periosteum
(per-ē-os'tē-ŭm 
)
[L. periosteum, periosteon, fr. Gr. periosteon, surrounding the bone]
The fibrous membrane that forms the covering of bones except at their articular surfaces. It consists of a dense external layer containing numerous blood vessels and an inner layer of connective tissue cells that function as osteoblasts when the bone is injured and also participate in new bone formation. Periosteum serves as a supporting structure for blood vessels nourishing bone and for attachment of tendons and ligaments.
alveolar p.Periodontal ligament.
p. externum Periosteum covering external surfaces of bones.
p. internum Interior periosteum lining the marrow canal of a bone.