Answer
The skull of the fetus is originally just mesenchyme and cartilage. As the baby develops the tissue of the skull ossifies and becomes bone. The upper part of the skull (clavarium) is not completely ossified until after birth. At birth, there are still six areas of unossified mesenchyme (fontanels) between the bones of the calvarium. These are the unpaired anterior, and unpaired posterior fontanels, plus the smaller, paired antero-parietals and the paired postero-parietal fontanels .
The fontanels keep the baby's skull flexible so that it can conform to the shape and size of the birth canal during birth. Then after birth, they facilitate the growth and development of the baby's brain to the large size determined by evolution. If the fontanels closed before birth, a human mother would need a much larger pelvis, and a wider birth canal to give birth to a human fetus
Work Step by Step
The soft spots in the baby's bead or (fontanels in its calvarium) close ( ossify) after birth and are reduced to the very thin connective tissue suture found between the bones of the adult skull. The posterior fontanel closes about two month after birth , but the anterior fontanel( the largest) may not be completely closed until 18 months postnatally. In any case, the dense connective tissue of collagen and elastic fibers that constitute fontanel matrix is not freely permeable to aqueous liquids. Therefore, there is no chance that washing a newborn baby's hair might place him/her at risk of having water leak into his/her brain.
