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N. W. INGALLS 



part of the interparietal, previously described in Cercopithecus, 

 is still present and now on the surface but otherwise sustaining 

 the same relations as before. It is significent that in certain cases 

 this part of the interparietal may be separate from the rest and 

 then the furrow limiting the first annectant gyrus in front is con- 

 nected with the anterior part of the interparietal above. This 

 limiting furrow of the annectant gyrus varies somewhat and with 

 it the size of the gyrus, being found at times very far forward. It 

 is further markedly influenced by the direction and depth of the 

 fossa parieto-occipitahs. 



sulcut gyri angularis 



Querfurche 



Fig. 10 Left hemisphere of Hylobates Mtilleri. 



The superior postcentral fissure is distinctly variable or may 

 even be absent. It is sometimes found in a very well defined form 

 uniting with, but much shallower than, the inferior, or between the 

 two there may be an annectant gyrus. When this occurs we have, 

 sharply defined, for the first time all the classical rami of the inter- 

 parietal. This superior postcentral, lying between areas 2 and 5, 

 is not the sulcus having the same name in Cercopithecus since 

 in the latter it lies between areas 1 and 2. The point is perhaps a 

 fine one. There is often an inverse proportion in the relative de- 

 velopment of this sulcus and the posterior extremity of the cal- 

 loso-marginal, compensatory in nature. Occasionally the first 

 annectant gyrus may be so large that its anterior limiting fur- 



