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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
  2. Ligaments Connecting the Sacrum and Ischium
(Fig. 320).
The Sacrotuberous.    The Sacrospinous.

The Sacrotuberous Ligament (ligamentum sacrotuberosum; great or posterior sacrosciatic ligament).—The sacrotuberous ligament is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends; attached by its broad base to the posterior inferior spine of the ilium, to the fourth and fifth transverse tubercles of the sacrum, and to the lower part of the lateral margin of that bone and the coccyx. Passing obliquely downward, forward, and lateralward, it becomes narrow and thick, but at its insertion into the inner margin of the tuberosity of the ischium, it increases in breadth, and is prolonged forward along the inner margin of the ramus, as the falciform process, the free concave edge of which gives attachment to the obturator fascia; one of its surfaces is turned toward the perineum, the other toward the Obturator internus. The lower border of the ligament is directly continuous with the tendon of origin of the long head of the Biceps femoris, and by many is believed to be the proximal end of this tendon, cut off by the projection of the tuberosity of the ischium.

Relations.—The posterior surface of this ligament gives origin, by its whole extent, to the Glutæus maximus. Its anterior surface is in part united to the sacrospinous ligament. Its upper border forms, above, the posterior boundary of the greater sciatic foramen, and, below, the posterior boundary of the lesser sciatic foramen. Its lower border forms part of the boundary of the perineum. It is pierced by the coccygeal nerve and the coccygeal branch of the inferior gluteal artery.

The Sacrospinous Ligament (ligamentum sacrospinosum; small or anterior sacrosciatic ligament).—The sacrospinous ligament is thin, and triangular in form; it is attached by its apex to the spine of the ischium, and medially, by its broad base, to the lateral margins of the sacrum and coccyx, in front of the sacrotuberous ligament with which its fibers are intermingled.

Relations.—It is in relation, anteriorly, with the Coccygeus muscle, to which it is closely connected; posteriorly, it is covered by the sacrotuberous ligament, and crossed by the internal pudendal vessels and nerve. Its upper border forms the lower boundary of the greater sciatic foramen; its lower border, part of the margin of the lesser sciatic foramen.
  These two ligaments convert the sciatic notches into foramina. The greater sciatic foramen is bounded, in front and above, by the posterior border of the hip bone; behind, by the sacrotuberous ligament; and below, by the sacrospinous ligament. It is partially filled up, in the recent state, by the Piriformis which leaves the pelvis through it. Above this muscle, the superior gluteal vessels and nerve emerge from the pelvis; and below it, the inferior gluteal vessels and nerve, the internal pudendal vessels and nerve, the sciatic and posterior femoral cutaneous nerves, and the nerves to the Obturator internus and Quadratus femoris make their exit from the pelvis. The lesser sciatic foramen is bounded, in front, by the tuberosity of the ischium; above, by the spine of the ischium and sacrospinous ligament; behind, by the sacrotuberous ligament. It transmits the tendon of the Obturator internus, its nerve, and the internal pudendal vessels and nerve.
  3. Sacrococcygeal Symphysis (symphysis sacrococcygea; articulation of the sacrum and coccyx)
.—This articulation is an amphiarthrodial joint, formed between the oval surface at the apex of the sacrum, and the base of the coccyx. It is homologous with the joints between the bodies of the vertebræ, and is connected by similar ligaments. They are:
The Anterior Sacrococcygeal.
The Posterior Sacrococcygeal.
The Lateral Sacrococcygeal.
The Interposed Fibrocartilage.
The Interarticular

The Anterior Sacrococcygeal Ligament (ligamentum sacrococcygeum anterius).—This consists of a few irregular fibers, which descend from the anterior surface of the sacrum to the front of the coccyx, blending with the periosteum.

The Posterior Sacrococcygeal Ligament (ligamentum sacrococcygeum posterius).—This is a flat band, which arises from the margin of the lower orifice of the sacral

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