76 ON THE EXTINCT MAMMALIA OF 



The condyloid foramen occupies a position in the angle of a rectangle between the 

 occipital condyle and the paramastoid process. 



The jugular foramen, occupying a position immediately behind the auditory bulla, 

 appears to be comparatively of small size. 



The foramen lacerum varies in size with the difference in development of the 

 auditory bulla in the different species of Oreodon. 



The stylo-mastoid foramen, oval foramen, and eustachian canal, occupy about the 

 same relative position as in the Deer. 



The spheno-orbital and optic foramina are likewise related to the oval foramen and 

 each other, as in the latter animal, but are proportionately more distant. 



The orbits are small compared with those of recent ruminants, and in this respect 

 resemble more those of the suilline animals. They are proportionately longer than 

 in either, and are directed more forward from the bottom. 



The floor of the orbit is as broad as in recent ruminants. About its middle it pre- 

 sents a wide entrance to the infra-orbital canal. 



The orbital entrance varies from vertically oval to round even in the same species 

 of Oreodon. In its direction outward it inclines forward and upward to about the 

 same extent it does in the Deer. 



The post-orbital arch is proportionately about as strong as in the Camel, and, as in 

 this, is directed from the forehead downward and backward to its conjunction with 

 the zygoma. 



The infra-orbital arch does not turn under below as in recent ruminants, but its 

 outer surface continues the incline of the orbital entrance to its inferior margin. 



The zygoma back of the orbital entrance extends considerably outward to it in 

 position, as it continues the infra-orbital arch backward, as in the Hog and Peccary. 



The margin of the orbital entrance is sub-acute. The upper margin is about as 

 much below the level of the forehead as in the Hog. Its anterior margin is furnished 

 with a vertical, compressed, mammillary lachrymal process, and is on a line with the 

 fore part of the second true molar tooth. Above the process there is an oblique 

 supra-orbital groove, varying in depth. 



A pair of lachrymal foramina exist internal to the lower part of the lachrymal 

 process, situated transversely ; a smaller, outer, round one, and a larger, inner, 

 oval one. 



In advance of the orbital entrance, as in the Deer and extinct Boothermm, and 

 to a less extent in the Sheep, Hog and Peccary, there is a lachrymal fossa. In 

 Oreodon it is of remarkable depth, and forms a hemispherical concavity, in great part 

 confined to the facial surface of the lachrymal bone. 



The face'of Oreodon, independent of the lower jaw, forms a demi-cone, the section 

 pf the cone corresponding with the alveolar border. In the same species it varies in 



