256 PROF. HUXLEY ON THE [JuDCll, 



question : in other words, the eminentia collateralis stands in the 

 same relation to n w as the hippocampus minor to / 1, or the hippo- 

 campus major to tn m. From the region especially named by ana- 

 tomists " eminentia collaterahs," the sulcus n, n, which may be con- 

 veniently termed the ' collateral ' sulcus, is continued forwards and 

 backwards, and preserves, as might be expected, a similar relation to 

 the parts which are the continuation of the eminentia collateralis, viz. 

 the floors of the descending and posterior cornua respectively, as it 

 had to that eminence. It is difficult to imagine a much more definite 

 proof, if any were wanted, that the hippocampus minor is in no sense 

 a continuation of the eminentia collateralis. 



In the brain whence the sections A to E were taken, the floors of 

 both the descending and the posterior cornua were partictilarly broad 

 (C, D) ; but even here the posterior cornu became a mere crescentic 

 slit posteriorly (B). However, the continuation of the collateral 

 sulcus was always directed upwards and outwards towards the bottom 

 of the slit*. 



A comparison of the views here given, of the inner face and of 

 sections, of Man's brain, with, as nearly as possible, corresponding 

 views of the brain of Ateles (woodcuts, figs. 1 and 2) is exceedingly 

 instructive. The principal sulci alone exist in Ateles ; so that its 

 brain furnishes a sort of sketch map of Man's. The calloso-marginal 

 sulcus, i, i, is easily recognizable; so is the occipito-parietal sulcus, 

 k, k; though the latter, instead of being straight and forming an 

 obtuse angle with the plane of the corpus callosum, as in Man, is 

 strongly convex forwards f, and, on the whole, makes an acute angle 

 with the same plane. As a consequence, the occipital lobe ipcc) is 

 much larger, proportionally, than in Man, while the quadrate lobule 

 is •pari passu smaller. The calcarine sulcus, I, I, has the same general 

 direction and the same bifurcated termination, as in Man. Anteriorly, 

 it ends just in front of the level of the posterior edge of the corpus 

 callosum (the prominent uncinate gyrus must be pushed aside to see 

 its termination) ; and it is, as in Man, separated from the dentate 

 sulcus by the narrow prolongation of the callosal gyrus downwards 

 into the temporal lobe, x. Lastly, the collateral sulcus, n n n, is 

 traceable — though interrupted at intervals — through the same extent, 

 as in Man ; and of the three parts into which it is broken, the pos- 

 terior is continued back even further than in him, and passes a little 

 on to the outer and posterior face of the hemisphere. The greater 



* I have recently had the opportunity of dissecting ten human hrains, and, in 

 all, I have found the calcarine and collateral sulci to present the relations described 

 above, with perfect constancy. On the other hand, nothing could be more vari- 

 able than the length and form of the posterior cornu of the lateral ventricle, 

 and the relative and absolute size of the hippocampus minor. In one of these 

 brains — that of a negro — the posterior cornua were almost absent, not exceeding 

 one-third of an inch in length, on either side. In another the cornua were both 

 1^ inch long and very wide, with a large hippocampus. Another had a posterior 

 cornu \ an inch long on the left side, 1 inch on the right. In yet another it was 

 much longer on the right than on the left side, &c. 



t I found this in both brains. M. Giatiolet represents the corresponding 

 sulcus in A. belzebuth as nearly straight. 



