306 ORIGINAL ARTICLES. 



fissure, is a very striking feature in the upper aspect of both the 

 Quadrumanous and the human brain ; but, in the Chimpanzee, the 

 point of the V is situated a little in front of the transverse axis 

 of the hemispheres, whilst in man it is, to a still greater extent, 

 behind that axis. Suppose the whole length of the hemispheres to 

 be represented by 100, then from the fore-part of the brain to the 

 point of the V, would measure, in the Chimpanzee, 49, and, in man, 

 57. It is obvious, on further examination, that whereas nearly one- 

 half of the upper surface of the cerebrum lies in front of the fissures 

 of Eolando in man, a very little more than one-third is so placed in 

 the Chimpanzee. In the Orang's brain, figured by Dr. Eolleston, 

 the proportion appears to be mid-way between the two. There can 

 be no reasonable doubt, that the part of the hemispheres situated in 

 front of these remarkable fissures in man, the Orang and the Chim- 

 panzee, and we may add, in still lower Quadrumana, are homologous 

 parts, in the truest sense of that term. The anterior cornua of the 

 lateral ventricles project into them, passing beyond the first ascend- 

 ing convolution on each side. The external perpendicular, or ver- 

 tical, fissure, figs. 4, 5, V, is particularly well developed in the 

 Chimpanzee's brain ; it is not bridged over, on the upper surface of 

 the hemispheres, by any superficial convolutions, so that its posterior 

 border, named by M. Gratiolet the operculum, is smooth and unin- 

 terrupted. It is continued, on the internal surface of the hemisphere, 

 as a distinct internal perpendicular fissure. In the particular human 

 brain which we have dissected for the purposes of this paper, the 

 external perpendicular fissure is obliterated, but it can be unmis- 

 takeably traced on the internal surface of the hemispheres, within the 

 longitudinal fissure, as the internal perpendicular, or vertical, fissure. 

 In the ape, this fissure cuts off 23 parts, posteriorly, out of 100 of the 

 length of the hemispheres as visible above ; in man, the corres- 

 ponding portion represents 20 parts out of 100 ; in the Orang 

 figured by Dr. Eolleston, the proportion seems to be intermediate. 

 There can be as little doubt here, as in regard to the parts in front 

 of the fissure of Eolando, that the portions of the hemispheres be- 

 hind the perpendicular fissure, in man, the Orang, and the Chim- 

 panzee, as well as in the lower apes, are strictly homologous parts 

 of the cerebrum. We shall see that the posterior cornua of the 

 lateral ventricles extend into them. Between the fissure of Eolando 

 on each hemisphere, and the perpendicular fissure, is an equally 

 homologous region which, in the Chimpanzee, occupies the remaining 

 28 parts out of 100, of the total length of the cerebrum ; whilst, in 

 man, it constitutes 23 parts, i. e. as seen directly from above ; but 

 this particular region, and also the part behind the perpendicular 

 fissure, it must be remembered, are just those which gain so much 

 in their vertical dimensions, in the human brain. If, in fact, we 

 measure longitudinally over the vertex, the relative spaces occupied 

 by these three regions, which may be distinguished as frontal, 

 parietal and occipital, though they do not exactly coincide with the 



