<prompt> Mastoid fontanelle closes by1-3 months3-6 months11-12 months18-24 months  <response>: Closure of Fontanelles:1. Anterior fontanelle by 18 months2. Posterior fontanelle by 2-3 months3. Sphenoidal fontanelle by 2-3 months and 4. Mastoid fontanelle by 12 months Reference: Chourasia; 6th edition; 12th page 