952 E\OLLTIONAL MODIMCATIONS 



verse diameter is also increased. Such modification a* thi* rewihs from the 

 de\-eIopments in the frontal lobe which tend t/j prrxJuce v>mething inter- 

 mediate between broad bramedness and (ong brained ncs». It is thus ev 

 in explanation of the . ;.ncies indicated b>' the dfa- 



indices of the ne high degree of broad ferainedness 



manifested by mycetes is due to expansifwi in the parietal region of tht 

 incident to accessions in sor .*.y. An additional el- 



in mycetes is the apparent - ion in the frontal lobe de^'ek^pment. 



In the case of the gibbon, where the axia! index rises to a xdathreiy 

 high figure, the espFanatron is also i retardatron of the f' 



do'elc^ment with - -i the higher 



asithiopoidsr both the orang . - refatf*.-e!y hL ^ es 



in their diametric indices due tc - bes wrthoat 



concomitant development in the : reas in man and 



gorilla the tendency" toward increase i .;nence in the frontal reg 



the brain makes itself apparent in a diametric fndex which is ojnsrderabFy 

 below that of their congeners in th- _ _ p. Exp . 



the frontal lobe, so important f- r of psychic specializs- 



tion, has made itself felt in t ndex of the gorilla and r. 



brain more than in any of the anthropoids. This index, which at first glance 

 seems to be so thoroughly inconsistent in the figures which it produces, does 

 as a matter of fact indicate a prices? f>f adaptive Sf)ecialization in the primate 

 order which has great signific . ation to the e\-oIiitionary process. 



The developmental conditions which it seems to denote in the adA"ance of 

 the brain are so well confirmed by other evidence as to leave no doubt con- 

 cerning the substantial correctness which these values present- A tabula- 

 tion of the diametric indices provides a most convincing demonstration to 

 indicate the adapti\'e \-icissitudes through which the brain has pasj?ed. 



