﻿140 ON THE CLASSIFICATION OF BIRDS. 



The anterior and the posterior toes of scansorial birds 

 are constructed for performing two very different func- 

 tions^ although both are essential to the act of climbing. 

 Those in front are formed for speed, and may be com- 

 pared to the arms of a man. When in the act of as. 

 cending a tree, his hold is secured in the first instance, 

 not by his foot, but by his arm, and in proportion to 

 his muscular strength and the firmness of his grasp 

 does he make his way upwards from branch to branch, 

 the foot merely serving to keeping him steady in the 

 progress he has first secured by his arms. This fact 

 every one must know, either from experience, observa- 

 tion, or reason. Hence we find that the long-armed 

 monkeys are the most expert climbers ; and the sloths, 

 whose hinder legs are not more than half as long as the 

 others, are the most expert, in ascending trees, of all 

 quadrupeds, monkeys alone excepted. These facts 

 establish the position upon which we shall argue. The 

 anterior toes of scansorial birds perform to them the 

 office of hands or arms ; it is these that are first ap- 

 plied to seize the bark of a tree, into the crevices or soft 

 covering of which the crooked claws enter, and obtain a 

 firm hold. It therefore follows that the more powerful 

 these anterior toes and claws are constructed, the more 

 facility the bird has in climbing. Now, the Dendro- 

 colapti and their congeners are the only scansorial 

 creepers that have two of the anterior toes of the same 

 length, so that the outer one is as long as the middle 

 {fig. 75.), and both, as if for giving additional strength, 

 are considerably united at their basal joint. Let us now 

 explain the reasons that, with such unusual strength in 

 the anterior toes, the hinder one is so small, while that 

 of the Sittince is enormous. It follows, from what has 

 already been said, that the functions of the hallux are 

 altogether different from those of the fore toes. In these, 

 and in all other birds, it is merely an organ of support. 

 And as the scansorial tribe, in climbing trees, assume a 

 semi-perpendicular attitude, they consequently require 



