As you know, embryology is a speculative science. This is the reason why the words "probably," "perhaps," and "most likely" appear often in texts. In the "Surgical Anatomy" section in a recent issue of the ARCHIVES (2000;135:314), the sentence "The distal third of the transverse colon to the anus arises from the hindgut" is not embryologically and anatomically correct.
The anal canal, with an approximate length of 4 cm, is perhaps a product of the cloaca.1 Anatomically, it is subdivided by the pectinate line (or close to the pectinate line) into 2 parts: the upper (proximal) 2 cm from the pelvic diaphragm to the pectinate line, and the lower (distal) 2 cm from the pectinate line to the anal verge. The hindgut is most likely responsible for the genesis of the upper 2 cm. Embryologically, the lower 2 cm is of ectodermal origin.