The Encyclopedia Americana (1920)/Sloth

SLOTH, an edentate mammal of the familyBradypodidæ. (See Edentata). The bestknown are the unau or two-toed sloth (Cholœpusdidactylus) of Brazil and the ai or three-toedsloth (Bradypus tridactylus) of northernSouth America. This family is distinguishedby the flat short head, and the elongated legs,furnished with powerful compressed and curvedclaws. No incisor teeth exist, but simplecolumnar molars without enamel are developed.The stomach is somewhat complex. The three-toedspecies are unique among mammals inpossessing nine cervical vertebræ. The long bonesare solid, and destitute of marrow or medullarycavities. Being adapted solely for an arboreallife, the fore-limbs exhibit a much greaterlength than the hind-limbs, and a powerfulmuscular organization. The forearm possessesan unusual degree of mobility, the feet beingstrong and the claws very powerful and permanentlyflexed. The usual mode of progressionof these animals is to move back downwardsuspended from the branches of trees, and theyare known to sleep in this curious position. Onthe ground the sloths are entirely out of theirelement; the feet being jointed in an obliquemanner to the limbs, the palms and soles arethus naturally turned inward, and the clawsthemselves are bent inward toward the solesof the feet. Three toes exist in this species,and its general color is a brownish gray, withdarker tints on the face and limbs. The furis of very coarse character, and when theanimals are living in their damp native forests istinted green from the presence upon it of aminute green plant or alga. The unau, as itsspecific name implies, has but two toes, and23 pairs of ribs exist, no mammal possessing agreater number than this. Its average lengthis about two feet, and its color is a lighter graythan that of the ai. The tail in both species iseither wanting, or at the most is rudimentary.The sloths are proverbially sluggish in theirmovements and are remarkably tenacious oflife. They are nocturnal and feed upon leavesand shoots which are secured with the slenderprehensile tongue. Generally only the twogenera mentioned above are recognized, butby some zoologists the three-toed sloths aresubdivided. The number of species is alsodoubtful. About 15 have been described, allconfined to South and Central America. TheMegathium and Mylodon (q.v.) were giganticsloth-like terrestrial mammals, the remains ofwhich are found abundantly in the Pleistocenedeposits of North and South America. ConsultFlower and Lydekker, ‘Mammals Living andExtinct’ (London 1891); Leidy, ‘Extinct SlothTribe of North America’ (Washington 1855);Bates, H. W., ‘Naturalist on the Amazon’(1910).