STRUCTURAL CULMINATION (/,i 



the three species does the (issure of Rolando show niorr than a siigticstion 

 ot its two major genulleetions. In all of the tluw tlu' most proniinent and 

 deep lissuring is seen in the parit-to-temporal area; in the frontal area onl\ 

 the beginnings of the superior frontal lissiire are apparent. The preeentral 

 fissure is well defined, whik' in the oeeijiital lobe two fissures are elearl\ 

 marked. These are the hssura oeeipitalis and the lateral oeeipital hssure. All 

 semblance ol the t\pieal eireiims\ l\ian arrangement of the sulci has now 

 disappeared. In the great anthropoids the lissural pattiMii has increased 

 consideral)l\- in its com])le\ity, although it retains all of the fundaments 

 which ha\e Ix'cn traced through the seiial approach to this k'\ el of the pri- 

 mate ortler. The latt-ral coinexity is still trilissural, tlu' hssure of SyKius, 

 the fissure ol Rolando and the simian lissure constituting the main 

 landmarks. 



As in all the Jiitcrmediate group, notable expansions are seen in the 

 occipital and frontal lobes; indeed, it is in tlu'sc regions that the greatest 

 degree of complcxitN has made itself apparent in the arrangement of the lis- 

 sures. The central sulcus of Rolando now manifests a delinite tendency to 

 display its maior genullections so characteristic of tlu- human brain. This 

 becomes progressi\ely accentuated m passing from the orang, in which the 

 genuflections are the least pronounced, through the chimpanzee to the 

 gorilla, w lu're the\ stand out in great prominence. As ni all jjrimatc brains, 

 the paricto-tem])()ral region shows a degree of lissural richness which is the 

 most ])ronounced. It is, howe\xr, m much less striking contrast to the 

 frontal region w ln-re the superior, middle and inlerior Irontal fissures are well 

 outliiu'd. 'file preeentral hssure has beconu' a di'ip sulcus l\ ing parallel to 

 the ctntral sulcus. In the occipital lobe the trans\ersc oeeijiital lissure is 

 deeper and has an inclination to develop several collateral branches. The 

 lateral occi])ital fissure is also pronounced. This becomes increasingly the 

 case in passing from the orang to the gorilla, in which latter the occipital 



