TEETH OF UNGULATA. 351 



The lower molars are like the upper ones reversed. The single 

 median longitudinal fold is external, and divides the convex outer 

 sides of the two lobes. The base of the fold extends, in some 

 species, across the molar for some distance before it contracts in 

 breadth, retreating toward the outer side, and the two lobes of 

 the crown accordingly continue to be completely divided for a 

 longer period, as in the Elk and Giraffe. 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 dif- 

 ferent 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 Cervidce than in the Bovidce. It is not developed in the 

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

 smaller species of Deer. The last true molar of the lower jaw is 

 characterised in all Ruminants by the addition of a third pos- 

 terior lobe. This is very small and simple in the Camel and the 

 Gnu, is relatively larger in the Bovidce and Cervidce, and pre- 

 sents, in the Megaceros and Sivatherium, a deeper central enamel 

 island or fold, which also characterises the smaller third lobe in 

 the Giraffe. The lower molars of the genus Auchenia are pecu- 

 liarly distinguished by the vertical ridge at the forepart of the 

 anterior lobe, which does not exist in the Camels of the Old 

 World. 



In all Ruminants, the outer contour of the entire molar series 

 is slightly zigzag, the anterior and outer angle of one tooth pro- 

 jecting beyond the posterior and outer angle of the next in 

 advance. All the three lower premolars have compressed, sub- 

 trenchant, and pointed crowns in the small Musk-deer ( Tragulus). 

 The true Musk (Moschus) more resembles the ordinary Deer 

 in its premolars. The aberrant Camelidce deviate most from 

 ruminant type in the position, shape, and number of the pre- 

 molars : the anterior one, fig. 278, s, is laniariform in both jaws. 



As phenomena of dentition serve to determine, or indicate, the 

 age of Hoofed beasts, a table is subjoined in which the charac- 

 teristic teeth are indicated by the symbols adopted in my ' Odon- 

 tography ' (v), and illustrated in figs.' 279 and 294, with reference 

 to those domesticated varieties raised for food, which are usually 

 exhibited, in competition, of prescribed ages, at the great cattle 



