XIII 



PHYLUM CHORDATA 



483 



shorter and thicker, hind-limb^ in which the second and third toes 

 are nearly as large as the fourth. 



The Phalangers (Phalangeridce) are climbing Marsupials which 

 have both fore- and hind-feet prehensile ; the second and 

 thif\l toes of the hind-foot slender and united by a web, as in the 

 Kangaroo, but the hallux, which is nailless, opposable to them ; 

 the fourth and fifth nearly equal. The tail is well developed and 

 prehensile. A 

 number of Phal- 

 angers (Flying 

 Phalangers) are 

 provided with 

 lateral folds of 

 skin extending 

 from the fore- to 

 the hind - limbs 

 and, acting as a 

 parachute, enab- 

 ling the animal, 

 as in the Flying 

 Squirrels, to per- 

 form flying leaps 

 from tree to tree. 

 The Koalas (Fig. 

 1123) differ from 

 the Phalangers 

 mainly in the 

 relatively thicker 

 body and the 

 vestigial tail. 



The Sloths 

 (Bradypodidce, 

 Fig. 1124) are 

 more completely 

 adapted, in the 

 structure of their 

 limbs, to an ar- 

 boreal life than any other group of the Mammalia. They have a 

 short, rounded head, with small pinnae, and long, slender limbs, the 

 anterior much longer than the posterior, with the digits, which are 

 never more than three in number, long, curved, and hook-like, 

 adapted for enabling the animal to hang and climb, body downwards, 

 among the branches of trees. In the three-toed Sloth there are three 

 toes in both manus and pes ; in the two-toed Sloth there are only 

 two in the manus, three in the pes. The tail is rudimentary. 

 The body is covered with long, coarse hairs, which differ from those 

 of other Mammals in being longitudinally fluted. On these hairs 



FIG. 1124. Unau, or Two-toed Sloth (Cholcepus didactylus). 

 (After Vogt and Specht.) 



