874 ^lAN 



Frontal Lobe oi- Pithecanthropus as Compared w rm That of 

 Gorilla and Homo Sapiens. As compared willi the priinalc Irontal lobe 

 nearest to that of man, i.e., the ironlhi, the brain ot pithecanthropus shows 

 nianilcst clifFcrcnces (Fig. 372). The frontal lobe as a whole is niLich less con- 

 spicuous in gorilla. It is actually- and rehitively sniaMer m size. The rchef of 

 its coiu'olutions is much less pronounced, its sha[)e is more pyrilorm as it 

 tapers towards its apex at the Irontal pole and it has no coronal constriction. 

 The left lobe of the Ja\an man is slightly larger than the right, which is 

 probabl\- indicative of unidexterity. AH of these dilFercnces point to a dis- 

 tinctly inferior dexclopment in the Irontal lobe oi gorilla as compared with 

 pithecanthropus. A comparison with the brain of Homo sapiens shows at 

 once what decisive gains the brain of modern races has made oxer its simple 

 prototype of primitue man (Fig. 3'"4). In size and general a])pearance the 

 brain of pithecanthropus resembles that of a three-year-old child. 



Fissures in the Frontal Lobe. The fissures in the frontal lobe which 

 may be idcntilit'd with certainty are the superior and middle frontal sulci. 

 They are tortuous and bound corrt's|)oiKlingly complex conxolutions. These 

 fi.ssures are most pronounced m tlu' prelrontal area and cannot be traced 

 back as far as the frontal region. The com (ilutions determined b\ the frontal 

 sulci are the superior, middle and inferior frontal g\res. The last of these is 

 of greatest importance since the mlerior Irontal coiuolution, espt'cially on 

 the left side, is almost universally regarded as the motor spia'ch center in 

 man. In connection with this con\-olution some authoritU'S ha\'e idi'iitilied 

 the anterior and ascending l)ranches of the S\l\ian fissure, if present m 

 pithecanthropus, howi'xcr, tlu'\ t'xist merel\ as tlu' laintest traces which 

 aiFord insufficient ground lor their acceptance as delinite cerebral landmarks. 

 in Ilomo sapiens, these sulci :ivv conspicuous and im|)art nuuh prominence 

 to the inferior frontal coiuolution. I'here is no indication oi tlu' precentral 

 fissure and hence no actual guide to tlu' Innits ol the pi'ecentral or motor 



