IRKITABILITY 



109 



each with three small bones, for the fingers and toes 

 (Fig. 65). 



Joints. — Wherever two bones come together to form a 

 joint, the one nearest the center of the body acts as a 

 support for the motion of the other one. At the shoul- 

 der, for example, the upper arm moves, the shoulder 

 remains quiet; at the elbow the lower arm moves, the 

 c 



Fig. 66.-^1, lengthening of biceps when arm is extended; C, clavicle ; S, scapula; 

 Sh, short head of biceps ; Lh, long head ; B, biceps. (Prom Fitz.) B, con- 

 traction of biceps to flex arm; S, scapula; J5, biceps; T, tendon; H, humerus; 

 U, ulna; i?, radius. (From Fitz.) 



upper arm is quiet; at the wrist the hand moves, the 

 lower arm is quiet. There is an advantage in this, 

 for it insures quickness and ease of movement for the 

 extremities. 



