Now that we’ve seen the ethmoid bone, we’ll return to the cavities for the paranasal sinuses, and see how they connect with the nasal cavity. We’ll look at the openings for the frontal and maxillary sinuses first.
Here’s the frontal sinus cavity, here’s the maxillary sinus cavity, seen through an artificial opening. The frontal and maxillary sinuses both open in this complex area beneath the middle concha, which we need to look at in more detail. In a dry skull there are two large irregular openings from the nasal cavity into the maxillary sinus, separated by this flake of bone, the uncinate process.
In the living body all of this opening, and much of this one, are closed off by soft tissue. The real opening of the maxillary sinus is back here. If we look in from in front, we can see that the opening is quite high on the medial wall of the maxillary antrum.
The frontal sinus opens into the nasal cavity by way of a narrow passage, the fronto-nasal duct. The fronto-nasal duct starts above the uncinate process, and runs upward and forward to reach the frontal sinus.
The frontal and maxillary sinuses open into the nasal cavity not directly, but into a narrow side chamber located here, called the infundibulum. The infundibulum isn’t apparent in a bony specimen. We’ll see it when we look at the soft tissues.
Now we’ll look at the openings for the other sinuses. The sphenoid sinus opens into the nasal cavity here, above and behind the superior concha. The ethmoid air cells, which are up in this region, have several small openings into the nasal cavity. Some of these are behind the middle concha some of them are below it.
There are two more openings to see in the lateral wall of the nasal cavity: the opening for the nasolacrimal duct, or tear duct, and an opening for nerves and blood vessels, the spheno-palatine foramen.
As we’ve seen, the bony passage for the naso-lacrimal duct starts here.
The naso-lacrimal duct, which is quite short, passes downwards and backwards to open beneath the inferior concha: here’s its opening.
The last opening to look at, the sphenopalatine foramen, is the inner end of a short tunnel for blood vessels and nerves to the nose and palate. On the inside it opens near the back of the superior meatus. We’ll go all the way round to the outside to see the other end of the sphenopalatine foramen which is here, in the depths of the pterygo-maxillary fissure.