Final answer:
A suture is a narrow fibrous joint that unites most bones of the skull.
Step-by-step explanation:
A suture is the correct answer. It is a narrow fibrous joint found between most bones of the skull. The adjacent flat bones of the skull join together and are united by a thin layer of dense connective tissue, forming sutures. These sutures are functionally classified as a synarthrosis, meaning they allow for very little movement between the cranial bones.