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 naU tends 

 to replace a claw. This condition is only gradually 

 acquired in the Primates, the lower forms having 

 pointed fingers, with naUs instead of claws. As already 

 suggested also, the hand in certain Primates tends to 

 become hook-hke, 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 bom 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 sufScient 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 taUs. 



Some minor adaptations to the arboreal life may 

 next be touched upon. As great freedom of movement 



