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N. W. INGALLS 



area 17, the first annectant gyrus and posterior limb of the inter- 

 parietal will be found on the surface to a varying extent. Such 

 an arrangement may occur in any of the forms under discussion, 

 biit most frequently in Cebus, Cynocephalus (fig. 7) and Semno- 

 pithecus. In Cebus, the entire extent of interparietal sulcus, 

 even including a sulcus occipitalis transversus, may be exposed on 

 the surface (Cunningham '92, fig. 46, EUiot Smith, '07, fig. 29). 

 In addition there may be found, lateral to the termination of the 

 interparietal, on the anterior sloping wall of the sulcus lunatus 



first annectant gyrus 



lunate 



callosomarginal 



parietooccipital , 



Fig. 7 Brain of Cynocephalus, from above and behind; cf. figures 5 and 6. 



one or two ill-defined Currows demarcating the second and third 

 annectant gyri, while even a fourth and fifth are figured by Ret- 

 zius ('06). The last two mentioned are, however, of doubtful 

 significance so far as homology is concerned. A further develop- 

 ment of the terminal portion of the interparietal, quite like the 

 conditions occuring in man will be met with later in the Simiidae. 

 Doubtless the most striking feature exhibited by the brain of the 

 lower Old World Apes is that great deep fissure which traverses 

 almost the entire lateral aspect of the hemisphere, the Aif enspalte 

 of Riidinger, the sulcus lunatus of Elliot Smith. Absent in the 



