The Transverse Rectal Folds, or Valves of Houston

These valves are reflections of the rectal mucosa, which contain some fibers of the circular muscle coat of the rectal wall. They are crescentic plications, which have a definite structure. They lie obliquely and transverse to the length of the rectum and project into the length of the rectal lumen. The valves are quite variable in number, location and degree of development. Usually there are three: an inferior, middle and superior but occasionally there are more. The inferior valve is usually located from 2.5 to 3.5 cm above the anal margin Occasionally, the valves are absent.

In the strict sense they are not valves, and the degree to which they are able to function is still debatable. Their purpose seems to be to serve as steps or spiral supports to modify the flow of the feces as they descend into the lower rectum.

They are lost after full surgical mobilization of the rectum, a manoeuvre that may provide about 5cm of additional length to the rectum.