The appendix is a small, blunt-ended tube composed of lymphatic tissue. It is considered part of the large intestine, although the tissues are different from the tissues of the large intestine. Appendicitis is an infection of the appendix that begins in the lymphoid nodules. Treatment often includes removal of the appendix, either with traditional surgery or laproscopically.
The spleen, with detailed cross section at right. (From Stedman’s Medical Dictionary. 27th Ed. Baltimore: Lippincott, Williams & Wilkins, 2000.)