194 Cc. W. M. POYNTER AND J. J. KEEGAN 
to force the conclusion that the gyrus frontalis superior in this 
series of brains is wider than in the average European brain 
and that the sulcus frontalis superior is more laterally placed. 
The continuous form of the sulcus frontalis superior in com- 
munication with the sulcus fronto-marginalis is found in 41 per 
cent. In the cases where the fissure is broken up there is some 
difficulty in interpreting the anterior element. 
The sulcus frontalis medius is represented in the majority of 
hemispheres, 75 per cent, by several shallow irregular elements, 
and in very few is there a longitudinal sulcus indenting the 
gyrus. Figures 1, 3 and 5 illustrate the usual condition. There 
is nothing in the series to impress one with the importance 
attributed to the suleus by Eberstaller (90). 
The sulcus frontalis inferior is characterized in this’ series of 
hemispheres by its great irregularity and its lack of conformity 
to any special type. The most frequent variety is that in which 
three elements are present, an anterior transverse, an inter- 
_ mediate horizontal and a posterior transverse. The last element 
in many instances cannot be distinguished from the praecentralis 
inferior, or sulcus diagonalis; communication with the latter 
occurs in 29.2 per cent of hemispheres. 
The sulcus radiatus has been variously interpreted by authors; 
more recently the tendency has been to view the anterior bi- 
furcation of the sulcus frontalis inferior as constituting the sul- 
cus radiatus. The much greater frequency with which only 
two transverse elements occur in this region has probably been 
responsible for the interpretation. In this series this condition 
is present in 58 per cent of adult hemispheres. In the other 
hemispheres, as seen in figure 1, a detached inferior portion of 
the bifurcation might be considered a third transverse sulcus; 
from the evidence of the group we are lead to consider the pos- 
terior of the two transverse sulci usually found in this region as 
the sulcus radiatus, or anterior bifurcation of the sulcus frontalis 
inferior, and the anterior the lateral part of the sulcus fronto- 
marginalis. 
The sulcus fronto-marginalis is represented by two quite dis- 
tinct elements, a lateral and an internal. The lateral element 
