CEEVICAL VERTEBRAE OF HESPERORNIS. 33 



Measurements. (No. 1207.) 



Length of centrum,.. . .-.--.- 30.0 mm 



Least diameter of centrum, at base, . _ . .. __ . . 10.0 



Transverse diameters of anterior articulation of centrum, 13.0-15.5 



Vertical diameters of anterior articulation of centrum, 6.5-1 1.0 



Transverse diameters of posterior articulation of centrum,. 11.0-15.0 



Vertical diameter of posterior articulation of centrum, 8.0' 



Transverse diameter of vertebra, across pre-zygapophyses, . . . - _ . 36.0 



Transverse diameter of vertebra, across post-zygapophyses, . . 32.0 



Greatest diameter of pre-zygapophyses, . . 12.0 



Least diameter of pre-zygapophyses, . . r 8.0 



Greatest diameter of post-zygapophyses, 13.0 



Least diameter of post-zygapophyses, 8.0 



Length of floor of neural canal, ----- - - 29.0 



Length of roof of neural canal, _____..__ 23.0 



Transverse diameter of neural canal, at anterior opening,.. 9.0 



Vertical diameter of neural canal, at anterior opening, 5.5 



Length of pleurapophysis, . 33.0 



Length of free portion of pleurapophysis, 23.0 



Diameter of pleurapophysis, at base,.. 7.5 



Transverse diameter of lateral foramen, __ 5.5 



Vertical diameter of lateral foramen, 8.0 



The Eleventh Vertebra. (Plate IV, figure 2.) 



The eleventh vertebra is shorter than the tenth, and appears much 

 shorter when seen from above, owing to the approach of the zygapophyses 

 toward each other, to aid in the flexure of the neck. Its inferior surface 

 is slightly less excavated than in the preceding vertebra, and the anterior 

 descending processes occupy a more anterior position. The diapophysis 

 is here developed into a prominent, tubercular, oblique ridge, running 

 backward, downward and outward, and forming the antero-lateral margin 

 of the vertebral outline, as seen from above. The neural spine is short, 

 and small. The ridge running from the side of the vertebra to the post- 

 zygajjophysis rises into a prominent tubercle on each side of the upper 

 surface of the vertebra. The post-zygapophyses are more oblique, and 

 the pleurapophyses rather shorter than in the preceding vertebra. 



The size and proportions of the eleventh vertebra of Hesperomis 

 regalis are given in the measurements below : 



