Video: Posterior and lateral views of the skull

For centuries, artists have been captivated by the human skull. From Renaissance vanity paintings to modern day tattoo art, images of the skull remind us that life is short and the time to live our dreams is now. Okay, but the purpose of this video tutorial is not to lead you to an existential crisis. Remember, there are still mundane things to learn like the anatomy of the human skull.

The skull is actually a very complex region with a lot of different structures, bony landmarks, and several foramina which allow for the passage of blood vessels and nerves. We can study the bone separately but it's also very useful to study the skull as a whole from different perspectives. This video tutorial will provide you with an overview of the posterior and lateral views of the skull.

The human skull consists of 22 bones that are mostly connected together by fibrous joints – so-called sutures. It comprises two main parts – the braincase, or the neurocranium, which surrounds and protects the brain and the facial skeleton, or viscerocranium, which provides support to the face. We'll start this tutorial with the posterior view of the skull and here we'll describe the bones and sutures visible from this perspective. Then we'll analyze the main bony landmarks of each of these bones in more detail. Then we'll move into the lateral view of the skull and follow the same logic. First, we'll talk about the bones and sutures, and after that, we'll take a closer look at the major bony landmarks. Finally, in our clinical notes section, we'll talk a little bit about skull fractures.

Let's start with the posterior view of the skull.

When looking at the skull from a posterior view, we're able to identify a few bones. Starting superiorly with the bones of the neurocranium, we can see the posterior parts of the two parietal bones. The name of these bones is derived from the Latin word for wall which makes sense because these bones form the superior and lateral walls of the cranium. Centrally, the squamous part of the occipital bone is the main structure visible in this view of the skull. The occipital bone is an unpaired bone that covers the back of the head or occiput. Lateral to the occipital bone on each side, we find a part of the temporal bones from which we'll have a much clearer view in the second part of this tutorial when we take a look at the lateral aspect of the skull. So the parietal, occipital, and temporal bones are the main bones of the neurocranium, evident in this posterior view of the skull. Besides that, we can see part of another bone of the neurocranium – the sphenoid bone.

From this posterior view, we can also catch a glimpse of some of the bones of the viscerocranium. Here we meet the paired palatine bones. This bone participates in building the three cavities within the skull – the oral cavity, the nasal cavity, and the orbits. As its name suggests, it also contributes to the formation of the hard palate, namely, its posterior part. Next, we can also identify the maxillae which are also known as the upper jaw bones. This is the paired bone that holds all 16 of our upper teeth – unless you've lost a few along the way. The mandible is the final bone that can be identified from the posterior perspective. It is an unpaired bone that is technically not part of the viscerocranium; however, it is sometimes still considered as such by some texts. The mandible is the largest, strongest, and lowest bone of the human facial skeleton and is commonly known as the jawbone.

Within this posterior view, we're also able to identify a few sutures between the bones we've just mentioned. Going from top to bottom, first we identify the sagittal suture, also known as the interparietal suture, because it connects the two parietal bones of the skull. The term is derived from the Latin word meaning arrow, perfectly describing its notched, arrow-like appearance. Inferior to the sagittal suture, we find the lambdoid suture which is central in this posterior view. It connects the parietal bones with the occipital bone. The name comes from its shape as it looks like one of the letters from the Greek alphabet – an uppercase lambda. Along with the lambdoid suture, small islands of bone may be observed. These bones are called sutural or wormian bones. The lambdoid suture is continuous laterally and inferiorly on both sides with the occipitomastoid suture where the occipital bone articulates with each temporal bone.

Now that we have an overall understanding of the bones and sutures visible from this perspective, let's take a closer look at some relevant bony landmarks, starting with the occipital bone.

The external occipital protuberance is a midline projection usually easily palpable in the median plane. It gives attachments to some muscles and the ligamentum nuchae. The external occipital crest descends from the external occipital protuberance towards the foramen magnum which is this large opening in the basal part of the occipital bone through which the spinal cord exits the cranial vault.

