98 MOSTLY MAMMALS 



To justify myself, and at the same time to enable my 

 readers properly to understand the structure of these 

 strange extinct edentates, it is necessary to enter into a 

 short dissertation on the subject of sloths, and likewise of 

 their distant cousins the ant-eaters. 



The external form and long shaggy hair of the sloths are 

 too well known to require description, and I pass on to 

 draw attention to certain peculiarities in regard to their 

 skeletons and teeth which will aid in explaining the reason 

 for the term ground-sloths. In the first place, then, sloths, 

 which are comparatively small animals, are characterised 

 by their peculiarly short and rounded heads, of an almost 

 spherical form. If the skull of one of these animals be 

 examined, a total absence of front teeth will be noticed ; 

 while the cheek-teeth comprise five pairs in the upper 

 and four in the lower jaw. 



As already stated, the teeth in all edentates are devoid 

 of the enamel so characteristic of those of other mammals ; 

 and in the sloths they form short cylinders, of which 

 the outer layer is harder than the central core, in con- 

 sequence of which their grinding surfaces become slightly 

 cup-shaped. In the three-toed sloths (Bradypus) the whole 

 of the teeth are of this extremely simple type ; but in 

 their two-toed cousins (Cholaepus) the first pair in each jaw 

 are longer than either of the others, and modified into a 

 somewhat tusk-like form, the upper ones wearing against 

 the front of the lower ones so as to produce by mutual 

 attrition an oblique bevelled surface at the top of each. 

 Both limbs of sloths are remarkable for their length and 

 slenderness, but the front pair are much longer than the 

 hinder ones. The narrow and curved feet terminate in 

 long hooked claws, which in the three-toed species are 

 three in number in each foot, although in the fore-feet of 



