AMERICAN NEGRO BRAIN 203 
seems to be more intimately related to the sulcus paracalearinus 
than to the sulcus limitans precunei in 46 per cent of instances. 
The sulcus incisura parieto-occipitalis is the most variable and 
inconstant of the group. In some cases it is only represented by 
a pit, in others it lies almost entirely on the lateral surface as a 
mesial branch of the ramus occipitalis. Quite frequently a 
slightly sunken gyrus arcuatus posterior and operculated lobulus 
parietalis inferior produce a shallow communication of the sul- 
cus incisura with the ramus occipitalis; this condition is very 
evident in both hemispheres of the fetal brain, probably because 
of the incomplete development of the gyrus arcuatus posterior. 
The sulcus calcarinus presents great variations in form and 
depth. Spitzka has called special attention to the straightness 
of the combined sulcus in the Eskimos, a similar condition is 
noted in five of these hemispheres. In several others a marked 
superior convexity is seen, this is not due to the displacement 
of the floor of the sulcus but to the excessive growth ofthe inferior 
lip of the gyrus lingualis producing a prominent operculum 
which conceals a portion of the cuneus but which does not 
necessarily reduce its size. This operculum also conceals the 
communication with the fossa parieto-occipitalis and often 
gives rise to the superficial appearance of a direct continuity 
of the sulcus calecarinus and the fossa. In every instance an 
examination of the depth of this communication reveals a union 
of these two sulci at right angles to each other. The gyrus 
cuneus has been considered by some anthropologists an index 
of inferiority on account of its superficial appearance in some 
apes and its reported more superficial position in the Negro. - 
In this series of Negro brains the gyrus cuneus can be made out 
in all but three hemispheres, but in the most prominent it lacks 
10 mm. of reaching the superficial surface. 
The sulcus interstriatus mesialis is variable. In 50 per cent of 
the hemisphereg it terminates in the groove of the transverse 
sinus at the occipital pole. In no instance does it extend across 
the groove to the lateral surface. The lateral extension seems 
to be somewhat greater in the males than in the females. The 
bridging gyrus cuneolingualis posterior is present in 58 per cent, 
