TEETH OF UNGULATA. 



357 



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 Rhi- 

 nocerotidce is, therefore, here 

 illustrated by the young 

 Hyrax capensis, fig. 287. 



The four premolars, p i, 

 2, 3, 4, are exposed above 



287 



?n 



Deciduous and permanent teeth, Hyrax. Nat. size. 



the four deciduous molars, 



di, 2, 3, 4, which they push 



out ; the first true molar, 



m i, 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 



.3.3 1.1 4^4 3.3 



oo'ii*-* ** ^ * ** ** 



O.O I . 1 O.O O,O 



= 42 (vol. ii. 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 i 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, 



