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DR ALEXANDER BRUCE 



large number both in the apical and in the reticular groups. The reticular group is 

 generally present at the re-entering angle between the anterior and the posterior cornua. 

 It is either continuous with the apical group or separated from it by a distinct interval. 

 Its cells are sometimes arranged in a triangle with its apex inwards, and its base 

 towards the formatio reticularis. Its cells lie generally with their long axis pointing 

 forwards and inwards. The apical group either lies at the tip of the lateral horn or 

 forms a triangle of considerable size, with its base inwards, and there is a tendency for 

 the cells to extend along the anterior surface of the lateral horn as a special anterior 

 group (D. 3, 74 ; fig. 6). No distinct difference in the size of the cells contained in the 

 apical and reticular groups could be made out. 



CL./n 



Fig. 6 (D. 3, 74, L. ). — This figure shows a large anterior group of cells in the intermedio-lateral 

 tract, the apical cells being few and the reticular ones being unrepresented. 



Fourth Dorsal Segment. — This segment was divided into 182 sections, and its 

 intermedio-lateral tract contains 3803 cells on the right side and 3623 on the left. 

 The groups of cells, as represented on the graph, show a return to the spire-like 

 arrangement of D. 2, with this difference, that the spires as a rule are higher than and 

 not quite so slender as in D. 2. The intervals between them are, however, very 

 distinct. There are nine groups on the left and ten on the right side. (An eleventh 

 group at the lower end of the segment is continued into the first group of D. 5, and 

 is therefore not enumerated here.) The greatest number of cells in any one section 

 (149 on the left side) is 82. This is the greatest number found in any one section of 

 the whole intermedio-lateral tract. In this group there is, in fifteen sections, a rise 

 from 5 cells to 82, and then a fall again to 2 cells. In section 149 

 (fig. 7) the connection and identity of the apical and reticular groups is clearly 

 established. On examining the sections in which this group was found, it is easy to 

 see that where an interval appears between the two sets of cells it is caused merely by 

 the presence of a bundle of nerve fibres, and is not due to any real difference in the 

 nature, of these cells. There is no constant difference in the size of the cells in the 



