23 



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 



FIG. 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, i, 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- 



