AN AMERICAN INDIAN BRAIN 411 



area on this side. The rhinal element of the sulcus is separated 

 in both hemispheres by a bridging gATus near the anterior 

 extremity. 



The sulcus lunatus can be very- plainly identified in the left 

 hemisphere. It is 35 millimeters in length and lies nearer the 

 lateral border about 3 centimeters from the occipital pole. It 

 has an arcuate or rather angular form and a slightly operculated 

 posterior lip. The area striata, delimited by knife sections, 

 lacked about 2 millimeters of reaching this lip but followed the 

 course of the fissure quite regularh\ In the right hemisphere the 

 tendency is towards a longitudinal disposition of the fissures in 

 this region, to which the boundary- of the area striata does not 

 bear any definite relation. The most prominent sulcus is inter- 

 preted as a modified s. prelunatus or s. occipitalis laterahs of 

 some authors. Comparison of the extent of.the area striata in 

 the two hemispheres shows \c\y iilainly a greater lateral extent 

 in the left hemis]iliere. 



The sulcus occipitalis paramesialis hes more upon the lateral 

 surface in the left hemisphere but is verj' prominent in both 

 hemispheres. This lateral position indicates that it bears a 

 relation to the lateral extension of the area striata. 



The sulcus occipitalis inferior courses on the tentorial surface 

 along the lateral border. It is verj' similar on the two sitles, a 

 deep, slightly operculated fissure about 40 millimeters in length, 

 communicating at the two extremities with the sulci of the 

 corresponding regions. 



The sulcus calcarinus in both hemispheres is separated from 

 the fossa parieto-occipitalis by a small bridging gyms cuneus 

 and from the sulcus retrocalcarinus by a larger bridging g^'rus. 



Tlie sulcus retrocalcarinus temiinates in both hemispheres in a 

 deep operculated polar element but separated by a prominent 

 bridging g>Tus. Landau ('15) interprets this polar element (s. 

 extrenms, s. occipitalis triradiatus, s. calcarinus externus of E. 

 Smith, s. occipitalis polaris), as the true posterior bifurcation as 

 described by Cunningham ('92), separated bj- the g>Tus cuneo- 

 lingualis posterior and homologous to the sulcus triradiatus of 

 ape brains. The prominence of this sulcus was noted by the 

 writer ('15) in the Negro brain, in which it was described as an 



