DORSAL VERTEBRAE OF HESPERORNIS. 45 



Vertical diameters of posterior articulation of centrum, . 9.0-14.5 mm 



Transverse diameter of vertebra, across pre-zygapophyses, 29.0 



Transverse diameter of vertebra, across diapopbyses, _ , 63.0 



Transverse diameter of vertebra, across parapopbyses, 32.0 



Transverse diameter of vertebra, across post-zygapophyses, 2 7.0 



Diameters of pre-zygapopbyses, 9.5-1 1.0 



Diameters of post-zygapopbyses, 7.5- 9.0 



Length of floor of neural canal, 23.0 



Lengtb of roof of neural canal, 21.0 



Transverse diameter of neural canal, at posterior opening, 8.0 



Vertical diameter of neural canal, at posterior opening, 7.5 



Lengtb of bypapopbysis, 19.0 



Diameters of articulation for bead of rib, 7.5- 9.0 



The Eighteenth, or First Dorsal, Vertebra. (Plate V, figure 2.) 



The eighteenth vertebra is a little longer than the seventeenth, and 

 its centrum is stouter, and less excavated at the sides. The hypapophysis 

 descends vertically, is longer than the centrum, and bears an oblique un- 

 synimetrical expansion at the end. The articular face for the head of the 

 rib is a little more elevated than in the preceding vertebra, but no larger. 

 The rib supported by this vertebra is represented in Plate VIII, figure 4, 

 and the adjoining sternal rib, in figure 16. The diapophyses are much as 

 in that vertebra, and are preceded by a deep pit, extending beneath the 

 posterior part of the pre-zygapophysis. A much smaller excavation is 

 situated just behind the base of the diapophysis. The neural spine was 

 somewhat larger than in the preceding vertebra, but is broken off in the 

 specimen figured. (Plate V, figures 2, 2 c.) The post-zygapophyses are 

 a little more approximate than in the seventeenth vertebra. 



The size of the present vertebra and of its various parts in Hesperornis 

 regalis is given in detail below : 



Measurements of Eighteenth Vertebra. No. 1207.) 



Length of centrum, 22.0 mm 



Transverse diameters of anterior articulation of centrum, 1 17.0-26.0 



Vertical diameters of anterior articulation of centrum, 7.5-1 1.0 



Transverse diameter of posterior articulation of centrum, 13.0 



Vertical diameter of posterior articulation of centrum, 10.0 



Transverse diameter of vertebra, across pre-zygapopbyses, _ 25.0 



Transverse diameter of vertebra, across diapopbyses, 61.5 



