Lymphatic vessels form a one way system in which lymph flows only toward the heart. Transport starts with lymphatic capillaries which weave between the tissue cells and blood capillaries in the loose connective tissues of the body. The largest collecting vessels unite and form lymphatic trunks.Lymph is delivered to one of two large ducts in the thoracic region which are the right duct and thoracic duct. The regional lymph nodes include cervical, axillary, and inguinal nodes. The lymphoid organs are grouped into two functional categories which are the primary and secondary lymphoid organs.The primary organs are where B and T cells mature- the red bone marrow and the thymus. The secondary organs include lymph nodes, the spleen, MALT that forms tonsils, Peyer's patches in the small intestine, and the appendix. Lymph nodes are bean shaped and are surrounded by a dense fibrous capsule. The soft spleen is about the size of a fist and is the largest lymphoid organ. The MALT is located in the mucous membrane throughout the body. Finally, the thymus is found in the inferior neck and extends into the superior thorax, where it overlies the heart deep to the sternum.