Robert Bennett Bean 367 
tering as an element. For each increase of 20 mm. in the length of the 
brain axis there is an increase of about one unit in the index. For ex- 
ample, the index for the left hemisphere of the male Caucasian brain is 
98, the length of the radius to the anterior association center is 70 
mm., that to the posterior association center is 71 mm. 70:71 ::98: 
100 is correct, considering the brain axis element 84 mm. Increase the 
latter and the index rises, reduce it and the index falls. The index varies, 
directly with the size of the anterior association center, and inversely 
with the size of the posterior association center. Increase 70 and the in- 
dex is increased; diminish 70 and the index is diminished. Increase 71 
and the index is diminished; diminish 71 and the index is increased. 
The index gives a simple numerical expression that may be used to ad- 
vantage in the comparison of brains, and in the comparison at present in 
hand it affords an excellent indication of existing differences. It is ob- 
served from the table that the index of the male Caucasian brain is the 
largest; the index of the female Caucasian comes next; with the female 
Negro third, and the male Negro the lowest. This indicates that the rela- 
tions of the brain axis and anterior association centers are similar to the 
index of the association centers, while the posterior association center is 
dissimilar in the two sexes and races. The index is shghtly larger on 
the left side, except in the female Caucasian. This may be due to the 
gyrus frontalis inferior, or to a larger motor area on the left side in the 
males. 
The relative differences of the association centers in the males of the 
two races on the right side are represented in Fig. 11, which is a com- 
posite of the 45° outline of the thirty-four male Caucasian and the forty- 
five male Negro brains The brain axis is practically the same length 
in each (167-8 mm.). A difference in the size and shape of the two out- 
lines is evident on the inferior surfaces of the frontal and occipital lobes 
below the axis, as well as above it, the Caucasian brain being further be- 
low the axis and more curved along the frontal lobe, while the Negro 
brain is further below the axis and more curved along the inferior surface 
of the occipital lobe, a difference which materially diminishes the size of 
the frontal lobe in the Negro and increases the size of the occipital. The 
flatness of the anterior association center is seen in the Negro outline, 
and the actual areas of the parts of these outlines are as follows: 
Area of the anterior lineal half of the composite Negro outline...48.4 sq. cm. 
Area of the anterior lineal half of the composite Caucasian 
EADS LAS peal a Res OOO MCRD CO.CC. CHOICE CORA DORER ARRON CROP eo lor t=O eGo 01k 
Area of the posterior lineal half of the composite Negro outline...48.2 sq. cm. 
Area of the posterior lineal half of the composite Caucasian 
OLE GIS RIED, OEIC EN ORT DICE O DIDIC ORO eRe ECR OG ORION 56.2 sq. cm. 
