FOREST COMMUNITIES 



425 



ing snakes tend to become elongate, a tendency which is also shown 

 by the arboreal agamid lizards of the Old World and by the unrelated 

 iguanid ones of tropical America (Fig. 116). 



Some heavy-bodied snakes, such as the vipers and pit vipers, have 

 developed prehensile tails in the tropics of both hemispheres; chame- 

 leons and a few other lizards are similarly supplied. The prehensile 

 tail has been developed independently by many different sorts of 

 arboreal mammals. In its typical form, a prehensile mammalian tail 

 is free from hair, and bears, near the outer end, sensitive ridges like 

 those of the palm of the hand which aid is giving a sure grip. Usually 

 these are on the ventral side, but in an arboreal mouse (Pogonomys) 



Fig. 116. — Tree agamid, Physignathus mentager, upper, and tree iguanid. 

 Iguana iguana, illustrating convergence of form in lizards of Asia and tropical 

 America. After Cope. 



of New Guinea, 7 and in the American tree porcupines, 8 they are dorsal. 

 Prehensile-tailed animals are especially abundant in heavily forested 

 regions of South America. There the opossum, arboreal anteaters, 

 numerous rodents, the kinkajou, the tree porcupine, and many, though 

 not all, monkeys, have a prehensile tail. 9 Outside tropical America, 

 monkeys lack the prehensile tail, but other groups of mammals have 

 it, for example, the climbing marsupials of Australia, some scaly ant- 

 eaters, certain mice, and the binturong (Ar otitis) , of the Sunda Is- 

 lands. 



Climbing mammals, primates excepted, tend to have relatively short 

 posterior legs; thus the ground-dwelling hares among rodents, and the 

 Indian cheetahs and the serval among cats, have long limbs in com- 

 parison with related climbing forms. Long hind legs are characteristic 



