A man is unable to hold typing paper between his index and middle fingers. Which of the following nerves was likely injured?

To hold a typing paper, the index finger is adducted by the palmar interosseous muscle, and the middle finger is abducted by the dorsal interosseous muscle. Both muscles are innervated by the ulnar nerve. Card test: Patient is asked to hold a card b/w two extended fingers while examiner tries to pull it. Power of palmar interossei (adductors) supplied by ulnar nerve can be judged.