496 ; The Making of Man. [June, 
the aspect of the body is distinctively horizontal. Life in trees 
does not necessarily produce a deviation from this horizontal - 
aspect, since it is retained by all arboreal mammals except those 
just mentioned. Yet it offers an opportunity for such a deviation, 
and this opportunity has been improved by the lemurs and apes. 
Their hands have developed a grasping power which is possessed 
by no other arboreal animal, and which opens to them new motor 
possibilities. They may assume a semi-erect or a fully erect 
attitude, by grasping upper branches with the hands. And this 
ability, in the higher apes, has led to the development of a mode 
of progression on the ground which is more or less intermediate 
between the quadrupedal and the bipedal modes. 
This fact is of great interest, as it seems to lead us directly to- 
wards the development of the bipedal habit, as attained in man. 
Though such a habit may be partly attained by tree-living ani- 
mals, a residence on the ground is essential to its full develop- 
ment. And it is significant, in this connection, that no existing 
-apes have fully given up the arboreal habit. 
Of the anthropoid apes, the orang and the chimpanzee dwell 
habitually in the trees. On the ground they are out of their true 
element. The same is the case with all the species of the gib- 
bons. All these creatures move with some difficulty om the 
ground, but freely and easily in the trees. The gorilla, on the 
contrary, seems to dwell more habitually on the surface. Its 
great weight tends to render an arboreal life unsuitable, and its 
hand is not so well adapted to climbing as that of the chimpar- 
zee. Yet it has only in part given up its arboreal residence. It 
ascends trees for food and, to some extent, to sleep, though there 
‘is some reason to believe that the adult males sleep occasionally, 
and perhaps habitually, on the ground. It seems to be in a tran 
sition state between the arboreal and the surface life-habit. 
Of the lower apes, the baboons make the ground their 
place of residence. They have not lost their climbing powe 
however, but can ascend trees with ease and rapidity. ost of 
the other apes dwell wholly, or nearly so, in the trees. 
