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 the}' 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 ver}' 

 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 marvellous wings of a modern bird. In 

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



