APTITUDES OF THE SLOTH. 191 



space. Kow, moreover, these bones, instead of being 

 firmly united as one bone, are so articulated with each 

 other as to permit a reciprocal rotatory movement, chiefly 

 performed, however, by the radius; and since to this bone 

 the carpal segment of the hand is mainly articulated, that 

 prehensile member can be turned prone or supine, as in 

 the human arm and hand. Six bones are preserved in 

 the carpus of three-toed sloth {Bradypus triclactylus)^ an- 

 swering to those called "lunare," "cuneiforme," "unci- 

 forme," and "pisiforme," also to the "scaphoides and 

 trapezium" united, and to the " trapezoides and magnum" 

 united. The scapho-trnpezium is characteristic of the 

 sloth-tribe, and is found in the extinct as well as existing 

 species. The articulation of the carpus with the radius, 

 and with the metacarpus, is such as to turn the palm of 

 the long hand inwards, and bring its outer edge to tlie 

 ground. The three fully-developed metacarpals are con- 

 fluent at their base, which is also anchylosed to the rudi- 

 ments of the first and fifth metacarpals; the proximal 

 phalanges of the digits answering to m*, iii^ and iv^ are 

 confluent with their metacarpals, and those digits appear 

 therefore to have only two joints. The last phalanx is 

 remarkably modified for the attachment of the yqyj long 

 and strong claw. 



AVith regard to the bladebone of the sloth, 51, it is 

 much broader in proportion to its length than in the swift 

 cloven-footed herbivores ; the spinous process is unusu- 

 ally short; the acromion is of moderate length, and unex- 

 panded at its extremity ; the supraspinal fossa is the 

 broadest, and has a perforation instead of the usual " su- 

 praspinal" notch. There is a short clavicular bone 

 attached to the acromion, but not attainino' to the ster- 

 num. 



