PARTS OF FEET. 61 



The leg and foot always consist of three princi- 

 pal pieces, independently of the toes : the femur or the 

 thigh-bone, the tibia or leg-bone, and the tarsus or 

 foot-bone. The tarsus, like the bones of the wings, 

 answering to the palm of the hand, is always very 

 much elongated ; and it is popularly called the leg, 

 though in fact it is the foot. Birds, in general, follow 

 the same law as the mammalia in the use of their 

 posterior extremities as organs of walking ; they are 

 digitigrade, or walk upon the toes, and not on the 

 tarsus ; and those which walk upon the latter have 

 even a more awkward and shambling gait than 

 the mammalia which have that habit ; indeed they 

 can hardly be said to walk at all. The knee joint, 

 or articulation of the tibia with the femur, which 

 bends forward only, appears to be inadequate to the 

 balancing even of a nearly inflexible spine in any but 

 a nearly vertical position. In man we have a flexible 

 spine, balanced with the whole length of the tarsus 

 on the ground, but it is in an erect position ; and 

 besides there is the astragalus or heel-bone in man, 

 which not only sustains the balance of the foot, but 

 gives a lever power to the tendo Achillis, which, when 

 pulled by the strong muscles to which it is attached, 

 throws the pressure of the body upon the balls of the 

 toes. The human foot is not, however, a fit subject 

 of comparison with the feet either of birds or of the 

 mammalia. 



Those birds which bring the whole length of the 

 tarsus to the ground when they walk, or attempt to 

 walk, are but few in number ; and they are all aquatic 

 birds, the proper functions of whose feet is swimming 

 and not walking. Their legs are articulated far 

 backward, and they have an oblique motion of the 

 joints for throwing the swimming feet at some dis- 



