112 ARBOREAL MAN 



more nearly than a true tree-climber, and moreover it 

 shows a definite tendency to carry out its arboreal 

 activities in an inverted position. It is therefore to be 

 presumed that the adoption of this habit has led to a 

 modification of its erector spinse muscle and its spinous 

 processes, and that by its slothful habits Xycticebus has, 

 in this respect, arrived at the state to which the Edentate 

 Sloths were bound by their inherited disabilities. 



The case of the Slow Lemurs is all the more interesting 

 since the absence of a dorso-himbar centre of movement, 

 and the presence of a practically uniform series of spines, 

 are seen in another group of arboreal Primates. Xj/ctice- 

 bus does not leap from branch to branch, it takes no spring 

 from its hind-limbs, it does not jump to its next arboreal 

 station, but reaches out for it and gras])s it, and upon 

 the ground it crawls and shuffles along. Now, much the 

 same conditions are seen in the Anthropoids. The Giant 

 Apes, though active enough and expert climbers, do not 

 spring from their hind-limbs, or leap about the branches 

 as the smaller monkeys do. Wallace has described the 

 Orang-utan in its natural state as " moving slowly along, 

 hanging from the ])ranches by its arms," and as " moving 

 along a large liml) of a tree in a semi-erect posture." 

 Both these modes of progression are typical of the An- 

 thropoids; the first, according to Wallace, is unusual in 

 Simla satyrus, but it is the one which is characteristic 

 of the smaller agile Anthropoids known as the Gibbons 

 (Hylobates). 



The Chimpanzee adopts the same methods of climbing, 

 methods which involve a semi-erect foot balance com- 

 bined with a dependence upon a powerful hand grasp. 

 More rapid translation from branch to branch, or from 

 tree to tree, is not performed by a spring from the resting 

 feet, but by a swing from the grasping hands. A group 

 of monkeys passing from tree to tree in the jungle will 

 jump those gaps where branches fail to meet, but a party 

 of Gibbons will swing themselves across the gap, releasing 



