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Chart 1 Giving the average values of the five diameters of the Norway rat 
cerebrum for each brain weight group. 
—- WB. oo LF 
pase W.D. x—-—x Ht. 
— ],G. 
The approximate value of each diameter can be caleulated by 
the following formulas: 
W. B (mm.) = Cy X V Brain weight (grams) (1) 
where Cy will be 12.8 for a brain weighing 1.3-1.6 grams. 
12.5 for a brain weighing 1.6-2.4 grams. 
W. D (mm.) = W. B mm.) — 1.25 mm. (2) 
L.G(mm.) = C, X ¥ Brain weight (grams) (3) 
where C, will be 12.2 for any brain weighing 1.3-2.4 grams. , 
ji PCat) Si C2(Gime ye 0 (4) 
Ht. (mm.) = Cy X ¥ Brain weight (grams) (5) 
where Cy will be 8.5 for a brain weighing 1.1-1.4 grams. 
8.2 for a brain weighing 1.4-1.9 grams. 
7.9 for a brain weighing 1.9-2.4 grams. 
At the first entry in this study, Group N XI (table 2), the 
relative volume of the cerebrum (W. B xX L. GX Ht.) is 
13.86 x 12.63 x 8.83 = 1546.92 (see also table 3 A) 
