What do we call the membrane-covered spaces between skull bones found only in infants?

The correct term for the membrane-covered spaces between the skull bones found only in infants is "fontanel." These fontanels, often referred to as "soft spots," are crucial during an infant's development. They allow for flexibility in the skull during childbirth, enabling the bones to overlap and facilitate the baby's passage through the birth canal. Additionally, the fontanels accommodate rapid brain growth during the early months and years of life. Over time, these areas gradually ossify and close as the infant matures, transitioning into a fully formed skull.

The other terms presented describe different anatomical features: "sinuses" are air-filled spaces within the bones of the skull; "fossa" refers to a depression or hollow in a bone or a surface in which another structure may sit; and "meatus" is a channel or passageway, often referring to openings in a bone. These distinctions illustrate why "fontanel" is the specific term related to the unique spaces found in an infant's skull.