Peterson: The Osteology of Promerycoch(erus. 183 



is almost identical, so far as comparisons can be made, with that in 

 Mesoreodon chelonyx described and figured by Professor Scott (/. c, 

 p. 136, PI. IV, Fig. 34). In smaller species of Merycoidodon the spine 

 and the acromion process are apparently slightly smaller, but probably 

 supported a clavicle. It thus seems that at least in one family of the 

 Artiodactyla the clavicle persisted, and was represented until well 

 into the Miocene. 



The Humerus (Fig. 27). — The humerus is rather short and heavy, 

 the proximal and distal ends being expanded and the distal trochlea 

 quite oblong, somewhat as in the hippopotamus. The head is very 

 large, well rounded, but not so hemispherical as in Merycoidodon 

 culbertsoni. 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 bi- 

 cipital 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 termi- 

 nating 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 shaft is short and heavy in comparison with that of 

 Merycoidodon. 



As stated above, the distal end of the humerus is much expanded, 

 especially transversely, the diameter being proportionally even greater 

 than in Merycoidodon. 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 prom- 

 inent than in the latter genus, but the tuberosity on the internal side 

 is large, indicating liberal attachments for ligaments and muscles. 

 The anconeal fossa is low and broad and there is no supratrochlear 

 foramen. 



" In Agriochcerus latifrons the external division of the trochlea is even smaller 

 than in the species under consideration (Wortman, Bull. Amer. Mus. Nat. Hist., 

 Vol. VII, 1895. P- 154). 



