STRUCTURE OF THE BRAIN IN RODENTS. 
707 
At A. (Plate 49, fig. 3) . 
B. 
C. 
D. 
E. 
Limbic lobe, 
mm. 
•376- 418 
•511 
•232 
•232 
•279 
Union with, extra-limbic, 
mm. 
•743 
•743 
•511 
•372 
•376 
Plence its depth is greatest at A and B, increasing upwards and outwards towards the 
extra-limbic portion, and thus forming a specially rich formation in Fekrieb/s region (7)5“ 
When these measurements are contrased with those of the same stratum in the Pig,t 
a great similarity is at once perceived. As before shown, the depth varies with the two 
kinds of arrangement observed by these cells, viz, : the clustered or the solitary. Thus 
in the Pig the clustered cells attained an average depth of * * * § 595 mm., whilst the dense 
confluent series in the Babbit average '506 mm. The depth, however, affords but an 
imperfect guide to the relative richness of the stratum in cells—a better notion is 
gained by the fact that the quarter-inch field will reveal in the confluent series as many 
as 90 to 100 cells, whilst the laminar series will give to the same power not over 
6 or 8 cells. 
2 . Form of cell. —The cell of this series is usually an elongate pyramid, although 
the oval and large fusiform cell is occasionally met with, as is also a bifurcate or horned 
cell; the latter, however, far less common than in the Sheep and Pig. It was stated 
as regards the form of these cells in the Pig, a striking uniformity in their contour was 
observable, “by far the greater proportion taking the form of an elongate pyramid, the 
few exceptions occurring being usually gigantic spindles.” J In this respect the 
ganglionic cells in the Babbit/s brain agree with those of the Pig and Sheep in 
not exhibiting the great irregularity in marginal conformation, which is a peculiar 
character of the same series of cells in Man. The group of ganglionic cells from the 
cortex of the Pig, figured in my last memoir, represents the typical form here.§ 
3. Size of cell. —The dimensions attained by these cells along this region from before 
backwards have a fair uniformity. The largest cells are found at G and D (Plate 49, 
fig. 3), where they measure 32/x long by 18p, broad, having a nucleus 13/x in length. 
Anterior to this they measure 24/rX 17/r, whilst posterior to it they diminish gradually 
in size to 26/x X 16/x behind the corpus callosum. With the exception of these slight 
variations I may state that throughout the upper limbic arc great uniformity in the size 
of the structural elements of this layer is maintained. When examining the structure 
of the parietal or extra limbic portion of the hemisphere we shall find still larger cells, 
* Vide fig’. 36, area 7, in brain of Rabbit. “The Functions of tbe Brain.” 
t Op>. cit., p. 62. 
X Op. cit., plate 7. 
§ Op. cit., page 43. 
