THE BRAIN OF MODERN MAN 779 



r(.'S|)cx't this latiTal smhu'f clilk'i's li-oin that ot t hi.' ^r'c'at anthropoids and other 

 priinatcs; nanirlx, the ahnost complete chsappc-araiK'c of thv most char- 

 acteristic of siiiiiaii hssuri.'s, tlu' sulcus simiaruin. I lius, the actual bouiidar\' 

 between the parietal and occipital lobes is lor the most part wanting in man. 

 The occipito-parietal incisurt% whose continuation upon the mesial surface 

 IS the occipito-parietal lissurt', marks the position ol this boundary. The 

 extent to which this incisure pro|i'cts laterally upon the coiufxity ol the 

 heniisplure \arK's 111 dillereiit iiidu iduals and also in the two hemispheres ol 

 the same brain. Olten it is scarcelx appart'iit bi'voiid tlu' superior longitudinal 

 lissure, or ma\ extend tor a distance Irom 3 to j cm. upon the lateral aspect. 

 In no instance, howe\er, doc-s this sulcus ha\e the prominence which tlic 

 simian hssure presents in the anthropoids. 



The Fissure 01^ S^l\ils. Of the primiti\'e anthropoid lissures, only 

 two may be disceriU'd with certainty upon tlu' lateral sLirlace ol the human 

 brain. These are the lissure ol SyKius and the hssure ol Rolando. Tiie 

 Rolandic fissure separates tlu' Irontal from the parietal lobe. The lissure of 

 SyKius separates thi- Irontal and the parietal lobi's Irom the temporal lobe. 

 The di\ ision between the i)arieto-temporal area and tin' occipital region is an 

 indecisive one. These three areas ol the bram become conlluent m a common 

 nn'cting-ground. Fhe hssure ol SyK'ius is the most ])romiiu'nt iissinx' ol the 

 human brain, it forms an angle ol something a little more than 45*^ with the 

 cerebral base line. This portion of it is know n as its posterior ramus. Upon the 

 basal surlace, between the orbital portion ol the Irontal lobe and the tip ol 

 the temporal lobe, is the horizontal limb ol the fissure. On the lateral surface 

 the hssure di\ idi'S into a short anti-rior limb, a longer anterior ascending limb 

 and the |)osterior limb alread\ mentioned. The ascending limb (ramus 

 anterior horizontalis I is about 2 cm. in K'ligth; it passes upward and slightly 

 lorward into the caudal portion of the inferior frontal coiu'olution. The 

 horizontal branch (^ranuis posterior) is the main lateral contiiuiation of the 



