intermembranous ossification

Intermembranous ossification is a process of bone formation that occurs within connective tissue, without the prior development of cartilage. This method is primarily responsible for the formation of the flat bones of the skull.12

The process begins with fibrous membranes rich in collagen and blood vessels. Specialized cells called osteoblasts secrete a matrix material known as osteoid into these membranes. This osteoid then hardens as inorganic salts are deposited, forming a spongy network of bony structures called trabeculae. New bone grows outward from centers within these membranes. In the skull, multiple ossification centers contribute to bone growth, and where these centers meet, they form cranial sutures visible in adults. This contrasts with endochondral ossification, where a cartilage model is gradually replaced by bone.2