A 38-year-old man had 28 removed 5 days ago after a posterior superior alveolar block. He now has a painful swelling of the right temple above the zygomatic arch and a second swelling of the cheek below the arch, giving an hourglass shape. He can open only 15 mm. Intraorally there is tender fullness high in the vestibule behind the tuberosity. His temperature is 38.4 C. Spread of infection into which space best explains these findings?