PELVIC ARTICULATIONS 



235 



ilium behind the auricular surface to the back of the lateral mass of the sacrum, 

 both lateral to and between the upper foramina and to the upper sacral articular 

 process, and the area between it and the first sacral foramen. Thfi. deepest fibres 

 of this group constitute the so-called interosseous ligament. The more superficial 

 fibres (long posterior sacro-iliac ligament) are oblique or vertical, and pass from 

 the posterior superior iliac spine to the second, third, and fourth tubercles on 

 the back of the sacrum, a more or less well-defined band which goes to the third 

 and fourth sacral tubercles being called sometimes the oblique sacro-iliac band 

 and sometimes the long straight band. 



The inferior sacro-iliac ligament (fig. 272) is covered behind by the upper 

 end of the sacro-tuberous ligament; it consists of strong fibres extending from 

 the lateral border of the sacrum below the articular facet to the posterior iliac 

 spines; some of the fibres are attached to the deep surface of the ilium and join 

 the interosseous ligament. 



Fig. 272. — Median Sagittal Section of the Pelvis, Showing Ligaments. 



Superior sacro-iliac liga- 

 ment 



Anterior sacro-iliac liga- 

 ment 



Inferior sacro-iliac liga- 

 ment 



Sacro-spinous ligament 



Sacro-tuberous ligament 

 A- 



The interosseous ligament is the strongest of all, and consists of fibres of 

 different lengths passing in various directions "between the two bones. Imme- 

 diately above the interspinous notch of the ilium the fibres of this ligament are 

 very strong, and form an open network, in the interstices of which is a quantity 

 of^fat in which the articular vessels ramify. 



The ear-shaped cartilaginous plate, which unites the bones firmly, is accu- 

 rately applied to the auricular surfaces of the sacrum and ilium. It is about /n 

 one-twelfth of an inch (2 mm.) thick in the centre, but becomes thinner toward / 

 the edges. Though closely adherent to the bones, it tears away from one entirely, .• 

 or from both partially, on the application of violence, sometimes breaking irregu- 

 larly so that the greater portion remains connected with one bone, leaving the 

 other bone rough and bare. It is usually one mass, and is only occasionally 

 formed of two plates with a synovial cavity between them. 



Because of the occasional presence of a more or less extensive synovial cavity ^'ittiij ^he 

 fibro-cartilage, and also of a synovial lining to the ligaments passing in front and behind the 

 articulation, the term 'diarthro-amphiarthrosis' has been given to this joint, and also to the 

 symphysis pubis. Testut mentions certain folds of synovial membrane fiUing up gaps which 

 here and there occur at the margin of the fibro-cartilage but they are not usually seen. 



The sacro-tuberous (great sciatic) ligament (figs. 271, 272, and 273) is at- 

 tached above to the posterior extremity of the crest of the ilium and the lateral 

 aspect of the posterior iliac spines. From this attachment some of its fibres 



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