474 ABDOMEN 



indeed, it is generally believed that the ligament is derived 

 from the posterior part of the muscle by the fibrous degenera- 

 tion of the muscular fasciculi. 



The sacro-tuberous and the sacro-spinous ligaments con- 

 vert the sciatic notches of the hip bone into foramina. 



Through the greater sciatic foramen pass the superior gluteal 

 vessels and nerve, the piriformis muscle, the pudendal and 

 inferior gluteal vessels and nerves, the nerve to the obturator 

 internus, the sciatic nerve, the nerve to the quadratus femoris, 

 and the posterior cutaneous nerve of the thigh. 



The lesser sciatic foramen transmits the tendon of the 

 obturator internus muscle, the pudendal vessels and nerve, 

 and the nerve to the obturator internus muscle. 



The sacro-iliac joint is a diarthrodial joint. The ligaments 

 of the joint should now be divided, and the two bones forcibly 

 wrenched asunder. It will then be seen that each articular 

 surface is covered with a plate of cartilage, and that a small 

 synovial space intervenes between and partially separates 

 the two plates. 



The sacro-iliac joint is not immovable. A slight amount 

 of movement can take place the sacrum rotating round an 

 imaginary line drawn transversely through its second piece. In 

 the erect posture the promontory of the sacrum is withdrawn 

 to the full extent from the symphysis ; when the body is bent 

 forwards, the symphysis and the promontory are approximated, 

 and, in consequence, the tension of the sacro-tuberous and 

 sacro-spinous ligaments is increased. 



Symphysis Ossium Pubis. The symphysis pubis is an 

 example of a synchondrosis. In addition to the intervening 

 disc of fibre-cartilage which connects the cartilage-covered 

 opposing surfaces of the two pubic bones, four ligaments are 

 present, viz. : 



i. Anterior pubic. 2. Posterior pubic. 3. Superior pubic. 4. Arcuate. 



Ligamentum Pubicum Anterius. The anterior pubic ligament 

 is strongly marked, and consists of two layers of fibres a 

 superficial and a deep. The superficial fibres are oblique, and 

 cross each other like the limbs of the letter X, mingling 

 with the decussating fibres of the superior crura of the 

 subcutaneous inguinal rings. The deep fibres are transverse 

 and extend across from one bone to the other. 



Ligamentum Pubicum Posterius The posterior pubic liga- 



