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CHAPTER VIII 
Plate VIII. — bones of the arm. 
Fig. 1. a, the humerus; the head, &, is a portion of a sphere, and 
exhibits an example of the ball and socket , or universal joint; c, the 
hinge-joint , instanced in the elbow; </, the radius; e, the idna. The 
radius belongs more peculiarly to the wrist, being the bone which 
supports the hand, and which turns with it in all its revolving mo¬ 
tions. The ulna principally belongs to the elbow-joint, for by it we 
perform all the actions of bending or extending the arm. 
Fig. 2. a, the humerus: 6, shows the connexion of the radius, 
with c, the ulna, at the elbow. The mode of articulation at the 
wrist is seen, Fig. 1. 
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