What two structures clearly divide the forearm flexors from the extensors?

• A. Brachioradialis and shaft of ulna
• B. Brachioradialis and radius
• C. Median nerve and ulnar nerve
• D. Flexor retinaculum and extensor retinaculum

Answer: (A)

The forearm is organized into a front (flexor) compartment and a back (extensor) compartment. The boundary between these two groups is most clearly seen along the lateral and medial sides: the brachioradialis sits at the outer edge of the forearm and marks where the flexor group ends and the extensor group begins, while the shaft of the ulna forms the medial border that helps separate the muscle masses along the forearm. Together these two structures create the clear division between flexors and extensors.

The other options don’t provide that compartmental boundary: the radius isn’t the dividing border for the forearm muscles, the nerves run through or between compartments rather than separating all flexors from extensors, and the retinacula are wrist structures, not forearm separators.