OF THE PELVIS. 



337 



is covered with a thin plate of cartilage, thicker on the sacrum than on the 

 ilium. The surfaces of these cartilages are usually in close contact, but not 

 united. Sometimes fine fibres are found running between portions of these sur- 

 faces, which in other cases may be, in the adult, rough and irregular, and sepa- 

 rated from one another by spaces containing synovial-like fluid. The ligaments 

 connecting these surfaces are the anterior and posterior sacro-iliac. 



The Anterior Sacro-iliac Ligament (Fig. 239) consists of numerous thin 

 ligamentous bands which connect the anterior surfaces of the sacrum and ilium. 



Aperture of communication 

 with 



PSOAS and ILIACUS. 



Femur. \ 



FIG. 239. Articulations of pel vis and hip. Anterior view. 



The Posterior Sacro-iliac (Fig. 240) is a strong interosseous ligament, situated 

 in a deep depression between the sacrum and ilium behind, and forming the chief 

 bond of connection between those bones. It consists of numerous strong fasciculi 

 which pass between the bones in various directions. Three of these are of large 

 size : the two superior, nearly horizontal in direction, arise from the first and 

 second transverse tubercles on the posterior surface of the sacrum, and are inserted 

 into the rough, uneven surface at the posterior part of the inner surface of the 

 ilium. The third fasciculus, oblique in direction, is attached by one extremity to 

 the third transverse tubercle on the posterior surface of the sacrum, and by the 

 other to the posterior superior spine of the ilium ; it is sometimes called the 

 sacro-iliac ligament. 



The position of the sacro-iliac joint is indicated by the posterior superior spine of the ilium. 

 This process is immediately behind the centre of the articulation. 



2. LIGAMENTS PASSING BETWEEN THE SACRUM AND ISCHIUM (Fig. 240). 



The Great Sacro-sciatic (Posterior). 

 The Lesser Sacro-sciatic (Anterior). 



The Great or Posterior Sacro-sciatic Ligament is situated at the lower and 

 back part of the pelvis. It is thin, flat, and triangular in form ; narrower in the 

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