Pathways between lymph vessels and sinuses in lymph nodes: a study in horses.

The pathways through which lymph flows from terminal afferent lymphatics to the lymph sinuses, and from the sinuses to initial efferent lymphatics, were studied in horse lymph nodes by using Microfil casts and electron microscopy. Terminal afferent lymphatics are continuous with the subcapsular sinus through oval holes, about 3 microns wide, along their length, and through larger openings near their end. Other terminal afferents penetrate into the node within trabeculae and are supported by processes across the lumen. They connect with trabecular and medullary sinuses through oval or round holes, generally 20-30 microns across. Some of these have processes, similar to the luminal strands of the adjacent sinuses, extending across them, apparently providing reinforcement. Initial efferent lymphatics receive lymph from medullary sinuses through holes which are similar to those in afferent lymphatics, though more common, especially near the origin of the vessel. Initial efferents within the medulla appear to be supported by the luminal strands of the surrounding medullary sinuses. It seems likely that these strands, like the trabeculae which surround the penetrating afferent lymphatics, may help to keep the lymphatic vessels open as the node swells while draining an area of infection.