THE EDENTATA PHTTOPHAGE. 331 



caudal vertebrse, and these ankylose with the proper saerals 

 to form the long sacruin. 



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

 and the hind foot is, more or less completely twisted, rest- 

 ing 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 grouj^s, one exist- 

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

 Sloths, or Tardigrada ; remarkable animals, which are con- 

 fined to the great forests of South America, where they 

 lead a purely arboreal life, suspended by their strong, hook- 

 like, 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, 

 being longer than the posterior, pair. In both the fore and 

 the hind limbs the internal and the external digits are 

 rudimentary, but the hind foot always has the three middle 

 toes completely developed ; while, in the fore foot, it some- 

 times happens that only two remain. The ungual pha- 

 langes are very long and hooked. 



The zygomatic arch is incomplete posteriorly, not being 

 united by bone with the squamosal. The cei-vical vertebrae 

 in this remarkable group 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, vertebrae in the neck. 



The pelvis is exceedingly spacious, and the acetabula are 

 directed backwards as weU as outwards. The femur is de- 

 void of a ligameutum teres. The distal end of the fibula 

 sends inwards a process which fits into a fossa situated 

 upon the outer surface of the astragalus, giving rise to that 

 kind of peg and socket 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. viii. p. 14.3), writes of the Ai, or three-toed Sloth : 



" In the greater number of animals, the principal articu- 



