Robert Bennett Bean 405 
The line passes through the longest diameter of the brain in 68% of the 
male Caucasian brains; 70% of the adult male Negro; none of the infant 
male Negro; 60% of the female Caucasian, and 334% of the female 
Negro. The line passes near the longest diameter, below in front and 
above behind, in 32% of the male Caucasian brains, 30% of the adult 
male Negro, 40% of the female Caucasian, 663% of the female Negro, 
and 100% of the infant male Negro. This gives a distinct gradation 
from the male Caucasian to the infant male Negro, the female Negro 
resembling most closely the infant type. In relation to the brain axis 
the infant has a larger amount of brain substance below the axis pos- 
teriorly, and a smaller amount below anteriorly, than is found in any of 
the others. When the brain axis does not exactly coincide with the long- 
est diameter of the brain, lines are drawn from the ends of the brain 
perpendicular to the axis, and in all cases the length of the axis between 
these lines coincides in length, practically, with the longest diameter of 
the brain. Refer to Figures 1 to 4 and 8 to 12 for evidence of these facts. 
The average distance between the lower border of the genu and the lower 
border of the frontal lobe is 22 mm. in the male Caucasian, 21 mm. in 
the male Negro, and 20 mm. in the female Negro. This difference, in 
connection with the extreme thinness of this part of the frontal lobe in 
the Negro, especially the Negro woman, indicates the frontal lobes to be 
even smaller than is apparent in the outlines, and by measurements taken 
from them. 
The brain axis is used because it is located definitely by three points 
that seem to be fairly constant in position, relatively; because it passes 
through the longest diameter of the brain in the majority of cases; be- 
cause it is a convenient line for measuring all parts of the brain in any 
position, thus facilitating speed and accuracy in brain measurements, and 
affording a just basis for comparison of any brain in the relation of its 
parts to each other and to other brains. By means of the brain axis a 
brain center is established which is constant within a small circle, and by 
a composite is shown to retain its position, relatively, in the brains meas- 
ured. It is located just above and anterior to the opening of the aque- 
duct of Sylvius into the third ventricle, a line drawn at an angle of 45° 
above the anterior end of the brain axis through the aqueduct of Sylvius 
passes through the brain center. It is just posterior to the gray commis- 
sure in the sulcus of Munro separating the alar from the basal lamina of 
the embryonic brain tube at a point that is perhaps as constant in posi- 
tion as any other during development. Shifting of the brain axis by ro- 
tation, antero-posteriorly or infero-superiorly, its usual variation when 
it changes, does not alter the position of the brain center. If its position 
