206 THE STRUCTURE AND LIFE OF BIRDS cuap. 
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 praaxial 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 przeaxial margin of the bone it causes the wing 
to face to the rear as it descends. 
Every one must have noticed that, wnen 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 
