Ischial tuberosity

The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known informally as the sit bones, 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.