1. Bone Development (during fetal development)
Intramembranous ossification
Takes place in connective tissue membrane
Endochondral ossification
Takes place in cartilage
Both methods of ossification
Produce woven bone that is then remodeled
After remodeling, formation cannot be distinguished as one or other

2. Intramembranous Ossification (8th week – 2 years of development)
Takes place in connective tissue membrane formed from embryonic mesenchyme
Forms many skull bones, part of mandible, diaphyses of clavicles
When remodeled, indistinguishable from endochondral bone.
Centers of ossification: locations in membrane where ossification begins (centers of ossification expand outwards to form a bone by gradually ossifying the membrane)
Fontanels: large membrane-covered spaces between developing skull bones; unossified (bones eventually grow together & all fontanels have closed by 2 years of age)

3. Intramembranous Ossification

4. Endochondral Ossification
Bones of the base of the skull, part of the mandible, epiphyses of the clavicles, and most of remaining bones of skeletal system
Cartilage formation begins at end of fourth week of development
Some ossification beginning at about week eight; some does not begin until years of age

5. Endochondral Ossification

6. Endochondral Ossification

7. Endochondral Ossification

8. Endochondral Ossification

9. Growth in Bone Length Growth in length occurs at the epiphyseal plate
Involves the formation of new cartilage by
Interstitial cartilage growth
Appositional growth on the surface of the cartilage
Closure of epiphyseal plate: epiphyseal plate is ossified becoming the epiphyseal line. Between 12 and 25 years of age
Articular cartilage: does not ossify, and persists through life
Appositional growth only
Interstitial growth cannot occur because matrix is solid
Occurs on old bone and/or on cartilage surface