WADING BIRDS. 85 



neck out forwards ;* and as the lengths of those bear a pro- 

 portion to each other, the balance of the bird is preserved, 

 and the flight rendered more easy. 



]^or is that all ; for the feet, which, from the stiffness of 

 the tarsal joints, cannot be so conveniently folded as those of 

 perching birds, answer many of the purposes of a tail. When 

 the bird descends they come down ; so that, in alighting, the 

 weight presses first on the points of the toes, and the bird 

 is let to its footing on the ground by its own feet as elastic 

 springs. 



When the bird is on the ground, and the axis of the body 

 nearly horizontal, which is the average position when feeding, 

 the centre of gravity is so far forward of the articulation of 

 the toes, that the pressure upon them is nearly in the same 

 ratio to their power of resistance through their whole length ; 

 and thus the whole foot is stable. If the centre of gravity 

 were thrown backward, the stability would be diminished, 

 just as that of a man is when he attempts to lean back with 

 his body straight and stiff; more so, indeed, for as soon as 

 the points of the toes are relieved of part of the pressure, 

 the elastic ligament begins to contract, and its tendency is to 

 throw the bird obliquely upwards and backwards. But as 

 the chief action of the birds while on their feet is either 

 walking or running, in which the anterior part of the body 

 is depressed and the head generally advanced, or seeking 

 for their, food below the axis of the body, their footing 

 becomes the firmer the more that they exert themselves in 

 either way. 



In taking wing, in which case the anterior part of the body 

 is always elevated, and the centre of gravity consequently 

 thrown backward, the action of the spring of the foot aids the 

 bird in getting into the air, a motion which, as the tail has 



* The neck of the heron during flight assumes a sigraoid flexure. M. 



