44 



THE CERATOPSIA 



a level with the zygapophysis at the base of the diapophysis. The latter is strong and well devel- 

 oped, and the spinous process is flat, narrow, but of considerable fore and aft extent, and slightly 

 expanded distally. The lateral aspect of the bone is peculiar as the entire complex of processes arises 

 above or behind the pedicels in marked contrast to any other Centrosaurus species. The zygapophyses 

 are large and strongly buttressed while the neural canal is much smaller than in cervical VIII, so 

 that behind the brachial enlargement the spinal cord was slender, in fact very slender for an animal 

 of this size. In Monoclontus crassus the equivalent vertebra is more erect and lacks the backward 

 offset and angulation of the processes. The zygapophyses are confluent as in M. crassus. The neural 

 arch is higher than in presacral VIII and is somewhat constricted above the neural canal. In its 

 anterior aspect the Yale vertebra resembles that of M. crassus but differs markedly when viewed from 

 the side. 



Measurements of Dorsal VI 



Height of centrum, anterior face 

 Width of centrum, anterior face 



Length of centrum 



Width across pedicels 



Vertical height over all 



Width across diapophyses 



Length of spinous process 



Neural canal height, anterior end 

 Neural canal width, anterior end 

 Length over zygapophyses 



(Figs. 14, 15) 



In this vertebra the centrum is somewhat wedge-shaped, when viewed from the side (possibly 

 due in part to crushing, although otherwise there is no evidence of it). The anterior face is nearly 

 plane (but the rim is partly eroded), the posterior face concave. Lateral pleurocoeles are present in 



Y.PM. 2015 



Fig. 14. — Dorsal IX of Monoclontus {Centrosaurus) flexus. Left lateral and anterior viaws, J4 natural size, az, 

 anterior zygapophysis; rl, diapophysis; h. capitular facet; n, neural canal; f, pleurocoele; fz, posterior zygapophysis; 

 s, neural spine; *, tubercular facet. 



1G Calculated from Hatcher's figure. 



17 Difference due in part to inclination of spinous process. 



18 Estimated length. 



