OF THE SACRUM AXD COCCYX 205 



The posterior sacro-coccygeal ligament (fig. 209) is a direct continuation of 

 tlie posterior common ligament of the column, consisting of a narrow band of 

 closely packed filjres, which become blended at the lower l)order of the first segment 

 of the coccyx with the filuni tcrminale and supracornual ligament. 



The supracornual ligament (fig. 209) is the prolongation of the supraspinous, 

 which becomes inseparably l)lcnded with the aponeurosis of the erector spinse opposite 

 the laminae of the third sacral vertebra, and is thus prolonged downwards upon the 

 back of the coccyx, passing over and roofing in the lower end of the spinal canal 

 where the laminse are deficient. The median fibres (the supraspinous ligament) 

 extend over the back of the coccyx to its tip, blending with the posterior sacro- 

 coccygeal ligament and filum terminale; the deeper fibres run across from the stunted 

 laminae on one side to the next below on the opposite side, and from the sacral 

 cornua on one side to the coccygeal on the opposite, some passing between the two 

 cornua of the same side, and bridging the aperture through which the fifth sacral 

 nerve passes. Its posterior sui'face gives origin to the gluteus maximus muscle. 



The intertransverse ligament (fig. 209) is merely a quantity of fibrous tissue 

 wliich passes from the transverse process of the coccyx to the lateral edge of the 

 sacrum below its angle. It is connected with the sacro-sciatic ligaments at their 

 attachments, and the fifth sacral nerve escapes behind it. It is perforated by twigs 

 from the lateral sacral artery and the coccygeal ner^'c. 



The arterial supply is from the lateral sacral and sacro-median arteries. 



The nerves come from the fourth and fifth sacral and coccygeal nerves. 



The movements permitted at this joint are of a simple forward and backward, 

 or hinge-like character. In the act of defecation, the bone is pushed back Ijv the 

 fa'cal mass, and, in parturition, l)y the foetus; but this backward movement is 

 controlled by the upward and f(^rward pull of the levator ani and coccygeus. The 

 external sphincter also tends to pull the coccyx forwards. 



(c) IXTERCOCCYGEAL JoiNTS 



The several segments of the coccyx are held together by the anterior and 

 posterior common ligaments, Avhich completely cover the bony nodules on their 

 anterior and posterior aspects. Laterally, the sacro-sciatic ligaments, being attached 

 to nearly the whole length of the coccyx, serve to connect them. Between the first 

 and second pieces of the coccyx there is a very perfect amjihiarthrodial joint, with 

 a well-marked intervertebral substance. 



(d) The Symphysis Pubis 

 Class, — A mph la rth ros is. 



The l)ones entering into this joint are the pubic ])ortions of the hip-bones. 

 This joint is shorter and l)roader in the female than in the male. The ligaments, 

 which completely surround the articulation, are: — 



Superior. Anterior. 



Inferior. Posterior. 



Interosseous cartilage. 



The superior ligament (figs. 210 and 211) is a well-marked stratum of 

 yellowish fibrc?^ whicli extends outwards along the crest of the pubes on each side, 

 blending in the middle line with the interosseous cartilage. It is continuous in 

 front with the deep transverse fibres of the anterior ligament, and behind Avith the 

 posterior ligament. It gives origin to the rectus abdominis tendon. 



The posterior ligament (fig. 212) is slight, and, excepting above and below, 

 consists of little more than thickened periosteum. Near the upper part is a Ijand 

 of strong fibres, reaching the whole width of the pubic bones, and continuous with 

 the thickened periosteal fibres along the ilio-pectineal line. BeloAv, many of the 

 upper and superficial fibres of the infrapubic ligament ascend over the back of the 



