Mesoderm

The middle layer of the 3 germ cell layers of the trilaminar embryo (ectoderm, mesoderm, endoderm). Each region of this early layer will later form different structures, this middle layer contributes all connective tissues of the body, except in the head region where neural crest also will contribute. Mesoderm outside the embryo and covering the amnion, yolk and chorion sacs is extraembryonic mesoderm.