1880. J NATURAL SCIENCES OF PHILADELPHIA. 1G9 



bj the first occipital fold it descends internally on the mesial side 

 of the hemisphere, separating the parietal from the occipital lobes. 

 In the Oraiig, the parieto-occipital fissure does not reach the cal- 

 carine, being separated from it by the " deuxieme plis de passage 

 interne " of Gratiolet, or " untere innere Scheitelbogen-Windung" 

 of Bischofl!^'. I have noticed this separation as an anomaly more 

 than once in man. 



According to Bischoff, this disposition obtains in the Gorilla, 

 and seems to be usual also in the Chimpanzee. In the female Chim- 

 panzee, however, on the left side I found the parieto-occipital 

 fissure passing into the calcarine, as in man. The frontal lobe is 

 easily distinguished from the parietal by the fissure of Rolando, 

 and from the temporal by the fissure of Sjdvius. In the Orang it 

 is higher, wider, and more arched than in the Chimpanzee. The 

 anterior central convolution in front of the central fissure runs 

 into the post-central convolution above and below, as in man. It 

 is difficult, however, to identify the three frontal convolutions 

 seen in man and the Chimpanzee, the frontal lobe of the Orang 

 dividing ratlier into two convolutions, the middle one being badly 

 defined. This is due somewhat to the length of the pre-central 

 fissure, which is as long as the fissure of Rolando, extending 

 farther upward than in man. There was nothing particularly 

 noticeable about the base of the frontal lobe ; on the mesial 

 surface it ran into the parietal. The part above the calloso- 

 marginal fissure in the Orang is not as distinctly divided into 

 convolutions as in man, though these are not constantly present 

 even in all human brains. The parietal lobe is separated from 

 the frontal by the central fissure, from the occipital and temporal 

 incompletely, by the parieto-occipital and Sylvian fissures. The 

 posterior-central convolution is well defined. The parietal fissure 

 in the Orang is more striking than that of man, resembling the 

 Gorilla's ; it is twice as long as the corresponding fissure in the 

 Chimpanzee, extending from the transverse occipital fissure, as is 

 sometimes the case in man, almost into the fissure of Rolando. It 

 is unbridged and without a break, and divides the parietal lobe 

 completely into upper and lower parietal lobules. The upper 

 parietal lobule is bounded externally by the parietal fissure ; 

 posteriorly it is separated from the occipital lobe, internally by 

 the parieto-occipital fissure ; externall}' it is continuous with the 

 occipital lobe, as the first occipital gyrus, anteriorlj' it is sepa- 



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