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 marvellous wings of a modern bird. In 
reptiles, this bone is divided into two weak, thin plates 
