The body of ischium enters into and constitutes a little more than two-fifths of the acetabulum. Its external surface forms part of the lunate surface of the acetabulum and a portion of the acetabular fossa. Its internal surface is part of the wall of the lesser pelvis; it gives origin to some fibers of the Obturator internus. Its anterior border projects as the posterior obturator tubercle; from its posterior border there extends backward a thin and pointed triangular eminence, the ischial spine, more or less elongated in different subjects. The external surface of the spine gives attachment to the Gemellus superior, its internal surface to the Coccygeus, Levator ani, and the pelvic fascia; while to the pointed extremity the sacrospinous ligament is attached. Above the spine is a large notch, the greater sciatic notch, converted into a foramen by the sacrospinous ligament; it transmits the Piriformis, the superior and inferior gluteal vessels and nerves, the sciatic and posterior femoral cutaneous nerves, the internal pudendal vessels, and nerve, and the nerves to the Obturator internus and Quadratus femoris. Of these, the superior gluteal vessels and nerve pass out above the Piriformis, the other structures below it. Below the spine is a smaller notch, the lesser sciatic notch; it is smooth, coated in the recent state with cartilage, the surface of which presents two or three ridges corresponding to the subdivisions of the tendon of the Obturator internus, which winds over it. It is converted into a foramen by the sacrotuberous and sacrospinous ligaments, and transmits the tendon of the Obturator internus, the nerve which supplies that muscle, and the internal pudendal vessels and nerve.