UREODON OF NEBRASKA. 



545 



The inferior incisors are oblique in their direction, but relatively not quite so 

 much so as in the Musk-deer, and on both sides they are arranged in the tangent 

 of a smaller circle than the upper ones. 



The true molars in both jaws have the same relation to one another as in the 

 Deer. 



The first premolar of the upper jaw has its posterior margin a little external to 

 the contiguous margin of the succeeding tooth, as if it had been pushed outwards 

 and backwards, in a jaw where but little space could be lost, to make the hiatus 

 between it and the canine. 



In the same manner, in the lower jaw, the latter tooth and the first premolar 

 appear pushed a little outwards and backwards in their relation to each other and 

 the succecling molar, so as to allow the formation of the hiatus anterior to the 

 canine. 



The crowns of the superior true molars are composed of four simple, pointed, 

 symmetrical, pyramidal lobes, as in Merycopotamus. In comparison with existing 

 Ruminants their form is most like those of the Deer, but they are more expanded, 

 and consequently are relatively of greater transverse breadth, more square, and the 

 interlobular depressions are more shallow. 



The outer lobes are not separated from one another as in Merycopotamus, but 

 are connected by a prominent buttress projecting externally, as in Anthracothe- 

 rium. The remaining anterior and posterior margins of the outer lobes are also 

 prominent externally, and with the exception of the posterior margin of the postero- 

 external lobe of the first and second teeth, form buttresses nearly or quite as large as 

 the middle one. The buttresses are laterally compressed, and expand towards their 

 base, where they become confluent by means of a basal ridge passing between them. 

 The latter ridge is sometimes obsolete, especially at the base of the postero-external 

 lobes of the posterior two molars. 



The external faces of the outer lobes are concave from side to side, slightly pro- 

 minent in the middle line, and incline at an angle of about 40°. The internal 

 faces are nearly vertical, but incline slightly outwards, and are angularly convex. 



The external faces of the inner lobes are concave, and have the same degree of 

 inclination as the corresponding faces of the outer lobes. The internal faces are 

 convex, and less angular than those of the outer lobes. 



The summits of the lobes are crescentic ridges elevated into a point at their 

 middle. The extremities of the outer crescents rest upon the external buttresses. 

 The anterior extremity of the antero-internal crescent, and the posterior of the 

 postero-internal crescent, are continuous with a short ridge descending to the sum- 

 mit of the corresponding buttresses of the outer lobes. The anterior horn of the 

 postero-internal crescent ends abruptly between the postero-external lobe, and the 

 posterior horn of the antero-internal crescent, which also terminates abruptly, but 

 is bent forward and ceases short of the posterior portion of the inner face of the 

 antero-external lobe. 



A basal ridge exists anteriorly and posteriorly upon the internal lobes, sometimes 

 continuous internally at the base of the postero-internal lobe of the second and 



