The lymphatics begin as a capillary plexus that wraps around the muscularis mucosae (Fig. 13.10). This plexus sends small branches into the mucosa to reach no higher than the bases of the crypts of Lieberkühn (2). These vessels pass into and through the submucosa and form another plexus around the muscularis propria. The efferent lymphatics from this system form increasingly larger channels, which eventually join lymphatic vessels in the mesocolon. There are generally four groups of external lymphatics: (a) epicolic, which lie on the colon; (b) paracolic, located along the marginal artery; (c) intermediate, located along the main colic vessels and their branches; and (d) principal, located along the superior and inferior mesenteric arteries.