THE VERTEBRAL COLUMN 41 



az 



Fie. 8. — Cervicals V and VI, coalesced (pathologic), of Monoclonius (Centrosaurus) fiexus, ]4 natural size, az, anterior 

 zygapophysis ; h, capitular facet; fz, posterior zygapophysis; /, neural spine of 5th cervical; /, tubercular facet. 



Measurements of Cervicals 



Length of centrum 



Height of centrum 



Breadth of centrum 



Breadth over diapophyses 

 Height over all 



In this bone the pedicels are longer, so that the diapophyses are higher with relation to the 

 centrum. All of the cervicals are simple in form, with a rather large neural canal. 



Cervical VIII 



The eighth presacral vertebra, in the Ceratopsia, has always been designated the first dorsal, 

 because of the change here in the length and character of the rib. Brown, 14 however, has used a new 

 system for differentiating the cervical from the dorsal region, contending that " in the cervical series 

 throughout the Dinosauria the capitular facets are invariably located on the centra of the vertebrae, 

 the change from the cervical to the dorsal series being marked by the rise of this facet from the 

 centrum to the neural arch. In Monoclonius the last vertebra having a capitular facet on the centrum 



is the ninth." 



Cervical VIII still has a very large neural canal to accommodate the brachial enlargement of the 

 spinal cord. The canal here has nearly twice the diameter of that of vertebra XV. The centrum 

 of VIII is somewhat biconcave and comparatively short, with a flattened lower surface and deeply 

 constricted lateral ones. It corresponds fairly well with the "anterior dorsal" of M. crassus, figured 

 by Hatcher, 1 "' although the diapophyses are relatively longer and more slender, and the neural canal 

 larger. They are equally simple in construction, but the Yale specimen is lighter in build. 



u Length of the coossified mass. 



14 Brown, B., 1917, p. 288. 



15 Hatcher, Marsh, Lull, 1907, Fig. 80. 



