192 Cc. W. M. POYNTER AND J. J. KEEGAN 
which compares favorably with other observations. The form 
of the sulcus praecentralis superior is very variable. A fairly 
constant posterior ramus has been described by Cunningham 
but was attributed by him to a posterior continuation of the 
sulcus frontalis superior. This sulcus which is represented in 
figures 3 and 5 may be more properly interpreted as a sulcus 
which has been called into existence by an excessive growth of 
the portion of the gyrus centralis anterior which gives rise to the 
superior genu of the sulcus centralis. In these cases it incises 
this prominent cortical region and gives to the gyrus an arcuate 
appearance. 
The sulcus praecentralis marginalis and sulcus praecentralis 
medius are so inconstant and variable as to make observation 
on so small a number of hemispheres valueless. 
The sulcus praecentralis inferior is much more strongly de- 
veloped than the superior; in the majority of hemispheres it is 
represented by two elements, as shown in figure 3. It is con- 
nected with the fissura Sylvii in 41 per cent of cases as compared 
-with 71 per cent given by Duckworth for Australian brains. 
A communication between the praecentralis inferior and the 
sulcus frontalis inferior occurs in 58.3 per cent. 
The sulcus frontalis superior and the sulcus frontalis medius 
are discussed together because of their intimate association in the 
anterior part of the frontal lobe. The description of the sulcus 
frontalis superior as given by Cunningham and Retzius is not 
entirely in accord with the condition found in this series. The 
point of variation is the direction taken by the sulcus and the 
location of its anterior termination. If a line be drawn through 
the centers of the two or three elements, or if the sulcus is con- 
tinuous following its general direction, this line will run parallel 
to the mesial border of the hemisphere at a distance from it of 
about 25 mm., and coincides with the juncture of the sulcus 
frontalis superior and the sulcus praecentralis superior poste- 
riorly and anteriorly with the sulcus fronto-marginalis. While 
this difference in the position of the sulcus frontalis superior may 
be due in part to the interpretation of the anterior elements, 
yet the difference is so evident in the majority of hemispheres as 
