TROGLOD^TES GORILLA 645 



Sl Kl ACE Al'I'EAKANCF. OF THE BrAIN OI GoRII.l.A 

 FISSL RES AND LOBES 



The ap[)caraiK-c of the hraiii in (gorilla elosely rcsemljlcs that in man. 

 Li si/e, li()\\f\cr, its diiiunsions are a little Ii'ss than one-half of the adult 

 human male. Its general outline' and hssural ]xittt'rns are conspicuously 

 humanoid. The deslii;n ol' tlu> hteral surface of the hemisphere is distinctly 

 quadriloliular, with three w ell-delined fissures separatinjjc four i'quallN- well- 

 delnucl lohes. The fissure ol S\ l\ ius sej^arates the parietal from the ti'mporal 

 lohe; the hssureot Rolando, tlu' |)arieta! from tlu' frontal lobe; and thesidcus 

 simiarum, tlu' occipital from the |)ari(.tal lobi'. The latter fissure may be 

 traced to the mesial surtace ol the hemispheri' where it occupies a pf)siti()n 

 identical with that ol tlu' paru'to-occipital fissure in tlu' human brain. 

 The hssurc ol S\l\iiis has all ol the ajjpearance characteristic of the 

 corresponding sulcus in man; while tiie Rolandic lissure has an e\en closer 

 correspondence to its human counler[)art. The entire region com|)risecl 

 within tlu' Rolandic, S\ Kian and simian sulci is richly coiuoluted and in it 

 arc all of the landmarks ol the similar temjjoro-parietal area in man. As in 

 most of the ]:)rimate.>, this region is highly convoluted, since it de\elops 

 in response to specializations in somesthetic sensibility and the special sense 

 of hearing. \n the occipital lobt' there is a marked degree of convolution, while 

 the fissural pattern is in man\ respects laid down as though in strict 

 accordance w ith a human |)rototype. This is true both ol the mesial and the 

 lateral occipital surfaces. 



More striking are the accessions to con\ olutional pattern and riclmessoi 

 fissural impression which occur in the frontal lobe. This feature distinguishes 

 the gorilla's lirain from the lower and intermediate primates, and gives it, at 

 least to superficial inspection, predominance o\ er the corresponding lobe in 

 the orang and chimpanzee. 



