RHINOCEROS TICHORHINUS. 



335 



Fiff. 125. 



Kirkdale, the remains of the large herbivorous quadru- 

 peds were chiefly those of young animals, and such as 

 would most easily fall a prey to the Hyeenas, and be 

 dragged by them into their den. 



Fig. 125 represents the 

 grinding surface of an upper 

 molar tooth of the Rhinoceros 

 tichorMnus, which was disco- 

 vered in the Kirkdale ca- 

 vern, and is now in the Bri- 

 tish Museum. This tooth is 

 the third of the series ; only 

 the crown had been formed 

 and had not made its ap- 

 pearance above the gum. 

 From its size, it was like- 

 wise evidently the germ of 

 a deciduous or milk tooth. 

 The comparison of figure 



124, with figure 112, of a similar germ of an upper 

 molar tooth of the Palaeotherium medium, will illustrate 

 the similarity of plan, and generic modification, of the 

 structure of the teeth of the Rhinoceros, as compared 

 with those of the more ancient Pachyderm. The outer 

 wall of the crown is more even and less deeply indented ; 

 the two valleys, a and 6, are wider in the Rhinoceros. 



Mastication first exposes the dentine at the summits of 

 the ridges, and produces the two peninsular folds of enamel 

 shewn in fig. 122. The continued wear of the tooth next 

 insulates the posterior division of the transverse peninsula 

 and simplifies it, as at b in the molar tooth from the cave 

 of Kent's Hole (fig. 126). As the shorter valley (a) is 

 deepest at its extremity, further attrition exposes the 



Deciduous upper molar ; nat. size ; Rhi- 

 noceros tichorliinus. Kirkdale cavern. 



