SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Human hands. Coloured X-ray of normal human hands, showing the bones of the hands and a faint image of the surrounding flesh. The bones of the hand consist of metacarpals (between the wrist and fingers) and phalanges (fingers). Each finger has three phalanges, but the thumbs (centre) have only two. The wrist contains eight bones, called carp- als. The skeletal structure of the human hand gives a delicacy of manipulation that is unique in the animal world. Key to this is the highly flexi- ble joint between the wrist and thumb, which gives humans an opposable thumb. This adaptation, along with upright posture, allowed our ancestors to use tools, facilitating the evolution of civilisation.
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