110 PROCEEDINGS OF THE ACADEMY OF [1S80. 



rated from the posterior central convolution more completely 

 than in man, by a fissure which runs parallel with the central 

 fissure. There is in the Orang, also, a fissure running parallel 

 with the parietal, which subdivides the u^pper parietal lobule into 

 inner and outer portions. The precuneus, or the space on the 

 mesial side of the parietal lobe between the parieto-occipital 

 fissures and the ascending branches of the calloso-marginal, is 

 well defined. The lower parietal lobule in the Orang divides 

 naturally into the supra-marginal and angular gyri. The supra- 

 marginal fold curves around the upper end of the posterior 

 branch of the fissure of Sylvius and runs into the superior tem- 

 l^oral g3'rus. The angular gyrus, which is very evident, arches 

 around the first temporal fissure, and becoming continuous with 

 the second occipital fold, passes then into the upper temporal 

 gyrus. The occipital lobe, separated from the parietal, internally, 

 by the parieto-occipital fissure, is continuous with upper parietal 

 lobule through the first occipital gyrus, and by the second 

 occipital gyrus with the angular. There are no sharp lines of 

 demarkation between the occipital and temporal lobes. In the 

 occipital lobe of my Orang the transverse occipital fissure was 

 present, and received the parietal fissure. The calcarine fissure 

 was well marked, but was separated in the Orang from the pai'ieto- 

 occipital fissure by the " deuxieme plis de passage interne " of 

 Gratiolet, the " untere innere Scheitelbogen-Windung " of Bischofl", 

 The cuneus of the Orang is therefore somewhat diff"erent from that 

 of man. In man I have seen these two fissures separated as an 

 anomal}-. The calcarine passed into the hippocampal fissure, so 

 tliat in the Orang, as in monkeys generally, the gyrus fornicatus 

 was separated from the hippocampal gyrus , whereas in man these 

 convolutions are continuous. This disposition has been noticed 

 in the Hylobates, in Ateles, and in one Chimpanzee, where 

 the calcarine did not reach the hippocampal. The first occi- 

 pital gyrus is very well developed, and, as the late Professor 

 Gratiolet observed, is one of the most strildng convolutions in 

 tlie brain of the Orang. It rises so to the surface that the 

 internal perpendicular fissure or external part of the parieto- 

 occipital fissure is almost entirely bridged over, the operculum so 

 characteristic of the monkey almost disappearing. It is con- 

 tinuous with the upper parietal lobule arching around the parieto- 

 occipital fissure. This convolution comes to the surface in the 



