Skull
. 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