54 HANDBOOK OF ANATOMY 



the tip of the transverse process of the fifth lumbar vertebra to 

 the iliac crest just behind its highest point. It is in reality a 

 thickened portion of the lumbar fascia. 



The Great Sciatic Ligament is triangular in shape. It is 

 attached to the posterior inferior spine of the ilium, the tuber- 

 osity of the ischium, and to the posterior aspects of the lower 

 part of the sacrum. It fills the gap between the innominate 

 bone and sacrum, and, by completing the great and small sciatic 

 notches, forms the great and small sacro-sciatic foramina. 



The Small Sciatic Ligament is also triangular ; it lies vent rally 

 to the great sciatic ligament, and is attached by its base to the 

 last two segments of the sacrum, and by its apex to the spine of 

 the ischium. 



The Symphysis Pubis is an immovable joint between the two 

 pubic bones. The articular surfaces are covered with cartilage 

 as usual, and have, in addition, an interarticular disc of cartilage 

 welding them firmly together. There are ligaments all round 

 the joint, the most important being the subpubic ligament, which 

 is in the arch of the pubis and separated from the triangular 

 ligament of the perineum by a small interval. The subpubic 

 ligament is attached to the interarticular ligament and the 

 descending rami of the pubic bones. There is no synovial 

 membrane. 



The Triangular Ligament of the perineum helps to complete 

 the pelvic walls, and stretches across between the descending 

 rami of the pubic bones. It occupies a horizontal position, and 

 has superior aud inferior surfaces. Posteriorly it fuses with the 

 deep fascia of the perineum. 



The Obturator Membrane fills the obturator foramen, leaving 

 superiorly a small canal, through which vessels and nerves pass. 



There are no muscles acting on these joints in the ordinary 

 way, the joints being for the sole purpose of preventing absolute 

 rigidity, so that the pelvis will "give" to the pull of the muscles 

 as required. 



The Hip- Joint takes place between the head of the femur and 

 the acetabulum of the innominate bone. 



It is a true ball-and-socket joint, so has movement round three 

 axjes : 



