The appendicular skeleton consists of the bones of the limbs, and the pectoral and pelvic girdles through which they are attached to the axial skeleton.

Functional differences between the two pairs of limbs reflect differences in their structure and in their attachment to the appendicular skeleton.

The forelimbs (arms) in man are not needed for locomotion, and hence are freed for manipulating the external environment and tools. The pectoral girdle is anchored to the appendicular skeleton only at the joint between the clavicle and sternum. This form of attachment is both weak and unstable but allows great flexibility and freedom of movement in the upper limb.

In contrast the attachment of the pelvic girdle to the sacrum is strong and stable. Balance and weight transfer are enhanced by the V shaped wedge of the sacrum fitting into the more or less rigid pelvis.