Appendix is a vestigial organ that is found in humans, a few species of great apes. About 6 cm long and 1 cm wide, it is a hollow organ that arises from the caecum. The walls of appendix are muscular and lined with a layer of lymphoid tissue and then an innermost layer of epithelium. It is structurally similar to colon and is also capable of peristalsis. The appendix has no function ; we do not know why humans have one. Since it vaguely resembles a lymph node, the appendix may function to prevent intestinal infections.