328 SLOTHS. 



much exceeds the others, as with its pecuhar form, to have re- 

 ceived the name of a canine. The Unau is the only species of 

 Bruta, which derives a weapon of offence and defence from 

 the dental system ; and, instead of affording the type(l) of the 

 dentition of its particular family, ought rather to be regarded as 

 manifesting the exceptional modification. 



The so-called canines of the Unau are separated by a 

 marked interval from the other teeth, especially in the upper 

 jaw; so that those above play upon the anterior part of those 

 below, contrary to the relative position, and mutual action of the 

 true canine teeth in the Quadrumana and Carnivora. They are of 

 a triedral form, (fig. 5. a,) with the margins of the oblique 

 abraded surface leading to the point, trenchant. The sockets 

 containing the long excavated base of each of these laniiform 

 molars, projects beyond the level of the outer surface of the jaw. 

 The second tooth (&) of the upper jaw is the smallest of the 

 series, it has an elliptical transverse section, and its grinding sur- 

 face slopes from before and behind to a sub-median transverse ridge. 

 The third (c), and fourth {d) molars, are a little larger, and have 

 two abraded surfaces, which converge to the median ridge. The 

 fifth molar (e), is the smallest, and has an oblique grinding surface. 

 In each tooth the ridge is formed by the hard dentine, and is 

 interrupted in the middle by an excavation of the soft dentine. 

 The second, third, and fourth teeth of the lower jaw correspond 

 with the third and fourth above ; and like the small upper molars, 

 are separated by short intervals : the last is the smallest and most 

 curved. 



The large laniiform molars are three-sided ; the upper one 

 has one of its sides turned outwards ; the lower, one of its angles : 

 the latter resembles the laniiform premolar in the lower jaw of 

 the slow Lemur, in working against the posterior surface of the 

 upper canine, which is an interesting analogy. The wedge-shaped 

 summits of the three lower small molars fit into the interspaces 

 of those of the four upper small molars, when the mouth is closed. 



The teeth of the Sloths consist of a central axis of vascular 



(1) Dr. Blainville, Osteographie des Paresseux, (pp. 32, 33.) 



