Baby Skull Anatomy: Bones, Sutures and Soft Spots

Which bones make up a baby’s skull?

• Frontal bone: Forms the forehead; in babies it is in two halves separated by a suture, which join during the first year.
• Parietal bones: Two large bones forming the top and sides of the head.
• Occipital bone: Forms the back of the head, where positional flattening is most common.
• Temporal bones: On each side of the head around the ears.

Other bones form the skull base, but the plates above and the sutures between them matter most for head shape.

What is a suture?

A suture is a flexible seam of fibrous tissue where two skull bones meet. Sutures allow the bones to shift slightly during birth and act as growth zones in infancy: as the brain grows, new bone is added along the suture edges so the skull expands in step with the brain.

What are the main skull sutures?

• Metopic: Between the two halves of the frontal bone, from the nose to the front soft spot.
• Sagittal: Along the top of the head between the parietal bones, front to back.
• Coronal: Between the frontal and parietal bones, from ear to ear over the top.
• Lambdoid: At the back, between the parietal and occipital bones.
• Squamous: On the sides, between the temporal and parietal bones.

When do skull sutures close?

The metopic suture closes first, usually starting between about 3 and 9 months, so a slight ridge in the middle of the forehead can be felt in some babies and is not always a problem. The sagittal, coronal and lambdoid sutures stay open for many years to allow brain growth and generally fuse in adulthood. Timing varies between individuals.

What are fontanelles?

Fontanelles are wider soft areas where several sutures meet, covered by a tough membrane. The front fontanelle is diamond-shaped and usually closes between 12 and 18 months; the back fontanelle is triangular and usually closes in the first 1–2 months. Smaller ones at the sides close early. Read more in when does the soft spot close.

Why is a baby’s skull flexible?

Flexibility helps the head pass through the birth canal and lets the skull keep pace with very rapid brain growth in the first year. The same softness makes the head sensitive to outside pressure: lying on one spot for long periods can cause flattening, known as deformational plagiocephaly, in which the sutures remain open. For the growth timeline, see when does a baby’s head shape settle.

What happens if a suture closes early?

Early fusion of one or more sutures is called craniosynostosis. Growth stops across the fused suture and continues at the open ones, producing typical shapes:

• Sagittal: A long, narrow head (scaphocephaly). See sagittal suture synostosis.
• Metopic: A triangular forehead with a prominent ridge (trigonocephaly). See metopic suture synostosis.
• One coronal suture: One side of the forehead flattened.
• Lambdoid: Rare one-sided flattening at the back that must be told apart from positional flattening.

Diagnosis and treatment are planned by a neurosurgical or craniofacial team. A helmet does not replace surgery but may be used after some techniques as part of the team’s plan.

When should you see a specialist?

• A hard ridge along a suture line
• A triangular forehead or one side of the forehead flattened
• A long, narrow head that is becoming more noticeable
• A front soft spot that seems to close very early
• A flat spot at the back or side that is increasing

You can book an appointment for assessment of positional head shape differences; babies with suspected craniosynostosis are referred to the appropriate doctor.

Frequently asked questions

How many bones are in a baby’s skull?

The part around the brain mainly includes the frontal bone (in two halves), two parietal bones, the occipital bone and two temporal bones, plus bones at the skull base.

What is a suture?

A flexible seam joining skull bones that acts as a growth zone during infancy.

When does the metopic suture close?

Usually between about 3 and 9 months. A slight forehead ridge alone is not necessarily a problem.

What is the difference between a fontanelle and a suture?

Sutures are narrow seams between bones; fontanelles are wider soft areas where several sutures meet.

My baby has a bony ridge on the head. Is it normal?

Some ridges, such as a mild metopic ridge, can be normal, but a prominent ridge or one that changes head shape should be checked by a pediatrician.