Thymus: The thymus is a pinkish-gray color, soft, and lobulated on its surfaces. The thymus is made up of two identical lobes and is located anatomically in the anterior superior mediastinum, in front of the heart and behind the sternum. The thymus provides an inductive environment for development of T-lymphocytes from hematopoietic progenitor cells. In addition, thymic stromal cells allow for the selection of a functional and self-tolerant T-cell repertoire. Therefore, one of the most important roles of the thymus is the induction of central tolerance.