between the 14th and 20th years, the remaining parts ossify in quick succession, and usually in the following order: first, in the root of the coracoid process, in the form of a broad scale; secondly, near the base of the acromion; thirdly, in the inferior angle and contiguous part of the vertebral border; fourthly, near the outer end of the acromion; fifthly, in the vertebral border. the base of the acromion is formed by an extension from the spine; the two nuclei of the acromion unite, and then join with the extension from the spine. the upper third of the glenoid cavity is ossified from a separate center (sub coracoid), which appears between the 10th and 11th years and joins between the 16th and the 18th years. further, an epiphysial plate appears for the lower part of the glenoid cavity, and the tip of the coracoid process frequently has a separate nucleus. these various epiphyses are joined to the bone by the 25th year. failure of bony union between the acromion and spine sometimes occurs (see os acromiale), the junction being effected by fibrous tissue, or by an imperfect articulation; in some cases of supposed fracture of the acromion with ligamentous union, it is probable that the detached segment was never united to the rest of the bone. "in terms of comparative anatomy the human scapula represents two bones that have become fused together; the (dorsal) scapula proper and the (ventral) coracoid. the epiphyseal line across the glenoid cavity is the line of fusion. they are the counterparts of the ilium and ischium of the pelvic girdle."— r. j. last – 'last's anatomy function the following muscles attach to the scapula: muscledirectionregion pectoralis minorinsertioncoracoid process coracobrachialisorigincoracoid process serratus anteriorinsertionmedial border triceps brachii (long head)origininfraglenoid tubercle biceps brachii (short head)origincoracoid process biceps brachii (long head)originsupraglenoid tubercle subscapularisoriginsubscapular fossa rhomboid majorinsertionmedial border rhomboid minorinsertionmedial border levator scapulaeinsertionmedial border trapeziusinsertionspine of scapula deltoidoriginspine of scapula supraspinatusoriginsupraspinous fossa infraspinatusorigininfraspinous fossa teres minororiginlateral border teres majororiginlateral border latissimus dorsi (a few fibers, attachment may be absent)origininferior angle omohyoidoriginsuperior border movements movements of the scapula are brought about by the scapular muscles. the scapula can perform six actions: elevation: upper trapezius and levator scapulae depression: lower trapezius retraction (adduction): rhomboids and middle trapezius protraction (abduction): serratus anterior upward rotation: upper and lower trapezius, serratus anterior downward rotation: rhomboids, levator scapulae, and pec minor clinical significance scapular fractures a winged scapula (left) left scapula, anterior surface. anatomic neck: red, surgical neck: purple because of its sturdy structure and protected location, fractures of the scapula are uncommon. when they do occur, they are an indication that severe chest trauma has occurred. scapular fractures involving the neck of the scapula have two patterns. one (rare) type of fracture is through the anatomical neck of the scapula. the other more common type of fracture is through the surgical neck of the scapula. the surgical neck exits medial to the coracoid process. an abnormally protruding inferior angle of the scapula is known as a winged scapula and can be caused by paralysis of the serratus anterior muscle. in this condition the sides of the scapula nearest the spine are positioned outward and backward. the appearance of the upper back is said to be wing-like. in addition, any condition causing weakness of the serratus anterior muscle may cause scapular "winging". scapular dyskenesis