Issues in anatomy: the external anal sphincter revisited.

Textbooks of anatomy often fail to reflect controversies or new developments in anatomy. This impinges on the conduct of examinations in anatomy with respect to whether the correct answer is what appears in the textbook or what is known in the research literature. The example of the external anal sphincter is addressed. Whereas textbooks portray this muscle as having three, essentially circular parts, past and more recent work denies this description. Rather, the sphincter consists of three loops; one formed by puborectalis, one stemming from the coccyx and one stemming from the pre-anal skin. Surgeons in training should recognise that anatomy is not a static science and that idealized descriptions that occur in textbooks do not necessarily reflect actual anatomy or controversies about it.