1900.] 



BBAIN OP "THE SlAMAtfG. 



189 



The mesial parieto-occipital fissure (M..F.Q., tig. 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 forvvardly 

 directed branch of which only an indication exists on the left side. 

 Slighter furrows pass forwards from the mesial parie to-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. 



3YL 



Brain of Siamang. Dorsal aspect. 



SYL., Sylvian fissure ; F.R., fissure of Rolando ; I. P., Intra-parietal ; 

 P.O., parieto-occipital ; B., frontalis inferior ; C, 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. 

 On 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 Man and the Chimpanzee, but 

 apparently not with the Gorilla. In a brain of H. leuciscus in my 

 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. 



As is the case with H. hoolock, the fissure of Kolando is inde- 

 pendent of other fissures at both ends of its oblique course. On 



