GUSTOIMAGES / SCIENCE PHOTO LIBRARY GUSTOIMAGES / SCIENCE PHOTO LIBRARY
Hand with thumb up. Coloured X-ray of a hand with its thumb up. Apart from the bones in each hand, an outline of the flesh (orange) is seen. The forearm bones are the radius (upper here) and the ulna. The hand consists of eight small wrist bones (carpals), five palm bones (metacarpals), and each finger has three phalanges. The thumb only has two such bones. This structure enables the human hand to be used with great flexibility, helped especially by the joint between the wrist and the opposable thumb. The hand's grip is powerful, but it is also capable of performing very delicate tasks. This hand signal can represent "yes" or "OK".
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