268 



VERTEBRATE SKELETON 



backwards in Pelycosaurs, forwards in many Therapsids, where it may be very 

 large. Pubis and ischium are usually plate-like; some are imperforate, some 

 have an obturator foramen in the pubis; in others it is merged in the fenestra. 

 Some have ischium and pubis suturally connected, sometimes the sutures are 

 obliterated. The acetabulum may be open or closed. 



ICHTHYOSAURiA, with the reduced use of the hind limbs, have a simplified 

 pelvis which has lost the connexion with the vertebral column and was embedded 

 in the muscles. All three bones apparently met in the acetabulum and are not 

 closely united with each other. All are 

 slender, the ilium directed downwards and 

 forwards, the ischium smaller than the pubis. 



Sauropterygia have a stronger pelvis, 

 the bones often loosely united. Some have 

 a long and slender ilium, others have it 

 large and stout and often fused with the 

 ischium, both bones being nearly flat. The 

 ventral elements remain largely cartilage, 

 the pubis being at least as large as the 

 ischium. Fenestra and obturator foramen 

 are united, the foramen sometimes being 

 indicated by a notch on the posterior border 

 of the pubis. Both pubis and ischium are 



Fig. 291. — Pelvis of Brontosaurus 

 (Marsh), a, acetabulum; il, ilium; is, 

 ischium; p, pubis. 



Fig. 292.- — Pelvis and hind leg of 

 Camptos'aurus (Marsh). /, femur; fb, 

 fibula; il, ilium; p, pubis; />/>, >post- 

 pubis; t, tibia; I-IV, digits. 



thickened near the acetabulum of which they form a part. Pubes and ischia 

 of the two sides either meet directlj' or with cartilage between them. 



DiNOSAURiA have all three bones meeting in the usually perforate acetab- 

 ulum. The long ilium is connected with the sacral and synsacral vertebrae, 

 the synsacrum containing a number of bones correlated to some extent with the 

 character of locomotion. The ventral bones differ in the two sub-orders. In 

 both there is no prepubis, the ischium is long and slender. Saurischia (figure 2qi . 

 closest to other reptiles) have a triradiate pelvis; pubes and ischia have a ventral 

 (often long) symphysis, and in some the pubis, directed forwards, has a small 

 preacetabular process and no postpubis. The ischium is long and slender. 



