In intramembranous ossification, red marrow appears in which location?

• A. In the spaces of woven bone that become trabeculae
• B. In the periosteum
• C. In the epiphyseal plate
• D. In the medullary cavity

Answer: (A)

Red marrow appears where hematopoietic tissue fills the spaces inside the newly formed woven bone as it organizes into trabeculae. In intramembranous ossification, mesenchyme differentiates directly into osteoblasts and lays down woven bone; the gaps between those trabeculae become marrow-filled spaces, producing red marrow. The periosteum is just the outer bone covering, not a marrow site; the epiphyseal plate relates to endochondral growth; and the medullary cavity, formed mainly in endochondral bones, typically houses marrow that shifts from red to yellow with age.