Origin: Lat. 1/ 3 of clavicle; acromion and spine of scapula. Insertion: Deltoid tuberosity of humerus.

Action:  Anterior fibers: flexion and medial rotation of humerus.

                 Middle fibers: ABD (15-90 degrees)

                 Posterior fibers: extension & external rotation of humerus.

Inervation: Axillary n. (C5, C6)

Blood Supply: Ant. & Post. circumflex humeral art.; acromial and deltoid branches of thoracoacromial trunk.

Origin: Supraspinous fossa of scapula.

Insertion: Superior facet of greater tubercle of humerus. 

Action: Initiates and assists deltoid in ABD of humerus (first 15 degrees); acts with other rotator cuff muscles in holding the head of humerus in glenoid fossa.

Inervation: Suprascapular n. (C4, C5, C6).

Blood Supply: Suprascapular and dorsal scapular arteries.

Origin: Infraspinous fossa of scapula.

Insertion: Middle facet of greater tubercle of the humerus.

Action: External Rotation of humerus; acts with rotator cuff muscles.

Inervation: Axillary n. 

Blood supply: Suprascapular and circumflex scapular aa.

Origin: Middle part of lateral border of scapula

Insertion: Inferior facet of greater tubercle of humerus.

Action: External rotation of humerus; acts with rotator cuff muscles.

Inervation: Axillary n.

Blood Supply:  Posterior humeral circumflex a.

Origin: Posterior surface of inferior angle of scapula

Insertion: Medial lip of intertubercular groove of humerus.

Action: Internal rotation of humerus.

Inervation: Lower subscapular n. (C5, C6)

Blood supply: Thoracodorsal a.

Origin: Subscapular fossa (med. 2/3 ant. surface of scapula) 

Insertion: Lesser tubercle of humerus.

Action: Most powerful IR of the humerus, ADD; acts with rotator cuff muscles.

Inervation: Upper and lower subscapular nerves. (C5, C6, C7).

Blood supply: Subscapular a.