The large intestine extends from the termination of the ileum to the anus. It is about five to six feet in length. Its calibre decreases from beginning to end except at the ampulla of the rectum where it is larger. It measures 28.5 cm. in circumference at the junction of colon and csecum, 20.5 cm. at the end of the ascending portion, 14.5 cm. in the descending portion. The large intestine is divided into the caecum, colon, and rectum. With the exception of the rectum it possesses three taeniae, these being groups of non-striated muscular fibres running lengthwise with the lumen of the intestine. Between the taeniae the walls are somewhat sacculated. The circular muscular fibres a re also accumulated in spots, leaving short intervals be-tween each other, thus forming constrictions and expansions (haustra coli) across the intestine (Fig. 8). The large bowel is further characterized by appendices epiploicae, external pouches, formed by the peritoneal covering containing fat. The caecum is the head of the colon or that part of the large bowel situated below the mouth of the ileum (Fig. 9). It lies in the right iliac fossa and is completely covered by the peritoneum. In the filled condition it touches the anterior abdominal wall.

Starting from the inner and back portion of the caecum lies the processus vermiformis or appendix, forming a narrow, somewhat bent, blind-ending tube. The appendix is movable and has its own mesentery (mes-enteriolum). Its length varies between 2 and 20 cm. and its width between 0.5 and 1 cm. The appendix opens into the caecum (ostium processus vermiformis), occasionally forming a crescentic fold (v a 1 v u 1 a processus vermiformis). In man it constitutes an entirely functionless organ which occasionally gives rise to manifold ailments. The appendix has no fixed position. J. D. Bryant 1 found it most often "inward," then "behind the caecum," "downward and inward," "into the true pelvis."

The Large Bowel Partly Opened along the Mesentery (Toldt)

Fig. 8. - The Large Bowel Partly Opened along the Mesentery (Toldt). a. Free taenia; b. taenia mesocolica; c. appendices epiploicae; d, the mucosa; e, the semilunar folds of the colon; f, the mesocolon.

Section of the Caecum and Ileum, showing the Entrance of the Latter into the Caecum (Toldt)

Fig. 9. - Section of the Caecum and Ileum, showing the Entrance of the Latter into the Caecum (Toldt). a. The semilunar folds of the colon; b, c, the ileocaecal valves (b, the upper, and c, the lower one); d, the end portion of the ileum; c. the posterior ileocaecal valve; f, the appendicular valve; g, the appendix.

1 J. D. Bryant: Annals of Surgery, February, 1893, p. 164.

Without distinct demarcation the caecum merges into the ascending colon. It passes vertically above the crest of the ileum and runs along the posterior abdominal muscles and the lower part of the right kidney. At this point just in front of the kidney and immediately beneath the liver the colon bends toward the left of the flexura coli dextra. The ascending colon is posteriorly adherent through connective tissue with the parts just mentioned, while the peritoneum covers only its anterior and partly also its lateral surfaces. In close proximity to its median wall lies the ascending part of the duodenum. Beginning at the flexura coli dextra the colon runs across the abdominal cavity from right to left (transverse colon), forming the longest segment of the large intestine. It passes from the hepatic flexure in the right hypochondrium transversely and slightly upward from right to left along the anterior abdominal wall to the splenic flexure in the left hypochondrium. This part of the colon is the most movable. It has a very long mesentery, called the transverse mesocolon. The usual position of the transverse colon corresponds to a line separating the umbilical and epigastric regions.

It is in relation by its upper surface with the lower part of the liver and gall bladder, the greater curvature of the stomach and the lower end of the spleen; by its under surface with the small intestine; by its anterior surface with the great omentum and abdominal wall; by its posterior surface with the transverse mesocolon; on the right side with the second part of the duodenum, and on the left besides the latter with some convolutions of the small intestine.

The transverse colon does not form a straight line connecting the right and left flexures, but is about twice as long as this line and therefore forms several curves. In the left hypochondrium especially, there is an S-shaped coil. The latter tills out the free space in the left hypochondrium which is left by the stomach in its various states of fulness. Beginning at the flexura coli sinistra the descending colon runs downward in front of the left kidney and the quadratus lumborum and iliac muscles until it reaches the left iliac fossa. The descending colon runs just in the opposite direction to the ascending colon, and like this is only partly covered by the peritoneum. The descending colon passes into the sigmoid colon or flexure (S Romanum), commencing above the iliac crest and ending below in the rectum at the brim of the true pelvis opposite the left sacro-iliac articulation. It is generally described as an S-shaped curve having an upper colic rim turned toward Poupart's ligament and the lower rectal rim, hanging down into the true pelvis. It has a complete peritoneal covering or mesentery. This part of the bowel is very movable, and its calibre is the narrowest of that of the large bowel.

