THE SYMPHYSIS PUBIS. 



339 



resist any tendency of the weight of the body to force the sacrum forward. A rather 

 distinct superficial band, the oblique sacro-iliac ligament^ (Fig- 362), passes 

 from the posterior superior iHac spine to the second and third sacral vertebrae. 

 Anterior and superior fibres are spread about the joint, and require no special 

 description. Some of them go to the pre-auricular sulcus of the ilium. 



The ilio-lumbar ligament^ (Fig. 359) is a triangular band of strong fibres 

 diverging from the apex and the front surface of the transverse process of the last 

 lumbar vertebra to the top of the crest of the ilium opposite to it and to the an- 

 terior surface, where it mingles with the anterior sacro-iliac fibres. A more or less 

 distinct bundle of diverging fibres to the top of the sacrum near the joint with the 

 ilium is the sacro-lumbar ligament (Fig. 359). 



THE SYMPHYSIS PUBIS. 

 The symphysis pubis is generally a typical half-joint, the fibro-cartilage coating 

 the opposed pubic surfaces being very dense and the central cavity small. In 

 section it appears as a linear cleft nearer the back than the front. Sometimes, 

 however, especially in women, a part of the surfaces is coated with hyaline cartilage. 

 The total breadth of the soft parts (greater in woman than in man) rarely exceeds 

 five millimetres. The cartilages are ensheathed in fibres, the deeper parts of which 



Fig. 360. 



Fig. 361. 



Superior Synovial 

 pubic ligament cavity 



Fibro-cartilage 



The symphysis pubis, anterior surface. 



Inferior 

 pubic ligament 



Frontal section through the symphysis pubis. 



are inseparable from them : those above and behind are of little consequence. 

 The anterior ones are in several layers, being in part composed of fibres from the 

 aponeurosis of the external oblique and of fibres of origin of the rectus. They are 

 in the main transverse, but those from the obliques run downward and inward, 

 sometimes making a distinct decussation. The inferior or si(bpiibic fibres are col- 

 lected into a dense transverse band, bounding by the lower side the pubic arch and 

 being joined by the upper to the fibro-cartilage. 



THE SACRO-SCIATIC LIGAMENTS. 



These are two layers of fibres passing from the sides of the sacrum to the 

 ischium and forming a partial wall for the pelvis at the sacro-sciatic notch, where the 

 bony walls are wanting. 



The great or posterior sacro-sciatic ligament^ (Fig. 362) is external to 

 the lesser, which it conceals to a large extent. It arises from the outer surface of 

 the pelvis, beginning at the inferior posterior spine of the ilium, where its fibres 

 mingle with those of the posterior sacro-iliacs, then from the posterior edge of the 

 border of the three lower pieces of the sacrum and from one or two of the coccyx. 

 From this broad origin it narrows as it passes forward, and at the same time twists 

 so that the outer surface becomes the inferior as it is inserted into the under side of 

 the tuberosity of the ischium. As it reaches the tuberosity the fibres at its inner 



Lig. sacroiliacum posterius longum. " Lig. iliolumbalc. '^ Lig. sacrotuberosum. 



