Skull is the bony framework of the head, enclosing the brain and forming the skeleton of the face. It lies above the neck and rests on the upper end of the vertebral column. Its bones protect delicate structures, support the teeth and provide attachment sites for muscles that move the jaw and head.
Where is the skull located?
The skull occupies the head, with the brain enclosed above and behind the facial skeleton. The scalp covers its upper and posterior surfaces, while muscles and other soft tissues cover much of the face. Below, the skull connects to the cervical spine, the part of the vertebral column within the neck.
The atlas, the uppermost cervical vertebra, supports the skull through joints with the occipital bone at its base. The hyoid bone lies below the skull in the anterior neck but is not a skull bone. It is suspended by muscles and ligaments rather than joined directly to another bone.
What are the main parts and bones of the skull?
The skull has two principal divisions: the neurocranium, which encloses the brain, and the viscerocranium, which forms the facial skeleton. These divisions meet around the eye sockets and nasal region rather than forming completely separate blocks.
The neurocranium includes the frontal bone, right parietal bone, left parietal bone, temporal bones, occipital bone, sphenoid bone and ethmoid. The frontal bone forms the forehead and contributes to the roofs of the eye sockets. The parietal bones form much of the roof and upper sides of the skull.
The facial skeleton includes the maxillae, which form the upper jaw; the zygomatic bones, which form the cheek prominences; and the mandible, which forms the lower jaw. Smaller bones contribute to the nose and eye sockets. For example, the left lacrimal bone contributes to the inner wall of the left eye socket, while the left inferior nasal concha forms a curved bony projection within the left nasal cavity.
What landmarks can be seen on the skull surface?
The calvaria is the dome-like roof of the neurocranium. Its outer surface is covered by the scalp, while its inner surface faces the brain and its protective membranes, collectively called the meninges. Much of the calvaria has compact outer and inner bone layers separated by diploë, a layer of spongy bone.
Several landmarks help orient the skull:
- The orbits are the bony eye sockets, situated on either side of the upper nose.
- The zygomatic arches are bridges of bone along the sides of the face, connecting the cheek region to the temporal bones.
- The external acoustic meatus is the ear canal; its medial part is bony and leads towards the eardrum.
- The mastoid process is a projection of the temporal bone behind the ear that provides muscle attachments.
- The external occipital protuberance is a prominence on the back of the occipital bone where ligaments and muscles attach.
The hard palate, the bony roof of the mouth, separates the oral cavity from the nasal cavity above. It is formed by parts of the maxillae and palatine bones.
What forms the skull base?
The skull base is the floor beneath the brain. Its internal surface has anterior, middle and posterior cranial fossae: depressions that accommodate different parts of the brain. The anterior fossa supports the frontal lobes, the middle fossa supports the temporal lobes, and the posterior fossa accommodates the cerebellum and brainstem.
Openings through the base allow nerves and blood vessels to pass between the cranial cavity, the space enclosing the brain, and neighbouring regions. A foramen is an opening in a bone. The foramen magnum is the large opening in the occipital bone through which the lower brainstem continues into the spinal cord.
Beside this opening are the occipital condyles, rounded joint surfaces that meet the atlas. Their position links the braincase directly to the supporting spine.
How do the skull bones join together?
Most skull bones meet at sutures, joints in which fibrous connective tissue holds adjacent bones together. The principal sutures of the cranial roof provide useful orientation landmarks.
| Suture | Bones joined | Position |
|---|---|---|
| Coronal suture | Frontal bone and parietal bones | Across the front of the cranial roof |
| Sagittal suture | Right and left parietal bones | Along the midline of the cranial roof |
| Lambdoid suture | Parietal bones and occipital bone | Across the posterior skull |
The mandible meets the temporal bones at the temporomandibular joints. These are synovial joints, meaning that their joint surfaces are enclosed within a capsule containing lubricating fluid. They allow opening, closing, forward, backward and side-to-side movements of the lower jaw.
The skull also forms synovial joints with the atlas. These atlanto-occipital joints permit much of the nodding movement of the head.
What does the skull do?
The neurocranium protects the brain and supports its surrounding membranes. The facial skeleton supports the eyes, forms the framework around the nasal cavity and provides the bony foundation of the mouth.
The jaws hold the teeth, and skull surfaces provide attachment sites for chewing muscles. Other attachments support muscles involved in facial expression and head movement. Openings and channels provide routes for nerves and blood vessels without leaving the entire braincase open.
How can you study the skull in the 3D model?
In the 3D model beside this article, rotate and zoom to compare the skull from the front, side and below. Select and isolate a structure to examine its shape, or fade it to compare its position with neighbouring structures.
Start by locating the forehead, cheek arches and lower jaw, then turn towards the skull base. Relating these external landmarks to the cranial roof and base helps connect the facial skeleton with the braincase.