The back part of the surface is subdivided by a narrow oblique fissure, the superior meatus of the nose, bounded above by a thin, curved plate, the superior nasal concha; the posterior ethmoidal cells open into this meatus. Below, and in front of the superior meatus, is the convex surface of the middle nasal concha; it extends along the whole length of the medial surface of the labyrinth, and its lower margin is free and thick.
The posterior area of the surface is segmented by a narrow, angled groove, the upper nasal channel, bounded above by a thin, curved plate, the superior nasal turbinate; the posterior ethmoidal cells open into this channel. Below, and in front of the upper nasal channel, is the convex surface of the middle nasal turbinate; it extends along the entire length of the medial surface of the labyrinth, and its lower edge is free and thick.