FEET OP BIRDS. 



405 



in walking, the head of a bird is in constant motion: whilst 

 the duck and other birds, whose legs are very short, have a 

 waddling gait. It may be observed that the more perfect- 

 ly predaceous birds are not the best formed for walking; be- 

 cause where they use their feet for that purpose, their talons, 

 which are required to be kept sharp for seizing and tearing 

 their prey, would be blunted; and accordingly the eagle, 

 when moving along the ground, supports itself partly by the' 

 motion of its win^s. 



In roosting, birds support themselves upon their perch 

 by means of one leg only, the other being folded close to 

 the body. They even maintain this attitude with greater 

 ease and security than if they rested upon both feet. ' The 

 true explanation of this curious fact was long ago given by 

 Borelli. On tracing the tendons (t, t Fig. 233) of the mus- 

 cles (m, m) which bend the claws, and enable them to grasp 

 an object, we find them passing over the outer angles of each 

 of the intervening joints, so that whenever these joints are 

 bent, as shown in Fig. 234, those tendons are put upon the 



stretch, and mechanically, or without any action of the inus- 

 cles, tend to close the foot. When the bird is on its perch, 

 this effect is produced by the mere weight of the body, 

 which of course, tends to bend all the joints of the limb on 

 which it rests; so that the greater that weight, the greater is 



