On this Wikipedia the language links are at the top of the page across from the article title. Left femur of extinct elephant, Alaska, Ice Age Bone in ribeye steak L0057714. Bertazzo S – SEM deproteined bone – wistar rat – x10k. A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals.

206 separate bones in the adult, not counting numerous small sesamoid bones. Their unique composition and design allows bones to be relatively hard and strong, while remaining lightweight. The elasticity of collagen improves fracture resistance. Bone is actively constructed and remodeled throughout life by special bone cells known as osteoblasts and osteoclasts. Within any single bone, the tissue is woven into two main patterns, known as cortical and cancellous bone, each with a different appearance and characteristics. The hard outer layer of bones is composed of cortical bone, which is also called compact bone as it is much denser than cancellous bone. Cancellous bone, also called trabecular or spongy bone, is the internal tissue of the skeletal bone and is an open cell porous network that follows the material properties of biofoams.

It was first illustrated accurately in the engravings of Crisóstomo Martinez. Bone marrow, also known as myeloid tissue in red bone marrow, can be found in almost any bone that holds cancellous tissue. Blood enters the endosteum, flows through the marrow, and exits through small vessels in the cortex. Bone is metabolically active tissue composed of several types of cells.