BONE HISTOGENESIS
“Histogenesis” designates the formation of a tissue. In the case of the bone tissue, this process is also called osteogenesis or ossification.
There are two basic modes of ossification: intramembranous ossification and endochondral ossification.
Intramembranous ossification occurs from mesenchymal tissue — the embryonic connective tissue. It contains stem-cells that can give rise to various types of connective tissue — cartilage, bone, adipose tissue, etc. as well as blood cells.
In various parts of the body, this mesenchyme is arranged in the form of a layers or membranes. The intramembranous ossification happens within these layers.
This type of ossification primarily gives rise to the flat bones, for example, the flat bones of the skull.
The second type of ossification – endochondral ossification – occurs during fetal life over models of bones made of cartilage. After the endochondral ossification process is complete, the cartilaginous skeleton gradually disappears and is replaced by the bony skeleton.
This type of ossification gives rise to long bones and some other types of bones, such as vertebrae.