THE BONES. 47 



feathers, and the bend of the leg beneath the tail 

 corresponding with c, the remaining part from that 

 point to the claws answering to our foot and toes. 



There are some other beautiful contrivances in 

 the limbs of birds which deserve attention. Look 

 at a bird fast asleep with its head under its wing, 

 resting usually oa one leg, and that again resting 

 upon a perch not thicker than one's finger. How 

 apparently difficult and uneasy is such a position; 

 and yet it is all made easy and safe to the bird, by 

 an admirable piece of internal mechanism, which 

 may be briefly thus explained. Connected with 

 the thigh-bones and leg, a set of muscles run down 

 to the very extremity of the toes, so contrived and 

 placed, that when, by pressure downwards, the limb 

 bends, these fine muscles are pulled in, and there- 

 fore contract the toes, thus making them grasp 

 more firmly whatever the bird is resting upon; just 

 as if a set of fine strings ran over pulleys to certain 

 hooks, and were acted upon at the other end by a 

 weight or pressure, and thereby made to draw in 

 the hooks. 



But there are some birds, and very large ones 

 too, such as Herons, Cranes, and certain other 

 wading birds, which sleep standing on one foot, the 

 leg being kept perfectly straight; and in these birds, 

 as the foot rests upon the ground, any grasping 

 power acting upon the toes would be useless. In 

 this case, therefore, what is required, is some con- 

 trivance to keep the leg firm, that it may not give 

 way, in consequence of any swinging or balancing 

 motion of the body, which would inevitably overset 

 the sleeper. Accordingly, the upper part of what 



