To the Editor.—In their article "Anal Cloacogenic Carcinoma: Classification and Clinical Behavior" (Archives 1981;116:456-459), Serota et al presented a diagram that indicates that there is nonkeratinized squamous epithelium above the dentate line of the anal canal. This is distinctly imprecise information. The epithelium is colonic columnar, as attested by standard textbooks and other publications. Marson and Dawson's Gastrointestinal Pathology, for example, states that "the anal canal above the pectinate line [dentate line] is lined by a continuation of the rectal mucosa...."1 A number of other works can be consulted for the same information. It is unfortunate, however, that many textbooks of anatomy and histology underemphasize the features of this important area.
In addition, the unqualified term "squamous epithelium" has no meaning. Squamous epithelium is either simple (a single layer of flattened epithelium) or stratified (layered, as in the anal mucosa below the dentate line). The two types are