The nasal cavities are narrow spaces, lined with mucous membranes, which extend from the nostrils to the apertures to the pharynx (choanae). The two cavities (left and right) are separated by a cartilaginous septum.
Both nasal cavities have inferior, middle and superior turbinates.
Then we have the paranasal sinuses, paired air-filled spaces, lying between the skull bones and the skin, which communicate with the nasal cavities by way of the ostia.
The sinuses have numerous important functions such as humidifying the air we breathe and acting as resonating chambers for our voice. They also have a protective function.