Your skull is a braincase welded to a face
A skull or cranium is usually bony armor around a vertebrate brain; some fish and amphibians keep it cartilaginous. In humans it joins neurocranium and facial skeleton from the first pharyngeal arch, with cranial bones, facial bones, and ear ossicles meeting at sutures.
The skull sits at the front end of the axial skeleton and grew out of the evolutionary trend toward concentrating nerves and senses in the head. It shields the brain, anchors muscles for the neck, face and jaw, fixes the eye sockets and ear canals so that vision can be stereoscopic and sounds can be located, shapes the nasal and oral cavities for smell, taste and eating, and even adds resonance to the voice. The English word probably comes from Old Norse, while cranium goes back to the Greek kranion.
Anatomists usually count 22 bones in the human skull: eight in the braincase, namely the occipital, frontal, sphenoid, ethmoid and paired parietals and temporals, and fourteen in the face, including the maxillae, nasal and cheek bones, and the mandible, the largest facial bone, which hinges on the temporal bones. Tallies differ because some sources treat paired bones as one or add the hyoid and ear ossicles. The bones meet at sutures, immovable fibrous joints with a little give from Sharpey's fibres, and small extra Wormian bones sometimes appear, most often along the lambdoid suture.
Air-filled paranasal sinuses lined with respiratory tissue lighten the skull, enrich the voice and warm and moisten inhaled air. Of the many openings, the largest is the foramen magnum in the occipital bone, through which the spinal cord passes. The roof and face bones form by intramembranous ossification directly from membrane, whereas the temporal bones and the endocranium supporting the brain form through cartilage.
Comparative anatomy shows the skull's long history. Jawless fish have only a partial cartilage basket around the brain, and sharks and rays a single cartilage case left open on top. Bony fish added dermal bone, and early tetrapods inherited a roof of plate-like bones from lobe-finned ancestors. Since then many bones have fused or vanished, often shaped by the forces of biting. Living amphibians have much-reduced skulls, while mammals and birds remodelled theirs to hold bigger brains; a bird's skull has five major bones and a single occipital condyle.
Source: Skull
