THE VERTEBRAL COLUMN 



39 



VI R 1 1 URAL COLUMN 



The vertebral formula agrees with that of Triceratops in that there are 21 presacral and 10 

 sacral vertebrae. In Centrosaurus the number of caudals has been determined by Brown 10 to be 46. 

 The exact number is apparently unknown in Triceratops. Of the presacrals 7 have heretofore been 

 described as cervicals and 14 as dorsals. To this Brown takes exception, however, claiming 9 as 

 belonging to the cervical series and 12 to the dorsal. His arguments will be discussed later. 



Vertebral Formulae 



Cervicals Dorsals Sacrals Caudals Total 



Triceratofs 7-9 14-12 10 45 ? 76 



Centrosaurus 7-9 14-12 10 46 77 



Anchiceratop 7-9 14-12 10 38 67 



Brachyceratop 8 ? 14 ? 6 50 78 



Protoceratop 7? 13 7-8 45 72 



Chasmosaurus 7-9 14-12 10 45 76 



Pentaceratop 7-9 14-12 10 28+ 59 + 



Coalesced Cervicals 



(Fig. 7) 



Centrosaurus conforms with the rule in the Ceratopsia, in having the three anterior cervicals 

 coalesced into a single mass. Each of these vertebrae bears a neural arch and the second and third 



Fig. 7. — Anterior cervicals of Monoclonius (Centrosaurus) flexus, J4 natural size, a, anterior; f, posterior; as, spine 

 of axis; h, capitular facet; if, intervertebral foramen; p, posterior zygapophysis; r, rib; s, spine of third cervical; 

 /, tubercular facet. 



a spine which as in Triceratops is bent sharply backward. The axial and third spines, although fused 

 throughout, are distinctly defined in the distal half, and their summits are broadened transversely. 

 In the Yale Centrosaurus the neural arch of the atlas arises as a rather heavy plate a little 

 forward of the center; in Triceratops it is seemingly lighter and arises farther back. The upper 

 outline of the neural spines is lost, but the intervertebral foramen between the axis and the third 



10 Brown, B., 1917, p. 289. 



