608 
Proceedings of the Royal Society of Edinburgh. [Sess. 
upper fourth of this segment) and all those of the middle cell system. In 
size and shape there is great variation. Many are large, polygonal cells, 
larger than intermedio-lateral tract cells; the post-central ones are very 
often smaller and more rounded in outline, but quite a fair proportion are 
as large and distinctly multipolar as the central and anterior cells. 
L 4. — Much as in L 3. In the lower part the middle cells are extending 
rather further forwards on the median aspect of the anterior horn. In the 
reticular formation groups are rare, but a few cells are generally to be seen. 
L 5. — [Note, segment destroyed ; description taken from examination of 
Fig. 9. 
SI— 357 R ( x32). 
a. Motor cells. 
The middle cells are scattered thickly over whole area not occupied 
by motor cells, the only other cells present. They are perhaps most 
abundant and of largest size in the central and reticular areas. 
a segment obtained from another cord of practically identical age.] — Very 
similar to L 3 and L 4. Individual sections may show few or many cells, 
and scattered or aggregated in any part of the base of anterior horn, central 
area, or base of posterior horn. They are extending further forwards now 
in the outer part of the lateral enlargement. The same variations in size. 
S 1. — See fig. 9. — The distribution is much as in the lower lumbar 
segments. Usually abundant, and anywhere within the large area shown 
in the accompanying figure. In the Clarke’s column area they are fairly 
common, though not so abundant as in other parts. In the lower part of 
