Cerebral Convolutions. 137 



The Brain of the Orang is more massive than that of the Chim- 

 panzee, and that of the Chimpanzee than that of the Gorilla : but the 

 Occipital Lobe in the Gorilla is larger than in either of the other two 

 (a point of inferiority, since this lobe is so small in Man) ; and the 

 Frontal lobe is lower : moreover the Convolutions are probably less 

 complicated in the Gorilla's Brain : therefore the Gorilla has the 

 least highly developed Brain of the three. 



In the Chimpanzee the Occipital lobe is large, its Operculum 

 complete the ascending branch of the Curved convolution generally 

 rises in front of the Fissure of Sylvius, and ascends a considerable 

 distance towards the superior border of the brain. The superior 

 External Bridging Convolution is generally absent ; the second is 

 large, but does not usually come to the surface. 



In the Orang the Occipital lobe is of moderate size. the Opercu- 

 lum scarcely perceptible the Curved convolution rises on a level 

 with the summit of the Fissure of Sylvius the superior Bridging 

 convolution is large and superficial the second present, but hidden. 



In Man the Occipital lobe is very small, and there is no trace of 

 an Operculum ; the origin of the ascending branch of the Curved 

 convolution is on a level with the summit of the Fissure of Sylvius, 

 and both the superior Bridging convolutions are large and superficial. 

 Therefore these three leaders will rank as follows 



1. Orang-Utang. 



2. Chimpanzee. 



3. Gorilla. 



The convolutions of the Brain are arranged after the same plan in 

 the Platyrrhine as in the Catarrhine Monkeys : and yet the former 

 have very distinctive Cerebral characteristics, and such as are not 

 found in the latter. Thus, besides the extreme reduction in the size 

 of the Frontal lobe, and the enormous development of the Parietal 

 in some, we find the second External Bridging convolution always 

 superficial in Cebus Capucinus ; the convolution limiting the summit 

 of the Fissure of Sylvius hidden in Ateles, without any part of the 

 fissure itself being covered ; and the ascending branch of the Curved 

 convolution continuous with the Superior Temporal in the same 

 Monkey arrangements which do not find a parallel in the Old 

 World Series. The highest group (Sapajous, Grat.) contains 

 Mycetes, Ateles, &c.; they take the first rank, owing to their having 

 a comparatively larger Frontal lobe, and both superior External 

 Bridging convolutions present. Next to these come Cebus Capucinus, 



