SWIFT. -263 



The swallow-tribe all have the foot less firm as a 

 perching foot, that is, less connected by membrane 

 between the bases of the toes, than the goat-suckers ; 

 and the articulations of the toes .with the tarsi have 

 more of the ball and socket form, and consequently 

 admit of more motion. This motion increases, and 

 the tarsus and to'es become shorter, and the claws 

 more crooked, from the lowest building swallows to 

 the swifts, which have the most perfect crab foot, that 

 is, the one best adapted for individually holding-on 

 upon slight inequalities of a perpendicular surface, and 

 at the same time the least fitted for perching on a twig, 

 or walking upon the ground, for which last office they 

 are not at all fitted, and the birds are consequently 

 quite helpless there. 



Swift hind toe reversed, but closed. 



The feet, admirably formed as they are, are not the 

 only organs by means of which these birds maintain 

 their perch upon perpendicular surfaces. The flying 

 feathers of their wings and tails are remarkably stiff 

 in the shafts and firm in the webs ; and though they 

 cannot, of course, take hold with their feathers, unless 

 when they, as it were, embrace a projection, yet the 



