Which of the following is identified as a muscle of the antebrachium?

The flexor carpi ulnaris and extensor carpi radialis are both muscles located in the antebrachium, which is the region of the forearm. Specifically, the extensor carpi radialis is classified as a muscle of the antebrachium that functions primarily to extend the carpal joint and can also assist in lateral movement of the wrist.

On the other hand, the flexor carpi ulnaris, while also a muscle of the antebrachium, does not share the same function as the extensor carpi radialis, which is focused on extension rather than flexion. The other two muscles listed, the rhomboid (often referred to as rector scapulae) and trapezius, are muscles of the shoulder region and are primarily involved in the movement of the scapula. Therefore, they do not pertain to the antebrachium.

In summary, the correct choice reflects a muscle directly associated with actions in the antebrachium, specifically involving wrist extension, which sets it apart from the other options provided.