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Anterior and lateral views of the Skull

Structures seen on the anterior and lateral views of the skull.

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Transcript

Humans are highly social beings and, from birth, faces form a key aspect of our social interactions. They give us clues about an individual’s emotions, ancestry, and even their health. They’re used by law enforcement in identification and by border control to identify travelers. But what lies deep to the skin? What determines a strong jawline, high cheekbones or a delicate nose? The things we used to identify our friends when we meet them at Starbucks? Well, that’s what we’re going to be looking at today as we discuss the bones that form the face. Specifically, we’re going to be talking about the bones that we see when we look at the skull from an anterior and a lateral perspective, but before we get onto that, let me explain some important terminology relating to the skull.

The skull is divided into two parts – the viscerocranium and the neurocranium – and I know these terms sound a bit scary, but trust me, they’re nothing to be scared about. The word viscerocranium simply refers to the bones that form the face and is also sometimes referred to as the splanchnocranium. The neurocranium, on the other hand, refers to the bones that house and protect the brain.

So, let’s also define some differences between terms such as the skull, cranium, and calvaria as they often cause a little bit of confusion.

The skull refers to the entire bony framework of the head including the mandible, the cranium refers to the skull without the mandible, and the calvaria refers to the skull cap which consists of the upper part of the neurocranium or the superior portions of the frontal, parietal and occipital bones.

Alright, now that you’re familiar with the parts of the skull, let me give you an overview of what we’ll be covering in today’s tutorial.

As I mentioned previously, we’re going to be covering the anterior and lateral views of the skull but more specifically, we’re going to be focusing on nine bones that can be seen between these two views.

So, first of all, we’ll focus on bones of the viscerocranium including the nasal bones, the maxillae, the zygomatic bones, and the mandible. Then, we’ll move on to the discuss some bones of the neurocranium – the frontal bone, the parietal bones, the temporal bones, the sphenoid bone, and the ethmoid bone. Next, we’ll talk about the bony orbit which encapsulates all of the structures of the eye, and then we’ll bring our tutorial to a close with some clinical notes relevant to the bones that form the face.

So, as I said, we’ll begin our tutorial with the bones of the viscerocranium.

So let’s start at the center of the face where we find two small paired bones known as the nasal bones, and these bones define your nose, determining its shape and size. And as you probably have guessed, yes, these are the anterior and the lateral views of your nasal bones. Now, the superior borders and main bodies form the bridge of the nose, while the inferior borders connect with the nasal cartilage to then form the superior margin of the nasal aperture which we will look at in more detail in different tutorials.

Moving upwards or laterally, we can see the maxillae highlighted in green from an anterior and lateral perspective. The maxillae is a paired bone consisting of the right and left maxilla which fuse in the midline. And it’s also known as the upper jaw and is a vital structure of the viscerocranium and it’s involved in the formation of the bony orbit as well as the nose and the palate, and it holds the upper or maxillary teeth, so therefore, plays an important role in mastication and communication. After all, without it, I couldn’t be talking to you right now.

Let’s have a look at some key features of the maxilla.

The first structure that I’d like to cover is this one over here, highlighted in green – and it’s also a paired structure – and it’s known as the infraorbital foramen or foramina in plural. It’s located in the maxilla and it serves as the pathway for the infraorbital nerve and blood vessels. Another feature of the maxilla is the anterior nasal spine which we can see here highlighted in green.

When looking at the skull, we’re able to see some of the projections of the maxilla. And the maxilla has four projections, and these include the zygomatic process, the alveolar process, the frontal process, and the palatine process. First, let’s have a little bit of a chat about the zygomatic process, which articulates with the zygomatic bone on either side of the face contributing to the formation of each orbit. Secondly, we have the alveolar process which forms half of what is known as the maxillary dental arch and holds the upper teeth.

Next, we can see the frontal process which articulates with the frontal bone and contributes towards the medial border of each orbit. And lastly, we have the palatine process. Keep in mind that the palatine process cannot be seen clearly from an anterior or lateral view as it is a horizontal extension found on the medial side of this bone, therefore, we need to look at it from an inferior or medial view as you can now see. Specifically, the palatine process contributes to the roof or the hard palate of the mouth as well as the floor of the nasal cavity.

Let’s move on now to another bone of the viscerocranium, and this bone is also a paired bone found on both sides of the face – and we can see it here highlighted in green. So, if you ever have someone tell you that you have really nice cheekbones, then this is the bone you need to thank – and it’s known as the zygomatic bone. Now, the zygomatic bone is also known as the zygoma and as you can see here, this is one of the most irregularly-shaped bones of your skull.

