Just so everyone knows, the term "sitz bones" is not a medical term, it's ischial tuberosity, but ain't nobody got time fer all that! Also, don't confuse them with a "sitz bath", which is something women do after having a baby and at other times, but that's not my area of expertise. I've heard all kinds of explanations as to how these bones got their names. A yoga teacher told me that "Mr. Sitz" (or something like that) named them, as far as I know that is definitely not true but it was said with such authority that I actually question myself. Funny how the delivery alone can make fiction into fact. Maybe you know, if so, write me! I tell people when a kid sits on your lap and their boney butt hurts your legs, those are the sitz bones. Or if you don't have a big "cushion" (you know what I'm saying) and your sitting on a metal bench you might feel your "sitz bones". Let's see what good ol' wikipedia says!
"The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known informally as the sitz bone, or as a pair the sitting bones) is a large swelling posteriorly on the superior ramus of the ischium. It marks the lateral boundary of the pelvic outlet. When sitting, the weight is frequently placed upon the ischial tuberosity. The gluteus maximus provides cover in the upright posture, but leaves it free in the seated position."
I like it! I totally agree! Wikipedia also has some nice drawings, which can help. So explore where these puppies are on your own. It's really important that you adventure out and explore your own body especially these sitting bones because they're the key to find your base, your vertical in a seated pose (check out my youtube on that! https://www.youtube.com/watch?v=UHDfE-8xeWA).
Now, where is my pelvic floor? It's the area of your body where the seams of your pants or shorts come together, if you wear female underwear (I won't judge!) it's where the quadrangle shape material is. If you're sitting of the front of your sitz bones you feel your pelvic floor on the support. Now, having said that, for some people sitting on the front of your sitz bones and finding the pelvic floor requires either flexibility and/or some props. For some ideas on that, click on my youtube channel "Beyond with Elizabeth" and watch "Seated Pose".
What does wikipedia say? "The pelvic floor or pelvic diaphragm is composed of muscle fibers of the levator ani, the coccygeus muscle, and associated connective tissue which span the area underneath the pelvis." I like the name "pelvic diaphragm" because like the other diaphragm there is a bandha associated with the pelvic floor (more on that later!) The picture really says it all...
Bon Voyage! Remember to have a sense of humor about it, we're only but a speck of dust in the the universe, if that.
Your Yoga Teacher