AN AMERICAN INDIAN BRAIN 409 



the left hemisphere does not seem to increase the regularity of 

 these elements. The greater tendency is towards a transverse 

 direction. 



The sulcus frontaUs mesiaUs is seen as an irregular system of 

 alternating transverse and longitudinal elements extending to the 

 frontal pole. The more posterior of these were chosen arbi- 

 trarily as a guide between the superior frontal area antl the 

 anterior frontal area. 



The orbital surface has the usual U-yye of fissuration, the only 

 unusual feature being the extension of the mesial limb of the 

 s. orbitalis transversus into the fossa Sylvii of both hemis])heres. 



The sulcus cinguli corresponding to E. Smith's chart is ver>' 

 poorly developed in its anterior two-thirds,, the more prominent 

 sulcus being the s. paracinguh. This might indicate a disap- 

 pearance of the s. cinguli due to an increased growth of the mesial 

 region, but was called to attention by Cole ('10) in a micro- 

 cephalic brain in which he suggested that the supracingulate 

 sulcus was the older. 



The sulcus postcentralis is a ver>' prominent fissure in both 

 hemispheres, extending from the mesial border to within a few 

 millimeters of the fissura cerebri lateralis. In the right hemi- 

 sphere there is ho communication with the s. interparietalis, 

 thus giving rise to a fissure veiy similar to the s. centralis. In 

 the left hemis])hore the posterior reflection of the two extremi- 

 ties forms an arcuate sulcus and a wide gjTUs centralis posterior 

 in the corresponding regions. 



The sulcus inter]mrietahs is contrasted on the two sides. In 

 the right hemisphere it appears as a fourth vertical sulcus in series 

 with the precentral, central and postcentral sulci. It communi- 

 cates across an almost superficial bridging g>Tus with the s. 

 paroccipitalis. The tendency in the left hemisphere is towards 

 a sagittal and more posterior arrangement. The sulcus is repre- 

 sented by two horizontal elements in intercommunication with 

 the s. postcentralis and the body of the s. paroccipitalis across 

 bridging g>Ti. 



The sulcus paroccipitalis is more lateral and more prominent 

 in the right hemisphere. The independence of this sulcus is 



