how does bones form in the foetus?

As you know, three germ layers are formed during embryonic development. The mesodermal and endodermal layer gives rise to the endoskeleton and other bones of the body. The development of bones begins about 13 weeks of pregnancy. The bones gradually become harder and muscle tissue begins to develop. At birth, a newborn's body has approximately 300 bones which later fuse and grow together to form 206 bones.