A non-ossified area of membranous bone, in particular of the skull in an infant. Fonticulus is the accepted Terminologia Anatomica name; fontanelle is widely preferred in the working medical parlance.

When should fontanelles close?

The posterior fontanelle usually closes by age 1 or 2 months. It may already be closed at birth. The anterior fontanelle usually closes sometime between 9 months and 18 months.

What are the six fontanelles?