SIMIA SAT^'RUS, THE ORANG-OUTANG 519 



Manx tacts alrevidx exist to prow the essential ix'lation ol the lateral 

 lobes of the eerebelhini to the arms and the legs. Similar inclieations |)oiiit to 

 expansions in the lU'opalliuin as a res|)onse to this linil) speeiali/ation. This 

 evidence seems to put bexond peradxeiiture tlu' C|Liestioii that api)(.'ndicular 

 speciali/ation sup]:)lK's the (k'\ I'lopmental moti\'e which underlies such far- 

 reachini; ditlerentiation in the central nerxous system. But limbs are ahnost 

 as ancient as the \frtcbrate stock itself. Tlu'\ are not characteristic of the 

 mammalian class alone. Some s])ecialized element intrinsic to the extremities, 

 and not necessarily apparent m their morpholouical structuri-, therefore, 

 must be sought to explain this pronounced de\elopment ol the mammalian 

 hemispheres, cerebral as well as cerebellar. Ho\ve\'er convergent or divergent 

 the fore- and hindlimbs of rt'ptilcs and birds, anii:)hibia and (ish may be in 

 structural comparison with those of mammals, there is a lunctional diver- 

 gence between them which is constant. In inlramammalian orders all mo\e- 

 ments of the limbs tend to be s\nchronized with the movements of the body 

 and w ith each other. Thert' appears to be little need of independent motion 

 on the part of one or the other limb. 



In the mammals, on the otiier hand, there is an increasing degree of 

 independent action in the lore- and hindlimbs and also in one loreiimb 

 independent of the other. Similarly, oiu- hindlimb may act inde])endentl\- 

 of all the others. Such iiuk'pendence of action strikes a new note in tlu' 

 motor organization of the extremities. The appendicular museulalurc liber- 

 ated itself from that dominating ck-peiuk'iic\ of interaction t'xisting between 

 the movable parts of tht' body. It gained a freedom which (k'ti'rmined a new 

 motor objective. Each limb, ha\ing acquired an indi\iduality ol its own, 

 develops a specilic s{)here of action. In this sense the fore and hind extremities 

 of mammals ditfer from those of lower xertebrates. Serving as more or k^ss 

 highly indi\ idualized instruments, the limi)s are capable of expressing what 

 amounts to a new physiological endowment. At the same time the\ retain 



