CERVICAL VERTEBRAE OF HESPERORXIS. 41 



is sub-oval in outline, with the long axis nearly vertical. The para- 

 pophysis supporting it is less prominent than in the fifteenth vertebra, and 

 does not extend in front of, nor below, the anterior articulation of the 

 centrum. The diapophyses are well developed, and somewhat ascending 

 (Plate IV, figure 7, b). They are flattened above, and strengthened by a 

 rounded ridge below. This ridge is united with the posterior portion of 

 the diapophysis, but anteriorly they are separated by a rounded groove, 

 which is shallow distally, but continues proximally into a deep excavation 

 under the anterior zygapophysis. 



The neural spine is well developed, and tubercular at the top, as in the 

 succeeding vertebra, but of less antero-posterior extent. It is irregularly 

 excavated at the base posteriorly by a fossa for the attachment of a liga- 

 ment. The post-zygapophyses are less projecting, and somewhat nearer 

 together than in the preceding vertebra. 



The posterior aspect of the sixteenth vertebra is well represented in 

 the following figure : 



Figcee 11. — Sixteenth vertebra of Hesperornis regalis, Marsh; (No. 1477), posterior view; natural size. rf. 

 diapophysis; p. parapophysis ; h. hypapophysis ; nc. neural canal ; s. neural spine ; z. pre-zygapophysis ; 

 z". post-zygapophysis. 



Full measurements of three specimens of the sixteenth vertebra of 

 Hesperornis regalis will be found in the following tables : 

 6 