The sigmoid flexure continues into the rectum, forming the terminal portion of the intestinal tube. It runs, coming from the left, in front of the os sacrum down to the bottom of the small pelvis. Only the upper half of the rectum is invested completely with peritoneum (mesorectum) and is attached to the sacral vertebra. The lower half passes between the organs occupying the pelvic floor, being adherent to them by connective tissue. It now runs posteriorly along the os coccyx and terminates in the anus. This part has an incomplete peritoneal covering (plica Douglasii) lying anteriorly and turning backward in order to ascend either over the vagina or the bladder (excavatio recto-uterina, excavatio rectovesica-lis). Below this point the rectum has very little mobility as it is covered all around by connective tissue. The entire rectum is about 18 to 22 cm. long. Its calibre varies. It is widest at the apex of the prostate, forming the ampulla of the rectum.

The longitudinal muscular fibres of the rectum are not arranged in taeniae as in the colon, but pass all around the lumen. The circular muscular fibres become more dense from above downward and increase to such a degree at the anal opening that they here form a thick ring (musculus sphincter ani internus). A short distance above this muscle there is also an accumulation of circular muscular fibres (musculus sphincter ani tertius). At the anus the walls of the rectum are connected with striated muscular fibres (sphincter ani externus and levator ani), which are both of importance in the act of defecation.

The colon is supplied by the three arteriae colicae, branches of the arteria mesenterica superior and arteria mesenterica inferior. The arteria colica sinistra originates from the arteria mesenterica inferior, while the arteria colica media and superior are tributaries of the arteria mesenterica superior. The veins accompany the artery and empty partly into the vena mesenterica superior, partly into the vena mesenterica inferior. The lymphatics of the colon are numerous and lie below the glands and all through the submucosa. The plexus mesentericus superior, a branch of the plexus cceliacus, provides the nervous supply of the caecum, ascending colon, and the right half of the transverse colon. The plexus mesentericus inferior, a branch of the plexus aorticus abdominalis, supplies the left half of the transverse colon, the descending colon, and the sigmoid flexure.

The rectum is supplied by the arteriae haemorrhoidales superior, media, and inferiores, branches of the arteria mesenterica inferior and arteria pudenda communis. The venous blood of the rectum is carried to the venae haemor-rhoidales principally into the vena mesenterica inferior, thus emptying into the vena portarum, partly, however, into the vena iliaca interna. In this way there is a separate communication (outside of the portal circulation) with the remaining vessels of the abdomen. The lymphatics of the rectum form a wide net, running partly to the glands lying behind the rectum, partly to the plexus lumbalis sinister. The nerves supplying the rectum originate from the sympathetic, being branches of the plexus mesenteri-cus inferior, the plexus sacralis (nervi haemorrhoidales inferior and medii), and the plexus hypogastricus superior.

Histology Of The Large Bowel

The large bowel consists, like the small bowel, of four coats: the serosa, muscularis, submucosa, and mucosa. The structure of these four coats corresponds to that of the small intestine, except that the longitudinal muscular fibres are arranged in. three groups (taeniae) running along the wall, as mentioned above. The mucosa of the large bowel differs from that of the small intestine in that there is an absence of the folds of Kerkring and of the villi. Lieberkiihn's glands are here somewhat longer and sometimes curved.

The mucous membrane of the rectum is thicker, more red, and succulent than that of the colon. There are numerous folds. One conspicuous fold is found 6 to 7 cm. above the anus (plica transversalis recti). In the neighborhood of the anus the folds take a longitudinal direction, and are called columnae Morgagnii seu recti. The lower region of the rectum contains the epithelial cells of the rectum, pavement-like epithelium, forming a gradual 2 transition from the mucous membrane of the digestive tract to that of the external skin. The upper portion of the rectum corresponds exactly to that of the colon.