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 ver}^ delicate, soft plumage. 

 Kingfishers and several related groups of birds make so 

 httle use of their feet, except in motionless perching, that 



Fig. 290. — Comb on toe of Chuck-wiir.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 ovv'ls. 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 zygodadyl. 



