206 THE STRUCTURE AND LIFE OF BIRDS chap. 



fastens firmly to the clavicle all along its length, and 

 then by a very short tendon attaches where I have 

 pointed out the mark of it on the humerus, on 

 its under side and its further or pmeaxial margin. 

 I have in several species found another less strong 

 attachment, also on the under side of the bone, 

 but near its postaxial margin ; and I cannot help 

 thinking that the bird can make the muscle act mainly 

 on the one or the other at his pleasure. In both cases 

 the wing would be lowered, but it would be rotated 

 differently ; working through its main tendon attached 

 to the prseaxial margin of the bone it causes the wing 

 to face to the rear as it descends. 



Every one must have noticed that, when the breast of 

 a chicken is carved, the greater part of the meat flakes 

 off clean from a thinner layer that lies below in the 

 angle between the upright keel and the nearly hori- 

 zontal sheet of bone below. This upper part (the 

 bird now lying upon its back) is the great pectoral 

 that lowers the wing, the part below is the Elevator, 

 muscle. The muscular fibres in the Great Pectoral may 

 be easily seen in an uncooked bird running forwards, 

 or, more strictly, forwards and inwards, converging 

 from both sides on a line of tendon in the middle. 

 The set of the fibres shows the direction in which 

 they pull. But since the muscle does not arise only 

 from the breastbone, but also from the clavicle, the 

 result of its action is not to draw the wing backwards 

 and downwards, but simply downwards. The forward 

 movement is, as I shall show, due to the action of 

 the air (see p. 213). To turn to the Elevator muscle. 

 Unassisted, it could not raise the wing since it 



