88 The Bird 



no matter how much change has occurred in their 

 shape and size. Take, for instance, the shoulder-blades. 

 When a tiger crouches they are very conspicuous, and 

 whether we take a frog, a turtle, a lizard, an armadillo, 

 a mouse, or a horse, we may always be sure of finding a 

 scapula in the region where we have observed it in the 

 bird. This is an important fact, and one which makes 

 the identification of many bones an easy matter. 



Thigh-girdle 



The shoulder-girdle which we have just examined 

 was not joined to the back-bone, but only saddled on 

 the ribs, the scapula extending backward, just clearing 

 them. What kept it in place in the chicken's skeleton 

 was the fact that it was strongly attached to the sternum, 

 and this in turn joined to the back-bone by means of 

 the ribs. But the pelvic arch or thigh-girdle is very 

 different. If the entire framework of the bird is to be 

 supported on two legs, the point of attachment of these 

 limbs must be solidly fixed to the back-bone of the body. 



Although there are as many bones supporting the leg 

 or thigh as there are bracing the shoulder, we would 

 never know this from examining our chicken. As in 

 other places in a bird's skeleton, the bones six in this 

 case have fused together in one solid piece, and only 

 in very young birds are they separate.* 



The names of the bones composing the pelvic girdle, 

 or arch, are the ilium, ischium, and pubis. The easiest 



* They were separate also in Archcenpteryx. 



