No. i.] OSTEOLOGY OF PCEBROTHERIUM. 41 



distal end, which embraces the lower end of the astragalus, 

 and between which and the sustentaculum there is a deep notch : 

 nothing of the kind is observable in Pcebrotheriiim, and the sus- 

 tentaculum itself is not so prominent. The fibular facet of the 

 calcaneum is longer, lower, and less abruptly truncated in front 

 than in the llama, and the cuboidal surface is likewise narrower. 

 The tuber calcis is proportionately thicker, of less depth, and 

 with the free end less thickened and rugose : its borders are also 

 more nearly parallel. 



The cuboid is decidedly higher and narrower than in the living 

 genera, and its facets differently proportioned ; that for the cal- 

 caneum being somewhat broader than that for the navicular, 

 while in the recent forms the reverse is the case, though the 

 difference is not very striking. The calcaneal facet in Pcebro- 

 therium is a broad overhanging shelf, strongly convex from before 

 backwards : a small fossa intervenes between it and the astras:- 

 alar surface, where the two are on the same level. The astrag- 

 alar facet is narrow and simply concave from before backward ; 

 in the middle of its course it is emarginated on both sides and 

 greatly narrowed, though not entirely interrupted, by the fossa 

 already mentioned, on the outer side and by another on the 

 inner side ; anteriorly it rises much higher above the calcaneal 

 facet than in the llama. The posterior hook of the cuboid is 

 very stout, but not quite so long as in the recent species, and 

 fits closely against the projection from the fourth metatarsal. 

 On the internal or tibial side of the cuboid are two facets for the 

 navicular, — the hinder one a large projecting ledge, the front 

 one a mere smooth surface. The distal end of the cuboid dis- 

 plays a large, somewhat triangular and concave surface for the 

 fourth metatarsal, which is not emarginated and interrupted as 

 in the camel. External to this is a minute facet for the rudi- 

 mentary fifth digit, but this facet is entirely lateral in position, 

 not at all distal. 



The navicular is entirely free from the cuboid, never showing 

 any tendency to coalesce with it ; it is comparatively high and 

 narrow, but of less antero-posterior depth than in the recent 

 forms, and is devoid of a posterior hook. The astragalar surface 

 is concave from before backwards, saddle-shaped from side to 

 side, and is emarginated in the middle by a fossa on the fibular 

 side. The posterior facet for the cuboid does not form a prom- 



