Medial Attachment of upper fibers (Clavicular portion): Anterior surface of sternal or medial one-half of the anterior clavicle.

Lateral Attachment of upper fibers: Outer or lateral lip of the intertubercular groove of the humerus, inferior to the greater tubercle of humerus.

Action of upper fibers: Flex and internally rotate the shoulder joint, and horizontally adduct the humerus toward the opposite shoulder. May also perform abduction and adduction of the shoulder depending on the position of the shoulder joint.

Medial Attachment of lower fibers (Sternal portion): Anterior surface of sternum, cartilages of first six ribs.

Lateral Attachment of lower fibers: Outer or lateral lip of the intertubercular groove of the humerus, inferior to the greater tubercle of humerus.

Action of lower fibers: Internal rotation, horizontal adduction, extension and adduction of the shoulder joint.

Nerve: Pectoral, lateral and medial branches.

Medial Attachment: Apex of coracoid process of scapula.

Lateral Attachment: Medial surface of middle of shaft of humerus, opposite deltoid tuberosity.

Action: Flexes, adducts and horizontally adducts the shoulder joint.

Nerve: Musculocutaneous.

Medial Attachment of anterior fibers: Anterior border, superior surface, lateral one-third of clavicle.

Medial Attachment of middle fibers: Lateral margin and superior surface of acromion.

Medial Attachment of posterior fibers: Inferior lip (edge) of the spine of scapula.

Lateral Attachment: Deltoid tuberosity of humerus.

Action: Abduction of the shoulder joint, performed chiefly by the middle fibers with stabilization (and assistance) by the anterior and posterior fibers.

In addition, the anterior fibers flex, internally rotate and horizontally adduct the shoulder joint.

The posterior fibers extend, externally rotate and horizontally abduct the shoulder joint.

Nerve: Axillary.

Medial Attachment: Spinous processes of last six thoracic vertebrae (T7-T12), through the thoracolumbar fascia from the lumbar (L1-L5) and sacral (S1-S5) vertebrae, the posterior aspect of the last three ribs (10-12), posterior iliac crest, and a slip from the inferior angle of the scapula.

Lateral Attachment: Medial aspect of the intertubercular groove of humerus, just below the lesser tubercle (twists).

Action: Internally rotates, adducts, extends and horizontally abducts the shoulder joint.

Nerve: Thoracodorsal.

Medial Attachment: Inferior third of lateral border of scapula.

Lateral Attachment: Medial aspect of the intertubercular groove of humerus (Crest of lesser tubercle of humerus) just medial to the latissimus dorsi tendon and intertubercular groove

Action: Internally rotates, adducts, and extends the shoulder joint. "The Latissimus dorsi’s helper"

Nerve: Lower subscapular.

Medial Attachment: Medial two-thirds of supraspinatus fossa of scapula.

Lateral Attachment: Superior aspect of the greater tubercle of humerus (superior facet of the greater tubercle of humerus ). 

Action: Abducts the shoulder joint, and stabilizes the head of the humerus in the glenoid cavity during movements of this joint.

Nerve: Suprascapular.

Medial Attachment: Medial aspect of infraspinatus fossa of scapula.

Lateral Attachment: Posterior aspect of the greater tubercle of humerus (middle facet on the posterior aspect of the greater tubercle of humerus).

Action: Externally rotates the shoulder joint and stabilizes the head of the humerus in the glenoid cavity during movements of the shoulder.

Nerve: Suprascapular.

Medial Attachment: Upper two-thirds, posterior surface of lateral border of scapula.

Lateral Attachment: Posterior aspect of the greater tubercle of humerus (inferior facet on the posterior aspect of the greater tubercle of humerus, below the infraspinatus attachment).

Action: Externally rotates the shoulder joint, and stabilizes the head of the humerus in the glenoid cavity during movements of this joint.

Nerve: Axillary.

Medial Attachment: Subscapular fossa on the anterior aspect of scapula.

Lateral Attachment: Lesser tubercle of humerus.

Action: Internally rotates the shoulder joint, and stabilizes the head of the humerus in the glenoid cavity during movements of the shoulder.

Nerve: Subscapular, upper and lower branches.