A 47 year old woman presents to the emergency depament with cramping/colicky abdominal pain. The current episode of pain began several hours ago, following a fatty meal. The pain began slowly, and rose in intensity to a plateau over the course of several hours. The patient repos that she had had several other episodes of similar pain during the past several months, with long intervening periods of freedom from pain. On physical examination, she is noted to have tenderness to deep palpation in the right upper quadrant of the abdomen near the rib cage. The patient also repos that she is experiencing shoulder/back pain at a site she identifies near the right lower scapula, but no tenderness can be elicited during the back and shoulder examination. Following appropriate diagnostic studies, the patient is taken to the surgical suite. During the surgery, the surgeon inses his fingers from right to left behind the hepatoduodenal ligament. As he does so, his fingers enter which of the following?