During fetal and post-natal life, bone development and growth occurs by two methods:

1. Endochondral (or cartilage-replacing) bone is formed by osteoblasts on a cartilaginous model of the bone. In this type of bone formation, growth occurs in cartilage and the structure is consolidated into bone.

2. Intramembranous bone is formed directly by osteoblasts in fibrous connective tissue without a preceding cartilage model.

All the bones below the skull are formed by endochondral ossification, except the clavicle. The vault of the skull and most of the facial skeleton are formed by intramembranous ossification, but the base of the skull and the bones surrounding the nose and internal ear are formed by endochondral ossification. Some skull bones form parts of the skull base and parts of the vault; they form by fusion of separate elements that develop by one of the two methods of bone formation. The clavicle has a mixed origin