What is the action of the abductor digiti I longus?

• A. Extend elbow, flex shoulder
• B. Abduct digit I, extend carpus
• C. Flex elbow
• D. Abduct manus, flex carpus

Answer: (B)

The abductor digiti I longus primarily functions to abduct the first digit (thumb) and extend the carpus (wrist). This action is vital for thumb movement, allowing for a greater range of motion and facilitating grip and manipulation of objects. The muscle originates on the radius and ulna, and its fibers extend toward the base of the first metacarpal, where it performs its action.

In contrast, other choices describe actions not associated with this muscle or involve different anatomical regions. For instance, elbow extension and shoulder flexion do not relate to the function of the abductor digiti I longus, as this muscle is focused on the movements of the thumb and wrist. Similarly, while flexing the elbow and abducting the manus may be relevant for other muscles, they do not apply in this case. Therefore, option B correctly identifies the specific actions of the abductor digiti I longus and highlights its key role in hand function.