The greater width of the semilunar segment exposed on the left side was, no doubt, owing to the gravitation of the cerebral lobes, but the greatest width of this segment was only three lines. The relations thus described are well shown in Pl. iii., fig. 3. The view of the base of the brain, as given in fig. 2, will enable us to complete our observations as to the relations of the cerebellum to the posterior lobes of the cerebrum. On looking at that figure, it will be seen that no cerebral surface comes into view on the outside of the lateral boundaries of the cerebellum. In a view of the base of the human brain, some cerebral substance is invariably seen in this situation; but the same is the case with a second orang's brain, with a chimpanzee's brain, and with the brains of several Cercopitheci, and an Inuus, in the Series belonging to the Christ Church Museum. The cerebellum does not project so far laterally as to cover the cerebral lobes in a basal view of any brain in Tiedemann's Icones which is above the rank of the Lemuridæ. Two figures[1] of the brain of the Gibbon given by M. Sandifort, which present a relation of the cerebral lobes to the cerebellum, much resembling that which I have described in the brain of the first of the two orangs in our museum, M. Gratiolet regards with suspicion, whilst he himself records the existence[2] of a similar relation of the two parts of the encephalon in the gorilla. M. Gratiolet gives the figure of the brain of the chimpanzee as drawn by Tyson, only to express a strong opinion as to its worthlessness; and as he condemns it, as well as the two figures of M. Sandifort, on grounds quite independent of the view they give of the cerebellum and its relations, we may, perhaps, be justified in disregarding any evidence which might be based upon these three figures, and in considering the condition and relation of the parts in the subject of this paper as an individual, rather than a specific, peculiarity.
The roof-like exterior of the skull of the gorilla would prepare us for meeting with quite another relation of cerebellum and cerebrum than that which we find in the subglobular skulls of the smaller anthropoid apes. For, though the transverse diameter in these latter skulls taken from one parietal protuberance, or rather from one spot homologous with such protuberance to the other, is only subequal to the transverse diameter, as taken from one supramastoid region to the other, it is yet never markedly inferior, as is the case with the gorilla, to a degree for which no development of mastoidal air-cells can account.
The evidence, then, for the lateral predominance of the cerebellar lobes rests upon the single instance, the subject of this paper, and upon the three representations which M. Gratiolet sees, upon other grounds, good cause for condemning. Against it, is to be set the evidence based upon the examination of several other simious brains as above specified, upon the unanimous assent of every one of the plates given by M. Gratiolet in his Mémoire sur des Plis Cerebraux, and upon Tiedemann's
