OSTEOGENESIS OF BONE (INTRAMEMBRANOUS VS. ENDOCHONDRAL) Intramembranous ossification (most flat bones of skull) Occurs w/in condensations of embryonic mesenchymal cells Differentiate into osteoblasts (takes place in primary ossification center) which surround capillaries Osteoid matrix is produced and then calcified forming trabeculae (islands of bone) of woven (primary) bone; its surface is surrounded by osteoblasts Trabecular growth leads to the fusion of adjacent ossification centers which gradually produce layers of compact bone that encloses spongy (cancellous) bone