968 



EVOLUTIONAL MOOIFICATIONS 



2 1 pvv cfiit, the cl()<i; of 2() i^cr cent, tlic Ifimir ol 23 ])ct cent, tlic spider 

 monkey 31 per cent, the baboon 31 per cent, \\\v ehinipanzee 33 per cent, 

 the gorilla 32 ])er cent and man 4~ ])er cent. The tabulation Irom which these 

 indices \\ere computed is gi\en in the appended table. The indices them- 

 selves dclinitely point to the fact that the expansion of the Irontal lobe is 

 the goal toward which the entire t'xolutionary process of the primate 

 brain has been directed. 



Planimetric Area Lndices of Neopallu .m 



* Temporo-parieto-occipital. 



E\oLi:iio.NAL Significance of Con\ 01 i i ioxai Puierns in the 

 Brain. This conclusion is further bornt'out In a comparison ot the con^■olu- 

 tional pattern in the frontal lobe w hich shows the same trend of de\ elopment 

 from a relatively simple area, through all thelnternu(liatestages,tothe highest 

 degree of comohition seen in tlu' human heir.:sphere. The obxious purpose of 

 this con\-olution is to increase the cell-cimtaininij; substance ol the bram and 

 thus to produce a more ellicient txllular structure lor the tiansaction ol those 

 functions necessary to the re<rulation of behavior. That the Irontal lobe 



