. Report of the geological exploration of the fortieth parallel . Transverse (liamctor of anterior articulation of tenth caudal vertebra, ^ertieal diameter of anterior articulation, Height of neural spine above floor of neural canal, Diameter of vertebra, across transverse processes, Antero-posterior extent of neural spine, Antero-posterior diameter of transverse process, at base, Antero-posterior extent on median line of the parts preserved of tenth and following vertebra, Diameter of the part preserved of eleventh vertebra, across transverseprocesses, °° The l
. Report of the geological exploration of the fortieth parallel . Transverse (liamctor of anterior articulation of tenth caudal vertebra, ^ertieal diameter of anterior articulation, Height of neural spine above floor of neural canal, Diameter of vertebra, across transverse processes, Antero-posterior extent of neural spine, Antero-posterior diameter of transverse process, at base, Antero-posterior extent on median line of the parts preserved of tenth and following vertebra, Diameter of the part preserved of eleventh vertebra, across transverseprocesses, °° The last six or seven vertebra; in tlie tail of Hesperornis regalis wereso interlocked by the expanded transverse processes, as shown in figure 23,below, that very little lateral motion was possible. The ln*])apophyses,also, of the last two free candals, would restiict vertical flexuie materiallv,so that the end of the tail would move mainly as a whole. This wouldgive great power, siniilai- to that in the Beavers tail, or in the flexibleblade of an oai-. Fig. FlOITRB 23.—Caudal vertebra) of Ilesperomia regalis, Marsh; seen from above, in position; two-thirds naturalsize. a. anterior convex face of first ; h. transverse process of fifth caudal; c. transverse processuf eleventh cuudul, or middle vertebra of the pygostylu. CHAPTER VII. THE LEGS AND FEET OF UESPERORXIS.(Plates XIII-XX.) The posterior liuibs of Hesperornis regalis preseut an admirableexample of adaptive structiu-e. The means of locomotion were confinedentirely to these extremities, and the life of Hesperornis was probably morecompletely aquatic than that of any known bird. It may fairly be ques-tioned whether it could even be said to walk on land, although somemovement on shore was of course a necessity. Considering the posteriorlimb as a whole, it will be found a nearly perfect piece, of machinery forpropulsion through the water. Provision was made for a very powerfulbackward sti-oke, followed by a quick
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