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Show 190 ON THE BRAIN OF THE SIAMANG. [Mar. 6, the left side it plainly stops short some little way above the Sylvian fissure ; on the right side a faint groove continues it into that fissure. Mesially neither fissure dips into the inter-cerebral sulcus. That of the right side comes a little closer than does that of the left; and it is curious that this detail is repeated in my brain of H. hoolock. The fissure of Rolando has no branches along its course, and is entirely unrelated to other fissures. The hemisphere measures along its curvature 3 | inches, and the fissure of Rolando arises 2-| inches from the anterior end. It is thus considerably behind the middle of the cerebrum. In H. hoolock, which has a longer brain, the corresponding figures are 3| and 2^. The frontal lobes are thus larger in H. syndactylus; they have a comparatively smooth appearance as in H. hoolock. Of the furrows traversing this lobe I recognize the praecentralis superior, the frontalis superior, and the frontalis inferior. The praecentralis superior is deeply cut but not extensive. On the left side it begins by being parallel to the fissure of Rolando. but ultimately bends much more forward. It is not connected with the frontalis superior. On the right side the fissure is more "'normal" in direction, and is connected with the second fissure referred to. It may be that the anterior half-the forwardly directed portion-of the supposed praecentralis is really the base of the frontalis superior; but I think that it is not for the following reasons : intermediate conditions are seen in two other Gibbons' brains in m y possession. In one (H. leuciscus) the two •prcecentrcdis fissures are quite parallel with the fissure of Rolando ; in the other brain (H. hoolock) both fissures have so diverged from the normal (?) that they are almost parallel to the inter-cerebral sulcus. The frontalis superior is represented by detached tracts which are deeply excavated. As is the case with tbe other two Gibbous' brains which I have examined, the frontalis inferior is a very strongly marked aud long fissure. O n the right side this fissure was forked posteriorly, and it is quite likely that this region really represents the praecentralis inferior, well developed in the other Gibbons, and on both sides. Intra-parietalfissure.-As can be seen from the drawingexhibited (fig. 2, p. 189), this fissure is very much the same on both sides of the brain; that portion of the complex furrow termed by D r Cunningham postcentralis superior is not well developed and is detached from the rest. It was also detached though very well developed in H. leuciscus; in H. hoolock it was perfectly confluent, the whole fissure being of the characteristic T-shape. I lay no stress upon these differences, which are in all probability individual. They only offer additional evidence of the unreliable nature of cerebral fissures for systematic purposes. |