532 UNGULATaS. 



circumference of this complex molar is also invested by a coat of 

 enamel (fig. 8, e) and a thinner layer of cement (ib. c). In some Rumi- 

 nants(l) a small vertical column (fig. 3, p), the analogue of the 

 large conical one in the Anoplothere, is developed at the internal 

 interspace of the two lobes of one or more of the upper true 

 molars, varying in height, and rarely reaching the summit of the new 

 formed crown. Different genera of Ruminants also differ in the 

 depth and sinuosity of the two outer longitudinal folds, and in the 

 depth and complexity of the two vertical folds, which likewise are 

 united in some species by a longer common base than in others, 

 producing thereby a continuity of the enamel and complete antero- 

 posterior bisection of the grinding surface during a longer period 

 of attrition. The upper molars also differ in their breadth or 

 antero-posterior diameter as compared with their thickness or 

 transverse diameter; but, as the summit of the crown is always 

 relatively broader in proportion to its thickness, care must be taken 

 to compare teeth of the different species that have been worn to 

 the same extent, or to allow for the difference. 



In the family of Sheep and Goats {Ovida, PI. 134, fig. 1) the 

 two outer depressions (o o) are broad and shallow with a very low 

 middle convexity, and are bounded by well defined, narrow promi- 

 nent longitudinal ridges, the posterior or third ridge being less 

 developed than the other two : there is no internal accessory 

 column : the breadth of the crown is greater in proportion to its 

 thickness than in the Cervidce or Bovidce. The vertical crescentic 

 folds of enamel forming the islands {e e) are narrow and simple : 

 the Goat and Argali offer a rudiment of a secondary fold at the 

 extremities of the insular crescents, which is rarely seen in the 

 Sheep. The little Musk-deer differs from the Sheep, principally 

 by the greater prominence of the middle longitudinal convexity on 

 the outer side of the anterior lobe, and the crescents are more 

 curved. 



The Antilopidce have the median convexity of the two outer 

 shallow depressions of the upper molars more marked than in the 

 OvidcB and the crescentic enamel-folds are wider ; in the Gnu 



(1) Cuvier specifies the Ox, Deer, and GiraiFe, loc, cit. p. 8. 



