Tuberosity of the ischium

Posteriorly, the superior ramus of the ischium forms a large swelling, the tuberosity of the ischium (or ischial tuberosity).

It marks the lateral boundary of the pelvic outlet.

When sitting, the weight is frequently placed upon the ischial tuberosity.

Divisions
The tuberosity is divided into two portions: a lower, rough, somewhat triangular part, and an upper, smooth, quadrilateral portion.


 * The lower portion is subdivided by a prominent longitudinal ridge, passing from base to apex, into two parts;
 * the outer gives attachment to the Adductor magnus,
 * the inner to the sacrotuberous ligament.


 * The upper portion is subdivided into two areas by an oblique ridge, which runs downward and outward;
 * from the upper and outer area the Semimembranosus arises;
 * from the lower and inner, the long head of the Biceps femoris and the Semitendinosus.