Let's take a look at the skull from an inferior perspective to get a better view of the external occipital crest and foramen magnum.

The occipital bone has three lines that serve as attachment points for muscles and ligaments. The superior nuchal lines extend laterally from each side of the external occipital protuberance and act as an attachment site for the occipitalis, trapezius, sternocleidomastoid, and splenius capitis muscles. Below them, we have two additional less distinct lines extending from the middle of the external occipital crest – the inferior nuchal lines. These lines serve as an attachment point for the rectus capitis posterior major and minor muscles. Above the superior nuchal lines, we find the supreme nuchal lines, which are often faintly marked. These lines are also known as the highest nuchal lines and extend from the superolateral aspects of the external occipital protuberance. The galea aponeurotica forms one of its attachments to the posterior skull at this point.

Another landmark on the posterior surface of the skull is the occipital condyles which are actually more visible from an inferior view as we can see here. These two structures allow the skull to articulate with the vertebral column at the atlanto-occipital joint.

When the skull is viewed from a posterior aspect, the temporal bones can be seen on the lateral extremities of the skull with a rounded eminence, the mastoid process being the prominent feature visible. You can find this bony prominence tucked just behind your ears. This process can be seen a little better from the lateral view of the skull. The mastoid foramen is a variably present foramen as well as being variable in its size, number, and position. It is most commonly located near the posterior margin of the mastoid process within the occipitomastoid suture. It transmits the emissary veins connecting to the sigmoid sinus and a small dural branch of the occipital artery.

Look carefully at the skull to identify the final bony landmark of the temporal bone that we can identify on this posterior view. This slender bony projection from the inferior surface of the temporal bone on each side is the styloid process. These processes serve as points of attachment for muscles and ligaments of the head and neck.

Onto the landmarks of the sphenoid bone. The small part of the sphenoid bone that we can observe from a posterior view is the pterygoid processes which are wing-like extensions of the basal surface of this bone. These are an important attachment site for some of the muscles of mastication. Parts of the maxillae, or upper jaw, are also discernible. The palatine process is a thick horizontal process that, together with its counterpart, forms part of the roof of the mouth and floor of the nasal cavity which we can see a little better in this sagittal section. This process contains the incisive foramen, also known as the anterior palatine foramen, a funnel-shaped opening that is continuous with the incisive canal which transmits the terminal branches of the sphenopalatine vessels and the nasopalatine nerve. The alveolar process of the maxilla is an inferior extension of the maxilla which contains eight cavities known as dental alveoli where the upper teeth are held.

The last structure that we're going to talk about in the posterior view of the skull is the mandible which also has a few landmarks visible from this perspective. The mandibular foramen is an opening on the internal surface of each ramus of the mandible. It allows for the passage of the inferior alveolar artery and nerve which supply the lower teeth. The body of the mandible contains two paired indentations on its inner surface which holds the salivary glands. The first is known as the sublingual fossa which as its name suggests is a shallow depression that houses the sublingual gland. Inferiorly and laterally, we find the second paired indentation of the mandible – the submandibular fossa – which as its name suggests is the location of the submandibular gland.

The final landmark of the posterior view of the skull that we'll meet today is the mental spines. These are small projections of bone located at the midline of the body of the mandible. They are a place of attachment for the muscles of the oral cavity.

So we're finished with the posterior view of the skull, but there's still a lot to cover in this tutorial. It's time to move on to the lateral view of the skull, starting with the bones that are visible from this perspective.

So in the lateral view of the skull, we can see the lateral wall of the cranium and half of the mandible. Let's first review the bones forming the lateral portion of the neurocranium.

