410 ZOOLOGY. 
(instead of compressed) claws or nails, could not be used in burrowing, foi 
the articulating surfaces between the tarsus and the first phalanx are flat 
instead of being rounded, thus excluding at once a vertical motion. They 
were furnished with longitudinal carinz, which did not allow of any lateral 
movement. The habits of Platyonyx were like those of the sloth, probably 
‘moving on the earth with more difficulty. Several species are described 
by Mr. Lund, the size of which varies from that of the ox (P. cuvieri) to 
that of the hog (P. minutus). 
The genus C@lodon had only four molars above and four below, shortened 
and unequal fingers, compressed nails, oblique feet, and a tail like that of 
the Megalonyx. One single species is known, C. maquinense, of the size 
of the tapir, from the caverns of Brazil. 
The genus Sphenodon had also four molars above and four below, 
originally conical and becoming cylindrical in being worn off. A single 
species of the size of the hog was found in the caverns of Brazil. 
I'am. 2. Brapypoprp is represented by a single living genus, Bradypus, 
or sloths. The dentition consists of four cylindrical molars above and 
three below of the same shape, and with sharp canines longer than the 
molars themselves. The fingers are united by a membrane, and only marked 
externally by enormous crooked nails, which, when at rest, are always bent 
towards the palm of the hand or the sole of the foot. The hind feet are 
obliquely articulated on the leg, and rest only upon their outer edge; the 
phalanges of the toes are articulated by a close ginglymus, and the first at 
a certain age become soldered to the bone of the metacarpus or metatarsus, 
which also in time present the same feature. To this inconvenience of the 
organization of the extremities another not less great is added, that is, their 
proportions. The arm and forearm are much longer than the thigh and 
leg, so that when these animals walk they are compelled to drag themselves 
along on their elbows. Their large pelvis and the inclination of their thighs 
to the sides prevent the approximation of their knees. Their gait is the 
necessary effect of such a disproportioned structure. They live in trees, 
and never remove from the one they are on until they have stripped it 
of every leaf, so painful to them is the requisite exertion to reach another. 
It is even asserted that, to avoid the trouble of a regular descent, they let 
themselves fall from the branches. The female produces but a single young 
at a birth. There are two mamme on the breast. The sloths possess 
great muscular power in their fore limbs, which, combined with the stout 
nails, constitutes an excellent means of defence. This is well known to 
hunters, who keep their dogs at a certain distance, in fear that they should 
be killed by them, which is often the case. The species that have three 
nails on the fore feet and a very short tail have received the sub-generic 
name of Acheus. The ai, of the size of a cat, Br. tridactylus (pl. 112, 
ig. 10), is an example of this section. Those species which have only 
two nails to the fore feet and possess no tail at all have been designated 
by the name of Cholepus, or Bradypus proper, of which the unau, B. didac- 
tylus (pl. 112, fig. 9), is the type. It is about one half larger than the ai. 
The sloths inhabit the warmer portions of South America. 
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