The thymus is a lymphoepithelial organ. It is located in the upper part of the mediastinum, and weighs 10 - 15 g in the adult human. The base lies on the pericardium and large blood vessels, while the upper limit is the neck where the thymus meets the equilateral lobe of the thyroid gland. At the back it is tied to the peritracheal fascia that is separated from large blood vessels. It consists of 2 equal lobes - right and left – and thymic bodies (corpora thymica).
Under the influence of thymic microenvironment and hormones, prothymocytes proliferate and mature from the stage of an early thymocyte, through thymocyte to the mature thymocyte. This process mainly occurs in the cortex.

Thymocytes are lymphocytes located in the cortical part of the thymus lobes