Chap, xvi 1 1.) THE PELVIS. 377 



The nerve relations of this joint are important. 

 It is supplied by the superior gluteal, by the lumbo- 

 sacral cord and first sacral nerve, and by the first and 

 second posterior sacral nerves (Morris). The lumbo- 

 sacral cord and the obturator nerve pass over the 

 front of the joint, the former being very closely con- 

 nected with the articulation. It will be understood 

 from these relations that in sacro-iliac disease pain is 

 felt over the sacral region (upper sacral nerves) and 

 in the buttock (gluteal nerve). Much pain is also 

 often complained of in the hip- or knee-joint, and 

 along the inner part of the thigh (obturator nerve). 

 In one or two reported cases there has been severe 

 pain in the calf and back of the thigh, with painful 

 twitchings in the muscles of those parts (lumbo- 

 sacral cord and connection with great sciatic nerve). 

 Dislocation of the sacrum at this joint is prevented by 

 the remarkable double-wedge-shaped outline of the 

 bone, and by the very dense ligaments that bind it 

 in its place. The thick end of the main wedge of the 

 sacrum is in front, and therefore the strongest liga- 

 ments are to be found behind the bone, as if to pre- 

 vent it from slipping forwards, or from becoming 

 rotated forwards on its transverse axis. 



Trendelenburg 's operation. In order to bring the 

 two pubic bones and the deficient soft parts together 

 in ectopia vesicae, Trendelenburg divides the sacro- 

 iliac synchondroses on either side. The knife is made 

 to cut the posterior sacro-iliac ligaments, the inter- 

 osseous and superior ligaments, and the interarticular 

 cartilage. The operation, which has been very 

 successful, is limited to children between the ages of 

 two and five. The distance between the anterior 

 superior iliac spines has in a child aged two and a- 

 half years been lessened two inches by this opera- 

 tion. 



Spiiia bi(i<!u. This term refers to certain con- 



