22 OF THE PELVIS. 



have received the names of anterior and posterior ligaments of the 

 symphysis pubis. 



25. The sacro-iliac or posterior symphyses are much more com- 

 plex than the preceding. There the sacrum is locked, like a double 

 wedge, between the coxal bones, so that it offers a very efficient re- 

 sistance to the weight of the body, which presses it from above down- 

 wards, and to the efforts of the pelvic viscera, which tend to force 

 it backwards; its articular surfaces, although uneven, are nevertheless 

 covered with a very thick diarthrodial cartilage, while those of the 

 iliac bones are wholly destitute of them. 



26. The name of posterior sacro-iliac ligament is given to a col- 

 lection of fibrous bundles, that are yellow, elastic, mixed with small 

 lumps of fat which fill up the uneven and rugous excavation that is 

 seen behind the cartilaginous surfaces. These fibrous bundles of 

 the same nature with the yellow ligaments of the vertebrae, are com- 

 posed of fibres decussating in every direction, and are united almost 

 intimately with the sacrum and coxal bones. Being of considerable 

 strength, they give an extraordinary solidity to the articulation which 

 they concur in forming. There is not, rigorously speaking, any an- 

 terior sacro-iliac ligament: a simple lamella of the pelvic periosteum 

 serves in its stead. 



27. Other small fibrous bands also serve, but less immediately, 

 to unite the bones of the pelvis behind. These are the sacro-sciatic, 

 and sacro-spinal ligaments; which, by passing from the posterior 

 spines of the ilium, and from the inferior half of the edge of the sa- 

 crum to the spine, and tuberosity of the ischium, convert the two 

 ischiatic notches into holes. 



28. The connections of the pelvis with the vertebral column and 

 with the coccyx, are effected by two amphiarthroses. 



2\h One, the sacro-coccygeal articulation, is composed, 1. Of an 

 elliptical fibro-cartilaginous lamina, which unites the point of the sa- 

 crum to the base of the coccyx; 2. Of the posterior sacro-coccygeal 

 ligament, a sort of prolongation or extension of the supra-spinal 

 ligament of the vertebrae, which closes the lower extremity of the 

 sacral canal; and 3. Of the anterior sacro-coccygeal ligament, 

 formed of two lateral bands united at their point on the front of the 

 second or third piece of the coccyx. Naturally very movable in 

 women, this articulation permits the coccyx to turn backwards, from 

 half an inch to an inch, while the child is passing through the lower 

 strait. 



30. The other, the sacro-vcrtebral articulation, differs from the 

 vertebral amphiarthroses, only in the thickness of its fibro-cartilage; 

 in the obliquity of the articular faces of the last lumbar vertebra, and 



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