Robert Bennett Bean 391 
the females of the two races. Compare these results with the results ob- 
tained above and there appears a greater racial difference in the relation 
of the genu to the splenium than in the relation of the body to the 
isthmus, or in the relation of the anterior to the posterior lineal halves of 
the corpus callosum. This may be expressed in a table. 
TABLE VIIb. 
Tue RELATION OF THE RATIOS OF THE PARTS OF THE CORPUS CALLOSUM. 
Genu to Splenium. Body to Isthmus. Lineal Halves. ~ 
Negro Cauca- wee, Relation Cauca- Relation Cauca-— Relation 
and sian verre of sian, Nero : sian weere of 
Caucasian. Ratio. ‘ * Ratio. Ratio. * Ratio. Ratio. * Ratio. 
ITAL ees ss LDS 120 131 160 164 97 122 102 119 
Females .... 150 alas) 130 io 160 97 110 100 110 
The racial difference is greater in the “relation of the ratios” of the 
genu and the splenium (130) than it is in the “relation of the ratios ” 
of the body and the isthmus (97), or of the lineal halves ( 119, 110). 
The sexual difference is slight in the relation of the ratios of the genu to 
the splenium (131 : 130 = 101); it is more marked in the “relation of 
the ratios” of the anterior lineal half to the posterior lineal half 
(119: 110 = 108) ; and it is least marked in the “ relation of the ratios ” 
of the body to the isthmus (97 :97 = 100). In other words the above 
table may be interpreted as follows: The genu of the Caucasian female is 
larger in proportion to the size of the splenium than it is in the Negro 
female, and this difference is greater than the racial difference in the 
females in the proportion of the body to the isthmus, or the anterior 
lineal half to the posterior lineal half of the corpus callosum, the same 
difference being noticed in the relative sizes of these, but in a lesser de- 
gree. The same racial differences are found in the males, but they are 
not so marked. The splenium and genu, then, exhibit the most notice- 
able racial differences. The most striking sexual differences are found 
in the anterior and posterior lineal halves, the anterior in proportion to 
the posterior being larger in the males than in the females. The ratio 
of the body to the isthmus is greatest in the Negro male, least in the 
Caucasian female and intermediate in the Caucasian inale and Negro 
female. This may be explained by the relative muscular power of the 
four classes, the commissural fibers of the motor areas forming the body 
of the corpus callosum. The greatest racial differences being found out- 
side of the motor areas and their commissural fibers gives strong presump- 
tive evidence that the great racial difference lies in the relation of the 
anterior to thé posterior association center. 
