1212 THE DIGESTIVE SYSTEM. 



but, on the contrary, are broken up (Fig. 950) into three bands, known as the 

 tseniae coli. These bands, which are about J inch (6 mm.) wide, begin at the base 

 of the vermiform process, and run along the surface of the gut at nearly equal 

 distances from one another until the rectum is reached. There they spread out 

 and form a layer of longitudinal muscular fibres, which is continuous all round the 

 tube (see p. 1229). The bands are about one-sixth shorter than the intestine to 

 which they belong ; consequently, in order to accommodate the bowel to the length 

 of the tsenise, the gut is tucked up, giving rise to a sacculated condition (Fig. 950). 

 Three -rows of pouches or saccules are thus produced, along the length of the tube, 

 between the tsenise. If the tseniae are dissected off, the sacculations largely disappear, 

 the intestine becomes cylindrical, and at the same time about one-sixth longer. 



The appendices epiploicae (Fig. 950) are little processes or pouches of peritoneum, 

 generally more or less distended with fat, except in emaciated subjects, which 

 project from the serous coat along the whole length of the large intestine, with the 

 exception of the rectum proper. 



When the interior of a piece of distended and dried large intestine is examined, its 

 saccules appear as rounded pouches, haustra, separated by crescentic folds, plicae 

 semilunares coli, corresponding to the creases on the exterior separating the saccules 

 from one another. 



The position of the three teeniae on the intestines is as follows : On the ascending, descending, 

 and iliac colons one taenia lies, on the anterior aspect of the gut, and two on the posterior aspect, 

 namely, one to the lateral side (postero- lateral), the other to the medial side (postero-medial). It 

 is chiefly along the first of these (the anterior) that the appendices epiploicae are found. On the 

 transverse colon their arrangement is different, but is rendered exactly similar by turning the 

 great omentum, with the colon, up over the thorax. On the transverse colon in the natural 

 position, the anterior taenia of the ascending and descending colons becomes the posterior (or 

 postero-inferior) termed tcenia libera, the postero-lateral becomes anterior or tcenia omentalis, 

 and the postero-medial becomes superior in position and is termed tcenia mesocolica. The anterior 

 and postero-lateral tseniae of the iliac colon pass below on to the front of the pelvic colon and 

 rectum. 



In formalin-hardened bodies portions of the large intestine, but particularly of the descending 

 and sigmoid colons, are often found fixed in what appears to be a state of contraction, when 

 they are reduced to a diameter of about or of an inch (16 to 19 mm.). Under similar con- 

 ditions parts of the small intestine are found correspondingly reduced. 



The appendices epiploicae, although generally said to be absent in the foetus, can be distinctly 

 seen as early as the seventh month, but at this time they contain no fat 



Structure of the Large Intestine. The tunica serosa is complete on the 

 vermiform process, caecum, transverse colon, and pelvic colon ; incomplete on the 

 ascending, descending, and iliac divisions of the colon and on the rectum. It will be 

 described in detail with each of these portions of the intestine. 



The tunica nmcosa is of a pale, or yellowish, ash colour in the colon, but 

 becomes much redder in the rectum. Unlike that of the small intestine, its surface 

 is smooth, owing to the absence of villi, but it is closely studded with the orifices 

 of numerous large intestinal glands. Solitary lymph nodules are also numerous, 

 particularly in the vermiform process (Fig. 955). 



Vessels and Nerves. The caecum and vermiform process receive their blood from the 

 ileo-colic artery ; the ascending colon from the right colic artery ; and the transverse colon from 

 the middle colic artery, which lies in the transverse mesocolon. These are all branches of the 

 superior mesenteric. The descending colon is supplied by the left colic, and the iliac and 

 pelvic colons by the sigmoid arteries, branches of the inferior mesenteric. The rectum derives 

 its blood from the three haemorrhoidal arteries, which will be described with that division of 

 the gut. 



The veins correspond largely to the arteries, and join the inferior and superior mesenteric 

 vessels, which send their blood into the portal vein. 



The lymph vessels of the large intestine arise from plexuses in the submucous and sub- 

 peritoneal coats, as in other parts of the alimentary canal. 



The deeper vessels escape chiefly along the entering blood-vessels, those from the lateral 

 aspects passing behind the intestine. 



The vessels pass medially to a series of glands lying along the medial border of the intestine 

 (" paracolic " glands (Jamieson)) ; thence they pass along the lines of the main arteries, passing 

 then to glands disposed at intervals about these vessels (intermediate and main glands). The 

 lymph vessels from the lower half of the descending colon, and from the iliac and pelvic colons, 

 join the left lymph trunk of the lumbar glands. Those of the rectum and caecum will be described 

 later. 



