Embryology · Skeleton, muscles, limbs and skin

Skull: neurocranium, viscerocranium, sutures and fontanelles !

Embryonic structure

A baby's skull is plates of bone joined by flexible seams (sutures) and soft spots (fontanelles) that let the brain grow.

Updated 2026-11-01

See it in 3D: Frontal bone · Parietal bones · Base of the skull · Temporal bones · Sphenoid bone · Ethmoid bone · Mandible · Maxillae · Nasal bones

What it is

The skull has two parts: the neurocranium, which protects the brain, and the viscerocranium, which forms the face. The vault ossifies directly in membrane, while the base passes through a cartilage stage first. Sutures and fontanelles allow moulding during birth and brain growth afterwards; their early closure is craniosynostosis.

Key facts

Vault (membranous neurocranium): intramembranous ossification of the flat bones.
Base (chondrocranium): endochondral ossification; in front of the sella turcica it comes from neural crest, behind it from paraxial mesoderm (occipital somites).
The frontal bone comes from neural crest; the parietal bones from paraxial mesoderm.
Viscerocranium: mostly neural crest of the first two pharyngeal arches (maxilla, mandible, ossicles).
Posterior fontanelle: closes around 1 to 2 months. Anterior fontanelle: around 18 months.
At birth the vault is large and the face small; the face grows with the paranasal sinuses and the teeth.

Structure

Membranous neurocranium: frontal, parietal bones, squamous temporal and part of the occipital.
Chondrocranium: sphenoid, ethmoid, petrous temporal and most of the occipital.
Main sutures: metopic (between the two frontal halves), coronal, sagittal and lambdoid.
Fontanelles: anterior (between frontal and parietal bones, the largest), posterior, and the sphenoid and mastoid ones on each side.

What it becomes

Sutures are growth zones: bone is added at their edges as the brain pushes outwards.
Fontanelles let the plates overlap during birth (moulding) and then return to place.
The anterior fontanelle is part of the infant exam: tense or bulging suggests raised intracranial pressure; sunken suggests dehydration.
As they close, sutures leave a rigid skull; the sagittal and coronal sutures fuse in adult life.

Markers

FGFR1
FGFR2
FGFR3
MSX2
TWIST1
RUNX2

Clinical notes

Craniosynostosis: early closure of a suture distorts the skull according to which one closes.
Cleidocranial dysplasia (RUNX2): large, late-closing fontanelles, absent clavicles and extra teeth.
Achondroplasia (FGFR3): the endochondral base stays small with a narrow foramen magnum; the membranous vault grows normally.
Microcephaly: a small skull because the brain does not grow; the sutures are not the cause.

Test yourself

Think of the answer, then tap the question to see it.

What type of ossification forms the bones of the skull vault?

Intramembranous: mesenchyme turns directly into bone without a cartilage model.

Around what age does the anterior fontanelle close?

In most children around 18 months; the posterior closes much earlier, around 1 to 2 months.

Where do the frontal and parietal bones come from?

The frontal bone derives from neural crest and the parietal bones from paraxial mesoderm.

Why does achondroplasia shrink the skull base but not the vault?

The base forms by endochondral ossification, which overactive FGFR3 slows; the vault is membranous.

Add to my cards (4)

See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Cranial sutures: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Cleidocranial dysplasia: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Langman's Medical Embryology, 13th ed., ch. 10: The Axial Skeleton (Wolters Kluwer, 2015).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.