FEET AND HANDS. 



5 2 5 



The hind feet of birds are less changed than the fore feet, but 

 still differ from the lizardlike foot in the number and character of 

 their toes. Some birds have four toes, others only three, and these 

 toes are usually able to curve so as to grasp the branches of trees, and 

 are armed with claws which help in climbing. In the birds which 

 run along the ground instead of flying, like the ostrich, there are 

 usually only two toes, which become very much thickened. Here, 

 as in the horse, we find increased speed in running obtained by re- 

 duction of the number of toes. The horse, as we saw, actually has 

 only one toe, and in some ostriches the second toe is so reduced that 

 they practically have only one also. 



Great as is the difference between the fore and hind limbs of the 

 bird, that between our own hands and feet is quite as important. 

 The fore feet of all animals have sometimes been called " hands," to 

 mark the fact that they correspond with what in a human being is 

 the hand, but in the animals we have considered we have had noth- 

 ing like a hand in the true sense of the word. In a true hand, the 

 inner finger is able to move in such a way as to face the other fingers, 

 and the hand is thus able to grasp any object far more firmly than if 

 the movement of all the fingers was similar, as 

 it is in the foot. Such an inner finger is 

 called an opposable thumb, and its presence 

 is absolutely necessary to a real hand. 



Let us see if we can understand how such 

 true hands arose. Besides the animals which 

 run about in various ways on the ground, those 

 that have taken to living in water and those 

 that have learned to fly in the air, there 

 are others that live almost entirely in trees, 

 climbing or springing from branch to branch, 

 and only occasionally walking on the ground. 

 These animals, the monkeys, which feed prin- 

 cipally on the fruits that grow on the trees 

 they inhabit, need agility in climbing rather 

 than swiftness in running, both for obtain- 

 ing their food and for escaping from their enemies, and so all their 

 feet have become specially adapted for firmly grasping the branches 

 of trees — i. e., they developed thumbs on all their feet; for this 

 reason they have been called the Quadrumana, or four-handed 

 animals. 



If we examine the hand and foot of a gorilla, given in Fig. 6 A 

 and B, we shall notice that the hand (A) differs very little from the 

 hand of man, given in Fig. V A. The feet of the ape, however, differ 

 considerably from those of man (cf. Fig. 6 B with Fig. 7 B). 



