24 



THE HUMAN BODY. 



surface slightly hollowed out, on which the head of the 



arm-bone plays. 



4. The arm-bone is called the humerus. It is a strong 

 bone, about a foot long in a grown man. It 

 has a round head, which plays on the joint 

 surface in the shoulder-blade. Its lower end 

 is joined to the two bones of the fore-arm. 



5. The bones of the fore-arm are called 

 the radius and the ulna. The 

 radius is on the thumb side, 

 and the ulna on the side of 

 the little finger. The radius 

 is joined to the humerus and 

 to the ulna in such a way that 

 it rolls over on the ulna, and 

 turns the palm of the hand 

 up or down. The ulna is 

 so joined to the humerus that 

 it can only move forward and 

 backward. The radius is joined 

 closely to the hand, and, when 

 it rolls over the ulna, carries 

 the hand with it. 



6. The hand is divided into the carpus, 

 or wrist, metacarpus, or palm, and pha- 

 langes, or fingers. 



7. The wrist has eight short bones, irregu- 2 ' TuE ULNA * 

 lar in size and shape. These are bound by ligaments into 

 a compact bunch. They glide a little on each other. 

 Though they seem to be put together without design, 

 they are really shaped and joined in such a way as to 

 give freedom of movement combined with strength. 



Fig. 9. 

 THE HUMERUS. 



Fig. 10. 

 1. THE RADIUS. 



