982 E\OLLTIOX.AL MODIFICATIONS 



St;.. . .. ... type. T' ' ^ame extremely long and powerful — 



longer ...v. ;nore f>o\ver; ...^:. ;nan the legs. Erectness was further 



iucr^^ii^rT because the thigh was more extended upon the pelvis. Standing and 

 wa.fv..,^ -^r^r-fir manifested definite improvements. Under these conditions 

 the toes a;.,^ ..^^.s touched the ground simultaneously, although the timing 

 r,.rmii[a was still infrahuman in t\"pe. In arboreal locomotion, the foot still 

 ,\ ;..... cd its grasping grip with shortened digits but opposable hallux. This 

 is true of all the great apes with the exception of the orang, which developed 

 a susj>ensr'" L'^ro in the foot due to its more strictly arboreal life. Adult 

 gorillas, t^f^^^.ci..y the older males, have definitely ground-gripping feet 

 with broad heels, flat arches and plantar eversion with some distal advance 

 of the great toe. Their pedal fulcrumation is well forward in the metatarsus. 

 Arboreal locomotion in all three of the great apes is predominantly br:' '"^^- 

 ing. This development imparted to the upper extremities those sptx.....z.ci- 

 tions which maintained the hands as part of the locomotor apparatus 

 and thus impeded their most effectual manual differentiation. The manus 

 retained its suspension grip well marked in the orang and chimpanzee, but 

 showed evident decline in the gorilla whose increasing tendency was to 

 assume a terrestrial habitat. Thus, however strong the incentr^e toward 

 terrestrial life may have been in the great apes, that inherent arboreal 

 commr"^""' "" set upon the primates in early Eocene times still kept them 

 true to .111 Liicir rigid simian inheritance. To be more than apes it was neces- 

 sars- for them to shed that stigma which tree fife stamped upon them. This 

 the modern apes never accomplished. The experimental efforts evident in 

 their anthropomorphous tendencies at length found a new opening. It was the 

 foot which led the way, producing a supporting structure having a well- 

 developed heel, a non-opp>osable hallux, and a heel-toe timing formula in 

 walking. At some later period in the Miocene the two great branches of the 

 orthograde primates parted company. The structural decision at this junc- 



