PELVIS. 



125 



anterior or internal surface are blended the 

 fibres of the ischio-coccygeus muscle, which 

 exclude it from the ischio-rectal fossa, and 

 render it rough when dissected. 



Soemmering describes the lower part of the 

 powerful lumbar fascia as a ligament connect- 

 ing the ilia to each other posteriorly and to 

 the lower spines of the sacrum. This fascia 

 does, doubtless, act powerfully in clasping 

 the ilia upon the sacrum between them. He 

 calls it the lateral sacro-iliac ligament, or the 

 posterior lateral iliac ligament. 



The important part which these three ac- 

 cessory ligaments play in the mechanism of 

 the pelvis will be hereafter shown. 



The movements of the sacro-iliac joint are 

 very limited indeed, its principal characteristic 

 being compactness and strength, with just 

 sufficient sliding motion downwards and back- 

 wards to break the shock of concussion pass- 

 ing from the lower extremities to the trunk. 

 This is said by some to be increased in preg- 

 nancy and by parturition. 



The pubic symphysis (fig. 80. 2) is an azygos 

 joint uniting the innominate bones by their 

 pubic portions in front. The osseous surfaces 

 composing it are oval, with the long diameter 

 directed downwards and backwards, and ge- 

 nerally an inch and a half long, by three 

 quarters broad. The planes of these sur- 

 faces not being directly opposed to each other, 

 leave a larger interval of separation in front 

 than behind. This interval is filled by a fibro- 

 cartilaginous disc, which is correspondingly 

 thicker in front, where the fibrous components 

 are so numerous and strong as to constitute 

 almost an interosseous ligament, and pass 

 from one bone to the other in an oblique and 

 concentric direction. Towards the central 

 and posterior part this disc is generally mainly 

 cartilaginous in structure, and is often, in 

 females, separated in the middle by a chink 

 forming two smooth, plane, oval contiguous 

 articular surfaces, of various dimensions, some- 

 times irregularly laminar, at others with a de- 

 licate investing membrane. In parturient wo- 

 men these surfaces often extend over nearly 

 the whole of the articulation, and are well 

 marked in a figure given by Dr. Hunter, in 

 the second volume of Medical Observations 

 and Inquiries. In males, this separation is 

 seldom present. The whole of the disc may, 

 however, by maceration, generally be separated 

 into two plates {fig. 82. a, a), of a denser and 

 more cartilaginous structure than the rest, 

 each strongly adherent to the bone by mammil- 

 liform fibrous processes (b), which pass into 

 corresponding depressions in the osseous sur- 

 faces (c), and are connected to each other on 

 opposite sides, by continuation of their fibres, 

 arranged in oblique and concentric layers, 

 which interlace obliquely with each other, (rf) 

 Dr. W. Hunter remarks, with Sandifort and 

 Albinos, that the two cartilaginous plates (a,ff), 

 covering the opposed surfaces of theossa pubis, 

 are usually connected by a structure rather liga- 

 mentous than cartilaginous ; and in a memoir 

 on the pubic symphysis, gives an engraving of 

 this arrangement. In several instances I have 



seen the fibrous processes which connect the 

 plates with the bone very well marked, leav- 



Ftg. 82. 



Symphysis pubis after maceration. 



a, cartilaginous plates of Dr. Hunter ; ft, mam- 

 millary processes on their osseous surface ; c, cor- 

 responding osseous depressions to receive them ; d, 

 inter-laminar concentric nbro-cartilaginous tissue 

 divided vertically in the centre. 



ing on the bone, after maceration, deep conical 

 pits. The above figure was taken from a ma- 

 cerated preparation of this joint. According 

 to the observations of Tenon, these processes 

 are directed into the bone downward and 

 backward, as well as outward, and tend to 

 prevent displacement of the cartilage in that 

 direction. The inter-laminar fibro-cartuUigin- 

 ous tissue is very elastic and yielding, swelling 

 out on the cut surface when lateral pressure 

 is made on the bone, somewhat in the manner 

 of the intervertebral discs. It often evinces 

 a tendency to split in a lamellar direction after 

 maceration. Around the circumference the 

 concentric fibres become much more numerous 

 and strong, and are continued into the peri- 

 pheral ligaments. These are an anterior, pos- 

 terior, a superior, and an inferior ligament. 



The anterior pubic ligament (fig. 80. rf) is a 

 thick layer, passing between the anterior sur- 

 faces of the bones, strengthened by and blended 

 with the oblique fibres of the aponeurosis of 

 the external oblique muscle continued to the 

 opposite pubic bone in front of the joint. 



The posterior pubic ligament is the most feeble. 

 It is composed of transverse fibres, somewhat 

 scattered, and is remarkable in being raised by 

 the posterior border of the pubic fibro-car- 

 tilage into a vertical ridge, in old persons often 

 very evident to the touch. It gives attachment 

 to the superior true ligaments of the bladder, 

 and the anterior fibres of the levator ani 

 muscle. 



The superior pubic ligament (e) is formed 

 by a thick, smooth layer of fibres often raised 

 by a central ridge like the posterior, passing 

 between the crests of the pubes, the super- 

 ficial fibres extending over the greater part of 

 the crests, and giving origin to the recti ab- 

 dominales and pyramidales abdominal muscles, 

 and lineaalba. 



