206 



EDEXTATES. 



ever, 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 breast-bone, although the ninth, and occasionally the eighth vertebra, is 

 furnished with a pair of free floating ribs, which stop short of the breast-bone. 

 There are several species of the genus characterised 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 (jn.lt. 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-coloured patch on the back cannot, however, as was once thought, 

 be regarded as a specific character. 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 

 that a captive specimen, when dragged from the branch to which it was clinging. 

 littered a shrill scream. 



