The body of the ischium is expanded inferiorly to form the ischial tuberosity.  It can be palpated through the lower medial part of the buttock, especially with the hip flexed as in sitting, when it becomes subcutaneous.  When standing the gluteus maximus muscle covers the tuberosity.  On sitting, the medial border of gluteus maximus clears the tuberosity, and supports the body’s weight.