EQUILIBRIUM OF ANIMALS : - BASE OF SUPPORT. 491 



the tarsus, c the bone of the metatarsus termed the canon (in 

 which the trace of a division into two pieces can be seen), 

 and p, pi, pt, the three phalanges of the toes, of which the 

 last is enveloped in the hoof, which is nothing else than a 

 large nail inclosing the whole extremity of the toe. In the 

 Horse this consolidation is carried still further than in the 

 Ruminants, for it has only one toe in each foot (fig. 233); but 

 we see the rudiment of an additional bone in the metatarsus 

 5, which is commonly termed the splint bone. 



653. But when an animal is supported upon two feet only, 

 whatever may be their degree of separation from each other, 

 the base of support cannot have sufficient extent, unless the 

 extremities touch the ground by a considerable surface. This 

 is the case with the foot of Man, and still more with that of 

 many Birds which habitually stand 

 upon one leg (fig. 234). In. order 

 that an animal may hold itself in 

 equilibrium upon a single limb, it 

 is necessary that the foot should 

 be placed vertically beneath the 

 centre of gravity of the body ; 

 and that its muscles should be so 

 arranged as to permit it to keep 

 this limb inflexible and immov- 

 able. Man can accomplish this, 

 for the centre of gravity of his 

 body is at about the middle of the 

 pelvis ; and to place this vertically 

 over one foot, it is sufficient for 

 him to bend himself a little from 

 the side which is not supported. 

 But the greater number of Qua- 

 drupeds are destitute of the power 

 of doing this ; and a large part 

 of them cannot even raise them- 

 selves on their hind legs, on 

 account of the direction of these members relatively to the 

 trunk; or if they can do so for an instant, they cannot 

 maintain themselves in this position. The reason of this is 

 very simple. The base of support, on account of the small- 

 ness of the feet, is very narrpw, and the centre of gravity of 





