STRUCTURE AND RELATIONSHIPS OF OPISTHOC(ELIAN DINOSAURS. 237 
CAUDAL VERTEBR&. 
Two anterior caudal vertebre were found in close apposition 
with the posterior end of the sacrum. The first has been so dis- 
torted in a diagonal direction that the structure of its centrum and 
zygapophyses can scarcely be determined. The second (Figs. 1 and 2, 
Plate LXXV) has suffered less from distortion, and is otherwise 
fairly well preserved. The centra are in general amphiccelous. The 
anterior end of the first is concave in its lower half, but is so badly 
distorted that it does not show whether or not it had the character-. 
istic convexity usually found in the upper half of the first centrum. 
The posterior end is slightly concave, a feature which the crushing 
has tended to lessen. In the second caudal the anterior end is 
uniformly concave, the posterior end slightly more so. There is no 
trace of the lateral cavities found in almost all the opisthoccelians. 
It cannot be determined whether or not these vertebrez were chevron- 
bearing. 
The neural arches are massive, broad on the anterior surface, but 
drawn to a rounded angle about the posterior opening of the neural 
foramen. Laterally there are traces of a slight ridge leading down- 
ward from the prezygapophyses to the base of the transverse process. 
The zygapophyses are slight for a vertebra of such dimensions; 
the anterior pair has been pushed upward by compressure. The 
articular facets normally face inward and slightly upward. The 
posterior pair in the second caudal bears distinct. evidence of a 
hyposphene. 
The neural spines are characteristically simple. They are laterally 
compressed at the base and expanded at the crest into a roughened 
knob. The anterior and posterior margins bear the strong rugosities for 
interspinous ligamental attachments which persist throughout the 
vertebral series. 
The caudal ribs are equally simple. The capitular element is rep- 
resented by a stout process arising from the lateral surface of the 
centrum above the middle. It is vertically compressed and appar- 
ently expanded into a rounded end. No trace of the tubercular 
element is to be seen. 
