Intramembranous ossification
![Transmission electron micrograph of a mesenchymal stem cell displaying typical ultrastructural characteristics.](/Images/godic/202501/20/MSC_high_magnification4038.jpg")
![Light micrograph of osteoprogenitor cells, most displaying a prominent Golgi apparatus, forming a nidus.](/Images/godic/202501/20/Bony_nidus_14038.jpg")
![Light micrograph of osteoblasts, most displaying a prominent Golgi apparatus, creating osteoid in the center of a nidus.](/Images/godic/202501/20/Bony_nidus_24039.jpg")
![Light micrograph of a nidus lined by osteoblasts that are creating rudimentary bone tissue.](/Images/godic/202501/20/Bony_nidus_34039.jpg")
Intramembranous ossification is one of the two essential processes during fetal development of the gnathostome (excluding chondrichthyans such as sharks) skeletal system by which rudimentary bone tissue is created. Intramembranous ossification is also an essential process during the natural healing of bone fractures and the rudimentary formation of bones of the head. Unlike endochondral ossification, which is the other process by which bone tissue is created during fetal development, cartilage is not present during intramembranous ossification.