Art Anatomy

The Structure of the Forearm

Here is a schematic diagram of the arrangement of the muscles on the forearm. The circle represents a cross-section of the forearm. (Imagine the forearm with the fingers pointing at you for the correct orientation.) The dividing forms, brachioradialis and the ulna, are represented by the large nodes at opposite poles.

Down one side of the circle are the four long flexor muscles, all on the medial epicondyle of the humerus; down the other are the four long extensors, all on the lateral epicondyle. Flexor carpi ulnaris can be paired with extensor carpi ulnaris, and flexor digitorum can be paired with extensor digitorum. Flexor carpi radialis can be paired with both extensors carpi radialis (longus and brevis), leaving only palmaris without a similarly-named extensor.

The thumb group, positioned between extensor carpi radialis and extensor digitorum, breaks the four long extensors into two groups of two.

Pronator teres and anconeus, both short muscles near the elbow, lie opposite each other on the circle in their proper positions on the forearm.

Last is little extensor digiti minimi, between extensor digitorum and extensor carpi ulnaris.

Arranged this way, the beautiful symmetry of the forearm is apparent. The left side contains only extensors (and excepting the thumb group, all the muscles originate on the lateral epicondyle). The right side contains only flexors, all of which originate on the medial epicondyle. No matter how the forearm is positioned, the order described on the circle still holds.

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