Feet and Legs 369 
forward, forming a four-tined grapple by which they 
hang themselves up in their hollow nesting-trees. Whip- 
poorwills and some other birds have a curious comb, 
or pecten, along the edge of the middle claw, which is 
perhaps of use in cleaning the long bristles about their 
mouths, or in arranging their very delicate, soft plumage. 
Ixingfishers and several related groups of birds make so 
little use of their feet, except in motionless perching, that 
Fra. 290.—Comb on toe of Chuck-will’s-widow. 
not only are the toes small and weak, but two of the 
front ones have grown together for over half their length. 
Perhaps the most interesting condition of toe struc- 
ture is found among the woodpeckers, parrots, cuckoos, 
and owls. In these groups we find a similar plan of gen- 
eral arrangement: two toes in front and two behind. 
With few exceptions it is the great, or first, toe and the 
fourth, or outer, toe which are reversed. This arrange- 
ment of toes is known as yoke-toed, or zygodactyl. 
