PELVIS 615 



and laterally, it is inserted into the medial lip of the iliac 

 crest at the posterior part of the iliac fossa. 



The synchondrosis between the body of the last lumbar 

 vertebra and the base of the sacrum corresponds, in every 

 respect, to the similar articulations between the bodies of 

 the vertebrae above. The opposed bony surfaces are each 

 coated by a thin layer of hyaline cartilage, and are firmly 

 united by an intervening disc of fibro-cartilage, which is dense 

 and laminated externally, but soft and pulpy towards the centre. 

 The dissector should observe that this disc is the thickest of 

 the series, and further, that it is wedge-shaped, being thicker 

 in front than behind. 



Sacro-coccygeal Articulation. This is a synchondrosis. 

 The articulating surfaces are each covered by a thin 

 cartilaginous plate, and these are united by a disc of fibro- 

 cartilage. The joint is strengthened in front by an anterior 

 ligament, which extends downwards from the front of the 

 sacrum to the anterior aspect of the coccyx, and by a posterior 

 ligament which, attached above to the posterior border of the 

 lower aperture of the sacral canal, proceeds downwards upon 

 the posterior aspect of the coccyx. The latter ligament is 

 much the stronger of the two. In addition, fibrous bands 

 will be found passing between the cornua of the sacrum 

 and the coccyx, and also between the lateral angles of the 

 sacrum and the transverse processes of the first piece of the 

 coccyx. 



As regards the coccygeal joints (when such exist), the union 

 of the different segments of the bone is brought about by 

 intervening cartilaginous discs and anterior and posterior 

 ligaments. 



Sacro-iliac Articulation. The sacrum is wedged in between 

 the two innominate bones, and is held fast in this position by 

 the sinuous form of the opposed articular surfaces, and by 

 the strong ligaments which pass between the bones. These 

 ligaments are : 



i. The anterior sacro-iliac. 2. The interosseous sacro-iliac. 3. The 

 long posterior sacro-iliac. 4. The short posterior sacro-iliac ligament. 

 5. The sacro-tuberous ligament. 6. The sacro-spinous ligament. 



Ligamentum Sacroiliacum Anterius. The anterior sacro- 

 iliac ligament is by no means strong. It is composed of a 

 series of short fibres stretching across the front of the joint, 

 and connecting the bones anteriorly. 



