Skull (overview)

The human skull can be defined as the skeletal framework of the head. It is composed of 22 bones (or 29 bones if the hyoid bone and three auditory ossicles (incus, malleus, and stapes) are included). The bones of the skull are joined together by fibrous joints with a fracture-like appearance called sutures. The primary function of the skull is to provide protection for the brain and sensory organs connected with it.

Most bones of the skull are immobile and are linked through previously mentioned sutures, except the mandible. It forms the lower jaw and is the only movable bone of the skull. It connects with the skull (temporal bones) at the temporomandibular joints.

Besides protecting the contents found within the cranial cavity, the skull also houses the upper part of the digestive tract (including the oral cavity), as well as the nasal cavity, which is the initial part of the respiratory tract. It also provides support for the soft tissue of the head and various facial structures.

Additionally, several skull bones contain air-filled cavities called the paranasal sinuses. These sinuses help to create voice resonance and aid in warming and moistening the inhaled air. 

Moreover, the skull contains numerous small canals and openings known as foramina. These foramina transmit various neurovascular structures, allowing them to enter and leave the cranial cavity. Finally, the bones of the skull serve as attachment sites to numerous muscles and ligaments.

The skull is composed of the following paired bones:

The skull is formed by the following unpaired bones:

All of these bones can be classified into two groups based on their primary function - the bones that form the cranial base and roof and protect the brain (bones of the neurocranium) and those that contribute to the facial skeleton (bones of the viscerocranium). Both parts of the skull are reviewed in the following slide.

Note: The hyoid bone is usually also considered a bone of the skull, and it will be reviewed later in this article.