The levator ani (pelvic diaphragm)



The levator ani  is a thin sheet of funnel-shaped muscle that is attached to the pelvic wall. It separates the pelvis from the perineum/ischiorectal fossa.


Let's trace the superior rim of this funnel as it circumvents the pelvic wall. This cross-section image shows its anterior attachment to the pubic bone.  Note the obturator internus and externus lining the obturator foramen. Trace the levator ani superiorly until it meets the obturator internus. This is the muscle's lateral attachment; it is an atypical attachment to a muscle sheath rather than to a bone. From the plane in the dissection window (<ctrl-p> to toggle the plane on and off), you can see that the lateral attachment bisects the obturator foramen. A medial view shows how the lateral attachment also places the superior half of obturator internus in the pelvis and the inferior half in the perineum. Use rollovers to identify the obturator superior and inferior to the levator ani. Note how the attachment extends to the ischial spine. Trace the levator up and down in the cross-section window to see the attachment to the coccyx. Rotate this image and trace the cross-section up and down. Use rollovers to re-identify highlighted structures.


Let's examine how the levator ani supports the pelvic organs. Rotate the image to an anterior view. Add in the bladder, urethra, and sphincter urethrae. Rotate the image to 295 degrees to appreciate how these urinary structures are related to the pubis and the levator ani. Rollover highlighted structures with your mouse to reinforce their identities. Note how the bladder is located between the heads of the femur. For orientation, use the slider to add back skin. Next, add the vagina, uterus, rectum, and anal sphincter. Use rollovers in both windows to distinguish the internal and external anal sphincters.


The external genitalia lie inferior to the pelvic diaphragm and are not associated with it. Instead, they attach to the inferior surface of the urogenital diaphragm. Use rollovers to identify the individual components. Rotate the image to see how the urogenital diaphragm (ischiocavernosus component is next to the bone) spans the plane between the left and right inferior rami of the coxal (hip) bone. (The urogenital diaphragm is completed by the fascia between the ischiocavernosus, external urethral sphincter, and superficial transverse perineal muscles. This fascia is not highlighted.)


©2011 Lawrence Rizzolo and William Stewart, Yale School of Medicine