NERVOUS SYSTEM. VERTEBRATA. 425 



its dual nature in the Baboons and lowlier Apes). The 

 resulting single sulcus is obviously the parieto-occipital 

 sulcus of Man. It is a simple linear sulcus, the lower end 

 of which is separated from the calcarine by a submer^M 

 gyrus (as in the human brain) ; its upper extremity is 

 surrounded by a broad arcus occipitalis which separates it 

 completely from the intraparietal sulcus. As occasionally 

 happens in the genus Papio, the occipital operculum is not 

 extensive enough to hide the arcus occipitalis or the 

 parieto-occipital sulcus. 



The inferior occipital operculum (i. e. the dorsal lip of 

 the inferior occipital sulcus) is much less developed than 

 it is in Macacus. In other respects the brain closely 

 resembles that of Macacus, with the exception that the 

 calcarine sulcus is not bifid. 0. C. 1338 F. 



D. 637. The brain o an Entellus Monkey (Semnopitliecus 

 entellus}, ( ? ). The left hemisphere has been separated. 



This closely resembles the preceding specimen. The 

 sulcus arcuatus is, however, triradiate in this case. 



The collateral series of sulci vary in the two brains in the 

 same way as we have already noted in Papio. 



0. C. 1338 Fa. 

 Presented by P. L. Sclater, Esq. 



D. 638. The brain of an Entellus Monkey (Semnopithecus 

 entellus) . 



This old specimen exhibits the same arrangement of 

 sulci as the preceding. 



In spite o its damaged condition it shows the relations 

 of the flocculus, paraflocculus, and the projecting " petrosal 

 lobule " better than the more recent specimens. 



0. C. 1338 F b. 



D. 639. The brain of an Entellus Monkey (Semnopithecus 

 entellus). The left hemisphere has been separated. 



In these hemispheres the arcus occipitalis has become 

 submerged under the occipital operculum, so that, at a 

 superficial glance, the Simian and the parieto-occipital 

 sulci seem to be confluent. 



