---
title: "Sphenoidal Fontanelle | Anatomy and Physiology I"
description: "Sphenoidal fontanelle is a small newborn skull opening near the temple that supports birth molding and closes as cranial bones fuse in A&P I."
canonical: "https://fiveable.me/anatomy-physiology/key-terms/sphenoidal-fontanelle"
type: "key-term"
subject: "Anatomy and Physiology I"
unit: "Unit 7"
---

# Sphenoidal Fontanelle | Anatomy and Physiology I

## Definition

The sphenoidal fontanelle is a small soft spot on a newborn skull near the temple, where cranial bones have not fully fused yet. In Anatomy and Physiology I, it shows how the skull forms and changes shape during birth and early growth.

## What It Is

The sphenoidal fontanelle is one of the soft spots in a newborn skull, and in Anatomy and Physiology I it is taught as part of how the axial skeleton develops before the cranial bones fully fuse. It is a small membranous gap on the side of the skull, near the junction of the frontal, parietal, sphenoid, and temporal bones. Because the bones have not yet locked together, the skull can be slightly more flexible in infancy.

That flexibility matters during fetal development and birth. The baby’s head has to pass through the birth canal, and a rigid skull would make that much harder. Fontanelles let the cranial bones shift a little and overlap temporarily, a process called molding. After birth, the brain grows quickly, so the skull also needs room to expand before the bones close and harden.

The sphenoidal fontanelle is usually one of the smaller fontanelles, and it closes early compared with the larger openings. As ossification continues, the surrounding cranial bones meet and form sutures, which are the fibrous joints between skull bones. The fontanelle is not a permanent hole, it is a developmental gap that disappears as normal bone growth finishes its job.

A good way to think about it is that the fontanelle is a temporary construction zone in the skull. The bones are being built by intramembranous ossification, but the final seams are still open so the head can grow and adapt. Once closure happens, the skull becomes more protective and stable.

In a newborn exam, a clinician may feel the fontanelle to check whether skull development seems normal. If it is unusually large, bulging, or slow to close, that can point to problems such as altered intracranial pressure or a developmental disorder. If it closes too early, that can also signal an issue with skull growth.

## Why It Matters

The sphenoidal fontanelle shows that the skull is not just a static box, it is a developing structure that has to balance protection, growth, and birth mechanics. That makes it a useful example when you are studying embryonic development of the axial skeleton and the way cranial bones form by intramembranous ossification.

It also connects anatomy to clinical reasoning. If you see a question about a newborn skull, a soft spot that is still open is normal, but the pattern of closure matters. A fontanelle that is very tense, sunken, or unusually wide can point to dehydration, increased pressure, or a growth problem, so the term often shows up in baby exam scenarios and developmental case questions.

This term also helps you separate fontanelles from sutures. Fontanelles are the open membranous spaces, while sutures are the fibrous seams that remain after the bones meet. That difference shows up a lot in lab practicals and bone ID questions.

If you are tracing how the skull changes from fetus to infant, the sphenoidal fontanelle gives you a clear before and after: open and flexible at birth, then replaced by fused bone as the cranial vault matures.

## Connections

### Fontanelle

Fontanelle is the broader term for the soft spots between infant skull bones. The sphenoidal fontanelle is one specific fontanelle, so this term sits under the larger idea of temporary openings that let the skull expand and mold during early development.

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

Cranial sutures are the fibrous joints that form when the skull bones meet and fuse. Fontanelles are open spaces before that fusion is complete, so if you understand one, it becomes easier to tell how the newborn skull changes into the adult skull.

### [Sphenoid Bone](/anatomy-physiology/key-terms/sphenoid-bone)

The sphenoidal fontanelle sits near the sphenoid bone, so skull anatomy questions often connect the two. The sphenoid is a central cranial bone, while the fontanelle is a temporary developmental gap near where several skull bones come together.

### [Anterior Fontanelle](/anatomy-physiology/key-terms/anterior-fontanelle)

The anterior fontanelle is larger and stays open longer than the sphenoidal fontanelle. Comparing the two helps you remember that not all fontanelles close at the same time, and each one has its own location and developmental timeline.

## On the AP Exam

A practical quiz question might point to a newborn skull diagram and ask you to identify the soft spot near the temple, or to name the structure that allows the infant skull to compress slightly during birth. In a lab practical, you may need to match the sphenoidal fontanelle with the correct location and distinguish it from the anterior fontanelle. In a short-answer or case question, you might explain why a fontanelle is open in infancy but should close as cranial ossification finishes. You can also be asked what a bulging or delayed-closing fontanelle suggests, so know both the normal function and the red-flag interpretation.

## Sphenoidal Fontanelle vs Anterior Fontanelle

These are both newborn skull openings, but they are not the same size or location. The anterior fontanelle is the larger, diamond-shaped soft spot on the top of the head, while the sphenoidal fontanelle is smaller and sits more laterally near the temple region.

## Key Takeaways

- The sphenoidal fontanelle is a temporary opening in the newborn skull near the temple region.
- It lets the skull flex during birth and gives the growing brain room before the cranial bones fully fuse.
- In Anatomy and Physiology I, it is part of embryonic development of the axial skeleton and intramembranous ossification.
- This fontanelle closes as the surrounding bones meet and form sutures, so it should not remain open forever.
- Changes in fontanelle size or closure can point to developmental or medical problems in an infant.

## FAQs

### What is the sphenoidal fontanelle in Anatomy and Physiology I?

It is a small soft spot on a newborn skull where cranial bones have not fused yet. In A&P I, it shows how the skull develops before the bones close into solid sutures.

### Where is the sphenoidal fontanelle located?

It is found on the side of the infant skull near the temple, where the frontal, parietal, sphenoid, and temporal bones come together. That location helps you tell it apart from the anterior fontanelle on the top of the head.

### Is the sphenoidal fontanelle the same as the anterior fontanelle?

No. They are both fontanelles, but the anterior fontanelle is larger and located at the top of the skull, while the sphenoidal fontanelle is smaller and more lateral. They also close on different timelines.

### Why do fontanelles exist in newborns?

They let the skull compress a little during birth and provide room for the brain to grow after delivery. Without them, the infant skull would be too rigid for normal birth and early development.

## Related Study Guides

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

## About This Document

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