Human Anatomy - Kotsan I. Ya. 2009

Muscles and fascia of the upper limb
Anterior compartment muscles of the forearm
First (superficial) layer of the anterior forearm muscles

The brachioradialis Muscle (m. brachioradialis) develops embryologically alongside the Posterior compartment Muscles of the forearm. However, because it is located on the anterolateral surface of the forearm and participates in its flexion, it is classified among the anterior forearm muscles. The brachioradialis originates from the humeral shaft just proximal to its lateral epicondyle and from the lateral intermuscular septum of the arm. At the midpoint of the forearm, the muscle belly transitions into a narrow, flat tendon that passes beneath the tendons of the abductor pollicis longus and extensor pollicis brevis, eventually inserting into the lateral surface of the distal end of the radius, just superior to its styloid process. Function: flexes the forearm at the elbow joint, pronates and (alternately) supinates it, and positions the forearm in mid-pronation-supination.

Innervation: radial nerve (C_V—С_VIII).

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Fig. 118. Anterior compartment muscles of the forearm (right upper limb)

a — superficial layer: 1 — brachioradialis muscle, 2 — pronator teres muscle, 3 — flexor carpi radialis muscle, 4 — palmaris longus muscle, 5 — flexor carpi ulnaris muscle, 6 — flexor digitorum superficialis muscle, 7 — bicipital aponeurosis; b — deep layer: 1 — supinator muscle, 2 — flexor pollicis longus muscle, 3 — flexor digitorum profundus muscle, 4 — lumbrical muscles

The pronator teres muscle (m. pronator teres) is the shortest of the superficial layer muscles (Figs. 118, 119). It originates from the medial epicondyle of the humerus, the forearm fascia, the medial intermuscular septum, and partially from the coronoid process of the ulna. This muscle inserts into the lateral and anterior surfaces of the middle third of the radius. Function: pronates and flexes the forearm.

Innervation: median nerve (С_V—T_hl).

The flexor carpi radialis muscle (m. flexor carpi radialis) is fusiform in shape, lies superficially beneath the Skin, and acts across multiple joints. The muscle originates from the medial epicondyle of the humerus, the medial intermuscular septum of the arm, and the forearm fascia. At approximately the middle of the forearm, it continues as a flat, long tendon that enters the hand beneath the flexor retinaculum and inserts into the Base of the second (and partially the third) metacarpal bone. Function: flexes the forearm at the elbow joint; flexes the hand at the radiocarpal and midcarpal joints; acting in synergy with the extensor carpi radialis, it can radially deviate (abduct) the hand.

Innervation: median nerve (С_V—Т_hІ).

The palmaris longus muscle (m. palmaris longus) is a variable muscle and may be absent in some individuals. It originates from the medial epicondyle of the humerus, the medial intermuscular septum of the arm, and the forearm fascia. It has a fusiform shape with a short muscle belly and a very long tendon that crosses into the hand beneath the flexor retinaculum to blend into the palmar aponeurosis. Function: tautens the palmar aponeurosis, flexes the hand and forearm.

Innervation: median nerve (С_V—Т_hІ).

The flexor carpi ulnaris muscle (m. flexor carpi ulnaris) arises from two heads—humeral and ulnar. The humeral HEAD originates from the medial epicondyle of the humerus and the medial intermuscular septum of the arm. The ulnar head originates from the olecranon of the ulna and the forearm fascia. In the proximal third of the forearm, both heads merge into a single belly that extends along the medial border of the forearm; its long tendon inserts into the pisiform bone, while some muscle fibers attach via ligaments to the hamate bone and the base of the fifth metacarpal bone. Function: flexes the forearm and hand; acting concurrently with the extensor carpi ulnaris, it ulnarly deviates (adducts) the hand.

Innervation: ulnar nerve (С_VII—С_VIII).