This review suggests revisiting nose anatomy by considering the ethmoidal labyrinths as part of the olfactory nose and not as paranasal sinuses.
Phylogenetically, the olfactory and respiratory organs of the most primitive vertebrates are separated. Exaptation, a mechanism of evolution, may explain the fusion of the olfactory and respiratory organs in dipnoi. The respiratory and olfactory noses remain anatomically separated by the transverse lamina in most mammals, whose olfactory labyrinth is a blind recess housing the ethmoturbinates. In humans, the partitioning between the olfactory cleft and the ethmoid labyrinth seems to be a consequence of ethmoid bone remodeling induced by the acquisition of an upright posture. The ethmoid bone is derived from the cartilaginous nasal capsule of primitive vertebrates and considered to be a highly conserved region among the bony elements of the skull base. It appears to be involved only in housing and protecting the olfactory function.
During the early stages of human fetal development, rupture of the oronasal membrane leads to the integration of the primary olfactory sac in the future respiratory organ. The cartilaginous nasal capsule appears in the tissue under the brain and around the olfactory channels. Its early fetal development is classically regarded as the beginning of paranasal sinus formation. From phylogenic and ontogenic perspectives, it may be regarded as the development of the olfactory labyrinth as modified by the remodeling process of the human face and skull base. The endochondral bony origin of the ethmoid labyrinths makes them substantially different from the other paranasal sinuses.