Anterior Compartment of the Arm

The anterior compartment of the arm (also called the flexor compartment) contains muscles responsible for flexion of the elbow and shoulder, as well as forearm supination. It is bounded by the brachial fascia and separated from the posterior compartment by the medial and lateral intermuscular septa. It also houses major neurovascular structures including the musculocutaneous nerve and brachial artery.

Boundaries

Structure	Description
Anterior	Brachial fascia and skin
Posterior	Humerus and intermuscular septa
Medial & Lateral	Medial and lateral intermuscular septa

Muscles of the Anterior Compartment

Muscle	Origin	Insertion	Function	Innervation
Biceps brachii	Long head: supraglenoid tubercle Short head: coracoid process	Radial tuberosity and bicipital aponeurosis	Flexes elbow, supinates forearm, weak shoulder flexion	Musculocutaneous nerve (C5–C6)
Brachialis	Distal anterior surface of humerus	Coronoid process and tuberosity of ulna	Main flexor of the elbow (regardless of forearm position)	Musculocutaneous nerve (C5–C6), radial nerve (partial)
Coracobrachialis	Coracoid process of scapula	Medial surface of humerus (midshaft)	Flexes and adducts the shoulder	Musculocutaneous nerve (C5–C7)

Musculocutaneous nerve: Innervates all three muscles; emerges as lateral cutaneous nerve of forearm
Brachial artery: Main arterial supply; gives off profunda brachii and nutrient branches
Median nerve and ulnar nerve: Pass through the compartment but do not innervate it
Basilic vein: Travels medially in the superficial fascia

Function

Elbow Flexion: Primarily by brachialis and biceps brachii
Forearm Supination: Biceps brachii (when forearm is flexed)
Shoulder Flexion and Adduction: Coracobrachialis and biceps (short head)

Blood Supply

Brachial artery: Continuation of axillary artery; supplies all muscles and gives branches to the humerus

Innervation

Musculocutaneous nerve (C5–C7): Sole motor nerve of this compartment

Clinical Significance

Compartment Syndrome: Increased pressure within the anterior compartment can compromise perfusion and nerve function, requiring fasciotomy
Biceps Tendon Rupture: Results in a “Popeye” deformity and loss of supination power
Musculocutaneous Nerve Injury: Rare but can cause weakness in elbow flexion and loss of lateral forearm sensation

Comparative Anatomy

In quadrupeds, the anterior compartment is less prominent due to reduced elbow flexion demands. In humans, it is well-developed to support carrying, lifting, and tool manipulation — functions dependent on controlled forearm positioning and strength.