Appendix (anatomy)

The appendix (: appendices or appendixes; also vermiform appendix; cecal [or caecal] appendix; vermix; or vermiform process) is a finger-like, blind-ended tube connected to the cecum, from which it develops in the embryo. The cecum is a pouch-like structure of the large intestine, located at the junction of the small and the large intestines. The term "vermiform" comes from Latin and means "worm-shaped". The appendix was once considered a vestigial organ, but this view has changed since the early 2000s. Research suggests that the appendix may serve an important purpose as a reservoir for beneficial gut bacteria. The human appendix averages in length, ranging from . The diameter of the appendix is , and more than is considered a thickened or inflamed appendix. The longest appendix ever removed was long. The appendix is usually located in the lower right quadrant of the abdomen, near the right hip bone. The base of the appendix is located beneath the ileocecal valve that separates the large intestine from the small intestine. Its position within the abdomen corresponds to a point on the surface known as McBurney's point. The appendix is connected to the mesentery in the lower region of the ileum, by a short region of the mesocolon known as the mesoappendix. Some identical twins—known as —can have a mirror-imaged anatomy, a congenital condition with the appendix located in the lower left quadrant of the abdomen instead of the lower right. Intestinal malrotation may also cause displacement of the appendix to the left side. While the base of the appendix is typically located below the ileocecal valve, the tip of the appendix can be variably located—in the pelvis, outside the peritoneum or behind the cecum. The prevalence of the different positions varies amongst populations with the retrocecal position being most common in Ghana and Sudan, with 67.3% and 58.3% occurrence respectively, in comparison to Iran and Bosnia where the pelvic position is most common, with 55.8% and 57.7% occurrence respectively.