706 
MR. W. BE VAN LEWIS ON THE COMPARATIVE 
cortical zone ; and lastly, with the increase from a four to a five-laminated cortex by 
the addition of a small angular layer, the latter lies immediately between the pyramidal 
layer and this stratum of large cells, which I therefore propose to consider as identical 
with the ganglionic series in Man. This intercalation of an angular layer between 
them and the pyramids suffices to distinguish them from the large pyramids of the 
lower half of the third layer in human brain. Another character common to this series 
and that of Man and higher animals is their distribution in confluent clusters, as a deep 
stratum on the one hand, or on the other, as the solitary or linear arrangement/"' The 
confluent and linear arrangement of these elements is as marked a feature here as it is 
in the Pig and Sheep. It has been noted that the great development of the ganglionic 
series in Man was found associated with the five-laminated, and not the six-laminated, 
cortex, and was peculiarly distributed over the upper limbic arc in its anterior half—so 
in the Babbit these cells vastly predominate in the four-laminated cortex, i.e. , before 
the intercalation of an angular layer occurs, and is richly distributed over the upper 
limbic arc and its immediate neighbourhood. To sum up the special features whereby 
I identify this layer with the common ganglionic series : — 
a. The large size and characteristic form of the cells. 
b. The histological structure of the stratum. 
c. Peculiar distribution of apex processes. 
d. Belationship to the angular layer. 
e. Arrangement in dense clusters or solitary cells. 
f Special development in certain areas. 
It now remains to consider how they differ histologically from the same series in higher 
animals, and this object will be best furthered by considering in detail the general 
structure of the ganglionic layer as regards—1, depth; 2, form of cell; 3, size of cell. 
1 . Depth of ganglionic layer. —Great variations in depth occur throughout this layer, 
corresponding to a more or less rich development of cells. Upon examining sections 
taken vertically through the hemisphere, as at B (Plate 49, fig. 3), one cannot fail to 
have the attention arrested by the rich development of these cells in the upper limbic 
arc, and their rapid diminution and thinning out in the outer regions of the extra 
limbic mass. Referring to our figure of the upper limbic arc in the Babbit (Plate 49, 
fig. 3 ), let us briefly examine the depth of this layer along the length of this arc, as 
also along the upper angle where it unites with the extra limbic portion. The depth 
attained is as follows :— 
* “ The Comparative Structure of the Cortex Cerebri.” Bevan Lewis. Phil. Trans., Part I., 1880, 
page 38. 
