OSTEOLOGY OF CARNIVOROUS DINOSAURS. 



59 



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articulated radius and ulna well out away from the body. The deltoid or radial 

 crest is strongly developed, as a short but high thin plate of bone, that is situated 

 on the anterior-external border immediately above the middle of the shaft. Viewed 

 from the front it renders the anterior surface deeply concave transversely (fig. 41). 

 Below this crest the shaft is constricted and angularly rounded in cross section. 

 The head is situated in about the middle of the proximal end with the articular 

 portion overhanging the posterior surface of the shaft. The radial and ulnar con- 

 dyles are well defined. Posteriorly they are separated by an unusually brOad but 

 shallow depression which continues somewhat upward on the shaft of the bone. 

 The articular ends of the humerus are rugosely roughened. A prominent rough- 

 ened oval shaped area on the postero- 

 external surface at the lower border of 

 the radial crest, probably represents the 

 point of insertion for the humero-radi- 

 alis muscle (pi. 6, figs. 2 and 4). The 

 measurements given, below were made 

 from the humerus of the right side, which 

 is the better preserved of the two : 



Measurements of humerus of Antrodemus valens. 



mm. 



Greatest length 310 



Greatest width of proximal end 118 



Greatest width of distal end 100 



Least diameter of shaft 38 



Ulna (it).— The ulna is expanded and 

 heavy proximally with a less expanded 

 distal end. It exceeds the radius in 

 length but is shorter than the humerus. 

 The proportion being as 1: :1.17. 



There is a heavy olecranon process (o. 

 fig. 42) that extends considerably above 

 the articular surface for the humerus. 

 The surface of this process is roughened 

 for muscular insertion. The olecranon 

 process is less well developed in Ceratosau- 

 rus nasicornis and appears to be entirely wanting on the ulna of Ornitholestes her- 

 manni, though robust in Ornithomimus . 



The articular surface for the humerus is comparatively narrow transversely, 

 with a shallow concave surface antero-posteriorly. The concavity on the proximal 

 end for the reception of the head of the radius is shallow. The shaft of the ulna is 

 slender, suboval in cross section, and in a distal direction, gradually expanding 

 into a moderately large end, the greatest diameter being antero-posteriorly. The 

 distal end is oblique to the longer axis of the bone, the surface of which looks down- 

 ward and forward in the articulated limb. On the inner anterior face of the distal 

 end, a prominent roughened protubrance presents a surface for union with the 

 radius. 



0.C. 



Fig. 41. — Right humerus op Antrodemus valens Leidy. 

 Cat. No. 4734, U.S.N. M. J nat. size. A, posterior view; 



B, ANTERIOR VIEW; ft. HEAD; T.C., RADIAL CREST; i.e.. INNER 

 condyle; O.C., OUTER CONDYLE. 



