The calvaria definition is a simple one — the calvaria is the topmost part of the neural cranium, which protects the cranial cavity that houses the brain. The calvaria is comprised of several different bones, including the parietal bones, the occipital bones, and the frontal bone, or forehead and is the primary part of the skull roof. The bones of the calvaria are comprised of layers of compact bone, which is separated by diploic veins, or cancellous bone that houses rich, red bone marrow until death. In a fetus and young child, the junctions at which the calvaria joins with other bones in the skull roof are soft and not yet melded together — this process, known as intramembranous ossification, completes after the first few years of life. The skull roof then becomes hard at the junctions and much more difficult to penetrate.