ROLLESTON ON THE BRAIN OF THE ORANG T7TANG. 213 



sively anthropic. These considerations make me suspect that more 

 weight has been attached to M. Gratiolet's words, as above quoted, than 

 he would have wished them himself to carry ; and anatomical investi- 

 gation seems to me but to strengthen the argument based upon these 

 literary considerations. For this " lobule of the marginal convolution" 

 is very frequently asymmetrical on the two sides of the same brain, and 

 its development in any two human brains taken at haphazard is pretty 

 sure to present the very greatest differences. Varying, as it does most 

 widely, in absolute size, it varies also showing "rien* de constant" in 

 its relation to certain other parts ; its value can hardly be high, there- 

 fore, as a serial characteristic. 



The convolution numbered 4 in Tig. 1 and Fig. 3, the "premier 

 pli ascendant" of Gratiolet, is separated by a vertical more or less in- 

 terrupted fissure from the horizontal-lying frontal lobes 2 and 3. Now, 

 a line drawn down the long axis of this fissure would fall a considerable 

 way in front of the commencement of the fissure of Sylvius. Such a line 

 in the human brain falls always far behind the commencement of that 

 fissure, joining it, indeed, some way behind the angle where the fissure 

 of Sylvius makes its bend horizontally backwards. The forward position 

 of this Hue speaks more strongly than can the vertical direction of the 

 fissure of Sylvius, of stunted antero -posterior growth of the frontal 

 lobes, and it deserves more attention than it has as yet received. 



The convolutions, No. 3, the superior frontal convolutions, are of all 

 the convolutions those in which by symmetry and simplicity, both 

 alike sure marks of degradation, the orang's brain contrasts to the 

 greatest disadvantage with man's. But this fourth and this fifth point we 

 shall leave to be elucidated by the reader for himself from an examina- 

 tion of our figures. We will state, however, the details which an 

 examination of the chimpanzee's brain, instituted with a view of see- 

 ing whether its convolutions were really more symmetrical and more 

 simple ^than those of the orang, elicited, in confirmation of !M. Gratiolet's 

 views. 



In the orang, and in the chimpanzee, both the frontal, 1, 2, 3, the 

 4 and 5 ascending parietal, and the superior bridging convolutions aa, 

 are asymmetrical on the two sides of the brain. The occipital d, the 

 temporo- sphenoidal b, and the convolutions b, b, b, named "pli courbe" 

 by M. Gratiolet, are symmetrical in the chimpanzee, but asymmetrical 

 in the orang. The occipital lobe is both more simple and more sym- 

 metrical in the chimpanzee than in the orang, but it is not larger in 

 size. Both ascending convolutions are a little more simple in the 

 chimpanzee than in the orang. But the sum total of advantage accruing 

 to the orang from this comparison is, on M. Gratiolet's own principles, 

 but slight. 



Having arrived at our last head- -that, namely, of such differentiae 

 as are detectible by dissection only — we will proceed to lay them before 



* Memoire, 1. c. 



