ASTRAPOTHERE. 



563 



in nearly the same manner as those of the pigs. The molars are more distinctly 

 rhinocerotic in structure, those of the upper jaw having taller crowns than those of 

 the homalodontothere, with a large posterior valley, and a well-developed projection 

 in the middle valley. The last of the series has the same triangular form as in 

 the majority of species of rhinoceros ; while the premolars are simpler than the 

 molars. In the lower jaw the molars form nearly simple crescents, very similar to 

 those of rhinoceroses, but the hinder crescent of the third of the series is more 

 elongated. 



The dentition may apparently be represented by the formula, i%, c J, p\ , m ; 

 the premolars being separated from the incisors or canines by a long gap. 



The front of the apex of the upper tusk is worn to an oblique facet by the 

 attrition of the lower canine. In the lower jaw the tusk is considerably smaller 



LOWER JAW OF THE ASTRAPOTHERE (much reduced). 



than in the upper jaw, but is still triangular in section, although with the sharp 

 edge in front. The inner surface is concave anteriorly and convex posteriorly ; 

 while the outer one is wholly convex, and passes imperceptibly into the small 

 hinder surface. The extremity of the latter is worn into a long oblique facet, in 

 the same manner as in the corresponding tooth of a peccary. The six lower 

 incisors are inclined forwards, and arranged in a circle so as to fill up the interval 

 between the tusks. Their crowns, which, vary in shape in the two species of the 

 genus, are short and spatulate, with the upper surface slightly concave, and the 

 lower one convex; a deep longitudinal groove traversing the middle of each of 

 these two surfaces, and uniting in a notch in the middle of the unworn crown. 

 The lower cheek-teeth call for no special remark, as they are very similar to those 

 of the rhinoceroses. In the lower jaw, the tusks certainly correspond to the 

 canines ; and it would appear at first sight that the same would hold good with 

 those of the upper jaw, but from the* analogy of the proterothere it is more prob- 

 able that the latter really belong to the incisor series. 



