RUMINANTS. 535 



of the two inner convexities. Bojanus has well illustrated these 

 characteristics of the upper molars of the Camel in his Memoir on 

 the Merycotherium{l) , a large extinct Cameloid genus of Ruminants 

 founded on fossil remains discovered in Siberia, and he has extended 

 the comparison to the Sheep, the Elk, and the Ox. 



Cuvier compares the lower molars of the Ruminants to the upper 

 ones reversed : in the lower true molars the single median longi- 

 tudinal fold is external and divides the convex outer sides of the two 

 lobes (fig 3*, o) : the base of the fold extends in some species across 

 the molar for some depth, before it contracts towards the outer side, 

 and the two lobes of the crown accordingly continue to be com- 

 pletely divided for a longer period, as in the Elk and Giraffe 

 (figs. 6 & 7) : the inner surface of the molar is gently sinuous, 

 the concavities being rarely so deep as those of the outer surface 

 of the upper molars : the lower molars are always thinner in 

 proportion to their breadth than those above, and the crescentic 

 islands are narrower and less bowed. The differences which the 

 lower molars present in different genera of Ruminants are analogous 

 to those in the upper molars, but are less marked : the accessory 

 small column when present, as in Bos, Urus, Megaceros and Alces, is 

 situated at the outer interspace of the convex lobes, and nearer the 

 base in the Cervidcs than in the Bovidcs : in the Giraffe it is present 

 in the first, but not in the second or third true molars ; it is not 

 developed in the Antelopes, Sheep or Camel, and is wanting in most 

 of the smaller species of Deer : other differences are expressed in 

 Plate 134. The last true molar of the lower jaw is characterised in 

 all Ruminants by the addition of a third posterior lobe : this is very 

 small and simple in the Camel and the Gnu, is relatively larger in 

 the Bovid(B and Cervidts, presents in the Megaceros and Sivatherium{2) 

 a deeper central enamel island or fold, which also characterises the 



(1) Nova Acta Nat. Curios. 4to. 1824, torn, xii, pt. i, p. 265, tab. xxi. 



(2) The last lower molar of this most gigantic of Ruminants is figured in PI. 133, 

 fig. 3. Cuvier (loc. cit. p. 5) describes the two lobes of the lower molars as being composed 

 of two half-cylinders forming crescentic ridges on the grinding surface, and the last lower 

 molar as having an additional half cylinder, and consequently a grinding surface of five 

 crescents : the crescentic ridges are formed by the vertical descending fold, which divides the 

 summit of the lobe, and the fact is that the third lobe of the last molar has also this fold ; but 

 it is shallower and the entire lobes are smaller. In most Ruminants the crescentic enamel island 

 or fold is therefore soon obliterated in the third lobej but in some species it is deeper and 



