42 TRANSACTIONS OF THE 



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former author applying the term Ch^lopus to the B. 

 didactylus ; and the latter author taking the B. tridac- 

 tylus as the type of his genus Acheus. 



The teeth of the three-toed sloth, although con- 

 structed on general principles like those of other phy- 

 tivorous quadrupeds, display remarkable peculiarities 

 in the arrangement of their various parts 5 they are 

 composed of bone, enamel and cement, or pars petrosa $ 

 but in place of being irregularly intermixed with each 

 other, there exists, first, a central cylinder of bone 

 which is surrounded by enamel, which itself is sur- 

 rounded or enveloped by a regular layer of cement. 

 The different densities of these constituent portions of 

 the tooth, occasion its crown to present, by detrition, 

 several irregular faces ; the central pillar of bone being 

 softest, wears away fastest and deepest, the central por- 

 tion of the crown is consequently hollow, whilst the ex- 

 ternal surface of the tooth or the cement being softer 

 than the enamel which it incloses, and harder than the 

 bone proper, remains less worn than the bone, and more 

 so than the enamel, and each portion projects propor- 

 tionably, the circumference of the tooth presenting a 

 bevelled edge. 



This structure renders the masticatory apparatus of 

 this species peculiarly appropriate for grinding vege- 

 tables ; accordingly, in my dissection of an adult sloth 

 (B. tridactylus,) which was killed soon after eating a 

 hearty meal of green leaves, its customary food, I ob- 

 served the stomach replete with vegetable matter, re- 

 duced to a fine pulpy consistence by mastication. Vid. 



