MORPHOLOGICAL REVISION OF THE SUBORDER. 



125 



it is seen that in order to make the facets in the chevrons fit the centrum, the chevron 

 must be turned very sharply to the rear. Just below the proximal end the chevron is 

 pierced by an elongate foramen (plate 21, fig. 9). 



The method of rib articulation: In the cervicals the head of the rib articulates 

 with a distinct process on the side of the intercentrum. The capitulum and tuber- 

 culum are widely separated; the ribs are short and not greatly curved. In the 

 anterior dorsal region the head passes in between the two adjacent centra and touches 

 the head of the intercentrum, but there is no articular face on the intercentrum, so it 

 is probable that the head of the rib was united to it by cartilage. The transverse 

 processes on the dorsals are short and grow shorter towards the rear, so that the 

 capitulum and tuberculum of the rib grow farther apart. In the posterior dorsals the 



transverse process is very short and stands out 

 I — ta-b — V^ ^'^ifA almost straight from the neural arch ; the capitu- 



lum and tuberculum are here farthest apart and 

 in a nearly vertical line. In the first lumbar the 

 head of the rib leaps suddenly from the notch 

 between the vertebrae and the end of the inter- 



— capit — \ j centrum to the articular face which appears on 



51 '^ b the edge of the centrum ; the head of the rib still 



capit 



Fig. 51. — The head of a rib from the anterior lumbar region of D. giganhomogenes. No. 1 12 University of Chicago, cafit, 



capitulum; tub, tuberculum; rt, anterior view ; 6, lateral view. 

 Fig. 52. — A mid- lumbar of the same specimen as fig. 51. a, lateral view ; ^, anterior view. Showing both rib articulation 



and intercentrum. itc, intercentrum ; cap!!, capitulum of rib ; tub, tuberculum of rib. 

 Fig. 53. — A posterior lumbar of the same specimen as fig. 51. a, lateral view ; b, anterior view. Lettering as in fig. 52. 



projects somewhat beyond the anterior edge of the centrum and retains its cartilaginous 

 connection with the intercentrum. In the posterior lumbars the change is progres- 

 sive, the transverse process shortens rapidly until it becomes a mere facet on the side 

 of the centrum and neural arch ; at the same time the facet on the edge of the centrum 

 enlarges. The capitulum and tuberculum enlarge, with the facets approaching each 

 other, until on the third or fourth presacral they unite into one, and the rib is reduced 

 to a slender process with a wide proximal end. At first the tuberculum and capitulum 

 lie at right angles to each other on the lumbars, and this continues until they are 

 fused. The space between the capitulum and the tuberculum is continued as a fora- 

 men as far back as the third or fourth presacral. 



The right side of t\\G. pelvis is almost perfectly preserved (plate 21, figs. 9 and 10). 

 The three bones are united by close sutures. All the bones are very thin except the 

 region of the acetabulum and the upper edge of the pubis, which is rounded and 

 thickened. The symphysis is very shallow, i. e., the bones of the two sides did not 



