268 STUDY OF NATURAL HISTORY. 
ing, throughout nature; and these gradations are so 
numerous and so combined with other qualities, that 
the variety thus produced becomes infinite. Thus 
it is among perching birds: all have the hind toe 
(which corresponds to the thumb of the quadru- 
manous Mammalia or monkeys) placed on the same 
plane as the sole of the foot, by which means they 
are enabled to grasp an object from behind, with as 
firm a hold as they do before with the-anterior toes: 
by this means the grasp is rendered firm; whereas, 
if only the fore-toes were employed, there would be 
wanted a support, or more properly a counteracting 
force, on the other side, to preserve the body steady. 
How important this structure is to the perching 
order, may be judged of by any one who should 
endeavour to grasp a broom or other round stick in his 
hand, by his four fingers only: he will think, perhaps, 
that it can be done very effectually; but a boy, 
with half his strength, will find no difficulty in 
wresting the stick from him. But if he again takes 
it, and applies his thumb in addition to his fingers, 
he will immediately perceive with what additional 
strength he now grasps the stick; and that no one, 
not physically stronger than himself, can take it 
from him. Applying this to the birds in question, 
we see that the toe of perching birds, like the 
thumb of the human hand, is on the same plane 
with the claws; and that both are more especially 
adapted for grasping round objects. This is why 
all weapons, or handles of utensils, are, for their 
more ready and convenient use, made round; and as 
the perching birds chiefly frequent and roost among 
branches, which are also round, their toes are es- 
