AMERICAN NEGRO BRAIN 207 
SUMMARY 
The frontal region has presented the greatest difficulty in the 
interpretation of the relation of the sulci to the cortical areas 
because the contrasts between adjoining areas are slight or 
impossible to detect. Such a relationship has been discovered 
in the occipital region and it is not unreasonable to suppose that 
similar, but as yet unidentified, factors have influenced the 
development and position of sulci in the frontal region. If 
we consider the center of the growth process to be in the frontal 
association area the result would be a migration of the surround- 
ing sulci in all directions from this center with probable dis- 
intregation of some of them. Going still further, it can be con- 
ceived that the interaction between this growth center and that 
of the parietal association area has been partly responsible for 
the system of vertical sulci in the Rolandic region. 
A growth activity in the frontal association area would affect 
the superior and inferior frontal regions. Downward expansion 
would result in a possible operculization to cover the insula, but 
might also force the sulcus frontalis inferior downwards until 
the gyrus frontalis inferior appeared less developed than before 
the growth occurred. The superior expansion would cause a 
migration of the sulcus frontalis superior towards the mesial 
border of the hemisphere, especially its anterior two-thirds. 
This would lead to a restriction of the lateral portion of the gyrus 
frontalis superior and to a decrease in the prominence of the 
sulcus frontalis mesialis. Similarly the sulcus fronto-marginalis 
would be effected, but the relation of this sulcus to the growth 
process is very similar to that of the sulcus occipitalis infe- 
rior in its region hence we may find disintegration as well as 
migration. 
Viewed in the light of the‘above reasoning, this series of Negro 
brains presents a number of interesting features. As has been 
noted, the sulcus frontalis superior is almost invariably parallel 
to the mesial border of the hemisphere and frequently in com- 
munication with the suleus fronto-marginalis; also in con- 
sequence of the unusually wide lateral aspect of the gyrus 
