204 ARTICULATIONS. 



IX. ARTICULATIONS OF THE PELVIS. 



The Ligaments connecting the bones of the pelvis with each other may be 

 divided into four groups. 1. Those connecting the sacrum and ilium. 2. Those 

 passing between the sacrum and ischium. 3. Those connecting the sacrum and 

 coccyx. 4. Those between the two pubic bones. 



1. ARTICULATION OF THE SACRUM AND ILIUM. 



The sacro-iliac articulation is an amphiarthrodial joint, formed between the 

 lateral surfaces of the sacrum and ilium. The anterior or auricular portion of 

 each articular surface is covered with a thin plate of cartilage, thicker on the 

 sacrum than on the ilium. The surfaces of these cartilages in the adult are rough 

 and irregular, and separated from one another by a soft yellow pulpy substance. 

 At an early period of life, occasionally in the adult, and in the female during 

 pregnancy, they are smooth and lined by a delicate 'synovial membrane. The 

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



The Anterior Sacro-iliac Ligament consists of numerous thin ligamentous bands, 

 which connect the anterior surfaces of the sacrum and ilium. 



The Posterior Sacro-iliac (fig. 128) is a strong interosseous ligament, situated 

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

 chief bond of connection between these 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 ex- 

 tremity to the third or fourth transverse tubercle on the posterior surface of the 

 sacrum, and by the other to the posterior superior spine of the ilium ; it is some- 

 times called the oblique sacro-iliac ligament. 



2. ARTICULATION OF THE SACRUM AND ISCHIUM. 



The Great or Posterior Sacro-sciatic . 

 The Lesser or Anterior Sacro-sciatic. 



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 middle 

 than at the extremities, attached by its broad base to the posterior inferior spine 

 of the ilium, to the third and fourth transverse tubercles on the sacrum, and to 

 the lower part of the lateral margin of that bone and the coccyx; passing 

 obliquely downwards, outwards, and forwards, it becomes narrow and thick, and, 

 at its insertion into the inner margin of the tuberosity of the ischium, it increases 

 in breadth, and is prolonged forwards along the inner margin of the ramus forming 

 the falciform ligament. The free concave edge of this ligament has attached to it 

 the obturator fascia, with which it forms a kind of groove, protecting the internal 

 pudic vessels and nerve. One of its surfaces is turned towards the perineum, the 

 other towards the Obturator internus muscle. 



The posterior surface of this ligament gives origin, by its whole extent, to fibres 

 of the Gluteus maximus. Its anterior surface is united to the lesser sacro-sciatic 

 ligament. Its superior border forms the lower boundary of the lesser sacro-sciatic 

 foramen. Its lower border forms part of the boundary of the perineum. This 

 ligament is pierced by the coccygeal branch of the sciatic artery. 



The Lesser or Anterior Sacro-sciatic Ligament, much shorter and smaller than 

 the preceding, is thin, triangular in form, attached by its apex to the spine of the 

 ischium, and internally, by its broad base, to the lateral margin of the sacrum 

 and coccyx, anterior to the attachment of the great sacro-sciatic ligament, with 

 which its fibres are intermingled. 