Similar to the maxilla, the zygomatic bone possesses several projections – the frontal process, the temporal process and the maxillary process. Each zygoma has a frontal process which articulates with the frontal bone via the frontozygomatic suture. The frontal process of the zygomatic bone also contributes towards the lateral border of each orbit. And both zygomatic bones also possess a temporal process, which articulates with the zygomatic process of the temporal bone on each side via the temporozygomatic suture to form the zygomatic arch. And finally, we have the maxillary processes, which articulate with the maxillary bone via the zygomaticomaxillary suture.

Now the last structure of the zygomatic bone we’re going to cover is this little hole which is known as the zygomaticofacial foramen. Now if we zoom in, we can clearly see it, and I can also show you some nerves and vessels passing through these foramina, and they include the zygomaticofacial nerve and its corresponding blood vessels.

The last bone of the viscerocranium we’ll look is the only bone in the entire cranium that doesn’t articulate with its adjacent skull bones via any sutures and, FYI, this is the bone responsible for giving Chris Pratt his strong jawline. So, if you guessed right, yes, this is your lower jaw, or if you want to be fancy, the mandible. So now in terms of the articulations, we can see here that the mandible is articulating dentally, which is known as the dental articulation. So, as you can see, the teeth that are rooted in the mandible are articulating with the maxillary teeth.

Another portion that will form an articulation is known as the temporomandibular joint, which happens right about here. And this is an articulation happening between the mandible and the neurocranium, more specifically, the temporal bone, and that’s why we call it the temporomandibular joint.

So, I also want to show you some of the landmarks and important structures related to the mandible, and here we can see the body of the mandible highlighted in green from an anterior and lateral view. And the body is the largest part of this bone and possesses the mental foramina. Now, these little holes that you’ll find within the body of the mandible are specifically found inferiorly to the second premolar tooth and they serve as exit points for certain structures including the mental artery and the mental branch of the inferior alveolar nerve.

The last structure of the mandible we’ll be talking about is the ramus of the mandible or rami, which is the plural for ramus because we have two. The ramus of the mandible exhibits several of its own structures including the coronoid process – this little triangular area highlighted in green – and the condylar process, which includes the head of the mandible which articulates with the temporal bone at the temporomandibular joint.

Alright, now that we’ve covered the bones of the viscerocranium, let’s move on to the bones of the neurocranium.

Highlighted in green, we can see the bone that defines your forehead from both an anterior and lateral perspective, and for the lack of a better name, we call it the frontal bone. The frontal bone, which is one of the bones that encases the brain, consists of three parts – the squamous part, the orbital part, and the nasal part. The squamous part makes up the largest portion of the frontal bone and encompasses the area of the forehead and houses the frontal sinuses. The orbital part is essentially the part of the frontal bone that contributes to the bony orbit, and the nasal part is the portion that articulates with the frontal processes of the maxilla and the nasal bones, and this is basically the portion that helps form the root of the nose.

So, let’s talk about some bony landmarks associated with the frontal bone – and the first one we can see here highlighted in green. And it’s a smooth and slightly elevated area above the nasal root and is known as the glabella. The other bony landmark that we find on the frontal bone is seen more specifically on the superior border of the orbit or the supraorbital margin, and this is known as the supraorbital notch. And this is an important structure because this is where the supraorbital blood vessels and nerve pass through.

Let’s move on to another bone of the neurocranium – the parietal bone.

The parietal bone is actually a paired bone found on both sides of the skull and it forms large parts of the top and sides of your head. And that’s why you see two little highlights here on the anterior view, but you can see this bone or these bones more clearly on a lateral view.

I want to use this opportunity to talk about some of the connections found between the parietal bones and the other bones. And the first one that can be seen anteriorly is found between the frontal bone and the two parietal bones forming this connection here that is known as the coronal suture. The parietal bones also connect with the temporal bones via the squamosal suture, and with the sphenoid bone via the sphenoparietal suture.

And moving on to the next bone, another paired bone as you can see here, which is the temporal bone. And the temporal bones form the base of the cranial vault along with this bone right here, the occipital bone, and they also ascend to participate in the lateral walls of the skull.

Now, let’s have a look at the different connections found between the temporal bones and the other bones of the skull.

