Atlas of Human Anatomy in Cross Section: Section 4. Upper Limb

Plate 4.15

Ronald A. Bergman, Ph.D., Adel K. Afifi, M.D., Jean J. Jew, M.D., and Paul C. Reimann, B.S.
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This section passes through the upper third of the forearm distal to the insertion of the arm muscles. The medially placed basilic (20) and the laterally placed cephalic (3) veins are seen.

The belly of palmaris longus (25) is decreasing in size and is tendinous in the next section.

Pronator teres muscle (5) arises from two heads. The humeral or chief head originates from the superior half of the ventral surface of the medial epicondyle and from the overlying fascia and intermuscular septa between it and the medial head of the triceps and flexor carpi radialis (26). The ulnar or deep head (accessory head) arises by an aponeurotic band from the medial border of the coronoid process of the ulna, medial to the tendon of the brachialis muscle. It is important to note that a fibrous arch extends between the humeral and ulnar heads through which the median nerve passes. At this point the median nerve can become trapped and compromised. The muscle inserts by a broad tendon that winds around the ventral surface of the radius (9) and attaches onto the middle third of its lateral surface. The muscle is innervated by a branch from the median nerve (2) before it passes between the two heads of the muscle. The nerve enters the proximal part of the middle third of the main belly of the muscle on its deep surface near the radial border. The branch to the ulnar head is proximal to its fusion with the humeral head.

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