Bone formation in which connective tissue serving as a membrane becomes a template for bone deposition without any intermediate formation of cartilage. Flat bones are embryonically formed in this way. When sufficient vascularity is present adjacent to the condensed mesenchyme, the osteoblasts begin to produce osteoid. A similar process takes place in healing of bone defects.
The formation of bone in or underneath a fibrous membrane, such as occurs in the formation of the cranial bones.