The vermiform ("worm-like") appendix is a vestigial organ in the right iliac fossa. Although there is considerable variability in its length and position, the base of the appendix is always found attached to the posteromedial surface of the caecum, approximately 2 cm below the ileocaecal valve. The base is the only part of the appendix which is fixed, the remainder being free, thus accounting for the great variability in the position of the body and tip (Figure 6.1). It is completely surrounded by peritoneum which is continuous with the mesentery of the small intestine, this connection being termed the mesoappendix. Again, the size of the mesoappendix is variable and the distal appendix may occasionally be devoid of a mesenteric covering. As was stated, the position of the appendiceal base is constant, the surface landmark of this being one third the way along a line drawn from the right anterior superior iliac spine to the umbilicus - McBurney's point. Internally, the base can be found by following the taeniae coli of the caecum to the base of the appendix where they converge to form a continuous appendiceal longitudinal muscle coat.

Histologically, the appendiceal lumen is lined by colonic-type columnar epithelium with abundant lymphoid follicles (which decrease with age) in the submucosa. There are continuous circular and longitudinal muscle coats.

Figure 6.1. The various positions of the appendix. Reproduced from Mann CV, Russell RCG, Williams NS. (eds.) Bailey and Love's short practice of surgery. Chapman & Hall: London, 1995.
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