Final answer:
Intramembranous ossification is the process of bone development from fibrous membranes. It forms the flat bones of the skull, mandible, and clavicles. Mesenchymal cells differentiate into osteoblasts, which secrete the extracellular matrix and deposit calcium to form spongy bone.
Step-by-step explanation:
Intramembranous ossification is the process of bone development from fibrous membranes. It is involved in the formation of the flat bones of the skull, the mandible, and the clavicles. Ossification begins as mesenchymal cells form a template of the future bone. They then differentiate into osteoblasts at the ossification center. Osteoblasts secrete the extracellular matrix and deposit calcium, which hardens the matrix. The non-mineralized portion of the bone or osteoid continues to form around blood vessels, forming spongy bone. Connective tissue in the matrix differentiates into red bone marrow in the fetus. The spongy bone is remodeled into a thin layer of compact bone on the surface of the spongy bone.