Three-dimensional organization of the lymphatics in the rabbit appendix. A scanning electron and light microscopic study.

The three-dimensional organization of the lymphatics in the rabbit appendix was demonstrated by scanning electron microscopy of lymphatic corrosion casts and intact tissues. In the glandular mucosa a polygonal network of lymphatics led into perpendicularly oriented lymphatics continuous with the lymphatics in the thymus-dependent area. In the thymus-dependent area a plexus consisting of anastomosing tubular lymphatics led into the upper ends of the perifollicular sinuses. Each follicle was surrounded by a well-developed perifollicular sinus. From the bottoms of the sinuses thin lymphatics descended into the submucosal lymphatics. The cast of submucosal lymphatics showed notches corresponding to the locations of bicuspid valves. Lymphocytes migrating through the lymphatics and high-endothelial venules were only observed in the thymus-dependent area. The results indicate that the potential capacity of the perifollicular sinuses as a reservoir and as a drainage route for fluid and lymphocytes is great, but that the lymphatics in the thymus-dependent area are sites for lymphocyte migration from the follicles into the lymphatics. The well-developed lymphatic network in the glandular layer suggests great participation in fluid flux.