Veterinary Histology and Embryology

PERIOSTEUM AND ENDOSTEUM

• Periosteum is a fibrous membrane investing the bones except at their articular surfaces.
• It consists of two layers, the outer of which is composed of course fibrous connective tissue containing few cells but numerous blood vessels and nerves.
• The inner layer is more cellular and less vascular and contains many elastic fibres.
• In the growing bones, the inner layer of periosteum is osteogenic and in the adult, this layer is converted into a row of flattened cells. Periosteum serves as a supporting bed for blood vessels and nerves going to bone and for anchorage of tendons and ligaments.
• Some of the periosteal fibres pass into the bone, either obliquely or at right angles to the long axis of bone and are termed as perforating fibres of Sharpy.
• Endosteum lines the surface of the cavities within a bone (Haversian canals) and also the surfaces of trabeculae in the marrow cavity. The cells of endosteal layer are like those of the periosteum and rest on a thin layer of connective tissue.