. Bulletin - United States National Museum. Science. A NEW WHALEBONE WHALE 23. Figure 13.—Anterior view of third dorsal, USNM 11976, of Pelocetus calvertensis. Abbr.: tr., transverse process. Third Dorsal: This dorsal (pi. 5, fig. 2) is notably larger and more massive than the second dorsal. A marked increase occurs in the dimensions of the diapophysis which projects outward and is inclined obliquely forward, its dorsal profile sloping to the extremity. The thickened basal portion of the right diapophysis (fig. 13) likewise arises from the transversely broadened pedicle (right, width 54 mm.) o
. Bulletin - United States National Museum. Science. A NEW WHALEBONE WHALE 23. Figure 13.—Anterior view of third dorsal, USNM 11976, of Pelocetus calvertensis. Abbr.: tr., transverse process. Third Dorsal: This dorsal (pi. 5, fig. 2) is notably larger and more massive than the second dorsal. A marked increase occurs in the dimensions of the diapophysis which projects outward and is inclined obliquely forward, its dorsal profile sloping to the extremity. The thickened basal portion of the right diapophysis (fig. 13) likewise arises from the transversely broadened pedicle (right, width 54 mm.) of the neural arch and the dorsoexternal angle of the centrum. The concave articular facet (length, 50 mm.) on the extremity of the diapophysis for reception of the tuberculum of the rib is elongated and is directed obliquely from above and in front downward and back- ward. The distance between the ends of the opposite diapophyses is 292 mm. The left pedicle of the neural arch measures 35 mm. anteroposteriorly at its base. The elongated prezygapophysial facet (pi. 6, fig. 3) is deeply concave in an anteroposterior direction, shallowly concave from side to side, and slopes obliquely inward and down- ward from its outer margin. The left metapophysis is a bluntly pointed anterior projection. The neural canal near its floor measures 75 mm. transversely. The antero- posterior increase in the thickness of the centrum (58 mm.) is proportionately greater than the increase in its transvese diameter anteriorly. The flattened facet (pi. 6, fig. 8) for the capitulum of the fourth rib is flush with the posterior face of the lateral surface of the centrum. Fourth Dorsal: A less noticeable increase in the thickness (67 mm.) of the centrum (pi. 6, fig. 4) of the fourth dorsal (USNM 11976) is observable and but very little if any change in the dorsoventral diameter (82 mm.) of the cen- trum anteriorly. The most marked change is seen in the shortening of the robust diapophysis (fig. 14) which i
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