612 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Sometimes scattered, but more often present as a small clump of cells. 
With them may be included the cells in the para-central area, which, although 
sometimes forming a distinct and separate aggregation of cells, can mostly 
not be separated off from the central cells. Many of the cells occurring in 
the reticular area at levels where the reticular group of the intermedio- 
lateral tract is not present (especially in the lower cervical region) may 
probably also be included here. 
(2) Anterior central cells in the base of the anterior horn — one of 
Waldeyer’s “ scattered ” cell groups. As this name implies, these are often 
simply scattered over the area in question, but sometimes they are gathered 
into small cell-nests, but rarely very compact ones. Although there is no 
sharp boundary between them posteriorly and the central cells, they are in 
the main larger cells, and are further distinguished by their shape. They 
are not so often definitely multipolar and of approximately equal diameter 
in different directions, but more frequently appear to be bipolar, with long- 
drawn-out processes. The axis of elongation may be variously oriented. 
With these would fall to be included the middle cells in the external 
central area of the lateral enlargements, particularly in the lumbo-sacral 
cord. Possibly also some of the para-central cells should be classed with 
this group, and not with the previous one. 
(3) Post-central cells. These lie in the area between Clarke’s column 
and the formatio-reticularis, or in the corresponding region of the grey 
matter at level where Clarke’s column is unrepresented. As with the 
anterior central cell, there is no sharp boundary between this series and 
the central middle cells. They are often continuous, or the cells may lie 
betwixt and between the two areas. But although many of the posterior 
cells may be as large, they are distinguished on the whole by being 
smaller in size than the central cells and less definitely polygonal, more 
rounded in outline. They are generally present either as a small clump 
or as a band of cells on the outer and posterior aspects of Clarke’s column. 
Posteriorly, it is very difficult to separate this group from the posterior- 
basal and posterior-marginal cells of Waldeyer. With this group may be 
included cells present in the area of Clarke’s column, particularly when that 
column is absent or only represented by occasional cells. Also some of the 
small cells found in the reticular formation, especially those lying between 
(vertically) the nuclei of the reticular group of the intermedio-lateral tract. 
These subdivisions may require modification from subsequent investiga- 
tions, particularly by tracing the course and termination of the cell pro- 
cesses. I have attempted to do this by means of Cajal’s silver impregnation 
methods, but, so far, have not succeeded. All I can affirm is that the fibres 
