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I. Orientation of Pelvis

II. Osteology

III. Joints

IV. Ligaments

V. Pelvic Musculature

VI. Perineum

[WebLecture Slide 39 320x240 pixels]

WebLecture Slide 39

The anal triangle contains the wedge-shaped ischiorectal fossa on either side of the anus which hold two extensive fat pads. This fat is liquid at body temperature allowing easy distention of the rectum and anus during defecation. The pudendal nerves and internal pudendal vessels course through the ischiorectal fossa heading for a fascial compartment called the pudendal canal. The pudendal canal is fused to the obturator fascia and passes its contents forwards along the inferior pubic rami. The inferior rectal nerve (a branch of the pudendal) and the inferior rectal vessels are also found in the ischiorectal fossa. 

The external anal sphincter surrounds the most inferior part of the anus and is bound to the overlying skin. The internal anal sphincter is not truly part of the anal triangle but is mentioned here to complete the anatomy of the anal sphincter. Like all sphincters, the anal sphincter is closed at relaxation. The tone of these sphincters keeps the lateral walls of the anal canal closed except when consciously relaxed during defecation or  while "pushing" during childbirth. 
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