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- 



