. Carnegie Institution of Washington publication. 108 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA Posterior to the axis the presacral vertebrae are very similar in form. They are of the same general type found in the Diadectidct and Pareiasauridce. The centrum is notochordal with wide funnels at the anterior and posterior ends; the lower line is shortened for the accommodation of intercentra. The neural arches are low and wide and swollen, so that the upper surface looks almost hemispherical. The spines are low and short, bifurcate in the anterior vertebrae, but more posteriorly, terminat-
. Carnegie Institution of Washington publication. 108 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA Posterior to the axis the presacral vertebrae are very similar in form. They are of the same general type found in the Diadectidct and Pareiasauridce. The centrum is notochordal with wide funnels at the anterior and posterior ends; the lower line is shortened for the accommodation of intercentra. The neural arches are low and wide and swollen, so that the upper surface looks almost hemispherical. The spines are low and short, bifurcate in the anterior vertebrae, but more posteriorly, terminat- ing bluntly as if they might have been attached to some dermal plate above. The zygapophyses are large and perfectly horizontal. There is no zygosphene or zygan- trum. The neural arch is coossified with the centrum. The transverse processes have elongate terminal faces for the single-head ribs; these are shorter than the rib heads, which were either attached to the intercentra directly or by cartilage. All the vertebrae were bound closely together by the wide overlapping of the zygapophyses and by strong ligaments lodged in a pit at the base of each neural spine behind. The transverse processes diminish in size in the posterior part of the series and the last four or five presacrals did not carry Fig. 47.—Labidosaurus. X §. a, dorsal vertebrae. 1, front view; 2, top view of same vertebra. b, rib of the anterior dorsal series. No. 4550 Am. Mus. c, shoulder girdle. CI, clavicle; 7c,interclavicle; Sep, scapula; Co, coracoid; Pe, procoracoid. After Williston. d, cervical and dorsal vertebra?. There are two sacral vertebrae which have more elevated and slender neural arches than the presacrals; they are not united into a sacrum. The caudal vertebra have more slender neural arches, resembling in this regard the sacrals rather than the presacrals. They diminish rapidly in size and are about seventeen in number (Broili). The ribs (fig. 47, b) have expanded pr
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