SLOTHS AND THEIR HAIR 315 



space not longer than the one between the second and 

 third. In the two-toed form, on the other hand, the first 

 tooth is taller than those behind, and has a bevelled 

 instead of a flat grinding surface, while the space dividing 

 it from the second much exceeds that between any of 

 the others. Again, the front of the upper jaw of the 

 two-toed sloth carries a T-shaped bone, corresponding to 

 the premaxillae of other mammals, which is totally wanting 

 in the other species. The front of the lower jaw of the 

 former is also prolonged so as to form a kind of spout, 

 of which there is no trace in the latter. In both these 

 respects the two-toed sloth comes much nearer to the 

 extinct ground-sloths than is the case with its three-clawed 

 cousin. 



Again, if the males of the three-toed sloth be examined, 

 there will be seen a patch in the middle of the back where, 

 owing to the absence of the long coarse external hair, 

 the presence of a soft orange and brown under-fur is 

 shown. It has been stated that this patch of under-fur 

 is made visible by the animals rubbing their backs against 

 boughs and wearing off the long hair, but it seems much 

 more probable that it is a sexual character. Of this under- 

 fur the two-toed sloth has but a very imperfect development. 



Apart from its extremely coarse and brittle nature, the 

 most striking peculiarity of the outer hair of the sloths is 

 its more or less decidedly green tinge. To see this in 

 perfection it is necessary to examine living animals, as it 

 tends to fade away more or less completely in skins 

 long exposed to the light, leaving the hair of a pale greyish 

 brown colour. 



Now green is a very rare colour among mammals, and 

 there ought, therefore, to be some special reason for its 

 development in the sloths. And, as a matter of fact, the 



