STRUCTURE OF THE BRAIN IN RODENTS. 
719 
Plane of Section. 
Length. 
Width. 
Nucleus. 
r 
r 
A 
Anterior to corpus callosum . 
... 32 
16 
13 
On a plane with Sylvian depression 
... 34 
16 
13 
Posterior to Sylvian depression . 
... 34 
17 
13 
Posterior border of corpus callosum . 
... 34 
16 
12 
Through superior parietal sulcus 
, . . 24 
18 
12 
Posterior to latter. 
... 31 
19 
13 
These nerve-cells are therefore larger than those of the corresponding series in the 
upper limbic arc (vide table of measurements), also larger than those of the lower 
limbic arc, which average for the olfactory gyrus 25/xX 13/x ; for the gyrus hippocampi 
31/rXl3/x; and for the modified olfactory type near the occipital pole 23/xXl3g. 
Larger cells occur occasionally, scattered widely apart, the largest registered attaining 
the dimensions of 60gXl8g. If these average dimensions he contrasted with those 
of the second cortical layer , in the region of the modified olfactory type (Plate 50, 
fig. 6, B), the important fact is disclosed that this peculiar formation consists of cells 
which attain a much higher average than that of the ganglionic cells. These globose 
inflated cells usually average 37gX32g, and frequently reach the dimensions of 
46gX27g. These are therefore the largest nervous elements to be found throughout 
the cortex cerebri. The lower limb of the rich ganglionic tract extending from the 
frontal pole along the limbic fissure beyond the Sylvian depression, possesses cells of 
a smaller size than those of the corresponding upper tract. Thus in front of the 
corpus callosum the nerve-cells near the limbic fissure measure 27g X 17/x, as contrasted 
with 32gXl6p, for those of the upper tract; r behind the Sylvian depression those 
of the lower tract measure 27p.Xl7g, whilst those of the upper tract measure 
34 [x X 17 ix. 
The rich aggregation of cells in the ganglionic layer along the median exposed 
portion of the vault results in a deep stratum, which near the frontal extremity 
measures *558 mm., and posteriorly and internal to the superior parietal sulcus 
'604 mm. If this be contrasted with the pale, solitary belt in five-laminated realms, 
measuring but T86 mm., its wealth of structure will be apparent. Another fact to be 
noted is that this layer of ganglionic cells is both deep ('604 mm.) and rich in cells in 
that area of the granule formation bounded externally by the primary parietal sulcus, 
and covers the median surface of this posterior region of the hemisphere as far back as 
the summit of the occipital pole. We must therefore conclude that although the 
ganglionic cells (next to those near the occipital pole) are the largest throughout the 
cortex cerebri, the distinctive feature relative to this formation is not the large size 
attained by the cells, as is the case in the highest of the Mammalian series—for they 
exhibit in the Babbit, as in the Pig and Sheep, a remarkable uniformity throughout; 
but, on the other hand, this formation is especially notable for its richness in nerve- 
mdccclxxxii. 4 z 
