Feathers 23 
The two lines of barbs which grow out on each side 
of the quill are very elastic and so intimately hooked to 
each other that they will bend some distance before sepa- 
rating. If we ever tried to force our way through a 
Fig. 21.—Model showing interlocking barbules and barbicels of feather, 
greatly enlarged. 
bramble of sweet-brier or blackberry-vines, we can more 
readily appreciate how these barbs and the interlocking 
barbules clutch each other. The thorns in the bramble 
catch our clothes and, when we move, the elasticity of the 
long stems tends to make them hold the tighter. 
We notice that one line of barbs—that along the 
inner curve of the quill—is much longer than that on the 
outer curve and we might think the air would force this 
