48 



BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



from the first to the fifth, the latter equaling the length of the twentieth of the 

 series, and in this diameter exceeding all others. 



The first two or three centra might be called platyccelian, though they soon 

 pass into the biconcave type, which continues throughout the dorsal series. The 



median cervicals have a much deeper concave 

 posterior end than the anterior end, but back of the 

 eighth the concavities of these ends become about 

 subequal. 



Viewed from below the ends are expanded, the 

 sides of the centra are pinched together, thus 

 making them concave longitudinally, with a strong 

 angular keel which widens at either end (fig. 16), 

 more especially the anterior, which is roughened 

 by coarse longitudinal striae. Proceeding toward 

 the dorsals the keel becomes progressively less 

 and less conspicuous. 



All of the cervicals have capitular facets on the 

 sides near the anterior end, as shown in figures 15 and 17, p. Well-developed dia- 

 pophyses extend outward from the sides of the neur apophyses. These have 

 heavy, expanded, articular ends, which look more downward than outward. The 

 diapophyses gradually increase in length proceeding posteriorly. On the side of 

 the centra near the posterior end, on a level with the parapophyses, is a roughened 



Pig. 15. — Median cervical vertebra of 

 Stegosaurus ungulatus Marsh. J Nat. 

 size, a, Side vtew. b, Same vertebra, 



FRONT VIEW, d, DiAPOPHYSIS; 71, NEURAL 



canal; p, parapophysis; s, neural spine; z, 



ANTERIOR ZYGAPOPHYSIS; Z', POSTERIOR zyga- 

 pophysis. After Marsh. 



Fig. 16. — Articulated cervical vertebrae of Stegosaurus stenops Marsh. Cat. no. 4934, U. S.N. M. Type, i Nat. 

 size. Inferior view, a, Atlas; ax, axis; 6, articular facet for cervical ribs; &,c', c 5 , c 6 , cervicals three to six; 

 p, parapophyses; r', left cervical rib to atlas; t" , left cervical Ri3 to axis; r, articulated cervical ribs belong- 

 ing to the fifth and sixth cervical vertebrae; z', posterior zygapophyses. 



protuberance which probably indicates the point of insertion of ligaments. 

 These projections are especially pronounced on the cervicals of the posterior half 

 of the neck. The neural canal remains large throughout the cervicals, changing 

 from a pear-shaped outline in the anterior ones to nearly circular openings in the 

 posterior members 