The frontal bone is a single bone whose name comes from the Latin word 'frons' meaning forehead, and as you can see, this bone creates the smooth curvature of the forehead so that name makes total sense. The frontal bone is also involved in the formation of the orbit and the bony part of the nose. We've already seen part of the parietal bone on the posterior view; however, in this lateral view, we have a better perspective of this roughly quadrilateral bone. As we've seen before, there is one on each side of the skull and together they form the superior and lateral walls of the cranium. The occipital bone which we've explored earlier in this tutorial is also visible posteriorly in this lateral view. The sphenoid bone, of which we saw a small part in the posterior view, is one of the most complex bones in the body. Its shape somewhat resembles that of a butterfly or bat with its wings extended. This bone is situated in the middle of the skull and part of it is visible from this perspective too as we can see here. Still a part of the neurocranium, the temporal bone is a major contributor to the lower portion of the lateral wall of the cranium.

Now let's take a look at the bones of the viscerocranium, or facial skeleton, that are visible in this lateral view of the skull.

The nasal bones are two small symmetrical midface bones that builds the bridge of the nose. The lacrimal bone, also a paired facial bone, makes up the most anterior part of the medial wall of the orbit. The lacrimal bone is the smallest bone of the skull having the size and shape of a fingernail. 'Lacrima' is Latin for tear, so the name of the bone corresponds with its relation to the nearby lacrimal structures. The zygomatic bone, or malar bone, is an irregularly-shaped bone with a rounded lateral surface that forms the prominence of the cheek. That's why it is commonly referred to as the cheekbone.

The maxilla is a central part of the viscerocranium. It is involved in the formation of the orbit, nose, and palate, and as we saw before, holds the upper teeth and plays an important role in mastication and communication. The mandible, also known as the lower jaw, is the only bone in the entire skull that doesn't articulate with its adjacent skull bones via sutures. So excluding the auditory ossicles, it's the only mobile bone of the skull. As we saw earlier, it is technically not part of the viscerocranium; however, it is sometimes still considered as such by some texts. The mandible comes in contact with the maxilla which is part of the viscerocranium via the teeth when the mouth is closed. It also articulates with the neurocranium via the temporal bone forming the temporomandibular joint.

Now let's look at the sutures that connect these bones.

The frontal bone articulates with the parietal bone at the coronal suture. The parietal bone then articulates with the occipital bone at the lambdoid suture – a suture we've already described previously on the posterior view. As we've also seen before, the lambdoid suture is continuous with the occipitomastoid suture where the occipital bone articulates with the temporal bone. The sphenoid bone articulates with a few bones. It articulates with the parietal bone at the sphenoparietal suture; it articulates with the frontal bone at the sphenofrontal suture; and finally, it articulates with the temporal bone at the sphenosquamous suture. The junction where the frontal, parietal, sphenoid, and temporal bones are in close proximity is the pterion. The squamous suture lies between the temporal and parietal bones bilaterally. From the pterion, it extends posteriorly, curves inferiorly, and continues as the parietomastoid suture. The final suture observed from the lateral aspect of the skull is the frontozygomatic suture. This is the tiny cranial suture between the zygomatic bone and the frontal bone.

Okay, now it's time to look at the main landmarks of the bones we've mentioned. Let's start with the frontal bone.

The supraorbital foramen or notch, depending on if it's an opening or just an indentation on the bone, is located at the edge of the superior orbital margin of the frontal bone. It transmits the supraorbital nerve, artery, and vein. Superomedial to each orbit is a rounded superciliary arch, usually more pronounced in males, between which there may be a median elevation – the glabella. Here from this lateral perspective is the sphenoid bone, or more specifically, the temporal surface of the greater wing. This little piece of bone is an important attachment site for one of the large muscles of mastication – the temporalis muscle.

Several parts of the temporal bone are noticeable from this perspective. The squamous part has the appearance of a large flat plate. It forms the anterior and superior parts of the temporal bone and contributes to the lateral wall of the cranium. The zygomatic process is an anterior bony projection from the lower surface of the squamous part of the temporal bone. Immediately below the origin of the zygomatic process is the tympanic part of the temporal bone. The tympanic part sits just anterior to the mastoid process of the temporal bone.

