<Li> Anterior fontanelle is a diamond - shaped membrane - filled space located between the two frontal and two parietal bones of the developing fetal skull . It persists until approximately 18 months after birth . It is at the junction of the coronal suture and sagittal suture . The fetal anterior fontanelle may be palpated until 18 months . In cleidocranial dysostosis, however, it is often late in closing or may never close . Examination of an infant includes palpating the anterior fontanelle . </Li> <Li> Two smaller fontanelles are located on each side of the head, more anteriorly the sphenoidal or anterolateral fontanelle (between the sphenoid, parietal, temporal, and frontal bones) and more posteriorly the mastoid or posterolateral fontanelle (between the temporal, occipital, and parietal bones). </Li> <P> During birth, fontanelles enable the bony plates of the skull to flex, allowing the child's head to pass through the birth canal . The ossification of the bones of the skull causes the anterior fontanelle to close over by 9 to 18 months . The sphenoidal and posterior fontanelles close during the first few months of life . The closures eventually form the sutures of the neurocranium . Other than the anterior and posterior fontanelles, the mastoid fontanelle and the sphenoidal fontanelle are also significant . </P> <P> In humans, the sequence of fontanelle closure is as follows: </P>

When do the fontanelle close on a baby