The concept of ethmoidal sinuses composed of ethmoidal air cells does not appear to fit with the embryological origin of the ethmoid. Post-natal formation of the paranasal sinuses, as visualized by MRI, appears to be fundamentally different from the embryological development of the ethmoid sinus. These two organs also appear to have very distinct functions: paranasal sinuses play a role in respiration and sanitization of the respiratory tract, while the ethmoid sinus plays a role in olfaction. However, human acquisition of bipedalism resulted in ethmoidal compartmentalization into olfactory clefts lined by olfactory mucosa and the ethmoidal labyrinth formed by a meshwork of ethmoturbinals that have lost their olfactory mucosa. Ethmoturbinals are septa that increase the surface area of olfactory mucosa in mammalian olfactory chambers. Embryological development of the human ethmoid sinus can be seen as the result of curved stacking of ethmoturbinal septa forming passages. Surgically, these passages can be accessed via the middle, superior and supreme meati. An ethmoidectomy technique following the ethmoturbinal passages can therefore be described. This structure of the ethmoidal labyrinth is both useful and necessary for the teaching of ethmoidal surgery.