290 THE ARTICULATIONS, OR JOINTS 



of the iliolumbar ligament. This ligament is in relation, in front, with the Psoas 

 muscle. The internal border of the lumbosacral ligament margins the foramen 

 of the last lumbar nerve. 



The iliolumbar ligament (ligamentum iliolumbale) (Fig. 238) passes horizontally 

 outward from f&gsa.pex of the transverse process of the last lumbar vertebra to 

 the crest of the ilium immediately in front of the sacroiliac articulation. It 

 is of a triangular form, thick and narrow internally, broad and thinner externallv. 

 It is in relation, in front, with the Psoas muscle; behind, with the muscles occupy- 

 ing the vertebral groove; above, with the Quadratus lumborum. It blends in 

 places with the lumbosacral ligament, and its crescentic inner margin marks 

 the limit of the foramen for the fourth lumbar nerve. These ligaments are thick 

 prolongations from the anterior layer of the lumbar fascia. 



X. 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 (ARTICULATIO SACROILIACA). 



The sacroiliac 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 hyaline cartilage, thicker 

 on the sacrum than on the ilium. These are in close contact with each other, 

 and to a certain extent united together by irregular patches of softer fibro- 

 cartilage, and at their upper and posterior part by fine fibres of interosseous 

 fibrous tissue. Throughout a considerable part of their extent, especially in 

 advanced life, they are not connected together, but are separated by a space 

 containing a synovial-like fluid, and hence the joint presents the characters of 

 a diarthrosis. 



The ligaments connecting these surfaces are the 



Anterior Sacroiliac. Posterior Sacroiliac. 



The anterior sacroib'ac ligament (ligamenta sacroiliaca anteriora) (Fig. 238) 

 consists of numerous thin bands which connect the anterior surfaces of the 

 sacrum and ilium. 



The posterior sacroiliac ligament (ligamentum sacroiliacum posterius) (Fig. 239)' 

 is a strong 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. The upper part of the ligament, the short sacroiliac (ligamentum 

 sacroiliacum posterius breve} is nearly horizontal in direction and passes from 

 the first and second transverse tubercles pn the posterior surface of the sacrum 

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

 ilium. The lower part (ligamentum sacroiliacum posterius longum), 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 oblique sacroiliac ligament. 



Surface Form. The position of the sacroiliac joint is indicated by the posterior superior- 

 spine of the ilium. This process is immediately behind the centre of the articulation. 



