CERVICAL VERTEBRA OF HESPERORNIS. 37 



The tubercle below the pre-zygapophysis begins in this vertebra to 

 assume the form of a true cliapophysis, or upper transverse process, but 

 presents no articular surface for a rib. The centrum is somewhat excavated 

 at the sides, and the excavation is bounded posteriorly by a rounded ridge. 

 The latter begins near the posterior end of the inferior surface, and runs 

 forward, upward and outward to the base of the cliapophysis, on the lower 

 part of which it is continued. Above this ridge, and behind the dia- 

 pophysis, there is a shallow fossa. 



This vertebra would be regarded by some anatomists as the last true 

 cervical. Its dimensions taken from three well preserved specimens of 

 Sesperornis regalis are given below : 



Measurements of the Fourteenth Vertebra. (No. 1207.) 



Length of centrum,. . 23.0 mm 



Least diameter of centrum, at base, 7.0 



Transverse diameters of anterior articulation of centrum. .. . 12.5-18.0 



Vertical diameters of anterior articulation of centrum, 1.0-1 1.5 



Trans verse diameters of posterior articulation of centrum, . - 11.0-15.0 



Vertical diameters of posterior articulation of centrum, . . 8.0-11.0 



Transverse diameter of vertebra, across pre-zygapophyses, _ . 58.0 



Transverse diameter of vertebra, across post-zygapopbyses, ._ 30.0 



Diameters of pre-zygapophyses, --- 12.0-11.0 



Diameters of post-zygapophyses, . _ . _ . . 11.0-11.0 



Length of floor of neural canal, 20.5 



Length of roof of neural canal, _ . 16.0 



Transverse diameter of neural canal, at anterior opening, 9.5 



Vertical diameter of neural canal, at anterior opening,.. 7.0 



Transverse diameter of neural canal, at posterior opening, . . 8.0 



Vertical diameter of neural canal, at posterior opening, 7.0 



Length of inferior descending processes, 17.0 



Measurements. (No. 1476.) 



Length of centrum, ...... 24.0' nm 



Least diameter of centrum, 8.0 



Vertical diameter of anterior articulation of centrum, 8.8 



Transverse diameters of posterior articulation of centrum, 10.5-15.0 



Vertical diameters of posterior articulation of centrum, _ 9.5-13.0 



Length of floor of neural canal, , 21.0 



Length of roof of neural canal, . .... 16.0 



Transverse diameter of neural canal, at anterior opening, 9.0 



Vertical diameter of neural canal, at anterior opening, S.O 



Transverse diameter of neural canal, at posterior opening, 9.0 



Vertical diameter of neural canal, at posterior opening, 8.0 



