The Framework of the Bird 89 



way to locate these is first to find the socket in which 

 fits the head of the thigh-bone. This is the deep cup- 

 shaped depression on each side, and all three bones join 

 in making the socket. The ilium lies along the back 

 and forms a sort of roof over the portion of the back- 

 bone in this region. If we look at the under side of this 

 bone, we may see the fused vertebrae more distinctly — 

 fourteen or fifteen of them. The two deep depressions 

 in which the kidneys of the bird were located are also 



Fig. 62. — Pelvic girdle of a bird. 



now visible. As the coracoid is the great pivot of the 

 wing, so the ilium helps most to bear the strain of hop- 

 ping and running. In the frog, which progresses by 

 hops or great leaps, the ilium is also largely developed; 

 indeed we can see it through the skin, thus giving the 

 broken-back appearance to that creature. 



Each side of the thigh-bone box is formed by the ischium, 

 which is closely fused with the ilium except in most of 

 the ostrich-like birds, the tinamous, and in reptiles, 

 where these bones are free throughout their entire length. 

 We can readily make out the pubis as a slender bar of 



