Middle cells of ethmoid bone

Within the complex architectural framework of the ethmoid bone are nestled the middle cells of ethmoid bone, a.k.a. middle ethmoidal air cells. These are a set of approximately 3 air-filled cavities that form a key part of the ethmoidal labyrinth. Together with both the anterior and posterior ethmoidal air cells, they form a sophisticated ethmoidal air cell network, positioned on either side of the nasal cavity's midline.

The anatomical arrangement of the ethmoidal air cells is meticulously designed. They are enclosed laterally by the orbital plate—a thin bony structure that separates them from the orbit. Medially, the ethmoidal labyrinth's medial wall marks their boundary with the nasal cavity. These cells are categorized into anterior, middle, and posterior groups, each with a unique position and a defined drainage pathway. Notably, the middle (alongside the anterior) ethmoidal air cells are strategically designed to facilitate drainage into the middle meatus of the nasal cavity. Specifically, the middle cells of ethmoid bone expand to create a prominence known as the ethmoidal bulla. This feature is conspicuously placed above the infundibulum—or the semilunar hiatus—within the middle meatus. As a result, these cells drain onto the ethmoidal bulla’s surface within the middle meatus.