The pelvis is the foundation of the riding seat.
– Sally Swift from “Centered Riding”
Pelvic anatomy
Pelvis - posterior view
The ischial tuberosity are the two bones of the pelvis that you sit on.
Each half of the pelvis is composed of three bones, the ilium, the ischium and the pubis, that have fused together during development. The topmost bone (the one that forms the pelvic rim) is the ilium. When you put your hands on your hips, they are resting on the iliac crest.
Side view of pelvis
Pelvic Anatomy Sacro-iliac Joint: This video gives a good 3D rotational view of the pelvic bones, as well as describing a reason that we are stiffer in movement as we age.
Amazing example of how the body can move – hips and spine. Belly dancing by Sadie from Denver, CO.