The coracobrachialis is a long, slender, fusiform-shaped muscle of the anterior arm compartment that is responsible for flexion and adduction of the arm at the shoulder joint. It is the smallest muscle in this compartment and acts as an antagonist to the deltoid.

The coracobrachialis arises from the apex of the coracoid process of the scapula, posterior to the origin of the short head of the biceps brachii. It then extends inferolaterally toward the humerus and inserts onto the midportion of its anteromedial surface between the origin sites of the brachialis and the medial head of the triceps brachii.

This muscle lies anterior to the subscapularis, teres major, latissimus dorsi, and medial head of the triceps brachii, and posterior to the pectoralis major. It lies medial to the brachialis and biceps brachii. Additionally, its anterior surface is crossed by the median nerve and brachial artery. And finally, the musculocutaneous nerve pierces the coracobrachialis as it travels from the posterior compartment into the anterior compartment of the arm.

While traditionally described as a single-headed muscle, recent cadaveric studies show the coracobrachialis can have two heads - a superficial head and a deep head - or, more rarely, a third accessory head. In our 3D model, we display a single-headed coracobrachialis.

Origin: apex of the coracoid process of the scapula; occasionally, it may also arise from the short head of the biceps brachii.

Insertion: midportion of the anteromedial surface of the humerus.

Action: flexion and adduction of the arm at the shoulder (glenohumeral) joint.

Innervation: musculocutaneous nerve (C5 - C7).

Blood supply: branches of the brachial artery, anterior circumflex humeral artery, and thoracoacromial artery (all are branches of the axillary artery).

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Coracobrachialis muscle