Clearly visible on the surface of this part is the bony external acoustic opening leading to the external acoustic meatus or ear canal. Here we can see the petrous part of the temporal bone which forms the part of the cranium between the sphenoid and the occipital bones. Internally, this part forms the division between the middle and posterior cranial fossa and houses the middle and internal ear; however, the external surface of the petrous part of the temporal bone is largely defined by the prominent mastoid process. For this reason, the petrous part of the temporal bone is also sometimes referred to as the petromastoid part. We've already seen this, of course, when we explored the posterior view of the skull. It is a large bony prominence that projects inferiorly from the inferior border of the petrous part of the temporal bone. It functions as an attachment site for muscles of the head and neck and contains air-filled spaces known as mastoid air cells. Medial to the mastoid process, the styloid process is a narrow, pointed projection which extends downwards and anteriorly from the inferior surface of the temporal bone. This process was also visible from the posterior view.

On the lateral surface of the skull are two curved lines known as the superior and inferior temporal lines. They begin as a single line from the posterior margin of the zygomatic process of the frontal bone and diverge as they arch backward through the parietal bone. These lines act as an attachment point for the temporal muscle and fascia. The temporal fossa, which is a shallow depression on the sides of the skull, lies below the inferior temporal line. This fossa contains the temporal muscle.

Moving onto the bones of the facial skeleton, as we saw before, the zygomatic bone is a visual centerpiece in this view. Medially, this bone assists in the formation of the inferior rim of the orbit through its articulation with the maxilla. Superiorly, its frontal process articulates with the zygomatic process of the frontal bone assisting in the formation of the lateral rim of the orbit. Laterally, the horizontal temporal process projects backward to articulate with the zygomatic process of the temporal bone, and in doing so, forms the zygomatic arch. The zygomatic arch functions to protect the eye and is an important attachment site for the masseter and part of the temporalis muscles of mastication. The zygomatic bone usually has a small opening on its lateral surface - the zygomaticofacial foramen – for the passage of the zygomaticofacial nerve and vessels.

Let's take a look at the visible bony landmarks of the maxilla now. The infraorbital foramen is an opening located below the infraorbital margin. It transmits the infraorbital artery and vein and the infraorbital nerve. From this lateral view of the skull, we can also spot the alveolar process of the maxilla which contains the upper teeth. So, go on, flash that Hollywood smile and let's take a look at that sparkling row of upper teeth.

The final bony structure that we're going to analyze in detail is the mandible. It consists of two parts – an anterior body and a posterior ramus. Starting anteriorly with the body of the mandible, it is somewhat U-shaped and extends posteriorly on either side. The superior border of the body of the mandible is known as the alveolar process. This is where you can find all 16 of your lower teeth. From this lateral view, we can also identify the mental protuberance at the center of the body which is responsible for the prominence of the chin. The mental foramen is located on the lateral surface of the body, one on each half of the mandible. It allows the inferior alveolar nerve and artery to exit the mandibular canal where they become the mental nerve and artery.

The angle of the mandible is where the inferior margin of the body of the mandible meets the posterior margin of the ramus. The rami of the mandible extend superiorly from the body on each side. On the superior part of the ramus, two processes extend upward. The condylar process is involved in the articulation of the mandible with the temporal bone at the temporomandibular joint. The coronoid process can be found anterior to the condylar process and is the point of attachment for the temporalis muscle. Between these two processes, there is a curved depression known as the mandibular notch. This notch allows for the passage of the masseteric vessels and nerve.

Okay, so we're finally done with all the bony landmarks that we wanted to cover today, and now, it's time for some clinical notes.

The bones of the skull may be fractured following an injury or trauma to the head. This happens when a force that's strong enough to break the bone hits the skull. Any type of impact to the head can cause a skull fracture. This includes being hit with an object, falling and hitting the ground, injuring the head in a car accident, or any other type of trauma. While mild breaks can cause a few problems and heal over time, severe breaks can lead to complications including bleeding, brain damage, leaking of cerebrospinal fluid, infection, and seizures.

