Periosteum is the thin yet tough outermost layer of bones. Its many collagen fibers support the bone and firmly connect it to the surrounding structures. Osteogenic cells in the periosteum play a vital role in the growth and repair of bony tissue.hysiology. The fibrous layer of the periosteum plays a vital role in connecting bones to the rest of the body. The collagen fibers of the periosteum not only wrap the entire bone, but also merge with the collagen fibers of the ligaments, joint capsules, and tendons that connect to the bone.