MUSCULAR POWER IN BIRDS. 52.> 



posture which gives them a strange and grotesque 

 appearance. 



I have ah'eady alhided to the lengthened legs 

 and feet of the waders, the utility of which to birds 

 frequenting marshy places, and shallow waters, is 

 very obvious. Their legs are not covered with 

 feathers, which would have been injured by con- 

 tinual exposure to wet. But birds of a truly 

 aquatic nature, have their toes webbed, that is, 

 united by a membrane ; a mechanism which qua- 

 lifies them to act as oars, and indeed gives them a 

 great advantage over all artificial oars that have 

 been constructed by human ingenuity ; for as soon 

 as the expanded foot has impelled the water behind 

 it, the toes collapse ; and while it is drawn forward, 

 it presents a very small surface to the opposing 

 water. Their plumage is so constructed as to pre- 

 vent the water from penetrating through it, and for 

 the purpose of preserving it in this condition, these 

 birds are provided with an oily fluid, which they 

 carefully spread over the whole surface of their 

 bodies. The swan, and many other water-fowls, 

 employ their wings as sails, and are carried forwards 

 on the water with considerable velocity, by the mere 

 impulse of the wind. 



Birds excel all other vertebrated animals in the 

 energy of their muscular powers. The promptitude, 

 the force, and the activity they display in all their 

 movements, and the unwearied vigour with which 

 they persevere for hours and days in the violent 

 exertions required for flight, far exceed those of 

 any quadruped, and imply a higher degree of irri- 

 tability, dependent probably on the great extent of 

 their respiratory functions, than is possessed by 



