BIRDS IN GENERAL. 7 



rise against the wind, because they have thus a 

 greater body of air on the under than the upper 

 side of the wing. For these reasons also, large 

 fowls do not rise easily, both because they have 

 not sufficient room at first for the motion of their 

 wings, and because the body of air does not lie 

 so directly under the wing as they rise. 



In order to move the wings, all birds are fur- 

 nished with two very strong pectoral muscles, 

 which lie on each side of the breast-bone. The 

 pectoral muscles of quadrupeds are trifling in 

 comparison to those of birds. In quadrupeds, as 

 well as in man, the muscles which move the 

 thighs and hinder parts of the body are by far the 

 strongest, while those of the arms are feeble ; but 

 in birds, which make use of their wings, the con- 

 trary obtains ; the pectoral muscles that move the 

 wings or arms are of enormous strength, while 

 those of the thighs are weak and slender. By 

 means of these, a bird can move its wings with a 

 degree of strength which, when compared to the 

 animal's size, is almost incredible. The flap of a 

 swan's wing would break a man's leg; and a 

 similar blow from an eagle has been known to lay 

 a man dead in an instant. Such, consequently, 

 is the force of the wing, and such its lightness, 

 as to be inimitable by art. No machines that 

 human skill can contrive are capable of giving 

 such force to so light an apparatus. The art of 

 flying, therefore, that has so often and so fruit- 

 lessly been sought after, must, it is feared, for 

 ever be unattainable ; since as man increases the 