So the first one is one that we’ve already talked about – the squamosal suture – and this connects the temporal bones with the parietal bones. Anteriorly, the suture becomes the sphenosquamosal suture, right here, where the temporal bone is now in connection with the sphenoid bone. Posteriorly, the squamosal suture becomes the parietomastoid suture which, as you can see, connects the mastoid process of the temporal bone with the parietal bone. And remember that the temporal bones also connect with the zygomatic bones via the temporomandibular suture and that they do this via the zygomatic processes.

The next bone on our list is not a paired bone although it does look like one when we view it from an anterior perspective, and this bone is known as the sphenoid bone. The sphenoid bone is also known as the wasp bone, and if we look at it in isolation from an anterior view, you can see why with its antenna-like structures and wings. And this pretty bone makes up most of the middle part of the base of the skull and contributes towards the floor of the middle cranial fossa.

Before we move on, let me show you two important parts of the sphenoid bone – the greater wings which we can see here and the lesser wings which we can see over here. And we’ll see how these parts contribute towards the bony orbit later on in this tutorial. But for now, I’m just going to let the wings of the sphenoid fly, and move on to another bone on our list. This one seen here highlighted in green which is the ethmoid bone.

The ethmoid bone contributes towards the medial wall of the bony orbit and if we look into the anterior nasal aperture, we can see several structures of the ethmoid bone including the superior and middle nasal conchae here, and the perpendicular plate here. And while we’re here, it’s worth mentioning the inferior nasal concha which we can see here. Note that the inferior nasal concha is not part of the ethmoid bone. It’s a bony structure by itself.

So now it’s time for us to move on and talk about the last topic on our list in this tutorial.

So, one of the things we clearly noticed when looking at the anterior view of the skull is this structure that you see on your screen known as the bony orbit. And the bony orbit is a skeletal cavity that is made up of several cranial structures and surrounds the soft tissue that makes up your eye. And before we look at the parts of the bony orbit, let me just show you some important structures starting with the superior orbital fissure. The superior orbital fissure transmits the oculomotor nerve, the trochlear nerve, the ophthalmic division of the trigeminal nerve, the abducens nerve, and the ophthalmic veins.

Next, we have the inferior orbital fissure. Several important structures pass through this fissure and they include the infraorbital nerve and the zygomatic nerve which both arise from the maxillary division of the trigeminal nerve, but it also transmits the infraorbital vessels.

So, the last structure that we’re going to be talking about is the optic canal. The optic canal transmits the optic nerve and the ophthalmic artery. So, it’s important to mention that the bony orbit is divided into four main parts – the roof, the lateral wall, the medial wall, and the floor. And what we’re going to do now is to look at each part of the bony orbit and define what bones contribute towards their formation.

The roof of the bony orbit is comprised of the orbital surface of the frontal bone and the lesser wing of the sphenoid bone. The lateral wall of the bony orbit is comprised by the orbital surface of the zygomatic bone and the greater wing of the sphenoid bone. The medial wall of the bony orbit is defined by the orbital plate of the ethmoid bone and the sphenoid bone also contributes to the medial wall of the bony orbit along with a few other bony structures such as the lacrimal bone. And there is some small contributions from other bones including the frontal bone and the maxilla.

And, finally, we’re going to move on to the floor of the bony orbit. Anteriorly, the floor is defined by the orbital surface of the maxilla and the orbital surface of the zygomatic bone. Posteriorly, it’s defined by the process of the palatine bone which is difficult to see from this perspective but I thought I’d include it on the list, anyway.

Alright, now that we’re finished learning about the bones of the skull, we can see from an anterior and lateral perspective, let’s get clinical. In today’s clinical notes, we are going to be talking about facial fractures, specifically, Le Fort fractures.

So, there are three different classifications of Le Fort fractures. We have type I which involves the separation of the alveolar part of the maxilla from the rest of the viscerocranium, there’s type II which involves the separation of the midface from the rest of the viscerocranium, and, finally, we have type III which involves the separation of the entire viscerocranium from the neurocranium. It’s worth noting that this is not a black and white classification system and that there can be some overlap between fracture types.

Alright, thanks for sticking with me throughout this tutorial. Before we conclude, let’s quickly summarize what we talked about today.

So, first, we looked at the bones of the viscerocranium including the nasal bones, the maxilla, the zygomatic bones, and the mandible. Then, we went on to discuss some bones of the neurocranium, the frontal bone, the parietal bones, the temporal bones, the sphenoid bone, and the ethmoid bone. Next, we discussed the bony orbit which encapsulates all the structures of the eye, and then we talked about Le Fort fractures which are a type of a facial fractures.

So that brings us to the end of our tutorial on anterior and lateral views of the skull. I hope you enjoyed it, thanks for watching, happy studying!

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