---
title: "Anterior Fontanelle | Anatomy and Physiology I"
description: "Anterior fontanelle is the soft spot between infant skull bones that allows head molding at birth and signals skull growth in Anatomy and Physiology I."
canonical: "https://fiveable.me/anatomy-physiology/key-terms/anterior-fontanelle"
type: "key-term"
subject: "Anatomy and Physiology I"
unit: "Unit 7"
---

# Anterior Fontanelle | Anatomy and Physiology I

## Definition

The anterior fontanelle is the soft, diamond-shaped gap on an infant’s skull where the frontal, parietal, and sphenoid regions meet. In Anatomy and Physiology I, it shows how skull bones form and fuse during early development.

## What It Is

The anterior fontanelle is the largest fontanelle on a newborn skull, a soft, diamond-shaped area where several cranial bones have not fused yet. You can feel it near the top front of an infant’s head, where the frontal and parietal bones meet, with the sphenoid area nearby. In Anatomy and Physiology I, this is one of the easiest examples of how the skull is built to grow first and fully harden later.

This soft spot exists because the bones of the skull vault do not begin life as one solid unit. During embryonic and early postnatal development, those bones form separately and are held together by fibrous connective tissue at sutures and fontanelles. That open space lets the skull expand as the brain grows rapidly in infancy.

The anterior fontanelle also matters during birth. Because the bones can shift slightly, the baby’s head can change shape as it moves through the birth canal. This is called molding, and it is normal. A newborn’s head may look a little elongated or uneven at first, then return closer to its usual shape after delivery.

Closure happens gradually as nearby cranial bones continue to ossify and the sutures narrow. The anterior fontanelle usually closes by about 12 to 18 months, but timing can vary. A fontanelle that closes too early, stays open too long, or feels unusually tense or sunken can point to a developmental or hydration issue, which is why clinicians check it during infant exams.

This term sits right at the intersection of skull anatomy and development. It is not just a “soft spot,” it is a clue that the infant skull is still changing as the skeleton matures.

## Why It Matters

The anterior fontanelle shows up whenever Anatomy and Physiology I connects bone structure to growth. It makes the process of skull development easy to see, because you can trace how intramembranous ossification builds the flat bones of the skull while flexible spaces remain open for a while.

It also gives you a concrete example of why cranial sutures are different from long-bone growth plates. The skull has to protect the brain, but it also has to leave room for rapid brain growth after birth. The anterior fontanelle solves that problem by staying open long enough for expansion, then closing when the bones are ready.

In a lab, model, or diagram question, this term helps you identify the correct region of the infant skull and explain what the open space does. In a clinical case, it can also help you connect anatomy to infant assessment, since changes in the fontanelle can reflect dehydration, pressure changes, or delayed closure. That makes it a practical bridge between skeleton anatomy and real-world health observation.

## Connections

### Fontanelle

The anterior fontanelle is one type of fontanelle, and it is the largest and most familiar one. If you understand the general idea of fontanelles as temporary gaps in the infant skull, the anterior fontanelle becomes the front, diamond-shaped example most often discussed in class and in infant anatomy visuals.

### [Cranial Sutures](/anatomy-physiology/key-terms/cranial-sutures)

Cranial sutures are the fibrous joints that connect skull bones, and the anterior fontanelle sits where several of those bones have not fully met yet. Sutures and fontanelles work together during skull growth, so a diagram often labels both when showing how the infant skull develops and later fuses.

### Ossification

Ossification is the process that turns developing tissue into bone, and it explains why the anterior fontanelle eventually closes. In the skull, ossification continues after birth, so the open area gets smaller as nearby bones mineralize and fuse. That timing is what makes fontanelle closure such a useful growth marker.

### [Hydrocephalus](/anatomy-physiology/key-terms/hydrocephalus)

Hydrocephalus can cause increased pressure in the skull, and an infant’s fontanelle may look or feel fuller than expected. This is not something you diagnose from the fontanelle alone, but it is one of the body clues clinicians notice when they evaluate head shape, growth, and pressure-related problems.

## On the AP Exam

A labeling quiz may show an infant skull and ask you to identify the soft spot at the front of the head. A short-answer question may ask why that area stays open for a while, and the best answer is that it allows skull molding at birth and space for rapid brain growth after birth. In a lab practical, you may need to point out the anterior fontanelle versus a cranial suture or another fontanelle. In a case-based question, you might explain why an unusually sunken or bulging fontanelle matters in a baby exam.

## Anterior Fontanelle vs Cranial Sutures

The anterior fontanelle is a soft, membranous gap where several skull bones meet, while cranial sutures are the fibrous joints between those bones. Sutures are the lines of connection, and the fontanelle is the open space at a junction before full fusion happens. On a diagram, the fontanelle looks like a larger area, not just a line.

## Key Takeaways

- The anterior fontanelle is the large soft spot on the front top of an infant’s skull.
- It exists because the skull bones have not fully fused yet, which allows brain growth after birth.
- The fontanelle also helps the baby’s head mold during childbirth.
- It usually closes by about 12 to 18 months as skull ossification continues.
- Changes in its size or feel can give clues about infant development or health.

## FAQs

### What is anterior fontanelle in Anatomy and Physiology I?

It is the soft, diamond-shaped area on a newborn’s skull where the frontal and parietal bones meet, with the sphenoid region nearby. In A&P I, it is used to show how the skull develops before the bones fully fuse.

### Why does the anterior fontanelle stay open after birth?

It stays open so the infant skull can expand as the brain grows rapidly. The open area also lets the head change shape slightly during delivery, which helps the baby pass through the birth canal.

### How is the anterior fontanelle different from a cranial suture?

A cranial suture is a fibrous joint between skull bones, while the anterior fontanelle is a larger gap where several bones meet before they fuse. Sutures are like the seam lines, and the fontanelle is the open junction between them.

### What does a bulging or sunken anterior fontanelle mean?

A fontanelle that looks unusually bulging or sunken can be a sign that something is off with pressure or fluid balance in an infant. In class, this comes up as an anatomy clue tied to infant assessment, not as a diagnosis by itself.

## Related Study Guides

- [7.5 Embryonic Development of the Axial Skeleton ](/anatomy-physiology/unit-7/5-embryonic-development-axial-skeleton/study-guide/FWwVKCt49KE3Byd7)

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