ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 113 



the cell-groups on the two sides, this resemblance does not amount to a perfect 

 symmetry. The largest group (the lowest on the right side) contains 578 cells, and the 

 largest number of cells in any one section is 58. 



At the upper extremity of the segment the intermedio-lateral tract is distributed on 

 the posterior border of the anterior cornu, a little internal to its lateral tip ; but, with 

 the progressive diminution of the number of large motor cells, its position relative to 

 these continues to shift outwards until, near the lower end of the segment, it comes to 

 lie at the apex of what is now the lateral horn proper. The cells in the upper part of 

 the segment lie for the most part within the grey matter, quite close to its margin, but 

 wherever their number undergoes a considerable increase they tend to project outwards 



Fig. 2 (D. 1, 175, R. ). — The cells of the intermedio-lateral tract form a large group, partly within 

 and partly without the cornu, a few being separated by a distinct interval from the main group. 

 The majority of the cells have their long axes in an oblique direction, and more or less parallel 

 to the posterior margin of the horn. 



into the white matter. In some groups the cells are, on the other hand, almost 

 entirely " outlying," or there may be a few outlying cells, while the main mass of the 

 cells is found in the grey matter. In the upper part of the segment the cells are 

 closely aggregated ; but at its lower part, where the lateral horn proper is fully con- 

 stituted, they are less compactly grouped, and tend to spread along the posterior, and, 

 even in some places, also along the anterior border of the horn. This anterior group 

 sometimes becomes separated off from the cells at the tip of the horn. Those on the 

 posterior margin spread further from the apex than the anterior ones, but they do not reach 

 the formatio reticularis. There is no indication of any reticular group in this segment. 



The long axes of the cells are in general parallel to the margin of the grey matter, 

 although the outlying cells assume the direction of the strands of connective tissue in 

 which they lie. 



TRANS. ROY. SOC. EDIN., VOL. XLV. PART I. (NO. 5). 15 



