42 



OREODON. 



internally the last premolar is excavated iuto a quadrilateral cul-de-sac, of which 

 the inner boundary is a pyramidal tubercle, the homologue of the postero-internal 

 lobe of a true molar. The outer apex of the tooth continues inward upon the sum- 

 mit of a pyramidal sub-lobe, apparently homologous with the antero-iuternal lobe of 

 a true molar. In advance of this sub-lobe, there is a broad notch sloping to the 

 base of the tooth. 



The second premolar exhibits internally a rudimentary form of the correspond- 

 in"' portion of the tooth behind. The tubercle has disappeared; and the sub-lobe 

 in advance of this has degenerated into an oblique ridge descending obliquely 

 backward from the summit of the tooth. The surface postero-internal to this ridge 

 is • sloping, and receives from it a slight abrupt offset. Anterior to the ridge, the 

 internal surface presents a simple, broad, sloping depression. 



The first premolar exhibits internally a simple ridge descending from the summit 

 obliquely backward, and dividing the surface into two depressions, of which the 

 anterior is the broader. 



In tracing upon the premolars, among our specimens, the effects of mastication, 

 it is observed that when the enamel is nearly obliterated from the triturating sur- 

 faces of the true molars, the bottom of the posterior cul-de-sac in the third premolar 

 is left as a small oval islet of enamel upon a broad shoe-formed surface of dentine ; 

 while the second premolar is worn so as to present a surface of dentine having the 

 form of a Greek e. (VI. 8.) 



As in existing ruminants, the inferior molar teeth of Oreodon are inserted by 

 two fangs placed one before the other. The last molar having a fifth lobe, the pos- 

 terior fang is proportion ably broad, and is constituted by a confluent pair. 



Canines. — (PI. II. Figs. 1, 3; III. 1, 2.) The possession of well developed 

 canine teeth in both jaws, is one of the most remarkable chai'acteristics of Oreodon. 

 The form of these teeth is peculiar ; neither those above nor below grow from per- 

 sistent pulps ; and only the crowns are capped with enamel. Those which I have 

 concluded to belong to the male of Oreodon, are more robust than those attributed 

 to the female. 



The upper canine, commencing at the extremity of its fang above the interval 

 of the first two premolars, curves forward, downward, and in a less degree outward. 

 In the male, it is directed more externally than in the female. The fang of the 

 upper canine renders the face slightly prominent along its course, and is trihedral, 

 with rounded margins, and approaches more or less a cylindroid form. In some 

 specimens it is flattened, or nearly so, upon the outer side, and exhibits one or two 

 slight flutings at the lower part. 



The crown is a trihedral pyramid, with the lateral margins acute, the anterior 

 margin subacute, and the summit pointed. Its sides are nearly equal; one being 

 directed outwardly, another inwardly and forward, arid the third posteriorly. The 

 first is nearly plane ; and the second is also nearly plane, and presents a median 

 obtuse ridge, which vanishes above in the fang, and below towards the point of the 

 crown. The remaining side is visible in only one specimen ; its enamel is worn 

 ofl', excepting a small portion at each basal angle; and it is quite plane and smooth, 

 and is a little larsrcr than the other sides. 



