MUSCLES AND PHENOMENA OF CONTRACTION. 139 



atlas, the power is applied where the muscles of the neck 

 are inserted into the skull, while the final weight of the 

 head might represent the "weight." A second illustra- 

 tion of this lever is found in the act of bowing. In this 

 case the fulcrum is at the hip joint, the "power " is applied 

 where the muscles of the hip are inserted to pull the body 

 backwards, while the forward weight of the body represents 

 the "weight." In such a lever little is gained except a 

 change of direction; a power pulling down may, with such 

 a lever, pull a weight up. 



In a lever of the second class the ' ' weight ' ' is between 

 the fulcrum and the u power." The ordinary wheelbarrow 

 is a lever of this class, having its fulcrum at the forward 

 wheel, the " weight " in the bed, and the " power " applied 

 where the hands grasp the handles. A crowbar in prying 

 upwards, as in rolling a barrel, is a further illustration. 

 There are not very many levers of this order in the body. 

 The best illustration of this lever is found in the ankle. 

 When the body is lifted the toes become the fulcrum, the 

 weight of the body rests on the astragalus, while the 

 4 ' power ' ' is applied at the end of the heel where the ten- 

 don Achilles of the calf of the leg is applied. It is evident 

 that by means of such a lever a greater weight may be lifted 

 than the power could lift directly, for the experience of 

 everyone will convince him that by means of a wheel- 

 barrow a man may lift a greater load than he could by 

 directly hoisting it with his arms. 



A lever of the third class has the ' ' power ' ' between the 

 fulcrum and the weight. Most of the levers of the body are 

 of this kind. The flexing of the forearm at the elbow is an 

 illustration of this class. Here the fulcrum is at the elbow, 

 the weight is in the hand where the object to be lifted is 

 held, and the power where the tendon of the biceps muscle 

 is imbedded in the radius. It is evident that in such a 

 muscle much power is lost, for the muscle, in order to raise 

 a certain weight at the end of the radius, would have to 

 pull much more than that weight by pulling on the radius 



