In the gorilla, chimpanzee, and orang, the island of Reil in the fissure of Sylvius is generally--at least, according to my experience--overlapped by the operculum, although there are instances in which this is not the case. In these three anthropoids, as Bastian justly observes, the fissure of Sylvius is much less horizontal than in man, and occupies a position more like that which it takes in the black sea-cat monkey, the wanderers, and other macacas. In the gorilla its direction is more horizontal than in the two other species of anthropoids. The central fissure, termed fissure of Rolando, is very marked, especially in the chimpanzee (Fig. 57 R); but it may also be easily traced in other species of anthropoids (Fig. 58, II., 56, R). The so-called simian fissure between the parietal and occipital lobes of the cerebrum (Meynart’s elongated external occipital fissure), presented in Fig. 58 _s c_, is very marked in the chimpanzee (Fig. 57, _d_). The frontal lobes of the gorilla brain are high, while those of the chimpanzee are short and low. It is said that those of the orang, which are high and short, terminate in a beak-shaped curvature, but this is not invariably the case. [Illustration: Fig. 60.--Longitudinal section of a gorilla’s brain (Bola and Pansch). _s.cm_, Colloso marginal fissure. _f, p_, Internal parieto-occipital fissure. _f, c_, Calcarine fissure, the posterior part of the hippocampal fissure. ] In the anthropoids we have been considering, and also in several of the lower species of apes, there are three other fissures of less importance in addition to those we have mentioned, namely, the fissure parallel to the fissure of Sylvius, and placed behind it, the _corpus callosum_ fissure, placed immediately above the _corpus callosum_ on the inner side of the hemisphere of the cerebrum, and the calcarine fissure (_Fissura calcarina_) (Fig. 60). The latter ends near the point of junction of the inner and lower surfaces of the posterior division of the hemisphere. The upper temporal convolution, termed by several anatomists _Gyrus supramarginalis_, is said by Gratiolet to be absent in anthropoids; but Rolleston, Bastian, and myself have all found it well developed[82] (Fig. 56, orang, and Fig. 58, gorilla).