Pathways of lymph flow to and from the medulla of lymph nodes in sheep.

Medullary sinuses are continuous with penetrating afferent lymphatics, and with the trabecular and tubular sinuses which penetrate through the cortex. Tubular sinuses are often associated with blood vessels, especially in the deep cortex, and they appear to be important in the transport of lymphocytes. The subcapsular sinus is continuous over the cortex and the medulla, although trabeculae and reticular processes appear to restrict the flow of afferent lymph to the subcapsular sinus over the medulla. Lymph leaves the medulla through up to 100 or more initial efferent lymphatics, some only 60 micron across. Almost all of these arise from sinuses adjacent to the capsule lining the hilus. Some efferents remain associated with the capsule for a short distance whereas others, especially in nodes with a deep hilar depression, leave immediately at an angle of 30-90 degrees.