. Bulletin - United States National Museum. Science. 20 UNITED STATES NATIONAL MUSEUM BULLETIN 247. , r« I Figure 12.—Posterior view of third cervical and axis, USNM 11976, of Pelocetus calvertensis. Abbr.: tr., transverse process. Neither transverse process is perforated by the foramen transversaria, and no trace of this aperture is visible on the anterior face of this process; on the posterior face (fig. 12), however, close to the base on each process is a circular depression approximately 35 x 20 mm. in diameter which indicates the former course of the cervical extension of the thoracic ret
. Bulletin - United States National Museum. Science. 20 UNITED STATES NATIONAL MUSEUM BULLETIN 247. , r« I Figure 12.—Posterior view of third cervical and axis, USNM 11976, of Pelocetus calvertensis. Abbr.: tr., transverse process. Neither transverse process is perforated by the foramen transversaria, and no trace of this aperture is visible on the anterior face of this process; on the posterior face (fig. 12), however, close to the base on each process is a circular depression approximately 35 x 20 mm. in diameter which indicates the former course of the cervical extension of the thoracic retia mirabile. It seems possible that this foramen may have been closed during growth by the exostosis which has affected several vertebrae in the column. The neural arch is stout, measuring 70 mm. antero- posteriorly at the apex of the coalesced arch, but actually 43 mm. on each pedicle at the level of the floor of the neural canal. A sharp edged anteroposterior crest on the dorsal surface of the neural arch persists as a vestige of the neural spine. The dorsal surface of the centrum is depressed and the ventral surface is excavated shallowly on each side of the broad median longitudinal ridge. Third Cervical: In contrast to the axis, the third cervical (fig. 12) is less massively constructed even though the centrum is rather broad (140 mm.), but its anteroposterior diameter (34 mm.) is less. The concave posterior surface of the centrum has raised margins. A median antero- posterior ridge on the dorsal and ventral face of the centrum separate shallow depressions. The relatively slender pedi- cles (pi. 4, fig. 7) of the neural arch (anteroposterior di- ameter, 18-20 mm.) support rather short anterior zyga- pophyses which are fused with corresponding lateral sur- faces on the neural arch of the axis. The postzygaphyses are elongated, rodlike and project at least 10 mm. beyond the level of the hinder face of the centrum. The neural canal is slightly wider (68 mm. posteriorly) th
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