Answer:
The internal nasal valve is defined as the junction between the septum and the caudal border of the upper lateral cartilage. Here, where the upper lateral cartilage diverges from the septum (become separate structures), the mucoperichondrium contains a fibrous aponeurosis that lends support to this area of the internal nasal valve. The angle is usually 10-15 degrees, and must be protected or reconstructed with a spreader graft to preserve flexible patency for a normal airway.