Video: Anatomy of the skull
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This is the face of Halloween. Since we were kids, you've probably seen this fella in every house, store, and is part of every costume around that time of year. In fact, we've seen it so much that ... Read more
This is the face of Halloween. Since we were kids, you've probably seen this fella in every house, store, and is part of every costume around that time of year. In fact, we've seen it so much that it doesn't seem spooky anymore. But now that you've decided to learn its anatomy, you might find that the skull is scarier than you thought. If we look at some questions on our quizzes at Kenhub, you will see that there are many, many structures to identify, like this one asking us to spell the bone highlighted in green or this one asking us to pick the image with the occipital bone highlighted, or even details related to the bones of the skull that are important to know such as this question asking which bone forms the upper jaw. Stay tuned. At the end of this tutorial, we will answer those questions with what we learn in this video on the introduction to the skull.
Even though it looks like one bone, the skull actually consists of about twenty-two to twenty-nine single bones which are mostly connected together by fibrous joints called sutures. I say twenty-two to twenty-nine because we can also consider the hyoid and inner ear bones, but in this video, we won't be covering those bones.
The skull is divided into two parts. The first is the braincase also known as the neurocranium which encloses the brain. From that, you probably can guess that one of the main functions of the braincase is to protect your brain. In addition to the braincase, there's the facial skeleton known as the viscerocranium which provides structure and support for soft tissues of the face and houses the teeth.
Let's first look at the structure of the braincase.
This part of the skull is composed of eight bones – the frontal bone, the ethmoid bone, the sphenoid bone, two parietal bones, two temporal bones, and one occipital bone. The braincase can be divided into two parts – the skullcap which we also called the calvaria and the cranial base. If we look at the top of the skull, you can see that the skullcap is made up of paired parietal bones and parts of the frontal bone as well as the occipital bone. From this view, you can also see these lines separating the bones of the skull. They are called sutures. There are thirty-three sutures that you can learn about, but for now, we will focus on the three largest ones.
The first one is the coronal suture found between the frontal and the parietal bone, the second one is the sagittal suture dividing both parietal bones, and the last one is the lambdoidal suture, which runs horizontally between the occipital bone and both parietal bones.
As we mentioned before, the other part of the braincase is the skull base which is the lower portion of the neurocranium. Looking at it from the inside, it can be subdivided into the anterior fossa, the middle fossa, and the posterior cranial fossa. The cranial base comprises of the frontal, ethmoid, sphenoid, occipital, and temporal bones. Now let's move to the front of the skull again where you can see the face.
The facial skeleton is referred to as the viscerocranium as all skull bones found at the lower front connect to the neurocranium, and those bones include two nasal bones, two lacrimal bones, two inferior nasal conchae, two maxillae, two palatine bones, two zygomatic bones which are known as the cheekbones, one vomer, and this bone here which is connected to the skull via the temporomandibular joint, but it is part of the facial skeleton, and that bone is the mandible.
You can also see here the frontal bone, which you may think is part of the facial skeleton. Well, technically it isn't. As we've seen before, this bone is part of the neurocranium. Just below it though, we can appreciate the maxillae, or the upper jaw, and the mandible, or the lower jaw. From this view, you can also clearly see two major landmarks of the facial skeleton – the orbits, also known as the eye sockets, and the nasal cavity.
Up until this point of the tutorial, we've been focusing mostly on showing you the bones of the skull from the anterior and superior views. You can, however, appreciate those bones that we've listed previously from other perspectives such as the lateral, posterior, and inferior views of the skull. Let's first look at the skull from the side or its lateral view.
The lateral aspect of the skull can be divided into three regions – the facial region, the temporal region, and the occipital region. The temporal region is subdivided by the zygomatic arch into the temporal fossa and the infratemporal fossa. The frontal bone, the parietal bone, the greater wing of the sphenoid bone, and the squamous part of the temporal bone meet at the pterion forming the floor of the temporal fossa.
It's time for us to rotate the skull and look at it from a posterior view. The posterior aspect of the skull is formed by the parietal bone superolaterally around here, this bone here which is the temporal bone, and the occipital bone centrally. Sometimes, this view of the skull is referred to as the occipital view.
If we look at the skull from an inferior view, we can see the base of the skull. This aspect of the skull contains a lot of important structures including the largest skull foramen – the foramen magnum. We can divide this part of the skull into five regions to make it easier to study. We have the anterior part which includes the hard palate and the upper jaw; the middle part with the sphenoid bone, the petrous processes of the temporal bones, and the basilar part of the occipital bone; the lateral parts which include the zygomatic arches, the mandibular fossae, the tympanic plates and the styloid and the mastoid processes; and we also have the posterior part and the only bone here is the occipital bone.
Now that we've looked at all the bones of the skull from all the main perspectives, it is time to briefly cover some important structures found on the skull – the holes. Yep, I said holes! As you've probably noticed, there are tons of holes in the skull. These are called foramen which is the singular and foramina which is the plural. Through these holes, many important blood vessels and nerves pass through. Of course, we couldn't finish this tutorial without mentioning some of the most relevant foramina.
Most foramina are located at the base of the skull, so we're going to look again at the images of the base of the skull, like this superior view, where you can find the first one known as the optic canal. It is centrally located in the sphenoid bone forming part of the middle cranial fossa. The optic nerve and the ophthalmic artery pass through the optic canal.
In the middle cranial fossa, we find the superior orbital fissure. Lots of things pass through this structure and they are the trochlea, abducens, oculomotor, and ophthalmic nerves which are connected to vision and eye movement. Still in the middle cranial fossa, we can also find the foramen rotundum where the maxillary nerve passes through, the foramen ovale which is the opening for the mandibular nerve, and the carotid canal which is the passage for the internal carotid artery.
In the posterior cranial fossa, it is worth noting the largest opening in the skull known as the foramen magnum. Here, the brainstem leaves the skull and becomes the spinal cord.
And that's it – a quick introduction to the anatomy of the skull.
Before you go, you need to check whether you can now answer the questions that we showed you at the beginning of this tutorial. Don't be nervous. you'll see just how easy it is.
So first we have the question which asks us to identify this bone here, which kind of looks like it's right where our cheeks should be, right? So, remember, back in this tutorial when we were exploring the anterior view of the skull, we said that this bone – the cheekbone – is the zygomatic bone. So, let's put this one in – and boom! We got it right! Even though the zygomatic bone is a relatively small bone, it has three foramina. You can learn more about them on our article on the zygomatic bone. If you scroll down, you can find a section for the foramina of this bone and you can see that they are the zygomaticofacial foramen, the zygomatico-orbital foramina, and the zygomaticotemporal foramen.
Now let's take a look at the second question which asks us to pick the occipital bone from these four images. Well, we said that the occipital bone is found at the back of the skull. This image shows something on the back of the head, but it can't be this one because this is clearly a suture. As you now know, sutures look like jagged lines. So, the right answer should be this one, where you can see the entire bone highlighted at the back of the head. To test more of your knowledge on the bones found at the back of your head, check out our quiz on the posterior and lateral skull.
The last question was asking us which bone forms the upper jaw. The upper and lower jaws were discussed on this video when we were talking about the facial skeleton. The mandible was the lower jaw, so that's not it, and the temporal, sphenoid, and ethmoid bones are a bit further to the back of the skull, So, that leaves us with the maxilla. Correct again.