Thymus Lobule

Taking a closer look at a single lobule, one can clearly see the division between the outer and inner layers. The outer cortex contains densely packed developing T-lymphocytes and epithelioreticular cells that provide a structural framework for development. Due to high cell density and small cell size, this zone is deeply stained. The medulla contains mature thymocytes that are larger and contain more cytoplasm. As a result, this zone is lightly stained. Where do immature T-cells enter the thymus?