THE SPINAL COLUMN OF BIRDS. 145 



immediately see that a solid uuyieldiug fouud- 

 atiou must be laid I'or the attachment of the 

 vokimiuous muscles of the thigh. The thigh, 

 as we have said, is articulated far beyond the 

 centre of gravity, the body is carried more 

 or less horizontally ; consequently, without an 

 adequate muscular power to sustain its weight 

 in this position, it would sink till the chest 

 touched the ground. Indeed, in some instances, 

 as the great auk and penguin, the bird cannot 

 maintain a horizontal attitude, so far back are 

 the short limbs placed, but is obliged to raise 

 itself into a perpendicular position as long as 

 it remains on the land. The jackass penguin, 

 as we have said, does, indeed, lean forward, 

 overbalanced, but then it uses its anterior fin- 

 like wings as crutches, and so runs on all fours. 

 In like manner the grebe is overbalanced, and 

 is unable to raise its body up. The breast 

 feathers of this bird are exceedingly close 

 and silky, and, resting on the ground, it slides 

 along, like a seal, pushing itself forward by 

 means of its hind-feet, which are each tri- 

 oared. This extreme backward position of 

 the hmbs, however awkward it may render 

 the birds on land, conduces most eminently to 

 their advantage in the water. 



