Haversian system is seen in

* Microscopically, the bone is of five types, namely lamellar (including both compact and cancellous), woven, fibrous, dentine and cement. 1. Lamellar bone: Most of the mature human bones, whether compact or cancellous, are composed of thin plates of bony tissue called lamellae. These are arranged in piles in a cancellous bone, but in concentric cylinders (Haversian system or secondary osteon) in a compact bone. 2. Woven Bone: seen in fetal bone, fracture repair and in cancer of bone 3. Fibrous bone is found in young foetal bones, but are common in reptiles and amphibia. 4. Dentine and 5. Cement occur in teeth. * Compact bone ( coical bone) In shaft (diaphysis) of long bone - lamellae arranged to form Haversian system - Bone marrow Yellow which stores fat after pubey. It is red before pubey - Hard and ivory-like * Cancelled bone spongy, or trabecular bone - In the epiphyses of long bone - arranged in a meshwork, so Haversian systems are not present - bone marrow red, produce RBCs, granular series of WBC and platelets - spongy * Nails are made of a tough protective protein called keratin - consists of the nail plate, the nail matrix and the nail bed below it, and the grooves surrounding it (Reference : BDC Handbook of General Anatomy , 5th edition, pg 39)