CONTRIVANCE IN THE LEG OF BIRDS. 219 



membered how fatiguing it is, to continue standing still 

 for any length of time full as much, I verily believe, as 

 to walk for the same space of time. But this cannot be 

 the case with quadrupeds, for the standing posture seems 

 to be one of rest to them. The horse after perfoj ming 

 his task seldom lies down immediately, and all day he 

 will stand in his stall without being fatigued. 



Dr. B. Because, his body resting on a wider base 

 of support, the tendency to fall in any direction is ob- 

 viously much lessened, and thus the equilibrium is pre- 

 served by a very little exertion of muscular power. 



In some animals which are sometimes obliged to 

 stand for a great length of time, we find curious contri- 

 vances for Assisting the action of the muscles. Thus, 

 the sea-birds, as the heron, which wade upon the shores 

 of the sea and in the marshes for fish and reptiles, their 

 natural food, had long excited the curiosity of naturalists, 

 by the length of time in which they would stand motion- 

 less, expecting their prey. At last it was found, that in 

 the lower extremity of the thigh-bone there is a deep 

 cavity into which a corresponding projection in the leg 

 can be shut at the pleasure of the animal. The thigh 

 and leg being thus firmly locked together, and to all in- 

 tents and purposes, constituting but one piece, no mus- 

 cular power is necessary to keep them extended. 



Emily. I should think some mechanical contrivance 

 was needed by all birds, to enable them to roost so long 

 as they do without loosing their hold. 



Dr. B. And such a one is possessed by all birds, 

 and is no less curious than that just described, which is 

 possessed by only a few. The muscle which bends 

 their talons, or draws them together so that they grasp 

 an object, coming from the thigh, passes over the back 

 part of the ancle-joint, or heel, proceeds along the foot, 

 and is inserted into the toes. 



Emily. So that when the ancle-joint is bent, as it 

 must be when the bird is perched, this muscle is bent 

 at the same time, and the talons which obey the con- 