A CT scan helps to determine the extent of the injury. Treatment depends on the severity of the fracture. Pain medication may be the only treatment necessary in mild fractures while neurosurgery may be required for more serious injuries. The clinical consequences of a skull fracture in the pterion area can be very serious. The bone in this area is particularly thin and overlies the anterior division of the middle meningeal artery which can be torn by a skull fracture in this area resulting in extradural or epidural hematoma and eventual death, if not treated. This is a collection of blood that forms between the inner surface of the skull and outer layer of the dura mater. It is typically biconvex in shape as you can see in this CT scan image.

Before I let you go, let's do a quick review of what we've learned today.

We started with the posterior view of the skull. Here we first had an overall view of the bones that are visible from this perspective. Beginning with the bones of the neurocranium, we identified both parietal bones, the occipital bone, the temporal bones, and part of the sphenoid bone. Also visible from this posterior view were some of the bones of the viscerocranium, namely, the palatine bones, the maxillae, and the mandible. Then we analyzed the sutures between these bones – the sagittal suture, the lambdoid suture, and the occipitomastoid suture.

We took a closer look at each of the bones and described their main bony landmarks. Several landmarks are visible on the occipital bone. These are the external occipital protuberance; the external occipital crest; the superior, inferior, and highest nuchal lines; and the occipital condyles. From the temporal bone, we can identify the mastoid process, the mastoid foramen, and the styloid process. Belonging to the sphenoid bone, we can see the pterygoid process. Both maxillae have palatine processes, an incisive foramen in the midline, and alveolar processes. And finally, on the mandible, we identified the mandibular foramen, the sublingual fossa, the submandibular fossa, and the mental spines.

Then we moved on to the second part of this tutorial – the lateral view of the skull. Here we also started by talking about all the bones that are visible from this perspective. Belonging to the neurocranium, we identified the frontal bone, the parietal bone, the occipital bone, the sphenoid bone, and the temporal bone; and from the viscerocranium or facial skeleton, we recognized the nasal bone, the lacrimal bone, the zygomatic bone, and the maxilla or upper jaw. The mandible or lower jaw is also very obvious in this view.

Several sutures can be found in this aspect of the skull. Anteriorly, we see the coronal suture, and posteriorly, the lambdoid suture. The sphenoid bone articulates with several other bones forming the sphenoparietal suture, the sphenofrontal suture, and the sphenosquamous suture. The junction where the frontal, parietal, sphenoid, and temporal bones are in close proximity is known as the pterion. The squamous suture is central in this perspective. Finally, we also identified the small frontozygomatic suture.

We also described various discernible bony landmarks. On the frontal bone, we found the supraorbital foramen or notch and the glabella. Regarding the sphenoid bone from this view, we can observe the temporal surface of its greater wing. A major contributor to this view of the cranium is the temporal bone which consists of several parts: the squamous part whose anterior projection is the zygomatic process, the tympanic part with the bony external acoustic opening leading to the external acoustic meatus. and the petromastoid part with two important bony projections – the mastoid process and the styloid process. Central in this view are the superior and inferior temporal lines which bounds the temporal fossa.

Moving onto the bony landmarks of the viscerocranium, we meet the zygomatic bone which has two projections – the frontal process and the temporal process – and a small opening known as the zygomaticofacial foramen. The zygomatic arch is formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone. At the maxilla, we find the infraorbital foramen and the alveolar process.

The last bone we talked about was the mandible. Anteriorly, on the body of the mandible, we find the alveolar part, the mental protuberances, and the mental foramen. The place where the inferior border of the body of the mandible meets the posterior border of the ramus is the angle of the mandible. Posteriorly on the ramus of the mandible, we find the condylar process, the coronoid process, and the mandibular notch.

Finally, we discussed a few clinical aspects related to skull fractures.

That's all for now. Hope you enjoyed this video. Happy studying and see you next time.