mesoderm /mes″ōdurm/ [Gk, mesos + derma, skin] , (in embryology) the middle of the three cell layers of the developing embryo. It lies between the ectoderm and the endoderm. Bone, connective tissue, muscle, blood, vascular and lymphatic tissue, and the pleurae of the pericardium and peritoneum are all derived from the mesoderm.
