Fontanels

• The skull of an infant, showing fontanels. (Credit: Medline Plus)
  
  Fontanels are the spaces between the cranial bones in infants. The bones are joined by membranes, which later ossify into bone. There are six fontanels: one anterior, one posterior, two sphenoid (or anterolateral) and two mastoid (or posterolateral). Most fuse by the first year, but the largest, the anterior fontanel, can be felt until age 2.
  
  

Other skull bones

• The frontal bone (forehead) and mandible (jaw) are separated into right and left bones at birth. They usually fuse together by age 5 or 6.
  
  

Deformity

• According to the Comer Children's Hospital of the University of Chicago, placing a newborn baby to sleep on its back every night, while a precaution against Sudden Infant Death Syndrome, can also cause the back of the head to flatten. To prevent this, turn a baby from side to side to back throughout the night.
  
  

Assessment

• Obstetric nurses examine babies after birth, especially a difficult birth, to make sure the cranial bones don't overlap each other.
  
  

Warnings

• Abnormally wide spaces between the bones can mean hydrocephalus or "water on the brain." Bulging fontanels can mean abnormally high pressure inside the cranium, and sunken fontanels can indicate dehydration.