deltoid

O: acromion and spine of scapula and lateral one-third of clavicle

I: deltoid tuberosity of humerus

A: flexion and medial rotation of arm (anterior fibers); abduction of arm (lateral fibers); extension and lateral rotation of arm (posterior fibers)

trapezius

O: external occipital protuberance, both nuchal lines, spinous processes of C1-T12

I: acromion, superior spine of scapula, posterior-lateral one-third of clavicle

A: elevate & rotate scapula upward and downward scapula

teres minor

O: lateral border of scapula

I: greater tubercle of humerus

A: lateral rotation of arm

teres major

O: inferior angle of scapula

I: medial lip of bicipital groove (intertubercular sulcus)

A: medial rotation of arm; also extension and adduction of arm

supraspinatus

O: supraspinous fossa of scapula

I: greater tubercle of humerus

A: aids deltoid in abduction

infraspinatus

O: infraspinous fossa of scapula

I: greater tubercle of humerus

A: modulates action of deltoid

O: subscapular fossa of scapula

I: lesser tubercle of humerus, anterior surface of joint capsule

A: modulates action of deltoid, rotates humerus medially

rhomboid minor

O: spinous processes of C7 & T1

I: medial border of scapula at medial angle (where spinous process meets vertebrae)

A: retraction of scapula

rhomboid major

O: spinous processes of T2-T5

I: medial border of scapula (spinous process down to inferior angle)

A: retraction of scapula