fontanelle

an opening in the SKULL of newborn and young infants in whom the BONE is not wholly formed and the SUTURES are incompletely fused. The largest of these is the anterior fontanelle, on the top of the head, which is about 2.5 cm square at birth. The fontanelles gradually close as bone is formed and are completely covered by the age of 18 months. If a baby is unwell, e.g. with a fever, the fontanelle becomes tense. If an infant is suffering from diarrhoea and possibly dehydrated, the fontanelle is abnormally depressed.