Anatomy of the Ribs, Shoulder Bone, and Clavicle Ribs • 12 pairs of ribs for the walls of the bony thorax. • All ribs articulate with the vertebral column posteriorly and downward toward the anterior body surface. • True Ribs = first 7 pairs • Attach directly to the sternum by costal cartilages. • False Ribs = next 5 pairs • Attach either indirectly or not at all to the sternum • Floating Ribs = Last 2 pairs • Lack sternal attachment Clavicular Notch Shoulder Girdle • Each shoulder girdle has 2 bones – a clavicle and a scapula. • The clavicle “collarbone” acts as a brace to hold the arm away from the top of the thorax and helps to prevent shoulder dislocation. • When the clavicle is broken the whole shoulder region caves in medially. Shoulder Girdle • The scapulae (shoulder blades) are commonly called wings due to triangular shape. • 2 important processes: • Acromin- enlarged end of the spine of the scapula • Connects the clavicle to the acromioclavicular joint. • Coracoid Process-beak like • Anchors some of the muscles of the arm. • Suprascapular notch- serves as a nerve passageway. • Glenoid Cavity- shallow socket that receives the head of the arm bone Shoulder Girdle Allows upper limb to have exceptionally free movement due to: 1. Each shoulder girdle attaches to the axial skeleton at only one point – the sternoclavicular joint. 2. The loose attachment of the scapula allows it to slide back and forth against the thorax as muscles act. 3. The glenoid cavity is shallow and the shoulder joint is poorly reinforced by ligaments • The drawback to exceptional flexibility is that the shoulder girdle is easily dislocated..
