Caecum and colon, illustration. The ileum (to the right) joins the ascending colon at the caecum. The worm-shaped vermiform appendix (pink) extends from and opens into the caecum. The colon shows two distinctive features, the haustra or successive saccules, and the teniae coli which is the outer smooth muscle layer arranged as three longitudinal strips. From Lizars, J. 1823 A system of anatomical plates of the human body. W.H. Lizars, Edinburgh.