THE ANATOMY OF THE SKULL
The skull is a bony structure that supports the face and forms a protective cavity for the brain. It is comprised of many bones, which are formed by intramembranous ossification, and joined by sutures (fibrous joints).
The Bones of the Skull:
The bones of the skull can be considered as two groups: those of the cranium (which consist of the cranial roof and cranial base) and those of the face.
NB: The six unpaired bones of the skull are: frontal, ethmoid, sphenoid, vomer, occipital and mandible.
Sutures of the Skull
The Sutures are a type of fibrous joint that are unique to the skull. They are immovable and fuse completely around the age of 20.
These joints are important in the context of trauma, as they represent points of potential weakness in the skull. The main sutures in the adult skull are:
- Coronal suture – The coronal suture is the articulation point of the frontal bone with the two parietal bones (it fuses the frontal bone with the two parietal bones).
- Sagittal suture – The sagittal suture is the articulation point between the two parietal bones (it fuses both parietal bones to each other).
- Lambdoid suture – The lambdoid suture is the articulation point between the occipital bone and the two parietal bones (it fuses the occipital bone to the two parietal bones).
- Squamous sutures - The squamous sutures are the articulation points between the each temporal bone and the parietal bone superior to it.
NB: In neonates, the incompletely fused suture joints give rise to membranous gaps between the bones, known as fontanelles. The two major fontanelles are:
- Frontal fontanelle – it is located at the junction of the coronal and sagittal sutures
- Occipital fontanelle – it is located at the junction of the sagittal and lambdoid sutures
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NB: There is only one movable joint in the skull. That is the joint connecting the lower jaw, or mandible, to the rest of the skull. All the other bones in the skull are firmly attached to one another by sutures. Sutures are rigid immovable connections holding bones tightly to one another. Some of the sutures in the skull take a few months-to-years after birth to completely form.