GROWTH OF THE CEREBRAL CORTEX 107 
TABLE 13 
Showing relations between the cortical area in the frontal section and the frontal 
diameter of the cerebrum (W. D). Column E gives relative lengths of the long 
side when the area is reduced to a rectangle with the short side equal to the cortical 
thickness. These values have almost a fixed ratio to the frontal diameter of the 
cerebrum (W. D) in each group, the average being 0.97. For the detailed expla- 
nation see also the text. Norway rat 
A B Cc D E F G 
CORTICAL CORTICAL 
BRAIN WEIGHT BRAIN AREA IN THICKNESS Cc W.D E 
GROUP WEIGHT FRONTAL IN FRONTAL D F 
SECTION SECTION 
grams mm.2 mm. mm. mm, 
N XI 1.163 22.3 1.88 11.9 12.7 0.94 
N XII 
N XIII 1.369 24.2 1.96 1263 13.0 0.95 
N XIV 1.430 25.4 1.95 13.0 13.2 0.98 
N XV 1.546 26.3 2.04 - 12.9 13.4 0.96 
N XVI 1.629 Daz 2.08 1321 1324 0.96 
N XVII 1.739 27.8 2.07 13.4 13.9 0.96 
N XVIII 1.829 29.6 2.08 14.2 14.2 1.00 
N XIX 1.972 28.2 2.00 14.1 14.3 0.99 
N XX 2.052 28 .2 1.96 14.4 14.4 1.00 
N XXI Qe Mi2 29.5 2.08 14.2 14.9 0.95 
Atyieramen (GOU pS) Niece INNCNOI) erates ee ctci= iets cccola Shasta tien) ses eee 0.97 
Awerarem (Gro upsy Ne Scull INe XN) eran sce atinea so. cteriansacc acti 0.98 
table 9) this percentage amounts to 44 per cent, which is equal 
to that seen in the mature Albino brain (Groups XVI to XIX, 
table 2), if we disregard one case of advanced age (Group XX). 
Q. Number of cells in a unit volume of the cortex. Norway rat 
compared with the Albino 
Reviewing table 10 which gives separately the numbers of 
nerve cells in the unit volume of 0.001 mm.’ of the lamina pyra- 
midalis and the lamina ganglionaris at a fixed locality in the 
frontal section of the cerebrum and counted by the same method 
used for the Albino rat and comparing these numbers with those 
in table 3 in part I, it is easily seen that, if the like brain weight 
groups of the two forms are paired, the number of cells in the 
unit volume of both layers is slightly lower in the Norway rat. 
