Bone II

Histology 2016-2017
Department of Anatomy &Histology: Dr.Rajaa Ali
***********************************************************BONE II

BONE FORMATION/OSSIFICATION
_ Ossifi cation is the process by which bone is formed from a soft tissue model (condensed mesenchyme or hyaline cartilage
model).
_ This process usually starts at the centre of the model, from which it spreads until the whole model is converted into
bone.
_ Bones are formed by two methods, namely,
1. Intramembranous ossifi cation, i.e. bone formation from condensed mesenchyme—membrane model. e.g. Flat bones
in the vault of skull, clavicle.
2. Endochondral ossifi cation, i.e. bone formation from cartilage—cartilage model. e.g. Long bones except clavicle.
Spongy or Cancellous
Bone (Decalcifi ed
Se ction).
(i) presence of bony trabeculae
separated by marrow space
containing bone marrow;
(ii) absence of Haversian systems and
lamellar arrangement;
(iii) presence of osteoblasts and
osteoclasts on the surface of bony
trabeculae;
(iv) osteocytes are seen embedded in
the matrix of the trabeculae.
Intramembranous Ossifi cation
Stage I: Condensation of mesenchyme
_ Condensation of loose mesenchyme occurs in the area where bone formation is to take place.