Transcription

This tutorial is on the foramina of the skull.   Foramina are openings which allow structures to pass through in the body.   If you just look at this model, you can just see these little holes here, which if you’ve watched the other tutorials I’ve done in the skull, you’ll have seen and probably wondered what they were. These are called foramen and the plural is ‘foramina’. And again, these are all Latin, coming from the Latin names that they have.

A foramen allows a structure to pass through, so things like blood vessels and nerves. In the skull, they’re really important to know because many important blood vessels pass through these foramina to supply the brain and several important nerves pass through them to carry information to and from the brain. It’s quite a complicated topic, so I’m going to break it into a few parts just to make things a bit more digestible.

 

This part, I’ll start from an external view, looking at the skull and the various foramina. I’ll go to an interior view and take a look at them from there. And then there are other parts of this tutorial which we’ll follow on. I’ll talk about all the different structures that pass through. It’s really important that you know about these because med schools in particular love to ask questions about which structures pass through which foramen.

 

To begin with, I’m going to talk about the foramina that you can see from the outside view of the skull.   Starting superiorly, looking into the orbits of the skull, we can see quite a few little holes, which are quite important to know.

 

Most medially, you’ve got this little hole here and this is called the optic canal. When I talk about these, you’ve got them on both sides.   They’re bilateral. You’ve got the optic canal here, which is most medial. You’ve got this big opening here, which isn’t technically a foramina. It’s referred to as a fissure. As you can see, it’s a big sort of opening in the skull.   This is the superior orbital fissure. If you look just inferior, you can probably guess, you’ve got the inferior orbital fissure.

 

In the orbit, you’ve got this optic canal, you’ve got this superior orbital fissure and you’ve got the inferior orbital fissure. These are bilateral, so they’re on both sides.

 

Just to demonstrate what structures pass through, I’ll just show you some nerve and some blood vessels. And again, I’ll be talking about these in detail in the next few parts because there’s quite a lot to get through.

 

As you can see there’s this big nerve here coming through the optic canal. You’ve got blood vessels and you’ve got all these little nerves coming through this fissure. And again, if we just zoom out a bit, you can see these vessels just emerging.

 

That’s the foramen, which you can see in the orbit. We’ll just get rid of that.

 

Just moving on to these ones here just inferiorly, you’ve got these little foramen which lie in the maxilla.   This is called the infraorbital foramen because it’s below, infra-, below the orbit. You’ve got these on both sides. These, you get the infraorbital nerves and vessels which pass through this.

 

The supraorbital foramen, which is just a little notch here is also referred to as the supraorbital notch.   Again, supra-, above the orbit. And this allows the supraorbital nerves and vessels to pass.

 

If you just move a little bit laterally, we’ve got this little hole here. This is the zygomatico facial foramen. And again, you’ve got this on both sides. This allows the zygomatico facial nerve to pass through. Try not to worry about what passes through in this tutorial. Just try and remember the names. I’m trying to remember them in terms of their position because all terms in anatomy are relatively logically named. It makes it a little bit easier to try and remember if you remember why they’re named that.   Infraorbit, below the orbit, infraorbital foramen.

 

And then right down here, you’ve got these little holes, these foramina. These are the mental foramen and they allow the mental nerves and vessels to pass.

 

Those are the foramina you can see externally.

 

Next one I’m going to do is I’m going to switch to a view inside the skull.   If you just see what I’m doing, I’m just going to get rid of the outside of the skull and we’re going to take a look from inside. I’m just going to bring it around and we can have a good look.

 

We’re now looking at the base of the skull from the inside. I got rid of the outside of the skull and we’re looking down at this base of the skull at the foramen from that perspective.   If I just go back to that.   Anterior is up here and this is posterior just so you can orientate yourselves.

 

Just before I start talking about the foramina of the skull, I’m just going to talk about the cranial fossa because you’ll often hear people referring to these.

 

Again, anatomy is like another language. It’s a lot of words you’ll hear repeatedly because they actually mean something in Latin. It’s useful to try and remember what these words mean.   A ‘fossa’ is just a ditch in Latin. It’s like a little hallowing.

 

If you look from a lateral view, you can see that there are three little ditches here in the brain, fossa. You’ve got the anterior one, which is the anterior cranial fossa, the middle cranial fossa and the posterior cranial fossa, which is most inferior also – so three cranial fossa. It’s useful to know about these because people will describe structures which pass through various cranial fossae (which is plural).

