The skull serves as a protective chamber for the brain and provides structural support for the face. It is a complex structure made up of multiple bones.
Major Bones of the Skull
The skull is composed of 22 bones, broadly categorized into cranial bones and facial bones. The cranial bones form the neurocranium. These include the frontal bone, forming the forehead and upper eye sockets, and two parietal bones, located on either side of the head behind the frontal bone, forming much of the top and sides of the skull.
The occipital bone makes up the posterior base of the skull and has a large opening for the spinal cord. Two temporal bones are situated on the sides and base of the skull, beneath the parietal bones, covering the area of the temples. The sphenoid bone sits below the frontal bone, spanning the width of the skull and contributing to the base and parts of the eye sockets. The ethmoid bone, located between the eyes at the roof of the nose, separates the nasal cavity from the brain.
Facial bones, also known as the viscerocranium, provide the structure for the face and support various sensory organs. The maxilla, a pair of bones, forms the upper jaw and much of the hard palate. The mandible is the lower jawbone, the largest and only movable bone of the face. The zygomatic bones form the prominences of the cheeks and contribute to the eye sockets. The nasal bones are two slender bones that form the bridge of the nose.
Primary Functions of the Skull
The skull’s primary function is to protect the delicate brain from external injury. This bony enclosure acts as a strong barrier against impacts and provides a stable environment for neurological processes. The skull also provides structural support for the face and serves as an anchor for various muscles.
The skull houses and protects several sensory organs, such as the eyes within their orbits and the inner structures of the ears. It also contributes to the formation of the nasal and oral cavities, which are involved in olfaction, taste, and digestion. The skull also provides attachment points for muscles of mastication, facial expression, and the neck, enabling functions like chewing, speaking, and head movement.
How Skull Bones Connect
In adults, the individual bones of the skull are joined by fibrous joints called sutures. These sutures are generally immovable, forming a rigid and protective structure around the brain. They are characterized by interlocking edges of adjacent bones, with fibrous connective tissue filling the narrow gaps between them.
Examples include the coronal suture, which connects the frontal bone with the parietal bones. The sagittal suture runs along the top of the skull, uniting the two parietal bones. The lambdoid suture fuses the occipital bone with the parietal bones at the back of the head.
Skull Development in Infants
The skull in infants exhibits unique characteristics to accommodate rapid brain growth and facilitate passage through the birth canal. Unlike adult skulls, infant skulls have unfused areas between the bones, known as fontanelles or “soft spots.” These gaps allow the skull bones to overlap slightly during birth, enabling the baby’s head to mold and pass more easily. They also permit the rapid expansion of the brain during infancy and childhood.
The two major fontanelles are the anterior fontanelle, located at the front top of the head, and the posterior fontanelle, found at the back of the head. The posterior fontanelle typically closes within two to three months after birth. The larger anterior fontanelle usually closes between 12 to 18 months of age.