TEETH OF UNGULATA. 



357 



287 



Deciduous and permanent teeth," Hyrax. Nat. size. 



The deciduous molars of the Rhinoceros are, in number as well 

 as in shape, similar to those in Hyrax, which bears the same re- 

 lation to the great Rhinoceros as the small existing Sloth does to 

 the extinct Megatherium. The change of dentition of the Rki- 

 nocerotidce is, therefore, here 

 illustrated by the young 

 Hyrax capensis, fig. 287. 



The four premolars, p l, 

 2, 3, 4, are exposed above 

 the four deciduous molars, 

 d l, 2, 3, 4, which they push 

 out; the first true molar, 

 m l, is in place ; the second, 

 m 2, and third, m 3, molars 

 are in different states of forwardness. The first premolar differs 

 from the rest only by a graduated inferiority of size, which, in 

 the last premolar, p 4, ceases to be a distinction between it and 

 the true molars. 



The dental formula of the Tapir is — 



* 3V c fT ; ^ 3V m 3l = 42 ^ vo1, iL p * 449 ' fig " 300 ' immature > 

 The median incisors above have a broad trenchant crown, k, 

 separated by a transverse channel from a large basal ridge ; the 

 wedge-shaped crowns of the opposite pair below fit into the 

 channel, and have no basal ridge ; the outer incisors above are 

 very large and like canines ; those below are unusually small. 

 The canines, /, have crowns much shorter than their roots, and 

 not projecting, like tusks, beyond the lips; they are pointed, with 

 an outer convex, separated by sharp edges from an inner, less 

 convex, surface. The lower canines form part of the same semi- 

 circular series with the incisors. The first three premolars above 

 have the outer part of the crown composed of two half-cones, the 

 posterior one having a basal ridge ; the anterior basal ridge rises 

 into a small cusp in the second premolar, which increases in size 

 in the third and fourth ; in this tooth the transverse depression 

 divides at the base of the anterior and outer demicone, and the 

 posterior division is continued into the interspace of the two 

 demicones; these, therefore, now become in m 1 and m 2 the outer 

 ends of the two transverse wedge-shaped eminences, giving their 

 summits a curve whose concavity is turned backward ; the last 

 molar, m 3, may be known by the shorter and more curved pos- 

 terior eminence. In the dentition of the lower jaw the double 

 transverse ridged structure prevails throughout the molar series, 



