OCR Text |
Show 1900.] BRAIN OF THE SIAMANG. 189 The mesial parieto-occipital fissure (M.P.O.,fig. 1, p. 188) on the left side of the brain passes straight downwards from the superior surface of the brain and joins the calcarine (CA.) below. On the right half there is a little complication : there is a forwardly directed branch of which only an indication exists on the left side. Slighter furrows pass forwards from the mesial parieto-occipital. In the form and direction of the mesial parieto-occipital fissure there are no noteworthy differences from the other brains with which I have compared it. Fig. 2. Brain of Siamang. Dorsal aspect. SYL., Sylvian fissure ; F.R., fissure of Rolando ; LP., Intra-parietal; P.O., parieto-occipital; B., frontalis inferior; 0., frontalis superior. The calcarine fissure (CA.) most obviously joins the mesial parieto-occipital fissure, as is shown in the accompanying drawing (fig. 1), and at a point nearer to the superior surface of the brain than it does in a brain of Hylobates hoolock which I have examined. O n the left side of the brain this fissure forked into a Y posteriorly. In this junction of the mesial parieto-occipital with the calcarine Hylobates syndactylus agrees with M a n and the Chimpanzee, but apparently not with the Gorilla. In a brain of H. leuciscus in m y possession there was no such junction ; the mesial parieto-occipital curved forwards parallel with the calcarine. The latter fissure was markedly Y-shaped, the three limbs of the Y being almost equal in length. A s is the case with H. hoolock, the fissure of Rolando is independent of other fissures at both ends of its oblique course. On |