32 ODONTOKNTTHES. 



Greatest diameter of post-zygapophysis, 12.0 mni 



Length of floor of neural canal, 31.5 



Length of roof of neural canal, 28.0 



Transverse diameter of neural canal, at anterior opening, 8.5 



Vertical diameter of neural canal, at anterior opening, 6.5 



Length of pleurapophysis, 31.0 



Length of free portion of pleurapophysis, . 20.0 



Diameter of pleurapophysis, at base, 9.0 



Vertical diameter of lateral foramen, 7.0 



Transverse diameter of lateral foramen, 5.5 



The Tenth Veetebea. (Plate IV, figure 1.) 

 The tenth vertebra is shorter and stouter than the ninth. The under 

 surface is perceptibly broader, and somewhat more deeply excavated in 

 front. The descending incurved processes, also, are longer than in the 

 ninth vertebra, but the tubercles at the posterior ends of the lateral ridges 

 are scarcely apparent. The ridge on the side of the centrum, above the 

 vertebrarterial groove, is very similar to the one on the last vertebra. The 

 neural spine is short, small, and low. The post-zygapophyses occupy a 

 slightly more anterior position in this vertebra than in the preceding ones, 

 a change that becomes more marked in the following vertebrae, where 

 the zygapophyses are brought nearer together, in order to facilitate the 

 dorsal flexure of the neck, near its base. The diapophysis is larger and 

 more prominent than in the ninth vertebra, and the pleurapophyses are 

 somewhat longer. 



The proportions of the tenth vertebra of Hesperornis regalis are fully 

 given in the accompanying measurements frorn two different specimens : 



Measurements of Tenth Vertebra. (No. 1206.) 



Length of centrum, . 32.0 mm 



Transverse diameters of anterior articulation of centrum, 12.0-17.5 



Vertical diameters of anterior articulation of centrum, _. 7.0-11.5 



Transverse diameters of posterior articulation of centrum, 12.0-16.0 



Vertical diameters of posterior articulation of centrum, 7.5-11.0 



Transverse diameter of vertebra, across pre-zygapophyses, . - _ 34.0 



Transverse diameter of vertebra, across post-zygapophyses, 32.0 



Greatest diameter of pre-zygapophysis, _ 14.5 



Least diameter of pre-zygapophysis, .. 8.0 



Length of floor of neural canal, . . 30.0 



Lensrth of roof of neural canal,.. _ 26.0 



