THE EDENTATA PHYTOPHAGA. 283 



Leaves are the cliief food of the former group, while the latter 

 delight chiefly iu ants, though some take, in addition, worms 

 and carrion. 



1. In the Phytophaga the long bones are without medul- 

 lary cavities. The lateral part of the zygomatic arch sends 

 down a remarkable vertical process. The acromial process of 

 the scapula coalesces with the coracoid. In the carpus, the 

 scaphoid and the trapezial bones anchylose and form one. The 

 ischia become united with the anterior caudal vertebrse, and 

 these anchylose with the proper sacrals to form the long sacrum. 



The ankle-joint has the character of a peg and socket, and 

 the hind-foot is, more or less completelj'' twisted, resting upon 

 its outer edge, and not upon its sole. 



Vascular canals connected with the pulp-cavity traverse 

 the dentine of the teeth. 



The Phytophaga are divisible into two groups, one exist- 

 ing, and the other extinct. The former consists of the Sloths, 

 or Tardigrada ; remarkable animals, which are confined to 

 the great forests of South America, where they lead a purely 

 arboreal life, suspended by their strong, hooklike, claws to the 

 branches of the trees. 



Their distinctive characters are these : The tail is short, 

 and the limbs exceedingly long and slender, the anterior be- 

 ing longer than the posterior pair. In both the fore-and the 

 hind-limbs the internal and the external digits are rudimen- 

 tary, but the hind-foot always has the three middle toes com- 

 pletely developed ; while, in the fore-foot, it sometimes hap- 

 pens that only two remain. The ungual phalanges are very 

 long and hooked. 



The zygomatic arch is incomplete posteriorly, not being 

 united by bone with the squamosal. The cervical vertebrae 

 in this remarkable grouj^ sometimes exceed, and sometimes 

 fall short of, the number (seven) which is so characteristic of 

 the Mammalia in general ; some species of Sloths having 

 nine, and others only six, vertebra in the neck. 



The pelvis is exceedingly spacious, and the acetabula are 

 directed backward as well as outward. The femur is devoid 

 of a ligamentwn teres. The distal end of the fibula sends in- 

 ward a process which fits into a fossa situated upon the outer 

 surface of the astragalus, giving rise to that kind of peg-and- 

 Bocket ankle-joint which is peculiar to these animals. 



A good deal of confusion prevails respecting the structure 

 of the ankle-joint in the Sloths. Cuvier (" Ossemens fossiles," 

 t, viiii, p. 143) writes of the Ai, or three-toed Sloth ; 



