CERVICAL VERTEBRiE OF HESPEROROTS. 43 



Diameters of post-zygapophyses, _ _ _■ 9.0-11.0 mm 



Length of floor of neural canal, 22.0 



Length of hypapophysis, 18.0 



Diameters of articulation for head of rib, 7.0- 9.0 



The Seventeenth Vertebra. (Plate V, figure 1.) 



The seventeenth vertebra, the last true cervical, is slightly longer than 

 the sixteenth, and has assumed the more general characters of the dorsal 

 vertebrae. The excavations at the sides of the centrum are rather less 

 pronounced than in the preceding vertebra. The hypapophysis is strong, 

 directed vertically downward, and is expanded at its distal end, as shown 

 in the figure below. 



Fro. 12. 



Figure 12. — Seventeenth vertebra of Eesperornis regcUis, Marsh ; (No. 1417), posterior view ; natural size. 



The posterior articulation of the centrum has a greater vertical extent 

 than in the sixteenth vertebra. The articular surface for the head of the 

 nb is larger, and a little more elevated, but not more prominent than in 

 that vertebra. The diapophyses are directed somewhat upward, and 

 supported beneath by a strong rounded ridge, above which as in the 

 preceding vertebra, is a groove, ending in a deep pit below the pre-zyga- 

 pophysis. The neural spine has a somewhat greater antero-posterior 

 extent, and is higher than in the last vertebra. It is thickened and 

 truncated at the top, as in the succeeding vertebrae. The posterior 

 zygapophyses are less prominent, and nearer together, than in the 

 sixteenth vertebra. 



