Infant Skull Anatomy: What Makes Up a Newborn Baby’s Skull

Although the skull may appear to be one bone, it is actually made of five connected bones that are separated to allow the baby's head to pass through the birth canal. The skull bones, joints, and fontanelles work together to allow your baby's brain to continue to grow after birth as well.

Bones of an Infant’s Skull

An infant’s skull is made up of five individual bones. These bony plates are able to overlap one another during birth so your child can fit through the birth canal. These bones include:

• Two frontal bones
• Two parietal bones
• One occipital bone 

The skull bones are held together by fibrous, flexible joints called sutures. 

Sutures: Joints in a Newborn Baby’s Skull

The joints in your baby's skull are known as sutures. These sutures are responsible for joining the skull bones together. During labor and birth, the sutures allow the skull bones to overlap so the baby's head fits through the birth canal. This protects the brain from being pressed on and damaged. The sutures in an infant's skull include:

• Coronal suture: The coronal suture runs from ear to ear over the top of the head. It connects both frontal bones to the parietal bones.
• Sagittal suture: The sagittal suture runs from the top of the head to the back of the head. It joins the two parietal bones together. 
• Metopic suture: The metopic suture runs from the top of the nose up to the top of the head. It connects the two frontal bones together.
• Lambdoid suture: The lambdoid suture runs across the back of the head. It joins both parietal bones to the occipital bone in the back of the skull. 

These sutures stay flexible and patent (open) as your baby ages, allowing their brain to grow normally. As the brain grows, the skull bones grow symmetrically into a circular shape, and the sutures allow this growth to take place.

When a suture fuses prematurely and is no longer flexible, your baby’s head growth could be affected. This can lead to a condition known as craniosynostosis. It occurs when one or more of the sutures in the skull fuses, leading to a misshapen skull and increased pressure on the brain. 

Fontanelles: Spaces in an Infant’s Skull

The fontanelles in your baby’s skull, often known as “soft spots,” are located in the spaces between the bones where the sutures intersect. These open spaces are covered with tough membranes to protect your baby’s brain. The fontanelles in your infant's skull include:

• Anterior fontanelle: The anterior fontanelle is located on the top of the head where the two frontal bones and two parietal bones meet. This fontanelle stays open anywhere from six months until two years.
• Posterior fontanelle: The posterior fontanelle is located toward the back of your baby’s skull where the two parietal bones meet the occipital bone. This fontanelle is usually the first to close. 

The fontanelles can also provide clues when a baby is seriously ill. The fontanelles usually feel flat and firm to the touch. A sunken anterior fontanelle appears as though it is sagging inward. This may indicate dehydration and needs to be treated right away.

A bulging anterior fontanelle appears as though the baby’s skin is pressing upward. This could mean that your little one is experiencing increased intracranial pressure and there is too much pressure on their brain. This is an emergency that requires immediate treatment. Your doctor will be able to assess your baby’s fontanelles by closely examining them and pressing them softly. 

Summary

Your baby's skull is made up of separate bones that can shift and overlap during labor to allow your baby to pass through the birth canal. These bones are held together by sutures, which remain flexible in your child's early years to provide room for their brain to grow.

Your baby's skull also has two fontanelles, or soft spots, which are where sutures intersect. When your baby is feeling unwell, the fontanelles can potentially help you figure out what's wrong.

A Word From Verywell

Your baby’s head is made up of five skull bones, four sutures, and two fontanelles. These components of the skull work together during the birth process to allow your baby’s head to fit through the birth canal.

The sutures remain flexible until your little one is a toddler to allow for rapid brain growth. If you have any concerns about the shape of your child’s head, don’t hesitate to reach out to your pediatrician. 

Frequently Asked Questions

Can an ultrasound show a newborn’s skull anatomy?

Cranial ultrasound can be performed on your child’s head to evaluate their skull. This test must be performed before their sutures have fused. If your doctor suspects that there is an abnormality in your child’s skull, they may recommend a cranial suture ultrasound to examine your child’s suture lines. It is faster than a CT scan and does not involve radiation. 

What happens to an infant’s skull anatomy as a baby grows?

As your baby grows, their skull continues to grow as well. The sutures usually stay open and flexible until the child’s second birthday. This allows their brain to grow quickly. By the time your child turns 2, their sutures will have fused and the fontanelles closed. 

What is the purpose of spaces in a newborn’s skull?

The open spaces in your baby’s head have two main purposes. First, they allow your baby to fit through the birth canal during labor and delivery. The skull bones are able to overlap and shift in order for your baby’s head to squeeze through without affecting the brain. Second, the open spaces allow the brain to grow normally.