The colon has a tubular, saccular shape caused by the presence of the haustral markings, semilunar folds or plica semilunares which are ridges that raise the mucosa so that the mucosa is not completely flat. The pleating effect is caused by the presence of the taenia coli which as mentioned are longitudinal mucle bands that run the length of the colon, and which are shorter thann the colon and hence the pleating effect and the sacculkar haustra. When the taenia contract they become even shorter and the haustrra become more apparent. The colon is characterized by the absence of villi on the mucosal surface, but the presence of mucosal infoldings called crypts of Lieberkuhn. The fatty excrescences called the appendices epiploica on the outer surface are unique and characteristic.