266 6. T. BETTANY ON THE GENUS MERYCOCHXERUS. 



Unfortunately the surface of the postero-inferior part of the orbit 

 and the suborbital arch are broken away on the right side in our 

 specimens, so that it is impossible to determine how the very deep 

 suborbital arch graduated into the much less deep middle portion of 

 the zygoma. Certainly the zygoma projected forward and was 

 intercalated between the prongs of a fork formed by the processes 

 of the malar. The two prongs of the fork seem gradually to have 

 diminished to nothing, while the zygoma descended to the same 

 level as the lower margin of the malar. The broken-off anterior 

 extremity of the zygoma, as we possess it, i3 about half the height of 

 the suborbital arch. Its external surface is smooth and gently 

 rounded. Its upper surface is as broad as its external is high ; in 

 front it is obliquely directed inwards ; but posteriorly its direction 

 changes until it is quite parallel with the middle line of the skull. 

 At the same time the internal height of the zygoma becomes very 

 much less than the external, and ultimately thins away to a sharp 

 edge. 



The upper surface of the zygoma in passing backwards now 

 becomes very much wider. Its inner edge curves round until it 

 passes transversely inwards to join with the lateral wall of the 

 cranium at about its anterior third ; while its external border rises 

 in a concave curve, passing inwards at the same time, till it has 

 reached a height of 2J inches above its origin, and of 3| inches 

 above the lowest part of the zygoma. 



This crest and arch differ from those of Oreodon in their much 

 greater proportional size and in their form. In Oreodon the 

 zygoma continues the direction of the infraorbital arch, or even 

 curves inwards to the cranial wall. In Merycoclioerus it diverges 

 considerably further from the middle line than the infraorbital arch. 

 In Oreodon the crest on the hinder part of the zygoma is very little 

 higher than the rest of the arch ; it is almost constituted by the 

 arch thinning in a vertical direction behind ; and its concave surface, 

 of no great extent, looks mainly inwards, only slightly forwards. In 

 Merycochcerus the crest is much higher than the rest of the zygoma, 

 and, far from being constituted by the compression of the latter, it 

 is set at right angles with its anterior part ; and its large concave 

 surface looks directly forwards. Its concave area is about six 

 square inches ; in a good-sized Oreodon it is only about one square 

 inch. 



The posterior aspect of the skull presents, in the middle line 

 below, the nearly vertical and circular occipital foramen, flanked by 

 the antero-posteriorly compressed occipital condyles. The upper 

 and posterior of the two surfaces produced by the compression of 

 the condyle, is separated from the lower and anterior by a blunt 

 ridge. The former is convex and oval, with an acute termination 

 below. The condyles are considerably separated from one another ; 

 and there appears to have been an emargination of the basioccipital 

 in the middle line. 



The lateral margins of the foramen are continued above into 

 blunt ridges, which soon join and then bifurcate to form strong 



