134 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



Jl 



Proceeding posteriorly the spinous processes of the caudals suffer a very rapid 

 reduction in their height (pi. 35, fig. 1), the twelfth being about one-fourth the height 

 of the first. Both the anterior and posterior borders of these processes are vertically 

 grooved, the bottoms of the grooves being roughened for the attachment of ligaments 

 (figs. 68 and 69) . The tops of all of the processes are squarely truncated, and without 



transverse thickening ex- 

 cept on the front and pos- 

 terior margins, the medi- 

 an portion presenting an 

 acutely edged border, es- 

 pecially pronounced in 

 this respect, posterior to 

 the eighth. 



The transverse proc- 

 esses are especially broad 

 anteroposteriorly and 

 placed well down on the 

 sides of the neural arch. 

 The first of the series are 

 slightly elevated above 

 the horizontal, but pro- 



Fig. 68.— First caudal vertebra of Ornithomimus sedens Marsh. Type, No. 4736 Ceedmg backward they 



U.S.N.M. J NAT. SIZE. A, VIEWED FRDM THE RIGHT SIDE; B, VIEWED FROM THE OTadUallV aSSUme ft llOri- 



ANTERIOR END; d, DIAPOPHYSIS; S, NEURAL SPINE; SU, SUTURE BETWEEN CENTRUM ■■•..-, 



AND SPINOUS PROCESS; Z, ANTERIOR ZYGAPOPHYSIS; z', POSTERIOR ZYGAPOPHYSIS. ZOntal, and finally Ul the 



most posterior ones are 

 depressed below the horizontal. Marsh has pointed out the diplosphenal 

 articulation of the caudal vertebrae and also that the first caudal bears a 

 chevron, the longest of the series, as in Orniihomimus altus. Osborn 1 describes 

 the chevron of the latter as "elongate and rod-like." The close resemblance 



Su- 



Fig. 69.— Caudal vertebrae 10, 11, and 12 of Ornithomimus sedens Marsh. Type, No. 4736, U.S.N.M. \ nat. size. A, 



VIEWED FROM THE RIGHT SIDE; B, TENTH CAUDAL VERTEBRA VIEWED FROM FRONT; d, DIAPOPHYSIS; S, NEURAL SPINE; 2, 

 ANTERIOR ZYGAPOPHYSIS; 2', POSTERIOR ZYGAPOPHYSIS. 10, 11, 12, CAUDALS 10, 11, and 12, RESPECTIVELY. 



of this chevron to the first of 0. sedens would indicate the above de- 

 scription not to be altogether accurate. None are especially elongate and cer- 

 tainly none are "rod-like," all being flattened transversely, and cimeter-like 

 in their general outline. The first, third, fourth, part of fifth, sixth, and 



Bull. Amer. Mus. Nat. Hiat., vol. 35, 1917, p. 748. 



