EDENTATA. 
123 
that, when these animals advance [on the ground], they are obliged to drag themselves forward on their 
elbows. The pelvis is so large, and the thighs so much directed outwards, that they cannot approxi- 
mate their knees. Their gait is the necessary consequence of so disproportioned [unusual] a struc- 
ture.* These animals inhabit trees, and never remove from that on which they are located until they have 
stripped it of every leaf, so painful to them is the requisite exertion to reach another ; it is even 
asserted that they let themselves fall from a branch to avoid the labour of descending. [The truth is, 
that these animals are modified for hanging by their limbs to the branches of trees, instead of sup- 
porting themselves upon the limbs like others : in this, their only natural posture, they are by no 
means slow in their movements ; and they inhabit the densely intertangled forests of South America, 
where hundreds of miles may be traversed by passing from one tree to another : clinging by the hinder 
claws, the posterior limbs securely embracing the bough, and generally by one of their fore-limbs also, 
they employ the other to hook towards them the foliage on which they browze, whence the great 
length of their arms : and it is observed that in more open places, where the trees are less contiguous, 
the Sloths take advantage of windy weather to effect their transits, when the boughs are blown 
together and commingled. Their long and coarse shaggy hair protects them from insects : and in 
short, as is well remarked by Professor Buckland, the peculiar conformation of these animals ought no 
more to excite our pity and compassion, than the circumstance of fishes being deprived of legs. They 
are just as admirably adapted and fitly organized for their appointed singular mode of life as any other 
animal whatever.] The female produces but one young one at a birth, which she carries on her back. 
The viscera of these animals are not less singular than the rest of their conformation. Their stomach 
[of enormous size] is divided into four compartments, somewhat analogous to the four stomachs of 
the ruminants, but without leaflets or other internal projecting parts ; while the intestinal canal is 
short, and without a coecum. 
M. F. Cuvier applies the name Acheus to such of them as have three claws on their fore-feet ; they 
have a very short tail. 
The Ai {Br. tridacfylus, Lin.) is the species in which all the 
peculiarities of its genus are developed to the greatest extent. 
Its thumb and little toe, reduced to small rudiments, arc 
concealed by the skin, and soldered to the metatarsus and 
metacarpus ; the clavicle, also, reduced to a rudiment, is sol- 
dered to the acromion. Its arms are twice as long as its legs ; 
the hair of its head, back, and limbs is long, coarse and un- 
elastic, bearing some resemblance to dried grass, which gives 
it a forbidding aspect. The colour is greyish, often spotted 
with brown and white, [particularly when young]. Size that 
of a Cat. It is the only known mammalian which has nine 
cervical vertebrae [the fact being, that the eighth and ninth 
support rudimental ribs (as shown at Fig. 2, p, 39), and are 
therefore dorsal vertebrae, as in all the rest of the class : the 
more complete rotation of the neck, however, thus acquired 
Fig-. 49.— The Ai, or Common Sloth 
by this extraordinary animal, having an obvious reference to its peculiar habits]. Some varieties of the Ai have 
been described as separate species, ditfering however in colour only : but the Bradypus torquatus, Geof., is very 
distinct, even in the bony structure of its head. 
M. F. Cuvier reserves the name Bradypm for those species which have two claws only on their 
fore-feet (the Cholapus, Ilhg.). Their canines are longer and more pointed, and they are quite desti- 
tute of tail. We know hut of one. 
The Unau {Br. didactylus, L.), which is rather less unfortunately {malheureusemenf) organized than the Ai. Its 
arms are shorter, its clavicles complete ; there are fewer bones of its fore and hind feet which become soldered 
together. Its muzzle is more elongated, &c. It is larger by one half than the Ai, and of an uniform greyish- 
brown, which inclines sometimes to reddish. 
These two animals are indigenous to the hot parts of America. Were it not for their stout claws, they would 
probably have been long since exterminated by the Carnivora of that country. [The lofty canopy from which 
they hang is beyond the reach of such enemies. In their affinities, the Sloths are closely related to the 
Myrmecophagce.'] 
* Sir A. Carlisle has observed that the arteries of the limbs com- 
mence by subdividing into numerous ramifications, which afterwards 
re-unite into a single trunk, from which the usual branches proceed. 
This structure being also met with in the Loris, the gait of which is 
almost equally sluggish, it is possible that it may exert some influence 
on this slowness of motion, [It occurs also in the Whale, and the 
generality of birds, being connected rather with the power of pro- 
tracting muscular exertion.] Independently of this, the Loris, the 
Ourang-outang, and the Coiata, all very slow animals, are remarkable 
for the length of their arms. [Still more so are the Gibbons, which 
are distinguished for the agility of their movements.] 
