OSTEOLOGY OF CARNIVOROUS DINOSAURS. 107 



Ilium (il.)— The ilium of Ceratosaurus, though of nearly the length of the 

 much larger Antrodemus ilium, is nearly a third narrower dorso-ventrally above 

 the acetabulum. It differs also in having a much narrower preacetabular notch. 

 The exact contours of the anterior and posterior ends of the ilium are unknown 

 at this time, both having been restored by Marsh as shown in figure 63. I am of 

 the opinion that the anterior end, instead of being rounded from above downward, 

 had a straight truncated outline following the lines of the Antrodemus ilium shown 

 in figure 2, plate 10. 



Both ilia are present and firmly attached to the sacrum, the right element 

 being the more complete. The bone as a whole has an inclination inward in its 

 upper part, this inclination being most pronounced posterior to the acetabulum. 

 The tops of the ilia do not rest against 

 the spinous processes of the sacrum, as 

 in Omithomimus along the center, but 



more closely resemble Tyrannosaurus, I'M'-- « s 



in being parallel to but removed from tiA/tlT #*^ -i^^ &&^ ^- " E * 5 *? 



them by 50 to 60 mm. of space, though nS ' 



flaring outward both front and back, /^ 



and thus rendering a considerable area m^^^^^^M^ 



of the bone concave from front to back. 

 The superior border when viewed from 

 the side (pi. 30) is considerably below 

 the tops of all the sacral spines, where- 

 as in Antrodemus, Ornitholestes, Gor- /ipp 

 gosaurus, and Omithomimus only the 

 posterior sacral processes project above. 

 The postacetabular portion is 

 strengthened on the inside by a strong, ^/ fflBk&«^ 

 inwardly turned flange, running ob- 

 liquely upward and backward from the FlG . 63 ._ PELVlS 0F C eratosa UEU nasicor™ marsh, type. 

 ischiac peduncle, which articulates with no. 4735, tj.s.n.m. j nat. size, viewed from the left 

 the posterior sacral vertebrae as shown s ™ KSH a } ' ACETABULUM = il >™™' is - ISCHIUM - *• PUBIS - < AFTER 

 in figure 1, plate 21. 



The iliac surface of the acetabulum is especially wide transversely, the outward 

 part being a thin shelf-like extension that comes to a sharp projecting edge. 



Measurements of the right ilium of Ceratosaurus nasicornis Marsh. 



mm. 



Greatest length (estimated) 650 



Height above middle of acetabulum 210 



Height above pubic peduncle 274 



Width of acetabular surface 95 



Length of pubic articulation 85 



Width of ischiac articulation 45 



Pubis (p.). — The pubes in Ceratosaurus are distinguished from those of all other 

 known Morrison and Upper Cretaceous Theropod dinosaurs by the presence of an 

 inclosed obturator foramen, such as is found in the Sauropodous dinosaurs and in 

 some of the Triassic Theropoda. The plate-like expansion of the ischial process of 



