CERVICAL VERTEBRiE OF IIESPERORNIS. 31 



on a line with the posterior margin of the articular surface. The tubercles 

 at the posterior end of the lower surface are small, and scarcely noticeable. 

 The ridge above the arterial groove upon the side of the centrum is much 

 as in the eighth vertebra. The articular surfaces of the centrum are slightly 

 broader below than in the preceding vertebra. 



The ridge strengthening the posterior zygapophysis is well developed, 

 and rises into a tubercle above the zygapophysis. This tubercle is espe- 

 cially developed in number 1206. The neural spine extends over slightly 

 less of the neural arch than in the eighth vertebra, and probably was not 

 as high. The outline of the arch is evenly concave between the post- 

 zygapophyses, and not notched on the median line. The diapophysis is 

 developed about as in the eighth cervical. The pleurapophyses are longer 

 than in the preceding' vertebra. 



The dimensions of the ninth vertebra of Hesperomis regalis are shown 

 in the tables given below : 



Measurements of JSFinth Vertebra. (No. 1206.) 



Length of centrum, 32.5 m 



Transverse diameter of anterior articulation of centrum, . 16.8 



Transverse diameter of posterior articulation of centrum, 12.2 



Vertical diameter of posterior articulation of centrum, 7.0 



Transverse diameter of vertebra, across pre-zygapophyses, ... 30.0 



Transverse diameter of vertebra, across post-zygapophyses, 33.0 



Diameters of post-zygapophyses, 10.5- 8.0 



Length of floor of neural canal, 33.0 



Length of pleurapophysis, 31.0 



Length of free portion of pleurapophysis, 22.0 



Measurements. (No. 1207.) 



Length of centrum, .. 31.0" 



Least diameter of centrum, at base, 10.0 



Transverse diameters of anterior articulation of centrum,. 13.0-16.0 



Vertical diameters of anterior articulation of centrum, 8.0-13.0 



Transverse diameter of posterior articulation of centrum, 12.2 



Vertical diameter of posterior articulation of centrum, 7.0 



Transverse diameters of vertebra, across pre-zygapophyses, 27.0-34.0 



Transverse diameter of vertebra, across post-zygapophyses, — 31.0 



Greatest diameter of pre-zygapophysis, 10.5 



Least diameter of pre-zygapophysis, 8.0 



