966 EVOLUTIONAL MODIFICATIONS 



larly the frontal and occipital regions. Not, however, that the temporal and 

 parietal areas are less characteristic in llieir laiulmarks, but rathtT that in 

 the process of expansion they iia\e Ix'cn sonicw hat o\ershaclo\vecI In' the rapid 

 strides of advance made by the frontal and occipital areas of the brain. 

 This advance mostly involves the prefrontal area, which is regarded by the 

 physiologists as rejircsenting the seat of such higher faculties as reason, 

 judgment and discrimination. This is tlu' region of the brain wherein those 

 syntheses of neural impulses are assembled which constitute the basis ol 

 human e\]3erience and personality. It is undoubtedI\ the case that diseases 

 atfccting this ])art of the brain do much to unseat the ]3rocess of reason and 

 judgment and ha\e far-reaching effects in changing in one direction or 

 another \hv personalitx' of the individual. Refcrcnct' need only be made to the 

 great xolume of clinical material already assembled in relation to tumors in 

 the frontal region of the brain, particularly in the prefrontal region, whose 

 outstanding clinical manifestations are marked changes in personality with 

 alterations in the validity of judgment and reason. It is most interesting in 

 this connection to note the tendency of expansion in the frontal lobes among 

 the mammals in what may be considered direct ])roportion to the develop- 

 ment of intelligence. W ithout ]>ausing here to dcline too much in detail the 

 meaning of intelligence, it may in general be stated that this attribute indi- 

 cates the capacity presented by an\ brain to select between alternative 

 courses of action, that is, to reason and linally form a judgment. 



If a number of mammals, those low in the ph\ letic scale as well as those 

 situated in the ui^j^cr lc\els, are contrasted by means of jjlanimetric estima- 

 tions of the areas on the lateral surface of the brain, and from such measure- 

 ments planimetric indices are constructed, thi' following interesting facts 

 are brought to light: The frontal lobe w Iumi compartxl in dilferent mammals 

 shows that the ant eater has a frontal index of i) per cent, the horse ol 13 

 per cent, the seal of 16 per cent, the leopard of 20 per cent, the brow n bear of 



