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which the length far surpasses that of the hinder-pair. Both pairs of limbs are 
furnished with long and slender feet, in which there are never more than three 
toes; while the toes themselves are invested for nearly their whole length in a 
common skin, and terminate in long curved claws of great strength. The thick 
coat of long, coarse, and somewhat brittle hair with which the whole of the body 
and limbs is invested, is generally of a brownish or dull ashy-grey colour, mingled 
with a greenish tint; each individual hair having a fluted or roughened external 
surface. The most remarkable feature connected with the pelage is, however, the 
growth of a vegetable—a kind of alga—on the hairs themselves; the alga attach- 
ing itself to the aforesaid flutings, and growing luxuriantly in the moist atmosphere 
of the South American forests, although quickly withering when the animals are 
brought to Europe. It is this extraneous vegetable growth which communicates 
the greenish tinge to the hair during life; and its object is doubtless to render the 
coloration of these creatures in still closer harmony with their inanimate surround- 
ings than would have been otherwise possible. It may be mentioned here that it 
is almost impossible to conceive that any sort of so-called natural selection could 
have given rise to this peculiar and unique kind of protective resemblance. In 
the region of the back between the shoulders many sloths exhibit a patch of fine 
woolly under-fur marked by longitudinal stripes of rich brown and orange; the ex- 
posure of such patches being due, according to Brehm, to the animals having abraded 
the long hair by rubbing or resting their backs against trees. The coloration of 
this patch of under-fur approximates to that obtaining in the coat of the ant-eaters, 
from which it may be inferred that both these groups of animals originally had 
bright-coloured fur, and that the long external dull-hued coat of the sloths has 
been a special development suited to the needs of their environment. 
The sloths have five pairs of teeth in the upper, and four in the lower jaw; 
the individual teeth, with the exception of the first pair in one of the two genera, 
being nearly cylindrical in form, and in all cases consisting of a core of ivory 
invested with a thick coating of cement. The skeleton is characterised by the 
presence of complete collar-bones ; while in the fore-arm the two bones are completely 
separate, and allow the hand to be supinated like that of man. The claws are, 
however, permanently fixed parallel to one another, so that the hand, like the foot, 
can be used merely as a claw. In the hind-limb the foot is articulated obliquely 
to the bones of the leg; so that when on the ground the animal can walk only on 
the outer sides of its feet. Of the soft parts, it will suffice to mention that the 
tongue is short and soft; while the large stomach, as in so many leaf-eaters and 
erass-feeders, is divided into several compartments. The windpipe is peculiar 
in being folded before reaching the lungs,—a feature found elsewhere only in 
certain birds. Finally, the female sloth has but a single pair of teats on the breast. 
Three-Toed The typical members of the family are commonly known as 
Sloths. three-toed sloths, or, from their native title, ais, and constitute the 
genus Bradypus, readily characterised by the presence of three toes on both the 
fore and the hind-feet. The teeth are all of nearly the same height, with their 
grinding surfaces deeply cupped ; the first tooth in the upper jaw being considerably 
smaller than either of the others, while the corresponding lower tooth is broad and 
compressed. The most remarkable peculiarity connected with the genus is, how- 

