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Pectoral girdle muscles
The muscles of the pectoral girdle are an extensive group of muscles that play an important role in anchoring the superior limb to the trunk. These muscles arise from three distinct embryonic primordia and attach the scapula and clavicle to the head, vertebral column, and ribs. The trapezius and sternocleidomastoid muscles develop from the caudal branchial arches and anchor the superior limb to the cranium, a second group of muscles (serratus anterior, levator scapulae, pectoralis minor, and subclavius) migrate onto the scapula and clavicle from the outermost layer of the hypaxial body wall and anchor the superior limb to the ribs and vertebral column. The final muscles in this group (rhomboideus major and minor) migrate from the proximal end of the developing limb bud to attach to the vertebral column. For their size, these muscles produce visibly minor movements of the skeleton, but they have a much more significant function. Even the most cursory examination of the skeleton reveals that the upper limb is only weakly united with the axial skeleton. As a result of this, the major function of these prominent muscles of the pectoral girdle is to anchor the upper limb to the axial skeleton and hold it stable so the prime movers of the limb can function optimally. The functional connections these muscles form with the head and rib cage also produce respiratory functions, which have become less obvious in the human bipedal stance.