. Bulletin. Natural history. Text-fig. 47. A. Flexor aspect of humerus of Plotosaiirus tuckeri (after Camp, 1942, fig. 10, X i/i)- B. Same of humerus of Mosasaurus conodon (reconstructed after USNM 11904 and 18255, X %o)- Abbreviations for text-figs. 47-49: ect, ectepicondyle; eg. ectepicondylar groove; ent, entepicondyle; Id, scar tor M. latissimus dorsi; pc, pectoral crest; pgp, postglenoid pro- cess. are short and rounded and have distinct grooves for the coracoids. The costal margins are much longer and converge posteriorly. Each has facets for five sternal ribs. ." Much less well pre
. Bulletin. Natural history. Text-fig. 47. A. Flexor aspect of humerus of Plotosaiirus tuckeri (after Camp, 1942, fig. 10, X i/i)- B. Same of humerus of Mosasaurus conodon (reconstructed after USNM 11904 and 18255, X %o)- Abbreviations for text-figs. 47-49: ect, ectepicondyle; eg. ectepicondylar groove; ent, entepicondyle; Id, scar tor M. latissimus dorsi; pc, pectoral crest; pgp, postglenoid pro- cess. are short and rounded and have distinct grooves for the coracoids. The costal margins are much longer and converge posteriorly. Each has facets for five sternal ribs. ." Much less well preserved, but probably similar sterna also occur in M. conodon (Martin, 1953), Plotosaiirus tuckeri (Camp, 1942, p. 14), Plate- carpus (Williston, 1899, p. 40), Ectenosaurus clidastoides (FHM 7937) and Tylosaurus proriger (Osborn, 1899a, fig. 9). The sternal ribs are flattened, strap-like structures linking the anterior thoracic ribs to the sternum. As noted above, five such bands of cartilage are present on each side of the sternum of Clidastes. At least five pairs occur in Plate- carpus (see Huene, 1911, pi. 3) and Ectenosaurus (FHM 7937), and according to Osborn (1899a, p. 180) there are ten in Tylosaurus. Only three pair of sternal ribs occur in Varanus. The tracheal rings have been reported in two excellent skeletons taken from the Niobrara Chalk. Osborn (1899a, p. 181, fig. 8) noted that in Tylosaurus ". . the trachea extends from below the axis, is imfortimately destroyed as far back as the fifth rib, and diverges into two bronchi just behind the ; Similar tracheal structures were seen by Williston (1899, p. 39, pi. 12) in a specimen of Platccarpus. HUMERUS The humerus of Clidastes liodontus and C. propython is a rectangular bone, longer than wide, and expanded at both ends. The glenoid articulating surface has its longest dimension and is convex in a dorsoventral direction. A tuberosity for the M. deltoideus lies in front of the glenoid condyle and is
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