I2l6 CLASS AVES. 



over the greater part of the acetabulum, of which, as already men- 

 tioned, the centre is unossified, and has an external articular surface 

 for the great trochanter of the femur termed the antitrochanter. 

 The ischium forms the hinder half of the inferior part of the aceta- 

 bulum, and is a moderately broad bar of bone directed downwards 

 and backwards, or occasionally backwards (fig. 1112). In the 

 Carinatse (fig. 1102) it generally unites inferiorly with the ilium, by 

 which means the upper part of the ilio-ischiatic notch is converted 

 into a foramen; but in the Ratitae (figs. 1107, 1112) there is no 

 such union. In Rhea alone, among existing Birds, the ischia unite 

 in a ventral symphysis. The pubis is generally a long and slender 



Fig. 1107. — Left side of the pelvis of the Emeu {Drom&us). Reduced. z7, Ilium ; is, Ischium ; 

 /', Pubis ; /, Pectineal process of do. ; a, Acetabulum. (After Marsh.) 



bone running parallel to the ischium, and entering into the anterior 

 part of the lower border of the acetabulum ; it frequently gives off 

 a pectineal process (fig. 1107), which is apparently homologous with 

 the preacetabular process of the pubis of the Ornithopodous Dino- 

 sauria. The Ostrich (Struthio) is peculiar among living Birds in 

 having a symphysis pubis ; while in Archceopteryx alone are the three 

 pelvic bones separate. The femur is a short thick bone, with its 

 head placed at right angles to the shaft, as in certain Dinosauria. 

 Its condyles are large, and antero-posteriorly elongated. A patella 

 is frequently present, and may be double. The fibula is always im- 

 perfect distally, and may be completely anchylosed to the tibia. 

 The latter, or tibio-tarsus as it should be correctly termed, is a very 

 characteristic bone ; and is always longer than the femur. Proxi- 

 mally this bone is expanded and produced into an anterior cnemial 

 process, like that of the Dinosauria, which may extend above the 

 knee-joint; and the distal extremity (fig. 1108, a) has a trochlea- 

 like surface, and consists of the astragalus of the tarsus, which has 

 been completely fused with the tibia. On the anterior surface of 



