36 OUR BODIES AND HOW WE LIVE 



a box or a door on its hinges. This is called a hinge joint. The 

 elbow joint is a good example of this forward and backward 

 movement ; we can only bend and extend it. 



Other hinge joints are found at the knee, and between 

 the lower jaw and the cranium. The last permits some 

 motion from side to side, and is therefore 

 called an imperfect hinge joint. 



Experiment 12. Sit in a chair and extend 

 the right leg. Place the right heel on the floor 

 and turn the foot from side to side. The thigh 

 bone can be felt rotating in the upper part of 

 the thigh. Note that while the thigh bone 

 moves through a small space, that described by 

 the tips of the toes is much larger. 



58. How Bones are fastened to Each 

 Other. The bones are fastened together, 

 kept in place, and their movements 

 limited, by tough and strong bands, or 

 straps, called ligaments, from a word 

 meaning to bind. They may be seen in 

 the movable joints, of the calf, sheep, 

 or chicken, and have the look of white, 

 silvery cords or bands. 

 A Powerful Some of the ligaments are as thin as 



at the thin tissue paper ; while otherS) as 



at the side of the knee, or at the shoulder, 

 are much thicker. Some cross each other, as in the knee- 

 joint ; while others go all round the joint, and completely 

 shut it up in a bag. This prevents the bones from being 

 easily dislocated, or slipped out of place. 



It is sometimes a difficult matter to carve a fowl, because 

 one has to cut through the ligaments before he can cut the 



