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 investigation 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[1] de constant" in its relation to certain other parts; its value can hardly be high, therefore, as a serial characteristic.
The convolution numbered 4 in Fig. 1 and Fig. 3, the "premier pli ascendant" of Gratiolet, is separated by a vertical more or less interrupted 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 line 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 examination of our figures. We will state, however, the details which an examination of the chimpanzee's brain, instituted with a view of seeing 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 symmetrical 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 differentiæ as are detectible by dissection only—we will proceed to lay them before
- ↑ Memoire, l. c.
