Fontanelles typically close by 18 to 24 months through which process?

• A. Ossification
• B. Calcification
• C. Fracture
• D. Tendon formation

Answer: (A)

Fontanelle closure happens as the skull sutures ossify. The soft spots are fibrous membranes between the skull bones, and over the first couple of years osteoblasts lay down bone in these membranes, turning them into bone in a process called intramembranous ossification. This replaces the fibrous tissue and fuses the sutures, with the anterior fontanelle typically closing around 18–24 months. Calcification occurs within the bone during ossification, but the driving process of closing the fontanelles is ossification itself. Fracture and tendon formation are unrelated to this normal skull development.