Anatomical Characters of the Unman Brain. 11 



is larger in Bean's tables than in mine in 7 white brains and one 

 black brain and smaller in 4 black and 2 white. The s])lcnium is 

 larger in 7 black and 4 white and is not smaller than mine in a single 

 instance in Bean's tables. This discrepancy between onr figiires is 

 snfficient to account for the racial differences in the corpus callosum 

 found in Bean's tables but not in mine, although the individual devia- 

 tions in both our charts are very great. I think my chart (Fig. 1) 

 shows conclusively, as far as possible with the method I employed, 

 that there is no variation in either genu or splenium of the corpus 

 callosum due to either race or sex. 



In order to determine the relative weight of the frontal lobe in 

 white and in negro brains I made numerous tests in separating this 

 lobe from the rest of the cerebrum to develop first an accurate method. 

 It was found that it is quite easy to break the cerebrum after it has 

 been hardened in formalin through the central sulcus along the motor 

 tract down through the basal ganglia with considerable precision. 

 The real test of the accuracy was made by comparing the results 

 <)btained on the right side with those on the left. If the half brains 

 are of equal weight the frontal lobes should be also of equal weight 

 if the method is a reliable one. It was found in over two-thirds of 

 the brains that the two frontal lobes weighed practically alike, i. e., 

 within 5 grams of each other, a variation which could be accounted 

 for by a slight difference in the amount of drainage and evaporation 

 of water from the specimens. In the remaining one-third of the brains 

 the difference between the two sides averaged 10 grams, which in 

 rough equals the weight of half of the precentral gyrus. Expressed 

 differently the probable observational error in the weight of the 

 frontal lobe compared with the whole hemisphere is less than one 

 per cent of its weight, so a deviation in the weight of the frontal 

 lobe due to race or sex would have to be fully two per cent in order 

 to be detected. 



Another source of error might be due to the fact that only hardened 

 brains were broken, or could be broken, with precision through the 

 central sulcus. It is well known that formalin causes the brain to 

 swell, and it has been sho^vn by Hrdlicka^^ that there is an unequal 



"Hrdlicka. Brains and Brain Preservatives. U. S. Nat Mus., XXX, Wasli- 

 ington, 190G. 



