The inner cell mass (ICM) is the part of the blastocyst that is fated to become the embryo, amnion, and yolk sac. In contrast, the trophectoderm cells of the blastocyst will contribute to extra-embryonic tissues, such as the placenta and umbilical cord. Cells of the ICM are pluripotent, meaning they can give rise to all the cell lineages (ectoderm, endoderm, and mesoderm) found in the body. The ICM is, thus, a source of embryonic stem cells.