Levator Ani Muscle
The levator ani is a broad, thin muscle, situated on the side of the pelvis. It is attached to the inner surface of the side of the lesser pelvis, and unites with its fellow of the opposite side to form the greater part of the floor of the pelvic cavity. It supports the viscera in pelvic cavity, and surrounds the various structures that pass through it. In combination with the coccygeus muscle, it forms the pelvic diaphragm. The levator ani muscle plays a crucial role in the preservation of urinary and bowel continence. Through its tonic activity the levator ani stabilizes the abdominal and pelvic organs and controls the opening and closing of the levator hiatus. While in quiescent state the urethra and the rectum are mechanically closed at the levator hiatus the muscle relaxes at the beginning of urination and defecation. Parts The levator ani is divided into three parts: Iliococcygeus muscle: It extends more laterally from the fascia of obturator internus muscle to the tailbone. Pubococcygeus muscle: It runs from the pubic bone (lateral of the origin of the puborectalis muscle) to the tendinous center of the perineum, anococcygeal body and tailbone. Puborectalis muscle: It originates lateral from the symphysis on both sides and encircles the rectum (anorectal junction). Origin and insertion The levator ani arises, in front, from the posterior surface of the superior ramus of the pubis lateral to the symphysis; behind, from the inner surface of the spine of the ischium; and between these two points, from the obturator fascia. Posteriorly, this fascial origin corresponds, more or less closely, with the tendinous arch of the pelvic fascia, but in front, the muscle arises from the fascia at a varying distance above the arch, in some cases reaching nearly as high as the canal for the obturator vessels and nerve. The fibers pass downward and backward to the middle line of the floor of the pelvis; the most posterior are inserted into the side of the last two segments of the coccyx; those placed more anteriorly unite with the muscle of the opposite side, in a median fibrous raphé (anococcygeal raphé), which extends between the coccyx and the margin of the anus. The middle fibers are inserted into the side of the rectum, blending with the fibers of the Sphincter muscles; lastly, the anterior fibers descend upon the side of the prostate to unite beneath it with the muscle of the opposite side, joining with the fibers of the sphincter ani externus and transversus perinei, at the central tendinous point of the perineum. The anterior portion is occasionally separated from the rest of the muscle by connective tissue. From this circumstance, as well as from its peculiar relation with the prostate, which it supports as in a sling, it has been described as a distinct muscle, under the name of levator prostatæ. In the female the anterior fibers of the levator ani descend upon the side of the vagina.