A 60-year-old alcoholic woman presents to the emergency room with fever, chills and shoness of breath. The sputum is rusty-yellow and contains numerous neutrophils, red blood cells and Gram-positive cocci. A chest X-ray shows diffuse haziness over both lungs. One week following admission, the patient develops empyema. This pulmonary condition is associated with the spread of bacterial infection to which of the following anatomic locations?