1, each one being spread over a 

 larger number of sections, especially on the left side. They number 12 to 15 on the 

 right, and 11 or 12 on the left. As in D. 1, though there is a general resemblance of 

 form on the two sides, the symmetry is not quite complete. The largest number of 

 cells in any one section is 58. 



a- '■ . 



Fig. 3 (D. 2, 4, R.). — The cells of the intermedio-lateral tract are 

 now at the apex of the lateral horn proper. The long axes of 

 the cells have no constant direction, and the cells are not so 

 closely compacted as in the previous figure. A small aberrant 

 group of post-postero-lateral cells {-p.p. I.) is seen near the 

 re-entrant angle between the lateral and the posterior cornua. 



Fig. 4 (D. 2, 169, L.).— This figure is taken from a 

 section through that portion of the tract in which 

 the reticular cells first appear. Their position at the 

 re-entrant angle of the grey matter and their partial 

 separation by a slight interval from the apical cells 

 is seen. 



As regards their distribution, the cells sometimes form a triangular group, the apex 

 of which occupies the tip of the lateral horn ; sometimes they stretch as a band along 

 the posterior margin of the lateral horn. There are a few outlying ceils in the white 

 matter (fig. 3). 



In the lower half of the segment, at section 165 on the left side, we have the first 

 definite appearance of the reticular group (fig. 4). At its commencement, which is 

 abrupt, it is apparently a separate group, but two sections below that at which it is 

 first observed it becomes continuous with the original group of intermedio-lateral cells, 

 and is hardly distinguishable from it in so far as size of cells is concerned. This 

 reticular group dies out again in section 174 on the left side. On the right side (fig. 

 5) it appears first in section 177, then gradually increases in size, spreads back along 



