vil FLIGHT - 
feathers themselves greatly reduces 
the work of the muscles and tendons 
in making, the adjustments that are 
required in order to render the wing 
impervious to air (fig. 55). 
The Active Machinery. 
The great muscles of flight lie below 
the shoulder joint, and yet upon them 
falls the task of raising the wing. All 
the great-mass of muscle lies behind 
the joint, and yet the wing must be 
lowered without being pulled back- 
ward. Besides this the muscles can 
incline the wing rightly for upward 
flight, for a downward swoop, for a 
sudden halt; they can adjust it to 
every varying breeze, to every current 
or eddy that can be turned to account. 
In addition to the breast muscles, 
there are many smaller ones which 
help in these niceties of adjustment. 
When we consider the number of 
these, each with its special office, each 
giving the wing a slightly different 
turn from any other, it is extraordinary 
that Professor Marey should state that 
“the muscular apparatus of the bird, 
like that of the insect, has nothing 
to do with the course of the wing; 
elevation and depression are almost the 
203 
Fic. 55. — Primary 
wing-feather of Heron 
(less than natural size). 
The outer web is nar- 
row. 
