236 



THE ARTICULATIONS 



pass downward and backward to be attached to the lateral borders and posterior 

 surfaces of the lovver three sacral vertebrae and upper two segments of the coccyx; 

 while others, after passing for a certain distance backward, curve forward and 

 downward to the ischium, forming the anterior free margin of the ligament 

 where it limits posteriorly the sciatic foramina. These fibres are joined by others 

 which arise from the posterior surfaces of the lower three sacral vertebrae and 

 upper pieces of the coccyx. At the ischium it is fixed to the medial border of the 

 tuberosity, and sends a thin sharp process upward along the ramus of the 

 ischium which is called the falciform process (fig. 273), and is a prolongation of 

 the posterior edge of the ligament. 



4:^great many fibres pass on directly into the tendon of the biceps muscle^ so that traction 

 on this muscle braces up the whole ligament, and the coccyx is thus made to moye on the sacrum. 

 The ligament may not unfairly be described as a tendinous expansion of the muscle, whereby 

 its action is extended and a more advantageous leverage given. It is broad and flat at its 

 attached ends, but narrower and thicker in the centre, looking like two triangular expansions 



Fig. 273. — Sacro-tuberous and Sacro-spinous Ligaments. (Posterior view.) 



Sacro-tuberouB ligament 



Sacro-spinous ligament 



Falciform process of sacro-tuberous 

 ligament 



Tendon of biceps muscle, continuous 

 with the sacro-tuberous ligament 



joined by a flat band, the larger triangle being at the ilium, and the smaller at the ischium 

 The fibres of the ligament are twisted upon its axis at the narrow part, so that some of the 

 superior fibres pass to the lower border. ^. 



'J'he post(!ri()r surface gives origin to the gluteus maximus muscle, and on it ramify the loopl^/. 

 from the posterior branches of the sacral nerves; its anterior surface is closely connected at its . 

 origin ,with the sacro-spinous ligament, and some fibres of the piriformis muscle arise from it^LV 

 below the obturator internus passes out of the pelvis under its cover, and the internal pudic 

 vessels and nerve pa,ss in. At the ilium, its posterior edge is continuous with the vertebra^_ 

 aponeurosis; while to the anterior edge is attached the thick fascia covering the gluteus mediusV!^"' 

 The obturator fa.scia is attached to its falciform edge. It is ))ierced by the coccygeal hranrhes of 

 the inferior gluteal {sciatic) artery and the inferior clunial {perforating cutaneous) nerve from the 

 second and third sacral. 



The sacro-spinous (small sciatic) ligament (figs. 271, 272, and 273) is tri- 

 angular and thin, springing by a broad base from the lateral border of the sacrum 

 and coccyx, from the front of the sacrum both above and below the level of the 

 fourth sacral foramen, and from the coccyx nearly as far as its tip. By its apex 

 it is attached to the front surface and the borders of the ischial spine as far out- 

 ward as its base. Its fibres decussate so that the lower ones at the coccyx be- ' 

 come the high(!st at the ischial spine; muscular fibres are often seen intermingled^ ^y\ 

 with the ligamentous. "^T^ ' 



The sacro-spinous ligament is situated in front of the sacro-tuberous ligament, with which 

 it is closely connected at the sacrum, and separates the greater from the lesser sciatic foramen. 



