410 ZOOLOGY. 



(instead of compressed) claws or nails, could not be used in burrowing, for 

 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 carinae, 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 Ccelodon 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. 



Fam. 2. Bradypodid^ 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 mammae 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 Achceus. The ai, of the size of a cat, B?: tridactylus {pi. 112, 

 fig. 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 Cholcepus, or Bradypus proper, of which the unau, B. didac- 

 tylus {pi. 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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