PROMKRYCOCHCERUS 



11 



The ribs have a comparatively small curvature and low tubercular facets, producing a wide rib 

 basket. The anterior five ribs are flat, while the others are more rounded, and the last is much 

 shortened, with no tubercular facet and with a sinuous curvature to the shaft. 



The three sternebrse present are heavy, broad, flat, and very deep, with rugose surfaces. 



The scapula is triangular in outline, with a medially situated spine, and the fossse are subequal. 

 The prominent spine is very heavy, becoming smaller toward the suprascapular border. Both the 

 acromion and the metacromion processes are well developed, the latter pointing downward and back- 

 ward, while the former is directed downward and forward. The glenoid cavity is relatively large; 

 the coracoid is heavy and rugose, with a moderately large coracoid process. The heavy glenoid 

 border is outwardly curved along its upper half and, with the spine, encloses a very concave, deep, 

 and subtriangular infraspinous fossa. The thin coracoid border is inwardly curved through a third 

 of its middle portion. 



From the size and shape of the spine and acromion process Peterson believed that a clavicle 

 persisted in this species, because Merycoidodon, with no greater relative development of these parts, 

 possessed a clavicle of considerable size. 



The short and heavy humerus is expanded at both ends, and the distal trochlea is oblong in 

 shape. 



The head is very large, well rounded, but not so hemispherical as in Merycoidodon culbertsom. The greater 

 tuberosity extends across the entire anterior face of the head, and is well produced above the articular surface, 

 terminating radially in a robust hook, which overhangs the deep and well-formed bicipital groove. The lesser 

 tuberosity is rather small, when compared with that of Merycoidodon, but, as in that form, it terminates in a 

 short curved tubercle, so as to nearly enclose the bicipital groove. The anterior face near the proximal end is 

 broad and rugose, the radial face is smooth and even, the ulnar face is more convex antero-posteriorly, and the 

 posterior face is rapidly rounded, so that a cross-section of the shaft is triangular with the apex behind. The 

 deltoid ridge is heavy, extending well down upon the shaft, and terminating in a rough, prominent ridge. Below 

 the termination of the deltoid ridge the antero-posterior diameter of the shaft decreases rapidly, so that in cross- 

 section it would be more oval in outline at this point. . . . The intercondylar ridge is prominent and broad, but 

 the external division of the trochlea is smaller and not so deep as in Merycoidodon. The internal epicondyle is 

 also less prominent than in the latter genus, but the tuberosity on the internal side is large. . . . The anconeal 

 fossa is low and broad and there is no supratrochlear foramen. 



The radius and ulna are short and heavy but otherwise similar in construction to those of 

 Merycoidodon. The shaft of the radius is anteroposteriorly compressed and transversely expanded. 

 The scaphoid facet is oblique, strongly concave transversely, and rapidly flexed back high up upon 

 the radial angle of the bone. The lunar facet is subtriangular and saddle-shaped. The olecranon 

 is long and heavy and has no tendinal sulcus. The cuneiform facet is wide, somewhat laterally con- 

 cave, and anteroposteriorly compressed, with a convex surface. The moderately small pisiform 

 articular facet is confined mainly to the border near the external angle. 



Peterson compared the carpals with those of P. montanus, to which they are very similar. The 

 scaphoid lacks an articular facet for the trapezium. The lunar has no proximal facet for the cunei- 

 form or for the scaphoid. The facet for the magnum is somewhat convex. The pisiform is rela- 

 tively smaller than that of M. culbertsonii. The small nodular trapezium is without a facet for 

 Mc. II, and there is no facet for a pollex. The metacarpals are short, stout, and broad. Mc. V is 

 slightly shorter than Mc. II. The phalanges are short, depressed, and flattened, while the unguals 

 are very short and wide. The phalanges of the second digit are somewhat larger than those of the 

 fifth. 



The more important differences in the hind limb, in comparison with that of Merycoidodon, 

 are the proportionally shorter tibia and fibula and the posterior shifting of the pelvis on the vertebral 

 column. 



Except for its greater size, the pelvis closely resembles that of Merycoidodon in general shape 

 and proportions. The ilium has a slightly greater outward curve anteriorly. The deep acetabulum 



