LOCOMOTION OF MAMMALIA. 71 



muscles of one arm and of the trunk, the force finally attained 

 and the swing being such as to propel the animal some distance 

 through the air; a bough is seized by the opposite out-stretched 

 arm, and the momentum is applied in aid of a repetition of 

 the action to gain a longer launch. I have myself witnessed, in 

 the London Zoological Gardens, an aerial leap of upwards of 

 fifteen feet so effected by the long arms of a captive Hylobat. 

 M. Duvaucel, observing them in their native forests, testifies to 

 their passing through a distance of forty feet from bough to 

 bough. Mr. Martin, when curator of the Zoological Society's 

 Museum, watching the same female Hylobates agilis which had 

 been the subject of my own study of the brachiating mode of 

 motion, states that, € a live bird being set at liberty in her pre- 

 sence, she marked its flight, made a long swing to a distant 

 branch, caught the bird with one hand in her passage, and at- 

 tained the branch with her other hand, her aim both at the bird 

 and the branch being as successful as if one object only had 

 gained her attention.' l 



In most of the Platyrhine monkeys the tail is prehensile, and 

 becomes, in Ateles more especially, a fifth independent organ of 

 grasping. 



In ordinary progression on the ground the Quadrumana move 

 as quadrupeds; but the higher tailless Catarrhines (Apes), in- 

 stead of setting the palm or outer margin of the fore-hands, 

 like the inferior families, to the ground, apply the back of the 

 second phalanges of the flexed fingers, the skin covering which 

 has a broad and thick callosity, whence these apes are sometimes 

 called collectively, ' knuckle-walkers.' The longer-armed kinds, 

 in slow movement, support the body upon the knuckles, as 

 upon a pair of crutches, and swing the hind-limbs forward 

 between them. In more rapid movement they sway the trunk 

 and hind-limbs in a sort of sidelong sweep, progressing by a kind 

 of shambling amble. The tracks of the Gorilla show this to be 

 the habitual mode of progression along the ground. 2 Station or 

 motion on the lower limbs only is shown to be difficult by its 

 awkwardness and the shortness of time during which it can be 

 maintained. The walk is a waddle from side to side, the huge 

 superincumbent body being balanced by swinging movements of 

 the long arms, or by clasping the hands behind the head. When 

 so pursued as to be driven to stand at bay, the Gorilla, like the 

 plantigrade Bear, raises himself on the hind-hands, so as to have 

 his powerful arms and fists free for the combat. 



1 xlyiii". 2 xiir\ p. 532. 



