OEEODON. 43 



The point and lateral margins of the crown of the upper canine were kept con- 

 stantly sharp, by being subjected to attrition only at the posterior part, where it 

 came in contact with the corresponding tooth of the lower jaw. 



The inferior canine is straight, and is directed from the end of its fang obliquely 

 upward, forward, and outward. 



The fang is variable in its form in diffei'ent specimens; in one its section is 

 transversely compressed and elliptical, in another cylindroidal, and in a third quad- 

 rilateral with rounded margins. 



The crown is a broad, transversely-compressed pyramid, with trenchant margins 

 converging to a slightly rounded but sharp summit. It is of about the same length 

 as that of the upper canine, but is a little broader. 



The inner face is convex; and the outer face is angularly convex, with one por- 

 tion directed outwardly, and the other antero-externally. 



The anterior margin is directed inward and forward, and at its outer part, 

 when the jaws are closed, comes into contact with the posterior face of the upper 

 canine, so as to suffer from attrition most in this position. The margins at the 

 bottom of the crown project slightly bej'ond the outline of the fang. 



The enamel of the canines is a little thicker externally than internally, and is 

 slightly corrugated ; and that upon the trenchant margins of the lower ones has a 

 slightly crenulated appearance. 



Incisors. — (PL II. Figs. 1, 2.) In only one specimen among the many under 

 investigation are the incisors preserved, and in this, their outer face alone is visible, 

 the other being enveloped in a matrix, the removal of which would endanger their 

 integrity. There are three incisors above, and four below, upon each side of the 

 median line. 



Of the superior incisors, the internal is smaller than the outer two, which are 

 nearly equal in size. Their outer face is convex, and they are trapezoidal or nearly 

 ovoid in outline, with the long diameter about one-fourth greater than the trans- 

 verse. The cutting edge and inner margin are convex, and the outer margin has 

 a slightly prominent talon. 



Of the inferior incisors, the internal is the smallest; the succeeding two are 

 nearly equal in size, and the external is a fifth larger than the others. The outer 

 face of the anterior three incisors is convex, and oblong quadrilateral. The cutting 

 edge of the first incisor is convex, that of the second slightly so, and that of the 

 third straight. The lateral margins have a more prominent talon than those of the 

 incisors above, and this is larger externally, and is situated about half-way down the 

 crown. The outer face of the external or fourth incisor is also convex, but is more 

 trapezoidal than the others. Its cutting edge is convex, and is above the level of 

 those of the incisors in advance of it. The lateral margins are oblique and nearly 

 straight. 



The .presence of eight incisors, in addition to well-developed and undoubted 

 canines, in the lower jaw of Oreodon, appears to indicate, in accordance with the 

 view of M. Cuvier, that the lateral or fourth incisors of existing ruminants, are true 

 physiological incisors ; and not transformed canines, as inferred by Mr. Owen, unless 



