A fontanelle is an anatomical

Human anatomy

Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...

 feature on an infant's skull

Human skull

The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...

.
Fontanelles are soft spots on a baby's head which, during birth, enable the bony plates of the skull to flex, allowing the child's head to pass through the birth canal. The ossification

Ossification

Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...

 of the bones of the skull causes the fontanelles to close over by 18 months up to a child's second birthday. The closures eventually form the sutures of the neurocranium.