BONE -

1. Bone is the hardest tissue in the body and supports various organs.
2. The inorganic salts present in the matrix are calcium phosphate, calcium carbonate, calcium fluoride, magnesium phosphate, etc.
3. If a bone is dried, its organic matter is destroyed and inorganic part is left behind.
4. On the other hand if a bone is kept in a dilute HCl for some time, its inorganic part is dissolved and organic part is left behind. Such a bone is called decalcified bone.

STRUCTURE OF DECALCIFIED MAMMALIAN BONE -

1. It consists of four parts : Periosteum, Matrix, Endosteum and Bone marrow.

1.      PERIOSTEUM -

1. It is a thick and tough sheath that forms an envelop around the bone.

2.      MATRIX -

1. It is composed of a protein called ossein.
2. The main salts found in the matrix are calcium phosphate, calcium carbonate, sodium chloride and magnesium phosphate.
3. Of these calcium phosphate is maximum in the vertebrae bone.
4. The Haversian canals a characteristic feature of the mammalian bones, are present in the matrix.
5. Each Haversian canal contains an artery, a vein, a lymph vessel, a nerve and some bone cells, all packed in with connective tissue.
6. The haversian canals are interconnected by transverse channel's the Volkmann's canals.

3.      ENDOSTEUM -

1. It is present outer to the bone marrow cavity.
2. Like the periosteum, it comprises white fibrous tissue and osteoblasts. But the white fibrous tissue is present here inner to osteoblasts.
3. The long bone thus grows in thickness from two sides. This type of growth is called bidirectional growth.

4.      BONE MARROW -

1. In long bones such as limb bones a cavity called bone marrow cavity is present inner to the endosteum.
2. The bone marrow cavity is filled with a soft kind of tissue which is called myelogenous or myeloid tissue.