188 MARVELS OF THE ANIMAL WORLD 



their hind limbs assuming the form of a rudder. 

 The whales, the porpoises, the dolphins, the mana- 

 tees, and the dugongs, however, are unique in the 

 fact that they have no hind limbs. 



Most mammals possessing four limbs apply both 

 pairs to the ground when walking, but a few of 

 them, such as the chimpanzee, the orang-utan, 

 the gorilla, the gibbons, the bears, the jerboas, 

 and the jumping-mice will sometimes assume an 

 upright pose and walk upon their hind legs alone. 

 As a rule, however, the above-mentioned apes walk 

 upon all fours with the knuckles of their hands 

 applied to the ground, while the hind feet may 

 either be spread out flat or have the toes tucked 

 underneath ; but in captivity the chimpanzee will 

 frequently make use of its fore -arms as crutches 

 and swing its body forward and between them. 

 The gait of the orang-utan is peculiar, and differs 

 from that of the other anthropoid apes inasmuch 

 as the creature turns the soles of its hind feet 

 inwards, and walks upon their outer sides. 



For sheer agility no monkey can vie with the 

 gibbons, their slender bodies and enormous length 

 of limbs at once proclaiming them to be expert 

 acrobats. Notwithstanding that they can assume 

 an upright pose and progress along the ground 

 by walking entirely upon their hind legs, yet they 

 rarely indulge in such a method of locomotion, as 

 they are almost entirely arboreal in habits. When 

 passing from tree to tree they make use of their 

 hands as hooks, hanging on to a bough and swing- 

 ing their bodies forward with their arms stretched 



