PROSENCEPHALON OF MAMMALS. 129 



cbscured by the minor intersylvian convolutions, which are ex- 

 posed in the Sheep and Elephant, and are concealed in higher 

 Quadrumana and Man, where they constitute the " gyri breves " of 

 Arnold ; l nor is that of the anterior lip by the interruption of 

 the ectosylvian fissure, s', in the Cat, fig. 91, whereby the sylvian 

 is divided into parallel vertical folds, which, w T ith the intervening 

 sylvian fissure, are overarched by the higher supersylvian fissure, 

 ib. 8. In Quadrumana the posterior part of the supersylvian 

 fissure, fig. 109, 8, sometimes runs into one, 9, behind and parallel 

 with the sylvian, 5. In Stenops the detached " post-sylvian," 9, is 

 short and straight, as in the Cat. 



6 In the Marmozets (Midas, Geof. Hapale, Bl. Jacclius vulgar is} 

 the sole superficial fissure on the exposed surface of the hemi- 

 sphere is the sylvian, figs. 109, 116, 5, and this determines the con- 

 tiguous part of the hemisphere, e, to be the homologue of the 

 sylvian fold. When the postsylvian fissure appears, as in 

 CaUitlirix, fig. 109, 9, the postsylvian fold, /, is defined : it is 

 certain that we now have the homologues of the folds so named 

 and numbered in Unsmiculates, ficrs. 90-92 ; and the advantage 



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of their determination would be lost were we to apply new names 

 to these folds and fissures as if they were distinct and superadded 

 parts in the quadrumanous and bimanous brains. The next fissure 

 which appears, in the Quadrumana., answers to that marked n, 8, 

 in Putorius, fig. 87, which is longitudinal and bends more or less 

 outward anteriorly : it divides, in fig. 116, Callitkrix, 8, the cerebral 

 surface above the sylvian and postsylvian fissures lengthwise, into 

 two pretty equal tracts, and tends to mark off an anterior part or 

 lobe of the hemisphere. 



' Proceeding with the more typical Quadrumana, we find that 

 the progressive expansion of the cerebrum, which has carried it 

 backward over the cerebellum, and augmented the outward and 

 downward extension of the part behind the sylvian fissure, has 

 also added so much to the anterior lobes as seems to have pushed 

 backward the rest of the hemisphere, and gives the sylvian, e, 

 and postsylvian, f } folds a more oblique direction from above, 

 downward and forward, than in most low r er Unauiculates. In 

 the Otter, indeed, and Lion, the sylvian and presylvian fissures 

 are similarly oblique : but the posterior part of the sylvian fold 

 does not project outward so far beyond the anterior part as in 

 Quadrumana : this development, together with the interruption 

 of the supersylvian fissure, and the extension of secondary 

 fissures at right angles and anterior to the sylvian fissure, tend 



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VOL. III. K 



