74 



PHYSIOLOGY FOR BEGINNERS 



CHAP. 



knee joint. The arrangement is also that of a lever of the 

 third class. The leg and foot form the weight, the fulcrum is at 

 the knee joint, and the power is applied between the two, but 

 close to the fulcrum. 



Movements at the Ankle Joint. The ankle joint is a 

 hinge joint allowing flexion and extension. Extension is pro- 

 duced by the muscles of the calf, which arise partly from the 

 lower end of the femur, but chiefly from the upper part of the 

 tibia and fibula ; they form the large belly of muscle of the 

 calf, and are inserted by a long and powerful tendon into the 

 heel bone. Flexion is prodiTced by the muscles lying just on 

 the outer side of the shin bone (tibia) on the front of the 



i II 111 



FIG. 36. Diagram of the actions of the ankle joint. 

 I., II., III., as a lever of the ist, 2nd, and 3rd class. 



leg. The main muscle arises from the upper part of the tibia, 

 and is inserted into the bones of the foot in front of the ankle 

 joint. Movements at the .inkle joint illustrate the three classes 

 of levers. 



I. When, the heel being raised from the ground, the foot is 



extended, so that the toes tap the ground, the weight 

 or resistance is at the toes, the power is applied by the 

 calf muscles at the heel, the fulcrum being at the 

 ankle joint between the two. Lever of the ist class. 



II. When the body is raised on the toes, the fulcrum is at 



the toes, the power is applied by the calf muscles at the 

 heel, and the weight is that of the whole body, which 

 falls on the foot at the ankle, between the heel and the 

 toes. Lever of the 2nd class. 



