OSTEOLOGY OF THE AEMOEED DINOSATJRIA. 



49 



The prezygapopliyses are wide apart and considerably raised above the 

 diapophyses in the anterior vertebrae, but brought more to their level in the posterior 

 cervicals. 



Neural spines are not 

 present, except in the most 

 posterior cervicals, although 

 there is a weak, median, crest- 

 like ridge, which eventually 

 develops into a true spinous 

 process. On account of the 

 damaged condition of these 

 processes I am unable to 

 determine the first vertebrae 

 having such a process. 



Dorsally the neural arch 

 consists of a broad, trans- 

 versely rounded surface 

 which extends upward and 

 backward, the posterior 



Fig. 17. — Posterior cervical vertebra op Stegosaurus ungulatus? 

 Marsh. Cat. no. 7348, U.S.N.M. J Nat. size. 1, Side view. 2, Oblique 

 front view, d, Diapophysis; n, neural canal; p, parapophysis; s, neu- 

 ral spine; z, anterior zygapophtsis; z' ', posterior zygapophysis. 



termination giving off the divergent branches of the post-zygapophyses. The 



height of the arch gradually increases posteriorly. 



Dorsal vertebrae (presacrals 11 to 26). 1 — The dorsal vertebrae of Stegosaurus are 



characterized by the great height of the neural arch and the upward thrust of the 



2 transverse processes. The 



centra of the posterior half of 

 the vertebral column are trans- 

 versely compressed, being shal- 

 lowly concave antero-poste- 

 riorly and somewhat flattened 

 vertically. All of the vertebrae 

 are without lateral cavities. 

 In the anterior dorsals the 

 depth of the concave articular 

 ends of the centra exceeds that 

 of the posterior ends, but pos- 

 terior to the median dorsal 

 region the two ends are sub- 

 equal in this respect. 



In the table of measure- 

 ments on page 53 it will be 

 observed that the centra grad- 

 ually increase in length from 

 the thirteenth to the twentieth, 



the latter being the longest of the entire vertebral series in No. 4934. From this 



point posteriorly they gradually decrease in length to the sacrum. 



1 All through the text and legends to the illustrations, the presacrals are numbered from the skull toward the sacrum, and 

 not from the sacrum forward as is the usual procedure in referring to the vertebrae as presacrals. 



Fig. 18. — Anterior dorsal vertebra of Stegosaurus sp. Cat. no. 6531, 

 U.S.N.M. J Nat. size. 1, Side view. 2, Front view, d, Diapophysis; 

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

 zygapophysis; z', posterior zygapophysis. 



