xii PHYLUM CHORDATA 531 



opposable to them ; the fourth and fifth nearly equal ; the 

 tail is well developed and prehensile. The koalas (Fig. 319) 

 differ from the phalangers mainly in the relatively thicker 

 body and the vestigial tail. 



The sloths (Bradypodidm) (Fig. 320) are more completely 

 adapted, in the structure of their limbs, to an arboreal life 



Fig. 319. — Koala {Phascolarctos cinereits). (After Vogt and Specht.) 



than any other group of the Mammalia. They have a 

 short, rounded head, with small pinna? 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. The tail is rudimentary. The body is covered with 

 coarse hairs. 



The ordinary ant-eaters (Myrmecophaga) have a greatly 



