STRUCTURAL CULMINATION 965 



lu'iiiispluial suilacf almost liw ol lissuial insi-ri])ti()n, it hccomc's possible, 

 at tlu' lU'xt stasia- m thr progrcssi\-c expansion ot the neopallmni, to note in 

 nixeetes a tlehnite ciuaclrilolKilar eonclition ni the hrani. A w cll-ck'hned (issiire 

 of Rolando separates the paiutal tioni the liontal lol)e. A ]3roniinent lissurc 

 of Syl\ nis (h\icles the parutal Ironi the ttinporal, and thi' ineipient suleus 

 simiarum sets the boLindan bt'tut'eii the oeeipital and the parietal regions. 

 Of these lour lobi's, the most hi(i;hl\ de\ eloped are tlie parietal and tlu' 

 temporal, wliile the e\|jansion in the frontal and tiie occipital re<i;ions seems 

 to be delinitelx' retarded. In tin- intermediate <;roup ot old-world monkeys, 

 the lobation in the eert'bral hemispheres iijjon the lateral surlaee is so striking 

 as scarcely to need hirther eomnient. Ihe tri-lissural pattern m allol'these 

 lorms ])roduees a decisixc c|iiadrilobular lateral surface in \\ hich, how e\er, the 

 parietal and temporal regions show the greatest degree of e\pansi\ e develop- 

 ment. This IS true not onl\ of the baboon and macacus, but e\en as much of 

 the gibbon. The lobular de\ elopment in the frontal region and in the occipital 

 region in these three lorms is not pronounced as com])ared w ith the temporal 

 and parit'tal areas, and in none ol these is the frontal lobe beginning to a.ssumc 

 the prominent proportions which it does in the upper grades of the priniate 

 series. 



In the three great anthropoids, a t|uadriloIjular arrangement on the 

 lateral surlaee is distinctl\ appart'iit, with t\ idi'ut accessions in the (k'\elo])- 

 nu'iit of both occipital and frontal lobes. It is not, howe\er, until the human 

 brain is reached that the full significance in these changing proportions ol the 

 scleral lobes of the brain becomes a])pareiit. The physiological significance 

 of that expansion, which has been progressively making itself lelt in the 

 hemispheres, now becomes more ()b^ ious. While the boundar\ lines between 

 these several lobes ot the brain are w ith more dilliculty discerned, because 

 of the greater richiuss ot the lissural j)attern and the high degree of com- 

 ])lexity of the com olutions, such progress as has occurred atlects particu- 



