LIGAMENTS OF THE PELVIS. 475 



The rest of the opening is filled "by the obturator liga- 

 ment. 



The structure of the innominatum is cellular internally, 

 with a compact layer externally. 



Its development is from three principal centres of ossifica- 

 tion, one for the ilium, one for the ischium, and one for the 

 puhis, all of which meet in the acetabulum ; and five addi- 

 tional or secondary points are noticed, one for the crest of 

 the ilium, one for the tuherosity of the ischium, one for the 

 anterior and inferior spine of the ilium, one for the angle 

 of the pubis, and one for the centre of the acetabulum. 

 These latter points appear at the twelfth year. Ossifica- 

 tion is noticed first in the ilium, at the same time or soon 

 after it occurs in the vertebrae ; about the third month in 

 the ischium, and between the fourth and fifth months in 

 the pubis, about the sixth year the rami of the ischium and 

 pubis are found nearly ossified, and join in the tenth year. 

 The three bones are complete in the acetabulum by the 

 twenty-fifth year. 



The osinnominatum articulates with its fellow, the 

 sacrum and the head of the femur. 



LIGAMENTS OF THE PELVIS. 



The mode of articulation Iretween the last lumbar verte- 

 bra and the sacrum, is the same as those of the other ver- 

 tebrae already described; by the inter vertebral, anterior and 

 posterior, capsular, yellow, supra spinous, and interspinous 

 ligaments, and synovial membranes. There is however an 

 additional ligament, consisting of a short, thick, strong fas- 

 ciculus extending from the transverse process of the last 

 lumbar vertebra to the posterior superior part of the base 

 of the sacrum, called lumbo-sacral ligament. The next liga- 

 ment connecting the vertebral column to the pelvis is the 

 ilio-lumbar. It arises from the transverse processes of the 

 two lower lumbar vertebrae, and is inserted into the poste- 

 rior crest of the ilium and into its posterior superior spinous 

 process. The ligaments of the pelvis are those connecting 

 the sacrum and ilium, those connecting the sacrum, coc- 



