230 BACKBONED ANIMALS. 
scales or hairs, developed, like them, in sacs in the skin. 
They afford protection to the bird, determine its contour 
or shape, and are the means of enabling it to soar in the 
air, the long pinions being arranged to offer the greatest 
Fic. 271.—Sparrow, showing the skeleton (Fig. 268) clothed in flesh, and 
the graceful outline produced by the coat of feathers. 
resistance. Taking a goose-feather (Fig. 272) as an ex- 
ample, we find that it is composed of several parts. The 
hollow, horny quill, 1, rests in a sac; this leads to the 
shaft, 2, which is horny, grooved, and filled with a sub- 
stance resembling wood-pith. From the sides of the shaft 
‘spring the barbs, 3, that are so delicate that it would nat- 
