Answer
The main function of the pectoral girdle is to attach the upper appendages ( upper limbs) to the axial skeleton. In addition, the structure of the girdle and its non-rigid moorings greatly facilitate the flexibility that humans demonstrate and utilize in play and work --swimming, throwing a ball, hammering, and painting. The bones of the pectoral girdle also provide points attachment for many important muscles.
Work Step by Step
The pectoral girdle is composed of two bones, the "S" shaped clavicle ( collar bone) and the "shield shaped" scapula (shoulder blade). The clavicle's shallow curves makes it very vulnerable to direct pressure. Consequently, it is frequently broken when a falling person tries to break his/her fall with outstretched forelimbs. The clavicle is located in a position anterior to the scapula. The former articulates with the sternum at the sternoclavicular joint.
The scapula articulates with the clavicle at the acromio-clavicular joint and with the humerus at the gleno-humeral or shoulder joint. Each scapula has a characteristic raised ridge or spine which can be easily palpated on upper back on both sides.
The bones of the pectoral girdle form important attachment points for many muscles. For instance, muscles that move the arm are attached to the supraspinatus fossa(supraspinatus muscle) and the infraspinatus fossa( infraspinatus muscle) of the scapula.
It should be noted that the bones of the pectoral girdle do not attach directly to the vertebral column. The sterno-clavicular joint is formed where medial end of clavicle meets manubrium of the sternum ; this is only direct attachment of the pectoral girdle to the axial skeleton. Muscles are mainly responsible for holding the pectoral girdle bones in place.
