The soft spot on the top of the head. At birth the skull is made of up of several plates of bone; it is not a single, solid bone. The spaces between the bone plates allow the skull to expand as the brain grows. Where four of these bony skull plates come together it forms a soft spot in the skull called a fontanelle. There is no bone in these soft spots, making these areas softer than the surrounding areas. There are usually two soft spots in the skull of a newborn, the anterior and the posterior fontanelle; both usually close by about 18 months of age.
