A fontanelle is the soft spot on a baby’s skull where the bone plates have not yet fully fused together. It helps the skull flex during birth and gives the brain room to grow after birth.

Simple meaning

  • It is a gap covered by tough membrane, not an open hole.
  • Babies usually have two main fontanelles: one at the top/front and one at the back.
  • The front one is the larger and usually closes later, often by around 18 months.

Why it matters

  • It supports normal skull and brain growth in infancy.
  • Doctors check it during baby exams because a fontanelle that is bulging or sunken can sometimes signal a health issue.
  • A gentle pulse can be normal.

Example

If you feel a soft, slightly springy area on the top of a newborn’s head, that is the fontanelle.

Word origin

The word comes from Old French and is related to the idea of a small spring or fountain.