40 Description of the Sivatherium, [Jan. 



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 hetween 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 hy which the 

 teeth differ from thos»e 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 ^hole 

 series heing 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 somewhat contracted : in the third molar, the width at the coronal 

 is 1 .93, at the bulge of the shaft 2.24.. The ridges 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 plates of enamel have a character which distinguishes them 

 from all known ruminants: the inner crescent, instead of sweeping in a 

 nearly simple curve, runs zig-zag-wise in large sinuous flexures, somewhat 

 resembling the form in the Elasmotherium. 



The three double molars differ from each other only in their relative 

 states of wearing. The antepenultimate, being most worn, has the 

 crescentic plates less curved, more approximate and less distinct: the 

 penultimate and last molars are less worn, and have the markings more 

 distinct. 



The three anterior or simple molars have the usual form, which holds 

 in Ruminantia, a single semi-cylinder, with but one pair of crescents. The 

 first one is much worn and partly mutilated : the second is more entire, 

 having been a shorter time in use, and finely exhibits the flexuous curves 

 in the sweep of the enamel of the inner crescent : the last one has the sim- 

 ple form of the permanent tooth, which replaces the last milk molar : it 

 also shews the wavy form of the enamel. 



Regarding the position of the teeth in the jaw ; the last four molars, 

 viz. the three permanent and the last of replacement, run in a straight 

 line, and on the opposite sides are parallel and equi-distant : the two 

 anterior ones are suddenly directed inwards, so as to be a good deal 

 approximated. If the two first molars were not thus inflected, the opposite 

 lines of teeth would form exactly two sides of a square : the length of the 

 line of teeth, and the intervals between the outer surfaces of the four last 

 molars, being almost equal, viz. 9.8 and 9.9 inches respectively. 



The plane of detrition of the whole series of molars from rear to front 

 is not horizontal, but in a slight curve, and directed upwards at a consider- 

 able angle with the base of the skull : so that when the head is placed, so 

 as to rest upon the occipital condyles and the last molars, a plane through 

 these points is cut by a chord along the curve of detrition of the whole 

 Beries of molars at an angle of about 4*5°. This is one of the marked 

 characters about the head: 



Dimensions of the Teeth. Length. Breadth. 



Inches. Inches. 



Last molar right side, 2.35 



Penultimate do 2.20 2.38 



Antepenultimate do 1.68 2.20 



Last simple molar, 1.55 2.24 



Second do. do 1.70 1.95 



First do. do 1.70 1.90 



