192 NATURAL HISTORY 



action of the tendon is easily observed by watching a common 

 fowl walk. At each step that it makes, on lifting its foot, the 

 claws are seen to be drawn together. When an eagle wishes 

 to drive his claws into its prey, he perches on it, and then sinks 

 down with the whole weight of his body, by which movement 

 the tendon is shortened and the claws forcibly pressed to- 

 gether. 



STERNUM. 



As the wing presents a very broad surface to the air, it is 

 necessary that very powerful muscles must be used to move it 

 with sufficient rapidity. The pectoral muscles are therefore 

 enormously developed, extending almost the whole length of 

 the body, as every one who has carved a fowl must have seen, 

 and in order to form an attachment for these immense muscles, 

 the ridge of the breast-bone is equally enlarged. It is the want 

 of these enlarged muscles that prevents man from flying, even 

 when he has attached wings to his arms. 



CLAW AND BEAK OF RAPACIOUS BLRD. 



