Medullary tissue is continuous from lobule to lobule throughout each lobe. Reticular cells and macrophages are present in addition to the lymphocytes, which are the dominant cell type within the lobules. Reticular cells are quite abundant. Their cytoplasm is eosinophilic, and their large, ovoid and light nuclei may contain one or two nucleoli. Thereby they create and maintain the microenvironment necessary for the development of T-lymphocytes in the cortex.
Macrophages occur in both cortex and medulla.
They are difficult to distinguish from the reticular cells in out preparations. The vast majority of them will be developing T-lymphocytes. They are also called thymic lymphocytes or thymocytes. Identify lymphocytes and thymic corpuscles. Take a close look at the medulla and try to find some cells which contain large and light nuclei.