44 



MUSCLES AND TENDONS 



joint depends largely upon the amount of motion per- 

 mitted in it. In a simple joint, for example, such as 



FIG. 36. Diagram illustrating 

 the muscles (drawn in thick 

 black lines) which pass before 

 and behind the joints, and by 

 their balanced contraction 

 keep the joints rigid and the 

 body erect. 



Extensor 

 muscle 

 Of thigh 



Knee cap 



Tibia 



Flexor 

 muscles 



Femur 



Fibula 



FIG. 37. Flexor and extensor muscles 

 of the left thigh (somewhat diagram- 

 matic). 



the hinge joint in the finger which permits only flexion 

 and extension, but two controlling muscles are essen- 

 tial, a flexor and an extensor. In a ball-and-socket joint. 



