Ethmoid bone

The ethmoid bone, shaped like a cube, sits at the front of the skull and connects with surrounding bones. It plays a key role in forming the inner walls of the eye sockets, the nasal septum, and both the roof and sidewalls of the nasal cavity. The ethmoid bone has a cribriform plate—a perforated, horizontal structure at the top of the nasal cavity—which allows olfactory nerves to pass through, enabling the brain to detect smells. From the center of the cribriform plate, a vertical part known as the perpendicular plate extends downward, forming the upper part of the nasal septum's bony framework.

On either side of the perpendicular plate of ethmoid bone, there are two box shaped parts, the lateral labyrinths, connected at the top by the cribriform plate. This arrangement looks a bit like the letter 'M', with the perpendicular pate forming the middle, and the ethmoidal labyrinths as the sides. Each labyrinth contains both external and internal walls and encases the ethmoidal air cells between them. The external side (or the orbital plate) contributes to the medial wall of the eye socket, while the internal side forms part of the lateral wall of the nasal cavity. Although the outer wall of the labyrinth is plain, the inner side, which faces the nasal cavity, features several key important anatomical structures such as the superior and middle conchae, related meatuses, the extension of the ethmoidal infundibulum into the frontonasal duct, and the ethmoidal bulla.