The large intestine is supplied by the branches of the inferior mesenteric artery, and the veins are of the same name. The large intestines are divided into the caecum, colon and rectum. =Caecum.=—The caecum is the commencement of the large intestines, it is a large blind pouch situated below the ileo caecal valve. _The ileo caecal valve_ is the valve between the exit of the small intestines and the commencement of the large intestines. The caecum is held mostly in place by the folds of the peritoneum. _The Vermiform Appendix._—The appendix is found only in the human, the higher apes, and the wombat, although in certain rodents a somewhat similar arrangement exists. The appendix is a long, narrow, worm shaped, musculo-membranous tube, which starts from the inner side of the posterior wall of the caecum, below and behind the termination of the ileum. It is the seat for a very common disease called appendicitis. It varies from one half to nine inches in length, its average being about three inches. Its diameter is from one eighth to one quarter of an inch. [Illustration: FIG. 24—The caecum and colon laid open to show the ileo-caecal valve. (Gray)] =The Colon.=—The colon is divided into three parts, the ascending, transverse and the descending colon. _The ascending colon_ is smaller than the caecum, with which it is continuous. It passes upward from its commencement at a point corresponding to the ileo-caecal valve, to the under surface of the right lobe of the liver, on the right of the gall bladder, where it is lodged in a shallow depression on the liver; here it bends abruptly inward to the left, forming the hepatic flexure. It is held to the posterior wall of the abdomen by folds of the peritoneum. _The transverse colon_ is the longest part of the small intestines, passes transversely from the right to the left across the abdomen, opposite the confines of the epigastric and umbilical regions, where it curves downward beneath the lower end of the spleen, forming the splenic flexure. In its course the transverse colon describes an arch, the concavity of which is directed backward toward the vertebral column and a little upward. This is the most movable part of the colon, only covered by peritoneum and held to the back wall by the folds of the peritoneum. The transverse colon is in relation, by its upper surface with the liver and gall bladder the great curvature of the stomach, and the lower end of the spleen; by its under surface with the small intestines; by its anterior surface with the anterior layers of the great omentum and the abdominal wall; its posterior surface on the right is in relation with the duodenum and on the left it is in contact with the convolutions of the jejunum and ileum.