THE SLOTHS 



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however, the presence of nine, instead of the usual seven, vertebrae in the neck; that 

 is to say, it is the tenth vertebra from the head which first carries ribs articulating 

 with the breastbone, although the ninth, and occasionally the eighth vertebra, is 

 furnished with a pair of free floating ribs, which stop short of the breastbone. 

 There are several species of the genus characterized by differences in coloration, or 

 by the relative length of the hair on the face; but the precise number of species is 



THE COMMON THREE-TOED SLOTH. 



(One-fourth natural size.) 



not yet definitely ascertained. In some kinds the coloration is uniform, while in 

 others there is a dark stripe across the shoulders; the presence of the above- 

 mentioned bright-colored patch on the back cannot, however, as was once thought, 

 be regarded as a specific characteristic. The typical B. tridactylus inhabits the drier 

 regions of the forests, while others, as noticed. below, frequent the permanently 

 flooded districts. As a rule, these animals appear to be silent; but it is recorded 

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