The Human Body

Skull

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Skull, term applied to the rigid cartilaginous or bony structure located anterior to the spinal column in all vertebrate animals, and serving to encase and protect the brain and to provide attachment for the muscles of the face and mouth. In lower vertebrates, such as cyclostomes and elasmobranchs, the skull is composed of cartilage throughout the lifetime of the organism; in teleost fishes and in more highly developed vertebrates, including humans, the skull is cartilaginous during embryonic and fetal life, becoming ossified early in postnatal life.

The adult human skull is divided into two regions, the cranial and the facial. The cranial region is the portion of the skull directly surrounding the brain; the facial region includes all the other bones of the skull.

Exteriorly the cranial bones include the two frontal bones, which constitute the forehead and which fuse together in adulthood; the two parietal bones, which constitute the top of the head and which in early childhood are separated from the frontal bones by a space called the anterior fontanel; the single occipital bone, constituting the back of the skull, which is pierced by a large opening through which the spinal cord enters the cranial cavity; and the two temporal bones, which constitute the temples and of the head and bear the zygomatic processes, or cheekbones. The human temporal bone represents the fusion of four bones found in lower mammals: the squamosal bone, which constitutes the side of the head and articulates with the jawbone; the petrosal bone, which contains the inner ear; the mastoid bone, which is behind the ear; and the tympanic bone, which surrounds the channel from the eardrum to the external ear.

Internally, the cranial bones include the ethmoid bone, which forms part of the septum of the nose and through which the olfactory nerves pass from the brain to the upper and middle turbinates; the sphenoid bone, which constitutes most of the floor of the cranial cavity and which houses the pituitary gland; and part of the occipital bone. The floor of the cranial cavity contains three terraced depressions, which contain the cerebellum and the frontal and temporal lobes of the cerebrum.

The facial bones include the two nasal bones, which constitute the upper portion of the bridge of the nose; the two lacrimal bones, which are located in each eye orbit next to the nose, close to the tear ducts; the maxillary bone, which constitutes the upper jaw; the mandible, which constitutes the lower jaw; the two palatine bones of the hard palate; the vomer, which, with a part of the ethmoid bone, constitutes the nasal septum; and the two inferior turbinates of the nose.

See: Disorders of the Human Skull