AN AMERICAN INDI.\N BRAIN 407 



sures. With this scheme it is hardh' necessary' to label the dif- 

 ferent fissures, for a comparison with E. Smith's figures in Cun- 

 ningham's Text-book of Anatomy will show the interpretation. 



The fissura cerebri lateralis is shar]3ly upturned and bifur- 

 cated in the left hemisphere at its posterior extremity, but hori- 

 zontal and single in the right. Since this bifurcation is caused 

 by an overgrowth of the posterior inferior parietal region, as has 

 been determined in the Negro brain by Poynter and Keegan 

 ('15), the two hemispheres are peculiarly contrasted in their 

 centers of greatest growth in the inferior parietal lobule, the left 

 being in the posterior region and the right in the anterior region. 

 This is further evidenced in the conformation of other sulci in 

 these areas, and will be discussed at a later point. In both 

 hemispheres there is a distinct operculation by the superior lip 

 in the region of the areii subcentralis. The anterior rami of 

 the fissure are completely separate on both sides, enclosing a 

 prominent pars triangularis. 



The sulcus centralis is unusual in its upi^er third in the left 

 hemisphere. It lacks several millimeters of reaching the mesial 

 border and in the superior third is displaced anteriorly in an 

 arcuate form, apparently due to an overgrowth of the gyrus 

 centralis posterior opposite the motor are^ of the lower limb. 

 According to Cole ('10), interniption of the sulcus by a sub- 

 merged or bridging g>'rus occurs at the posterior arch of the 

 supeiior genu in poorly convoluted brains and just above in 

 well developed brains. This brain shows the gyrus exactly at 

 the apex of the superior genu in both hemispheres, narrower and 

 more prominent in the left. An examination of a large number 

 of Negro and Caucasian brains failed to corroborate Cole's 

 conclusion. The gA'rus is always at the same point, varying only 

 in depth and width. The maximum depth of the sulcus cen- 

 tralis is about the same as the sulcus interparietalis. The 

 greater depth of the latter is stated by Appleton ('10) to be a 

 distinctive feature of Australian and simian brains. It is a 

 question whether this would not simply indicate an overgrowth 

 of the parietal lobe in a human brain and not an undergrowth 

 of any region. 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 26, NO. 4 



