THK Bl^AlN 01 MODERN MAN 787 



the cephalic angle of the IoIjc a short distance above the Sylvian fissure with 

 w liieh it is sometimes continuous. It extends for about an inch ])arallel with 

 the lissure of Rolando and then curves backward and slightly upward, across 

 the parietal surface into the occipital lobe. This sulcus usually appears in 

 three distinct parts whicii form tiie superior and inferior postcentral sulci and 

 tile horizontal intraparietal lissure. The inferior postcentral sulcus, situated 

 behind and parallel to the lower part of the (issurc of Rolando, is separated 

 in about ~2 per cent of cases from the superior jiostcentrai sulcus. The 

 superior postcentral sulcus lies behind and parallel whh the Rolandic sulcus, 

 ch)rsal to the horizontal liml) of the intraparietal sulcus. The horizontal mtra- 

 parietal sulcus passes backward and slightly upward. It js often continuous 

 at its cephalic cxtremit\ w ith the postcentral sulcus. The convolutions on 

 the lateral surface of the |xirietal lobe are thrt'c in number, the jjosteentral, 

 the sujx'rior parietal and tlu' inferior parietal, the last being subdi\ided 

 into certain accessory gyres. The postcentral or ascendmg parietal conxolu- 

 tion constitutes the caudal wall of the Rolandic fissure. It is bounded cau- 

 dall\ by the postcentral sulcus in its two subdivisions. The lower extremity 

 of this gyre is connected with the precentral convolution in front and the 

 inferior parietal gyre behind b\ means of annectent gyres. The superior 

 parit'tal gyrus is situated caudal to the superior postcentral sulcus, dorsal to 

 the horizontal limb of the intraparietal sulcus. The inferior parietal gyrus 

 is situated between the inferior postct'iUral sulcus, the Sylvian fissure, 

 and llu' horizontal limlj of tlu' Intraparulal fissure. I his coinolution is more 

 complex in its configuration than either of the preceding gyres. It is sub- 

 divided by the upturned end of the Sylvian fissure, also by the caudal ter- 

 mination of the first and second temporal sulci. The extremities ol tht^sc 

 fissures determine the position of the supramarginal and angular gyres. The 

 supramarginal gyrus passes around the upturned end of the Sylxian fissure; 

 the angular gyrus bears a similar relation to the upturned end of the superior 



