1 84 



THE GROWTH OF THE BRAIN. 



concerning the individuals whose encephalic develop- 

 ment appears to be symmetrical, what degree of perfec- 

 tion is thus accomplished. The results of examination 

 with this idea in view may be given in two ways : either 

 by summing the weights of all the right and left hemi- 

 spheres in a given series, and from these finding the 

 average amount by which one hemisphere exceeds the 

 other ; or by determining the number of cases in which 

 the two hemispheres weigh the same, and also the num- 

 ber in which one half exhibits an excess of weight. 



TABLE 43. To SHOW THE AVERAGE AMOUNT IN GRAMMES BY 



WHICH EITHER HEMISPHERE EXCEEDS THE OTHER. 



Taking the simplest method, we have an expression 

 of facts like this in the above table (43), where, for 

 example, all the male brains weighed by Broca had on 

 the average right hemispheres which were 1-93 grammes 

 heavier than the left ; whereas Boyd found the left 

 hemispheres to show an average excess of 3*7 grammes. 

 Taking the weight of the male brain as 1,360 grammes, 

 then 37 grammes is only -27 per cent, which is really 

 very small. Using the second arrangement, the facts 

 are expressed by the following table (44) from Fran- 

 ceschi. 



