Which areas in a child's cranium are non-calcified?

The area in a child's cranium that remains non-calcified is the fontanelles. Fontanelles are the soft spots on a newborn's skull where the bones have not yet fused together. They serve a crucial purpose during childbirth, allowing the baby's head to compress and pass through the birth canal more easily. Additionally, fontanelles provide space for rapid brain growth during the early stages of life.

In contrast, the other options refer to different anatomical features: sinuses are air-filled spaces that develop within the bones of the skull, cranial sutures are the fibrous joints connecting the bones of the skull, and the mandibular symphysis is the joint where the two halves of the mandible meet and fuse. These areas are all typically calcified or solidified in a child’s skull as they grow, contrasting with the soft, pliable nature of the fontanelles.