What does the periosteum contain?

Periosteum is a membrane that lines the outer surface of all bones, except at the joints of long bones.Endosteum lines the inner surface of all bones.

Periosteum consists of dense irregular connective tissue. Periosteum is divided into an outer "fibrous layer" and inner "cambium layer" (or "osteogenic layer"). The fibrous layer contains fibroblasts, while the cambium layer contains progenitor cells that develop into osteoblasts. These osteoblasts are responsible for increasing the width of a long bone and the overall size of the other bone types. After a bone fracture the progenitor cells develop into osteoblasts and chondroblasts, which are essential to the healing process.