Final answer:
The muscle attached to the anterior ulna shaft is the flexor carpi ulnaris.
Step-by-step explanation:
The muscle that is attached to the anterior ulna shaft is the flexor carpi ulnaris. This muscle is located in the anterior compartment of the forearm and is responsible for flexing the wrist and ulnar deviation. It originates on the humerus and inserts onto the pisiform bone (a small bone of the hand) and the hamate bone (a bone of the wrist).