SKELETON 



121 



meet at the acetabulum which is perforate in recent species. The 

 lower end of the ilium separates as a distinct bone (pars acetabularis). 

 The pelvis of the dinosaurs (fig. 129) has the same great extension 

 of the ilium forward and back as is seen in the birds, and a correspond- 

 ing increase of the sacrum (p. 59), the result of the partially upright 

 position. The ischia are greatly elongate and are directed backward, 

 being frequently united below. The pubic bones are remarkable in 

 being directed forward and downward and in having strong post- 



FiG. 129. — Pelvis and hind limb of Camplosaiirus, after Marsh. /, femur; /J, fibula; i7, 

 ilium; is, ischium; />, pubis; pp, postpubis; /, tibia; 7-/F, digits. 



pubic processes which are parallel to the ischium. Frequently the 

 ilium gives off an iliac spine near the acetabulum. 



The pterodactyls had the same elongate ilium as the dinosaurs, 

 the ischium being fused to it so as to exclude the pubis from the acet- 

 abulum, the latter^ being usually loosely articulated to the ischium 

 and meeting its fellow in the median line below. The pelvic opening 

 was very small. The pelvic bones of the ichthyosaurs were weak, 

 long and slender, and apparently were imbedded in the muscles. 



* This pubis is sometimes regarded as a prepubis, the ischium being called an ischio- 

 pubis. 



