The skull consists of five thin, curved, bony plates that are held
together by fibrous material called sutures. These sutures allow a baby's skull
to expand with the growing brain. Usually, the area within a baby's skull
doubles in the first 6 months of life and doubles again by age 2. Some sutures
begin to close at about this time. After age 2, the skull and brain grow at a
much slower rate.
The sutures ossify (gradually harden) to join the skull bones
together. The spaces where sutures meet are called fontanelles. At birth, they
are covered with a membrane (a thin layer of tissue), which are often called
"soft spots." See an illustration of the
sutures and fontanelles .
Babies born with certain conditions may have irregular fontanelles
and sutures. For example, a baby born with
congenital hydrocephalus may have wider sutures than
normal, and the tissue covering the fontanelles may bulge.