611 
1907-8.] Middle Cells of Grey Matter of Spinal Cord. 
paratively few in number, and may be scattered irregularly ; but small 
groups are often found, most commonly in the central area, about on a 
level with the central canal, and in the post-central area, between Clarke’s 
column and the reticular group of the intermedio-lateral tract. In the 
lumbar segments the middle cells are abundant, particularly centrally and 
in the base of the anterior horn. Their field extends anteriorly, until in 
the lower sacral region they come to be found over the whole area of the 
anterior cornua in addition to their more usual situations. 
At all levels, as studied in serial sections, the distribution of the middle 
cells is seemingly erratic and casual. No regular plan of arrangement can 
be made out, and there is most certainly no segmentation (as Argutinski 
described) like that so well seen in the intermedio-lateral tract. The cells 
are sometimes just dotted here and there singly ; sometimes they are 
scattered fairly thickly and evenly over the whole or part of the regions 
they are to be found in ; or, again, they may occur more thickly in one part, 
or be aggregated into a distinct little cell group or nest, but even then 
these cell groups are seldom so closely packed as are the cell groups of the 
intermedio-lateral tract. The duration of any one of these types of cell 
arrangement is inconstant ; and although there are levels where cells seem 
for a bit to be almost persistent in one place, this much can be stated as 
a general rule, that no middle cell group lasts through more than a very 
few serial sections. If traced further, the group is found either to shift to 
some other area or to die out altogether. Occasionally there appears to be 
a variation in number of cells parallel with the oscillations of the inter- 
medio-lateral tract, but closer study shows that this is by no means absolute, 
and is probably only a local accidental variation. 
Without expressing any opinion as regards function, I am inclined to 
divide the cells I have described collectively as middle cells into three 
groups, basing this division merely on the distribution and arrangement of 
the cells and on the microscopic appearances of the cell bodies. These 
divisions are, however, not very sharply defined either as regards the 
character of the individual cells or in the cell distribution. Still they seem 
to warrant such a division being made, and to suggest at least that the 
cells of the three groups may be functionally different. The groups 1 
would make are — 
(1) The middle cells proper, or central cells, occurring chiefly in the 
central area of the grey matter. These cells are of medium size and very 
similar to those of the apical group of the intermedio-lateral tract, multi- 
polar, polygonal or rounded polygonal in outline, with a comparatively large 
nucleus and a few chromatic granules round it in the cell substance. 
