208 OMNIVOR.E. 



The first or wood-pecker's foot is zygodactylic, or " yoked," 

 two of the toes being turned back, and two forward, and the 

 two front ones are joined together at their bases. As that 

 foot has two bearings in the front and two behind, it enables 

 the bird to perch or to walk lengthwise on a branch ; and, 

 with the feet alternately holding on, and the tail bearing as a 

 prop, to walk up the trunk of a tree, or even to move side- 

 wise round it, though slowly. The legs are placed behind the 

 centre of gravity, so that the weight of the bird both assists 

 in compressing the claws into the fissures of the bark, and 

 presses the tail against the tree under them ; and while the 

 centre of gravity remains higher than the feet, the bird is 

 stable, without that exertion of the body which would prevent 

 the use of the beak and of the wings, if these should be neces- 

 sary. But if the head were turned downwards, or the body 

 even much out of the upward position, the principle of stability 

 would be changed into a means of falling. Hence, though 

 these birds can run upwards, they come down only backwards, 

 and that rather slowly and awkwardly ; and they can get 

 round only in an ascending spiral : hence they beat and hunt 

 the trees from the roots upwards. There are some very 

 curious modifications of these feet, but as they belong not to 

 British birds, they do not come within our province. 



The second foot (that of the nuthatch) is anisodactytic, or 

 " unequally yoked," and is by far the more curious foot of the 

 two, though at a cursory glance it seems not to differ much 

 from a common foot with three toes before and one behind. 

 It has, in fact, the power of two feet, and of two feet com- 

 bined ; so that the bird keeps its hold better with one foot 

 than other birds can do with two, and with the two, better 

 than other birds could do if they had even four. The middle 

 and exterior toes are united together at their bases, and admit 

 of a position half reversed, or midway between the other two ; 

 the hinder toe is long and strong, and all the toes have strong 



