Scheme of the thymus medulla (human)

A-B: medullar epithelioreticular cells; C-D-E: development stages of thymic corpuscles (or Hassall bodies) (1): branching (-->) epithelioreticular cells in the medulla forming a meshwork (cytoreticulum) that normally is populated by thymocytes; (2): specialized epithelioreticular cells (2) often localize concentrically close together and that results in the formation of a Hassall's corpuscle consisting of aggregated flattened cells (2) that contain keratohyalin (observed as granules) ; (3): centrally within the expanding corpuscle necrotic cells (3) might be present; in the larger bodies the amount of necrotic cells increases and eventually the corpuscle results in a cystic structure bordered by a 1-2 layered wall of flattened epithelioreticular cells (2) ; (4): blood vessel in close contact with a corpuscle (4)