(3.23)

In a minute we’ll look at the individual named bones that form the facial skeleton. Before we do that, we need to take a look at some of the features of the inside of the skull.

This special skull has been cut away at a series of levels that are just above the floor of the cranium. The way it’s been cut reflects the fact that there are two big steps in the floor of the cranium, formed by the sphenoid ridges, and the petrous temporal bones. These divide the floor of the cranial cavity into three parts, the anterior cranial fossa, the middle cranial fossa, and the posterior cranial fossa.

We saw the posterior cranial fossa in the previous section. In this section we’ll look at the main features of the anterior and middle cranial fossae. The bone that forms this upward bulge in the floor of the anterior fossa is the same bone that forms the roof of the orbit

This midline crest is called the crista galli. On either side of it is a depression, the base of which is formed by these small areas of thin, perforated bone, the cribriform plates. The cribriform plate forms the very narrow roof of the nasal cavity. Here we can see it from below. The filaments of the olfactory nerve, which transmits the sense of smell, pass through the openings in the cribriform plate.

This flat area behind the cribriform plates is the roof of a cavity that we'll see later, the sphenoid sinus. Now we'll move back to the middle cranial fossa.

The bone that forms the side wall and floor of the middle cranial fossa also forms, on the outside of the skull, the wall of the temporal fossa, and of the infratemporal fossa.

We’ve seen that this is the roof of the orbit. The bone that forms the anterior wall of the middle temporal fossa also forms part of the orbit: it forms this posterior part of the lateral orbital wall.

This complicated raised area in the middle is called the sella turcica. The main features of the sella turcica are this deep depression, the pituitary fossa for the pituitary gland, this shallow groove for the two optic nerves, and these four projections, the anterior, and posterior clinoid processes. This sloping surface behind the posterior clinoid processes, the dorsum sellae, is continuous with the base of the occiput.

The floor of the middle cranial fossa is marked by numerous openings for nerves and blood vessels, which we’ll come back to later in this section.