DORSAL VERTEBRiE OF HESPERORXIS. 49 



Its articular faces are perceptibly larger. The hypapophysis is shorter 

 and weaker, and the parapophyses are higher on the side of the 

 vertebra, than in the last. The diapophyses point directly outward, and 

 somewhat upward. They are thin, and scarcely grooved in front, and 

 there is only a rudimentary pit at the base, but behind, there is a more 

 pronounced depression. In number 1476, there is a pit on one side, and 

 none on the other. The neural spine begins to increase slightly in height 

 in this vertebra. Its base is broad, and it expands but little antero- 

 posteriorly toward the top. The fossa at its base behind is large, and 

 most of its anterior border is decidedly roughened for ligamentary 

 attachment. The centrum of this vertebra is constricted, and has a 

 medullary cavity, as shown in the figure below. 



Figtbe 13. — Transverse vertical section of twentieth vertebra; (No. 1471). Front view; natural size. 

 d. diapophysis ; c. outline of posterior end of centrum; m. medullary cavity; nc. neural canal; s. neural 

 spine ; z'. outline of post-zygapophysis. 



The dimensions of two well preserved examples of the twentieth 

 vertebra in Hesperornis regalis are as follows : 



Measurements of Twentieth Vertebra. (Ho. 1207.) 



Length of centrum, 24.5 mm 



Transverse diameters of anterior articulation of centrum, 1 7.0-25.0 



Vertical diameters of anterior articulation of centrum, 10.0-12.5 



Transverse diameters of posterior articulation of centrum, 14.0-21.5 



Vertical diameters of posterior articulation of centrum, 11.5-15.2 



Transverse diameter of vertebra, across pre-zygapophyses, 20.0 



Transverse diameter of vertebra, across diapophyses, 61.0 



1 



