Deltoid

( Triangularly shaped)

O : acromial extermeity of clavicle(anterior fibers), acromion of scapula (lateral fibers), and spine of scapula (posterior fibers)

I : Deltoid tuberosity of humerus

Action : Lateral fibers abduct arm at shoulder joint; anterior fibers flex and medially rotate arm at shoulder joint: posterior fibers extend and laterally rotate arm at shoulder joint

innervation : axillary nerve

Subscapularis

(sub = below

Scapularis = scapula)

O : Subscapular fossa of scapula

I : Lesser tubercle of humerus

Action: Medially rotates arm at shoulder joint.

innervation : upper and lower subscapular nerve

Supraspinatus

(supra = above ; spina- = spine(of the scapula))

O:  supraspinous fossa of scapula

I : greater tubercle of humerus

Actions : assists deltoid muslce in abducting arm at shoulder joint

innervation : suprascapular nerve

Infraspinatus

(infra = below)

O : infraspinous fossa of scapula

I :  Greater tubercle of humerus.

action : laterally rotates art at shoulder joint.

innervation : suprascapular nerve.

Teres major

(teres = long and round)

O : inferior angle of scapula

I : Medial lip of intertubercular sulcus of humerus

Actions : extends arm at shoulder joint and assists in adduction and medial rotation of art at shoulder joint.

Innervation : lower subscapular nerve

O : Inferior lateral border of scapula

I : greater tubercle of humerus

Action : laterally rotates and extends arm at shoulder joint

Innervation : axillary nerve

Coracobrachialis

( coraco- = coracoid process [of the scapula];

brachi- = arm)

O :  coracoid process of scapula

I :  Middle of medial surface of shaft of humerus

Action : flexes and adducts arm at shoulder joint

innervation : musculocutaneous nerve.