Surgical Anatomy of the Rectum, Anal Canal, Perineum, and Colon

Abstract

The two levator ani muscles form a funnel whose outlet begins at the level of the puborectal sling and there forms a sharp angle — about 90° — backward. The medial fibers of the levator ani form a muscular sling which arises from the pubic bone and encircles the anorectal flexure. This muscle sling, called the “puborectal,” plays a crucial role in maintaining fecal continence. The sphincter ani externus muscle forms the lower part of the funnel of the pelvic floor. It consists of three parts (subcutaneous, superficial, and deep) which cannot be distinguished clearly but merge into each other. Muscle fibers running from the tip of the coccyx to the external sphincters are called the anococcygeal ligament. Cranial to this ligament are the left and right ischiorectal spaces, which are located caudal to the pelvic floor. The levator ani and sphincter externus ani muscles are supplied with blood by branches of the pudendal artery.