74 Description of the Bones of a new Fossil Animal. 



in the rhinoceros it is one third, in the elephant one fourth ; in 

 the Ruminantia, on the contrary, these crests are but slightly de- 

 veloped. The deltoid protuberances of this humerus are much 

 more strongly developed than those of the same bone in the me- 

 gatherium ; the internal protuberance is continued down the an- 

 terior surface of the shaft in a longitudinal crest, which is most 

 elevated at its lower extremity, or sixty inches above the elbow 

 joint. On the outer side of this elevation is a still bolder protu- 

 berance, whose free border curves outwards and backwards, and 

 which, being opposed inferiorly and posteriorly by the crest of 

 the external condyle, forms a groove or channel sufficiently capa- 

 cious to receive the arm of a man ; and running in a curve half 

 around the bone, from the posterior to the anterior surface of the 

 humerus, affords a lodgment for a large and powerful flexor mus- 

 cle of the fore-arm. A shallow trace of this groove is observable 

 in the humerus of the Megalonyx laqueatus, and is more forci- 

 bly developed in the chlamyphorus, (vid. Harlan's Medico-Phys- 

 ical Researches, p. 47.) The shaft of the humerus is slightly 

 concave posteriorly, and somewhat depressed in its antero-poste- 

 rior diameter. 



The radio-humeral articulating surface is peculiar, consisting 

 of two distinct facets, an exterior hemispherical head, projecting 

 one and a half inches below the internal articular face, which 

 is slightly concave in its transverse and convex in its antero-pos- 

 terior diameter, exacting a corresponding peculiarity in the artic- 

 ulating surface of the ulna, rendering the structure and arrange- 

 ment of this joint somewhat sui generis. There is a broad de- 

 pression just above the condyles posteriorly, to accommodate the 

 motions of the olecranon. The following are the dimensions of 

 this humerus : 



Total length of the bone, .... 



Greatest diameter of the shaft, 



Antero-posterior diameter of shaft, . 



Circumference of the shaft, .... 



Diameter of the superior head, 



Transverse diameter of the condyloid crests, . 



Long diameter of the head, .... 



Transverse diameter of the radio-humeral articula- 

 ting surfaces, ...... 6 



Vide Plate II, figs. 1 and 2 — vertical view of its head. 



