258 STfel'CTfBE OF 



the sky with the one, and the top of the rock or the 

 tower with the other. 



The feet correspond: the syndactylic foot, with 

 its soldered toes, forms a steady base for resting by 

 pressure upon a horizontal perch ; and the foot of the 

 swift, which is the opposite extreme, in all the birds 

 which prey upon insects on the wing, is the best 

 adapted for holding-on upon the slightest inequalities 

 of an upright surface. Although, therefore, the feet 

 of all these birds are small, apparently feeble, and 

 not adapted for locomotion, there are no feet better 

 adapted to the habits of their owners. 



The general character in which the "crab" foot, or 

 foot of the Fissirostres, differs from that of all other birds, 

 is the equality of the three front toes, and the reversi- 

 bility of the back one. In most birds the middle toe 

 and the external front one, have each four phalanges 

 of bone, while the inner one has only three, and in 

 some of them, more particularly in the zygodactylic 

 birds, the feet of which remain yet to be noticed, the 

 outer toe is reversible backwards, so that it acts in 

 concert with the hind one and in opposition to the 

 other two. But in the crab foot, the back one is 

 reversible, so that all the four points can be turned 

 forward, or rather into the circumference of a circle, in 

 which the articulation of the toes with the tarsus forms 

 a fifth point. 



The feet with the reversible outer toe, have the 

 strongest action in opposite directions toward the 

 centre of the foot, and therefore they grasp firmly any 

 substance to which that is applied, although the tarsal 

 joint is straight, or even the bird suspended by the 

 leg at full length, or standing up with it in the same 

 position. But the greatest action of the crab foot is 

 concentrated upon the articulation of the tarsus in 



