Which of the following examples represent a bony joint, or synostosis? Multiple Choice A synostosis develops at the ends of the tibia and fibula to help hold them together. Cranial sutures form as a synostosis when the baby's fontanels close. A synostosis occurs in the jaw when a child's permanent teeth come in. An infant is born with right and left mandibular bones, but they soon fuse into a single bone. When the two maxillary bones unite to form the anterior two-thirds of the hard palate, a synostosis develops.