264 ANISODACTYLIC FEET. 



pressure both of the wings and tail assists in tighten- 

 ing the hold taken with the claws ; so that, even 

 though the surface to which they cling overhangs, these 

 birds can stick to itj^ery firmly. The preceding figure 

 of the swift's foot will show the structure. 



ANISODACTYLIC FEET. 



As " crab " feet, more especially in that form 

 which they have in the swallows and swifts, are 

 the best fitted for holding-on while the body gene- 

 rally of the bird is steady, upon an upright or an 

 overhanging surface, so feet of the form now to be 

 described are the best adapted for motion upon such 

 surfaces. Birds which have them are all, generally 

 speaking, tree birds, or at all events woodland birds. 

 But, like the birds with feet of the immediately pre- 

 ceding form, they admit of subdivision into those 

 which feed more exclusively upon the bark of trees, 

 and those which feed more exclusively on the wing. 

 They are the same, or nearly the same, as the tenui- 

 rostres of Cuvier. 



But, although that illustrious naturalist has taken 

 the form of the bill as their distinguishing character 

 as a tribe, and though their wings, which are in 

 general very powerful, might also be made both a 

 general character of the whole and a means of divid- 

 ing them into different sections, yet the foot is 

 unquestionably their most prominent and remarkable 

 character. Their feet are entitled to the preeminence, 

 not because they are, as in those birds which cannot 

 fly, the only active organs except the bill, and not 

 because they are efficient organs of locomotion upon 

 the ground ; for, generally speaking, these birds are 

 not only very bad walkers, but they are seldom, if 

 ever, found upon horizontal surfaces. Indeed they 



