Brachialis

Location and anatomy

The brachialis muscle (also known as Casserio's muscle) belongs to the deep layer of muscles on the anterior surface of the arm. It occupies the lower two thirds of the arm and is covered by the deep fascia.

• Origin (Origo) — anterior surface of the distal half of the humerus, as well as the medial and lateral intermuscular septa (septum intermusculare mediale et laterale).
• Insertion (Insertio) — ulnar tuberosity (tuberositas ulnae) and coronoid process (processus coronoideus). Some of the muscle bundles weave into the anterior wall of the elbow joint capsule.

Function

The muscle is the primary flexor of the forearm at the elbow joint. Some of its bundles weave into the elbow joint capsule to protect it from impingement.

Blood supply and innervation

• Blood supply is provided by branches of the brachial artery (a. brachialis), superior and inferior ulnar collateral arteries (aa. collaterales ulnaris superior et inferior), and the radial recurrent artery (a. recurrens radialis).
• Innervation is supplied by the musculocutaneus nerve — n. musculocutaneus (C5–C7). The lateral part often receives additional branches from the radial nerve (n. radialis).

Topography and adjacent structures

The brachialis muscle serves as an important topographical landmark on the upper extremity:

• In the arm: located in the deep (subfascial) layer. Superficially, it is covered by the biceps brachii muscle (m. biceps brachii). The m. brachialis itself covers the deepest layer — the elbow joint and its capsule.
• Neurovascular bundle: the brachial artery (a. brachialis) runs along the surface of the muscle in the medial (brachial) sulcus. The lateral cutaneous nerve of the forearm (n. cutaneus antebrachii lateralis) emerges from the slit between the biceps and brachialis muscles.
• In the cubital fossa (fossa cubiti): the brachialis muscle, together with the supinator (m. supinator), forms its floor. Here, the brachial artery lies in the groove between the m. brachialis and the pronator teres (m. pronator teres), located beneath the bicipital aponeurosis (aponeurosis m. bicipitis brachii).
• Lateral sulcus: deep between the brachial and brachioradialis (m. brachioradialis) muscles lie the radial nerve (n. radialis) and the radial collateral artery. Upward and laterally, between m. brachialis and m. brachioradialis, runs the radial recurrent artery.

Clinical significance

The elbow flexion function can be impaired in compression neuropathies of the musculocutaneous nerve. The primary site of nerve entrapment is where it passes through the coracobrachialis muscle. This condition occurs in strength athletes, including armwrestlers and weightlifters, due to muscle hypertrophy or repetitive stereotyped movements — elbow flexion with forearm pronation.

Class and exam questions

What else to study on this topic

• Biceps brachii muscle (m. biceps brachii)
• Cubital fossa (fossa cubiti)
• Musculocutaneous nerve (n. musculocutaneus)
• Brachial artery (a. brachialis)

Other topics in the "Anatomical Structures" section

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