THE Yl'RTF.KRAL COLUMN 



45 



the upper part of the centrum. The zygapophyses arc confluent, the anterior pair forming a V-shapcd 

 surface which looks upward and somewhat backward. 1'hc posterior sulfates arc smaller and nearly 

 horizontal, with a slight division between the two halves, which look slightly outward as well as 

 downward. The diapophyses are broad fore and aft and flattened. The capitular facet, one-third of 

 the way out on the anterior border, is buttressed by the prezygapophysis. The tubercular facet is 



az 



Y\ G . 1 5. — Right lateral view of dorsal IX of Monoclones (Centrosaurus) nasicomus, J4 natural size, az, anterior zygapo- 

 physis; A, capitular facet; fz, posterior zygapophysis; s, neural spine; /, tubercular facet. 



terminal. The spinous process arises behind the pedicel so that its anterior edge is about over the 

 posterior margin of the neural arch. It is flattened and its antero-posterior diameter is nearly twice 

 that of the diapophyses. The thickness of each is about equal. A median ridge rises from the 

 neural canal to the junction of the zygapophyses. In this, as in the general form of the latter, the 

 offset to the rear of the base of the spinous process, and the depth of the lateral pleurocoeles, the 

 vertebra differs markedly from that of M. crassus figured by Hatcher. 19 



Measurements of Dorsal IX 



Centrum, length at top 71.0 mm. 



Centrum, width of anterior face 97.5 



Centrum, height of anterior face 7°. 5 



Width over diapophyses 244.0 



Width over capitular facets 114.4 



Length of spinous process 166.0 



Neural canal, height of anterior end 25.0 



Neural canal, width of anterior end 13.0 



10 Hatcher, Marsh, Lull, 1907, Fig. 79. 



