CERVICAL VERTEBRA OF HESPERORXIS, 21 



neural arch, and continued outward and backward. Between this ridge 

 and the neural spine, the surface of the vertebra is excavated posteriorly, 

 but the posterior edge of the neural arch is considerably thickened, and 

 rises in a ridge connecting the post-z}-gapophyses with the base of the 

 neural spine. Over the post-zygapophyses, this ridge is developed into a 

 projecting tubercle. The lateral foramen for the vertebral artery is small, 

 and over-arched by a strong bridge of bone, from which a short, stout, 

 obtuse pleurapophysis projects backward, and somewhat downward. The 

 floor of the foramen is continued as a groove for a short distance backward 

 upon the side of the vertebra, bounded below by a well developed nearly 

 horizontal ridge. A similar, but much smaller, ridge is seen above ; and, 

 over this, a slight ridge appears on some specimens, extending a little 

 farther back on the vertebra. 



The measurements given below show the principal dimensions of the 

 third cervical vertebra of Hesperornis regalis, in the type specimen, number 

 1200, and in two other skeletons : 



Measurements of Third Vertebra. (No. 1200.) 



Length of centrum, 22.5 mm 



Transverse diameter of anterior articulation of centrum, 9.0 



Vertical diameters of anterior articulation of centrum, 1 6.0- 8.0 



Transverse diameters of posterior articulation of centrum, 9.8- 8.2 



Vertical diameters of posterior articulation of centrum, T.0- 9.6 



Transverse diameter of vertebra, across pre-zygapophyses, 19.0 



Transverse diameter of vertebra, across lateral foramina, 20.0 



Transverse diameter of vertebra, across post-zygapophyses, 22.5-21.0 



Diameters of pre-zygapophyses,.- - 5.0- 9.0 



Diameters of post-zygapophyses, -.- .. 7.0-8.0 



Length of floor of neural canal, .. ' 22.0 



Length of roof of neural canal, 21.0 



Length of hypapophysis, 6.5 



Measurements. (No. 1206.) 

 Length of centrum, 24.0 mm 



Transverse diameter of anterior articulation of centrum,. 10.0 



Transverse diameters of posterior articulation of centrum, 9.0- 9.5 



Vertical diameters of posterior articulation of centrum, 6.0- 8.0 



1 Where two measurements of the same part are given together, as in this case, they 

 refer to the greatest and least dimensions of the portion named. 



