In this section we’ll look at the upper part of the air passage. We’ll look at the external nose, the nasal cavities, the paranasal sinuses, and the nasopharynx. We’ll start by looking at the bony structures that surround these spaces.
The bony opening for the nose is called the piriform aperture. Inside it there are two nasal cavities, a right and a left, separated in the midline by the nasal septum. To get a better look inside we’ll divide the skull in the frontal plane along this line.
There’s a lot to see here. Let’s get ourselves oriented. Here’s the hard palate. Here’s the floor of the anterior cranial fossa. Here are the medial walls of the orbits. Here are the two nasal cavities. The septum dividing them is a little off center, which is not unusual. The roof of each cavity, formed by the cribriform plate, is very narrow.
The medial wall of each nasal cavity, formed by the septum, is smooth and featureless, so is the floor. By contrast the lateral wall is marked by a number of features, most notably by these three delicate bony projections, the conchae, also known as the turbinate bones. This is the inferior concha, this is the middle concha, this is the much smaller superior concha.
The three conchae partially divide the air passage into three parts, the inferior meatus, the middle meatus, and the superior meatus. Here’s the back of the orbital cavity. Below it is the hollow space in the maxilla, the maxillary antrum, which we’ll look at later.
At about the level of the floor of the orbit, the nasal cavity becomes much narrower. The narrowing is caused by the presence of this collection of small hollow spaces, the ethmoid air cells. We’ll see more of these in a minute.
To see more of the septum and the nasal cavity we’ll look at it in a skull that’s been divided just to the left of the mid-line. Here’s the bony part of the nasal septum. It’s formed by this part of the ethmoid bone, the perpendicular plate, and by this small bone that we haven’t encountered up till now, the vomer. The lowest part of the septum is formed by the maxilla and by the palatine bone.
Here’s the divided left cribriform plate. This projection above it is something we’ve seen before: it’s the crista galli. The frontal section we were looking at was divided here, just behind the crista galli.
Now we’ll remove the septum to get a good look at the lateral wall of the nasal cavity. The roof of the nasal cavity runs along this line, rising to its highest point along the length of the cribriform plate. Here are the conchae again, superior, middle, and inferior.
There are several openings in the lateral walll of the nasal cavity. They’re partly hidden by the conchae. We’ll see these in a minute. The lateral wall of the nasal cavity is formed partly by the maxilla, partly by the ethmoid bone, and partly by the perpendicular part of the palatine bone. Further back, where the nasal cavity becomes the nasopharynx, the lateral wall is formed by the medial pterygoid plate.