The skull (latin: cranium) is the skeleton of the head composed usually of 22 bones. The main function of the skull is to provide protection for the brain and the sensory organs connected with it. The skull also incorporates the upper parts of the digestive (mouth) and respiratory tracts (nose), and supports the soft tissue of the head. The human skull consists of two major parts: the neurocranium and the viscerocranium.
The neurocranium consists of bones of the skull that are in contact with the brain. There are eight bones forming the neurocranium. These are four single bones (sphenoid, occipital, frontal, ethmoid) and two paired bones (temporal, parietal bones).
The viscerocranium (or splanchnocranium) is composed of the facial bones of the skull. Six of them are paired (maxilla, zygomatic bone, palatine bone, lacrimal bone, nasal bone, inferior nasal concha) and three are unpaired bones (vomer, mandible and hyoid bone).
There are also three tiny bones, the auditory ossicles (malleus, incus and stapes), located within each middle ear, which is housed in the skull, specifically, within the right and left temporal bones.
The bones of the skull are connected to each other with the help of fibrous junctions called sutures. The bones of the skull grow and fuse together during fetal and childhood development, forming a single skull. However, the mandible remains separate from the rest of the skull and is the only movable bone of the skull.
There are around 33 sutures in the human skull. The most important sutures in the skull are the coronal suture, sagittal suture and the lambdoidal suture.
There is only one synovial joint between bones of the skull. It is the temporomandibular joint (TMJ), which is formed between the head of the mandible and the mandibular fossa of the temporal bone.
The skull is rich with openings, including foramina and canals, serving mostly as passages for nerves and blood vessels. The largest opening of the skull is the foramen magnum in the base of the skull, through which the spinal cord as an extension of the medulla oblongata exits the cranial cavity.