The ilium in dinosaurs and birds. Bulletin of the AMNH ; v. 48, article 5.

Abstract

"One. The saurischian pars preacetabularis ilii is an extension of the external iliac surface. 2. The ornithischian pars preacetabularis is an exaggeration of the anterior iliac spine. 3. The bird pars preacetabularis may have been derived for that of the Ornithischia by a movement medially and the building up of a surface ventral to the original process. 4. The saurischian pars preacetabularis passed dorsal to the pubo-ischio-femoralis internus. That of the Ornithischia did so primitively but later picked up a portion of its origin. In the birds the entire origin of the muscle is from the pars preacetabularis, which is now medial to the muscle, in strong contrast to the saurischian process, which is lateral to it"--P. 144-145.