All the paranasal sinuses, and the nasolacrimal duct for the tears, open into the nasal cavity. To see their openings into openings into the nasal cavity, we’ll remove the conchae. The inferior concha was here. Here beneath it is the opening for the nasolacrimal duct. Beneath the middle concha, which was here, is a deep groove called the semilunar hiatus.
To see where this leads, we’ll retract its lower border with this thread. The semilunar hiatus leads into a narrow, irregular shaped side chamber called the infundibulum. The infundibulum receives the openings of the frontal sinus, and the maxillary sinus.
Sometimes the more anterior ethmoid air cells open into the infundibulum too. Sometimes, as in this case, they open separately, below the middle concha. Here’s where the superior concha was . The more posterior ethmoid air cells open below the superior concha. The sphenoid sinus, which is this cavity, opens forwards into the highest part of the nasal cavity, the spheno-ethmoidal recess.
Here’s the frontal sinus cavity, in a different specimen. The opening to the fronto-nasal duct is behind here. To see the other sinus cavities we’ll take a look from the outside, at a dissection in which all the facial soft tissues have been removed.
Here’s the maxillary sinus cavity, opened from in front. The opening from the sinus into the infundibulum is all the way up here on the medial wall. Here are the ethmoid air cells, with the lamina papyracea removed. This bony opening in the medial wall of the orbit also exposes the infundibulum.