76 



A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



The third vertebra has the posterior zygapophyses more obliquely placed. 

 The spine is stout and short, somewhat diamond-shaped in section, with the edges 

 anteroposterior. The sides are very rugose and there is on each side a triangular 

 flap extending to the rear to increase the surface for the attachment of the nuchal 

 ligament. The transverse process is short and there is a very short face for the 

 tuberculum of the rib on its distal end. There is no face for the capitulum, though 

 there was a well-developed head on the rib; it must have been attached to the inter- 

 centrum. The lower edge of the transverse process is not free from the centrum, 

 but attached to it by a broad thin plate of bone, as is so characteristic for the whole 

 group. The centrum is round in section and there are no median or lateral keels 



on the surface. It is shorter be- 

 low than above, leaving a space 

 for the intercentrum. 



On the fourth cervical the 

 anterior zygapophyses are ob- 

 lique, but the posterior ones are 

 horizontal. The spine is shorter 

 and stouter than that of the 

 third. The transverse process 

 is wider, but still supports only 

 a single facet for the rib. On 

 the anterior edge of the centrum, 

 near the bottom, is a facet for 

 the capitulum of the rib. 



In the fifth the facet for the 

 capitulum is united with the one 

 on the transverse process by a very narrow ridge; this corresponds with the fact 

 that the capitulum and tuberculum are practically united in the rib. 



All the vertebrae of the presacral series have the strong hyposphene-hypantrum 

 articulation in addition to zygapophyses. This structure was first described by 

 Cope in the dinosaurian genus Amphicceltas as follows: 



"The anterior zygapophyses are separated by a deep fissure, while the posterior 

 zygapophyses are united on the middle line. From the latter, from the point of 

 junction, there descends a vertical plate which rapidly expands laterally, forming a 

 wed<*e whose base looks downward. The supero-lateral faces are flat, and articulate 

 with corresponding facets on the inferior side of the anterior zygapophyses, which 

 look downward and inward, on each side of the fissure above described. When in 

 relation, the anterior zygapophyses occupy a position between the posterior zyga- 

 pophyses above, and the hyposphene, as I have termed the inferior reversed wedge, 

 below. This arrangement accomplishes the purpose effected by the zygosphenal 

 articulation — that is, the strengthening of the articulation between the neural arches, 

 but in a different way. The additional articulation is placed at the opposite 

 extremity of the vertebra, and it is the anterior zygapophysis instead of the posterior 

 which is embraced." 



In the sixth the two facets on the transverse process are completely united and 

 the vertebra has taken on the character of a true dorsal. The wide, wing-like 

 transverse processes bear a single face which slopes downward and forward as well 

 as inward. The upper part of this facet is much broader in the anterior vertebra?, 

 but gradually decreases until in the mid-dorsals and posterior dorsals it is only at 

 the extreme upper end that this can be noticed. Throughout the series the rib 

 heads are not so long as the faces on the transverse processes; there was evidently 



Fig. 24. — Dorsal vertebra of Dtadictes sp. X J. No. 4840 Am. Mus. 

 a, anterior view; b, lateral view. 



