Mastoid Fontanelle

The mastoid fontanelle is one of two areas of an infant's head where the skull bones have not completely covered the brain. It is also known as one of the soft spots. There is one mastoid fontanelle on each side of the head, just beneath the parietal bone and between the front of the occipital bone and the lower rear edge of the temporal bone. The mastoid fontanelle has usually disappeared (because the plates of the skull grow and fuse together) by the time the infant is about a year old.