CERVICAL VERTEBRAE OF IIESPERORXIS. 19 



may have existed here, completing the foramen. In the succeeding 

 cervical vertebra?, this foramen is well developed, and may conveniently 

 be termed the lateral foramen. It is formed by the diapophysis above and 

 the parapophysis below, and closed externally by their union with the 

 intervening pleurapophysis. In life, this aperture probably protected both 

 the vertebral artery and y-ein, and the main trunk of the sympathetic 

 nerve, as in most recent birds. A hypapophysis extending over about the 

 posterior half of the centrum is indicated, but is not preserved. The 

 posterior articular surface is nearly square in outline, with rounded comers. 

 It is only slightly oblique, the lower portion projecting but little beyond 

 the upper margin. As in ordinary birds, it is distinctly concave vertically, 

 and convex transversely. 



The neural arch was surmounted by a well developed neural spine, 

 which is broken off in the present specimen. The pre-zygapophyses are 

 small, oval, convex facets, slightly raised above the surrounding bone, and 

 looking outward and upward at an angle of about 45°. The post- 

 zygapophyses are much larger. They are concave, and look nearly 

 directly downward. The neural canal is somewhat depressed, perhaps in 

 part by crashing. The post-zygapophyses extend within about two milli- 

 meters of the posterior articular surface of the centrum. They are 

 strongly supported above by a ridge arising upon the side of the neural 

 arch, and running outward and backward over the post-zygapophyses. 

 No vascular or pneumatic foramina are visible upon this vertebra. 



This description of the axis of Hesperomis regalis is derived mainly 

 from the specimen, number 1207, in which the series of presacral vertebra? 

 is nearly complete. The following measiu'ements are taken from the same 

 vertebra : 



Measurements of Axis. (Xo. 1207.) 



Length of centrum, including odontoid process, 29.0 mm 



Length of centrum, , 21.0 



Least transverse diameter of centrum (approximate), 2.0 



Length of odontoid process, 8.0 



Transverse diameter of odontoid process, at base, - 7.2 



Vertical diameter of odontoid process, at hase. 4.0 



Transverse diameter of anterior articulation of centrum. 13.0 



