than in man, a point to be recollected in connexion with the relations stated to exist between the transverse d and antero-posterior diameters c, of the cerebellum.
It is under our third head, that, namely, of the differences which M. Gratiolet's work has enabled us to describe, and we might almost say to discover, that the most important points of our comparison will be found. Under this head will fall the points which were mentioned in the last number[1] of this Journal, as the second and third points of difference, absolutely distinguishing the brain of man from that of the ape; and under it also may be ranged those which M. Gratiolet[2] lays stress upon, as indicating a relative inferiority in the African to the Asiatic ape.
To begin with "the external perpendicular fissure." This fissure or a part of it is visible in Fig. i., below a; in Fig iii., between a and a. It is well represented in most of the simious brains figured by M. Gratiolet; it may be seen in Fig. i., Fig. ii., Fig. iii., Fig. vi., at f, in Tab. i. of Tiedemann's Icones of the brain of the Simia Nemestrina, Simia Rhesus, Simia sabæa, and Cebus capucinus. It will be seen a little later that it is not beside the purpose to remark that it may also be better seen in Tiedemann's[3] figure of the brain of an Orang on one side than it is on either side of his representation of the brain of a Chimpanzee; and that it is very well-marked on both sides, in a drawing of a brain of a young orang given by Professor Wagner, in a work[4] written with express and constant reference to M. Gratiolet's labours. Lastly, this fissure is very well seen in the representation of the brain of the Chimpanzee given by Professor Owen in his paper in the Linnæan Society's Proceedings, Jan. 21, 1857, Fig. iv., p. 19, and in his Reade Lecture, Fig. vii., p. 25.
The inward prolongation of this fissure is never filled up, see 16, Fig. iv. It is upon the degree to which its outward prolongation is filled up or not filled up, bridged or not bridged over, that the absence or presence of an external perpendicular figure, the existence or non-existence of an "operculum," depends.
In the figures referred to, and to some extent in those appended to this paper, the anterior edge of the occipital lobes is seen to rise wave-like as it were against the table-land of the fronto-parietal lobes. The wave-like edge is the "operculum." Along the middle line on each in Fig. i., Fig. iii., and Fig. iv., the wave-like edge, speaking of disruption of continuity between the occipital lobes and the mass of brain anterior to them, is absent; a convolution, a, a, passes across what would else be a chasm. This convolution is the "premier pli de passage" of Gratiolet; it comes according to that authority thus to the surface, and thus bridges the chasm in Man, in the Orang, and in the Ateles, but in no other ape. Our first canon can be immediately applied in the estimation of the value
