OSTEOLOGY OF CAENIVOEOUS DINOSAURS. 



65 



Plate 13. 



The pelvis of Antrodemus comprises the ilium, ischium, and pubis. These 

 articulate to form the acetabulum. In very old individuals these bones are some- 

 times found coossified, especially the ilium and pubis, a condition that also obtains 

 in certain members of the Sauropoda. The most striking featm-e of the pelvis is 

 the union of the distal ends of the pubes to form a triangular foot-like end, on 

 which it is thought the animal rested its weight when assuming a squatting postm-e. 



nium (il.). — In general form the ilium resembles that of other members of the 

 Theropoda. In the present skeleton the right ilium was found attached to the 

 sacrum. The left ilium was 

 detached but not far removed 

 from the sacrum and the other 

 pelvic elements, and is the 

 most perfect of the pair. In 

 figure 2, plate 10, is sho\\Ti a 

 lateral view of the left ilium 

 which for the first time gives 

 the correct contour of the 

 anterior end. Upon investi- 

 gation it is found that all of 

 the figures previously pub- 

 lished of tliis bone are in- 

 correct. The greatest dis- 

 crepancy observed is in the 

 contom* of the anterior end, 

 compare figure 2, plate 10, 

 with figure 46, for instead of 

 having a convex border from 

 above downward, it presents 

 an irregular but truncated 

 end, resembling somewhat the 

 ilium of Tyrannosaurus. 



In the Dinosaurs of North 

 America (pis. 10 and 11) 

 Marsh figures the left side of the pelvis of this same individual, but since the left 

 ilium was only recently removed from its sandstone bed it is to be inferred that 

 the reversed figure of the right was used in making* the illustration. A recent 

 examination of this bone shows that the anterior border is incomplete, though it 

 is not so indicated in the figures, and this fact will account for the inaccuracy of 

 previously published illustrations, one of which is shown in figure 46. 



The ilium has the same elongate form, with a general contour similar to the 

 ilia of Ceratosaurus and Tyrannosaurus. The superior border is gently convex 

 toward the anterior end, and but little expanded transversely. Above the pubic 

 peduncle tliis border is 15 mm. wide, but near the posterior end it increases to 30 



Fig. 46.— Pelvis of Antrodemus valens Leidy. No. 4734, U.S.N.M. ■}, 

 NAT. SIZE. Lateral view, o, acetabuhjm; i7, ilium; is, ischium; p, pubis 



ANTERIOR END OF ILIUM INCORRECTLY RESTORED. (AFTER MARSH.) 



