Cranial sutures are fibrous bands of tissue that connect the bones of the skull.

An infant's skull is composed of 6 separate bones (the frontal bone, the occipital bone, 2 parietal bones, and 2 temporal bones), called cranial bones. These bones are held together by strong, fibrous, elastic tissues called cranial sutures. The spaces within the fibrous tissues between the bones (sometimes referred to as "soft spots") are called fontanels (the anterior fontanel and the posterior fontanel). The cranial bones remain separate bones for approximately 12 to 18 months. Then the separate cranial bones grow together (fuse) and remain fused throughout adulthood.

The fibers (sutures) and spaces between the cranial bones (fontanels) are necessary for the infant's brain growth and development. During childbirth, the flexibility of the fibers allows the bones to overlap their edges so the head can pass through the birth canal without compressing and damaging the infant's brain.

During infancy and childhood, the flexibility of the fibers allows the rapid growth of the brain without constriction while protecting the brain from minor impacts to the head (such as when the infant is learning to hold his head up, roll over, and sit up). Without the flexibility of the sutures and fontanels, the child's brain would be constricted within the cranial bones and could not grow adequately. The child would suffer brain damage.

Feeling the cranial sutures and fontanels is one way that physicians and nurses determine the child's growth and development. They are able to assess the pressure within the brain by feeling the tension of the fontanels. The fontanels should feel flat and firm. Bulging fontanels indicate increased pressure within the brain. In this case, investigation with imaging techniques such as CT scan or MRI scan is warranted and surgery may be necessary to relieve the increased pressure. Sunken, depressed fontanels indicate dehydration.