Which color line marks the posterior border of the maxillary sinus?

• A. Purple Line
• B. Light Blue Line
• C. Green Line
• D. Red Line

Answer: (B)

The posterior border is the back wall of the maxillary sinus—the boundary that faces the infratemporal fossa and sits near the pterygomaxillary fissure. On standard diagrams, the line that runs along this back wall is drawn in light blue, so it marks the posterior border. The other colored lines typically correspond to the other borders (such as the anterior facial wall, the orbital or superior border, and the inferior border near the alveolar process), which is why only the light blue line identifies the posterior boundary.