This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The position and direction of the appendix have been variously described and much discussed. This has arisen from the fact that it is so curled, curved, and twisted on itself that it is impossible to say that it points in any definite direction, and that, being so mobile, it may be found in almost any position, swinging around with its point of attachment to the caecum as the axis. We agree with Cunningham when he says that it runs generally in one of three directions: (1) over the brim into (or towards) the pelvis; (2) upward behind the caecum; (3) upward and inward toward the spleen. As he says, each of these has been considered the normal position by one or more observers. It is evident that, as the appendix comes off close to the ileum, this is its most fixed and constant point. In certain cases the caecum retains its high fetal position and then the appendix will be higher than usual. If the appendix is long and straight, its tip may reach to or beyond the median line; it may lie in contact with the rectum, ovary, tube, or bladder; it may lie low down close to Poupart's ligament or curved upward behind the colon, reaching in front of the kidney and nearly or quite to the liver. When retro-caecal it lies on the quadratus lumborum; when lower it may lie on the iliacus or psoas muscle. If it goes over the brim of the pelvis it lies on the external iliac artery. The external iliac vein is below and to the inner side and is largely protected from injury in operating by the stronger and tougher artery.
There are three folds and three fossae formed by the peritoneum in the neighborhood of the caecum.
1. The superior ileocaecal (ileocolic) fold runs from the upper surface of the mesentery just above the ileum to the upper anterior surface of the caecum. In it runs the ileocaecal (anterior) artery. Beneath it, with its opening toward the left, is the superior ileocaecal fossa (Fig. 424).
2. The inferior ileocaecal fold passes from the termination of the ileum to the front of the meso-appendix; it contains a small recurrent branch of the appendicular artery. Beneath it and between it and the meso-appendix is the inferior ileocaecal fossa, which may sometimes contain the appendix.
3. The retrocolic fold is not constant and may be multiple. It passes from the lower and outer surface of the caecum to the peritoneum beneath. It binds down the end of the caecum and not infrequently must be divided before the caecum and appendix can be raised; the fossae on each side of it are called the retrocolic fossae.
The lymphatics of the caecum and appendix drain into a group located in the mesentery of the ileocaecal angle, accompanying the ileocolic artery. According to Poirier and Cuneo there are three sets: an anterior caecal, a posterior caecal, and an appendicular.
The anterior caecal lymphatics drain the anterior surface of the caecum and, after traversing one or two small nodes, pass in the ileocaecal fold up to the main ileocaecal group.
The posterior caecal lymphatics drain the posterior portion of the caecum and, after traversing three to six small nodes, empty likewise into the ileocaecal group.
The appendicular lymphatics form four or five trunks which accompany the artery between the layers of the meso-appendix. They then pass across the posterior surface of the ileum to empty into the ileocaecal group.
Poirier and Cuneo state that these lymph-trunks from the appendix pass through one to three nodes placed in the retro-ileal portion of the meso-appendix, but Kelly and Hurdon state that in the majority of cases these trunks empty into one or two nodes some distance above the ileum in the ileocaecal angle, forming a part of the ileocaecal chain. These latter authors state that there are three sets of lymph-capillaries in the appendix: a superficial or subperitoneal set, another between the submucous and muscular layers, and a deep set in the mucosa around the glands of Lieberkuhn.
The three great lymph-streams, anterior caecal, posterior caecal, and appendicular, are quite distinct from each other and from the surrounding lymphatics of the pelvis and colon; when these latter are involved it is not by a lateral extension from these three streams but by direct infection from the regions which they themselves drain. From the ileocaecal nodes the lymphatics follow the arteries to the nodes at the root of the mesentery and empty into the receptaculum chyli. They do not follow the veins to the liver, hence infection of the liver is not caused through the lymph-channels in appendicitis.