Inflexible layers of dense connective tissues that hold the bones tightly together.

In adults, these joints or sutures, do not allow any movement; while in new-born babies and very young children, some fibrous joints, or fontanelles known as "soft spots", are movable before they have solidified.

These fontanelles on a baby’s head enable the soft bony plates of the skull to flex during the second stage of labor making it possible for the head to pass through the birth canal.

As the baby matures, the sutures close and the fontanelles gradually harden and are usually completely hardened by the child's second birthday.