Review Question - QID 219850

A 23-year-old male presents to the emergency department after an assault which resulted in lacerations over his right antecubital fossa and torso. On exam, the patient has greater than 10 mm two-point discrimination along the thumb, index, and long finger with 4 mm two-point discrimination along the small and ulnar half of the ring finger. He cannot flex the thumb at the interphalangeal joint or abduct the index finger. He can abduct the small finger and extend the thumb interphalangeal joint. Which anatomical variant explains the physical exam findings in this patient?