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The picture below shows a schematic long bone (i.e. the femur), which demonstrates where the compact and spongy bone types are located, as well as some other anatomical features. Compact bone is very strong and dense, having no spaces within it other than the Haversian canals. Compact bone is found along the perimeter of the bone organ (i.e. the femur). Spongy bone, however, has numerous spaces within it which accounts for it being named, "spongy." It is found mainly within the middle of the ends of the bone. Be aware that spongy bone is not soft and pliable like a sponge (it's hard like any other bone type), but rather just has many spaces giving the appearance of a sponge.
The epiphyseal plates (also called growth plates) are the areas where the bone grows, allowing it to extend in length. These are what fuse after puberty to stop your growth. The marrow cavity is the hollow centre area of the bone which holds bone marrow. Bone marrow is both seen as a fat storage medium (yellow marrow) and a hematopoietic and immunopoietic medium (red marrow). Hematopoietic means the production of erythrocytes, while immunopoietic means the production of immune cells (i.e. leukocytes). The periosteum is the connective tissue which surrounds all bones. The articular cartilage is the substance that protects the ends of the bones and provides a smooth gliding surface, allowing for smooth movement of the joints.
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Special thanks to Hans Christoffersen for the preparation of this page.
Send comments to:
Sandra K. Ackerley (),
Department of Zoology, University of Guelph, Guelph, Ontario,
Canada N1G 2W1.
Latest page update: April 5, 2000.