1900.] 



BBAItt OF tHE SIAMANG. 



189 



The mesial parieto-occipital fissure (M..1P.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 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. 



-SY1. 



Brain of Siamang. Dorsal aspect. 



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

 P.O., parieto-occipital ; B., frontalis inferior ; 0., frontalis superior. 



The calcarine fissure (CA.) most obviously joins the mesial 

 parieto-occipital Assure, 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 hooloclc which I have examined. 

 On the left side of the brain this fissure forked into ay posteriorly. 

 In this junction of the mesial parieto-occipital with the calcarine 

 Hylobates syndactylies 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 II. hooloclc, the fissure of Kolamlo is inde- 

 pendent of other fissures :it both ends of its oblique course. On 



