1886. } Birds to the Power of Flight. 27 
tively larger than in those of less power of flight. Conversely, other 
things being constant, those birds in which the pectoral muscles 
form a larger percentage of the weight of the body, would have 
a greater power of flight. 
This being true the question naturally rises: What is the varia- 
tion in the development of the pectoral muscles for the different 
species of birds, and is this variation by natural families or by 
individual species ? 
In the solution of our problem the shape of the wing plays an 
important part. The long, narrow, sharp-pointed wing is most 
advantageous to continued flight, and the shorter, rounded, less- 
compact form is least so. Between these two extremes there is 
an indefinite shading of the one form into the other, with more 
or less resulting advantage as the case may be. 
The pectoral muscles may be relatively large, yet if the wing 
be of impeding form, so that considerable force is lost in over- 
coming the consequent disadvantage, the resulting power of 
flight is much lessened. 
In this paper I have taken the weight of the whole body as a 
constant basis and found the percentage by weight of the pec- 
toral muscles in the body. The data are derived from the dissec- 
tion of 119 birds, having in all cases possible taken an average 
for each species from three individuals. 
There are represented seven orders, twenty-five families and 
fifty-three species. It will be seen that variation is not by natural 
families but by individual species. This is explained by the fact 
that though certain species may have structures so allied as to 
join them together in a family, yet because of their distinct habits 
of life they may differ considerably in their power of flight. 
List of species examined, arranged in order of — of 
pectoral muscles to total weight of body : 
Broad-winged hawk....... 5-98 per cent. Maryland yellow-throat....7.50 pr cent, 
Buteo pennsylvanicus. Geothlypis trichas. 
Seh OW iy sss. sce 6.14 |o Blaejay. 5.4 FOE Me 
Scops asio. Cyanocitta cristata. 
Mallard duck.,... HO 3% Sony POWs nesr a 
Anas boschas.. Melospiza fasciata. 
House wren 6.87 © — Mud hen or cdot; 6. scssi is 7.89 ” 
Troglodytes edon. Fulica americana. ; 
Catbird. 222 z 7.12 *& Brown thrush.. 8.00 ~~ 
Mimus carolinensis. — - 44 Harporhynchus rufus. 
