Aspects of this topic are discussed in the following places at Britannica.
...these two segments of the large intestine. The internal cavity of the rectum is divided into three or four chambers; each chamber is partly segmented from the others by permanent transverse folds (valves of Houston) that help to support the rectal contents. A sheath of longitudinal muscle surrounds the outside wall of the rectum, making it possible for the rectum to shorten in length.
We welcome your comments. Any revisions or updates suggested for this article will be reviewed by our editorial staff. Contact us here.
Regular users of Britannica may notice that this comments feature is less robust than in the past. This is only temporary, while we make the transition to a dramatically new and richer site. The functionality of the system will be restored soon.