Fontanels

At birth, the skull is incompletely developed, and the cranial bones are separated by fibrous membranes. These membranous areas are called "fontanels" or, more commonly, "soft spots." They permit some movement between the bones, so that the developing skull is partially compressible and can slightly change shape. This action enables an infant's skull to pass more easily through the birth canal. Eventually the fontanels close as the cranial bones grow together. The posterior fontanel usually closes about two months after birth; the sphenoid fontanel closes at about three months, the mastoid fontanel closes near the end of the first year, but the anterior one may not close until the middle or end of the second year.