 

From a superior view, which I’m now showing you again looking down at the skull, you’ve got the anterior cranial fossa which is this part. This anterior cranial fossa forms the roof of the nasal cavity and the central part.   This central part of the anterior cranial fossa forms the roof of the nasal cavity. You’ve got the cribriform plate and the crista galli, which you might remember from my other tutorials.

 

And then laterally, these lateral portions house the frontal lobes of the brain.   That’s the anterior cranial fossa.

 

And then you’ve got the middle cranial fossa. It’s this entire bit, which I’m showing you with the mouse.   All around here, this is the middle cranial fossa. Posteriorly, you’ve got the dorsum sellae, this structure here. That’s the back of the middle cranial fossa, this dorsum sellae, which you might remember from another tutorial.

 

And then you’ve got the posterior cranial fossa right at the back, which contains the brain stem and cerebellum. It’s the most inferior fossa.

 

Just again looking laterally …anterior, middle and posterior. Let’s get rid of that. If I bring in the brain, you can see how it just sits in this fossa. I’ll just get rid of the outer membrane and now you can see the cerebellum and the brain stem sitting in the posterior cranial fossa. You can see the temporal lobe sitting in the middle cranial fossa and you can see the frontal lobe sitting in the anterior cranial fossa.

 

Now that I’ve covered that, we can go back to talking about the foramen or foramina. Just to remind you, I’m going to be doing this in few parts.   If you’re getting a bit bored by this and you want to see all the cranial nerves and how they pass through, I’ll be using views like this from the base of the skull, showing you what kinds of structures pass through and views like this showing you how the cranial nerves pass through. But this tutorial, I’m just focusing on the foramina themselves.

 

Again, looking superiorly down at the base of the skull, I’m just going to work from anterior to posterior and talk about these foramina.

 

These holes here right at the front are the optic canals. You saw them from the outside.   These little holes here, which sit medially in the orbit. That’s the optic canal. And then if you remember the superior orbital fissure, that’s this here. And just going back to the external view, the superior orbital fissure here, which you can see.

 

Then we’ve got a few more which you couldn't see from the external view that I showed you just before. You’ve got these holes in the middle cranial fossa.   Posteriorly and laterally in the middle cranial fossa, you’ve got a little round hole on either side here. This is called the foramen spinosum. That’s the most lateral and posterior in the middle cranial fossa. And then you’ve got this big oval-shaped structured – well, not structure, hole. It’s just aptly named the foramen ovale.

 

And then – you can’t quite see it from here, so I’m going to rotate the skull around.   You can see just below the superior orbital fissure, you can see this little round hole here. And again, this is named the foramen rotunda because of its shape. That lies anterior to the foramen ovale.

 

You’ve got the spinosum, the ovale, the rotundum and then you’ve got this huge laceration here. This is called the foramen lacerum. In life, this is actually filled with cartilage.   No structures actually pass through this one.

 

Again, laterally, you’ve got the foramen spinosum, then you’ve got the foramen ovale and then you’ve got the foramen rotunda.

 

That’s the foramen of the middle cranial fossa.

 

Now we’re just going to look at the foramen that you’ve got in the posterior cranial fossa. This one here is the internal auditory meatus. And then if you work yourself slightly inferiorly and posteriorly, you’ve got another foramen, which is the jugular foramen. Quite a few structures pass through that.

 

Working even further down, more inferiorly, you’ve got the hypoglossal canal. And then obviously, you’ve got this huge one in the middle and that’s the foramen magnum.   Again, ‘magnum’ in Latin means ‘great’, so it’s the ‘great foramen’. The brain stem passes through here and this is where it becomes the spinal cord. This is the foramen magnum.

 

Just looking at this view (because in a lot of atlases, you’ve got this superior view), you’ve got the – I can’t quite see it. You’ve got the internal auditory meatus, you’ve got the jugular foramen and then you’ve got the hypoglossal canal and the big foramen magnum.

 

Just to very quickly recap what I’ve been over, you’ve got the optic canal at the front, the superior orbital fissure, the foramen rotundum, you’ve got the foramen spinosum, the foramen ovale, the foramen lacerum in the middle cranial fossa. And then in the posterior cranial fossa, you’ve got the internal auditory meatus, the jugular foramen and the hypoglossal canal, as well as the big foramen magnum down here.