Skull, the bony framework of the head, composed of 22 bones in adults. The skull protects the brain and other vital organs within the cranial cavity. It also serves as a attachment site for many muscles that control head and neck movement. The human skull is divided into two main parts: the cranium, which encloses and protects the brain; and the facial skeleton, which includes all bones below the orbit (eye socket) including those that form the nose, mouth, cheeks, and jaws.
The cranium is further subdivided into two parts: the neurocranium, which encloses and protects the brain; and the viscerocranium (also called splanchnocranium), which forms most of face. The neurocranium is made up of eight bones: frontal bone, 2 parietal bones, temporal bones (2), occipital bone , sphenoid bone , ethmoid bone . All except frontal bone & ethmoid are paired. The viscerocranium is made up of 14 bones: maxilla (2), palatine (2), zygomatic or malar bone(2), nasal bone(2), lacrimalbone(2), inferior concha(2) & vomer . Of these only maxilla & palatine are paired while rest are single bones. In addition there are 3 small accessory sinuses-frontal sinus , ethmoidal sinus & sphenoidal sinus present in some people in cavities within frontal , ethmoidal & sphenoidal bones respectively.
Developmentally skulls result from intramembranous ossification involving transformation of mesenchymal cells to osteoblasts . This occurs directly without an intervening cartilage stage unlike long tubular Bones like femur . Most flat Bones of skull develop this way with exception being mandible which has a cartilaginous model before it starts ossifying endochondrally i.e., around a hyaline cartilage template.
Calvaria or top part of skull develops from membranous ossification whereas base of skull develops by endochondral ossification i.e., around a cartilaginous model Craniosynostosis refers to premature Fusion of one or more sutures between plates of developing calvaria results in abnormal shapes like scaphocephaly resulting due to premature fusion sagittal suture , oxycephaly resulting from premature fusion coronal sutures & trigonocephaly when metopic suture fuses prematurely . Treatment involves surgical correction soon after birth so as to allow normal growth remaining unfused sutures .