84 The Bird 



ture is in external appearance from a bird. Their keels 

 and sternums are very much alike. This is called par- 

 allelism, and sometimes it gives a great deal of trouble 

 to naturalists when they are trying to find the right 

 relationships between living animals. 



Shoulder-girdle 



It will be remembered that mention was made of the 

 trios of bones which radiate near the juncture with the 

 body, of each wing and each leg, — girdles or arches they 

 are called. The pectoral, or shoulder, girdle meets the 

 upper arm-bone of each wing at the shoulder-joint. If 

 we run our hand along the back of our shoulders, we 

 will feel a prominent bone, called the shoulder-blade, and 

 in almost the same place in our chicken we notice a very 

 long and thin bone. This is the scapula, and is one of 

 the pectoral-girdle trio, the other two being known as 

 coracoid and clavicle. 



The coracoid is a short, but stout, column of bone 

 joined to the shoulder-blade and extending down and 

 backward to the breast-bone. This coracoid bone is 

 especially developed in birds as compared with other 

 creatures. When their forefathers began to scale through 

 the air, thus putting a great strain on the muscles of 

 the breast, '^Nature seized on these coracoid bones, giving 

 them such strength and thickness that they have become 

 the pivots upon which, at each swift vibration through 

 the air, turn the mar\'e]lous wings of a modern bird. In 

 reptiles, this bone is divided into two weak, thin plates 



