94 THE FAUNA OF 
the condition described as the opposable thumb and 
great toe. At the same time the extremities of the 
digits tend to be flattened, giving more gripping power, 
and with the flattening of the finger-tips a nail tends 
to replace a claw. This condition is only gradually 
acquired in the Primates, the lower forms having 
pointed fingers, with nails instead of claws. As already 
suggested also, the hand in certain Primates tends to 
become hook-like, the thumb being absent or minute. 
Only in man among the Primates is the great toe not 
opposable. 
But this condition of one (or more) digit being 
opposable to the other is not confined to the Primates. 
In the opossums and phalangers, primitive mammals 
whose young are born in a very undeveloped state, the 
great toe is also opposable. Again, in parrots among 
birds, and the chameleon among lizards, a gripping 
hand and foot is produced by certain digits being 
opposable to the others. 
Still another adaptation to arboreal life is seen in 
the prehensile tail. This also occurs in widely separ- 
ated groups. We find it in the chameleon, in the New 
World monkeys, in opossums, in some of the South 
American ant-eaters, in the South American tree-por- 
cupines, in the kinkajou, and so forth. Like the hook- 
shaped hand it tends rather to occur in relatively sluggish 
forms than in those whose agility is sufficient to enable 
them to recover easily from a false movement. Thus 
Brehm notes that the ‘five-handed’ New World 
monkeys are not nearly such good climbers as the 
four-handed monkeys of the Old World, which never 
have prehensile tails. 
Some minor adaptations to the arboreal life may 
next be touched upon. As great freedom of movement 
