Bones of the cranium
Introduction0:00–0:45
The cranium, or skull, is the bony structure that protects the structures found inside our head, and it’s divided into two parts: the viscerocranium and the neurocranium.
Viscera- refers to the organs within the body cavities, so the viscerocranium is the lower and anterior part of the skull that forms the orbits, the nasal cavities, and the oral cavities; in other words, the facial skeleton.
Neuro-, on the other hand, refers to the nervous system, so the neurocranium, also called the cranial cavity, is the superior and posterior part of the skull that houses the brain, and its membranous coverings - the cranial meninges - and also blood vessels and the proximal parts of the cranial nerves.
Let’s look at the viscerocranium first, which is actually made up of 15 bones! Only three of them are unpaired bones, and they sit on the midline: the mandible, ethmoid, and vomer; then there are six pairs of paired, symmetrical bones: the maxillae, the inferior nasal conchae, as well as the zygomatic, palatine, nasal, and lacrimal bones.
Viscerocranium & Neurocranium0:45–3:23
Most of these bones articulate with each other by fibrous - or immovable - joints; except for the mandible, which articulates only with the temporal bones by a synovial - or movable - joint.
Next, the neurocranium is made up of eight bones: the frontal, ethmoid, sphenoid, and occipital bones, which are singular and placed in the midline; then two temporal and two parietal bones, which are bilaterally paired.
All these bones articulate by fibrous joints. In addition, the neurocranium can be further divided into the calvaria - or skullcap - and the cranial base, which would be like the roof and the floor of the neurocranium, respectively.
The cranial base is where the foramen magnum is found, where the spinal cord is continuous with the brain. Alright, so let’s get started with the bones of the viscerocranium.
If you get face to face with a skull, you'll see the most bones of the viscerocranium. The maxillary bones occupy most of the surface.
On each side there are the zygomatic bones, which form the skeleton of the cheek. Medial to the superior part of the maxillary bones, there's the nasal bones, and laterally there's the lacrimal bones.
Now, if you look inside the piriform aperture, which is the opening to the nasal cavity, you can see the nasal septum formed by the ethmoid bone superiorly, and the vomer inferiorly.
You can also see the middle nasal conchae, which are also part of the ethmoid bone; and the inferior nasal conchae, which are their own separate bones.
The most inferior bone of the face is the mandible. The only bones you won't see from this view, are the palatine bones, which are behind the maxillary bones.Let's begin with the maxillary bones.
Maxilla3:23–4:35
These are two big irregular bones placed in the middle part of the face that form the upper jaw and help form the boundaries of the orbits, the nasal cavity, and the mouth.
They articulate with one another on the midline, at the intermaxillary suture. The inferior border of each bone is called the alveolar process; that consists of a number of cavities, or alveoli, for the upper or maxillary teeth.
The anterior border of both bones together form the piriform or nasal aperture. The superior border helps form the lower orbital margin, and the posterior border articulates with the sphenoid to help form the infratemporal fossa.
Laterally, the maxilla articulates with the zygomatic bones, and anterior to this articulation and inferior to each orbit there’s the infraorbital foramina, through which the infraorbital nerve and vessels pass.
Superior and anteriorly, the maxilla frontal process articulates with the nasal, frontal, and lacrimal bones.Moving on to the zygomatic bones, these are two quadrilateral bones situated inferior and lateral to the orbits, so they’re also called malar or cheekbones.
Zygomatic bone4:35–5:35
In the center, they have a small opening called the zygomaticofacial foramen, through which the zygomaticofacial vessels and nerves pass in order to reach the cheeks, and make us blush when complimented.
The zygomatic bones articulate with other bones of the facial skeleton through four processes: the frontal process, which articulates superiorly with the frontal bone; the orbital process, which articulates with the maxillary and sphenoid bone to form the floor of the orbit and also forms the lateral and inferior rims of the orbit; the maxillary process, which articulates inferiorly with the maxillary bone; and the temporal process, which articulates with the temporal bone to form the zygomatic arch, and contributes the inferior boundary of the temporal fossa.Okay now, moving forward to the unpaired bones, let's take a look at the mandible.
Mandible5:35–6:50
It's the bone that forms the lower jaw and results from the union of two bones in the midline at the mandibular symphysis.
The mandible consists of two parts: the body, which is horizontal, and a vertical ramus on each side. The angle where each ramus joins the body is called the angle of the mandible, where part of the masseter muscle inserts.
The body of the mandible presents the mental protuberance, which defines the shape of our chin. A bit lateral and posterior to the mental protuberance, there’s the mental foramen, a hole through which the mental vessels and nerve pass.
The superior border of the body is called the alveolar process that supports the mandibular teeth. The superior border of each ramus has a coronoid process anteriorly, which is thin and triangular, with the mandibular notch posterior to it.
The mandibular notch is a concave depression that separates the coronoid process from the condyloid process posterior to it, which is thick and round-shaped, and articulates with the mandibular fossa of the temporal bone to form the temporomandibular joint.
Okay so, before we move on, feel free to pause the video and see if you can label the bones on this frontal view of the skull!Alright, now let’s switch gears and look at the bones of the neurocranium, starting with the frontal bone.
Quiz6:50–7:09
Frontal bone7:09–9:06
The frontal bone forms the skeleton of the forehead and protects the frontal lobes of the brain. It’s an unpaired flat bone that has two parts: the squamous part, which is flat and vertically oriented; and the horizontally oriented orbital part, which forms the anterior floor of the cranial cavity and the roof of the orbits.
An external view of the bone shows, right where these two portions of the frontal bone bind are the supraorbital margins, a ridge above the orbit, on each side.
