70 THE FLIGHT OF BIRDS 
slopes more outward in strong than in weak flyers, 
and, as a rule, more inMig birds than in small. At 
the shoulder-joint the coracoid is met by two other 
bones, the clavicle or merrythought (which varies 
much in make and strength), and the scapula or 
shoulder-blade, and the three bones together form a 
first-rate pivot, so that the strong wing-beats do not 
shatter the bird’s framework. 
Fia. 20. 
Clavicle of (1) Tern; (2) Eagle. Drawn to scale. 
Muscles and Quality of Muscle. 
From the keel and from the outer part of the 
sternum (thus covering up the small Elevator 
muscle), and also from the clavicle, springs the Great 
Pectoral—the Depressor muscle; it attaches by a 
short tendon to the front part of the under-surface 
of the humerus (upper-arm bone), and, attaching 
where it does, its pull tends to lower the front part 
of the wing relatively to the back. And springing 
as it does not only from the breastbone but also from 
the clavicle, it pulls the wing, not downward and 
backward, but simply downward. The underlying 
Elevator sends out a long tendon that passes 
