HIPPOPOTAMUS. • 141 



or that most posterior, is in the same state of advancement, 

 having just pierced the bone : the oldest tooth in the head or 

 the first permanent molar is just worn to that state when the 

 development of the trefoil crown is most perfect ; the second 

 permanent molar is just showing this appearance on its two 

 front pillars ; the front false or pointed molars are unworn, 

 and exhibit in all their perfection the richly embossed surface, 

 which is peculiar to these teeth in the Hippopotami. The 

 first false molar or milk tooth seems to have retained its posi- 

 tion in many of our fossils, long after the fall of the other 

 milk teeth, and long after the arrival of the animal at the 

 adult state. In some of our skulls, which are the remains of 

 very old animals, we observe the alveolus of this tooth very 

 distinct, and having the appearance more of having been 

 broken off in the fossil than of having been lost previous to 

 the death of the animal, m which case, moreover, a fillmg in 

 of the pit from the growth of the bone would be more or less 

 evident in the fossil. From the natural wear of the tusks 

 upon each other, the truncated extremity of the upper 

 one, which in the Hippopotamus Sivalensis is described as 

 reniform, occurs on the convex or outer side of the tusk; 

 and this must be the case wherever the tusk belongs to the 

 upper jaw. Amongst a very extensive and very large collec- 

 tion, containing, as we before remarked, three perfect skulls, 

 with a number of fragments of nearly perfect lower jaws, with 

 a great number of pieces of both more or less mutilated, the 

 reniform tusk is an invariable appendage to the upper, and 

 the pjrriform to the lower jaw. Our collection, however, ex- 

 hibits one solitary instance of the anterior extremity of a 

 reniform tusk truncated on the inner or concave surface ; 

 this, unfortiuiately, is a separate fragment, unattached to 

 any portion of the jaw, and bearing in itself no further mark 

 of its having existed in the lower jaw than this truncation of 

 the extremity. It is difficult to imagine any fortuitous cir- 

 cumstance that would have produced such an anomaly, and 

 it is at the same time difiicult to come to a conclusion con- 

 trary to the facts elicited by such an extensive collection of 

 remains, in which we see no sign of the reniform character 

 of the canine in the lower jaw ; should the truncation alluded 

 to not be accidental, or be caused by some deformity in the po- 

 sition in the alveolus, we have yet to discover a variety of the 

 Hippopotamus with the reniform tusk in the lower jaw. The 

 fact of the existence of this fragment, however, may be as 

 well noted, as we observe peculiarities of form in other frag- 

 ments of the bones of the head that may ultimately prove to 

 belong to different species. We have contented ourselves 

 with drawing our comparisons from the bones of the head, 



