Slide 23 - Decalcified Bone in cross-section, with a portion of marrow cavity in the center.  The inorganic components of the matrix have been removed, leaving the fibrous constituents (staining bright red-orange) and the cells (staining purple).  On the outer surface of the bone lies a densecollagenous periosteum  (bright pink), with strands of skeletal muscle attached to it.  (Notice the peripheral nuclei of the muscle; cross-striations may be difficult to see because of the effect of the decalcification treatment on them.)  The bone is organized into Haversian systems, i.e., small vascular channels surrounded by several concentric lamellae. Notice also some peripheral (circumferential) layers of bone, lying immediately beneath the periosteum; these constitute a sheath around the entire shaft of the bone and are known as periosteal bone.  There are also a few circumferential layers immediately next to the marrow cavity:  the endosteal bone.  Find where these show best.

Notice that the periosteum is two-layered:  an outer dense fibrous layer (pink) and an inner cellular layer (purple nuclei).  The inner layer is also vascular with branches entering the bone itself and communicating with the blood vessels of the Haversian canals, and ultimately with the blood vessels of the marrow.  Osteoprogenitor cells lying in both cellular periosteum and marrow become osteoblasts and deposit additional circumferential lamellae on the outer and inner surfaces.  Such cells also extend inwardly as an inner lining of the Haversian canals. 

In the bone, note that some blood vessels run  perpendicularly to the plane of Haversian systems; these are Volkmann’s canals, bearing blood vessels from the surfaces of the bone to anastomose with the vessels of the Haversian systems.  Look also for interstitial lamellae lying between Haversian systems (in X section) and representing the remnants of an earlier arrangement of the bony structure.  Remember that bone is constantly laid down, resorbed, and laid down again in remodeling during development and that the tissue as a whole is metabolically very active in the adult.  (Interstitial lamellae are best seen in #24, ground bone)