?| DESCRIPTION OF THE SIVATHERIUM, 



Now in detail of individual parts ; and to commence with the most 

 important and characteristic, the teeth : 



There are six molars on either side of the upper jaw. The third of the 

 series, or last milk molar, has given place to the corresponding permanent 

 tooth, the detrition of which and of the last molar is well advanced and 

 indicates the animal to have been more than adult. 



The teeth are in every respect those of a ruminant with some slight 

 individual peculiarities. 



The three posterior or double molars are composed of two portions or 

 semi-cylinders, each of which incloses, when partially worn down, a double 

 crescent of enamel the convexity of which is turned inwards. The last molar, 

 as is normal in ruminants, has no additional complication, like that in the 

 corresponding tooth of the lower jaw. The plane of grinding slopes from 

 the outer margin inwards. The general form is exactly that of an ox or 

 camel, on a large scale. The ridges of enamel are unequally in relief, and 

 the hollows between them unequally scooped. Each semi-cylinder has 

 its outer surface, in horizontal section, formed of three salient knuckles, 

 with two intermediate sinuses ; and its inner surface, of a simple arch or 

 curve. But there are certain peculiarities by which the teeth differ from 

 those of other ruminants. 



In correspondence with the shortness of jaw, the width of the teeth 

 is much greater in proportion to the length than is usual in the family : 

 the width of the third and fourth molars being to the length as 2.24 and 2.2 

 to 1.55 and 1.68 inches, respectively : and the average width of the whole 

 series being to the length as 2.13 to 1 .76 inches. Their form is less prismatic : 

 the base of the shaft swelling out into a bulge or collar, from which the 

 inner surface slopes outward as it rises : so that the coronal becomes some- 

 what contracted : in the third molar, the width at the coronal is 1 .93, at 

 the bulge of the shaft 2.24. The rido-es and hollows on the outer surface 

 descend less upon the shaft, and disappear upon the bulge. There are no 

 accessary pillars on the furrow of junction at the inner side. The crescentic 