In the medial part of each one, the supraorbital nerve and vessels pass through the supraorbital foramen or notch. Now, seen from the inside of the cranial cavity, the squamous part of the frontal bone presents impressions on its surface that correspond to the frontal lobes, and in the midline there’s the sagittal sinus that ends on the frontal crest.
The frontal crest provides attachment to the falx cerebri. Now, the frontal bone articulates to a number of bones.
Inferiorly in the middle part of the frontal bone is an area called the Glabella, and below this is where the frontal bone articulates with the nasal, maxillary, and lacrimal bones.
On the lateral end of the supraorbital margins, there are the zygomatic processes, which articulate with the zygomatic bones on each side.
In the middle, the orbital part articulates with the ethmoid bone. The ethmoid bone is unpaired and found in the midline.
It forms part of: the nasal septum, the lateral walls and roof of the nasal cavities, the medial wall of the orbits, and the anterior cranial fossa.
Next, let’s look at the temporal bones! These bones are highly irregular, bilateral bones on each side of the cranium, corresponding to where the ears are located.
Temporal bone9:06–10:47
Each temporal bone consists of a squamous, tympanic, mastoid, and petrous part. The squamous part is flat, and it has a smooth, convex external surface where the temporalis muscle attaches.
From the lower portion of the squamous part, the zygomatic process arises, and it articulates with the temporal process of the zygomatic bone, forming the zygomatic arch.
The squamous part also has a depression called the mandibular fossa to articulate with the mandible. Right behind this articular surface, there’s the tympanic part, which forms most of the external acoustic meatus and provides an attachment surface for the tympanic membrane.
The mastoid part of the temporal bone is the most posterior part, and gives attachment points to the occipitalis muscle and the posterior auricular muscle.
The mastoid part has the mastoid process, which is posterior to the external acoustic meatus, and lateral to the styloid process, which belongs to the petrous part.
The mastoid process and the styloid process serve as attachment points for muscles and ligaments. From an internal and superior view of the temporal bone, we can see an opening on the petrous part, which is called the internal acoustic meatus.
We can also see how it articulates with the sphenoid bone anteriorly, the occipital bone posteriorly, and the parietal bone superiorly.Now that we’ve looked at each bone separately, let’s take a look at how they interact to form the calvaria, or the skull cap, which is the roof of the neurocranium.
Calvaria10:47–12:31
It’s formed by four bones: the squamous part of the frontal bone, both parietal bones, and the squamous part of the occipital bone.
Seen from the outside, in other words, in a superior view, the calvaria is a smooth convex surface, and the most relevant features here are the sutures between the bones that comprise it, which are all synarthrosis joints.
Between the frontal and both parietal bones, there’s the coronal suture; between both parietal bones, there’s the sagittal suture, in the midline; and between both parietal bones and the occipital bone, there’s the lambdoid suture, named after the Greek letter lambda, to which it is similar.
Where the lambdoid suture meets the sagittal suture, this point is called the lambda. Then where the sagittal suture meets the coronal suture, this point is called the Bregma.
These are very important spots because, in newborns, the sutures are not fused yet and the gaps are called the anterior and posterior fontanelles, which provide space for the brain to grow and develop properly.
Posterior to the bregma there is the vertex, which is the most superior part of the calvaria. Going even further posteriorly, where the calvaria meets the base of the cranium, we have the external occipital protuberance.
Finally, on a lateral view of the skull cap, you can see the squamous or squamosal suture that connects the temporal and parietal bones.
At the anterior end of this suture, the frontal, parietal, temporal, and sphenoid bones join to form a letter “H”, this is called the pterion.Now feel free to take a quick break and pause the video to test your knowledge!
Quiz12:31–12:47
Can you label the missing parts on the following image?##SummaryAll right, as a quick recap… The cranium is divided into two parts: the viscerocranium and the neurocranium.
Review12:47–13:57
The viscerocranium is the lower and anterior part of the skull, made up of 15 bones, that forms the facial skeleton. Only three of them are unpaired bones, and they sit on the midline: the mandible, ethmoid, and vomer; then there are six pairs of paired, symmetrical bones: the maxillae, the inferior nasal conchae, as well as the zygomatic, palatine, nasal, and lacrimal bones.
The neurocranium is the superior and posterior part of the skull, made up of eight bones: the frontal, ethmoid, sphenoid, and occipital bones, which are singular and placed in the midline; then two temporal and two parietal bones, which are bilaterally paired.
The calvaria, which is the roof of the neurocranium, is formed by four bones: the squamous part of the frontal bone, both parietal bones, and the squamous part of
Figure 1: Bones of the cranium A. lateral and B. anterior views.
Figure 2: Anatomy of the maxillary and zygomatic bones, A. anterior and B. lateral views.
Figure 3: Anatomy of the frontal bone, A. lateral, B. anterior, and C. superior views.
Figure 4: Anatomy of the ethmoid bone, A. anterior view and B. lateral view.
Figure 5: Anatomy of the temporal bone, A. lateral view, and B. superior view.
Figure 6: Anatomy of the mandible, A. lateral and B. anterior view.
Figure 7: Anatomy of the calvaria, A. lateral and B. superior view.
Illustrator: Elizabeth Shapiro, MSMI, CMI
Editor: Leah Lebranche
Editor: Andrew Horne
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- "Costanzo Physiology, 7th edition" Elsevier (2021)
- "Moore’s Clinically Oriented Anatomy, 9th edition" Wolters Kluwer (2023)
- "Primary Intraosseous Cavernous Hemangioma of the Cranium: A Systematic Review of the Literature" World Neurosurg (2022)
- "Headache or facial pain attributed to disorder of the cranium, eyes, ears, nose, sinuses, teeth, mouth, or other facial structure" Headache and Migraine in Practice (2022)
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