Now let's move on to the middle layer. Actually not the middle layer. Let's discuss the internal layer. So this is the innermost layer found in that developing organism, in that developing embryo. And this is called the endoderm. Now, the endoderm layer gives rise to the epithelial layer of the lungs, our digestive system, the pancreas, the bladder, the liver, and it also forms the thyroid and the parathyroid gland as well as the thymus.