THE DESCRIPTIONS of anal anatomy in current textbooks on surgery and proctology are remarkably diverse. Not only are there departures in terminology, but in many instances details of considerable surgical significance are not given proper emphasis or are omitted entirely. The need for clear and uniform concepts has led to this presentation of the essential points with which he who ventures to dissect the nether parts of his fellow man should be familiar. It is based on certain fundamental contributions to this subject,1 tempered by a personal study of postmortem and surgical material.
THE ANAL MUSCULATURE
The four muscles of importance in anal surgery are the external sphincter, the internal sphincter, the longitudinal muscle and the levator ani. It is amazing how frequently the relationship of these muscles is misrepresented, despite the thorough and conclusive studies of Milligan and Morgan,1a Blaisdelllb and others. The proper relationship is