The fore and hind limbs of all terrestrial vertebrates are built on a basic pentadactyl plan. The evolution of pentadactyl limbs was one of the adaptations that arouse in connection with terrestrial life. This type of limb consists of a long bone, followed by a pair of long placed side By side, a set of nine small bones in three rows, five thin long bones and finally five digits (' penta' meaning 'five' and dactyl' meaning 'digits'). Each digit is made up of a small bones. This shows a generalized fore and hind pentadactyl limbs, and gives the names of the corresponding parts.
The fore limb or arm consists of the upper arm, lower arm, wrist and hand. In humans, the two bones of the lower arm ( the ulna and radius) can partly rotate around each other so that the hand can be held palm upwards or downwards. In Addition, the thumb can be rotated to a position opposite the fingers ( this feature is found in other primaries). This allows the hand to grasp and manipulate objects precisely, a feature Important in the evolution of humans.
The hind limb or leg consists of the high shank, ankle and foot. The thigh bone is the largest and strongest bone in the body. The bones of the foot are not as dexterous as those of the hand. However , they form an arch which enables the foot to withstand tremendous forces.
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