CHAPTER XIII 
WINGS 
the ground, and, ages before this, a many-rayed mem- 
brane stretched across the primitive fin, aided its owner 
in cleaving a way through the water. So, like a palimp- 
sest, if we look beneath the outer covering of feathers, 
we see, in the wing of the modern bird, the three fingers 
hinting of widely different ancestral habits. 
The general structure and appearance of the bills, the 
feet, and wings of various birds is the result of a function 
characteristic of each. The bills are used to procure 
food, the feet to walk or perch, and the wings to propel 
the bird through the air. But, as we have seen in the 
case of the bill, these organs are put to many other uses 
besides the one for which they were primarily adapted. 
This is only what we should expect when we consider the 
relative high position which avian intelligence holds, and 
the remarkable extremes of environment with which 
these structures—hill, feet, and wings—are brought into 
close touch. 
The photograph of the young heron’s wing shows 
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