Occipital roof development in the Japanese musk shrew, Suncus murinus

The occipital squama of the Japanese musk shrew, Suncus murinus, consists only of membrane bone which arises from the periosteal bony band of the supraoccipital cartilage. No cartilaginous tectum posterius, generally forming the dorsal border to the foramen magnum, was found in the developing chondrocranium. Also additional intramembranous ossification centres were occasionally observed, and could be interpreted as being the primordium of the interparietal bone. These observations indicate that the membrane bone is homologous not with the interparietal bone but with the tectum posterius, i.e. the membranous supraoccipital bone. This is an instance of interchangeability between cartilage and membrane bone in a mammal.