212 THE STRUCTURE AND LIFE OF BIRDS cHAp, 
Wood-pigeons! the three pairs of breast muscles 
represented three thirteenths of the whole—z., a little 
less than one quarter,.a very large proportion, the 
average, among birds, being less than a fifth, The 
Elevator is very small compared with the Depressor, 
often so light that the most delicate scales are re- 
quired if trustworthy results are to be obtained. The 
differences in different species are very striking. In 
the Wood-pigeon I have found the weight of the small 
muscle to be a little less than one fifth of the greater, 
in the starling just over one ninth. 
Movements of the Wing partly due to the Action 
of the Air. 
The muscle which lowers the wing rotates the 
humerus, as I have shown, so that the under surface 
of the wing looks dackward and downward. And 
since the whole expanse of feathers lies to rearward 
of the bones, the action of the air will tend to turn 
the wing round in the same direction, just as the 
wind swings a sign-board. When once an upward 
1 These figures do not agree with those given by two German 
investigators, Legal and Reichel, in the Jahres-Berichte der 
Schlesischen Gesellschaft fiir Vaterlandcultur, 1879. They 
é I 100 : ; 
ive —— (= —— = more nearl than 3) to represent the 
ae a3 \ 348 y ites 4) to ee 
relative weights of the three pairs of pectoral muscles and of 
the whole body. This seems impossible, nor is it clear why in 
the pigeon the breast muscles should weigh so enormously 
heavier in proportion to the weight of the body than in any 
other bird. -In the case of other-species their figures are not so 
startling, and they may be more trustworthy. 
