122 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



In recent birds (figs. 56, 60) the pelvic bones are fused. The 

 ilium is greatly elongate and usually fused with the synsacrum (p. 

 59) ; ischium and pubis directed backward. The pubes, lying in the 

 position of the postpubes of the dinosaurs, never meet below except in 

 the ostriches. In the embryo (fig. 130), they are at first directed 



J^p 



Fig. 130. Fig. 131. 



Fig. 130. — Development of pelvis of chick, after Miss Johnson. A, chick of 6 days. 

 B, older; C, 20 days; cartilage dotted, bone white, o, acetabulum; i7, ilium; in, ischiadic 

 nerves; w, ischium; on, obturator nerve; p, pubis; pp, pectineal process. 



Fig. 131. — Pelvis of Galeopiihecus, after Leche. ah, acetabular bone; t, ischium; t7, 

 ilium; p, pubis; cartilage dotted. 



forward and only attain the final position later. A pectineal process 

 arises from the acetabular region and extends forward, simulating the 



dinosaur pubis. 



In the mammals, obturator fora- 

 men and ischio-pubic fenestra are 

 united, the opening being bounded 

 on the medial side by processes from 

 ischium and pubis. All three bones 

 may meet in the acetabulum, but 

 more often the extension of ilium and 

 ischium excludes the pubis from the 

 Left side of pelvis of fossa. A peculiarity is the common 

 occurrence of an additional bone (tig. 

 131, a6) in the formation of the 

 acetabulum (acetabular or cotyloid 

 bone). This lies between ilium and pubic bone and may 

 fuse with any of the elements. In marsupials and mono- 

 tremes the interpubic cartilage persists for some time, or through life, 

 but elsewhere it disappears and the elements unite by symphysis. 



-3 



Fig. 132 



duck-bill. Ornithorhynchus, a, ace- 

 tabulum; il, ilium; is, ischium; m, 

 marsupial bone; of, obturator fora- 

 men; p, OS pubis; 5^1;, sacral vertebra. 



