PELVIC ARTICULATIONS AND LIGAMENTS.
—The articulations of the pelvis arrange them selves into ; 1. those connecting the pelvis with the spinal column, or lumbo-pelvic articu lations ; 2. those of the pelvic bones with each other, or proper pelvic articulations ; 3. those connecting thein with the thigh bones, or fentoro-pelvic articulations. The second class of articulations are those with which we have more immediately to do. The first class may be alluded to as necessary for elucidation of the subject. The last class come more particularly under the consideration of the hip joint.
The ligantents of the pelvis are of twc kinds : 1. those which are closely connect& with the several articulations, or intimate figs. ments ; and, 2. those which connect distant portions of its osseous structure, and are com plementary to the articulations or accessory ligaments. The fornier will be best described with the articulations of which they form part.
Luntbo-pelvic articulations.— The sacrum, and through it the pelvis, is united to the last lumbar vertebra by exactly the same mean: as the vertebrx to each other, viz.:—First, by an amphi-arthrodial joint, composed of a thick disc of fibro-cartilage intervening between, and adherent to, their opposing articular surfaces ; and strengthened by a continuation of the anterior and posterior common ligaments to the sacrum. Secondly, by two arthrodialjoints invested with capsular ligaments, one for each of the articular pro cesses. Thirdly, by the lowest members of the ligamenta =Vara connecting the laminw of the vertebrm with those of the sacrum, and by the lowest inter-spinous and supra spinous ligainents connecting their spines. And, lastly, by an accessory ligament, which is a representative of the inter-transverse or oblique transverso-costal ligaments. This extends from the loNN er border of the last lumbar transverse process on each side, to the lateral masses of the base of the sacrum, its fibres expanding to the sacro-iliac sy m physis and iliac crest. It is called the sacro vertebral or tuntho-sacraitigament.
The fibro-cartilaginous disc is composed, like the other intervertebral plates, of an obliquely intersecting layer of fibres externally, and of a central, soft, pulpy portion, and differs only by gradually becoming much thicker ante riorly, like the body of the last lumbar ver tebra itself. This allows of the curve of the spinal column at this part, uhich is the most salient point of the sacro-vertebral angle.
The movements of this joint are a limited antero-posterior motion with slight lateral flexure, somewhat less than that of the rest of the spinal column.
Proper Or intra -pelvic articulations. — These consist of a joint uniting the sacrum and coccyx by a miniature amphi-arthrosis ; of a joint on each side uniting the sacrum to the innominate bone posteriorly ; and a single joint in front, uniting the innotninate bones to each other. The three latter joints are of the kind usually denominated " sym physis," and considered by many as included also in the class "amphi-arthrosis." The sacro-iliac joints, however, most fre quently presenting two contiguous surfaces and two separate plates ofincrusting cartilage, o ugh t rather, as Albinus remarked, to be considered as "arthrodial" forms of articulation, while the pubic symphysis occupies an intermediate or transitional position between the pro-carti laginous or mixed, and the arthrodialjoints.
The sacro-coccygeal joint is composed of a fibro-cartilaginous disc, and an anterior and posterior ligament. The fibro-cartilaginous disc is a miniature of the intervertebral, inter vening between and adherent to the opposed articular surfaces of these bones, being, how ever, less evidently pulpy in the centre. Ac cording to Cruveilhier, there is sometimes found a synovial membrane in the centre of this joint. The anterior sacro-coccygeal liga ment consists of a thin layer of fibres passing from one bone to the other in front of the joint, and spreading over the whole coccy geal surface. The posterior sacro-coccygeal liganient is much stronger and more developed.