SOME REMARKABLE TYPES 53 



as in the apes in question, so that when the body is held in an 

 upright position the fingers reach to the middle N of the calf. On 

 occasion, and for a few yards, these apes can walk on the hind- 

 limbs alone, but with difficulty. When at rest, however, the 

 hands are used, as in man, for conveying food to the mouth, and 

 for other purposes. They are also used for climbing. 



The only other land mammals which are bipedal are the 

 kangaroos and the jerboas, and certain other little animals closely 

 related thereto. In these animals, and especially in the kangaroos 

 and jerboas, the hind-legs are of great length, enabling the ground 

 to be covered by a series of leaps often of prodigious length 

 (Fig. 16). The tail in these leapers is of great length, and strong 

 enough to form a support to the body when at rest it forms the 

 third leg of a tripod. In the kangaroo, indeed, it serves as a 

 "leg" during walking, which is performed "on all-fours," and 

 after the following fashion. First the fore-legs are put down, 

 then the hind-legs are brought forward, one on each side of the 

 fore-legs, the body and hind-legs being at the same time lifted 

 off the ground and driven forward by means of the tail. Then 

 the fore-limbs are thrust forward for a second step, and so on. 



In the rabbit and hare we have an indication of the stages 

 by which this two-legged stage came about, since in these 

 animals, and especially in the hare, the hind-legs are much longer 

 than the fore-legs. 



In the bipedal whales and porpoises it is the fore-limbs which 

 become specially developed, while the hind-legs have totally 

 disappeared. These fore-limbs are, however, used, not as 

 supports to the body which is sufficiently buoyed up by the 

 water but as balancing organs. 



While most four-legged animals, it will be noticed, move the 

 right fore-leg and the left hind-leg forwards, more or less in unison, 

 some animals, such as the tiger, camel and giraffe, move the 

 right fore- and right hind-leg in unison that is not the fore- and 

 hind-legs of opposite but of the same sides. Some breeds of 

 horses, known as " pacers," have this peculiar method of walking 

 and running. 



Flight, as a means of locomotion among the mammalia, we 

 have already discussed, but we propose to return to this theme for 



