Merriam-Webster Collegiate Dictionary - fontanel

 or ~le  noun  Etymology: Middle English fontinelle a bodily hollow or pit, from Anglo-French funtainele, diminutive of funtaine fountain  Date: 1741 a membrane-covered opening in bone or between bones; specifically any of the spaces closed by membranous structures between the uncompleted angles of the parietal bones and the neighboring bones of a fetal or young skull