abductor pollicis, radioulna-prepollox

The abductor pollicis radioulna-prepollox (m. abductor pollicis) is a specialized muscle found in certain tetrapods that originates on the distal radioulna (the fused forearm bone) and inserts on the palmar prepollex (a small sesamoid or accessory bone medial to the first digit). It abducts the thumb region.

This muscle is positioned in the distal forearm to proximal hand region, running from its origin on the distal radioulna to its insertion on the palmar prepollex. It spans the wrist and acts on the thumb or its homolog in the species bearing it.

This muscle performs abduction of the thumb or pre-thumb structure (prepollex), drawing it away from the midline of the limb. In the animals where it is found, this contributes to manipulative ability and digit positioning.

As a structure studied primarily in comparative anatomy, clinical information specific to this muscle is limited. Injury to the distal radioulna or to the prepollex region in relevant species would be expected to affect this muscle's function.

The human abductor pollicis longus inserts on the base of the first metacarpal, while the abductor pollicis radioulna-prepollox inserts on the prepollex — an accessory structure not present in the human hand. This distinction reflects the diversity in digit and thumb architecture across tetrapod vertebrates.