CONDYLAETHRA. 449 



The humerus is rather robust. Its muscular ridges are well developed. 

 The deltoid extends two-thirds the length, and the external epicondylar 

 ridge rises as it disappears, and is most prominent near its origin. The head 

 is an anteroposterior oval supplemented by the very large greater tuberosity, 

 and the small but prominent lesser one. The edge of the former is raised, 

 and near its posterior end overhangs a distinct large round facet for the teres 

 minor tendon. The ridge for the insertion of the teres major rises to the 

 inferior overhanging edge of the head a little posterior to this facet. The 

 subscapularis facet of the lesser tuberosity is large and transversely lenticu- 

 lar in shape. It is bounded below by a strong angular ridge. There is a low 

 ridge in the fundus of the wide bicipital groove. The inner side of the shaft 

 for some distance above the condyle is flat. An inch above the condyle 

 its section is triangular. The epicondyles are not prominent ; the internal 

 is a small tuberosity, which is continued into the narrow and short bridge 

 that incloses the epitrochlear foramen. 



The condyles have greater transverse extent than in most Diplarthra, 

 resembling rather that of Proboscideans and Carnivora. The internal flange 

 is prominent, and the external cylinder is quite convex in longitudinal 

 direction, as in Oredon, but less prominently. 



The Phenacodus primavus displays its primitive and Proboscidian char- 

 acter in the relations of the bones of the cubitus. Instead of having the 

 ulna more slender than the radius, as in Hycracotherium and the modern Peris- 

 sodactyla, or equal to it in diameter, as in Hyrachyus, the shaft of the ulna 

 is more robust than that of the radius. The olecranum is not acuminate, 

 but is obliquely truncate, and is flattened below. The middle of the shaft is 

 compressed ; its internal side is nearly flat, or a little concave, while a ridge 

 marks the middle of the external side. This ridge becomes an angle on the 

 distal third of the bone, and almost disappears. Above this ridge there is 

 a wide, rather shallow, groove, which is bounded above by the angular 

 external edge of a narrow superior truncation on which the radius rests. 

 At the distal extremity the external face has a shallow median groove. On 

 the inner side the tuberosity which is applied to the radius is three centi- 

 meters from the extremity. The carpal facet on the latter is a narrow oval, 



convex in both directions. 

 29 o 



