140 
ON THE CLASSIFICATION OF BIRDS. 
The anterior and the posterior toes of scansorial birds 
are constructed for performing two very different func- 
hons, a,lthough 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, cither from experience, observa- 
tion, or reason. JHence we find that the long-armed 
monkeys are the most expert climbers ; and the kloths 
whose hinder legs are not more than half as long as the 
others, are the most expert, in ascending trees, of aU 
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 olitain a 
firm hold. It therefore follows that the more powerful 
ffiese anterior toes and claws are constructed, the more 
facility the bird has in climbing. Now, the Dendrn- 
outaph and their congeners are tlie 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 
{Jig. 75.) and both, as if for giving adilitional strength 
are considerably united at their basal joint. Let us now 
explain the reasons that, with such unusual strength in 
tlie anterior toes, the hinder one is so small, while that 
of the SHtino! 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 
