The appearance of the muscularis externa is different from that of the small intestine . The inner circular layer of muscle forms the usual sheath around the large intestine, but the outer longitudinal muscle layer forms three flattened strands, the taenia coli . Only a thin layer of longitudinal muscle surrounds the inner circular muscle layer between the taenia coli . The vermiform appendix is a small blind-ending diverticulum from the cecum. The most important of its features is the thickening of its walls primarily due to large accumulations of lymphoid nodules in the lamina propria.
Intestinal villi are usually absent, and crypts are comparatively rare .
There is often fatty tissue in the submucosa. The muscularis externa is thinner than in the remainder of the large intestine. The mucosa has a characteristic surface relief of 5-10 longitudinal folds, the anal columns , each of which contains a terminal branch of the superior rectal artery and vein . This line defines sections of the anal canal with different arterial and nerve supplies, different venous and lymphatic drainages and different embryological origins. Crypts disappear below the pectinate line and the epithelium changes from the tall, columnar type seen in other parts of the large intestine to a stratified squamous epithelium .