The fore and him limbs were evolved basically for bearing the weight of the body and for locomotion as is seen in quadrupeds cows or dogs. The two pairs of limbs are therefore built on the same basic principle.
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Each limb is made up of a basal segment or girdle and a free part divided into proximal, middle and distal segments. The girdle attaches the limb to the axial skeleton. The distal segment carries five digits. Tables 1.1 show homologous parts of upper and lower limbs.
However, with the evolution of the erect posture in man, the function of weight bearing was taken over by the lower limbs. Thus the upper limbs, especially the hand, became free and gradually evolved into organs having great mainpulative skills.
This has became possible because of a wide range of mobility at the shoulder. The whole upper limbs works as a jointed lever. The human hand is a grasping tool. It is exquisite adaptable to preform various complex functions under the control of a large area of the brain. The unique position of man as a master mechanic of the animal world is because of the skilled movements of this hands.
Medical Book PDF: Human Anatomy 6th