The channels in the lymph node medulla that separate the medullary cords and are crossed by a reticulum of cells and fibers and bounded by littoral cells; lymph flows through the medullary sinus from the cortical sinuses and into the efferent lymphatic vessels.
Comment:
Lymph flows into the medullary sinuses from cortical sinuses, and into efferent lymphatic vessels. Medullary sinuses contain histiocytes (immobile macrophages) and reticular cells.[WP]