TROGLODYTES NIGER, THE CHIMPANZEE 567 



The indices as computed on this basis arc: 



Forcbrain index, displaces 310 c.c 83 per cent 



Midbrain index, displaces 4 c.c 5 per cent 



Hindbrain index, displaces 55 c.c 12 per cent 



A forcbrain index of 83 per cent ibv weight) assigns this animal to the 

 distinctly manual group, an estimation which accords well with the actual 

 behavior of the chimpanzee. 



Surface Appearance of the Brain in Chimpanzee 



The pattern and appearance of the cerebral hemisphere in the chim- 

 panzee may be said to l)e that of a human brain in miniature. W ith a few 

 notable exceptions, the convolutional design of this anthropoid corresponds 

 cIosel\ to that of man, and might easily be mistaken lor the latter were it 

 not for its diminutive size, actually being about one-quarter the volume 

 of the human brain. The characterization of the chimpanzee's hemisphere as 

 a human miniature applies equally to the other two great anthropoid apes. 

 The chimpanzee, however, does retain marks of its inherent primitiveness 

 which arc considerably more pronounced than in the case of the gorilla, 

 although less defined than in the orang. A careful comparison of all the 

 markings on the surfaces of the endbrain and the brain stem would almost 

 certainly place the chimpanzee below the gorilla and somewhat above the 

 orang-outang. 



fissures and lobes 



The fissural pattern on the lateral surface of the hemisphere is anthro- 

 poid in type, as determined by the presence of three principal fissures, 

 namely, the fissure of Sylvius whose long horizontal limb has less of 

 the usual simian obliquity, the central fissure of Rolando which divides 



