PELVIC ARCH 



119 



more oblique, sloping upwards and backwards from the aceta- 

 bulum. 



The pelvis of Crocodiles exhibits special characteristics and is 

 of particular interest, as in some points it resembles that of 

 certain extinct forms. The pubes, which have at first a trans- 

 verse position, become later directed forwards much more 

 markedly than in Chelonians and Lizards^ and thus the ischio- 

 pubic foramina (in which the obturator foramina are included) are 

 very wide, and are separated from one another by a fibrous cord 

 (Fig. 96). A symphysis, both of the pubis and ischium, is formed, 

 but the former is not present in the adult. The acetabulum is 

 perforated, and the pubis is separated from it by a cartilaginous 

 pars acetabular is, not represented in lower Vertebrates, formed 

 from the acetabular process of the ilium. The epipubis is- 

 possibly represented by a cartilaginous apophysis at the anterior 

 (distal) end of the pubis, but it never becomes ; separately 

 differentiated. 



The ilium becomes greatly broadened out in the antero- 

 posterior direction dorsally, where it is attached to the sacrum ; and 

 this is of special interest as a similar extension of the ilium 

 occurs still more markedly in Dinosaurians and Birds (Fig. 97). 



Birds. — The pelvis of Birds is chiefly characterised by the 

 relatively large development of the iliac region and by the position 

 of the delicate pubis, which in the course of development becomes 



Fig. 97.— Belyk of ApUn/x ausi/ralis. Lateral view. (After Marsh. ) 



il, ilium ; i-i, ischium ; ^J, spinous process from the pars acetabularis ; p^, pubis ; 



a, acetabulum. 



directed backwards, parallel to the ischium and post-acetabular 

 process of the ilium, and is often united with the ischium 



