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N. W. INGALLS 



in all ways, since it represents the posterior extremity of the prim- 

 itive sulcus which we see in its earliest form in what is also known 

 as the sulcus lateralis in the Lemuroidea (cf. Perodicticus) . Be- 

 yond the point where this branch is joined to the interparietal, 

 this latter sulcus or even the sulcus laterahs is of a newer formation ; 

 it is less constant and in the forms we are considering, the Cer- 

 copithecidae, it is distinctly shallower, so much so in fact, that 

 one could even speak of an annectant gyrus in many cases. The 

 branch just referred to is to be seen in the left hemisphere of 

 Pithecida (fig. 2). On account of the great growth disturbances 



sulcus gyri angularis 



Fig. 6 Right hemisphere of Cynocephalus; cf. figures 5 and 7. 



occuring in this region, considerable distortion of the primitive 

 conditions in Pithecia is inevitable, and the depth to which this 

 branch of the interparietal is buried will be determined in part 

 by the degree to which the first annectant gyrus is submerged. 

 It may be present, but this is doubtful, on the right side of the 

 example of Pithecia figured. This dorsal branch of the interparietal 

 sulcus is an important furrow and will be encountered again in 

 Semnopithecus and Hylobates, where, with the reemergence of the 

 first annectant gyrus, it also rises to the surface. The other branch 

 of the interparietal is less marked and less constant. It is located 

 somewhat anterior to the first mentioned branch, is usually quite 



