Posterior Muscles of Human Trunk

infraspinatus

origin: infraspinous fossa of scapula insertion: greater tubercle of humerus action: lateral rotation of arm

latissimus dorsi

origin: lower vertebrae, last 3 to 4 ribs, and iliac crest insertion: arm action: prime mover of shoulder extension; adducts and medially rotates arm

trapezius

origin: occipital bone; vertebrae insertion: acromion and spinous process of scapula; clavicle action: extension of head; superior fibers elevate scapula (as in shrugging the shoulders)

teres minor

origin: scapula insertion: greater tubercle of humerus action: lateral rotation of arm

subscapularis

origin: scapula insertion: humerus action: adduction and flexion of shoulder

teres major

origin: scapula insertion: humerus action: extension and adduction of shoulder

rhomboids -- major and minor

origin: spinous processes of vertebrae insertion: medial border of scapula action: pulls scapula medially (retraction); scapula elevation

supraspinatus

origin: supraspinous fossa of scapula insertion: greater tubercle of humerus action: abduction of shoulder

levator scapulae

origin: transverse processes of C1-C4 insertion: medial border of scapula action: elevates and adducts scapula