Crania

Crania, the plural of cranium, refers to the skulls that enclose the brain. In humans and many vertebrates, the cranium is divided into the neurocranium, which forms the braincase, and the viscerocranium, or facial skeleton.

The neurocranium comprises eight bones: frontal, two parietal, two temporal, occipital, sphenoid, and ethmoid. The calvaria—the skull cap—consists of the frontal, parietal, and occipital bones. The cranial base forms the floor and includes portions of the sphenoid, temporal, occipital, and ethmoid bones. The viscerocranium consists of 14 facial bones: two maxillae, two zygomatics, two nasal bones, two lacrimals, two inferior nasal conchae, two palatines, the vomer, and the mandible.

Joints and growth: Sutures join cranial bones in the infant and young child; fontanelles are softer gaps that allow growth. The cranial bones gradually fuse during childhood and adolescence, with some variation among individuals.

Functions: The cranium protects the brain and sensory organs, supports facial structures, and provides attachments for muscles of mastication and head movement.

Clinical relevance: Fractures can damage brain or vessels; craniosynostosis is the premature fusion of sutures; hydrocephalus and raised intracranial pressure may occur with skull and brain abnormalities; congenital anomalies can affect skull shape and function.

Evolution and variation: In Homo sapiens, the braincase is relatively large and rounded. Skull morphology varies across individuals and species, reflecting genetics, development, and functional demands.