Sloths and Manatees. 89 



differ in the possession of short round heads, not pro- 

 longed into a snout, with a lower jaw of one piece, 

 even from a very early age, and also by having a very 

 remarkable down-directed process of the malar or 

 cheek-bone. They are strictly vegetable-feeders, and 

 have sacculated stomachs. Their whole organisation 

 is adapted to an arboreal life, and they live suspended 

 from the branches of trees by their long and strong 

 hook-like claws. They are clad with coarse hair of 

 a dirty white or brownish colour, and have two or 

 three toes only. The peculiarity of their neck verte- 

 brae has been alluded to before ( 49). They have no 



incisor teeth and ^^- molars, which are simple and 



nearly flat-topped. 



The Megatherium, a fossil sloth from South 

 America, must have been little less in size than a 

 large hippopotamus. In many respects it and its 

 allies seem like passage forms from the sloths to the 

 armadillos. 



57. Order 5, Sirenia or Manatees, constitute a 

 small group of sea-weed-eating marine animals, of a 

 somewhat fish-like habit and form, usually found near 

 the mouths of rivers. They have a thick skin, sparsely 

 covered with bristles, and flat-crowned grinding teeth. 

 They have no hind limbs, and the fore-limbs are 

 converted into paddles. The heart in some is deeply 

 cleft, the right and left ventricles being nearly separate 

 from each other (fig. 43). One animal of this group, 

 the Rhytina, which inhabited some islands in Behring's 

 Strait, has become extinct within the last century. 

 Another, the dugong, inhabits the Indian Ocean, 



