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Show 74 MR. F. E. BEDDARD ON THE [Feb. 7, But later Dr. Benham found this precise arrangement in the brain of Anthropopithecus calvus and in another Chimpanzee. Whether the Gorilla's brain shows the same variability or not I am unable to state; but at any rate there was no such junction in three of the brains which I examined. On the other hand, in the brain of a common Chimpanzee this junction was obvious on both sides. Calloso-mctrginal fissure.-This is long and deeply engraved upon the brain-surface. It follows the margin of the corpus callosum and bends down anteriorly with it. Posteriorly it ends with the corpus callosum. So far there is no difference from the Chimpanzee. A number of branches arise from the upper margin of the fissure and run at right angles to it towards the upper margin of the brain. Two or three of these actually bend over and appear right and left upon the upper surface of the hemispheres. So far as concerns the parietal lobe, only one of these fissures is absolutely constant; it is to be found in all m y five brains. The fissure in question cuts the surface of the brain just behind the fissure of Rolando. Exactly the same statement may be made with regard to the Chimpanzee brain. But there is this difference between the two Anthropoid Apes, that whereas in the Gorilla the calloso-marginal sulcus is continued back behind the point of origin of the transverse fissure just referred to, this is at least not always the case with the Chimpanzee. In two brains of the latter animal which I have before me the calloso-marginal fissure ends in this superficial fissare. Lntra-parietal fissure.-In the Gorilla, as in the Chimpanzee, this is sometimes a continuous and T-shaped fissure. The horizontal part of the T runs roughly-in some cases, indeed, more accurately-parallel to the fissure of Rolando. The stem of the T joins the Simian fissure behind. Dr. Cunningham divides this complex fissure in the humau brain into four separate ones, since in the foetal brain they are not confluent. In the Gorilla that portion of the system which Cunningham terms " sulcus postcentrals superior," and which lies most mesially of the various component parts, is sometimes separate from the rest. This was the case with the right half of the brain belonging to the College of Surgeons (fig. 1), in which, moreover, the furrow in question was prolonged anteriorly to reach the fissure of Rolando. The same arrangement was observed in the same hemisphere of a second brain (fig. 5) and in the left hemisphere of a third (fig. 7), save that in neither of these was there a junction with the fissure of Rolando. In two other brains these various sections were confluent. There is thus in the Gorilla precisely the same variability in respect of these fissures that occurs in the Chimpanzee. It is no more the " usual condition" in the Gorilla than it is in the Chimpanzee for the sulcus postcentralis superior to be confluent with the rest of this system of fissures. Sulci of the frontal lobe.-It may be convenient to describe these furrows in some elaboration in a given brain and then to describe |
