STRUCTURAL CULMIXATIOX Q45 



spheres has in general a tri-fissural design in which three chief fissures are 

 present: first, the fissure of Sylvius, second, the fissure of Rolando and third, 

 the simian fissure. The position and angulation of these fissures arc charac- 

 teristic in the primate brain. The SyKian fissure in its lateral portion extends 

 backward and upward at an angle something less than 45 degrees with the 

 base line of the brain. The fissure of Rolando extends forward Jrom the 

 superior longitudinal fissure at an angle varying from 6~.j to 84 degrees. 

 The sulcus simiarum leaves the superior longitudinal fissure at an angle of 

 about go degrees. This latter sulcus is believed to have no counterpart in 

 the human brain. Nevertheless, distinguished authorities such as Elliot 

 Smith maintain that the sulcus lunatus, on the lateral surface of the occipital 

 lobe of man, is a vestige of this great simian fissure. In many instances the 

 human parietal incisure of the occipito-parietal fissure corresponds in striking 

 degree to the more proximal portion of the sulcus simiarum of the higher 

 anthropoids. 



Nor are the similarities, which link the primates together on the basis 

 of their fissural patterns, limited to these three major fissures alone. W ith 

 few exceptions, the identifications may be carried to the secondary fissures. 

 In many lower primates and also in the intermediate group, these secondary 

 fissures have no such prominence as they attain in man. If the brains of 

 such simians be compared with the fetal brain of man in which the secondary 

 fissures are making their appearance, the correspondence between the anthro- 

 poid and human brain may be recognized. Further development of the 

 brain in man adds much complexity both to its convolutions and fissures. 

 But an essential correspondence of fissural pattern exists in all primates. 



The Lobation of the Primate Brain. The lobation in apes and man 

 is identical throughout the series. As seen upon the lateral convexity of the 

 hemispheres, this lobation expresses itself in four distinct divisions: the 

 frontal lobe, the parietal lobe, the temporal lobe and the occipital lobe. 



