From the surrounding 794 mesoderm the petrous bone is formed by a process of chondrification and ossification.
It has been already stated that the mesoderm is a composite tissue.
The formation of the mesoderm in Teleosts is not definitely understood.
The origin and part played by the mesoderm appeared the most obscure.
The mesoderm is a plate of cells lying between the endodermic and ectodermic plates.
As these cœlom cavities develop in the mesoderm the cells lining them become distinctly epithelial.
To these a third intermediate layer is soon added, the mesoderm.
This double disposition of the cloaca is accomplished by gradual changes in the entoderm and mesoderm.
The mesoderm is, if we may judge from the number of organs which are derived from it, much the most important of the three layers.
The external muscular and fibrous coats of the gall-bladder are developed from the mesoderm of the mesogastrium.
mesoderm mes·o·derm (měz'ə-dûrm', měs'-)
The middle embryonic germ layer, lying between the ectoderm and the endoderm, from which connective tissue, muscle, bone, and the urogenital and circulatory systems develop.
The middle of the three primary germ layers of the embryos of vertebrates and other complex animals. In vertebrates, the mesoderm gives rise to the muscles, bones, cartilage, connective tissue, blood, blood and lymph vessels, dermis, kidneys, and gonads. The mesoderm develops during gastrulation from either the ectoderm or the endoderm. The embryos of simpler animals lack a mesoderm. Compare ectoderm, endoderm.