ANATOMY or THE ANTHKOPOID APES. 199 



extent ; the length is generally (according to Quain's ' Anatomy ') about an inch, la 

 the Chimpanzee, on the other hand, these fissures on each side are very long ; in both 

 of the specimens which I examined they extended to within one-sixth to half an inch 

 of the furrow lying between the cerebrum and cerebellum ; and as figured by Hart- 

 mann ^ they pass in an almost straight course across the brain, being traceable up to 

 the median furrow of the brain. In the brain of " Sally," on the other hand, these 

 fissures, although recognizable laterally, were connected with the median furrow (on 

 Plate XXIII. fig. 3, P.o.f.) by an irregular bent fissure on one side only. A closer 

 comparison of the two brains showed an interesting reason for this difl'erence. In the 

 Common Chimpanzee the parieto-occipital fissure is deep, and its posterior wall is said 

 to be markedly convoluted. This was so, at any rate, with one of the two individuals 

 whose brains are among my stores at the Gardens. If that part of the brain of 

 Troglodytes caZuws lying between the letters P.o.f. \ and P.O./. in fig. 3 of Plate XXIII., 

 the median longitudinal furrow of the brain, were infolded, we should get a very close 

 resemblance to the brain of Troglodijtes nlger. 



The Sylvian fissure of Troglodytes calvus presents, at any rate, one very interesting 

 point. It has been more than once pointed out that the posterior and longer of the 

 two branches of the Sylvian fissure is more upright in the Chimpanzee than in Man. 

 This was undoubtedly the case with the two brains examined by myself, the angle of 

 inclination being pretty much the same in both. In the brain of Troglodytes calvus, 

 however (Plate XXIII. fig. 2 F.s.), the posterior limb of the Sylvian fissure was much 

 more upright than in the Common Chimpanzee, resembling therefore that of the Gorilla, 

 the Gibbon, and the Orang, though not so upright as iu the latter. 



The fissure in the brain of Troglodytes calvus, which appears to correspond to the 

 anterior branch of the Sylvian fissure as figured by Gratiolet^, is quite as large as in the 

 Common Chimpanzee, but more horizontal in direction. I take it, however, that this is 

 not the true anterior branch of the Sylvian fissure. For this long fissure, which lies in 

 front of (below) the true anterior branch of the Sylvian fissure, is not continuous with 

 the posterior branch of the Sylvian fissure, as can be seen by raising the temporo- 

 sphenoidal lobe. Comparing the brains of the Chimpanzees with that of the Orang 

 and the Gibbon, the true anterior branch of the Sylvian fissure (F.s.a.) is seen to be 

 very short. In Troglodytes calvus it is directed more upwards than in 1\ niger. 



The fissure of Rolando certainly varies in position in the Common Chimpanzee. 

 In one of the two specimens which I have before me this fissure is not much behind 

 the transverse axis of the brain ; this is the case also with the brain of Troglodytes 

 calvus. But in another Common Chimpanzee the point of the V formed by the two 

 converging furrows is distinctly (more than half an inch) behind the transverse axis. 



' ' Anthropoid Apes,' fig. 37, p. 192. 



^ ' Memoire sur les plis cerebraux de I'homme et des primates,' pi. vi. figs. 2, 6. 



