Which muscle is innervated by the ulnar nerve?

The Flexor carpi ulnaris is indeed innervated by the ulnar nerve, making it the correct answer. This muscle is important for wrist flexion and also assists with adduction of the wrist. The ulnar nerve plays a key role in the functioning of muscles in the forearm and hand, particularly those responsible for fine motor movements.

In contrast, the Flexor carpi radialis is innervated by the median nerve, which is distinct from the ulnar nerve's responsibility. The Biceps brachii is also not innervated by the ulnar nerve; it is primarily innervated by the musculocutaneous nerve. The Palmaris longus, while also a flexor of the wrist, is innervated by the median nerve, not the ulnar nerve.

Thus, the role of the ulnar nerve is specifically associated with the Flexor carpi ulnaris, making this the correct choice in understanding muscle innervation in the forearm.