210 ORIGINAL ARTICLES. 



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* 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. Gratioletf 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/, in Tab. i. of 

 Tiedemann's Icones of the brain of the Simia Nemestrina, Simia Rhesus, 

 Simia sabcea, 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^ 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§ 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 Linnaean 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 pre- 

 sence 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 



* Nat. Hist. Rev., i., p. 83. f Memoire, pp. 51, 62. 



% Tiedemann ap. Wagner, Icones Zoot., Taf. viii., figs. 2 and 3. 

 § Vorstudien zu einer Wissenschaftliehen Morphologie und Physiologie des Mensch- 

 lichen Gehirns als Seolenorgan. Von Rudolph Wagner. Gottingen. 1860. 



