X] THE ORGANS OF LOCOMOTION 117 



in the bod}-. It occurs when the leg is fixed on the ground and 

 the body is passing over it. The ground is the fulcrum, the 

 gastrocnemius is the power, and the body through the elbow or 

 hock joints is the weight. 



Power 



A i 



Fulcrum Weight or 



resistance 



In the third kind of lever the fulcrum is at one end but is 

 nearer to the power than to the weight. 



Power 



i 



A I 



Fulcrum Weight or 



resistance 



In the body it is the lever of flexion, and the nearer the power 

 to the fulcrum the greater is the degree of flexion obtained for 

 the same expenditure of muscular force. It is the lever of speed 

 and Avhat is gained in sj)eed is lost in power. In one sense there- 

 fore it is a wasteful lever. In the horse it is commoner than the 

 other two levers, since in that animal the movements of the limbs 

 are directed principally^ towards carrying a comparatively light 

 weight a considerable distance and in a short time. The following 

 are examples. In the flexion of the elbow the weight is the leg 

 below the elbow, the power is the flexor brachii muscle (which is 

 inserted on the radius) and the fulcrum is the elbow joint. In 

 the flexion of the hock the weight is the limb below the hock, 

 the power is the flexor metatarsi, and the fulcrum is the hock 

 joint. 



In the three classes of lever as drawn above the power and 

 weight are represented as working at right angles to the lever. 

 In the actual levers of the body this is not the case. But the 

 nearer the force is to being at right angles to the lever the greater 

 is the mechanical advantage. 



Thus if AP in the diagram represents the line of action of 

 the force exerted by a muscle attached to a bone FA at A and 

 causing by its contraction movement of the bone round the 

 joint at F, the mechanical advantage may be represented by 

 PxFA where FA is at right angles to the line of action of P. 



