AMERICAN NEGRO BRAIN 199 
between the ramus parietalis and the sulcus parietalis superior, 
obscuring the identity of the latter sulcus. 
The ramus occipitalis shows in nearly every hemisphere the 
typical form of a sagittal arcuate sulcus with terminal anterior 
and posterior transverse bifurcations, the mesial limbs and body 
of which serve to define the gyrus arcuatus posterior; this can be 
well seen in figure 5. In no case is there a sharply defined 
bridging gyrus separating the sulcus transversus; in 16.6 per 
cent there is a possible communication with the sulcus lunatus. 
The mesial operculation caused by the lobulus parietalis inferior 
will be discussed later. 
The sulcus lunatus, sulcus prelunatus and sulcus occirpitalis 
will be discussed together on account of their intimate relation- 
ship. The findings in this region in this series of brains confirm. 
in general the work of Smith. An examination of the extent of 
the area striata was not possible in every case; consequently 
the identification of the sulcus lunatus is in some instances less 
positive than it might otherwise be. There is a noticeably 
greater tendency to prominent and typical development in the 
left hemispheres; this accords with both Smith’s (’04) and 
Murphy’s (’10) observations. The area striata extends on to the 
lateral surface of the hemisphere in every case in which it was 
examined, but not to any great extent; its limit frequently coin- 
cides with one or two shallow grooves concentric with the sul- 
cus lunatus. 
The most interesting feature of this region is the unusual 
prominence of the sulcus prelunatus and the series of forms 
presented illustrating the mode of transition from a very short 
element to a typical sulcus occipitalis lateralis. It has an average 
length of 25 mm. and depth of 10 mm. It extends anteriorly 
to within a few millimeters of the ramus ascendens sulcus tem- 
poralis medius, and by its posterior communication with the 
sulcus lunatus, it forms an angle enclosing the lateral limb of 
the sulcus transversus. It thus forms a distinct boundary 
between the gyrus parietalis inferior and the gyrus occipitalis 
lateralis. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 25, NO. 3 
