noun🔗ShareOne of the three tissue layers in the embryo of a metazoan animal. Through embryonic development, it will produce many internal organs of the adult, e.g. muscles, spine and circulatory system."During the early development of a puppy, the mesoderm layer gives rise to its heart, bones, and muscles. "biologyanatomyphysiologymedicineorganismbodyscienceChat with AIVocabulary GamePractice Reading