A germ layer is a group of cells in an embryo that interact with each other as the embryo develops and contribute to the formation of all organs and tissues. ... All other animals are triploblastic, as endoderm and ectoderm interact to produce a third germ layer, called mesoderm.
They also form muscles and bones, and that includes the cardiac muscle as well. ... The mesoderm forms our muscles, including the heart muscle, our skeletal system, and our genitourinary tracts. And the ectoderm forms our skin and related structures, along with our nervous system.