H^'LOBATES HOOLOCK, THE GIBBON 



415 



of these cortical areas is relatively simple. It is most complex in the parietal 

 region and least conspicuous in the frontal lobes. In respect to fissural devel- 

 opment, the gibbon shows less advance than either the baboon or macacos. 



FIG. 194. BASE OF BRAIN, HYLOBATES HOOLOCK. 



[Actual Length, 70 mm.] 



Key to Diagram, o.c, Optic Chiasm. 



On the Other hand, there is a richness of convolutional pattern in the occipi- 

 tal lobe, which does not exist in cither of the other two forms. This fact, 

 taken in conjunction with the much reduced appearance of the superior 

 colliculus of the midbrain, indicates that in the gibbon most of the actual 

 supervision of vision has been transferred to the occipital lobe. The fissures 

 in the temporal lobe, especially the superior temporal fissure, are well devel- 

 oped and this latter has connected \\ith its extremity a well-defined angular 

 gyrus. 



The fissures of the basal surface of the frontal and temporal lobes give 

 these regions an extremely simple appearance. In fact, the impression obtained 

 from a survey of the cerebral hemispheres in gibbon allies this form much 



