42 
MR, W. BEVAN LEWIS OX THE COMPARATIVE 
in size with those which constitute the whole thickness of this stratum in the Pig; 
whilst none of the smaller cells crowding the upper portion of this layer in Man, the 
Monkey, and the Cat are here present. The nerve-cells of this layer vary much in 
contour : we find them oval, oblong, pyriform, and pyramidal, and a few even elongate 
spindles. By far the more frequent form assumed is that of the pyramidal or a slight 
modification of the pyramid. The junction of every main branch with its cell is 
marked by the gradual increase in size of the branch where it blends with the cell, 
occasioned by the continuation of a funnel-shaped prolongation of protoplasm from the 
cell into its branch. This gradual blending of the cell with its branch is a safe 
criterion to follow if any doubt arise as to the actual junction betwixt the two. The 
average number of processes thrown off by these cells (inclusive of basal and apex 
process), as seen in vertical sections, is six. As many as eight or more are often seen; 
but, from reasons already adduced,'" no approximate knowledge can be obtained of 
the absolute number of primary branches. The apex arising from the gradual attenua¬ 
tion of the cell lies more or less parallel with the radial fasciculi, and is therefore 
directed outwards or directly towards the superficial layer of the cortex. The basal 
process appears to conform in every respect to the corresponding process in the large 
ganglionic cell. The smaller branches arise from various points of the periphery 
of the cell, more especially near the base, and radiate outwards, dividing and sub¬ 
dividing into extremely delicate fibrils occupying an extensive zone around the cell. 
Each cell contains an oval nucleus (deeply stained by aniline and carmine), which is 
invariably centric in position. The cells of this layer frequently have a number of 
small nuclei arranged around or upon them : these elements pertain to the pericellular 
lymph spaces.! As to the general arrangement of the cells of the third layer, no 
regular grouping is apparent: they are scattered very irregularly through the greater 
depth of this layer except at its deeper portions, where they lie in dense clusters 
between the advancing sheaves of apical processes given off from the ganglionic cells 
of the subjacent stratum. These latter bundles of nerve-fibres consequently occupy 
somewhat pale spaces almost devoid of cells, forming well marked septa betwixt the 
cells of the deeper regions of this layer. The peculiar angular cell is found sparsely 
scattered throughout the whole depth of the third layer as in the cortex of higher 
animals. 
Ganglionic layer (Plate 6, D).—We now arrive at a region of the cortex where the 
most striking and characteristic features develop themselves, and where the distinc¬ 
tive characters impressed upon the architecture of the cortex in Man and the lower 
Mammalia come out most prominently. Any one accustomed to the microscopic 
* “ Cortical Lamination of the Motor Area of the Brain,” Proc. Royal Soc., No. 185. 
f See on this subject Obersteiner's views, “Ueber einige Lymphraume ira Gehirne” (Sitzb. d. k. 
Akad. d. Wissensch., Abth. i., Jan. Heft, 1870). Also an article by the writer entitled, " The Relationships 
of the Herve-Cells of the Cortex to the Lymphatic System of the Brain,” Proc. Royal Soc., Xo. 
182, 1877. 
