Brachialis muscle

Structure

Origin

The brachialis originates from the anterior surface of the distal half of the humerus, near the insertion of the deltoid muscle, which it embraces by two angular processes. Its origin extends below to within 2.5 cm of the margin of the articular surface of the humerus at the elbow joint.

Insertion

Its fibers converge to a thick tendon which is inserted into the tuberosity of the ulna, and the rough depression on the anterior surface of the coronoid process of the ulna.

Innervation

The brachialis muscle is innervated by the musculocutaneous nerve (also Casserio nerve), which runs on its superficial surface, between it and the biceps brachii. However, in 70-80% of people, the muscle has double innervation with the radial nerve (C5-T1). The divide between the two innervations is at the insertion of the deltoid.

Blood supply

The brachialis is supplied by muscular branches of the brachial artery and by the recurrent radial artery.

Variation

The muscle is occasionally doubled; additional muscle slips to the supinator, pronator teres, biceps brachii, lacertus fibrosus, or radius are more rarely found.