BONE HISTOGENESIS
The development of bones – bone histogenesis – that happens initially in embryos and continues after birth is called osteogenesis or ossification.
There are two basic mechanisms of ossification called intramembranous and endochondral ossification. Osteogenesis begins in humans around the sixth or seventh weeks of embryonic development.
Intramembranous ossification develops inside the mesenchyme, the precursor of connective tissue found in embryos. Many bones, especially flat bones of the skull and face, as well as other bone formats such as the clavicles and mandible are formed according this mechanism.
Endochondral ossification uses cartilage models of the future bones. Bone-forming cells penetrate the cartilage model and form bone tissue on the surface cartilage matrix. The cartilage model is then gradually replaced by bone tissue.
This type of ossification originates a large part of long bones as well as of other types of bones, such as the vertebrae. As will be seen in the next pages, these bones are formed by both ossification mechanisms.
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