SULCUS LUNATUS 133 
tend so far forward as the sulcus lunatus in man, thus this sulcus 
does not limit the striate area frontally. In explanation of this 
fact he refers to the findings of both Ziehen (14) and Kappers 
(op. cit.), who have shown that the sulci are more conservative 
in their migrations than the neighboring cortical zones. 
The key to the situation may be found in the last state- 
ment. The striate area is pushed backward during the evolu- 
tion of the distinctively human parieto-occipital ‘association’ 
fields. The more conservative lunate sulcus, if it survive at 
all in the altered conditions of cortical tension attendant upon 
this unfolding process, does not accurately follow the retreating 
area striata. However, it is to be noted that the more oper- 
culated the lunate sulcus be (e.g., the more successful it has been 
in retaining its original anthropoid shape amid the changing 
human conditions), the nearer does the striate area approach 
its lip. The very fact that the area striata never extends beyond 
this sulcus, but does sometimes terminate at its lip, even in 
Europeans, makes the distribution of the stria of Gennari a 
most important point in this issue.! 
I would thus advocate the addition to van Valkenburg’s 
list of a fifth and most important criterion—one emphasised by 
Elliot Smith from the outset, viz: The area striata never extends 
beyond the sulcus in question, though it may fall short of it, 
for reasons already noted; and its forward extension is in direct 
relation to the degree of operculation. 
January 31, 1915. 
'[ have seen the area striata extend to the lip of the lunate sulcus in two 
specimens obtained at autopsy this autumn—both sulci were on the right side 
and both subjects were adults of American parentage and of European extraction. 
