





309 



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 

 Glutseus 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 pos- 

 terior 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 sacro- 

 sciatic 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 con- 

 nected; 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 sacrotuberoua 

 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 trans- 

 mits 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 homol- 

 ogous with the joints between the bodies of the vertebrae, and is connected by 

 similar ligaments. They are: 



The Anterior Sacrococcygeal. The Lateral Sacrococcygeal. 



The Posterior 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 





