Which of the following heads contribute to the proximal attachment of the flexor carpi ulnaris?

The flexor carpi ulnaris has two heads that contribute to its proximal attachment: the humeral head and the ulnar head. The humeral head originates from the medial epicondyle of the humerus via the common flexor tendon, while the ulnar head arises from the olecranon and the posterior border of the ulna. Both of these heads join together to form a robust muscle that plays a key role in flexing and adducting the wrist.

The humeral head is crucial due to its attachment to the prominent structure of the upper arm, allowing for powerful movements, while the ulnar head provides additional stability and strength from the ulna's bony structure. This dual attachment is essential for the muscle to perform its functions effectively, making option B the correct choice.